Electron emitter and method of fabricating the same

Abstract

To provide an electron emitter and a method of fabricating the electron emitter.SOLUTION: According to certain embodiments, an electron emitter includes a tip with a planar region having a diameter in a range of approximately (0.05-10) micrometers. The electron emitter tip is configured to release field emission electrons. The electron emitter further includes a work-function-lowering material applied onto the tip.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. patent application Ser. No. 62 / 372,084, filed Aug. 8, 2016, and U.S. patent application Ser. No. 62 / 531,793, filed July 12, 2017, which are incorporated by reference in their entireties herein.

[0002] The present invention relates generally to the field of charged particle sources, and more particularly to electron emitters for use in electron beam devices and methods of fabricating the same. [Background technology]

[0003]

[0003] In the manufacturing process of integrated circuits (ICs), unfinished or finished circuit components are inspected to ensure that they are manufactured as designed and are free of defects. Inspection systems that use optical microscopes typically have a resolution of a few hundred nanometers, limited by the wavelength of light. As the physical size of IC components continues to shrink to less than 100 nanometers or even less than 10 nanometers, inspection systems capable of higher resolution than those that use optical microscopes are needed.

[0004]

[0004] Charged particle (e.g., electron) beam microscopes such as scanning electron microscopes (SEMs) or transmission electron microscopes (TEMs), capable of sub-nanometer resolution, serve as practical tools for inspecting IC components with feature sizes of less than 100 nanometers. In an SEM, electrons from a single primary electron beam or multiple primary electron beams can be focused onto a predefined scan location on a wafer under inspection. The primary electrons interact with the wafer and may be backscattered or may cause the wafer to emit secondary electrons. The intensity of the electron beam, including the backscattered and secondary electrons, may vary based on the characteristics of the internal and / or external structure of the wafer, thereby indicating whether the wafer is defective.

[0005]

[0005] However, due to its high resolution, the throughput of a typical electron beam inspection tool is low. This limits the application of electron beam inspection tools to large-scale wafer inspection. One approach to improve the throughput is to increase the beam current of the primary electron beam so that it can scan a larger area on the wafer or can be split into multiple beamlets to scan multiple separate areas simultaneously. Current electron emitters, such as Schottky emitters, can generate bright illumination but only have a small emission area as the emission area from which electrons can be emitted. This limits the maximum beam current achievable at a given brightness. Moreover, the emission area can be easily deformed during high brightness operation (i.e., high temperature and / or high electric field), which causes instability or reduces the emission area for the emitted electron beam. Therefore, current electron emitters cannot meet high throughput requirements. Summary of the Invention

[0006]

[0006] Embodiments of the present invention relate to an electron emitter and a method of fabricating the same. In some embodiments, an electron emitter is provided. The electron emitter includes a tip with a planar region having a diameter in the range of about (0.05-10) micrometers. The electron emitter further includes a work-function-lowering material coated on the tip.

[0007] In some embodiments, a thermal field emission cathode is provided. The thermal field emission cathode includes an emitter, the emitter further includes a tip configured to release field emission electrons, the tip having a planar area with a diameter in the range of about (0.05-10) micrometers. The thermal field emission cathode also includes a work function reducing material coated on the tip. The thermal field emission cathode further includes a heating component configured to provide thermal energy to the emitter.

[0008] In some embodiments, a method of fabricating an electron emitter is provided. The method includes applying a restraint to an electron emitter having a tip. The method also includes forming a planar region on the tip under the restraint. The method further includes removing the restraint.

[0009] In some embodiments, a method of fabricating an electron emitter is provided that includes coating a work function reducing material on a tip of an electron emitter having a base material. The work function reducing material includes at least one of an oxide compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium, a nitride compound of zirconium, titanium, niobium, scandium, vanadium, or lanthanum, and an oxynitride compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, niobium, or thorium.

