Charged Particle Beam Apparatus and Method Thereof Having High-Speed Focus Correction Function

Abstract

A system and method for imaging a sample using a charged particle beam device are disclosed. The device may include a charged particle source configured to emit charged particles, wherein the emitted charged particles form a primary charged particle beam along a primary optical axis; an objective lens including a magnetic lens; a charged particle detector disposed downstream of the objective lens with respect to the path of the primary charged particle beam and disposed along a horizontal plane substantially perpendicular to the primary optical axis; and a voltage control plate disposed between the charged particle detector and a magnetic pole piece of the magnetic lens. The voltage control plate may include a horizontal portion including an aperture and an elongated portion extending downward from the aperture into a hole of the charged particle detector with respect to the path of the primary charged particle beam.

Description

Technical Field

[0001] Cross - reference to Related Applications

[0001] This application claims priority to U.S. Patent Application No. 63 / 351,273, filed on June 10, 2022, which is hereby incorporated by reference in its entirety.

[0002]

[0002] Embodiments provided herein disclose a charged particle beam apparatus, and more specifically, an electron beam inspection apparatus with a high - speed focus adjustment function for imaging a three - dimensional (3D) structure on a substrate.

Background Art

[0003]

[0003] In the manufacturing process of integrated circuits (ICs), incomplete or completed circuit components are inspected to ensure that they are manufactured as designed and are defect - free. Inspection systems using charged particle (e.g., electron) beam microscopes or optical microscopes, such as a scanning electron microscope (SEM), may be used. As the complexity of device architectures increases, accurate inspection of 3D structures has become more important. A high - landing - energy beam may be used to image high - aspect - ratio structures, and the focus of such a high - energy beam may be adjusted between the top and bottom surfaces of the 3D structure. However, the focus adjustment technology may interfere with signal detection or signal collection by a charged particle detector (e.g., a backscattered electron detector).

Summary of the Invention

[0004]

[0004] One aspect of the present disclosure relates to a charged particle beam apparatus for imaging a sample. The charged particle beam apparatus may include a charged particle source configured to emit charged particles, and the emitted charged particles form a primary charged particle beam along a primary optical axis. The apparatus may further include an objective lens including a magnetic lens, a charged particle detector disposed downstream of the objective lens with respect to the path of the primary charged particle beam and disposed along a horizontal plane substantially perpendicular to the primary optical axis, and a voltage control plate disposed between the charged particle detector and the magnetic pole piece of the magnetic lens. The voltage control plate may include a horizontal portion including an opening and an elongated portion extending downward from the opening into the hole of the charged particle detector with respect to the path of the primary charged particle beam.

[0005]

[0005] Another aspect of the present disclosure relates to a method for imaging a sample using a charged particle beam apparatus. The method may include forming a primary charged particle beam from charged particles emitted by a charged particle source, detecting signal electrons generated from the sample by an interaction between the primary charged particle beam and the sample using a charged particle detector, and adjusting an electrical signal applied to a voltage control plate. The voltage control plate may include a horizontal portion including an opening and an elongated portion extending downward from the opening into the hole of the charged particle detector with respect to the path of the primary charged particle beam.

[0006]

[0006] 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 a charged particle beam apparatus to cause the charged particle beam apparatus to perform a method. The method may include forming a primary charged particle beam from charged particles emitted by a charged particle source, detecting signal electrons generated from the sample by an interaction between the primary charged particle beam and the sample using a charged particle detector, and adjusting an electrical signal applied to a voltage control plate. The voltage control plate may include a horizontal portion including an opening and an elongated portion extending downward from the opening into the hole of the charged particle detector with respect to the path of the primary charged particle beam.

[0007]

[0007] Another aspect of the present disclosure relates to an electro-optical assembly. The electro-optical assembly may include an objective lens including a magnetic lens, a charged particle detector disposed downstream of the objective lens with respect to the path of a primary charged particle beam and disposed along a horizontal plane substantially perpendicular to the primary optical axis, and a voltage control plate disposed between the charged particle detector and the magnetic pole piece of the magnetic lens. The voltage control plate may include a horizontal portion including an opening and an elongated portion extending downward from the opening into the hole of the charged particle detector with respect to the path of the primary charged particle beam, and the opening and the elongated portion form a cavity configured to allow the primary charged particle beam to pass through.

[0008]

[0008] Another aspect of the present disclosure relates to a plate insertable between a charged particle detector and a magnetic pole piece of an objective lens of a charged particle beam apparatus. The plate may include a horizontal portion including an opening and an elongated portion extending downward from the opening into the hole of the charged particle detector with respect to the path of the primary charged particle beam, and the opening and the elongated portion form a cavity configured to allow the primary charged particle beam to pass through.

[0009]

[0009] Other advantages of the embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings. In the following description, specific embodiments of the invention are described by way of illustration and example.

Brief Description of the Drawings

[0010]

Figure 1

[0010] It is a schematic diagram showing an exemplary electron beam inspection (EBI) system consistent with an embodiment of the present disclosure.

Figure 2

[0011] It is a schematic diagram showing an exemplary electron beam tool that may be part of the exemplary electron beam inspection system of FIG. 1 consistent with an embodiment of the present disclosure.

Figure 3

[0012] Schematic diagram of an exemplary charged particle beam apparatus equipped with a charged particle detector, which is consistent with embodiments of the present disclosure.

Figure 4

[0013] Schematic diagram showing a part of an exemplary charged particle beam apparatus equipped with a voltage control plate, which is consistent with embodiments of the present disclosure.

Figure 5

[0014] Schematic diagram showing a part of an exemplary charged particle beam apparatus equipped with a voltage control plate, which is consistent with embodiments of the present disclosure.

Figure 6A

[0015] Schematic top view of an exemplary voltage control plate, which is consistent with embodiments of the present disclosure.

Figure 6B

[0016] Schematic cross-sectional view along axis A-A' (shown in FIG. 6A) of an exemplary voltage control plate, which is consistent with embodiments of the present disclosure.

Figure 6C

[0016] Schematic cross-sectional view along axis A-A' (shown in FIG. 6A) of an exemplary voltage control plate, which is consistent with embodiments of the present disclosure.

Figure 7

[0017] Process flowchart representing an exemplary method of imaging a sample using a charged particle beam with a high landing energy in the charged particle beam apparatus of FIG. 4 or FIG. 5, which is consistent with embodiments of the present disclosure.

Embodiments for Carrying Out the Invention

[0011]

[0018] Here, exemplary embodiments are referred to in detail, and the examples are shown in the accompanying drawings. The following description refers to the accompanying drawings, and unless otherwise stated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following description of the exemplary embodiments do not represent all implementations. Instead, they are merely examples of apparatuses and methods that conform to aspects related to the disclosed embodiments, as described in the appended claims. For example, some embodiments are described in relation to the use of electron beams, but the present disclosure is not so limited. Other types of charged particle beams can be applied as well. Moreover, other imaging systems such as optical imaging, photographic detection, X-ray detection, etc. can be used.

[0012]

[0019] An electronic device is constructed of 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 sizes of these circuits have decreased dramatically, and as a result, even more circuits can be fitted onto the substrate. For example, the IC chip of a smartphone is about the size of a fingernail, yet it can contain over two billion transistors, and the size of each transistor is less than 1 / 1000 the size of a human hair.

[0013]

[0020] The creation of these extremely small ICs is a complex and expensive process that requires a great deal of time and often involves hundreds of individual steps. Even an error in one step can result in a defect in the completed IC, rendering the completed IC useless. Therefore, one of the goals of the manufacturing process is to avoid such defects in order to maximize the number of functional ICs created by the process, i.e., to improve the overall yield of the process.

[0014]

[0021] One factor in improving yield is to monitor the chip fabrication process to ensure that a sufficient number of functional integrated circuits are produced. One way to monitor the process is to inspect the chip circuit structure at various stages of its formation. The inspection can be performed using a scanning electron microscope (SEM). The SEM can be used to image these extremely small structures and actually take a "picture" of the structure. The image can be used to determine whether the structure was correctly formed and whether the structure was formed in the correct location. If there are defects in the structure, the process can be adjusted to reduce the likelihood of the defects recurring.

[0015]

[0022] In existing inspection systems such as SEMs, 3D structures such as high aspect ratio (HAR) contact holes may be imaged using an electron beam with a particularly high landing energy. For a given set of conditions, a higher landing energy of the incident electrons results in an increased interaction volume with the sample and can generate more backscattered electrons, which can provide information related to features below the surface within the sample. However, it can be difficult to focus an electron beam with a high landing energy to form high-resolution images of the top and bottom surfaces of such structures while maintaining measurement accuracy and throughput.

[0016]

[0023] In a complex device architecture such as a 3D-NAND device, 3D structures that can have a depth of several micrometers (μm) may be inspected or measured using a beam with a high landing energy. The interaction volume, and thus the backscattered signal electron intensity, may increase by using an electron beam with a high landing energy. However, when adjusting the focal length of an electron beam with a high landing energy to image the top and bottom surfaces of a 3D structure, the inspection process may become significantly longer compared to the inspection of a two-dimensional planar structure. In some cases, although the focus of an electron beam with a high landing energy can be adjusted or corrected by applying a voltage signal to an electrostatic lens, the amount of adjustment of the focal length per unit voltage applied may be undesirably small. In other words, a very large voltage signal may be applied to slightly adjust the focal length of a beam with a high landing energy. Applying a large voltage signal to an electrostatic lens can, among other things, adversely affect the detection efficiency of a backscattered electron detector, thereby affecting the inspection throughput.

