Systems and methods of particle contamination reduction in charged-particle beam systems

Abstract

Systems and methods of increasing gas flow across a substrate in a charged-particle beam apparatus are disclosed. The apparatus may include a vacuum chamber comprising a first gas inlet fluidly connected with a charged-particle beam optics column and configured to direct a first gas flow downstream in the charged-particle beam optics column toward a substrate at a first flow velocity and a second gas inlet configured to direct a second gas flow toward the substrate at a second flow velocity. The first and the second gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.

Description

SYSTEMS AND METHODS OF PARTICLE CONTAMINATION REDUCTION IN CHARGED- PARTICLE BEAM SYSTEMSCROSS-REFERENCE To RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 608,004 which was filed on December 08, 2023 and which is incorporated herein in its entirety by reference.FIELD

[0002] The description herein relates to charged-particle beam apparatuses, and more particularly, to systems and methods of mitigating particle contamination in operation of vacuum systems.BACKGROUND

[0003] In manufacturing processes of integrated circuits (ICs), unfinished or finished circuit components are inspected to ensure that they are manufactured according to design and are free of defects. Inspection systems utilizing optical microscopes or charged particle (e.g., electron) beam microscopes, such as a scanning electron microscope (SEM) can be employed. As the physical sizes of IC components continue to shrink, and their structures continue to become more complex, particle contamination on critical surfaces poses a significant challenge in improving throughput, yield, and cost-efficiency.

[0004] Particle contamination through particle suspension or particle resuspension on surfaces operating in vacuum environment is detrimental to the system as well as the end-products fabricated using such systems. As an example, a stable high-voltage environment is desirable for normal operation of a SEM inspection apparatus. The stability of the electron source may be impacted by the presence of contaminants or unwanted particles whether pre-existing or generated by internal sources. Contaminants can cause electrostatic discharge (ESD), which may disturb the system voltage output and electric field strength and can generate contaminants, further deteriorating the system stability. In addition to ESD, particulate contaminants can cause other issues including aperture clogging, lens damage, wafer yield loss, among other things.SUMMARY

[0005] Embodiments of the present disclosure provide systems and methods for mitigating particle contamination in charged-particle beam systems during vent-up cycles. One aspect of the disclosure is directed to a charged-particle beam apparatus comprising a vacuum chamber. The vacuum chamber may include a first gas inlet fluidly connected with a charged-particle beam optics column and configured to direct a first gas flow downstream in the charged-particle beam optics column toward a substrate at a first flow velocity, and a second gas inlet configured to direct a second gas flow toward the substrate at a second flow velocity. The first and the second gas flows merge to form a lateral gasflow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.

[0006] Another aspect of this disclosure is directed to a method of increasing gas flow across a substrate in a charged-particle beam apparatus. The method may include causing a first gas flow downstream in a vacuum chamber toward a substrate at a first flow velocity, and causing a second gas flow toward the substrate at a second flow velocity, wherein the first and the second gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.

[0007] Yet another aspect of this disclosure is directed to a charged-particle beam apparatus comprising a first gas inlet fluidly connected with a charged-particle beam optics column and configured to direct a first gas flow downward in the charged-particle beam optics column toward a substrate at a first flow velocity, a second gas inlet located upstream from the substrate and configured to direct a second gas flow toward the substrate at a second flow velocity, and a third gas inlet located downstream from the substrate and configured to direct a third gas flow toward the substrate at a third flow velocity. The first, the second, and the third gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity, the second flow velocity, or the third flow velocity.

[0008] Yet another aspect of this disclosure is directed to a non-transitory computer readable medium storing a set of instructions that is executable by one or more processors of a charged-particle beam apparatus to cause the charged-particle beam apparatus to perform a method of increasing gas flow across a substrate in a charged-particle beam apparatus. The method may include causing a first gas flow downstream in a vacuum chamber toward a substrate at a first flow velocity, and causing a second gas flow toward the substrate at a second flow velocity, wherein the first and the second gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.

[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed embodiments, as may be claimed.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 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.

[0011] Fig. 1A is a diagrammatic representation of an exemplary charged-particle beam inspection system, consistent with embodiments of the present disclosure.

[0012] Fig. IB is a schematic diagram illustrating an exemplary wafer loading sequence in the charged-particle beam inspection system of FIG. 1A, consistent with embodiments of the present disclosure.

[0013] Fig. 2 is a schematic diagram illustrating an exemplary charged-particle beam tool that can be a part of the exemplary charged-particle beam inspection system of Fig. 1A, consistent with embodiments of the present disclosure.

[0014] Fig. 3A is a schematic illustration of a portion of an exemplary charged-particle beam apparatus and the gas flows during venting-up from vacuum, consistent with embodiments of the present disclosure.

[0015] Fig. 3B is a schematic illustration of an exemplary protective gas blanket formed above a critical surface in a charged-particle beam apparatus of Fig. 3A, consistent with embodiments of the present disclosure.

[0016] Fig. 4A is a schematic diagram of a portion of a charged-particle beam apparatus comprising an exemplary purge ring, consistent with embodiments of the present disclosure.

[0017] Fig. 4B is a schematic illustration of the top-view of the purge ring of Fig. 4A, consistent with embodiments of the present disclosure.

[0018] Fig. 5A is a schematic diagram of a portion of a charged-particle beam apparatus comprising an exemplary purge ring, consistent with embodiments of the present disclosure.

[0019] Fig. 5B illustrates a sectional top-view of a portion of the charged-particle beam apparatus along section A- A' of Fig. 5A, consistent with embodiments of the present disclosure.

[0020] Fig. 5C is a schematic diagram of a portion of a charged-particle beam apparatus comprising two purge rings, consistent with embodiments of the present disclosure.

[0021] Fig. 6A is a schematic diagram of a portion of a charged-particle beam apparatus comprising an exemplary purge ring, consistent with embodiments of the present disclosure.

[0022] Fig. 6B illustrates a sectional top-view of a portion of the charged-particle beam apparatus along section A- A' of Fig. 6A, consistent with embodiments of the present disclosure.

[0023] Fig. 6C is a schematic diagram of a portion of a charged-particle beam apparatus comprising two purge rings, consistent with embodiments of the present disclosure.

[0024] Fig. 7 is a flowchart illustrating an exemplary venting-up sequence of a charged-particle beam apparatus including one or more purge rings, consistent with embodiments of the present disclosure.

[0025] Fig. 8 is a flowchart illustrating an example method of increasing gas flow across a substrate in a charged-particle beam apparatus, consistent with embodiments of the disclosure.DETAILED DESCRIPTION

[0026] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the invention. Instead, they are merely examples of apparatuses, systems, and methods consistent with aspects related to subject matter that may berecited in the appended claims. Without limiting the scope of the present disclosure, some embodiments may be described in the context of providing detection systems and detection methods in systems utilizing electron beams (“e-beams”). However, the disclosure is not so limited. Other types of charged-particle beams (e.g., including protons, ions, muons, or any other particle carrying electric charges) may be similarly applied. Furthermore, other imaging systems may be used, such as optical imaging, photodetection, x-ray detection, extreme ultraviolet inspection, deep ultraviolet inspection, or the like.

[0027] Electronic devices are constructed of circuits formed on a piece of silicon called a substrate. The semiconductor material may include, for example, silicon (Si), gallium arsenide (GaAs), indium phosphide (InP), or silicon germanium (SiGe), or the like. Many circuits may be formed together on the same piece of silicon and are called integrated circuits or ICs. With advancements in technology, the size of these circuits has decreased dramatically so that many more of them can fit on the substrate. For example, an IC chip in a smart phone can be as small as a fingernail and yet may include over 2 billion transistors, the size of each transistor being less than one-thousandth the width of a human hair.

[0028] Making these extremely small ICs is a complex, time-consuming, and expensive process, often involving hundreds of individual steps. Errors in even one step have the potential to result in 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.

[0029] 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 carried out using a scanning electron microscope (SEM). A SEM can be used to image these extremely small structures, in effect, taking a “picture” of the structures. The image can be used to determine if the structure was formed properly and also if it was formed in the proper location. If the structure is defective, then the process can be adjusted so the defect is less likely to recur. Defects may be generated during various stages of semiconductor processing. For the reason stated above, it is important to find defects accurately, efficiently, and as early as possible. To enhance throughput (e.g., the number of samples processed per hour), it is desirable to conduct inspection as quickly as possible.

[0030] The working principle of a SEM is similar to a camera. A camera takes a picture by receiving and recording brightness and colors of light reflected or emitted from people or objects. A SEM takes a “picture” by receiving and recording energies or quantities of electrons reflected or emitted from the structures. Before taking such a “picture,” an electron beam may be provided onto the structures, and when the electrons are reflected or emitted (“exiting”) from the structures, a detector of the SEM may receive and record the energies or quantities of those electrons to generate an image. To take such a“picture,” some SEMs use a single electron beam (referred to as a “single-beam SEM”), while some SEMs use multiple electron beams (referred to as a “multi-beam SEM”) to take multiple “pictures” of the wafer. By using multiple electron beams, the SEM may provide more electron beams onto the structures for obtaining these multiple “pictures,” resulting in more electrons exiting from the structures. Accordingly, the detector may receive more exiting electrons simultaneously, and generate images of the structures of the wafer with a higher efficiency and a faster speed.

[0031] With continuous scaling and increased design and process complexity, there is an increasing need for semiconductor manufacturing process control. This need calls for not only advance methods and more capable tools, but also additional intra-wafer, inter-wafer, and across-lot sampling in order to capture process variations and / or changes in process signatures. Integrated circuits (ICs) are expected to perform more complex tasks with higher efficiency and faster processing speeds with each new process technology node, which necessitates complex device architectures to accommodate a higher density of active devices. A “technology node,” in the context of semiconductor device industry (e.g., “10 nm”), refers to the smallest size of a feature, such as a gate of a transistor or a halfpitch of a metal line, which can be reproducibly printed on a semiconductor wafer.

[0032] With the reduction in the size of the features fabricated on a semiconductor wafer, particle contamination in charged-particle beam systems poses a bigger challenge. In some cases, the contaminants or undesirable particles may be larger than the size of an entire device itself, and suspension of such particles on the wafer during device fabrication may render the device dead. In some cases, particle contamination may also impact the performance and stability of critical components of an apparatus such as, but not limited to, electron source in an electron-beam apparatus, reticles in a photolithography apparatus, etc. As an example, a stable, high-voltage environment may be desirable for normal operation of the electron source configured to generate electrons or electron beams in a SEM to inspect wafer surfaces. Any disturbance in the electric field strength or the system voltage, such as due to contamination on the tip of the electron source, may affect the output of the electron source, thereby impacting the quality, throughput, or the secondary electron images generated by SEM. Additionally, particulate contamination near regions of high electric fields may induce electrical arcing, which can damage or degrade a SEM system or samples being inspected by the SEM system.

