Scanning electron microscope and scanning electron microscope system

Abstract

Embodiments of the utility model include a scanning electron microscope (SEM) having an electron gun configured to generate an electron beam directed toward a sample stage along an axis passing through a lens barrel of the SEM. In some embodiments, the SEM includes a first backscattered electron (BSE) detector mounted along an axis. In some examples, the SEM also includes a second BSE detector mounted off-axis, where the second BSE detector surrounds a bottom portion of the post. In some examples, the second BSE detector includes a plurality of blades having a flat shape or an arcuate shape in a side view. Further, in some embodiments, the plurality of blades are arranged in a circular configuration in an upper view.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to a scanning electron microscope, a scanning electron microscope system. BACKGROUND

[0002] The electronics industry continues to demand smaller, faster electronic devices that can simultaneously support a large number of increasingly complex and sophisticated functions. As a result, there is a continuing trend in the semiconductor industry to produce integrated circuits (ICs) that are low cost, high performance, and low power. To date, these goals have been achieved in large part by scaling down the size of semiconductor ICs (e.g., minimum feature size) and thereby increasing production efficiency and reducing associated costs. However, this scaling also increases the complexity of the semiconductor manufacturing process. Thus, to achieve continued progress in semiconductor ICs and devices, similar progress in semiconductor manufacturing processes and techniques is needed.

[0003] In one example related to photolithographic patterning, a photomask (or mask) used for a photolithography process has a circuit pattern defined thereon. The mask is used to transfer the circuit pattern to a substrate, e.g., as part of a photolithography system. For advanced technology nodes with highly scaled feature sizes, the pattern on the mask needs to be very precise, and the photolithographic patterning process is more sensitive to mask defects. In various cases, the mask is repaired to eliminate defects, and further inspected to verify the repaired defects. However, available techniques for performing such verification are limited in their ability to provide accurate and reliable structure information.

[0004] Therefore, the prior art has not proven fully satisfactory in all respects. SUMMARY

[0005] Some embodiments of the present application provide a scanning electron microscope (SEM) comprising: an electron gun configured to generate an electron beam directed along an axis through a column of the SEM toward a sample stage; a first backscattered electron (BSE) detector mounted along the axis; a second BSE detector mounted off the axis, wherein the second BSE detector encircles a bottom of the column.

[0006] Further embodiments of the present application provide a scanning electron microscope system comprising: a sample stage; an electron gun configured to provide an electron beam directed through an electron column toward the sample stage; an in-lens energy selective backscattered (EsB) detector; an out-of-lens EsB detector encircling a bottom of the electron column; and a computer coupled to receive data from the in-lens EsB detector and the out-of-lens EsB detector. BRIEF DESCRIPTION OF DRAWINGS

[0007] Aspects of the disclosure can be best understood from the following detailed description when read in conjunction with the accompanying drawings. It is to be noted, however, that the various features illustrated in the figures are not necessarily drawn to scale. In fact, the dimensions can be arbitrarily increased or decreased for the sake of discussion.

[0008] Figure 1 A simplified block diagram of embodiments of an integrated circuit (IC) manufacturing system and IC manufacturing flow related thereto according to some embodiments is provided;

[0009] Figure 2 A more detailed block diagram of the shown mask room is provided according to various aspects of the disclosure; Figure 1

[0010] Figure 3 A scanning electron microscope (SEM) according to some embodiments is shown;

[0011] Figure 4 A platform according to some embodiments is shown, depicting top and side views of various types or configurations of surround EsB detectors;

[0012] Figure 5 An exemplary example, such as a photomask, according to some embodiments is shown;

[0013] Figure 6 A platform according to some embodiments is shown, depicting a plurality of BSE images taken at different EHT voltages and including corresponding grayscale intensity values;

[0014] Figure 7 A Gaussian filter is used to differentiate between thickness of non-metal on metal according to some embodiments is shown;

[0015] Figure 8 A system and processing flow implementing a 3D image algorithm according to some embodiments is shown; and

[0016] Figure 9 A method for implementing a 3D image algorithm according to some embodiments is shown. Figure 8 DETAILED DESCRIPTION

[0017] ​​The following disclosure provides many different embodiments, or examples, for implementing different characteristics of the provided subject matter. The specific examples of components and arrangements are intended to be examples for purposes of simplifying the disclosure. These are only examples and are not intended to be limiting. For example, in instances where a first feature is formed over or on a second feature in the following description, embodiments can include instances in which the first and second features are formed in direct contact, and embodiments in which additional features can be formed between the second feature. The first and second features can be such that the first and second features can not be in direct contact. Additionally, the disclosure can repeat reference numerals and / or letters in various examples. This repetition of reference numerals and / or letters is for the purpose of simplicity and clarity and does not itself dictate a relationship between the various embodiments and / or configurations discussed.

[0018] Also for ease of explanation, spatially relative terms such as "beneath", "below", "lower", "above", "upper" and the like can be used herein for describing the orientation of one component or feature to another component or feature, as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0019] Additionally, in the following discussion, dimensions of a given layer or other feature (e.g., such as thickness, width, length, etc.) can sometimes be used, in which such terms should be interpreted as meaning within ±10% of the value cited or between the values being compared. For example, if a dimension A is described as "substantially equal" to dimension B, it will be understood that dimension A is within ±10% of dimension B. As another example, if a layer is described as having a thickness of about 100 nm, it will be understood that the thickness of the layer can be in a range of 90-110 nm.

[0020] As noted above, photomask (reticle) patterns need to be very precise, and photolithographic patterning processes are more sensitive to reticle defects for advanced technology nodes. In various instances, reticles are repaired to eliminate defects, and further inspected to verify the repaired defects. As an example, when defects such as flaking occur during reticle production, chromium (Cr) deposition (e.g., via electron beam induced deposition, EBID) can be performed to fill in missing patterns. The deposited Cr layer can then be covered with a tetraethyl orthosilicate (TEOS) capping layer, which can also be deposited via EBID, to prevent Cr degradation. Available techniques for verifying / inspecting such repairs are limited in their ability to provide accurate and reliable structural information. For example, existing techniques for verification / inspection processes using conventional scanning electron microscopes (SEMs) are unable to provide detailed imagery of sample sidewalls, at least because such techniques are unable to capture backscattered electron (BSE) imagery of sidewalls. As a result, effective localization and identification of defects would be challenging, particularly on sidewalls and after repair and capping using a TEOS capping layer. In other words, it is not possible to accurately inspect sample sidewall profiles using conventional BSE imagery. As a result, existing techniques have not proven fully satisfactory in all respects.

[0021] Embodiments of the present disclosure provide advantages over the prior art, although it should be understood that other embodiments can provide different advantages and that not all embodiments necessarily exhibit the same advantages discussed herein, and that not all embodiments need to exhibit a particular advantage. For example, embodiments discussed herein include systems and methods for detecting thickness and sidewall profile of a target sample. In some embodiments, an electron microscope (e.g., SEM) is provided with a 360-degree surround BSE detector that enables acquisition of BSE imagery of sidewalls of a target sample, as described below. The disclosed BSE detector includes an out-lens detector that surrounds a bottom portion of an electron column of the electron microscope (e.g., adjacent to a bottom portion of an objective lens). In various embodiments, the out-lens detector includes a plurality of blades (which can have a flat shape or an arc shape) strategically positioned at various angles and that provide capture of backscattered electrons from a full 360-degree range around a target sample. In various embodiments, an energy filtering grid can also be provided to allow selection of a specified energy band of BSEs to be detected. Thus, the disclosed BSE detector can also be referred to as an energy selective backscatter (EsB) detector. The energy selective out-lens EsB detector grid (e.g., energy filtering grid) can be used to improve signal-to-noise ratio and enhance contrast and resolution of BSE imaging. In some examples, the out-lens detector is also optically coupled to a photomultiplier tube (PMT), which can include a high quantum efficiency GaAs photocathode for electron multiplication and conversion to an electrical signal.

[0022] In some embodiments, a real-time adjustable electron high tension (EHT) voltage controller is provided, in which a variable EHT voltage can be used to produce BSE imagery with different gray scale intensities, which can be used to determine film thickness (or height), as discussed herein. In some examples, a Gaussian filter can be used to distinguish different thicknesses at different gray scale intensities. Further, in some examples, the systems and methods disclosed herein include a 3D image algorithm (or overlay algorithm) that integrates a trained machine learning (ML) model with real-time BSE imagery. In examples, the 3D image algorithm can take BSE imagery as input and use a trained ML model to estimate surface thickness and sidewall profile, thereby providing a 3D image that can be used for reliable inspection of a sample sidewall. In various embodiments, real-time BSE imagery can be taken at multiple EHT voltages, e.g., using a real-time adjustable EHT voltage controller, in order to build up a 3D image.

