Image generation for investigation of semiconductor samples

Abstract

To provide a system and method of examination of a semiconductor specimen.SOLUTION: A method comprises: obtaining a sequence of frames of an area of the specimen acquired by an electron beam tool configured to scan the area from a plurality of directions, the sequence comprising a plurality of sets of frames each acquired from a respective direction; and registering the plurality of sets of frames and generating an image of the specimen based on a result of the registration. The registering step comprises: performing, for each direction, a first registration among the set of frames acquired therefrom, and combining the registered set of frames to generate a first composite frame, thereby giving rise to a plurality of first composite frames respectively corresponding to the plurality of directions; and performing a second registration among the plurality of first composite frames, and combining the registered plurality of first composite frames to generate the image of the specimen.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The subject matter of the present disclosure generally relates to the field of inspection of semiconductor samples, and more specifically, to the generation of images that can be used for the inspection of semiconductor samples.

Background Art

[0002] Current requirements for high density and high performance associated with the very large scale integration of manufactured devices require submicron features, improved transistor and circuit speeds, and improved reliability. As semiconductor processes advance, pattern dimensions such as line widths and other types of critical dimensions are continuously shrinking. Such requirements necessitate the formation of device features with high precision and high uniformity, and as a result, careful monitoring of the manufacturing process, including the automated inspection of devices while still in the form of semiconductor wafers.

[0003] Inspection can be performed by using non-destructive inspection tools during or after the production of the sample to be inspected. Inspection generally includes directing light or electrons onto the wafer and detecting the light or electrons from the wafer to generate a specific output (e.g., an image, a signal, etc.) regarding the sample. Various non-destructive 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 can include a plurality of inspection steps. During the manufacturing process, the inspection steps can be performed multiple times, for example, after the production or processing of a particular layer. Additionally or alternatively, each inspection step can be repeated multiple times, for example, for different wafer locations or for the same wafer location with different inspection settings.

[0005] The investigation process is used at various steps during semiconductor manufacturing to detect and classify defects in a sample and to perform metrology-related operations. The effectiveness of the investigation can be improved by automating the process, for example, by defect detection, automatic defect classification (ADC), automatic defect review (ADR), automatic metrology-related operations, and the like. SUMMARY OF THE INVENTION

[0006] According to certain aspects of the subject matter of this disclosure, a computerized system for investigating a semiconductor sample is provided, the system obtaining a sequence of frames of an area of the semiconductor sample, the sequence of frames being acquired by an electron beam tool configured to scan the area from a plurality of directions, the sequence of frames including a plurality of sets of frames, each set of frames being acquired from a respective direction; obtaining the sequence; aligning the plurality of sets of frames and generating an image of the semiconductor sample based on the result of the alignment; in response to a determination to perform a first alignment among the sets of frames acquired from each direction, performing the first alignment among the sets of frames acquired from that direction for each direction, combining the aligned sets of frames to generate a first composite frame, thereby resulting in a plurality of first composite frames respectively corresponding to a plurality of directions; performing a second alignment among the plurality of first composite frames and combining the aligned plurality of first composite frames to generate an image of the area of the semiconductor sample; and including a processing and memory circuit (PMC) configured to perform the foregoing, the generated image having reduced image artifacts with respect to frames scanned from a given direction among the plurality of directions, and the image being usable for investigating the semiconductor sample.

[0007] In addition to the above features, the system according to this aspect of the subject matter of this disclosure can include one or more of the following features (i) through (xii) in any desired combination or permutation that is technically possible. (i) Aligning a set of multiple frames to generate an image of a semiconductor sample can further include, in response to a decision not to perform a first alignment, for each direction, combining the set of frames obtained therefrom to generate a second composite frame, thereby resulting in a plurality of second composite frames respectively corresponding to a plurality of directions, and performing a second alignment among the plurality of second composite frames and combining the aligned plurality of second composite frames to generate an image of the semiconductor sample. (ii) This system can further include an electron beam tool. (iii) A sequence of frames can be obtained by sequentially scanning a region from a plurality of directions and obtaining one or more frames from each direction during all scans. (iv) The electron beam tool can be configured to compensate for at least a part of the offset between frames obtained from different directions by adjusting the synchronization between the scanning process and the imaging process of the electron beam tool. (v) The decision can be based on the following factors: namely, the number of frames included in the set of frames, and at least one of the layers and / or materials of the sample to be investigated. (vi) The first alignment can be performed to correct the drift between the sets of frames obtained from each direction caused by one or more physical effects between the electron beam of the electron beam tool and the semiconductor sample. (vii) The one or more physical effects can be selected from the group consisting of thermal expansion, charging effects, and tool tolerances. (viii) The first alignment can include performing pattern matching between the sets of frames using a normalized cross-correlation function. (ix) The search range 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. (x) The second alignment can be performed to correct the offset between a plurality of first composite frames caused by scanning the area from a plurality of directions. (xi) During the pattern matching performed in the second alignment, the search direction used in the current frame can be based on the scanning direction at the time of acquisition of the current frame. (xii) The plurality of directions can include pairs of two or more opposite directions, and performing the second alignment involves aligning two first composite frames corresponding to the opposite directions of a given pair for each given pair of opposite directions, combining the two aligned first composite frames to obtain a composite frame, thereby resulting in two or more composite frames corresponding to 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.

[0008] According to other aspects of the subject matter of this disclosure, a method for investigating a semiconductor sample is provided, the method being performed by a processing and memory circuit (PMC) and obtaining a sequence of frames of an area of the semiconductor sample, the sequence of frames being acquired by an electron beam tool configured to scan the area from a plurality of directions, the sequence of frames including a plurality of sets of frames, each set of frames being acquired from a respective direction, obtaining the sequence; aligning the plurality of sets of frames and generating an image of the semiconductor sample based on the alignment result; in response to a determination to perform a first alignment among the sets of frames acquired from each direction, for each direction, performing a first alignment among the sets of frames subsequently acquired therefrom, combining the aligned sets of frames to generate a first composite frame, thereby resulting in a plurality of first composite frames respectively corresponding to a plurality of directions; performing a second alignment among the plurality of first composite frames and combining the aligned plurality of first composite frames to generate an image of the area of the semiconductor sample; and generating, the generated image having reduced image artifacts with respect to frames scanned from a given direction among the plurality of directions, the image being usable for investigating the semiconductor sample.

[0009] This aspect of the subject matter of this disclosure can include one or more of the features (i) through (xii) listed above with respect to the system, in a desired combination or permutation that is technically possible with necessary modifications.