[0033] Particles, whether pre-existing in the system due to lack of proper and regular cleaning routines or generated by internal sources, may cause a number of challenges such as electrical arcing, dielectric breakdown, or electrostatic discharge (ESD), based on the type of particle, its location, or both. Electrical arcing can occur when a conductive contaminant (e.g., moisture, conductive dust, debris) forms a low resistance path between surfaces with different voltages such as in electrodes of a SEM, for example. The ionized air formed by the electrical arc can conduct extremely high current, causing electrical failure, mechanical damage, or both. In some cases, the high current can generate excessive localized heat to melt the electrodes and release particles or debris, and may prolong thearcing due to cascading contamination effects. In addition to pre-existing particles in a vacuum system, pump-down and vent-up mechanisms of vacuum chambers may introduce particulate contamination as well. The change in gas flow and gas pressure may lead to particulate contamination in the form of particle suspension from incoming gas flow or particle resuspension of pre-existing particles due to a strong turbulent incoming flow.

[0034] One of several ways to protect a critical surface such as a wafer surface from particle suspension during a system vent-up procedure may include parking the substrate (e.g., wafer) beneath the electron-optical column (i.e., the SEM module). The gas flow through the SEM module may form a protective gas cover, also referred to herein as a gas curtain, over the wafer surface, which may push away incoming airborne contaminants or particles, thus protecting the wafer surface from particle suspension. However, such a venting design may suffer from several challenges. The effectiveness of the protective gas cover formed may be determined based on the flow rate or flow velocity of the venting gas configured to form the gas cover. While a stronger gas flow through the electron-optical column of a SEM may help form a stronger gas cover, the turbulence of the strong gas flow may cause pre-existing particles to resuspend on surfaces within the electron-optical column or on the wafer surface, or both, which may be detrimental to the process and product yield. Therefore, it is desirable to provide systems and methods of venting up vacuum systems that can provide a strong protective gas cover over critical surfaces while mitigating the risk of particle resuspension or contamination within the electron-optical column.

[0035] Some aspects of the present disclosure may address some above-mentioned challenges by providing an additional source of venting gas to allow formation of a strong protective gas cover over the wafer surface while preventing particle contamination through resuspension of pre-existing particles within the electron-optical column of a vacuum system such as a SEM. In some embodiments, the system may include a first gas flow configured to vent up the electron-optical column and a second gas flow configured to form the protective gas cover over the wafer top surface. The first gas flow may be directed downstream through the electron-optical column and the second gas flow may be directed downstream or upstream towards the wafer top surface. The two gas flows may merge to form a lateral gas flow over the top surface of the wafer, and the lateral gas flow may be directed radially outward to push the gas toward the edges of the substrate (or a critical surface). The flow velocity of the merged lateral gas flow may be higher than the individual flow velocity of the first or the second gas flows. The second gas flow may be configured to flow through a purge ring installed within a shield (e.g., high-voltage shield) above the substrate (e.g., wafer) or within a substrate holder below the substrate. The first and the second gas flow rates or flow velocity may be individually controlled by a controller configured to regulate the gas flow through a gas flow control mechanism.

[0036] 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 arenot necessarily required to achieve such exemplary objects or advantages, and some embodiments may not achieve any of the stated objects or advantages.

[0037] 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. 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.

[0038] Reference is now made to Fig. 1A, which illustrates an exemplary charged-particle beam inspection system 100 (e.g., electron beam inspection (EBI) system) consistent with embodiments of the present disclosure. EBI system 100 may be used for imaging or metrology. As shown in Fig. 1A, charged particle beam inspection system 100 includes a main chamber 10, a load-lock chamber 20, an electron beam tool 40, and an equipment front end module (EFEM) 30. Electron beam tool 40 is located within main chamber 10. While the description and drawings are directed to an electron beam, it is appreciated that the embodiments are not used to limit the present disclosure to specific charged particles.

[0039] EFEM 30 includes a first loading port 30a and a second loading port 30b. EFEM 30 may include additional loading port(s). First loading port 30a and second loading port 30b 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 are collectively referred to as “wafers” hereafter). In some embodiments, a semiconductor wafer may be referred to as a substrate. One or more robot arms (not shown) in EFEM 30 transport the wafers to load-lock chamber 20.

[0040] Load-lock chamber 20 is connected to a load / lock vacuum pump system (not shown), which removes gas molecules in load-lock chamber 20 to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transport the wafer from load-lock chamber 20 to main chamber 10. Main chamber 10 is connected to a main chamber vacuum pump system (not shown), which removes gas molecules in main chamber 10 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by electron beam tool 40. In some embodiments, electron beam tool 40 may comprise a single-beam inspection tool.

[0041] Controller 50 may be electronically connected to electron beam tool 40 and may be electronically connected to other components as well. Controller 50 may be a computer configured to execute various controls of charged particle beam inspection system 100. Controller 50 may also include processing circuitry configured to execute various signal and image processing functions. While controller 50 is shown in Fig. 1A as being outside of the structure that includes main chamber 10, load-lock chamber 20, and EFEM 30, it is appreciated that controller 50 can be part of the structure.

[0042] In some embodiments, controller 50 may include one or more processors (not shown). A processor may be a generic or specific electronic device capable of manipulating or processing information. For example, the processor may include any combination of any number of a central processing unit (or “CPU”), a graphics processing unit (or “GPU”), an optical processor, a programmable logic controllers, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a Programmable Logic Array (PLA), a Programmable Array Logic (PAL), a Generic Array Logic (GAL), a Complex Programmable Logic Device (CPLD), a Field- Programmable Gate Array (FPGA), a System On Chip (SoC), an Application-Specific Integrated Circuit (ASIC), a neural processing unit (NPU), and any type of circuit capable of data processing. The processor may also be a virtual processor that includes one or more processors distributed across multiple machines or devices coupled via a network.

[0043] In some embodiments, controller 50 may further include one or more memories (not shown). A memory may be a generic or specific electronic device capable of storing codes and data accessible by the processor (e.g., via a bus). For example, the memory may include any combination of any number of a random-access memory (RAM), a read-only memory (ROM), an optical disc, a magnetic disk, a hard drive, a solid-state drive, a flash drive, a security digital (SD) card, a memory stick, a compact flash (CF) card, or any type of storage device. The codes may include an operating system (OS) and one or more application programs (or “apps”) for specific tasks. The memory may also be a virtual memory that includes one or more memories distributed across multiple machines or devices coupled via a network.

[0044] While the present disclosure provides examples of main chamber 10 housing an electron beam inspection system, it should be noted that aspects of the disclosure in their broadest sense, are not limited to a chamber housing an electron beam inspection system. Rather, it is appreciated that the foregoing principles may be applied to other chambers as well.

[0045] Reference is now made to Fig- IB, which is a schematic diagram illustrating an exemplary wafer loading sequence in charged particle beam inspection system 100 of Fig. 1A, consistent with embodiments of the present disclosure. In some embodiments, charged particle beam inspection system 100 may include a robot arm 11 located in EFEM 30 and a robot arm 12 located in main chamber 10. In some embodiments, EFEM 30 may also include a pre-aligner 60 configured to position a wafer accurately before transporting the wafer to load-lock chamber 20.

[0046] In some embodiments, first loading port 30a and second loading port 30b, for example, may receive wafer FOUPs that contain wafers. Robot arm 11 in EFEM 30 may transport the wafers from any of the loading ports to pre-aligner 60 for assisting with the positioning. Pre-aligner 60 may use mechanical or optical aligning methods to position the wafers. After pre-alignment, robot arm 11 may transport the wafers to load-lock chamber 20.

[0047] After the wafers are transported to load-lock chamber 20, a load lock vacuum pump (not shown) may remove gas molecules in load-lock chamber 20 to reach a first pressure below the atmospheric pressure. After reaching the first pressure, a robot arm 12 may transport the wafer from load-lock chamber 20 to a wafer stage 80 of electron beam tool 40 in main chamber 10. Main chamber 10 may be connected to a main chamber vacuum pump system (not shown), which removes gas molecules in main chamber 10 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer may be subject to inspection by the electron beam tool.

[0048] In some embodiments, main chamber 10 may include a parking station 70 configured to temporarily store a wafer before inspection. For example, when the inspection of a first wafer is completed, the first wafer may be unloaded from wafer stage 80, and then robot arm 12 may transport a second wafer from parking station 70 to wafer stage 80. Afterwards, robot arm 12 may transport a third wafer from load-lock chamber 20 to parking station 70 to temporarily store the third wafer until the inspection for the second wafer is finished.

[0049] In some embodiments, to improve the overall throughput of inspection system, charged particle beam inspection system 100 may perform a thermal conditioning of a wafer before loading the wafer onto wafer stage 80. This pre-inspection thermal conditioning may occur in pre-aligner 60, load-lock chamber 20, parking station 70, or any other place suitable for thermally conditioning the wafer before moving it to wafer stage 80.

[0050] Reference is now made to Fig- 2, which illustrates a schematic diagram illustrating an exemplary configuration of electron beam tool 40 that can be a part of the exemplary charged particle beam inspection system 100 of Fig. 1, consistent with embodiments of the present disclosure.Electron beam tool 40 (also referred to herein as apparatus 40) may comprise an electron emitter, which may comprise a cathode 203, an extractor electrode 205, a gun aperture 220, and an anode 222. Electron beam tool 40 may further include a Coulomb aperture array 224, a condenser lens 226, a beam-limiting aperture array 235, an objective lens assembly 232, and an electron detector 244. Electron beam tool 40 may further include a sample holder 236 supported by motorized stage 234 to hold a sample 250 to be inspected. It is to be appreciated that other relevant components may be added or omitted, as needed.

[0051] In some embodiments, electron emitter may include cathode 203, an anode 222, wherein primary electrons can be emitted from the cathode and extracted or accelerated to form a primary electron beam 204 that forms a primary beam crossover 202. Primary electron beam 204 can be visualized as being emitted from primary beam crossover 202.

[0052] In some embodiments, the electron emitter, condenser lens 226, objective lens assembly 232, beam-limiting aperture array 235, and electron detector 244 may be aligned with a primary optical axis 201 of apparatus 40. In some embodiments, electron detector 244 may be placed off primary optical axis 201, along a secondary optical axis (not shown).

