Field emission electron source, its manufacturing method and electron beam device using the same

Abstract

The present invention: improves the ratio of an emission angle current density to the total current of a field emission electron source in which a (100) plane of hexaboride single crystal or transition metal carbide single crystal is used as an electron emission surface; and improves current stability. Formed at a distal end of a tip of hexaboride single crystal or transition metal carbide single crystal of a <100> axis constituting an electron source is a top facet of a first (100) plane, surrounded by such side facets as to be constituted of at least four {n11} planes and at least four {n10} planes where n = an integer 1, 2, or 3, the total surface area of the side facets of the {n11} planes being > than the total surface area of the {n10} side facets. Furthermore formed is a microcrystal having a top facet of a second (100) plane, inside the top facet plane of the first (100) plane. Electrons are mainly emitted from the top facet of the second (100) plane.

Description

[Technical Field]

[0001] The present invention relates to a field emission electron source for an electron beam device such as an electron microscope, a method for manufacturing the same, and an electron beam device using the same. [Background technology]

[0002] Electron microscopes have spatial resolution beyond the optical limit, allowing observation of microstructures and composition analysis on the nm to pm order. For this reason, they are widely used in engineering fields such as materials, physics, medicine, biology, electricity, and mechanics. Among electron microscopes, the scanning electron microscope (SEM) is an instrument that can easily observe the surface of a sample.

[0003] The electron sources used in electron beam devices such as scanning electron microscopes include thermionic emitters (TE), field emitters (FE), and Schottky emitters (SE). Of these electron sources, field emitters (FE) are the most monochromatic and can emit high-brightness electron beams, which reduces chromatic aberration in the electron optical system and makes them the electron source for high-spatial resolution scanning electron microscopes. W tips, which use tungsten {310} crystal faces with sharpened needle-shaped electrodes (tips), are widely used for these field emitter electron sources.

[0004] Figure 1 shows the energy diagram that is the emission principle of a field emission electron source. A high electric field is applied by concentrating an external electric field F at the tip of the W-tip, and electrons e in the W-tip are emitted into a vacuum by quantum mechanically passing through an effectively thinned energy barrier. Since it can operate at room temperature, the full width at half maximum energy of the extracted electrons e is ΔE FE The electron beam emitted from the narrow electron emission surface at the very sharp tip has a high density, resulting in a brightness of 10 8 (A / cm 2 sr) and has high characteristics.

[0005] In order to further narrow the full width at half maximum energy ΔE and increase the brightness B, a field emission electron source using nanowires of hexaborides such as LaB6, which has a lower work function Φ than W, has also been proposed (for example, Patent Document 1). Because the work function barrier is lower than that of W, electrons can be transmitted and emitted in a lower electric field, and the full width at half maximum energy ΔE FE It is possible to further reduce

[0006] The inventors have previously used hexaboride single crystals such as CeB6 produced by the floating zone method or the like, and formed their tips into a hemispherical shape using electrolytic polishing, field evaporation, etc., followed by heat treatment at 700-1400°C to form a {310} crystal face of CeB6 with a low work function, to develop and disclose a cold field emitter (CFE) that emits field emissions at room temperature (Patent Document 2). This hexaboride single crystal field emitter has better monochromaticity than conventional W field emitter electron sources, and a high angular radiation current density J relative to the total current It (μA). Ω (μA / sr) ratio J Ω / It is 6 to 13 (1 / sr) or more and the radiation angular current density J Ω This invention can improve the chromatic aberration of scanning electron microscopes, especially at low accelerating voltages, and enables high spatial resolution observation of the extreme surfaces of samples and of light element materials such as carbon-based compounds. Furthermore, because the size of hexaboride single crystals produced by the floating zone method and other techniques is on the order of 0.1 mm to several mm, they can be assembled into electron sources by hand or machine, offering the advantage of being cheaper, easier, and with higher yields than electron sources using nanowires with diameters of tens to hundreds of nanometers.