[0017]

[0024] As one of the methods for achieving focus adjustment for imaging a 3D structure, there is an example of using an electron detector simultaneously as an electrode to adjust the electrostatic field in the vicinity of the sample, thereby adjusting the focal distance of the primary electron beam. However, such a configuration may have several drawbacks. For example, the voltage signal applied to the electron detector to adjust the electrostatic field may change the landing energy of the backscattered electrons that were originally supposed to be detected. When the voltage applied to the electron detector changes, it may further affect, for example, the photon emission intensity of the scintillator, thereby generating a low-quality image and leading to inaccurate inspection and measurement of the imaged structure. Furthermore, in such a configuration, the charge or contaminants accumulated on the inner surface of the central hole of the backscattered electron detector may affect the rotational symmetry and smoothness, and higher-order electric fields such as quadrupole fields may be induced. The higher-order electric fields may interfere with the electrostatic field experienced by the primary electron beam and may adversely affect the size or shape of the probe spot. Although the inner surface of the backscattered electron detector may be cleaned, it may be difficult to polish the inner surface to maintain smoothness. In contrast, the voltage control plate can be configured to provide a better inner surface, for example, by reprocessing, polishing, or cleaning its inner surface. The charge or contaminants accumulated on the inner surface of the central hole of the backscattered electron detector may affect the rotational symmetry and smoothness, and higher-order electric fields such as quadrupole fields may be induced. The higher-order electric fields may interfere with the electrostatic field experienced by the primary electron beam and may adversely affect the size or shape of the probe spot. The ability to clean or polish the inner surface of the voltage control plate enables maintaining the ellipticity of the inner surface in addition to a smooth surface, thereby making it possible to reliably obtain high-quality images while maintaining throughput. The voltage control plate may be an insertable plate made of a conductive material such as metal or a non-magnetic material. Therefore, although the dual function of the electron detector may have the potential to improve inspection throughput, the quality of the generated image may be affected, and the inspection system may become insufficient.Therefore, it may be desirable to perform focus correction of a high landing energy electron beam while maintaining the resolution and throughput of the SEM and the electron detection ability of the detector to inspect the top and bottom surfaces of the 3D structure.

[0018]

[0025] Some embodiments of the present disclosure relate to an apparatus and method for imaging a sample with a high landing energy charged particle beam. The apparatus may include a voltage control plate disposed between a backscattered electron detector and a magnetic pole piece of a magnetic lens of a compound objective lens. The voltage control plate may include a horizontal portion having an aperture and an elongated portion extending downward from the aperture into a central hole of the backscattered electron detector. The voltage control plate may include a cavity formed by the inner surfaces of the aperture and the elongated portion. The voltage control plate may be configured to receive a voltage signal that, when applied or adjusted, affects the electrostatic field experienced by the primary electron beam passing through the cavity, thereby adjusting the focal length of the primary electron beam that will be incident on the sample. The focal length of the primary electron beam can be adjusted using the voltage control plate without interfering with the backscattered collection efficiency, and thus high imaging quality can be obtained while maintaining the accuracy and throughput of inspection and measurement.

[0019]

[0026] In the drawings, the relative dimensions of components may be enlarged for clarity. In the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and only the differences with respect to individual embodiments are described. As used herein, unless otherwise specifically stated, the term "or" includes all possible combinations, except where the combination is not feasible. For example, if it is described that a component may include A or B, then unless otherwise specifically stated or infeasible, the component may include A or B or both A and B. As a second example, if it is described that a component may include A, B, or C, then unless otherwise specifically stated or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A, B, and C.

[0020]

[0027] Referring now to FIG. 1, FIG. 1 illustrates an exemplary electron beam inspection (EBI) system 100 that is consistent with an embodiment of the present disclosure. As shown in FIG. 1, the charged particle beam inspection system 100 includes a main chamber 10, a load lock chamber 20, an electron beam tool 40, and an equipment front end module (EFEM) 30. The electron beam tool 40 is located within the main chamber 10. It should be understood that although the description and drawings are directed to electron beams, the embodiments are not used to limit the present disclosure to specific charged particles.

[0021]

[0028] 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 a wafer front opening unified pod (FOUP) that contains a wafer to be inspected (e.g., a semiconductor wafer or a wafer made of other materials) or a sample (hereinafter, wafers and samples are collectively referred to as "wafers"). One or more robot arms (not shown) of the EFEM 30 transfer the wafer to the load lock chamber 20.

[0022]

[0029] The loading / lock chamber 20 is connected to a loading / lock vacuum pump system (not shown), and the loading / lock vacuum pump system removes gas molecules in the loading / lock chamber 20 so as to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transfer the wafer from the loading / lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pump system (not shown), and the main chamber vacuum pump system removes gas molecules in the main chamber 10 so as to reach a second pressure below the first pressure. After reaching the second pressure, 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.

[0023]

[0030] The controller 50 can be electronically connected to the electron beam tool 40 and can also be electronically connected to other components. The controller 50 can be a computer configured to perform various controls of the charged particle beam inspection system 100. The controller 50 may also include a processing circuit configured to perform various signal and image processing functions. In FIG. 1, the controller 50 is shown as being external to the structure including the main chamber 10, the loading / lock chamber 20, and the EFEM 30, but it is understood that the controller 50 can also be a part of the structure.

[0024]

[0031] The present disclosure provides an example of the main chamber 10 that houses the electron beam inspection system, but it should be noted that the aspects of the present disclosure are not limited to the chamber that houses the electron beam inspection system in a broad sense. Rather, it is understood that the foregoing principles can also be applied to other chambers.

[0025]

[0032] Referring now to FIG. 2, FIG. 2 shows a schematic diagram illustrating an exemplary configuration of an electron beam tool 40 that can be part of the exemplary charged particle beam inspection system 100 of the present disclosure that is consistent with an embodiment of the present disclosure. The electron beam tool 40 (also referred to herein as apparatus 40) can include an electron emitter that can include a cathode 203, an extraction electrode 205, a gun aperture 220, and an anode 222. The electron beam tool 40 can 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 can 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 related components can be added or omitted as necessary.

[0026]

[0033] In some embodiments, the electron emitter can include a cathode 203 and an anode 222, and primary electrons can be emitted from the cathode, extracted or accelerated, and form a primary electron beam 204 that forms a primary beam crossover 202. The primary electron beam 204 can be visualized as being emitted from the primary beam crossover 202.

[0027]

[0034] In some embodiments, the electron emitter, the condenser lens 226, the objective lens assembly 232, the beam limiting aperture array 235, and the electron detector 244 can be aligned with the primary optical axis 201 of the apparatus 40. In some embodiments, the electron detector 244 can be disposed off the primary optical axis 201 along a secondary optical axis (not shown).

[0028]

[0035] Depending on the embodiment, the objective lens assembly 232 may include a modified swing objective retarding immersion lens (SORIL), which includes a magnetic 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 general imaging process, the primary electron beam 204 emitted from the tip of the cathode 203 is accelerated by the acceleration voltage applied to the anode 222. A part of the primary electron beam 204 passes through the apertures of the gun aperture 220 and the Coulomb aperture array 224, and is focused by the condenser lens 226 so as to completely or partially pass through the aperture of the beam limiting aperture array 235. The electrons passing through the aperture of the beam limiting aperture array 235 are focused by the modified SORIL lens to form a probe spot on the surface of the sample 250, and may be 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.

[0029]

[0036] In the objective lens assembly 232, the excitation coil 232d and the pole piece 232a may generate a magnetic field. A part of the sample 250 scanned by the primary electron beam 204 is immersed in this magnetic field and may be electrically charged, and then an electric field is generated thereby. This electric field may reduce the energy of the colliding primary electron beam 204 on or near the surface of the sample 250. The control electrode 232b is electrically insulated from the pole piece 232a and controls, for example, the electric field on and above the sample 250 to reduce the aberration of the objective lens assembly 232, control the focusing situation of the signal electron beam to increase the detection efficiency, or avoid an arc discharge to protect the sample. One or more deflectors of the beam manipulator assembly can deflect the primary electron beam 204 to facilitate beam scanning on the sample 250. For example, in the scanning process, the deflectors 240a, 240b, 240d, and 240e are controlled to deflect the primary electron beam 204 to different positions on the upper surface of the sample 250 at different times to provide data for reconstructing images of different parts of the sample 250. Note that in different embodiments, the order of 240a to 240e may be different.

[0030]

[0037] Backscattered electrons (BSE) and secondary electrons (SE) may be emitted from a portion of the sample 250 when receiving the primary electron beam 204. The beam separator can direct a secondary or scattered electron beam, including backscattered electrons and secondary electrons, towards the sensor surface of the electron detector 244. The detected secondary electron beam can form a corresponding beam spot on the sensor surface of the electron detector 244. The electron detector 244 can generate a signal (e.g., voltage, current) representing the intensity of the received secondary electron beam spot and provide the signal to a processing system such as the controller 50. The secondary electron beam or backscattered electron beam and the intensity of the resulting secondary electron beam spot can vary depending on the external or internal structure of the sample 250. Also, as discussed above, the primary electron beam 204 can be deflected to different positions on the upper 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 position of the sample 250, the processing system can reconstruct an image reflecting the internal or external structure of the wafer sample 250.

[0031]

[0038] In some embodiments, the controller 50 may include an image processing system, which may include an image acquirer (not shown) and a 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 a combination thereof. The image acquirer can be communicatively coupled to the electronic detector 244 of the device 40 through media such as, among other things, a conductor, an optical fiber cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, a wireless radio or a combination thereof. In some embodiments, the image acquirer can receive a signal from the electronic detector 244 and construct an image. Accordingly, the image acquirer can acquire an image of the area of the sample 250. The image acquirer can also perform various post-processing functions such as contour generation, superimposing an indicator on the acquired image and the like. The image acquirer can be configured to perform adjustments such as brightness and contrast of the acquired image. In some embodiments, the storage can 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 can be coupled to the image acquirer and used to store the scanned raw image data as the original image and to store the post-processed image.

