Image generation for inspection of semiconductor samples

Abstract

The present application discloses image generation for inspecting semiconductor samples. A system and method for inspecting semiconductor samples are provided, including: obtaining a frame sequence of a region of the sample, the frame sequence being acquired by an electron beam tool configured to scan the region from multiple directions, the sequence comprising multiple frame groups, each group of frames being acquired from a corresponding direction; and registering the multiple frame groups, and generating an image of the sample based on the result of the registration, including: for each direction, performing a first registration between the frame groups acquired from the direction, and combining the registered frame groups to generate a first composite frame, thereby generating multiple first composite frames corresponding to the multiple directions respectively; and performing a second registration between the multiple first composite frames, and combining the registered multiple first composite frames to generate the image of the sample.

Description

Technical Field

[0001] The presently disclosed subject matter relates generally to the field of inspecting semiconductor samples, and more particularly, to the generation of images that can be used to inspect semiconductor samples. Background Art

[0002] The current demand for high density and high performance associated with ultra-large scale integration of manufacturing devices requires sub-micron features, increased transistor and circuit speeds, and improved reliability. As semiconductor processes advance, pattern dimensions such as line widths and other types of critical dimensions continue to shrink. Such demands require the formation of device features with high accuracy and consistency, which in turn necessitates careful monitoring of the manufacturing process, including automated inspection of the device while it is still in semiconductor wafer form.

[0003] Inspection can be provided by nondestructive inspection tools during or after the manufacture of the sample to be inspected. Inspection generally involves generating some output (e.g., image, signal, etc.) for the sample by directing light or electrons toward a wafer and detecting light or electrons from the wafer. Various nondestructive inspection tools include, by way of non-limiting example, scanning electron microscopes, atomic force microscopes, optical inspection tools, and the like.

[0004] The inspection process may include multiple inspection steps. During the manufacturing process, the inspection steps may be performed multiple times, for example after the manufacture or processing of certain layers, etc. Additionally or alternatively, each inspection step may be repeated multiple times, for example for different wafer positions, or for the same wafer position with different inspection settings.

[0005] Inspection processes are used at various steps during semiconductor manufacturing to detect and classify defects on samples and to perform metrology-related operations. The effectiveness of inspection can be improved by automating the process(es), such as defect detection, automatic defect classification (ADC), automatic defect review (ADR), automated metrology-related operations, and the like. Summary of the invention

[0006] According to certain aspects of the subject matter of the present disclosure, a computerized system for inspecting a semiconductor sample is provided, the system including a processing and memory circuit (PMC), the processing and memory circuit (PMC) being configured to: obtain a frame sequence of an area of ​​the semiconductor sample, the frame sequence being acquired by an electron beam tool configured to scan the area from multiple directions, the frame sequence including multiple groups of frames, wherein each group of frames is acquired from a corresponding direction; and align the multiple groups of frames, and generate an image of the semiconductor sample based on a result of the alignment, including: in response to a determination to perform a first alignment between the groups of frames acquired from each direction, for each direction, performing a first alignment between the groups of frames acquired from the direction and combining the aligned groups of frames to generate a first composite frame, thereby producing multiple first composite frames corresponding to the multiple directions respectively; and performing a second alignment between the multiple first composite frames, and combining the multiple aligned first composite frames to generate an image of the area of ​​the semiconductor sample; wherein the generated image has reduced image artifacts with respect to a frame scanned from a given direction in the multiple directions, and wherein the image can be used to inspect the semiconductor sample.

[0007] In addition to the above features, the system according to this aspect of the disclosed subject matter may include one or more of the following listed features (i) to (xii), in any desired combination or arrangement technically possible:

[0008] (i). Aligning multiple groups of frames and generating an image of the semiconductor sample may further include, in response to a determination not to perform the first registration, combining, for each direction, a group of frames acquired from the direction to generate a second composite frame, thereby producing a plurality of second composite frames corresponding to the plurality of directions, respectively; and performing a second registration between the plurality of second composite frames, and combining the registered plurality of second composite frames to generate an image of the semiconductor sample.

[0009] (ii). The system may further include an electron beam tool.

[0010] (iii). A frame sequence can be obtained by continuously scanning an area from multiple directions and acquiring one or more frames from each direction during each scan.

[0011] (iv). The electron beam tool may be configured to compensate at least part of the offset between frames acquired from different directions by adjusting the synchronization between the scanning process and the imaging process of the electron beam tool.

[0012] (v). The determination may be based on at least one of the following factors: the number of frames included in the frame group and the layer and / or material of the sample to be inspected.

[0013] (vi). A first registration may be performed to correct for drift between the sets of frames acquired from each direction caused by one or more physical effects between the electron beam of the electron beam tool and the semiconductor sample.

[0014] (vii). The one or more physical effects may be selected from the group consisting of thermal expansion, charging effects and tool tolerances.

[0015] (viii). The first registration may include performing image matching between the frame groups using a normalized cross-correlation function.

[0016] (ix). The search range used for the current frame during image matching may be based on at least one previous drift identified in at least one preceding frame of the current frame.

[0017] (x). A second registration may be performed to correct for shifts between the plurality of first composite frames caused by scanning the region from a plurality of directions.

[0018] (xi). The search direction used for the current frame during image matching performed in the second registration may be based on the scanning direction when the current frame was acquired.

[0019] (xii). The multiple directions may include two or more pairs of opposite directions, and performing the second alignment may include: for each given pair of opposite directions, aligning two first composite frames corresponding to the opposite directions in the given pair, and combining the two aligned first composite frames to obtain a composite frame, thereby generating two or more composite frames corresponding to the two or more pairs of opposite directions; and aligning the two or more composite frames and combining the aligned two or more composite frames to generate an image of the semiconductor sample.

[0020] According to other aspects of the subject matter of the present disclosure, a method for inspecting a semiconductor sample is provided, the method being performed by a processing and memory circuit (PMC) and comprising: obtaining a frame sequence of an area of ​​the semiconductor sample, the frame sequence being acquired by an electron beam tool configured to scan the area from multiple directions, the frame sequence comprising multiple groups of frames, wherein each group of frames is acquired from a corresponding direction; and registering the multiple groups of frames and generating an image of the semiconductor sample based on a result of the registration, comprising: in response to a determination to perform a first registration between the groups of frames acquired from each direction, for each direction, performing a first registration between the groups of frames acquired from the direction and combining the registered groups of frames to generate a first composite frame, thereby producing a plurality of first composite frames corresponding to the multiple directions respectively; and performing a second registration between the plurality of first composite frames, and combining the registered plurality of first composite frames to generate an image of the area of ​​the semiconductor sample; wherein the generated image has reduced image artifacts with respect to a frame scanned from a given direction of the multiple directions, and wherein the image can be used to inspect the semiconductor sample.

[0021] This aspect of the disclosed subject matter may comprise, mutatis mutandis, one or more of the features (i) to (xii) listed above with respect to the system, in any desired combination or permutation technically possible.