[0010] According to other aspects of the subject matter of this disclosure, there is provided a non-transitory computer-readable medium including instructions that, when executed by a computer, cause the computer to perform a method of investigating a semiconductor sample, the method comprising obtaining a sequence of frames of a region of the semiconductor sample, the sequence of frames being obtained by an electron beam tool configured to scan the region from a plurality of directions, the sequence of frames including a plurality of sets of frames, each set of frames being obtained from a respective direction; obtaining the sequence; aligning the plurality of sets of frames and generating an image of the semiconductor sample based on the alignment result; in response to a determination to perform a first alignment among the sets of frames obtained from each direction, performing the first alignment among the sets of frames obtained from each direction, combining the aligned sets of frames to generate a first composite frame, thereby resulting in a plurality of first composite frames respectively corresponding to a plurality of directions; performing a second alignment among the plurality of first composite frames, and combining the aligned plurality of first composite frames to generate an image of the region of the semiconductor sample; and generating, the generated image having reduced image artifacts with respect to frames scanned from a given direction among the plurality of directions, the image being usable for investigating the semiconductor sample.

[0011] This aspect of the subject matter of this disclosure can include one or more of features (i) through (xii) listed above with respect to the system, in any desired combination or permutation that is technically possible with the necessary changes.

[0012] To understand this disclosure and how it can be actually implemented, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings.

Brief Description of the Drawings

[0013]

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DETAILED DESCRIPTION OF THE INVENTION

[0014] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be understood by those skilled in the art that the subject matter of the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to obscure the subject matter of the present disclosure.

[0015] Unless otherwise specified, as will be apparent from the following discussion, throughout this specification, discussions using terms such as "perform", "obtain", "scan", "determine", "acquire", "align", "generate", "combine", "compensate", "adjust", "correct", etc. refer to computer actions and / or processes that manipulate data and / or transform data into other data, where the data is represented as a physical quantity such as an electron and / or the data represents a physical object. The term "computer" should be broadly construed to include, by way of non-limiting example, any kind of hardware-based electronic device having data processing capabilities, including the investigation systems, image generation systems, and respective parts thereof disclosed in this application.

[0016] As used herein, the term "investigation" should be broadly construed to include any kind of measurement-related operations, as well as operations related to the detection and / or classification of defects in samples during production. Investigations are performed by using non-destructive investigation tools during or after the production of the sample to be investigated. By way of non-limiting example, the investigation process can include one or more of the following operations, namely, in-situ scanning (in single or multiple scans), sampling, review, measurement, classification, and / or other operations performed on the sample or a part thereof using the same or different investigation tools. Similarly, investigations can be performed prior to the production of the sample to be investigated and can include, for example, generating investigation strategies and / or other setup operations. Note that, unless otherwise specified, the term "investigation" or its derivatives as used herein are not limited with respect to the resolution or size of the inspection area. Various non-destructive investigation tools include, by way of non-limiting example, scanning electron microscopes, atomic force microscopes, optical inspection tools, etc.

[0017] As used herein, the term "measurement" should be broadly construed to include any type of measured property and characteristic of a sample provided by using an investigation and / or measurement tool during or after the production of the sample to be inspected. By way of non-limiting example, the measurement process can include generating a measurement strategy and / or performing in-situ measurements by, for example, scanning (single or multiple scans), reviewing, measuring, and / or other operations performed on the sample or a portion thereof using the same or different tools. Measurement results such as measured images are analyzed, for example, by utilizing image processing techniques. Note that, unless otherwise specified, the term "measurement" or its derivatives used herein are not limited with respect to measurement techniques, measurement resolution, or the size of the inspection area.

[0018] As used herein, the terms "non-transitory memory" and "non-transitory storage medium" should be broadly construed to include any volatile or non-volatile computer memory suitable for the subject matter of the present disclosure.

[0019] As used herein, the term "sample" should be broadly construed to include any type of wafer, mask, and other structures, combinations thereof and / or portions thereof used to produce semiconductor integrated circuits, magnetic heads, flat panel displays, and other semiconductor manufacturing products.

[0020] As used herein, the term "defect" should be broadly construed to include any type of abnormality or undesirable feature formed on or within the sample.

[0021] Unless otherwise specified, it should be understood that specific features of the subject matter of the present disclosure described in the context of separate embodiments can also be provided in combination in a single embodiment. Conversely, various features of the subject matter of the present disclosure described in the context of a single embodiment can also be provided separately or in any suitable sub-combination. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the methods and apparatuses.

[0022] With this in mind, turn attention to FIG. 1, which shows a functional block diagram of an inspection system according to a particular embodiment of the subject matter of the present disclosure.

[0023] The inspection system 100 shown in FIG. 1 can be used for the inspection of semiconductor samples (e.g., wafers and / or parts thereof) as part of a sample manufacturing process. According to a particular embodiment of the subject matter of the present disclosure, the illustrated inspection system 100 includes a computer-based system 101 that can generate one or more images of a semiconductor sample during sample manufacturing (hereinafter, for brevity, referred to as manufacturing process (FP) images or simply images). The FP images can be used for the inspection of semiconductor samples. System 101 is also referred to herein as an image generation system.

[0024] As described above, the inspections referred to herein can be interpreted to include any kind of measurement-related operations, as well as operations related to the detection and / or classification of defects in samples during manufacturing. By way of example, the generated FP images can be used for inspections such as, for example, defect detection, and / or automatic defect review (ADR), and / or automatic defect classification (ADC), and / or automatic measurement-related operations. In some embodiments, system 101 can be configured to perform one or more measurement operations on the generated images. By way of example, the measurement operations can include critical dimension (CD) measurements on a sample or a part thereof. In such a case, system 101 is also referred to as a measurement system and is a subsystem of inspection system 100.

[0025] System 101 can be operably connected to one or more inspection tools 120 configured to scan a semiconductor sample and capture a frame / image of the sample for inspection of the sample. In some embodiments, at least one of the inspection tools 120 has a measurement function and can be configured to perform a measurement operation on the captured image. Such an inspection tool is also referred to as a measurement tool.

[0026] As used herein, the term "measurement operation" should be broadly construed to include measurement operation procedures used to extract measurement information related to one or more structural elements on a semiconductor sample. By way of example, the measurement information to be extracted can represent one or more of the following, namely, dimensions (e.g., line width, line spacing, contact diameter, element size, edge roughness, gray level statistics, etc.), element shape, distance within an element or distance between elements, relative angle, overlay information related to elements corresponding to different design levels, etc. In some embodiments, the measurement operation can include a measurement operation such as critical dimension (CD) measurement performed on a specific structure on the sample.

[0027] As used herein, the term "inspection tool" should be broadly construed to include any tool that can be used in an inspection-related process, including, by way of non-limiting example, imaging, scanning (single or multiple scans), sampling, review, measurement, classification, and / or other processing performed on a sample or a portion thereof.