[0053] Objective lens assembly 232, in some embodiments, may comprise a modified swing objective retarding immersion lens (SORIL), which includes a pole piece 232a, a control electrode 232b, a beam manipulator assembly comprising deflectors 240a, 240b, 240d, and 240e, and an exciting coil 232d. In a general imaging process, primary electron beam 204 emanating from the tip of cathode 203 is accelerated by an accelerating voltage applied to anode 222. A portion of primary electron beam 204 passes through gun aperture 220, and an aperture of Coulomb aperture array 224, and is focused by condenser lens 226 so as to fully or partially pass through an aperture of beam-limiting aperture array 235. The electrons passing through the aperture of beam- limiting aperture array 235 may be focused to form a probe spot on the surface of sample 250 by the modified SORIL lens and deflected to scan the surface of sample 250 by one or more deflectors of the beam manipulator assembly. Secondary electrons emanated from the sample surface may be collected by electron detector 244 to form an image of the scanned area of interest.

[0054] In objective lens assembly 232, exciting coil 232d and pole piece 232a may generate a magnetic field. A part of sample 250 being scanned by primary electron beam 204 can be immersed in the magnetic field and can be electrically charged, which, in turn, creates an electric field. The electric field may reduce the energy of impinging primary electron beam 204 near and on the surface of sample 250. Control electrode 232b, being electrically isolated from pole piece 232a, may control, for example, an electric field above and on sample 250 to reduce aberrations of objective lens assembly 232 and control focusing situation of signal electron beams for high detection efficiency, or avoid arcing to protect sample. One or more deflectors of beam manipulator assembly may deflect primary electron beam 204 to facilitate beam scanning on sample 250. For example, in a scanning process, deflectors 240a, 240b, 240d, and 240e can be controlled to deflect primary electron beam 204, onto different locations of top surface of sample 250 at different time points, to provide data for image reconstruction for different parts of sample 250. It is noted that the order of 240a-e may be different in different embodiments.

[0055] Backscattered electrons (BSEs) and secondary electrons (SEs) can be emitted from the part of sample 250 upon receiving primary electron beam 204. A beam separator 240c can direct the secondary or scattered electron beam(s), comprising backscattered and secondary electrons, to a sensor surface of electron detector 244. The detected secondary electron beams can form corresponding beam spots on the sensor surface of electron detector 244. Electron detector 244 can generate signals (e.g., voltages, currents) that represent the intensities of the received secondary electron beam spots, and provide the signals to a processing system, such as controller 50. The intensity of secondary or backscattered electron beams, and the resultant secondary electron beamspots, can vary according to the external or internal structure of sample 250. Moreover, as discussed above, primary electron beam 204 can be deflected onto different locations of the top surface of sample 250 to generate secondary or scattered electron beams (and the resultant beam spots) of different intensities. Therefore, by mapping the intensities of the secondary electron beam spots with the locations of sample 250, the processing system can reconstruct an image that reflects the internal or external structures of sample 250.

[0056] In some embodiments, controller 50 may comprise an image processing system that includes an image acquirer (not shown) and a storage (not shown). The image acquirer may comprise one or more processors. For example, the image acquirer may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. The image acquirer may be communicatively coupled to electron detector 244 of apparatus 40 through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, among others, or a combination thereof. In some embodiments, the image acquirer may receive a signal from electron detector 244 and may construct an image. The image acquirer may thus acquire images of regions of sample 250. The image acquirer may also perform various post-processing functions, such as generating contours, superimposing indicators on an acquired image, and the like. The image acquirer may be configured to perform adjustments of brightness and contrast, etc. of acquired images. In some embodiments, the storage may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer readable memory, and the like. The storage may be coupled with the image acquirer and may be used for saving scanned raw image data as original images, and post-processed images.

[0057] In some embodiments, controller 50 may include measurement circuitries (e.g., analog-to- digital converters) to obtain a distribution of the detected secondary electrons and backscattered electrons. The electron distribution data collected during a detection time window, in combination with corresponding scan path data of a primary electron beam 204 incident on the sample (e.g., a 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 sample 250, and thereby can be used to reveal any defects that may exist in the wafer.

[0058] In some embodiments, controller 50 may control motorized stage 234 to move sample 250 during inspection. In some embodiments, controller 50 may enable motorized stage 234 to move sample 250 in a direction continuously at a constant speed. In other embodiments, controller 50 may enable motorized stage 234 to change the speed of the movement of sample 250 over time depending on the steps of scanning process.

[0059] As is commonly known in the art, interaction of charged particles, such as electrons of a primary electron beam with a sample may generate signal electrons containing compositional and topographical information about the probed regions of the sample. Secondary electrons (SEs) may beidentified as signal electrons with low emission energies, and backscattered electrons (BSEs) may be identified as signal electrons with higher emission energies. Because of their low emission energy, an objective lens assembly may direct the SEs along electron paths and focus the SEs on a detection surface of in-lens electron detector placed inside the SEM column. BSEs traveling along electron paths may be detected by the in-lens electron detector as well. In some cases, BSEs with large emission angles, however, may be detected using additional electron detectors, such as a backscattered electron detector, or remain undetected, resulting in loss of sample information needed to inspect a sample or measure critical dimensions.

[0060] Detection and inspection of some defects in semiconductor fabrication processes, such as buried particles during photolithography, metal deposition, dry etching, or wet etching, among other things, may benefit from inspection of surface features as well as compositional analysis of the defect particle. In such scenarios, information obtained from secondary electron detectors and backscattered electron detectors to identify the defect(s), analyze the composition of the defect(s), and adjust process parameters based on the obtained information, among other things, may be desirable for a user.

[0061] Reference is now made to Fig. 3A, which is a schematic illustration of a portion of an exemplary charged-particle beam tool 300, consistent with embodiments of the present disclosure. Charged-particle beam tool 300 (also referred to as apparatus 300 may comprise a charged-particle source such as, an electron source configured to emit primary electrons from a cathode and extracted using an extractor electrode to form a primary electron beam along a primary optical axis. Apparatus 300 may further comprise an anode, a condenser lens, a beam-limiting aperture array, a signal electron detector, a compound objective lens, a scanning deflection unit comprising primary electron beam deflectors, and a control electrode, none of which are illustrated for brevity purposes. In the context of this disclosure, signal electron detectors may be an in-lens electron detector located inside the electron-optical column 310 and may be arranged rotationally symmetric around a primary optical axis. In some embodiments, signal electron detector(s) may be referred to as through-the-lens detector, immersion lens detector, upper detector, or a secondary electron detector. It is to be appreciated that relevant components may be added, omitted, or reordered, as appropriate.

[0062] An electron source (not shown) may include a thermionic source configured to emit electrons upon being supplied thermal energy to overcome the work function of the source, a field emission source configured to emit electrons upon being exposed to a large electrostatic field, etc. In the case of a field emission source, the electron source may be electrically connected to a controller, such as controller 50 of Fig. 1A, configured to apply and adjust a voltage signal based on a desired landing energy, sample analysis, source characteristics, among other things. An extractor electrode may be configured to extract or accelerate electrons emitted from a field emission gun, for example, to form primary electron beam that forms a virtual or a real primary beam crossover (not illustrated) along primary optical axis. Primary electron beam may be visualized as being emitted from the primary beam crossover. In some embodiments, controller 50 may be configured to apply and adjust a voltagesignal to extractor electrode to extract or accelerate electrons generated from electron source. An amplitude of the voltage signal applied to extractor electrode may be different from the amplitude of the voltage signal applied to cathode. In some embodiments, the difference between the amplitudes of the voltage signal applied to extractor electrode and to cathode may be configured to accelerate the electrons downstream along primary optical axis while maintaining the stability of the electron source.

[0063] Apparatus 300 may include vacuum chambers 301 and 302. Vacuum chamber 301 may comprise electron-optical column 310. Vacuum chamber 302 may include control electrode 320, a shield 330, a substrate 340 placed on a substrate holder 350, and a substrate table 360. It is to be appreciated that, although not illustrated, vacuum chambers 301 and 302 may comprise more elements. It is to be also appreciated that, in some embodiments, apparatus 300 may include a single vacuum chamber instead of two vacuum chambers.

[0064] Electron-optical column 310, also referred to as a charged-particle beam optics column, may include a charged-particle source such as an electron source, a plurality of aperture arrays, electromagnetic or static lens arrays, a condenser lens, an objective lens assembly, microstigmators, microdeflector, charged-particle detectors, among other things, which may be sensitive to particle contamination. In the context of this disclosure, components or surfaces sensitive to particulate contamination are referred to as “critical” components or surfaces. As an example, control electrode 320, substrate 340, substrate holder 350, internal surfaces of electron-optical column 310 may comprise critical components or critical surfaces. A component or a surface may be “critical” if the functionality of the component or the surface is impacted by the presence of a contaminant such as, but not limited to, dust particles, debris, or any airborne contaminants.

[0065] As used in the context of this disclosure, “downstream” refers to a direction along the path of primary electron beam starting from the electron source towards substrate 340. With reference to positioning of an element of a charged-particle beam apparatus (e.g., apparatus 300 of Fig. 3A), “downstream” may refer to a position of an element located below or after another element, along the path of primary electron beam starting from the electron source, and “immediately downstream” refers to a position of a second element below or after a first element along the path of primary electron beam such that there are no other active elements between the first and the second element. For example, as illustrated in Fig. 3A, substrate 340 may be positioned immediately downstream of shield 330 or control electrode 320 such that there are no other optical or electron-optical elements placed between substrate 340 and shield 330. As used in the context of this disclosure, “upstream” may refer to a position of an element located above or before another element, along the path of primary electron beam starting from the electron source, and “immediately upstream” refers to a position of a second element above or before a first element along the path of primary electron beam such that there are no other active elements between the first and the second element. As an example, control electrode 320 or shield 330 may be placed immediately upstream from substrate 340. As usedherein, “active element” may refer to any element or component, the presence of which may modify the electromagnetic field between the first and the second element, either by generating an electric field, a magnetic field, or an electromagnetic field.

[0066] Apparatus 300 may include a gas inlet 305 fluidly connected to vacuum chamber 301 or electron-optical column 310. Gas inlet 305 may be configured to introduce venting gas 315 into vacuum chamber 301 or electron-optical column 310 to vent-up electron-optical column 310 to atmospheric pressure from a vacuum environment. During operation of the charged-particle beam apparatus (e.g., a SEM) for an inspection or a metrology measurement, electron-optical column 310 or vacuum chamber 301 may be held in a vacuum environment. Venting up a system or a vacuum chamber (e.g., an electron-optical column or a SEM module) refers to a process in which the internal gas pressure of the chamber is restored from vacuum or near vacuum to atmospheric pressure. Pumping down a system or a vacuum chamber refers to a process of reducing internal gas pressure of the system or the vacuum chamber from an atmospheric pressure level to an operational state of vacuum.

