Objective lens cooling system

Abstract

An improved magnetic lens cooling system is disclosed, wherein the magnetic lens assembly can include a coil, a housing that accommodates the coil, and a pole piece that is separated from the housing such that there is a gap between the housing and the pole piece, and wherein the magnetic lens assembly can be configured to have a vacuum pressure in the gap.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application No. 63 / 435,771, filed December 28, 2022, and incorporated herein by reference in its entirety.

[0002]

[0002] Embodiments provided herein disclose an objective lens assembly, and more particularly, an objective lens cooling system for minimizing thermal deformation of the objective lens assembly, for example, in an inspection apparatus. [Background technology]

[0003]

[0003] During the integrated circuit (IC) manufacturing process, unfinished or finished circuit components are inspected to ensure they are manufactured as designed and are free of defects. Inspection systems using optical microscopes or charged particle (e.g., electron) beam microscopes, such as scanning electron microscopes (SEMs), may be employed. As IC components become smaller, the accuracy of defect detection becomes increasingly important. Therefore, accurately controlling the charged particle beam to a targeted location on a sample is essential to meet the increasing demands for high-precision inspection and metrology. Summary of the Invention

[0004] Some embodiments provide a charged particle beam inspection apparatus including a charged particle beam source configured to generate a primary charged particle beam for scanning a sample and an objective lens assembly configured to influence the charged particle beam. The objective lens assembly may include a coil, a housing that accommodates the coil, and a pole piece separated from the housing such that there is a gap between the housing and the pole piece. Here, the objective lens assembly may be configured to have a vacuum pressure in the gap.

[0005] Some embodiments provide a magnetic lens assembly that may include a coil, a housing that accommodates the coil, and a pole piece that is separated from the housing such that there is a gap between the housing and the pole piece, wherein the magnetic lens assembly is configured to have a vacuum pressure in the gap.

[0006]

[0006] Other advantages of embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings, in which certain embodiments of the present invention are set forth by way of illustration and example.

[0007]

[0007] The above and other aspects of the present disclosure will become more apparent from the description of illustrative embodiments taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary charged particle beam inspection system consistent with an embodiment of the present disclosure. [Figure 2A]

[0009] 2 is a schematic diagram illustrating an example multi-beam tool consistent with an embodiment of the present disclosure that may be part of the example charged particle beam inspection system of FIG. 1. [Figure 2B]

[0010] 2 is a schematic diagram illustrating an example single beam tool consistent with an embodiment of the present disclosure that may be part of the example charged particle beam inspection system of FIG. 1. [Figure 3]

[0011] 1 is a cross-sectional view of a conventional magnetic lens assembly. [Figure 4]

[0012] 1 is a cross-sectional view of an exemplary magnetic lens assembly consistent with an embodiment of the present disclosure. [Figure 5A]

[0013] 5 is a schematic diagram illustrating an exemplary fluid channel formed within a housing of the magnetic lens assembly of FIG. 4, consistent with an embodiment of the present disclosure. [Figure 5B]

[0014] 5 is a schematic diagram illustrating an exemplary housing of the magnetic lens assembly of FIG. 4, consistent with an embodiment of the present disclosure. [Figure 6A]

[0015] 5 is a schematic diagram illustrating an exemplary coupling structure within the magnetic lens assembly of FIG. 4, consistent with an embodiment of the present disclosure. [Figure 6B]

[0016] 5 is a schematic diagram illustrating an exemplary pipe within the magnetic lens assembly of FIG. 4, consistent with an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009]

[0017] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which like numbers in different drawings represent the same or similar elements unless otherwise specified. The implementations described in the following description of exemplary embodiments do not represent all implementations consistent with the present invention. Instead, they are merely examples of apparatus and methods consistent with aspects related to the present invention as recited in the appended claims. For example, although some embodiments are described in connection with the use of electron beams, the present disclosure is not so limited. Other types of charged particle beams (e.g., including protons, ions, muons, or any other particles carrying an electric charge) may be similarly applied. Furthermore, other imaging systems, such as optical imaging, photon detection, x-ray detection, ion detection, etc., may also be used.

[0010]

[0018] Electronic devices are composed of circuits formed on a piece of semiconductor material called a substrate. The semiconductor material can include, for example, silicon, gallium arsenide, indium phosphide, or silicon germanium. Many circuits can be formed together on the same piece of silicon and are called integrated circuits, or ICs. The dimensions of these circuits have been dramatically reduced so that many more circuits can fit on a substrate. For example, the IC chip in a smartphone can be as small as a thumbnail, yet contain over 2 billion transistors, each smaller than 1 / 1000 the size of a human hair.

[0011]

[0019] Fabricating ICs with these tiny structures or components is a complex, time-consuming, and expensive process, often involving hundreds of individual steps. An error in just one step can result in a defect in the finished IC, rendering it unusable. Therefore, one of the goals of a manufacturing process is to avoid such defects and maximize the number of functional ICs produced by the process, i.e., to improve the overall yield of the process.

[0012]

[0020] One component of improving yield is monitoring the chip fabrication process to ensure that a sufficient number of functional integrated circuits are being produced. One way to monitor the process is to inspect the chip circuit structures at various stages in their formation. Inspection can be done using a scanning charged particle microscope ("SCPM"). For example, an SCPM can be a scanning electron microscope (SEM). An SCPM can actually take a "picture" of the structures on the wafer and can be used to image those tiny structures. This image can be used to determine if the structures were properly formed in the correct location. If the structures are defective, the process can be adjusted to make the defect less likely to recur.

[0013]

[0021] As IC components become increasingly miniaturized, defect detection accuracy becomes increasingly important. Therefore, accurately controlling a charged particle beam to a targeted location on a sample is essential to meet the increasing demands for high-precision inspection and metrology. In a charged particle beam imaging or inspection system, such as an SCPM, an electromagnetic lens with electromagnetic coils (e.g., the coils are housed in a ferromagnetic base) can be used to focus a charged particle beam onto a wafer. Current passing through the electromagnetic coils can generate a magnetic field that focuses or defocuses the charged particle beam. The amount of heat generated can be proportional to the current passing through the coils and the number of coils. In conventional magnetic lens assemblies, the pole pieces of the electromagnetic lens assembly are not thermally isolated from the heat source, e.g., the coils of the electromagnetic lens assembly. For example, heat generated by the coils can be transferred to the pole pieces by thermal convection, using the air between the pole pieces and the coil as a heat transfer medium. This allows the heat generated by the coils to be transferred to the pole pieces. However, even slight temperature changes in the pole pieces can cause thermal expansion or physical deformation of the pole pieces. Such thermal expansion and dimensional deformation of the pole pieces can destabilize the magnetic field induction by the pole pieces, and further make it difficult to position a precisely focused charged particle beam at a target position on a sample, thereby making it difficult to obtain accurate inspection images. Therefore, a cooling mechanism that can efficiently cool the coils while minimizing heat transfer to the pole pieces is needed. Thermal management issues can be accentuated in multi-beam inspection tools. While using multiple beams for wafer inspection, each beam capable of imaging a different point on the wafer, is useful for improving wafer inspection throughput, multi-beam inspection tools can experience excessive heat generation. Focusing multiple beams may require a greater number of electromagnetic coils or a higher current to be passed through the electromagnetic coils, necessitating improved heat dissipation systems and methods.

