Method and system for generating calibration data for wafer analysis - Patents.com

Abstract

To provide methods and systems for generating calibration data for wafer analysis.SOLUTION: Disclosed herein is a computer-implemented method for generating calibration data usable for analysis of a sample. The method includes: (i) identifying targets in an image frame pertaining to a scanned area of the sample; (ii) computing displacements of the targets relative to positions thereof as given by, or derived from, reference data of the scanned area; (iii) based at least on the computed target displacements, determining values of coordinate transformation parameters (CTPs) relating to coordinates of the image frame to coordinates of the scanned area as given by, or derived from, the reference data; and (iv) using at least the CTPs to obtain displacements of multiple segments in the image frame, thereby generating a displacement mapping of the image frame or at least a part thereof.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] cross reference This application claims priority to U.S. Patent Application No. 16 / 990,593, filed August 11, 2020, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

[0002] The present disclosure generally relates to methods and systems for generating calibration data for wafer analysis. [Background technology]

[0003] Process diagnostic tools for semiconductor production, such as inspection, metrology, and review systems, often have a wide field of view (FOV) to parallelize data acquisition from the sample being analyzed (e.g., wafer, photomask, or reticle) and achieve high processing speeds (throughput). A movable stage can be used to move the inspection sample relative to the imaging device, thereby enabling coverage of a large area of ​​the sample. For example, a mechanical stage can move the wafer along a first direction, while the imaging device collects data points along a second direction that is perpendicular to the first direction. Thus, slice-by-slice coverage of the wafer (or one or more areas thereof) is achieved, thereby facilitating the construction of a two-dimensional image.

[0004] As design rules shrink, analyzing small structures on a sample becomes increasingly difficult. Stringent performance requirements are imposed on analysis systems, particularly on the localization accuracy of patterns on the sample. For example, wafer inspection systems will require higher localization accuracy to associate analysis parameters (e.g., of analysis algorithms) and, more generally, analysis algorithms with specific locations on the wafer. Summary of the Invention [Problem to be solved by the invention]

[0005] This challenge is made doubly difficult by temporal physical effects and imperfections that adversely affect localization accuracy and play an ever-more important role as design rules shrink. These include, for example, mechanical vibrations, thermal fluctuations, thermal expansion of the stage, mechanical tension release of the optical module and stage, mechanical-optical drift, atmospheric density instabilities, and jittering and / or acceleration (of the stage and / or sub-stages configured to enable movement of the stage along (different) respective directions), which in turn cause additional mechanical vibrations.

[0006] Other defects may include misalignment of the stage axes: for example, the scanned wafer may be moved along a direction that is slightly offset relative to the wafer's y-axis (as defined by the die rows on the wafer), and / or, for example, the FOV of the imaging device (imager) may be slightly offset relative to the wafer's x-axis. [Means for solving the problem]

[0007] Aspects of the present disclosure, according to some embodiments thereof, relate to methods and systems for generating calibration data for sample analysis (e.g., analysis of wafers, photomasks, reticles). More particularly, but not by way of limitation, aspects of the present disclosure, according to some embodiments thereof, relate to methods and systems for generating position calibration data for analysis of patterned wafers.

[0008] Thus, according to an aspect of some embodiments there is provided a computer-implemented method for generating calibration data usable for analyzing a sample, the method comprising: - identifying a target within an image frame associated with a scanned area of ​​a sample (e.g., a wafer, a photomask, or a reticle); - calculating the displacement of the target relative to a target position given (i.e., specified) by or derived from reference data of the scan area; - determining, based at least on the calculated target displacement, values ​​of coordinate transformation parameters (CTP) relating the coordinates of the image frame to the coordinates of the scan area given by or derived from the reference data; - obtaining the displacements of a number of segments in the image frame using at least the CTP, thereby generating a displacement mapping of the image frame or at least a portion thereof.

[0009] According to some embodiments of the method, the CTP comprises at least three independent parameters.

[0010] According to some embodiments of the method, at least three independent parameters each characterize a respective correlation that persists across image frames.

[0011] According to some embodiments of the method, the CTP includes one or more of parameters characterizing a global shift, a linear scaling, a fixed angle skewing, and a rotation.

[0012] According to some embodiments of the method, the reference data includes one or more of the design data, CTP and / or displacement mapping generated from scan data of the sample obtained during recipe setup, and data obtained from scanning another sample of the same design (as the sample to be analyzed) or containing architectural features similar to those within the scanned area.

[0013] According to some embodiments of the method, prior to calculating the displacement of the target, the reference data is calibrated based on current system coordinates, which may have been generated taking into account previously acquired scan data (e.g., from a previously scanned area along the same slice). According to some such embodiments, the calibration includes scaling the reference data coordinates.

[0014] According to some embodiments of the method, at least some of the segments have a size of a pixel.

[0015] According to some embodiments of the method, the sample is a patterned (first) wafer.

[0016] According to some embodiments of this method, the scan area is positioned along a slice extending through a first die of the wafer, and the method further includes repeating the method with respect to other scan areas of the first die positioned along the slice.

[0017] According to some embodiments of the method, the CTP of at least one of the scan area and one or more other scan areas (i.e., at least one area) is determined taking into account one or more previously determined CTPs of previously scanned areas along the slice.

[0018] According to some embodiments of this method, the method further includes initial operations including optimizing (i) the height of the image frame (along the slice, respectively, relative to the scan area) and (ii) the selection of the CTP to achieve the required accuracy at maximum or substantially maximum throughput.

[0019] According to some embodiments of this method, the method further includes saving the generated CTP and, optionally, a displacement mapping of the image frame associated with the previously scanned area along the slice.

[0020] According to some embodiments of this method, the method further includes generating displacement mappings for additional image frames respectively associated with additional scan areas along the slice located on additional dies along the die row including the first die. The displacement mappings for the first group of additional image frames can be generated directly based at least on calculated displacements of targets therein (i.e., in the image frames) relative to corresponding positions of the targets given by the reference data. The displacement mappings for the second group of image frames can be generated based at least on calculated displacements of targets in the image frames relative to calibrated positions of corresponding targets in the corresponding image frames associated with scan areas on each previously scanned die (e.g., on an adjacent die) in the die row.

[0021] According to some embodiments of this method, the previously scanned die is the last scanned die.

[0022] According to some embodiments of this method, the method includes repeating it for each slice, thereby generating calibration data for one or more die rows of the wafer.

[0023] According to some embodiments of this method, the method further includes generating displacement mappings of additional areas of other dies along the die row in the slice containing the first die. For every predetermined number of dies along the die row, a displacement mapping of the image frame of the next die in the die row is generated directly from the reference data. For the remaining dies in the die row, the displacement mapping of the image frame of each one is determined based at least on calibration data of corresponding image frames in adjacent and previously scanned dies in the die row.

[0024] According to some embodiments of the method, if a (given) image frame associated with one of the other scan areas along the slice or one of the additional scan areas along the slice is characterized by (i) an insufficient number of identifiable targets and / or (ii) an insufficient uniform distribution of identifiable targets, such that (i.e., in that sense) the required accuracy of the displacement mapping of the given image frame is not achievable solely based on the displacements of the identifiable targets in the given image frame, then the displacement mapping of the given image frame is interpolated or extrapolated based on or further taking into account calibration data of image frames associated with scan areas near the scan area associated with the given image frame.

[0025] According to some such embodiments of the method, the method further comprises scanning the sample.

[0026] According to some embodiments of the method, the method can be performed at run-time as the sample is being scanned.

[0027] According to some embodiments of the method, the method can be performed off-tool using stored scan data of the sample.

[0028] According to some embodiments of this method, the reference image has a width (perpendicular to the mechanical scanning direction) of at least about 100 pixels.

[0029] According to some embodiments of the method, the reference image has a width of at least about 1000 pixels.

[0030] According to an aspect of some embodiments, there is provided a computer-implemented method for analysis of a sample, the method including generating calibration data associated with image frames of areas along a slice of the sample by performing the method disclosed above, and using the calibration data to associate one or more defect detection algorithms with respective sub-frames within the image frames, the calibration data including CTP and / or displacement mapping of the image frames.

[0031] According to an aspect of some embodiments, there is provided a non-transitory computer-readable medium having stored therein instructions executable by a computerized system (such as the computerized systems and sample analysis systems described below) to perform the above-described method for generating calibration data usable for sample analysis.

[0032] According to an aspect of some embodiments, there is provided a computerized system for generating calibration data usable for analyzing a sample, the system including a displacement analysis module, the displacement analysis module comprising: - calculating the displacement of targets identified in one or more image frames associated with one or more scan areas of the sample, respectively, relative to target positions provided by or derived from reference data for the one or more areas; - determining, based at least on the calculated target displacements, values ​​of coordinate transformation parameters (CTP) relating coordinates of one or more image frames to coordinates of the scan area provided by or derived from reference data of one or more areas, respectively; - configured to use at least the CTP to determine displacements of a number of segments in one or more image frames, thereby generating one or more displacement mappings of the one or more image frames or at least one or more portions thereof;

[0033] According to some embodiments of the computerized system, the CTP includes at least three independent parameters.

[0034] According to some embodiments of the computerized system, each of the at least three independent parameters characterizes a respective correlation that persists across each of the image frames.

[0035] According to some embodiments of the computerized system, the CTP includes one or more of parameters characterizing a global shift, a linear scaling, a fixed angle skewing, and a rotation.

[0036] According to some embodiments of the computerized system, the reference data includes one or more of the design data, CTP and / or displacement mapping generated from scan data of the sample obtained during strategy development, and data obtained from scanning another sample of the same design (as the sample to be analyzed) or containing architectural features similar to the features within one or more scan areas.

[0037] According to some embodiments of the computerized system, prior to calculation of the target displacement, the reference data is calibrated based on current system coordinates, which may have been generated taking into account previously acquired scan data (e.g., from a previously scanned area along the same slice). According to some such embodiments, the calibration includes scaling the reference data coordinates.

[0038] According to some embodiments of the computerized system, at least some of the segments have a size of a pixel.

[0039] According to some embodiments of the computerized system, the sample is a patterned (first) wafer.

[0040] According to some embodiments of the computerized system, the scan area is positioned along a slice extending through a first die of the wafer, and the displacement analysis module is further configured to generate calibration data for image frames respectively associated with other scan areas of the first die positioned along the slice.

[0041] According to some embodiments of the computerized system, the CTP of the scan area and at least one of the one or more other scan areas (i.e., at least one area) is determined taking into account one or more previously determined CTPs of previously scanned areas along the slice.

[0042] According to some embodiments of the computerized system, the displacement analysis module is further configured to perform initial operations including optimizing (i) the height of the image frame (along the slice, respectively, relative to the scan area) and (ii) the selection of the CTP to achieve the required accuracy at maximum or substantially maximum throughput.

[0043] According to some embodiments of the computerized system, the computerized system is configured to store the generated CTP and, optionally, a displacement mapping of the image frames related to previously scanned areas along the slice.

[0044] According to some embodiments of the computerized system, the computerized system is further configured to generate displacement mappings for additional image frames, each associated with an additional scan area along the slice, located on an additional die along the die row containing the first die. The displacement mappings for the first group of additional image frames can be generated directly based at least on calculated displacements of targets therein (i.e., in the image frames) relative to corresponding positions of the targets given by the reference data. The displacement mappings for the second group of image frames can be generated based at least on calculated displacements of targets in the image frames relative to calibrated positions of corresponding targets in the corresponding image frames, associated with scan areas on each previously scanned die (e.g., on an adjacent die) in the die row.

