Method of scanning a sample with non-circular beam spots

Abstract

Systems, methods, and non-transitory computer readable mediums for scanning a sample with non-circular beam spots may include generating an elongated electron beam; orientating the elongated electron beam such that a length of the elongated electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the elongated electron beam; detecting electrons emitted from the sample during the scanning; and determining a characteristic of the pattern based on the detected electrons.

Description

METHOD OF SCANNING A SAMPLE WITH NON-CIRCULAR BEAM SPOTSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 609,855 which was filed on December 13, 2023 and which is incorporated herein in its entirety by reference.FIELD

[0002] The description herein relates to the field of metrology and inspection and charged particle systems, and more particularly to systems and methods for scanning a sample with non-circular beam spots.BACKGROUND

[0003] In manufacturing processes of integrated circuits (ICs), unfinished or finished circuit components are inspected to ensure that they are manufactured according to design, which have the correct dimensions and are free of defects. A metrology / inspection system utilizing an optical microscope typically has resolution down to a few hundred nanometers; and the resolution is limited by the wavelength of light. As the physical sizes of IC components continue to reduce down to sub- 100 or even sub-10 nanometers, metrology / inspection systems capable of higher resolution than those utilizing optical microscopes are needed.

[0004] A charged particle (e.g., electron) beam microscope, such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), capable of resolution down to less than a nanometer, serves as a practicable tool for inspecting and measuring IC components having a feature size that is sub-100 nanometers. With a SEM, electrons of a single primary electron beam, or electrons of a plurality of primary electron beams, can be focused on locations of interest of a wafer under the metrology or inspection mode. The primary electrons interact with the wafer and may be backscattered or may cause the wafer to emit secondary electrons. The intensity of the electron beams comprising the backscattered electrons and the secondary electrons may vary based on the properties of the internal and external structures of the wafer. The signal may be used to extract the pattern dimension in metrology mode and also may indicate whether the wafer has defects in inspection mode.SUMMARY

[0005] Embodiments of the present disclosure provide systems, methods, and non-transitory computer readable mediums for scanning a sample. Embodiments may include generating an elongated electron beam; orientating the elongated electron beam such that a length of the elongated electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the elongatedelectron beam; detecting electrons emitted from the sample during the scanning; and determining a characteristic of the pattern based on the detected electrons.

[0006] Embodiments may include generating a non-circular electron beam; orientating the noncircular electron beam such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; and determining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.

[0007] Embodiments may include generating a non-circular electron beam; orientating the sample such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; and determining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 is a schematic diagram illustrating an exemplary electron beam metrology or inspection (EBM or EBI) system, consistent with embodiments of the present disclosure.

[0009] Fig. 2A is a schematic diagram illustrating an exemplary multi-beam system that is part of the exemplary charged particle beam metrology or inspection system of Fig. 1, consistent with embodiments of the present disclosure.

[0010] Fig. 2B is a schematic diagram illustrating an exemplary single -beam system that is part of the exemplary charged particle beam metrology or inspection system of Fig. 1, consistent with embodiments of the present disclosure.

[0011] Fig. 3 is an exemplary image depicting various pixel sizes and pattern edge positions.

[0012] Fig. 4 is an exemplary graph depicting measured critical dimension (CD) values from a pattern of a sample with respect to scan time.

[0013] Fig. 5A is a diagram illustrating an ion beam intensity profile from the short axis (X direction) and the long axis (Y direction) directions for an ion source aperture and stencil mask with a same shape

[0014] Fig. 5B is a diagram illustrating an ion beam intensity profile from the short axis (X direction) and the long axis (Y direction) directions for an ion source aperture and stencil mask with a different shape.

[0015] Fig. 6 shows an exemplary schematic of a scanning process using a circular beam.

[0016] Fig. 7A shows an exemplary charged particle beam system, consistent with embodiments of the present disclosure.

[0017] Fig. 7B illustrates an exemplary multi-pole structure having a quadrupole configuration, consistent with embodiments of the present disclosure.

[0018] Fig. 7C illustrates an exemplary multi-pole structure having an octupole configuration, consistent with embodiments of the present disclosure.

[0019] Fig. 7D illustrates exemplary multi-pole structures, consistent with embodiments of the present disclosure.

[0020] Fig. 7E illustrates an exemplary schematic of a quadrupole lens, consistent with embodiments of the present disclosure.

[0021] Fig. 8 shows a strategy to set the voltages of quadrupoles so that the elongated beam may be self-aligned with a pattern, consistent with embodiments of the present disclosure.

[0022] Fig. 9 shows exemplary charged particle beam spots and pixels, consistent with embodiments of the present disclosure.

[0023] Fig. 10 shows an exemplary charged particle beam system, consistent with embodiments of the present disclosure.

[0024] Fig. 11 shows an exemplary schematic of a Wien filter, consistent with embodiments of the present disclosure.

[0025] Fig. 12 shows the impact of a Wien filter, which may stretch the beam along one direction, consistent with embodiments of the present disclosure.

[0026] Fig. 13 shows an exemplary schematic of using layout data (e.g., GDS-RSS) to design a beam spot shape and pixel size distribution over the entire wafer, consistent with embodiments of the present disclosure.

[0027] Fig. 14 shows an exemplary schematic of applying an elongated beam spot functionality in a multi-beam system, consistent with embodiments of the present disclosure.

[0028] Fig. 15 shows exemplary graphs of simulated beam spot shapes varying with quadrupole lens excitation, consistent with embodiments of the present disclosure.

[0029] Fig. 16 shows exemplary graphs of resolutions at the sagittal focal plane as a function of varying quadrupole lens excitation, consistent with embodiments of the present disclosure.

[0030] Figs. 17A-17D show exemplary graphs of simulated signals and exemplary beam spots, consistent with embodiments of the present disclosure.

[0031] Fig. 18 shows an exemplary process for scanning a sample, consistent with embodiments of the present disclosure.DETAILED DESCRIPTION

[0032] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the disclosure. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the subject matter recited in the appended claims. For example, although some embodiments are described in the context of utilizing electron beams, the disclosure is not so limited. Other types of charged particle beamsmay be similarly applied. Furthermore, other imaging systems may be used, such as optical imaging, photodetection, x-ray detection, extreme ultraviolet inspection / metrology, deep ultraviolet inspection / metrology, or the like, in which they generate corresponding types of images.

[0033] Electronic devices are constructed of circuits formed on a piece of silicon called a substrate. Many circuits may be formed together on the same piece of silicon and are called integrated circuits or ICs. The size of these circuits has decreased dramatically so that many more of them can fit on the substrate. For example, an IC chip in a smart phone can be as small as a thumbnail and yet may include over 2 billion transistors, the size of each transistor being less than 1 / 1000th the size of a human hair.

[0034] Making these extremely small ICs is a complex, time-consuming, and expensive process, often involving hundreds of individual steps. Errors in even one step have the potential to result in incorrect dimensions and defects in the finished IC rendering it useless. Thus, one goal of the manufacturing process is to accurately measure the pattern size in each step and avoid such defects to maximize the number of functional ICs made in the process, that is, to improve the overall yield of the process.

[0035] One component of improving yield is monitoring the chip making process to ensure that it is producing a sufficient number of functional ICs. One way to monitor the process is to measure and inspect the chip circuit structures at various stages of their formation. Metrology or inspection may be carried out using a scanning charged particle microscope (SCPM), such as a scanning electron microscope (SEM). A SEM can be used to image these extremely small structures, in effect, taking a “picture” of the structures of the wafer. The image can be used to determine if the structure was formed properly, and also if it was formed at the proper location. If the structure is defective, then the process can be adjusted so the incorrect dimension and defect are less likely to recur. Incorrect dimensions and defects may be generated during various stages of semiconductor processing. For the reason stated above, it is important to find the incorrect dimensions and defects accurately and efficiently as early as possible.

[0036] The working principle of a SEM is similar to a camera. A camera takes a picture by receiving and recording brightness and colors of light reflected or emitted from people or objects. A SEM takes a “picture” by receiving and recording energies or quantities of electrons reflected or emitted from the structures. Before taking such a “picture,” an electron beam may be projected onto the structures, and when the electrons are reflected or emitted (“exiting”) from the structures, a detector of the SEM may receive and record the energies or quantities of those electrons to generate an image. To take such a “picture,” some SEMs use a single electron beam (referred to as a “single-beam SEM”), while some SEMs use multiple electron beams (referred to as a “multi-beam SEM”) to take multiple “pictures” of the wafer. By using multiple electron beams, the SEM may project more electron beams onto the structures for obtaining these multiple “pictures,” resulting in more electrons exiting from thestructures. Accordingly, the detector may receive more exiting electrons simultaneously, and generate images of the structures of the wafer with a higher efficiency and a faster speed.

[0037] In typical systems, a circular beam is used in a scanning electron microscope (SEM). Efforts were made in typical systems to remove all the aberrations that make the beam have an elliptical or other non-circular shape. In e-beam metrology, the performance of a SEM is evaluated by how stably and accurately the critical dimension (CD) is measured over a long time span. Typical systems use a circular beam to scan a one-dimensional (ID) line on a sample, where many points along the edge of the line are located and used to determine the mean CD of the line pattern.

[0038] Typical systems, however, suffer from constraints. The throughput in typical systems is low due to the many scans required to locate the line edge for the CD determination. Moreover, the high current density risks damage to the sample (e.g., radiation damage) or images with reduced accuracy due to charging effects.

[0039] Typical SEMs use a circular beam spot for both ID and two-dimensional (2D) patterns. For 2D patterns, to resolve the pattern edge in two directions, small beam spots that are equal in size in two orthogonal directions are required. For ID patterns, since the edge of a pattern is only along one direction, it is not necessary to use a round beam spot. As long as the resolution in a direction perpendicular to the pattern is sufficiently small, an accurate CD value may be extracted from a ID pattern.

[0040] The disclosed embodiments provide systems and methods that address some or all of these disadvantages by generating a charged particle beam (e.g., electron beam) with an elongated beam spot. That is, the disclosed embodiments provide systems and methods that include favorable aberrations into the electron profile to improve the performance of metrology and inspection by generating a non-circular electron beam. The beam spot may be elongated in a direction parallel to the length of line patterns. As a result, the throughput may be boosted by more than ten times the throughput achieved with a circular beam spot. By breaking the symmetry of the beam spot, a non- circular beam may largely increase the throughput for a ID pattern while still maintaining high CD accuracy as long as the resolution perpendicular to the pattern is not adjusted. Moreover, a non- circular beam may reduce radiation damage and charging effects in the sample that may otherwise occur with a circular beam.

[0041] Relative dimensions of components in drawings may be exaggerated for clarity. Within the following description of drawings, the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described.