[0022] According to other aspects of the subject matter of the present disclosure, a non-transitory computer-readable medium is provided, the non-transitory computer-readable medium including instructions, which, when executed by a computer, cause the computer to perform a method for inspecting a semiconductor sample, the method comprising: obtaining a frame sequence of an area of ​​the semiconductor sample, the frame sequence being acquired by an electron beam tool configured to scan the area from multiple directions, the frame sequence comprising multiple groups of frames, wherein each group of frames is acquired from a corresponding direction; and registering the multiple groups of frames and generating an image of the semiconductor sample based on a result of the registration, comprising: in response to a determination to perform a first registration between the groups of frames acquired from each direction, for each direction, performing a first registration between the groups of frames acquired from the direction and combining the registered groups of frames to generate a first composite frame, thereby generating a plurality of first composite frames corresponding to the multiple directions respectively; and performing a second registration between the plurality of first composite frames, and combining the registered plurality of first composite frames to generate an image of the area of ​​the semiconductor sample; wherein the generated image has reduced image artifacts compared to a frame scanned from a given direction in the plurality of directions, and wherein the image can be used to inspect the semiconductor sample.

[0023] This aspect of the disclosed subject matter may comprise, mutatis mutandis, one or more of the features (i) to (xii) listed above with respect to the system, in any desired combination or permutation technically possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to understand the present disclosure and to know how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0025] Figure 1 A generalized block diagram of an inspection system according to certain embodiments of the disclosed subject matter is shown.

[0026] Figure 2A A generalized flow chart for generating images that can be used to inspect semiconductor samples according to certain embodiments of the disclosed subject matter is shown.

[0027] Figure 2B A generalized flow chart illustrating an alternative process for frame registration and image generation according to some embodiments of the disclosed subject matter is shown.

[0028] Figure 3 A generalized flow chart of a second registration performed in a two-step registration process according to some embodiments of the disclosed subject matter is shown.

[0029] Figure 4 An example of a sequence of frames of a target area on a sample is shown, according to some embodiments of the disclosed subject matter.

[0030] Figure 5 A schematic diagram illustrating an image generation process in bidirectional scanning according to some embodiments of the presently disclosed subject matter is shown.

[0031] Figure 6 A schematic diagram illustrating an image generation process in four-directional scanning according to some embodiments of the presently disclosed subject matter.

[0032] Figure 7 Two graphs are shown that illustrate drift and offset between frames according to certain embodiments of the disclosed subject matter. DETAILED DESCRIPTION

[0033] In the following specific embodiments, many details are set forth to provide a thorough understanding of the present disclosure. However, those skilled in the art will appreciate that the subject matter of the present disclosure can be practiced without these specific details. In other cases, well-known methods, procedures, components and circuits are not described in detail to avoid obscuring the subject matter of the present disclosure.

[0034] Unless specifically stated otherwise, as will be apparent from the following discussion, it should be understood that terms such as "perform," "obtain," "scan," "determine," "acquire," "align," "generate," "combine," "compensate," "adjust," "correct," and the like, used throughout this specification discussion, refer to computer actions and / or processes that manipulate data and / or transform data into other data, the data being represented as physical data (such as electronic, quantitative) and / or the data representing physical objects. The term "computer" should be interpreted expansively to cover any kind of hardware-based electronic device with data processing capabilities, including, by way of non-limiting example, inspection systems, image generation systems, and corresponding portions thereof disclosed in this application.

[0035] The term "inspection" used in this specification should be interpreted broadly to cover any kind of metrology-related operations, as well as operations related to the detection and / or classification of defects in samples during sample manufacturing. Inspection is provided by using a non-destructive inspection tool during or after the manufacture of the sample to be inspected. By way of non-limiting example, the inspection process may include one or more of the following operations: runtime scanning (single or multiple scans), sampling, evaluation, measurement, classification and / or other operations provided with respect to the sample or part thereof using the same or different inspection tools. Similarly, the inspection may be provided before the manufacture of the sample to be inspected, and may include, for example, the generation of (multiple) inspection recipes and / or other setup operations. Note that, unless specifically stated otherwise, the term "inspection" or its derivatives used in this specification are not limited in resolution or size of the inspection area. By way of non-limiting example, a variety of non-destructive inspection tools include scanning electron microscopes, atomic force microscopes, optical inspection tools, and the like.

[0036] The term "metrology" as used in this specification should be interpreted expansively to cover any kind of measurement characteristics and features in a sample provided during or after the manufacture of the sample to be inspected by using inspection and / or metrology tools. By way of non-limiting example, the metrology process may include generating measurement recipes and / or performing runtime measurements, such as by scanning (single or multiple scans), evaluating, measuring and / or other operations provided on the sample or part thereof using the same or different tools. For example, by analyzing the measurement results, such as images of the measurements, using image processing techniques. Note that, unless specifically stated otherwise, the term "metrology" or its derivatives as used in this specification are not limited to measurement techniques, measurement resolution or size of the inspection area.

[0037] The terms "non-transitory memory" and "non-transitory storage medium" as used herein should be interpreted expansively to cover any volatile or non-volatile computer memory suitable for the subject matter of the present disclosure.

[0038] The term "sample" as used in this specification should be interpreted expansively to cover any kind of wafers, masks and other structures, combinations and / or portions of which are used to manufacture semiconductor integrated circuits, magnetic heads, flat panel displays and other semiconductor manufactured articles.

[0039] The term "defect" as used in this specification should be interpreted expansively to cover any kind of abnormal or undesirable feature formed on or within a sample.

[0040] It should be understood that, unless otherwise specifically stated, some features of the subject matter of the present disclosure described in the context of a separate embodiment may also be provided in combination with a single embodiment. On the contrary, the various features of the subject matter of the present disclosure described in the context of a separate embodiment may also be provided individually or in any suitable sub-combination. In the following specific embodiments, many details are set forth in order to provide a thorough understanding of the present method and apparatus.

[0041] Focus on this and pay attention Figure 1 , Figure 1 A functional block diagram of an inspection system according to some embodiments of the disclosed subject matter is shown.

[0042] Figure 1 The inspection system 100 shown in the figure can be used to inspect a semiconductor sample (e.g., a wafer and / or a portion thereof) as part of a sample manufacturing process. According to certain embodiments of the disclosed subject matter, the inspection system 100 shown includes a computer-based system 101 that is capable of generating one or more images of a semiconductor sample during sample manufacturing (hereinafter referred to as a manufacturing process (FP) image, or just an image for simplicity). The FP image can be used to inspect the semiconductor sample. The system 101 is also referred to herein as an image generation system.

[0043] As described above, the inspection mentioned herein may be interpreted as covering any kind of metrology-related operations, as well as operations related to the detection and / or classification of defects in a sample during the manufacture of the sample. For example, the generated FP image may be used for inspection, such as, for example, defect detection and / or automatic defect assessment (ADR) and / or automatic defect classification (ADC) and / or metrology-related operations. In some embodiments, the system 101 may be configured to perform one or more metrology operations on the generated image. For example, the metrology operation may include a critical dimension (CD) measurement on a sample or a portion thereof. In this case, the system 101 is also referred to as a metrology system, which is a subsystem of the inspection system 100.