[0032]

[0039] In some embodiments, the controller 50 may include a measurement circuit (e.g., an analog / digital converter) to obtain the detected distributions of secondary electrons and backscattered electrons. The electron distribution data collected during the detection time window can be combined with the corresponding scanning path data of the primary beam 204 incident on the surface of the sample (e.g., wafer) and used to reconstruct an image of the wafer structure being inspected. The reconstructed image can be used to reveal various features of the internal or external structure of the sample 250, and thus can be used to reveal any defects that may be present in the wafer.

[0033]

[0040] 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 continuously move the sample 250 in a certain direction at a constant speed. In other embodiments, the controller 50 can cause the motorized stage 234 to be able to change the speed at which the sample 250 moves over time according to the steps of the scanning process.

[0034]

[0041] Referring now to FIG. 3, this figure shows a schematic diagram of an exemplary charged particle beam apparatus 300 (also referred to as apparatus 300) that is consistent with embodiments of the present disclosure. The apparatus 300 may include a charged particle source such as an electron source configured to emit primary electrons from a cathode 301, extract them using an extractor electrode 302, and form a primary electron beam 300B1 along a primary optical axis 300-1. The apparatus 300 may further include an anode 303, a condenser lens 304, a beam limiting aperture array 305, signal electron detectors 306 and 313, a composite objective lens 307, a scanning deflection unit including primary electron beam deflectors 308, 309, 310, and 311, and a control electrode 314. In some embodiments, the signal electron detector 313 may be a backscattered electron detector, and the signal electron detector 306 may be a secondary electron detector. It should be understood that the associated components may be added, omitted, or rearranged as appropriate.

[0035]

[0042] The electron source (not shown) may include a thermionic source configured to emit electrons when supplied with thermal energy to overcome the work function of this radiation source, a field emission source configured to emit electrons when exposed to a large electrostatic field, and the like. In the case of a field emission source, the electron source may be electrically connected to a controller such as the controller 50 of FIG. 2, which is a controller configured to apply and adjust a voltage signal, particularly based on a desired landing energy, sample analysis, and radiation source characteristics. The extractor electrode 302 may be configured to extract or accelerate electrons emitted, for example, from a field emission gun to form a primary electron beam 300B1 that forms a virtual or actual primary beam crossover (not shown) along the primary optical axis 300-1. The primary electron beam 300B1 may appear to be emitted from the primary beam crossover. In some embodiments, the controller 50 may be configured to apply and adjust a voltage signal to the extractor electrode 302 to extract or accelerate electrons generated from the electron source. The amplitude of the voltage signal applied to the extractor electrode 302 may be different from the amplitude of the voltage signal applied to the cathode 301. In some embodiments, the difference between the amplitude of the voltage signal applied to the extractor electrode 302 and the amplitude of the voltage signal applied to the cathode 301 may be configured to accelerate electrons in the downstream direction along the primary optical axis 300-1 while maintaining the stability of the electron source. As used in the context of the present disclosure, "downstream" refers to the direction along the path of the primary electron beam 300B1 starting from the electron source and towards the sample 315. With respect to the positioning of the elements of a charged particle beam device (e.g., the device 300 of FIG. 3), "downstream" may refer to the position of one element being arranged under or behind another element along the path of the primary electron beam starting from the electron source, and "immediately downstream" refers to the position of the second element being under or behind the first element along the path of the primary electron beam 300B1 such that no other active elements are present between the first and second elements. For example, as shown in FIG. 3, the signal electron detector 306 may be positioned immediately downstream of the beam limiting aperture array 305 such that no other optical or electro-optical elements are arranged between the beam limiting aperture array 305 and the electron detector 306.As used in connection with the present disclosure, "upstream" may refer to the position of an element being disposed above or in front of another element along the path of a primary electron beam starting from an electron source, and "immediately upstream" refers to the position of a second element being above or in front of a first element along the path of the primary electron beam 300B1 such that no other active element exists between the first element and the second element. As used herein, an "active element" may refer to any element or component that, by its presence, may change an electrostatic or electromagnetic field between a first element and a second element by generating an electric, magnetic, or electromagnetic field.

[0036]

[0043] Apparatus 300 may include a condenser lens 304 configured to receive a portion or a substantial portion of the primary electron beam 300B1 and focus the primary electron beam 300B1 onto a beam-limiting aperture array 305. The condenser lens 304 may be substantially similar to the condenser lens 226 of FIG. 2 and may perform substantially similar functions. Although shown as a magnetic lens in FIG. 3, the condenser lens 304 may be, among other things, an electrostatic lens, a magnetic lens, an electromagnetic lens, a composite electromagnetic lens. The condenser lens 304 may be electrically coupled to a controller 50 as shown in FIG. 2. The controller 50 may apply an electrical excitation signal to the condenser lens 304 to adjust the focusing power of the condenser lens 304 based on factors including, but not limited to, the operating mode, the application, the desired analysis, the material of the sample being inspected.

[0037]

[0044] The apparatus 300 may further include a beam limiting aperture array 305 configured to limit the beam current of the primary electron beam 300B1 passing through one of the plurality of beam limiting apertures of the beam limiting aperture array 305. Although only one beam limiting aperture is shown in FIG. 3, the beam limiting aperture array 305 may include any number of apertures having a uniform or non-uniform aperture size, cross-section, or pitch. In some embodiments, the beam limiting aperture array 305 may be disposed substantially perpendicular to the primary optical axis 300-1 downstream of the condenser lens 304 or (as shown in FIG. 3) immediately downstream of the condenser lens 304. In some embodiments, the beam limiting aperture array 305 may be configured as a conductive structure with a plurality of beam limiting apertures. The beam limiting aperture array 305 may be electrically connected to the controller 50 via a connector (not shown), and the controller 50 may be configured to instruct supplying a certain voltage to the beam limiting aperture array 305. The voltage supplied may be a reference voltage such as, for example, a ground potential. The controller 50 may also be configured to maintain or adjust the supplied voltage. The controller 50 may be configured to adjust the position of the beam limiting aperture array 305.

[0038]

[0045] Apparatus 300 may include one or more signal electron detectors 306 and 313. Signal electrons may be generated by the interaction of primary charged particles, such as electrons of the primary electron beam 300B1, with the surface of the sample 315. The signal electrons may include, among other things, secondary electrons, backscattered electrons, or Auger electrons. The signal electron detectors 306 and 313 may be configured to detect substantially all secondary electrons and a portion of the backscattered electrons, based at least in part on the emission energy or emission angle. In some embodiments, the signal electron detectors 306 and 313 may be configured to detect secondary electrons, backscattered electrons, or Auger electrons. The signal electron detector 313 may be disposed downstream of the signal electron detector 306. In some embodiments, the signal electron detector 313 may be disposed downstream of the objective lens 307. The secondary electron beam 300B4 may include signal electrons having a low emission energy (typically 50 eV or less), and the backscattered electron beam 300B2 may include signal electrons having a high emission energy (typically greater than 50 eV). In some embodiments, 300B4 may include secondary electrons, low-energy backscattered electrons, or high-energy backscattered electrons. Although not shown, it should be understood that a portion of the backscattered electrons may be detected by the signal electron detector 306, and a portion of the secondary electrons may be detected by the signal electron detector 313. For the inspection of 3D structures, such as deep holes, trenches, or contact holes, a primary electron beam with a high landing energy may be used, which generates signal electrons with a high emission energy. The signal electron detector 313 may be used to detect a portion of the signal electrons with a high emission energy, such as backscattered electrons.

[0039]

[0046] The apparatus 300 may further include a composite objective lens 307 configured to focus the primary electron beam 300B1 onto the surface of the sample 315. The controller 50 may apply an electrical excitation signal to the coil 307C of the composite objective lens 307 to adjust the focusing power of the composite objective lens 307 based on factors including, but not limited to, the primary beam energy, the application, the desired analysis, and the material of the sample being inspected. The composite objective lens 307 may be further configured to focus signal electrons, such as secondary electrons or backscattered electrons, onto the detection surface of a signal electron detector (e.g., signal electron detector 306 or 313). The composite objective lens 307 may be substantially similar to the objective lens assembly 232 of FIG. 2 and may perform substantially the same functions. In some embodiments, the composite objective lens 307 may include an electromagnetic lens including a magnetic lens 307M, and an electrostatic lens 307ES formed by the control electrode 314, the pole piece 307P, and the sample 315.

[0040]

[0047] As used herein, a composite objective lens is an objective lens that generates overlapping magnetic and electrostatic fields in the vicinity of a sample to focus a primary electron beam. In the present disclosure, the condenser lens 304 may also be a magnetic lens, but references to magnetic lenses such as 307M refer to objective magnetic lenses, and references to electrostatic lenses such as 307ES refer to objective electrostatic lenses. As shown in FIG. 3, the magnetic lens 307M and the electrostatic lens 307ES may, for example, cooperate to focus the primary electron beam 300B1 onto the sample 315 to form the composite objective lens 307. The lens body and coil 307C of the magnetic lens 307M may generate a magnetic field, while an electrostatic field may be generated, for example, by generating a potential difference between the sample 315 and the pole piece 307P. In some embodiments, the control electrode 314, or other electrodes disposed between the pole piece 307P and the sample 315, may also be part of the electrostatic lens 307ES.