[0007] As a result of further investigations by the inventors, the hexaboride single crystal <100> When a (100) facet was formed on the tip of a hexaboride single crystal, and field emission electrons from the (100) facet were probed, it was found that the emission current was more stable than that from the {310} facet. This is mainly because the (100) facet has a slightly higher work function than the {310} facet, making it less susceptible to work function fluctuations due to adsorbed gases. Furthermore, the higher atomic surface density compared to the {310} facet makes the structure more stable and suppresses atomic vibrations. Heating the facet makes it easier to form a flat, large-area facet, reducing the degree of electric field concentration. Furthermore, local work function changes due to gas adsorption and desorption during field electron emission are averaged within the large facet, reducing the overall fluctuations. <100> The current stability can be improved by forming a (100) facet at the tip of the hexaboride single crystal tip of the axis and probing the electron beam emitted from the (100) facet.

[0008] However, the high work function and low electric field concentration mean that the (100) plane is less likely to emit electrons than the {310} plane. In addition, electrons emitted from the {310} planes formed on the side of the tip around the (100) plane are wasted outside the optical axis of the electron microscope, resulting in a large angular emission current density J relative to the total current It (μA). Ω The problem was that the ratio of (μA / sr) was significantly reduced to less than 1 (1 / sr).

[0009] If the total current It (μA) is too large, electrons that are unnecessarily emitted off the optical axis will hit the extraction electrode inside the electron microscope, generating electron beam stimulated desorption gas from the electrode surface, which will then impinge on and adsorb to the surface of the field emission electron source, causing work function fluctuations and impairing current stability.

[0010] Therefore, the inventors have studied methods for improving this problem and have found that <100> At the tip end of the hexaboride single crystal of the axis, a top facet of a (100) plane is formed surrounded by side facets composed of at least four {n11} planes with a high work function, where n=1, 2, or 3, and at least four {n10} planes with a low work function, and the total area of ​​the side facets of the {n11} planes is greater than the total area of ​​the side facets of {n10}. This reduces unnecessary emission current from the side facets, and reduces the radiation angular current density J of the probe current extracted from the electron emission section of the top (100) plane of the electron source of the hexaboride single crystal tip. Ω It has been disclosed that the ratio of the total current It (μA) emitted from the electron source to the total current It (μA) emitted from the electron source can be improved to 2.6 to 4 (1 / sr), thereby realizing a stable electron source with less current fluctuation than conventional electron sources (Patent Document 3). [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 05660564 [Patent Document 2] Patent No. 06694515 [Patent Document 3] International Publication No. 2022 / 064557 Summary of the Invention [Problem to be solved by the invention]

[0012] As mentioned in the background art, when a field emission electron source using a hexaboride single crystal such as CeB6 is probed for field emission electrons from the (100) plane, the emission current is more stable than that from the {310} plane, and the radiation angular current density J Ω (μA / sr) to the total current It (μA) J ΩIncreasing / It can further improve stability. Furthermore, as a result of further investigations by the inventors, it has been found that when field emission electrons from the (100) plane are probed in transition metal carbide single crystals such as HfC, ZrC, and TiC, which have a work function lower than that of W and the same cubic crystal structure as hexaboride single crystals such as CeB6, the stability of the emission current is higher than that of field emission electrons from the {310} plane. Field emission electron sources using these low work function materials have a radiation angular current density J Ω (μA / sr) to the total current It (μA) J Ω The higher the / It is, the more the generation of electron-beam stimulated desorption gas can be suppressed, and the stability is improved. Ω Improvements in / It are expected, and new technologies to suppress gas adsorption on the electron emission surface are also expected.