[0044] The system 101 may be operably connected to one or more inspection tools 120 configured to scan semiconductor samples and capture frames / images of the semiconductor samples for inspection of the samples. In some embodiments, at least one of the inspection tools 120 has metrology capabilities and may be configured to perform metrology operations on the captured images. Such inspection tools are also referred to as metrology tools.

[0045] The term "metrology operation" as used in this specification should be interpreted expansively to cover any metrology operation procedure for extracting metrology information about one or more structural elements on a semiconductor sample. For example, the extracted metrology information may indicate one or more of the following: dimensions (e.g., line width, line spacing, contact diameter, element size, edge roughness, grayscale statistics, etc.), element shape, distance within or between elements, related angles, coverage information associated with elements corresponding to different design levels, etc. In some embodiments, the metrology operation may include measurement operations such as, for example, critical dimension (CD) measurements performed on certain structures on the sample.

[0046] The term "inspection tool" as used herein should be interpreted expansively to cover any tool that can be used for inspection-related processes, including, by way of non-limiting example, imaging, scanning (single or multiple scans), sampling, evaluation, measurement, classification and / or other processes provided with respect to a sample or portion thereof.

[0047] For example, the sample may be inspected by one or more low-resolution inspection tools (e.g., optical inspection systems, low-resolution SEMs, etc.). The resulting data (referred to as low-resolution image data) providing low-resolution image information of the sample may be transmitted to the system 101 directly or via one or more intermediate systems. Alternatively or in addition, the sample may be inspected by a high-resolution tool (e.g., a scanning electron microscope (SEM) or an atomic force microscope (AFM) or a transmission electron microscope (TEM)). The resulting data (referred to as high-resolution image data) providing high-resolution image information of the sample may be transmitted to the system 101 directly or via one or more intermediate systems.

[0048] Without limiting the scope of the present disclosure in any way, it should also be noted that inspection tool 120 may be implemented in the form of various types of inspection machines, such as optical imaging machines, electron beam machines, etc. In some cases, the same inspection tool may provide low-resolution image data and high-resolution image data.

[0049] According to certain embodiments, one of the inspection tools is an electron beam tool, such as, for example, a scanning electron microscope (SEM). A SEM is an electron microscope that generates an image of a sample by scanning a surface with a focused electron beam. The electrons interact with the atoms in the sample, thereby generating various signals that contain information about the surface morphology and composition of the sample. The position of the beam is combined with the intensity of the detected signal to generate an image. The SEM is capable of accurately measuring features during the manufacture of semiconductor wafers. For example, a SEM tool can be a critical dimension scanning electron microscope (CD-SEM) for measuring the critical dimensions of structural features in an image.

[0050] One of the problems with using SEM for CD metrology involves charging effects. When scanned by an electron beam, semiconductor samples collect charge, and the accumulation of surface charge on the sample caused by the electron beam can cause scanning failures and image artifacts, such as, for example, gross image distortion and / or image washout. Such image artifacts can lead to a greater inability to accurately measure critical integrated device dimensions in the semiconductor industry. As CDs become smaller and smaller as lithography advances, charge accumulation is expected to become a larger variable error component of CD-SEM metrology. Artifacts caused by charge can be more significant relative to size and feature edge profile, and inaccuracies caused by image artifacts can form a significant problem in integrated circuit manufacturing.

[0051] In particular, scanning a sample from a given direction (e.g., from left to right) can result in non-uniform charging of the sample, which can affect CD measurements. For example, assume that there is a line structure in a region of the sample. When scanning the region from a particular direction perpendicular to the longitudinal axis of the structure, such as from left to right, the electron beam interacts differently with different surface structures and / or different materials, thus resulting in different local charging in the region. For example, in some cases, the edge of the line structure will likely emit more electrons, thus resulting in a positive charge on the surface. Due to the positive charge of the edge surface, as the beam moves along the edge of the line structure to the center and toward the other edge, at least a portion of the beam may be attracted by the positively charged adjacent edge surface, thus changing its original path and being redirected to the adjacent surface instead of the original target destination. In this case, the amount of electrons that actually arrive at the target location will be different from the amount that should have arrived, thereby affecting the accuracy of the SEM signal generated for the target location. For example, in an ideal situation, a SEM signal representing a line structure will typically have two peaks, which represent two line edges, respectively. However, due to local charging effects, the second peak (ie, the second one from the scan direction) will appear with reduced amplitude compared to the first peak and may have some artifacts.

[0052] Different measures for reducing charging effects involve physically changing / transforming the features to be measured, or creating stacks or coatings that can neutralize the charge. However, these measures all require physically changing the wafer structure, which is complex to implement. According to certain embodiments of the disclosed subject matter, image generation methods and systems are presented that are used to reduce / eliminate image artifacts caused by charging effects, rather than attempting to eliminate the charging effects themselves.

[0053] like Figure 1As shown in FIG. 1 , system 101 includes a processor and memory circuit system (PMC) 102, which is operably connected to a hardware-based I / O interface 126. PMC 102 is configured to provide the processing necessary for operating the system (for more details, see Figure 2A , Figure 2B and Figure 3 ), and includes a processor (not shown separately) and a memory (not shown separately). The processor of PMC 102 can be configured to execute several functional modules according to computer-readable instructions, which are implemented on a non-transitory computer-readable memory included in the PMC. Such functional modules are hereinafter referred to as being included in the PMC.

[0054] According to some embodiments, the functional modules included in the PMC 102 may include a first registration module 104 and a second registration module 106. The PMC 102 may be configured to obtain a frame sequence of a region of the semiconductor sample via the I / O interface 126. The frame sequence may be obtained by an electron beam tool (e.g., one of the inspection tools 120) configured to scan the region from multiple directions. The frame sequence includes multiple groups of frames, where each group of frames is acquired from a corresponding direction. The PMC 102 may be configured to register the multiple groups of frames and generate an image of the semiconductor sample based on the (multiple) results of the registration.

[0055] Specifically, the first registration module 104 can be configured to, in response to a determination to perform a first registration between the frame groups acquired from each direction, perform a first registration between the frame groups acquired from the direction for each direction, and combine the registered frame groups to generate a first composite frame, thereby generating multiple first composite frames corresponding to multiple directions respectively.

[0056] The second registration module 106 can be configured to perform a second registration between the plurality of first composite frames and combine the registered plurality of first composite frames to generate an image of the region of the semiconductor sample. The image generated by the above process has reduced image artifacts with respect to the frame scanned from a given direction in the plurality of directions. The image can be used to inspect the semiconductor sample as described above.

[0057] The operation of the system 101, PMC 102 and the functional modules therein will refer to Figure 2A , Figure 2B and Figure 3 Further details are given.

[0058] According to some embodiments, the system 101 may include a storage unit 122. The storage unit 122 may be configured to store any data necessary for operating the system 101, such as data related to input and output of the system 101, and intermediate processing results generated by the system 101. For example, the storage unit 122 may be configured to store frames generated by the inspection tool 120 and / or its derivatives. Thus, the frames may be retrieved from the storage unit 122 and provided to the PMC 102 for further processing.

