Lateral recess measurement in semiconductor samples

Abstract

A system and method for measuring a lateral recess in a semiconductor sample are provided, comprising: obtaining a first image acquired by collecting SE emitted from a surface of the sample and a second image acquired by collecting BSE scattered from an internal region of the sample between the surface and a target second layer, the sample being scanned using an electron beam having a landing energy selected to penetrate to a depth corresponding to the target second layer; generating a first GL waveform based on the first image, and generating a second GL waveform based on the second image; estimating a first width of the first layer based on the first GL waveform, and generating a second width relative to at least the target second layer based on the second GL; and measuring the lateral recess based on the first width and the second width.

Description

Technical Field

[0001] The presently disclosed subject matter relates generally to the field of inspection of semiconductor specimens, and more particularly, to critical dimension (CD) metrology with respect to lateral recesses in the specimens. Background Art

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

[0003] Inspection can be provided by using non-destructive inspection tools during or after fabrication 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 to a wafer and detecting the light or electrons from the wafer. As non-limiting examples, a variety of non-destructive inspection tools include scanning electron microscopes, atomic force microscopes, optical inspection tools, etc.

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

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

[0006] According to certain aspects of the presently disclosed subject matter, there is provided a computerized system for measuring lateral recesses in a semiconductor sample, the semiconductor sample comprising a stack of one or more first layers of a first type and one or more second layers of a second type deposited alternately with each other, the second layers being at least partially etched so as to form a lateral recess between each given second layer and two adjacent first layers thereof, the system comprising: an electron beam tool configured to: scan the semiconductor sample with an electron beam having a landing energy specifically selected to penetrate to a predefined depth corresponding to a target second layer of the sample; and acquire a first image by collecting secondary electrons (SE) emitted from a surface of the sample, and acquire a second image by collecting secondary electrons (SE) emitted from a surface of the sample at a depth between the surface and the target second layer; and acquiring a second image by using backscattered electrons (BSE) scattered from an internal region between the sample and the target, the first image providing information on a surface profile of the sample and the second image providing information on an internal structure of the internal region; and a processing and memory circuit (PMC) operably connected to the electron beam tool and configured to: generate a first GL waveform providing information on a grayscale (GL) intensity distribution of the first image and a second GL waveform providing information on a GL intensity distribution of the second image; estimate a first width of the one or more first layers based on the first GL waveform, and estimate a second width relative to at least the target second layer based on the second GL waveform; and measure a lateral recess relative to the target second layer based on the first width and the second width.

[0007] In addition to the above features, the system according to this aspect of the presently disclosed subject matter may include one or more of the features (i) to (x) listed below in any desired combination or permutation that is technically possible:

[0008] (i) The semiconductor sample includes a gate-all-around (GAA) device. The first layer is made of silicon, and the second layer is made of silicon germanium.

[0009] (ii) the target second layer is a top second layer among the one or more second layers, and the lateral concavity to be measured is a top lateral concavity formed between the top second layer and an adjacent first layer.

[0010] (iii) the target second layer is a subsequent second layer after the top second layer, and the measured lateral concavity is an average lateral concavity of a top layer formed between the top second layer and an adjacent first layer and a subsequent lateral concavity formed between the subsequent second layer and the adjacent first layer.

[0011] (iv) the PMC is further configured to measure an average lateral concavity of a subsequent second layer relative to the top second layer, and to derive a subsequent layer lateral concavity based on the average lateral concavity and the top layer lateral concavity.

[0012] (v) The SE is collected by an array of SE detectors, and the BSE is collected by at least one BSE detector.

[0013] (vi) The landing energy that penetrates to the predefined depth corresponding to the target second layer is specifically selected based on a comparison between the number of BSEs relative to a reference sample without lateral recesses and the number of BSEs relative to the semiconductor sample of interest.

[0014] (vii) estimating the first width includes estimating first topological points on the first GL waveform by calculating derivatives along the first GL waveform, and applying a predefined derivative threshold on the first GL waveform to generate the first topological points, and measuring the first width between the first topological points.

[0015] (viii) estimating the second width includes estimating second topological points on the second GL waveform by applying a predefined GL threshold on the second GL waveform, generating the second topological points, and measuring the second width between the second topological points.

[0016] (ix) The PMC is further configured to calibrate the measured lateral recess relative to reference measurement data obtained from the TEM.

[0017] (x) The calibration is based on a correlation previously derived between corresponding measurement data from the electron beam tool and the reference measurement data obtained from a TEM.

[0018] According to other aspects of the presently disclosed subject matter, there is provided a method of measuring lateral recesses in a semiconductor sample, the semiconductor sample comprising a stack of one or more first layers of a first type and one or more second layers of a second type deposited alternately with each other, the second layers being at least partially etched so as to form lateral recesses between each given second layer and two adjacent first layers, the method being performed by a processing and memory circuit (PMC) and comprising: obtaining a first image acquired by collecting secondary electrons (SE) emitted from a surface of the sample and a second image acquired by collecting backscattered electrons (BSE) scattered from an inner region of the sample between the surface and the target second layer, wherein a first image is obtained by collecting secondary electrons (SE) emitted from a surface of the sample and a second image is obtained by collecting backscattered electrons (BSE) scattered from an inner region of the sample between the surface and the target second layer, wherein the second layer is at least partially etched so as to form a lateral recess between each given second layer and two adjacent first layers, the method being performed by a processing and memory circuit (PMC) and comprising: obtaining a first image acquired by collecting secondary electrons (SE) emitted from a surface of the sample and a second image obtained by collecting backscattered electrons (BSE) scattered from an inner region of the sample between the surface and the target second layer, wherein the second image is obtained by collecting a backscattered electron (BSE) scattered from an inner region of the sample between the surface and the target second layer, wherein the backscattered electrons (BSE) are scattered from the ... Scanning the semiconductor sample with an electron beam of a landing energy specifically selected to penetrate to a predefined depth corresponding to the target second layer, and wherein the first image provides information on the surface contour of the sample and the second image provides information on the internal structure of the internal region; generating a first grayscale (GL) waveform providing information on the GL intensity distribution of the first image and a second GL waveform providing information on the GL intensity distribution of the second image; estimating a first width of the first layer based on the first GL waveform, and estimating a second width relative to at least the target second layer based on the second GL; and measuring a lateral recess relative to the target second layer based on the first width and the second width.

[0019] This aspect of the disclosed subject matter may comprise one or more of the features (i) to (x) listed above with respect to the system mutatis mutandis in any desired combination or permutation that is technically possible.