[0041]

[0048] As disclosed in this specification, a magnetic pole piece of a magnetic lens (e.g., magnetic lens 307M) is a piece of magnetic material near the magnetic pole of the magnetic lens, while a magnetic pole is an end of the magnetic material where the external magnetic field is strongest. As shown in FIG. 3, apparatus 300 includes magnetic pole pieces 307P and 307O. As an example, magnetic pole piece 307P may be a piece of magnetic material near the N pole of magnetic lens 307M, and magnetic pole piece 307O may be a piece of magnetic material near the S pole of magnetic lens 307M. When the direction of the current in magnetic lens coil 307C changes, the polarity of the magnetic pole may also change. In the context of the present disclosure, the positioning of an electron detector (e.g., signal electron detector 313 in FIG. 3, or signal electron detector 413 in FIG. 4), a beam deflector (e.g., beam deflectors 308 - 311 in FIG. 3), and an electrode (e.g., control electrode 314 in FIG. 3) may be described with reference to the position of magnetic pole piece 307P disposed closest to the point where primary optical axis 300-1 intersects sample 315. The magnetic pole piece 307P of magnetic lens 307M may include a magnetic pole made of a soft magnetic material such as an electromagnet that substantially focuses the magnetic field inside the cavity of magnetic lens 307M. Magnetic pole pieces 307P and 307O may be, for example, high-resolution magnetic pole pieces, multi-purpose magnetic pole pieces, or high-contrast magnetic pole pieces.

[0042]

[0049] As shown in FIG. 3, the pole piece 307P may include an opening 307R configured such that the primary electron beam 300B1 can pass through it and signal electrons can reach the signal electron detector 306. The opening 307R of the pole piece 307P may have a circular cross-section, be substantially circular, or be non-circular. In some embodiments, the geometric center of the opening 307R of the pole piece 307P may be aligned with the primary optical axis 300-1. In some embodiments, as shown in FIG. 3, the pole piece 307P may be the most downstream horizontal portion of the magnetic lens 307M and may be substantially perpendicular to the primary optical axis 300-1. The pole pieces (e.g., 307P and 307O) are one of the prominent features of the magnetic lens compared to the electrostatic lens. Since the pole piece is a magnetic component adjacent to the pole of the magnetic lens, and since the electrostatic lens does not generate a magnetic field, the electrostatic lens does not have a pole piece.

[0043]

[0050] The apparatus 300 may further include a scanning deflection unit having primary electron beam deflectors 308, 309, 310, and 311 configured to dynamically deflect the primary electron beam 300B1 on the surface of the sample 315. In some embodiments, the scanning deflection unit having primary electron beam deflectors 308, 309, 310, and 311 may be referred to as a beam manipulator or a beam manipulator assembly. By dynamically deflecting the primary electron beam 300B1, a desired area or a desired region of interest of the sample 315 may be scanned, for example, in a raster scan pattern, to generate SE and BSE for sample inspection. One or more of the primary electron beam deflectors 308, 309, 310, and 311 may be configured to deflect the primary electron beam 300B1 in the X-axis, or the Y-axis, or a combination of the X-axis and the Y-axis. As used herein, the X-axis and the Y-axis form orthogonal coordinates, and the primary electron beam 300B1 propagates along the Z-axis or the primary optical axis 300-1.

[0044]

[0051] As the requirements for the data processing and computing capabilities of electronic devices increase, integrated circuit (IC) chips are required to perform more complex tasks faster and more efficiently. To meet these requirements, an increase in device density (the number of devices per unit area of the wafer) is necessary, which can be achieved, among other strategies, by fabricating 3D structures. 3D structures may be inspected using a charged particle beam with a high landing energy, but the throughput is limited by the speed of adjusting the focus to image the top and bottom surfaces of the 3D structure, and the device may become insufficient for inspection or measurement applications. A backscattered electron detector, which is placed near the sample and configured to detect signal electrons with a high emission energy, may be used as an electrode to control the electrostatic field experienced by the primary electron beam. However, doing so causes the landing energy of the backscattered electrons on the detection surface of the backscattered electron detector to vary, which may adversely affect the gain of the detector or the collection efficiency of the detector. Therefore, in order to obtain a high-resolution image while maintaining the throughput, it may be desirable to control the electrostatic field to adjust the focal length of the electron beam with a high landing energy without affecting the collection efficiency of the backscattered electron detector.

[0045]

[0052] Referring now to FIG. 4, this figure shows a schematic diagram of a portion of an exemplary charged particle beam apparatus 400 (also referred to as apparatus 400) that is consistent with an embodiment of the present disclosure. Compared to apparatus 300, apparatus 400 may additionally include a voltage control plate 420. Apparatus 400 may further include a backscattered electron detector 413 (similar to the signal electron detector 313 of FIG. 3) and a control electrode 414 (similar to the control electrode 314 of FIG. 3).

[0046]

[0053] Backscattered electrons (BSE) (e.g., the signal electrons of beam 400B2) are generated by elastic scattering events of incident electrons from deeper layers beneath the surface, such as the bottom of a deep trench or a high aspect ratio hole, and may have a high emission energy between 50 eV and the incident energy of the primary electron beam. Therefore, in order to obtain high-quality imaging of 3D structures, it may be desirable to maintain a high backscattered electron detection efficiency. In some embodiments, apparatus 400 may include a signal electron detector such as backscattered electron detector 413 disposed between sample 415 and objective lens 407. Backscattered electron detector 413 may be disposed along a plane 413P that is substantially perpendicular to the primary optical axis 400-1. It should be understood that the horizontal plane 413P along which backscattered electron detector 413 extends, represented by the dashed (dotted-dashed) line, is an imaginary plane for purposes of visual aid and explanation only. Plane 413P represents the central plane of backscattered electron detector 413 with respect to the thickness of backscattered electron detector 413 in a direction parallel to the primary optical axis 400-1. In the context of the present disclosure, the term "substantially perpendicular" refers to the positioning of an element such that, even if present, it has an offset to the extent that it can be ignored and does not adversely affect the intended function and expected performance of the element, and is sufficiently perpendicular with an offset. As an example, the substantially perpendicular backscattered electron detector 413 may form an angle of 90° ± 0.05° with respect to the primary optical axis 400-1, and as a result, for example, the orientation of backscattered electron detector 413 may not affect the detection efficiency of the detector. The backscattered electron detector may form an angle between 89.95° and 90.05° with respect to the primary optical axis 400-1 so that the electrostatic field is not affected. A larger offset in the angle between the backscattered electron detector (e.g., backscattered electron detector 413) and the primary optical axis (e.g., primary optical axis 400-1) (e.g., more than ±0.1° from 90°) may generate an additional deflection field, which may shift the primary electron beam and increase the landing angle, adversely affecting the resolution of the generated image.

[0047]

[0054] In some embodiments, the backscattered electron detector 413 may include a central aperture aligned with the primary optical axis 400-1. As shown in FIG. 4, the central aperture of the backscattered electron detector 413 may have an inner diameter d1. In some embodiments, the inner diameter d1 of the backscattered electron detector 413 may be smaller than the diameter of the aperture (e.g., aperture 307R in FIG. 3) of the objective lens 407 (similar to the objective lens 307 in FIG. 3). However, in some embodiments, the inner diameter d1 may be determined based on factors including, but not limited to, the field of view (FOV), the working distance of the device, resolution requirements, mechanical limitations, or physical space constraints.

[0048]

[0055] The apparatus 400 may further include a voltage control plate 420. In some embodiments, the voltage control plate 420 may be a conductive element configured to receive an electrical signal. In some embodiments, the voltage control plate 420 may be made of a non-magnetic material. The voltage control plate 420 may be electrically connected to the voltage control unit 425 or the controller 50 or both. The voltage control unit 425 or the controller 50 may include a circuit configured to apply an electrical signal, such as a voltage signal, to the voltage control plate 420. The voltage control unit 425 or the controller 50 may further include a circuit configured to adjust the applied electrical signal. Adjusting the applied electrical signal may include adjusting the voltage, and as a result, adjusting the electrostatic field experienced by the passing primary electrons, thereby adjusting the focal length of the primary electron beam incident on the surface of the sample 415.

[0049]

[0056] In some embodiments, the voltage control plate 420 may be made using a conductive material such as, among other things, metal. The voltage control plate 420 may be disposed downstream of the pole piece 407P of the objective lens 407 and upstream of the backscattered electron detector 413, with reference to the path of the primary electron beam 400B1 along the primary optical axis 400-1. The voltage control plate 420 may be disposed along a plane that is substantially perpendicular to the primary optical axis 400-1 and substantially parallel to the horizontal plane 413P. It should be understood that the objective lens 407 may be a compound objective lens including a magnetic lens and an electrostatic lens, and that the pole piece (e.g., pole piece 407P) refers to the pole piece of the magnetic lens of the objective lens 407.

[0050]

[0057] FIG. 6A shows a top view of an exemplary voltage control plate 620 similar to the voltage control plate 420. The voltage control plate 620 may include an aperture 622 aligned with the primary optical axis 600-1. As used herein, the term "aligned" refers to the positioning of the voltage control plate 620 such that the geometric center of the aperture 622 coincides with the primary optical axis 600-1. In some embodiments, as shown in FIGS. 4 and 5 (described below), the diameter of the aperture 622 of the voltage control plate 620 may be smaller than the diameter of the hole of the backscattered electron detector 413, but large enough for the primary electron beam 400B1 and the secondary electron beam 400B4 to pass through without being blocked or impeded in the path of the primary or secondary electrons. The voltage control plate 620 may be made from a seamless, one-piece component of a material such as, but not limited to, metal or other conductive materials. For example, the voltage control plate 620 may be made from a single continuous metal sheet, and the aperture 622 may be formed by removing metal from the corresponding location. The aperture 622 may be formed in the horizontal portion 621 by a material removal process including, but not limited to, etching, cutting, drilling, punching, among other material removal techniques. In some embodiments, although not shown, two or more pieces of conductive material may be attached to each other to form a voltage control plate 620 including an aperture 622 having a desired diameter.

