Charged particle beam device having a wide field of view and method thereof

Abstract

A system and method for imaging a sample using a charged particle beam device is disclosed that may include a charged particle source configured to emit charged particles, an aperture plate configured to form a primary charged particle beam from the emitted charged particles along a primary optical axis, a plurality of primary charged particle beam deflectors configured to deflect the primary charged particle beam to be incident on a surface of the sample and define a center of a field of view (FOV), and a controller including circuitry configured to apply a first excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors to cause the primary charged particle beam to scan a portion of the FOV of the sample and to apply a second excitation signal to cause the primary charged particle beam deflector to compensate for off-axis aberrations of the primary charged particle beam in the portion of the FOV.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. patent application Ser. No. 63 / 331,644, filed April 15, 2022, which is incorporated by reference in its entirety into this specification.

[0002]

[0002] The embodiments provided herein disclose charged particle beam devices, and more specifically, disclose electron beam metrology and inspection devices having a wide field of view (FOV) for detecting defects and acquiring high resolution images. [Background technology]

[0003]

[0003] During the manufacturing process of integrated circuits (ICs), unfinished or finished circuit components are inspected to ensure that they are manufactured as designed and are free of defects. Inspection systems using charged particle (e.g., electron) beam microscopes or optical microscopes, such as scanning electron microscopes (SEMs), may be used. As the physical size of IC components continues to shrink, the accuracy of defect detection and yield becomes more important. The imaging FOV may be increased to increase throughput, but doing so may introduce off-axis aberrations of the primary electron beam, which may adversely affect imaging quality and overall image resolution. Summary of the Invention

[0004]

[0004] One aspect of the disclosure relates to a charged particle beam device for imaging a sample. The device may include a charged particle source configured to emit charged particles, an aperture plate configured to form a primary charged particle beam from the emitted charged particles along a primary optical axis, a plurality of primary charged particle beam deflectors configured to deflect the primary charged particle beam to be incident on a surface of the sample and define a center of a field of view (FOV), and a controller. The controller may include a circuit configured to apply a first excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors to cause the primary charged particle beam to scan a portion of the FOV of the sample, and to apply a second excitation signal to cause the primary charged particle beam deflector to compensate for off-axis aberrations of the primary charged particle beam in the portion of the FOV of the sample.

[0005] Another aspect of the present disclosure relates to a method for imaging a sample using a charged particle beam device, which may include forming a primary charged particle beam from charged particles emitted by a charged particle source, deflecting the primary charged particle beam by a primary charged particle beam deflector to be incident on a surface of the sample and define a center of a field of view (FOV), applying a first excitation signal to the primary charged particle beam deflector to cause the primary charged particle beam to scan a portion of the FOV of the sample, and applying a second excitation signal to cause the primary charged particle beam deflector to compensate for off-axis aberrations of the primary charged particle beam in the portion of the FOV.

[0006]

[0006] Yet another aspect of the present disclosure relates to a charged particle beam device for imaging a sample. The device may include a charged particle source configured to emit charged particles, an aperture plate configured to form a primary charged particle beam from the emitted charged particles along a primary optical axis, a plurality of primary charged particle beam deflectors configured to deflect the primary charged particle beam to be incident on a surface of the sample and define a center of a field of view (FOV), a plurality of beam separators, and a controller. The controller may include a circuit configured to apply a first excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors such that the primary charged particle beam scans a portion of the FOV of the sample, and to apply a second excitation signal to a first beam separator of the plurality of beam separators such that the first beam separator compensates for off-axis chromatic aberration of the primary charged particle beam in the portion of the FOV.

[0007]

[0007] Yet another aspect of the present disclosure relates to a method for imaging a sample using a charged particle beam device, which may include forming a primary charged particle beam from charged particles emitted by a charged particle source, deflecting the primary charged particle beam by a primary charged particle beam deflector to be incident on a surface of the sample and define a center of a field of view (FOV), applying a first excitation signal to the primary charged particle beam deflector such that the primary charged particle beam scans a portion of the FOV of the sample, and applying a second excitation signal to a first beam separator of a plurality of beam separators such that the first beam separator compensates for off-axis chromatic aberration of the primary charged particle beam in the portion of the FOV.

[0008]

[0008] Yet another aspect of the present disclosure relates to a charged particle beam device for imaging a sample, which may include a charged particle source configured to emit charged particles, an aperture plate configured to form a primary charged particle beam from the emitted charged particles along a primary optical axis, a number of primary charged particle beam deflectors configured to deflect the primary charged particle beam to be incident on a surface of the sample, and a controller. The controller may include circuitry configured to cause a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors to perform a first beam alignment of the primary charged particle beam to a first location within a field of view (FOV) of the sample, perform a second beam alignment of the primary charged particle beam to a second location different from the first location, scan a first region of the sample with the primary charged particle beam, where the first region includes a first portion of the FOV that includes the second location, and after scanning the first region, perform a third beam alignment of the primary charged particle beam to a third location at least a threshold distance away from the second location, and scan a second region of the sample with the primary charged particle beam, where the second region includes a second portion of the FOV that includes the third location.

[0009]

[0009] Yet another aspect of the present disclosure relates to a method for imaging a sample using a charged particle beam device, which may include forming a primary charged particle beam from charged particles emitted by a charged particle source of the charged particle beam device, performing a first beam alignment of the primary charged particle beam to a first location in a field of view (FOV) of the sample, performing a second beam alignment of the primary charged particle beam to a second location different from the first location, scanning a first region of the sample with the primary charged particle beam, the first region including a first portion of the FOV including the second location, after scanning the first region, performing a third beam alignment of the primary charged particle beam to a third location at least a threshold distance away from the second location, and scanning a second region of the sample with the primary charged particle beam, the second region including a second portion of the FOV including the third location.

[0010]

[0010] Yet another aspect of the present disclosure relates to a non-transitory computer-readable medium storing a set of instructions executable by one or more processors of the charged particle beam device to cause the charged particle beam device to perform a method of imaging a sample. The method may include activating a charged particle source to emit charged particles and form a primary charged particle beam from the emitted charged particles, deflecting the primary charged particle beam to be incident on a surface of the sample and defining a center of a field of view (FOV), applying a first excitation signal to a primary charged particle beam deflector to cause the primary charged particle beam to scan a portion of the FOV of the sample, and applying a second excitation signal to cause the primary charged particle beam deflector to compensate for off-axis aberrations of the primary charged particle beam in the portion of the FOV.

[0011]

[0011] Yet another aspect of the present disclosure relates to a non-transitory computer-readable medium storing a set of instructions executable by one or more processors of the charged particle beam device to cause the charged particle beam device to perform a method of imaging a sample. The method may include activating a charged particle source to emit charged particles and form a primary charged particle beam from the emitted charged particles, deflecting the primary charged particle beam to be incident on a surface of the sample and defining a center of a field of view (FOV), applying a first excitation signal to a primary charged particle beam deflector to cause the primary charged particle beam to scan a portion of the FOV of the sample, and applying a second excitation signal to a first beam separator of a plurality of beam separators to cause the first beam separator to compensate for off-axis chromatic aberration of the primary charged particle beam in the portion of the FOV.

[0012]

[0012] Yet another aspect of the present disclosure relates to a non-transitory computer-readable medium storing a set of instructions executable by one or more processors of the charged particle beam device to cause the charged particle beam device to perform a method of imaging a sample, which may include activating a charged particle source to emit charged particles and form a primary charged particle beam from the emitted charged particles, performing a first beam alignment of the primary charged particle beam to a first location within a field of view (FOV) of the sample, performing a second beam alignment of the primary charged particle beam to a second location different from the first location, scanning a first region of the sample with the primary charged particle beam, the first region including a first portion of the FOV that includes the second location, after scanning the first region, performing a third beam alignment of the primary charged particle beam to a third location at least a threshold distance away from the second location, and scanning a second region of the sample with the primary charged particle beam, the second region including a second portion of the FOV that includes the third location.

[0013]

[0013] Other advantages of the embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0013] In the following description, by way of illustration and example, certain embodiments of the invention are set forth. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary electron beam inspection (EBI) system consistent with embodiments of the present disclosure. [Diagram 2]

[0015] FIG. 2 is a schematic diagram illustrating an example electron beam tool that may be part of the example electron beam inspection system of FIG. 1 consistent with embodiments of the present disclosure. [Diagram 3]

[0016] FIG. 1 is a schematic diagram illustrating an exemplary electron beam tool for imaging a large field of view (FOV) of a sample consistent with embodiments of the present disclosure. [Figure 4A]

[0017] FIG. 1 is a schematic diagram illustrating an exemplary wide FOV consistent with embodiments of the present disclosure. [Figure 4B] FIG. 1 is a schematic diagram illustrating an array of 3×3 sub-FOVs consistent with an embodiment of the present disclosure. [Figure 4C]

[0018] FIG. 1 is a schematic diagram illustrating an exemplary 3×3 array of sub-FOVs consistent with embodiments of the present disclosure. [Figure 4D] FIG. 1 is a schematic diagram illustrating an exemplary 3×3 sub-FOV array consistent with embodiments of the present disclosure. [Figure 4E]

[0019] FIG. 1 is a schematic diagram illustrating an exemplary 5×5 sub-FOV array consistent with embodiments of the present disclosure. [Figure 4F] FIG. 1 is a schematic diagram illustrating an exemplary 5×5 sub-FOV array consistent with an embodiment of the present disclosure. [Diagram 5]

[0020] 1 is a process flow diagram illustrating an exemplary method for imaging a wide FOV of a sample consistent with embodiments of the present disclosure. [Figure 6]

[0021] 1 is a process flow diagram illustrating an exemplary method for imaging a wide FOV of a sample consistent with embodiments of the present disclosure. [Figure 7]

[0022] 1 is a process flow diagram illustrating an exemplary method for imaging a wide FOV of a sample consistent with embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015]

[0023] 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 stated. The implementations described in the following description of exemplary embodiments do not represent all implementations. Instead, the implementations are merely examples of apparatuses and methods consistent with aspects related to the disclosed embodiments, as described in the appended claims. For example, although some embodiments are described in relation to the use of electron beams, the disclosure is not so limited. Other types of charged particle beams can be applied as well. Moreover, other imaging systems can be used, such as optical imaging, photo detection, x-ray detection, and the like.

[0016]

[0024] Electronic devices are built with circuits formed on a piece of silicon called a substrate. Many circuits can 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 more and more circuits can fit on a substrate. For example, an IC chip in a smartphone is about the size of a thumbnail, yet can contain over 2 billion transistors, each less than 1 / 1000 the size of a human hair.

[0017]

[0025] Creating these tiny ICs is a time-consuming, complex, and expensive process, often involving hundreds of individual steps. An error in even one step can introduce defects into the finished IC, rendering it useless. Thus, one of the goals of a manufacturing process is to avoid such defects in order to maximize the number of functioning ICs produced by the process, i.e., to increase the overall yield of the process.

[0018]

[0026] One factor in improving yield is monitoring the chip creation process to ensure that it produces a sufficient number of functioning integrated circuits. One way to monitor the process is to inspect the chip circuit structures at various stages of their formation. Inspection can be done using a scanning electron microscope (SEM). An SEM can be used to image these extremely small structures, in effect taking a "picture" of the structure. The image can be used to determine if the structure was formed correctly, and if it was formed in the correct place. If the structure is defective, the process can be adjusted to make it less likely that the defect will reoccur.

[0019]

[0027] Integrated circuits (ICs) are expected to perform more complex tasks more efficiently and at faster processing speeds with each new process technology node, requiring complex device architectures to accommodate a higher density of active elements. In the semiconductor device industry, a "technology node" (e.g., "10 nm") refers to the smallest size of a feature that can be reproducibly printed on a semiconductor wafer, such as a transistor gate or the half pitch of a metal line. Extreme ultraviolet (EUV) lithography systems use photons with a wavelength of 13.5 nm, making it possible to print such nanoscale features.

