Vacuum chamber for cold field emission electron source

Abstract

An electron source assembly with an improved vacuum chamber for an electron source is provided. The electron source assembly includes an electron source having an emitter tip at which electrons are generated. The electron source also includes a vacuum chamber configured to enclose the electron source and including an exhaust barrier coating on an inner surface of the vacuum chamber. The vacuum chamber has undergone a heat treatment in a hydrogen atmosphere and a gas removal treatment at high vacuum and high temperature. The electron source assembly also includes a vacuum pump connected to the vacuum chamber and configured to vacuumize the vacuum chamber to a pressure lower than 1.0 x 10-11 Torr.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to PCT application PCT / CN2022 / 136706, which was filed on December 5, 2022 and is incorporated herein by reference in its entirety. Technical Field

[0003] The embodiments provided herein relate to charged particle beam sources of charged particle beam systems, and more particularly to improved vacuum chambers for electron sources using cold field emission. Background Art

[0004] During the manufacturing process 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 using optical microscopes or charged particle (e.g., electron) beam microscopes such as scanning electron microscopes (SEM) can be employed. As the physical dimensions of IC components continue to shrink, the accuracy of defect detection, imaging resolution, and throughput become increasingly important. In an SEM, a primary electron beam with relatively high energy is decelerated to a relatively low landing energy and impinges on a sample, and is focused to form a probe point on the sample. Due to this focused probe point of the primary electrons, secondary electrons will be generated from the surface. The primary electrons are detected by an electron detector to generate an SEM image of the sample.

[0005] The quality and resolution of the image are greatly affected by the stability of the primary electron beam generated by the electron source. A cold field emission source can provide an electron beam with small beam energy spread, high coherence, high lifetime, and excellent brightness due to a significantly small emission area. Thus, a cold field emission source can be a desirable electron source for high-resolution imaging in an SEM system. However, contamination of the electron source can affect the performance of the cold field emission source. Therefore, maintaining a high level of vacuum cleanliness is desirable for high imaging resolution and high detection throughput. Summary of the Invention

[0006] The embodiments provided herein disclose a charged particle beam device, and more particularly disclose an improved vacuum chamber for an electron source.

[0007] One aspect of the present disclosure relates to an electron source assembly having an improved vacuum chamber for an electron source. The electron source assembly includes an electron source having an emitter tip at which electrons are generated. The electron source further includes a vacuum chamber configured to enclose the electron source and including an exhaust barrier coating on an inner surface of the vacuum chamber. The vacuum chamber has undergone a heat treatment in a hydrogen environment and a gas removal treatment at high vacuum and high temperature. The electron source assembly further includes a vacuum pump connected to the vacuum chamber and configured to pump down the vacuum chamber to a pressure lower than 1.0×10 -11 Torr.

[0008] Another aspect of the present disclosure relates to a method of treating a vacuum chamber for use at high vacuum levels. The method includes the step of performing a heat treatment of the vacuum chamber in a hydrogen environment. The method further includes the step of performing a gas removal treatment of the vacuum chamber at high vacuum measurement and high temperature, and the step of coating an inner surface of the vacuum chamber with a coating of an exhaust barrier material.

[0009] Other advantages of embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings, which illustrate, by way of example, certain embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 FIG. is a schematic diagram showing an example charged particle beam inspection system consistent with embodiments of the present disclosure.

[0011] Figure 2 FIG. shows an example configuration of an electron beam tool capable of being part of a charged particle beam inspection system consistent with embodiments of the present disclosure as Figure 1 FIG. is a schematic diagram of an example configuration of an electron source assembly consistent with embodiments of the present disclosure.

[0012] Figure 3A and Figure 3B FIG. is a flowchart showing an example method of treating a vacuum chamber for an electron source using cold field emission consistent with embodiments of the present disclosure.

[0013] Figure 4 FIG. is a flowchart showing an example method of treating a vacuum chamber for an electron source using cold field emission consistent with embodiments of the present disclosure. DETAILED DESCRIPTION

[0014] Reference will now be made in detail to exemplary embodiments, which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which, unless otherwise indicated, the same reference numerals in different drawings denote the same or similar elements. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the present invention. On the contrary, they are merely examples of apparatuses and methods consistent with aspects of the present invention as recited in the appended claims.

[0015] An electronic device is composed of circuits formed on a silicon wafer (referred to as a substrate). The semiconductor material can include, for example, silicon, gallium arsenide, indium phosphide, or silicon germanium, etc. Many circuits can be formed together on the same silicon wafer and are referred to as integrated circuits or ICs. The sizes of these circuits have been significantly reduced so that more circuits can be installed on the substrate. For example, the IC chip in a smart phone can be as small as a fingernail, but it can include more than 10 billion transistors, and the size of each transistor is smaller than 1 / 1000 of the size of a human hair.