[0042] As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a component may include A or B, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or A and B. As a second example, if it is stated that a component may include A, B, or C, then, unlessspecifically stated otherwise or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0043] Without limiting the scope of the present disclosure, some embodiments may be described in the context of providing detectors and detection methods in systems utilizing electron beams. However, the disclosure is not so limited. Other types of charged particle beams may be similarly applied. Furthermore, systems and methods for detection may be used in other imaging systems, such as optical imaging, photon detection, x-ray detection, ion detection, etc.

[0044] Fig. 1 illustrates an exemplary electron beam metrology / inspection (EBM / EBI) system 100 consistent with embodiments of the present disclosure. EBM / EBI system 100 may be used for imaging. As shown in Fig. 1, EBM / EBI system 100 includes a main chamber 101, a load / lock chamber 102, an electron beam tool 104, and an equipment front end module (EFEM) 106. Electron beam tool 104 is located within main chamber 101. EFEM 106 includes a first loading port 106a and a second loading port 106b. EFEM 106 may include additional loading port(s). First loading port 106a and second loading port 106b receive wafer front opening unified pods (FOUPs) that contain wafers (e.g., semiconductor wafers or wafers made of other material(s)) or samples to be inspected (wafers and samples may be used interchangeably). A “lot” is a plurality of wafers that may be loaded for processing as a batch.

[0045] One or more robotic arms (not shown) in EFEM 106 may transport the wafers to load / lock chamber 102. Load / lock chamber 102 is connected to a load / lock vacuum pump system (not shown) which removes gas molecules in load / lock chamber 102 to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) may transport the wafer from load / lock chamber 102 to main chamber 101. Main chamber 101 is connected to a main chamber vacuum pump system (not shown) which removes gas molecules in main chamber 101 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to metrology / inspection by electron beam tool 104. Electron beam tool 104 may be a single -beam system or a multi-beam system.

[0046] A controller 109 is electronically connected to electron beam tool 104. Controller 109 may be a computer configured to execute various controls of EBM / EBI system 100. While controller 109 is shown in Fig. 1 as being outside of the structure that includes main chamber 101, load / lock chamber 102, and EFEM 106, it is appreciated that controller 109 may be a part of the structure.

[0047] In some embodiments, controller 109 may include one or more processors (not shown). A processor may be a generic or specific electronic device capable of manipulating or processing information. For example, the processor may include any combination of any number of a central processing unit (or “CPU”), a graphics processing unit (or “GPU”), an optical processor, a programmable logic controllers, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a Programmable Logic Array (PLA), a Programmable Array Logic (PAL), a Generic Array Logic (GAL), a Complex Programmable Logic Device (CPLD), a Field-Programmable Gate Array (FPGA), a System On Chip (SoC), an Application-Specific Integrated Circuit (ASIC), and any type circuit capable of data processing. The processor may also be a virtual processor that includes one or more processors distributed across multiple machines or devices coupled via a network.

[0048] In some embodiments, controller 109 may further include one or more memories (not shown). A memory may be a generic or specific electronic device capable of storing codes and data accessible by the processor (e.g., via a bus). For example, the memory may include any combination of any number of a random-access memory (RAM), a read-only memory (ROM), an optical disc, a magnetic disk, a hard drive, a solid-state drive, a flash drive, a security digital (SD) card, a memory stick, a compact flash (CF) card, or any type of storage device. The codes may include an operating system (OS) and one or more application programs (or “apps”) for specific tasks. The memory may also be a virtual memory that includes one or more memories distributed across multiple machines or devices coupled via a network.

[0049] Embodiments of this disclosure may provide a single charged-particle beam imaging system (“single -beam system”). Compared with a single-beam system, a multiple charged-particle beam imaging system (“multi-beam system”) may be designed to optimize throughput for different scan modes. Embodiments of this disclosure provide a multi-beam system with the capability of optimizing throughput for different scan modes by using beam arrays with different geometries and adapting to different throughputs and resolution requirements.

[0050] Reference is now made to Fig. 2A, which is a schematic diagram illustrating an exemplary electron beam tool 104 including a multi-beam metrology / inspection tool that is part of the EBM / EBI system 100 of Fig. 1, consistent with embodiments of the present disclosure. In some embodiments, electron beam tool 104 may be operated as a single-beam metrology / inspection tool that is part of EBM / EBI system 100 of Fig. 1. Multi-beam electron beam tool 104 (also referred to herein as apparatus 104) comprises an electron source 201, a Coulomb aperture plate (or “gun aperture plate”) 271, a condenser lens 210, a source conversion unit 220, a primary projection system 230, a motorized stage 209, and a sample holder 207 supported by motorized stage 209 to hold a sample 208 (e.g., a wafer or a photomask) to be measured or inspected. Multi-beam electron beam tool 104 may further comprise a secondary projection system 250 and an electron detection device 240. Primary projection system 230 may comprise an objective lens 231. Electron detection device 240 may comprise a plurality of detection elements 241, 242, and 243. A beam separator 233 and a deflection scanning unit 232 may be positioned inside primary projection system 230.

[0051] Electron source 201, Coulomb aperture plate 271, condenser lens 210, source conversion unit 220, beam separator 233, deflection scanning unit 232, and primary projection system 230 may be aligned with a primary optical axis 204 of apparatus 104. Secondary projection system 250 and electron detection device 240 may be aligned with a secondary optical axis 251 of apparatus 104.

[0052] Electron source 201 may comprise a cathode (not shown) and an extractor or anode (not shown), in which, during operation, electron source 201 is configured to emit primary electrons from the cathode and the primary electrons are extracted or accelerated by the extractor and / or the anode to form a primary electron beam 202 that form a primary beam crossover (virtual or real) 203. Primary electron beam 202 may be visualized as being emitted from primary beam crossover 203.

[0053] Source conversion unit 220 may comprise an image-forming element array (not shown), an aberration compensator array (not shown), a beam-limit aperture array (not shown), and a pre-bending micro-deflector array (not shown). In some embodiments, the pre-bending micro-deflector array deflects a plurality of primary beamlets 211, 212, 213 of primary electron beam 202 to normally enter the beam-limit aperture array, the image-forming element array, and an aberration compensator array. In some embodiments, apparatus 104 may be operated as a single -beam system such that a single primary beamlet is generated. In some embodiments, condenser lens 210 is designed to focus primary electron beam 202 to become a parallel beam and be normally incident onto source conversion unit 220. The image-forming element array may comprise a plurality of micro-deflectors or micro-lenses to influence the plurality of primary beamlets 211, 212, 213 of primary electron beam 202 and to form a plurality of parallel images (virtual or real) of primary beam crossover 203, one for each of the primary beamlets 211, 212, and 213. In some embodiments, the aberration compensator array may comprise a field curvature compensator array (not shown) and an astigmatism compensator array (not shown). The field curvature compensator array may comprise a plurality of micro-lenses to compensate field curvature aberrations of the primary beamlets 211, 212, and 213. The astigmatism compensator array may comprise a plurality of micro-stigmators to compensate astigmatism aberrations of the primary beamlets 211, 212, and 213. The beam-limit aperture array may be configured to limit diameters of individual primary beamlets 211, 212, and 213. Fig. 2A shows three primary beamlets 211, 212, and 213 as an example, and it is appreciated that source conversion unit 220 may be configured to form any number of primary beamlets. Controller 109 may be connected to various parts of EBM / EBI system 100 of Fig. 1, such as source conversion unit 220, electron detection device 240, primary projection system 230, or motorized stage 209. In some embodiments, as explained in further details below, controller 109 may perform various image and signal processing functions. Controller 109 may also generate various control signals to govern operations of the charged particle beam metrology / inspection system.

[0054] Condenser lens 210 is configured to focus primary electron beam 202. Condenser lens 210 may further be configured to adjust electric currents of primary beamlets 211, 212, and 213 downstream of source conversion unit 220 by varying the focusing power of condenser lens 210. Alternatively, the electric currents may be changed by altering the radial sizes of beam-limit apertures within the beam-limit aperture array corresponding to the individual primary beamlets. The electric currents may be changed by both altering the radial sizes of beam-limit apertures and the focusing power of condenser lens 210. Condenser lens 210 may be an adjustable condenser lens that may beconfigured so that the position of its first principal plane is movable. The adjustable condenser lens may be configured to be magnetic, which may result in off-axis beamlets 212 and 213 illuminating source conversion unit 220 with rotation angles. The rotation angles change with the focusing power or the position of the first principal plane of the adjustable condenser lens. Condenser lens 210 may be an anti-rotation condenser lens that may be configured to keep the rotation angles unchanged while the focusing power of condenser lens 210 is changed. In some embodiments, condenser lens 210 may be an adjustable anti -rotation condenser lens, in which the rotation angles do not change when its focusing power and the position of its first principal plane are varied.

[0055] Objective lens 231 may be configured to focus beamlets 211, 212, and 213 onto a sample 208 for metrology / inspection and may form, in the current embodiments, three probe spots 221, 222, and 223 on the surface of sample 208. Coulomb aperture plate 271, in operation, is configured to block off peripheral electrons of primary electron beam 202 to reduce Coulomb effect. The Coulomb effect may enlarge the size of each of probe spots 221, 222, and 223 of primary beamlets 211, 212, 213, and therefore deteriorate metrology / inspection resolution.

[0056] Beam separator 233 may, for example, be a Wien filter comprising an electrostatic deflector generating an electrostatic dipole field and a magnetic dipole field (not shown in Fig. 2A). In operation, beam separator 233 may be configured to exert an electrostatic force by electrostatic dipole field on individual electrons of primary beamlets 211, 212, and 213. The electrostatic force is equal in magnitude but opposite in direction to the magnetic force exerted by magnetic dipole field of beam separator 233 on the individual electrons. Primary beamlets 211, 212, and 213 may therefore pass at least substantially straight through beam separator 233 with at least substantially zero deflection angles.

[0057] Deflection scanning unit 232, in operation, is configured to deflect primary beamlets 211, 212, and 213 to scan probe spots 221, 222, and 223 across individual scanning areas in a section of the surface of sample 208. In response to incidence of primary beamlets 211, 212, and 213 or probe spots 221, 222, and 223 on sample 208, electrons emerge from sample 208 and generate three secondary electron beams 261, 262, and 263. Each of secondary electron beams 261, 262, and 263 typically comprise secondary electrons (having electron energy < 50eV) and backscattered electrons (having electron energy between 50eV and the landing energy of primary beamlets 211, 212, and 213). Beam separator 233 is configured to deflect secondary electron beams 261, 262, and 263 towards secondary projection system 250. Secondary projection system 250 subsequently focuses secondary electron beams 261, 262, and 263 onto detection elements 241, 242, and 243 of electron detection device 240. Detection elements 241, 242, and 243 are arranged to detect corresponding secondary electron beams 261, 262, and 263 and generate corresponding signals which are sent to controller 109 or a signal processing system (not shown), e.g., to construct images of the corresponding scanned areas of sample 208.