[0023] Accordingly, the embodiments disclosed herein provide a variety of benefits and advantages. For example, the 360-degree surround BSE detector provides higher precision and higher resolution images of the target sample, including the sidewall profile of the target sample. Further, the use of different gray scale intensities provides in-line gating check points for the mask defects, even for those defects that include TEOS protected top cap layer sidewall coverage. This ensures real-time detection and correction of defects, reducing the need for manual inspection and improving the overall quality of the product. Further, the use of the disclosed system provides faster detection and correction of defects, reducing the time and cost involved in manual inspection and correction. The systems and methods disclosed herein also improve the efficiency of the manufacturing process by reducing the need for manual inspection and correction and by providing higher precision images that enable faster and more accurate detection of defects. It should be noted that while the various examples shown and described herein can be discussed in the context of photomask (mask) repair or inspection, embodiments of the disclosure can similarly be used in other applications to achieve similar benefits. For example, the disclosed embodiments can also be used as a mask in-line process monitor, for mask in-line structure verification, for mask optical proximity correction (OPC) design, or for mask critical dimension (CD) SEM measurement, among other applications. Additional embodiments and advantages will be apparent to those skilled in the art upon reading the present disclosure.

[0024] To provide further context regarding the present disclosure, Figure 1 A simplified block diagram of an embodiment of an integrated circuit (IC) manufacturing system 100 and an IC manufacturing flow associated therewith is provided, which can benefit from various aspects of the present disclosure. The IC manufacturing system 100 includes a plurality of entities, such as a design house 120, a mask house 130, and an IC manufacturer 150 (i.e., a wafer foundry), which interact with each other in the design, development, and manufacturing cycle and / or manufacturing-related services. An integrated circuit (IC) device 160. The plurality of entities are connected through a communication network, which can be a single network or various different networks, such as an intranet and the Internet, and can include wired and / or wireless communication channels. Each entity can interact with and can provide services to and / or receive services from the other entities. One or more of the design house 120, the mask house 130, and the IC manufacturer 150 can have common ownership and can even coexist in a common facility and use common resources.

[0025] In various embodiments, a design room 120, which can include one or more design teams, generates an IC design layout 122. The IC design layout 122 can include various geometric patterns designed for fabricating an IC device 160. For example, the geometric patterns can correspond to patterns of metal, oxide, or semiconductor layers that make up various parts of the IC device 160 to be fabricated. The layers combine to form various functions of the IC device 160. For example, various portions of the IC design layout 122 can include features such as active regions, gate electrodes, source and drain regions, metal lines or vias for metal interconnects, openings for bond pads, and other features known in the art. Techniques form the various layers within or on a semiconductor substrate, such as a silicon die, and various material layers disposed on the semiconductor substrate. In various examples, the design room 120 implements a design flow to form the IC design layout 122. The design process can include logic design, physical design, and / or placement and routing. The IC design layout 122 can be represented in one or more data files having information related to the geometric patterns to be used to fabricate the IC device 160. In some examples, the IC design layout 122 can be expressed in an Open Artwork System Interchange Standard (OASIS) file format, a GDSII file format, or a DFII file format.

[0026] In some embodiments, the design room 120 can transmit the IC design layout 122 to the mask room 130, e.g., via the network connection described above. The mask room 130 can then use the IC design layout 122 to manufacture one or more masks for fabricating various layers of the IC device 160 according to the IC design layout 122. In various examples, the mask room 130 performs mask data preparation 132, in which the IC design layout 122 is converted to a form that can be physically written by a mask writer, mask manufacturing 144, in which the design layout prepared by the mask data preparation 132 is modified to conform to manufacturing with a particular mask writer and / or mask manufacturer, and then mask inspection 145. In some examples, the mask data preparation 132 and the mask manufacturing 144 are shown as separate components; however, in some embodiments, the mask data preparation 132 and the mask manufacturing 144 can be collectively referred to as mask data preparation. Figure 1

[0027] ​For example, mask data preparation 132 includes applying one or more resolution enhancement techniques (RET), such as phase shift mask (PSM), off-axis illumination (OAI), optical proximity correction (OPC), and inverse lithography technology (ILT) to compensate for potential lithography errors, such as errors caused by diffraction, interference, or other process effects. In some embodiments, RET (e.g., such as OPC or ILT) can be used to modify the mask layout to compensate for processing limitations used in IC manufacturing, and which become apparent as process technology nodes scale down. Without RET, a simple scaling down of a layout design used on a larger node would often result in inaccurate or poorly shaped features. In various examples, OPC can be used to adjust line widths according to the density of surrounding geometry, add "dog-bone" end caps to line ends to prevent line end shortening, correct e-beam proximity effects, or for other purposes. OPC can also be used to add sub-resolution assist features (SRAFs) such as scattering bars, serifs, and / or hammerheads to the IC design layout 122, such that after the lithography process, the final pattern on the chip is improved with enhanced resolution and accuracy. While some features of mask data preparation 132 have been described, it should be understood that the above description has been simplified for the purpose of clarity and that mask data preparation can include additional processes and / or features.

[0028] After the mask data preparation 132 and during the mask manufacturing 144, a mask or a set of masks can be manufactured based on the modified IC design layout. For example, based on the modified IC design layout, a pattern is formed on a mask (photomask or reticle) using an electron beam (e-beam) or a multi- e-beam mechanism. The mask can be formed through a variety of techniques. In one embodiment, the mask is formed using binary technology. In some embodiments, the mask pattern includes opaque regions and transparent regions. A beam of radiation (e.g., an ultraviolet (UV) beam) used to expose a layer of radiation-sensitive material (e.g., photoresist) coated on a chip is blocked by the opaque regions and transmitted through the transparent regions. In one example, a binary mask includes a transparent substrate (e.g., fused quartz) and an opaque material (e.g., chromium) coated in the opaque regions of the mask. In some examples, the mask is formed using phase-shift technology. In a phase-shift mask (PSM), various features in the pattern formed on the mask are configured to have a preconfigured phase difference to enhance image resolution and imaging quality. In various examples, the phase-shift mask can be an attenuated PSM or an alternating PSM.

[0029] At various stages during the mask manufacturing process, and after the mask manufacturing, the mask or set of masks can be inspected (through mask inspection 145). In some embodiments, the mask inspection 145 is performed using a SEM with a 360-degree surround BSE detector, as described herein. If a defect is found during the inspection process, the defective mask or set of masks can be returned to the mask manufacturing 144 for further processing to fix the defect.

[0030] In some embodiments, IC manufacturer 150, such as a semiconductor foundry, uses the pellicles (or pellicon) manufactured by pellicle chamber 130 to transfer one or more pellicle patterns to production wafers 152 and thus manufacture IC devices 160 on production wafers 152. IC manufacturer 150 can include IC manufacturing facilities, which can include numerous manufacturing facilities for manufacturing a variety of different IC products. For example, IC manufacturer 150 can include a first manufacturing facility for front-end manufacturing (i.e., front-end-of-line (FEOL) manufacturing) of a plurality of IC products, while a second manufacturing facility can provide back-end manufacturing for a plurality of IC products. Interconnection and packaging of IC products (i.e., back-end-of-line (BEOL) manufacturing) and a third manufacturing plant can provide other services for foundry business. In various embodiments, the semiconductor chips (i.e., production wafers 152) within and / or on which IC devices 160 are manufactured can include silicon substrates or other substrates having material layers formed thereon. Further, the pellicles (or pellicon) can be used for a variety of processes. For example, the pellicles (or pellicon) can be used in ion implantation processes to form various doped regions in the semiconductor chips, in etching processes to form various etched regions in the semiconductor chips, and / or in other suitable processes.

[0031] As Figure 1 Further shown, and in some examples, IC manufacturer 150 can use the pellicles (or pellicon) manufactured by pellicle chamber 130 to transfer one or more pellicle patterns to development design wafers 154. After processing development design wafers 154, development design wafers 154 can be transferred to a test lab (a metrology lab or parametric test lab) for empirical analysis 156. In some embodiments, empirical data collected from development design wafers 154 can be transferred to pellicle chamber 130, where IC design layout 122 can be further modified (if necessary) based on the empirical data. In some embodiments, IC manufacturer 150 can use production wafers 152 or development design wafers 154 to collect correction data for empirical analysis 156. In addition to chip inspection, and in various examples, empirical analysis 156 can include pellicle inspection using a SEM with a 360-degree surround BSE detector, as described herein. If defects are found in the pellicles through empirical analysis 156, the defective pellicles or pellicon set can be returned to pellicle manufacturing 144 for further processing to repair the defects. Alternatively, IC manufacturer 150 itself can include facilities for pellicle repair.