[0014]

[0022] Embodiments of the present disclosure may provide a magnetic lens assembly that can minimize heat transfer from the coil to the pole pieces. According to some embodiments of the present disclosure, the pole pieces may be thermally isolated from a heat source, such as the coil of the magnetic lens assembly. In some embodiments, the magnetic lens assembly may be configured to have a gap between the pole pieces and a housing that houses the coil, and the gap is maintained under vacuum. Because the gap between the pole pieces and the housing that houses the coil is in a vacuum state, heat transfer from the coil to the pole pieces due to thermal convection can be minimized. As a result, according to some embodiments of the present disclosure, the amount of heat transferred from the coil to the pole pieces can be reduced. In some embodiments, the magnetic lens assembly may be configured to eliminate one heat dissipation path (e.g., thermal convection through air) from the coil, but it will be understood that the efficiency of heat dissipation from the coil may not be affected by the loss of the heat dissipation path. In some embodiments, the heat from the coil is concentrated in a cooling fluid circulating through the housing that houses the coil. As a result, the efficiency of heat dissipation may not be reduced by the loss of the heat dissipation path (i.e., thermal convection through air). Indeed, in some embodiments, heat from the coil is concentrated in the cooling fluid rather than dissipated, thereby fully utilizing the cooling fluid's ability to dissipate heat from the coil, thereby increasing heat dissipation efficiency, thereby allowing for efficient dissipation of heat from the coil while maintaining minimal heat transfer to the pole pieces, according to some embodiments of the present disclosure.

[0015]

[0023] In the context of this disclosure, a low thermal conductivity material is one that has a thermal conductivity of between 1 and 10 W.m under standard measurement conditions. -1 .K -1 High thermal conductivity materials can be defined as materials with thermal conductivity values ​​in the range of 20 to 2000 W.m under standard measurement conditions. -1 .K -1 Thermal conductivity may be defined as a material having a thermal conductivity value in the range

[0016]

[0024] The relative dimensions of components in the drawings may be exaggerated 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. Other objects and advantages of the present disclosure may be realized by the elements and combinations described in the embodiments discussed herein. However, embodiments of the present disclosure are not necessarily required to achieve such exemplary objects or advantages, and some embodiments may not achieve any of the described objects or advantages.

[0017]

[0025] Without limiting the scope of the present disclosure, some embodiments may be described in connection with providing scan deflection systems and methods in systems utilizing electron beams ("e-beams"). Some scan deflection systems may use electric fields to influence charged particle beams. However, the present disclosure is not so limited. Other types of charged particle beams may be applied as well. For example, the systems and methods may be applicable to optical systems, photons, muons, x-rays, ions, or any other particles that carry an electric charge. Deflection may be used, for example, to scan the beam over a surface in a cathode ray tube (CRT), lithography machine, scanning charged particle microscope (SCPM), or other analytical instrument. Although some embodiments are discussed with respect to deflection systems that use electric fields to influence the beam, deflection may also be achieved, for example, by magnetic fields.

[0018]

[0026] As used herein, unless otherwise stated, the term "or" includes all possible combinations unless impracticable. For example, if a component is described as including A or B, the component may include A or B, or A and B, unless otherwise stated or impracticable. As a second example, if a component is described as including A, B, or C, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A, B, and C, unless otherwise stated or impracticable. A phrase such as "at least one of" does not necessarily modify all of the subsequent list, and does not necessarily modify each member of the list; so, "at least one of A, B, and C" should be understood to include only one A, only one B, only one C, or any combination of A, B, and C. The phrase "one of A and B" or "either one of A and B" should be interpreted in the broadest sense to include one of A or one of B.

[0019]

[0027] FIG. 1 illustrates an exemplary electron beam inspection (EBI) system 100 consistent with embodiments of the present disclosure. The EBI system 100 can be used for imaging. As shown in FIG. 1, the EBI system 100 includes a main chamber 101, a load / lock chamber 102, a beam tool 104, and an equipment front-end module (EFEM) 106. The beam tool 104 is disposed within the main chamber 101. The EFEM 106 includes a first load port 106a and a second load port 106b. The EFEM 106 may include additional load ports. The first load port 106a and the second load port 106b receive wafer front-opening unified pods (FOUPs) containing wafers (e.g., semiconductor wafers or wafers made of other materials) or samples (wafers and samples may be used interchangeably) to be inspected. A "lot" is a plurality of wafers that can be loaded for processing as a batch.

[0020]

[0028] One or more robot arms (not shown) in the EFEM 106 can transfer wafers to the load / lock chamber 102. The load / lock chamber 102 is connected to a load / lock vacuum pumping system (not shown), which removes gas molecules from the load / lock chamber 102 to reach a first pressure lower than atmospheric pressure. After the first pressure is reached, one or more robot arms (not shown) can transfer the wafers from the load / lock chamber 102 to the main chamber 101. The main chamber 101 is connected to a main chamber vacuum pumping system (not shown), which removes gas molecules from the main chamber 101 to reach a second pressure lower than the first pressure. After the second pressure is reached, the wafers are subjected to inspection by the beam tool 104. The beam tool 104 can be a single beam system or a multi-beam system.

[0021]

[0029] A controller 109 is electronically connected to the beam tool 104. The controller 109 may be a computer configured to perform various controls of the EBI system 100. While the controller 109 is illustrated in Figure 1 as being external to the structure including the main chamber 101, the load / lock chamber 102, and the EFEM 106, it will be understood that the controller 109 may be part of the structure.

[0022]

[0030] In some embodiments, the controller 109 may include one or more processors (not shown). A processor may be a general-purpose or specialized electronic device capable of manipulating or processing information. For example, a processor may include any number of central processing units (i.e., "CPUs"), graphics processing units (i.e., "GPUs"), optical processors, programmable logic controllers, microcontrollers, microprocessors, digital signal processors, intellectual property (IP) cores, programmable logic arrays (PLAs), programmable array logic (PALs), general purpose array logic (GALs), complex programmable logic devices (CPLDs), field programmable gate arrays (FPGAs), systems-on-chips (SoCs), application-specific integrated circuits (ASICs), and any combination of any type of circuitry capable of processing data. A processor may also be a virtual processor, including one or more processors distributed across multiple machines or devices coupled via a network.

[0023]

[0031] In some embodiments, the controller 109 may further include one or more memories (not shown). Memory may be a general-purpose or specific electronic device capable of storing code and data accessible to a processor (e.g., via a bus). For example, memory may include any number of random access memories (RAMs), read-only memories (ROMs), optical disks, magnetic disks, hard drives, solid-state drives, flash drives, security digital (SD) cards, memory sticks, compact flash (CF) cards, or any combination of any type of storage device. The code and data may include an operating system (OS) and one or more application programs (i.e., "apps") for specific tasks. Memory may also be a virtual memory, which includes one or more memories distributed across multiple machines or devices coupled via a network.

[0024]

[0032] FIG. 2A shows a schematic diagram of an exemplary multi-beam beam tool 104A (also referred to herein as apparatus 104A) and image processing system 290 that may be configured for use in EBI system 100 (FIG. 1) consistent with an embodiment of the present disclosure.

[0025]

[0033] The beam tool 104A includes a charged particle source 202, a gun aperture 204, a condenser lens 206, a primary charged particle beam 210 emitted from the charged particle source 202, a source conversion unit 212, multiple beamlets 214, 216, and 218 of the primary charged particle beam 210, a primary projection optics 220, a motorized wafer stage 280, a wafer holder 282, multiple secondary charged particle beams 236, 238, and 240, a secondary optics 242, and a charged particle detection device 244. The primary projection optics 220 may include a beam separator 222, a deflection scanning unit 226, and an objective lens 228. The charged particle detection device 244 may include detection subregions 246, 248, and 250.

[0026]

[0034] The charged particle source 202, the gun aperture 204, the condenser lens 206, the source conversion unit 212, the beam separator 222, the deflection scanning unit 226, and the objective lens 228 may be aligned with a primary optical axis 260 of the apparatus 104A. The secondary optics 242 and the charged particle detection device 244 may be aligned with a secondary optical axis 252 of the apparatus 104A.