[0058] In some embodiments, detection elements 241, 242, and 243 detect corresponding secondary electron beams 261, 262, and 263, respectively, and generate corresponding intensity signal outputs (not shown) to an image processing system (e.g., controller 109). In some embodiments, each detection element 241, 242, and 243 may comprise one or more pixels. The intensity signal output of a detection element may be a sum of signals generated by all the pixels within the detection element.

[0059] In some embodiments, controller 109 may comprise image processing system that includes an image acquirer (not shown), a storage (not shown). The image acquirer may comprise one or more processors. For example, the image acquirer may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. The image acquirer may be communicatively coupled to electron detection device 240 of apparatus 104 through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, among others, or a combination thereof. In some embodiments, the image acquirer may receive a signal from electron detection device 240 and may construct an image. The image acquirer may thus acquire images of sample 208. The image acquirer may also perform various post-processing functions, such as generating contours, superimposing indicators on an acquired image, and the like. The image acquirer may be configured to perform adjustments of brightness and contrast, etc. of acquired images. In some embodiments, the storage may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer readable memory, and the like. The storage may be coupled with the image acquirer and may be used for saving scanned raw image data as original images, and post-processed images.

[0060] In some embodiments, the image acquirer may acquire one or more images of a sample based on an imaging signal received from electron detection device 240. An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a single image comprising a plurality of imaging areas. The single image may be stored in the storage. The single image may be an original image that may be divided into a plurality of regions. Each of the regions may comprise one imaging area containing a feature of sample 208. The acquired images may comprise multiple images of a single imaging area of sample 208 sampled multiple times over a time sequence. The multiple images may be stored in the storage. In some embodiments, controller 109 may be configured to perform image processing steps with the multiple images of the same location of sample 208.

[0061] In some embodiments, controller 109 may include measurement circuitries (e.g., analog-to- digital converters) to obtain a distribution of the detected secondary electrons. The electron distribution data collected during a detection time window, in combination with corresponding scan path data of each of primary beamlets 211, 212, and 213 incident on the wafer surface, can be used to reconstruct images of the wafer structures under metrology / inspection. The reconstructed images canbe used to reveal various features of the internal or external structures of sample 208, and thereby can be used to reveal any defects that may exist in the wafer.

[0062] In some embodiments, controller 109 may control motorized stage 209 to move sample 208 during inspection / metrology of sample 208. In some embodiments, controller 109 may enable motorized stage 209 to move sample 208 in a direction continuously at a constant speed. In other embodiments, controller 109 may enable motorized stage 209 to change the speed of the movement of sample 208 over time depending on the steps of scanning process.

[0063] Although Fig. 2A shows that apparatus 104 uses three primary electron beams, it is appreciated that apparatus 104 may use one, two, or more number of primary electron beams. The present disclosure does not limit the number of primary electron beams used in apparatus 104. In some embodiments, apparatus 104 may be a SEM used for lithography. In some embodiments, electron beam tool 104 may be a single-beam system or a multi-beam system.

[0064] For example, as shown in Fig. 2B, an electron beam tool 100B (also referred to herein as apparatus 100B) may be a single -beam metrology / inspection tool that is used in EBM / EBI system 10, consistent with embodiments of the present disclosure. Apparatus 100B includes a wafer holder 136 supported by motorized stage 134 to hold a wafer 150 to be inspected. Electron beam tool 100B includes an electron emitter, which may comprise a cathode 103, an anode 121, and a gun aperture 122. Electron beam tool 100B further includes a beam limit aperture 125, a condenser lens 126, a column aperture 135, an objective lens assembly 132, and a detector 144. Objective lens assembly 132, in some embodiments, may be a modified SORIL lens, which includes a pole piece 132a, a control electrode 132b, a deflector 132c, and an exciting coil 132d. In an imaging process, an electron beam 161 emanating from the tip of cathode 103 may be accelerated by anode 121 voltage, pass through gun aperture 122, beam limit aperture 125, condenser lens 126, and be focused into a probe spot 170 by the modified SORIL lens and impinge onto the surface of wafer 150. Probe spot 170 may be scanned across the surface of wafer 150 by a deflector, such as deflector 132c or other deflectors in the SORIL lens. Secondary or scattered primary particles, such as secondary electrons or scattered primary electrons emanated from the wafer surface may be collected by detector 144 to determine intensity of the beam and so that an image of an area of interest on wafer 150 may be reconstructed.

[0065] There may also be provided an image processing system 199 that includes an image acquirer 120, a storage 130, and controller 109. Image acquirer 120 may comprise one or more processors. For example, image acquirer 120 may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. Image acquirer 120 may connect with detector 144 of electron beam tool 100B through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, or a combination thereof. Image acquirer 120 may receive a signal from detector 144 and may construct an image. Image acquirer 120 may thus acquire images of wafer 150. Image acquirer 120 may also perform various post-processing functions, such as generating contours,superimposing indicators on an acquired image, and the like. Image acquirer 120 may be configured to perform adjustments of brightness and contrast, etc. of acquired images. Storage 130 may be a storage medium such as a hard disk, random access memory (RAM), cloud storage, other types of computer readable memory, and the like. Storage 130 may be coupled with image acquirer 120 and may be used for saving scanned raw image data as original images, and post-processed images. Image acquirer 120 and storage 130 may be connected to controller 109. In some embodiments, image acquirer 120, storage 130, and controller 109 may be integrated together as one electronic control unit.

[0066] In some embodiments, image acquirer 120 may acquire one or more images of a sample based on an imaging signal received from detector 144. An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a single image comprising a plurality of imaging areas that may contain various features of wafer 150. The single image may be stored in storage 130. Imaging may be performed on the basis of imaging frames.

[0067] The condenser and illumination optics of the electron beam tool may comprise or be supplemented by electromagnetic quadrupole electron lenses. In some embodiments, the condenser and illumination optics of the electron beam tool may comprise or be supplemented by electromagnetic octupole lenses. For example, as shown in Fig. 2B, electron beam tool 100B may comprise a first quadrupole lens 148 and a second quadrupole lens 158. In some embodiments, the quadrupole lenses are used for controlling the electron beam. For example, first quadrupole lens 148 can be controlled to adjust the beam current and second quadrupole lens 158 can be controlled to adjust the beam spot size and beam shape.

[0068] Fig. 2B illustrates a charged particle beam apparatus in which an inspection / metrology system may use a single primary beam that may be configured to generate secondary electrons by interacting with wafer 150. Detector 144 may be placed along optical axis 105, as in the embodiment shown in Fig. 2B. The primary electron beam may be configured to travel along optical axis 105. Accordingly, detector 144 may include a hole at its center so that the primary electron beam may pass through to reach wafer 150.

[0069] Fig. 3 is an exemplary image 300 depicting various pixel sizes and pattern edge positions.

[0070] In typical systems, pixel sizes are the same size in the X direction and in the Y direction. For example, sampling plan 300(a) includes pixels 302(a) that are the same size in the X direction and in the Y direction. Sampling plan 300(a) is not desirable because it samples a short portion of line pattern 310 of sample 308. As a result, the critical dimension (CD) of line pattern 310 cannot be accurately determined by sampling plan 300(a). Moreover, the dense sampling shown in sampling plan 300(a) results in large radiation damage (e.g., due to a highly concentrated beam density in each small beam spot) and heavily charging the sample 308 (e.g., electrons from one beam may be stored in the sample 308 and affect the scanning of an adjacent pixel of sample 308).

[0071] Sampling plan 300(b) includes pixels 302(b) that are the same size in the X direction and in the Y direction. Sampling plan 300(b) may be more desirable than sampling plan 300(a) because sampling plan 300(b) samples a longer portion of line pattern 310. As a result, the CD of line pattern 310 may be more accurately determined by sampling plan 300(b). Moreover, sampling plan 300(b) suffers from the same negative effects of dense sampling as in sampling plan 300(a). Sampling plan 300(b) results in large radiation damage (e.g., due to a highly concentrated beam density in each small beam spot) and heavily charging the sample 308 (e.g., electrons from one beam may be stored in the sample 308 and affect the scanning of an adjacent pixel of sample 308).

[0072] At the same time, the resolution is most determined by the resolution perpendicular to the pattern (e.g., in the X direction). In other words, using small pixels along the pattern will not improve the measurement accuracy.

[0073] Sampling plan 300(c) includes asymmetrical pixel sizes with larger pixel sizes 302(c) than sampling plans 300(a) or 300(b). While the pixel size of sampling plan 300(c) in the X direction is the same as in sampling plans 300(a) and 300(b), the pixel size of sampling plan 300(c) in the Y direction is greater than the pixel size of sampling plans 300(a) and 300(b) (e.g., as seen by the greater spacing in the Y direction between beam spots in sampling plan 300(c)).

[0074] Advantageously, sampling plan 300(c) has a reduced sampling density and a reduced e-beam dose (e.g., due to the larger beam spot size), thereby resulting in reduced radiation damage and reduced negative charging effects (e.g., less radiation damage and less negative charging effects compared to sampling plans 300(a) and 300(b)). Sampling plan 300(c) allows edge variation and edge roughness of line pattern 312 to be determined. Sampling plan 300(c) also results in increased throughput due to less sampling data that needs to be obtained.

[0075] Sampling plan 300(c), however, also suffers from constraints. While the throughput of sampling plan 300(c) is higher than sampling plans 300(a) or 300(b), the throughput of sampling plan 300(c) is still relatively low due to the higher number of sampling that needs to occur to scan line pattern 312 of sample 308. At the same time, the beam spots 302(c) in sampling plan 300(c) are still circular and thus the longer pixel size in the Y direction does not result in more information or optimized throughput.

[0076] Fig. 4 is an exemplary graph 400 depicting measured CD values 402 from a pattern of a sample with respect to scan time 404.

[0077] Curve 410 corresponds to sampling plan 300(b) of Fig. 3 and curve 420 corresponds to sampling plan 300(c) of Fig. 3. As shown by curve 410, the measured CD of the pattern using sampling plan 300(b) decreases over time because the pattern shrinks as a result of radiation damage.

[0078] As shown by curve 420, the measured CD of the pattern using sampling plan 300(c) does not decrease over time due to the reduced radiation damage and reduced charging effects. As discussed above, sampling plan 300(c) results in reduced radiation damage and reduced charging effects due to,at least in part, the increased spacing in the Y direction between each beam during scanning. As a result, the pattern barely shrinks, and the measured CD values do not decrease much over time.

[0079] Fig. 5A is a diagram illustrating an ion beam intensity profile from the short axis (X direction) and the long axis (Y direction) directions for an ion source aperture and stencil mask with a same shape.