[0032] Referring to Figure 2 wherein various aspects of the present disclosure are provided Figure 1 A more detailed block diagram of pellicle chamber 130 is shown. In Figure 2In one example, the dome room 130 includes a dome design system 180, which is operable to perform [operations related to / specifications]. Figure 1 The preparation of the shroud data 132 or the shroud inspection 145 are related to and in conjunction with the reference. Figures 6-9 The described methods and / or processes are associated with the described functions, which are discussed below. Specifically, according to various embodiments, the mask design system 180 can receive data from the mask inspection 145 and is operable to perform functions associated with the 3D imaging algorithm to estimate surface thickness and sidewall profiles. In some embodiments, similar functions associated with the 3D imaging algorithm may also be provided at the IC manufacturer 150 (e.g., such as at empirical analysis 156). More generally, and according to various embodiments, an information processing system that communicates with a SEM having a 360-degree surround BSE detector and is configured to receive data from the SEM can implement the functions associated with the 3D imaging algorithm, as described herein.

[0033] Such an information processing system is illustrated in the context of a mask design system 180 and may include an information processing system, such as a computer, server, workstation, or other suitable device. System 180 includes a processor 182 communicatively coupled to system memory 184, a mass storage device 186, and a communication module 188. System memory 184 provides non-transient, computer-readable memory for processor 182 to facilitate the execution of computer instructions. Examples of system memory 184 may include random access memory (RAM) devices, such as dynamic RAM (DRAM), synchronous DRAM (SDRAM), solid-state memory devices, and / or various other memory devices known in the art. Computer programs, instructions, and data are stored in mass storage device 186. Examples of mass storage device 186 may include hard disks, optical disks, magneto-optical disks, solid-state memory devices, and / or various other mass storage devices. Communication module 188 is operable to transmit information, such as IC design layout files, to other components in IC manufacturing system 100 (e.g., design room 120). Examples of communication module 188 may include an Ethernet card, an 802.11 WiFi device, a cellular data radio, and / or other suitable devices known in the art. In various embodiments, other information processing systems with similar components may be implemented, for example at IC manufacturer 150 (e.g., at empirical analysis 156) or elsewhere, enabling the information processing system to communicate with a SEM that receives data from a 360-degree surround BSE detector.

[0034] In operation, the mask design system 180 is configured to manipulate the IC design layout 122 according to various design rules and constraints prior to the IC design layout 122 being transferred to the mask 190 by the mask manufacturing 144. For example, in one embodiment, the mask data preparation 132 (including, as one example, OPC) can be implemented as software instructions executed on the mask design system 180. In such an embodiment, the mask design system 180 receives a first GDSII file 192 containing the IC design layout 122 from the design room 120. After the mask data preparation 132 is complete, the mask design system 180 transmits a second GDSII file 194 containing the modified IC design layout to the mask manufacturing 144 (i.e., to the mask manufacturer). In alternative embodiments, the IC design layout 122 can be transmitted between components in the IC manufacturing system 100 in alternative file formats (such as DFII, CIF, OASIS, or any other appropriate file type). Furthermore, in alternative embodiments, the mask design system 180 and the mask room 130 can include additional and / or different components. Once mask manufacturing and inspection is complete, the mask can be transferred to the IC manufacturer 150.

[0035] Referring now to the drawings Figure 3SEM 300. While embodiments of the disclosure are not limited in this regard, in some cases, SEM 300 can be implemented by the reticle inspection 145, by the IC manufacturer 150 (e.g., at the metrology analysis 156), or by another facility of the IC manufacturing system 100. As shown, the SEM 300 includes an electron gun 302 that generates an electron beam 304 that is directed along an axis through a column of the SEM 300 to a sample 306 mounted on a sample stage 308. In some embodiments, the sample 306 can include a reticle (photomask or photolithographic mask), such as a binary reticle, a phase shift mask (PSM), an EUV reticle, a DUV, or other type of reticle. In various embodiments, the electron gun 302 can include different types of emitters, such as a tungsten filament, a solid-state hexaboride crystal, and a field emission gun. Electrons emitted by the electron gun 302 are accelerated toward an anode with an EHT voltage (e.g., in a range of about 0.1 keV to about 30 keV) that can be adjusted in real-time (e.g., by an EHT controller through the SEM 300). A condenser lens, a plurality of apertures, an objective lens 315, deflection coils, and / or other components are configured to focus and project the electron beam 304 onto the sample 306. In an example, the stage 308 is configured to secure the sample 306 to the stage 308 through a vacuum system and to provide precise positioning and movement of the sample 306 along X, Y, and / or Z directions (e.g., through a motor coupled to the stage 308) during focusing, leveling, and / or measurement operations. In some embodiments, a vacuum system (e.g., including a mechanical pump, a turbo pump, an ion pump, or other type of pump) is coupled to the SEM 300 to provide a high vacuum environment for the SEM 300 (e.g., including the column, a chamber that houses the stage 308 and the sample 306) and to provide other vacuum functions (e.g., to secure the sample 306 to the stage 308).

[0036] The SEM 300 also includes a detector system that can include a variety of different types of detectors, such as a secondary electron detector, a backscatter electron detector, an energy selective backscatter detector, and / or an X-ray detector, each of which is configured for different purposes. In an example, the detector system includes a secondary electron detector that is configured to detect secondary electrons that are emitted from the sample 306 when the electron beam 304 is incident on the sample 306. In some embodiments, the secondary electron detector includes a scintillator that converts the secondary electrons into photons that are detected by a photomultiplier tube (PMT). In an example, the detector system includes a backscatter electron detector that is configured to detect backscattered electrons that are emitted from the sample 306 when the electron beam 304 is incident on the sample 306. In some embodiments, the backscatter electron detector includes a scintillator that converts the backscattered electrons into photons that are detected by a PMT. In an example, the detector system includes an energy selective backscatter detector that is configured to detect backscattered electrons that are emitted from the sample 306 when the electron beam 304 is incident on the sample 306. In some embodiments, the energy selective backscatter detector includes a scintillator that converts the backscattered electrons into photons that are detected by a PMT. In an example, the detector system includes an X-ray detector that is configured to detect X-rays that are emitted from the sample 306 when the electron beam 304 is incident on the sample 306. In some embodiments, the X-ray detector includes a scintillator that converts the X-rays into photons that are detected by a PMT. Figure 3In the example of FIG. 3, the SEM 300 includes a secondary electron (SE) detector 310 that detects signals from interactions between the electron beam 304 projected on the sample 306 and atoms at or near the surface of the sample 306. Thus, the signals captured by the SE detector 310 can be used to provide high resolution images of the surface of the sample 306. The SE detector 310 is mounted on the axis of the electron beam 304 and can be equivalently referred to as an in-lens SE detector 310. The illustrated SEM 300 also includes an energy selective backscatter (EsB) detector 312 positioned above the in-lens SE detector 310. The EsB detector 312 is also mounted along the axis of the electron beam 304 and can be equivalently referred to as an in-lens EsB detector 312 or an in-lens energy selective BSE detector 312. In-lens detectors generally include detectors positioned inside the column of the SEM 300 that are arranged rotationally symmetrically about an optical axis (e.g., the axis of the electron beam 304). Thus, in various embodiments, the in-lens SE detector 310 and the in-lens EsB detector 312 are configured to detect backscattered electrons (BSEs) that enter the column of the SEM 300. In particular, the EsB detector 312 can detect signals from interactions between the electron beam 304 and atoms deeper within the sample 306. In other words, the EsB detector 312 is used to collect higher energy electrons (e.g., as compared to the SE detector 310). The signals captured by the EsB detector 312 can be used to provide BSE images to visualize different elements within the sample 306 (e.g., to provide compositional contrast or grayscale variations). To prevent the EsB detector 312 from detecting secondary electrons (SEs), an energy filtering grid 314 is positioned in front of the EsB detector 312 (e.g., between the SE detector 310 and the EsB detector 312). In some examples, the filtering grid 314 can be used to filter energies between about 0 and 1500 eV through appropriate biasing of the filtering grid 314. Thus, by activating (turning on) a voltage provided to the filtering grid 314, secondary electrons (SEs) will be rejected (e.g., shown as rejected electrons 316) and backscattered electrons (BSEs) (e.g., shown as BSE electrons 318) will be detected by the EsB detector 312. This energy filtering can be important for enhancing topographical contrast and composite images of the sample 306. In addition to being able to reject lower energy secondary electrons (SEs), the filtering grid 314 can also be used to select a desired energy band of BSEs for detection.