[0020]

[0028] Although effective, EUV lithography can present some challenges, notably local critical dimension (CD) variations due to stochastic effects, stochastic defects, or tight tolerance and process windows. In EUV lithography, the incidence of stochastic defects is low and the dimensional variations to be detected are typically in the range of a few nanometers, making it very difficult to detect such defects. However, the size or size variations of the defects that can render a device non-functional are also small, making it important to detect these defects that are very difficult to detect. Existing critical dimension scanning electron microscope (CD-SEM) imaging techniques can provide high resolution, but can be inadequate due to throughput limitations that limit the area of ​​the wafer that can be scanned with high resolution in a given time. One way to improve throughput is to increase the area of ​​the wafer that is scanned between wafer movements, called the field of view (FOV), because this results in less wafer movement during scanning of a given area, resulting in increased throughput. Although increasing the FOV can improve throughput, in part by reducing time-consuming wafer movement, doing so can result in reduced imaging resolution, for example, due to increased off-axis aberrations of the primary electron beam that accompany scanning through a large FOV. Off-axis aberrations of the incident primary electron beam can include astigmatism, off-axis chromatic aberration, field curvature, or coma, among others. It would therefore be desirable to provide a system and method for increasing the FOV while maintaining high resolution within a wide FOV, for example, by minimizing one or more types of off-axis aberrations during scanning of the sample.

[0021]

[0029] Some embodiments of the present disclosure relate to a system and method for imaging a wide FOV of a sample. The method may include splitting the wide FOV into multiple sub-FOVs, which can be scanned by a primary electron beam of a CD-SEM device. Off-axis aberrations, such as astigmatism, field curvature, and off-axis chromatic aberration, of the primary electron beam can be dynamically compensated during scanning by adjusting an excitation signal to one or more of multiple primary electron beam deflectors. The method may further include applying an excitation signal to a beam separator to compensate for energy dispersion of the primary electron beam caused by a Wien filter configured to deflect secondary electrons toward an electron detector while allowing the primary electron beam to pass undeflected toward the sample. The method may further include scanning multiple sub-FOVs of the wide FOV in a sequence such that adverse effects due to charge accumulation in successively scanned sub-FOVs are minimized or substantially mitigated.

[0022]

[0030] In the drawings, the relative dimensions of the components may be exaggerated for clarity. Within the following description of the drawings, the same or similar reference numbers refer to the same or similar components or entities and only describe the differences for the individual embodiments. As used herein, unless specifically stated otherwise, the term "or" encompasses all possible combinations unless infeasible. For example, if it is stated that a component may include A or B, the component may include A or B or A and B, unless specifically stated otherwise or infeasible. As a second example, if it is stated that a component may include A, B, or C, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A, B, and C, unless specifically stated otherwise or infeasible.

[0023]

[0031] Reference is now made to Figure 1, which illustrates an exemplary electron beam inspection (EBI) system 100 consistent with embodiments of the present disclosure. As shown in Figure 1, the charged particle beam inspection system 100 includes a main chamber 10, a load-lock chamber 20, an electron beam tool 40, and a front-end equipment module (EFEM) 30. The electron beam tool 40 is located within the main chamber 10. Although the description and drawings are directed to electron beams, it should be understood that the embodiments are not intended to limit the present disclosure to any particular charged particle.

[0024]

[0032] The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include additional load ports. The first load port 30a and the second load port 30b receive wafer front-opening integrated pods (FOUPs) containing wafers (e.g., semiconductor wafers or wafers made of other materials) or samples to be inspected (hereinafter, wafers and samples are collectively referred to as "wafers"). One or more robotic arms (not shown) of the EFEM 30 transfer the wafers to the load-lock chamber 20.

[0025]

[0033] The load-lock chamber 20 is connected to a load / lock vacuum pumping system (not shown) that removes gas molecules in the load-lock chamber 20 to reach a first pressure below atmospheric pressure. After the first pressure is reached, one or more robot arms (not shown) transfer the wafer from the load-lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pumping system (not shown) that removes gas molecules in the main chamber 10 to reach a second pressure below the first pressure. After the second pressure is reached, the wafer is inspected by the electron beam tool 40. In some embodiments, the electron beam tool 40 may include a single beam inspection tool. In other embodiments, the electron beam tool 40 may include a multi-beam inspection tool.

[0026]

[0034] The controller 50 may be electronically connected to the electron beam tool 40 and may also be electronically connected to other components. The controller 50 may be a computer configured to perform various controls of the charged particle beam inspection system 100. The controller 50 may also include processing circuitry configured to perform various signal and image processing functions. Although the controller 50 is shown in FIG. 1 as being external to the structure including the main chamber 10, the load lock chamber 20, and the EFEM 30, it will be understood that the controller 50 may also be part of the structure.

[0027]

[0035] It should be noted that while the present disclosure provides an example of a main chamber 10 housing an electron beam inspection system, aspects of the present disclosure are not limited in their broadest sense to chambers housing electron beam inspection systems, rather, it is understood that the principles discussed above may be applied to other chambers as well.

[0028]

[0036] Reference is now made to Figure 2, which shows a schematic diagram illustrating an exemplary configuration of an electron beam tool 40 that may be part of the exemplary charged particle beam inspection system 100 of Figure 1 consistent with an embodiment of the present disclosure. The electron beam tool 40 (also referred to herein as apparatus 40) may include an electron emitter that may include a cathode 203, an extraction electrode 205, a gun aperture 220, and an anode 222. The electron beam tool 40 may further include a Coulomb aperture array 224, a condenser lens 226, a beam limiting aperture array 235, an objective lens assembly 232, and an electron detector 244. The electron beam tool 40 may further include a sample holder 236 supported by a motorized stage 234 for holding a sample 250 to be inspected. It should be understood that other relevant components may be added or omitted as desired.

[0029]

[0037] In some embodiments, the electron emitter may include a cathode 203 and an anode 222, where primary electrons may be emitted from the cathode and extracted or accelerated to form a primary electron beam 204 that forms the primary beam crossover 202. The primary electron beam 204 may be visualized as being emitted from the primary beam crossover 202.

[0030]

[0038] In some embodiments, the electron emitter, condenser lens 226, objective lens assembly 232, beam-limiting aperture array 235, and electron detector 244 may be aligned with the primary optical axis 201 of apparatus 40. In some embodiments, the electron detector 244 may be positioned off-axis from the primary optical axis 201 along a secondary optical axis (not shown).

[0031]

[0039] In some embodiments, the objective lens assembly 232 may include a modified swing objective retarding immersion lens (SORIL), which includes a pole piece 232a, a control electrode 232b, a beam manipulator assembly including deflectors 240a, 240b, 240d, and 240e, and an excitation coil 232d. In a typical imaging process, a primary electron beam 204 emitted from the tip of the cathode 203 is accelerated by an acceleration voltage applied to the anode 222. A portion of the primary electron beam 204 passes through the gun aperture 220 and the apertures of the Coulomb aperture array 224, and is focused by the condenser lens 226 to pass fully or partially through the apertures of the beam-limiting aperture array 235. Electrons passing through the apertures of the beam-limiting aperture array 235 may be focused by a modified SORIL lens to form a probe spot on the surface of the sample 250 and deflected by one or more deflectors of the beam manipulator assembly to scan the surface of the sample 250. Secondary electrons emitted from the sample surface may be collected by the electron detector 244 to form an image of the scanned area of ​​interest.

[0032]

[0040] In the objective lens assembly 232, the excitation coil 232d and the pole piece 232a may generate a magnetic field. A portion of the sample 250 scanned by the primary electron beam 204 may be immersed in this magnetic field and become electrically charged, which in turn generates an electric field. This electric field may reduce the energy of the impinging primary electron beam 204 on or near the surface of the sample 250. The control electrode 232b is electrically isolated from the pole piece 232a and may control the electric field on and above the sample 250, for example, to reduce aberrations of the objective lens assembly 232, control the focusing condition of the signal electron beam to increase detection efficiency, or avoid arcing to protect the sample. One or more deflectors of the beam manipulator assembly may deflect the primary electron beam 204 to facilitate beam scanning on the sample 250. For example, in a scanning process, deflectors 240a, 240b, 240d, and 240e may be controlled to deflect primary electron beam 204 to different locations on the top surface of sample 250 at different times to provide data for reconstructing images of different portions of sample 250. Note that in different embodiments, the order of 240a-240e may be different.

[0033]

[0041] Backscattered electrons (BSE) and secondary electrons (SE) may be emitted from a portion of the sample 250 upon receiving the primary electron beam 204. A beam separator may direct the secondary or scattered electron beam, including the backscattered electrons and the secondary electrons, to a sensor surface of the electron detector 244. The detected secondary electron beam may form a corresponding beam spot on the sensor surface of the electron detector 244. The electron detector 244 may generate a signal (e.g., voltage, current) representative of the intensity of the received secondary electron beam spot and provide the signal to a processing system, such as the controller 50. The intensity of the secondary or backscattered electron beam and the resulting secondary electron beam spot may vary depending on the external or internal structure of the sample 250. Also, as discussed above, the primary electron beam 204 may be deflected to different locations on the top surface of the sample 250 to generate secondary or scattered electron beams (and resulting beam spots) of different intensities. Therefore, by mapping the intensity of the secondary electron beam spot to the location of the sample 250 , the processing system can reconstruct an image reflecting the internal or external structure of the wafer sample 250 .

[0034]

[0042] In some embodiments, the controller 50 may include an image processing system, which includes an image acquirer (not shown) and storage (not shown). The image acquirer may include one or more processors. For example, the image acquirer may include a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, and the like or combinations thereof. The image acquirer may be communicatively coupled to the electronic detector 244 of the device 40 through a medium such as electrical conductors, fiber optic cables, portable storage media, IR, Bluetooth, the Internet, a wireless network, a wireless radio, or combinations thereof, among others. In some embodiments, the image acquirer may receive signals from the electronic detector 244 and construct an image. Thus, the image acquirer may acquire an image of an area of ​​the sample 250. The image acquirer may also perform various post-processing functions such as generating contours, superimposing indicators on the acquired image, and the like. The image acquirer may be configured to perform adjustments such as brightness and contrast of the acquired image. In some embodiments, the storage may be a storage medium such as a hard disk, a 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 to store raw scanned image data as original images, and to store post-processed images.

[0035]

[0043] In some embodiments, the controller 50 may include measurement circuitry (e.g., analog-to-digital converters) to obtain a distribution of detected secondary and backscattered electrons. The electron distribution data collected during the detection time window, in combination with corresponding scan path data of the primary beam 204 incident on the sample (e.g., wafer) surface, may be used to reconstruct an image of the wafer structure under inspection. The reconstructed image may be used to reveal various features of the internal or external structure of the sample 250, and thus any defects that may be present in the wafer.

[0036]

[0044] In some embodiments, the controller 50 can control the motorized stage 234 to move the sample 250 during inspection. In some embodiments, the controller 50 can cause the motorized stage 234 to move the sample 250 continuously in one direction at a constant speed. In other embodiments, the controller 50 can cause the motorized stage 234 to vary the speed at which the sample 250 moves over time depending on the step of the scanning process.

[0037]

[0045] Reference is now made to Figure 3, which is a schematic diagram of an exemplary electron beam tool 300 consistent with embodiments of the present disclosure. The electron beam tool 300 (also referred to herein as apparatus 300) may be used as a metrology tool, inspection tool, or review tool configured to detect the presence of physical defects such as micro-bridging between features, discontinuous lines, merging contact holes, missing contact holes, roughness of line edges, among other defects.

[0038]

[0046] The apparatus 300 may include an electron source 302 configured to generate electrons when activated. In some embodiments, the controller 50 may activate, deactivate, or control the electron source 302 or elements thereof by applying one or more electrical signals to the electron source 302 or adjusting the electrical signals to adjust characteristics of the electrons generated by the electron source 302. The characteristics of the generated electrons may include, among others, the number, intensity, acceleration, and direction of emission. The electron source 302 may include a cathode 303, an extractor electrode 305, and an anode 322.

[0039]

[0047] In some embodiments, the apparatus 300 may further include an aperture plate 323 configured to block ambient electrons exiting the electron source 302 to form the primary electron beam 304 along the primary optical axis 301. The aperture plate 323 may include a plate with a single aperture of a predetermined size and positioned such that the geometric center of the aperture is aligned with the primary optical axis 301. In some embodiments, the aperture plate 323 may include one or more apertures, and the aperture used to form the primary electron beam 304 may be aligned with the primary optical axis 301.