[0016] Manufacturing these ICs with so many extremely small transistors is a complex, time-consuming, and expensive process, usually involving hundreds of individual manufacturing steps. Even an error in one step may cause defects in the finished IC, making it unusable. Therefore, one goal of the manufacturing process is to avoid such defects so as to maximize the number of functional ICs manufactured in the process, that is, to increase the overall yield of the process.

[0017] One element in increasing the yield is to monitor the chip manufacturing process to ensure that it is producing a sufficient number of functional ICs. One way to monitor the process is to inspect the chip circuit structure at various stages of its formation. The inspection can be carried out using inspection tools such as a scanning charged particle microscope. For example, the scanning charged particle microscope can be a scanning electron microscope (SEM). The SEM can be used to create images of these extremely small structures, effectively taking "photos" of these structures. The image can be used to determine whether the structure is correctly formed and whether it is formed in the correct position. If the structure is defective, the process can be adjusted so that the defect is less likely to occur again.

[0018] Obtaining high-resolution images of good quality using SEM begins with an electron source (also known as an electron gun) that has high brightness, small energy spread, and small virtual size. Two types of electron sources are commonly used in SEM systems: thermionic sources and field emission sources. Thermionic emission electron sources generate electrons by heating a filament (e.g., a tungsten hairpin filament or a LaB6 crystal), similar to how light is produced by an incandescent lamp. However, although thermionic emission electron sources are inexpensive and easy to use, they have several drawbacks, including shorter lifetime, higher operating temperature, lower brightness, wider beam energy spread, etc., which may cause degraded image quality.

[0019] In contrast, field emission sources (also known as field emission guns) use a strong electrostatic field to induce electron emission from the tip of an electron emitter. Field emission sources offer excellent brightness due to significantly smaller emission area, small beam energy spread, higher coherence, and long lifetime, making them the desired electron source for high-resolution imaging in SEM. There are two types of field emission sources - Schottky emitters and cold field emitters. Schottky emitters are thermally assisted field emission sources that combine the advantages of thermionic emission and field emission technologies. However, due to the relatively high operating temperature (although not as high as thermionic sources (e.g., about 1800 K at the tip of the emitter)), Schottky emitters also have some drawbacks similar to thermionic emission sources, such as larger beam energy spread and shorter lifetime of the emitter material. Cold field emission sources (also known as cold field emission guns or CFEGs) operate at room temperature without heating, e.g., about 300 K, and are capable of providing a similar level of brightness as Schottky emitters, while also offering smaller beam energy spread and a much longer lifetime of the emitter material. However, the performance of CFEGs is more susceptible to contamination on the surface of the emitter tip than other emitter types. The tip of a CFEG emitter tends to attract residual gases and contaminants to the emitter surface, which may cause emission noise and unwanted variations in the electron beam current.

[0020] CFEG emitters are typically placed in a high-vacuum environment (e.g., in an ultra-high-vacuum gun chamber), and to mitigate contamination issues, they are also periodically cleaned. For example, the emitter is heated periodically to purify the emission surface. This technique is referred to as "flashing" or "flash heating". During flashing, the SEM may have to be turned off or be in an inactive state, which can affect throughput. Additionally, flashing can increase the temperature of the vacuum chamber, which can cause higher outgassing in the vacuum chamber and introduce more residual gases and contaminants that can re-contaminate the emission surface. Thus, the efficiency and availability of CFEGs in systems that require high throughput may be limited. Accordingly, it is desirable to provide a gun chamber with a low outgassing rate to improve the performance of an SEM system with a CFEG. One aspect of the present disclosure includes an improved gun chamber having a reduced outgassing rate. For example, the gun chamber can be processed by an improved manufacturing process described in Figure 4 such that the gun chamber can provide ultra-high-vacuum (UHV) or extreme-high-vacuum (XHV) conditions to support a cold field emission electron source.

[0021] For clarity, the relative dimensions of components in the figures may be exaggerated. In the following description of the drawings, like or similar reference numerals refer to like or similar components or entities, and only differences relative to individual embodiments are described. As used herein, unless otherwise expressly stated, the term "or" encompasses all possible combinations unless infeasible. For example, if it is stated that a component can include A or B, then the component can include A, or B, or A and B, unless otherwise expressly stated or infeasible. As a second example, if it is stated that a component can include A, B, or C, then the component can include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C, unless otherwise expressly stated or infeasible.