[0037] According to embodiments of the present disclosure, and as Figure 3As shown, the SEM 300 also includes a 360-degree surround BSE detector assembly 320, which enables the acquisition of BSE images of the sidewalls of the sample 306, as described herein. An energy filter grid 322 is disposed in front of the surround BSE detector assembly 320 to allow selection of a specific energy band of the BSE to be detected by the surround BSE detector assembly 320 (e.g., by activating or activating the filter grid 322 by providing an appropriate voltage to the filter grid 322). Therefore, in various embodiments, the 360-degree surround BSE detector assembly 320 may also be referred to as an energy-selective backscatter (EsB) detector assembly 320 or a 360-degree surround EsB detector assembly 320. In various embodiments, the filter grid 322 may also be used to improve the signal-to-noise ratio and enhance the contrast and resolution of the BSE imaging. The 360-degree surround EsB detector assembly 320 is an out-lens detector (e.g., located outside the pillars of the SEM 300 and configured to detect backscattered electrons (BSEs) that do not enter the pillars of the SEM 300). Additionally, the surround EsB detector assembly 320 includes multiple EsB detectors (e.g., Figure 3 The blades 320A, 320B, or Figure 4The blades 402A-402D, 404A-404D, and 406A-406L (described below) are mounted off-axis from the electron beam 304 and surround (or encircle) the bottom portion of the column of the SEM 300 (e.g., adjacent to the bottom portion of the objective lens 315). As described above, multiple EsB detectors (e.g., blades, also referred to as secondary detectors) are separated or spaced apart from each other and are each mounted off-axis, while the overall 360-degree surround EsB detector assembly 320 is located on the axis of the electron beam 304. Unlike the high-angle backscattered electrons detected by the EsB detector 312, the backscattered electrons (BSE) detected by the surround EsB detector assembly 320 can be referred to as low-angle backscattered electrons. Like the EsB detector 312, the signal captured by the surround EsB detector assembly 320 can be used to provide BSE images to visualize different elements within the sample 306 (e.g., to provide compositional contrast or grayscale variations). However, the BSE image generated by the surround EsB detector assembly 320 may include data associated with the sidewalls of sample 306 and may be further used to generate a 3D image of the surface of sample 306, as described in more detail below. In various examples, each of the plurality of EsB detectors in the surround EsB detector assembly 320 (e.g., each of the blades) may be used to independently acquire or provide images, wherein the independently acquired images may be combined to provide a complete image of the EsB detector assembly 320 and sample 306. Additionally, in some embodiments, the BSE images generated by EsB detector 312 and the surround EsB detector assembly 320 may be combined to provide synthetic contrast or grayscale variations, and / or generate a 3D image of the surface of sample 306.

[0038] like Figure 3 As shown, the surround-type EsB detector assembly 320 is also optically coupled to one or more photomultiplier tubes (PMTs) 324 for electron multiplication and conversion into electrical signals, which are used to generate BSE images associated with the surround-type EsB detector assembly 320. In some embodiments, the PMT 324 comprises a high-quantum-efficiency GaAs photocathode, compared to at least some existing PMTs that include photocathodes composed of dual or multi-alkali metals. In some cases, the GaAs photocathode of the PMT 324 comprises GaAs nanowires to provide higher quantum efficiency, as well as longer lifetime and higher stability. Additionally, in some embodiments, the PMT 324 comprises a microchannel plate (MCP) made of GaAs, which can be directly integrated onto the surface of the photocathode to enhance performance. Such an MCP will provide higher gain, better spatial resolution, and lower noise compared to at least some existing MCPs (e.g., glass MCPs).

[0039] Generally, the SEM 300 can be coupled to the computer 305, and the computer 305 can include components related to the above reference. Figure 2 The system described in System 180 is a similar information processing system. Therefore, Computer 305 may similarly include a processor, mass storage device, communication module, and / or other suitable components known in the art, communicatively coupled to system memory. The computer can receive user input from an input device 307 (e.g., keyboard, mouse, or other input device) coupled to Computer 305. Furthermore, Computer 305 may be coupled to Display 309 (e.g., computer monitor). In various examples, Computer 305 may receive signals and / or images (e.g., surface images, BSE images, or other images) acquired by SE detector 310, EsB detector 312, EsB detector assembly 320, X-ray detector, or other detectors and provide the images to Display 309 for user viewing.

[0040] refer to Figure 4 Table 400, illustrating various embodiments, depicts top and side views of a surround-type EsB detector assembly 320 of various types or configurations. As previously described, each of the various types or configurations shown in Table 400 includes an external-lens BSE detector configured to surround the bottom portion of a pillar of the SEM 300 (e.g., adjacent to the bottom of objective lens 315). In some examples, each type or configuration shown in Table 400 has multiple blades strategically positioned at different angles (e.g., having a flat or curved shape in the side view), which provide the ability to capture backscattered electrons from a full 360-degree range around the sample 306, thereby obtaining a BSE image of the sidewalls of the sample 306.

[0041] In row 402 or table 400, a first configuration of the surround EsB detector assembly 320 includes a circular configuration with four blades 402A, 402B, 402C, and 402D. In some embodiments, blades 320A, 320B ( Figure 3) can include any of the blades 402A-402D. As shown in the top view of row 402, the blades 402A and 402B define an outer circle portion and the blades 402C and 402D define an inner circle portion that is coaxial with the outer circle portion. In examples, and with reference to the top view, the width Wl of the blades 402A / 402B can be less than the width W2 of the blades 402C / 402D. However, in other cases, the width Wl of the blades 402A / 402B can be greater than the width W2 of the blades 402C / 402D. In other examples, the width Wl of the blades 402A / 402B and the width W2 of the blades 402C / 402D can be substantially equal to each other. In some instances, the blades 402A and 402B can be substantially identical to each other (e.g., have similar dimensions, shapes, widths, etc.) and the blades 402C and 402D can be substantially identical to each other (e.g., have similar dimensions, shapes, widths, etc.). In some embodiments, and as shown in the side view of row 402, the inner circular portion of the blades 402C / 402D can be substantially flat. In various embodiments, the outer circular portion of the blades 402A / 402B can have a substantially flat shape or an arcuate shape (in the side view). Further, in some embodiments, and regardless of whether the shape of the blades 402A / 402B is flat or arcuate, the blades 402A / 402B of the outer circular portion can be tilted or rotated relative to the blades 402C / 402D of the inner circular portion, as shown. In various examples, a tilt angle Θ1 is defined between a substantially horizontal plane 405 (in the side view) corresponding to the orientation of the blades 402C / 402D and the surface of the tilted or rotated blades 402A / 402B. In some embodiments, the tilt angle Θ1 is in a range between about 0-50 degrees. Thus, in at least some cases (e.g., when the tilt angle Θ1 is equal to about 0 degrees), all four of the blades 402A, 402B, 402C, 402D can be oriented in a substantially horizontal direction (in the side view).

[0042] In row 404 or table 400, a second configuration of the wrap-around EsB probe assembly 320 includes a circular configuration with four blades 404A, 404B, 404C, 404D. In some embodiments, the blades 320A, 320B( Figure 3) can include any of the blades 404A-404D. In contrast to the first configuration of row 402, and as shown in the top view of row 404, the four blades 404A, 404B, 404C, 404D collectively define a circular second blade configuration. In examples, each of the blades 404A, 404B, 404C, 404D can be substantially identical to one another (e.g., have similar dimensions, shapes, widths, etc.). Although in some cases, one or more of the blades 404A, 404B, 404C, 404D can be different than the others. In various embodiments, each of the blades 404A, 404B, 404C, 404D can have a substantially flat shape or an arcuate shape (in the side view). As shown in the side view of row 404, in some embodiments and regardless of the flat or arcuate shape of the blades 404A, 404B, 404C, 404D, the blades 404A, 404B, 404C, 404D can be tilted or rotated such that a tilt angle Θ2 is defined between a substantially horizontal plane 407 (in the side view) and the surface of the tilted or rotated blades 404A / 404B / 404C / 404D. In some embodiments, the tilt angle Θ2 is in a range between about 0-50 degrees. Thus, in at least some cases (e.g., when the tilt angle Θ2 is equal to about 0 degrees), all four of the blades 404A, 404B, 404C, 404D can be oriented in a substantially horizontal direction (in the side view).