[0028] As an example, the sample can be investigated with one or more low-resolution investigation tools (e.g., an optical inspection system, a low-resolution SEM, etc.). The resulting data providing information on the low-resolution image of the sample (referred to as low-resolution image data) can be sent to system 101 directly or via one or more intermediate systems. Alternatively or additionally, the sample can be investigated with a high-resolution tool (e.g., a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM)). The resulting data providing information on the high-resolution image of the sample (referred to as high-resolution image data) can be sent to system 101 directly or via one or more intermediate systems.

[0029] It should also be noted that, without in any way limiting the scope of the present disclosure, the investigation tool 120 can be implemented as various types of investigation apparatuses such as an optical imaging apparatus, an electron beam apparatus, etc. In some cases, the same investigation tool can provide both low-resolution image data and high-resolution image data.

[0030] According to a particular embodiment, one of the investigation tools is an electron beam tool such as, for example, a scanning electron microscope (SEM). An SEM is a type of electron microscope that creates an image of a sample by scanning a surface with a focused electron beam. The electrons interact with the atoms of the sample, creating various signals that contain information about the surface topography and composition of the sample. The position of the beam is combined with the intensity of the detected signals to create an image. An SEM can accurately measure features during the production of semiconductor wafers. As an example, the SEM tool can be a critical dimension scanning electron microscope (CD-SEM) used to measure the critical dimensions of structural features within an image.

[0031] One of the problems when using SEM for CD measurement is related to the effect of charging. When a semiconductor sample is scanned by an electron beam, it accumulates charge, and the accumulation of surface charge on the sample caused by the electron beam can cause scanning defects and image artifacts such as distortion of the entire image and / or image disappearance. Such image artifacts are increasingly making it impossible to accurately measure the dimensions of integrated devices important in the semiconductor industry. Since CD is becoming smaller and smaller with the progress of lithography technology, it is expected that the charge accumulation will increase the indeterminate error component in CD-SEM measurement. Artifacts induced by charging may be more serious than dimensions and feature edge profiles, and the inaccuracies caused by image artifacts can pose serious problems for the production of integrated circuits.

[0032] In particular, when scanning a sample from a given direction (e.g., from left to right), non-uniform charging of the sample may be induced, which can affect CD measurements. As an example, assume that there is a line structure in a certain area of the sample. When scanning the area from one specific direction perpendicular to the longitudinal axis of the structure, e.g., from left to right, the electron beam interacts differently with different surface structures and / or different materials, thereby causing different local charging in that area. For example, in some cases, the edges of the line structure are most likely to emit more electrons, thereby creating a positive charge on the surface. Due to the positive charge on the edge surface, when the beam moves from the edge along the center of the line structure towards the other edge, at least a part of the beam is attracted by the positively charged adjacent edge surface, thereby changing the original route and potentially redirecting it towards an adjacent surface other than the originally targeted destination. In such a case, the amount of electrons actually reaching the target location is different compared to the amount that was originally assumed to reach, thereby affecting the accuracy of the SEM signal generated for the target location. For example, in an ideal situation, the SEM signal representing the line structure would generally have two peaks, each representing one of the two line edges. However, due to the influence of local charging, the second peak (i.e., the second one from the scanning direction) will appear with a reduced amplitude and perhaps some artifacts compared to the first peak.

[0033] Various means for reducing the effect of charging include physically modifying / converting the feature to be measured or creating a stack or coating that can neutralize the charge. However, all of these means require physical modifications to the wafer structure, which are complex to implement. According to certain embodiments of the subject matter of the present disclosure, instead of attempting to eliminate the effect of charging itself, an image generation method and system for reducing / eliminating image artifacts caused by the effect of charging are proposed.

[0034] As shown in FIG. 1, system 101 includes a processor and memory circuit (PMC) 102 operably connected to a hardware-based I / O interface 126. PMC 102 is configured to perform the processing necessary to operate the system, as will be described in more detail with reference to FIGS. 2A, 2B, and 3, and includes a processor (not shown individually) and a memory (not shown individually). The processor of PMC 102 can be configured to execute several functional modules according to computer-readable instructions implemented in the non-transitory computer-readable memory included in the PMC. Such functional modules are hereinafter referred to as being included in the PMC.

[0035] According to certain embodiments, the functional modules included in PMC 102 can include a first alignment module 104 and a second alignment module 106. PMC 102 can be configured to obtain a sequence of frames of an area of a semiconductor sample via I / O interface 126. The sequence of frames can be obtained with an electron beam tool (e.g., one of inspection tools 120) configured to scan the area in a plurality of directions. The sequence of frames includes a set of frames, and each set of frames is obtained from a respective direction. PMC 102 can be configured to align the sets of frames and generate an image of the semiconductor sample based on the result of the alignment.

[0036] Specifically, in response to a determination to perform a first alignment within a set of frames obtained from each direction, the first alignment module 104 performs a first alignment within the set of frames obtained therefrom for each direction, combines the sets of aligned frames to generate a first composite frame, thereby resulting in a plurality of first composite frames respectively corresponding to a plurality of directions.

[0037] The second alignment module 106 can be configured to perform a second alignment among a plurality of first composite frames and combine the aligned plurality of first composite frames to generate an image of a region of a semiconductor sample. The generated image, such as that resulting from the process described above, has reduced image artifacts with respect to frames scanned from a given direction among a plurality of directions. The image can be used for the investigation of the semiconductor sample as described above.

[0038] The operation of the system 101, the PMC 102, and the functional modules therein will be described in further detail with reference to FIGS. 2A, 2B, and 3.

[0039] According to certain embodiments, the system 101 can include a storage unit 122. The storage unit 122 can be configured to store data necessary to operate the system 101, such as data related to the input and output of the system 101, as well as intermediate processing results generated by the system 101. By way of example, the storage unit 122 can be configured to store frames made by the investigation tool 120 and / or derivatives thereof. As a result, the frames can be retrieved from the storage unit 122 and provided to the PMC 102 for further processing.

[0040] In some embodiments, the system 101 can 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 the sample, including frame / image data of the sample, can be presented to the user (e.g., by a display forming part of the GUI 124). Options for defining specific operation parameters can be provided to the user via the GUI. In some cases, the user can further view operation results on the GUI, such as the generated image and / or further investigation results (e.g., measurements related to the generated image).