[0027]

[0035] The charged particle source 202 can emit one or more charged particles, such as electrons, protons, ions, muons, or any other particles that carry an electric charge. In some embodiments, the charged particle source 202 can be an electron emitter. For example, the charged particle source 202 can include a cathode, an extractor, or an anode, and primary electrons can be emitted from the cathode and extracted or accelerated to form a primary charged particle beam 210 (in this case, a primary electron beam) with a (virtual or real) crossover 208. For ease of explanation and to avoid ambiguity, some of the descriptions herein use electrons as an example. However, it should be noted that any charged particle, not limited to electrons, can be used in any embodiment of the present disclosure. The primary charged particle beam 210 can be visualized as it is being emitted from the crossover 208. The gun aperture 204 can block charged particles surrounding the primary charged particle beam 210 to reduce the Coulomb effect, which can cause an increase in the size of the probe spot.

[0028]

[0036] The source conversion unit 212 may include an array of image-forming elements and an array of beam-limiting apertures. The array of image-forming elements may include an array of micro-deflectors or micro-lenses. The array of image-forming elements may form multiple (virtual or real) parallel images of the crossover 208 along with the multiple beamlets 214, 216, and 218 of the primary charged particle beam 210. The array of beam-limiting apertures may limit the multiple beamlets 214, 216, and 218. Although three beamlets 214, 216, and 218 are shown in FIG. 2A , embodiments of the present disclosure are not limited thereto. For example, in some embodiments, the apparatus 104A may be configured to generate a first number of beamlets. In some embodiments, the first number of beamlets may be in the range of 1 to 1000. In some embodiments, the first number of beamlets may be in the range of 200 to 500. In an exemplary embodiment, the apparatus 104A may generate 400 beamlets.

[0029]

[0037] The condenser lens 206 can focus the primary charged particle beam 210. The currents of the beamlets 214, 216, and 218 downstream of the source conversion unit 212 can be varied by adjusting the focusing power of the condenser lens 206 or by changing the radius of the corresponding beam-limiting apertures in the array of beam-limiting apertures. The objective lens 228 can focus the beamlets 214, 216, and 218 onto a wafer 230 for imaging, and can form multiple probe spots 270, 272, and 274 on the surface of the wafer 230.

[0030]

[0038] The beam separator 222 may be a Wien filter-type beam separator that generates an electrostatic dipole field and a magnetic dipole field. In some embodiments, when applied, the force that the electrostatic dipole field exerts on the charged particles (e.g., electrons) in the beamlets 214, 216, and 218 may be substantially equal in magnitude and opposite in direction to the force that the magnetic dipole field exerts on the charged particles. Thus, the beamlets 214, 216, and 218 may pass through the beam separator 222 in a straight line with a zero deflection angle. However, the total dispersion of the beamlets 214, 216, and 218 generated by the beam separator 222 may also be non-zero. The beam separator 222 may separate the secondary charged particle beams 236, 238, and 240 from the beamlets 214, 216, and 218 and direct the secondary charged particle beams 236, 238, and 240 to the secondary optics 242.

[0031]

[0039] The deflection scanning unit 226 can deflect the beamlets 214, 216, and 218 to scan probe spots 270, 272, and 274 on the surface area of ​​the wafer 230. In response to the beamlets 214, 216, and 218 impinging on the probe spots 270, 272, and 274, secondary charged particle beams 236, 238, and 240 can be emitted from the wafer 230. The secondary charged particle beams 236, 238, and 240 can include charged particles (e.g., electrons) having a distribution of energies. For example, the secondary charged particle beams 236, 238, and 240 can be secondary electron beams including secondary electrons (energy ≦50 eV) and backscattered electrons (energy between 50 eV and the landing energy of the beamlets 214, 216, and 218). The secondary optics 242 can focus the secondary charged particle beams 236, 238, and 240 onto detection subregions 246, 248, and 250 of the charged particle detection device 244. The detection subregions 246, 248, and 250 can be configured to detect the corresponding secondary charged particle beams 236, 238, and 240 and generate corresponding signals (e.g., voltages, currents, etc.) that are used to reconstruct SCPM images of structures on or below the surface area of ​​the wafer 230.

[0032]

[0040] The signals generated may represent the intensities of the secondary charged particle beams 236, 238, and 240 and may be provided to an image processing system 290 in communication with the charged particle detection device 244, the primary projection optics 220, and the motorized wafer stage 280. The speed of movement of the motorized wafer stage 280 may be synchronized and adjusted with the beam deflection controlled by the deflection scanning unit 226 so that the movement of the scanning probe spots (e.g., scanning probe spots 270, 272, and 274) systematically covers the area of ​​interest on the wafer 230. Such synchronization and adjustment parameters may be adjusted to accommodate various materials of the wafer 230. For example, different materials of the wafer 230 may have different resistance-capacitance characteristics that may cause different signal sensitivities to the movement of the scanning probe spots.

[0033]

[0041] The intensities of the secondary charged particle beams 236, 238, and 240 may vary depending on the external or internal structure of the wafer 230 and may therefore indicate whether the wafer 230 contains defects. Furthermore, as described above, the beamlets 214, 216, and 218 may be projected onto different locations on the top surface of the wafer 230 or onto different sides of a local structure of the wafer 230 to generate secondary charged particle beams 236, 238, and 240 that may have different intensities. Thus, by mapping the intensities of the secondary charged particle beams 236, 238, and 240 with areas of the wafer 230, the image processing system 290 can reconstruct an image that reflects the characteristics of the internal or external structure of the wafer 230.

[0034]

[0042] In some embodiments, image processing system 290 may include an image acquirer 292, storage 294, and a controller 296. Image acquirer 292 may include one or more processors. For example, image acquirer 292 may include a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. Image acquirer 292 may be communicatively coupled to charged particle detection device 244 of beam tool 104A via a medium such as electrical conductors, fiber optic cable, portable storage media, IR, Bluetooth, the Internet, a wireless network, wireless radio, or a combination thereof. In some embodiments, image acquirer 292 may receive signals from charged particle detection device 244 and construct an image. In this manner, image acquirer 292 may acquire an SCPM image of wafer 230. Image acquirer 292 may also perform various post-processing functions, such as generating contours and overlaying indicators on the acquired image. Image acquirer 292 may be configured to adjust the brightness and contrast of the acquired image, etc. In some embodiments, storage 294 may be a storage medium such as a hard disk, a flash drive, cloud storage, random access memory (RAM), or other type of computer-readable memory. Storage 294 may be coupled to image acquirer 292 and may be used to save the scanned raw image data as original images and post-processed images. Image acquirer 292 and storage 294 may be connected to controller 296. In some embodiments, image acquirer 292, storage 294, and controller 296 may be integrated into one control unit.

[0035]

[0043] In some embodiments, the image acquirer 292 may acquire one or more SCPM images of the wafer based on the imaging signal received from the charged particle detection device 244. The imaging signal may correspond to a scanning motion for performing charged particle imaging. The acquired image may be a single image including multiple imaging areas. The single image may be stored in the storage 294. The single image may be an original image that may be divided into multiple regions. Each of these regions may include an imaging area that includes a feature of the wafer 230. The acquired image may include multiple images of a single imaging area of ​​the wafer 230 sampled multiple times over a temporal sequence. The multiple images may be stored in the storage 294. In some embodiments, the image processing system 290 may be configured to perform image processing steps using multiple images of the same location on the wafer 230.

[0036]

[0044] In some embodiments, image processing system 290 may include measurement circuitry (e.g., an analog-to-digital converter) to obtain a distribution of detected secondary charged particles (e.g., secondary electrons). The charged particle distribution data collected during the detection time window may be used in combination with corresponding scan path data of beamlets 214, 216, and 218 incident on the wafer surface to reconstruct an image of the wafer structure under inspection. The reconstructed image may be used to reveal various features of the internal or external structure of wafer 230, and thereby reveal any defects that may be present in the wafer.