[0020] According to other aspects of the presently disclosed subject matter, there is provided a non-transitory computer-readable storage medium tangibly embodying a program of instructions that, when executed by a computer, causes the computer to perform a method of measuring a lateral recess in a semiconductor sample, the semiconductor sample comprising a stack of one or more first layers of a first type and one or more second layers of a second type deposited alternately with each other, the second layers being at least partially etched so as to form a lateral recess between each given second layer and two of its adjacent first layers, the method comprising: obtaining a first image acquired by collecting secondary electrons (SE) emitted from a surface of the sample and obtaining a second image acquired by collecting backscattered electrons (SEs) scattered from an inner region of the sample between the surface and a target second layer; A second image acquired by a BSE (Borne electron beam), wherein the semiconductor sample is scanned using an electron beam having a landing energy specifically selected to penetrate to a predefined depth corresponding to the target second layer, and wherein the first image provides information of a surface profile of the sample and the second image provides information of the internal structure of the internal region; generating a first grayscale (GL) waveform providing information of a GL intensity distribution of the first image and a second GL waveform providing information of a GL intensity distribution of the second image; estimating a first width of the first layer based on the first GL waveform, and estimating a second width relative to at least the target second layer based on the second GL; and measuring a lateral recess relative to the target second layer based on the first width and the second width.

[0021] This aspect of the inventively disclosed subject matter may comprise one or more of the features (i) to (x) listed above with respect to the system mutatis mutandis in any desired combination or permutation that is technically possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to understand the present disclosure and to see how it may be carried out in practice, embodiments will be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0023] Figure 1 A generalized block diagram of an inspection system in accordance with certain embodiments of the presently disclosed subject matter is shown.

[0024] Figure 2A A generalized flow chart for measuring lateral recesses in a semiconductor sample is shown, in accordance with certain embodiments of the presently disclosed subject matter.

[0025] Figure 2B A generalized flow chart for acquiring a first image and a second image according to some embodiments of the presently disclosed subject matter is shown.

[0026] Figure 3A generalized flow chart for measuring per-layer lateral concavity and / or measuring average lateral concavity according to certain embodiments of the presently disclosed subject matter is shown.

[0027] Figure 4 A schematic diagram of a GAA structure is shown in accordance with some embodiments of the presently disclosed subject matter.

[0028] Figure 5 Examples of first and second images of a GAA structure are shown, in accordance with some embodiments of the presently disclosed subject matter.

[0029] Figure 6 Examples of first and second GL waveforms according to some embodiments of the presently disclosed subject matter are shown.

[0030] Figure 7 An exemplary graph illustrating a correlation between the difference in the number of BSEs received from a reference sample relative to a sample of interest and the level of landing energy used, according to certain embodiments of the presently disclosed subject matter. DETAILED DESCRIPTION

[0031] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, those skilled in the art will appreciate that the subject matter currently disclosed may be practiced without these specific details. In other cases, well-known methods, processes, components, and circuits are not described in detail in order to avoid obscuring the subject matter currently disclosed.

[0032] Unless otherwise specifically stated, as will be clear from the following discussion, it will be understood that terms such as "measure," "scan," "acquire," "generate," "estimate," "derive," "select," "calculate," "apply," "calibrate," etc., utilized 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, such as electronic, quantities and / or the data representing physical objects. The term "computer" should be broadly interpreted to encompass any kind of hardware-based electronic device with data processing capabilities, including, as non-limiting examples, the inspection systems, metrology systems, and corresponding portions thereof disclosed in this application.

[0033] The term "inspection" used in this specification should be broadly interpreted to cover any kind of metrology-related operations and operations related to the detection and / or classification of defects in the sample during the manufacture of the sample. Inspection is provided by using a non-destructive inspection tool during or after the manufacture of the sample to be inspected. As a non-limiting example, the inspection process may include one or more of the following operations: runtime scanning (in a single or multiple scans), sampling, inspection, measurement, classification and / or other operations provided with respect to the sample or part thereof using the same or different inspection tools. Similarly, inspection may be provided before manufacturing the sample to be inspected, and may include, for example, generating (multiple) inspection schemes and / or other setup operations. It should be noted that, unless otherwise specifically stated, the term "inspection" or its derivatives used in this specification are not limited in terms of the resolution or size of the inspection area. As non-limiting examples, various non-destructive inspection tools include scanning electron microscopes, atomic force microscopes, optical inspection tools, and the like.

[0034] The term "metrology" as used in this specification should be broadly interpreted 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. As a non-limiting example, the metrology process may include generating a measurement plan and / or performing runtime measurements, such as scanning (in a single or multiple scans), inspection, measurement and / or other operations provided on the sample or part thereof by using the same or different tools. For example, the measurement results (such as the measured image) are analyzed by using image processing techniques. It should be noted that unless otherwise specifically stated, the term "metrology" or its derivatives used in this specification are not limited by the measurement technique, the measurement resolution or the size of the inspection area.

[0035] 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 presently disclosed subject matter.

[0036] The term "sample" used in this specification should be broadly interpreted to cover any kind of wafers, masks and other structures, as well as combinations and / or portions thereof, used to manufacture semiconductor integrated circuits, magnetic heads, flat panel displays and other semiconductor products.

[0037] The term "defect" as used in this specification should be interpreted broadly to cover any kind of abnormal or undesirable feature formed on or within a sample.

[0038] It will be appreciated that, unless specifically stated otherwise, certain features of the presently disclosed subject matter described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the presently disclosed subject matter described in the context of a single embodiment may also be provided individually or in any suitable subcombination. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the methods and apparatus.

[0039] With this in mind, turn to Figure 1 , showing a functional block diagram of an inspection system according to certain embodiments of the presently disclosed subject matter.

[0040] As part of the sample fabrication process, Figure 1 The inspection system 100 shown in the figure is used to inspect semiconductor samples (e.g., wafers and / or portions thereof). As described above, the inspection referred to 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 the sample during the manufacture of the sample. According to certain embodiments of the presently disclosed subject matter, the inspection system 100 shown includes a computer-based system 101, which is capable of automatically performing one or more metrology operations on images obtained during the manufacture of the sample. System 101, also referred to as a metrology system, is a subsystem of the inspection system 100. Specifically, according to certain embodiments, the metrology operations may include critical dimension (CD) measurements relative to lateral recesses formed in the semiconductor sample.