[0040]

[0048] As used in the context of this disclosure, "downstream" refers to a direction along the path of the primary electron beam (e.g., primary electron beam 304 in FIG. 3) starting from the electron source (e.g., electron source 302 in FIG. 3) toward the sample (e.g., sample 350 in FIG. 3). With respect to the positioning of elements of a charged particle beam device (e.g., device 300 in FIG. 3), "downstream" may refer to the position of one element being located below or after another element along the path of the primary electron beam starting from the electron source, and "immediately downstream" refers to the position of a second element being below or after a first element along the path of the primary electron beam 304 such that there are no other active elements between the first and second elements. As used in the context of this disclosure, "upstream" may refer to the location of an element being located above or before another element along the path of the primary electron beam starting from the electron source, and "immediately upstream" refers to the location of a second element being above or before a first element along the path of the primary electron beam 302 such that there are no other active elements between the first and second elements. As used herein, "active element" may refer to any element or component whose presence may generate an electric, magnetic, or electromagnetic field, thereby modifying the electromagnetic field between the first and second elements.

[0041]

[0049] The apparatus 300 may include a Coulomb aperture array 324 disposed downstream of the aperture plate 323 to further block peripheral electrons of the primary electron beam 304 and form the primary electron beam 304-1. The Coulomb aperture array 324 may be substantially similar to the Coulomb aperture array 224 of FIG. 2 and may perform substantially similar functions. The Coulomb aperture array 324 may include a plate containing one or more apertures to allow a portion of the primary electron beam 304 to pass through such that Coulomb interactions between electrons in the primary electron beam 304-1 are minimized while maintaining desired beam characteristics. The apertures of the Coulomb aperture array 324 may be uniform or non-uniform in shape, size, pitch, or cross-section, and may be arranged in a regular pattern to form an array or may be in an irregular pattern. The geometric center of the apertures used to form the primary electron beam 304-1 may be aligned with the primary optical axis 301. In some embodiments, the position of the Coulomb aperture array 324 may be adjustable along an axis substantially perpendicular or substantially parallel to the primary optical axis 301. Adjusting the position of the Coulomb aperture array 324 horizontally along a plane perpendicular to the primary optical axis 301 may allow for selection of a desired aperture. Adjusting the position of the Coulomb aperture array 324 vertically along the primary optical axis 301 may allow for adjustment of the number of electrons allowed to pass through the aperture, thereby adjusting the beam size. In some embodiments, the position of the Coulomb aperture array 324 may be adjusted horizontally or vertically, or both, as desired.

[0042]

[0050] The apparatus 300 may further include a focusing lens 326 configured to focus the primary electron beam 304-1 after exiting the Coulomb aperture array 324. The focusing lens 326 may include an electrostatic lens, an electromagnetic lens, or a compound lens. In some embodiments, the controller 50 may be configured to adjust the excitation of the focusing lens 326 by adjusting one or more electrical signals applied to the focusing lens 326. Adjusting the excitation of the focusing lens 326 may allow the focusing power of the focusing lens 326 to be adjusted. In some embodiments, the focusing lens 326 may be an adjustable focusing lens, which may be configured such that a first principal plane (not shown) is adjustable. In some embodiments, the adjustable focusing lens (e.g., the focusing lens 326) may be electromagnetic. In an alternative embodiment, the focusing lens 326 may be an anti-rotation focusing lens, which allows the focusing power to be changed without affecting the rotation angle of the electron beam (e.g., the primary electron beam 304-1) passing through the lens. In some embodiments, the focusing lens 326 may be an adjustable anti-rotation focusing lens, which may include an anti-rotation lens with an adjustable first principal plane. The adjustable anti-rotation lens may include, for example, two or more lenses. Adjustable focusing lenses and anti-rotation lenses are further described in International Application No. PCT / EP2017 / 084429, which is incorporated herein by reference in its entirety.

[0043]

[0051] The apparatus 300 may further include an astigmatism corrector 330 configured to partially or completely compensate for astigmatism. In the context of this disclosure, astigmatism refers to an imaging artifact that distorts an image and occurs when charged particles (usually electrons) in a charged particle beam are subjected to non-uniform magnetic fields as they traverse their path toward the sample surface. Factors that can cause astigmatism include, but are not limited to, asymmetries of the pole pieces in an electromagnetic lens, impurities, contaminants, charge buildup in the material from which the lens is made, and the like. One solution to correct astigmatism is to use an astigmatism corrector, such as the astigmatism corrector 330, or a micro-astigmatism corrector that introduces a compensating field to offset the non-uniformity that causes astigmatism. The astigmatism corrector may include a magnetic or electromagnetic multi-pole structure to generate the compensating field. Commonly used multipole structures include, but are not limited to, quadrupole, hexapole, octapole, and 12-pole astigmatism correctors. In some embodiments, the controller 50 may adjust the electrical signal applied to the astigmatism corrector 330 to adjust the compensation field, thereby minimizing or compensating for astigmatism. The astigmatism corrector 330 may be located downstream from the focusing lens 326.

[0044]

[0052] The apparatus 300 may include a beam-limiting aperture array 335 configured to further block peripheral electrons of the primary electron beam 304-1 and pass a portion of the primary electron beam 304-1 to form the primary electron beam 304-2. The beam-limiting aperture array 335 may include a plurality of beam-limiting apertures. The apertures of the beam-limiting aperture array 335 may be configured to block peripheral electrons of the primary electron beam 304-1 based on a desired probe size or probe current of the probe beam incident on the sample surface. The beam-limiting aperture array 335 may be electrically connected to the controller 50 such that the controller 50 can provide an electrical signal to adjust the aperture size and thereby the beam size or beam current passing through the apertures of the beam-limiting aperture array 335. In some embodiments, the beam-limiting aperture array 335 may be located downstream of the astigmatism corrector 330. The beam-limiting aperture array 335 may be positioned such that the apertures through which the primary electron beam 304-2 passes are aligned with the primary optical axis 301. In some embodiments, the active apertures of the aperture plate 323, the active apertures of the Coulomb aperture array 324, and the active apertures of the beam-limiting aperture array 335 may be aligned with each other and with the primary optical axis 301. In this context, an active aperture refers to an aperture through which a primary electron beam (e.g., primary electron beam 304 or 304-1) passes.

[0045]

[0053] The apparatus 300 may further include an objective lens 332 disposed downstream of the beam-limiting aperture array 335 and configured to focus the primary electron beam 304-2 exiting the beam-limiting aperture array 335 onto the surface of the sample 350. In some embodiments, the objective lens 332 may include a modified swing objective retarding immersion lens (SORIL) lens, which includes a pole piece 332a, a control electrode 340e (also referred to herein as a beam scanning deflector), a beam manipulator assembly including primary electron beam deflectors 340a, 340b, 340c, 340d, and an excitation coil 332c. In a typical imaging process, the primary electron beam 304 emitted from the tip of the cathode 303 is accelerated by an acceleration voltage applied to the anode 322. A portion of the primary electron beam 304 passes through the aperture plate 323 and the apertures of the Coulomb aperture array 324 and is focused by the collection lens 326 to pass fully or partially through the apertures of the beam-limiting aperture array 335. The electrons passing through the apertures of the beam-limiting aperture array 335 may be focused by a modified SORIL lens to form a probe spot on the surface of the sample 350 and deflected by one or more deflectors of the beam manipulator assembly to scan the surface of the sample 250. Secondary electrons emitted from the sample surface may be collected by an electron detector 344 to form an image of the scanned area of ​​interest.

[0046]

[0054] In some embodiments, the excitation coil 332c and the pole piece 332a in the objective lens 332 may generate a magnetic field. The portion of the sample 350 scanned by the primary electron beam 304-2 may be immersed in this magnetic field and become electrically charged, which in turn generates an electric field. This electric field may reduce the energy of the impinging primary electron beam 304-2 on or near the surface of the sample 350. A control electrode is electrically isolated from the pole piece 332a and may control the electric field on and above the sample 350, for example, to reduce aberrations of the objective lens 332, control the focusing of the signal electron beam to increase detection efficiency, or avoid arcing to protect the sample from potential damage. One or more deflectors 340a-e of the beam manipulator assembly may deflect the primary electron beam 304-2 to facilitate beam scanning on the sample 350. For example, in a scanning process, deflectors 340a, 340b, 340c, 340d, and 340e may be controlled to deflect the primary electron beam 304 to different locations on the top surface of the sample 350 at different times to provide data for reconstructing images of different portions of the sample 350. It should be understood that the order of arrangement of the deflectors 340a-e may be different in different embodiments.

[0047]

[0055] The apparatus 300 may further include a beam separator 346. In some embodiments, as shown in FIG. 3, the beam separator 346 may be positioned closer to the sample 350 and may be configured to deflect the secondary electrons (or secondary electron beam) towards the electron detector 344 while passing the primary electron beam 304-2 with a zero deflection angle. The beam separator 346 may be a Wien filter type beam separator including an electrostatic deflector that generates an electrostatic dipole field and a magnetic dipole field (neither of which are shown in FIG. 3). When applied, the force acting on the electrons of the primary electron beam 304-2 by the electrostatic dipole field may be equal in magnitude and opposite in direction to the force acting on the electrons by the magnetic dipole field, and thus cancel each other out. Thus, the primary electron beam 304-2 may pass straight through the beam separator 346 with a zero deflection angle. However, the total energy dispersion of the primary electron beam 304-2 produced by the beam separator 346 may not be zero.

[0048]

[0056] In some embodiments, the apparatus 300 may include one or more beam separators. As shown in FIG. 3, in addition to the beam separator 346, the apparatus 300 may include a beam separator 348 disposed upstream of the beam separator 346. In some embodiments, the beam separator 348 may be of the Wien filter type and may be configured to compensate for the energy dispersion of the primary electron beam 304-2 caused by the beam separator 346. In some embodiments, the beam separator 348 may be disposed upstream of the electron detector 344 and upstream of the objective lens 332. In some embodiments, the beam separator 348 may be disposed downstream of the beam limiting aperture array 335. In some embodiments, the beam separator 348 may be disposed between the beam limiting aperture array 335 and the electron detector 344.

[0049]

[0057] With each new generation, commonly referred to as a technology "node" in the semiconductor device industry, the number, density, performance, and complexity of transistors and electronic circuits increase. Increasing the density of transistors in integrated circuits requires patterning smaller three-dimensional features on the semiconductor substrate. In general, smaller technology nodes result in smaller feature sizes, producing smaller transistors that are faster and more power efficient. As a general guide, a technology or process "node" can refer to the characteristics of a transistor, including, for example, the gate length or half pitch of a metal line. One device manufacturing technique that enables such small features to be formed is extreme ultraviolet (EUV) lithography, which uses photons with a wavelength of 13.5 nm and a high numerical aperture (NA) to transfer a pattern from a reticle or mask to a wafer with high fidelity.

[0050]

[0058] Although useful and effective, high NA EUV lithography techniques may present some challenges, especially local critical dimension (CD) variations due to stochastic effects, stochastic defects, or tight tolerance and process windows. In EUV lithography, the incidence of stochastic defects is low, and the dimensional variations to be detected are typically in the range of a few nanometers. Due to its high resolution, CD-SEM (Critical Length Scanning Electron Microscope) imaging may be a desirable imaging technique to detect stochastic defects such as micro-bridges, broken lines, contact hole junctions, or protrusions that occur during the EUV lithography process. However, existing CD-SEM imaging techniques may be inappropriate or inefficient due to limitations in the area of ​​the sample that can be scanned, called the field of view (FOV). While increasing the FOV may seem an obvious solution to overcome the limitations of CD-SEM imaging for stochastic defects, doing so may reduce imaging resolution since at least the off-axis aberrations of the primary electron beam increase with wider FOV scanning. Off-axis aberrations of the incident primary electron beam may include astigmatism, off-axis chromatic aberration, field curvature, or coma. It may therefore be desirable to provide a system and method that increases the FOV while maintaining high resolution within a wide FOV and minimizes one or more types of off-axis aberrations during scanning of the sample. Furthermore, a wider FOV may help improve imaging throughput by reducing the time involved in moving and settling the wafer stage each time a new location is scanned.