[0041] As will be described in further 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 can include frame data (and / or derivatives thereof) created by the inspection tool 120 and / or frame data stored in one or more data repositories. The frame data can include one or more of the following: frames captured by the inspection tool during the production process, frames derived from the captured frames as obtained at various preprocessing stages, and computer-generated design database frames (e.g., simulated frames, synthetic frames, etc.). Note that in some cases, the frames can include frame data and associated numerical data (e.g., metadata, manually created attributes, etc.). Further note that the frame data can include data related to the layer of interest of the sample and / or one or more additional layers.

[0042] The system 101 is further configured to process the received frames and send the result or a part thereof (e.g., the generated image and / or CD measurements on the image) to the storage unit 122 and / or the inspection tool 120 via the I / O interface 126.

[0043] In some embodiments, in addition to the inspection tool 120, the inspection system 100 can include one or more inspection modules that can be used for the inspection of semiconductor samples, 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 measurement-related module, and / or other inspection modules, etc. The one or more inspection modules can be implemented as a stand-alone computer, or their functions (or at least a part thereof) can be integrated into the inspection tool 120. In some embodiments, the generated images, such as those obtained from the system 101, can be used in the inspection tool 120 and / or one or more inspection modules (or a part thereof) for further inspection of the sample.

[0044] Those skilled in the art will readily understand that the teachings of the subject matter of the present disclosure are not restricted by the system shown in FIG. 1, and equivalent functions and / or modified functions may be integrated or divided in other ways and may be implemented in any suitable combination of software and firmware and / or hardware.

[0045] The investigation system shown in FIG. 1 can be implemented in a distributed computing environment, and the functional modules as included in PMC 102 may be distributed across several local and / or remote devices and may also be linked through a communication network. It should be noted that in other embodiments, at least some of the investigation tool 120, the storage unit 122, and / or the GUI 124 are external to the investigation system 100 and can operate by performing data communication with the system 101 via the I / O interface 126. The system 101 can be implemented as a stand-alone computer that can be used in cooperation with the investigation tool. Alternatively, each function of the system 101 can be at least partially integrated with one or more investigation tools 120, thereby facilitating and enhancing the functions of the investigation tool 120 in the investigation-related process.

[0046] Referring to FIG. 2A, a generalized flowchart is shown that generates an image that can be used for the investigation of a semiconductor sample according to a particular embodiment of the subject matter of the present disclosure.

[0047] As described above, the effects of charging on the sample caused by the electron beam can cause scanning defects and image artifacts such as distortion of the entire image and / or image disappearance. Such image artifacts can affect the accuracy and effectiveness of the investigation of the sample. For example, when scanning the sample from a specific direction (e.g., from left to right) by an electron beam tool, non-uniform charging of the sample may be induced, which may affect the accuracy of CD measurement.

[0048] According to a particular embodiment of the subject matter of the present disclosure, an image generation method and system are proposed for reducing / eliminating image artifacts caused by the effects of charging, thereby providing an image with reduced artifacts and feature uniformity, and accordingly improving the investigation results of the sample.

[0049] Specifically, a sequence of frames of an area of a semiconductor sample can be obtained (202) (e.g., from the inspection tool 120 by the PMC 102 via the I / O interface 126). The sequence of frames can be obtained by an electron beam tool configured to scan the area from multiple directions. As an example, the sequence of frames can be SEM frames captured by an SEM tool. For example, the SEM tool can be a critical dimension scanning electron microscope (CD-SEM) used to measure the critical dimensions of structural elements / features in an image. The sequence of frames includes a set of multiple frames, and each set of frames is obtained from each of the multiple directions.

[0050] In some embodiments, the multiple directions can include one or more pairs of opposite directions. The opposite directions of a pair refer to two directions that are completely opposite to each other (e.g., 180 degrees from each other), such as a first direction from left to right and a second direction from right to left, or a first direction from top to bottom and a second direction from bottom to top. As an example, in some cases, the multiple directions include one pair of opposite directions. In such a case, the sequence of images is captured from two opposite directions, which is also called two-direction scanning. For example, the first set of frames is obtained from a first direction (e.g., from left to right), and the second set of frames is obtained from a second direction (e.g., from right to left).

[0051] As another example, the multiple directions can include a number of pairs of opposite directions. For example, the sequence of images can be obtained from two pairs of opposite directions, namely, a first pair between left and right, and a second pair between top and bottom. This is also called four-direction scanning. As a result, four sets of frames are obtained from the four directions respectively. Similarly, for example, one or more additional pairs of directions, such as directions along the diagonal, can be added, and as a result, additional sets of frames can be obtained from such directions. This method of scanning an area of a sample from multiple directions can generally be called N-direction scanning (N≥2).

[0052] In some embodiments, the number (and exact directions) of directions required to scan a given semiconductor sample or region thereof can be specifically determined. As an example, such determination can be made based on a particular layer of the sample and / or particular structural elements / features included in the target region of the sample. For example, a two-direction scan may be sufficient in the case of a structural element such as a line. In such a case, the frame can be obtained by scanning a region of the sample from a direction that is normal / perpendicular to the main direction of the structural element (e.g., the longitudinal axis of the line). In another example, when the structural element includes a contact having a circular shape, a four-direction scan or a scan in more directions may be used to correct for possible artifacts caused by the effects of charging from different directions. Therefore, in some embodiments of the present disclosure, the proposed method can further include determining a plurality of directions used to scan a region of the sample. As an example, the determination may be made manually by the user as a tool setting, or automatically by the system 101 as part of an image generation method. Alternatively, the determination can be a default determination. For example, the system can, by default, always perform a two-direction scan or a four-direction scan, etc. Thus, this default determination can be regarded as a pre-determination or pre-setting of the system.

[0053] As used herein, a structural element or feature has a geometric shape or geometry with a contour and can, in some cases, refer to an original object on the sample that is combined with other objects (and thus forms a pattern). Examples of structural elements can include features of common shapes such as contacts, line structures, and the like.

[0054] Next, referring to FIG. 4, an example of a sequence of frames of a target region of a sample according to a particular embodiment of the subject matter of the present disclosure is shown.

[0055] According to certain embodiments, a sequence of frames can be obtained by sequentially scanning an area from multiple directions and obtaining one or more frames from each direction during all scans. FIG. 4 shows an example of a sequence of frames obtained by a four-direction scan including a first pair of left-to-right and right-to-left directions and a second pair of top-to-bottom and bottom-to-top directions. Specifically, 400 shows an example where the target area of the sample is sequentially scanned from four directions, and each time, one frame is obtained from each direction. As shown in the illustration, frame 1 is obtained from the first direction from left to right, frame 2 is obtained from the second direction from right to left, frame 3 is obtained from the third direction from top to bottom, and frame 4 is obtained from the fourth direction from bottom to top. Then, the sequence continues in a similar manner, and frames 5-8 repeat in this order.