[0037]

[0045] In some embodiments, the charged particles may be electrons. When electrons of the primary charged particle beam 210 are projected onto the surface of the wafer 230 (e.g., probe spots 270, 272, and 274), the electrons of the primary charged particle beam 210 may interact with particles of the wafer 230 and penetrate the surface of the wafer 230 to a certain depth. Some electrons of the primary charged particle beam 210 may interact with the material of the wafer 230 elastically (e.g., in the form of elastic scattering or collisions) and be reflected or bounced off the surface of the wafer 230. The elastic interaction preserves the total kinetic energy of the interacting objects (e.g., electrons of the primary charged particle beam 210), and the kinetic energy of the interacting objects is not converted into other forms of energy (e.g., heat, electromagnetic energy, etc.). The reflected electrons resulting from such elastic interactions may be referred to as backscattered electrons (BSE). Some electrons of the primary charged particle beam 210 may interact with the material of the wafer 230 inelastically (e.g., in the form of inelastic scattering or collisions). Inelastic interactions do not conserve the total kinetic energy of interacting objects, but rather convert some or all of the kinetic energy of the interacting objects into other forms of energy. For example, inelastic interactions can cause the kinetic energy of some electrons in the primary charged particle beam 210 to cause electronic excitation and transitions in atoms of a material. Such inelastic interactions can also produce electrons that leave the surface of the wafer 230, which may be called secondary electrons (SEs). The yield or emission rate of BSEs and SEs depends, among other things, on the material under inspection and the irradiation energy of the electrons of the primary charged particle beam 210 that are irradiated onto the surface of the material. The energy of the electrons of the primary charged particle beam 210 can be imparted in part by their acceleration voltage (e.g., the acceleration voltage between the anode and cathode of the charged particle source 202 in FIG. 2A). The amount of BSEs and SEs can be greater or less than (and even the same as) the injected electrons of the primary charged particle beam 210.

[0038]

[0046] Another example of a charged particle beam device will now be discussed with reference to Figure 2B. Beam tool 104B (also referred to herein as device 104B) may be an example of beam tool 104 and may be similar to beam tool 104A shown in Figure 2A. However, unlike device 104A, device 104B may be a single-beam tool that uses only one primary electron beam at a time to scan one location on the wafer.

[0039]

[0047] 2B, the apparatus 104B includes a wafer holder 136 supported by a motorized stage 134 for holding a wafer 150 to be inspected. The beam tool 104B includes an electron emitter, which may include a cathode 103, an anode 121, and a gun aperture 122. The beam tool 104B further includes a beam-limiting aperture 125, a condenser lens 126, a column aperture 135, an objective lens assembly 132, and a detector 144. The objective lens assembly 132 may, in some embodiments, be a modified SORIL lens including a pole piece 132a, a control electrode 132b, a deflector unit 132c, and an excitation coil 132d. In the detection or imaging process, electron beam 161 emitted from the tip of cathode 103 may be accelerated by the voltage on anode 121, pass through gun aperture 122, beam-limiting aperture 125, condenser lens 126, be focused by a modified SORIL lens to a probe spot 170, and impinge on the surface of wafer 150. Probe spot 170 may be scanned across the surface of wafer 150 by a deflector, such as deflector unit 132c in the SORIL lens or other deflector. Secondary or scattered particles, such as secondary electrons or scattered primary electrons emitted from the wafer surface, reveal the intensity of the beam and may be collected by detector 144 so that an image of the region of interest on wafer 150 can be reconstructed.

[0040]

[0048] An image processing system 199 may also be provided, including the image acquirer 120, the storage 130, and the controller 109. The image acquirer 120 may include one or more processors. For example, the image acquirer 120 may include a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, or the like, or a combination thereof. The image acquirer 120 may be connected to the detector 144 of the beam tool 104B via a medium such as electrical conductors, a fiber optic cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, wireless radio, or a combination thereof. The image acquirer 120 may receive signals from the detector 144 and construct an image. In this manner, the image acquirer 120 may acquire an image of the wafer 150. The image acquirer 120 may also perform various post-processing functions, such as averaging the image, generating contours, and superimposing indicators on the acquired image. The image acquirer 120 may be configured to adjust the brightness and contrast of the acquired image, etc. The storage 130 may be a storage medium such as a hard disk, random access memory (RAM), cloud storage, or other types of computer-readable memory. The storage 130 may be coupled to the image acquirer 120 and may be used to store scanned raw image data as original images and post-processed images. The image acquirer 120 and the storage 130 may be connected to the controller 109. In some embodiments, the image acquirer 120, the storage 130, and the controller 109 may be integrated into one electronic control unit.

[0041]

[0049] In some embodiments, the image acquirer 120 can acquire one or more images of the sample based on an imaging signal received from the detector 144. The imaging signal can correspond to a scanning motion to perform charged particle imaging. The acquired image can be a single image including multiple imaging areas that can include various features of the wafer 150. The single image can be stored in the storage 130. The imaging can be performed based on imaging frames.

[0042]

[0050] The condenser and illumination optics of an electron beam tool can include or be supplemented by electromagnetic quadrupole electron lenses. For example, as shown in FIG. 2B , electron beam tool 104B can include a first quadrupole lens 148 and a second quadrupole lens 158. In some embodiments, the quadrupole lenses can be used to control the electron beam. For example, first quadrupole lens 148 can be controlled to adjust the beam current, and second quadrupole lens 158 can be controlled to adjust the beam spot size and beam shape.

[0043]

[0051] FIG. 2B illustrates a charged particle beam device that may use a single primary beam configured to generate secondary electrons by interacting with a wafer 150. As in the embodiment illustrated in FIG. 2B, a detector 144 may be positioned along the optical axis 105. The primary electron beam may be configured to travel along the optical axis 105. Accordingly, the detector 144 may include a hole in its center through which the primary electron beam can pass to reach the wafer 150. FIG. 2B illustrates an example of a detector 144 with an opening in its center. However, some embodiments may use a detector positioned off the optical axis along which the primary electron beam travels. For example, as in the embodiment illustrated in FIG. 2B above, a beam separator 222 may be provided to direct the secondary electron beam toward the off-axis detector. As illustrated in FIG. 2A, the beam separator 222 may be configured to redirect the secondary electron beam toward an electron detection device 244.

[0044]

[0052] Images generated by SCPM can be used for defect inspection. For example, a generated image capturing a test device area of ​​a wafer can be compared to a reference image capturing the same test device area. The reference image may be predetermined (e.g., by simulation) and may not contain known defects. If the difference between the generated image and the reference image exceeds an acceptable level, a potential defect can be identified. As another example, SCPM can scan multiple areas of a wafer, each containing identically designed test device areas, and generate multiple images capturing those test device areas as manufactured. The multiple images can be compared to each other. If the difference between the multiple images exceeds an acceptable level, a potential defect can be identified.

[0045]

[0053] Reference is now made to FIG. 3, which is a cross-sectional view of a conventional magnetic lens assembly. As shown in FIG. 3, the magnetic lens assembly 300 may include a coil 310, a bobbin 320, and a pole piece 330. In FIG. 3, the longitudinal axis of the magnetic lens assembly 300 may coincide with the primary optical axis 301. The coil 310 may be an electromagnetic coil and may be disposed within the bobbin 320. The bobbin 320 may include a cooling system that absorbs heat generated by the coil 310. As shown in FIG. 3, the bobbin 320 includes a tube 322 as the cooling system. The tube 322 may be fitted into a groove 321 formed in the bobbin 320 and may circulate a fluid that absorbs heat generated by the coil 310. The tube 322 may be attached within the groove 321 with a thermally conductive material, such as epoxy. Fluid is supplied to the tube 322 from outside the system (e.g., a fluid resource), circulates through the tube 322 and the bobbin 320, absorbing heat generated by the coil 310, and the heated fluid is discharged from the bobbin 320.