[0051]

[0059] In existing SEM-based wafer metrology techniques, such as CD-SEM imaging, a focused primary electron beam (e.g., primary electron beam 304-2 in FIG. 3) may be scanned across a region of interest on a sample (e.g., sample 350 in FIG. 3). The region of interest may include underlying subsurface structures, defects, nodes, topographical features, and the like. The scanned region of interest may form a field of view (FOV) of the sample. As mentioned above, CD-SEM imaging allows for high-resolution imaging, but the FOV is small, typically 10 μm or less. To detect fewer and smaller sized stochastic defects introduced by EUV lithography, it may be desirable to increase the FOV and maintain resolution within the FOV to efficiently perform CD-SEM imaging.

[0052]

[0060] 4A and 4B, which respectively show schematic diagrams of an exemplary wide FOV and an array of sub-FOVs that make up the wide FOV, consistent with embodiments of the present disclosure. It should be understood that while the size of the FOV is expressed in units of length, such as micrometers (μm), the field of view refers to an "area," and generally refers to a square region of interest on the sample surface. As an example, a 10 μm FOV refers to a square region of the sample that is approximately 10 μm on a side, and thus the area of ​​the FOV is approximately 100 μm. 2 may be also possible.

[0053]

[0061] 4A illustrates an exemplary wide FOV 400, which may be larger in size than a conventional FOV in a CD-SEM. For example, the wide FOV 400 may be 10 μm or larger, 20 μm or larger, 30 μm or larger, 40 μm or larger, 50 μm or larger, 60 μm or larger, 70 μm or larger, 80 μm or larger, 100 μm or larger, or any size suitable for detecting defects while maintaining inspection throughput and resolution. In some embodiments, the wide FOV 400 may be at least 2 times larger than the conventional FOV, at least 5 times larger than the conventional FOV, at least 10 times larger than the conventional FOV, at least 20 times larger than the conventional FOV, at least 40 times larger than the conventional FOV, at least 50 times larger than the conventional FOV, at least 80 times larger than the conventional FOV, or at least 100 times larger than the conventional FOV.

[0054]

[0062] FIG. 4B illustrates an exemplary wide FOV 410 that includes multiple sub-FOVs 401-409. As used herein, a sub-FOV refers to a portion of the wide FOV that the primary electron beam 304-2 can scan. Although the exemplary wide FOV 410 of FIG. 4B illustrates a 3×3 array of sub-FOVs, it should be understood that other array configurations are possible. For example, the wide FOV 410 may include, but is not limited to, a 2×2 array, or a 4×4 array, or a 5×5 array (as shown in FIGS. 4C-4E), or an m×n array, where m and n are integers and m=n or m≠n.

[0055]

[0063] Enabling imaging of the wide FOV 410 using the apparatus 300 may include scanning the sub-FOVs 401-409. In some embodiments, the beam deflectors of the beam manipulation assembly (e.g., beam deflectors 340a-e of FIG. 3) may be configured to deflect the primary electron beam 304-2 such that it scans an area of ​​the sample to form the wide FOV. In some embodiments, configuring the beam deflectors 340a-e may include applying or adjusting one or more signals to adjust the deflection, scan frequency, among others. One of the challenges of enabling imaging of a wide FOV using a CD-SEM is maintaining resolution while increasing the size of the FOV. Those skilled in the art of semiconductor device inspection and metrology will appreciate that as the FOV of a CD-SEM inspection tool increases, imaging resolution decreases due to, among others, increasing off-axis aberrations such as astigmatism, chromatic aberration, field curvature, and coma.

[0056]

[0064] Some techniques to minimize the impact of off-axis aberrations on resolution degradation may include, but are not limited to, optimizing one or more beam deflectors 340a-e to adjust scanning characteristics, or splitting a wide FOV (e.g., wide FOV 410 in FIG. 4B) into multiple sub-FOVs (e.g., sub-FOVs 401-409 in FIG. 4B), or both. In some embodiments, achieving a wide FOV may include two types of beam movement: moving the primary electron beam 304-2 from one sub-FOV to another (slow scan) and scanning the primary electron beam 304-2 within each sub-FOV (fast scan or quick scan).

[0057]

[0065] In some embodiments, the beam deflectors 340a, 340d, and 340e may be configured to slow scan the primary electron beam 304-2 to move a probe spot formed by the primary electron beam 304-2 (shown as a solid black circle in the center of the sub-FOV 405 in FIG. 4B ) from the center of the sub-FOV 405 to the center of the sub-FOV 401. As shown, the center of the sub-FOV 405 may coincide with the center of the wide FOV 410. The dotted line connecting the centers of the sub-FOV 405 and 401 represents an exemplary deflection path of the primary electron beam 304-2. The beam deflectors 340a, 340d, and 340e may be electrostatic deflectors configured to deflect the primary electron beam 304-2 from the center of the wide FOV 410 (which coincides with the center of the sub-FOV 405) to be incident on the region of the sample represented by the sub-FOV 401. The controller 50 may apply or adjust applied signals to the beam deflectors 340a, 340d, and 340e to deflect the primary electron beam 304-2 from the center of the sub-FOV 405 to the center of the sub-FOV 401. Enabling the slow scan step may further include aligning the primary electron beam 304-2 with respect to the center of the sub-FOV 401 before fast scanning the primary electron beam 304-2 within the sub-FOV 401. The beam deflectors 340b and 340c may be configured to cause the primary electron beam 304-2 to fast scan the sub-FOV 401 after the primary electron beam 304-2 is aligned with the center of the sub-FOV 401. In some embodiments, rapidly scanning the sub-FOV 401 may include adjusting signals to the beam deflectors 340b and 340c such that the primary electron beam 304-2 scans from the left edge of the sub-FOV 401 to the right edge of the sub-FOV 401 (represented by the solid horizontal line) as shown in FIG. 4B. Upon reaching the right edge of a first row within the sub-FOV 401, the primary electron beam 304-2 may be deflected and positioned to the left edge of a second row vertically below the first row (represented by the dashed line). The row-to-row scan pattern may be repeated to scan the sub-FOV 401.After scanning sub-FOV 401, controller 50 applies signals to beam deflectors 340a, 340d, and 340e to allow the primary electron beam 304-2 to be deflected to the center of adjacent sub-FOV 402, which is scanned using the fast scan regime, similar to sub-FOV 401. It should be understood that the numbering of sub-FOVs 401-409 may indicate the order in which the sub-FOVs are scanned, but does not necessarily do so. As an example, sub-FOV 406 may be scanned immediately after sub-FOV 401 is scanned, among other reasons, to increase the physical distance between two successive scans of the sub-FOVs, so that charge build-up can dissipate. In some cases, the overlap of the scan areas of adjacent sub-FOVs may adversely affect image resolution or even cause defects due to charging, among other issues.

[0058]

[0066] Although it is useful to minimize the effects of off-axis aberrations, in some cases, the off-axis aberrations may still be undesirably large for a wide FOV. Splitting a wide FOV into multiple sub-FOVs that can be scanned individually may not provide sufficient resolution to detect stochastic defects associated with EUV lithography techniques. This may be because a primary electron beam (e.g., primary electron beam 304-2 in FIG. 3) configured to scan an area of ​​a sample within a sub-FOV (e.g., sub-FOV 401 in FIG. 4B) may have off-axis aberrations that may adversely affect the resolution of the generated image. Therefore, it may be desirable to provide a method and system for compensating for off-axis aberrations of the primary electron beam 304-2 during scanning of the sub-FOV.

[0059]

[0067] Referring back to FIG. 3 , the apparatus 300 may be configured to compensate for one or more off-axis aberrations of the primary electron beam 304-2 during scanning of an area of ​​the sample 350. The off-axis aberrations may include coma, astigmatism, off-axis chromatic aberration, or field curvature. In some embodiments, an aberration compensation mechanism may be used to reduce one or more off-axis aberrations in each sub-FOV of the wide FOV. The aberration compensation mechanism may be configured to dynamically compensate for one or more off-axis aberrations in each sub-FOV of the wide FOV, thereby allowing imaging of the wide FOV while dynamically compensating for off-axis aberrations to allow detection of defects, including but not limited to stochastic defects caused by EUV lithography techniques.

[0060]

[0068] In some embodiments, the deflectors of the beam manipulator assembly may be configured to compensate for astigmatism in the sub-FOV. In some embodiments, any one of the deflectors 340a-e may be configured to compensate for astigmatism. The controller 50 may apply an electrical excitation signal to any one of the deflectors 340a-e to deflect the primary electron beam 304-2 such that the astigmatism is compensated. The electrical excitation signal may include, for example, a voltage signal. In some embodiments, the excitation signal applied to a deflector to compensate for astigmatism may be an auxiliary excitation signal, such as a voltage signal, that is added to the primary excitation signal applied to that deflector. The auxiliary excitation signal may be substantially smaller than the primary excitation signal applied to the deflector. In this context, substantially smaller refers to 10% or less of the primary excitation signal. For example, if the primary excitation signal is 100V, the auxiliary excitation signal may be 10V or less.

[0061]

[0069] In some embodiments, the supplemental excitation signal for compensating for astigmatism may be a predetermined signal based on the astigmatism of the primary electron beam 304-2. In some embodiments, the astigmatism may be determined based on a trained model, such as via simulation or artificial learning, or a machine learning model. Information related to the simulated astigmatism values ​​may be stored in a database or in a storage module within the network, such that the processor or controller 50 may access and utilize the stored information to adjust the electrical signals applied to the corresponding deflectors.

[0062]

[0070] In some embodiments, the predetermined auxiliary excitation signal for compensating for astigmatism in a sub-FOV may be a constant signal, such that the excitation signal is uniform throughout the sub-FOV. For example, if the predetermined auxiliary excitation signal for a sub-FOV 401 is 10V and the primary excitation signal is 100V, then the excitation signal for the sub-FOV 401 may be 110V at each probe location within the sub-FOV 401. In some embodiments, the predetermined auxiliary excitation signals for one or more sub-FOVs may be substantially similar or dissimilar based on, among other things, the position of the sub-FOV relative to the primary optical axis, the position of the probe spot, or the distribution of electrons in the primary electron beam 304-2.

[0063]

[0071] In some embodiments, the predetermined auxiliary excitation signal for compensating for astigmatism may vary within the sub-FOV, so that the excitation signal at the pixel in the sub-FOV may not be uniform. In the context of the present disclosure, the probe location within the sub-FOV may be referred to as a pixel of the sub-FOV. The controller 50 may be configured to adjust the excitation signal applied to the deflector associated with compensating for astigmatism. In some embodiments, the controller 50 may be configured to adjust the excitation signal for each pixel by applying a predetermined auxiliary excitation signal, which may be similar or dissimilar.

[0064]

[0072] In some embodiments, astigmatism may be compensated for by applying an excitation signal to the astigmatism corrector 330, or by applying an excitation signal including the auxiliary excitation signal to one of the deflectors 340a-e, or by applying an excitation signal to the astigmatism corrector 330 and one of the deflectors 340a-e.

[0065]

[0073] Referring back to FIG. 3 , the deflectors of the apparatus 300 may be configured to compensate for the field curvature aberration in the sub-FOV. In some embodiments, any one of the deflectors 340a-e may be configured to compensate for the field curvature aberration. The controller 50 may apply an electrical excitation signal to any one of the deflectors 340a-e to deflect the primary electron beam 304-2 such that the field curvature aberration is compensated. The electrical excitation signal may include, for example, a voltage signal. In some embodiments, the excitation signal applied to a deflector to compensate for the field curvature may be an auxiliary excitation signal, such as a voltage signal, that is added to the primary excitation signal applied to that deflector. The auxiliary excitation signal may be significantly smaller than the primary excitation signal applied to the deflector.