[0056] 410 shows another example where the target area of the sample is sequentially scanned from four directions, and each time, two frames are obtained from each direction. As shown in the illustration, frames 1 and 2 are obtained from the first direction from left to right, frames 3 and 4 are obtained from the second direction from right to left, frames 5 and 6 are obtained from the third direction from top to bottom, and frames 7 and 8 are obtained from the fourth direction from bottom to top.

[0057] Scans in different orders can have different advantages. For example, when scanning in the manner shown in 400, it can be expected that the charge spreads more uniformly across the surface of the sample, and thus it is advantageous for reducing the effect of the accumulated charge and the image artifacts caused thereby. On the other hand, when scanning in the manner shown in 410, the amount of drift between the two frames captured from each direction can be reduced (as described above, when they are captured, adjacent frames are not impaired by a large number of drifts).

[0058] For illustrative purposes, only eight frames are shown in the example sequence, but it should be understood that any example sequence can continue in a similar iterative manner. It should also be understood that the number of frames acquired from each direction per scan is not limited to one or two frames as shown in the example. The order of scanning for multiple directions can further be different from that illustrated above and can have different advantages compared to that described above. As a result, other suitable numbers of frames combined with different scanning orders may be adapted and applied in the present disclosure.

[0059] Continuing with the description of FIG. 2, a sequence of frames including a set of multiple frames acquired from multiple directions can be aligned, and an image of the semiconductor sample can be generated based on the result of the alignment (204) (e.g., by PMC102). In some embodiments, the alignment can include a first alignment among the frames within each set of frames acquired from each direction and a second alignment between the frames from multiple directions (i.e., the aligned and combined frames). In some cases, the first alignment can be optional. For example, as will be described in more detail below, it can be determined whether it is necessary to perform the first alignment.

[0060] According to a particular embodiment, in response to the determination to perform a first alignment among the sets of frames acquired from each direction, for each direction, within the set of frames acquired from each direction, a first alignment can be performed (e.g., by the first alignment module 104 included in PMC102), resulting in a set of aligned frames (206). The sets of aligned frames can be combined to generate a first composite frame for each direction (206). Therefore, a plurality of first composite frames respectively corresponding to multiple directions can be obtained.

[0061] According to certain embodiments, the first alignment is performed for the purpose of correcting drift between frames within a set of frames acquired from a given direction, and the drift is caused by one or more physical effects between the electron beam of an electron beam tool and a semiconductor sample. By way of example, the one or more physical effects can be selected from the group consisting of thermal expansion, the effect of charging, and tool tolerances.

[0062] Thermal expansion refers to a physical phenomenon in which a semiconductor sample, such as a wafer, is placed on an inspection stage installed in a chamber where a constant temperature is maintained and scanned by an electron beam, causing the wafer to be continuously heated, thereby causing physical expansion of the wafer surface. Such thermal expansion can cause the original target location of the beam to drift. The effect of charging refers to the physical phenomenon of the accumulation of surface charges on the sample caused by the interaction between the electron beam and the sample as described above. Due to the continuous scanning process, the entire surface of the area is continuously charged (this is also called area charging as opposed to local charging as described above), thereby affecting at least a part of the actual destination of the beam on the sample, which causes drift between frames. Tool tolerances refer to specific physical differences related to the electron beam tool itself or differences between different tools. For example, in some cases, there may be particles in the tool during scanning and / or there may be mechanical differences in the component assembly, and these factors can, together or separately, result in drift between frames.

[0063] It should be noted that the above physical effects are listed for illustration and exemplification purposes only and should in no way be considered as limiting the scope of the present disclosure. In different embodiments, other physical effects that may cause possible drift may be added in addition to or instead of the above.

[0064] In some embodiments, the first alignment can include performing pattern matching between frames within a set of frames acquired from a given direction. Pattern matching generally refers to checking for the presence of components of a particular pattern or structure. For example, pattern matching can be performed by identifying a particular structural element or pattern within a first frame of the set and searching for the identified pattern within each of the remaining frames of the set. Pattern matching can be performed in various ways using various algorithms. By way of example, in the present disclosure, a normalized cross-correlation function can be used to extrapolate or predict the expected location of a pattern.

[0065] In some cases, the search range (e.g., search radius and / or search direction) used in the current frame during pattern matching to find a matching pattern 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 particular structural element (e.g., a line, a contact, or at least a portion thereof) is identified in the first frame. When searching for the particular element within the second frame, the search range including the search radius and / or search direction can be defined, for example, by default or by the user, since there is no reference drift to consider. After the element is found within the second frame, a first drift between the two frames (with respect to the relative distance and direction between the locations of the element in the first and second frames) can be recognized. When searching for the same structural element within the third frame, the first drift can be used as a reference when determining a particular search range therein. Similarly, when searching for the same element within the fourth frame, the first drift and / or the second drift can be used as a reference to determine the search range, thereby enabling a more efficient and accurate search.

[0066] After the first alignment is performed, a set of aligned frames is obtained for each direction. The sets of aligned frames can be combined to generate a first composite frame for each direction. Therefore, a plurality of first composite frames corresponding to a plurality of directions can be obtained. The combination of the frames can be performed in various ways. As an example, the sets of aligned frames can be combined by summing the aligned frames, optionally averaging the frames during the summing, and / or applying weights to the frames during the summing.

[0067] A second alignment is performed among the plurality of first composite frames (e.g., by a second alignment module 106 included in PMC102), which can result in a plurality of aligned first composite frames (208). The plurality of aligned first composite frames can be combined to generate an image of an area of the semiconductor sample (208). The image resulting from the above process has reduced image artifacts (e.g., caused by non-uniform charging of the sample when scanned from one direction) with respect to the frames scanned from a given direction among the plurality of directions. Such a generated image can be used for the investigation of the semiconductor sample.

[0068] According to certain embodiments, the second alignment is performed to correct for offsets between a plurality of first composite frames resulting from scanning the region from a plurality of directions. Offsets caused by directional scanning may be related to the scanning mechanism of the electron beam tool. By way of example, scanning from different directions may be performed with different scanning coils of the tool, and there may be a processing delay between the scanning coils, which may be translated into such an offset. For instance, when starting a scan in a given direction, there is always an acceleration phase when the beam starts to increase in speed from rest, which causes a delay in the signal being formed. Signals acquired during the acceleration phase will be on different sides of the frame formed when scanning from different directions, thereby causing an offset between frames acquired from different directions. This is merely one example of such physical phenomena that may cause an offset between frames acquired from different directions, and it should be noted that the present disclosure is not limited to specific factors or phenomena that cause the offset.

