Thermal deformation compensation in charged-particle beam apparatus

Abstract

A component for mounting a lens in a charged-particle beam apparatus has a coefficient of thermal expansion (CTE) and a shape configured to cause the component to deflect by a predictable amount in a Z direction when subject to a predetermined non-zero temperature change such that a working distance of the lens remains substantially unchanged over the predetermined non-zero temperature range.

Description

THERMAL DEFORMATION COMPENSATION IN CHARGED-PARTICLE BEAM APPARATUSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 613,590 which was filed on December 21, 2023 and US application 63 / 661,544 which was filed on June 18, 2024 which are incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The description herein generally relates to methods and samples for thermal deformation compensation in components of a charged-particle beam apparatus.BACKGROUND

[0003] The performance of a charged-particle beam apparatus, such as, for example, a scanning electron microscope (SEM) can be influenced by variations in atmospheric temperature. Atmospheric temperature changes can cause thermal drift, which is a slow, gradual change in the position of the particle beam or the specimen stage that can lead to a loss of precision in imaging and may require frequent recalibration. Different components of a charged-particle beam apparatus may be made of materials having different coefficients of thermal expansion (CTE) and may expand and contract at different rates with temperature changes. This can cause misalignment or changes in the focal length of lenses, potentially affecting image resolution. Moreover, the refocusing procedure is typically time consuming.SUMMARY

[0004] Some embodiments provide a component for mounting a lens in a charged-particle beam apparatus is disclosed. The component may include a first part having a first coefficient of thermal expansion (CTE) and a second part having a second CTE different from the first CTE. The first and second parts may be arranged such that a working distance of the lens, mounted to a body of the charged-particle beam apparatus using the component, remains substantially unchanged over a nonzero predetermined temperature range.

[0005] Some embodiments provide a component for mounting a lens in a charged-particle beam apparatus includes a first part having a first coefficient of thermal expansion (CTE), a second part having a second CTE different from the first CTE, and a third part having a third CTE different from the first CTE. The second and third parts may be fixed to opposite sides of the first part. The first, second, and third parts may be arranged such that a working distance of the lens coupled to the charged-particle beam apparatus using the first, second, and third parts remain substantially unchanged over a non-zero predetermined temperature range.

[0006] Some embodiments provide a component for mounting a lens in a charged-particle beam apparatus, includes a first part including a first cylindrical portion that extends along an optical axis of the charged-particle beam apparatus and a first annular flange that extends from one end of the first cylindrical portion substantially perpendicular to the optical axis. The first annular flange may include an end surface and a central cavity that extends from the end surface along the optical axis. The component may also include a second part. The second part may include a second cylindrical portion having a second cavity that extends along the optical axis and a second annular flange extending around the second cavity from one end of the second cylindrical portion. The first part and the second part may be arranged such that a working distance of the lens coupled to the charged-particle beam apparatus using the first and second parts remain substantially unchanged over a non-zero predetermined temperature range.

[0007] Some embodiments provide an apparatus for mounting a lens in a charged-particle beam apparatus. The apparatus may include a component coupling the lens to a body of the charged-particle beam apparatus. The component may have a coefficient of thermal expansion (CTE) and a shape configured to cause the component to deflect by a predictable amount in a Z direction when subject to a predetermined non-zero temperature change such that a working distance of the lens remains substantially unchanged over the predetermined non-zero temperature range.

[0008] Some embodiments provide an apparatus for mounting a lens in a charged-particle beam apparatus. The apparatus may include an annular component having a central axis aligned with an optical axis of the charged-particle beam apparatus and include an outer portion disposed radially outwards of an inner portion. The outer portion may be coupled to an electron column of the charged- particle beam apparatus and the inner portion may be coupled to the lens. The component may be configured to deflect by a predictable amount in a Z direction when subject to a predetermined nonzero temperature change such that a working distance of the lens remains substantially unchanged over the predetermined non-zero temperature range.

[0009] Some embodiments provide a charged particle beam system. The charged particle beam system may include a lens, a body, and a component for mounting the lens to the body of the charged- particle beam system. The component may include a first part having a first coefficient of thermal expansion (CTE), and a second part having a second CTE different from the first CTE. The first and second parts may be arranged such that a working distance of the lens, mounted to a body of the charged-particle beam system using the component, remains substantially unchanged over a non-zero predetermined temperature range.

[0010] Other advantages of the embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present disclosure.BRIEF DESCRIPTION OF FIGURES

[0011] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments, taken in conjunction with the accompanying drawings.

[0012] FIG. 1 is a schematic illustration of an exemplary charged particle beam inspection or metrology system, consistent with some embodiments of the present disclosure.

[0013] FIG. 2A is a schematic illustration of an exemplary multi-beam tool that may be part of the charged particle beam inspection system of FIG. 1.

[0014] FIG. 2B is a schematic illustration of an exemplary single -beam tool that may be part of the charged particle beam inspection system FIG. 1.

[0015] FIGs. 3A-3F are schematic illustrations depicting an exemplary coupling mechanism of an objective lens to the tool of FIGs. 2 A or 2B.

[0016] FIGs. 4A-4B are schematic illustrations of exemplary coupling mechanisms of the objective lens to the tool, consistent with some embodiments of the present disclosure.

[0017] FIGs. 5A-5C are schematic illustrations of exemplary coupling mechanisms of the objective lens to the tool, consistent with some embodiments of the present disclosure.

[0018] FIG. 6 is a schematic illustration of an exemplary coupling mechanism of the objective lens to the tool, consistent with some embodiments of the present disclosure.

[0019] FIGs. 7A-7C are schematic illustrations of exemplary coupling mechanisms of the objective lens to the tool, consistent with some embodiments of the present disclosure.

[0020] FIG. 8 is a schematic illustration of an exemplary coupling mechanism of the objective lens to the tool, consistent with some embodiments of the present disclosure.

[0021] FIGs. 9A-9B are schematic illustrations of exemplary coupling mechanisms of the objective lens to the tool, consistent with some embodiments of the present disclosure.

[0022] FIGs. 10A-10C are exemplary configurations of compensators of an objective lens coupling mechanism, consistent with some embodiments of the present disclosure.DETAILED DESCRIPTION

[0023] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the disclosed embodiments as recited in the appended claims. For the sake of brevity, embodiments of the current disclosure may be the described with reference to an electron beam apparatus, such as, a scanning electron microscope. However, this is only exemplary, and aspects of the current disclosure may be applied to any charged-particle beam apparatus. For example, although some embodiments are described in the context of utilizing electronbeams, the disclosure is not so limited. Features of the current disclosure may also be applied to other types of apparatuses or devices that use other types of charged-particle beams (e.g., including protons, ions, muons, or any other particle carrying electric charges). Furthermore, other imaging systems may be used, such as optical imaging, photon detection, x-ray detection, ion detection, etc.

[0024] Electronic devices are constructed of circuits formed on a piece of semiconductor material called a substrate. The semiconductor material may include, for example, silicon, gallium arsenide, indium phosphide, or silicon germanium, or the like. Many circuits may be formed together on the same piece of silicon and are called integrated circuits or ICs. The size of these circuits has decreased dramatically so that many more of them can be fit on the substrate. For example, an IC chip in a smartphone can be as small as a thumbnail and yet may include over 2 billion transistors, the size of each transistor being less than 1 / 1000th the size of a human hair.

[0025] Making these ICs with extremely small structures or components is a complex, timeconsuming, and expensive process, often involving hundreds of individual steps. Errors in even one step have the potential to result in defects in the finished IC, rendering it useless. Thus, one goal of the manufacturing process is to avoid such defects to maximize the number of functional ICs made in the process; that is, to improve the overall yield of the process.

[0026] One component of improving yield is monitoring the chip-making process to ensure that it is producing a sufficient number of functional integrated circuits. One way to monitor the process is to inspect the chip circuit structures at various stages of their formation. Inspection can be conducted using a scanning charged-particle microscope (“SCPM”). For example, an SCPM may be a scanning electron microscope (SEM). A SCPM can be used to image these extremely small structures, in effect, taking a “picture” of the structures of the wafer. The image can be used to determine if the structure was formed properly in the proper location. If the structure is defective, then the process can be adjusted, so the defect is less likely to recur.

[0027] As the physical sizes of IC components continue to shrink, accuracy and yield in defect detection becomes increasingly important. In the context of an SEM used for inspection in semiconductor fabrication, resolution refers to the microscope’s ability to distinguish and display minute details in the sample being observed. Resolution is typically described in terms of spatial resolution, which is the smallest distance between two points on a sample's surface that can be distinguished as separate entities in the SEM image. The resolution of an SEM is a critical performance parameter in the semiconductor industry where extremely small features need to be accurately characterized. Performance of an SEM can be influenced by variations in temperature. For example, atmospheric temperature changes can cause temperature changes in the various components of the SEM, resulting in a gradual change in the position of the electron beam or the specimen stage resulting in a loss of precision in imaging. Similarly, dissimilar materials in the SEM may expand and contract differently resulting a loss of resolution.

[0028] Although the effect of atmospheric temperature variations may be reduced, for example, by housing the SEM in a controlled environment, eliminating such variations may be difficult. As feature sizes of the samples continue to decrease, accurately imaging these small features in the presence of unavoidable ambient temperature variations may be important. For example, the focal length and resolution of an SEM may change (increase or decrease) over time during an imaging session due to different thermal expansion of the SEM components. This changing resolution of the SEM over time may result in a loss of image sharpness and degradation of image quality over time. Embodiments of the present disclosure provide techniques to compensate for the different thermal expansion of components of an SEM (or another charged-particle beam apparatus) and thereby reduce image degradation over time.

[0029] Relative dimensions of components in drawings may be exaggerated for clarity. Within the following description of drawings, the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described. Other objects and advantages of the disclosure may be realized by the elements and combinations as set forth 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 stated objects or advantages.