[0059] In some embodiments, the system 101 may optionally include a computer-based graphical user interface (GUI) 124 configured to enable user-specified inputs related to the system 101. For example, a visual representation of a sample including frame / image data of the sample may be presented to the user (e.g., via a display forming component of the GUI 124). The user may be provided with the option of defining certain operating parameters via the GUI. In some cases, the user may also see the results of the operation, such as a generated image, and / or other inspection results (e.g., measurements on the generated image) on the GUI.

[0060] As will be further described in detail with reference to FIG. 2 , the system 101 is configured to receive a sequence of frames via the I / O interface 126. The frames may include frame data (and / or derivatives thereof) generated by the inspection tool 120 and / or frame data stored in one or more data storage locations. The frame data may include one or more of the following: frames captured by the inspection tool during the manufacturing process, frames derived from captured frames obtained through various pre-processing stages, and frames based on computer-generated design data (e.g., simulated frames, synthesized frames, etc.). Note that in some cases, the frames may include frame data and associated digital data (e.g., metadata, hand-crafted attributes, etc.). Further note that the frame data may include data related to a layer of interest of the sample and / or one or more additional layers of the sample.

[0061] The system 101 is further configured to process the received frames and send the results or parts thereof (eg, the generated images and / or CD measurement data on the images) to the storage unit 122 and / or the inspection tool 120 via the I / O interface 126 .

[0062] In some embodiments, in addition to the inspection tool 120, the inspection system 100 may include one or more inspection modules, such as, for example, a defect detection module and / or an automatic defect review module (ADR) and / or an automatic defect classification module (ADC) and / or a module related to metrology and / or other inspection modules that can be used to inspect semiconductor samples. One or more inspection modules may be implemented as stand-alone computers, or the functionality of the one or more inspection modules (or at least portions thereof) may be integrated with the inspection tool 120. In some embodiments, the generated image as obtained from the system 101 may be used by the inspection tool 120 and / or one or more inspection modules (or portions thereof) for further inspection of the sample.

[0063] Those skilled in the art will readily appreciate that the teachings of the subject matter of the present disclosure are not limited to Figure 1 The system shown in FIG. 1 is bound by the system; equivalent and / or modified functionality may be consolidated or decomposed in another manner and may be implemented in any suitable combination of software and firmware and / or hardware.

[0064] Note that in Figure 1 The inspection system shown in can be implemented in a distributed computing environment, wherein the above-mentioned functional modules included in the PMC 102 can be distributed on several local and / or remote devices and can be linked via a communication network. It is further noted that in other embodiments, at least some of the (multiple) inspection tools 120, storage unit 122 and / or GUI 124 can be external to the inspection system 100 and operate in data communication with the system 101 via the I / O interface 126. The system 101 can be implemented as (multiple) independent computers used in conjunction with the inspection tools. Alternatively, the corresponding functions of the system 101 can be at least partially integrated with one or more inspection tools 120, thereby facilitating and enhancing the functionality of the inspection tools 120 in processes related to the inspection.

[0065] refer to Figure 2A , depicts a generalized flow chart for generating images that can be used to inspect semiconductor samples according to certain embodiments of the disclosed subject matter.

[0066] As described above, the charging effects on the sample caused by the electron beam may lead to scanning failures and image artifacts, such as, for example, gross image distortion and / or image clean-up. Such image artifacts may affect the accuracy and effectiveness of sample inspection. For example, scanning a sample from a particular direction (e.g., from left to right) by an electron beam tool may result in uneven charging of the sample, which may affect the accuracy of CD measurements.

[0067] According to certain embodiments of the presently disclosed subject matter, image generation methods and systems are presented for reducing / eliminating image artifacts caused by charging effects, thereby providing images with reduced artifacts and feature consistency, and thus improving inspection results of samples.

[0068] Specifically, a sequence of frames of an area of ​​a semiconductor sample may be obtained (202) (e.g., from inspection tool(s) 120, by PMC 102 via I / O interface 126). The sequence of frames may be obtained by an electron beam tool configured to scan the area from a plurality of directions. For example, the sequence of frames may be SEM frames captured by a SEM tool. For example, the SEM tool may be a critical dimension scanning electron microscope (CD-SEM) for measuring critical dimensions of structural elements / features in an image. The sequence of frames includes a plurality of frame groups, wherein each frame group is acquired from a corresponding direction in the plurality of directions.

[0069] In some embodiments, the plurality of directions may include one or more pairs of opposite directions. A pair of opposite directions refers to two directions that are diametrically opposed to each other (e.g., the angle between the two is 180 degrees), such as, for example, a first direction is left to right, and a second direction is right to left, or a first direction is top to bottom, and a second direction is bottom to top. For example, in some cases, the plurality of directions include a pair of opposite directions. In such a case, the image sequence is captured from two opposite directions, which is also referred to as bidirectional scanning. For example, a first frame group is acquired from a first direction (e.g., from left to right), and a second frame group is acquired from a second direction (e.g., from right to left).

[0070] As another example, the multiple directions may include multiple pairs of opposite directions. For example, an image sequence may be acquired from two pairs of opposite directions, the first pair being between left and right, and the second pair being between top and bottom. This is also referred to as four-way scanning. Thus, four frame groups are acquired from four directions, respectively. Similarly, one or more pairs of additional directions may be added, such as, for example, directions along a diagonal line, etc., and, therefore, additional frame groups may be acquired from such directions. Such a manner of scanning a sample area from multiple directions may be generally referred to as N-way scanning (N≥2).

[0071] In some embodiments, it may be specifically determined how many directions (and which specific directions) are needed for scanning a given semiconductor sample or a region thereof. For example, such a determination may be made based on a specific layer of the sample and / or a specific structural element / feature included in the target region of the sample. For example, bidirectional scanning may be sufficient for structural elements such as, for example, lines. In such a case, a frame may be acquired by scanning a region of the sample from a direction normal to / perpendicular to the main direction of the structural element (e.g., the longitudinal axis of the line). In another example, in the case where the structural element includes a circular-shaped contact, four-way scanning or more directions of scanning may be used to compensate for possible artifacts caused by charging effects caused by different directions. Therefore, in some embodiments of the present disclosure, the proposed method may further include determining a plurality of directions for scanning a region of the sample. For example, the determination may be made by a user in the form of a manual configuration in a tool, or may be made automatically by the system 101 in the form of a part of an image generation method. Alternatively, it may be a default determination, for example, the system may default to always performing bidirectional scanning or four-way scanning, etc. This default determination may therefore be considered a pre-determination or pre-configuration of the system.

[0072] As used herein, a structural element or feature may refer to any original object on a sample that has a contoured geometric shape or geometric structure, in some cases combined with other objects (thus forming a pattern). Examples of structural elements may include features of general shape, including, for example, contacts, line structures, and the like.

[0073] Reference now Figure 4 , illustrating an example of a frame sequence of a target area on a sample according to some embodiments of the disclosed subject matter.