[0045] According to some embodiments of the computerized system, the previously scanned die is the most recently scanned die.

[0046] According to some embodiments of the computerized system, the displacement analysis module is further configured to generate calibration data associated with the scanned area of ​​the wafer for each slice, thereby generating calibration data for one or more die rows of the wafer.

[0047] According to some embodiments of the computerized system, the displacement analysis module is further configured to generate displacement mappings of additional areas of other dies along the die row in the slice containing the first die. For every predetermined number of dies along the die row, a displacement mapping of the image frame of the next die in the die row is generated directly from the reference data. For the remaining dies in the die row, the displacement mapping of the image frame of each one is determined based at least on calibration data of corresponding image frames in adjacent and previously scanned dies in the die row.

[0048] According to some embodiments of the computerized system, the displacement analysis module is further configured to interpolate or extrapolate the displacement mapping of the image frame based on or further taking into account calibration data of image frames associated with scan areas near the scan area associated with the image frame (if the image frame associated with one of the other scan areas along the slice or one of the additional scan areas along the slice is characterized by (i) an insufficient number of identifiable targets and / or (ii) an insufficient uniform distribution of identifiable targets, such that the required accuracy of the displacement mapping of the image frame is not achievable solely based on the displacement of the identifiable targets in the image frame).

[0049] According to some embodiments of the computerized system, the displacement analysis module is further configured to generate the displacement mapping at runtime as the wafer is being scanned. According to some such embodiments, the computerized system may be configured to receive (and generate the displacement mapping based on) scan data of the wafer in real time or near real time from a wafer inspection tool that scans the wafer. Alternatively, the computerized system may be configured to scan the wafer.

[0050] According to some embodiments of the computerized system, the imager of the computerized system has a FOV of at least about 100 pixels.

[0051] According to some embodiments of the computerized system, the imager of the computerized system has a FOV of at least about 1000 pixels.

[0052] According to some embodiments of the computerized system, the computerized system can be configured to generate the displacement mapping off-tool using stored scan data of the sample.

[0053] According to an aspect of some embodiments, there is provided a sample analysis system (eg, a wafer analysis system) that includes a computerized system for generating calibration data as described above.

[0054] According to some embodiments of the sample analysis system, the sample analysis system further includes: - a scanning device including an imager and configured to scan an area of ​​the sample. - processing and memory circuitry including a computerized system and a sample analysis module (e.g., a wafer analysis module), the sample analysis module configured to detect potential defects in one or more areas of the region taking into account displacement mapping of the one or more areas generated by the displacement analysis module of the computerized system;

[0055] According to some embodiments of the sample analysis system, the imager is or includes an optical-based imager.

[0056] According to some embodiments of the sample analysis system, the optically-based imager includes a large field of view scanning tool (ie, corresponding to at least 1000 pixels).

[0057] According to some embodiments of the sample analysis system, the imager includes a scanning electron microscope.

[0058] According to some embodiments of the sample analysis system, the processing and memory circuitry further includes an image processing module. - receiving image frame data of one or more areas imaged by the imager; - identifying resolvable targets within one or more zones; - configured to send image data of the identified targets to a displacement analysis module;

[0059] According to an aspect of some embodiments, there is provided a non-transitory computer-readable medium comprising instructions executable by a processing circuit of a system for generating calibration data usable for analyzing a sample. The instructions may include: - identifying a target within an image frame corresponding to a scanned area of ​​the sample; - calculating the displacement of the target relative to a target position given by or derived from reference data for the scan area; - determining, based at least on the calculated target displacement, values ​​of coordinate transformation parameters (CTP) relating coordinates of the image frame to coordinates of the scan area provided by or derived from the reference data; - configured to obtain, using at least the CTP, the displacement of a number of segments in the image frame, thereby generating a displacement mapping of the image frame or at least a part thereof.

[0060] According to an aspect of some embodiments, there is provided a wafer analysis method incorporating the above-described methods, which may be a process diagnostic task, which may be any of wafer inspection, metrology, and / or review.

[0061] As will be apparent to those skilled in the art, the techniques, systems, methods, and computer program products of the present disclosure are applicable not only to wafer analysis, but also to the analysis of photomasks and reticles used in semiconductor production, and therefore, the scope of the present disclosure is understood to encompass not only wafer analysis, but also the analysis of photomasks and reticles used in wafer production.

[0062] Particular embodiments of the present disclosure may include some, all, or none of the advantages discussed above. One or more other technical advantages will be readily apparent to those skilled in the art from the figures, descriptions, and claims contained herein. Furthermore, while certain advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages.

[0063] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure pertains. In case of conflict, the present patent specification, including definitions, shall prevail. As used herein, the indefinite articles "a" and "an" mean "at least one" or "one or more," unless the context clearly dictates otherwise.

[0064] Unless otherwise specifically stated, it will be understood that, as will be apparent from this disclosure, according to some embodiments, terms such as "processing," "calculating," "computing," "determining," "estimating," "evaluating," "measuring," etc. can refer to the actions and / or processes of a computer or computing system, or similar electronic computing device, that manipulate and / or transform data represented as physical (e.g., electronic) quantities in the registers and / or memory of the computing system into other data similarly represented as physical quantities in the memory, registers, or other such information storage, transmission, or display device of the computing system.

[0065] Embodiments of the present disclosure may include an apparatus for performing the operations herein. The apparatus may be specially constructed for the desired purposes, or may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored on a computer-readable storage medium such as, but not limited to, a floppy disk, an optical disk, a CD-ROM, any type of disk including a magneto-optical disk, a read-only memory (ROM), a random access memory (RAM), an electrically programmable read-only memory (EPROM), an electrically erasable and programmable read-only memory (EEPROM), a magnetic or optical card, or any other type of medium suitable for storing electronic instructions and capable of being coupled to a computer system bus.

[0066] The processes and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the desired method. The desired structure for a variety of these systems will be apparent from the description below. Additionally, embodiments of the present disclosure are not described with reference to any particular programming language. It will be understood that a variety of programming languages ​​can be used to implement the teachings of the present disclosure as described herein.

[0067] Aspects of the disclosure may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The disclosed embodiments may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media, including memory storage devices.

[0068] Some embodiments of the present disclosure are described herein with reference to the accompanying drawings. The description, together with the drawings, will make apparent to those skilled in the art how some embodiments can be practiced. The drawings are for illustrative purposes only, and no attempt is made to show structural details of the embodiments beyond those necessary for a basic understanding of the present disclosure. For clarity, some objects shown in the drawings are not to scale. Moreover, two different objects in the same drawing may be shown at different scales. In particular, the scale of some objects may be greatly exaggerated compared to other objects in the same drawing. [Brief explanation of the drawings]

[0069] [Figure 1A] 1A-1C are diagrams that schematically illustrate example displacement mapping, according to some embodiments. [Figure 1B] 1A-1C are diagrams illustrating schematic diagrams of dies of a wafer according to some embodiments. [Figure 2] FIG. 1 is a diagram that schematically illustrates a linear coordinate transformation associated with wafer analysis, according to some embodiments. [Figure 3A] FIG. 10 is a diagram illustrating an example coordinate transformation relating coordinates parameterizing an image frame associated with a scanned wafer area to coordinates parameterizing a reference data area corresponding to the wafer area, according to some embodiments. [Figure 3B] FIG. 10 is a diagram illustrating an example coordinate transformation relating coordinates parameterizing an image frame associated with a scanned wafer area to coordinates parameterizing a reference data area corresponding to the wafer area, according to some embodiments. [Figure 3C] FIG. 10 is a diagram illustrating an example coordinate transformation relating coordinates parameterizing an image frame associated with a scanned wafer area to coordinates parameterizing a reference data area corresponding to the wafer area, according to some embodiments. [Figure 3D] FIG. 10 is a diagram illustrating an example coordinate transformation relating coordinates parameterizing an image frame associated with a scanned wafer area to coordinates parameterizing a reference data area corresponding to the wafer area, according to some embodiments. [Figure 3E] FIG. 10 is a diagram illustrating an example coordinate transformation relating coordinates parameterizing an image frame associated with a scanned wafer area to coordinates parameterizing a reference data area corresponding to the wafer area, according to some embodiments. [Figure 3F] 3A-3E are graphical representations of displacement mappings resulting from the coordinate transformations of FIGS. 3A-3E, according to some embodiments. [Figure 4A] FIG. 1 is a block diagram of a computerized system for generating calibration data for wafer inspection, according to some embodiments. [Figure 4B] FIG. 4B is a block diagram of a displacement analysis module of the system of FIG. 4A according to some embodiments. [Figure 5A] 1A-1C are diagrams illustrating schematic image frames of a scan area of ​​a die of a (patterned) wafer, according to some embodiments. [Figure 5B] FIG. 5B is a schematic graphical representation of reference data corresponding to the image frame of FIG. 5A, according to some embodiments. [Figure 5C] FIG. 5B is a schematic graphical representation of reference data corresponding to the image frame of FIG. 5A, according to some embodiments. [Figure 5D] FIG. 5B is a diagram illustrating the image frame of FIG. 5A partitioned into segments, according to some embodiments. [Figure 5E] 5B and 5C, according to some embodiments. FIG. [Figure 6] 1A-1C are diagrams that schematically illustrate scanned slices extending through a die, according to some embodiments. [Figure 7] 1A-1C are diagrams that schematically illustrate adjacent slices along a die row of a wafer that are scanned in alternating directions, according to some embodiments. [Figure 8] 1 is a flow diagram of a coordinate transformation-based method for generating calibration data for wafer analysis, according to some embodiments. [Figure 9] 1 is a flow chart illustrating run-time calibration of system coordinates while scanning a wafer using the computerized systems and methods of the present disclosure, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0070] The principles, uses, and implementation of the teachings herein may be better understood with reference to the accompanying description and figures. Upon perusal of the description and figures presented herein, those skilled in the art will be able to practice the teachings herein without undue effort or experimentation. In the figures, like reference numerals refer to like parts throughout.

[0071] In the description and claims of this application, the words "include" and "have" and forms thereof are not limited to the members of the list with which the words may be associated.

[0072] As used herein, the term "substantially" can be used to specify that a first property, quantity, or parameter is close to or equal to a second or target property, quantity, or parameter. For example, a first object and a second object can be said to be of "substantially the same length" if the length of the first object is at least 80% (or other predefined threshold percentage) and not more than 120% (or other predefined threshold percentage) of the length of the second object. In particular, the first object and the second object being "substantially the same length" also includes the first object having the same length as the second object.

[0073] According to some embodiments, the target quantity can refer to an optimal parameter that, in principle, can be obtained using mathematical optimization software. Thus, for example, the value assumed by a parameter can be said to be "substantially equal" to the maximum possible value that the parameter can assume if the value of the parameter is equal to at least 80% (or some other predefined threshold percentage) of the maximum possible value. In particular, the value assumed by the parameter is also included in the description "substantially equal" to the maximum possible value that the parameter can assume if the value of the parameter is equal to the maximum possible value.

[0074] As used herein, the term "about" can be used to specify a quantity or parameter value (e.g., the length of an element) within a continuous range of values ​​near (and including) a given (specified) value. According to some embodiments, "about" can specify a parameter value between 80% and 120% of the given value. For example, stating that "the length of the element is equal to about 1 m" is equivalent to stating that "the length of the element is between 0.8 m and 1.2 m." According to some embodiments, "about" can specify a parameter value between 90% and 110% of the given value. According to some embodiments, "about" can specify a parameter value between 95% and 105% of the given value.

[0075] As used herein, according to some embodiments, the terms "substantially" and "about" may be interchangeable.