[0069] The second alignment can be performed in a manner similar to the first alignment, for example, by performing pattern matching between a plurality of first composite frames corresponding to a plurality of directions. The pattern matching can be performed in a manner similar to the method described above with reference to block 206. Specifically, in some embodiments, the search direction used in the current frame during pattern matching can be based on the direction of scanning at the time of acquisition of the current frame in order to find a matching pattern.

[0070] As an example, assume that four first composite frames corresponding to four scanning directions are obtained after a first alignment. When searching for a specific pattern in one of the frames, the preferred search direction can be defined based on the scanning direction in which the specific composite frame was generated. For example, if the first composite frame is generated based on a set of frames obtained from a first direction (e.g., left to right), the preferred search direction in such a frame can be defined to be consistent with the first direction. For example, the search radius (e.g., left - right dimension) set for the X direction can be made larger compared to the search radius (e.g., up - down dimension) set for the Y direction.

[0071] In some embodiments, the plurality of directions can include pairs of two or more opposite directions. In such a case, the second alignment can be performed in a two - step alignment process as shown in FIG. 3. Specifically, for each given pair of opposite directions, two first composite frames corresponding to the opposite directions of the given pair can be aligned. The two aligned first composite frames can be combined to obtain a composite frame, thereby resulting in two or more composite frames corresponding to two or more pairs of opposite directions (302). As will be illustrated below with reference to FIG. 6, two or more composite frames can be aligned, and the two or more aligned composite frames can be combined to generate an image of the semiconductor sample (304).

[0072] Next, referring to FIG. 7, two graphs are shown that illustrate drift and offset between frames according to a particular embodiment of the subject matter of the present disclosure.

[0073] As shown in the illustration, 702 shows a graph of a one-directional scan of the sample, i.e., a scan of the sample from only one given direction. A set of frames including eight frames has been acquired from the given direction. The X-axis of the graph represents the frame numbers of the eight frames in the set, e.g., frames 1 to 8. The Y-axis represents the amount of drift caused between the frames within the set. As described above, the drift between the frames within the set may be caused by one or more physical effects between the electron beam of the electron beam tool and the sample, such as thermal expansion, the effect of charging, and tool tolerances. In some cases, the drift between the frames appears to be in a linear relationship. This is particularly true when the drift is caused at least in part by the effect of thermal expansion. As shown in graph 702, the amount of drift for each specific frame forms a linear regression.

[0074] On the other hand, 704 shows a graph of a two-directional scan of the sample, i.e., a scan of the sample from two directions (e.g., a pair of opposite directions). An eight-frame sequence including two sets of frames is acquired, with each set including four frames acquired from each respective direction. Specifically, the sample is sequentially scanned from two directions as shown in 400 of FIG. 4. Therefore, a first set of frames including frames 1, 3, 5, and 7 is acquired from the first direction, and a second set of frames including frames 2, 4, 6, and 8 is acquired from the second direction. Since each set of frames is collected every other frame within the sequence, the amount of drift between every two adjacent frames within the set of the two-directional scan is expected to be twice the amount of drift between every two adjacent frames within the set of the one-directional 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.

[0075] Therefore, when performing the first alignment, the search radius used in pattern matching should be defined accordingly to correct such drift. For example, in a two-direction scan, the search radius should be at least twice that of a one-direction scan, and in a four-direction scan, the search radius should be at least four times that of a one-direction scan.

[0076] As described above, the second set of frames shown in graph 704 includes frames 2, 4, 6, and 8 obtained from the second direction. As shown, there is an offset between the amount of drift of the second set of frames compared to the amount of drift of the first set of frames. For example, the offset between the drift of frame 1 (obtained from the first direction) and the drift of frame 2 (obtained from the second direction) is approximately 16 nm, and the same applies to the offset between frame 3 and frame 4. This offset between frames obtained from different directions may be caused by a directional scan (i.e., scanning of the sample from different directions) as described above, which may be related to the scanning mechanism of the electron beam tool. The second alignment is for correcting such an offset as described above.

[0077] As shown in FIG. 7, the offset between frames acquired from different directions can be very large compared to the drift between frames acquired from the same direction. Therefore, in some cases, different means may be employed to compensate for such an offset in addition to or instead of the second alignment. According to certain embodiments, tool setting optimization can be performed to address this issue. As is known, an electron beam tool can generally be recognized as including, among other things, a scanning module and an imaging module. The scanning module can be configured to physically scan the surface of a sample using an electron beam, thereby enabling a signal to be detected based on electrons emitted from the sample. The imaging module can be configured to convert the detected signal into a digital format that can be represented by frames. The two modules are typically required to be accurately synchronized so that the generated frames can accurately reflect the generated signal.

[0078] In some embodiments of the present disclosure, accordingly, it is proposed to adjust / conform the synchronization between the scanning process and the imaging process to compensate for at least part of the offset between frames acquired from different directions. The exact adjustment or conformance can be based on offset data obtained from a reference sample.

[0079] For example, in the example of graph 704 of FIG. 7, the second set of frames can be imaged using a pre-set delay based on the generated signal from the scanning process, while for the first set of frames, no delay is required. Similarly, in the example of FIG. 4, if there are four sets of frames acquired from four directions, the delay between the imaging process and the scanning process can be configured differently to generate different sets of frames.

[0080] According to certain embodiments, when performing alignment of a set of multiple frames acquired from multiple directions and generation of an image of a semiconductor sample, an alternative process may be implemented instead of steps 206 and 208, as described with respect to block 204 of FIG. 2A. This may be appropriate in some cases when it is determined not to perform the first alignment, as will be described in detail with respect to FIG. 2B.

[0081] Next, referring to FIG. 2B, a generalized flowchart of an alternative process for frame alignment and image generation according to certain embodiments of the subject matter of the present disclosure is shown.

[0082] As described above, in some embodiments, the determination can be made to decide whether to perform the first alignment. By way of example, the determination can be based on the following factors: the number of frames included in the set of frames, and at least one of the layers of the sample to be investigated (as a manufacturing step in the manufacturing process) and / or the material. For example, in some cases, only one frame is acquired from each direction, i.e., each set of frames includes a single frame. In such cases, there is no need to perform the first alignment within each set of frames. In another example, a particular layer of the sample may not be subject to drift problems due to its physical properties such as, for example, the material of the layer, charge, temperature, etc. In some cases, the layer and / or material of the sample may be used together or separately to determine the need to perform the first alignment.

[0083] Note that the determination referred to in this specification regarding the first alignment can 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 setting). Alternatively, the determination can be a default determination, i.e., the system can always perform the first alignment by default or not perform the first alignment by default. Thus, this default determination can be regarded as a pre-determination or pre-setting of the system.