[0046]

[0054] In a conventional architecture, the magnetic lens assembly 300 can utilize air as another heat dissipation medium from the coil 310, in addition to fluid. As shown in FIG. 3 , the magnetic lens assembly 300 includes an O-ring 325 configured to seal air within a space that contains the bobbin 320 containing the coil 310. In FIG. 3 , an air jacket is formed that contains the bobbin 320 and the coil 310 by introducing pressurized air and sealing the air with the O-ring 325. As shown in FIG. 3 , the coil 310 and bobbin 320 can be surrounded by air. In this conventional structure, air can be trapped in the space between the coil 310 / bobbin 320 and the pole piece 330 sealed with the O-ring 325. In the magnetic lens assembly 300, heat generated by the coil 310 can also be dissipated by thermal convection using the air sealed by the O-ring 325 as a heat transfer medium. However, when heat is dissipated outside the coil 310 by thermal convection, the heat from the coil 310 may be transferred to the pole pieces 330, which may still cause thermal expansion of the pole pieces 330 and deformation of the geometry of the pole pieces 330. As a result, the magnetic lens assembly 300 still faces beam placement accuracy errors due to the thermal expansion or deformation of the pole pieces 330. Therefore, there is a need for a cooling mechanism that can efficiently cool the coil 310 while minimizing heat transfer to the pole pieces 330.

[0047]

[0055] FIG. 4 is a cross-sectional view of an exemplary magnetic lens assembly consistent with embodiments of the present disclosure. In some embodiments, magnetic lens assembly 400 can be an objective lens (e.g., objective lens 228 of FIG. 2A) or an objective lens assembly (e.g., objective lens assembly 132 of FIG. 2B). As shown in FIG. 4, magnetic lens assembly 400 can include a coil 410, a housing 420, and a pole piece 430. In FIG. 4, a longitudinal axis of magnetic lens assembly 400 can coincide with a primary optical axis 401. In some embodiments, primary optical axis 401 can be a primary optical axis, such as primary optical axis 260 of device 104A of FIG. 2A or optical axis 105 of FIG. 2B.

[0048]

[0056] In some embodiments, the coil 410 may be an electromagnetic coil configured to adjust the focus of a single or multiple charged particle beams. The coil 410 may include a conductor such as a wire in the shape of a coil, spiral, helix, or the like. A current may be passed through the coil 410 to generate a circular magnetic field around the conductor. In a coil configuration, the conductor may be wound multiple times to increase the magnetic field density. The coil 410 may include a conductor including, but not limited to, copper, aluminum, silver, or the like. In some embodiments, the conductive wire, such as copper wire, may be encapsulated in an insulating material. Due to the large amount of heat generated by passing a current through the coil 410, a thermal gap filler material may be applied between each layer of the coil. The thermal gap filler material may provide a current of 1 W.m to dissipate localized heat. -1 .K -1 5 x 10 to provide thermal conductivity and electrical insulation between the two layers of conductor coil. 12 It may include a thermal gap filler gel, putty, or pad having an electrical resistance of ohms or greater, although it should be understood that other suitable thermal gap filler materials may also be used.

[0049]

[0057] In some embodiments, housing 420 may be configured to house coil 410. As shown in Figure 4, housing 420 may be configured to house the entire coil 410. In some embodiments, housing 420 may be configured to house at least a portion of coil 410. In some embodiments, housing 420 may be configured to include a bobbin around which coil 410 is wound.

[0050]

[0058] According to some embodiments of the present disclosure, the housing 420 may have a channel 421 or multiple channels 421. As referred to herein, a channel may be a path through which a fluid may pass or circulate, and may include multiple channels. In some embodiments, the housing 420 includes multiple channels 421 through which a fluid may circulate. The fluid may include a cooling fluid, including but not limited to a coolant, a cooling liquid, water, a gas, a compressed gas, or a mixture thereof. It should be understood that the terms channel, multiple channels, channel, and cooling channel may be used interchangeably herein.

[0051]

[0059] In some embodiments, the housing 420 with cooling channels 421 can provide a cooling capacity of 20-2000 W.m under standard measurement conditions. -1 .K -1 The cooling channels 421 may comprise a single material having a thermal conductivity within the range of 0.1 to 1.0, such as, but not limited to, materials including aluminum, titanium, copper, graphite, aluminum nitride, aluminum carbide, metal alloys, metal ceramic composites, etc. In some embodiments, the housing 420 with the cooling channels 421 may comprise multiple materials having different thermal conductivities and machinability, for example, a portion of the housing 420 may comprise aluminum and the cooling channels 421 may comprise titanium. Other combinations are possible.

[0052]

[0060] In some embodiments, the housing 420 having the plurality of channels 421 may comprise a monolithic structure. A monolithic structure, as referred to herein, may be defined as a structure made from a single material. For example, the monolithic structure may be formed by a subtractive manufacturing process or an additive manufacturing process. A subtractive manufacturing process is a process of creating a three-dimensional (3D) object by sequentially cutting material from a block of material, either by hand or using a computer numerically controlled (CNC) machine. An additive manufacturing process is a process of creating a three-dimensional part by layering material together under computer-guided control, for example, 3D printing. In some embodiments, the housing 420 having the channels 421 may comprise an additively manufactured monolithic structure. An additively manufactured housing 420 having the channels 421 may comprise a single metal, such as, for example, aluminum or titanium.

[0053]

[0061] In some embodiments, the channel 421 may be disposed on the exterior surface of the housing 420 and may be disposed vertically, horizontally, or circumferentially around the housing 420. In some embodiments, the channel 421 may be disposed within the housing 420 and may be disposed vertically, horizontally, or circumferentially within the housing 420, as shown in FIG. 4 . Other channel layouts and configurations may be used as appropriate. FIG. 5A is a schematic diagram illustrating exemplary fluid channels formed within the housing 420 of the magnetic lens assembly 400 of FIG. 4 , consistent with embodiments of the present disclosure. FIG. 5A shows a cross-section of the housing 420 along section line A-A′ in FIG. 4 . In FIG. 5A , the channel 421 is configured to circulate fluid near the coil 410 below the channel 421. While FIGS. 4 and 5A illustrate the channel 421 being disposed above the coil 410, it will be understood that the channel 421 may be formed vertically, horizontally, or circumferentially along any path within the housing 420.

[0054]

[0062] 5A, the channel 421 can include an inlet terminal 426 and an outlet terminal 427. In some embodiments, the inlet terminal 426 can be configured to be coupled to an input channel that supplies fluid into the channel 421, and the outlet terminal 427 can be configured to be coupled to an outlet channel that discharges the circulated fluid from the channel 421. The fluid referred to herein can include, among other things, a liquid, a coolant, a cooling liquid, a gas, a compressed gas, or a mixture thereof. The fluid can be configured to absorb heat generated by passing a large current through the electromagnetic coil 410. The fluid can circulate through the channel 421 before being discharged out of the system via the outlet terminal 427.

[0055]

[0063] Input channel 422_1 and output channel 422_2 are shown in FIG. 5B, which is a schematic diagram illustrating housing 420 of magnetic lens assembly 400 of FIG. 4, consistent with an embodiment of the present disclosure. In some embodiments, input channel 422_1 is coupled to an inlet terminal of a channel internal to housing 420 (e.g., inlet terminal 426 of channel 421). In some embodiments, input channel 422_1 extends outside housing 420 to receive fluid from a fluid supply (not shown). In some embodiments, output channel 422_2 is coupled to an outlet terminal of a channel internal to housing 420 (e.g., outlet terminal 427 of channel 421). In some embodiments, output channel 422_2 extends outside housing 420 to discharge circulated fluid out of housing 420.