[0022] Now referring to Figure 1 , Figure 1 illustrates an example charged particle beam inspection system 100 consistent with embodiments of the present disclosure. The charged particle beam inspection system 100 can be an electron beam inspection (EBI) system. As shown in Figure 1 , the charged particle beam inspection system 100 includes a main chamber 10, a load lock chamber 20, an electron beam tool 40, and an equipment front-end module (EFEM) 30. The electron beam tool 40 can be located within the main chamber 10. Although the specification and drawings are directed to electron beams, it should be understood that these embodiments are not intended to limit the present disclosure to specific charged particles and charged particle beam devices. For example, the charged particle can refer to an electron, an ion, or any positively or negatively charged particle, and the charged particle beam device can refer to an electron beam device, or an ion beam device, or any device that uses electrons and ions, such as an SEM or a focused ion beam (FIB) combined with an SEM.

[0023] The EFEM 30 includes a first feed port 30a and a second feed port 30b. The EFEM 30 may include additional (multiple) feed ports. The first feed port 30a and the second feed port 30b receive a wafer front-opening unified pod (FOUP) that contains wafers (e.g., semiconductor wafers or wafers made of (multiple) other materials) or samples to be inspected (hereinafter, wafers and samples are collectively referred to as "wafers"). One or more robotic arms (not shown) in the EFEM 30 transfer the wafers to the load lock chamber 20.

[0024] The load lock chamber 20 is connected to a load / lock vacuum pump system (not shown) that removes gas molecules from the load lock chamber 20 to achieve a first pressure below atmospheric pressure. After achieving the first pressure, one or more robotic arms (not shown) transfer the wafers from the load lock chamber 20 to the main chamber 10. In some embodiments, the main chamber 10 may also be connected to a main chamber vacuum pump system (not shown) that removes gas molecules from the main chamber 10 to achieve a second pressure below the first pressure. After achieving the desired vacuum level, the wafers are inspected by the electron beam tool 40. In some embodiments, the electron beam tool 40 may include a single-beam inspection tool. In other embodiments, the electron beam tool 40 may include a multi-beam inspection tool.

[0025] The controller 50 may be electrically connected to the electron beam tool 40 and may also be electrically connected to other components. The controller 50 may be a computer configured to perform various controls of the charged particle beam inspection system 100. The controller 50 may also include processing circuitry configured to perform various signal and image processing functions. Although the controller 50 is Figure 1 shown to be external to the structure including the main chamber 10, the load lock chamber 20, and the EFEM 30, it can be understood that the controller 50 can be part of the structure.

[0026] In some embodiments, controller 50 may include one or more processors (not shown). A processor may be a general-purpose electronic device or a special-purpose electronic device capable of manipulating or processing information. For example, a processor may include any number of central processing units (CPUs), graphics processing units (GPUs), optical processors, programmable logic controllers, microcontrollers, microprocessors, digital signal processors, intellectual property (IP) cores, programmable logic arrays (PLAs), programmable array logic (PALs), generic array logic (GALs), complex programmable logic devices (CPLDs), field-programmable gate arrays (FPGAs), systems-on-a-chip (SoCs), application-specific integrated circuits (ASICs), and any combination of any type of circuit capable of performing data processing. A processor may also be a virtual processor that includes one or more processors distributed across multiple machines or devices coupled via a network.

[0027] In some embodiments, controller 50 may also include one or more memories (not shown). A memory may be a general-purpose electronic device or a special-purpose electronic device (e.g., via a bus) capable of storing code and data accessible by a processor. For example, a memory may include any number of random access memories (RAMs), read-only memories (ROMs), optical discs, magnetic discs, hard drives, solid-state drives, flash drives, secure digital (SD) cards, memory sticks, compact flash (CF) cards, or any combination of any type of storage device. The code may include an operating system (OS) and one or more applications (or “apps”) for specific tasks. A memory may also be a virtual memory that includes one or more memories distributed across multiple machines or devices coupled via a network.

[0028] Although the present disclosure provides an example of the main chamber 10 that houses an electron beam inspection system, it should be noted that aspects of the present disclosure are not limited, in their broadest sense, to a chamber that houses an electron beam inspection system. Instead, it should be understood that the foregoing principles may also be applied to other chambers.