[0080] Fig. 5B is a diagram illustrating an ion beam intensity profile from the short axis (X direction) and the long axis (Y direction) directions for an ion source aperture and stencil mask with a different shape.

[0081] Figs. 5A and 5B are related to ion machining methods with non-axially symmetric ion beams. Diagram 500A shows an asymmetrical beam created by projecting a rectangular stencil mask onto a sample. Diagram 500B shows a symmetrical beam created by projecting a square stencil mask onto a sample. The effective resolution in the direction of interest (e.g., the X direction) of asymmetrical beams may remain unchanged as compared to symmetrical beams, such that the scanning throughput may be greatly increased by increasing the beam size in the direction (e.g., the Y direction) orthogonal to the direction of interest (e.g., the X direction).

[0082] Fig. 6 shows an exemplary schematic 600 of a scanning process using a circular beam.

[0083] Schematic 600 shows beams 610, 620, and 630 at times ti, tz, and ta, respectively, during scanning. Beams 610, 620, and 630 each have circular beam spots 612, 622, and 632, respectively, which land on sample 640. Sample 640 may have line patterns 642 and 644.

[0084] Beam spot size and probe current are two critical factors that affect scanning throughput. For metrology, a large current density (e.g., a large probe current per beam spot area) causes radiation damage and charging issues on the pattern. Using the upper limits of current density and a larger beam spot size would cover the same region on a sample in less time, thereby leading to a higher scanning throughput. However, the resolution of the resulting image would decrease. Thus, there are trade-offs between image resolution and throughput.

[0085] To achieve a more accurate CD, the beam spot size should be small in the direction of interest. For line patterns 642 and 644, the direction of interest may be the X direction. The CD is mostly affected by the direction of resolution perpendicular to the direction of the length of line patterns 642 and 644. For example, the CD is mostly affected by the resolution in the X direction. If a circular spot is used, then decreasing the beam spot size in one direction also decreases the beam spot size in the orthogonal direction. As a result, smaller pixel sizes are needed and more scanning is required to obtain the same amount of information from sample 640. For a ID pattern, the beam spot size along the length of line patterns 642 and 644 (in the Y direction) does not contribute to CD accuracy. Therefore, using circular beam spots actually limits the throughput without gaining more useful information.

[0086] Fig. 7A shows an exemplary charged particle beam system 700A (e.g., electron beam tool 104 of Fig. 2A, electron beam tool 100B of Fig. 2B), consistent with embodiments of the present disclosure.

[0087] In some embodiments, charged particle beam system 700A may include an extractor 702, a gun fixed aperture 704, an anode 706, a gun moving aperture 708, condenser lens 710, stigmator 712, column aperture 714, and objective lens 716. In some embodiments, charged particle beam system 700A may include a sample 718 and charged particle beams 720. In some embodiments, sample 718 may include line patterns 742 and 744. Stigmator 712 may include an octupole electrode working as a pair of orthogonal quadrupole lens (e.g., quadrupole lens 148 of Fig. 2B, quadrupole lens 158 of Fig. 2B, etc.).

[0088] In some embodiments, a quadrupole lens (of stigmator 712) may be used to intentionally shift the focus in two directions (e.g., X and Y directions) so that they are not at the same level. By doing so, two focal planes may be created. One focal plane is called a meridional focal plane and the other focal plane is called a sagittal focal plane. At both planes, the resolution perpendicular to (in the X direction) line patterns 742 and 744 is similar or substantially the same as the resolution value without the quadrupole lens. For example, diagram 750 shows arrows 752, 754, 756, and 758, which represent forces in the quadrupole lens. These forces may shift the focus in the quadrupole lens to generate charged particle beams with various beam spot shapes (e.g., circular, non-circular, etc.).

[0089] For example, arrows 752 and 756 show directions in which forces are exerted on a charged particle beam to “compress” the beam (e.g., in the X direction) and arrows 754 and 758 show directions in which forces are exerted on a charged particle beam to “expand” the beam (e.g., in the Y direction). The forces in the quadrupole lens may be adjusted by adjusting the voltage on the electrodes of the quadrupole lens. The voltage on the electrodes of the quadrupole lens may be adjusted to achieve a target beam spot shape.

[0090] In some embodiments, charged particle system 700A may generate a charged particle beam (e.g., electron beam) with an elongated beam spot 760. For example, beam spot 760 may be elongated in a direction parallel to the length of line patterns 742 and 744 (in the Y direction). In some embodiments, the charged particle beam spot size may be elongated in one direction (the Y direction) more than ten times the length of the charged particle beam in the orthogonal direction (the X direction) (e.g., the aspect ratio of the charged particle beam spot may be greater than 10:1; the length of the elongated beam spot may be more than 90 nm; etc.). As a result, the throughput may be boosted by more than ten times the throughput achieved with a circular beam spot (e.g., a circular beam spot with a diameter substantially equal to the width of the elongated beam spot) (e.g., the throughput may increase 34x using a beam spot with a length of 90 nm without sacrificing the resolution in the direction of the width of the beam spot). By breaking the symmetry of the beam spot, a non-circular beam may largely increase the throughput for a ID pattern while still maintaining high CD accuracy as long as the resolution perpendicular to the pattern (the resolution in the X direction) is not adjusted.Moreover, a non-circular beam may reduce radiation damage and charging effects in the sample that may otherwise occur with a circular beam.

[0091] In some embodiments, charged particle system 700A may generate one or more charged particle beams with elongated beam spots to scan a ID pattern (e.g., line patterns), where the length of the elongated beam spot is parallel to the length of the line pattern. In some embodiments, the pixel shape may be adjusted to reduce radiation damage and charging effects, while the beam orientation may be adjusted to be parallel to the length of the ID line patterns.

[0092] In some embodiments, charged particle beam system 700A may include a high signal-to-noise detector to compensate for a decrease in the current density of a charged particle beam. For example, the current density of an elongated beam spot may decrease compared to the current density of a circular beam spot. The signal from the elongated beam spot may decrease due to the decrease in electrons per unit area on the pattern. The high signal-to-noise detector may suppress the noise to compensate for the decreased signal from the elongated beam spot.

[0093] In some embodiments, the voltage on the electrodes of the octupole for the two orthogonal quadrupole lens may be adjusted to rotate the beam.

[0094] Fig. 7B illustrates an exemplary multi-pole structure 700B having a quadrupole configuration, consistent with embodiments of the present disclosure. Fig. 7C illustrates an exemplary multi-pole structure 700C having an octupole configuration, consistent with embodiments of the present disclosure.

[0095] For example, when one voltage is applied to all electrodes, the multi-pole structure is configured to function as an electrostatic lens. If the multi-pole structure 700B has four segmented electrodes (i.e., a quadrupole structure) and two voltages of the same absolute value, but opposite polarities, are applied to the two pairs of opposite electrodes, the multi-pole structure 700B is configured to function as a stigmator having a quadrupole field that is changeable in value, but fixed in direction. For example, in Fig. 7B, when voltage VI is applied to electrodes 700Bel and 700Be3, and when voltage -VI is applied to electrodes 700Be2 and 700Be4, the multi-pole structure 700B functions as such kind of a stigmator. The quadrupole field can be changed in value by varying voltage V 1.

[0096] In some embodiments, the multipole field can be changed in value and direction by varying voltages VI and V2. If the multi-pole structure has four segmented electrodes (i.e., a quadrupole structure) and two voltages having the same absolute value and opposite polarities are applied to one pair of opposite electrodes, and other two voltages of the same absolute value and opposite polarities are applied to the other pair of opposite electrodes, the multi-pole structure is configured to function as a deflector. For example, in Fig. 700B, when voltage VI is applied to 700Be2, voltage -VI is applied to 700Be4, voltage V2 is applied to 700Bel, and voltage -V2 is applied to 700Be3, the multipole structure functions as a deflector. The dipole field can be changed in value and direction by varying voltages V 1 and V2.

[0097] In some embodiments, voltage VI may be applied to opposite facing electrodes (e.g., electrodes 700Bel and 700Be3, electrodes 700Be2 and 700Be4) and voltage -VI may be applied to the other opposite facing electrodes (e.g., electrodes 700Be2 and 700Be4, electrodes 700Bel and 700Be3) to rotate or orient the beam spot (e.g., in increments of 90 degrees, such as 0, 90, 180, and 360 degrees). For example, switching VI from electrodes 700Bel and 700Be3 to electrodes 700Be2 and 700Be4 and -V 1 electrodes 700Be2 and 700Be4 to electrodes 700Bel and 700Be3 can rotate the beam spot by 90 degrees.

[0098] If the multi-pole structure 700C has an eight segmented electrode (i.e., an octupole structure) and two voltages that have the same absolute value and opposite in polarity are applied to two pairs of opposite electrodes and other two voltages that have the same absolute value and opposite in polarity are applied to other two pairs of opposite electrodes, the multi-pole structure 700C is configured to function as a stigmator whose quadrupole field is changeable in both value and direction. For example, in Fig. 7C, when voltage VI is applied to electrodes 700Cel and 700Ce5, -VI is applied to electrodes 700Ce3 and 700Ce7, voltage V2 is applied to electrodes 700Ce2 and 700Ce6, and -V2 is applied to electrodes 700Ce4 and 700Ce8, the multi-pole structure functions as such kind of a stigmator.

[0099] In some embodiments, switching the applied voltages VI to different pairs of opposite facing electrodes (e.g., electrodes 700Cel, 700Ce2, 700Ce5, 700Ce6 and electrodes 700Ce3, 700Ce4, 700Ce7, 700Ce8) and applied voltage -VI to other different opposite facing electrodes (e.g., electrodes 700Ce3, 700Ce4, 700Ce7, 700Ce8 and electrodes 700Cel, 700Ce2, 700Ce5, 700Ce6) can cause the beam spot to rotate (e.g., in increments of 45 degrees, such as 0, 45, 90, 135, 180, 225, 270, 315, and 360 degrees). In some embodiments, using a multipole structure with more electrodes than the quadrupole structure 700B (e.g., octupole structure 700C) may provide greater flexibility for rotating and orienting the beam.

[0100] Fig. 7D illustrates exemplary multi-pole structures, consistent with embodiments of the present disclosure.

[0101] In some embodiments, quadrupole structure 702D may include electrodes 71 ID, 712D, 713D, and 714D, applied voltages Vx and -Vx, and electric fields Ex. Quadrupole structure 704D may include electrodes 721D, 722D, 723D, and 724D, applied voltages Vy and -Vy, and electric field Ey. In some embodiments, quadrupole structure 702D and quadrupole structure 704D may be combined to be orthogonal to each other with a 45-degree angle difference, resulting in an octupole structure 706D and electric fields Er. By combining two quadrupole structures, the resultant quadruple field may be rotated by 0 from 0 to 360 degrees, thereby adjusting the beam orientation.