[0076] For ease of illustration, a three-dimensional Cartesian coordinate system (with orthogonal axes x, y, and z) is introduced in some of the figures. Note that the orientation of the coordinate system relative to the objects shown may change from one figure to the next. Furthermore, the symbol

number

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[0077] Referring to the figures, in the flow diagrams, optional operations may appear within boxes drawn with dashed lines. Introduction

[0078] Disclosed herein are systems and methods for generating (at runtime, as well as "off-tool") displacement mapping of a scanned area of ​​a wafer. According to some embodiments, the disclosed systems and methods aim to address temporal instabilities (e.g., due to the temporal physical effects and defects listed in the "Background") that adversely affect runtime wafer analysis. Ideally (i.e., in the absence of temporal instabilities), the data points (collected by the imaging device used to scan the wafer) would form a grid that is fixed in time. In contrast, temporal instabilities generally result in a grid (of collected data points) that is not fixed in time. The resulting uncertainty in the (position) coordinates of each grid point is on the order of tens or even hundreds of nanometers, thereby violating design criteria for advanced technology nodes.

[0079] As used herein, a computational task (e.g., generating a displacement mapping) may be said to be performed "off-tool" if it is performed after the completion of the scan from which the scan data (on which the computational task is processed) was obtained. Thus, a computational task performed on scan data of a sample is performed off-tool if it is performed after the scan of the sample from which the scan data was obtained.

[0080] FIG. 1A schematically illustrates an exemplary displacement mapping 10, according to some embodiments. An (image) frame 12 associated with a scanned wafer area (such as area 110a in FIG. 1B ) is shown. Frame 12 is shown partitioned (divided) into frame segments 14, as indicated by a dashed grid 16 superimposed on frame 12. Each of frame segments 14 may correspond to a single pixel. Additionally, a dash-dot grid 26 is superimposed on frame 12. Dashed-dot grid 26 is generated based on reference data (such as a CAD-based simulated image (not shown)) corresponding to the wafer area represented by frame 12. Dashed-dot grid 26 is partitioned into reference data (RD) segments 24. The reference data specifies the expected positions of the segments according to a default coordinate system that is available before the start of the scan.

[0081] It can be seen that grid 16 and grid 26 differ from one another due to physical effects and imperfections, as discussed above and in further detail below. Each of the RD segments 24 of dash-dotted grid 26 corresponds to a respective frame segment from frame segment 14. Superimposing (dashed) grid 26 on (dashed) grid 16 provides a graphical representation of the displacement of each of frame segments 14 relative to its respective reference datum. For example, the displacement of frame segment 14c relative to its reference datum location (indicated by RD segment 24c) is indicated by arrow 32c. Similarly, the displacement of frame segment 14d relative to its reference datum location (indicated by RD segment 24d) is indicated by arrow 32d. Notably, arrows 32c and 32d can be seen to differ from one another in both length and orientation, which reflects the sensitivity of the disclosed method and system to displacements and deformations of the scanned image (image frame) at the sub-pixel level.

[0082] Reference is now made to FIG. 1B, which also serves as an introduction to terminology. Depicted is a die 102a of a wafer 100 (only partially shown), such as a wafer used in the manufacture of integrated circuits and other microdevices. As used herein, unless otherwise specified, the term "wafer" will be used to refer to a "processed" or "patterned" wafer (including electronic circuits fabricated thereon). Wafer 100 includes multiple dies 102 (only die 102a is shown in full). Dies 102 may be arranged on the wafer in a die row (row of dies). Dies 102a are shown in the commonly implemented rectangular shape, but it will be understood that other shapes are applicable. Dies 102 may further include partial edge dies that reside at the circular wafer boundary. Similar to the term "wafer," unless otherwise specified, the term "die" will be used to refer to a small block of semiconductor material on which electronic circuits are fabricated.

[0083] Additionally, edge 104 of wafer 100 is shown in FIG. 1B.

[0084] Wafer 100 is configured to be cut ("diced") into separate dies. Each of the dies can contain copies of the same electronic circuitry, or some of the dies can each contain different electronic circuitry. It will be understood that the scope of the present disclosure encompasses both options.

[0085] Each row of dies (die rows) to be scanned is partitioned into adjacent (scan) slices 106, such as adjacent slices 106a and 106b extending (along the y-axis) through the die 102a. According to some embodiments, each of the slices 106 can have a width that corresponds to or substantially corresponds to the x-dimension of the field of view (FOV) of the imaging device. In other words, each of the slices 106 can represent a partial “coverage” of the wafer 100 by a respective scan path along the wafer 100. Note that while the slices 106 are shown as straight lines in FIG. 1B, the scan path is not limited to a straight line and can follow any curve, as desired, for example, in the case of a helical scan with an R-θ stage. According to some embodiments (not shown in FIG. 1B), adjacent slices can partially overlap to ensure complete (i.e., 100%) coverage of the die. Various areas 110 of the die 102a are shown. One of the areas 110, namely area 110a, is shown partitioned (divided) into segments 112. While segments 112 are shown as rectangles, it will be understood that other shapes are possible. Each of segments 112 may correspond to a group of adjacent pixels or even a single pixel in an image frame associated with area 110a, such as frame 12 in FIG. 1A.

[0086] Depending on the scanning strategy, the die may be partially or completely scanned. Furthermore, the die 102 may vary in size (due to design). In particular, according to some embodiments, dies along the same die row may vary in width. As a result, the width of a slice may vary along its length. More specifically, according to some embodiments, the imaging device may be configured to adjust (at runtime) the FOV of the imaging device according to the width of the die currently being scanned. Additionally, the spacing between dies on a wafer (e.g., wafer 100) may also vary. Depending on the scanning strategy, areas between the dies, such as area 120 in FIG. 1B, may also be scanned.

[0087] To achieve high throughput, a large FOV (e.g., on the order of thousands to tens of thousands of pixels) can be used to parallelize data acquisition and analysis. However, the larger the FOV, the greater the variation between the optical paths taken by light rays returning (e.g., reflected, scattered) from different locations (field points) on the wafer. In particular, the larger the FOV, the greater the variation in the optical path lengths taken by different rays, resulting in greater distortions to the image frame due to the temporal physical effects listed above.

[0088] Ensuring that these distortions are efficiently accounted for is a challenge; that is, ensuring that every segment (e.g., every pixel) of an image frame can be efficiently associated with the segment's reference data location (i.e., the location determined by the reference data). Additional related challenges arise when the image frame is not densely and / or uniformly filled with resolvable objects or does not contain a unique pattern. In particular, an image frame may include one or more non-resolvable sub-frames (that do not contain any resolvable objects), each of which may include, for example, hundreds of thousands or even millions of pixels.

[0089] To this end, the present disclosure teaches methods for obtaining a coordinate transformation that relates the coordinates of an image frame associated with a scanned wafer area to the coordinates of reference data that describe the wafer, and in particular the scanned wafer area. According to some embodiments, the coordinate transformation relates each pixel of the image frame to a corresponding reference data coordinate (e.g., in units of μm or nm), thereby enabling a displacement mapping to be obtained. The displacement mapping specifies the displacement of each pixel relative to its reference data position, thereby enabling the generation of calibration data with a resolution down to a single pixel (in the sense that the calculated displacement of a pixel can differ from each of the surrounding pixels).

[0090] A coordinate transformation, and consequently a displacement mapping, is generated based on the calculated displacement of the target in the image frame relative to the (identifiable) target's reference data position. Advantageously, the generated displacement mapping can also take into account sub-frames of the image frame that do not contain alignment targets, such as sub-frames consisting of unresolved arrays, low contrast features, saturated features, etc.

[0091] To specify a coordinate transformation, values ​​for the coordinate transformation parameters {C} must be provided. For example, a two-dimensional global translation (shift) can be specified by two values ​​representing translations along the x- and y-axes. The selection of a set of coordinate transformation parameters (CTP) can be based on prior knowledge of the architecture and temporal behavior of the analysis system and the wafer characteristics.

[0092] For a given set of CTPs (e.g., global displacements and rotations), a value of the CTP can be obtained based on the calculated target displacements (also called "displacement data"). More precisely, displacement data fitting can be utilized to obtain an (optimal) value of the CTP. According to some embodiments, high-precision displacement mapping can be achieved even when limited to linear coordinate transformations. As shown in FIG. 2, linear coordinate transformations include global shifts (e.g., along the x- and y-axes), linear scaling (along the x- and y-axes), fixed-angle skewing (with respect to the x- and y-axes), and rotations.

[0093] Global shift can result, for example, from inaccurate positioning of the wafer on the stage (the stage plane is assumed to be parallel to the xy plane). Linear scaling can result from changes in magnification or changes in scan speed. Assuming the stage is intended to be moved along the y axis, x skewing can result from a slight (angular) offset in the stage translation direction, or low frequency jitter (of the stage) parallel to the x axis. y skewing can result from wafer rotation, or low frequency jitter (of the stage) parallel to the y axis. Note that to first order, rotation and skewing are indistinguishable.

[0094] More generally, it should be appreciated that a set of CTPs can include transformation parameters that characterize correlations that persist across an image frame (ie, along its height and width).

[0095] 3A-3E schematically illustrate an exemplary coordinate transformation M relating coordinates of an image frame of a scanned wafer area to coordinates of a reference data area of ​​the wafer area. More specifically, FIG. 3A schematically illustrates a rectangular area A (marked with a dashed line) of a die of a wafer (such as area 110a of wafer 100) intended to be scanned. Additionally, targets T1, T2, T3, and T4 within area A are shown. The origin O of the coordinate system (i.e., the point whose coordinates are given by x=0 and y=0) is also shown.

[0096] For ease of illustration and to make the discussion more concrete, a constant x-skew without other physical effects and defects is assumed. Referring to FIG. 3B, the dashed arrow g represents the direction of actual movement of the stage on which the scanned wafer was positioned, thereby indicating the degree of skew. Due to the skew, area A will only be partially scanned. FIG. 3C schematically illustrates scan area S, which is the area that is actually scanned. Because the skew is constant across scan area S (i.e., does not change within the "acquisition" time of scan area S), scan area S has the shape of a parallelogram.

[0097] FIG. 3D shows an (image) frame I obtained from an imaging device and corresponding to a scan area S. Frame I is shown partitioned into pixels P. The horizontal and vertical axes of FIG. 3D are labeled u and v, respectively, to emphasize that frame coordinates may generally differ from wafer coordinates (i.e., x and y in FIG. 3B). Furthermore, the origin of the frame coordinate system

number

[0098] 3E shows a schematic representation of a "deformed" image I' corresponding to frame I when presented with respect to reference coordinates, or wafer coordinates, which in this example are the same thing. The deformed image I' can be obtained from frame I using coordinate transformation M (or its inverse, depending on how coordinate transformation M was defined).

[0099] Furthermore, pixel P in frame I A and P B , and the corresponding pixel P of the deformed image I'. A ' and P B ' is shown in Figure 3E.

[0100] As will be explained in detail below, the coordinate transformation M is obtained using a numerical fitting method based on the calculated displacements of the targets in frame I. Targets T1, T2, T3, and T4 shown in FIG. 3D are also shown in FIG. 3E to illustrate their displacements. More specifically, if the position of target T1 is given by vector (u1, v1) in FIG. 3D and the position of target T1 is given by vector (x1, y1) in FIG. 3E, the displacement of target T1 is given by the difference of the two vectors (u1-x1, v1-y1).