[0043] In row 406 of the table 400, a third configuration of the wrap-around EsB detector assembly 320 includes a circular configuration having twelve blades 406A-406L. In some embodiments, the blades 320A, 320B( Figure 3) can include any of the blades 406A-406L. In contrast to the first configuration of row 402, but similar to the second configuration of row 404, and as shown in the top view of row 406, the twelve blades 406A-406L collectively define a circular third blade configuration. In examples, each of the twelve blades 406A-406L can be substantially identical to one another (e.g., have similar dimensions, shapes, widths, etc.). Although in some cases, one or more of the twelve blades 406A-406L can be different from the others. In various embodiments, each of the twelve blades 406A-406L can have a substantially flat shape or an arcuate shape (in the side view). As shown in the side view of row 406, in some embodiments, regardless of whether the blades 406A-406L are flat or arcuate in shape, each of the twelve blades 406A-406L can be tilted or rotated such that an angle of tilt Θ3 (in the side view) is defined between the substantially horizontal plane 409 and the surface of the tilted or rotated blades 406A-406L. In some embodiments, the angle of tilt Θ3 is in a range between about 0-50 degrees. Thus, in at least some cases (e.g., when the angle of tilt Θ3 is equal to about 0 degrees), all twelve of the blades 406A-406L can be oriented in a substantially horizontal direction (in the side view).

[0044] While some examples of various types or configurations of the wrap-around EsB probe assembly 320 have been provided, it should be appreciated that other configurations can be equally implemented without departing from the scope of the present disclosure. For example, in some cases, as a variation of the first configuration of row 402, an intermediate circular portion (consisting of two blades similar in shape to the inner and outer circular portions) can be interposed between the outer and inner circular portions. In other words, a first blade of the intermediate circular portion can be inserted between blades 402B and 402D, and a second blade of the intermediate circular portion can be inserted between blades 402A and 402C. In other cases, and as a variation of the second configuration of row 404 and the third configuration of row 406, the configuration of the wrap-around EsB probe assembly 320 can include another number of blades collectively defining a circular blade configuration. For example, in some embodiments, the wrap-around EsB probe assembly 320 includes a circular configuration having two blades, six blades, eight blades, ten blades, or another number of blades.

[0045] As previously mentioned, the SEM 300 (including the surround-type EsB detector assembly 320) can be used in any of a variety of different applications, such as mask repair or inspection, online mask process monitoring, online mask structure verification, mask OPC design, or for mask CDSEM measurements. In particular, for advanced technology nodes, mask patterns need to be very precise (e.g., virtually free of mask defects). Therefore, as an illustrative case, an example of using the SEM 300 (including the surround-type EsB detector assembly 320) for mask repair or inspection is now provided.

[0046] If defects are found in the mask, it may be necessary to selectively remove layers or deposit layers on the mask. Figure 5 An exemplary sample 505 (or mask 505) is shown, which may include the sample 306 discussed above. Therefore, sample 505 may also include a mask, such as a binary mask, phase-shifted mask (PSM), EUV mask, DUV mask, or other type of mask. In one embodiment, mask 505 includes a quartz substrate 502. As an example, when defects such as peeling occur during mask production, chromium (Cr) deposition (e.g., via electron beam induced deposition, EBID) can be performed to fill the missing pattern. Figure 5 In this example, the selectively deposited Cr layer 504 is shown to be formed over a substrate 502 to repair various defects. The deposited Cr layer 504 can then be covered with a corresponding tetraethyl orthosilicate (TEOS) capping layer 506, which can also be deposited via EBID to protect the Cr layer 504 from degradation (e.g., during subsequent photolithography processes). While a target thickness for the TEOS capping layer 506 can be defined (e.g., about 10 nm), in practice, the thickness of the TEOS capping layer 506 may not always conform to the target thickness and / or the thickness of the TEOS capping layer 506 along the top surface. And / or along the sidewalls of a given Cr layer 504, or between different Cr layers 504, it can be non-uniform (e.g., as shown in the image). Figure 5 (as roughly depicted in the text). As previously mentioned, the available techniques for verifying / inspecting such repairs are limited in their ability to provide accurate and reliable structural information, particularly along the sidewalls of the repaired area (e.g., the TEOS capping layer 506 on the sidewalls of the Cr layer 504).

[0047] The SEM 300 can obtain various types of imagery and information about a sample (e.g., the sample 505 or the sample 305 discussed above). By way of illustration, consider now that the SEM 300 (including the surround EsB detector assembly 320) is used to inspect a TEOS cap layer (e.g., such as the TEOS cap layer 506) formed over various Cr layers (e.g., such as the Cr layer 504), which has been deposited to repair a mask defect (e.g., such as a missing pattern). By way of example, and with reference to Figure 6 wherein a plurality of BSE images 602, 604, 606, 608, 610, 612, 614, 616, 618, 620 are shown taken by the SEM 300 using different EHT voltages, which can be adjusted in real-time by the EHT voltage controller of the SEM 300. In the illustrative example, each of the BSE images 602, 604, 606, 608, 610, 612, 614, 616, 618, 620 includes a 3x3 array of Cr squares (e.g., similar to the Cr layer 504) (e.g., similar to the TEOS cap layer 506) of various thicknesses covered by the TEOS cap layer. In particular, the variable EHT voltage can be used to produce (or take) the BSE images 602, 604, 606, 608, 610, 612, 614, 616, 618, 620 with varying gray scale intensities, which can be used to determine the film thickness (or height) of the TEOS cap layer formed over the 3x3 array of Cr squares. In other applications, the varying gray scale intensities can be used to determine the film thickness (or height) or to identify an alternative layer composition or type. In some embodiments, the BSE images 602, 604, 606, 608, 610, 612, 614, 616, 618, 620 can be captured by the EsB detector 312. In some cases, the BSE images can be taken by, for example, the surround EsB detector assembly 320 or by a combination of the EsB detector 312 and the surround EsB detector assembly 320 to enhance the quality of the BSE images. Of course, in accordance with embodiments of the present disclosure, the BSE images produced by the surround EsB detector assembly 320 can include data associated with sidewalls of the sample (e.g., data about the TEOS cap layer formed over the sidewalls of the Cr layer) and can also be used to generate 3D images of the surface of the sample, as further described below.

[0048] Still referring to Figure 6BSE image 602 was taken at an EHT voltage of 0.2 keV, BSE image 604 was taken at an EHT voltage of 0.4 keV, BSE image 606 was taken at an EHT voltage of 0.6 keV, BSE image 608 was taken at an EHT voltage of 0.8 keV, BSE image 610 was taken at an EHT voltage of 1.0 keV, BSE image 612 was taken at an EHT voltage of 1.1 keV, BSE image 614 was taken at an EHT voltage of 1.2 keV, BSE image 616 was taken at an EHT voltage of 1.3 keV, BSE image 618 was taken at an EHT voltage of 1.4 keV, and BSE image 620 was taken at an EHT voltage of 1.5 keV. In the BSE images, each Cr square of the 3x3 array of Cr squares has a number below it representing the measured thickness (nm) of the TEOS cap layer deposited on the corresponding Cr square. As shown, the various measured thicknesses of the TEOS cap layer include 2.6 nm, 4.6 nm, 7.6 nm, 9.7 nm, 12.8 nm, 15.5 nm, 16.8 nm, 19.7 nm, and 22.4 nm.

[0049] Figure 6 Also shown is table 622, which includes the gray scale intensity values of each TEOS cap layer formed on the respective Cr squares of the 3x3 array of Cr squares in BSE images 602, 604, 606, 608, 610, 612, 614, 616, 618, 620. The first row of table 622, 'Height (nm)', includes the rounded values of the various measured thicknesses of the TEOS cap layer formed on each Cr square, where 3 nm in table 622 corresponds to 2.6 nm in the BSE images, 5 nm in table 622 corresponds to 4.6 nm in the BSE images, 8 nm in table 622 corresponds to 7.6 nm in the BSE images, 10 nm in table 622 corresponds to 9.7 nm in the BSE images, 13 nm in table 622 corresponds to 12.8 nm in the BSE images, 16 nm in table 622 corresponds to 15.5 nm in the BSE images, 17 nm in table 622 corresponds to 16.8 nm in the BSE images, 20 nm in table 622 corresponds to 19.7 nm in the BSE images, and 22 nm in table 622 corresponds to 22.4 nm in the BSE images. Thus, each row in table 622 corresponds to a different one of the Cr squares in the 3x3 array of Cr squares, as identified by the thickness of the TEOS cap layer given for each row of table 622.