[0030] As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a component includes A or B, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or A and B. As a second example, if it is stated that a component includes A, B, or C, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. Expressions such as “at least one of’ do not necessarily modify an entirety of a following list and do not necessarily modify each member of the list, such that “at least one of A, B, and C” should be understood as including only one of A, only one of B, only one of C, or any combination of A, B, and C. The phrase “one of A and B” or “any one of A and B” shall be interpreted in the broadest sense to include one of A, or one of B.

[0031] All relative terms such as “about,” “substantially,” “approximately,” etc., indicate a possible variation of ±10% (unless noted otherwise or another variation is specified). For example, a feature disclosed as being about “w” units wide (or long, thick, etc.) may vary in width from (w - O.lw) to (w + O.lw) units. Similarly, a width within a range of about A-B units can have a width between (A - 10%) and (B + 10%). Further, a width varying from, or between, A-B units includes the endpoints (e.g., A and B). In some cases, the specification or figures provide context to some of the relative terms used.

[0032] FIG. 1 illustrates an exemplary electron beam inspection (EBI) system 100 consistent with embodiments of the present disclosure. EBI system 100 is a type of charged-particle beam apparatus. EBI system 100 may be used for imaging. As shown in FIG. 1, EBI system 100 includes a mainchamber 101, a load / lock chamber 102, a beam tool 104, and an equipment front end module (EFEM) 106. Beam tool 104 is located within main chamber 101. EFEM 106 includes a first loading port 106a and a second loading port 106b. EFEM 106 may include additional loading port(s). First loading port 106a and second loading port 106b receive wafer front opening unified pods (FOUPs) that contain wafers (e.g., semiconductor wafers or wafers made of other material(s)) or samples to be inspected (wafers and samples may be used interchangeably). A “lot” is a plurality of wafers that may be loaded for processing as a batch.

[0033] One or more robotic arms (not shown) in EFEM 106 may transport the wafers to load / lock chamber 102. Load / lock chamber 102 is connected to a load / lock vacuum pump system (not shown) which removes gas molecules in load / lock chamber 102 to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) may transport the wafer from load / lock chamber 102 to main chamber 101. Main chamber 101 is connected to a main chamber vacuum pump system (not shown) which removes gas molecules in main chamber 101 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by beam tool 104. Beam tool 104 may be a single-beam system or a multi-beam system.

[0034] A controller 109 is electronically connected to beam tool 104. Controller may be a device or a system that is configured for regulating, managing, and coordinating the operation of EBI system 100. It may receive input from sensors or other sources (e.g., an operator), processes this information, and then makes decisions or adjustments based on predefined parameters or algorithms. In some embodiments, controller 109 may serve as the central unit that coordinates and controls the functions and parameters of EBI system 100. Controller 109 may assist in ensuring precise and accurate performance during electron beam microscopy or other applications. Non-limiting functions of controller 109 may include: beam control (e.g., managing the generation, intensity, and focus of the electron beam by, for example, regulating parameters like beam current, accelerating voltage, and spot size); stage movement and positioning (e.g., by allowing for precise manipulation and alignment of the sample position under the electron beam); image acquisition and processing (e.g., by overseeing the acquisition of images and allowing for adjustments of, for example, contrast, brightness, and other imaging parameters); vacuum system operation (e.g., by ensuring that the appropriate level of vacuum is maintained for suitable electron beam interactions with the sample); detector management (e.g., by coordinating the operation and signal processing of secondary electron detectors, backscatter detectors, etc.); temperature control (e.g., by assisting in the management of cooling systems, etc. to regulate the temperature within the electron beam chamber, etc.); safety and interlocks (e.g., by incorporating or managing safety features and interlocks to ensure that the instrument operates within safe parameters and to prevent potential damage to the system or samples, etc.); data logging (e.g., record and store data related to instrument settings, operating conditions, and acquired images for future reference or analysis); calibration and alignment (e.g., it may include tools or functions forinstrument calibration and alignment to ensure accurate and reliable performance); user interface (e.g., a user interface through which operators can interact with the electron beam apparatus). In some embodiments, controller 109 may serve only a portion of the above-described functions, and in some embodiments, controller 109 may serve other or additional functions.

[0035] Controller 109 may be a physical system or device that include some or all of: one or more microprocessors or microcontrollers; one or more memories (e.g., random access memory (RAM); read-only memory (ROM), etc.); input / output (I / O) ports (e.g., to interface with sensors, actuators, and other components of EBI system 100); analog and digital inputs; analog and digital outputs; user interface (e.g., a graphical user interface (GUI), a touch screen, buttons, knobs, or a combination of these); display (e.g., a display screen to provide feedback, status updates, and information to the operator); control buttons and keypad (e.g., to allow an operator to input commands or set parameters for EBI system 100); communication ports (e.g., to enable the controller to communicate with external devices or networks); power supply; control algorithms and software (e.g., programs and algorithms that dictate how the controller processes input data and makes decisions to control EBI system 100); safety interlocks (e.g., components designed to ensure safe operation by monitoring critical conditions and shutting down EBI system 100 if necessary to prevent damage or hazards); diagnostic and monitoring systems (e.g., sensors and monitoring circuits that provide feedback on the status and performance of various components of EBU system 100); enclosure and housing (e.g., the components that make up the controller may be housed in a protective enclosure to shield it from environmental factors and potential physical damage).

[0036] In some embodiments, controller 109 may include one or more processors (not shown). A processor may be a generic or specific electronic device capable of manipulating or processing information. For example, the processor may be an electronic device capable of manipulating or processing information and may include any combination of any number of a central processing unit (or “CPU”), a graphics processing unit (or “GPU”), an optical processor, a programmable logic controllers, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a Programmable Logic Array (PLA), a Programmable Array Logic (PAL), a Generic Array Logic (GAL), a Complex Programmable Logic Device (CPLD), a Field-Programmable Gate Array (FPGA), a System On Chip (SoC), an Application-Specific Integrated Circuit (ASIC), a neural processing unit (NPU), and any other type circuit capable of data processing. In some embodiments, the processor may also be a virtual processor that includes one or more processors distributed across multiple machines or devices coupled via a network.

[0037] In some embodiments, controller 109 may further include one or more memories (not shown). A memory may be a generic or specific electronic device capable of storing codes and data accessible by the processor (e.g., via a bus). For example, the memory may include any combination of any number of a random-access memory (RAM), a read-only memory (ROM), an optical disc, a magnetic disk, a hard drive, a solid-state drive, a flash drive, a security digital (SD) card, a memory stick, acompact flash (CF) card, or any type of storage device. The codes and data may include an operating system (OS) and one or more application programs (or “apps”) for specific tasks. The memory may also be a virtual memory that includes one or more memories distributed across multiple machines or devices coupled via a network. Although not a requirement, in some embodiments, controller 109 may be a computer configured to execute various controls of EBI system 100. While controller 109 is shown in FIG. 1 as being outside of the structure that includes main chamber 101, load / lock chamber 102, and EFEM 106, it is appreciated that controller 109 may be a part of the structure.

[0038] FIG. 2 A illustrates a schematic diagram of an example multi-beam beam tool 104A (also referred to herein as apparatus 104A) and an image processing system 290 that may be configured for use in EBI system 100 (FIG. 1), consistent with embodiments of the present disclosure.

[0039] Beam tool 104 A comprises a charged particle source 202, a gun aperture 204, a condenser lens 206, a primary charged particle beam 210 emitted from charged particle source 202, a source conversion unit 212, a plurality of beamlets 214, 216, and 218 of primary charged particle beam 210, a primary projection optical system 220, a motorized wafer stage 280, a wafer holder 282, multiple secondary charged particle beams 236, 238, and 240, a secondary optical system 242, and a charged particle detection device 244. Primary projection optical system 220 can comprise a beam separator 222, a deflection scanning unit 226, and an objective lens 228. Charged particle detection device 244 can comprise detection sub-regions 246, 248, and 250.

[0040] Charged particle source 202, gun aperture 204, condenser lens 206, source conversion unit 212, beam separator 222, deflection scanning unit 226, and objective lens 228 can be aligned with a primary optical axis 260 of apparatus 104A. Secondary optical system 242 and charged particle detection device 244 can be aligned with a secondary optical axis 252 of apparatus 104A.

[0041] Charged particle source 202 can emit one or more charged particles, such as electrons, protons, ions, muons, or any other particle carrying electric charges. In some embodiments, charged particle source 202 may be an electron source. For example, charged particle source 202 may include a cathode, an extractor, or an anode, wherein primary electrons can be emitted from the cathode and extracted or accelerated to form primary charged particle beam 210 (in this case, a primary electron beam) with a crossover (virtual or real) 208. For ease of explanation without causing ambiguity, electrons are used as examples in some of the descriptions herein. However, it should be noted that any charged particle may be used in any embodiment of this disclosure, not limited to electrons. Primary charged particle beam 210 can be visualized as being emitted from crossover 208. Gun aperture 204 can block off peripheral charged particles of primary charged particle beam 210 to reduce Coulomb effect. The Coulomb effect may cause an increase in size of probe spots.

[0042] Source conversion unit 212 can comprise an array of image-forming elements and an array of beam-limit apertures. The array of image-forming elements can comprise an array of micro-deflectors or micro-lenses. The array of image-forming elements can form a plurality of parallel images (virtual or real) of crossover 208 with a plurality of beamlets 214, 216, and 218 of primary charged particlebeam 210. The array of beam-limit apertures can limit the plurality of beamlets 214, 216, and 218. While three beamlets 214, 216, and 218 are shown in FIG. 2A, embodiments of the present disclosure are not so limited. 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 a range from 1 to 1000. In some embodiments, the first number of beamlets may be in a range from 200-500.

[0043] Condenser lens 206 can focus primary charged particle beam 210. The electric currents of beamlets 214, 216, and 218 downstream of source conversion unit 212 can be varied by adjusting the focusing power of condenser lens 206 or by changing the radial sizes of the corresponding beam-limit apertures within the array of beam-limit apertures. Objective lens 228 can focus beamlets 214, 216, and 218 onto a wafer 230 for imaging, and can form a plurality of probe spots 270, 272, and 274 on a surface of wafer 230.