[0101] 3F is a schematic graphical depiction of the displacement mapping D resulting from the coordinate transformation M. More specifically, frame I is shown partitioned into pixels P. Within each of the pixels P is a respective arrow representing the direction and relative magnitude of the pixel's displacement with respect to the pixel's location in image I'.

[0102] 3A-3E, the width L of frame I (and of area A) can correspond to (i) the full width (i.e., x-dimension) of the FOV of the imaging device used to scan the wafer, or (ii) a fraction (i.e., a portion) of the width of the FOV. As described in more detail below, the height of frame I (and of area A) can be selected to achieve the required (or desired) accuracy of the displacement mapping D (e.g., so that the displacement of each pixel is determined to the required accuracy). system

[0103] According to an aspect of some embodiments, a computerized system is provided that generates calibration data usable for inspection of wafers, such as wafer 100. FIG. 4A presents a block diagram of such a computerized system, computerized system 400, according to some embodiments. According to some embodiments, system 400 may be combined with or connected to an inspection machine used to inspect wafers (e.g., during different stages of the wafer's production). According to some embodiments, system 400 may be integrated into an inspection system that incorporates some or all of the functionality and / or features described herein below. According to some embodiments, as shown in FIG. 4A, system 400 may be configured to additionally perform process diagnostic tasks, such as wafer inspection, metrology, and / or review.

[0104] The system 400 includes a processing circuit 402 including one or more processors, and a memory circuit 404 including one or more memories and operatively associated with the processing circuit 402. The processing circuit 402 includes at least a displacement analysis module 410. The displacement analysis module 410 is configured to determine the displacement of a segment in an image frame relative to a scanned wafer area.

[0105] As used herein, the term "processing and memory circuitry" can be used to refer together to a processing circuit and a memory circuit functionally associated with the processing circuit, such as processing circuitry 402 and memory circuitry 404.

[0106] More specifically, the displacement analysis module 410 is configured to determine values ​​of coordinate transformation parameters (CTP) that specify a coordinate transformation that relates a first set of coordinates to a second set of coordinates. The first set of coordinates may parameterize an image frame of the scanned wafer area. The second set of coordinates may parameterize a corresponding area specified by the wafer's reference data (possibly after scaling according to the latest system coordinates, as described below). The coordinate transformation is configured to account for temporal physical effects and defects that affect the wafer and setup during wafer scanning, as well as defects that may already be present in the wafer before the wafer is scanned (e.g., warpage due to induced stresses during production). As explained above, the physical effects and defects "appear" in the image frame. To remove the defects, the image frame is calibrated.

[0107] The memory circuit 404 can include non-volatile and volatile memory components. The memory circuit 404 can have stored therein instructions executable by the displacement analysis module 410 to determine the CTP value, as described above. According to some embodiments, the memory circuit 404 can be configured to function as a "tracking" database and temporarily store the CTP and, optionally, the displacement mapping of the image frame (generated by the displacement analysis module 410). In particular, the memory circuit 404 can be configured to temporarily store the displacement mapping of image areas that are densely populated with resolvable objects. The stored displacement mapping can be used to generate displacement mappings for adjacent image areas that are sparsely populated, as described below in the specification of FIG. 6.

[0108] According to some embodiments, processing circuitry 402 further includes an image processing module 414. According to some embodiments, processing circuitry 402 further includes a wafer analysis module 416. The functionality of image processing module 414 and wafer analysis module 416 is described below.

[0109] Each of the displacement analysis module 410, the image processing module 414, and the wafer analysis module 416 may be implemented by one or more processors. According to some embodiments, each of the one or more processors may be dedicated to the module and independent of the processors of the other modules. Alternatively, according to some embodiments, one or more of the processors may be "shared" by several of the modules. The above-listed modules may further include software and / or firmware processing modules.

[0110] According to some embodiments, the system 400 further includes a controller 420, a movable stage 422, and an imager 424 (e.g., an imaging device). The controller 420 is functionally associated with the stage 422, the imager 424, and the processing circuitry 402. More specifically, the controller 420 may be configured to control and synchronize the operation and functionality of the above-listed modules and components during scanning of a wafer. For example, the stage 422 may be configured to support an inspection sample, such as the wafer 100, and mechanically move the inspection sample along a scan path set by the controller 420, which may also control the imager 424. The stage 422 may include a multi-axis substage that allows the wafer to move along any scan path (including curved scan paths) imposed by the controller 420.

[0111] The imager 424 is configured to scan a wafer, such as wafer 100. The imager 424 may include scanning, imaging, and / or detection devices as known in the art of wafer analysis. More specifically, the imager 424 may include a light source for producing a light beam configured to impinge on the wafer and one or more sensors configured to detect light returned from the wafer. According to some embodiments, the produced light beam may be coherent, for example, if the light source is a laser. According to some embodiments, the light beam may be incoherent. According to some embodiments, the imager 424 may have a large FOV (e.g., on the order of thousands to tens of thousands of pixels). As used herein, according to some embodiments, a scanning tool such as the imager 424 is said to have a large FOV if the FOV corresponds to at least 1,000 pixels, 5,000 pixels, or 10,000 pixels. Each possibility corresponds to a separate embodiment. According to some embodiments, the imager 424 may be configured to produce multiple scanning spots, for example, using a diffractive optical element.

[0112] According to some embodiments, the operation of the imager 424 can be based on multi-spot scanning. Alternatively, according to some embodiments, the operation of the imager 424 can be based on flood illumination, in which case the imager 424 can include a one-dimensional or two-dimensional pixel array camera.

[0113] Additionally or alternatively, imager 424 may include a charged particle source for producing a beam of charged particles configured to impinge on the wafer and one or more sensors configured to detect charged particles deflected from the wafer. According to some embodiments, imager 424 may be or include a multi-beam and / or multi-channel charged particle imaging system. According to some embodiments, imager 424 includes a scanning electron microscope (SEM).

[0114] By way of example, to perform scanning, wafer 100 can be placed on a movable stage, such as stage 422. In such an embodiment, wafer 100 is moved by stage 422 during scanning of wafer 100. For example, stage 422 can move along one or more of the x-axis, y-axis, and z-axis as required by the analysis protocol and scanning strategy. (Here, x-axis and y-axis are defined to be parallel to the "axis" of wafer 100, and z-axis is defined to be perpendicular to wafer 100.) Additionally or alternatively, imager 424 can be repositioned to image different portions of wafer 100. Scanning can be based on scan instructions sent to imager 424 from a (scanning) strategy database 430.

[0115] According to some embodiments, prior to the start of a scan (of the wafer), e.g., during setup, an alignment module (e.g., in controller 420 or different therefrom) may be used to align wafer 100 on stage 422. According to some embodiments, alignment may be performed using anchor points from reference data.

[0116] The imager 424 is configured to transmit the scanned image data (image frame data) of the wafer 100 obtained thereby to the image processing module 414. The image processing module 414 is configured to identify predefined landmarks (which may be defined by a scanning strategy) within the image frames associated with the scanned wafer area, such as area 110a of the wafer 100. More specifically, according to some embodiments, the image processing module 414 may be configured to: (i) calculate the expected position of the landmark based on the latest system coordinates and the reference data position of the landmark; (ii) generate a cropped image of the landmark including surrounding margins; and (iii) send the cropped image to the displacement analysis module 410.

[0117] According to some embodiments, the image processing module 414 may be configured to enlarge the margins around the cropped image to ensure that the target object is actually located completely within the cropped image, the degree of enlargement being determined taking into account the level of inaccuracy in the latest system coordinates (i.e., the system's current coordinate system).

[0118] The displacement analysis module 410 is configured to receive reference data corresponding to the target images from the strategy database 430 and, if necessary, calibrate the reference data according to the latest system coordinates. In particular, the calibration may include scaling the reference data coordinates. The displacement analysis module 410 is further configured to (i) calculate a (maximum) matching score between the cropped image and the corresponding (possibly scaled) reference data using a pattern recognition method (e.g., image correlation), (ii) compare the matching score with a (predefined) threshold, and, if the matching score exceeds the threshold, (iii) calculate the displacement of each of the targets based on the cropped image of the target (and its position with respect to the latest system coordinates) received from the image processing module 414 and the corresponding reference data. Thus, a target can be considered "identified" if its calculated matching score is greater than the threshold.

[0119] According to some embodiments, during scanning, the displacement analysis module 410 can send calibration data to the controller 420 for run-time correction and / or adjustment of scanning parameters such as die row origin, scan path, etc. (beginning of scan, new slice), etc. In particular, the calibration data can be used to update system coordinates.

[0120] 4B, the displacement analysis module 410 may include a target displacement module 410a and a displacement mapping module 410b. The target displacement module 410a is configured to receive (cropped) images of targets in the scanned wafer area from the image processing module 414. The target displacement module 410a is further configured to receive reference data corresponding to the targets (e.g., from the strategy database 430). The target displacement module 410a uses the received images and reference data to calculate the displacement of the targets relative to the reference data position of the targets.

[0121] The displacement mapping module 410b is configured to receive the calculated target displacements from the target displacement module 410a. The displacement mapping module 410b is further configured to determine a value of the CTP based on the calculated target displacements. Based on the determined value of the CTP, the displacement mapping module 410b can generate a high (spatial) resolution displacement mapping.

[0122] As described below in the Methods subsection, the calibration data (related to the wafer) generated by system 400 can be used to improve detection of potential defects on the wafer. In particular, the greater localization accuracy provided by the calibration data allows analysis parameters, and more generally, analysis algorithms, to be better correlated to specific locations on the wafer. The calibration data can additionally be used to improve the reporting accuracy of the locations of detected defects. Furthermore, the calibration data can also be relevant to tasks other than defect detection, such as, for example, improving the positioning accuracy of a defect review tool or metrology tool, or another inspection device (e.g., an SEM or multi-beam inspection device) used to inspect the wafer.

[0123] Without limiting the scope of the present disclosure in any way, according to some embodiments, system 400 can be used in process diagnostic tasks. In particular, according to some embodiments, system 400 can be used in inspection tasks, in which a wafer, or one or more dies, are partially or completely scanned to detect potential defects. Additionally or alternatively, according to some embodiments, system 400 can be used for review tasks, in which it is determined whether a potential defect is a defect of interest. Review tasks generally require higher-resolution scanning compared to inspection tasks and therefore may utilize electron beam inspection. Such review tools typically inspect a small portion of the wafer at higher resolution (but with lower throughput).

[0124] Whenever the term "inspection" or its derivatives are used in this disclosure, it will be understood that the inspection referred to is not limited with respect to the resolution or size of the area inspected. In particular, it will be understood that, according to some embodiments, system 400 may be equally applicable to review tools and lower resolution wafer inspection tools. It will be understood that the same applies to the term "analysis," which, according to some embodiments, is used interchangeably with the term "inspection."

[0125] 5A schematically illustrates an (image) frame 500 of a scanned area of ​​a (patterned) die, such as area 110a, according to some embodiments. Frame 500 can include anywhere between thousands and hundreds of millions of pixels. According to some embodiments, the width of the scanned area can correspond to the full width of the FOV of imager 424. According to some embodiments, the width of the scanned area can correspond to a portion of the width of the FOV of imager 424.

[0126] FIG. 5B schematically illustrates a reference image corresponding to the scan area of ​​FIG. 5A , according to some embodiments. As is known in the art, a reference image can be derived from corresponding reference data, such as design data, by mathematically transforming the reference data to generate a graphical representation thereof. More specifically, FIG. 5B schematically illustrates a “reference data” (RD) area 500′ corresponding to frame 500. RD area 500′ is shown as “shrunken” along both the x-axis and the y-axis compared to frame 500. RD area 500′ can be generated using the corresponding reference data and updated system coordinates. The updated system coordinates specify a pixel width and pixel height estimated prior to the capture of frame 500.