[0029] Now referring Figure 2 , Figure 2 FIG. is a schematic diagram showing an example configuration of an electron beam tool 40 consistent with an embodiment of the present disclosure, the electron beam tool 40 being capable of serving as Figure 1 a part of a charged particle beam inspection system 100 of C. The electron beam tool 40 (also referred to herein as device 40) may include an electron source that includes a cathode 203, an anode 220, and a gun aperture 222. The electron source may be placed in a vacuum chamber (e.g., Figure 3Ainto the gun chamber 310). The electron beam tool 40 may also include a Coulomb aperture array 224, a condenser lens 226, a beam limiting aperture array 235, an objective lens assembly 232, and an electron detector 244. The electron beam tool 40 may also include a sample holder 236 supported by a motorized stage 234 to hold a sample 250 to be inspected. It should be understood that other related components may be added or omitted as needed.

[0030] In some embodiments, the electron source may include a cathode 203 and an extractor anode 220, where primary electrons can be emitted from the cathode and extracted or accelerated to form a primary electron beam 204, which forms a primary beam crossover 202 (virtual or real). The primary electron beam 204 can be visualized as being emitted from the primary beam crossover 202.

[0031] In some embodiments, the electron source, the condenser lens 226, the objective lens assembly 232, the beam limiting aperture array 235, and the electron detector 244 may be aligned with the main optical axis 201 of the apparatus 40. In some embodiments, the electron detector 244 may be placed off the main optical axis 201 along a secondary optical axis (not shown).

[0032] In some embodiments, the objective lens assembly 232 may include a modified swing - out retarding immersion lens (SORIL) that includes pole pieces 232a, a control electrode 232b, a deflector 232c (or more than one deflector), and an excitation coil 232d. During a general imaging process, the primary electron beam 204 emitted from the tip of the cathode 203 is accelerated by a voltage applied to the anode 220. A portion of the primary electron beam 204 passes through the gun aperture 222 and the apertures of the Coulomb aperture array 224 and is focused by the condenser lens 226 so as to completely or partially pass through the apertures of the beam limiting aperture array 235. The electrons passing through the apertures of the beam limiting aperture array 235 are focused by the modified SORIL lens to form a probe point on the surface of the sample 250 and are deflected by the deflector 232c to scan the surface of the sample 250. Secondary electrons emitted from the sample surface can be collected by the electron detector 244 to form an image of the scanned area of interest.

[0033] In the objective lens assembly 232, the excitation coil 232d and the pole piece 232a can generate a magnetic field, which leaks out through the gap between the two ends of the pole piece 232a and is distributed in the region around the optical axis 201. The portion of the sample 250 scanned by the primary electron beam 204 can be immersed in the magnetic field and can be charged, which in turn generates an electric field. This electric field can reduce the energy of the primary electron beam 204 impinging on the vicinity of and on the surface of the sample 250. The control electrode 232b, which is electrically isolated from the pole piece 232a, controls the electric field above and on the sample 250 to reduce the aberration of the objective lens assembly 232 and control the focusing of the signal electron beam for high detection efficiency. The deflector 232c can deflect the primary electron beam 204 to facilitate beam scanning on the wafer. For example, during scanning, the deflector 232c can be controlled to deflect the primary electron beam 204 to different positions on the top surface of the sample 250 at different time points to provide data for image reconstruction of different portions of the sample 250.

[0034] Backscattered electrons (BSE) and secondary electrons (SE) can be emitted from portions of the sample 250 after receiving the primary electron beam 204. The electron detector 244 can capture the BSE and SE and generate an image of the sample based on the information collected from the captured signal electrons. If the electron detector 244 is deviated from the main optical axis 201, a beam splitter (not shown) can direct the BSE and SE to the sensor surface of the electron detector 244. The detected signal electron beam can form a corresponding secondary electron beam spot on the sensor surface of the electron detector 244. The electron detector 244 can generate a signal (e.g., voltage, current) representing the intensity of the received signal electron beam spot and provide this signal to a processing system, such as the controller 50. The intensity of the secondary electron beam or backscattered electron beam and thus the resulting beam spot can vary according to the external or internal structure of the sample 250. Additionally, as described above, the primary electron beam 204 can be deflected to different positions on the top surface of the sample 250 to generate secondary signal electron beams or backscattered signal electron beams (and thus the resulting beam spots) of different intensities. Therefore, by mapping the intensity of the signal electron beam spots to the positions of the primary electron beam 204 on the sample 250, the processing system can reconstruct an image of the sample 250 that reflects the internal or external structure of the sample 250.