[0010]

[0010] Additional objects and advantages of the disclosed embodiments will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the embodiments. The objects and advantages of the disclosed embodiments will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

[0011]

[0011] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed embodiments as set forth in the claims. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating an exemplary electron beam tool consistent with embodiments of the present invention. [Diagram 2]

[0013] FIG. 2 is a schematic diagram illustrating an exemplary thermal field emission cathode for use in the exemplary electron beam tool of FIG. 1. [Figure 3A]

[0014] FIG. 1 is a schematic diagram showing a conventional tungsten emitter tip without any coating material. [Figure 3B]

[0015] FIG. 2 is a schematic diagram illustrating an emitter tip coated with a work function reducing material consistent with embodiments of the present invention. [Figure 4]

[0016] 4 is a flow chart of an exemplary method for preparing an electron emitter consistent with embodiments of the present invention. [Diagram 5]

[0017] 4 is a flow chart of an exemplary method for preparing an electron emitter consistent with embodiments of the present invention. [Figure 6]

[0018] FIG. 3 is a schematic diagram illustrating a fixture or jig attached to the emitter tip of the thermal field emission cathode of FIG. 2, consistent with embodiments of the present invention. [Figure 7]

[0019] 4 is a flow chart of an exemplary method for preparing an electron emitter consistent with embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013]

[0020] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which the same numbers in different drawings represent the same or similar elements unless otherwise stated. The embodiments set forth in the following description of exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of apparatus and methods consistent with aspects related to the present invention as recited in the claims.

[0014]

[0021] This application discloses an electron emitter capable of generating an electron beam with high brightness and beam current, as well as a method for preparing or fabricating the electron emitter. The disclosed electron emitter can be used in many technologies, such as integrated circuit (IC) manufacturing processes. FIG. 1 is a schematic diagram illustrating an exemplary electron beam tool 10 consistent with embodiments of the present invention. As shown in FIG. 1, the electron beam tool 10 includes a motorized stage 134 and a wafer holder 136 supported by the motorized stage 134 for holding a wafer 150 to be inspected. The electron beam tool 10 further includes a cathode 100, an anode 120, a gun aperture 122, a beam-defining aperture 124, a condenser lens 126, a source conversion unit 128, an objective lens assembly 132, a beam separator 138, and an electron detector 140. The source conversion unit 128, in some embodiments, can include a micro-deflector array 129 and a beamlet definition plate 130. The objective lens assembly 132, in one embodiment, can include a modified swing objective retarding immersion lens (SORIL), which includes a pole piece 132a, a control electrode 132b, a deflector 132c, and an excitation coil 132d. The electron beam tool 10 can further include an energy dispersive X-ray spectrometer (EDS) detector (not shown) for characterizing materials on the wafer.

[0015]

[0022] When the electron beam tool 10 operates, a wafer 150 to be inspected is mounted or placed on a wafer holder 136 supported by a motorized stage 134. A voltage is applied between the anode 120 and the cathode 100, causing the cathode 100 to emit an electron beam 160. The emitted electron beam passes through a gun aperture 122 and a beam-defining aperture 124, both of which can determine the size of the electron beam entering a condenser lens 126 that is present below the beam-defining aperture 124. The condenser lens 126 can focus the emitted electron beam 160 before the electron beam 160 enters a source conversion unit 128. A micro-deflector array 129 can split the emitted beam into multiple primary electron beams 160a, 160b, and 160c. The number of multiple primary beams is not limited to three, and the micro-deflector array 129 can be configured to split the emitted beam into a larger number of primary electron beams. The beamlet limiting plate 130 can set the size of the multiple primary electron beams before entering the objective lens assembly 132. The deflector 132c deflects the primary electron beams 160a, 160b, and 160c to facilitate beam scanning on the wafer. For example, in a scanning process, the deflector 132c can be controlled to deflect the primary electron beams 160a, 160b, and 160c simultaneously onto different positions on the top surface of the wafer 150 at different times to provide data for image reconstruction for different portions of the wafer 150.

[0016]

[0023] The excitation coil 132d and the pole piece 132a generate a magnetic field that starts at one end of the pole piece 132a and ends at the other end of the pole piece 132a. The portion of the wafer 150 being scanned by the primary electron beam 160 can be immersed in the magnetic field and can be charged, which in turn generates an electric field. The electric field reduces the energy of the primary electron beam 160 colliding with the wafer near the surface of the wafer before colliding with the wafer. The control electrode 132b is electrically isolated from the pole piece 132a and controls the electric field on the wafer to prevent micro-arching of the wafer and ensure proper beam focus.