[0084] According to certain embodiments, in response to a determination not to perform the first alignment, a set of frames obtained from each direction can be combined to generate a second composite frame, thereby resulting in a plurality of second composite frames respectively corresponding to a plurality of directions (210). The second alignment can be performed among the plurality of second composite frames, and the aligned plurality of second composite frames can be combined to generate an image of the semiconductor sample (212).

[0085] FIG. 5 shows a schematic diagram of an image generation process in two-direction scanning according to a particular embodiment of the subject matter of the present disclosure.

[0086] As illustrated, a sequence of four frames (frames 1-4) is obtained that includes two frames (frames 1 and 3) obtained from a first direction (e.g., left to right) and two frames (frames 2 and 4) obtained from a second direction (e.g., right to left). A determination can be made as to whether a first alignment 510 should be performed on the frames obtained from the same direction. In response to an affirmative determination, frames 1 and 3 are aligned and the two aligned frames are combined to generate a composite frame 502 (when the first alignment is performed, it is called the first composite frame as described above). Similarly, frames 2 and 4 are aligned and the two aligned 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 a composite frame 502 (when the first alignment is not performed, it is called the second composite frame as described above). Similarly, frames 2 and 4 are combined to generate a composite frame 504. Then, a second alignment 520 is performed on the two composite frames 502 and 504, and the two aligned composite frames are combined to generate an image 506 of the sample.

[0087] FIG. 6 shows a schematic diagram of an image generation process in four-direction scanning according to a particular embodiment of the subject matter of the present disclosure.

[0088] As illustrated, a sequence of eight frames (frames 1-8) is obtained by scanning a sample from four directions, each including a set of four frames obtained from each direction. Each set includes two frames, namely, frame 1 and 5 obtained from a first direction (e.g., left to right), frame 2 and 6 obtained from a second direction (e.g., right to left), frame 3 and 7 obtained from a third direction (e.g., top to bottom), and frame 4 and 8 obtained from a fourth direction (e.g., bottom to top). Clearly, the four directions include two pairs of opposite directions.

[0089] Similarly, as described above with reference to FIG. 5, it is possible to determine whether to perform the first alignment 510, and based on the result of the determination, the two frames from each set are first aligned and then combined or simply combined to generate a composite frame for a given direction. Therefore, four composite frames 602, 604, 606, and 608 can be generated.

[0090] Since there are two pairs of opposite directions, a second alignment 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 that are a pair are first aligned, and the two aligned first composite frames are combined to obtain a composite frame. For example, the composite frames 602 and 604 corresponding to the opposite directions from left to right and from right to left are aligned and combined to generate a composite frame 610 (525). Similarly, the other two composite frames 606 and 608 are aligned and combined to generate a composite frame 612 (525). Therefore, two composite frames are generated corresponding to the two pairs of opposite directions. Then, the two composite frames 610 and 612 are aligned and combined to generate an image 614 of the semiconductor sample (530).

[0091] According to a particular embodiment, the image generation process as described above with reference to FIGS. 2A, 2B, and 3 can be included as part of an investigation strategy that can be used by the system 101 and / or the investigation tool 120 for investigating a sample during execution, for example, by performing a measurement operation on the sample. In such a case, the subject matter of the present disclosure further includes a system and method for generating an investigation strategy during the strategy setting phase, and the strategy includes steps as described with reference to FIGS. 2A, 2B, and 3 (and their various embodiments). It should be noted that the term "investigation strategy" should be broadly interpreted to include any strategy that can be used in an investigation tool for performing operations related to any type of investigation as described above.

[0092] For example, examples shown in this disclosure such as frames obtained from a particular exemplified direction, alignment algorithms, pattern matching algorithms, and the listed physical effects as described above are shown for illustrative purposes and should in no way be construed as limiting this disclosure. In addition to or instead of the above, other examples can be used.

[0093] Among the advantages of certain embodiments of the image generation process described herein may be providing an image of a sample having reduced image artifacts (e.g., image artifacts caused by non-uniform charging of the sample when scanned from one direction). Such generated images can provide better results with higher accuracy, for example, when used in the investigation of semiconductor samples such as CD measurements.

[0094] It should be understood that the present disclosure in its application is not limited to the details set forth in the description contained herein or shown in the drawings.

[0095] It will also be understood that the system according to the present disclosure can be realized, at least in part, by a properly programmed computer. Similarly, the present disclosure contemplates a computer program readable by a computer for performing the method of the present disclosure. The present disclosure further contemplates a non-transitory computer-readable memory tangibly embodying a program of instructions executable by a computer for performing the method of the present disclosure.

[0096] The present disclosure allows for other embodiments and can be practiced and carried out in various ways. Therefore, it should be understood that the syntax and terminology used herein are for the purpose of description and should not be regarded as limiting. Thus, those skilled in the art will understand that the concepts on which the present disclosure is based can be readily utilized as a basis for designing other structures, methods, and systems for carrying out some of the objectives of the subject matter of the present disclosure.

[0097] Those skilled in the art will readily understand that various modifications and changes can be applied to the embodiments of the present disclosure as described above without departing from the scope defined in the appended claims and by the claims.

Description of Reference Numerals

[0098] 100 Investigation system 101 Computer-based system 102 Processor and Memory Circuit (PMC) 104 First Alignment Module 106 Second Alignment Module 120 Investigation Tool 122 Storage Unit 124 GUI 126 I / O Interface 502, 504 Composite Frame 506 Image 510 First Alignment 520 Second Alignment 602, 604, 606, 608 Composite Frame 610, 612 Composite Frame 614 Image 702, 704 Graph

Claims

1. A computerized system for investigating a semiconductor sample, the system being to obtain a sequence of frames of an area of the semiconductor sample, the sequence of frames being obtained by an electron beam tool configured to scan the area from a plurality of directions, the sequence of frames including a set of a plurality of frames, each set of frames being obtained from a respective direction, obtaining the sequence; registering the sets of the plurality of frames and generating an image of the semiconductor sample based on the result of the registration; in response to a determination to perform a first registration among the sets of frames obtained from each direction, for each direction, performing the first registration among the sets of frames subsequently obtained therefrom, combining the registered sets of frames to generate a first composite frame, thereby resulting in a plurality of first composite frames respectively corresponding to the plurality of directions; performing a second registration among the plurality of first composite frames and combining the plurality of registered first composite frames to generate the image of the area of the semiconductor sample, the second registration being performed to correct an offset between the plurality of first composite frames related to a scanning mechanism of the electron beam tool caused by directional scanning from the plurality of directions, generating; including a processing and memory circuit (PMC) configured to perform; wherein the generated image of the semiconductor sample has reduced image artifacts with respect to frames scanned from a given direction among the plurality of directions, and the image is usable for investigating the semiconductor sample, the computerized system.