[0102] Fig. 7E illustrates an exemplary schematic of a quadrupole lens, consistent with embodiments of the present disclosure.

[0103] Fig. 7E shows a round lens 702E, a quadrupole lens 704E, and charged particle beam 706E. Fig. 7E shows a schematic 71 IE of the beam in plane Pl and a schematic 712E of the beam in planeP2, where 714E is the meridional plane, 715E is the sagittal plane, and 716E is the plane if there is no quadrupole lens in the system. Schematic 713E shows the beam in the P3 plane with a quadrupole lens and schematic 723E shows the beam in plane P3 without a quadrupole lens in the system.

[0104] Fig. 8 shows a strategy to set the voltages of quadrupoles so that the elongated beam can be self-aligned with the pattern, consistent with embodiments of the present disclosure.

[0105] View 810 shows a beam spot 812 that is not aligned with the sample 814 and has an effective resolution 816 in the X direction. View 820 shows a beam spot 822 that is not aligned with the sample 824 and has an effective resolution 826 in the X direction. View 830 shows a beam spot 832 that is aligned with the sample 834 and has an effective resolution 836 in the X direction. As shown in views 810, 820, and 830, the effective resolution in the X direction (the direction of interest) is shortest when the beam spot is aligned with the sample.

[0106] In some embodiments, self-alignment in a charged particle system may occur by loading a wafer into the SEM, calibrating the SEM, adding an additional stigmator voltage, and rotating the quadrupole field generated by the stigmator (e.g., by adjusting the voltage on the electrodes for two orthogonal quadrupole lens such that the resultant quadrupole field can be rotated to any direction in the X-Y plane), thereby minimizing the resolution and sharpness. In some embodiments, the sample may be rotated or orientated such that an edge of the line pattern on the sample is parallel to the length of the beam spot. In some embodiments, self-alignment in a charged particle system may occur by programming the stigmator setting such that the elongated beam may be aligned with a pattern automatically.

[0107] Fig. 9 shows exemplary charged particle beam spots and pixels, consistent with embodiments of the present disclosure.

[0108] View 910 shows a beam spot 912 with a pixel 914, view 920 shows a beam spot 922 with a pixel 924, and view 930 shows a beam spot 932 with a pixel 934.

[0109] In some embodiments, using different pixel sizes may reduce radiation damage and charging effects, thereby resulting in a more stable measured CD value of the patterns. For example, for wafers that are easily charged and damaged by radiation, it may be more advantageous to use charged particle beams that do not overlap in two pixels (e.g., beam spot 912 and pixel 914 may be preferred to minimize overlap by the charged particle beams). In some embodiments, beam spot 912 and pixel 914 may increase throughput (e.g., because the sample does not need to be scanned as many times compared to smaller pixel sizes) and reduce radiation damage of the patterns. However, for some other types of wafers, views 920 or 930 may be preferred.

[0110] For example, using beam spots that overlap areas of the sample in two pixels (e.g., views 920 and 930) may result in smoother generated images due to areas of the sample being measured multiple times by charged particle beams.

[0111] Fig. 10 shows an exemplary charged particle beam system 1000, consistent with embodiments of the present disclosure.

[0112] In some embodiments, charged particle beam system 1000 may include an extractor 1002, a gun fixed aperture 1004, an anode 1006, a gun moving aperture 1008, condenser lens 1010, stigmator 1012, column aperture 1014, objective 1016, and a Wien filter 1070. In some embodiments, charged particle beam system 1000 may include a sample 1018 and charged particle beams 1020. In some embodiments, sample 1018 may include line patterns (e.g., line patterns 742 and 744 of Fig. 7A). Stigmator 1012 (e.g., stigmator 712 of Fig. 7 A) may include quadrupole lens (e.g., quadrupole lens 148 of Fig. 2B, quadrupole lens 158 of Fig. 2B, etc.).

[0113] In some embodiments, a Wien filter 1070 may be used to improve the signal from the charged particles (e.g., electrons). Wien filters are further described in U.S. Patent No. 8,436,317, which is incorporated by reference in its entirety.

[0114] Fig. 11 shows an exemplary schematic of a Wien filter 1100, consistent with embodiments of the present disclosure. Fig. 11 shows the working principle of the Wien filter, which consists of an orthogonal electrostatic and magnetic dipole.

[0115] A magnetic dipole field Bi and an electric dipole field Ei are respectively generated by a pair of magnetic pole-pieces 1101 and 1102 with opposite polarities and a pair of electrodes 1103 and 1104 with opposite potentials. Both of the dipole fields are perpendicular to each other and superimposed along and perpendicular to a straight optical axis, which lies on the Z-axis. Each magnetic pole-piece may be formed by a permanent magnet or electromagnetic magnet. For simplicity, hereinafter the reference regarding a magnet is expressed by the related magnetic polepiece thereof. In the example Wien filter 1100, two grounded pole-pieces, which include a N polepiece 1101 and a S pole -piece 1102, will generate a magnetic dipole field Bi in the Y direction, while two electrodes, which include an electrode 1103 at +Vd potential and an electrode 1104 at -Vd potential, will generate an electric dipole field Ei in the X direction. For the electrons moving along the Z-axis and with a same velocity, the magnetic and electric dipole fields Bi and Ej, respectively exert the electric force Fe and magnetic force Fm on these particles.

[0116] For the nominal electron energy, at the center of Wien filter 1100, the Ei field and Bi field may balance each other. Away from center, the electrostatic potential changes and cannot balance the Bi field, which leads to an effective quadrupole field (e.g., stretching / compressing the beam in the X direction in Fig. 11). Due to the energy dispersion of the electron beam, even for the on-axis beam, the Ei field and Bi field cannot balance each other for other electron energies (see, e.g., Fig. 12). The dispersion caused by Wien filter 1100 is also along the X direction in Fig. 11 (Ei field).

[0117] The impact from the quadrupole field of Wien filter 1100 may be compensated by the stigmator (e.g., another quadrupole, of stigmator 1012 of Fig. 10) for the nominal energy. After compensation, the beam spot will not be circular due to the energy dispersion. The energy dispersion has a direction (see, e.g., Fig. 12). The direction of the energy dispersion on the wafer may be rotated by rotating the Wien filter field (e.g., rotating the magnetic field and the electric field). Rotating the Wien filter to deflect the signal electrons to different detector regions in flooding mode and ininspection mode is further described in U.S. Patent No. 11,513,087, which is incorporated by reference in its entirety.

[0118] In some embodiments, Wien filter 1100 may be rotated. In some embodiments, stigmator 1020 and Wien filter 1070 may be rotated or aligned to elongate the beam spot.

[0119] In some embodiments, the size of the beam spot in the direction of interest (the X direction) will remain substantially the same as the size of the beam spot without the Wien filter or additional quadrupole lens. In some embodiments, with a rotationally symmetric secondary electron (SE) / backscattered electron (BSE) detector, the beam may be aligned in any direction to match the pattern on the sample.

[0120] In some embodiments, the patterns on the wafer may be designed to be either parallel or perpendicular to a certain direction. In some embodiments, the Wien filter alignment may be fixed and the secondary electron (SE) I backscattered electron (BSE) detector may be designed to be non- symmetrical to improve the signal-to-noise ratio. In some embodiments, the pattern alignment and energy dispersion from the Wien filter may be designed to be parallel with or perpendicular to each other. If parallel, the Wien filter does not need to be rotated. If perpendicular, the wafer may be rotated 90 degree to match with the energy dispersion of the Wien filter.

[0121] In some embodiments, the wafer may be placed onto a rotational holder. In some embodiments, the patterns on the wafer may be designed in any direction. The wafer may be rotated to match the pattern direction and the energy dispersion from the Wien filter.

[0122] Fig. 12 shows an exemplary simulated electron profile on the wafer with a Wien filter in the system, consistent with embodiments of the present disclosure.

[0123] Simulated electron profile 1200 shows that Wien filter lens has aberration effects. At different energies, a beam spot 1210 may be dispersed in a certain direction (from ai to aa). The beam spot 1210, with compensation by the stigmator (e.g., stigmator 712 of Fig. 7A, stigmator 1012 of Fig. 10), may be stretched by the Wien filter (e.g., Wien filter 1070 of Fig. 10, Wien filter 1100 of Fig. 11) due to the energy dispersion. In some embodiments, arrow 1212 may represent the chromatic aberration introduced by a Wien filter, the arrow pointing from a lower energy to a high energy.

[0124] Fig. 13 shows an exemplary schematic 1300 of a wafer 1310, consistent with embodiments of the present disclosure.

[0125] In some embodiments, a layout design may be stored in a layout file for a wafer design. The layout file can be in a Graphic Database System (GDS) format, Graphic Database System II (GDS II) format, an Open Artwork System Interchange Standard (OASIS) format, a Caltech Intermediate Format (CIF), etc. The wafer design may include patterns or structures for inclusion on the wafer. The patterns or structures can be mask patterns used to transfer features from the photolithography masks or reticles to a wafer. In some embodiments, a layout in GDS or OASIS format, among others, may comprise feature information stored in a binary file format representing planar geometric shapes, text, and other information related to the wafer design.

[0126] In some embodiments, a layout design may be used to pre-design the beam spot shape and orientation across sample 1310. For example, the layout data may indicate that sample 1310 includes patterns 1312, 1314, and 1316 (e.g., the layout data may indicate the pattern coordinates on sample 1310). Based on the layout data, the charged particle system may generate or orient beam spots 1322, 1324, and 1326, which correspond to the shapes of patterns 1312, 1314, and 1316, respectively, as described above. Advantageously, throughput may significantly increase. Additionally, using the selfalignment functionality of the beam spot, the width of the beam spot (e.g., the shorter length of the beam spot) may be used to measure the pattern edge, thereby increasing both the accuracy and the stability of the pattern measurement.

[0127] Fig. 14 shows an exemplary schematic 1400 of a sample 1410, consistent with embodiments of the present disclosure.

[0128] Schematic 1400 may include patterns 1412, 1414, 1416, 1418, 1420, 1422, 1424, and 1426 and beam spots 1442, 1444, 1446, and 1448. As shown in schematic 1400, the embodiments of the present disclosure may be extended to a multi-beam system (e.g., electron beam tool 104 of Fig. 2A).

[0129] Fig. 15 shows exemplary graphs 1500a, 1500b, 1500c, 1500d, 1500e, and 1500f of simulated beam spot shapes varying with quadrupole lens excitation, consistent with embodiments of the present disclosure.

[0130] Graph 1500a shows a simulated beam spot 1502a with zero excitation of the quadrupole lens (stigmator at 0 V). As shown in graph 1500a, beam spot 1502a has a circular shape at zero excitation of the quadrupole lens.