[0044] Beam separator 222 can be a beam separator of Wien filter type generating an electrostatic dipole field and a magnetic dipole field. In some embodiments, if they are applied, the force exerted by the electrostatic dipole field on a charged particle (e.g., an electron) of beamlets 214, 216, and 218 can be substantially equal in magnitude and opposite in a direction to the force exerted on the charged particle by magnetic dipole field. Beamlets 214, 216, and 218 can, therefore, pass straight through beam separator 222 with zero deflection angle. However, the total dispersion of beamlets 214, 216, and 218 generated by beam separator 222 can also be non-zero. Beam separator 222 can separate secondary charged particle beams 236, 238, and 240 from beamlets 214, 216, and 218 and direct secondary charged particle beams 236, 238, and 240 towards secondary optical system 242.

[0045] Deflection scanning unit 226 can deflect beamlets 214, 216, and 218 to scan probe spots 270, 272, and 274 over a surface area of wafer 230. In response to the incidence of beamlets 214, 216, and 218 at probe spots 270, 272, and 274, secondary charged particle beams 236, 238, and 240 may be emitted from wafer 230. Secondary charged particle beams 236, 238, and 240 may comprise charged particles (e.g., electrons) with a distribution of energies. For example, secondary charged particle beams 236, 238, and 240 may be secondary electron beams including secondary electrons (energies < 50 eV) and backscattered electrons (energies between 50 eV and landing energies of beamlets 214, 216, and 218). Secondary optical system 242 can focus secondary charged particle beams 236, 238, and 240 onto detection sub-regions 246, 248, and 250 of charged particle detection device 244. Detection sub-regions 246, 248, and 250 may be configured to detect corresponding secondary charged particle beams 236, 238, and 240 and generate corresponding signals (e.g., voltage, current, or the like) used to reconstruct an inspection image of structures on or underneath the surface area of wafer 230.

[0046] The generated signals may represent intensities of secondary charged particle beams 236, 238, and 240 and may be provided to image processing system 290 that is in communication with charged particle detection device 244, primary projection optical system 220, and motorized waferstage 280. The movement speed of motorized wafer stage 280 may be synchronized and coordinated with the beam deflections controlled by deflection scanning unit 226, such that the movement of the scan probe spots (e.g., scan probe spots 270, 272, and 274) may orderly cover regions of interests on the wafer 230. The parameters of such synchronization and coordination may be adjusted to adapt to varied materials of wafer 230. For example, different materials of wafer 230 may have different resistance-capacitance characteristics that may cause different signal sensitivities to the movement of the scan probe spots.

[0047] The intensity of secondary charged particle beams 236, 238, and 240 may vary according to the external or internal structure of wafer 230, and thus may indicate whether wafer 230 includes defects. Moreover, as discussed above, beamlets 214, 216, and 218 may be projected onto different locations of the top surface of wafer 230, or different sides of local structures of wafer 230, to generate secondary charged particle beams 236, 238, and 240 that may have different intensities. Therefore, by mapping the intensity of secondary charged particle beams 236, 238, and 240 with the areas of wafer 230, image processing system 290 may reconstruct an image that reflects the characteristics of internal or external structures of wafer 230.

[0048] In some embodiments, image processing system 290 may include an image acquirer 292, a storage 294, and a controller 296. Image acquirer 292 may comprise one or more processors. For example, image acquirer 292 may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, or the like, or a combination thereof. Image acquirer 292 may be communicatively coupled to charged particle detection device 244 of beam tool 104A through a medium such as an electric conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, or a combination thereof. In some embodiments, image acquirer 292 may receive a signal from charged particle detection device 244 and may construct an image. Image acquirer 292 may thus acquire inspection images of wafer 230. Image acquirer 292 may also perform various post-processing functions, such as generating contours, superimposing indicators on an acquired image, or the like. Image acquirer 292 may be configured to perform adjustments of brightness and contrast of acquired images. In some embodiments, storage 294 may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer-readable memory, or the like. Storage 294 may be coupled with image acquirer 292 and may be used for saving scanned raw image data as original images, and postprocessed 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 together as one control unit.

[0049] In some embodiments, image acquirer 292 may acquire one or more inspection images of a wafer based on an imaging signal received from charged particle detection device 244. An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a single image comprising a plurality of imaging areas. The single image may be storedin storage 294. The single image may be an original image that may be divided into a plurality of regions. Each of the regions may comprise one imaging area containing a feature of wafer 230. The acquired images may comprise multiple images of a single imaging area of wafer 230 sampled multiple times over a time sequence. The multiple images may be stored in storage 294. In some embodiments, image processing system 290 may be configured to perform image processing steps with the multiple images of the same location of wafer 230.

[0050] When electrons of primary charged particle beam 210 are projected onto a surface of wafer 230 (e.g., probe spots 270, 272, and 274), the electrons of primary charged particle beam 210 may penetrate the surface of wafer 230 for a certain depth, interacting with particles of wafer 230. Some electrons of primary charged particle beam 210 may elastically interact with (e.g., in the form of elastic scattering or collision) the materials of wafer 230 and may be reflected or recoiled out of the surface of wafer 230. An elastic interaction conserves the total kinetic energies of the bodies (e.g., electrons of primary charged particle beam 210) of the interaction, in which the kinetic energy of the interacting bodies does not convert to other forms of energy (e.g., heat, electromagnetic energy, or the like). Such reflected electrons generated from elastic interaction may be referred to as backscattered electrons (BSEs). Some electrons of primary charged particle beam 210 may inelastically interact with (e.g., in the form of inelastic scattering or collision) the materials of wafer 230. An inelastic interaction does not conserve the total kinetic energies of the bodies of the interaction, in which some or all of the kinetic energy of the interacting bodies convert to other forms of energy. For example, through the inelastic interaction, the kinetic energy of some electrons of primary charged particle beam 210 may cause electron excitation and transition of atoms of the materials. Such inelastic interaction may also generate electrons exiting the surface of wafer 230, which may be referred to as secondary electrons (SEs). Yield or emission rates of BSEs and SEs depend on, e.g., the material under inspection and the landing energy of the electrons of primary charged particle beam 210 landing on the surface of the material, among others. The energy of the electrons of primary charged particle beam 210 may be imparted in part by its acceleration voltage (e.g., the acceleration voltage between the anode and cathode of charged particle source 202 in FIG. 2A). The quantity of BSEs and SEs may be more or fewer (or even the same) than the injected electrons of primary charged particle beam 210.

[0051] In some embodiments, image processing system 290 may include measurement circuits (e.g., analog-to-digital converters) to obtain a distribution of the detected secondary charged particles (e.g., secondary electrons). The charged particle distribution data collected during a detection time window, in combination with corresponding scan path data of beamlets 214, 216, and 218 incident on the wafer surface, can be used to reconstruct images of the wafer structures under inspection. The reconstructed images can be used to reveal various features of the internal or external structures of wafer 230, and thereby can be used to reveal any defects that may exist in the wafer.

[0052] Another example of a charged particle beam apparatus will now be discussed with reference to FIG. 2B. Beam tool 104B (also referred to herein as apparatus 104B) may be an example of beamtool 104 and may be similar to beam tool 104A shown in FIG. 2A. However, different from apparatus 104A, apparatus 104B may be a single -beam tool that uses only one primary electron beam to scan one location on the wafer at a time.

[0053] As shown in FIG. 2B, apparatus 104B includes a wafer holder 136 supported by motorized stage 134 to hold a wafer 150 to be inspected. Beam tool 104B includes an electron emitter 110 which may comprise a cathode 103 and an anode 121, and a gun aperture 122. Beam tool 104B further includes a beam limit aperture 125, a condenser lens 126, a column aperture 135, an objective lens assembly 132, and a detector 144. Objective lens assembly 132, in some embodiments, may be a modified SORIL lens, which includes a pole piece 132a, a control electrode 132b, a deflector unit 132c, and an exciting coil 132d. In a detection or imaging process, an electron beam 161 emanating from the tip of cathode 103 may be accelerated by anode 121 voltage, pass through gun aperture 122, beam limit aperture 125, condenser lens 126, and be focused into a probe spot 170 by the modified SORIL lens and impinge onto the surface of wafer 150. Probe spot 170 may be scanned across the surface of wafer 150 by a deflector, such as deflector unit 132c or other deflectors in the SORIL lens. Secondary or scattered particles, such as secondary electrons or scattered primary electrons emanated from the wafer surface may be collected by detector 144 to determine intensity of the beam and so that an image of an area of interest on wafer 150 may be reconstructed.

[0054] There may also be provided an image processing system 199 that includes an image acquirer 120, a storage 130, and controller 109. Image acquirer 120 may comprise one or more processors. For example, image acquirer 120 may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. Image acquirer 120 may connect with detector 144 of beam tool 104B through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, or a combination thereof. Image acquirer 120 may receive a signal from detector 144 and may construct an image. Image acquirer 120 may thus acquire images of wafer 150. Image acquirer 120 may also perform various post-processing functions, such as image averaging, generating contours, superimposing indicators on an acquired image, and the like. Image acquirer 120 may be configured to perform adjustments of brightness and contrast, etc. of acquired images. Storage 130 may be a storage medium such as a hard disk, random access memory (RAM), cloud storage, other types of computer readable memory, and the like. Storage 130 may be coupled with image acquirer 120 and may be used for saving scanned raw image data as original images, and postprocessed images. Image acquirer 120 and storage 130 may be connected to controller 109. In some embodiments, image acquirer 120, storage 130, and controller 109 may be integrated together as one electronic control unit.

[0055] In some embodiments, image acquirer 120 may acquire one or more images of a sample based on an imaging signal received from detector 144. An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a singleimage comprising a plurality of imaging areas that may contain various features of wafer 150. The single image may be stored in storage 130. Imaging may be performed on the basis of imaging frames.