[0041] The system 101 is operably connected to one or more inspection tools 120, which are configured to scan semiconductor samples and capture images thereof to inspect the samples. In some embodiments, at least one of the inspection tools 120 has metrology capabilities and can be configured to perform metrology operations on the captured images. Such inspection tools are also referred to as metrology tools.

[0042] The term "metrology operation" as used in this specification should be interpreted broadly to cover any metrology operation process for extracting metrology information related to one or more structural elements on a semiconductor sample. For example, the metrology information to be extracted may indicate one or more of the following: dimensions (e.g., line width, line spacing, contact diameter, size of elements, edge roughness, grayscale statistics, etc.), shape of elements, distances within or between elements, related angles, overlap information associated with elements corresponding to different design levels, etc. In some embodiments, the metrology operation may include a measurement operation, such as, for example, a CD measurement performed relative to certain structures on the sample.

[0043] The term "inspection tool(s)" as used herein should be broadly interpreted to cover any tool that can be used for inspection-related processes, including, by way of non-limiting example, imaging, scanning (in a single or multiple scans), sampling, inspection, measurement, classification and / or other processes provided with respect to a sample or portion thereof.

[0044] As an 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 providing information of a low-resolution image of the sample (also referred to as low-resolution image data) 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 providing information of a high-resolution image of the sample (also referred to as high-resolution image data) may be transmitted to the system 101 directly or via one or more intermediate systems.

[0045] Without limiting the scope of the present disclosure in any way, it should also be noted that the inspection tool 120 can be implemented as various types of inspection machines, such as optical imaging machines, electron beam machines, etc. In some cases, the same inspection tool can provide low-resolution image data and high-resolution image data.

[0046] 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 a type of electron microscope that generates an image of a sample by scanning the sample with a focused electron beam. The electrons interact with the atoms in the sample, thereby generating various signals containing information about the surface morphology and / or composition of the sample. The position of the beam is combined with the intensity of the detected signals to generate an image. The SEM is capable of accurately measuring features during the manufacture of semiconductor wafers. As an example, the SEM tool can be a critical dimension scanning electron microscope (CD-SEM) for measuring critical dimensions of structural features in an image.

[0047] System 101 includes a processor and memory circuit (PMC) 102 operatively connected to a hardware-based I / O interface 126. PMC 102 is configured to provide the processing necessary for operating the system (e.g., Figure 2A , Figure 2B and Figure 3 102 and includes a processor (not shown separately) and a memory (not shown separately). The processor of PMC 102 may be configured to execute several functional modules according to computer-readable instructions 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.

[0048] As previously mentioned, in some embodiments, the system 101 may be configured to measure lateral recesses in a semiconductor sample. A lateral recess (also referred to as a cavity recess) refers to a recess formed from the lateral side of a semiconductor sample. Specifically, in some embodiments, a semiconductor sample may include a stack of two types of layers: one or more first layers of a first type and one or more second layers of a second type, which are deposited alternately with each other to form a superlattice layer stack. The two types of layers may be made of different materials. During the manufacturing process, it may be necessary to selectively recess only one type of material from the superlattice layer stack. For example, the second layer may be at least partially etched, thereby forming a lateral recess between each given second layer and two first layers adjacent to the given second layer. In some cases, the sample manufacturer is particularly interested in measuring the lateral recess (e.g., the width of the lateral recess, also referred to as the cavity depth), which is one of the geometric parameters that has a great influence on the performance of the final device. It can also provide an indication of the progress of etching, as well as facilitate fine-tuning and control of the manufacturing process.

[0049] This recess, etched from the lateral side of the sample, is hidden and buried in the stack and therefore cannot be seen from top-down images such as those typically taken by inspection tools. Current process control relies on expensive, slow and destructive cross-sectional electron microscopy (such as using metrology tools like TEM), or optical inspection techniques (such as optical critical dimension (OCD) scatterometers) that rely on specific spectra and provide indirect and less accurate measurements.

[0050] The semiconductor sample that may include a layer stack structure as described above may be a logic device or a memory device. As an example, the sample may be a logic device, such as, for example, a gate-all-around field effect transistor (GAAFET), which is also referred to herein as a gate-all-around (GAA) device or transistor. As another example, the sample may be a memory device, such as, for example, a 3D NAND (NOT-AND), which is a type of non-volatile flash memory in which memory cells are vertically stacked in multiple layers. As a further example, the sample may be a memory device, such as, for example, a 3D storage class memory (3D SCM).

[0051] For exemplary and illustrative purposes, certain embodiments of the presently disclosed subject matter are described herein for GAA devices. This is by no means intended to limit the present disclosure in any way. It will be appreciated that the proposed methods and systems may be applied to lateral recess measurements in other semiconductor samples having structures similar to those described above.

[0052] GAA devices are field effect transistors (such as, for example, nanosheet (NS), forked sheet (FS), and complementary field effect (CFET) transistors) in which a gate material surrounds a channel region on all sides. Figure 4A schematic diagram of a GAA structure is shown in accordance with some embodiments of the presently disclosed subject matter.

[0053] The GAA structure 410 includes a stack of two types of layers: a plurality of first layers 402 (i.e., silicon layers) and a plurality of second layers 404 (i.e., silicon germanium layers, also referred to as SiGe layers) formed on a semiconductor substrate 406. The stacked structure includes a periodic arrangement of silicon layers deposited on the silicon germanium layers, thereby forming a superlattice layer stack. A plurality of such stacked structures may be formed on a wafer spaced apart from one another, such as on a wafer. Figure 4 Two exemplary GAA structures 400 and 410 are shown formed on a substrate 406. Once these layers are fully grown, special chemicals are used to selectively etch the silicon germanium, but do not react with silicon. The lateral sides of the multiple silicon germanium layers are etched to remove at least a portion of these layers. The etching process can be gradual, and eventually, only the silicon layer is left hanging as a bridge between the source and drain.

[0054] During the etching process, a lateral recess is formed between each given second layer and two first layers adjacent to the given second layer. For example, a lateral recess or cavity recess 408 is formed between the second silicon germanium layer and its adjacent silicon layer. As described above, in some cases, it is particularly important to measure the lateral recess (e.g., the width 412 of the lateral recess, also referred to as the cavity depth), which has a great impact on the final device performance. For exemplary purposes, GAA structures 400 and 410 are shown as having lateral recesses of different widths to show what happens to the GAA device at different etching time points during the etching process.