[0067] Generally, the vent-up process of an entire system (e.g., apparatus 300) includes venting up of electron-optical column 310 (placed in vacuum chamber 301) and venting up of vacuum chamber 302, among other things. Venting up of electron-optical column 310, also referred to as the SEM module here, includes injecting extremely clean dry air (XCDA) or nitrogen (Nz) via gas inlet 305 into electron-optical column 310. The venting gas flow travels downstream (as indicated by the dashed arrows in Fig. 3A) towards vacuum chamber 302, which is fluidly connected with vacuum chamber 301. Vacuum chamber 302 may include a recessed substrate table 360, and substrate holder 350 holding substrate 340. Although not illustrated, vacuum chamber 302 may further include a gas inlet mechanism configured to inject venting gas into vacuum chamber 302. The flow of venting gas 315 in electron-optical column 310 or vacuum chamber 301 serves two functions, i.e., venting up the electron-optical column 310, and generating an overpressure in the electron-optical column 310. The overpressure prevents contaminated gas from flowing into electron-optical column 310 and minimizes exposure of critical components in electron-optical column 310 to contaminants or airborne particles. In the context of this disclosure, “overpressure” in a system refers to an overall positive internal gas pressure above atmospheric pressure or higher internal gas pressure of the system with reference to a gas pressure of other connected systems.

[0068] Particle contamination is one of the major challenges faced by the semiconductor industry, and even more so as the technology nodes get smaller. Unintentionally present particles or contaminants can be a nuisance in device fabrication, device inspection, wafer metrology, among other aspects of semiconductor device manufacturing. Particles on critical surfaces, whether preexisting in the system due to inadequate cleaning or generated by internal sources or processes, may cause functional damage of systems or of devices produced using the systems. For example, a stable high-voltage environment is desirable for efficient operation of an electron source in a SEM and presence ofunwanted particles may cause electrostatic discharge (ESD), which can disturb the system voltage and electric field strength. In some cases, ESD may further generate particles by inducing localized heating of electrodes to release particles from the melted metal surfaces, which in turn may form more weak spots for ESDs. Particle contamination may thus cause a deteriorated and unstable high voltage system. Other examples of functional damage caused by particle contamination include, but are not limited to, aperture clogging, damage to the lens assembly, wafer yield loss, machine down time, or device throughput loss. Therefore, it is desirable to minimize particulate contamination in every aspect of semiconductor device fabrication including inspection before, during, and after device fabrication.

[0069] One of several sources of particulate contamination in vacuum systems used in semiconductor device fabrication is particle resuspension due to change in internal gas pressure such as, for example during a pump-down or a vent-up process. As previously described, critical surfaces may be sensitive to particulate contamination in that the contaminant may alter one or more of the surface’ s optical, mechanical, electrical, chemical, structural properties or its desired functionality. As an example, a dust particle or debris on a critical surface (e.g., wafer surface) during device fabrication may cause a physical or an electrical defect, rendering the end device non-functional. An increased gas flow laterally across the critical surface may be desirable to “drive-away” or “push-off’ the contaminants landing on the critical surface. Increasing the lateral gas flow may include increasing the gas flow (e.g., flow of venting gas 315) through SEM electron-optical column (e.g., electron-optical column 310 of Fig. 3A). However, increasing gas flow of venting gas 315 may cause turbulence 318 inside the electron-optical column 310, resulting in increased contaminant resuspension in the electron- optical column 310. In the context of this disclosure, lateral gas flow across a surface refers to the direction of gas flowing radially outward and substantially parallel to a horizontal plane along which the surface extends. In Fig. 3A, the direction indicated by arrow 319 indicates a lateral gas flow of venting gas 315 across the top surface of substrate 340 (e.g., a wafer placed on a substrate / wafer holder).

[0070] Fig. 3B illustrates a system 370, analogous to system 300 of Fig. 3A, which comprises vacuum chambers 375 and 378 fluidly connected with each other. Vacuum chamber 375 may be a vacuum chamber housing substrate holder 350 and vacuum chamber 378 may comprise a robot arm chamber. The gas flow in the robot arm chamber or vacuum chamber 378 may be considerably stronger and more turbulent compared to the venting gas flow (e.g., venting gas 315) in vacuum chamber 375 due to relatively strong incoming venting flow from chamber venting inlets (not shown). In some cases, stronger gas flow in vacuum chamber 378 may be desirable for faster vent-ups of system 370.

[0071] The risk of particle resuspension during a vent-up process in a SEM apparatus may be related to the shear velocity of the venting gas. For example, for an average shear velocity, particle resuspension during vent-up may be negligible (e.g., less than 0.0001% of 4-pm particles may bemoved by the gas flow). While the shear velocity may be higher in smaller regions on the surfaces of control electrode (e.g., control electrode 320 of Fig. 3A), which could potentially cause resuspension of larger particles, the risk may be mitigated by proper cleaning procedures, or a particle-free venting gas flow in the SEM module. A wafer stage or the substrate holder, which may be a critical surface, may be placed such that it is substantially perpendicular to the downstream flow of venting gas. In such a scenario, the top surface of substrate holder (e.g., substrate holder 350 of Fig. 3A), which makes the direct, normal-angle contact with the venting flow from the SEM module may experience the highest shear velocity of the venting gas, and thus, particles in the SEM venting gas may be deposited or retained on the top surface of the substrate holder. As another example, the gas flow in the robot arm chamber (e.g., vacuum chamber 378 of Fig. 3B) is considerably more turbulent and stronger due to the relatively strong incoming venting gas flow from the chamber venting inlets, as previously mentioned. With exposed moving components such as, but not limited to, joints, bearings, or hydraulic lifting systems, the vacuum robot arm (not shown) may be a source of particle contamination as well. Therefore, a turbulent-flow environment around a relatively dirty robot arm may lead to noticeable particle resuspension, which may induce contamination of critical surfaces as the gas flow exits the robot arm chamber and flows downstream.

[0072] During a vent-up process of a SEM apparatus (e.g., system 370), it may be desirable to park critical surfaces such as substrate holder 350 or substrate 340 beneath electron-optical column 310 to protect the surface from particle contamination. In some existing systems, the flow of venting gas 315 downward through electron-optical column 310 may form a protective gas cover 380, also referred to herein as a “gas curtain,” above the top surface of substrate 340. Gas cover 380 may be formed below the control electrode (e.g., control electrode 320 of Fig. 3A) and above substrate 340 or substrate holder 350 (if a substrate is not placed on the substrate holder). The protective gas cover 380 may be configured to provide protection to control electrode 320 and portions of shield 330 in addition to substrate 340 placed on substrate holder 350. Within the protective gas cover 380, gas flow diverges from control electrode 320 towards the edges of substrate 340 (or substrate holder 350), and diverts the venting gas flow from vacuum chamber 378 around critical surfaces. If the venting gas flow of vacuum chamber 378 is stronger, such as for faster vent-ups, a stronger gas curtain may be desirable to handle more aggressive chamber venting flow from vacuum chamber 378 which is expected to induce more airborne contaminants.

[0073] One of several ways to form an effective protective gas cover 380 over critical surfaces in vacuum chamber 375 may include providing a high flow velocity of venting gas 315 through vacuum chamber 375 to increase the lateral gas flow across a critical surface. In this context, flow velocity refers to the distance that the gas travels in a specific timeframe and may be represented in meters / second (m / s), or centimeters / sec (cm / s), or millimeters / sec (mm / s). However, if the flow velocity of venting gas 315 passing through electron-optical column 310 is too high, the risk of particle resuspension and surface contamination may be higher. In some existing systems, providingan increased lateral gas flow across a critical surface may include increasing the flow of venting gas through the electron-optical column. While the increased lateral gas flow across the critical surface may reduce the particulate suspension on the critical surface, it may cause particulate resuspension on critical surfaces in electron-optical column 310 while passing through. Therefore, it is desirable to provide systems and methods of increasing the gas flow across a critical surface to reduce contaminants landing on the critical surface while minimizing contaminant resuspension on other critical surfaces.

[0074] Reference is now made to Fig. 4A, which illustrates an exemplary system 400 comprising an electron-optical column 410, a control electrode 420, a purge ring 425, a shield 430, a substrate 440 placed on a substrate holder 450, and a substrate table 460. Although not illustrated, it is to be appreciated that system 400 may also include one or more vacuum chambers such as vacuum chambers 375 and 378 of Fig. 3B, venting-up and pump-down mechanisms, among other things. Electron-optical column 410 may be substantially similar to and may perform substantially similar functions as electron-optical column 310 of Fig. 3A. Electron-optical column 410 may be placed in a vacuum chamber or connected thereto.

[0075] In some embodiments, shield 430 may comprise a magnetic shield configured to mitigate or prevent exposure of the charged-particle beam to stray magnetic fields which may cause magnetic disturbance. For example, in a charged-particle beam apparatus such as a SEM, an electron beam may be projected on a surface of a substrate. A magnetic lens may be used to focus or deflect the electron beam by a magnetic force on the substrate surface by means of a magnetic field. The electrons of the electron beam, interacting with the magnetic field by a magnetic Lorentz force, may be susceptible to magnetic disturbances. Further, in some systems, the actuators of a substrate positioning device may be magnetic actuators. Such actuators, upon actuation, generate stray magnetic fields that may affect the electron beam in a SEM. The interaction of stray magnetic fields with the electron beam may result in a loss of accuracy of the electron beam, or loss of throughput of the apparatus, or both. Shield 430 may be configured to reduce the impact of magnetic stray fields towards the propagation path of the electron beam and towards the magnetic lens in electron-optical column 410. In some embodiments, shield 430 may be configured to provide shielding from high-voltage effects, thermal effects, among other things. Shield 430 may be made from mu-metal, a material having high magnetic permeability, or any other suitable material. Shield 430 may be in the form of a plate, a disc, a tube, or any suitable form.