[0051]

[0058] FIG. 6B shows a cross-sectional view of the voltage control plate 620 along the axis A-A' (shown in FIG. 6A). As shown in FIG. 6B, the voltage control plate 620 may further include a vertically elongated portion 624 that extends downward from the opening 622 along the primary optical axis 600-1 and extends substantially perpendicular to the horizontal portion 621 of the voltage control plate 620. The elongated portion 624 may be substantially parallel to the primary optical axis 600-1, along which the primary electron beam 600B1 travels toward the sample (e.g., sample 415 of FIG. 4). The traveling direction of the primary electron beam 600B1 is indicated by the solid arrow in FIG. 6B. The elongated portion 624 may have an inner diameter substantially similar to the diameter of the opening 622. The elongated portion 624 may be cylindrical such that the inner diameter is uniform throughout the length L and is approximately the same as the diameter of the opening 622. In such a configuration, the opening 622 and the elongated portion 624 may form a cavity 628 having a diameter substantially the same as the diameter of the opening 622 for the passage of primary electrons and secondary electrons. The cavity 628 may be defined by the space between imaginary planes 625 and 626 that respectively represent the upstream end and the downstream end of the voltage control plate 620. It should be understood that the imaginary planes 625 and 626, represented by dashed lines, are visual aids for illustrative purposes only. The imaginary plane 625 located closer to the objective lens (e.g., objective lens 407 of FIG. 4) may define the upper boundary line of the cavity 628, and the imaginary plane 626 located closer to the sample (e.g., sample 415 of FIG. 4) may define the lower boundary line of the cavity 628 of the voltage control plate 620. As used herein, the "cavity" of the voltage control plate refers to the space defined by the aperture 622 and the elongated portion 624 of the voltage control plate 620 configured to allow the primary electron beam 600B1 to pass through, and this space is rotationally symmetric about the primary optical axis 600-1. The terms "within the cavity of the voltage control plate" or "inside the cavity of the voltage control plate" refer to the space confined within the imaginary planes 625 and 626 and the inner surfaces of the aperture 622 and the elongated portion 624 directly exposed to the primary electron beam 600B1.The imaginary planes 625 and 626 may be substantially perpendicular to the primary optical axis 600-1. FIGS. 4, 5, 6A, 6B, and 6C show a cylindrical cavity, but the cross-section of the cavity 628 may be cylindrical, conical, alternating cylinders, alternating cones, or any suitable cross-section.

[0052]

[0059] As shown in FIG. 6B, the voltage control plate 620 may be formed or fabricated from a single seamless integrated part of a conductive material such that the horizontal portion 621 and the elongated portion 624 form a continuous structure. The voltage control plate 620 may be fabricated such that the inner surface of the opening 622 of the horizontal portion 621 and the inner surface of the elongated portion 624 are substantially aligned with each other.

[0053]

[0060] Alternatively, as shown in FIG. 6C, the horizontal portion 631 and the elongated portion 634 may be joined together to form the voltage control plate 630. In some embodiments, the horizontal portion 631 and the elongated portion 634 may be joined using a joining mechanism such as, but not limited to, welding, gluing, adhesion, brazing, or hardware assembly, or other suitable mechanisms. The voltage control plate 630 may be fabricated, formed, or assembled such that the inner surface of the opening 632 of the horizontal portion 631 and the inner surface of the elongated portion 634 are substantially aligned with each other. It should be understood that the horizontal portion 631 and the elongated portion 634 may be formed from the same material, especially to avoid problems related to contact resistance, thermal coefficient mismatch, and differences in electrical conductivity.

[0054]

[0061] Returning to FIG. 4, the voltage control plate 420 of the apparatus 400 may include a seamless integral voltage control plate (e.g., the voltage control plate 620 of FIG. 6B) or a combined voltage control plate (e.g., the voltage control plate 630 of FIG. 6C). The primary electron beam 400B1 may include an electron beam with a high landing energy. The voltage control plate 420 may be disposed between the objective lens 407 and the backscattered electron detector 413. In some embodiments, the voltage control plate 420 may be disposed between the pole piece 407P of the objective lens 407 and the backscattered electron detector 413. The voltage control plate 420 may be positioned upstream of the backscattered electron detector 413, such that the elongated portion (e.g., the elongated portion 624 of FIG. 6B or the elongated portion 634 of FIG. 6C) extends downward into the space defined by the central hole of the backscattered electron detector 413. The diameter d1 of the central hole of the backscattered electron detector 413 may be slightly larger than the outer diameter of the elongated portion of the voltage control plate 420. The centers of the central hole of the backscattered electron detector 413 and the opening (e.g., the opening 622 of FIG. 6B) of the voltage control plate 420 may be aligned with the primary optical axis 400-1.

[0055]

[0062] In practice, the voltage control plate 420 and the backscattered electron detector 413 may be electrically insulated from each other. In some embodiments, the diameter d1 of the central hole of the backscattered electron detector 413 may be sufficiently larger than the outer diameter of the elongated portion of the voltage control plate 420 to provide electrical insulation. In addition to or instead of this, a portion of the outer surface of the backscattered electron detector 413 may be coated with an electrically insulating material to provide electrical insulation between the voltage control plate 420 and the backscattered electron detector 413. In some embodiments, a portion of the non-detection surface of the backscattered electron detector 413 may be coated with an insulating material. In some embodiments, the entire non-detection surface of the backscattered electron detector 413 may be coated with an insulating material. The voltage control plate 420 may be disposed in contact with the portion of the surface of the backscattered electron detector 413 coated with the insulator. Examples of the insulating material for coating the surface of the backscattered electron detector 413 include, but are not limited to, dielectrics, ceramics, glass, or other suitable insulating materials. However, in some embodiments, the voltage control plate 420 may not be disposed in contact with the surface of the backscattered electron detector 413 coated with the insulator. Instead, it may be attached to or coupled to the objective lens 407. In some embodiments, the voltage control plate 420 may be neither disposed in contact with the backscattered electron detector 413 nor coupled to the objective lens 407, but may be a stand-alone structure. In such a configuration, the voltage control plate 420 may be held in a predetermined position by attaching the voltage control plate 420 to the frame of the apparatus 400 or any suitable holding mechanism such that the voltage control plate 420 is coaxial with the primary optical axis 400-1.

[0056]

[0063] The apparatus 400 may include a voltage control plate 420 configured to adjust the focal length of the primary electron beam 400B1 that is to be incident on the sample. The voltage control plate 420 may include a conductive plate that is electrically insulated from the backscattered electron detector 413. Electrical insulation may allow a voltage signal to be applied to the voltage control plate 420 without, among other things, affecting the landing energy of the backscattered electrons on the backscattered electron detector 413. Adding a voltage control plate 420 between the objective lens 407 and the backscattered electron detector 413 may have a number of advantages over existing focus correction techniques in charged particle beam apparatuses. As used herein, the voltage control plate, also referred to as a conductive plate or an aperture plate, may have some or all of the advantages discussed herein, among other things. i. Independent control of focal length - A voltage control plate (e.g., voltage control plate 420) that can independently apply or adjust the voltage to the plate allows the focal length of the primary electron beam to be controlled without affecting the gain of the signal electron detector (e.g., backscattered electron detector 413 in FIG. 4) or the landing energy of the backscattered electrons on the backscattered electron detector, as shown in FIGS. 4 and 5. ii. Small focus adjustment voltage - The inner diameters of the aperture (e.g., aperture 622 in FIG. 6B) and the cavity (e.g., cavity 628 in FIG. 6B) are smaller than the inner diameter of the backscattered electron detector, but large enough for the primary electron beam and the secondary electron beam to pass through. Since the inner diameter is small, the focal length of the primary electron beam passing through the voltage control plate can be clearly adjusted by simply applying a small voltage signal to the voltage control plate. As an example, by applying a voltage signal of less than 100 V, the focal length of the primary electron beam can be adjusted by up to 10 μm. iii. Wide range of focal lengths - Since the inner diameter of the aperture of the voltage control plate is small, the focusing force per unit voltage applied may be large. This allows a wider range of focal lengths to be obtained by applying a small voltage signal. iv. Improvement in safety - When the voltage control plate is disposed between the objective lens and the backscattered electron detector, stray electrons (primary or secondary) can be blocked, and hardware including wiring associated with the backscattered electron detector or the back surface can be substantially prevented from being exposed to the stray electrons. By blocking the incidence of stray electrons on the back surface of the backscattered electron detector, potential electrical or mechanical failures or the risk of undesirable charge accumulation can be minimized. v. Improvement in reliability - When the inspection apparatus is used for a long time, contaminants, debris, or charges may accumulate on the surface exposed to primary electrons or secondary electrons. The charge or contaminants accumulated on the inner surface of the central hole of the backscattered electron detector may affect the rotational symmetry and smoothness, and higher-order electric fields such as quadrupole fields may be induced. The higher-order electric fields may interfere with the electrostatic field experienced by the primary electron beam and may adversely affect the size or shape of the probe spot. Although the inner surface of the backscattered electron detector may be cleaned, it may be difficult to polish the inner surface to maintain smoothness. In contrast, it may be easier to polish or clean the inner surface of the voltage control plate made of metal, thereby reliably obtaining high-quality images while maintaining throughput. vi. Improvement in stability - In measurement applications, the overall magnification stability of the electron optical system influences the stability and can minimize the effort spent on calibrating the charged particle system. The adjustment amount of the voltage applied to the voltage control plate to adjust the focal length of the primary electron beam may be small and may not affect the overall magnification of the electron optical system. This is because the voltage control plate can be disposed close to the sample, and thus the voltage required to adjust the focusing force of the voltage control plate may be small, which may not adversely affect the overall magnification of the lenses of the electron optical system. vii. Design flexibility - The concentricity of the voltage control plate, backscattered electron detector, control electrode (e.g., control electrode 414 in FIG. 4), or objective lens can be controlled during the assembly process or adjusted by an appropriate mechanism to avoid induced deflection fields with tolerances that may adversely affect the probe spot characteristics.