[0035] In some embodiments, the controller 50 may include an image processing system that includes an image collector (not shown) and a memory (not shown). The image collector may include one or more processors. For example, the image collector may include a computer, a server, a mainframe, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image collector may be communicatively coupled to the electronic detector 244 of the device 40 via a medium (such as an electrical conductor, an optical fiber cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, radio, etc., or a combination thereof). In some embodiments, the image collector may receive signals from the electronic detector 244 and may construct an image. Thus, the image collector may acquire an image of an area of the sample 250. The image collector may also perform various post-processing functions, such as generating contours, superimposing indicators on the acquired image, etc. The image collector may be configured to adjust the brightness, contrast, etc. of the acquired image. In some embodiments, the storage device may be a storage medium, such as a hard disk, a flash drive, a cloud storage device, a random access memory (RAM), other types of computer-readable memories, etc. The storage device may be coupled to the image collector and may be used to save the scanned raw image data as a raw image and a post-processed image.

[0036] In some embodiments, the controller 50 may include measurement circuitry (e.g., an analog-to-digital converter) to obtain the distribution of the detected secondary electrons. The electron distribution data collected during the detection time window, combined with the corresponding scan path data of the primary beam 204 incident on the surface of the sample (e.g., a wafer), can be used to reconstruct an image of the inspected wafer structure. The reconstructed image can be used to reveal various features of the internal or external structure of the sample 250 and, thereby, can be used to reveal any defects that may be present in the sample 250 (such as a wafer).

[0037] In some embodiments, the controller 50 may control the motional stage 234 to move the sample 250 during inspection. In some embodiments, the controller 50 may enable the motional stage 234 to continuously move the sample 250 in a certain direction at a constant speed. In other embodiments, the controller 50 may enable the motional stage 234 to change the moving speed of the sample 250 over time depending on the steps of the scanning process.

[0038] Now refer to Figure 3A and Figure 3B , Figure 3A and Figure 3B show a system that is consistent with embodiments of the present disclosure and can be used for Figure 2An example configuration of the electron source assembly 300 of the electron beam tool 40 shown in [description]. In some embodiments, the electron source assembly 300 may include a gun chamber 310, a vacuum pump port 320, an electron source 330 having a emitter tip 335, and an extractor electrode 338. The gun chamber 310 may be a closed vacuum chamber. In some embodiments, the gun chamber 310 may be Figure 2 a part of a large vacuum chamber for an electron optical device column (not shown) of the device 40 shown in [description]. The gun chamber 310 may house the electron source 330 and the extractor electrode 338. The electron source 330 may be electrically connected to a power supply 360. During an operation of the electron assembly 300 for inspection or imaging, the power supply 360 may be configured to generate an electrostatic field to extract electrons from the emitter tip 335, or to focus the extracted electrons, or both. The extracted electrons may form an electron beam 302 traveling along the main optical axis 301. In some embodiments, the power supply 360 is communicatively connected to a controller 50 that is configured to control the electron source 330. Controlling the power supply 360 may include adjusting the excitation voltage, current, or power generated by the power supply 360 to regulate electron beam characteristics, which may include, but are not limited to, the number of electrons, electron beam distribution, etc.

[0039] As described above, various types of electron sources may be used for SEM, including thermionic emission sources, Schottky emission sources, and cold field emission sources (also referred to as cold field emission guns or CFEGs). Among these types of electron sources, CFEGs generally offer the best performance characteristics - including excellent brightness, small beam energy spread, and long emitter life - due to their lower operating temperature (e.g., room temperature, which is close to 300K). In some embodiments, the electron source 330 may include a CFEG.

[0040] However, the performance of a CFEG can be severely affected by contamination on the surface of the emitter tip. For example, the tip of a CFEG emitter (e.g., emitter tip 335) is prone to attracting residual gases and contaminants to the surface, and since the emitter is maintained at a relatively low temperature compared to a thermionic emitter or a Schottky emitter, contaminants can be more easily accumulated on the surface of the tip of the CFEG. These accumulated contaminants can cause emission noise and undesirable variations in the electron beam current generated by the electron source 330. This contaminant-induced degradation can occur rapidly. For example, some CFEGs have a 50% decay time of the emission current less than 100 hours. Cleaning the surface of the emitter tip 335 can alleviate the contamination problem to some extent, but does not provide a complete solution. Some currently available techniques for cleaning the surface of the emitter tip include a process called "flashing", which involves resistively heating the emitter tip and the support filament to which the emitter tip is attached to a temperature in the range from 700 °C to 2000 °C for a short period of time by passing a current through the emitter tip. However, unless the heating is sufficiently localized, this cleaning process may increase the overall temperature of the gun chamber 310, which may cause a higher outgassing from the materials of the gun chamber 310. This increased outgassing can cause a temporary reduction in the vacuum level in the gun chamber 310, thereby causing contaminants to re-adsorb and re-accumulate on the emitter tip 335.