[0074] According to some embodiments, the sequence of frames may be acquired by sequentially scanning the area from multiple directions and obtaining one or more frames from each direction during each scan. Figure 4 An example of a sequence of frames acquired in a four-directional scan is shown, the four-directional scan including a first pair of directions from left to right and right to left, and a second pair of directions from top to bottom and bottom to top. Specifically, 400 shows an example in which a target area of ​​a sample is scanned sequentially from four directions, and one frame is acquired from each direction at a time. As shown, frame 1 is acquired from a first direction from left to right, frame 2 is acquired from a second direction from right to left, frame 3 is acquired from a third direction from top to bottom, and frame 4 is acquired from a fourth direction from bottom to top. Subsequently, the sequence continues in a similar manner, and frames 5 to 8 are repeated in this order.

[0075] Another example in which the target area of ​​the sample is sequentially scanned from four directions and two frames are acquired from each direction at a time is shown in 410. As shown, frames 1 and 2 are acquired from a first direction from left to right, frames 3 and 4 are acquired from a second direction from right to left, frames 5 and 6 are acquired from a third direction from top to bottom, and frames 7 and 8 are acquired from a fourth direction from bottom to top.

[0076] Different scanning orders may have different advantages over each other. For example, when scanning in the manner shown in 400, the charge can be expected to be spread more evenly across the surface of the sample, thereby reducing the effects of concentrated charging and resulting image artifacts, while scanning in the manner shown in 410 can reduce the amount of drift between the two frames captured from each direction (because they are captured in adjacent frames, so there is no problem of multiple drift).

[0077] Although only eight frames are shown in the sequence of the examples for illustrative purposes, it should be understood that the sequence in any example can continue in a similar repetitive manner. It should also be understood that the number of frames acquired from each direction in each scan is not limited to one or two frames as shown in the examples. The order of scanning in multiple directions may also be different from that described above and may have different advantages as described above. Therefore, any other suitable combination of the number of frames and different scanning orders may be applicable and applied in the present disclosure.

[0078] Continuing with the description of FIG. 2 , a frame sequence including a plurality of frame groups acquired from a plurality of directions may be registered and an image of a semiconductor sample may be generated ( 204 ) based on the result of the registration (e.g., by PMC 102 ). In some embodiments, the registration may include a first registration between frames in each frame group acquired from each direction, and a second registration between frames from a plurality of directions (i.e., registered and combined frames). In some cases, the first registration may be optional. For example, it may be determined whether the first registration needs to be performed, as will be described in further detail below.

[0079] According to some embodiments, in response to a determination to perform a first registration between the frame groups acquired from each direction, for each direction, a first registration may be performed (206) between the frame groups acquired from the direction (e.g., by a first registration module 104 included in the PMC 102), thereby generating a registered frame group. The registered frame groups may be combined (206) to generate a first composite frame for each direction. Thus, a plurality of first composite frames may be acquired corresponding to a plurality of directions, respectively.

[0080] According to some embodiments, the first registration is performed to correct for drift between frames in a frame set acquired from a given direction, the drift being caused by one or more physical effects between an electron beam of an electron beam tool and a semiconductor sample. For example, the one or more physical effects may be selected from the group consisting of: thermal expansion, charging effects, and tool tolerances.

[0081] Thermal expansion refers to the physical phenomenon that when a semiconductor sample (such as a wafer) is placed on an inspection platform located in a chamber maintained at a stable temperature and scanned by an electron beam, the wafer is continuously heated, which causes the physical expansion of the wafer surface. Such thermal expansion may cause the original target position of the beam to drift. The charging effect as described above refers to the physical phenomenon of the accumulation of surface charge on the sample caused by the interaction between the electron beam and the sample. Due to the continuous scanning process, the surface of the entire area is charged in an uninterrupted manner (this is also called regional charging, as opposed to local charging as described above), thereby affecting at least a portion of the actual destination of the beam on the sample, which causes drift between frames. Tool tolerance refers to certain physical differences associated with the electron beam tool itself, or differences between different tools. For example, in some cases, there may be particles on the tool during scanning, and / or there may be mechanical differences in the assembly of parts, which factors can jointly or individually cause drift between frames.

[0082] It should be noted that the above physical effects are listed for illustrative and exemplary purposes only and should not be considered to limit the scope of the present disclosure in any way. In different embodiments, in addition to or in place of the above physical effects, other physical effects that may cause possible drift may be applied.

[0083] In some embodiments, the first registration may include performing pattern matching between frames in a group of frames acquired from a given direction. Pattern matching generally refers to checking for the presence of a component of a pattern or structure. For example, pattern matching can be performed by identifying a specific structural element or pattern in the first frame of the group and searching for the identified pattern in each of the remaining frames of the group. Pattern matching can be performed in different ways using a variety of algorithms. For example, a normalized cross-correlation function can be used in the present disclosure to infer or predict the expected position of a pattern.

[0084] In some cases, in order to find a matching pattern, the search range (e.g., search radius and / or search direction) used in the current frame during pattern matching can be based on at least one previous drift identified in at least one previous frame of the current frame. For example, assume that a set of frames acquired from a given direction includes four frames. A specific structural element (e.g., a line, a contact, or at least a portion thereof) is identified in the first frame. When searching for a specific element in the second frame, the search range, including the search radius and / or the search direction, can be defined by default or by the user, for example, because there is no reference drift to consider. Once the element is found in the second frame, the first drift between the two frames can be identified (based on the relative distance and direction between the element positions in the first frame and the second frame). When searching for the same structural element in the third frame, the first drift can be used as a reference when determining a specific search range therein. Similarly, when searching for the same element in the fourth frame, the first drift and / or the second drift can be used as a reference for determining the search range, thereby enabling a more efficient and more accurate search.

[0085] Once the first registration is performed, a registered set of frames is obtained for each direction. The registered set of frames can be combined to generate a first composite frame for each direction. Therefore, multiple first composite frames can be obtained corresponding to multiple directions, respectively. The combination of frames can be performed in various ways. For example, the registered set of frames can be combined by summing the registered frames, and the frames are selectively averaged and / or weighted during the summation.

[0086] A second registration may be performed (208) between the plurality of first composite frames (e.g., by a second registration module 106 included in the PMC 102) to generate a plurality of registered first composite frames. The plurality of registered first composite frames may be combined (208) to generate an image of a region of the semiconductor sample. The image produced by the above process has reduced image artifacts (e.g., caused by uneven charging of the sample when the sample is scanned from one direction) compared to a frame scanned from a given direction of the plurality of directions. Such a generated image may be used to inspect the semiconductor sample.

[0087] According to certain embodiments, the second registration is performed to correct the offset between multiple first composite frames caused by scanning the area from multiple directions. The offset caused by directional scanning can be related to the scanning mechanism of the electron beam tool. For example, scanning from different directions can be implemented with different scanning coils in the tool, and there may be process delays between the scanning coils, which can be converted into such offsets. For example, when scanning is started in a given direction, there is always an acceleration period when the beam starts to accelerate from rest, and the acceleration period causes a delay in the signal formed. When scanning from different directions, the signals acquired during the acceleration period reside on different sides of the formed frame, thus causing an offset between frames acquired from different directions. It should be noted that this is only an example of such a physical phenomenon that can cause an offset between frames acquired from different directions, and the present disclosure is not limited to any specific factor or phenomenon that causes the offset.