[0127] The double arrow w and difference interval Δw indicate the contraction of the RD area 500′ along the x-axis. The double arrow h and difference interval Δh indicate the contraction of the RD area 500′ along the y-axis. While the frame 500 has been linearly expanded compared to the RD area 500′, it should be understood that this particular choice of deformation (between the frame 500 and the RD area 500′) is intended as a simple and straightforward example for ease of illustration and to make the discussion more concrete.

[0128] The term "reference data," as used herein, should be broadly interpreted to encompass any data indicative of the physical design of a (patterned) wafer and / or data derived from the physical design (e.g., by simulation, geometric and Boolean operations, etc.). According to some embodiments, the reference data for a wafer can include "design data" for the wafer, such as, for example, CAD data in various formats. The design data may be provided in various formats, such as GDSII format, OASIS format, etc.

[0129] According to some embodiments, wafer reference data can include data obtained by fully or partially scanning the wafer during recipe setup. Additionally, the first wafer manufactured for a particular design can be scanned during recipe setup, and the resulting scan data can be processed to generate reference data or additional reference data for subsequently manufactured wafers of the same design (as the first wafer). Such "self-generated" reference data is essential when design data is not available, but can also be beneficial even when design data is available.

[0130] According to some embodiments, reference data for the wafer can be used in combination with data acquired at runtime when generating a displacement mapping for an image frame. For example, scan data for one die or multiple dies with the same architecture during runtime can be used in generating a displacement mapping for another die with the same architecture, as described in more detail below.

[0131] Moreover, according to some embodiments, the calibration data generated for a scanned first area can be used in generating a displacement mapping for a scanned second area, particularly in embodiments where the second area is scanned shortly after (e.g., immediately after) the first area and is located near (e.g., adjacent to) the first area along the same slice. For example, the global shift and constant skewing values ​​determined for the first area can be used in generating the displacement mapping for the second area, thereby reducing the computational load required in generating the CTP for the second area (since the number of CTPs that need to be calculated is reduced).

[0132] More specifically, reference data or additional reference data (e.g., to be used in analyzing multiple wafers of a particular architecture) can be self-generated, for example, by partially or completely scanning one or more sample wafers from multiple sample wafers. Image processing tools can be applied to the resulting scanned data to discover (or find) unique patterns that are “easy” to identify (detect) within the respective surrounding search areas. The discovered unique patterns (or, more precisely, images and their exact locations) can be stored, for example, in the recipe database 430 for future use as reference data. As used herein, a pattern can be referred to as “unique” even if it is unique only along one axis (e.g., the x-axis or the y-axis). In particular, a pattern that exhibits uniqueness only along one axis (e.g., the x-axis) can still serve as reference data and be used for x-axis calibration.

[0133] According to some embodiments, the image processing module 414 and displacement analysis module 410 can be further configured to "self-generate" reference data (particularly to find alignment targets that are easy to identify), as described above, particularly when design data is not available.

[0134] According to some embodiments, the reference data may further include reference data associated with or derived from other types of wafers (i.e., of a different architecture than the wafer to be analyzed), but known to contain patterns in common with the wafer to be analyzed.

[0135] 5A, a number of frame targets 510 (i.e., targets imaged within frame 500) are shown schematically and within frame 500. Each of frame targets 510 is shown enclosed within a respective dotted box (e.g., of 32x32 pixels) from dotted box 512. For example, frame target 510a (from frame target 510) is enclosed within dotted box 512a. Each of frame targets 510 may include a pattern that is relatively easy to identify within its environment, for example, by image processing module 414 (using appropriate image processing algorithms).

[0136] Each of the frame targets 510 can be associated with a corresponding RD target (from the RD targets 510') in the RD zone 500'. The RD targets 510' are shown in Figures 5B and 5C surrounded by a dash-dotted box 512'. For example, the RD target 510a' (from the RD target 510') is surrounded by a dash-dotted box 512a'. Figure 5C schematically illustrates the RD zone 500' with a dotted box 512 (representing the location of the frame target 510) superimposed. The dotted box 512 superimposed on the RD zone 500' visually indicates the displacement of each of the frame targets 510 relative to the RD targets 510'.

[0137] By way of non-limiting example and for clarity, all of the frame targets 510 are shown as rectangular (i.e., the dotted box 512 is rectangular) and as being the same size. However, it will be understood that other options are possible. According to some embodiments, the frame targets may differ in height and / or width from one another. More generally, any shape constructed from pixels is, in principle, feasible.

[0138] The displacement analysis module 410 (e.g., target displacement module 410a) is configured to calculate the displacement of each of the frame targets 510 relative to the corresponding RD target (from RD target 510'). According to some embodiments, the displacement analysis module 410 can utilize image registration methods known in the art to calculate the displacement of each of the frame targets 510, e.g., frame target 510a, for example, by maximizing over the cross-correlation coefficient between frame target 510a and RD target 510a' (corresponding to frame target 510a).

[0139] The calculated displacement of a (frame) target indicates the displacement of the target relative to where the target "should have been" according to the reference data. In other words, the calculated displacement indicates the displacement of the target relative to where the target would have been in the absence of physical effects and defects.

[0140] It should be noted that in embodiments where the format of the scan data (e.g., the format of the image frame) and the format of the reference data are different, intermediate processing of at least one of the formats may be required before performing image registration.

[0141] Additional details and different ways in which the displacement analysis module 410 can perform image registration are described below in the description and methods subsection of FIG.

[0142] 5D , frame 500 is shown partitioned (divided) into frame segments 520 (i.e., sub-images of frame 500), as indicated by dashed grid 522. According to some embodiments, frame segments 520 may vary in size and / or shape to account for various image deformations. According to some embodiments, each of frame segments 520 may correspond to a pixel. According to some embodiments, at least some or all of the segments may correspond to a number of pixels, such that all pixels within a segment share the same size and shape, in which case partitioning of frame 500 into frame segments 520 may be performed by displacement analysis module 410.

[0143] The displacement analysis module 410 (e.g., displacement mapping module 410b) is further configured to generate a displacement mapping that specifies the displacement of each of the frame segments 520 (or at least a portion of the frame segments 520) based on the calculated displacement of the frame target 510. More specifically, the displacement analysis module 410 is configured to use the calculated displacement of the frame target 510 to derive a coordinate transformation that relates the coordinates (i.e., u and v) that parameterize the frame 500 to the coordinates (i.e., x and y) that parameterize the RD area 500′. In other words, the displacement analysis module 410 is configured to determine a value for each parameter C of the set of CTP{C} that parameterize the coordinate transformation.

[0144] As a non-limiting example intended to make the discussion more concrete, in Figures 5A-5D, u = (1 + α) · x and v = (1 + β) · y, where α > 0 and β > 0. Therefore, the coordinate transformation can be characterized by the values ​​of two parameters α and β (i.e., {C} = {α, β}). In particular, the scaling of the axes can be different (i.e., α ≠ β). That is, the pixel size along the wafer translation axis (i.e., y-axis) can be determined by the stage motion, while the pixel size along the other axis (i.e., x-axis) can be determined by the optical magnification.

[0145] It will be understood that, in general, either α or β may be negative. Setting both α and β as positive is purely to ensure that the signs of α and β correspond to expansion (rather than contraction), and is consistent with Figures 5A-5D. In modern wafer analysis systems, α and β are typically 10 -3 It may be less than.

[0146] Various methods by which the value of CTP can be obtained (e.g., fitting methods) are discussed in the Methods subsection.

[0147] FIG. 5E schematically illustrates displacement mapping corresponding to the coordinate transformation specified above, according to some embodiments. Frame segments 520 are indicated by dashed grids 522. Additionally, RD segments 520′ corresponding to frame segments 520 are shown. That is, each of RD segments 520′ can be obtained by applying a coordinate transformation from frame segment 520 to its corresponding segment. RD segments 520′ are indicated by dashed-dotted grids 522′. Portions of frame segments 520 are “filled” with a first pattern to make them easier to distinguish. Portions of RD segments 520′ are “filled” with a second pattern to make them easier to distinguish.

[0148] According to some embodiments, the location of a segment can be specified by the "centroid" coordinates of the segment. (i,j) (from frame segment 520) can be said to be located at the intersection of a first horizontal line (not shown) extending along the center of the ith row of frame segment 520 and a first vertical line (not shown) extending along the center of the jth column of frame segment 520. Similarly, RD segment 520' (k,l) The frame segment 520 (from the RD segment 520') can be said to be located at the intersection of a second horizontal line (not shown) extending along the center of the kth row of the RD segment 520' and a second vertical line (not shown) extending along the center of the lth column of the RD segment 520'. (i,j) (i.e., the displacement of the corresponding RD segment 520' (i,j) ) is the corresponding displacement of the "center of gravity", i.e., Δx i =u i -x i =α x i and Δy j =v j -y j =β·yj.

[0149] Displacement Arrow A (7,8) and A (10,14) are frame segments 520, respectively. (7,8) and 520 (10,14) Displacement arrow A indicates the displacement of (7,8) and A (10,14) Each of points from the "centre of gravity" of the corresponding RD segment to the "centre of gravity" of its corresponding (frame) segment.

[0150] FIG. 6 illustrates a die 602 (such as die 102a) according to some embodiments. Further illustrated is a slice 606 of the die 602, as well as an adjacent area 610 (such as area 110) along the length of the slice 606. The motion arrow m indicates the scan direction (i.e., the direction of movement of the stage 422). A close-up of area 610a shows its architecture and a target 630a therein. The system 400 is configured to generate a displacement mapping of an image frame associated with area 610 by implementing the process described above in the description of FIGS. 5A-5E.

[0151] Area 610b is also shown. According to some embodiments, a displacement mapping cannot be generated with the required accuracy from the image frame associated with area 610b. According to some embodiments, this may be due to an insufficient number of alignment targets included in area 610b, in the sense that there are too few alignment targets to generate a displacement mapping with the required accuracy. Additionally or alternatively, according to some embodiments, this may be due to the distribution of alignment targets in area 610b perhaps not being sufficiently uniform to generate a displacement mapping with the required accuracy (i.e., for the displacements of all frame segments to be determined with the required accuracy).

[0152] According to some embodiments, when generating the displacement mapping corresponding to area 610b, the displacement analysis module 410 can be configured to additionally take into account previously acquired calibration data (e.g., a set of CTPs) corresponding to areas in slice 606 that are positioned near area 610b. In other words, the displacement analysis module 410 can be configured to use extrapolation techniques based on calibration data from other areas along slice 606 when generating the displacement mapping corresponding to area 610b.

[0153] According to some embodiments, when generating a displacement mapping corresponding to area 610b, the displacement analysis module 410 can be configured to additionally take into account calibration data corresponding to all areas along slice 606 in the die 602 that were scanned before area 610b (or at least all areas from the image frame for which a displacement mapping can be generated with the required accuracy).

[0154] According to some embodiments, when generating the displacement mapping corresponding to area 610b, displacement analysis module 410 can be configured to additionally take into account calibration data corresponding to areas along slice 606 located on one or more previously scanned dies within the same die row.