[0055] According to certain embodiments, a new method is proposed to measure lateral recesses in the above semiconductor samples using the penetration capability of an electron beam tool with a relatively high voltage landing energy. The proposed measurement method is non-destructive and provides direct measurement with improved accuracy and throughput (TpT).

[0056] In some embodiments, the inspection tool 120 may be an electron beam tool (e.g., SEM) configured to scan a semiconductor sample using an electron beam having a landing energy specifically selected to penetrate to a predefined depth corresponding to a target second layer of the sample. The electron beam tool is further configured to acquire a first image by collecting secondary electrons (SE) emitted from the surface of the sample, and to acquire a second image by collecting backscattered electrons (BSE) scattered from an internal region of the sample between the surface and the target second layer. The first image provides information of the surface profile of the sample, and the second image provides information of the internal structure of the internal region.

[0057] The functional modules included in the PMC 102 may include an image processing module 104 and a measurement module 106. The PMC 102 may be configured to obtain a first image and a second image acquired by an electron beam tool via an I / O interface 126. The image processing module 104 may be configured to generate a first GL waveform providing information of a grayscale (GL) intensity distribution of the first image, and to generate a second GL waveform providing information of a GL intensity distribution of the second image. The measurement module 106 may be configured to estimate a first width of one or more first layers based on the first GL waveform, and to estimate a second width relative to at least a target second layer based on the second GL waveform. The measurement module 106 may be further configured to measure a lateral concavity relative to the target second layer based on the first width and the second width.

[0058] The operation of system 100, system 101, PMC 102 and the functional modules therein will be referred to as Figure 2A , Figure 2B and Figure 3 Further details.

[0059] According to certain embodiments, the system 101 may include a storage unit 122. The storage unit 122 may be configured to store any data required to operate the systems 100 and 101, such as data related to input and output of the systems 100 and 101, and intermediate processing results generated by the system 101. As an example, the storage unit 122 may be configured to store images (e.g., the first image and the second image) generated by the inspection tool 120 and / or derivatives thereof. Thus, the images may be retrieved from the storage unit 122 and provided to the PMC 102 for further processing.

[0060] In some embodiments, the system 101 may optionally include a computer-based graphical user interface (GUI) 124 configured to enable user-specified input related to the system 101. For example, a visual representation of the sample may be presented to the user (e.g., via a display forming part of the GUI 124), including an image of the sample and / or its corresponding waveform. The user may be provided with the option of defining certain operating parameters via the GUI. In some cases, the user may also view the results of the operation (such as lateral concavity measurements) and / or further test results on the GUI.

[0061] As described above, the system 101 is configured to receive an image of the sample via the I / O interface 126. The image may include image data (and / or derivatives thereof) generated by the inspection tool 120 and / or image data stored in the storage unit 122 or one or more data repositories. In some cases, the image data may refer to an image captured by the inspection tool during the manufacturing process, and / or a pre-processed image derived from a captured image obtained through various pre-processing stages, etc. It is noted that in some cases, the image may include associated digital data (e.g., metadata, hand-crafted attributes, etc.). It is further noted that some of the image data may include data related to a layer of interest and / or data related to one or more additional layers of the sample.

[0062] The system 101 is further configured to process the received image and send the results (eg, CD measurements on the image) to a storage unit 122 and / or an inspection tool 120 via an I / O interface 126 .

[0063] 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 automated defect review module (ADR) and / or an automated defect classification module (ADC) and / or a metrology-related module and / or other inspection modules that may be used to inspect semiconductor samples. One or more inspection modules may be implemented as stand-alone computers, or their functionality (or at least a portion thereof) may be integrated with the inspection tool 120. In some embodiments, measurements obtained from the system 101 may be used by the inspection tool 120 and / or one or more inspection modules (or a portion thereof) for further inspection of the sample.

[0064] Those skilled in the art will readily appreciate that the teachings of the presently disclosed subject matter are not limited to Figure 1 The system constraints shown in ; equivalent and / or modified functions may be combined or divided in another manner, and may be implemented in any suitable combination of software and firmware and / or hardware.

[0065] Please note that Figure 1 The inspection system shown in can be implemented in a distributed computing environment, wherein the aforementioned functional modules included in PMC102 can be distributed across several local and / or remote devices and can be linked via a communication network. It should be 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 communicate data with the system 101 via the I / O interface 126. The system 101 can be implemented as (multiple) independent computers for use 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 inspection-related processes.

[0066] Reference now Figure 2A , shows a generalized flow chart for measuring lateral recesses in a semiconductor sample, according to certain embodiments of the presently disclosed subject matter.

[0067] As described above, the lateral recess is measured relative to a semiconductor sample having a specific type of structure. As an example, the sample may include a stack of one or more first layers of a first type and one or more second layers of a second type. The first and second layers are deposited alternately with each other. The second layers are at least partially etched during the manufacturing process, thereby forming a lateral recess between each given second layer and its two adjacent first layers.

[0068] This type of sample can be a logic device (such as a GAA device) or a memory device (such as, for example, 3D NAND, 3D SCM, etc.). As an example of such a specially structured sample, a GAA device is Figure 4 Schematically represented as described above.

[0069] A first image and a second image of the sample may be obtained (202) (e.g., by PMC 102 from inspection tool 120 via I / O interface 126 or from storage unit 122). The first image and the second image may be obtained by an electron beam tool (such as a SEM). For example, the SEM tool used herein may be a critical dimension scanning electron microscope (CD-SEM) configured to measure critical dimensions of structural elements / features of the sample based on the captured images. According to certain embodiments, the sample may be scanned (210) using an electron beam (e.g., by electron beam tool 120) having a landing energy specifically selected to penetrate to a predefined depth corresponding to a target second layer of the sample, such as Figure 2B , which shows a generalized flow chart for acquiring a first image and a second image according to some embodiments of the presently disclosed subject matter.

[0070] In a SEM, different types of signals are generated when an electron beam hits a sample. Secondary electrons (SE) originate from the surface or near-surface region of the sample. They are the result of the inelastic interaction between the primary electron beam and the sample and have lower energy than backscattered electrons. Specifically, SEs are generated when incident electrons excite electrons in the sample and lose some of their energy in the process. The excited electrons move toward the surface of the sample, and if the excited electrons still have enough energy, they escape from the surface as secondary electrons. The shallow depth of generation of the detected SE makes it ideal for examining the topography of the surface of the sample.