[0088] The second registration may be performed in a similar manner as the first registration, for example by performing pattern matching between the plurality of first composite frames corresponding to the plurality of directions. The pattern matching may be performed in a similar manner as described above with reference to block 206. Specifically, in some embodiments, the search direction used in the current frame during pattern matching to find a matching pattern may be based on the scanning direction when acquiring the current frame.

[0089] For example, assume that four first composite frames corresponding to four scanning directions are acquired after the first registration. When searching for a particular pattern in one of these frames, a preferred search direction can be defined based on the scanning direction that generated the particular composite frame. For example, if the first composite frame is generated based on a set of frames acquired from a first direction (e.g., left to right), then the preferred search direction in such frames can be defined to be consistent with the first direction. For example, the search radius set for the X direction (e.g., the left-right dimension) can be larger than the search radius set for the Y direction (e.g., the top-bottom dimension).

[0090] In some embodiments, the plurality of directions may include two or more pairs of opposite directions. In such a case, the second registration may be performed in a two-step registration process, such as Figure 3 Specifically, for each given pair of opposite directions, two first composite frames corresponding to the opposite directions in the given pair may be registered. The two registered first composite frames may be combined (302) to obtain a composite frame, thereby generating two or more composite frames corresponding to the two or more pairs of opposite directions. The two or more composite frames may be registered, and the registered two or more composite frames may be combined (304) to generate an image of the semiconductor sample, as will be described below with reference to Figure 6 Example.

[0091] Reference now Figure 7 , illustrates two graphs illustrating drift and offset between frames according to certain embodiments of the disclosed subject matter.

[0092] As shown, 702 shows a chart of a unidirectional scan of a sample, i.e., the sample is scanned only from a given direction. A group of frames including eight frames is acquired from a given direction. The X-axis of the chart represents the frame numbers of the eight frames in the group, for example, frames 1-8. The Y-axis represents the amount of drift caused between the frames in the group. As described above, the drift between the frames in the group can be caused by one or more physical effects between the electron beam of the electron beam tool and the sample, such as, for example, thermal expansion, charging effects, tool tolerances, and the like. In some cases, the drift between frames presents a linear relationship. This is especially true when the drift is at least partially caused by the effect of thermal expansion. As shown in chart 702, a linear regression is formed about the amount of drift for each particular frame.

[0093] On the other hand, 704 shows a diagram of bidirectional scanning of a sample, i.e., scanning the sample from two directions (e.g., a pair of opposite directions). A sequence of eight frames is acquired, including two groups of frames, where each group includes four frames acquired from a corresponding direction. Specifically, the sample is sequentially scanned from two directions, with Figure 4 400 of FIG. 702. Thus, a first set of frames including frames 1, 3, 5, and 7 are acquired from a first direction, and a second set of frames including frames 2, 4, 6, and 8 are acquired from a second direction. Because each set of frames is collected every other frame in a sequence, it is expected that the amount of drift between every two adjacent frames in a set in a bidirectional scan is twice the amount of drift between every two adjacent frames in a set in a unidirectional scan. For example, the drift between frame 1 and frame 2 in graph 702 is about 1 nm, while the drift between frame 1 and frame 3 in graph 704 is about 2 nm.

[0094] Therefore, when performing the first registration, in order to correct such drift, the search radius used in the pattern matching should be defined accordingly. For example, in a bidirectional scan, the search radius should be at least twice the search radius of a unidirectional scan, and in a four-directional scan, the search radius should be at least four times the search radius of a unidirectional scan.

[0095] As described above, the second set of frames as shown in graph 704 includes frames 2, 4, 6, and 8 acquired from the second direction. As shown, there is an offset between the drift of the second set of frames and the drift of the first set of frames. For example, the offset between the drift of frame 1 (acquired from the first direction) and the drift of frame 2 (acquired from the second direction) is about 16nm, and the offset between frame 3 and frame 4 is also the same. As described above, this offset between frames acquired from different directions can be caused by directional scanning (i.e., scanning the sample from different directions), which may be related to the scanning mechanism of the electron beam tool. The second registration as described above is to correct for such an offset.

[0096] As in Figure 7 As shown in , the shift between frames acquired from different directions can be much larger than the drift between frames acquired from the same direction. Therefore, in some cases, in addition to or instead of the second registration, different measurement methods can be taken to compensate for such shifts. According to certain embodiments, tool configuration optimization can be performed to solve this problem. As known, an electron beam tool can be generally considered to include, among other things, a scanning module and an imaging module. The scanning module can be configured to physically scan the surface of the sample using an electron beam, resulting in a signal being detected based on electrons emitted from the sample. The imaging module can be configured to convert the detected signal into a digital form that can be represented by a frame. The two modules usually need to be fully synchronized so that the generated frames can accurately reflect the generated signals.

[0097] In some embodiments of the present disclosure, it is proposed to adjust / debug the synchronization between the scanning process and the imaging process accordingly in order to compensate at least part of the offset between frames acquired from different directions. The accurate adjustment or debugging may be based on the offset data obtained from the reference sample.

[0098] For example, in Figure 7 In the example of graph 704 of , the second set of frames can be imaged with a preconfigured delay relative to the signal generated from the scanning process, while no delay is required for the first set of frames. Figure 4 In the example of FIG. 1 , when there are four sets of frames acquired from four directions, the delay between the imaging process and the scanning process may be configured differently to generate different sets of frames.

[0099] According to some embodiments, when performing registration of multiple sets of frames acquired from multiple directions and generating an image of a semiconductor sample, as described with respect to Figure 2A As described in block 204 of FIG. 1 , an alternative process may be implemented to replace steps 206 and 208. This is applicable when it is determined in some cases that a first registration is not to be performed, as will be described with respect to FIG. Figure 2B Described in detail.

[0100] Now turn to Figure 2B , shows a generalized flow chart of an alternative process for frame registration and image generation according to certain embodiments of the presently disclosed subject matter.

[0101] As described above, in some embodiments, a determination may be made to decide whether to perform a first registration. For example, the determination may be based on at least one of the following factors: the number of frames included in the frame group, and the layers (such as manufacturing steps in a manufacturing process) and / or materials of the sample to be inspected. For example, in some cases, only one frame is acquired from each direction, i.e., each group of frames includes a single frame. In such a case, it is not necessary to perform a first registration within each group of frames. In another example, certain layers of the sample may not have drift issues due to the physical properties of the layers, such as, for example, the material of the layer, charging, temperature, etc. In some cases, the layers and / or materials of the sample may be used together or individually to determine whether it is necessary to perform a first registration.

[0102] It should be noted that the determination regarding the first registration mentioned herein may be made automatically by the system 101 (e.g., as part of the proposed method) or manually by the user (e.g., as an adjustable system configuration). Alternatively, it may be a default determination, i.e., the system may default to always performing the first registration or default to not performing the first registration. Such a default determination may therefore be considered a pre-determination or pre-configuration of the system.