[0131] Graph 1500b shows a simulated beam spot 1502b with excitation of the quadrupole lens at a stigmator applied voltage of 4V, graph 1500c shows a simulated beam spot 1502c with excitation of the quadrupole lens at a stigmator applied voltage of 8V, graph 1500d shows a simulated beam spot 1502d with excitation of the quadrupole lens at a stigmator applied voltage of 12V, graph 1500e shows a simulated beam spot 1502e with a excitation of the quadrupole lens at a stigmator apphed voltage of 16V, and graph 1500f shows a simulated beam spot 1502f with excitation of the quadrupole lens at a stigmator applied voltage of 20V. As shown in graphs 1502b-f, increasing the excitation of the quadrupole lens in one direction causes the beam spot shape to be elongated in one direction while the resolution in the orthogonal direction remains substantially unchanged.

[0132] In some embodiments, adding 20V to the quadrupole lens results in a beam spot that is elongated to as much as 90 nm in one direction, resulting in a throughput boost of about 34 times.

[0133] Fig. 16 shows exemplary graphs 1600 of resolutions 1612 at the sagittal focal plane as a function of varying quadrupole lens excitation 1614, consistent with embodiments of the present disclosure.

[0134] Graph 1600 shows curve 1602 and curve 1604. In some embodiments, curve 1602 represents the resolution at the sagittal focal plane in the pattern length axis direction (the Y direction) and curve1604 represents the resolution at the sagittal focal plane in the pattern width axis direction (the X direction).

[0135] As shown in graph 1600, the resolution along the pattern length axis direction increases substantially linearly with the excitation of the quadrupole lens, while the resolution of pattern width axis direction remains at a substantially low and constant value. In some embodiments, adding an additional quadrupole lens may not sacrifice of the resolution along the direction of interest (the X direction, perpendicular to the length of the ID line pattern).

[0136] Fig. 17A shows an exemplary graph 1700A of simulated signals for a stigmator voltage of 0V, Fig. 17B shows a top view of a beam spot and sample corresponding to the stigmator setting of Fig. 17A, Fig. 17C shows an exemplary graph 1700C of simulated signals for a stigmator voltage of 20V, and Fig. 17D shows a top view of a beam spot and sample corresponding to the stigmator setting of Fig. 17C, consistent with embodiments of the present disclosure.

[0137] Diagram 1700 shows an electron beam 1710, sample 1712, and patterns 1714.

[0138] Each of graphs 1700A and 1700C show simulated signals for secondary electrons (SE) less than 40eV, backscattered electrons (BSE) greater than 50 eV, and SE and BSE combined. Beam spot 1700B corresponds to the stigmator setting (0V) of graph 1700A and beam spot 1700D corresponds to the stigmator setting (20V) of graph 1700C.

[0139] In some embodiments, the elongated electron beam spot 1700D may be used in CD measurement. Figs. 17A and 17C compare the simulated signals with the voltages of the stigmator between 0 V and 20 V. As shown in Figs. 17A and 17C, the signals at different stigmator excitations are substantially the same. This result follows because at the two stigmator excitations, the resolutions perpendicular (e.g., in the Y direction) to the sample 1712 are the same. At a stigmator voltage of 20 V, with the beam spot 1700D elongated parallel to the pattern, the throughput may be increased and the radiation and charging effects may be reduced.

[0140] Fig. 18 shows an exemplary process 1800 for scanning a sample (e.g., sample 208 of Fig. 2A, wafer 150 of Fig. 2B, sample 718 of Fig. 7A, sample 1018 of Fig. 10, sample 1310 of Fig. 13, sample 1410 of Fig. 14, sample 1712 of Figs. 17B and 17D), consistent with embodiments of the present disclosure.

[0141] In some embodiments, the elongated beam may be used in defect inspection. In some embodiments, the elongated beam may be used in voltage contrast defect inspection. In some embodiments, the elongated beam may be used in flooding mode to improve the throughput in singlebeam systems and in multi-beam systems. Then, in some embodiments, the beam spot shape may be easily restored to a circular shape using the quadrupole lens to inspect defects in inspection mode.

[0142] At step 1802, a charged particle system (e.g., electron beam tool 104 of Fig. 2A, electron beam tool 100B of Fig. 2B, charged particle system 700A of Fig. 7A, charged particle system 1000 of Fig. 10) may generate a charged particle beam (e.g., electron beam) with an elongated beam spot (e.g., beam spot 760 of Fig. 7A, beam spots 812, 822, and 832 of Fig. 8, beam spots 912, 922, and932 of Fig. 9, beam spots 1322 and 1324 of Fig. 13, beam spots 1442, 1444, 1446, and 1448 of Fig. 14, beam spot 1700D of Fig. 17D).

[0143] In some embodiments, the charged particle beam system may include a stigmator (e.g., stigmator 712 of Fig. 7A, stigmator 1012 of Fig. 10), which may include quadrupole lens (e.g., quadrupole lens 148 of Fig. 2B, quadrupole lens 158 of Fig. 2B, etc.).

[0144] In some embodiments, a quadrupole lens may be used to intentionally shift the focus in two directions (e.g., X and Y directions) so that they are not at the same level. By doing so, two focal planes may be created. One focal plane is called a meridional focal plane and the other focal plane is called a sagittal focal plane. At both planes, the resolution perpendicular to (in the X direction) line patterns (e.g., line patterns 742 and 744 of Fig. 7A, patterns 1312 and 1314 of Fig. 13, patterns 1412, 1414, 1416, 1418, 1420, 1422, 1424, 1426 of Fig. 14) on the sample is similar or substantially the same as the resolution value without the quadrupole lens. For example, forces in the quadrupole lens may shift the focus in the quadrupole lens to generate charged particle beams with various beam spot shapes (e.g., circular, non-circular, etc.). It is appreciated that other multipole lens may be used, such as an octupole lens.

[0145] The forces may be exerted on a charged particle beam to “compress” the beam (e.g., in the X direction) and or to “expand” the beam (e.g., in the Y direction). The forces in the quadrupole lens may be adjusted by adjusting the voltage on the electrodes of the quadrupole lens. The voltage on the electrodes of the quadrupole lens may be adjusted to achieve a target beam spot shape.

[0146] In some embodiments, the beam spot may be elongated in a direction parallel to the length of the line patterns (in the Y direction). In some embodiments, the charged particle beam spot size may be elongated in one direction (the Y direction) more than ten times the length of the charged particle beam in the orthogonal direction (the X direction) (e.g., the aspect ratio of the charged particle beam spot may be greater than 10: 1; the length of the elongated beam spot may be 90nm; etc.). As a result, the throughput may be boosted by more than ten times the throughput achieved with a circular beam spot (e.g., a circular beam spot with a diameter substantially equal to the width of the elongated beam spot) (e.g., the throughput may increase 34x using a beam spot with a length of 90nm without sacrificing the resolution in the direction of the width of the beam spot). By breaking the symmetry of the beam spot, a non-circular beam may largely increase the throughput for a ID pattern while still maintaining high CD accuracy as long as the resolution perpendicular to the pattern (the resolution in the X direction) is not adjusted. Moreover, a non-circular beam may reduce radiation damage and charging effects in the sample that may otherwise occur with a circular beam.

[0147] At step 1804, the charged particle system may orient the elongated electron beam such that a length of the elongated electron beam is parallel to an edge of a pattern on the sample. For example, the voltage on the electrodes of the quadrupole lens may be adjusted to rotate the beam.

[0148] In some embodiments, self-alignment in a charged particle system may occur by loading a wafer into the SEM, calibrating the SEM, adding an additional stigmator voltage, and rotating thequadrupole field generated by the stigmator (e.g., by adjusting the voltage on the octupole electrodes for two orthogonal quadruple lens such that the combined quadrupole field may be rotated to any direction in the X-Y plane ), thereby minimizing the resolution and sharpness. In some embodiments, the sample may be rotated or orientated such that an edge of the line pattern on the sample is parallel to the length of the beam spot.

[0149] At step 1806, the elongated electron beam may be used to scan the pattern. In some embodiments, the charged particle system may generate one or more charged particle beams with elongated beam spots to scan a ID pattern (e.g., line patterns), where the length of the elongated beam spot is parallel to the length of the line pattern. In some embodiments, the pixel shape may be adjusted to reduce radiation damage and charging effects, while the beam orientation may be adjusted to be parallel to the length of the ID line patterns.

[0150] In some embodiments, using different pixel sizes may reduce radiation damage and charging effects, thereby resulting in a more stable measured CD value of the patterns. For example, for wafers that are easily charged and damaged by radiation, it may be more advantageous to use charged particle beams that do not overlap in two pixels (e.g., beam spot 912 and pixel 914 of Fig. 9 may be preferred to minimize overlap by the charged particle beams). In some embodiments, using charged particle beams that do not overlap in two pixels may increase throughput (e.g., because the sample does not need to be scanned as many times compared to smaller pixel sizes) and reduce radiation damage of the patterns. However, for some other types of wafers, using beam spots that overlap areas of the sample in two pixels (e.g., views 920 and 930 of Fig. 9) may result in smoother generated images due to areas of the sample being measured multiple times by charged particle beams.

[0151] At step 1808, the charged particle system may detect electrons emitted from the sample during the scanning and at step 1710, the charged particle system may determine a characteristic of the pattern (e.g., a CD of the pattern) based on the detected electrons.

[0152] In some embodiments, the charged particle beam system may include a Wien filter (e.g., Wien filter 1070 of Fig. 10, Wien filter 1100 of Fig. 11). In some embodiments, the Wien filter may be used to improve the signal from the charged particles (e.g., electrons). The working principle of the Wien filter includes an orthogonal electrostatic and magnetic dipole.

[0153] In some embodiments, Wien filter 1100 may be rotated. In some embodiments, the stigmator and the Wien filter may be rotated or aligned to elongate the beam spot. In some embodiments, the size of the beam spot in the direction of interest (the X direction) will remain substantially the same as the size of the beam spot without the Wiens filter or additional quadrupole lens. In some embodiments, with a rotationally symmetric secondary electron (SE) / backscattered electron (BSE) detector, the beam may be aligned in any direction to match the pattern on the sample.

[0154] In some embodiments, a layout design may be stored in a layout file for a wafer design. The layout file can be in a Graphic Database System (GDS) format, Graphic Database System II (GDS II) format, an Open Artwork System Interchange Standard (OASIS) format, a Caltech IntermediateFormat (CIF), etc. The wafer design may include patterns or structures for inclusion on the wafer. The patterns or structures can be mask patterns used to transfer features from the photolithography masks or reticles to a wafer. In some embodiments, a layout in GDS or OASIS format, among others, may comprise feature information stored in a binary file format representing planar geometric shapes, text, and other information related to the wafer design.