[0056]

[0064] In some embodiments, channel 421 may include a single loop surrounding housing 420. In some embodiments, channel 421 may include multiple loops surrounding housing 420 based on the application and system cooling requirements. In some embodiments, channel 421 may include one or more input channels and a single output channel. For example, additional input channels may be used. In some embodiments, channel 421 may include a single input channel and multiple output channels. Other combinations of numbers and configurations of input and output channels may be designed and employed as appropriate.

[0057]

[0065] In some embodiments, the channel 421 may comprise an enclosed passageway, such as a channel having a circular or elliptical cross-section and a wall thickness. The cross-sectional shape and cross-sectional area may be determined based on the application, space availability, material compatibility, or cooling requirements of the system. The channel 421 may comprise a uniform or non-uniform wall thickness. It should be understood that the size, shape, cross-section, area, total volume, and other related dimensions of the channel 421 may be determined and designed as needed.

[0058]

[0066] Referring again to FIG. 4 , the magnetic lens assembly 400 may further include a pole piece 430. In some embodiments, the pole piece 430 may be configured to induce the magnetic field generated by the coil 410. As shown in FIG. 4 , the pole piece 430 may be configured to surround the housing 420 that contains the coil 410 therein. In some embodiments, the pole piece 430 may also be configured with a gap 431 for inducing the magnetic field, as shown in FIG. 4 . In some embodiments, the pole piece 430 may include a ferromagnetic material, including but not limited to, cobalt, nickel, iron, chromium dioxide, or alloys thereof. Ferromagnetic materials, as used herein, may refer to materials that have a large positive susceptibility to an external magnetic field. Ferromagnetic materials exhibit a strong attraction to the magnetic field and can retain their magnetic properties even after the external field is removed. In some embodiments, the pole piece 430 may include a material with low thermal conductivity, including but not limited to, ceramic materials such as cerium oxide, silica, fused silica, quartz, and zirconium dioxide. In some embodiments, the pole piece 430 may comprise a material coated with a low thermal conductivity material, such as, for example, cerium oxide.

[0059]

[0067] According to some embodiments of the present disclosure, the pole piece 430 can be thermally isolated from the housing 420 such that there is a gap between the housing 420 and the pole piece 430. In FIG. 4 , the inner surface of the pole piece 430 facing the housing 420 is shown separated from the outer surface of the housing 420 by a distance d. In some embodiments, the pole piece 430 is separated from the housing 420 on all sides. In some embodiments, the distance d between the housing 420 and the pole piece 430 can vary depending on the location on the outer surface of the housing 420 or on the inner surface of the pole piece 430. According to some embodiments of the present disclosure, the gap between the housing 420 and the pole piece 430 can be maintained under vacuum pressure during operation of the magnetic lens assembly 400. In some embodiments, the vacuum pressure can be ultra-high vacuum (UHV) pressure. In some embodiments, the vacuum pressure can be in the range of 10e-11 Torr to 10e-6 Torr. In some embodiments, the magnetic lens assembly 400 may be disposed in a vacuum chamber (not shown), which may provide a vacuum pressure (e.g., UHV) to maintain the gap between the housing 420 and the pole piece 430 under the vacuum pressure provided by the vacuum chamber. In some embodiments, the vacuum chamber may be evacuated of air or gas using a vacuum pump. In some embodiments, a vacuum chamber present in the inspection system may be utilized as the vacuum chamber for supplying UHV pressure to the magnetic lens assembly 400. For example, the vacuum chamber may be the main chamber 101 of the EBI system 100 shown in FIG. 1 .

[0060]

[0068] Because the gap between the housing 420 and the pole piece 430 is a vacuum, heat transfer from the coil 410 to the pole piece 430 due to thermal convection can be minimized, thereby reducing the amount of heat transferred from the coil 410 to the pole piece 430. Because thermal isolation is a function of the vacuum level, not the distance between the housing 420 and the pole piece 430, some embodiments can utilize a minimum distance (e.g., distance d) between the housing 420 and the pole piece 430 to thermally isolate the pole piece 430. That is, as the vacuum pressure increases, better thermal isolation can be achieved regardless of the actual distance between the housing 420 and the pole piece 430.

[0061]

[0069] It will be appreciated that while the magnetic lens assembly 400 of FIG. 4 eliminates one heat dissipation path from the coil 410 (e.g., thermal convection through air), the efficiency of heat dissipation from the coil 410 may not be affected by the loss of the heat dissipation path. Because the heat dissipation from the coil 410 may be concentrated in the cooling fluid circulating through the channels 421, the efficiency of heat dissipation may not be reduced by the loss of the air dissipation path. In some embodiments, the heat from the coil 410 may be concentrated in the cooling fluid without dissipation, thereby fully utilizing the cooling fluid's ability to dissipate heat from the coil 410, thereby increasing the efficiency of heat dissipation. This allows for more efficient dissipation of heat from the coil 410 while maintaining a minimal level of heat transfer to the pole piece 430, thereby minimizing thermal expansion or dimensional deformation of the pole piece 430, according to some embodiments of the present disclosure.

[0062]

[0070] Referring again to FIG. 4 , consistent with some embodiments of the present disclosure, the magnetic lens assembly 400 may further include a coupling structure 440 that couples the housing 420 to the pole piece 430. As shown in FIG. 4 , the coupling structure 440 may be configured to position the housing 420 in an interior space of the pole piece 430 while separating the pole piece 430 from the housing 420. FIG. 6A is a schematic diagram illustrating an example coupling structure 440 that couples the housing 420 to the pole piece 430, consistent with embodiments of the present disclosure. As shown in FIG. 6A , the coupling structure 440 may include a screw 441 configured to secure the housing 420 relative to the pole piece 430. According to some embodiments of the present disclosure, the housing 420 may be coupled to the pole piece 430 using the coupling structure 440 in a manner that can minimize heat transfer to the pole piece 430. In some embodiments, a head portion of the screw 441 directly or indirectly contacts an outer surface of the pole piece 430, and a tip portion of the screw 441 is disposed within a recess formed in the housing 420. In some embodiments, as shown in FIG. 6A , the screw 441 can be configured so that the bottom surface of the head portion of the screw 441 contacts the outer surface of the pole piece 430, while the side surface of the head portion does not contact the structure 433 surrounding the head portion. As shown in FIG. 6A , the recess can be configured to receive the tip portion of the screw 441. In some embodiments, the screw 441 is configured to be inserted into a hole formed in the pole piece 430 when the housing 420 is fixed to the pole piece 430. In some embodiments, the screw 441 can be configured to have a width W1 narrower than the width W2 of the hole formed in the pole piece 430 so that the screw 441 does not contact the inner wall forming the hole in the pole piece 430 during installation. Because the screw 441 does not contact the inner wall of the pole piece 430, heat transfer from the coil 410 to the pole piece 430 through the screw 410 can be minimized when the housing 420 is fixed to the pole piece 430.