[0057]

[0064] In a charged particle beam inspection system such as an SEM, one of several ways to adjust the image resolution may include, among other things, adjusting the working distance of the objective lens. In this context, the working distance refers to the distance between the magnetic pole piece (e.g., magnetic pole piece 407P in FIG. 4) and the surface of the sample (e.g., sample 415 in FIG. 4). By reducing the working distance of the objective lens, a higher image resolution can be obtained. However, in a high landing energy beam system using a backscattered electron detector for inspecting 3D structures, reducing the working distance to obtain a higher resolution may, among other things, cause the tool to become inadequate due to limitations in throughput, focusing power, detector collection efficiency, or physical space constraints. For inspection or metrology applications, it can be beneficial to obtain high-resolution images while maintaining throughput and accuracy for feature detection or defect detection measurements during wafer inspection.

[0058]

[0065] FIG. 4 shows a schematic diagram of an apparatus 400 configured to image a sample using a high landing energy charged particle beam 400B1 that is consistent with an embodiment of the present disclosure. The apparatus 400 may be configured to image the sample 415 with higher throughput and higher signal electron detection efficiency using fast focus correction with a voltage control plate 420.

[0059]

[0066] As shown in FIG. 4, the elongated portion of the voltage control plate 420 (e.g., the elongated portion 624 in FIG. 6B) may extend downward into the central hole of the backscattered electron detector 413, such that the downstream end of the elongated portion of the voltage control plate 420 is a horizontal plane 413P along which the backscattered electron detector 413 extends and is aligned. In such a configuration, the diameter d1 of the central hole of the backscattered electron detector 413 may be small, and by collecting backscattered electrons over a wide range of emission angles and emission energies, a higher backscattered electron collection efficiency becomes possible. In the apparatus 400, the working distance (WD1) between the magnetic pole piece 407P and the sample 415 may be increased to accommodate the voltage control plate 420. This configuration may be useful in applications where higher throughput and higher BSE detector collection efficiency are desired while maintaining high image quality and measurement accuracy. The diameter of the central hole of the backscattered electron detector 413 may be smaller, but it should be understood that this diameter may be large enough to allow the primary electron beam 400B1 and the secondary electron beam 400B4 to pass through without being obstructed.

[0060]

[0067] Referring now to FIG. 5, this figure shows a schematic view of a portion of an exemplary charged particle beam apparatus 500 that is consistent with an embodiment of the present disclosure. The apparatus 500 may be configured to image a sample 515 using fast focus correction with a voltage control plate 520.

[0061]

[0068] In some embodiments, the apparatus 500 may include an objective lens 507 configured to focus a primary electron beam 500B1 onto the surface of the sample 515, a voltage control plate 520 configured to receive an electrical signal from a voltage control unit 525, a backscattered electron detector 513 configured to detect a signal electron beam 500B2, a control electrode 514, a secondary electron detector 506 configured to detect a signal electron beam 500B4, and a controller 50 (similar to the controller 50 in FIGS. 2 and 3). Although not shown, it should be understood that the apparatus 500 may include other components as appropriate.

[0062]

[0069] The voltage control plate 520 of the apparatus 500 may include a seamless integral voltage control plate (e.g., the voltage control plate 620 of FIG. 6B) or a coupled voltage control plate (e.g., the voltage control plate 630 of FIG. 6C). In some embodiments, the voltage control plate 520 may be configured to adjust the focal length of the primary electron beam 500B1 that will be incident on the sample 515. The primary electron beam 500B1 may include an electron beam with a high landing energy.

[0063]

[0070] As shown in FIG. 5, the elongated portion of the voltage control plate 520 (e.g., the elongated portion 624 of FIG. 6B) may extend downward into the central hole of the backscattered electron detector 513, such that the downstream end of the elongated portion of the voltage control plate 520 extends beyond the horizontal plane 513P. The plane 513P similar to the plane 413P represents the central plane of the backscattered electron detector 513 based on the thickness of the backscattered electron detector 513 in a direction parallel to the primary optical axis 500-1. In such a configuration, the diameter d2 of the central hole of the backscattered electron detector 513 may be larger than the diameter d1 of the backscattered electron detector 413 to receive the voltage control plate 520 while maintaining electrical insulation. In the apparatus 500, the working distance (WD2) between the magnetic pole piece 507P and the sample 515 may be shorter than WD1, which may enable acquisition of a high-resolution image. This configuration may be useful in applications where a higher image resolution is desired while maintaining high throughput and measurement accuracy. The electron collection efficiency of the backscattered electron detector 513 may be lower than that of the backscattered electron detector 413.

[0064]

[0071] Referring now to FIG. 7, this figure shows a process flow chart representing an exemplary method 700 for imaging a sample that is consistent with an embodiment of the present disclosure. One or more steps of method 700 may be performed by a controller 50 of the EBI system 100 as shown, for example, in FIG. 2. For example, the controller 50 may instruct a module of a charged particle beam apparatus to operate a charged particle source to generate a primary charged particle beam (e.g., an electron beam), apply an electrical signal to a voltage control plate, and perform other functions.

[0065]

[0072] In step 710, a charged particle source may be operated to emit charged particles. The charged particles may pass through an aperture to form a charged particle beam (e.g., the primary charged particle beam 400B1 of FIG. 4 or the primary charged particle beam 500B1 of FIG. 5). The electron source may be operated by a controller (e.g., controller 50 of 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., the primary optical axis 400-1 of FIG. 4 or the primary optical axis 500-1 of FIG. 5). The electron source may be remotely operated, for example, by supplying power to the electron source through a control circuit 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., the Coulomb aperture array 224 of FIG. 2) and a beam limiting aperture array (e.g., the beam limiting aperture array 305 of FIG. 3) to adjust the beam size or beam current of the primary electron beam and form a probe beam (e.g., sample 415 of FIG. 4 or sample 515 of FIG. 5) incident on the sample.

[0066]

[0073] In step 720, a signal electron detector (e.g., the backscattered electron detector 413 in FIG. 4 or the backscattered electron detector 513 in FIG. 5) may detect signal electrons (e.g., the backscattered electron beam 400B2 in FIG. 4 or the backscattered electron beam 500B2 in FIG. 5). Backscattered electrons (BSE) are generated by elastic scattering events of incident electrons from deeper layers beneath the surface, such as the bottom of a deep trench or the bottom of a high aspect ratio hole, and may have a high emission energy between 50 eV and the incident energy of the primary electron beam. The backscattered electron detector may be disposed between the sample and the objective lens. The diameter of the central hole of the backscattered electron detector may be varied based on the desired collection efficiency. For example, when the diameter of the central hole of the backscattered electron detector is smaller, it may be possible to collect BSE having a wider emission angle and emission energy.

[0067]

[0074] The charged particle beam apparatus (e.g., the apparatus 400 in FIG. 4 or the apparatus 500 in FIG. 5) may include a voltage control plate (e.g., the voltage control plate 420 in FIG. 4 or the voltage control plate 520 in FIG. 5) configured to receive an electrical signal. This electrical signal may be a voltage signal applied by a voltage control unit (e.g., the voltage control unit 425 in FIG. 4 or the voltage control unit 525 in FIG. 5). The voltage control plate may include a conductive plate made of a conductive material such as metal. In some embodiments, the voltage control plate may be made of a non-magnetic material.

[0068]

[0075] In step 730, the voltage control unit may adjust the voltage signal applied to the voltage control plate to adjust the electrostatic field experienced by the primary electron beam passing through the cavity (e.g., the cavity 628 in FIG. 6B). Changes in the electrostatic field may affect the focal length of the passing primary electron beam that will be incident on the sample. The voltage control plate is a separate element, and the voltage to this plate may be independently applied and controlled without affecting the landing energy of the backscattered electrons on the backscattered electron detector. The voltage control plate and the backscattered electron detector may be electrically insulated from each other.

[0069]

[0076] A non-transitory computer-readable medium storing instructions for a processor of a controller (e.g., controller 50 of FIG. 1) to perform operations such as image inspection, image acquisition, operation of a charged particle source, adjustment of the electrical excitation of an aberration corrector, adjustment of the electron landing energy, adjustment of the objective lens excitation, application of an electrical signal to a voltage control plate to change the electrostatic field experienced by the primary electron beam, adjustment of an electrical signal to adjust the focal length of the primary electron beam, control of the movement of a stage, operation of a beam deflector to deflect the primary electron beam, application of an electrical excitation signal including an AC voltage, etc. may be provided. General forms of non-transitory media include, for example, floppy disks, flexible disks, hard disks, solid state drives, magnetic tapes, or any other magnetic data storage media, CD-ROM (Compact Disc Read Only Memory), any other optical data storage media, any physical medium having a pattern of holes, RAM (Random Access Memory), PROM (Programmable Read Only Memory), EPROM (Erasable Programmable Read Only Memory), FLASH-EPROM, or any other flash memory, NVRAM (Non-Volatile Random Access Memory), caches, registers, any other memory chip or cartridge, and network versions thereof.