[0071] Alternatively, backscattered electrons (BSE) are reflected back after the elastic interaction between the beam and the sample. This type of electron originates from a wide area within the interaction volume. They are the result of elastic collisions of electrons with atoms, which causes a change in the trajectory of the electrons. Specifically, when the electron beam hits the sample, the atoms in the sample deflect some of the electrons from their original path in an elastic manner (without energy loss). These essentially elastically scattered primary electrons (which are high-energy electrons) that bounce back from the sample are called BSEs.

[0072] As described above, BSE originates from deeper regions of the sample, while SE originates from the surface region. Therefore, BSE and SE carry different types of information. For example, BSE images are highly sensitive to differences in atomic number and therefore can carry information about the internal structure and / or composition of the sample (i.e., this is referred to as the penetration ability of BSE to probe deep into the sample when provided with sufficient landing energy), while SE images can provide more detailed surface information.

[0073] According to certain embodiments of the presently disclosed subject matter, a first image as described above may be acquired (212) by collecting secondary electrons (SE) emitted from the surface of the sample (e.g., by an SE detector array of the electron beam tool 120). It should be noted that the surface of the sample may refer to the outer surface of the sample facing and exposed to the electron beam, or may refer to the surface region of the sample ranging from the outer surface to a depth near the surface. Therefore, the first image is also referred to herein as an SE image. A second image as described above may be acquired by collecting backscattered electrons (BSE) scattered from an inner region of the sample between the surface and a second layer of the target (e.g., by at least one BSE detector of the electron beam tool 120). Therefore, the second image is also referred to herein as a BSE image. Therefore, the first image may provide information about the surface contour (e.g., surface topography) of the sample, while the second image may provide information about the internal structure (and / or composition) of an inner region of the sample.

[0074] like Figure 4 As shown, the sample may include a plurality of first layers and a plurality of second layers deposited alternately with each other. As an example, the GAA structure 410 includes three first layers 402 (i.e., silicon layers) and three second layers 404 (i.e., silicon germanium layers), so three lateral recesses are formed on each lateral side of the structure, each lateral recess corresponding to a corresponding cavity formed between a corresponding second layer and two adjacent first layers. For example, the lateral recess 408 shown is the second lateral recess among the three lateral recesses, which is formed between the middle second layer (i.e., the second silicon germanium layer) and the top first layer and the bottom first layer adjacent to the middle second layer.

[0075] According to certain embodiments, the lateral concavity relative to the target second layer can be measured by using an electron beam having a landing energy specifically selected to penetrate to a predefined depth corresponding to the target second layer. Specifically, the currently proposed method can be used to measure the average concavity of the sample (i.e., the average concavity of a plurality of lateral concavities included in the sample) and / or the lateral concavity specific to each layer (the lateral concavity belonging to a specific target second layer (such as, for example, the top second layer, the middle second layer, etc.)), as will be described in further detail below.

[0076] As an example, in order to measure a specific lateral recess belonging to the top second layer 404, the landing energy of the electron beam may be specifically selected to penetrate a predefined depth 414 corresponding to (or near) the top second layer 404. For example, the landing energy may be selected to penetrate a depth corresponding to the bottom (or near) of the target second layer (e.g., the top second layer in this example), such as Figure 4 In such cases, the lateral concavity measured is the per-layer lateral concavity, i.e., the top layer lateral concavity belonging to the second layer from the top.

[0077] As another example, to measure the average lateral concavity relative to the middle second layer, the landing energy of the electron beam may be specifically selected to penetrate a predefined depth 416 corresponding to the middle second layer (or thereabouts). In such a case, the measured lateral concavity is the average lateral concavity between the top layer lateral concavity and the middle layer lateral concavity. Similarly, when the landing energy of the electron beam is set to be able to penetrate a predefined depth 418 corresponding to the bottom second layer, the measured lateral concavity is the average lateral concavity of the three per-layer lateral concavities (top layer lateral concavity, middle layer lateral concavity, and bottom layer lateral concavity).

[0078] In some embodiments, the landing energy of the electron beam may first be set to be suitable for measuring the penetration depth of the top layer lateral concavity, as described above, and after the measurement is completed, the landing energy of the electron beam may be reset to be suitable for measuring the penetration depth of the average lateral concavity between the top layer lateral concavity and the middle layer lateral concavity. The middle layer lateral concavity may then be derived based on these two measurements, such as by using the reference Figure 3 described in further detail.

[0079] In some embodiments, in order to select a level of landing energy that can penetrate to a specific expected depth of the target second layer corresponding to the sample to be inspected, a reference sample having a structure similar to the sample but without a recess formed in any of the second layers may be simulated and used as a reference. A sample of interest having a lateral recess at a specific second layer may also be simulated. According to certain embodiments, a landing energy that penetrates to a predefined depth corresponding to the target second layer may be specifically selected based on a comparison between the number of BSEs relative to the reference sample (without lateral recesses) and the number of BSEs relative to the sample of interest (with lateral recesses at a specific layer).

[0080] Figure 7 An exemplary graph illustrating a correlation between the difference in the number of BSEs received from a reference sample relative to a sample of interest and the level of landing energy used, according to certain embodiments of the presently disclosed subject matter.

[0081] Can simulate with reference Figure 4 A reference GAA device having a similar structure to the described GAA (e.g., having a superlattice stack) but without a lateral recess formed in the second layer (SiGe layer) and a GAA of interest having lateral recesses at the first SiGe layer, the second SiGe layer, and the third SiGe layer, respectively, are obtained to obtain a pattern. A simulation may be performed to simulate scanning of the reference GAA and the GAA of interest using different landing energies, respectively, and the number of BSEs received from the two simulated scans may be calculated and compared. Figure 7 The graph in shows the difference (Y-axis) between the number of BSEs received from two scans relative to different levels of landing energy (X-axis) for the scans for different second layers of the sample. For example, the curve for layer 1 refers to the difference (Y-axis) between the number of BSEs received from a scan of a reference GAA and the number of BSEs received from a scan of a GAA of interest having a lateral recess at the first (i.e., top) SiGe layer relative to different levels of landing energy (X-axis) for the scans. The curve for layer 2 refers to the difference (Y-axis) between the number of BSEs received from a scan of a reference GAA and the number of BSEs received from a scan of a GAA of interest having a lateral recess at the second SiGe layer relative to different levels of landing energy (X-axis) for the scans. The curve for layer 3 refers to the difference (Y-axis) between the number of BSEs received from a scan of a reference GAA and the number of BSEs received from a scan of a GAA of interest having a lateral recess at the third SiGe layer relative to different levels of landing energy (X-axis) for the scans.