[0050] The second row of table 622, '0.2 keV', corresponds to BSE image 602, the third row of table 622, '0.4 keV', corresponds to BSE image 604, the fourth row of table 622, '0.6 keV', corresponds to BSE image 606, the fifth row of table 622, '0.8 keV', corresponds to BSE image 608, the sixth row of table 622, '1.0 keV', corresponds to BSE image 610, the seventh row of table 622, '1.1 keV', corresponds to BSE image 612, the eighth row of table 622, '1.2 keV', corresponds to BSE image 614, the ninth row of table 622, '1.3 keV', corresponds to BSE image 616, the tenth row of table 622, '1.4 keV', corresponds to BSE image 618, and the eleventh row of table 622, '1.5 keV', corresponds to BSE image 620.

[0051] As previously mentioned, the TEOS capping layer formed over each Cr square of the 3x3 array of Cr squares can be deposited using EBID. In various embodiments, the deposition rate of the TEOS used to form the TEOS capping layer can be adjusted by varying the dwell time of the electron beam used during EBID. For example, by increasing the dwell time of the electron beam, a higher deposition rate (and thickness) of the TEOS capping layer can be achieved. In various embodiments, the target thickness of the TEOS capping layer formed over each Cr square can be approximately 10 nm, and the varying gray scale intensity of the BSE images can be used to detect any deviations from the target thickness. Of course, in other embodiments, a different target thickness can be used equally without departing from the scope of the present disclosure.

[0052] In table 622, the gray scale intensity values can range from 0 to 255, where 0 corresponds to a black pixel of the corresponding BSE image and 255 corresponds to a white pixel of the corresponding BSE image. Thus, different values in table 622 indicate different gray scales as compared to the background material (e.g., silicon, or in some cases quartz). Further, in table 622, bins 624A-624H, for a given EHT voltage, adjacent gray scale intensity values are plotted around, where the adjacent gray scale intensity values correspond to consecutive thickness values of the TEOS capping layer. Specifically, the adjacent gray scale intensity values shown in each bin 624A-624H represent a sufficient change (delta) in the gray scale intensity values to be able to distinguish between a bright layer (metal, e.g., Cr) and a dark layer (non-metal, e.g., ethyl silicate). In each bin 624A-624H, the lower row of gray scale intensity values are the smaller gray scale intensity values (corresponding to the dark, non-metal layer), and the upper row of gray scale intensity values are the larger gray scale intensity values (corresponding to the bright, metal layer). In some embodiments, the change (delta) in adjacent gray scale intensity values in each bin 624A-624H ranges from about 1.5X to about 3.8X. In some cases, it can be generally stated that the change (delta) in adjacent gray scale intensity values in each bin 624A-624H represents about a 2-fold (or more) difference in the gray scale intensity values.

[0053] In summary, with reference to bin 624A and at 0.6 keV EHT, it can be understood that backscattered electrons cannot pass through a 5 nm TEOS capping layer on the Cr film, resulting in the Cr film appearing as a dark square (similar to the image background) in BSE image 606 having a TEOS capping layer of 5 nm or greater thickness. In contrast, and still with reference to bin 624A and at 0.6 keV EHT, backscattered electrons can pass through a 3 nm TEOS capping layer on the Cr film, resulting in the Cr square in BSE image 606 having a bright (or brighter) appearance having a TEOS capping layer of 3 nm thickness. Bin 624A-1 in BSE image 606 indicates a region having a bright (metal) region.

[0054] With reference to bin 624B and at 0.8 keV EHT, backscattered electrons cannot pass through an 8 nm TEOS capping layer on the Cr film, resulting in the Cr square in BSE image 608 having a dark appearance (similar to the image background) having a TEOS capping layer of 8 nm or greater thickness. In contrast, and still with reference to bin 624B and at 0.8 keV EHT, backscattered electrons can pass through a 5 nm TEOS capping layer on the Cr film, resulting in the Cr square in BSE image 608 having a bright (or brighter) appearance having a TEOS capping layer of 5 nm or less thickness. Bin 624B-1 in BSE image 608 indicates a set of bright (metal) regions.

[0055] Referring to grid 624C and at 1.0 keV EHT, backscattered electrons cannot pass through a 10 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in BSE image 610 with TEOS top cap layer appearing dark (similar to the image background) with a thickness of 10 nm or greater. In contrast, and still referring to grid 624C and at 1.0 keV EHT, backscattered electrons can pass through an 8 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in BSE image 610 having a bright (or lighter) appearance with a TEOS top cap layer of 8 nm or less. Grid 624C-1 in BSE image 610 represents a set of bright (metallic) regions.

[0056] Referring to grid 624D and at 1.1 keV EHT, backscattered electrons cannot pass through a 10 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in BSE image 612 with TEOS top cap layer appearing dark (similar to the image background) with a thickness of 10 nm or greater. In contrast, and still referring to grid 624D and at 1.1 keV EHT, backscattered electrons can pass through an 8 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in BSE image 612 having a bright (or lighter) appearance with a TEOS top cap layer of 8 nm or less. Grid 624D-1 in BSE image 612 represents a set of bright (metallic) regions.

[0057] Referring to grid 624E and at 1.2 keV EHT, backscattered electrons cannot pass through a 10 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in BSE image 614 with TEOS top cap layer appearing dark (similar to the image background) with a thickness of 10 nm or greater. In contrast, and still referring to grid 624E and at 1.2 keV EHT, backscattered electrons can pass through an 8 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in BSE image 614 having a bright (or lighter) appearance with a TEOS top cap layer of 8 nm or less. Grid 624E-1 in BSE image 614 represents a set of bright (metallic) regions.

[0058] Referring to the grid 624F and at 1.3 keV EHT, backscattered electrons cannot pass through a 10 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in the BSE image 616 with the TEOS top cap layer appearing dark (similar to the image background) with a thickness of 10 nm or more. In contrast, and still referring to the grid 624F and at 1.3 keV EHT, backscattered electrons can pass through an 8 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in the BSE image 616 having a bright (or brighter) appearance with a TEOS top cap layer of 8 nm or less in thickness. The grid 624F-1 in the BSE image 616 represents a set of bright (metallic) regions.

[0059] Referring to the grid 624G and at 1.4 keV EHT, backscattered electrons cannot pass through a 16 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in the BSE image 618 with the TEOS top cap layer appearing dark (similar to the image background) with a thickness of 16 nm or more. In contrast, and still referring to the grid 624G and at 1.4 keV EHT, backscattered electrons can pass through a 13 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in the BSE image 618 having a bright (or brighter) appearance with a TEOS top cap layer of 13 nm or less in thickness. The grid 624G-1 in the BSE image 618 represents a set of bright (metallic) regions.

[0060] Referring to the grid 624H and at 1.5 keV EHT, backscattered electrons cannot pass through a 17 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in the BSE image 620 with the TEOS top cap layer appearing dark (similar to the image background) with a thickness of 17 nm or more. In contrast, and still referring to the grid 624H and at 1.5 keV EHT, backscattered electrons can pass through a 16 nm TEOS top cap layer on the Cr film, resulting in the Cr squares in the BSE image 620 having a bright (or brighter) appearance with a TEOS top cap layer of 16 nm or less in thickness. The grid 624H-1 in the BSE image 620 represents a set of bright (metallic) regions.

[0061] In view of the discussion of Figure 6 It is apparent that, by using the variable EHT voltage of the SEM 300, different thicknesses of the non-metal (e.g., TEOS) on the metal (e.g., Cr film) can be distinguished in the BSE images. In other words, the variable EHT voltage used to generate (or take) the BSE images 602, 604, 606, 608, 610, 612, 614, 616, 618, 620 with varying gray scale intensities can be readily used to determine and / or distinguish the film thickness (or height) of the TEOS top cap layer formed on the 3x3 array of Cr squares.

[0062] While the variation in grayscale intensity of the BSE image provided by modulating the EHT voltage offers a way to distinguish the thickness of non-metallic elements on a metallic surface, as described above, other embodiments are also possible. For example, in some cases, a Gaussian filter can be used to distinguish the thickness of non-metallic elements on a metallic surface. A Gaussian filter also has the ability to substantially eliminate noise. As an illustration, and with reference to... Figure 7 The example BSE image 702 is shown therein. Similar. Figure 6 The BSE image 702 comprises a 3×3 array (e.g., Cr layer 504) of Cr blocks covered by TEOS capping layers of various thicknesses (e.g., similar to TEOS capping layer 506). For the BSE image 702 acquired at a given EHT voltage, a region of interest 704 can be identified for processing using a Gaussian filter. As shown, the region of interest 704 comprises the interface region between a given Cr block (with a TEOS capping layer) and a background material (e.g., such as silicon, or in some cases quartz). In the exemplary example, processing the region of interest 704 using a Gaussian filter results in image map 706, where the X-axis of image map 706 includes pixel values ​​(or grayscale intensity values) ranging from 0 to 255, and the Y-axis of image map 706 includes the total count, as previously discussed. Image 706 includes a bimodal histogram with two distinct peaks 707 and 709 (or groups of 707 and 709), corresponding to the Cr blocks within the region of interest 704 and the corresponding peaks in the background material. Thus, the example of image 706 illustrates successful distinction between bright (metallic) and dark (non-metallic) layers. Furthermore, in some cases, BSE images 702 can be captured at various EHT voltages to provide varying image patterns, as described below.