[0063]

[0071] In some embodiments, the coupling structure 440 may further include a standoff 442 configured to maintain a distance between the housing 420 and the pole piece 430. As shown in FIG. 6A , the standoff 442 may also be configured to allow a screw 441 to be inserted into a hole formed therein. In some embodiments, a width W3 of the hole in the standoff 442 may be wider than a width W1 of the screw 441 so that the screw 441 does not come into contact with an inner wall defining the hole in the standoff 442 during installation. This can minimize heat transfer from the coil 410 to the pole piece 430 via the screw 441 and the standoff 442. In some embodiments, the coupling structure 440 may include a material with low thermal conductivity. In some embodiments, materials with low thermal conductivity may include polystyrene, polyethylene terephthalate (PET), polyetheretherketone (PEEK), fiberglass, paper, polycarbonate, polyester, low-density polyethylene, high-density polyethylene, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), glass, silicone, styrofoam, steatite, etc. In some embodiments, the screws 441 that secure the housing 420 to the pole piece may include a material with high mechanical strength. In some embodiments, the screws 441 may include stainless steel 303, stainless steel 304, stainless steel 316, stainless steel 316L, titanium grade 2, titanium grade 5, aluminum, brass, bronze, carbon fiber, ceramic, fiberglass, iron, lead, nickel, nickel alloy, plastic, etc. In some embodiments, the standoffs 442 may comprise a low thermal conductivity material such as polystyrene, polyethylene terephthalate (PET), polyetheretherketone (PEEK), fiberglass, paper, polycarbonate, polyester, low density polyethylene, high density polyethylene, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), glass, silicone, styrofoam, steatite, or the like.In some embodiments, the magnetic lens assembly 400 may have one or more coupling structures 440 for securing the housing 420 relative to the pole piece 430. While Figure 5 illustrates three coupling structures 440 mounted within the housing 420, it will be understood that any number of coupling structures 440 may be utilized. While the coupling structures 440 are discussed with reference to Figure 6A, it will be understood that any configuration that similarly minimizes heat transfer from the coil 410 to the pole piece 430 may be utilized.

[0064]

[0072] Similarly, other components of the magnetic lens assembly 400 may be configured to minimize heat transfer to the pole piece 430. For example, fluid input or output channels may be provided to minimize heat transfer to the pole piece 430. FIG. 6B is a schematic diagram illustrating exemplary fluid channels in the magnetic lens assembly 400 of FIG. 4 , consistent with embodiments of the present disclosure. According to some embodiments of the present disclosure, the fluid channel 422 may be an input channel (e.g., input channel 422_1) configured to supply fluid to the channel 421, or an output channel (e.g., output channel 422_2) configured to discharge fluid from the channel 421. As shown in FIG. 6B , in some embodiments, the fluid channel 422 may be configured as a fluid tube. The fluid channel 422 may be connected to an inlet terminal of the channel 421 (e.g., inlet terminal 426 in FIG. 5A ) or an outlet terminal of the channel 421 (e.g., outlet terminal 426 in FIG. 5A ). In some embodiments, an O-ring 428 may be utilized when connecting the fluid channel 422 to the channel 421 of the magnetic lens assembly 400 to prevent fluid leakage. The O-ring 428 may be disposed at the interface of two contacting surfaces. For example, FIG. 6B shows a first O-ring 428_1 disposed at the interface between the fluid channel 422 and the housing 420 and a second O-ring 428_2 disposed at the interface between the fluid channel 422 and a structure 432 disposed outside the pole piece 430. According to some embodiments of the present disclosure, the fluid channel 422 may be coupled to the channel 421 in a manner that can minimize heat transfer to the pole piece 430. In some embodiments, the fluid channel 422 is configured to pass through a hole formed in the pole piece 430. In some embodiments, the fluid channel 422 may be configured to have a width W4 that is narrower than a width W5 of the hole formed in the pole piece 430 so that the fluid channel 422 does not contact the inner wall forming the hole in the pole piece 430 when installed. Because the fluid channel 422 does not contact the inner wall of the pole piece 430, heat transfer from the coil 410 to the pole piece 430 through the fluid channel 422 can be minimized.In some embodiments, as shown in Figure 6B, the fluid channel 422 can be positioned such that the fluid channel 422 does not directly contact the pole piece 430. Figure 6B shows that the fluid channel 422 is not fixed to the pole piece 430, but only passes through the pole piece 430. As an example, as shown in Figure 6B, the fluid channel 422 can be fixed to a structure 432 disposed outside the pole piece 430. In some embodiments, the fluid channel 422 can include a low thermal conductivity material, such as titanium grade 5.

[0065]

[0073] In some embodiments, as shown in FIG. 5B , the magnetic lens assembly 400 may have two fluid channels 422_1 and 422_2 connected to the channel 421. For example, the first fluid channel 422_1 may be connected to the inlet terminal 426 of the channel 421 as shown in FIG. 5A , and the second fluid channel 422_2 may be connected to the outlet terminal 427 of the channel 421 as shown in FIG. 5A . While FIG. 5B shows two fluid channels 422_1 and 422_2 located in the housing 420, it will be understood that any number of fluid channels 422 may be utilized. While the fluid channels 422 were discussed with reference to FIG. 6B , it will be understood that any configuration that similarly minimizes heat transfer from the coil 410 to the pole piece 430 may be utilized.

[0066]

[0074] 5B , consistent with some embodiments of the present disclosure, magnetic lens assembly 400 may further include a wire tube 450 that provides wire to coil 310. In some embodiments, wire tube 450 may be configured to provide wire to coil 310 from outside the system. In some embodiments, wire tube 450 may also be configured to minimize heat transfer to pole piece 430, similar to fluid channel 422 shown in FIG. 6A . For example, wire tube 450 may be configured as a tube with a path for wire provided therein. In some embodiments, wire tube 450 may be positioned such that wire tube 450 does not directly contact pole piece 430, similar to the configuration of fluid channel 422 in FIG. 6B .

[0067]

[0075] According to some embodiments of the present disclosure, the magnetic lens assembly 400 may further include a thermal insulation layer (not shown) between the housing 420 and the pole piece 430. In some embodiments, the thermal insulation layer may be configured to further reduce heat transfer to the pole piece 430. In some embodiments, the thermal insulation layer may be configured to reduce heat transfer by radiation caused by a temperature difference between two objects, such as between the housing 420 and the pole piece 430. In some embodiments, the thermal insulation layer may be configured to block infrared energy transfer from the heat source, i.e., the coil 410, to the pole piece 430. In some embodiments, the thermal insulation layer may be a multi-layer insulation material. For example, the thermal insulation layer may include an aluminum layer coated on one side of the thermal insulation layer. The thermal insulation layer may include a fiberglass layer on another side of the thermal insulation layer. In some embodiments, the thermal insulation layer may be formed on either the outer surface of the housing 420 or the inner surface of the pole piece 430.

[0068]