[0155] In some embodiments, a layout design may be used to pre-design the beam spot shape and orientation across the sample. For example, the layout data may indicate the pattern coordinates on the sample. Based on the layout data, the charged particle system may generate, adjust, or orient beam spots, which correspond to the shapes of patterns. Advantageously, throughput may significantly increase. Additionally, using the self-alignment functionality of the beam spot, the width of the beam spot (e.g., the shorter length of the beam spot) may be used to measure the pattern edge, thereby increasing both the accuracy and the stability of the pattern measurement.

[0156] In some embodiments, the charged particle beam system may include a high signal-to-noise detector to compensate for a decrease in the current density of a charged particle beam. For example, the current density of an elongated beam spot may decrease compared to the current density of a circular beam spot. The signal from the elongated beam spot may decrease due to the decrease in electrons per unit area on the pattern. The high signal-to-noise detector may suppress the noise to compensate for the decreased signal from the elongated beam spot.

[0157] A non-transitory computer readable medium may be provided that stores instructions for a processor of a controller (e.g., controller 109 of Figs. 1, 2A, 2B, etc.) for controlling the electron beam tool or other systems, or components thereof, consistent with embodiments in the present disclosure. These instructions may allow the one or more processors to carry out beam generating, beam shaping, beam rotating, image processing, data processing, beamlet scanning, graphical display, operations of a charged particle beam apparatus, or another imaging device, or the like for providing operations consistent with those described above for Fig. 18. In some embodiments, the non- transitory computer readable medium may be provided that stores instructions for a processor to perform the steps of process 1800. Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, hard disk, solid state drive, magnetic tape, or any other magnetic data storage medium, a Compact Disc Read Only Memory (CD-ROM), any other optical data storage medium, any physical medium with patterns of holes, a Random Access Memory (RAM), a Programmable Read Only Memory (PROM), and Erasable Programmable Read Only Memory (EPROM), a FLASH-EPROM or any other flash memory, Non-Volatile Random Access Memory (NVRAM), a cache, a register, any other memory chip or cartridge, and networked versions of the same.

[0158] The embodiments may further be described using the following clauses: 1. A method for scanning a sample, the method comprising: generating an elongated electron beam;orientating the elongated electron beam such that a length of the elongated electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the elongated electron beam; detecting electrons emitted from the sample during the scanning; and determining a characteristic of the pattern based on the detected electrons.2. The method of clause 1, wherein the elongated electron beam has an aspect ratio that is greater than ten to one.3. The method of any one of clauses 1-2, further comprising orientating the sample such that the edge of the pattern is parallel to the length of the elongated electron beam.4. The method of any one of clauses 1-3, wherein the edge of the pattern is a length of the pattern.5. The method of any one of clauses 1-4, wherein the pattern is a line pattern.6. The method of any one of clauses 1-5, wherein the characteristic is a critical dimension of the pattern.7. The method of any one of clauses 1-6, wherein generating the elongated electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.8. The method of clause 7, wherein the voltage is adjusted to exert a force on the elongated electron beam.9. The method of any one of clauses 7-8, wherein orientating the elongated electron beam comprises rotating the elongated electron beam.10. The method of clause 9, wherein rotating the elongated electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.11. The method of any one of clauses 1-10, further comprising compensating for a signal from the elongated electron beam using a high signal-to-noise detector.12. The method of any one of clauses 1-11, wherein a pixel corresponding to the elongated electron beam comprises a size such that scanning overlap on the sample by the elongated beam is minimized.13. The method of any one of clauses 1-11, wherein a pixel corresponding to the elongated electron beam comprises a size such that the elongated beam overlaps areas on the sample during scanning.14. The method of any one of clauses 1-13, further comprising deflecting, using a Wien filter, signal electrons to regions of a detector.15. The method of any one of clauses 1-14, further comprising, prior to generating the elongated electron beam, designing a shape of the elongated electron beam using layout data.16. A method for scanning a sample, the method comprising: generating a non-circular electron beam; orientating the non-circular electron beam such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; anddetermining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.17. The method of clause 16, wherein the non-circular electron beam has an aspect ratio that is greater than ten to one.18. The method of any one of clauses 16-17, further comprising orientating the sample such that the edge of the pattern is parallel to the length of the non-circular electron beam.19. The method of any one of clauses 16-18, wherein the edge of the pattern is a length of the pattern.20. The method of any one of clauses 16-19, wherein the pattern is a line pattern.21. The method of any one of clauses 16-20, wherein the characteristic is a critical dimension of the pattern.22. The method of any one of clauses 16-21, wherein generating the non-circular electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.23. The method of clause 22, wherein the voltage is adjusted to exert a force on the non-circular electron beam.24. The method of any one of clauses 22-23, wherein orientating the non-circular electron beam comprises rotating the non-circular electron beam.25. The method of clause 24, wherein rotating the non-circular electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.26. The method of any one of clauses 16-25, further comprising compensating for a signal from the non-circular electron beam using a high signal-to-noise detector.27. The method of any one of clauses 16-26, wherein a pixel corresponding to the non-circular electron beam comprises a size such that scanning overlap on the sample by the non-circular beam is minimized.28. The method of any one of clauses 16-26, wherein a pixel corresponding to the non-circular electron beam comprises a size such that the non-circular beam overlaps areas on the sample during scanning.29. The method of any one of clauses 16-28, further comprising deflecting, using a Wien filter, signal electrons to regions of a detector.30. The method of any one of clauses 16-29, further comprising, prior to generating the non-circular electron beam, designing a shape of the non-circular electron beam using layout data.31. A method for scanning a sample, the method comprising: generating a non-circular electron beam; orientating the sample such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; anddetermining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.32. The method of clause 31, wherein the non-circular electron beam has an aspect ratio that is greater than ten to one.33. The method of any one of clauses 31-32, further comprising orientating the non-circular electron beam such that a length of the non-circular electron beam is parallel to the edge of the pattern.34. The method of any one of clauses 31-33, wherein the edge of the pattern is a length of the pattern.35. The method of any one of clauses 31-34, wherein the pattern is a line pattern.36. The method of any one of clauses 31-35, wherein the characteristic is a critical dimension of the pattern.37. The method of any one of clauses 31-36, wherein generating the non-circular electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.38. The method of clause 37, wherein the voltage is adjusted to exert a force on the non-circular electron beam.39. The method of any one of clauses 37-38, wherein orientating the non-circular electron beam comprises rotating the non-circular electron beam.40. The method of clause 39, wherein rotating the non-circular electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.41. The method of any one of clauses 31-40, further comprising compensating for a signal from the non-circular electron beam using a high signal-to-noise detector.42. The method of any one of clauses 31-41, wherein a pixel corresponding to the non-circular electron beam comprises a size such that scanning overlap on the sample by the non-circular beam is minimized.43. The method of any one of clauses 31-41, wherein a pixel corresponding to the non-circular electron beam comprises a size such that the non-circular beam overlaps areas on the sample during scanning.44. The method of any one of clauses 31-43, further comprising deflecting, using a Wien filter, signal electrons to regions of a detector.45. The method of any one of clauses 31-44, further comprising, prior to generating the non-circular electron beam, designing a shape of the non-circular electron beam using layout data.46. A non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of a computing device to cause the computing device to perform a method for scanning a sample, the method comprising: generating an elongated electron beam; orientating the elongated electron beam such that a length of the elongated electron beam is parallel to an edge of a pattern on the sample;scanning the pattern with the elongated electron beam; detecting electrons emitted from the sample during the scanning; and determining a characteristic of the pattern based on the detected electrons.47. The non-transitory computer readable medium of clause 46, wherein the elongated electron beam has an aspect ratio that is greater than ten to one.48. The non-transitory computer readable medium of any one of clauses 46-47, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform orientating the sample such that the edge of the pattern is parallel to the length of the elongated electron beam.49. The non-transitory computer readable medium of any one of clauses 46-48, wherein the edge of the pattern is a length of the pattern.50. The non-transitory computer readable medium of any one of clauses 46-49, wherein the pattern is a line pattern.51. The non-transitory computer readable medium of any one of clauses 46-50, wherein the characteristic is a critical dimension of the pattern.52. The non-transitory computer readable medium of any one of clauses 46-51, wherein generating the elongated electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.53. The non-transitory computer readable medium of clause 52, wherein the voltage is adjusted to exert a force on the elongated electron beam.54. The non-transitory computer readable medium of any one of clauses 52-53, wherein orientating the elongated electron beam comprises rotating the elongated electron beam.55. The non-transitory computer readable medium of clause 54, wherein rotating the elongated electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.56. The non-transitory computer readable medium of any one of clauses 46-55, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform compensating for a signal from the elongated electron beam using a high signal-to-noise detector.57. The non-transitory computer readable medium of any one of clauses 46-56, wherein a pixel corresponding to the elongated electron beam comprises a size such that scanning overlap on the sample by the elongated beam is minimized.58. The non-transitory computer readable medium of any one of clauses 46-56, wherein a pixel corresponding to the elongated electron beam comprises a size such that the elongated beam overlaps areas on the sample during scanning.59. The non-transitory computer readable medium of any one of clauses 46-58, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform deflecting, using a Wien filter, signal electrons to regions of a detector.60. The non-transitory computer readable medium of any one of clauses 46-59, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform, prior to generating the elongated electron beam, designing a shape of the elongated electron beam using layout data.61. A non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of a computing device to cause the computing device to perform a method for scanning a sample, the method comprising: generating a non-circular electron beam; orientating the non-circular electron beam such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; and determining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.62. The non-transitory computer readable medium of clause 61, wherein the non-circular electron beam has an aspect ratio that is greater than ten to one.63. The non-transitory computer readable medium of any one of clauses 61-62, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform orientating the sample such that the edge of the pattern is parallel to the length of the non-circular electron beam.64. The non-transitory computer readable medium of any one of clauses 61-63, wherein the edge of the pattern is a length of the pattern.65. The non-transitory computer readable medium of any one of clauses 61-64, wherein the pattern is a line pattern.66. The non-transitory computer readable medium of any one of clauses 61-65, wherein the characteristic is a critical dimension of the pattern.67. The non-transitory computer readable medium of any one of clauses 61-66, wherein generating the non-circular electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.68. The non-transitory computer readable medium of clause 67, wherein the voltage is adjusted to exert a force on the non-circular electron beam.69. The non-transitory computer readable medium of any one of clauses 67-68, wherein orientating the non-circular electron beam comprises rotating the non-circular electron beam.70. The non-transitory computer readable medium of clause 69, wherein rotating the non-circular electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.71. The non-transitory computer readable medium of any one of clauses 61-70, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform compensating for a signal from the non-circular electron beam using a high signal-to-noise detector.72. The non-transitory computer readable medium of any one of clauses 61-71, wherein a pixel corresponding to the non-circular electron beam comprises a size such that scanning overlap on the sample by the non-circular beam is minimized.73. The non-transitory computer readable medium of any one of clauses 61-71, wherein a pixel corresponding to the non-circular electron beam comprises a size such that the non-circular beam overlaps areas on the sample during scanning.74. The non-transitory computer readable medium of any one of clauses 61-73, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform deflecting, using a Wien filter, signal electrons to regions of a detector.75. The non-transitory computer readable medium of any one of clauses 61-74, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform, prior to generating the non-circular electron beam, designing a shape of the non-circular electron beam using layout data.76. A non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of a computing device to cause the computing device to perform a method for scanning a sample, the method comprising: generating a non-circular electron beam; orientating the sample such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; and determining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.77. The non-transitory computer readable medium of clause 76, wherein the non-circular electron beam has an aspect ratio that is greater than ten to one.78. The non-transitory computer readable medium of any one of clauses 76-77, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform orientating the non-circular electron beam such that a length of the non- circular electron beam is parallel to the edge of the pattern.79. The non-transitory computer readable medium of any one of clauses 76-78, wherein the edge of the pattern is a length of the pattern.80. The non-transitory computer readable medium of any one of clauses 76-79, wherein the pattern is a line pattern.81. The non-transitory computer readable medium of any one of clauses 76-80, wherein the characteristic is a critical dimension of the pattern.82. The non-transitory computer readable medium of any one of clauses 76-81, wherein generating the non-circular electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.83. The non-transitory computer readable medium of clause 82, wherein the voltage is adjusted to exert a force on the non-circular electron beam.84. The non-transitory computer readable medium of any one of clauses 82-83, wherein orientating the non-circular electron beam comprises rotating the non-circular electron beam.85. The non-transitory computer readable medium of clause 84, wherein rotating the non-circular electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.86. The non-transitory computer readable medium of any one of clauses 76-85, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform compensating for a signal from the non-circular electron beam using a high signal-to-noise detector.87. The non-transitory computer readable medium of any one of clauses 76-86, wherein a pixel corresponding to the non-circular electron beam comprises a size such that scanning overlap on the sample by the non-circular beam is minimized.88. The non-transitory computer readable medium of any one of clauses 76-86, wherein a pixel corresponding to the non-circular electron beam comprises a size such that the non-circular beam overlaps areas on the sample during scanning.89. The non-transitory computer readable medium of any one of clauses 76-88, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform deflecting, using a Wien filter, signal electrons to regions of a detector.90. The non-transitory computer readable medium of any one of clauses 76-89, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform, prior to generating the non-circular electron beam, designing a shape of the non-circular electron beam using layout data.91. A system for scanning a sample, the system comprising: a memory storing a set of instructions; and one or more processors configured to execute the set of instructions to cause the system to perform operations comprising: generating an elongated electron beam;orientating the elongated electron beam such that a length of the elongated electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the elongated electron beam; detecting electrons emitted from the sample during the scanning; and determining a characteristic of the pattern based on the detected electrons.92. The system of clause 91, wherein the elongated electron beam has an aspect ratio that is greater than ten to one.93. The system of any one of clauses 91-92, wherein the operations further comprise orientating the sample such that the edge of the pattern is parallel to the length of the elongated electron beam.94. The system of any one of clauses 91-93, wherein the edge of the pattern is a length of the pattern.95. The system of any one of clauses 91-94, wherein the pattern is a line pattern.96. The system of any one of clauses 91-95, wherein the characteristic is a critical dimension of the pattern.97. The system of any one of clauses 91-96, wherein generating the elongated electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.98. The system of clause 97, wherein the voltage is adjusted to exert a force on the elongated electron beam.99. The system of any one of clauses 97-98, wherein orientating the elongated electron beam comprises rotating the elongated electron beam.100. The system of clause 99, wherein rotating the elongated electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.101. The system of any one of clauses 91-100, wherein the operations further comprise compensating for a signal from the elongated electron beam using a high signal-to-noise detector.102. The system of any one of clauses 91-101, wherein a pixel corresponding to the elongated electron beam comprises a size such that scanning overlap on the sample by the elongated beam is minimized.103. The system of any one of clauses 91-101, wherein a pixel corresponding to the elongated electron beam comprises a size such that the elongated beam overlaps areas on the sample during scanning.104. The system of any one of clauses 91-103, wherein the operations further comprise deflecting, using a Wien filter, signal electrons to regions of a detector.105. The system of any one of clauses 91-104, wherein the operations further comprise, prior to generating the elongated electron beam, designing a shape of the elongated electron beam using layout data.106. A system for scanning a sample, the system comprising: a memory storing a set of instructions; andone or more processors configured to execute the set of instructions to cause the system to perform operations comprising: generating a non-circular electron beam; orientating the non-circular electron beam such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; and determining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.107. The system of clause 106, wherein the non-circular electron beam has an aspect ratio that is greater than ten to one.108. The system of any one of clauses 106-107, wherein the operations further comprise orientating the sample such that the edge of the pattern is parallel to the length of the non-circular electron beam.109. The system of any one of clauses 106-108, wherein the edge of the pattern is a length of the pattern.110. The system of any one of clauses 106-109, wherein the pattern is a line pattern.111. The system of any one of clauses 106-110, wherein the characteristic is a critical dimension of the pattern.112. The system of any one of clauses 106-111, wherein generating the non-circular electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.113. The system of clause 112, wherein the voltage is adjusted to exert a force on the non-circular electron beam.114. The system of any one of clauses 112-113, wherein orientating the non-circular electron beam comprises rotating the non-circular electron beam.115. The system of clause 114, wherein rotating the non-circular electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.116. The system of any one of clauses 106-115, wherein the operations further comprise compensating for a signal from the non-circular electron beam using a high signal-to-noise detector.117. The system of any one of clauses 106-116, wherein a pixel corresponding to the non-circular electron beam comprises a size such that scanning overlap on the sample by the non-circular beam is minimized.118. The system of any one of clauses 106-116, wherein a pixel corresponding to the non-circular electron beam comprises a size such that the non-circular beam overlaps areas on the sample during scanning.119. The system of any one of clauses 106-118, wherein the operations further comprise deflecting, using a Wien filter, signal electrons to regions of a detector.120. The system of any one of clauses 106-119, wherein the operations further comprise, prior to generating the non-circular electron beam, designing a shape of the non-circular electron beam using layout data.121. A system for scanning a sample, the system comprising: a memory storing a set of instructions; and one or more processors configured to execute the set of instructions to cause the system to perform operations comprising: generating a non-circular electron beam; orientating the sample such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; and determining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.122. The system of clause 121, wherein the non-circular electron beam has an aspect ratio that is greater than ten to one.123. The system of any one of clauses 121-122, wherein the operations further comprise orientating the non-circular electron beam such that a length of the non-circular electron beam is parallel to the edge of the pattern.124. The system of any one of clauses 121-123, wherein the edge of the pattern is a length of the pattern.125. The system of any one of clauses 121-124, wherein the pattern is a line pattern.126. The system of any one of clauses 121-125, wherein the characteristic is a critical dimension of the pattern.127. The system of any one of clauses 121-126, wherein generating the non-circular electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.128. The system of clause 127, wherein the voltage is adjusted to exert a force on the non-circular electron beam.129. The system of any one of clauses 127-128, wherein orientating the non-circular electron beam comprises rotating the non-circular electron beam.130. The system of clause 129, wherein rotating the non-circular electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.131. The system of any one of clauses 121-130, wherein the operations further comprise compensating for a signal from the non-circular electron beam using a high signal-to-noise detector.132. The system of any one of clauses 121-131, wherein a pixel corresponding to the non-circular electron beam comprises a size such that scanning overlap on the sample by the non-circular beam is minimized.133. The system of any one of clauses 121-131, wherein a pixel corresponding to the non-circular electron beam comprises a size such that the non-circular beam overlaps areas on the sample during scanning.134. The system of any one of clauses 121-133, wherein the operations further comprise deflecting, using a Wien filter, signal electrons to regions of a detector.135. The system of any one of clauses 121-134, wherein the operations further comprise, prior to generating the non-circular electron beam, designing a shape of the non-circular electron beam using layout data.