[0056] The condenser and illumination optics of the electron beam tool may comprise or be supplemented by electromagnetic quadrupole electron lenses. For example, as shown in FIG. 2B, electron beam tool 104B may comprise a first quadrupole lens 148 and a second quadrupole lens 158. In some embodiments, the quadrupole lenses may be used for controlling the electron beam. For example, first quadrupole lens 148 may be controlled to adjust the beam current and second quadrupole lens 158 may be controlled to adjust the beam spot size and beam shape.

[0057] FIG. 2B illustrates a charged-particle beam apparatus that may use a single primary beam configured to generate secondary electrons by interacting with wafer 150. Detector 144 may be placed along optical axis 105, as in the example shown in FIG. 2B. The primary electron beam may be configured to travel along optical axis 105. Accordingly, detector 144 may include a hole at its center so that the primary electron beam may pass through to reach wafer 150. FIG. 2B shows an example of detector 144 having an opening at its center. However, some embodiments may use a detector placed off-axis relative to the optical axis along which the primary electron beam travels. For example, as in the example shown in FIG. 2A, discussed above, a beam separator 222 may be provided to direct secondary electron beams toward a detector placed off-axis. Beam separator 222 may be configured to divert secondary electron beams toward an electron detection device 244, as shown in FIG. 2A.

[0058] Typically, at least some of the components of beam tools 104A and 104B may be made of materials having different coefficient of thermal expansions (CTEs). Coefficient of thermal expansion (CTE) is a material property that quantifies how much a material expands or contracts when subjected to a change in temperature. It is a measure of the relative change in size or volume of a material for a given change in temperature. More specifically, CTE is defined as the fractional change in length (or volume) of a material per degree of temperature change. It is typically expressed in units of per degree Celsius (°C) or per degree Fahrenheit (°F). When materials with different CTEs are combined in a system (e.g., beam tool 104A, 104B), it can lead to mechanical stress, dimensional changes, and potential structural issues as the system experiences temperature variations. For example, when the system experiences a temperature change (e.g., as a result of an atmospheric temperature change, etc.), each material expands or contracts at its own rate based on its CTE. If adjacent materials have different CTEs, this may lead to the development of thermal stresses at the interfaces between the materials. This thermal stress can potentially lead to cracking or delamination at the interfaces. The differential expansion or contraction of materials may also cause the system to deform or warp. For instance, if one material expands more than another, it may exert mechanical forces on the surrounding materials, leading to bending or distortion. In systems where precision is critical, such as beam tools 104A, 104B, differences in CTEs can result in dimensional changes (e.g., a change infocal distance or the distance between a lens and the sample) leading to the need for frequent adjustments to the focal distance.

[0059] For example, the objective lens of beam tools 104A and 104B (e.g., objective 228 of FIG. 2A, objective lens assembly 132 of FIG. 2B) may be an electromagnetic device configured to focus the electron beam onto the sample. Typically, the objective lens may include components made of varied materials having different CTEs. For example, objective lens assembly 132 (of FIG. 2B) may include a pole piece 132a (e.g., made of a high-permeability material such as, for example, iron or a similar alloy), a control electrode 132b, a deflector unit 132c, and an exciting coil 132d (e.g., copper wire wound around the pole pieces to form a coil). Other embodiments of an objective lens may include additional or different components. Typically, the objective lens is positioned between the vacuum chamber top and the electron column of the charged-particle beam system (e.g., beam tool 104A, 104B). The electron column is a vertical section of the electron beam system (e.g., SEM) that contains the various lenses, apertures, and other components that control and manipulate the electron beam. It may include the electron source (electron gun), condenser lenses, scanning coils, and other elements that manipulate the electron beam. The objective lens, positioned between the electron source and the vacuum chamber (or sample chamber), may be located at the bottom of the electron column. The vacuum chamber houses the sample (e.g., wafer 230 of FIG. 2A and wafer 150 of FIG. 2B) and maintains a high vacuum environment. In some embodiments, the walls of the electron column may be made of iron alloy (or another relatively high permeability material such as, for example, a nickel alloy, or a cobalt alloy). During a temperature transient, the components of the apparatus including the components that make up the objective lens, the electron column, and the vacuum chamber may expand and contract by different amounts and change the distance between the objective lens and the sample.

[0060] The distance along the optical axis (e.g., optical axis 260 of FIG. 2A and optical axis 105 of FIG. 2B) between the objective lens and the sample is known as the working distance. The working distance affects several aspects of imaging using an electron beam apparatus. For example, the working distance influences the depth of field, which is the range of distances along the optical axis where the sample remains in acceptable focus. A longer working distance generally results in a larger depth of field. The working distance may also affect the effective magnification of the apparatus. As the working distance increases, the apparent size of the sample in the image may decrease. The working distance may also impact the achievable resolution of the apparatus. Generally, shorter working distances may lead to higher resolution because the electron beam is more focused. Typically, an electron beam apparatus is designed to operate within a specific range of working distances. Deviations outside this range can result in loss of image quality or difficulties in focusing.

[0061] FIG. 3A is a simplified schematic illustration of an exemplary electron beam apparatus 300 showing an objective lens 350 positioned at the bottom of electron column 330. It should be noted that only components relevant to the discussion below are shown in FIG. 3A. As illustrated in FIG.3 A, objective lens 350 is disposed between an electron beam source 310 and a sample 370 positioned in a vacuum chamber 360. Electron beam source 310 may be similar to charged-particle beam source 202 of FIG. 2A and electron emitter 110 of FIG. 2B. As discussed with reference to FIGs. 2A and 2B, electron beam source 310 may generate an electron beam directed along an optical axis 302 towards a sample 370 through objective lens 350 and other components (e.g., condenser lens 320, etc.) of apparatus 300. These other components between the objective lens 350 and the electron beam source 310 (which are not shown in FIG. 3 A) may be similar to those discussed with reference to FIGS. 2A and 2B. In some embodiments, as illustrated in FIG. 3A, electron column 330 may have a substantially cylindrical body portion 332 with a flange-like portion 334 at its bottom end. In a 3D view, the electron column 330 may be generally shaped like a top hat with the flange-like portion 334 forming an annular ring (or rim) around the cylindrical body portion 332. The flange-like portion 334 of electron column 330 may be attached to the top wall 362 of the vacuum chamber 360 that houses the sample 370. In some embodiments, objective lens 350 may be coupled to the bottom surface of the flange-like portion 334 (of electron column 330).

[0062] In some embodiments, as illustrated in FIG. 3A, the flange-like portion 334 may have a substantially cylindrical recess 336 at its bottom end centered around the optical axis 302. In some such embodiments, the objective lens 350 may be coupled to the bottom surface of the flange-like portion 334 within the recess 336 and the top wall 362 of the vacuum chamber 360 may be coupled to the bottom surface of the flange-like portion 334 outside the recess 336. However, this is merely exemplary, and the bottom surface of the flange-like portion 334 may have any configuration. For example, in some embodiments, the recess 336 may be eliminated (e.g., the bottom surface of the flange-like portion 334 may be a substantially flat surface), and the top wall 362 of the vacuum chamber 360 may be coupled to the substantially flat bottom surface of the flange-like portion 334 around the objective lens 350. In some embodiments, as illustrated in FIG. 3B, the bottom surface of the flange-like portion 334 may have multiple nested cylindrical recesses 336A, 336B centered around the optical axis 302. In some such embodiments, the objective lens 350 may be coupled to the bottom surface of one of the recesses (e.g., the inner-most recess 336A) and the top wall 362 of the vacuum chamber 360 may be coupled to the bottom surface of the flange-like portion 334 outside the recesses.

[0063] As explained previously, objective lens 350 includes multiple components. It should be noted that only the external surface of the outer-most component (e.g., the field guide) of objective lens 350 is shown in FIGs. 3A and 3B. As illustrated in FIGs. 3A and 3B, in some embodiments, the field guide of objective lens 350 may be generally shaped like an inverted circus tent with a cylindrical body and a conical bottom end forming a tip A. Tip A of objective lens 350 may be the part of the lens closest to the sample 370. With reference to FIG. 3A, the distance between the tip A (of objective lens 350) and the surface of the sample 370 may be the previously described working distance (d). As explained previously, a stable working distance (d), that does not vary significantly as the result of atemperature variation during operation, is important for the efficient functioning of electron beam apparatus 300.

[0064] In some embodiments, an adapter plate 340 may be positioned between the bottom surface of the flange-like portion 334 and the top of the objective lens 350. Although not shown in FIGs. 3A and 3B, in some embodiments, mechanical fasteners (e.g., screws, etc.) may be used to couple the objective lens 350 to the bottom of the flange-like portion 334. In some embodiments, these fasteners may pass through the adapter plate 340. In general, adapter plate 340 may be made of a non-magnetic material to magnetically decouple the objective lens from the body of the electron column 330 and vacuum chamber 360. In some embodiments, adapter plate 340 may be made of aluminum or an aluminum alloy. In some embodiments, adapter plate 340 may be made of a material having a relative permeability close to that of air.

[0065] In some embodiments, electron column 330, adapter plate 340, and objective lens 350 may exhibit mechanical performances similar to perforated circular and annular plates and cones of considerable thickness with constrained circular boundaries. The contained boundary may be free, guided, simply supported, or fixed, and may include small deflection considerations of axisymmetric uniform or non-uniform thermal loads. Due to the effect of the constraint on their deflection during a temperature change, the expansion of these components may be different from that expected from unconstrained linear predictions. This effect may be described by their respective effective coefficients of thermal expansions. The effective coefficient of thermal expansion for an unconstrained body may be the same as its coefficient of thermal expansion. The effective coefficient of thermal expansion for a constrained body may depend on the material properties of the body (e.g., CTE, modulus of elasticity, etc.) and the nature of the constraint (fixed, simply supported, etc.). In general, when a body is constrained, its expansion may be restricted or exacerbated (e.g., due to warpage, etc.), and the effective coefficient of thermal expansion takes into account the change in deflection resulting from the constraint. For bodies having complex geometries and constraints (e.g., electron column 330, adapter plate 340, and objective lens 350), the effective coefficient of thermal expansion may be calculated using numerical methods (e.g., finite element analysis).