[0103] According to some embodiments, in response to a determination not to perform the first registration, the frame groups acquired from each direction may be combined (210) to generate a second composite frame, thereby generating a plurality of second composite frames corresponding to the plurality of directions, respectively. A second registration may be performed between the plurality of second composite frames, and the registered plurality of second composite frames may be combined (212) to generate an image of the semiconductor sample.

[0104] Figure 5 A schematic diagram illustrating an image generation process in bidirectional scanning according to some embodiments of the presently disclosed subject matter is shown.

[0105] As illustrated, a sequence of four frames (frames 1-4) is acquired, including two frames (frames 1 and 3) acquired from a first direction (e.g., from left to right), and two frames (frames 2 and 4) acquired from a second direction (e.g., from right to left). For frames acquired from the same direction, a determination may be made whether to perform a first registration 510. In response to an affirmative determination, frames 1 and 3 are registered, and the two registered frames are combined to generate a composite frame 502 (termed as a first composite frame, as described above when the first registration is performed). Similarly, frames 2 and 4 are registered, and the two registered frames are combined to generate a composite frame 504. Alternatively, in response to a negative determination, frames 1 and 3 are simply combined (e.g., summed) to generate the composite frame 502 (termed as a second composite frame, as described above when the first registration is not performed). Similarly, frames 2 and 4 are combined to generate the composite frame 504. A second registration 520 is then performed on the two composite frames 502 and 504, and the registered two composite frames are combined to generate an image 506 of the sample.

[0106] Figure 6 A schematic diagram illustrating an image generation process in four-directional scanning according to some embodiments of the presently disclosed subject matter.

[0107] As illustrated, a sequence of eight frames (frames 1-8) is acquired by scanning the sample from four directions, including four groups of frames each acquired from a corresponding direction. Each group includes two frames: frames 1 and 5 acquired from a first direction (e.g., from left to right), frames 2 and 6 acquired from a second direction (e.g., from right to left), frames 3 and 7 acquired from a third direction (e.g., from top to bottom), and frames 4 and 8 acquired from a fourth direction (e.g., from bottom to top). Obviously, the four directions include two pairs of opposite directions.

[0108] Similarly, as mentioned above Figure 5 As described above, a determination may be made whether to perform a first registration 510, and based on the result of the determination, for a given direction, two frames from each group may be first registered and then combined, or simply combined to generate a composite frame. Thus, four composite frames 602, 604, 606, and 608 may be generated.

[0109] Because there are two pairs of opposite directions, the second registration between the four composite images can be performed in two steps 525 and 530. First, for each pair of opposite directions, the two first composite frames corresponding to the two opposite directions in the pair are first registered, and the registered two first composite frames are combined to obtain a composite frame. For example, the composite frames 602 and 604 corresponding to the opposite directions of left to right and right to left are registered and combined (525) to generate a composite frame 610. Similarly, the other two composite frames 606 and 608 are registered and combined (525) to generate a composite frame 612. Therefore, two composite frames corresponding to two pairs of opposite directions are generated. The two composite frames 610 and 612 are then registered and combined (530) to generate an image 614 of the semiconductor sample.

[0110] According to certain embodiments, as described above with reference to Figure 2A , Figure 2B and Figure 3 The described image generation process may be included as part of an inspection recipe that may be used by the system 101 and / or the inspection tool 120 for inspecting a sample at runtime, such as, for example, performing metrology operations on the sample. In such a case, the subject matter of the present disclosure also includes systems and methods for generating an inspection recipe during a recipe setup phase, wherein the recipe includes the following: Figure 2A , Figure 2B and Figure 3 Described steps (and their various embodiments). It should be noted that the term "inspection recipe" should be interpreted expansively to cover any recipe that can be used by an inspection tool for performing operations related to any kind of inspection as described above.

[0111] It should be noted that the examples shown in the present disclosure, such as, for example, frames acquired from specific exemplified directions, registration algorithms, pattern matching algorithms, and enumerated physical effects, etc., as described above, are shown only for exemplary purposes and should not be considered to limit the present disclosure in any way. Other examples may be used in addition to or in place of the above.

[0112] One of the advantages of certain embodiments of the image generation process as described herein is providing an image of a sample with reduced image artifacts (e.g., image artifacts caused by non-uniform charging of the sample when scanning the sample from one direction). Such generated images can provide better results with higher accuracy when used for inspection of semiconductor samples (such as, for example, CD measurement).

[0113] It will be understood that the disclosure is not limited in its application to the details set forth in the description contained herein or shown in the drawings.

[0114] It will also be understood that the system according to the present disclosure can be implemented at least in part on a suitably programmed computer. Likewise, the present disclosure contemplates a computer-readable computer program for performing the method of the present disclosure. The present disclosure further contemplates a non-transitory computer-readable memory that tangibly embodies a computer-executable instruction program for performing the method of the present disclosure.

[0115] The present disclosure is capable of other embodiments and can be practiced and executed in various ways. Therefore, it will be understood that the wording and terminology employed herein are for descriptive purposes and should not be considered restrictive. Thus, it will be understood by those skilled in the art that the concepts upon which the present disclosure is based can be easily used as a basis for designing other structures, methods and systems for performing several purposes of the subject matter of the present disclosure.

[0116] It will be easily appreciated by those skilled in the art that various modifications and changes may be applied to the embodiments of the present disclosure as described above without departing from the scope of the present disclosure as defined in and by the accompanying claims.

Claims

1. A computerized system for inspecting a semiconductor sample, the system comprising a processing and memory circuit system (PMC), the processing and memory circuit system (PMC) being configured to: obtaining a frame sequence of a region of the semiconductor sample, the frame sequence being acquired by an electron beam tool configured to scan the region from a plurality of directions, the frame sequence comprising a plurality of frame groups, wherein each group of frames is acquired from a corresponding direction; as well as Registering the plurality of frame groups and generating an image of the semiconductor sample based on a result of the registration, comprising: In response to a determination to perform a first registration between the groups of frames acquired from each direction, for each direction, performing the first registration between the groups of frames acquired from the direction, and combining the registered groups of frames to generate a first composite frame, thereby generating a plurality of first composite frames corresponding to the plurality of directions respectively; and performing a second registration between the plurality of first composite frames and combining the registered plurality of first composite frames to generate the image of the region of the semiconductor sample, wherein the second registration is performed to correct for shifts between the plurality of first composite frames caused by directional scanning from the plurality of directions and related to a scanning mechanism of the electron beam tool; Wherein the generated image has reduced image artifacts compared to a frame scanned from a given direction of the plurality of directions, and wherein the image can be used for inspection of the semiconductor sample.