[0017]

[0024] The backscattered primary and secondary electrons may be emitted from a portion of the wafer 150 upon receiving the primary electron beams 160a, 160b, and 160c. The beam separator 138 may direct the secondary and / or scattered electron beams 170a, 170b, and 170c, including the backscattered secondary electrons, to a sensor surface of the electron detector 140. The detected electron beams 170a, 170b, and 170c may form corresponding beam spots 180a, 180b, and 180c on the sensor surface of the electron detector 140. The electron detector 140 may generate a signal (e.g., voltage, current, etc.) representative of the intensity of the received beam spot and provide the signal to a processing system (not shown in FIG. 1). The intensity of the secondary and / or scattered electron beams 170a, 170b, and 170c and the resulting beam spots may vary depending on the external and / or internal structure of the wafer 150. Moreover, as described above, primary electron beams 160a, 160b, and 160c can be projected onto different locations on the top surface of wafer 150 to generate secondary and / or scattered electron beams 170a, 170b, and 170c (and resulting beam spots) of different intensities. Thus, by mapping the intensity of the beam spots by position on wafer 150, a processing system can reconstruct an image reflecting the internal and / or external structure of wafer 150.

[0018]

[0025] 1 illustrates the electron beam tool 10 as a multi-beam inspection tool that uses multiple primary electron beamlets to simultaneously scan multiple locations of the wafer 150, it is also contemplated that the electron beam tool 10 can be a single-beam inspection tool that uses only one primary electron beam to scan one location of the wafer 150 at a time. Moreover, the electron beam tool 10 can also be implemented as an electron beam lithography (EBL) system, such as an electron beam direct write (EBDW) system. This application does not limit the particular system or technology field to which the disclosed electron emitters are applied.

[0019]

[0026] Regardless of whether the electron beam tool 10 is used to inspect a wafer or to perform electron beam lithography, the disclosed electron emitter can emit a larger beam current to improve the throughput of the electron beam tool 10. FIG. 2 is a schematic diagram illustrating a cathode 100 used in the exemplary electron beam tool of FIG. 1. In exemplary embodiments, the cathode 100 can be a thermal field emission cathode, e.g., a Schottky cathode, that uses a combination of heat and an electric field to emit electrons. Referring to FIG. 2, the cathode 100 includes an electron emitter 102, a filament 110, two electrodes 112, and a base 114.

[0020]

[0027] The base 114 is made of an electrically insulating material, such as a ceramic or a thermal ceramic. In some embodiments, the electrically insulating material is zirconium dioxide (ZrO 2 ), aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), etc. The base 114 supports two electrodes 112. Each electrode 112 is embedded at one end in the base 114. The electrodes 112 are made of a conductive material, such as a nickel-iron alloy.

[0021]

[0028] The filament 110 is a conductive wire made of, for example, tungsten or rhenium. Two ends of the filament 110 are welded to two electrodes 112, respectively. The filament 110 can also be bent at its center. The bent angle of the filament 110 can be in the range of 10 to 100 degrees. The electron emitter 102 is attached to the center of the filament 110 such that the filament 110 is convex with respect to the electron emitter 102 at its center.

[0022]

[0029] The electron emitter 102 includes an emitter tip 104 having an apex 106. The apex 106 can be a planar region. The emitted electrons are in a narrow energy band and are emitted from the apex 106 in an emission cone. Typically, to escape the electron emitter 102, the electrons must gain enough energy to overcome an energy barrier imposed by the atoms and / or molecules present at the surface of the apex 106. The amount of energy required to overcome the energy barrier is known as the work function of the electron emitter 102. In exemplary embodiments, the emitter tip 104 and especially the speck 106 can be coated with a thin layer of a coating material 108 to lower the work function. In the present invention, the material that constitutes the body of the electron emitter 102 is referred to as the "base material" and the coating material 108 is referred to as the "work function lowering material."

[0023]

[0030] When the cathode 100 is implemented as a Schottky cathode, current is supplied to the filament 110 through the electrode 112. The filament 110 heats the electron emitter 102, thermally exciting the electrons in the electron emitter 102 so that they can escape across a work function barrier. Additionally or alternatively, the cathode 100 and anode 120 can generate a strong electric field at the emitter tip 112, which facilitates the emission of electrons by tunneling through the work function barrier. By adjusting the emitter temperature and / or the strength of the electric field, the cathode 100 can vary the beam current emitted from the electron emitter 102.