[0013] The object of the present invention is to solve the above-mentioned problems and to provide a field emission electron source of a hexaboride single crystal or a transition metal carbide single crystal that combines monochromaticity and long-term stability of emission current by utilizing a stable electron beam emitted from a local region of an electron emission surface that is stable in a desired shape and time variation and that is less affected by gas adsorption, and by employing a technique for suppressing the mixing of unstable electron beams emitted from other than the emission surface, and to provide an electron beam device such as an electron microscope that requires high resolution and long-term stability and can be used for various applications. [Means for solving the problem]

[0014] In order to solve the above-mentioned problems, the present invention provides a field emission electron source comprising: <100> The tip of the axial hexaboride single crystal or transition metal carbide single crystal is formed with a first (100) top facet surrounded by side facets such that the total area of ​​the side facets of the {n11} planes is greater than the total area of ​​the side facets of {n10}, and the tip is made of at least four {n11} planes, where n is an integer of 1, 2, or 3, and at least four {n10} planes, and the total area of ​​the side facets of the {n11} planes is greater than the total area of ​​the side facets of {n10}. A field emission electron source is used, characterized in that a microcrystal having a second (100) top facet is formed within the first (100) top facet, and electrons are emitted from the second (100) top facet.

[0015] Here, single crystals containing LaB6 or CeB6 as the main component of hexaboride single crystals, and single crystals containing HfC, ZrC, or TiC as the main component of transition metal carbide single crystals, have a low work function, high heat resistance, and the cubic crystal structure necessary for forming the microcrystals with the second (100) top facet at the tip end described above, and are therefore suitable materials for the present invention.

[0016] Furthermore, the problem can be effectively solved by making the top facet of the second (100) plane smaller than that of the first (100) plane, with the ratio of one side of the top facet of the first (100) plane to that of the second (100) plane being 0.05 to 0.35, and by making the microcrystals forming the top facet of the second (100) plane either cubic with sides formed of {100} planes or trapezoidal with sides formed of {111} planes, with one side of the top facet of the second (100) plane being in the range of 10 to 60 nm, and by making the height of the microcrystals being 0.7 times or more the length of one side of the top facet of the second (100) plane.

[0017] Furthermore, the top facet of the first (100) plane has a side length of 1.5 μm or less and a multi-step structure of four or less steps, which effectively suppresses the surface diffusion of adsorbed gas from the tip sidewall toward the electron emission surface, thereby solving the problem.

[0018] In order to solve the above-mentioned problems, the present invention provides a method for manufacturing an electron source, which comprises the steps of: <100> The tip of a rod made of a hexaboride single crystal or a transition metal carbide single crystal having a crystalline orientation is electrolytically polished to form a conical tip. This tip is then heated while a strong positive electric field is applied to the tip, forming a first (100) top facet at the tip, which is composed of at least four {n11} planes, where n = 1, 2, or 3, and at least four {n10} planes, and is surrounded by side facets such that the total area of ​​the side facets of the {n11} planes > the total area of ​​the side facets of {n10}. This problem can then be solved by primarily reducing the electric field to form a microcrystal with a second (100) top facet within the first (100) top facet at the tip tip.

[0019] Furthermore, in order to solve the above-mentioned problems, the present invention provides an electron beam apparatus including an electron source, a sample stage on which a sample is placed, and an electron optical system that converges electrons emitted from the electron source into a beam shape and irradiates the sample on the sample stage, the electron source comprising: <100> This problem can be solved by forming a first (100) top facet surrounded by side facets such that the tip end of the axial hexaboride single crystal, transition metal carbide single crystal, or transition metal carbide single crystal is composed of at least four {n11} planes, where n is an integer of at least 1, 2, or 3, and at least four {n10} planes, and the total area of ​​the side facets of the {n11} planes > the total area of ​​the side facets of {n10}, and further forming a microcrystal having a second (100) top facet within the first (100) top facet. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a new field emission electron source that combines monochromaticity and long-term stability of emission current, and an electron beam device such as an electron microscope that is equipped with this field emission electron source and can be used for various applications that require high resolution and long-term stability. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is an energy diagram illustrating the operating principle of a field emission electron source used in an electron beam device such as an electron microscope. [Figure 2] 1 is a perspective view showing the crystal structure (unit cell) of a hexaboride single crystal used in an electron source according to Example 1. FIG. [Figure 3] 1 is a perspective view showing the crystal structure (unit lattice) of a transition metal carbide single crystal used in the electron source according to Example 1. FIG. [Figure 4] FIG. 1 is a schematic diagram showing a rectangular pillar or cylindrical rod cut along the