[0066]

[0074] In some embodiments, the predetermined auxiliary excitation signal for compensating for field curvature aberrations in a sub-FOV may be a constant signal, such that the excitation signal is uniform across the entire sub-FOV. For example, if the predetermined auxiliary excitation signal for a sub-FOV 401 is 10V and the primary excitation signal is 100V, then the excitation signal for the sub-FOV 401 may be 110V at each probe location within the sub-FOV 401. In some embodiments, the predetermined auxiliary excitation signals for one or more sub-FOVs may be substantially similar or dissimilar based on, among other things, the position of the sub-FOV relative to the primary optical axis, the position of the probe spot, or the distribution of electrons in the primary electron beam 304-2.

[0067]

[0075] In some embodiments, the predetermined auxiliary excitation signal for compensating for the field curvature aberration may vary within the sub-FOV, so that the excitation signal at the pixels within the sub-FOV may not be uniform. The controller 50 may be configured to adjust the excitation signal applied to the deflector associated with compensating for the field curvature aberration. In some embodiments, the controller 50 may be configured to adjust the excitation signal for each pixel by applying a predetermined auxiliary excitation signal, which may be similar or dissimilar.

[0068]

[0076] In some embodiments, the apparatus 300 may be configured to compensate for field curvature aberrations by adjusting the excitation signal to the objective lens 332, or adjusting the excitation signal to the beam deflector 340e, or adjusting the excitation signal to the collection lens 326, or adjusting the lens field excitation signal to one of the beam deflectors 340a-d, or a combination thereof. In the context of the present disclosure, adjusting the excitation signal may include, but is not limited to, adding an auxiliary excitation signal to the primary excitation signal, or varying the primary excitation signal to perform aberration compensation.

[0069]

[0077] With reference to FIG. 3, the beam separator 348 may be configured to compensate for off-axis chromatic aberration for each sub-FOV. In some embodiments, the beam separator 348 may be configured to compensate for the energy dispersion and off-axis chromatic aberration of the primary electron beam 304-2 caused by the beam separator 346. As illustrated in FIG. 3, the beam separator 348 may be disposed upstream of the beam separator 346 and downstream of the beam-limiting aperture array 335. The electrostatic and magnetic forces exerted by the beam separator 346 on the incoming primary electron beam 304-2 may be balanced, so that a portion of the primary electron beam 304-2 can pass through the beam separator 346 undeflected. However, the primary electron beam 304-2 includes electrons with an energy distribution, for example, 1 eV or less, and some electrons may experience energy dispersion when passing through. In some embodiments, the beam separator 348 may be configured to compensate for an energy dispersion of the primary electron beam 304-2 caused by the beam separator 346. In some embodiments, the energy dispersion of the primary electron beam 304-2 may be determined based on characteristics of the primary electron beam 304-2, and the excitation signal to the beam separator 348 may be based on the determined energy dispersion of the primary electron beam 304-2. The excitation signal may also include a component that compensates for off-axis chromatic aberration of the primary electron beam 304-2.

[0070]

[0078] In some embodiments, two or more deflectors of the apparatus 300 may be configured to reduce coma. In some embodiments, an excitation signal may be applied to at least the deflectors 340a and 340e to reduce coma of the primary electron beam 304-2, or an excitation signal may be applied to at least the deflectors 340d and 340e to reduce coma of the primary electron beam 304-2. In some embodiments, an excitation signal applied to the deflectors 340a, 340d, and 340e may reduce coma of the primary electron beam 304-2.

[0071]

[0079] As mentioned above, one of several ways to maintain high imaging resolution in a wide FOV includes splitting the wide FOV into multiple sub-FOVs and dynamically compensating for one or more off-axis aberrations while scanning the sub-FOVs. Additionally or alternatively, the scanning order of the sub-FOVs may also be adjusted in some cases to minimize the adverse effects of "charging" or "charge accumulation" and thereby improve the overall image quality. It should be appreciated that illuminating a sample surface with charged particles, such as electrons, may cause accumulation of charged particles within the surface since there is no charge dissipation mechanism. The accumulated charged particles may adversely affect the overall imaging quality and in some cases may prevent the detection of defects and disqualify the defect inspection device. Therefore, it may be desirable to provide a method to minimize the effects of charging when scanning a wide FOV to detect or image defects.

[0072]

[0080] 4C and 4D, which illustrate exemplary 3×3 array sub-FOVs 401-409 consistent with embodiments of the present disclosure. In some embodiments, the wide FOV may be divided into symmetric array sub-FOVs, such as a 3×3 array, or a 5×5 array, or a 7×7 array. In some embodiments, the wide FOV may be divided into asymmetric array sub-FOVs, such as a 2×4 array, or a 3×5 array. Although FIGS. 4C and 4D show a symmetric 3×3 array, it should be understood that the wide FOV may be divided into other array-like arrangements represented by m×n arrays, where m and n are integers, and where m=n or m≠n. It should be understood that the boundaries defining the squares shown in FIGS. 4A-4D are for illustrative, illustrative, and visual aid purposes only. However, in practice, the primary electron beam (e.g., primary electron beam 304-2) may be deflected a range of distances from a reference point to scan an area confined within or represented by the sub-FOV.

[0073]

[0081] Figure 4C illustrates a wide FOV 450 that includes multiple sub-FOVs 401-409. In the embodiment illustrated in Figure 4C, the numbering of the sub-FOVs indicates the order or sequence for scanning the sub-FOVs 401-409 within the wide FOV 450. In some embodiments, scanning the wide FOV 450 with the primary electron beam 304-2 may include, but is not limited to, aligning the primary electron beam 304-2 with the center of the wide FOV 450, adjusting the position of the primary electron beam 304-2 from the center of the wide FOV 450 to the center of the sub-FOV 401, aligning the primary electron beam 304-2 with the center of the sub-FOV 401, scanning the primary electron beam 304-2 across the sub-FOV 401, adjusting the position of the primary electron beam 304-2 to align with the center of the sub-FOV 402 after scanning the sub-FOV 401, and scanning the primary electron beam 304-2 across the sub-FOV 402. It should be understood that scanning the wide FOV 450 may include more or fewer steps as needed.

[0074]

[0082] To mitigate the effects of charging in a wide FOV (e.g., wide FOV 450), the scanning order of the sub-FOVs may be adjusted such that the physical spacing between successively scanned sub-FOVs is maximized. The physical spacing and time lapse between successive scans allows accumulated charge to dissipate. Thus, increasing the spatial and physical spacing between two successively scanned sub-FOVs increases the time between the two scans, and thus can reduce problems associated with charge accumulation.

[0075]

[0083] In some embodiments, consecutively scanned sub-FOVs, such as sub-FOV 401, sub-FOV 402, may be physically or spatially separated by at least a threshold distance. The threshold distance of separation may depend on factors including, but not limited to, probe beam intensity, sample material, presence of defects, type of defects present, among others, while taking into account overall imaging quality and inspection throughput. In some embodiments, a wide FOV may be divided into multiple sub-FOVs of substantially equal size. In such a case, the threshold distance may be expressed in sub-FOV units. For example, the threshold distance between two consecutively scanned sub-FOVs may be one sub-FOV, or two sub-FOVs, or three sub-FOVs, or any distance therebetween, or any suitable distance. It should be understood that in this context, the distance between two sub-FOVs refers to the horizontal distance along the surface of the sample between the geometric centers of the two sub-FOVs.

[0076]

[0084] As shown in FIG. 4C, subFOV 402, which may be scanned after scanning subFOV 401, is located diagonally opposite subFOV 401, which is the maximum distance in a square array arrangement. It should be understood that the distance between two consecutively scanned subFOVs may be maximized, although this is not always possible. For example, the physical distance between subFOV 402 and subFOV 403 may be smaller than the physical distance between subFOV 410 and subFOV 402, but the distance between subFOV 402 and subFOV 403 is the maximum distance possible within wide FOV 450. As indicated above, the numbering of the subFOVs within wide FOV 450 represents the order of scanning.

[0077]

[0085] In some embodiments, as shown in FIG. 4D, the physical distance between successively scanned sub-FOVs, such as sub-FOV 401, sub-FOV 402, sub-FOV 403, and sub-FOV 404, may be uniform or substantially uniform. In this context, a substantially uniform separation distance refers to negligible variation in the separation distance between two successively scanned sub-FOVs across a wide FOV. It should be understood that the physical separation distance between successively scanned sub-FOVs, such as sub-FOV 401, sub-FOV 402, may not be the maximum possible physical separation. It should also be understood that the physical separation between sub-FOV 408 and sub-FOV 409 may be different, or more specifically, shorter, than the physical separation between sub-FOV 407 and sub-FOV 408, for example. FIG. 4D shows a wide FOV 460 divided into multiple sub-FOVs 401-409 arranged in an array pattern such that the physical spacing between successively scanned sub-FOVs is uniform distances apart, yet maximized.

[0078]

[0086] 4E and 4F, which show example scan patterns of sub-FOVs within a wide FOV consistent with embodiments of the present disclosure. FIGS. 4E and 4F show example scan patterns within wide FOV 470 and wide FOV 480, respectively. Wide FOVs 470 and 480 include a 5×5 symmetric array of sub-FOVs 401-425. Scan patterns 472 and 482 are represented by dashed lines connecting the centers of sub-FOVs to be scanned consecutively. Scan pattern 472 may include a “skip” pattern, in which primary electron beam 304-2 scans a sub-FOV, such as sub-FOV 401, and then is deflected to scan a sample area at least one sub-FOV away along the X-axis, or the Y-axis, or a combination of the X-axis and the Y-axis. In a wide FOV 470, the scan pattern 472 may include a combination of skip patterns and other regular or irregular patterns such that the maximum possible physical spacing is maintained between two successively scanned sub-FOVs while maintaining a substantially uniform separation distance based on the scan area.

[0079]

[0087] In some embodiments, the scan pattern 482 for the wide FOV 480 may include a "star" pattern. The dashed lines represent this pattern and the shortest path to the desired sub-FOV to scan, but it should be understood that other paths may also be implemented. In some embodiments, the scan pattern may include a star pattern, a skip pattern, or any combination of regular or irregular patterns, or any combination of multiples thereof.

[0080]

[0088] In some embodiments, the scan pattern 472 or 482 may be a pre-determined pattern based on factors including, but not limited to, the total scan area, information related to the type of defects, information related to the number of defects, desired imaging resolution, among others. In some embodiments, the pre-determined pattern may be based on a simulated pattern generated by a trained model, such as a machine learning model or an artificial intelligence based model.

[0081]

[0089] In some embodiments, the controller 50 of the apparatus 300 may be configured to deflect the primary electron beam 304-2 such that the primary electron beam 304-2 follows a path based on a predetermined scan pattern. One or more beam deflectors 340a-e controlled by the controller 50 may be configured to deflect the primary electron beam 304-2 by applying an excitation signal thereto. The applied excitation signal may be, for example, a voltage signal to an electrostatic beam deflector such as deflector 340a.

[0082]

[0090] 5, which illustrates a process flow diagram depicting an exemplary method 500 for imaging a wide FOV of a sample consistent with embodiments of the present disclosure. One or more steps of the method 500 may be performed by a controller 50 of an EBI system 100, such as that shown in FIG. 2. For example, the controller 50 may instruct modules of a charged particle beam device to operate a charged particle source to generate a charged particle beam (e.g., an electron beam), apply electrical signals to a beam deflector, apply electrical signals to a beam separator, and perform other functions.

[0083]

[0091] In step 510, a charged particle source (e.g., electron source 302 in FIG. 3) may be activated to emit charged particles. The charged particles may pass through an aperture to form a charged particle beam (e.g., primary charged particle beam 304 in FIG. 3). The electron source may be activated by a controller (e.g., controller 50 in FIG. 3). For example, the electron source may be controlled to emit primary electrons to form an electron beam along a primary optical axis (e.g., primary optical axis 301 in FIG. 3). The electron source may be activated remotely by providing power to the electron source through a control circuit, for example, using software, an application, or a set of instructions for a processor of the controller. The primary electron beam may pass through a Coulomb aperture array (e.g., Coulomb aperture array 324 in FIG. 3) and a beam-limiting aperture array (e.g., beam-limiting aperture array 335 in FIG. 3) to adjust the beam size or beam current of the primary electron beam and form a probe beam (e.g., primary charged particle beam 304-2 in FIG. 3).