[0024]

[0031] Schottky cathodes are capable of producing a bright electron beam. The emitter used in a typical Schottky cathode, i.e., a typical Schottky emitter, is <100> , <110> , <111> or <310> The Schottky emitter is made from a single crystal of tungsten oriented in the axial direction. The Schottky emitter can also be made from other base materials such as molybdenum, iridium, or rhenium. The Schottky emitter can also be coated with a work function lowering material, including compounds such as oxides, nitrides, and carbon compounds of zirconium, titanium, hafnium, yttrium, niobium, vanadium, thorium, scandium, beryllium, or lanthanum. For example, by making the apex surface of the Schottky emitter a (100) crystal plane of tungsten and using zirconium oxide (ZrO) as the work function lowering material, the work function of the Schottky emitter can be lowered from 4.5 eV to 2.8 eV. The reduction in the work function makes the Schottky emitter a brighter electron source. The operating temperature of such a ZrO-coated tungsten emitter, i.e., the temperature at the apex of the emitter, is in the range of (300-1,800) K.

[0025]

[0032] Although a tungsten Schottky emitter can generate a bright electron beam, the electric field and temperature applied to the emitter can cause surface self-diffusion at the apex of the emitter. Specifically, at the high operating temperature of the Schottky emitter, the base material and coating material tend to evaporate from the apex of the emitter, which changes the original planar surface of the apex into a curved surface. Meanwhile, the high electric field moves the base material and coating material at the apex, thus shrinking the surface of the apex, e.g., sharpening the tip of the emitter. Thus, the combined effect of high temperature and high electric field tends to make the apex have an irregular surface. FIG. 3A is a schematic diagram showing a tip 204 of a conventional tungsten emitter without coating material. As shown in FIG. 3A, the tip 204 includes an apex 206, which has an original planar surface (not shown). However, when the tungsten emitter continues to operate under high temperature and high electric field, the surface of the apex 206 is gradually deformed, which causes instability for electron emission and reduces the beam current.

[0026]

[0033] 2, in the disclosed embodiments, to reduce surface deformation, the base material of the electron emitter 102 can be selected from transition metal carbide compounds and / or transition metal boride compounds. For example, the transition metal carbide compounds can be hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, or niobium carbide compounds. For example, the transition metal boride compounds can be hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, niobium, or lanthanum boride compounds.

[0027]

[0034] Compared to tungsten, transition metal carbides or borides have a higher melting point, higher hardness, and lower work function. For example, hafnium carbide has a melting point of 4,163K and a work function in the range of (3.3-3.6) eV. These properties of transition metal carbides and transition metal borides make these compounds less susceptible to surface changes under high temperatures and / or high electric fields.

[0028]

[0035] In some embodiments, a work function reducing material can be coated onto the transition metal carbide and transition metal boride to further reduce its work function. The work function reducing material can include at least one of oxide compounds of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium.

[0029]

[0036] Alternatively or additionally, the work function reducing material may include at least one of a nitride compound of zirconium, titanium, niobium, scandium, vanadium, or lanthanum.

[0030]

[0037] Alternatively or additionally, the work function reducing material may include at least one of an oxynitride compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, niobium, or thorium.

[0031]

[0038] FIG. 3B is a schematic diagram showing an emitter tip 104 coated with a work function reducing material 108 consistent with embodiments of the present invention. The base material of the emitter tip 104 includes transition metal carbides and / or transition metal borides. The work function reducing material 108 includes the work function reducing materials disclosed above, and can reduce the work function of the transition metal carbides and / or transition metal borides from about 3.3 eV to about 2.3 eV, for example. Due to the reduced work function, the angular intensity of the electron beam emitted from the apex 106, defined as the electron current (i.e., beam current) divided by the solid angle through which the electrons are emitted, can reach a range of (15-400) mA / Sr. Moreover, the electric field that needs to be applied to the emitter tip 104 to achieve a given brightness can be reduced. Such a weaker electric field reduces the chance of surface deformation at the apex 106. As illustrated by FIG. 3B, the planar surface of apex 106 can remain without deformation for extended periods of time.

[0032]

[0039] In the disclosed embodiments, the emission area of ​​the electron emitter 102, i.e., the planar area at the apex 106, may also be enlarged to increase the angular intensity of the electrons emitted from the apex 106. Referring back to FIG. 2, in some embodiments, the apex 106 may be configured to have a diameter in the range of about (0.05-10) micrometers. For example, the angular intensity of the electron beam emitted from a tungsten emitter with such an apex diameter may reach the range of (1-25) mA / Sr.