[0100] crystal axis from a hexaboride single crystal or a transition metal carbide single crystal grown along the

[0100] crystal axis according to Example 1. [Figure 5] 1 is a perspective view showing a state in which the metal tube according to Example 1 is mounted on an assembly table with rods of hexaboride single crystal and transition metal carbide single crystal. FIG. [Figure 6] FIG. 1 is a perspective view illustrating the positional relationship between a metal tube with a rod of hexaboride single crystal or transition metal carbide single crystal attached to an assembly table, a pressure welding tool, and a stereomicroscope, illustrating a method for joining a metal tube and a rod of hexaboride single crystal or transition metal carbide single crystal according to Example 1. [Figure 7] 1A to 1C are diagrams illustrating the joining structure of a metal tube and a square prism rod made of a hexaboride single crystal or a transition metal carbide single crystal in Example 1, where (a) is a plan view, (b) is a perspective view, and (c) is a cross-sectional front view. [Figure 8] FIG. 2 is a front view of a structural body serving as a prototype of the electron source, illustrating the assembly structure of the electron source according to the first embodiment. [Figure 9] 1A and 1B are diagrams for explaining an alignment jig used when assembling an electron source according to Example 1; FIG. 1A is a perspective view of the alignment jig that aligns the metal tube, the filament, and the alignment jig that aligns them; and FIG. 1B is a perspective view of the alignment jig that aligns the metal tube to which the filament is spot-welded, the stem, and the alignment jig that aligns them. [Figure 10]1A to 1C are diagrams illustrating another example of the joining structure of a metal tube and a cylindrical rod of a hexaboride single crystal or a transition metal carbide single crystal according to Example 1, where (a) is a plan view, (b) is a perspective view, and (c) is a front cross-sectional view. [Figure 11] 10 is a front cross-sectional view illustrating a state in which the electron source structure is immersed in an electrolytic polishing solution, illustrating a process of sharpening the rod tip of the electron source according to Example 1 by electrolytic polishing to form a tip. FIG. [Figure 12] 1 is a front cross-sectional view of a hexaboride tip, a transition metal carbide single crystal, and an electrolytic polishing solution, illustrating the principle of electrolytic polishing the rod end of the electron source according to Example 1 to form a tip. FIG. [Figure 13] 1 is a front view of an electron source made of a hexaboride single crystal or a transition metal carbide single crystal according to Example 1. FIG. [Figure 14] 1A and 1B are diagrams showing the process of forming the electron emission surface at the tip end of Examples 2 and 3, where (a) is an oblique view showing the tip end shape after electrolytic polishing, (b) is an oblique view showing the tip end shape after the first stage of thermal field treatment, and (c) is an oblique view showing the tip end shape after the second stage of thermal field treatment. [Figure 15] 10A and 10B are diagrams showing the range of process conditions for the manufacturing method of Example 2, where FIG. 10A shows the range of process conditions for the first-stage thermal electric field treatment, and FIG. 10B shows the range of process conditions for the second-stage thermal electric field treatment. [Figure 16] 1A and 1B are cross-sectional views of the tip end illustrating the mechanism by which a microcrystal having a second (100) top facet is formed within a first (100) top facet in the manufacturing methods of Examples 2 and 3. (a) is a cross-sectional view illustrating the state of the top facet when the first-stage thermal electric field treatment is performed, and (b) is a cross-sectional view illustrating the state of the top facet when the second-stage thermal electric field treatment is performed. [Figure 17] 10A and 10B are diagrams showing the range of process conditions for the manufacturing method of Example 3, where FIG. 10A shows the range of process conditions for the first-stage thermal electric field treatment, and FIG. 10B shows the range of process conditions for the second-stage thermal electric field treatment. [Figure 18]These are field emission microscope images of the tip of the transition metal carbide single crystal using HfC in Example 4, where (a) is a field emission microscope image of the tip after the first heat treatment, and (b) is a field emission microscope image of the tip after the second heat treatment. [Figure 19] 10 is a graph showing the measured radial current density JΩ (μA / sr) versus total current It (μA) in the case where only the top facet of the first (100) plane is formed and in the case where a microcrystal having the top facet of the second (100) plane is formed in the field emission electron source of the transition metal carbide single crystal using HfC in Example 4. [Figure 20] 10 is a graph comparing the stability of the radiation angular current density JΩ (μA / sr) in the case where only the top facet of the first (100) plane is formed and the case where the microcrystal having the top facet of the second (100) plane is formed in the field emission electron source of the transition metal carbide single crystal using HfC of Example 4. [Figure 21] 10A and 10B are graphs showing the change in the electron emission characteristics of the field emission electron source depending on the size (length of one side) of the microcrystals having the second (100) top facet of Example 5, where (a) is a graph showing the change in the electric field strength at the center of the tip, (b) is a graph showing the change in the radiation angular current density JΩ (μA / sr), and (c) is a graph showing the change in the light source diameter. [Figure 22] 10A and 10B are graphs showing the change in electron emission characteristics of the field emission electron source depending on the ratio of the height of the microcrystal to the length of one side of the top facet of the second (100) plane of Example 5, where (a) is a graph showing the change in electric field strength at the center of the tip, and (b) is a graph showing the change in the radiation angular current density JΩ (μA / sr). [Figure 23]1 shows the results of an investigation into the relationship between the side length of the first (100) plane top facet of Example 5 being 170 nm and the side length being 340 nm, where (a) is a graph showing the change in electric field strength at the center of the tip depending on the size (side length) of the microcrystal having the second (100) plane top facet, (b) is a graph showing the change in electric field strength ratio versus the ratio of the side length of the second (100) plane top facet to the first (100) plane top facet, and (c) is a graph showing the change in radial angular current density JΩ (μA / sr) versus the ratio of the side length of the second (100) plane top facet to the first (100) plane top facet. [Figure 24] FIG. 10 is a perspective view of a tip in Example 6, in which the first apex (100) facet at the tip end is made to have a multi-stage structure. [Figure 25] FIG. 10 is a schematic cross-sectional view of an electron beam apparatus (a scanning electron microscope equipped with a field emission electron source using a tip of the hexaboride single crystal or transition metal carbide of the present invention) according to Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0022] In the following explanation, crystal planes and crystal orientations are expressed in accordance with Miller indices, with a single plane indicated by ( ) and equivalent plane groups indicated by {}. Crystal axis directions are indicated by [ ] and equivalent axes by < >.