[0076] The following clauses may be used to further describe the embodiments: 1. A coil and a housing that accommodates the coil; a pole piece separated from the housing such that there is a gap between the housing and the pole piece; a magnetic lens assembly configured to have a vacuum pressure in the gap; 2. The magnetic lens assembly of clause 1, wherein the vacuum pressure is an ultra-high vacuum pressure. 3. A magnetic lens assembly according to clause 1 or 2, wherein the housing is coupled to the pole pieces via a low thermal conductivity material. 4. The magnetic lens assembly of clause 3, wherein the low thermal conductivity material comprises polystyrene, polyethylene terephthalate (PET), polyether ether ketone (PEEK), glass fiber, paper, polycarbonate, polyester, polyethylene low density, polyethylene high density, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), glass, silicone, styrofoam, or steatite. 5. A magnetic lens assembly as described in any one of clauses 1 to 4, wherein the housing is coupled to the pole piece via a screw and a standoff disposed between the housing and the pole piece. 6. The magnetic lens assembly of clause 5, wherein the standoff comprises polystyrene, polyethylene terephthalate (PET), polyether ether ketone (PEEK), fiberglass, paper, polycarbonate, polyester, polyethylene low density, polyethylene high density, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), glass, silicone, styrofoam, or steatite. 7. The magnetic lens assembly of clause 5, wherein the screws comprise stainless steel 303, stainless steel 304, stainless steel 316, stainless steel 316L, titanium grade 2, titanium grade 5, aluminum, brass, bronze, carbon fiber, ceramic, fiberglass, iron, lead, nickel, nickel alloy, or plastic. 8. A magnetic lens assembly described in any one of clauses 5 to 7, wherein the screw has a portion that is inserted into a hole formed in the housing, and that portion of the screw has a width that is narrower than the width of the hole formed in the housing. 9. A magnetic lens assembly as described in any one of clauses 1 to 8, further comprising a thermal insulating layer between the housing and the pole piece. 10. The magnetic lens assembly of clause 9, wherein the thermal insulating layer comprises a layer having fiberglass or aluminum. 11. Housing an inlet terminal configured to receive a fluid; a channel formed within the housing and configured to circulate a fluid received by the inlet terminal; an outlet terminal configured to release fluid from the channel; 11. The magnetic lens assembly of any one of clauses 1-10, further comprising: 12. The magnetic lens assembly of clause 11, wherein the housing further includes an input tube configured to supply fluid to the channel via the inlet terminal, the input tube not contacting the pole piece when installed. 13. A magnetic lens assembly according to any one of clauses 1 to 12, wherein the housing is enclosed within a vacuum environment provided within the pole piece. 14. A charged particle beam source configured to generate a primary charged particle beam for scanning a sample; an objective lens assembly configured to affect the charged particle beam; 1. A charged particle beam inspection apparatus comprising: an objective lens assembly comprising: A coil and a housing that accommodates the coil; a pole piece separated from the housing such that there is a gap between the housing and the pole piece; wherein the objective lens assembly is configured to have a vacuum pressure in the gap. 15. A charged particle beam inspection apparatus according to clause 14, wherein the vacuum pressure is an ultra-high vacuum pressure. 16. A charged particle beam inspection apparatus according to clause 14 or 15, wherein the housing is coupled to the pole piece via a low thermal conductivity material. 17. A charged particle beam inspection apparatus as described in clause 16, wherein the low thermal conductivity material includes polystyrene, polyethylene terephthalate (PET), polyether ether ketone (PEEK), glass fiber, paper, polycarbonate, polyester, polyethylene low density, polyethylene high density, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), glass, silicon, styrofoam, or steatite. 18. A charged particle beam inspection apparatus according to any one of clauses 14 to 17, wherein the housing is coupled to the pole piece via a screw and a standoff disposed between the housing and the pole piece. 19. A charged particle beam inspection apparatus as described in clause 18, wherein the standoff comprises polystyrene, polyethylene terephthalate (PET), polyether ether ketone (PEEK), fiberglass, paper, polycarbonate, polyester, polyethylene low density, polyethylene high density, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), glass, silicone, styrofoam, or steatite. 20. A charged particle beam inspection apparatus as described in clause 19, wherein the screws include stainless steel 303, stainless steel 304, stainless steel 316, stainless steel 316L, titanium grade 2, titanium grade 5, aluminum, brass, bronze, carbon fiber, ceramic, fiberglass, iron, lead, nickel, nickel alloy or plastic. 21. A charged particle beam inspection device described in any one of clauses 18 to 20, wherein the screw has a portion that is inserted into a hole formed in the housing, and that portion of the screw has a width that is narrower than the width of the hole formed in the housing. 22. A charged particle beam inspection device according to any one of clauses 14 to 21, wherein the objective lens assembly further comprises a thermal insulating layer between the housing and the pole piece. 23. A charged particle beam inspection apparatus as described in clause 22, wherein the thermal insulation layer comprises a layer having glass fiber or aluminum. 24. Housing an inlet terminal configured to receive a fluid; a channel formed within the housing and configured to circulate a fluid received by the inlet terminal; an outlet terminal configured to release fluid from the channel; 24. The charged particle beam inspection device of any one of clauses 14 to 23, further comprising: 25. The charged particle beam inspection apparatus of clause 24, wherein the housing further includes an input tube configured to supply fluid to the channel via the inlet terminal, the input tube not contacting the pole piece when installed. 26. A magnetic lens assembly according to any one of clauses 14 to 25, wherein the housing is enclosed within a vacuum environment provided within the pole piece.

[0069]

[0077] The block diagrams in the figures may illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block in the schematic diagrams may represent a specific arithmetic or logical operation that may be implemented using hardware, such as electronic circuits. The blocks may also represent modules, segments, or portions of code that include one or more executable instructions for implementing the specified logical function. It should be understood that in some alternative implementations, the functions shown in the blocks may occur in an order different from that shown in the figures. For example, depending on the functionality involved, two blocks shown in succession may be executed or implemented substantially simultaneously, or the two blocks may be executed in the reverse order. Some blocks may also be omitted. It should also be understood that each block and combination of blocks in the block diagrams may be implemented by a dedicated hardware-based system that performs the specified function or act, or a combination of dedicated hardware and computer instructions.

[0070]

[0078] It is to be understood that the embodiments of the present disclosure are not limited to the exact configurations described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope of the present invention. While the present disclosure has been described in connection with various embodiments, other embodiments will become apparent to those skilled in the art from consideration of the specification and practice of the techniques disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

Claims

1. A coil and a housing that accommodates the coil; a pole piece separated from the housing such that there is a gap between the housing and the pole piece; 10. A magnetic lens assembly comprising: a magnetic lens assembly having a vacuum pressure in the gap;

2. The magnetic lens assembly of claim 1 , wherein the vacuum pressure is an ultra-high vacuum pressure.

3. The magnetic lens assembly of claim 1 , wherein the housing is coupled to the pole pieces via a low thermal conductivity material.

4. 4. The magnetic lens assembly of claim 3, wherein the low thermal conductivity material comprises polystyrene, polyethylene terephthalate (PET), polyetheretherketone (PEEK), glass fiber, paper, polycarbonate, polyester, polyethylene low density, polyethylene high density, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), glass, silicone, expanded polystyrene, or steatite.

5. The magnetic lens assembly of claim 1 , wherein the housing is coupled to the pole piece via a screw and a standoff disposed between the housing and the pole piece.

6. 6. The magnetic lens assembly of claim 5, wherein the standoff comprises polystyrene, polyethylene terephthalate (PET), polyetheretherketone (PEEK), fiberglass, paper, polycarbonate, polyester, polyethylene low density, polyethylene high density, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), glass, silicone, expanded polystyrene, or steatite.

7. 6. The magnetic lens assembly of claim 5, wherein the screw comprises stainless steel 303, stainless steel 304, stainless steel 316, stainless steel 316L, titanium grade 2, titanium grade 5, aluminum, brass, bronze, carbon fiber, ceramic, fiberglass, iron, lead, nickel, nickel alloy, or plastic.

8. 6. The magnetic lens assembly of claim 5, wherein the screw has a portion that is inserted into a hole formed in the housing, the portion of the screw having a width that is narrower than a width of the hole formed in the housing.

9. The magnetic lens assembly of claim 1 further comprising a thermal barrier between the housing and the pole piece.

10. The magnetic lens assembly of claim 9 , wherein the thermal insulation layer comprises a layer comprising fiberglass or aluminum.

11. The housing includes: an inlet terminal for receiving a fluid; a channel formed within the housing and received by the inlet terminal for circulating the fluid; an outlet terminal for discharging the fluid from the channel; The magnetic lens assembly of claim 1 further comprising:

12. The magnetic lens assembly of claim 11 , wherein the housing further comprises an input tube that supplies the fluid to the channel through the inlet terminal, the input tube not contacting the pole piece when installed.

13. The magnetic lens assembly of claim 1 , wherein the housing is enclosed within a vacuum environment provided within the pole piece.

14. a charged particle beam source that generates a primary charged particle beam for scanning the sample; an objective lens assembly for influencing said charged particle beam; 1. A charged particle beam inspection apparatus comprising: A coil and a housing that accommodates the coil; a pole piece separated from the housing such that there is a gap between the housing and the pole piece; wherein the objective lens assembly has a vacuum pressure in the gap.

15. The charged particle beam inspection system of claim 14, wherein the vacuum pressure is an ultra-high vacuum pressure.

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