[0066] FIG. 3C shows a portion of a region of FIG. 3A between the objective lens 350 and the flange-like portion 334. FIG. 3C will be used to describe the effect of an exemplary temperature change (AT) on the thermal deflection of tip A in the vertical direction along the optical axis 302 (e.g., the Z-direction), and the resulting variation in the working distance (d) of apparatus 300. In the discussion below, temperature change (AT) is assumed to be a positive temperature change (e.g., an increase in temperature from Ti to Tz), and the bottom surface of the flange-like portion 334 of electron column 330 is considered a fixed reference surface. In other words, the deflection in the vertical direction (or Z-direction) of a location R at the bottom of the flange-like portion 334 due to temperature change (AT) is assumed to be zero. In the discussion below, the material of the flange-like portion 334 is considered to have a CTE of (X334, the material of the adapter plate 340 is considered to have a CTE of (X340, and the effective CTE of the objective lens 350 is considered to be Cteo- The effective CTE (X350 of objective lens 350, made of multiple subcomponents with different materials, may be roughly approximated as the weighted average of the individual CTEs and their respective volume fractions based on some assumptions. Numerical modeling techniques (e.g., finite element analysis) may also be used more accurately predict

[0067] The thermal expansion (Af) of a component having a CTE and a length due to an increase in temperature from Ti to T2 (a temperature change of AT) is I aAT. Therefore, assuming that the individual components behave independently and linearly with respect to thermal expansion, the length marked fain the flange-like portion 334 will change in the +Z direction by Afa= CZ3311:,AT, the length marked €bin the adapter plate 340 will change in the -Z direction by A€b= OG ir, ( i, AT, and the length marked fcin the objective lens 350 will change in the -Z direction by Afc= CX350 ( cAT. Thus, the total deflection of tip A with reference to location R will be the algebraic sum of these thermal deformations (Afa, Afb, and Afc). In other words, the thermal deformation of tip A in the Z direction can be approximated to be +CZ3311aAT - CX3101 i,AT - CX350ICAT. In some embodiments, this thermal deformation (as a result of a temperature increase of AT) may cause a net deflection of tip A in the -Z direction and result in a decrease of working distance (d). Similarly, based on the same assumptions, a temperature decrease of AT may cause a net deflection of tip A in the +Z direction and result in an increase in working distance (d).

[0068] It should be noted that the analysis above assumes that each component (e.g., electron column 330, vacuum chamber 360, adapter plate 340, and objective lens 350, etc.) is free to thermally deform independently without constraint from the other components. However, in reality, since the different components are coupled together, relative thermal expansion between these components induces thermal stresses and strains that may cause some or all of these components to deform by bending or warping. For example, similar to a bimetal thermostat (composed of two different metals or alloys bonded together) that bends when it is subjected to a temperature change, the components of apparatus 300 may also bend as a result of the thermal stresses induced due to a temperature change (AT). In some embodiments, such thermal stress induced bending may result in additional deflection of tip A in the Z-direction and lead to a further variation (increase or decrease) in the working distance (d). In some embodiments, the deflection of tip A as a result of bending may be a sizable portion of the total deflection of tip A due to temperature change.

[0069] FIG. 3D is schematic illustration of the bending of the apparatus components as a result of a temperature change. As shown in FIG. 3D, the bending of the components can also result in a vertical deflection of tip A. It should be noted that the bending (or warpage) of the components is exaggerated in FIG. 3D to illustrate its effect on the deflection of tip A. It should also be noted that the amount and direction of bending (e.g., concave-up as shown in FIG. 3D or convex-up) depends on, among otherfactors, the relative CTE mismatch between the components (e.g., flange-like portion 334 of electron column 330, top wall 362 of vacuum chamber 360, objective lens 350, etc.), the relative stiffness (thickness, modulus of elasticity, size, etc.) of the components, and the magnitude and direction of the temperature change. For example, an increased CTE mismatch and increased AT will result in increased warpage. See, e.g., “Bond Layer Properties and Geometry Effect on Interfacial Thermomechanical Stresses in Bi-material Electronic Packaging Assembly,” Sujan et al., AAME 2018, AATEC Web of Conferences, 202, available at https: / / doi.org / 10.105 / mateconf / 201820201004). Numerical simulations (e.g., finite element analysis) may be used to determine the deflection of tip A based on the material properties and the geometry of the components of apparatus 300.

[0070] As described above, when a structure (such as an exemplary electron beam apparatus 300) is subjected to a temperature change (e.g., temperature increase), its different components experience thermal expansions that may be exacerbated by their constraints (or boundary conditions) that prevent them from freely expanding or contracting. Representing structural components as equivalent disk springs is a simplification technique that may be used to understand the complex behavior of a structure under thermal loads. This representation simplifies the analysis by focusing on the overall stiffness and flexibility characteristics of the components.

[0071] FIGs. 3E and 3F are schematic illustrations of an exemplary electron beam apparatus 300 that will be used to describe the effect of an exemplary temperature increase on the thermal deflection of tip A (in the vertical direction along the optical axis 302) using an approximated disk spring model. FIG. 3E illustrates the undeformed configuration of apparatus 300 (e.g., before the temperature increase), and FIG. 3F illustrates the deformed configuration of the apparatus 300 after the temperature increase. In FIGs. 3E and 3F, objective lens 350 is represented using its constituent inner and outer pole pieces 350A and 350B. Inner and outer pole pieces 350A and 350B are annular components that extend around the optical axis 302. In some embodiments, as illustrated in these figures, these pole pieces may have a generally L-shaped cross-sectional shape. Tip A (that was used to describe working distance (d) in FIGs 3A-3D) may be assumed to be at the opening of the inner pole piece 350A.

[0072] Using an equivalent spring simplification, the electron column 300 and the inner and outer pole pieces 350A and 350B of apparatus 300 may be represented as equivalent disk springs with a constrained outer diameter. As illustrated using dashed lines in FIG. 3F, due to the temperature increase, the inner diameter of equivalent disk spring 330' (representing the electron column 330) deflects upwards (e.g., in the +Z direction), while the inner diameters of equivalent springs 350A', 350B' (representing the inner and outer pole pieces 350A, 350B) deflect downwards (e.g., in the -Z direction). Notably, if the upward deflection of the inner diameter of equivalent disk spring 330' is not equal to the downward deflection of the outer diameter of equivalent spring 350A', the distance of tip A from the sample (e.g., working distance (d)) will change due to the temperature increase.

[0073] It should be noted that although only the electron column and the pole pieces are represented as equivalent springs in FIGs. 3E and 3F, this is only a simplification. In reality, many components of apparatus 300 that contribute to the axial deflection of tip A may be represented as equivalent disk springs to understand the deflection of tip A. Moreover, although the outer diameters of equivalent springs 330', 350A', 350B' are described as being constrained, this is also only exemplary. In general, the inner or outer ends of the equivalent springs may be constrained. Typically, numerical simulations (e.g., Finite Element simulations) may be used to understand the axial deflection of tip A along optical axis 302 as a result of a temperature change. It should be noted that the thermal deflection of the equivalent disk springs will remain linear (and therefore follow Hooks law) as long as the spring thickness is much smaller than the diameter of the spring.

[0074] In embodiments of the current disclosure, an electron beam apparatus is configured to reduce the deflection (or the net dimensional change) of tip A (e.g., towards or away from the sample) due to a temperature change. For example, the structure (e.g., geometry, configuration, etc.) and materials (CTE, etc.) of the components of an electron beam apparatus are configured to reduce the deflection of tip A. For example, as illustrated in FIGs. 4A and 4B, in some exemplary embodiments, a compensating ring 400 may be provided to at least partially counteract the deflection of tip A that occurs due to bending (e.g., in the configuration of FIG. 3D). In some embodiments, compensating ring 400 may be provided as an addition to adapter plate 340, and in some embodiments, compensating 400 may be provided as an alternative to adapter plate 340. In some embodiments, the compensating ring 400 may be an annular ring that is coupled to the underside (e.g., bottom surface) of the top wall 362 of the vacuum chamber 360. When the electron beam apparatus 300A (of FIG. 4A) experiences a temperature change, the compensating ring 400 may tend to induce a warpage in the components (e.g., in the flange-like portion 334) that is opposite in direction to the warpage the component would have experienced without the compensating ring 400. The dimensions (thickness t, width w, etc.) of the compensating ring 400 and the properties (modulus of elasticity E, CTE a, etc.) of the material of the compensating ring 400 may be such that, when apparatus 300A is subjected to a temperature change, the compensating ring 400 at least partially compensates for the Z-direction deflection that tip A would have experienced without the compensating ring 400 (e.g., the deflection that tip A experiences in apparatus 300 of FIG. 3D). For example, if simulations of apparatus 300 of FIG. 3D (e.g., without a compensating ring 400) indicates that tip A would deflect downward (e.g., in the -Z direction) by, for example, 5 nanometers (nm), compensating ring 400 (in apparatus 300A of FIG. 4A) may be selected to decrease this downward deflection of tip A (e.g., to make the downward deflection < 5nm). In general, the compensating ring 400 may be selected to reduce the deflection of tip A by any amount (e.g., < 4nm, < 3nm, < 2nm, < Inm, etc.). In some embodiments, the compensating ring 400 may be selected to make the net deflection of tip A as a result of a temperature change close to zero. In some embodiments, the compensating ring 400 may be selected to reduce the deflection of the tip A such that the working distance of the apparatus 300A stays within anacceptable focal range during an expected temperature change. Typically, numerical simulations may be used to select the suitable dimensions and material of the compensating ring 400 to reduce the deflection of tip A during expected temperature variations of the apparatus.