[0023] As a result of intensive research by the inventors, the present invention has been achieved by forming a field emission electron source. <100> The tip of a hexaboride single crystal or transition metal carbide single crystal of the shaft has a first (100) top facet surrounded by side facets, the top facet being composed of at least four {n11} planes (where n = 1, 2, or 3) and at least four {n10} planes, and the total area of ​​the side facets of the {n11} planes is greater than the total area of ​​the side facets of {n10} planes. Furthermore, a microcrystal having a second (100) top facet is formed within the first (100) top facet, and electrons are emitted from the second (100) top facet. The reason for this is explained below.

[0024] As disclosed by the inventors in Patent Document 3, a field emission electron source using a (100) plane has a higher stability of emission current than a field emission electron source using a (310) plane, but the radiation angular current density J relative to the total current It (μA) is low. Ω The low ratio of (μA / sr) is an issue, and we showed that the solution is to reduce electron emission from the surrounding area other than the (100) facet at the top. Therefore, by developing a new manufacturing method, <100> The tip of the single crystal shaft has a top facet of a (100) plane surrounded by side facets consisting of at least four {n11} planes, where n = 1, 2, or 3, and at least four {n10} planes, and the total area of ​​the side facets of the {n11} planes with a high work function is greater than the total area of ​​the side facets of the {n10} planes with a low work function. The electron source tip has been successfully fabricated, and the angular radiation current density J relative to the total current It (μA) is Ω (μA / sr) ratio J Ω / I was able to increase it to 2.6~4.