[0063] Figure 7 Table 722 is also shown, which includes an image of the region of interest (similar to region of interest 704) corresponding to the interface area between each Cr block (with a TEOS capping layer) and the background material in the 3x3 Cr block array. Each Cr block in the 3x3 Cr block array is identified in Table 722 by the thickness of the corresponding TEOS capping layer formed above the corresponding Cr block (displayed along the top of the platform). (See also: ...) Figure 6The various thicknesses of the TEOS capping layer formed over the respective Cr cubes of the 3x3 array of Cr cubes discussed include 3 nm, 5 nm, 8 nm, 10 nm, 13 nm, 16 nm, 17 nm, 20 nm, and 22 nm. In various embodiments, the BSE images can be captured at various EHT voltages that can be adjusted in real-time in order to produce BSE images (with varying gray scale intensities) for processing using a Gaussian filter to distinguish between non-metals over metals. In Table 722, exemplary EHT voltage values are shown as 1.0 keV, 1.1 keV, and 1.2 keV. In general, the examples shown in Table 722 illustrate that the range of EHT voltage values provided 1.0 to 1.2 keV EHT can be used to analyze the gray scale intensity values based on using a Gaussian filter. More specifically, as shown in Table 722, for each row corresponding to 1.0 keV EHT, 1.1 keV EHT, and 1.2 keV EHT, a Gaussian filter can be used to produce a plurality of image plots (one for each Cr cube and corresponding to each TEOS capping layer thickness). As described above, when an image plot displays two distinct populations (a bimodal histogram), a successful distinction between bright layers (metals) and dark layers (non-metals) is shown. Otherwise, if an image plot contains only one population, it will be interpreted as a dark layer (non-metal). Thus, for the row corresponding to 1.0 keV EHT, image plot 708 (corresponding to 8 nm TEOS capping layer thickness) includes a bimodal histogram, as do the image plots corresponding to TEOS capping layer thicknesses less than 8 nm. Similarly, for the row corresponding to 1.1 keV EHT, image plot 710 (corresponding to 10 nm TEOS capping layer thickness) includes a bimodal histogram, as do the image plots corresponding to TEOS capping layer thicknesses less than 10 nm. Further, for the row corresponding to 1.2 keV EHT, image plot 712 (corresponding to 13 nm TEOS capping layer thickness) includes a bimodal histogram, as do the image plots corresponding to TEOS capping layer thicknesses less than 13 nm. Thus, the Gaussian filter technique can also be used to distinguish between non-metals over metals. More specifically, although the analysis procedure for distinguishing between non-metals over metals as discussed with reference to FIGS. 6A-6C and 7A-7C varies, both techniques can be used to produce comparable results. Figure 6 and Figure 7

[0064] As previously described, some embodiments include Figure 8 ​The system and processing flow illustrated herein provide a 3D imagery algorithm (or overlay algorithm) for integrating a machine learning (ML) system 802 (including a trained ML model) with real-time BSE imagery. In some examples, the ML system 802 may be trained and utilize artificial neural networks (e.g., convolutional neural networks (CNNs or ConvNets)), which define mathematical models for modeling complex relationships between inputs and outputs or for finding patterns in data. In some embodiments, the ML model (including CNNs) may be trained based on real input imagery data and / or on synthetic training data. In an example, the 3D imagery algorithm disclosed herein may take a BSE image of a sample (e.g., such as sample 505 or 305) (e.g., BSE images 602-620 and 702 as described above) as input and use the ML system 802 (including a trained ML model) to estimate surface thickness and sidewall profiles to provide a 3D image 804 that can be used for reliable inspection of the sample sidewalls, as previously discussed. In various embodiments, real-time BSE images can be captured at multiple EHT voltages, as shown in the reference above. Figure 6 and Figure 7 Various EHT voltages (or subsets thereof and / or at different EHT voltages) are discussed, using a real-time adjustable EHT voltage controller to build 3D images 804.

[0065] refer to Figure 9 The document illustrates a method 900 for implementing a 3D imaging algorithm that can be used to provide a 3D image 804, as described above. It should be understood that method 900 is merely an example and is not intended to limit this disclosure to what is expressly shown in method 900. Furthermore, additional process steps may be implemented before, during, and after method 900, and some of the described process steps may be replaced or eliminated according to various embodiments of method 900.

[0066] The method begins at block 902, where data is collected and processed. In some embodiments, the collected data includes BSE images taken by the EsB detector 312 (in-lens BSE images) and the surround EsB detector assembly 320 (out-of-lens BSE images). Specifically, as described above, the out-of-lens BSE images provided by the surround EsB detector assembly 320 include data associated with the sidewall of the sample (e.g., including sidewall profile and thickness information) and can be used with the in-lens BSE images to generate a 3D image (e.g., 3D image 804) by the ML system 802. Additionally, as described above, the in-lens and out-of-lens BSE images can be collected using multiple EHT voltages. In various embodiments, the collected data can undergo pre-processing, which can include filtering, normalization, and segmentation, among others. Thereafter, in some examples, the data can be further processed to extract various features. For example, the in-lens and out-of-lens BSE images can be analyzed to determine the thickness of a non-metal layer (e.g., TEOS) on a metal layer (e.g., Cr). In various embodiments, the techniques used to determine and / or distinguish the thickness of the non-metal on the metal can include one or both of the techniques described above with reference to Figure 6 and Figure 7 That is, in some embodiments, the varying grayscale intensities of the BSE images provided by modulating the EHT voltage can be used to distinguish the thickness of the non-metal on the metal, a Gaussian filter can be used to generate an image map that can be analyzed to distinguish the thickness of the non-metal on the metal, or a combination of both techniques. Generally speaking, in some embodiments, the features that can be extracted from the data include sidewall profile estimates, surface thickness, intensity, texture, and / or shape features.

[0067] The method 900 proceeds to block 904, where the data is provided to the ML system 802 for processing. The data provided to the ML system 802 can include the in-lens and out-of-lens BSE images (which can be pre-processed), data related to the extracted features (as described above), and / or other data. In some examples, the data received by the ML system 802 can be split into a training data set and a validation data set. In some embodiments, the training and validation data can be collected and / or provided to the ML system 802 separately or together. The ML system 802 can use the training data to provide a trained ML model, and the validation data can be used to evaluate the prediction accuracy, precision, and recall of the trained ML model. Based on the training and evaluation, and in some embodiments, the ML system 802 can perform an optimization process to fine-tune the parameters of the ML model.

[0068] Method 900 then proceeds to block 906, where ML system 802 uses the ML model to generate a 3D image (e.g., such as 3D image 804) that includes, among other information, non-metal (e.g., TEOS) formed on top of and on sidewall surfaces of metal (e.g., Cr). Thus, the generated 3D image can be used for reliable inspection of the sample sidewall as compared to at least some existing implementations. In particular, method 900 can effectively locate and identify defects on the mask, particularly on the sidewall and after repair and capping using a TEOS top cap layer. Moreover, method 900 can also be used for real-time detection and correction of defects, reducing the need for manual inspection, improving overall product and process quality. It is additionally noted that while method 900 has been discussed in the context of photomask (mask) repair or inspection, in other embodiments, method 900 can be used for other applications (e.g., such as a mask on-line process monitor, for mask on-line structure verification, for mask OPC design, or for mask CDSEM measurement, or other applications) to achieve similar advantages.

[0069] With respect to the description provided herein, systems and methods for detecting thickness and sidewall profile of a target sample are disclosed. In some embodiments, a SEM with a surround lens outer BSE detector is provided. In various embodiments, the lens outer detector includes a plurality of blades (which can have a flat shape or an arc shape) strategically positioned at various angles and which provide capture of backscattered electrons from a full 360-degree range around the target sample. In various embodiments, an energy filtering grid can also be provided to allow selection of a specified energy band of BSEs to be detected, thereby providing an EsB detector. In some instances, the lens outer EsB detector is also optically coupled to a PMT, which can include a high quantum efficiency GaAs photocathode for electron multiplication and conversion to an electrical signal. In some embodiments, a real-time adjustable EHT voltage controller is provided, where a variable EHT voltage can be used to generate BSE images with different gray scale intensities, which can be used to determine film thickness (or height). Moreover, various embodiments provide a 3D image algorithm (or overlay algorithm) that integrates a trained ML model with real-time BSE images to estimate surface thickness and sidewall profile, thereby providing a 3D image that can be used for reliable inspection of the sample sidewall. Thus, the embodiments disclosed herein provide a variety of benefits and advantages, such as higher precision and higher resolution images of the target sample (including sidewall profile of the target sample), real-time detection and correction of defects (reducing the need for manual inspection) and improving overall quality of the product), and reducing processing time and cost of manual inspection and correction, among others.