[0070]

[0077] Embodiments of the present disclosure can be further described using the following clauses. 1. A charged particle beam apparatus, A charged particle source configured to emit charged particles, wherein the emitted charged particles form a primary charged particle beam along a primary optical axis, the charged particle source, and An objective lens including a magnetic lens, and A charged particle detector disposed downstream of the objective lens with respect to the path of the primary charged particle beam and disposed along a horizontal plane substantially perpendicular to the primary optical axis, A voltage control plate disposed between a charged particle detector and a magnetic pole piece of a magnetic lens, a horizontal portion including an opening, and an elongated portion extending downward from the opening into a hole of the charged particle detector with respect to the path of a primary charged particle beam, the voltage control plate including: A charged particle beam device. 2. The apparatus according to clause 1, wherein the elongated portion includes an inner diameter substantially the same as the diameter of the opening of the horizontal portion. 3. The apparatus according to clause 2, wherein the diameter of the opening is smaller than the diameter of the hole of the charged particle detector. 4. The apparatus according to any one of clauses 1 to 3, wherein the opening and the elongated portion form a cavity configured to allow a primary charged particle beam to pass through. 5. The apparatus according to clause 4, wherein the cavity includes a cylindrical cavity that is rotationally symmetric about a primary optical axis. 6. The apparatus according to any one of clauses 4 and 5, wherein the inner surface of the elongated portion forming the cavity and the inner surface of the opening are aligned with each other. 7. A circuit, applying an electrical signal to the voltage control plate, adjusting the electrical signal so as to affect an electrostatic field experienced by a primary charged particle beam passing through the cavity, and the electrical signal includes a voltage signal, and further includes a controller including a circuit configured as described above. The apparatus according to any one of clauses 4 to 6. 8. The apparatus according to clause 7, wherein the adjustment of the electrical signal is configured such that the voltage control plate adjusts the focal length of a primary charged particle beam that will be incident on the sample. 9. The apparatus according to any one of clauses 7 and 8, wherein the focal length of the primary charged particle beam is adjusted by up to 10 μm by an applied voltage signal of 100 V or less. 10. The apparatus according to any one of clauses 1 to 9, wherein the charged particle detector and the voltage control plate are electrically insulated from each other. 11. The downstream end of the elongated portion extends into the hole of the charged particle detector and extends beyond a horizontal plane along which the charged particle detector extends, the horizontal plane including a central plane with respect to the thickness of the charged particle detector, the apparatus according to any one of clauses 1 to 10. 12. The downstream end of the elongated portion extends into the hole of the charged particle detector and is substantially aligned with a horizontal plane along which the charged particle detector extends, the horizontal plane including a central plane with respect to the thickness of the charged particle detector, the apparatus according to any one of clauses 1 to 10. 13. The apparatus according to any one of clauses 1 to 12, further including a control electrode disposed downstream of the charged particle detector. 14. The apparatus according to clause 13, wherein the voltage control plate, the charged particle detector, the control electrode, and the objective lens are coaxial. 15. The apparatus according to any one of clauses 1 to 14, wherein the voltage control plate includes a conductive plate. 16. The apparatus according to any one of clauses 1 to 15, wherein the horizontal portion of the voltage control plate is formed from a seamless, integral substrate. 17. The apparatus according to any one of clauses 1 to 16, wherein the horizontal portion of the voltage control plate is formed by joining two or more plates. 18. The apparatus according to any one of clauses 1 to 17, wherein the elongated portion is fluidly connected to the horizontal portion of the voltage control plate. 19. The apparatus according to any one of clauses 1 to 18, wherein the elongated portion is joined to the horizontal portion using hardware assembly, welding, gluing, adhesion, or brazing. 20. The apparatus according to any one of clauses 1 to 19, wherein the charged particle detector includes a backscattered electron detector configured to detect backscattered electrons. 21. The apparatus according to any one of clauses 3 to 20, wherein the elongated portion includes an outer diameter that is smaller than the diameter of the hole of the charged particle detector. 22. The apparatus according to any one of clauses 6 to 21, wherein the inner surface of the elongated portion and the inner surface of the opening can be configured to provide a superior surface compared to the inner surface of the hole of the charged particle detector. 23. The device according to any one of clauses 6 to 22, wherein the inner surface of the elongated portion and the inner surface of the opening are configurable to maintain the ellipticity of the cavity. 24. The device according to clause 23, wherein the ellipticity of the cavity allows the primary charged particle beam to pass through the cavity without substantial deflection. 25. The device according to any one of clauses 1 to 24, wherein the voltage control plate comprises a non-magnetic material. 26. A method for 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; detecting signal electrons generated from the sample by interaction of the primary charged particle beam with the sample using a charged particle detector; adjusting an electrical signal applied to a voltage control plate, the voltage control plate comprising: a horizontal portion including an opening; and an elongated portion extending downward from the opening into a hole of the charged particle detector with respect to the path of the primary charged particle beam. 27. The method according to clause 26, wherein the voltage control plate is disposed between the charged particle detector and the pole piece of the objective lens. 28. The method according to any one of clauses 26 and 27, wherein the elongated portion comprises an inner surface that is substantially the same as the diameter of the opening of the horizontal portion. 29. The method according to clause 28, wherein the diameter of the opening is smaller than the diameter of the hole of the charged particle detector. 30. The method according to any one of clauses 26 to 29, wherein the opening and the elongated portion form a cavity configured to allow the primary charged particle beam to pass through. 31. The method according to clause 30, wherein the cavity includes a cylindrical cavity that is rotationally symmetric about a primary optical axis. 32. The method according to any one of clauses 30 and 31, wherein the inner surface of the elongated portion and the inner surface of the opening are aligned with each other. 33. Applying a voltage signal to the voltage control plate; Further comprising adjusting a voltage signal so as to affect an electrostatic field experienced by a primary charged particle beam passing through the cavity, the method according to any one of clauses 30 to 32. 34. The method according to clause 33, wherein the focal length of the primary charged particle beam that will be incident on the sample is adjusted by adjusting the voltage signal. 35. The method according to clause 34, wherein when the voltage signal is adjusted by 100 V or less, the focal length of the primary charged particle beam is adjusted by up to 10 μm at most. 36. The method according to any one of clauses 26 to 35, wherein the voltage control plate and the charged particle detector are electrically insulated from each other. 37. The method according to clause 36, wherein electrically insulating the voltage control plate and the charged particle detector includes forming an electrical insulation layer on the non-detection surface of the charged particle detector. 38. The downstream end of the elongated portion extends into the hole of the charged particle detector and is a horizontal plane that extends beyond the horizontal plane along which the charged particle detector extends, and the horizontal plane includes a central plane with reference to the thickness of the charged particle detector, the method according to any one of clauses 26 to 37. 39. The downstream end of the elongated portion extends into the hole of the charged particle detector and is a horizontal plane that is substantially aligned with the horizontal plane along which the charged particle detector extends, and the horizontal plane includes a central plane with reference to the thickness of the charged particle detector, the method according to any one of clauses 26 to 37. 40. The method according to any one of clauses 26 to 39, wherein the voltage control plate and the charged particle detector are aligned with the primary optical axis. 41. The method according to any one of clauses 26 to 40, wherein the voltage control plate includes a conductive plate. 42. The method according to any one of clauses 26 to 41, wherein the horizontal portion of the voltage control plate is formed from a seamless integral base material. 43. The method according to any one of clauses 26 to 42, wherein the horizontal portion is formed by joining two or more plates. 44. The method according to any one of clauses 26 to 43, wherein the elongated portion is fluidly connected to the horizontal portion of the voltage control plate. 45. The method according to any one of clauses 26 to 44, wherein the elongated portion is coupled to the horizontal portion using hardware assembly, welding, gluing, adhesion, or brazing. 46. The method according to any one of clauses 26 to 45, wherein the charged particle detector includes a backscattered electron detector configured to detect backscattered electrons. 47. The method according to any one of clauses 26 to 46, wherein the elongated portion includes an outer diameter that is smaller than the diameter of the hole of the charged particle detector. 48. The method according to any one of clauses 32 to 47, further comprising modifying the inner surface of the elongated portion and the inner surface of the opening to provide a superior surface compared to the inner surface of the hole of the charged particle detector. 49. The method according to clause 48, wherein modifying includes cleaning, polishing, or reworking the inner surface of the elongated portion and the inner surface of the opening to maintain the ellipticity of the cavity. 50. The method according to clause 49, wherein maintaining the ellipticity of the cavity enables the primary charged particle beam to pass through the cavity without substantial deflection. 51. The method according to any one of clauses 26 to 50, wherein the voltage control plate includes a non-magnetic material. 52. A non-transitory computer-readable medium storing a set of instructions executable by one or more processors of a charged particle beam apparatus to cause the charged particle beam apparatus to perform a method, the method comprising: obtaining a signal from a charged particle detector, the signal resulting from the charged particle detector detecting signal electrons generated from a sample due to an interaction between a primary charged particle beam and the sample; and adjusting an electrical signal applied to a voltage control plate to enable adjustment of a focal length of a primary charged particle beam that will be incident on the sample, the voltage control plate including: a horizontal portion including an opening; and an elongated portion extending downward from the opening into a hole of the charged particle detector with respect to a path of the primary charged particle beam. 53. The opening and the elongated portion form a cavity configured to allow a primary charged particle beam to pass through, the non-transitory computer-readable medium according to clause 52. 54. A set of instructions executable by one or more processors of a charged particle beam device causes the charged particle beam device to further apply a voltage signal to a voltage control plate, and adjust the voltage signal so as to affect an electrostatic field experienced by a primary charged particle beam passing through the cavity, the non-transitory computer-readable medium according to clause 53. 55. By adjusting the voltage signal, the focal length of a primary charged particle beam that will be incident on a sample is adjusted, the non-transitory computer-readable medium according to clause 54. 56. When the voltage signal is adjusted by 100 V or less, the focal length of the primary charged particle beam is adjusted by up to 10 μm, the non-transitory computer-readable medium according to clause 55. 57. The voltage control plate and the charged particle detector are electrically insulated from each other, the non-transitory computer-readable medium according to any one of clauses 52 to 56. 58. Electrically insulating the voltage control plate and the charged particle detector includes forming an electrical insulating layer on a non-detection surface of the charged particle detector, the non-transitory computer-readable medium according to clause 57. 59. The downstream end of the elongated portion extends into a hole of the charged particle detector and is a horizontal plane that extends beyond a horizontal plane along which the charged particle detector extends, the horizontal plane including a central plane with reference to the thickness of the charged particle detector, the non-transitory computer-readable medium according to any one of clauses 52 to 58. 60. The downstream end of the elongated portion extends into a hole of the charged particle detector and is a horizontal plane that is substantially aligned with a horizontal plane along which the charged particle detector extends, the horizontal plane including a central plane with reference to the thickness of the charged particle detector, the non-transitory computer-readable medium according to any one of clauses 52 to 58. 61. An electron-optical assembly, an objective lens including a magnetic lens, A charged particle detector arranged downstream of the objective lens with respect to the path of the primary charged particle beam and arranged along a horizontal plane substantially perpendicular to the primary optical axis, and A voltage control plate arranged between the charged particle detector and the magnetic pole piece of the magnetic lens, A horizontal portion including an opening, and An elongated portion extending downward from the opening into the hole of the charged particle detector with respect to the path of the primary charged particle beam, and An electron-optical assembly including a voltage control plate in which the opening and the elongated portion form a cavity configured to allow the primary charged particle beam to pass through. 62. The assembly according to clause 61, wherein the elongated portion includes an inner diameter substantially the same as the diameter of the opening of the horizontal portion. 63. The assembly according to clause 62, wherein the diameter of the opening is smaller than the diameter of the hole of the charged particle detector. 64. The assembly according to any one of clauses 61 to 63, wherein the cavity includes a cylindrical cavity that is rotationally symmetric about the primary optical axis. 65. The assembly according to any one of clauses 61 to 64, wherein the inner surface of the elongated portion forming the cavity and the inner surface of the opening are aligned with each other. 66. A circuit, Applying an electrical signal to the voltage control plate, Adjusting the electrical signal so as to affect the electrostatic field experienced by the primary charged particle beam passing through the cavity, and the electrical signal includes a voltage signal, and further including a controller including a circuit configured as such. The assembly according to any one of clauses 61 to 65. 67. The assembly according to clause 66, wherein the adjustment of the electrical signal is configured such that the voltage control plate adjusts the focal length of the primary charged particle beam that will be incident on the sample. 68. The assembly according to any one of clauses 66 and 67, wherein the focal length of the primary charged particle beam is adjusted by up to 10 μm by an applied voltage signal of 100 V or less. 69. The charged particle detector and the voltage control plate are electrically insulated from each other, and the assembly according to any one of clauses 61 to 68. 70. The downstream end of the elongated portion extends into the hole of the charged particle detector and is a horizontal plane that extends beyond the horizontal plane along which the charged particle detector extends. The horizontal plane includes a central plane based on the thickness of the charged particle detector, and the assembly according to any one of clauses 61 to 69. 71. The downstream end of the elongated portion extends into the hole of the charged particle detector and is a horizontal plane that is substantially aligned with the horizontal plane along which the charged particle detector extends. The horizontal plane includes a central plane based on the thickness of the charged particle detector, and the assembly according to any one of clauses 61 to 69. 72. The assembly according to any one of clauses 61 to 71, further including a control electrode disposed downstream of the charged particle detector. 73. The voltage control plate, the charged particle detector, the control electrode, and the objective lens are coaxial, and the assembly according to clause 72. 74. The voltage control plate includes a conductive plate, and the assembly according to any one of clauses 61 to 73. 75. The horizontal portion of the voltage control plate is formed from a seamless integral substrate, and the assembly according to any one of clauses 61 to 74. 76. The horizontal portion of the voltage control plate is formed by joining two or more plates, and the assembly according to any one of clauses 61 to 74. 77. The elongated portion is fluidly connected to the horizontal portion of the voltage control plate, and the assembly according to any one of clauses 61 to 76. 78. The elongated portion is joined to the horizontal portion using hardware assembly, welding, gluing, adhesion, or brazing, and the assembly according to any one of clauses 61 to 76. 79. The charged particle detector includes a backscattered electron detector configured to detect backscattered electrons, and the assembly according to any one of clauses 61 to 78. 80. The assembly according to any one of clauses 63 to 79, wherein the elongated portion includes an outer diameter that is smaller than the diameter of the hole of the charged particle detector. 81. The assembly according to any one of clauses 65 to 80, wherein the inner surface of the elongated portion and the inner surface of the opening can be configured to provide a superior surface as compared to the inner surface of the hole of the charged particle detector. 82. The assembly according to any one of clauses 65 to 81, wherein the inner surface of the elongated portion and the inner surface of the opening can be configured to maintain the ellipticity of the cavity. 83. The assembly according to clause 82, wherein due to the ellipticity of the cavity, a primary charged particle beam can pass through the cavity without being substantially deflected. 84. The assembly according to any one of clauses 61 to 83, wherein the voltage control plate includes a non-magnetic material. 85. A plate that can be inserted between a charged particle detector and a pole piece of an objective lens of a charged particle beam apparatus, including a horizontal portion including an opening, and an elongated portion that extends downward from the opening into the hole of the charged particle detector with respect to the path of the primary charged particle beam, wherein the opening and the elongated portion form a cavity configured such that a primary charged particle beam can pass through.