[0082] As shown, when the landing energy is very low (e.g., less than 2keV), the difference in the BSE received from the two scans is close to 0, which means that the landing energy is insufficient for the electrons to penetrate into any of the second layers with the recesses, and thus there is no difference between the number of BSEs received from the two scans. As the landing energy increases, the electrons begin to reach the top second layer of the sample (e.g., the top SiGe layer), and the difference between the number of BSEs received from the two scans (the scan of the reference GAA and the GAA of interest with the recess at the top SiGe layer) is expected, indicating that there is a lateral recess in the top second layer in the GAA of interest relative to the reference GAA without the recess at the top second layer (e.g., fewer electrons are received from the GAA of interest because there is less material to interact with the electrons and the electrons are scattered due to the recess).

[0083] Thus, in the curve for layer 1, it can be seen that as the landing energy increases from approximately 2keV to 3.5keV, the difference between the number of BSEs received from the two scans increases, indicating that electrons with landing energies within this range are penetrating the top SiGe layer, while not yet reaching the second and third SiGe layers (as shown, the curves for layers 2 and 3 remain close to 0 within this energy range). An electron beam with a landing energy selected approximately within this range can be used to measure each recess of the top SiGe layer.

[0084] As the landing energy continues to increase (e.g., from approximately 3.5 keV to 4.0 keV), the electrons are able to reach the second SiGe layer, where the difference between the number of BSEs received from the two scans (the scan of the reference GAA and the scan of the GAA of interest with recess at the second SiGe layer) continues to increase in the curve for Layer 2, as shown. An electron beam with a landing energy selected approximately within this range can be used to measure the average recess of the top SiGe layer and the second SiGe layer.

[0085] When the landing energy is increased between 4.0keV and 6.0keV, the electrons are able to reach the third SiGe layer, where in the graph for layer 3, the difference between the number of BSEs received from the two scans (the scan of the reference GAA and the scan of the GAA of interest with a recess at the third SiGe layer) starts to increase as shown. An electron beam with a landing energy selected approximately within this range can be used to measure the average recess of the top SiGe layer, the second SiGe layer, and the third SiGe layer. At relatively high landing energies (about 20keV, Figure 7 In the case of the 3D image (not shown), the sensitivity of the electrons to the three different layers is almost the same, indicating that the BSE signal is only sensitive to the average recess on the three layers. In the case of measuring the average recess of the GAA device, this relatively high level of landing energy can be used.

[0086] continue Figure 2A As described above, once the first image and the second image are obtained (as described above with reference to blocks 202 and Figure 2B ), then (for example, by Figure 1 The image processing module 104 in the embodiment of the present invention generates (204) a first gray level (GL) waveform providing information of gray level intensity distribution of the first image and a second GL waveform providing information of GL intensity distribution of the second image.

[0087] Based on the first GL waveform (e.g., Figure 1 The first width of the one or more first layers can be estimated (206) based on the second GL waveform. A second width relative to at least the target second layer can be estimated (206) based on the first width and the second width (e.g., by Figure 1 The measurement module 106 in the embodiment measures (208) a lateral concavity of the second layer relative to the target.

[0088] Reference now Figure 5 , showing examples of first and second images of a GAA structure according to some embodiments of the presently disclosed subject matter.

[0089] As shown, image 502 is an exemplary first image (i.e., SE image) obtained by collecting SE emitted from the surface of the sample, and image 504 is an exemplary second image (i.e., BSE image) obtained by collecting BSE scattered from the internal area of ​​the sample between the surface and the target second layer. The first image provides information on the surface profile (e.g., surface topography) of the sample. As shown, image 502 presents SE image representations of four GAA structures. For each GAA structure, the grayscale intensity varies in a direction perpendicular to the longitudinal axis of the GAA structure, thereby representing the variation in the surface profile of the GAA in that direction. For illustrative purposes, Figure 4 Schematically illustrated is a surface profile 420 of the GAA 400. As shown, the surface profile 420 represents the outer surface topography of the first layer (ie, the silicon layer) exposed to the electron beam during scanning.

[0090] As described above, the second image provides information about the internal structure (and / or composition) of the sample in the internal region between the surface and the target second layer. Image 504 presents a BSE image representation of four GAA structures. For each GAA structure, the change in grayscale intensity in the BSE image can reflect the hidden lateral recess structure (i.e., the penetration ability of the BSE) relative to the remaining portion of the second layer (i.e., SiGe layer) during the etching process.

[0091] Reference now Figure 6, showing examples of first and second GL waveforms according to certain embodiments of the presently disclosed subject matter.

[0092] As shown in the figure, Figure 5 , a first GL waveform 602 is generated that provides information about the GL intensity distribution of the first image 502 (e.g., its particular GAA structure), and a second GL waveform 604 is generated that provides information about the GL intensity distribution of the second image 504. The first GL waveform and the second GL waveform are generated along a direction perpendicular to the longitudinal axis of the GAA structure.

[0093] A first width of one or more first layers (eg, width 512, such as Figure 5 As an example, estimating the first width may include estimating a first topological point on the first GL waveform. A topological point refers to a point on a signal waveform (e.g., a GL waveform) that is identified as corresponding to a specific position on the geometry of the sample. For example, the first topological point may represent an estimated edge / boundary of the first layer (e.g., representing the outer boundary of the widest silicon layer, or the average boundary of three silicon layers). Specifically, in some embodiments, the first topological point may be estimated by calculating a derivative along the first GL waveform, applying a predefined derivative threshold on the first GL waveform, generating a first topological point, and measuring a first width between two topological points.

[0094] For example, in Figure 6 In this example, two points on the first waveform 602 corresponding to the derivative threshold are identified as 606 and 608. The topological points 606 and 608 may represent the estimated edge / boundary of the first layer (i.e., the silicon layer). A first width 610 between the two points 606 and 608 may be measured, which represents the estimated width 412 of the first layer of the GAA structure.

[0095] A second width (eg, width 514, such as width 516) relative to at least the target second layer may be estimated based on the second GL waveform. Figure 5 ). As described above, in the case where the target second layer is the top second layer, the estimated second width refers to the width of the target second layer. In the case where the target second layer is a subsequent second layer after the top second layer (such as, for example, a middle second layer or a bottom second layer), the estimated second width refers to the average width of the second layers up to the target second layer. As an example, estimating the second width may include estimating a second topological point on the second GL waveform. For example, the second topological point may represent an estimated edge / boundary relative to at least the target second layer. Specifically, in some embodiments, the second topological point may be estimated by applying a predefined GL threshold on the second GL waveform and measuring the second width between the second topological points.