[0155] According to some embodiments, the calibration data (or at least the CTP) corresponding to the scan area can be temporarily stored in the memory circuit 404 (e.g., in a volatile memory component thereof). The displacement analysis module 410 (more specifically, the displacement mapping module 410b) can be configured to request some or all of the stored CTP and / or displacement mapping from the memory circuit 404 when tasked with generating a displacement mapping corresponding to an area containing an insufficient number of alignment targets. According to some embodiments, the stored calibration data can be deleted from the memory circuit 404 when the stored calibration data is no longer useful for extrapolation and / or interpolation purposes. In particular, according to some embodiments, the stored CTP can be deleted after a period greater than the intrinsic timescale (coherence time) of the relevant temporal physical effects affecting the wafer or setup (and parameterized by the CTP).

[0156] Optionally, according to some embodiments, the generation of the displacement mapping for area 610b can be delayed to also take into account calibration data for areas along slice 606 that were scanned after area 610b (image frames from which a displacement mapping of the required accuracy can be generated). In other words, displacement analysis module 410 can be further configured to utilize interpolation techniques (based on calibration data from areas above and below area 610b along slice 606) when generating the displacement mapping for area 610b.

[0157] With further reference to Figure 7, during scanning of a die row of a wafer, the die row may be scanned slice by slice in alternating directions (e.g., from the "bottom" of the wafer to the "top" of the wafer and from top to bottom), as indicated by arrows u and d. In describing Figure 7, terms such as "top," "bottom," "up," "down," "right," and "left" should be understood with reference to directions "defined" by the page of the figure (i.e., the page that contains Figure 7). Thus, a first element may be said to be positioned above a second element if it is positioned closer to the top of the page compared to the second element.

[0158] As previously discussed, the displacement analysis module 410 is configured to determine a CTP value associated with a pair of sets of coordinates. The first set of coordinates in the pair can parameterize an image frame of the scanned wafer area (i.e., an image frame associated with the scanned wafer area), while the second set of coordinates can serve as a “reference.” According to some embodiments, the second set of coordinates (in the pair) can also parameterize a second image frame. The second image frame can be of a previously scanned wafer area (e.g., area 710”) that corresponds to the wafer area (e.g., area 710′) in the image frame parameterized by the first set of coordinates. In particular, the previously scanned wafer area (shown in the image frame parameterized by the second set of coordinates) can be located on a die (e.g., die 702”) adjacent to the die (e.g., die 702′) that includes the wafer area shown in the image frame parameterized by the first set of coordinates.

[0159] As an example, dies 702' and 702" are adjacent and located along slice 706 of die row 704 of wafer 700 (such as wafer 100). Dies 702' and 702" share the same architecture up to the defect. Slice 706 is shown scanned from top to bottom (as indicated by arrow d). Area 710' and area 710" are "corresponding" areas in the sense that they share the same architecture up to the defect. Area 710" is scanned before area 710'.

[0160] According to some embodiments, the coordinate transformation is determined by identifying a target in an image frame associated with area 710' and calculating its displacement relative to the position of the corresponding target in an image frame associated with area 710" (e.g., by maximizing over the correlation coefficients of the target images as described above). Based on the calculated target displacement, a value for CTP is determined. The CTP can then be used to obtain the displacement of a number of segments in the image frame associated with area 710' relative to their corresponding positions in the image frame associated with area 710", thereby generating a displacement mapping for the image frame associated with area 710'.

[0161] The resulting coordinate transformation is configured to account for both temporary and permanent physical effects and defects that manifest as variations between image frames associated with areas 710" and 710'. Thus, the image frame associated with area 710" is used to generate a displacement mapping corresponding to area 710'. Similarly, the image frame associated with area 710''' that corresponds to area 710" can be used to generate a displacement mapping corresponding to area 710". Area 710''' is located on die 702''' (on slice 706) adjacent to and positioned above die 702'' in die row 704.

[0162] Conversely, for slices scanned from the bottom to the top of die row 704, such as slice 706', which is the leftmost slice of die row 704, image frames associated with areas of die 702' can be used to generate displacement mapping associated with corresponding areas of die 702", and image frames associated with areas of die 702" are used to generate displacement mapping associated with corresponding areas of die 702'".

[0163] Finally, a coordinate transformation associated with a "first scan" area along a slice (i.e., an area in the bottom die if the slice is scanned bottom-up, or an area in the top die if the slice is scanned top-down) can relate coordinates that parameterize the image frame of the (first scan) area to coordinates that parameterize reference data (such as design data for the first scan area). For example, a CTP of first scan area 710t (corresponding to areas 710', 710" and 710'") in top die 702t of die row 704 can relate its image frame to its reference data.

[0164] According to some embodiments in which wafer analysis module 416 is or includes a defect detection module, wafer analysis module 416 can be configured to take into account the generated displacement mapping (related to the coordinates of the image frame of the corresponding area), for example, as part of a die-to-die (D2D) or cell-to-cell (C2C) defect detection protocol. Furthermore, wafer analysis module 416 can be configured to apply a specific defect detection algorithm to each sub-frame within the image frame according to the generated displacement mapping.

[0165] Alternatively, according to some embodiments, the displacement analysis module 410 can be configured to determine a set of CTPs that directly associates sets of coordinates of image frames of all corresponding areas along a slice (e.g., areas 710′, 710″, 710′″, and the rest of the corresponding areas along slice 706) to a common (and single) set of coordinates. The common set of coordinates can parameterize reference data (common to all areas as they correspond to each other), such as design data. The reference data can be stored in a recipe database, such as recipe database 430. According to some such embodiments in which the wafer analysis module 416 is or includes a defect detection module, the wafer analysis module 416 can be configured to take the displacement mapping (generated for the common set of coordinates) into account as part of a die-to-database (D2DB) defect detection protocol. Furthermore, the wafer analysis module 416 can be configured to apply a specific defect detection algorithm to each sub-frame within the image frame according to the generated displacement mapping.

[0166] Additionally, according to some embodiments, one or more of the CTPs associated with non-transient effects, such as a fixed offset in the stage translation direction, can be "carried over" from one scanned slice to the next scanned slice, thereby potentially improving accuracy.

[0167] According to some embodiments, the two above-mentioned approaches for generating displacement mapping (i.e., via die-to-die or cell-to-cell comparison, or via die-to-database comparison) can be combined. For example, according to some such embodiments, one CTP can associate coordinates that parameterize two image frames, both acquired at runtime, and another CTP can associate each image frame acquired at runtime (particularly of an area of ​​a middle die in a die row) with respective reference data, such as design data.

[0168] As a non-limiting example, the (first) distance between die 702′ and the bottom die 702b is assumed to be equal to the (second) distance between die 702″ (adjacent to die 702′) and the top die 702t. That is, the number of dies between die 702′ and the bottom die 702b is assumed to be equal to the number of dies between die 702″ and the top die 702t. Displacement mapping of image frames associated with areas of die 702′ and bottom die 702b along a slice scanned from bottom to top (e.g., slice 706′) can be generated using reference data, such as design data. Displacement mapping of image frames associated with areas of the remaining dies in die row 704 can be generated based on image alignment relative to corresponding image frames associated with previously scanned areas in one or more dies positioned below it (along these same slices (i.e., scanned from bottom to top)).

[0169] For example, the CTP of the image frame of the area of ​​die 702" can be generated based on image alignment to corresponding image frames of previously scanned areas of die 702' along the slice scanned from bottom to top. And the CTP of the image frame of the area of ​​die 702''' can be generated based on image alignment to corresponding image frames of previously scanned areas of die 702" along the slice scanned from bottom to top. Similarly, the CTP of the image frame of the area of ​​each die located between bottom die 702b and die 702' can be generated based on image alignment to corresponding image frames of previously scanned areas of each adjacent die located below it along the slice scanned from bottom to top.

[0170] Note that for each image frame associated with an area of ​​die 702', along a slice scanned from bottom to top, the displacement of the target (frame) is calculated relative to its position given by the reference data for the respective area (possibly after scaling the reference data based on the latest system coordinates). In contrast, for each image frame associated with an area of ​​die 702″, along a slice scanned from bottom to top, the displacement of the (frame) target is calculated relative to the calibrated position of the corresponding (frame) target in the image frame associated with the previously scanned area of ​​die 702′. Nevertheless, it is emphasized that not only in the former case but also in the latter case, the reference data is taken into account when calculating the target displacement (and, therefore, the displacement mapping), since the calibrated positions (for which the target displacement is calculated) (in the above example) are calculated (directly) based on the reference data (up to the scaling). Therefore, it can be said that the displacement mapping of the image frame associated with die 702″ (generated based on the calculated displacement of the (frame) target (in the image frame) relative to the calibrated position of the corresponding (frame) target in the corresponding image frame associated with die 702′) is derived from the reference data.

[0171] Similarly, the displacement mapping of the image frame associated with die 702''' (generated based on the calculated displacement of the (frame) target (in the image frame) relative to the calibrated position of the corresponding (frame) target in the corresponding image frame associated with die 702") can be said to be derived from the reference data, since the calibrated target position (for which the displacement of the target (in the image frame associated with die 702''') is calculated) is itself derived from the reference data, as described in the previous paragraph.

[0172] More generally, target displacements calculated relative to the calibrated positions of corresponding targets can be said to be derived from the reference data. Similarly, CTPs and displacement mappings generated based on target displacements calculated relative to the calibrated positions of corresponding targets can be said to be derived from the reference data.

[0173] In general, in any "chain" (i.e., sequence) of displacement mappings generated based on registering image frames relative to one another, the displacement mapping of the "first" image frame in the chain can be generated based on reference data. Thus, all displacement mappings can be said to be derived from the reference data. The displacement mapping of the first image can be said to be generated (obtained) directly from the reference data. The displacement mappings of the remaining frames can be said to be generated indirectly from the reference data, since calculations of inter-image registration are involved.

[0174] Continuing with FIG. 7 , displacement mapping of image frames associated with areas of die 702″ and top die 702t can be generated using reference data, such as design data, along slices scanned from top to bottom (e.g., slice 706). Displacement mapping of image frames associated with areas of the remaining dies in die row 704 can be generated based on image alignment (along these same slices (i.e., scanned from top to bottom)) relative to corresponding image frames associated with previously scanned areas of one or more dies above it.

[0175] For example, the CTP of an image frame associated with an area of ​​die 702′ can be generated based on image registration to corresponding image frames of each previously scanned area of ​​die 702″ along a slice scanned from top to bottom. Similarly, the CTP of an image frame of an area of ​​each die located between bottom die 702b and die 702″ can be generated based on image registration to corresponding image frames of previously scanned areas of each adjacent die located above it along a slice scanned from top to bottom.

[0176] It should be noted that the accuracy of the displacement mapping of an image frame generated based on a chain of displacement mappings (each of which is generated using calibration data of a corresponding and previously scanned area along a slice) may decrease with the length of the chain. On the other hand, direct generation of the displacement mapping from reference data may be relatively computationally expensive, given that die-to-die or cell-to-cell image alignment is performed by default (i.e., in any case) for defect detection when the displacement mapping is generated, for example, as part of a defect inspection protocol.

[0177] Thus, according to some embodiments, to balance the above considerations (while achieving the necessary or desired accuracy), for every predetermined number of dies, the displacement mapping of the image frame of the next die (to be scanned) can be generated directly from reference data (such as design data), while the displacement mapping of the image frames of the remaining dies can be generated based on image alignment relative to corresponding image frames from each previously (and potentially adjacent) scanned die. method

[0178] 8 shows a flow diagram of a computerized method 800 for generating calibration data usable for wafer analysis, according to some embodiments. Method 800 can be implemented using a system configured to generate calibration data usable for wafer analysis, such as system 400.