2. A computerized system for investigating a semiconductor sample, the system being to obtain a sequence of frames of an area of the semiconductor sample, the sequence of frames being obtained by an electron beam tool configured to scan the area from a plurality of directions, the sequence of frames including a set of a plurality of frames, each set of frames being obtained from a respective direction, obtaining the sequence; aligning a set of the plurality of frames and generating an image of the semiconductor sample based on a result of the alignment; in response to a determination not to perform a first alignment, for each direction, combining the set of frames obtained therefrom to generate a second composite frame, thereby resulting in a plurality of second composite frames respectively corresponding to the plurality of directions; performing a second alignment among the plurality of second composite frames, and combining the aligned plurality of second composite frames to generate the image of the semiconductor sample, wherein the second alignment is performed to correct an offset between a plurality of first composite frames related to a scanning mechanism of the electron beam tool caused by a directional scan from the plurality of directions, including generating; including a processing and memory circuit (PMC) configured to perform; a computerized system, wherein the generated image of the semiconductor sample has reduced image artifacts with respect to frames scanned from a given direction among the plurality of directions, and the image is usable for investigation of the semiconductor sample.

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

4. The computerized system according to claim 1, wherein a sequence of the frames is obtained by sequentially scanning the area from the plurality of directions and obtaining one or more frames from each direction during all scans.

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

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

7. The computerized system according to claim 1, wherein the first alignment is performed to correct for drift between sets of the 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.

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

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

10. The computerized system according to 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 according to claim 1, wherein a search direction used in a current frame during pattern matching performed in the second alignment is based on a scanning direction at the time of acquisition of the current frame.

12. The plurality of directions includes pairs of two or more opposite directions, and performing the second alignment includes for each given pair of opposite directions, aligning two first composite frames corresponding to the opposite directions of the given pair, combining the two aligned first composite frames to obtain a composite frame, thereby resulting in two or more composite frames corresponding to the two or more pairs of opposite directions; and aligning the two or more composite frames, combining the two or more aligned composite frames to generate the image of the semiconductor sample. The computerized system according to claim 1.

13. A computerized method for investigating a semiconductor sample, the method being executed by a processing and memory circuit (PMC), Obtaining a sequence of frames of the region of the semiconductor sample, wherein the sequence of frames is obtained by an electron beam tool configured to scan the region from a plurality of directions, the sequence of frames includes a set of a plurality of frames, and each set of frames is obtained from a respective direction, obtaining a sequence; Aligning the sets of the plurality of frames and generating an image of the semiconductor sample based on the result of the alignment; In response to a determination to perform a first alignment among the sets of frames obtained from each direction, for each direction, performing the first alignment among the sets of frames obtained therefrom, and combining the aligned sets of frames to generate a first composite frame, thereby resulting in a plurality of first composite frames respectively corresponding to the plurality of directions; Performing a second alignment among the plurality of first composite frames, and combining the aligned plurality of first composite frames to generate the image of the region of the semiconductor sample, wherein the second alignment is performed to correct an offset between the plurality of first composite frames related to a scanning mechanism of the electron beam tool caused by a directional scan from the plurality of directions, including generating; including; A computerized method, wherein the generated image of the semiconductor sample has reduced image artifacts with respect to frames scanned from a given direction among the plurality of directions, and the image is usable for investigation of the semiconductor sample.

14. A computerized method for investigating a semiconductor sample, wherein the method is executed by a processing and memory circuit (PMC), Obtaining a sequence of frames of the region of the semiconductor sample, wherein the sequence of frames is obtained by an electron beam tool configured to scan the region from a plurality of directions, the sequence of frames includes a set of a plurality of frames, and each set of frames is obtained from a respective direction, obtaining a sequence; Aligning the sets of the plurality of frames and generating an image of the semiconductor sample based on the result of the alignment; In response to the decision not to perform the first alignment, for each direction, the set of frames thus obtained is combined to generate a second composite frame, thereby resulting in a plurality of second composite frames respectively corresponding to the plurality of directions, performing a second alignment among the plurality of second composite frames, and combining the aligned plurality of second composite frames to generate the image of the semiconductor sample, wherein the second alignment is performed to correct an offset between a plurality of first composite frames related to a scanning mechanism of the electron beam tool caused by a directional scan from the plurality of directions, and the generating includes the generating, including, wherein the generated image of the semiconductor sample has reduced image artifacts with respect to frames scanned from a given direction among the plurality of directions, and the image is usable for investigation of the semiconductor sample, a computerized method.

15. The computerized method according to claim 13, wherein the decision is based on the following factors: the number of frames included in the set of frames, and at least one of the layers and / or materials of the sample to be investigated.

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

17. The computerized method according to claim 13, wherein a search direction used in a current frame during pattern matching performed in the second alignment is based on a scanning direction at the time of acquisition of the current frame.

18. the plurality of directions includes pairs of two or more opposite directions, and performing the second alignment includes for each given pair of opposite directions, aligning two first composite frames corresponding to the opposite directions of the given pair, and combining the aligned two first composite frames to obtain a composite frame, thereby resulting in two or more composite frames respectively corresponding to the two or more pairs of opposite directions, Aligning the two or more composite frames and combining the aligned two or more composite frames to generate the image of the semiconductor sample The computerized method according to claim 13, comprising:

19. A non-transitory computer-readable storage medium tangibly embodying a program of instructions that, when executed by a computer, cause the computer to perform a method of investigating a semiconductor sample, the method comprising: Obtaining a sequence of frames of an area of the semiconductor sample, the sequence of frames being obtained by an electron beam tool configured to scan the area from a plurality of directions, the sequence of frames including a set of a plurality of frames, each set of frames being obtained from a respective direction; Aligning the sets of the plurality of frames and generating an image of the semiconductor sample based on the result of the alignment; In response to a determination to perform a first alignment among the sets of frames obtained from each direction, for each direction, performing the first alignment among the sets of frames obtained therefrom, and combining the aligned sets of frames to generate a first composite frame, thereby resulting in a plurality of first composite frames respectively corresponding to the plurality of directions; Performing a second alignment among the plurality of first composite frames and combining the aligned plurality of first composite frames to generate the image of the area of the semiconductor sample, the second alignment being performed to correct an offset between the plurality of first composite frames related to a scanning mechanism of the electron beam tool caused by directional scanning from the plurality of directions, including generating; including The generated image of the semiconductor sample has reduced image artifacts with respect to frames scanned from a given direction among the plurality of directions, and the non-transitory computer-readable storage medium, wherein the image is usable for investigating the semiconductor sample

Images