[0033]

[0040] Traditionally, it has been difficult to increase the size of the apex of a tungsten tip because the mechanical strength of tungsten is relatively low. As explained above, transition metal carbides or transition metal borides have a higher hardness than tungsten. Therefore, compared with tungsten emitters, it is easier to polish emitter tips made of transition metal carbides or transition metal borides. Moreover, the methods 500 and 700 described below can be used to increase the size of the apex of an emitter tip, whether the emitter tip is made of tungsten, transition metal carbides, transition metal borides, or other types of base materials.

[0034]

[0041] Due to the increased angular intensity of the emitted electrons, the disclosed electron emitter 102 may help improve the throughput of the electron beam tool 10. For example, if the electron beam tool 10 is a single beam inspection tool, a primary electron beam with a higher angular intensity may be used to scan a larger area on the wafer 150 or perform voltage contrast (VC) defect inspection of high aspect ratio contacts (HARCs). As another example, if the electron beam tool 10 is a multiple beam inspection tool, the higher angular intensity may make it feasible to split the primary electron beam into multiple beamlets so that multiple locations on the wafer 150 can be scanned simultaneously. Moreover, as with single beam inspection tools, the higher angular intensity may enable the multi-beam inspection tool to perform voltage contrast defect inspection. As yet another example, if the electron beam tool 10 is an EBDW system, the higher angular intensity may provide a larger beam current, which improves lithography efficiency.

[0035]

[0042] Next, exemplary methods of preparing or fabricating the disclosed electron emitters are disclosed. FIG. 4 is a flow chart of an exemplary method 400 of preparing an electron emitter according to some embodiments of the present invention. For example, the electron emitter can be the electron emitter 102 shown in FIG. 2. The base material of the electron emitter can include at least one of a transition metal carbide compound or a transition metal boride compound. The transition metal carbide compound can be a carbide compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, or niobium. The transition metal boride compound can be a boride compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, niobium, or lanthanum. The method 400 can be performed to coat a work function lowering material (e.g., work function lowering material 108) on an emitter tip (e.g., emitter tip 104) of the electron emitter to lower the work function of the electron emitter.

[0036]

[0043] Referring to FIG. 4, method 400 may include one or more of the following steps 410-430. In step 410, an end portion of an emitter wire or rod is etched to form an emitter tip of an electron emitter. The base material of the emitter wire / rod includes a transition metal carbide compound or a transition metal boride compound. In some embodiments, the emitter wire / rod may be electrochemically etched using any etching method known in the art. In some embodiments, step 410 may be omitted if the emitter tip is already formed, such as when the electron emitter is a commercially available emitter that already has an emitter tip.

[0037]

[0044] In step 420, a thermal treatment is performed on the electron emitter to desorb contaminants on the surface of the emitter tip. For example, the electron emitter can be heated by passing a direct current through it, bombarding it with electrons, contacting a hot filament directly with the electron emitter, or resistively heating the electron emitter by field emission. The invention does not limit the manner in which the thermal treatment is performed.

[0038]

[0045] In step 430, the emitter tip is coated with a layer of work function reducing material (e.g., work function reducing material 108). In disclosed embodiments, the work function reducing material can include at least one of an oxide compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium.

[0039]

[0046] Alternatively or additionally, the work function reducing material may include at least one of a nitride compound of zirconium, titanium, niobium, scandium, vanadium, or lanthanum.

[0040]

[0047] Alternatively or additionally, the work function reducing material may include at least one of an oxynitride compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, niobium, or thorium.

[0041]

[0048] 5 is a flow chart of an exemplary method 500 of preparing an electron emitter according to some embodiments of the present invention. For example, the electron emitter can be the electron emitter 102 shown in FIG. 2. The electron emitter can already include an emitter tip (e.g., emitter tip 104) suitable for emitting electrons, and the method 500 can be used to increase the size of the apex (e.g., apex 106) of the electron emitter. The base material of the electron emitter can include tungsten, molybdenum, iridium, rhenium, transition metal carbide compounds, transition metal boride compounds, or other types of base materials.

[0042]

[0049] Referring to FIG. 5, the method 500 can include one or more of the following steps 510-550. In step 510, a restraint is applied to the emitter tip. The restraint is used to help the emitter tip withstand mechanical strain when the emitter tip is under stress, to enhance the mechanical strength of the base material at the emitter tip, to relieve stress directly applied by the apex enlargement process on the base material of the emitter tip, and / or to hold the emitter tip from moving. In this way, the apex can be ground without breaking or damaging the emitter tip. In some embodiments, the restraint can be in the form of a fixture, jig, or clamp that holds around, is secured to, attached to, mounted on, or glued to the emitter tip.