[0179] According to some embodiments, the method 800 includes the following operations. - operation 810, in which a (frame) target is identified in an image frame (e.g., frame 500) of a first area (e.g., area 110a) of a die of a wafer (e.g., wafer 100). The target can be identified using corresponding reference data. - operation 820, in which the displacement of the target (ie the image of the target in the image frame) relative to the corresponding target position given by or derived from the target reference data is calculated. - operation 830, in which CTP values ​​relating the coordinates of the image frame to the coordinates of the reference data are determined based at least on the target displacements calculated in operation 820; - operation 840, in which (at least) the determined value of the CTP is used to obtain the displacement of a number of segments (e.g. pixels) within the image frame, thereby generating a displacement mapping of the image frame or at least a part thereof. - Optional operation 850, where the CTP and, optionally, other obtained calibration data may be saved. - optional operation 860, in which operations 810 to 850 are repeated successively for additional areas (image frames), which may be located along slices extending through the die.

[0180] Operation 810 may be performed by an image processing module, such as image processing module 414 or similar. Each of operations 820, 830, and 840 may be performed by a displacement analysis module, such as displacement analysis module 410 or similar. In particular, according to some embodiments, operation 820 may be performed by a target displacement module, such as target displacement module 410a or similar. According to some such embodiments, operations 830 and 840 may be performed by a displacement mapping module, such as displacement mapping module 410b or similar.

[0181] Each of the targets to be identified in operation 810 may (i) constitute a unique pattern within its environment along one or both of the x-axis and y-axis, and (ii) exhibit high contrast along one or both of the x-axis and y-axis. The targets to be identified may be specified by a scanning strategy. The scanning strategy may include identification information for each of the targets. The identification information associated with the targets may be a cropped image of the target obtained during strategy setup, multiple representative cropped images of the target, a CAD-simulated image, or other parameterized values ​​of image pattern recognition properties that can be used for identification purposes. The identification information may be stored in a (scanning) strategy database, such as strategy database 430.

[0182] On the one hand, the more alignment targets utilized in operation 810, the better the induced noise suppression (i.e., the averaging-out of transient and / or local measurement noise) and thus the more accurate the CTP and displacement mapping determinations in operations 830 and 840, respectively. On the other hand, the more alignment targets utilized in operation 810, the greater the computational load and, as a result, the greater the scanning delays, which may result in lower throughput and / or the need for additional computational resources. Thus, according to some embodiments, if a die or one or more areas thereof is characterized by a high density of alignment targets, only a subset of the alignment targets may be utilized in operation 810 (as long as the subset is sufficient to achieve the required accuracy). The number and selection of alignment targets (to be used in operation 810) can be determined during strategy setup.

[0183] Prior to calculating the displacement, the reference data may be calibrated based on the latest system coordinates in operation 820. In particular, the reference data coordinates may be scaled according to the latest system coordinates.

[0184] According to some embodiments, in operation 820, the displacement of the target (i.e., the image of the target in the image frame) can be calculated with sub-pixel accuracy. For example, using image correlation techniques, a correlation coefficient between the image of the target and its reference image (obtained from reference data describing the target) can be calculated for each relative shift between the two images. The sub-pixel displacement can then be obtained by interpolating the correlation coefficients and taking the maximum value. If the format of the scan data is different from the format of the reference data, at least one of two intermediate processes may be required before calculating the correlation coefficient.

[0185] According to some embodiments, in operation 820, the displacements of the targets may be obtained by calculating the displacements of the targets relative to their respective positions specified by the reference data (possibly after scaling), in which case the displacements (and, consequently, the CTP and displacement mapping) may be said to be obtained directly from the reference data. According to some embodiments, the displacements of the targets may be obtained by calculating the displacements of the targets relative to the calibrated positions of the corresponding targets in the corresponding image frames, in which case the displacements (and, consequently, the CTP and displacement mapping) may be said to be obtained indirectly (or derived) from the reference data, as described above with respect to the chain of displacement mappings (in the description of FIG. 7).

[0186] In operation 830, extraction of CTPs {C} from the calculated target displacements can be performed using fitting methods (optimization algorithms) known in the art, such as least-squares regression, the Nelder-Mead Downhill Simplex method, etc., which minimize the difference between the calculated target displacements and the corresponding displacements specified by the "trial" coordinate transformation. In this regard, it should be noted that fast fitting methods have the advantage of not reducing inspection tool throughput. Before analyzing a new type of wafer (e.g., with a different die geometry and a different pattern type), a different set of CTPs can be selected to optimize calculation time while meeting accuracy requirements. (Generally, accuracy requirements reflect the complexity and intricacy of the wafer's patterns.) The objective is generally to arrive at a minimum set of critical CTPs whose associated errors are within the required accuracy.

[0187] According to some embodiments, the CTP corresponds to a linear coordinate transformation of the form: x→u=T x +S x (xx c )+Φ x ·y y→v=T y +S y (yy c)+Φ y x

[0188] where T x and T y parameterize the global translation along the x-axis and y-axis, respectively, and S x and S y parameterize the linear scaling along the x and y axes, respectively, and Φ x and Φ y parameterize the x-skewing and y-skewing, respectively. x and Φ y Since is constant (i.e., independent of coordinates within the image area), the skewing described by the above coordinate transformation is uniform (at a fixed angle). Rotations about an axis parallel to the z axis, when limited to sufficiently small angles (i.e., limited to first order in x and y), can be expressed as Φ x and / or Φ y Therefore, the rotation coefficients do not appear in the above equations. The coordinates x and y are reference coordinates, i.e., they parameterize the RD area corresponding to the image frame, while the coordinates u and v parameterize the image frame. c and y c labels the center of the RD region.

[0189] It should be noted that the choice of CTP may depend on the dimensions (e.g., height) of the image frame for which the displacement mapping is to be generated. More specifically, the larger the image frame dimensions, the more complex the coordinate transformation (relating the displacement of a frame segment to its reference data position) may be, and as a result, the number of CTPs required to achieve the required (or desired) accuracy may increase proportionately.

[0190] The size of the segments can be determined depending on the desired (spatial) resolution of the image frame. Each segment can contain multiple pixels. If maximum resolution is required, each segment will correspond to a single pixel. According to some embodiments, the lower the required resolution, the less accurate the displacement mapping needs to be, which means that relatively fewer calculations of target displacements can be performed and / or fewer CTPs can be utilized in generating the displacement mapping.

[0191] According to some embodiments, the set of CTPs can include additional parameters (beyond the six listed in the above formula). In particular, according to some embodiments, the set of CTPs can include any parameter related to continuous transformations, which can contribute when considering the displacement of a segment across an image frame relative to the segment's reference data position. According to some embodiments, the importance of a particular CTP can be evaluated using experimental design or other methods, such as machine learning-based methods, to further reduce residuals. The option of incorporating additional parameters to meet accuracy requirements or further reduce residuals reflects the flexibility of the disclosed method.

[0192] According to some embodiments, the width of the image frame corresponds to or is included in the FOV of an imager, such as imager 424. In particular, the width of the image frame can correspond to only a portion of the FOV of the imager. That is, the image frame can depict a scan area that is smaller in width than the width of the scan slice in which the scan area is included. According to some embodiments, each segment of the image frame corresponds to a single pixel.

[0193] According to some embodiments, in operation 860, for a given m, where m is an integer greater than 1, the mth iteration may be performed on the (m+1)th area adjacent to the mth area on which the (m-1)th iteration was performed. According to some embodiments, at least some of the areas in operation 860 may overlap.

[0194] For example, according to some embodiments, where method 800 includes operation 860, method 800 may further include an operation of determining in advance the number of image frames associated with the die slices to meet desired criteria (e.g., the required accuracy of the displacement mapping). Fixing the number of image frames is equivalent to determining the height of the image frames. As described above, the higher the required accuracy, the greater the number of CTPs that may be required to generate the displacement mapping with the required accuracy. In particular, higher accuracy may require taking into account additional CTPs characterized by short coherence times, which may result in a limited image frame height (so that the correlation exhibited by the additional CTPs persists across the entire y-dimension of each image frame). According to some embodiments, the image frame height, together with the selection of CTPs, may be optimized to achieve the required accuracy of the displacement mapping with maximum throughput.

[0195] The method 800 can be repeated for additional slices to scan one or more regions of the wafer or to scan the entire wafer.

[0196] According to an aspect of some embodiments, the method 800 may be performed as part of a process diagnostic task, such as wafer inspection, metrology, and / or review.

[0197] According to an aspect of some embodiments, a wafer analysis method is provided. The wafer analysis method may include, for example, determining the presence of potential defects on the wafer or reviewing the potential defects in a provided list of potential defects. The wafer analysis method is performed taking into account the calibration data generated by method 800. In other words, the method includes method 800. The method may be implemented using a system such as system 400. In particular, generating the calibration data from the acquired scan data may be performed using a displacement analysis module such as displacement analysis module 410 (as well as an image processing module such as image processing module 414). The analysis may be performed using a wafer analysis module such as wafer analysis module 416.

[0198] It should be noted that the disclosed method can be applied at any stage of the wafer manufacturing process where an imager can recognize a pattern on the wafer.

[0199] 9 presents a flow diagram 900 illustrating the calibration (i.e., updating) of system coordinates (i.e., the coordinate system of the system) during a scan of a wafer performed using a system such as system 400 according to method 800, in accordance with some embodiments. At the start of a scan of a wafer or one or more regions thereof, a default coordinate system 902 is utilized that serves as the initial coordinate system for the wafer. The default coordinate system 902 may be stored in a database 906, such as recipe database 430.

[0200] The default coordinate system 902 may be sent to an alignment module of the system, which, in operation 910, may use the default coordinate system 902 to align the wafer with respect to the axes of the stage on which it is placed (e.g., stage 422) (so that the die row is parallel to the direction of stage translation during scanning). By modifying the default coordinate system 902 to take into account the alignment of the wafer, updated system coordinates 914 are generated. The system coordinates 914 are iteratively updated during the scanning of the wafer, as described below.

[0201] Before starting the scan, in operation 918, mechanical scan parameters (defined by the scan strategy and initially specified relative to the default coordinate system 902) may be adjusted according to the latest (i.e., current) system coordinates 914. The mechanical scan parameters may, for example, specify the scan path. More generally, operation 918 is performed repeatedly at the start of the scan for each slice, as described in more detail below.

[0202] Scanning each slice can be performed as described above in the description of method 800 and FIG. 6 . For each resolvable captured (image) frame, a target displacement 922 is calculated. According to some embodiments, the target displacement 922 can be calculated in a processing circuit, such as processing circuit 402, using reference data from database 906. That is, by calculating the displacement of each identified target (e.g., frame target 510a) in the captured frame relative to the target's position specified by the reference data (e.g., RD ​​target 510a′) and the latest system coordinates 914. In particular, the RD area (e.g., RD ​​area 500′) corresponding to the captured frame (e.g., image frame 500) can be located and aligned with respect to the latest system coordinates 914. The targets can be identified in an image processing module, such as image processing module 414. The target displacement 922 can be calculated in a displacement analysis module, such as displacement analysis module 410, or more precisely, in a target displacement module, such as target displacement module 410a.

[0203] According to some alternative embodiments, for a given captured frame of the last scanned area, at least a portion of the target displacement 922 may be calculated based on the (corresponding) calibrated frame of the previously scanned area. The previously scanned area may be of the same design as the last scanned area. In particular, according to some embodiments, the previously scanned area may be located along the same slice as the last scanned area, but on a die adjacent to the die containing the last scanned area.

[0204] The target displacement 922 is then utilized to calculate a CTP 926 using a displacement analysis module such as displacement analysis module 410, or more precisely, using a displacement mapping module such as displacement mapping module 410b. The CTP 926 is then utilized to generate a displacement mapping 930 of the captured frame.