[0076] Fig. 4B illustrates a corresponding top-view of an exemplary shield 430 used in system 400 of Fig. 4A. Shield 430 may comprise a central opening 432 configured to allow the primary charged- particle beam to propagate through to substrate 440. Shield 430 may be placed such that the central opening 432 of shield 430 surrounds control electrode 420. In some embodiments, the geometric center of central opening 432 of shield 430 and the center of control electrode 420 may be aligned with the primary optical axis 401 of system 400. In some embodiments, control electrode 420 andshield 430 may be coplanar or substantially coplanar. In this context, “coplanar” refers to the positioning of two or more components such that their respective centers of gravity lie on the same plane and “substantially coplanar” refers to the positioning of two or more components such that their respective centers of gravity lie approximately on the same plane. As an example, shield 430 and control electrode 420 may be coplanar or substantially coplanar such that their respective centers of gravity lie on a virtual two-dimensional plane 430P. It is to be appreciated that plane 430P is an imaginary, virtual plane shown as a visual aid and for illustrative purposes only.

[0077] In some embodiments, in addition to venting gas 415 supplied through gas inlet 405, system 400 may include purge ring 425 configured to provide venting gas 422 during vent-up of system 400 (e.g., SEM tool). Purge ring 425 may comprise a second gas inlet configured to direct venting gas 422 towards substrate 440. Gas inlet 405 and purge ring 425 may be configured to direct venting gas 415 and venting gas 422, respectively, toward substrate 440 such that the two gas flows merge to form a lateral flow across the top surface of substrate 440. The merged lateral flow (indicated by the curved arrows in Fig. 4A) pushes the gas radially outward toward the edges of substrate 440 to minimize particle contamination on critical surfaces which could be caused by particle retention, particle suspension, or particle resuspension.

[0078] In some embodiments, purge ring 425 may be mechanically coupled with shield 430. In some embodiments, shield 430 may comprise an opening configured to receive purge ring 425 such that purge ring 425 sits partially or fully within the opening. An opening in shield 430 to receive purge ring 425 may be a recessed portion with apertures or holes to allow passage of venting gas 422. In some embodiments, purge ring 425 may be held in place by a coupling mechanism such as, but not limited to, welding, flex coupling, rigid coupling, among other techniques. Although not illustrated in Fig. 4A, it is to be appreciated that system 400 may include one or more gas flow regulation mechanisms. For example, gas flow through gas inlet 405 or purge ring 425 may be regulated through separate flow valves controlled by a controller (e.g., controller 50 of Fig. 2). One or more flow valves may be activated or deactivated individually via a controller to regulate the gas flow during vent-up of system 400.

[0079] Purge ring 425 may be configured to provide additional venting gas 422 during venting up of system 400. The gas flow of venting gas 422 may form a gas curtain (e.g., gas cover 380 of Fig. 3B) to protect one or more critical surfaces from particle contamination. The venting gas 422 flow rate may be adjusted individually. In this context, the gas flow rate refers to the volumetric flow or volume of gas passing through a cross-section within a specific timeframe and may be represented as nanoliters / min (nl / min) or milliliters / min (ml / min). The ability to individually regulate the flow rate of venting gas 422 through purge ring 425 may serve two functions — form a stronger gas curtain to protect one or more critical surfaces and facilitate faster venting up of system 400 without increasing the risk of particle resuspension. The faster vent-ups may allow an increase in the throughput or overall system usability. In some embodiments, the flow rate of venting gas 422 from purge ring 425may be higher or substantially higher compared to the flow rate of venting gas 415, resulting in formation of a stronger gas cover and accordingly, better protection from particle contamination. This may be accomplished without affecting or increasing the risk of particle resuspension within electron- optical column 410 because venting gas 422 is configured to flow through a physically-separated and individually-controlled purge ring 425.

[0080] As previously described, in some existing systems, the flow rate of venting gas flowing through an electron-optical column may be limited to maintain a laminar gas flow to minimize particle resuspension. The gas curtain formed by the slow flowing venting gas may be inadequate to provide protection from particle suspension on a critical surface such as a substrate or a substrate holder. One of several issues with the vent-up procedures in existing systems is that the venting gas through electron-optical column is configured to form a gas cover to protect particle contamination of critical surfaces as well as maintain a laminar gas flow within the electron-optical column to minimize particle resuspension on critical surfaces within the electron-optical column. Providing additional venting gas through purge ring 425 may overcome one or more of the issues associated with particle resuspension on critical surfaces.

[0081] In some embodiments, the additional venting gas through purge ring 425 may allow decoupling the “SEM module overpressure” function from the “gas curtain” function. In the context of this disclosure, the “SEM module overpressure” refers to a relatively positive gas pressure within the SEM module in comparison to the gas pressure outside the SEM module. The SEM module overpressure may be desirable to prevent gas flowing upstream into the SEM module from neighboring positive pressure regions including vacuum chamber 378, for example. The “gas curtain” refers to a cover or a layer of gas formed by a laminar, radially outward flow of venting gas directly above a critical surface such as a substrate or a substrate holder. In some existing systems, the venting gas through the SEM module (i.e., the electron-optical column) serves to create the SEM module overpressure and to form the gas curtain. However, using purge ring 425 to provide additional venting gas (e.g., venting gas 422), as discussed herein, may allow decoupling the SEM module overpressure function from the gas curtain function. A low flow rate of venting gas 415 may be maintained in the SEM module (e.g., electron-optical columns 310 and 410 of Fig. 3A and Fig. 4A, respectively) to maintain a laminar gas flow to minimize particle resuspension and an overpressure to prevent backflow of gases into the SEM module. A high flow rate of venting gas 422 through purge ring 425 may be directed toward a substrate to form a strong gas curtain (e.g., gas cover 380 of Fig. 3B), providing protection of critical surfaces from particle contamination.

[0082] In some embodiments, the composition of venting gas 422 may comprise extremely clean dry air (XCDA), Nitrogen (Nz), ionized gas, or an inert gas, or mixtures thereof as suitable. In some embodiments, the composition of venting gas 422 may be substantially similar to the composition of venting gas used for venting up vacuum chamber 378 or robot arm chamber. In some embodiments, the amount of venting gas 422 through purge ring 425 may be relatively small compared to theamount of venting gas used for venting up vacuum chamber 378. In such a scenario, the composition of venting gas 422 may comprise nitrogen. In some embodiments, purge ring 425 may be used to introduce ionized gases to regulate the charges present on the surface of a substrate (e.g., a wafer). For example, in an application including wafer inspection using a SEM apparatus, venting gas 422 may include a mixture of an ionized gas and a purging gas directed toward the wafer before or after wafer inspection. It is appreciated that in such applications for wafer charge control, gas flowing through purge ring 425 may not necessarily be used for venting up a system, instead it may be used to regulate the charges present on the substrate.

[0083] In some embodiments, the temperature of venting gas 422 flowing through purge ring 425 may be adjustable based on the thermal conditioning of substrate or substrate holder (e.g., an electrostatic chuck). Gas flowing through purge ring 425 may be heated up or cooled down to compensate the temperature mismatch between a substrate (e.g., a wafer) and the substrate holder (e.g., an electrostatic chuck). For example, a wafer introduced into vacuum chamber 375 from load lock may be colder due to the cold load induced by the fast pumping-down in load lock. The temperature mismatch between the cold wafer and the chuck configured to receive the wafer may lead to wafer distortion, and resultantly image distortion during wafer inspection. In such a scenario, it might be desirable to adjust the temperature of the chuck to minimize the temperature mismatch between the incoming wafer and the chuck. Venting gas 422 flowing through purge ring 425 may be pre-cooled to a predetermined temperature prior to being introduced into the gas supply mechanism. In some embodiments, the temperature of the substrate (e.g., a wafer) or the substrate holder may rise during wafer inspection or a metrology measurement. The temperature rise may cause an undesirable thermal drift as it may affect the image quality. The pre-cooled purge gas may be introduced through purge ring 425 to provide a controlled cooling of the substrate or the substrate holder to compensate the temperature rise.

[0084] System 400 may comprise substrate table 460, also referred to herein as a mirror block or an encoder block. A substrate table may be referred to as a mirror block if the position of substrate table 460 is determined based on an interferometer position measurement system. If the position of substrate table 460 is determined based on an encoder position measurement system, substrate table 460 may be referred to as an encoder block. In some embodiments, substrate holder 450 may be placed in a recess in substrate table 460 and substrate 440 may be placed on top of substrate holder 450. In some embodiments, vacuum may be developed in spaces between substrate table 460 and substrate holder 450 and between substrate holder 450 and substrate 440 so that substrate 440 and substrate holder 450 are clamped in place by atmospheric pressure above substrate 440. In some embodiments, the recess in substrate table 460 may be slightly larger than substrate holder 450 and substrate 440 to accommodate variations in substrate size and placement. The difference between the size of the recess and substrate holder 450 or substrate 440 may form a narrow groove or a trench (discussed with reference to Figs. 5A and 5B) around the edges of substrate 440.

[0085] Reference is now made to Fig. 5A, which illustrates an exemplary system 500 comprising an electron-optical column 510, a control electrode 520, a purge ring 525, a shield 530, a substrate 540 placed on a substrate holder 550, and a substrate table 560. Although not illustrated, it is to be appreciated that system 500 may also include one or more vacuum chambers such as vacuum chambers 375 and 378 of Fig. 3B, venting-up and pump-down mechanisms, among other things. Electron-optical column 510 may be substantially similar to and may perform substantially similar functions as electron-optical column 310 of Fig. 3A. Electron-optical column 510 may be placed in a vacuum chamber or connected thereto.

[0086] In some embodiments, substrate holder 550 may comprise purge ring 525. As illustrated in Fig. 5A, purge ring 525 may be placed within substrate holder 550 such that venting gas 522 is released in trench 555 toward the internal walls of the recess of substrate table 560, travels upward and radially outward towards the edges of substrate 540. Venting gas 515 traveling downward through electron-optical column 510 toward the top surface of substrate 540 and venting gas 522 from purge ring 525 located inside substrate holder 550 may merge to form a lateral flow above top surface of substrate 540 and directed radially outward to minimize or prevent particle suspension on top surface of substrate 540. The flow rate of venting gas 515 may be low to maintain a laminar flow through electron-optical column 510. In some embodiments, the flow rate of venting gas 515 may be less than 1 nl / min (nanoliters / minute), or less than 0.9 nl / min, or less than 0.8 nl / min, or less than 0.7 nl / min, or less than 0.6 nl / min, or less than 0.5 nl / min, or less than 0.4 nl / min, or less than 0.3 nl / min, or less than 0.2 nl / min, or a suitable range to avoid turbulence, and thereby increasing the risk of particle resuspension on critical surfaces inside electron-optical column 510. The flow rate of venting gas 522 through purge ring 525 may be considerably higher than the flow rate of venting gas 515. The high flow rate of venting gas 522 may enable formation of a strong protective gas cover (e.g., gas cover 380 of Fig. 3B) over the top surface of substrate 540. The low flow rate of venting gas 515 may maintain a positive internal gas pressure to substantially prevent the backflow of venting gas 522 or chamber venting gas inside electron-optical column 510.