[0096] For example, in Figure 6 In this example, a predefined GL threshold (e.g., 70%) is applied on the second waveform 604, and two topological points 616 and 618 are identified. A second width 620 between the two points 616 and 618 can be measured, which represents Figure 5 The estimated width 514 is illustrated in FIG.

[0097] The lateral recess relative to the target second layer may be measured based on the first width 610 and the second width 620 (eg, by subtracting the second width from the first width).

[0098] In some embodiments, the measured lateral recess may be further calibrated relative to reference measurement data of a reference semiconductor sample obtained from a transmission electron microscope (TEM). Such calibration may improve the accuracy of the measurement. In some cases, the calibration may be performed based on a correlation previously derived between corresponding measurement data from an electron beam tool and reference measurement data obtained from a TEM.

[0099] Now turn to Figure 3 , shows a generalized flow chart for measuring per-layer lateral concavity and / or measuring average lateral concavity according to certain embodiments of the presently disclosed subject matter.

[0100] As described above, in the case where the target second layer is the top second layer of one or more second layers, the above reference Figure 2A The method described herein measures (302) a top lateral recess formed between a top second layer and its adjacent first layer. In this case, the landing energy of the electron beam needs to be specifically selected to penetrate to a depth corresponding to the top second layer. In other words, in this case, Figure 2A The resulting measured lateral concavity is referred to as the top layer lateral concavity.

[0101] After the measurement of block 302 is completed, the landing energy of the electron beam may be reset to be able to penetrate the subsequent second layer corresponding to the top second layer (e.g., the middle second layer or the bottom second layer, as in Figure 4 , and an average lateral concavity relative to a subsequent second layer may be measured (304). For example, when the subsequent second layer is an intermediate second layer, the measured lateral concavity refers to an average lateral concavity averaged between the top layer lateral concavity and the intermediate layer lateral concavity. In this case, the lateral concavity of each layer of the subsequent second layer may be derived (306) based on the average lateral concavity and the top layer lateral concavity.

[0102] According to some embodiments, as mentioned above Figure 2A , Figure 2B and Figure 3The described measurement process may be used as part of an inspection protocol used by the system 101 and / or the inspection tool 120 for runtime inspection of a sample, such as, for example, performing metrology operations on the sample (in this case, referred to as a metrology protocol). Thus, the presently disclosed subject matter also includes systems and methods for generating an inspection protocol during a protocol setup phase, wherein the recipe includes a method as described in reference Figure 2A , Figure 2B and Figure 3 (and its various embodiments) described herein. It should be noted that the term "inspection protocol" should be interpreted broadly to cover any protocol that can be used by an inspection tool to perform operations related to any kind of inspection as described above.

[0103] It should be noted that the examples shown in the present disclosure, such as, for example, the exemplary GAA structure, the acquired first image and the second image, the generated GL waveform, and the specific manner of the estimated width and / or topological point as described above, are shown for exemplary purposes and should not be considered to limit the present disclosure in any way. In addition to or in place of the above, other appropriate examples / implementations may be used.

[0104] It should be noted that although certain embodiments of the measurement process disclosed in the present invention are described with respect to measuring lateral recesses in a semiconductor sample having a specific structure, i.e., the sample comprises a stack of two types of layers: one or more first layers of a first type and one or more second layers of a second type deposited alternately with each other, wherein the second layers are at least partially etched, this is not intended to limit the measurement process disclosed herein to be applied only to such structured samples. Alternatively, in some cases, a sample comprising only one material and thus not stratified may have lateral recesses formed on its lateral sides, and the measurement process disclosed herein may be similarly applied to such a sample for the purpose of measuring its lateral recesses.

[0105] As an example, the measurement process in this case may include: obtaining a first image obtained by collecting secondary electrons (SE) emitted from the surface of the sample and a second image obtained by collecting backscattered electrons (BSE) scattered from an internal region of the sample between the surface and a target depth (e.g., corresponding to the bottom (or vicinity) of a lateral recess of the sample), wherein the semiconductor sample is scanned using an electron beam having a landing energy specifically selected to penetrate to the target depth, wherein the first image provides information on a surface profile of the sample and the second image provides information on an internal structure of the internal region; generating a first grayscale (GL) waveform providing information on a GL intensity distribution of the first image and a second GL waveform providing information on a GL intensity distribution of the second image; estimating a first width of a first layer based on the first GL waveform and estimating a second width relative to at least a target second layer based on the second GL; and measuring the lateral recess in the sample based on the first width and the second width.

[0106] One of the advantages of certain embodiments of the measurement process as described herein is to provide a direct measurement of a lateral recess formed in the above-mentioned semiconductor sample, which is non-destructive and has improved accuracy and throughput (TpT). This is achieved at least by using the penetration capability of the BSE signal in combination with the SE signal of an electron beam tool, wherein the electron beam tool is configured with an electron beam having a landing energy of a relatively high voltage.

[0107] It will be understood that the present disclosure is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings.

[0108] It will also be understood that the system according to the present disclosure may be implemented at least in part on a suitably programmed computer. Likewise, the present disclosure contemplates a computer program that can be read by a computer to perform the method of the present disclosure. The present disclosure further contemplates a non-transitory computer-readable memory that tangibly embodies a program of instructions that can be executed by a computer to perform the method of the present disclosure.

[0109] The present disclosure can have other embodiments and can be practiced or carried out 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. Therefore, those skilled in the art will appreciate that the concepts upon which the present disclosure is based can be easily used as the basis for designing other structures, methods and systems for carrying out several purposes of the presently disclosed subject matter.

[0110] Those skilled in the art will easily appreciate that various modifications and changes may be applied to the embodiments of the present disclosure as described above without departing from the scope of and defined by the appended claims.