[0043]

[0050] FIG. 6 is a schematic diagram illustrating an exemplary fixture or jig 109 attached to the emitter tip 104 of FIG. 2 in accordance with some embodiments of the present invention. Referring to FIG. 6, the fixture or jig 109 can be a wax, for example, a thermal wax, applied onto the emitter tip 104. The wax 109 forms a layer around the emitter tip 104. This wax layer has a suitable thickness to effectively reduce stress on the base material of the emitter tip 104. If the emitter tip 104 is pre-coated with the work function reducing material 108, the wax 109 can be applied directly onto the work function reducing material 108. Alternatively, the work function reducing material 108 can first be removed from the emitter tip 104, and the wax 109 is then applied to the base material of the emitter tip 104.

[0044]

[0051] 5, in step 520 of method 500, a planar region with a desired size may be formed at a vertex under constraints. Alternatively, if the vertex already has a planar region before performing method 500, the planar region may be expanded to reach the desired size.

[0045]

[0052] The flat area can be formed or enlarged using a variety of methods. In some embodiments, the restraint can generate sufficient force to form or enlarge the flat area at the apex. For example, a fixture / jig / clamp can be applied on the emitter tip to directly form the flat area. In other embodiments, the emitter tip that has been subjected to restraint can be polished to form or enlarge the flat area. This polishing can be performed electrolytically or mechanically using any polishing method known in the art.

[0046]

[0053] A restraint (e.g., fixture, jig, clamp, wax, etc.) is applied to the emitter tip so that the emitter tip can withstand greater strain or stress without breaking or becoming damaged. Thus, a flat area with a diameter in the range of, for example, (0.05-10) micrometers can be formed at the apex without damaging the emitter tip.

[0047]

[0054] In step 530, after forming a planar region with the desired size at the apex, the inhibitor is removed from the emitter tip. For example, if the inhibitor is in the form of wax, the wax can be melted with heat and washed off with acetone.

[0048]

[0055] In step 540, a thermal treatment is performed on the electron emitter to desorb contaminants on the surface of the emitter tip. This step is similar to step 420 of method 400.

[0049]

[0056] In step 550, the emitter tip is coated with a layer of work function reducing material (e.g., work function reducing material 108). The work function reducing material can be selected based on the type of base material. For example, if the base material is tungsten, molybdenum, iridium, or rhenium, the work function reducing material can be oxides, nitrides, and carbon compounds of zirconium, titanium, hafnium, yttrium, niobium, vanadium, thorium, scandium, beryllium, or lanthanum.

[0050]

[0057] As another example, when the base material is a transition metal carbide compound or a transition metal boride compound, the work function reducing material can include an oxide compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium, a nitride compound of zirconium, titanium, niobium, scandium, vanadium, or lanthanum, and / or an oxynitride compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, niobium, or thorium.

[0051]

[0058] FIG. 7 is a flow chart of an exemplary method 700 of preparing an electron emitter, according to some embodiments of the present invention. For example, the electron emitter can be the electron emitter 102 shown in FIG. 2. Unlike the method 600, the method 700 can be performed to prepare an electron emitter with a desired apex size from an emitter wire or rod without an emitter tip (e.g., emitter tip 104) suitable for emitting electrons. The emitter wire or rod is made of a basic material that constitutes the electron emitter to be prepared. Referring to FIG. 7, the method 700 can include one or more of the following steps 710-760.

[0052]

[0059] In step 710, an end portion of the emitter wire or rod is etched to form an emitter tip of the electron emitter. Step 710 is similar to step 410 of method 400.

[0053]

[0060] In step 720, suppression is applied to the newly formed emitter tip. Step 720 is similar to step 510 of method 500.

[0054]

[0061] In step 730, a planar region with a desired size under constraint is formed at the apex of the emitter tip. Step 730 is similar to step 520 of method 500.

[0055]

[0062] In step 740, after forming a planar region with a desired size at the vertex, the suppression is removed from the emitter tip. Step 740 is similar to step 530 of method 500.

[0056]

[0063] In step 750, a thermal treatment is performed on the electron emitter to desorb contaminants on the surface of the emitter tip, which is similar to step 420 of method 400 and step 540 of method 500.