[0071]

[0078] It will be understood that the embodiments of the present disclosure are not limited to the structure as described above and shown in the accompanying drawings, and various modifications and variations can be made without departing from its scope. The present disclosure has been described in connection 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. The specification and examples are to be regarded as illustrative only, and the true scope and spirit of the invention are intended to be indicated by the following claims.

[0072]

[0079] The foregoing description is intended to be illustrative and not restrictive. Accordingly, it will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the following claims.

Claims

1. A charged particle source configured to emit charged particles, wherein the emitted charged particles form a primary charged particle beam along a primary optical axis, the charged particle source; An objective lens including a magnetic lens; A charged particle detector disposed downstream of the objective lens with respect to the path of the primary charged particle beam and disposed along a horizontal plane substantially perpendicular to the primary optical axis; A voltage control plate disposed between the charged particle detector and a magnetic pole piece of the magnetic lens, the voltage control plate having a horizontal portion including an opening and an elongated portion extending downward from the opening into a hole of the charged particle detector with respect to the path of the primary charged particle beam; A charged particle beam apparatus comprising:

2. The apparatus according to claim 1, wherein the elongated portion includes an inner diameter substantially the same as a diameter of the opening of the horizontal portion.

3. The apparatus according to claim 2, wherein the diameter of the opening is smaller than a diameter of the hole of the charged particle detector.

4. The apparatus according to claim 1, wherein the opening and the elongated portion form a cavity configured to allow the primary charged particle beam to pass therethrough.

5. The apparatus according to claim 4, wherein the cavity includes a cylindrical cavity that is rotationally symmetric about the primary optical axis.

6. The apparatus according to claim 5, wherein an inner surface of the elongated portion forming the cavity and an inner surface of the opening are aligned with each other.

7. The apparatus according to claim 5, further comprising a controller having a circuit configured to apply an electrical signal to the voltage control plate and adjust the electrical signal so as to affect an electrostatic field experienced by the primary charged particle beam passing through the cavity, the electrical signal including a voltage signal.

8. The apparatus according to claim 7, wherein the adjustment of the electrical signal is configured such that the voltage control plate adjusts a focal length of the primary charged particle beam that is to be incident on a sample.

9. The apparatus according to claim 7, wherein the focal length of the primary charged particle beam is adjusted by up to 10 μm by the applied voltage signal of 100 V or less.

10. The apparatus according to claim 1, wherein the charged particle detector and the voltage control plate are electrically insulated from each other.

11. The downstream end of the elongated portion extends into the hole of the charged particle detector and extends beyond the horizontal plane. The charged particle detector extends along the horizontal plane. The horizontal plane includes a central plane with reference to the thickness of the charged particle detector, the apparatus according to claim 1.

12. The downstream end of the elongated portion extends into the hole of the charged particle detector and is substantially aligned with the horizontal plane. The charged particle detector extends along the horizontal plane. The horizontal plane includes a central plane with reference to the thickness of the charged particle detector, the apparatus according to claim 1.

13. The elongated portion includes an outer diameter. The outer diameter is smaller than the diameter of the hole of the charged particle detector, the apparatus according to claim 3.

14. The inner surface of the elongated portion and the inner surface of the opening can be configured to provide a superior surface compared to the inner surface of the hole of the charged particle detector, the apparatus according to claim 6.

15. A method for imaging a sample using a charged particle beam apparatus, comprising: forming a primary charged particle beam from charged particles emitted by a charged particle source; detecting signal electrons generated from the sample by the interaction between the primary charged particle beam and the sample using a charged particle detector; adjusting an electrical signal applied to a voltage control plate, the voltage control plate having a horizontal portion including an opening and an elongated portion extending downward from the opening into the hole of the charged particle detector with reference to the path of the primary charged particle beam; A method comprising.

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