[0075] In some embodiments, the compensating ring 400 and the flange-like portion 334 (of electron column 330) may have substantially the same CTE (e.g., (X334 ~ CUoo). In some embodiments, they may be made of the same material (e.g., an iron alloy). In some such embodiments, if the CTE mismatch between the flange-like portion 334 and the top wall 362 (ACC362-334) cause these components to warp in a concave manner (when viewed from the top, see FIG. 3D) during a temperature change, the CTE mismatch between the top wall 362 and compensating ring 400 (ACC362-400) may tend to induce a warpage in the opposite direction (e.g., convex when viewed from the top) and thereby reduce the deflection of tip A resulting from the warpage. In some embodiments, as illustrated in FIG. 4B, the thermal expansion forces in the flange-like portion 334 and the compensator ring 400 resulting from a temperature change may counteract each other to squeeze top wall 362, thereby resulting in minimal (or no) change in the Z-axis position of tip A. It should be noted that (X334 ~ C oo is not a requirement, and in general the compensating ring 400 and the flange-like portion 334 may have any CTE (e.g., even different CTEs). For example, in some embodiments where the flexural stiffness (which is the resistance to bending and is a function of material properties and geometry) of the compensating ring 400 is smaller than the flexural stiffness of the flange-like portion 334 (e.g., k4oo < kss i), the material of the compensating ring 400 may be chosen such that the CTE mismatch between the top wall 362 and the compensating ring 400 (A0C362-400) is greater than the CTE mismatch between the top wall 362 and the flange-like portion 334 (ACC362-334) so that the warpage resulting from ACC362-400 at least partially counteracts the warpage resulting from A0C362-334. Similarly, in some embodiments, when k334 > k400, the material of the compensating ring 400 may be chosen such that the CTE mismatch between the top wall 362 and the compensating ring 400 is smaller than the CTE mismatch between the top wall 362 and the flange-like portion 334.

[0076] It should be noted that although compensating ring 400 is illustrated as a washer-like annular ring having a constant width (w) and thickness (t), this is only exemplary. In some embodiments, the width (w) or thickness (t) of compensating ring 400 may vary. For example, in some embodiments, the compensating ring may have multiple concentric annular regions (e.g., of widths wi, W2, etc.) of different thicknesses. In some embodiments, the compensating ring may be wedge shaped such that its thickness (t) increases or decreases radially inward (e.g., towards optical axis 302). In some embodiments, the compensating ring may be made of multiple materials (e.g., having different CTEs), for example, to induce warpage in a desired direction. For example, a first thickness (ti) of the compensating ring may be made of a material having a first CTE (CCi) and a second thickness (tz) may be made of a material having a second CTE (0C2) greater than or less than the first CTE (OCi). The second thickness (tz) may be equal to or different from (e.g., less than or greater than) the firstthickness (ti). In some embodiments, such a multi-material compensating ring may be provided to induce warpage in a desired direction to the assembly and thereby reduce tip deflection. Generally, numerical simulations may be used to determine a suitable geometry and the material of the compensating ring 400.

[0077] As explained with reference to FIGs, 3A-3C, the thermal expansion of the components of apparatus 300 during a temperature variation may result in a deflection of the tip A in the vertical direction (e.g., along the optical axis 302). In some embodiments, the objective lens 350 may be coupled to the electron column 330 with components that compensate for the deflection of the tip A in the vertical direction (and horizontal direction, in some embodiments). For example, as schematically illustrated in FIG. 5A, in some embodiments, in an exemplary apparatus 300B, the objective lens 350 may be coupled to the flange-like portion 334 of the electron column 330 using multiple compensator pieces, for example, first and second compensator pieces 510, 520. In general, any number of first and second compensator pieces 510, 520 may be used to couple the objective lens 350 to the electron column 330. For example, in some exemplary embodiments, four first compensator pieces 510 in the form of rods and a single second compensator piece 520 in the form of an annular ring may be used. However, this is only exemplary, and in some embodiments, a different number (e.g., 1, 2, 3, 5, 6, etc.) of first compensator pieces 510 and second compensator pieces 520 may be used. In some embodiments, the annular second compensator piece 520 may extend around, and may be coupled to, the objective lens 350, and the multiple first compensator pieces 510 may couple the second compensator piece 520 to the bottom surface of the flange-like portion 334 of the electron column 330.

[0078] As described with reference to FIG. 3C, as a result of an increase (or decrease) in temperature of AT, the different components (e.g., flange-like portion 334, first compensator pieces 510, second compensator piece 520, objective lens 350, etc.) of apparatus 300B will thermally expand (or contract) as a function of its respective CTE (a), length (€), and the temperature variation (AT). The dimensions (e.g., length f, diameter, etc.) and CTE of the first and second compensator pieces 510, 520 in apparatus 300B (of FIGs. 5A-5B) are selected such that the deflection of the tip A (e.g., in the Z-direction) is reduced as compared to the deflection of the tip A of apparatus 300 of FIGs. 3A-3C. In general, the first and second compensator pieces 510, 520 may be configured to reduce the tip deflection by any amount, for example, compared to the tip deflection of apparatus 300 of FIGs. 3A- 3C. In some embodiments, the dimensions, and materials of the first and second compensator pieces 510, 520 may be selected such that the tip deflection during an expected temperature change of apparatus 300B is close to zero. In some embodiments, the electron column 330 and the outer field guide of objective lens 350 may be made of the same material or materials having a similar CTE (approximately equal to (XA). In some embodiments, the first compensator piece 510 may be made of a material with a CTE lower that (XA (e.g., OCs 10 < (XA), and the second compensator piece 520 may bemade of a material having a CTE higher than (XA (e.g., (X520 > (XA). In some embodiments, the electron column 330 and the outer field guide of objective lens 350 may be made of an iron alloy. In some such embodiments, the first compensator piece 510 may be made of quartz (or another relatively low CTE and low magnetic permeability material such as, for example, a ceramic, or alumina) and the second compensator piece 520 may be made of aluminum or an aluminum alloy (or another material having a low magnetic permeability and relatively high CTE).

[0079] In the embodiments of FIGs. 5A and 5B, the bottom surface of the flange-like portion 334 includes a recess 336 and one end (e.g., a first end 512) of each first compensator piece 510 is attached to the bottom surface of the flange-like portion 334 within the recess 336. However, this is not a requirement. In some embodiments, as illustrated in FIG. 5B, the first end 512 of each first compensator piece 510 may be coupled to the bottom surface of the flange-like portion 334 outside the recess 336. Similarly, in the example of FIG. 5A, the second compensator piece 520 is coupled to the bottom-most end 352 of the objective lens 350. This is also not a requirement. For example, in some embodiments, as illustrated in FIG. 5C, the second compensator piece 520 may be coupled to the objective lens 350 at a different location, for example, at a location 354 between the two vertical ends of the objective lens 350. In general, the coupling location, the dimensions, and materials of the first and second compensator pieces 510, 520 may be selected such the resulting thermal expansion (and contraction) of these components will collectively reduce the deflection of tip A. It should be noted that the configuration of the first and second compensator pieces 510, 520 illustrated in FIGS. 5A-5C are only exemplary. In general, the first and second compensator pieces may have any suitable configuration to reduce the deflection of tip A resulting from a temperature variation. In some cases, the configuration (e.g., shape), number, dimensions, and materials of the compensator pieces may be selected based on numerical simulations.

[0080] In some exemplary embodiments, in addition to the compensator pieces, a compensating ring (as discussed with reference to apparatus 300A of FIGs. 4A and 4B) may also be incorporated to counteract the deflection of tip A that occurs due to bending of the components during a temperature change. FIG. 6 illustrates an exemplary apparatus 300C having first and second compensator pieces 510, 520 and a compensating ring 400. In some embodiments, the compensating ring 400 may be an annular ring that is coupled to the underside (e.g., bottom surface) of the top wall 362 of the vacuum chamber 360. However, as explained with reference to compensator ring 400 of FIGs. 4A and 4B, other configurations of the compensator ring are also contemplated. The first and second compensator pieces 510, 520 may be similar in structure and function in an analogous manner as discussed with reference to FIGs. 5A-5D, and the compensating ring 400 may be similar in structure and function in an analogous manner as discussed with reference to FIGs. 4A and 4B. For example, when apparatus 300C experiences a temperature change, the compensating ring 400 may tend to induce a warpage in the components (e.g., in the flange-like portion 334) that is opposite in direction to the warpage the component would have experienced without the compensating ring 400. As discussed with referenceto FIGs. 5A-5D, the first and second compensator pieces 510, 520 may assist in reducing the deflection of tip A resulting from the thermal expansion and contraction of the constituent components of the apparatus 300C. Meanwhile, the compensating ring 400 may assist in reducing the deflection of the tip A resulting from the thermal strain induced warpage of the constituent components. In general, the first and second compensator pieces may have any suitable configuration to reduce the deflection of tip A resulting from a temperature variation. As discussed previously, in some cases, the configuration (e.g., shape), number, dimensions, and materials of the first and second compensator pieces 510, 520, and the compensating ring 400 may be chosen based on numerical simulations.

[0081] FIG. 7A illustrates another exemplary apparatus 300D where a single compensator piece, or a compensator 600, is used to couple the objective lens 350 to the electron column 330 such that the deflection of the tip A as a result of a temperature variation is reduced (e.g., compared to the apparatus 300 of FIGs. 3A-3C). In a 3D view, compensator 600 may be generally top hat shaped having a cylindrical portion 610 with an annular flange forming a rim 620 at one end of the cylindrical portion 610. Compensator 600 may be coupled to the objective lens 350 such that the inner cylindrical surface of cylindrical portion 610 (of compensator 600) mates with the external cylindrical surface of the objective lens 350. During a temperature variation, compensator 600 may deform and deflect in a manner similar to the column base 330 since both structures have a similar structure and are similarly constrained. During a temperature variation, to compensate for the downward deflection (e.g., in the -Z direction) of tip A, the cylindrical portion 610 of the compensator 600 may displace upward (e.g., in the +Z direction). The amount of upward deflection may be selected by selecting the material and dimensions of compensator 600. Specifically, the material and dimensions of the compensator 600 may be selected such that the deflection of tip A resulting from the thermal expansion (and contraction) of the components of apparatus 300D is reduced (e.g., as compared to the deflection of tip A in apparatus 300 of FIGs. 3A-3C). In some embodiments, the material and configuration of compensator 600 may selected to make the deflection of tip A resulting from an expected temperature variation of apparatus 300D close to zero. In some embodiments, the compensator 600 may be made of aluminum or an aluminum alloy to reduce the deflection of tip A resulting from typical thermal variations of apparatus 300D. Using a compensator 600 made of aluminum may make the fabrication of the compensator 600 easier. Typically, the configuration (e.g., shape, etc.), dimensions, and the material of the compensator 600 may be selected based on numerical simulations.