[0057]

[0064] In step 760, the emitter tip is coated with a layer of work function reducing material (e.g., work function reducing material 108). This step is similar to step 550 of method 500.

[0058]

[0065] The following clauses may be used to further describe embodiments. Clause 1. A tip having a flat area having a diameter in the range of about (0.05 to 10) micrometers; a work function reducing material coated on the tip; an electron emitter. Clause 2. The electron emitter of clause 1, wherein the tip comprises single crystal tungsten. Clause 3. Single crystal tungsten <100> The electron emitter of claim 2 having a crystal orientation of Clause 4. The electron emitter of clause 1, wherein the tip comprises at least one of a transition metal carbide compound or a transition metal boride compound. Clause 5. The electron emitter of clause 4, wherein the transition metal carbide compound is a carbide compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, or niobium. Clause 6. The electron emitter of clause 4, wherein the transition metal boride compound is a boride compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, niobium, or lanthanum. Clause 7. The work function reducing material, At least one of oxide compounds of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium Electron emitters according to any one of clauses 4 to 6, including Clause 8. The work function reducing material, At least one of the nitride compounds of zirconium, titanium, niobium, scandium, vanadium, or lanthanum Electron emitters according to any one of clauses 4 to 6, including Clause 9. The work function reducing material, At least one of the oxynitride compounds of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, niobium, or thorium Electron emitters according to any one of clauses 4 to 6, including Clause 10. A tip configured to release field emission electrons, the tip having a planar area with a diameter in the range of about (0.05-10) micrometers; a work function reducing material coated on the tip; an emitter including: a heating component configured to provide thermal energy to the emitter; A thermal field emission cathode comprising: Clause 11. The thermal field emission cathode of clause 10, wherein the tip comprises single crystal tungsten. Clause 12. Single crystal tungsten <100> 12. The thermal field emission cathode of claim 11, having a crystal orientation of Clause 13. The thermal field emission cathode of clause 10, wherein the tip comprises at least one of a transition metal carbide compound or a transition metal boride compound. Clause 14. The thermal field emission cathode of clause 13, wherein the transition metal carbide compound is a carbide compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, or niobium. Clause 15. The thermal field emission cathode of clause 13, wherein the transition metal boride compound is a boride compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, niobium, or lanthanum. Clause 16. The work function reducing material, At least one of oxide compounds of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium 16. The thermal field emission cathode of any one of clauses 13 to 15, comprising: Clause 17. The work function reducing material, At least one of the nitride compounds of zirconium, titanium, niobium, scandium, vanadium, or lanthanum 16. The thermal field emission cathode of any one of clauses 13 to 15, comprising: Clause 18. The work function reducing material, At least one of the oxynitride compounds of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, niobium, or thorium 16. The thermal field emission cathode of any one of clauses 13 to 15, comprising: Clause 19. A thermal field emission cathode according to any one of clauses 10 to 18, wherein the heating means comprises a filament attached to the emitter. Article 20. Base Two electrodes embedded in the base; A conductive wire including two ends and a central portion, the two ends of the conductive wire being connected to two electrodes respectively, an emitter being attached to the central portion of the conductive wire, and the conductive wire being convex toward the emitter at the central portion; 20. The thermal field emission cathode of any one of clauses 10 to 19, further comprising: Clause 21. Applying suppression to an electron emitter having a tip; forming a planar region on the tip under restraint; Removing inhibitions; A method comprising: Clause 22. Forming a flat area on the tip Polishing the tip of the electron emitter to form a flat area. The methods of clause 21, including: Clause 23. Suppression of electron emitters Attach a fixture or jig to the tip 2. The method of any one of clauses 21 and 22, Clause 24. Forming a flat area on the tip Using a fixture or jig to form a flat area The methods of clause 23, including: Article 25. Suppression of electron emitters Apply wax to the tip (c) the method of any one of clauses 21 to 23, Clause 26. Heating the electron emitter after inhibition is removed, the heating removing contaminants on the tip. 26. The method of any one of clauses 21 to 25, further comprising: Clause 27. Coating work function reducing material on tip after heating The method of clause 26 further comprising: Clause 28. The method of any one of clauses 21 to 27, wherein the electron emitter comprises single crystal tungsten. Clause 29. Single crystal tungsten <100> 29. The method of claim 28, wherein the crystal orientation is Clause 30. The method of any one of clauses 21 to 27, wherein the electron emitter comprises at least one of a transition metal carbide compound or a transition metal boride compound. Clause 31. The method of clause 30, wherein the transition metal carbide compound is a carbide compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, or niobium. Clause 32. The method of clause 30, wherein the transition metal boride compound is a boride compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, niobium, or lanthanum. Clause 33. Coating a work function reducing material on the tip after the inhibition is removed, the work function reducing material comprising at least one of oxide compounds of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium. The method of clause 30 further comprising: Clause 34. Coating a work function reducing material on the tip after the inhibition is removed, the work function reducing material comprising at least one of a nitride compound of zirconium, titanium, niobium, scandium, vanadium, or lanthanum. The method of clause 30 further comprising: Clause 35. Coating a work function reducing material on the tip after the inhibition is removed, the work function reducing material comprising at least one of an oxynitride compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, niobium, or thorium. The method of clause 30 further comprising: Clause 36. Etching end portions of electron emitters to form tips 36. The method of any one of clauses 21 to 35, further comprising: Clause 37. The method of any one of clauses 21 to 36, wherein the planar area of ​​the tip has a diameter within the range of about (0.05 to 10) micrometers. Clause 38. Coating a work function reducing material on the tip of the electron emitter having a base material; The work function reducing material is an oxide compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium; a nitride compound of zirconium, titanium, niobium, scandium, vanadium, or lanthanum; Oxynitride compounds of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, niobium, or thorium The method includes at least one of the following: Clause 39. The method of clause 38, wherein the base material of the electron emitter comprises at least one of a transition metal carbide compound or a transition metal boride compound. Clause 40. The method of any one of clauses 38 and 39, wherein the transition metal carbide compound is a carbide compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, or niobium. Clause 41. The method of any one of clauses 38 and 39, wherein the transition metal boride compound is a boride compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, niobium, or lanthanum. Clause 42. Heating the electron emitter to remove contaminants on the tip before coating the work function reducing material on the tip. 42. The method of any one of clauses 38 to 41, further comprising: Clause 43. Etching an end portion of the electron emitter to create a tip before heating the electron emitter to remove contaminants on the tip. The method of clause 42 further comprising:

[0059]

[0066] It will be appreciated that the present invention is not limited to the exact construction described above and illustrated in the accompanying drawings, but various modifications and changes can be made without departing from the scope thereof, which should be limited only by the claims.

Claims

1. applying a suppression to an electron emitter having a tip; forming a planar area on the tip under the restraint; and removing said inhibition; and A method comprising:

2. forming the planar region on the tip portion; polishing the tip of the electron emitter to form the flat area; The method of claim 1 , comprising:

3. applying the suppression to the electron emitter, Attaching a fixture or jig to the tip. The method of claim 1 or 2, comprising:

4. forming the planar region on the tip portion; forming the planar area using the fixture or the jig; The method of claim 3 , comprising:

5. applying the suppression to the electron emitter, applying wax onto said tip; The method of any one of claims 1 to 4, comprising:

6. heating the electron emitter after the inhibition is removed, which heating removes contaminants on the tip. The method of claim 1 , further comprising:

7. coating a work function reducing material on said tip after said heating; The method of claim 6 further comprising:

8. The method of claim 1 , wherein the electron emitter comprises single crystal tungsten.

9. 9. The method of claim 8, wherein the single crystal tungsten has a <100> crystallographic orientation.

10. The method of claim 1 , wherein the electron emitter comprises at least one of a transition metal carbide compound or a transition metal boride compound.

11. the transition metal carbide compound is a carbide compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, or niobium; 11. The method of claim 10, wherein the transition metal boride compound is a boride compound of hafnium, zirconium, tantalum, titanium, tungsten, molybdenum, niobium, or lanthanum.

12. coating a work function reducing material on the tip after the inhibition is removed, the work function reducing material comprising at least one of an oxide compound of zirconium, hafnium, titanium, scandium, yttrium, vanadium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium, or thorium. The method of claim 10 further comprising:

13. Etching an end portion of said electron emitter to form said tip. The method of claim 1 , further comprising:

14. The method of any one of claims 1 to 13, wherein the planar region of the tip has a diameter in the range of 0.05 to 10 micrometers.

15. 15. An electron emitter comprising a tip with a planar region formed by the method of any one of claims 1 to 14.

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