[0159] It will be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

CLAIMS1. A non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of a computing device to cause the computing device to perform a method for scanning a sample, the method comprising: generating an elongated electron beam; orientating the elongated electron beam such that a length of the elongated electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the elongated electron beam; detecting electrons emitted from the sample during the scanning; and determining a characteristic of the pattern based on the detected electrons.

2. The non-transitory computer readable medium of claim 1, wherein the elongated electron beam has an aspect ratio that is greater than ten to one.

3. The non-transitory computer readable medium of claim 1, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform orientating the sample such that the edge of the pattern is parallel to the length of the elongated electron beam.

4. The non-transitory computer readable medium of claim 1, wherein the edge of the pattern is a length of the pattern.

5. The non-transitory computer readable medium of claim 1, wherein the pattern is a line pattern.

6. The non-transitory computer readable medium of claim 1, wherein the characteristic is a critical dimension of the pattern.

7. The non-transitory computer readable medium of claim 1, wherein generating the elongated electron beam comprises adjusting a voltage on electrodes of a multipole lens of a charged particle beam system, wherein the multipole lens has at least four electrodes.

8. The non-transitory computer readable medium of claim 7, wherein the voltage is adjusted to exert a force on the elongated electron beam.

9. The non-transitory computer readable medium of claim 7, wherein orientating the elongated electron beam comprises rotating the elongated electron beam.

10. The non-transitory computer readable medium of claim 9, wherein rotating the elongated electron beam comprises adjusting a voltage on the electrodes of the multipole lens of the charged particle beam system.

11. The non-transitory computer readable medium of claim 1, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform compensating for a signal from the elongated electron beam using a high signal-to-noise detector.

12. The non-transitory computer readable medium of claim 1, wherein a pixel corresponding to the elongated electron beam comprises a size such that scanning overlap on the sample by the elongated beam is minimized.

13. The non-transitory computer readable medium of claim 1, wherein a pixel corresponding to the elongated electron beam comprises a size such that the elongated beam overlaps areas on the sample during scanning.

14. The non-transitory computer readable medium of claim 1, wherein the set of instructions that is executable by at least one processor of a computing device to cause the computing device to further perform deflecting, using a Wien filter, signal electrons to regions of a detector.

15. A non-transitory computer readable medium that stores a set of instructions that is executable by at least one processor of a computing device to cause the computing device to perform a method for scanning a sample, the method comprising: generating a non-circular electron beam; orientating the non-circular electron beam such that an edge of the non-circular electron beam is parallel to an edge of a pattern on the sample; scanning the pattern with the non-circular electron beam; and determining a characteristic of the pattern based on detected electrons emitted from the sample during scanning.

Images