[0082] In some embodiments, as illustrated in FIG. 7A, the compensator 600 may be attached to the flange-like portion 334 of electron column 330 such that the cylindrical portion 610 of the compensator 600 (with the objective lens 350) is positioned within the recess 336 on the bottom surface of the flange-like portion 334 with the rim 620 positioned outside the recess 336. However, this is not a requirement, and other configurations are also contemplated. For example, in someembodiments, as illustrated in FIG. 7B, multiple nested recesses 336A, 336B may be provided on the bottom surface of the flange-like portion 334 (as discussed with reference to FIG. 3B), and the cylindrical portion 610 of the compensator 600 may be positioned within the inner recess 336A with the rim 620 positioned on the bottom surface of the outer recess 336B. In the embodiments of FIGs. 7A and 7B, cylindrical portion 610 of compensator 600 is dimensioned such that the inner cylindrical surface of compensator 600 mates with substantially the entire vertical length of objective lens 350. However, such a configuration of compensator 600 is only exemplary. For example, FIG. 7C illustrates an example where a compensator 600' couples to the objective lens 350 at a small region 354 near the top of the objective lens 350. In the example of FIG. 7C, compensator 600' has an annular washer-like configuration with an external surface having multiple stepped surfaces. As illustrated in FIG. 7C, in some such embodiments, the bottom surface of the flange-like portion 334 (of electron column 330) may include multiple stepped recesses configured to receive the stepped external surfaces of the compensator 600' therein.

[0083] The objective lens 350 may be coupled to compensator 600, 600', and the compensator may be coupled to the electron column 330 in any manner. In some embodiments, mechanical fasteners may be used to couple these components together. For example, one or more fasteners may extend through some or all of these components to couple them together. For example, multiple fasteners may extend through compensator 600, 600' and the flange-like portion 334 to couple the objective lens 350 to the electron column 330. In addition to openings for the fasteners, compensator 600, 600' may also include additional openings, for example, to pass cooling fluid conduits to the objective lens 350.

[0084] In some exemplary embodiments, in addition to compensator 600, 600' of FIGS. 7A-7C, a compensating ring 400 (as discussed with reference to apparatus 300A of FIGs. 4A and 4B) may also be incorporated to counteract the deflection of tip A that occurs due to bending of components during a temperature change. FIG. 8 illustrates an exemplary apparatus 300E having a compensator 600 and a compensating ring 400. Compensator 600 may be similar in structure and function in an analogous manner as discussed with reference to FIGs. 7A-7B, and the compensating ring 400 may be similar in structure and function in an analogous manner as discussed with reference to FIGs. 4A and 4B. As discussed with reference to FIGs. 7A-7C, compensator 600 may assist in reducing the deflection of tip A resulting from the thermal expansion and contraction of the constituent components of the apparatus 300E. Meanwhile, the compensating ring 400 may assist in reducing the deflection of the tip A resulting from the thermal strain induced warpage of the constituent components. Although compensator 600 of FIGs. 7A-7B is illustrated in apparatus 300E of FIG. 8, this is only exemplary. In some embodiments, compensator 600' of FIG. 7B may be used in apparatus 300E. Generally, the configuration (e.g., shape), dimensions, and materials of the compensator 600, 600' and compensating ring 400 may be chosen based on numerical simulations.

[0085] FIG. 9A illustrates an exemplary apparatus 300F where the objective lens 350 is coupled to the underside of the electron column 330 using a compensator 900. As in FIG. 3E, the objective lens350 is represented by its constituent inner and outer pole pieces 350A, 350B in FIG. 9A. FIG. 9B is an illustration of apparatus 300F (of FIG. 9A) after a temperature change (e.g., a temperature increase). As described with reference to FIG. 3F, the components of apparatus 300F are represented as equivalent disk springs with constrained outer diameters in FIG. 9B. For example, the electron column 330 is represented using an equivalent disk spring 330', the compensator 900 using an equivalent disk spring 900', and the inner and outer pole pieces 350A, 350B using equivalent disk springs 350A', 350B'. Tip A of objective lens 330 (that defines working distance (d) of lens 330 from the sample) may be considered as the opening of the inner pole piece 350A. As illustrated using dashed lines in FIG. 9B, as a result of the temperature increase, the inner diameters of equivalent disk springs 330' and 900' deflect in the +Z direction (e.g., upwards) while the inner diameters of equivalent disk springs 350A', 350B' deflect in the -Z direction. As described with reference to FIG. 3F, if the total upward deflection of the components is not equal to the downward deflection of the tip A, the working distance (d) of the objective lens 330 will change as a result of the temperature change.

[0086] In embodiments of the current disclosure, the compensator 900 is configured such that it reduces (e.g., minimizes or negates) the net temperature induced deflection of the objective lens 330 (e.g., tip A) as a result of a temperature change (e.g., temperature increase or decrease). For example, in apparatus 300F of FIGs 9A and 9B, compensator 900 may be configured such that the upward displacement of the inner diameter of equivalent disc spring 900' compensates for the downward displacement of the tip A as a result of the temperature increase. In other words, if apparatus 300F did not have the compensator 900, tip A would have moved towards the sample as a result of the temperature increase. The inclusion of the compensator 900 in apparatus 300F reduces the downward displacement of the tip A. In some embodiments, the compensator 900 may be configured such that the tip A does not move in the axial direction along optical axis 302 during an expected temperature change.

[0087] In general, the shape or the material properties of compensator 900 may be selected to reduce the axial deflection of the tip A due to a temperature change. For example, in some embodiments, the coefficient of thermal expansion (CTE) of compensator 900 may be higher than that of the components attached to it (e.g., column base 330, inner and outer pole pieces 350A, 350B, etc.). In some embodiments, the compensator 900 may be made of aluminum or an aluminum alloy. However, it is also contemplated that compensator 900 may be made of another suitable material, such as, for example a plated copper alloy. Alternatively, or additionally, in some embodiments, the compensator 900 may have a shape that is adapted to counteract the axial deflection of tip A. In some embodiments, as illustrated in FIG. 9A, compensator 900 may have a stepped shape resembling two annular disks stacked one of top of another. In some embodiments, compensator 900 may have a conical, cupped (e.g., resembling a shallow dish or bowl), or a top-hat like shape. These geometriesmay have any suitable form (e.g., perforated, monolithic, frame-like, etc.) and, in some embodiments, may include multiple parts.

[0088] It should be noted that although features of the current disclosure are described as being used to couple the objective lens to the electron column to reduce the deflection of the objective lens tip due to a temperature variation, this is only exemplary. In general, aspects of the current disclosure may be used to couple any component of a charged-particle beam apparatus to similarly reduce deflections induced due to a temperature variation. For example, in some embodiments, aspects of the current disclosure may be used to couple any lens of a charged-particle beam apparatus to a body of the apparatus such the variation in the focal length of the lens caused as a result a temperature variation is reduced. Temperature variations during the operation of a charged-particle beam apparatus are common and difficult to avoid. For example, such temperature variations may arise when a cleanroom door housing the apparatus is momentarily opened, when an HVAC system of the facility turns on or off, when operators enter the cleanroom or touch the apparatus, etc. Embodiments of the current disclosure may enable the apparatus to tolerate such unavoidable temperature variations while reducing the need for frequent refocusing and recalibration which may reduce throughput and efficiency of the apparatus.

[0089] Schematic illustrations and 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 a schematic diagram may represent certain arithmetical or logical operation processing that may be implemented using hardware such as an electronic circuit. Blocks may also represent a module, segment, or portion of code that comprises one or more executable instructions for implementing the specified logical functions. It should be understood that in some alternative implementations, functions indicated in a block may occur out of the order noted in the figures. For example, two blocks shown in succession may be executed or implemented substantially concurrently, or two blocks may sometimes be executed in reverse order, depending upon the functionality involved. Some blocks may also be omitted. It should also be understood that each block of the block diagrams, and combination of the blocks, may be implemented by special purpose hardware -based systems that perform the specified functions or acts, or by combinations of special purpose hardware and computer instructions.