[0041] Accordingly, it is desirable to reduce the outgassing rate of the materials used to fabricate the gun chamber 310 such that a high level of vacuum cleanliness can be maintained to achieve high imaging resolution and high inspection throughput using a CFEG. Thus, in some embodiments, the gun chamber 310 can be constructed of materials suitable for high-level vacuum (such as but not limited to stainless steel) and can be evacuated using one or more vacuum pumps via the vacuum pump port 320. In some embodiments, the gun chamber 310 can be specially treated such that it can be evacuated to a high-level vacuum state to provide a longer mean free path for electrons traveling downstream in the electron optical device column, to improve the reliability and stability of the electron source, to extend the operating life of the electron source, and for other advantages. For example, as described in further detail below, when the electron source assembly 300 includes a cold emission electron source, the gun chamber 310 may need to be evacuated to ultra-high vacuum (UHV) or extreme high vacuum (XHV) conditions. In some embodiments, a gun chamber using a CFEG can be evacuated to a pressure lower than 1.0×10 -11 Torr. To achieve such a high level of vacuum condition, in some embodiments, the gun chamber 310 can be fabricated by an improved manufacturing process (e.g., as described below Figure 4The process steps described in) are processed to reduce the outgassing rate of the material so that a high level of vacuum cleanliness can be maintained. In some embodiments, the gun chamber 310 may include an outgassing barrier coating 315 to reduce outgassing from the surface of the gun chamber 310, as Figure 3B shown, because the outgassing barrier coating 315 can fill the pores on the surface of the gun chamber 310 through which absorbed gas molecules can penetrate. The outgassing barrier coating 315 may include a material having the following properties - (i) low hydrogen permeability and strong hydrogen resistance, (ii) being less likely to generate secondary electrons when primary electrons strike the coating, (iii) improving the surface finish of the gun chamber, and (iv) a low outgassing rate of the coating material itself. In some embodiments, titanium nitride (TiN) may be used for the outgassing barrier coating 315. In some embodiments, the outgassing barrier coating 315 may be made of other materials including but not limited to titanium carbide, titanium dioxide, chromium oxide, zirconium oxide, silicon carbide, silicon nitride, or aluminum alloy.

[0042] Now refer to Figure 4 , Figure 4 which is a flow chart of an exemplary process for fabricating and processing the gun chamber 310 shown in for consistency with embodiments of the present disclosure. As described above, the CFEG provides better performance than other types of electron emitters. However, the gun chamber (such as the gun chamber 310 in Figure 3A and Figure 3B ) should be able to provide ultra-high vacuum (UHV) or extremely high vacuum (XHV) conditions while maintaining a high level of vacuum cleanliness. In some embodiments, the gun chamber using the CFEG can be evacuated to a pressure lower than 1.0×10 Figure 3A and Figure 3B Torr. To achieve such a high level of vacuum conditions while fully utilizing the advantages of the CFEG, the gun chamber can be processed by the improved manufacturing process described in -11 . Figure 4

[0043] In step 410, the gun chamber (such as the gun chamber 310 shown in Figure 3A ) can be fabricated from raw materials. In some embodiments, the gun chamber is fabricated by a casting process or a forging process. In some embodiments, the gun chamber may be constructed of a material suitable for high-level vacuum (such as but not limited to stainless steel).

[0044] In step 420, the gun chamber can be heat-treated in a hydrogen environment to remove organic contaminants from the gun chamber. For example, the gun chamber can be baked in a furnace filled with hydrogen. Hydrogen can react with the contaminants and remove the contaminants from the surface of the gun chamber. It can remove some of the contaminants that cannot even be easily removed by conventional ultrasonic cleaning.

[0045] In step 430, a hydrogen removal process is performed on the gun chamber under high vacuum and high temperature to reduce the outgassing of the gun chamber. As described above, a cold field emission gun requires ultra-high vacuum (UHV) or extremely high vacuum (XHV) conditions. At such a high level of vacuum (e.g., lower than 1.0×10 -10 Torr), the outgassing of absorbed gases from the gun chamber material can be problematic. For example, hydrogen may be present in the stainless-steel body of the gun chamber, and this hydrogen can be outgassed into the internal volume of the gun chamber. Although the gun chamber (such as Figure 3A the gun chamber 310) can be connected to a vacuum pump, such as a molecular pump or an ion pump, via a port (such as Figure 3A the vacuum pump port 320), it is difficult for these hydrogen molecules to be removed by these vacuum pumps under ultra-high vacuum (UHV) or extremely high vacuum (XHV) conditions. Therefore, step 430 is designed to prepare the gun chamber while the gun chamber is being fabricated by removing these absorbed gas molecules (especially hydrogen) from the surface and body of the gun chamber. Baking the gun chamber at a high temperature (e.g., 500 to 1200 °C) and in a high-vacuum apparatus (e.g., 1.0×10 -5 to 1.0×10 -7 Torr) for a long time can permanently remove the gases in the chamber, especially hydrogen. The time required to perform this hydrogen removal process may vary depending on the material and size of the gun chamber. For example, in some cases, for every 1 mm increase in the thickness of the gun chamber, an additional hour or so of processing may be involved. Generally, performing step 430 at a higher baking temperature and a higher vacuum level can result in a lower outgassing rate of the gun chamber.