[0087] Fig. 5B illustrates a top view of system 500 along A-A' shown in Fig. 5A, consistent with some embodiments of the present disclosure. As illustrated, purge ring 525 may be located within substrate holder 550 and on the outer edge of substrate holder 550 to allow introduction of venting gas 522 directly into trench 555. In some embodiments, purge ring 525 may be located radially inward toward the center of substrate holder 550. In such cases, a path (e.g., a tubing or a passage) for venting gas 522 may be provided to direct the venting gas from purge ring 525 to trench 555. In some embodiments, the width 555w and the depth of trench 555 may be uniform around the edges of substrate 540 or substrate holder 550. In some embodiments, trench width 555w may be fixed or constant along the depth of the trench. In this context, the width of a trench refers to the horizontal distance between the internal walls of recess of a substrate table and the edges of the substrate or substrate holder, and the depth of a trench refers to the vertical distance between the top surface of asubstrate or a substrate holder (if the substrate is absent) and the base of the recess of the substrate table. In some embodiments, the depth of a trench (e.g., trench 555) may be substantially similar to the depth of the recess of substrate table (e.g., substrate table 560). In some alternative embodiments, the depth of a trench may be more or less than the depth of the recess of table substrate.

[0088] In some embodiments, substrate holder 550 may include more than one purge ring 525 (not shown). For example, a first purge ring may be configured to introduce a mixture of ionized gases and inert gases and a second purge ring may be configured to introduce a venting gas such as, but not limited to, XCDA or Nitrogen. It is to be appreciated that the size of the purge ring(s), number of purge rings, location of purge ring(s), spacing between the purge rings, material of fabrication, or gases introduced through the purge ring(s) may be adjusted, as appropriate. It is to be further appreciated that although the substrate table is circular in Fig. 5B, it may be rectangular, or any desired shape.

[0089] Reference is now made to Fig. 5C, which illustrates an exemplary system 500_2 comprising a plurality of purge rings, consistent with some embodiments of the present disclosure. In comparison to system 500, system 500_2 includes an additional purge ring 525_2 located in shield 530. In some embodiments, a downward flow or a downstream flow and an upward flow or an upstream flow of gas may be merged to form a lateral gas flow across a critical surface. The downward flow or downstream flow of gas may comprise flow of venting gas 515 through electron-optical column 510 toward substrate 540, or flow of venting gas 522_2 from purge ring 525_2 located inside shield 530 toward substrate 540, or both. The upward flow of gas may comprise flow of purge gas 522 from purge ring 525 located inside substrate holder 550 toward substrate 540. In some embodiments, venting gas 522_2, venting gas 515, and venting gas 522 may merge to form a lateral gas flow across the top surface of substrate 540. The flow velocity of the merged lateral gas flow may be higher than any of the individual gas flows. The merged gas flow may form a protective gas cover above a critical surface (e.g., top surface of substrate 540 or substrate holder 550 if substrate is absent) to prevent particle suspension or particle contamination of critical surfaces. In some embodiments, the flow velocity of venting gas 515 may be low to maintain a laminar gas flow downward through electron- optical column 510 to minimize particle resuspension and to maintain an overpressure to prevent the backflow of venting gases. The flow velocity of venting gases 522_2 and 522 may be individually and separately adjusted to adjust the venting speed, or the strength of protective gas cover (e.g., gas cover 380 of Fig. 3B), or both.

[0090] Reference is now made to Fig. 6A, which illustrates an exemplary system 600 comprising an electron-optical column 610, a control electrode 620, a purge ring 625, a shield 630, a substrate 640 placed on a substrate holder 650, and a substrate table 660. Although not illustrated, it is to be appreciated that system 600 may also include one or more vacuum chambers such as vacuum chambers 375 and 378 of Fig. 3B, venting-up and pump-down mechanisms, among other things. Electron-optical column 610 may be substantially similar to and may perform substantially similarfunctions as electron-optical column 310 of Fig. 3A. Electron-optical column 610 may be placed in a vacuum chamber or connected thereto.

[0091] Purge ring 625 may be located inside substrate table 660 and around trench 655 such that purge ring 625 may introduce venting gas 622 directly into trench 655. In some embodiments, purge ring 625 may be configured to provide venting gas 622 through openings on the inner vertical walls of recess of substrate table and through openings in the horizontal base of the recess as well. Venting gas 622 flowing upwards toward substrate 640 may merge with venting gas 615 flowing downward through electron-optical column 610 to form a lateral gas flow across the top surface of substrate 640. The lateral gas flow across the top surface of substrate 540 may serve as a gas cover (e.g., gas cover 380 of Fig. 3B) to prevent or mitigate particle suspension. Particulates may be pushed off towards the outer edges and away from any critical surface by the lateral gas flow directed radially outward. In some embodiments, substrate table 660 may include more than one purge rings 625 (not shown). For example, a first purge ring may be configured to introduce a mixture of ionized gases and inert gases and a second purge ring may be configured to introduce a venting gas such as, but not limited to, XCDA or Nitrogen. It is appreciated that the size of the purge ring(s), number of purge rings, location of purge ring(s), spacing between the purge rings, material of fabrication, or gases introduced through the purge ring(s) may be adjusted, as appropriate. Fig. 6B illustrates a top view of a portion of system 600 along section A-A' shown in Fig. 6A.

[0092] Reference is now made to Fig. 6C, which illustrates an exemplary system 600_2 comprising a plurality of purge rings, consistent with some embodiments of the present disclosure. In comparison to system 600, system 600_2 includes an additional purge ring 625_2 located in shield 630. In some embodiments, a downward flow or a downstream flow and an upward flow or an upstream flow of gas may be merged to form a lateral gas flow across a critical surface. The downward flow or downstream flow of gas may comprise flow of venting gas 615 through electron-optical column 610 toward substrate 640, or flow of venting gas 622_2 from purge ring 625_2 located inside shield 630 toward substrate 640, or both. The upward flow of gas may comprise flow of purge gas 622 from purge ring 625 located inside substrate table 660 toward substrate 640. In some embodiments, venting gas 622_2, venting gas 615, and venting gas 622 may merge to form a lateral gas flow across the top surface of substrate 640. The flow velocity of the merged lateral gas flow may be higher than any of the individual gas flows. The merged gas flow may form a protective gas cover above a critical surface (e.g., top surface of substrate 640 or substrate holder 650 if substrate is absent) to prevent particle suspension or particle contamination of critical surfaces. In some embodiments, the flow velocity of venting gas 615 may be low to maintain a laminar gas flow downward through electron- optical column 610 to minimize particle resuspension and to maintain an overpressure to prevent the backflow of venting gases. The flow velocity of venting gases 622_2 and 622 may be individually and separately adjusted to adjust the venting speed, or the strength of protective gas cover (e.g., gas cover 380 of Fig. 3B), or both.

[0093] Reference is now made to Fig- 7, which illustrates a venting sequence 700 of an exemplary system including one or more purge rings, consistent with some embodiments of the present disclosure. A venting sequence, as referred to in this context, refers to a sequence of steps or functions performed by a system to vent-up a system from negative internal pressure (i.e., a vacuum) to positive internal pressure (atmospheric pressure or higher). It is appreciated that although the exemplary vacuum system may include a SEM inspection or a metrology tool, the venting sequence may be applied to other vacuum systems as well.

[0094] In step 710, controller 50 may be configured to activate one or more valves to allow venting gas to flow in the electron-optical column of a charged-particle beam apparatus (e.g., a SEM). The venting gas flowing through the electron-optical column (e.g., electron-optical columns 310, 410, 510, or 610 of Figs. 3A, 4A, 5A, or 6A, respectively) may serve to create an overpressure while venting up the electron-optical column. Controller 50 may be further configured to adjust the flow rate or gas flow velocity of venting gas allowed through a corresponding valve to maintain a non-turbulent flow through the electron-optical column. The non-turbulent flow of venting gas may allow venting up the electron-optical column without the risk of particle resuspension on critical surfaces within the electron-optical column.

[0095] In step 720, controller 50 may be configured to activate one or more valves to allow venting gas to flow through the corresponding purge ring (e.g., purge rings 425, 525, 525_2, 625, 625_2 of Figs. 4A, 5A, 5C, 6A, or 6C, respectively). In some embodiments, controller 50 may be further configured to cause a first time-delay 715 between steps 710 and 720. In some embodiments, the first time-delay may be in the range of 0.5 to 5.0 seconds, or 0.5 to 4.5 seconds, or 0.5 to 4.0 seconds, or 0.5 to 3.5 seconds, or 0.5 to 3.0 seconds, or 0.5 to 2.5 seconds, or 0.5 to 2.0 seconds, or 0.5 to 1.5 seconds, or 0.5 to 1.0 second, or any suitable time range. In some preferred embodiments, the first time-delay may be between 1.5 to 2 seconds. The first time-delay may allow the flow of venting gas through the electron-optical column to generate an overpressure (a positive internal gas pressure through the electron-optical column) to minimize the backflow of purge gas through one or more purge rings into the electron-optical column. Controller 50 may be further configured to adjust the flow rate or gas flow velocity of venting gas flowing through one or more purge rings such that the flow rate is higher in comparison with the flow rate of venting gas through the electron-optical column. The higher flow rate of venting gas through one or more purge rings may enable forming a stronger protective gas cover (e.g., gas cover 380 of Fig. 3B) to minimize particle suspension or retention on a critical surface such as a wafer. In some embodiments, the flow rate through one or more purge rings may be adjusted to adjust the venting up speed of a system as well. In some embodiments, where more than one purge ring may be used to vent up a system (e.g., system 500_2 or 600_2 of Figs. 5C or 6C, respectively), controller may be configured to individually adjust the flow rate, the timing of activation or deactivation of the corresponding valves, or the choice of gas flowing through the purge rings.

[0096] In step 730, controller may be configured to activate a valve to allow venting gas to flow in robot arm chamber (e.g., vacuum chamber 378 of Fig. 3B). The venting gas introduced in the robot arm chamber may vent-up the robot arm chamber from vacuum to atmospheric pressure or higher. Controller 50 may be further configured to adjust the flow rate or gas flow velocity of venting gas to adjust the venting speed. In some embodiments, controller 50 may be further configured to cause a second time-delay 725 between steps 720 and 730. In some embodiments, the second time-delay may be less than 0.5 seconds, or less than 0.45 seconds, or less than 0.40 seconds, or less than 0.35 seconds, or less than 0.30 seconds, or less than 0.25 seconds, or less than 0.2 seconds, or less than 0.15 seconds, or any suitable time range. In some preferred embodiments, the second time-delay may be 0.1 seconds.