[0084]

[0092] In step 520, the probe beam may be deflected from the primary optical axis such that the deflected probe beam scans over a surface of a sample (e.g., sample 350 of FIG. 3) to form a field of view (FOV). The controller may be configured to apply excitation signals to one or more beam deflectors (e.g., primary charged particle beam deflectors 340a-e of FIG. 3) in a beam manipulator assembly of the inspection apparatus (e.g., apparatus 300 of FIG. 3) to deflect the probe beam. The applied excitation signals may cause the deflected probe beam to scan across a region of interest (ROI) to form the FOV of the image.

[0085]

[0093] It may be desirable to form a wide FOV using dynamic aberration compensation mechanisms to detect defects such as stochastic defects created by EUV lithography. One of several challenges associated with increasing FOVs in critical dimension scanning electron microscopes (CD-SEMs) is that imaging resolution decreases as the size of the FOV increases. This loss of imaging resolution may be due to off-axis aberrations of a probe beam, such as a primary electron beam. Off-axis aberrations may include astigmatism, field curvature aberration, chromatic aberration, or coma. Thus, it may be desirable to provide a method to compensate for one or more types of off-axis aberrations of the probe beam to maintain imaging resolution when increasing the size of the imaging FOV to detect nanoscale defects. A wide FOV may be imaged by scanning multiple portions of the wide FOV and dynamically compensating for off-axis aberrations in each portion. A portion of the wide FOV (e.g., wide FOV 410 in FIG. 4B) is referred to herein as a sub-FOV (e.g., sub-FOVs 401-409 in FIG. 4B).

[0086]

[0094] In step 530, the controller may apply excitation signals to one or more beam deflectors to deflect the probe beam to scan the sub-FOV. The controller may apply excitation signals to one or more deflectors, such as primary beam deflectors 340a, 340d, and 340e, to adjust the position of the probe beam from the center of the wide FOV to the center of the sub-FOV. The probe beam may be aligned to the center of the sub-FOV before scanning the entire sub-FOV.

[0087]

[0095] In step 540, after aligning the probe beam, the controller may adjust or apply excitation signals to the primary beam deflectors to compensate for off-axis aberrations of the probe beam while scanning across the sub-FOV. For example, the controller may adjust excitation signals to one or more beam deflectors 340a-e to compensate for astigmatism or field curvature aberrations while performing a quick scan across the sub-FOV.

[0088]

[0096] The electrical excitation signal may include, for example, a voltage signal. In some embodiments, the excitation signal applied to a deflector to compensate for astigmatism may be an auxiliary excitation signal, such as a voltage signal, that is added to the primary excitation signal applied to that deflector. The auxiliary excitation signal may be significantly smaller than the primary excitation signal applied to the deflector. In this context, significantly smaller refers to 10% or less of the primary excitation signal. For example, if the primary excitation signal is 100V, the auxiliary excitation signal may be 10V or less.

[0089]

[0097] The auxiliary excitation signal may be a predetermined voltage signal. The predetermined auxiliary excitation signal for compensating for field curvature or astigmatism in a sub-FOV may be a constant signal, so that the excitation signal is uniform across the sub-FOV. In some embodiments, the predetermined auxiliary excitation signal for compensating for field curvature may vary within the sub-FOV, so that the excitation signal at the pixels in the sub-FOV may not be uniform. The controller 50 may be configured to adjust the excitation signal applied to the deflector associated with compensating for off-axis aberrations. In some embodiments, the controller 50 may be configured to adjust the excitation signal for each pixel by applying a predetermined auxiliary excitation signal, which may be similar or dissimilar.

[0090]

[0098]

[0023] Referring now to Figure 6, this figure shows a process flow diagram illustrating an exemplary method 600 for imaging a wide FOV of a sample consistent with embodiments of the present disclosure. One or more steps of the method 600 may be performed by, for example, a controller 50 of an EBI system 100 as shown in Figure 2. For example, the controller 50 may instruct modules of a charged particle beam device to operate a charged particle source to generate a charged particle beam (e.g., an electron beam), apply electrical signals to a beam deflector, apply electrical signals to a beam separator, and perform other functions.

[0091]

[0099] In step 610, a charged particle source (e.g., electron source 302 in FIG. 3) may be activated to emit charged particles. The charged particles may pass through an aperture to form a charged particle beam (e.g., primary charged particle beam 304 in FIG. 3). The electron source may be activated by a controller (e.g., controller 50 in FIG. 3). For example, the electron source may be controlled to emit primary electrons to form an electron beam along a primary optical axis (e.g., primary optical axis 301 in FIG. 3). The electron source may be activated remotely by providing power to the electron source through a control circuit, for example, using software, an application, or a set of instructions for a processor of the controller. The primary electron beam may pass through a Coulomb aperture array (e.g., Coulomb aperture array 324 in FIG. 3) and a beam-limiting aperture array (e.g., beam-limiting aperture array 335 in FIG. 3) to adjust the beam size or beam current of the primary electron beam and form a probe beam (e.g., primary charged particle beam 304-2 in FIG. 3).

[0092]

[0100] In step 620, the probe beam may be deflected from the primary optical axis such that the deflected probe beam scans over a surface of a sample (e.g., sample 350 of FIG. 3) to form a field of view (FOV). The controller may be configured to apply excitation signals to one or more beam deflectors (e.g., primary charged particle beam deflectors 340a-e of FIG. 3) in a beam manipulator assembly of the inspection apparatus (e.g., apparatus 300 of FIG. 3) to deflect the probe beam. The applied excitation signals may cause the deflected probe beam to scan across a region of interest (ROI) to form the FOV of the image.

[0093]

[0101] In step 630, the controller may apply excitation signals to one or more beam deflectors to deflect the probe beam to scan the sub-FOV. The controller may apply excitation signals to one or more deflectors, such as primary beam deflectors 340a, 340d, and 340e, to adjust the position of the probe beam from the center of the wide FOV to the center of the sub-FOV. The probe beam may be aligned to the center of the sub-FOV before scanning the entire sub-FOV.

[0094]

[0102] In step 640, the controller may apply an excitation signal to a beam separator (e.g., beam separator 348 in FIG. 3) to compensate for energy dispersion caused by another beam separator (e.g., beam separator 346 in FIG. 3) and off-axis chromatic aberration of the primary probe beam. The beam separator may be an electromagnetic beam separator, such as a Wien filter. The beam separator 346 may be configured to deflect secondary electrons generated by the interaction of the primary electrons of the probe beam with the sample toward a secondary electron detector (e.g., detector 344 in FIG. 3). The beam separator 348 may include a compensating Wien filter configured to compensate for energy dispersion and off-axis chromatic aberration.

[0095]

[0103] 7, which illustrates a process flow diagram depicting an exemplary method 700 for imaging a wide FOV of a sample consistent with embodiments of the present disclosure. One or more steps of the method 700 may be performed by, for example, a controller 50 of an EBI system 100 as shown in FIG. 2. For example, the controller 50 may instruct modules of a charged particle beam device to operate a charged particle source to generate a charged particle beam (e.g., an electron beam), apply electrical signals to a beam deflector, apply electrical signals to a beam separator, and perform other functions.

[0096]

[0104] In step 710, a charged particle source (e.g., electron source 302 in FIG. 3) may be activated to emit charged particles. The charged particles may pass through an aperture to form a charged particle beam (e.g., primary charged particle beam 304 in FIG. 3). The electron source may be activated by a controller (e.g., controller 50 in FIG. 3). For example, the electron source may be controlled to emit primary electrons to form an electron beam along a primary optical axis (e.g., primary optical axis 301 in FIG. 3). The electron source may be activated remotely by providing power to the electron source through a control circuit, for example, using software, an application, or a set of instructions for a processor of the controller. The primary electron beam may pass through a Coulomb aperture array (e.g., Coulomb aperture array 324 in FIG. 3) and a beam-limiting aperture array (e.g., beam-limiting aperture array 335 in FIG. 3) to adjust the beam size or beam current of the primary electron beam and form a probe beam (e.g., primary charged particle beam 304-2 in FIG. 3).

[0097]

[0105] In step 720, in a first beam alignment, the probe beam may be aligned with a first location of the FOV (e.g., the center of FOV 470 in FIG. 4E). The first location may be the center of the FOV. The controller may be configured to apply an excitation signal to one or more beam deflectors (e.g., primary charged particle beam deflectors 340a-e in FIG. 3) in a beam manipulator assembly of the metrology apparatus (e.g., apparatus 300 in FIG. 3). In some embodiments, the center of the FOV may be determined based on the spot or area where the probe beam lands on the sample when no scanning is being performed.

[0098]

[0106] In step 730, in a second beam alignment, the probe beam may be repositioned or deflected to align with the center of a portion of the FOV, such as the first sub-FOV (sub-FOV 401 in FIG. 4E). The controller may apply excitation signals to one or more beam deflectors to align the probe beam with the center of the first sub-FOV. In some embodiments, the controller may apply excitation signals to beam deflectors 340a, 340d, and 340e to deflect the beam from the center of the FOV to the center of the sub-FOV. The center of the sub-FOV may be at a different location than the center of the FOV.

[0099]

[0107] In step 740, after aligning the probe beam to the center of the first sub-FOV, the controller may apply excitation signals to one or more beam deflectors, such as beam deflectors 340b and 340c, to cause the probe beam to scan the entire first sub-FOV. In some embodiments, the excitation signals applied to one or more beam deflectors 340a, 340b, 340c, 340d, or 340e may be adjusted to compensate for astigmatism or field curvature aberration, or both, while the probe beam is scanning the first sub-FOV.

[0100]

[0108] In step 750, after scanning the first sub-FOV, the controller may apply an excitation signal to one or more beam deflectors to deflect the probe beam to align it with the center of a second sub-FOV (e.g., sub-FOV 402 in FIG. 4E). The second sub-FOV may be at least a threshold distance away from the first sub-FOV to allow dissipation of charge and minimize or mitigate adverse effects of charge build-up from a previous scan to a subsequent scan. The separation distance between successively scanned sub-FOVs may be maximized and uniform. The separation threshold distance may depend on factors including, but not limited to, probe beam intensity, sample material, the presence of defects, the type of defects present, among others, while taking into account overall imaging quality and inspection throughput. In some embodiments, the wide FOV may be divided into multiple sub-FOVs of substantially equal size. In such cases, the threshold distance may be expressed in sub-FOV units. For example, the threshold distance between two consecutively scanned sub-FOVs may be one sub-FOV, or two sub-FOVs, or three sub-FOVs, or any distance therebetween, or any suitable distance.

[0101]

[0109] In step 760, after aligning the probe beam to the center of the second sub-FOV, the controller may apply excitation signals to one or more beam deflectors, such as beam deflectors 340b and 340c, to cause the probe beam to scan the entire second sub-FOV. In some embodiments, the excitation signals applied to one or more beam deflectors 340a-e may be adjusted to compensate for astigmatism or field curvature aberration, or both, while the probe beam is scanning the second sub-FOV.

[0102]

[0110] A non-transitory computer readable medium may be provided that stores instructions for a processor of a controller (e.g., controller 50 of FIG. 1 ) to perform image inspection, image acquisition, actuating a charged particle source, adjusting electrical excitation of an astigmatism corrector, adjusting electron landing energy, adjusting objective lens excitation, applying excitation signals to one or more beam deflectors, applying excitation signals to one or more beam separators, controlling movement of a stage, actuating beam deflectors to deflect the primary electron beam, applying electrical excitation signals including AC voltages, and the like. Common forms of non-transitory media include, for example, floppy disks, flexible disks, hard disks, solid state drives, magnetic tape or any other magnetic data storage media, CD-ROMs (Compact Disc Read Only Memory), any other optical data storage media, any physical media with a pattern of holes, RAM (Random Access Memory), PROMs (Programmable Read Only Memory), EPROMs (Erasable Programmable Read Only Memory), FLASH-EPROMs or any other flash memory, NVRAMs (Non-Volatile Random Access Memory), caches, registers, any other memory chips or cartridges, and networked versions thereof.