[0070] Accordingly, one of the embodiments of the present disclosure describes a scanning electron microscope (SEM) including an electron gun configured to generate an electron beam directed along an axis through a column of the SEM toward a sample stage. In some embodiments, the SEM includes a first backscattered electron (BSE) detector mounted along the axis. In some examples, the SEM further includes a second BSE detector mounted off-axis, wherein the second BSE detector is wrapped around a bottom portion of the column.

[0071] In embodiments of the present disclosure, the second backscattered electron detector surrounds the bottom portion of the column adjacent to a bottom portion of an objective lens of the scanning electron microscope.

[0072] In embodiments of the present disclosure, the first backscattered electron detector is configured to detect backscattered electrons that enter the column, and wherein the second backscattered electron detector is configured to detect backscattered electrons that do not enter the column.

[0073] In embodiments of the present disclosure, the second backscattered electron detector includes a 360 degree wrap-around backscattered electron detector.

[0074] In embodiments of the present disclosure, the scanning electron microscope further includes a first energy filter grid positioned in front of the first backscattered electron detector to provide a first energy selective backscattered electron detector, and a second energy filter grid positioned in front of the second backscattered electron detector to provide a second energy selective backscattered electron detector.

[0075] In embodiments of the present disclosure, the scanning electron microscope further includes one or more photomultiplier tubes coupled to the second backscattered electron detector, wherein the one or more photomultiplier tubes include a gallium arsenide photocathode having gallium arsenide nanowires and a microchannel plate integrated onto a surface of the gallium arsenide photocathode composed of gallium arsenide.

[0076] In embodiments of the present disclosure, the second backscattered electron detector has a plurality of blades having a flat shape or an arcuate shape in a side view.

[0077] In embodiments of the present disclosure, the second backscattered electron detector has a plurality of blades arranged in a circular configuration in a top view.

[0078] In embodiments of the present disclosure, the circular configuration includes an inner circular portion composed of a first pair of blades of the plurality of blades and an outer circular portion coaxial with the inner circular portion, the outer circular portion composed of a second pair of blades of the plurality of blades.

[0079] In embodiments of the present utility model, each of the plurality of blades is substantially identical to each other.

[0080] In embodiments of the present utility model, the scanning electron microscope further comprises an electronic high voltage controller, wherein the first backscattered electron detector and the second backscattered electron detector are configured to capture a plurality of backscattered electron images while adjusting the gallium arsenide voltage of the scanning electron microscope in real time through the gallium arsenide voltage controller.

[0081] In embodiments of the present utility model, it is configured to communicate with an information processing system and configured to provide the plurality of backscattered electron images as an input to a machine learning system executing on the information processing system to generate a 3D image of the sample.

[0082] In another embodiment, a system including a sample platform, an electron gun configured to provide an electron beam directed through an electron column to the sample platform is discussed. In some embodiments, the system further includes an in-lens energy selective backscatter (EsB) detector and an out-of-lens EsB detector surrounding a bottom portion of the electron column. In some examples, the system further includes a computer coupled to receive data from the in-lens EsB detector and the out-of-lens EsB detector.

[0083] In embodiments of the present utility model, the in-lens energy selective backscatter detector is configured to detect backscattered electrons that enter the electron column, and wherein the out-of-lens energy selective backscatter detector is configured to detect backscattered electrons that do not enter the electron column.

[0084] In embodiments of the present utility model, the system further comprises one or more photomultiplier tubes coupled to the out-of-lens energy selective backscatter detector, wherein the one or more photomultiplier tubes include a gallium arsenide photocathode having gallium arsenide nanowires and a microchannel plate composed of gallium arsenide integrated onto a surface of the gallium arsenide photocathode.

[0085] In embodiments of the present utility model, the out-of-lens energy selective backscatter detector includes a plurality of blades having a flat shape or an arc shape in a side view, and wherein the plurality of blades are arranged in a circular configuration in a top view.

[0086] In embodiments of the present application, the in-lens energy selective backscatter detector and the out-of-lens energy selective backscatter detector are configured to take a plurality of backscattered electron images at varying electron high tension voltages, the plurality of backscattered electron images defining a portion of the data, and wherein the computer is configured to receive and process the data using a machine learning system executing on the computer to produce a 3D image of a sample disposed on the sample stage.

[0087] In another embodiment, a method is discussed that includes taking a plurality of backscattered electron (BSE) images using an in-lens energy selective backscatter (EsB) detector and an out-of-lens EsB detector at a plurality of electron high tension (EHT) voltages. In some embodiments, the out-of-lens EsB detector surrounds a bottom portion of an electron column of an electron microscope. In some examples, the method further includes providing data associated with the plurality of BSE images to a machine learning (ML) system for one or more of training and validation of a ML model. In some embodiments, the method further includes producing a 3D image of a sample using the ML model. In various examples, the 3D image includes sidewall thickness and profile information of a non-metal formed on a sidewall surface of a metal.

[0088] In embodiments of the present application, the data associated with the plurality of backscattered electron images includes a feature of the sample determined based at least in part on varying gray scale intensities of the plurality of backscattered electron images.

[0089] In embodiments of the present application, the out-of-lens energy selective backscatter detector includes a plurality of blades having a flat shape or an arc shape in a side view, and wherein the plurality of blades are arranged in a circular configuration in a top view.

[0090] The foregoing summary is directed to features of several embodiments so that one of ordinary skill in the art can better understand the aspects of the present disclosure. Those of ordinary skill in the art should appreciate that they can readily use the present disclosure as a basis for designing or modifying other processes and structures to accomplish the same goals as the embodiments introduced herein and / or to achieve the same advantages. Those of ordinary skill in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.

Claims

1. A scanning electron microscope, characterized by, Comprising: an electron gun configured to produce an electron beam directed along an axis through a column of the scanning electron microscope toward a sample stage; a first backscatter electron detector mounted along the axis; a second backscatter electron detector mounted off the axis, wherein the second backscatter electron detector encircles a bottom portion of the column.

2. The scanning electron microscope of claim 1, wherein, the second backscatter electron detector encircles the bottom portion of the column adjacent to a bottom portion of an objective lens of the scanning electron microscope.

3. The scanning electron microscope of claim 1, wherein, the first backscatter electron detector is configured to detect backscattered electrons that enter the column, and wherein the second backscatter electron detector is configured to detect backscattered electrons that do not enter the column.

4. The scanning electron microscope of claim 1, wherein, the second backscatter electron detector comprises a 360 degree encircling backscatter electron detector.

5. The scanning electron microscope of claim 1, wherein, Further comprising: a first energy filtering grid in front of the first backscatter electron detector to provide a first energy selective backscatter electron detector; and a second energy filtering grid in front of the second backscatter electron detector to provide a second energy selective backscatter electron detector.

6. The scanning electron microscope of claim 1, wherein, Further comprising: one or more photomultiplier tubes coupled to the second backscatter electron detector, wherein the one or more photomultiplier tubes comprise a gallium arsenide photocathode having gallium arsenide nanowires and a microchannel plate comprised of gallium arsenide integrated onto a surface of the gallium arsenide photocathode.

7. The scanning electron microscope of claim 1, wherein, the second backscatter electron detector has a plurality of blades having a flat shape or an arc shape in a side view.

8. The scanning electron microscope of claim 1, wherein, the second backscatter electron detector has a plurality of blades arranged in a circular configuration in an upper view.

9. The scanning electron microscope of claim 1, wherein, Further comprising: an electron high voltage controller; wherein the first backscatter electron detector and the second backscatter electron detector are configured to capture a plurality of backscatter electron images while adjusting an electron high voltage of the scanning electron microscope in real time through the electron high voltage controller.

10. A scanning electron microscope system, characterized by, Comprising: a sample stage; an electron gun configured to provide an electron beam directed through an electron column toward the sample stage; an in-lens energy selective backscatter detector; an out-of-lens energy selective backscatter detector encircling a bottom of the electron column; and a computer coupled to receive data from the in-lens energy selective backscatter detector and the out-of-lens energy selective backscatter detector.

Images