[0205] The CTPs 926 and / or displacement mapping 930 can be used to update the system coordinates 914. According to some embodiments, the updates can include short-term corrections 934 to the system coordinates 914. The short-term corrections 934 to the system coordinates 914 are temporary and are used to account for transient physical effects affecting the wafer and / or the setup (e.g., the stage 422 and / or the imager 424). For example, one or more CTPs from the CTPs 926 (characterized by (i) being determined for the last captured frame (or multiple most recently captured frames) and (ii) being associated with one or more physical effects with a sufficiently long coherence time to affect the next frame or frames to be captured) can be used to temporarily update the system coordinates 914. The transient updates associated with each such CTP can be “released” (i.e., removed) after a period longer than the respective coherence time has elapsed. These CTPs can then be recalculated based on the most recent scan data (i.e., scan data associated with the most recently captured frame, e.g., the last captured frame).

[0206] When the scanning of a slice is completed, before starting the scanning of the next slice, operation 918 can be repeated to take into account long-term physical effects and defects affecting the wafer and / or the setup that were detected during the scanning of the last scanned slice. More generally, assessments of previously detected long-term physical effects can be improved during the scanning of a slice. These updated assessments can be used in operation 918 to adjust the mechanical scanning parameters before starting the scanning of the next slice.

[0207] The calibration data and corresponding scan data generated at each stage of the scan can be sent to database 906. For each resolvable captured frame, its associated CTP 926 can be sent to database 906. The calibration data can be subjected to long-term analysis (i.e., not run-time) to improve the scanning strategy and / or modify the default coordinate system 902, potentially resulting in faster defect coordinate calculation speeds.

[0208] As used herein, according to some embodiments, the term "sample" encompasses patterned wafers, optical photomasks, and reticles with respect to objects to be analyzed using the methods and / or systems of the present disclosure.

[0209] As used herein, according to some embodiments, the term "calibration data" may include, with respect to an image frame, calculated CTP and / or generated displacement mapping associated with the image frame. According to some embodiments, calibration data obtained during scanning may be used as reference data in subsequent stages of scanning.

[0210] As used herein, according to some embodiments, the terms "frame" and "image frame" may be used interchangeably.

[0211] As used herein, according to some embodiments, the term "frame target," when referring to an image frame, will be understood to refer to a sub-frame of the image frame, where the sub-frame of the image frame shows a sub-area of ​​the wafer area corresponding to the image frame, and the sub-frame of the image frame shows image pattern recognition characteristics (i.e., high contrast edges, pattern uniqueness, etc.) that are desirable in the alignment target.

[0212] As used herein, according to some embodiments, the term "target" when used in reference to a scanned image (e.g., an image frame) can be used to refer to an image of a target. In particular, according to some embodiments, when used in reference to an image frame, the terms "target" and "frame target" can be used interchangeably.

[0213] As used herein, according to some embodiments, the terms "coordinate transformation" and "coordinate mapping" may be used interchangeably.

[0214] As used herein, according to some embodiments, the terms "identifiable target" and "alignment target" may be used interchangeably.

[0215] As used herein, according to some embodiments, an image area (e.g., a sub-frame of an image frame) may be referred to as "resolvable" when it contains (an image of) at least one resolvable object. Similarly, according to some embodiments, an image area may be referred to as "non-resolvable" when it does not contain (an image of) a resolvable object.

[0216] Although this disclosure focuses on wafer scanning and inspection, it will be apparent to those skilled in the art that the disclosed systems and methods are also applicable to optical photomasks and reticles used in wafer manufacturing.

[0217] It should be understood that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination, or as appropriate, in other described embodiments of the present disclosure. A feature described in the context of one embodiment should not be considered an essential feature of that embodiment, unless expressly designated as such.

[0218] Although the operations of methods according to some embodiments may be described in a particular order, the methods of the present disclosure may include performing some or all of the described operations in a different order. The methods of the present disclosure may include some of the described operations or all of the described operations. No particular operation in a disclosed method should be considered an essential operation of the method unless expressly designated as such.

[0219] While the present disclosure has been described in connection with specific embodiments thereof, it is apparent that numerous alternatives, modifications, and variations may exist that will be apparent to those skilled in the art. Consequently, the present disclosure encompasses all such alternatives, modifications, and variations that fall within the scope of the appended claims. It is to be understood that the present disclosure is not necessarily limited in its application to the details of construction and arrangement of the components and / or methods described herein. Other embodiments may be practiced, and an embodiment may be carried out in various ways.

[0220] The phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. Citation or identification of a reference in this application shall not be construed as an admission that such reference is available as prior art to the present disclosure. Section headings are used herein to facilitate understanding of the specification and should not be construed as necessarily limiting. [Explanation of symbols]

[0221] 10 Displacement Mapping 12 frames 14 Frame Segments 14c Frame Segment 14d Frame Segment 16 dashed grid 24 Reference Data (RD) segments 24c RD segment 24d RD segment 26 Dash-dotted grid 32c Arrow 32d arrow 100 wafers 102 Die 102a Die 104 Edge 106 slices 106a slice 106b slice 110 areas 110a area 112 segments 120 areas 400 Computerized Systems, Systems 402 Processing Circuit 404 Memory Circuit 410 Quantile Analysis Module 410a Target Displacement Module 410b Displacement Mapping Module 414 Image Processing Module 416 Wafer Analysis Module 420 Controller 422 Movable stage, stage 424 Imager 430 Policy Database 500 frames, image frames 500' RD area 510 Frame Target 510' RD target 510a Frame Target 510a' RD target 512 dotted box 512' dashed-dotted box 512a Dotted Box 512a' dash-dotted box 520 frame segments 520 (i、j) Frame Segment 520 (7,8) Frame Segment 520 (10,14) Frame Segment 520' RD segment 520' (i,j) RD segment 522 dashed grid 522' dashed-dotted grid 602 Die 606 slices 610 Adjacent Areas 610a area 610b area 630a Target 700 wafers 702' Die 702" die 702'' die 702t Upper die 702b Bottom Die 704 Die Row 706 slices 706' slice 710' area 710” area 710''' area 710t First Scan Area 900 Flowchart 902 Default Coordinate System 906 Database 910 operation 914 System Coordinates 918 operations 922 Target Displacement 926 CTP 930 Displacement Mapping 934 Short-Term Fix A (7,8) Displacement Arrows A (10,14) Displacement Arrows

Claims

1. 1. A computer-implemented method for generating calibration data usable for analyzing a sample, the method comprising: Identifying a target within an image frame associated with a scanned area of ​​the sample; calculating a displacement of the target relative to a position of the target given by or derived from reference data for the scan area; determining, based at least on the calculated target displacement, values ​​of coordinate transformation parameters (CTP) relating coordinates of the image frame to coordinates of the scan area provided by or derived from the reference data; obtaining displacements of multiple segments within the image frame using at least the CTP, thereby generating a displacement mapping of the image frame or at least a portion thereof; Including, A method wherein at least some of the segments have a size of a pixel.

2. The method of claim 1 , wherein the CTP comprises at least three independent parameters.

3. The method of claim 2 , wherein each of the at least three independent parameters characterizes a respective correlation that persists across the image frames.

4. The method of claim 2 , wherein the CTP includes one or more of parameters characterizing a global shift, a linear scaling, a fixed angle skewing, and a rotation.

5. 2. The method of claim 1, wherein the reference data comprises one or more of design data, CTP and / or displacement mapping generated from scan data of the sample obtained during strategy development, and data obtained from scanning another sample of the same design or containing architectural features similar to features within the scan area.

6. The method of claim 1 , wherein prior to calculating the displacement of the target, the reference data is calibrated based on current system coordinates generated taking into account previously acquired scan data.

7. The method of claim 1 , wherein the sample is a patterned wafer.

8. 8. The method of claim 7, wherein the scan area is located along a slice extending through a first die of the wafer, and the method further comprises repeating it for other scan areas of the first die located along the slice.

9. 9. The method of claim 8, wherein the CTP of at least one of the scan area and the other scan area is determined taking into account one or more previously determined CTPs of previously scanned areas along the slice.

10. 9. The method of claim 8, further comprising an initial operation comprising optimizing (i) the height of the image frame along the slice, respectively associated with the scan area, and (ii) the selection of the CTP, to achieve the required accuracy at maximum or substantially maximum throughput.

11. generating displacement mappings for additional image frames respectively associated with additional scan areas along the slice, the additional image frames being positioned on additional dies along the die row including the first die, wherein the displacement mappings for the first group of additional image frames are generated directly based at least on calculated displacements of targets in the additional image frames relative to corresponding positions of the targets provided by reference data; 9. The method of claim 8, wherein the displacement mapping of the second group of image frames is generated based at least on calculated displacements of targets in the image frames relative to calibrated positions of corresponding targets in the corresponding image frames associated with the scan area of ​​each previously scanned die in the die row.

12. The method of claim 11 , wherein the previously scanned die is the most recently scanned die.

13. 12. The method of claim 11, wherein the method is repeated for each slice, thereby generating calibration data for one or more die rows of the wafer.

14. 9. The method of claim 8, wherein if an image frame associated with one of the other scan areas along the slice is characterized by an insufficient number of identifiable targets and / or an insufficiently uniform distribution of identifiable targets, such that the required accuracy of the displacement mapping of the image frame is not achievable solely based on the displacement of identifiable targets in the image frame, the displacement mapping of the image frame is interpolated or extrapolated based on or further taking into account calibration data of image frames associated with scan areas near the scan area associated with the image frame.

15. The method of claim 1 , further comprising scanning the sample and generating the calibration data at run-time as the sample is being scanned.

16. 1. A computerized system for generating calibration data usable for analyzing a sample, the system including a displacement analysis module, the displacement analysis module comprising: calculating a displacement of the target identified in one or more image frames corresponding to one or more areas of the sample, respectively, relative to a target position given by or derived from reference data for the one or more areas; determining, based at least on the calculated target displacements, values ​​of coordinate transformation parameters (CTPs) relating coordinates of the one or more image frames to coordinates of scan areas provided by or derived from the reference data of the one or more areas, respectively; using at least the CTP to determine displacements of multiple segments within the one or more image frames, thereby generating one or more displacement mappings of the one or more image frames or at least one or more portions thereof; It is configured as follows: A computerized system wherein at least some of the segments have a size of a pixel.

17. a scanning device including an imager and configured to scan an area of ​​the sample; 17. A processing and memory circuit comprising the computerized system of claim 16 and a sample analysis module configured to detect potential defects in one or more zones of the region taking into account displacement mapping of the one or more zones generated by the displacement analysis module of the computerized system. A sample analysis system comprising:

18. 20. The sample analysis system of claim 17, wherein the imager comprises an optically based imager, optionally wherein the imager comprises a large field of view scanning tool, and / or wherein the imager comprises a scanning electron microscope.

19. 1. A non-transitory computer-readable medium containing instructions executable by a processing circuit of a system for generating calibration data usable for analyzing a sample, the instructions providing the system with: identifying targets in image frames corresponding to scanned areas of the sample; calculating a displacement of the target relative to a position of the target given by or derived from reference data for the scan area; determining, based at least on the calculated target displacement, values ​​of coordinate transformation parameters (CTP) relating coordinates of the image frame to coordinates of the scan area provided by or derived from the reference data; obtaining displacements of multiple segments within the image frame using at least the CTP, thereby generating a displacement mapping of the image frame or at least a portion thereof; It is configured as follows: A non-transitory computer-readable medium, wherein at least some of the segments have a size of a pixel.

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