Claims

1. A computerized system for measuring lateral recesses in a semiconductor sample comprising a stack of one or more first layers of a first type and one or more second layers of a second type deposited alternately with each other, the second layers being at least partially etched so as to form a lateral recess between each given second layer and its two adjacent first layers, the system comprising: An electron beam tool, the electron beam tool being configured to: scanning the semiconductor sample using an electron beam having a landing energy specifically selected to penetrate to a predefined depth corresponding to a target second layer of the sample; as well as Acquire a first image by collecting secondary electrons emitted from a surface of the sample, and acquire a second image by collecting backscattered electrons scattered from an inner region of the sample between the surface and the target second layer, the first image providing information on a surface profile of the sample, and the second image providing information on an inner structure of the inner region; and processing and memory circuitry operatively connected to the electron beam tool and configured to: generating a first grayscale waveform providing information of a grayscale intensity distribution of the first image and a second grayscale waveform providing information of a grayscale intensity distribution of the second image; estimating a first width of the one or more first layers based on the first grayscale waveform, and estimating a second width relative to at least the target second layer based on the second grayscale waveform; as well as A width of the lateral recess relative to the target second layer is measured based on the first width and the second width.

2. The computerized system of claim 1, wherein the semiconductor sample comprises a gate-all-around device, and wherein the first layer is made of silicon and the second layer is made of silicon germanium.

3. The computerized system of claim 1, wherein the target second layer is a top second layer among the one or more second layers, and the lateral recess is a top lateral recess formed between the top second layer and an adjacent first layer thereof.

4. A computerized system according to claim 3, wherein the processing and memory circuit is further configured to measure the width of the average lateral concavity of a subsequent second layer after the top second layer, and derive the subsequent layer lateral concavity based on the average lateral concavity and the top layer lateral concavity.

5. The computerized system of claim 1 , wherein the target second layer is a subsequent second layer following a top second layer, and the lateral concavity is an average lateral concavity of a top layer lateral concavity formed between the top second layer and an adjacent first layer and a subsequent lateral concavity formed between the subsequent second layer and an adjacent first layer.

6. The computerized system of claim 1, wherein the secondary electrons are collected by a secondary electron detector array and the backscattered electrons are collected by at least one backscattered electron detector.

7. A computerized system according to claim 1, wherein the landing energy that penetrates to the predefined depth corresponding to the target second layer is specifically selected based on a comparison between the number of backscattered electrons relative to a reference sample without lateral recesses and the number of backscattered electrons relative to the semiconductor sample.

8. A computerized system according to claim 1, wherein estimating the first width includes estimating first topological points on the first grayscale waveform by calculating derivatives along the first grayscale waveform, applying a predefined derivative threshold on the first grayscale waveform to generate the first topological points, and measuring the first width between the first topological points.

9. A computerized system according to claim 1, wherein estimating the second width includes estimating second topological points on the second grayscale waveform by applying a predefined grayscale threshold on the second grayscale waveform, generating the second topological points, and measuring the second width between the second topological points.

10. The computerized system of claim 1, wherein the processing and memory circuitry is further configured to calibrate the lateral recess relative to reference measurement data obtained from a transmission electron microscope.

11. The computerized system of claim 10, wherein the calibration is based on a correlation previously derived between corresponding measurement data from the electron beam tool and the reference measurement data obtained from the transmission electron microscope.

12. A computerized method of measuring lateral recesses in a semiconductor sample comprising a stack of one or more first layers of a first type and one or more second layers of a second type deposited alternately with each other, the second layers being at least partially etched so as to form lateral recesses between each given second layer and its two adjacent first layers, the method being performed by a processing and memory circuit and comprising: obtaining a first image acquired by collecting secondary electrons emitted from a surface of the sample and a second image acquired by collecting backscattered electrons scattered from an internal region of the sample between the surface and a target second layer, wherein the semiconductor sample is scanned using an electron beam having a landing energy specifically selected to penetrate to a predefined depth corresponding to the target second layer, and wherein the first image provides information of a surface profile of the sample and the second image provides information of an internal structure of the internal region; generating a first grayscale waveform providing information of a grayscale intensity distribution of the first image and a second grayscale waveform providing information of a grayscale intensity distribution of the second image; estimating a first width of the first layer based on the first gray level waveform, and estimating a second width relative to at least the target second layer based on the second gray level; as well as A width of the lateral recess relative to the target second layer is measured based on the first width and the second width.

13. The computerized method of claim 12, wherein the target second layer is a top second layer of the one or more second layers, and the lateral recess is a top lateral recess formed between the top second layer and an adjacent first layer thereof.

14. The computerized method of claim 13, further comprising measuring a width of an average lateral concavity of a subsequent second layer relative to the top second layer, and deriving a subsequent layer lateral concavity based on the average lateral concavity and the top layer lateral concavity.

15. The computerized method of claim 12, wherein the target second layer is a subsequent second layer following a top second layer, and the lateral concavity is an average lateral concavity of a top layer lateral concavity formed between the top second layer and an adjacent first layer and a subsequent lateral concavity formed between the subsequent second layer and an adjacent first layer.

16. A computerized method according to claim 12, wherein the landing energy that penetrates to the predefined depth corresponding to the target second layer is specifically selected based on a comparison between the number of backscattered electrons relative to a reference sample without lateral recesses and the number of backscattered electrons relative to the semiconductor sample.

17. A computerized method according to claim 12, wherein estimating the first width includes estimating first topological points on the first grayscale waveform by calculating derivatives along the first grayscale waveform, applying a predefined derivative threshold on the first grayscale waveform to generate the first topological points, and measuring the first width between the first topological points.

18. A computerized method according to claim 12, wherein estimating the second width includes estimating second topological points on the second grayscale waveform by applying a predefined grayscale threshold on the second grayscale waveform, generating the second topological points, and measuring the second width between the second topological points.

19. The computerized method of claim 12, further comprising calibrating the lateral recess relative to reference measurement data obtained from a transmission electron microscope.

20. 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 measuring lateral recesses in a semiconductor sample, the semiconductor sample comprising a stack of one or more first layers of a first type and one or more second layers of a second type deposited alternately with each other, the second layers being at least partially etched so as to form lateral recesses between each given second layer and two adjacent first layers thereof, the method comprising: obtaining a first image acquired by collecting secondary electrons emitted from a surface of the sample and a second image acquired by collecting backscattered electrons scattered from an internal region of the sample between the surface and a target second layer, wherein the semiconductor sample is scanned using an electron beam having a landing energy specifically selected to penetrate to a predefined depth corresponding to the target second layer, and wherein the first image provides information of a surface profile of the sample and the second image provides information of an internal structure of the internal region; generating a first grayscale waveform providing information of a grayscale intensity distribution of the first image and a second grayscale waveform providing information of a grayscale intensity distribution of the second image; estimating a first width of the first layer based on the first gray level waveform, and estimating a second width relative to at least the target second layer based on the second gray level; as well as A width of the lateral recess relative to the target second layer is measured based on the first width and the second width.

Images