2. A computerized system for inspecting a semiconductor sample, the system comprising a processing and memory circuit system (PMC), the processing and memory circuit system (PMC) being configured to: obtaining a frame sequence of a region of the semiconductor sample, the frame sequence being acquired by an electron beam tool configured to scan the region from a plurality of directions, the frame sequence comprising a plurality of frame groups, wherein each group of frames is acquired from a corresponding direction; as well as Registering the plurality of frame groups and generating an image of the semiconductor sample based on a result of the registration, comprising: In response to a determination that the first registration is not performed between the frame groups acquired from each direction, for each direction, combining the frame groups acquired from the directions to generate a second composite frame, thereby producing a plurality of second composite frames respectively corresponding to the plurality of directions; and performing a second registration between the plurality of second composite frames and combining the registered plurality of second composite frames to generate the image of the semiconductor sample, wherein the second registration is performed to correct for an offset between the plurality of first composite frames caused by directional scanning from the plurality of directions and related to a scanning mechanism of the electron beam tool; Wherein the generated image has reduced image artifacts compared to a frame scanned from a given direction of the plurality of directions, and wherein the image can be used for inspection of the semiconductor sample.

3. The computerized system of claim 1, further comprising the electron beam tool.

4. The computerized system of claim 1, wherein the sequence of frames is acquired by sequentially scanning the area from the plurality of directions and obtaining one or more frames from each direction during each scan.

5. The computerized system of claim 3, wherein the electron beam tool is configured to compensate at least in part for the offset between frames acquired from different directions by adjusting synchronization between a scanning process and an imaging process of the electron beam tool.

6. The computerized system of claim 1, wherein the determination is based on at least one of the following factors: a number of frames included in the frame set, and a layer and / or material of a sample to be inspected.

7. The computerized system of claim 1, wherein the first registration is performed to correct for drift between the sets of frames acquired from each direction caused by one or more physical effects between an electron beam of the electron beam tool and the semiconductor sample.

8. The computerized system of claim 7, wherein the one or more physical effects include thermal expansion, charging effects, and tool tolerances.

9. The computerized system of claim 1, wherein the first registration comprises performing pattern matching between the sets of frames using a normalized cross-correlation function.

10. The computerized system of claim 9, wherein a search range used in a current frame during the pattern matching is based on at least one previous drift identified in at least one previous frame of the current frame.

11. The computerized system of claim 1 , wherein a search direction used in a current frame during pattern matching performed in the second registration is based on a scan direction when the current frame was acquired.

12. The computerized system of claim 1, wherein the plurality of directions comprises two or more pairs of opposite directions, and wherein performing the second registration comprises: for each given pair of opposite directions, registering two first composite frames corresponding to the opposite directions in the given pair, and combining the registered two first composite frames to obtain a composite frame, thereby generating two or more composite frames corresponding to the two or more pairs of opposite directions; as well as The two or more composite frames are registered, and the registered two or more composite frames are combined to generate the image of the semiconductor sample.

13. A computerized method of inspecting a semiconductor sample, the method being performed by a processing and memory circuit (PMC) and comprising: obtaining a frame sequence of a region of the semiconductor sample, the frame sequence being acquired by an electron beam tool configured to scan the region from a plurality of directions, the frame sequence comprising a plurality of frame groups, wherein each group of frames is acquired from a corresponding direction; as well as Registering the plurality of frame groups and generating an image of the semiconductor sample based on a result of the registration, comprising: In response to a determination to perform a first registration between the frame groups acquired from each direction, for each direction, performing the first registration between the frame groups acquired from the direction, and combining the registered frame groups to generate a first composite frame, thereby generating a plurality of first composite frames respectively corresponding to the plurality of directions; and performing a second registration between the plurality of first composite frames and combining the registered plurality of first composite frames to generate the image of the region of the semiconductor sample, wherein the second registration is performed to correct for shifts between the plurality of first composite frames caused by directional scanning from the plurality of directions and related to a scanning mechanism of the electron beam tool; Wherein the generated image has reduced image artifacts compared to a frame scanned from a given direction of the plurality of directions, and wherein the image can be used for inspection of the semiconductor sample.

14. A computerized method of inspecting a semiconductor sample, the method being performed by a processing and memory circuit (PMC) and comprising: obtaining a frame sequence of a region of the semiconductor sample, the frame sequence being acquired by an electron beam tool configured to scan the region from a plurality of directions, the frame sequence comprising a plurality of frame groups, wherein each group of frames is acquired from a corresponding direction; as well as Registering the plurality of frame groups and generating an image of the semiconductor sample based on a result of the registration, comprising: In response to a determination that the first registration is not performed between the frame groups acquired from each direction, for each direction, combining the frame groups acquired from the directions to generate a second composite frame, thereby producing a plurality of second composite frames respectively corresponding to the plurality of directions; and performing a second registration between the plurality of second composite frames and combining the registered plurality of second composite frames to generate the image of the semiconductor sample, wherein the second registration is performed to correct for an offset between the plurality of first composite frames caused by directional scanning from the plurality of directions and related to a scanning mechanism of the electron beam tool; Wherein the generated image has reduced image artifacts compared to a frame scanned from a given direction of the plurality of directions, and wherein the image can be used for inspection of the semiconductor sample.

15. The computerized method of claim 13, wherein the determination is based on at least one of the following factors: the number of frames included in the frame set, and a layer and / or material of the sample to be inspected.

16. The computerized method of claim 13, wherein a search range used in a current frame during pattern matching performed in the first registration is based on at least one previous drift identified in at least one previous frame of the current frame.

17. The computerized method of claim 13, wherein a search direction used in a current frame during pattern matching performed in the second registration is based on a scan direction when the current frame was acquired.

18. The computerized method of claim 13, wherein the plurality of directions comprises two or more pairs of opposite directions, and wherein performing a second registration comprises: for each given pair of opposite directions, registering two first composite frames corresponding to the opposite directions in the given pair, and combining the registered two first composite frames to obtain a composite frame, thereby generating two or more composite frames corresponding to the two or more pairs of opposite directions; as well as The two or more composite frames are registered, and the registered two or more composite frames are combined to generate the image of the semiconductor sample.

19. A non-transitory computer-readable storage medium tangibly embodying a program of instructions which, when executed by a computer, causes the computer to perform a method of inspecting a semiconductor sample, the method comprising: obtaining a frame sequence of a region of the semiconductor sample, the frame sequence being acquired by an electron beam tool configured to scan the region from a plurality of directions, the frame sequence comprising a plurality of frame groups, wherein each group of frames is acquired from a corresponding direction; as well as Registering the plurality of frame groups and generating an image of the semiconductor sample based on a result of the registration, comprising: In response to a determination to perform a first registration between the set of frames acquired from each direction, for each direction, performing the first registration among the set of frames acquired from the direction, and combining the registered frame groups to generate a first composite frame, thereby generating a plurality of first composite frames corresponding to the plurality of directions respectively; and performing a second registration between the plurality of first composite frames and combining the registered plurality of first composite frames to generate the image of the region of the semiconductor sample, wherein the second registration is performed to correct for shifts between the plurality of first composite frames caused by directional scanning from the plurality of directions and related to a scanning mechanism of the electron beam tool; Wherein the generated image has reduced image artifacts compared to a frame scanned from a given direction of the plurality of directions, and wherein the image can be used for inspection of the semiconductor sample.

Images