[0103]

[0111] The embodiments of the present disclosure can be further described using the following clauses. 1. A charged particle beam device comprising: a charged particle source configured to emit charged particles; an aperture plate configured to form a primary charged particle beam along a primary optical axis from the emitted charged particles; a plurality of primary charged particle beam deflectors configured to deflect the primary charged particle beam so as to be incident on the surface of the sample and define a center of a field of view (FOV); A controller, applying a first excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors to cause the primary charged particle beam to scan a portion of the FOV of the sample; and and a controller including circuitry configured to apply a second excitation signal to cause the primary charged particle beam deflector to compensate for off-axis aberrations of the primary charged particle beam in that portion of the FOV of the sample. 2. The apparatus of claim 1, wherein the second excitation signal comprises a predetermined voltage signal. 3. The apparatus of claim 2, wherein the predetermined voltage signal is based on a simulation from a trained machine learning model. 4. An apparatus as described in any one of clauses 2 and 3, wherein the predetermined voltage signal is constant across a portion of the FOV of the sample. 5. An apparatus described in any one of clauses 2 and 3, wherein the predetermined voltage signal varies based on the location of a probe spot within a portion of the FOV, the probe spot being formed by a primary charged particle beam incident on the sample. 6. An apparatus as described in clause 5, wherein a varying predetermined voltage signal enables dynamic compensation of off-axis aberrations of the primary charged particle beam in a portion of the FOV of the sample. 7. An apparatus according to any one of clauses 1 to 6, wherein the plurality of primary charged particle beam deflectors include electrostatic beam deflectors or magnetic deflectors. 8. An apparatus described in any one of clauses 1 to 7, wherein a portion of the FOV includes a sub-FOV, and the FOV includes a plurality of sub-FOVs arranged in a two-dimensional array. 9. The apparatus of claim 8, wherein each sub-FOV of the plurality of sub-FOVs is scanned by the primary charged particle beam. 10. An apparatus as described in clause 9, wherein prior to scanning each sub-FOV of the plurality of sub-FOVs, the primary charged particle beam is aligned with the centre of each corresponding sub-FOV. 11. The apparatus of any one of clauses 8 to 10, wherein the two-dimensional array comprises a symmetric array of sub-FOVs. 12. The apparatus of any one of clauses 8 to 11, wherein the controller includes circuitry further configured to apply a second excitation signal to compensate for off-axis aberrations of the primary charged particle beam while the primary charged particle beam deflector is scanning a sub-FOV among the plurality of sub-FOVs. 13. The apparatus of any one of clauses 8 to 11, wherein the controller includes circuitry further configured to apply the second excitation signal multiple times during scanning of the sub-FOV so as to compensate for off-axis aberrations of the primary charged particle beam while the primary charged particle beam deflector is scanning that sub-FOV of the multiple sub-FOVs. 14. An apparatus according to any one of clauses 1 to 13, wherein the off-axis aberrations include astigmatism or field curvature of the primary charged particle beam. 15. The controller is a circuit comprising: applying a second excitation signal to the first primary charged particle beam deflector such that the first primary charged particle beam deflector compensates for the field curvature aberration of the primary charged particle beam; a circuit further configured to apply a third excitation signal to a second primary charged particle beam deflector different from the first primary charged particle deflector, such that the second primary charged particle beam deflector compensates for astigmatism of the primary charged particle beam; 15. The apparatus of claim 14, wherein the first and second primary charged particle beam deflectors are electrostatic beam deflectors. 16. An apparatus described in any one of clauses 1 to 15, further comprising a plurality of beam separators, a first beam separator of the plurality of beam separators configured to compensate for energy dispersion of the primary charged particle beam in a portion of the FOV, the energy dispersion being caused by a second beam separator of the plurality of beam separators. 17. The apparatus of claim 16, wherein the first beam separator is further configured to compensate for off-axis chromatic aberration of the primary charged particle beam in a portion of the FOV of the sample. 18. An apparatus according to any one of clauses 16 and 17, wherein the first beam separator is disposed upstream of the second beam separator, the first and second beam separators comprising electromagnetic beam separators. 19. An apparatus described in any one of clauses 17 to 18, wherein the first beam separator is further configured to receive an excitation signal from the controller, and in response to receiving the excitation signal, the first beam separator compensates for energy dispersion and off-axis chromatic aberration of the primary charged particle beam in a portion of the FOV of the sample. 20. A method of imaging a sample using a charged particle beam device, comprising: forming a primary charged particle beam from charged particles emitted by a charged particle source; deflecting the primary charged particle beam with a primary charged particle beam deflector so as to be incident on a surface of the sample and define a center of a field of view (FOV); applying a first excitation signal to a primary charged particle beam deflector to cause the primary charged particle beam to scan a portion of the FOV of the sample; applying a second excitation signal to cause the primary charged particle beam deflector to compensate for off-axis aberrations of the primary charged particle beam in that portion of the FOV. 21. The method of clause 20, wherein applying the second excitation signal includes applying a predetermined voltage signal to a primary charged particle beam deflector. 22. The method of claim 21, wherein the predetermined voltage signal is constant across a portion of the FOV of the sample. 23. The method of claim 21, wherein the predetermined voltage signal varies based on a location of a probe spot within a portion of the FOV, the probe spot being formed by a primary charged particle beam incident on the sample. 24. A method according to clause 23, in which varying a predetermined voltage signal enables dynamic compensation of off-axis aberrations of the primary charged particle beam in a portion of the FOV of the sample. 25. The method of any one of clauses 20 to 24, wherein the off-axis aberrations include astigmatism or field curvature aberrations of the primary charged particle beam. 26. Applying a second excitation signal to the first primary charged particle beam deflector so that the first primary charged particle beam deflector compensates for the field curvature aberration of the primary charged particle beam; 26. The method of claim 25, further comprising applying a third excitation signal to a second primary charged particle beam deflector different from the first primary charged particle deflector, such that the second primary charged particle beam deflector compensates for astigmatism of the primary charged particle beam. 27. A method according to any one of clauses 20 to 26, wherein a portion of the FOV includes a sub-FOV, and the FOV includes a plurality of sub-FOVs arranged in a two-dimensional array. 28. An apparatus as described in clause 27, wherein each sub-FOV of the plurality of sub-FOVs is scanned by the primary charged particle beam. 29. The method of claim 28, wherein prior to scanning each sub-FOV of the plurality of sub-FOVs, the primary charged particle beam is aligned with the center of each corresponding sub-FOV. 30. The method of any one of clauses 27 to 29, wherein the two-dimensional array comprises a symmetric array of sub-FOVs. 31. The method of any one of clauses 20 to 30, further comprising applying an excitation signal to the first beam separator to compensate for energy dispersion of the primary charged particle beam in a portion of the FOV, the energy dispersion being caused by the second beam separator. 32. The method of claim 31, further comprising compensating for energy dispersion and off-axis chromatic aberration of the primary charged particle beam in a portion of the FOV by applying an excitation signal to the first beam separator. 33. The method of any one of clauses 31 and 32, wherein the first beam separator is positioned upstream of the second beam separator, and the first and second beam separators comprise electromagnetic beam separators. 34. A charged particle beam device comprising: a charged particle source configured to emit charged particles; an aperture plate configured to form a primary charged particle beam along a primary optical axis from the emitted charged particles; a plurality of primary charged particle beam deflectors configured to deflect the primary charged particle beam so as to be incident on the surface of the sample and define a center of a field of view (FOV); A plurality of beam separators; A controller, applying a first excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors to cause the primary charged particle beam to scan a portion of the FOV of the sample; and a controller including circuitry configured to apply a second excitation signal to a first beam separator of the plurality of beam separators such that the first beam separator compensates for off-axis chromatic aberration of the primary charged particle beam in a portion of the FOV. 35. The apparatus described in clause 34, further comprising a second beam separator disposed downstream of the first beam separator, wherein the second excitation signal further compensates for energy dispersion of the primary charged particle beam in a portion of the FOV, the energy dispersion being caused by the second beam separator. 36. The apparatus of claim 35, wherein the first and second beam separators comprise electromagnetic beam separators or Wien filters. 37. An apparatus according to any one of clauses 34 to 36, further comprising a charged particle detector configured to detect secondary charged particles generated from the sample by interaction of the primary charged particle beam with the sample. 38. An apparatus as described in clause 37, wherein the first beam separator is positioned upstream of the charged particle detector. 39. An apparatus according to any one of clauses 37 and 38, wherein the second beam separator is configured to deflect the secondary charged particles for detection by the charged particle detector, allowing the primary charged particle beam to pass undeflected. 40. The apparatus of any one of clauses 34 to 39, wherein the second excitation signal includes a voltage signal and a current signal. 41. The apparatus of any one of clauses 34-40, wherein the second excitation signal comprises a predetermined excitation signal based on simulation from a trained machine learning model. 42. An apparatus described in any one of clauses 34 to 41, wherein the controller includes circuitry further configured to apply a third excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors so that the primary charged particle beam deflector compensates for astigmatism of the primary charged particle beam in a portion of the FOV of the sample. 43. The apparatus of clause 42, wherein the controller includes circuitry further configured to apply a fourth excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors such that the primary charged particle beam deflector compensates for field curvature aberration of the primary charged particle beam in a portion of the FOV of the sample. 44. The apparatus of claim 43, wherein the third and fourth excitation signals comprise predetermined voltage signals. 45. An apparatus according to any one of clauses 34 to 44, wherein the primary charged particle beam deflector of the plurality of primary charged particle beam deflectors comprises an electrostatic beam deflector. 46. ​​A method of imaging a sample using a charged particle beam device, comprising: forming a primary charged particle beam from charged particles emitted by a charged particle source; deflecting the primary charged particle beam with a primary charged particle beam deflector so as to be incident on a surface of the sample and define a center of a field of view (FOV); applying a first excitation signal to a primary charged particle beam deflector to cause the primary charged particle beam to scan a portion of the FOV of the sample; applying a second excitation signal to a first beam separator of the plurality of beam separators such that the first beam separator compensates for off-axis chromatic aberration of the primary charged particle beam in a portion of the FOV. 47. The method of claim 46, further compensating for energy dispersion of the primary charged particle beam in a portion of the FOV by applying a second excitation signal, the energy dispersion being caused by a second beam separator of the plurality of beam separators arranged downstream of the first beam separator. 48. The method of claim 47, wherein the first and second beam separators comprise electromagnetic beam separators or Wien filters. 49. A method according to any one of clauses 46 to 48, further comprising detecting, using a charged particle detector, secondary charged particles generated from a portion of the FOV of the sample by interaction of the primary charged particle beam with the sample. 50. The method of claim 49, wherein the first beam separator is positioned upstream of the charged particle detector. 51. A method according to any one of clauses 48 to 50, further comprising using a second beam separator to deflect the secondary charged particles for detection by a charged particle detector and allowing the primary charged particle beam to pass undeflected. 52. The method of any one of clauses 46-51, wherein applying the second excitation signal includes applying a voltage signal and a current signal. 53. The method of any one of clauses 46-52, wherein the second excitation signal comprises a predetermined excitation signal based on simulation from a trained machine learning model. 54. The method of any one of clauses 46 to 53, further comprising applying a third excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors such that the primary charged particle beam deflector compensates for astigmatism of the primary charged particle beam in a portion of the FOV of the sample. 55. The method of claim 54, further comprising applying a fourth excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors such that the primary charged particle beam deflector compensates for field curvature aberration of the primary charged particle beam in a portion of the FOV of the sample. 56. The method of clause 55, wherein the third and fourth excitation signals comprise predetermined voltage signals. 57. The method of any one of clauses 46 to 56, wherein the primary charged particle beam deflector of the plurality of primary charged particle beam deflectors comprises an electrostatic beam deflector. 58. A method of imaging a sample using a charged particle beam device, comprising: forming a primary charged particle beam from charged particles emitted by a charged particle source of a charged particle beam device; performing a first beam alignment of a primary charged particle beam with a first location within a field of view (FOV) of the sample; performing a second beam alignment of the primary charged particle beam with a second location different from the first location; scanning a first area of ​​the sample with a primary charged particle beam, the first area including a first portion of the FOV that includes the second location; performing a third alignment of the primary charged particle beam after scanning the first area with a third location at least a threshold distance away from the second location; and scanning a second region of the sample with the primary charged particle beam, the second region comprising a second portion of the FOV that includes a third location. 59. The method of claim 58, wherein the first location comprises a center of the FOV of the sample. 60. A method according to any one of clauses 58 and 59, wherein the first region comprises a first sub-FOV and the second region comprises a second sub-FOV of the sample FOV. 61. A method according to any one of clauses 58 to 60, wherein the FOV comprises an array of sub-FOVs, the array comprising a two-dimensional symmetric array. 62. The method of clause 61, wherein the threshold distance comprises a separation distance between the centres of adjacent sub-FOVs in the array. 63. A method according to any one of clauses 58 to 62, wherein the second location comprises a centre of a first sub-FOV and the third location comprises a centre of a second sub-FOV of samples. 64. A charged particle beam device comprising: a charged particle source configured to emit charged particles; an aperture plate configured to form a primary charged particle beam along a primary optical axis from the emitted charged particles; a plurality of primary charged particle beam deflectors configured to deflect the primary charged particle beam so as to be incident on the surface of the sample; a controller, the controller controlling a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors to: performing a first beam alignment of the primary charged particle beam with a first location within a field of view (FOV) of the sample; performing a second beam alignment of the primary charged particle beam with a second location different from the first location; scanning a first region of the sample with the primary charged particle beam, the first region including a first portion of the FOV that includes the second location; performing a third alignment of the primary charged particle beam with a third location at least a threshold distance away from the second location after scanning the first area; and a controller including circuitry configured to scan a second region of the sample with the primary charged particle beam, the second region including a second portion of the FOV that includes a third location. 65. The apparatus of clause 64, wherein the first location comprises a centre of the FOV of the sample. 66. An apparatus according to any one of clauses 64 and 65, wherein the first region comprises a first sub-FOV and the second region comprises a second sub-FOV of the sample FOV. 67. An apparatus according to any one of clauses 64 to 66, wherein the FOV comprises an array of sub-FOVs, the array comprising a two-dimensional symmetric array. 68. The apparatus of clause 67, wherein the threshold distance comprises a separation distance between the centers of adjacent sub-FOVs in the array. 69. An apparatus according to any one of clauses 64 to 68, wherein the second location comprises a centre of a first sub-FOV and the third location comprises a centre of a second sub-FOV of the sample. 70. An apparatus according to any one of clauses 64 to 69, further comprising a charged particle detector configured to detect secondary charged particles generated from the sample by interaction of the primary charged particle beam with the sample. 71. An apparatus described in any one of clauses 64 to 70, further comprising a first beam separator configured to receive an excitation signal from the controller, the excitation signal being received causing the first beam separator to compensate for off-axis chromatic aberration of the primary charged particle beam in a portion of the FOV being scanned. 72. The apparatus of clause 71, further comprising a second beam separator disposed downstream of the first beam separator and configured to deflect the secondary charged particles for detection by the charged particle detector. 73. The apparatus of claim 72, wherein the first and second beam separators comprise electromagnetic beam separators or Wien filters. 74. An apparatus according to any one of clauses 64 to 73, wherein the plurality of primary charged particle beam deflectors include electrostatic beam deflectors or magnetic deflectors. 75. The controller including the circuit further comprises: applying a first excitation signal to cause the primary charged particle beam deflector to perform a first beam alignment; applying a second excitation signal to cause the primary charged particle beam deflector to perform a second beam alignment; applying a third excitation signal to cause the primary charged particle beam deflector to scan the primary charged particle beam over a first region of the sample; applying a fourth excitation signal to cause the primary charged particle beam deflector to perform a third beam alignment after scanning the first region of the sample; An apparatus described in any one of clauses 64 to 74, configured to apply a fifth excitation signal to cause the primary charged particle beam deflector to scan a second region of the sample with the primary charged particle beam. 76. A non-transitory computer readable medium storing a set of instructions executable by one or more processors of a charged particle beam device to cause the charged particle beam device to perform a method of imaging a sample, the method comprising: activating a charged particle source to emit charged particles and forming a primary charged particle beam from the emitted charged particles; Deflecting a primary charged particle beam so as to be incident on a surface of a sample and define a center of a field of view (FOV); applying a first excitation signal to a primary charged particle beam deflector to cause the primary charged particle beam to scan a portion of the FOV of the sample; and applying a second excitation signal to cause the primary charged particle beam deflector to compensate for off-axis aberrations of the primary charged particle beam in that portion of the FOV. 77. The non-transitory computer-readable medium of clause 76, wherein applying the second excitation signal includes applying a predetermined voltage signal to a primary charged particle beam deflector. 78. The non-transitory computer-readable medium of clause 77, wherein the predetermined voltage signal is constant across a portion of the FOV of the sample. 79. The non-transitory computer-readable medium of clause 77, wherein the predetermined voltage signal varies based on a location of a probe spot within a portion of the FOV, the probe spot being formed by a primary charged particle beam incident on the sample. 80. The non-transitory computer-readable medium of clause 79, wherein varying a predetermined voltage signal enables dynamic compensation of off-axis aberrations of a primary charged particle beam in a portion of a FOV of a sample. 81. A set of instructions executable by one or more processors of a charged particle beam device, the charged particle beam device further comprising: applying a second excitation signal to the first primary charged particle beam deflector to cause the first primary charged particle beam deflector to compensate for the field curvature aberration of the primary charged particle beam; A non-transitory computer readable medium according to any one of clauses 76 to 80, further comprising applying a third excitation signal to a second primary charged particle beam deflector different from the first primary charged particle deflector to cause the second primary charged particle beam deflector to compensate for astigmatism of the primary charged particle beam. 82. A non-transitory computer-readable medium according to any one of clauses 76 to 81, wherein a portion of the FOV includes a sub-FOV, and the FOV includes a plurality of sub-FOVs arranged in a two-dimensional array. 83. The non-transitory computer-readable medium of claim 82, wherein each sub-FOV of the plurality of sub-FOVs is scanned by the primary charged particle beam. 84. The non-transitory computer-readable medium of clause 83, wherein prior to scanning each sub-FOV of the plurality of sub-FOVs, the primary charged particle beam is aligned with a center of each corresponding sub-FOV. 85. The non-transitory computer-readable medium of any one of clauses 82-84, wherein the two-dimensional array includes a symmetric array of sub-FOVs. 86. A non-transitory computer-readable medium according to any one of clauses 76 to 85, wherein the set of instructions executable by one or more processors of the charged particle beam device further causes the charged particle beam device to apply an excitation signal to the first beam separator to compensate for energy dispersion of the primary charged particle beam in a portion of the FOV, the energy dispersion caused by the second beam separator. 87. The non-transitory computer-readable medium of claim 86, wherein the excitation signal is applied to the first beam separator to compensate for energy dispersion and off-axis chromatic aberration of the primary charged particle beam in a portion of the FOV. 88. The non-transitory computer-readable medium of any one of clauses 86 and 87, wherein the first beam separator is positioned upstream of the second beam separator, and the first and second beam separators include electromagnetic beam separators. 89. A non-transitory computer readable medium storing a set of instructions executable by one or more processors of a charged particle beam device to cause the charged particle beam device to perform a method of imaging a sample, the method comprising: activating a charged particle source to emit charged particles and forming a primary charged particle beam from the emitted charged particles; Deflecting a primary charged particle beam so as to be incident on a surface of a sample and define a center of a field of view (FOV); applying a first excitation signal to a primary charged particle beam deflector to cause the primary charged particle beam to scan a portion of the FOV of the sample; and applying a second excitation signal to a first beam separator of the plurality of beam separators such that the first beam separator compensates for off-axis chromatic aberration of the primary charged particle beam in a portion of the FOV. 90. A non-transitory computer readable medium storing a set of instructions executable by one or more processors of a charged particle beam device to cause the charged particle beam device to perform a method of imaging a sample, the method comprising: activating a charged particle source to emit charged particles and forming a primary charged particle beam from the emitted charged particles; performing a first beam alignment of a primary charged particle beam with a first location within a field of view (FOV) of the sample; performing a second beam alignment of the primary charged particle beam with a second location different from the first location; scanning a first area of ​​the sample with a primary charged particle beam, the first area including a first portion of the FOV that includes the second location; performing a third beam alignment of the primary charged particle beam with a third location at least a threshold distance away from the second location after scanning the first area; scanning a second region of the sample with the primary charged particle beam, the second region including a second portion of the FOV that includes a third location.