[0090] The embodiments may be further described using the following clauses:1. A component for mounting a lens in a charged-particle beam apparatus, comprising: a first part having a first coefficient of thermal expansion (CTE); and a second part having a second CTE different from the first CTE, wherein the first and second parts are arranged such that a working distance of the lens, mounted to a body of the charged-particle beam apparatus using the component, remains substantially unchanged over a non-zero predetermined temperature range.2. The component of clause 1, wherein the body has a third CTE, and wherein the first CTE is less than the third CTE and the second CTE is greater than the third CTE.3. The component of any of clauses 1-2, wherein the first part includes multiple subparts symmetrically arranged about an optical axis of the charged-particle beam apparatus, and the second part is an annular ring extending around the lens.4. The component of clause 3, wherein one end of each subpart of the multiple subparts is coupled to the body of the charged-particle beam apparatus and an opposite end of each subpart is coupled to the second part.5. The component of clause 3, wherein each subpart of the multiple subparts has a rod shape.6. The component of clause 3, wherein the body is made of an iron alloy, a nickel alloy, or a cobalt alloy, each subpart of the multiple subparts is made of quartz, alumina, or a ceramic, and the second part is made of aluminum or an aluminum alloy.7. The component of any of clauses 1-2, wherein the body of the charged-particle beam apparatus is an annular flange symmetrically positioned about an optical axis of the charged-particle beam apparatus, the annular flange including a surface extending substantially perpendicular to the optical axis, and wherein the component is fixed to a region of the surface and an annular region of the surface radially outwards of the region is coupled to a wall of a vacuum chamber of the charged- particle beam apparatus.8. The component of clause 7, wherein the surface of the annular flange includes a recess that is centrally positioned about the optical axis.9. The component of clause 8, wherein the region is a portion of the surface within the recess.10. The component of clause 8, wherein the region is a portion of the surface outside the recess.11. The component of clause 7, further comprising a compensator, wherein the annular region of the surface is fixed to a top surface of the wall of the vacuum chamber and the compensator is fixed to a bottom surface of the wall of the vacuum chamber, and wherein the compensator is an annular part that extends around the optical axis.12. The component of clause 11, wherein the compensator and the annular flange have substantially the same CTE.13. A component for mounting a lens in a charged-particle beam apparatus, comprising: a first part having a first coefficient of thermal expansion (CTE); a second part having a second CTE different from the first CTE; and a third part having a third CTE different from the first CTE, wherein the second and third parts are fixed to opposite sides of the first part, wherein the first, second, and third parts are arranged such that a working distance of the lens coupled to the charged-particle beam apparatus using the first, second, and third parts remain substantially unchanged over a non-zero predetermined temperature range.14. The component of clause 13, wherein the second CTE and the third CTE are substantially the same.15. The component of clause 13, wherein the second CTE is different from the third CTE.16. The component of any of clauses 13-15, wherein the first part is a top wall of a vacuum chamber of the charged-particle beam apparatus, the second part is an annular flange symmetrically positioned about an optical axis of the charged-particle beam apparatus and fixed to a top surface of the top wall, and the third part is an annular ring attached to a bottom surface of the top wall.17. The component of clause 16, wherein the annular ring is symmetrically positioned about the optical axis.18. The component of any one of clauses 13-15, further comprising one or more first compensator parts and a second compensator part, wherein the lens is connected to the second part using the one or more first compensator parts and the second compensator part.19. The component of clause 18, wherein the one or more first compensator parts include multiple first compensator parts symmetrically arranged about an optical axis of the charged-particle beam apparatus, and the second compensator part is an annular ring extending around the lens.20. The component of clause 19, wherein one end of each first compensator part of the multiple first compensator parts is fixed to the second part and an opposite end of each first compensator part is fixed to the second compensator part.21. A component for mounting a lens in a charged-particle beam apparatus, comprising: a first part including a first cylindrical portion that extends along an optical axis of the charged-particle beam apparatus and a first annular flange that extends from one end of the first cylindrical portion substantially perpendicular to the optical axis, the first annular flange including an end surface and a central cavity that extends from the end surface along the optical axis; and a second part, the second part including a second cylindrical portion having a second cavity that extends along the optical axis and a second annular flange extending around the second cavity from one end of the second cylindrical portion, wherein the first part and the second part are arranged such that a working distance of the lens coupled to the charged-particle beam apparatus using the first and second parts remain substantially unchanged over a non-zero predetermined temperature range.22. The component of clause 21, wherein the lens is disposed in the second cavity and the second annular flange of the second part is fixed to the end surface of the first part.23. The component of any of clauses 21-22, wherein the second cylindrical portion of the second part is disposed in the central cavity of the first part.24. The component of clauses 21 or 22, wherein an annular region of the end surface of the first annular flange is coupled to a vacuum chamber of the charged-particle beam apparatus.25. The component of clause 24, further including an annular compensator ring, wherein the annular region of the end surface of the first annular flange is coupled to a top surface of a top wall of the vacuum chamber, and the compensator ring is coupled to a bottom surface of the top wall.26. An apparatus for mounting a lens in a charged-particle beam apparatus, comprising:a component coupling the lens to a body of the charged-particle beam apparatus, the component having a coefficient of thermal expansion (CTE) and a shape configured to cause the component to deflect by a predictable amount in a Z direction when subject to a predetermined non-zero temperature change such that a working distance of the lens remains substantially unchanged over the predetermined non-zero temperature range.27. The apparatus of clause 26, wherein the component has an annular shape and a circumferential region of the component is constrained.28. The apparatus of clause 26, wherein the CTE of the component is higher than a CTE of the body and a CTE of a part of the lens that the component is attached to.29. The apparatus of clause 26, wherein the component is made of aluminum.30. The apparatus of clause 26, wherein the body is an underside of an electron column of the charged-particle beam apparatus.31. The apparatus of clause 26, wherein the component is attached to the body using mechanical fasteners or an adhesive.32. The apparatus of clause 26, wherein the component has an annular shape with an outer portion disposed radially outwards an inner portion, wherein the inner portion is spaced apart from the outer portion in the Z direction.33. The apparatus of clause 32, wherein the outer portion of the component is coupled to the body and the inner portion of the component is coupled to the lens.34. The apparatus of clause 26, wherein the component is radially symmetric about an optical axis of the charged-particle beam apparatus.35. An apparatus for mounting a lens in a charged-particle beam apparatus, comprising: an annular component having a central axis aligned with an optical axis of the charged-particle beam apparatus and including an outer portion disposed radially outwards of an inner portion, wherein the outer portion is coupled to an electron column of the charged-particle beam apparatus and the inner portion is coupled to the lens, and wherein the component is configured to deflect by a predictable amount in a Z direction when subject to a predetermined non-zero temperature change such that a working distance of the lens remains substantially unchanged over the predetermined nonzero temperature range.36. The apparatus of clause 35, wherein the component has a coefficient of thermal expansion (CTE) higher than a CTE of the electron column and a body of the lens.37. The apparatus of clause 35, wherein the inner portion of component is spaced apart from the outer portion in the Z direction.38. The apparatus of clause 35, wherein the component is made of aluminum.39. The apparatus of clause 35, wherein the component is radially symmetric about the optical axis.40. The apparatus of clause 35, wherein the charged-particle beam apparatus is a scanning electron microscope.41. A charged particle beam system, comprising: a lens; a body; and a component for mounting the lens to the body of the charged-particle beam system, wherein the component includes: a first part having a first coefficient of thermal expansion (CTE); and a second part having a second CTE different from the first CTE, wherein the first and second parts are arranged such that a working distance of the lens, mounted to a body of the charged-particle beam system using the component, remains substantially unchanged over a non-zero predetermined temperature range.42. The charged particle beam system of clause 41, wherein the body has a third CTE, and wherein the first CTE is less than the third CTE and the second CTE is greater than the third CTE .43. The charged particle beam system of clause 42, wherein the first part includes multiple subparts symmetrically arranged about an optical axis of the charged-particle beam system, and the second part is an annular ring extending around the lens.44. The charged particle beam system of clause 43, wherein one end of each subpart of the multiple subparts is coupled to the body of the charged-particle beam system and an opposite end of each subpart is coupled to the second part.45. The charged particle beam system of clause 43, wherein each subpart of the multiple subparts has a rod shape.46. The charged particle beam system of clause 43, wherein the body is made of an iron alloy, a nickel alloy, or a cobalt alloy, each subpart of the multiple subparts is made of quartz, alumina, or a ceramic, and the second part is made of aluminum or an aluminum alloy.

[0091] It will be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure has been described in connection with various embodiments, other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the technology described herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

Claims

CLAIMS1. An apparatus for mounting a lens in a charged-particle beam apparatus, comprising: a component coupling the lens to a body of the charged-particle beam apparatus, the component having a coefficient of thermal expansion (CTE) and a shape configured to cause the component to deflect by a predictable amount in a Z direction when subject to a predetermined nonzero temperature change such that a working distance of the lens remains substantially unchanged over the predetermined non-zero temperature range.

2. The apparatus of claim 1, wherein the component has an annular shape and a circumferential region of the component is constrained.

3. The apparatus of claim 1, wherein the CTE of the component is higher than a CTE of the body and a CTE of a part of the lens that the component is attached to.

4. The apparatus of claim 1, wherein the component is made of aluminum.

5. The apparatus of claim 1, wherein the body is an underside of an electron column of the charged- particle beam apparatus.

6. The apparatus of claim 1, wherein the component is attached to the body using mechanical fasteners or an adhesive.

7. The apparatus of claim 1, wherein the component has an annular shape with an outer portion disposed radially outwards an inner portion, wherein the inner portion is spaced apart from the outer portion in the Z direction.

8. The apparatus of claim 7, wherein the outer portion of the component is coupled to the body and the inner portion of the component is coupled to the lens.

9. The apparatus of claim 1, wherein the component is radially symmetric about an optical axis of the charged-particle beam apparatus.

10. A charged particle beam system, comprising: a lens; a body; and a component for mounting the lens to the body of the charged-particle beam system, wherein the component includes: a first part having a first coefficient of thermal expansion (CTE); and a second part having a second CTE different from the first CTE, wherein the first and second parts are arranged such that a working distance of the lens remains substantially unchanged over a non-zero predetermined temperature range.

11. The charged particle beam system of claim 10, wherein the body has a third CTE, and wherein the first CTE is less than the third CTE and the second CTE is greater than the third CTE .

12. The charged particle beam system of claim 11, wherein the first part includes multiple subparts symmetrically arranged about an optical axis of the charged-particle beam system, and the second part is an annular ring extending around the lens.

13. The charged particle beam system of claim 12, wherein one end of each subpart of the multiple subparts is coupled to the body of the charged-particle beam system and an opposite end of each subpart is coupled to the second part.

14. The charged particle beam system of claim 12, wherein each subpart of the multiple subparts has a rod shape.

15. The charged particle beam system of claim 12, wherein the body is made of an iron alloy, a nickel alloy, or a cobalt alloy, each subpart of the multiple subparts is made of quartz, alumina, or a ceramic, and the second part is made of aluminum or an aluminum alloy.

Images