[0046] In step 440, a coating (such as Figure 3B the outgassing barrier coating 315 shown in Figure 3A and Figure 3B the gun chamber 310) can be created on the surface of the gun chamber (such as Figure 3A and Figure 3B the gun chamber 310). This coating can be created on the inner surface of the gun chamber. In some embodiments, the coating can be created on both the inner and outer surfaces of the gun chamber. This coating can effectively reduce the permeability of absorbed gas molecules (e.g., hydrogen) because the coating can fill the pores on the surface of the gun chamber that can permeate absorbed gas molecules. For example, even after step 430, some hydrogen may still be present in the gun chamber material. The coating can effectively prevent hydrogen from permeating into the gun chamber. The coating can include materials with the following properties: (i) low hydrogen permeability and strong hydrogen resistance, (ii) being less likely to generate secondary electrons when primary electrons strike the coating, (iii) improving the surface finish of the gun chamber, and (iv) a low outgassing rate of the coating material itself. In some embodiments, titanium nitride (TiN) can be used for the coating. In some embodiments, other materials can be used for the coating, including but not limited to titanium carbide, titanium dioxide, chromium oxide, zirconium oxide, silicon carbide, silicon nitride, or aluminum alloy.

[0047] Embodiments of the present disclosure may also be described using the following terms:

[0048] 1. A method of processing a vacuum chamber for use at a high vacuum level, comprising:

[0049] Performing a heat treatment of the vacuum chamber in a hydrogen environment;

[0050] Performing a gas removal treatment of the vacuum chamber at high vacuum measurement and high temperature; and

[0051] Coating an inner surface of the vacuum chamber with a coating of an exhaust barrier material.

[0052] 2. The method according to clause 1, wherein the high vacuum level comprises a pressure lower than 1.0×10 -11 Torr.

[0053] 3. The method according to clause 1, wherein the heat treatment of the vacuum chamber in the hydrogen environment removes organic contaminants from the vacuum chamber.

[0054] 4. The method according to clause 1, wherein the gas removal treatment of the vacuum chamber reduces the exhaust of the vacuum chamber.

[0055] 5. The method according to clause 1, wherein the exhaust barrier material comprises titanium nitride.

[0056] 6. The method according to clause 1, wherein the exhaust barrier material comprises at least one of titanium carbide, titanium dioxide, chromium oxide, or zirconium oxide.

[0057] 7. The method according to clause 1, wherein the exhaust barrier material comprises at least one of silicon carbide or silicon nitride.

[0058] 8. The method according to clause 1, wherein the exhaust barrier material comprises aluminum.

[0059] 9. The method according to clause 1, wherein the gas removal treatment is performed at the high temperature in a range of 500 to 1200 °C.

[0060] 10. The method according to clause 1, wherein the gas removal treatment is performed at the high vacuum in a range of 1.0×10 -5 to 1.0×10 - 7 Torr.

[0061] 11. A method of processing a gun chamber for use with a cold field emission electron source, comprising:

[0062] Bake the gun cavity in a furnace filled with hydrogen;

[0063] Bake the gun cavity under high vacuum and high temperature; and

[0064] Apply a coating of an exhaust barrier material to the surface of the gun cavity.

[0065] 12. The method according to clause 11, wherein baking the gun cavity in a furnace filled with hydrogen removes organic contaminants from the surface of the gun cavity.

[0066] 13. The method according to clause 11, wherein baking the gun cavity under high vacuum and high temperature removes the gas absorbed in the gun cavity.

[0067] 14. The method according to clause 11, wherein the gas is hydrogen.

[0068] 15. The method according to clause 11, wherein the exhaust barrier material comprises titanium nitride.

[0069] 16. The method according to clause 11, wherein the exhaust barrier material comprises at least one of titanium carbide, titanium dioxide, chromium oxide, or zirconium oxide.

[0070] 17. The method according to clause 11, wherein the exhaust barrier material comprises at least one of silicon carbide or silicon nitride.

[0071] 18. The method according to clause 11, wherein the exhaust barrier material comprises aluminum.