[0097] Reference is now made to Fig- 8, which illustrates a process flowchart representing an exemplary method 800 of increasing gas flow across a substrate in a charged-particle beam apparatus such as apparatus 300 of Fig. 3A, consistent with embodiments of the present disclosure.

[0098] In step 810, a controller (e.g., controller 50 of Fig. 2) may activate one or more valves to cause a first gas to flow downstream in a vacuum chamber (e.g., electron-optical column 310 of Fig. 3A). The gas flowing through the electron-optical column may comprise a venting gas (e.g., venting gas 315 of Fig. 3 A) configured to vent-up the electron-optical column from operating vacuum pressure to atmospheric pressure or higher. Some examples of venting gas, though not limited, include XCDA, Nitrogen, or a mixture of gases suitable for venting up vacuum systems. The controller may be further configured to adjust the flow rate or flow velocity of the venting gas through the electron-optical column. In some embodiments, the flow rate or flow velocity may be adjusted to maintain a laminar (non-turbulent) flow of venting gas. The non-turbulent flow may cause the electron-optical column to vent-up while mitigating particle contamination on critical surfaces (e.g., lens surfaces within the electron-optical column).

[0099] In step 820, the controller may activate one or more valves to cause a second gas to flow toward the substrate at a second flow velocity. In some embodiments, the valves configured to regulate the flow of second gas may be different from the valve configured to regulate the flow of first gas. The second gas may be a venting gas flowing through a purge ring (e.g., purge ring 425 or 525 of Figs. 4A or 5A, respectively). In some embodiments, the purge ring may be located inside a shield (e.g., high voltage shield 430 of Fig. 4A) or inside a substrate holder (e.g., high voltage shield 530 of Fig. 5A). In some embodiments, the second gas (e.g., venting gas) may be flown toward the substrate from two purge rings simultaneously, as illustrated in systems 500_2 and 600_2 of Figs. 5C and 6C, respectively. In some embodiments, the second flow velocity may be higher than the first flow velocity.

[0100] In some embodiments, the first and the second gas flows merge to form a lateral gas flow across a top surface of a substrate (e.g., substrate 340 of Fig. 3A). The lateral gas flow may be directed radially outward and provide a protective gas cover (e.g., gas cover 380 of Fig. 3B) tomitigate particle contamination on critical surfaces (e.g., top surface of a substrate or a wafer, or a substrate holder). The lateral gas flow directed radially outward may have a higher velocity than the first or the second flow velocity.

[0101] In some embodiments, the second gas flow may be directed downstream or downwards toward the top surface of the substrate from a purge ring (e.g., purge ring 425) located inside the shield, as illustrated in Fig. 4A. In some embodiments, the second gas flow may be directed upstream or upwards toward the top surface of the substrate from a purge ring (e.g., purge ring 525) located inside a substrate holder (e.g., substrate holder 550), as illustrated in Fig. 5A. In some embodiments, one or more purge rings may be used to introduce venting gas to form the protective gas cover over the top surface of the substrate. For example, as illustrated in Fig. 5C, venting gas may be introduced through purge rings 525 and 525_2 located inside the substrate holder and the shield, respectively, to vent-up the system.

[0102] In some embodiments, the controller may be configured to cause a time-delay between activation of a first valve to introduce venting gas flowing through the electron-optical column (e.g., venting gas 315, 415, 515, 615 of Figs. 3A, 4A, 5A, 6A, respectively) and activation of the second valve to introduce venting gas flowing through a purge ring.

[0103] A non-transitory computer-readable medium may be provided that stores instructions for a processor of a controller (e.g., a central processing unit or electronic control unit that is configured to control a charged particle beam apparatus) for performing a method according to the exemplary flowcharts or other methods consistent with embodiments of the present disclosure. For example, the instructions stored in the non-transitory computer-readable medium may be executed by the circuitry of the controller for performing the methods in part or in their entireties. Common forms of non- transitory media include, for example, a floppy disk, a flexible disk, hard disk, solid-state drive, magnetic tape, or any other magnetic data storage medium, a Compact Disc Read-Only Memory (CD- ROM), any other optical data storage medium, any physical medium with patterns of holes, a Random Access Memory (RAM), a Programmable Read-Only Memory (PROM), and Erasable Programmable Read-Only Memory (EPROM), a FLASH-EPROM or any other flash memory, Non-Volatile Random Access Memory (NVRAM), a cache, a register, any other memory chip or cartridge, and networked versions of the same.

[0104] 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, twoblocks 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.