[0104]

[0112] It will be understood that the embodiments of the present disclosure are not limited to the exact structures described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure has been described in conjunction with various embodiments, and other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as merely exemplary, with a true scope and spirit of the invention being indicated by the following claims.

[0105]

[0113] The above description is intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications can be made as described without departing from the scope of the claims set forth below.

Claims

1. 1. A charged particle beam device, comprising: a charged particle source configured to emit charged particles; an aperture plate configured to form a primary charged particle beam along a primary optical axis from the emitted charged particles; a plurality of primary charged particle beam deflectors configured to deflect the primary charged particle beam so as to be incident on a surface of a sample and define a center of a field of view (FOV); A controller, applying a first excitation signal to a primary charged particle beam deflector of the plurality of primary charged particle beam deflectors to cause the primary charged particle beam to scan a portion of the FOV of the sample; and and a controller including circuitry configured to apply a second excitation signal such that the primary charged particle beam deflector compensates for off-axis aberrations of the primary charged particle beam in the portion of the FOV of the sample.

2. The apparatus of claim 1 , wherein the second excitation signal comprises a predetermined voltage signal.

3. The apparatus of claim 2 , wherein the predetermined voltage signal is based on a simulation from a trained machine learning model.

4. The apparatus of claim 2 , wherein the predetermined voltage signal is constant across the portion of the FOV of the sample.

5. 3. The apparatus of claim 2, wherein the predetermined voltage signal varies based on a location of a probe spot within the portion of the FOV, the probe spot being formed by the primary charged particle beam incident on the sample.

6. The apparatus of claim 5 , wherein the varying predetermined voltage signal enables dynamic compensation of the off-axis aberrations of the primary charged particle beam in the portion of the FOV of the sample.

7. The apparatus of claim 1 , wherein the plurality of primary charged particle beam deflectors comprises electrostatic beam deflectors or magnetic deflectors.

8. The apparatus of claim 1 , wherein the portion of the FOV includes a sub-FOV, and the FOV includes a plurality of sub-FOVs arranged in a two-dimensional array.

9. The apparatus of claim 8 , wherein each sub-FOV of the plurality of sub-FOVs is scanned by the primary charged particle beam.

10. The apparatus of claim 9 , wherein prior to scanning each sub-FOV of the plurality of sub-FOVs, the primary charged particle beam is aligned with a center of each corresponding sub-FOV.

11. The apparatus of claim 8 , wherein the two-dimensional array comprises a sub-FOV symmetric array.

12. 10. The apparatus of claim 8, wherein the controller comprises circuitry further configured to apply the second excitation signal to compensate for the off-axis aberrations of the primary charged particle beam while the primary charged particle beam deflector is scanning a sub-FOV of the plurality of sub-FOVs.

13. 10. The apparatus of claim 8, wherein the controller comprises circuitry further configured to apply the second excitation signal multiple times during scanning of the sub-FOV to compensate for the off-axis aberrations of the primary charged particle beam while the primary charged particle beam deflector is scanning the sub-FOV of the plurality of sub-FOVs.

14. The apparatus of claim 1 , wherein the off-axis aberrations include astigmatism or field curvature aberrations of the primary charged particle beam.

15. 1. A non-transitory computer readable medium storing a set of instructions executable by one or more processors of a charged particle beam device to cause the charged particle beam device to perform a method of imaging a sample, the method comprising: activating a charged particle source to emit charged particles and forming a primary charged particle beam from the emitted charged particles; Deflecting the primary charged particle beam so that it is incident on a surface of the sample to define a center of a field of view (FOV); applying a first excitation signal to a primary charged particle beam deflector such that the primary charged particle beam scans a portion of the FOV of the sample; and applying a second excitation signal such that the primary charged particle beam deflector compensates for off-axis aberrations of the primary charged particle beam in the portion of the FOV.

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