[0072] 19. The method according to clause 11, wherein the high temperature ranges between 500 °C and 1200 °C.

[0073] 20. The method according to clause 11, wherein the high vacuum ranges between 1.0×10 -5 Torr and 1.0×10 - 7 Torr.

[0074] 21. An electron source assembly, comprising:

[0075] An electron source having an emitter tip at which electrons are generated;

[0076] A vacuum cavity configured to enclose the electron source and comprising an exhaust barrier coating on the inner surface thereof, wherein the vacuum cavity has undergone heat treatment in a hydrogen environment and gas removal treatment under high vacuum and high temperature; and

[0077] A vacuum pump is connected to the vacuum chamber and configured to evacuate the vacuum chamber to a pressure lower than 1.0×10 -11 Torr.

[0078] 22. The electron source assembly according to clause 21, wherein the electron source is a cold field emission gun.

[0079] 23. The electron source assembly according to clause 21, wherein the exhaust barrier coating includes titanium nitride.

[0080] 24. The electron source assembly according to clause 21, wherein the exhaust barrier coating includes at least one of titanium carbide, titanium dioxide, chromium oxide, or zirconium oxide.

[0081] 25. The electron source assembly according to clause 21, wherein the exhaust barrier coating includes at least one of silicon carbide or silicon nitride.

[0082] 26. The electron source assembly according to clause 21, wherein the exhaust barrier coating includes aluminum.

[0083] 27. The electron source assembly according to clause 21, wherein the gas removal treatment is performed at the high temperature in the range of 500 to 1200 °C.

[0084] 28. The electron source assembly according to clause 21, wherein the gas removal treatment is performed under the high vacuum in the range of 1.0×10 -5 to 1.0×10 -7 Torr.

[0085] It should be understood that the embodiments of the present disclosure are not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The present disclosure has been described in connection with various embodiments, and other embodiments of the present invention will be apparent to those skilled in the art by considering the specification and the practice of the invention disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0086] The above description is intended to illustrate and not to limit. Therefore, it should be apparent to those skilled in the art that the modifications as described can be made without departing from the scope of the following claims.

Claims

1. An electron source assembly, comprising: An electron source having an emitter tip at which electrons are generated; A vacuum chamber configured to enclose the electron source and including an exhaust barrier coating on an inner surface of the vacuum chamber, wherein the vacuum chamber has undergone a heat treatment in a hydrogen environment and a gas removal treatment at high vacuum and high temperature; And A vacuum pump, which is connected to the vacuum chamber and configured to evacuate the vacuum chamber to a pressure lower than 1.0×10 -11 Torr.

2. The electron source assembly according to claim 1, wherein the electron source is a cold field emission gun.

3. The electron source assembly according to claim 1, wherein the exhaust barrier coating comprises titanium nitride.

4. The electron source assembly according to claim 1, wherein the exhaust barrier coating comprises at least one of titanium carbide, titanium dioxide, chromium oxide, zirconium oxide, silicon carbide or silicon nitride.

5. The electron source assembly according to claim 1, wherein the exhaust barrier coating comprises aluminum.

6. The electron source assembly according to claim 1, wherein the gas removal treatment is performed at the high temperature in a range of 500 to 1200 °C.

7. The electron source assembly according to claim 1, wherein the gas removal treatment is carried out under the high vacuum within a range of 1.0×10 -5 to 1.0×10 -7 Torr.

8. A method of treating a vacuum chamber for use at a high vacuum level, comprising: Performing a heat treatment on the vacuum chamber in a hydrogen environment; Performing a gas removal treatment on the vacuum chamber at high vacuum measurement and high temperature; And Coating an inner surface of the vacuum chamber with a coating of an exhaust barrier material.

9. The method according to claim 8, wherein the high vacuum level comprises a pressure lower than 1.0×10 -11 Torr.

10. The method according to claim 8, wherein the heat treatment on the vacuum chamber in the hydrogen environment removes organic contaminants from the vacuum chamber.

11. The method according to claim 8, wherein the gas removal treatment on the vacuum chamber reduces the exhaust of the vacuum chamber.

12. The method according to claim 8, wherein the exhaust barrier material comprises titanium nitride.

13. The method according to claim 8, wherein the exhaust barrier material comprises at least one of titanium carbide, titanium dioxide, chromium oxide, zirconium oxide, silicon carbide, silicon nitride or aluminum.

14. The method according to claim 8, wherein the gas removal treatment is performed at the high temperature in a range of 500 to 1200 °C.

15. The method according to claim 8, wherein the gas removal treatment is carried out under the high vacuum measurement in the range of 1.0×10 -5 to 1.0×10 -7 Torr.

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