[0105] The embodiments may further be described using the following clauses:1. A charged-particle beam apparatus, comprising: a vacuum chamber, comprising: a first gas inlet fluidly connected with a charged-particle beam optics column and configured to direct a first gas flow downstream in the charged-particle beam optics column toward a substrate at a first flow velocity; and a second gas inlet configured to direct a second gas flow toward the substrate at a second flow velocity, wherein the first and the second gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.2. The apparatus of clause 1, wherein the first flow velocity is lower than the second flow velocity.3. The apparatus of any one of clauses 1 and 2, wherein the first gas flow is configured to cause the charged-particle beam optics column to vent-up.4. The apparatus of any one of clauses 1-3, further comprising a shield located immediately upstream from the substrate, the shield comprising an opening configured to receive the second gas inlet.5. The apparatus of clause 4, wherein the second gas inlet comprises a purge ring mechanically coupled to the shield by a coupling mechanism.6. The apparatus of clause 5, further comprising a substrate chamber configured to house the substrate, the substrate chamber being fluidly connected to the charged-particle beam optics column.7. The apparatus of clause 6, further comprising a third gas inlet configured to direct a third gas flow inside the substrate chamber to vent-up the substrate chamber.8. The apparatus of clause 7, further comprising a controller including circuitry configured to: activate a first valve configured to regulate the first gas flow through the first gas inlet; activate a second valve configured to regulate the second gas flow through the second gas inlet; and activate a third valve configured to regulate the third gas flow through the third gas inlet.9. The apparatus of clause 8, wherein:activation of the first valve enables the first gas flow through the charged-particle beam optics column, activation of the second valve enables the second gas flow through the purge ring, and activation of the third valve enables the third gas flow into the substrate chamber.10. The apparatus of any one of clauses 8 and 9, wherein the controller including circuitry further configured to cause a first time-delay between the activation of the first and the second valve.11. The apparatus of clause 10, wherein the controller including circuitry further configured to cause a second time-delay between the activation of the second and the third valve.12. The apparatus of clause 11, wherein the first and the second time-delays are predetermined.13. The apparatus of any one of clauses 11 and 12, wherein the first time-delay is longer than the second time-delay.14. The apparatus of any one of clauses 7-13, wherein a gas composition of the second gas flow and a gas composition of the third gas flow are substantially similar.15. The apparatus of clause 14, wherein the gas composition of the second gas flow and the gas composition of the third gas flows are different.16. The apparatus of any one of clauses 14 and 15, wherein the gas composition of the second gas flow comprises nitrogen, extremely clean dry air (XCDA), an inert gas, or an ionized gas.17. The apparatus of any one of clauses 1-5, wherein the purge ring is located downstream from the substrate.18. The apparatus of clause 17, further comprising a substrate holder configured to support the substrate.19. The apparatus of clause 18, further comprising a substrate table, wherein the substrate holder is placed in a recess in the substrate table.20. The apparatus of clause 19, wherein upon placement of the substrate holder in the recess, a trench is formed between edges of the substrate holder and inner walls of the substrate table forming the recess.21. The apparatus of clause 20, wherein the substrate holder comprises the purge ring configured to direct the second gas flow in the trench.22. The apparatus of clause 20, wherein the substrate table comprises the purge ring configured to direct the second gas flow in the trench.23. The apparatus of any one of clauses 2-22, wherein the lateral gas flow is directed radially outward.24. The apparatus of any one of clauses 2-23, wherein the first and the second gas flows increase a gas pressure in the vacuum chamber.25. A method of increasing gas flow across a substrate in a charged-particle beam apparatus, the method comprising:causing a first gas flow downstream in a vacuum chamber toward a substrate at a first flow velocity; and causing a second gas flow toward the substrate at a second flow velocity, wherein the first and the second gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.26. The method of clause 25, wherein the first flow velocity is lower than the second flow velocity.27. The method of any one of clauses 25 and 26, wherein the first gas flow is configured to cause a charged-particle beam optics column to vent-up.28. The method of any one of clauses 25-27, wherein causing the first gas flow downstream comprises directing the first gas flow using a first gas inlet fluidly connected with a charged- particle beam optics column, and wherein causing the second gas flow toward the substrate comprises directing the second gas flow using a second gas inlet different from the first gas inlet.29. The method of clause 28, wherein the second gas inlet comprises a purge ring located upstream from the substrate.30. The method of clause 29, wherein the purge ring is mechanically coupled to a shield by a coupling mechanism.31. The method of clause 30, further comprising causing a third gas flow through a third gas inlet and configured to vent-up a substrate chamber housing the substrate, wherein the substrate chamber is fluidly connected to the charged-particle beam optics column.32. The method of clause 31, wherein: causing the first gas flow comprises activating a first valve configured to regulate the first gas flow through the first gas inlet; causing the second gas flow comprises activating a second valve configured to regulate the second gas flow through the second gas inlet; and causing the third gas flow comprises activating a third valve configured to regulate the third gas flow through the third gas inlet.33. The method of clause 32, wherein: activating the first valve enables the first gas flow through the charged-particle beam optics column toward the substrate; activating the second valve enables the second gas flow through the purge ring toward the substrate; and activating the third valve enables the third gas flow into the substrate chamber.34. The method of any one of clauses 32 and 33, further comprising causing a first time- delay between activating the first and the second valve.35. The method of clause 34, further comprising causing a second time-delay between activating the second valve and the third valve.36. The method of clause 35, wherein the first time-delay is longer than the second time-delay.37. The method of any one of clauses 31-36, wherein a gas composition of the second gas flow and a gas composition of the third gas flow are substantially similar.38. The method of any one of clauses 31-36, wherein a gas composition of the second gas flow and a gas composition of the third gas flow are different.39. The method of any one of clauses 37 and 38, wherein the gas composition of the second gas flow comprises nitrogen, extremely clean dry air (XCDA), an inert gas, or an ionized gas.40. The method of clause 28, wherein the second gas inlet comprises a purge ring located downstream from the substrate.41. The method of clause 40, wherein the purge ring is located inside a substrate holder configured to support the substrate, and wherein the substrate holder is placed in a recess in a substrate table.42. The method of clause 41, wherein placing the substrate holder in the recess forms a trench between edges of the substrate holder and inner walls of the substrate table forming the recess.43. The method of clause 42, wherein the purge ring is configured to direct the second gas flow in the trench.44. The method of clause 42, wherein the purge ring is located inside the substrate table and is configured to direct the second gas flow in the trench.45. The method of any one of clauses 25-44, wherein the lateral gas flow is directed radially outward.46. The method of any one of clauses 25-45, wherein the first and the second gas flows increase a gas pressure in the vacuum chamber.47. A charged-particle beam apparatus, comprising: a first gas inlet fluidly connected with a charged-particle beam optics column and configured to direct a first gas flow downward in the charged-particle beam optics column toward a substrate at a first flow velocity; a second gas inlet located upstream from the substrate and configured to direct a second gas flow toward the substrate at a second flow velocity; and a third gas inlet located downstream from the substrate and configured to direct a third gas flow toward the substrate at a third flow velocity, wherein the first, the second, and the third gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity, the second flow velocity, or the third flow velocity.48. The apparatus of clause 47, wherein the first flow velocity is lower than the second or the third flow velocity.49. The apparatus of any one of clauses 47 and 48, wherein the first gas flow is configured to cause the charged-particle beam optics column to vent-up.50. The apparatus of any one of clauses 47-49, further comprising a shield located immediately upstream from the substrate, the shield comprising an opening configured to receive the second gas inlet.51. The apparatus of clause 50, further comprising: a substrate holder configured to support the substrate; and a recessed substrate table, wherein the substrate holder is placed in a recess in the substrate table.52. The apparatus of clause 51, wherein upon placement of the substrate holder in the recess, a trench is formed between edges of the substrate holder and inner walls of the substrate table forming the recess.53. The apparatus of clause 52, wherein the second gas inlet comprises a first purge ring mechanically coupled to the shield by a coupling mechanism, and wherein the third gas inlet comprises a second purge ring configured to direct the third gas flow in the trench.54. The apparatus of clause 53, wherein the second purge ring is located inside the substrate holder.55. The apparatus of clause 53, wherein the second purge ring is located inside the substrate table.56. The apparatus of clause 55, further comprising a substrate chamber configured to house the substrate, the substrate chamber being fluidly connected to the charged-particle beam optics column.57. The apparatus of clause 56, further comprising a fourth gas inlet configured to direct a fourth gas flow inside the substrate chamber to vent-up the substrate chamber.58. The apparatus of clause 57, further comprising a controller including circuitry configured to: activate a first valve configured to regulate the first gas flow through the first gas inlet; activate a second valve configured to regulate the second gas flow through the second gas inlet; activate a third valve configured to regulate the third gas flow through the third gas inlet; and activate a fourth valve configured to regulate the fourth gas flow through the fourth gas inlet.59. The apparatus of clause 58, wherein: activation of the first valve enables the first gas flow through the charged-particle beam optics column; activation of the second valve enables the second gas flow through the first purge ring; activation of the third valve enables the third gas flow through the second purge ring; and activation of the fourth valve enables the fourth gas flow into the substrate chamber.60. The apparatus of clause 59, wherein the controller including circuitry is further configured to cause a first time-delay between the activation of the first valve and one of the second valve or the third valve.61. The apparatus of clause 60, wherein the controller including circuitry is further configured to cause a second time-delay between the activation of one of the second or the third valve and the fourth valve.62. The apparatus of clause 61, wherein the first and the second time-delays are predetermined.63. The apparatus of any one of clauses 61 and 62, wherein the first time-delay is longer than the second time-delay.64. The apparatus of any one of clauses 47-63, wherein a gas composition of the second or the third gas flow comprises Nitrogen, extremely clean dry air (XCDA), an inert gas, or an ionized gas.65. The apparatus of any one of clauses 47-64, wherein the lateral gas flow is directed radially outward.66. The apparatus of any one of clauses 47-65, wherein the first and the second gas flows increase a gas pressure in the vacuum chamber.67. A non-transitory computer readable medium storing a set of instructions that is executable by one or more processors of a charged-particle beam apparatus to cause the charged-particle beam apparatus to perform a method of increasing gas flow across a substrate in a charged- particle beam apparatus, the method comprising: causing a first gas flow downstream in a vacuum chamber toward a substrate at a first flow velocity; and causing a second gas flow toward the substrate at a second flow velocity, wherein the first and the second gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.68. The non-transitory computer readable medium of clause 67, wherein the first flow velocity is lower than the second flow velocity.69. The non-transitory computer readable medium of any one of clauses 67 and 68, wherein causing the first gas flow downstream comprises directing the first gas flow using a first gas inlet fluidly connected with a charged-particle beam optics column, and wherein causing the second gas flow toward the substrate comprises directing the second gas flow using a second gas inlet different from the first gas inlet.70. The non-transitory computer readable medium of clause 69, wherein the second gas inlet comprises a purge ring located upstream from the substrate, and wherein the purge ring is mechanically coupled to a shield by a coupling mechanism.71. The non-transitory computer readable medium of clause 70, wherein the method further comprises causing a third gas flow through a third gas inlet and configured to vent-up a substrate chamber housing the substrate, and wherein the substrate chamber is fluidly connected to the charged-particle beam optics column.72. The non-transitory computer readable medium of clause 71, wherein: causing the first gas flow comprises activating a first valve configured to regulate the first gas flow through the first gas inlet; causing the second gas flow comprises activating a second valve configured to regulate the second gas flow through the second gas inlet; and causing the third gas flow comprises activating a third valve configured to regulate the third gas flow through the third gas inlet.73. The non-transitory computer readable medium of clause 72, wherein: activating the first valve enables the first gas flow through the charged-particle beam optics column toward the substrate; activating the second valve enables the second gas flow through the purge ring toward the substrate; and activating the third valve enables the third gas flow into the substrate chamber.74. The non-transitory computer readable medium of any one of clauses 72 and 73, wherein the method further comprises: causing a first time-delay between activating the first and the second valve, and causing a first second time -delay between activating the second and the third valve.75. The non-transitory computer readable medium of clause 74, wherein the first time-delay is longer than the second time-delay.76. The non-transitory computer readable medium of any one of clauses 71-75, wherein a gas composition of the second gas flow and a gas composition of the third gas flow are substantially similar.77. The non-transitory computer readable medium of any one of clauses 71-75, wherein a gas composition of the second gas flow and a gas composition of the third gas flow are different.78. The non-transitory computer readable medium of any one of clauses 76 and 77, wherein the gas composition of the second gas flow comprises nitrogen, extremely clean dry air (XCDA), an inert gas, or an ionized gas.79. The non-transitory computer readable medium of clause 69, wherein the second gas inlet comprises a purge ring located downstream from the substrate.80. The non-transitory computer readable medium of clause 79, wherein the purge ring is located inside a substrate holder configured to support the substrate, and wherein the substrate holder is placed in a recess in a substrate table.81. The non-transitory computer readable medium of clause 80, wherein placing the substrate holder in the recess forms a trench between edges of the substrate holder and inner walls of the substrate table forming the recess.82. The non-transitory computer readable medium of clause 81, wherein the purge ring is configured to direct the second gas flow in the trench.83. The non-transitory computer readable medium of clause 81, wherein the purge ring is located inside the substrate table and is configured to direct the second gas flow in the trench.84. The non-transitory computer readable medium of any one of clauses 67-83, wherein the lateral gas flow is directed radially outward.85. The non-transitory computer readable medium of any one of clauses 67-84, wherein the first and the second gas flows increase a gas pressure in the vacuum chamber.

[0106] 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 invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A charged-particle beam apparatus, comprising: a vacuum chamber, comprising: a first gas inlet fluidly connected with a charged-particle beam optics column and configured to direct a first gas flow downstream in the charged-particle beam optics column toward a substrate at a first flow velocity; and a second gas inlet configured to direct a second gas flow toward the substrate at a second flow velocity, wherein the first and the second gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.

2. The apparatus of claim 1, wherein the first flow velocity is lower than the second flow velocity.

3. The apparatus of claim 1, wherein the first gas flow is configured to cause the charged- particle beam optics column to vent-up.

4. The apparatus of claim 1, further comprising a shield located immediately upstream from the substrate, the shield comprising an opening configured to receive the second gas inlet.

5. The apparatus of claim 4, wherein the second gas inlet comprises a purge ring mechanically coupled to the shield by a coupling mechanism.

6. The apparatus of claim 5, further comprising a substrate chamber configured to house the substrate, the substrate chamber being fluidly connected to the charged-particle beam optics column.

7. The apparatus of claim 6, further comprising a third gas inlet configured to direct a third gas flow inside the substrate chamber to vent-up the substrate chamber.

8. The apparatus of claim 7, further comprising a controller including circuitry configured to: activate a first valve configured to regulate the first gas flow through the first gas inlet; activate a second valve configured to regulate the second gas flow through the second gas inlet; andactivate a third valve configured to regulate the third gas flow through the third gas inlet.

9. The apparatus of claim 8, wherein: activation of the first valve enables the first gas flow through the charged-particle beam optics column, activation of the second valve enables the second gas flow through the purge ring, and activation of the third valve enables the third gas flow into the substrate chamber.

10. The apparatus of claim 8, wherein the controller including circuitry further configured to cause a first time-delay between the activation of the first and the second valve.

11. The apparatus of claim 10, wherein the controller including circuitry further configured to cause a second time-delay between the activation of the second and the third valve.

12. The apparatus of claim 11, wherein the first and the second time-delays are predetermined.

13. The apparatus of claim 11, wherein the first time-delay is longer than the second time-delay.

14. The apparatus of claims 7, wherein a gas composition of the second gas flow and a gas composition of the third gas flow are substantially similar.

15. A non- transitory computer readable medium storing a set of instructions that is executable by one or more processors of a charged-particle beam apparatus to cause the charged-particle beam apparatus to perform a method of increasing gas flow across a substrate in a charged- particle beam apparatus, the method comprising: causing a first gas flow downstream in a vacuum chamber toward a substrate at a first flow velocity; and causing a second gas flow toward the substrate at a second flow velocity, wherein the first and the second gas flows merge to form a lateral gas flow across a top surface of the substrate, the lateral gas flow having a flow velocity higher than the first flow velocity or the second flow velocity.

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