[0025] However, even in this structure, the top (100) facet is flat, and although the area is smaller, the {n10} faces, such as the {310} faces of the side facets adjacent to the top (100) facet, are sharp, making the structure prone to electric field concentration. Ω / It was difficult to make it any higher.

[0026] Therefore, in an embodiment of the present invention, by further improving the manufacturing method of Patent Document 3, a top facet of a first (100) plane is formed, which is composed of at least four {n11} planes, where n=an integer of 1, 2, or 3, and at least four {n10} planes, and is surrounded by side facets such that the total area of ​​the side facets of the {n11} planes > the total area of ​​the side facets of {n10}, and further, by forming a microcrystal having a top facet of a second (100) plane within the top facet of the first (100) plane, an electric field is concentrated at the top facet of the second (100) plane, increasing electron emission from the highly stable (100) plane. In addition, since the electric field applied to the {n10} plane of the side facet is relatively weaker, emission of unnecessary off-axis current can be suppressed, and J Ω / We found that we can improve it even more.

[0027] The present invention will be described below by way of examples with reference to the drawings. In the examples of the electron beam device, a scanning electron microscope (SEM) will be used as an example. However, the present invention is not limited to this and can be applied to electron beam devices including transmission electron microscopes (TEM), scanning transmission electron microscopes (STEM), electron beam exposure devices, electron beam 3D printers, and X-ray tubes. In the drawings, the scale of each component has been appropriately changed to make the configuration of the invention easier to understand. [Example]

[0028] In Example 1, the structure of a field emission electron source (hereinafter sometimes simply referred to as an electron source) of the present invention and its assembly method will be described with reference to Figures 2 to 13. The method for forming the first and second (100) top facets at the tip end, which is a feature of the present invention, will be described in Example 2 and subsequent examples.

[0029] First, as the material of the electron source of the present invention, rare earth hexaboride single crystals or transition metal carbide single crystals are used. Specifically, as the hexaboride single crystal, elements of the lanthanoid series such as La, Ce, Pr, Nd, Sm, Eu, Gd, etc. can be used, and they are represented by chemical formulas such as LaB6, CeB6, PrB6, NdB6, SmB6, EuB6, GdB6, etc. Fig. 2 shows a schematic diagram of the unit cell 200 thereof. The unit cell 200 has a cubic crystal structure in which six blocks of boron atoms 2 are located at the body center of the simple cubic lattice of metal atoms 1. These materials generally have a high melting point (for example, LaB6: 2483 K, CeB6: 2463 K), a low vapor pressure, a high hardness, are resistant to ion bombardment, and are suitable as electron source materials with a lower work function than W (for example, LaB6, CeB6: about 2.6 eV < W: about 4.3 eV). Among these, LaB6 and CeB6 are materials that are particularly widely used as thermionic electron source materials. As the hexaboride single crystal, single crystals mainly composed of LaB6 or CeB6 can be effectively used.

[0030] On the other hand, as the transition metal carbide single crystal, single crystals mainly composed of HfC, ZrC, or TiC can be effectively used. Fig. 3 shows a schematic diagram of the unit cell 201 thereof. The unit cell 201 has a cubic crystal structure in which carbon atoms 3 of metal atoms 1 are alternately arranged. These materials have a higher melting point than the hexaboride single crystal (for example, HfC: 4163 K, ZrC: 3805 K, TiC: 3443 K), a low vapor pressure, a high hardness, are resistant to ion bombardment, and are suitable as electron source materials with a lower work function than W (for example, HfC, ZrC, TiC: about 3.3 eV).

[0031] In this embodiment, an example using mainly CeB6 of the hexaboride single crystal and HfC of the transition metal carbide single crystal will be described. Among the rare earth hexaboride single crystals, CeB6 has f electrons with strong energy localization and a high density of states directly below the Fermi level, a high electron density for supplying the emission current, and is particularly suitable as a material for the hexaboride single crystal for fabricating a field emission electron source. On the other hand, HfC is the material with the highest melting point among the transition metal carbide single crystals and is particularly suitable.

[0032] The manufacturing method of the present invention is generally the same for hexaboride single crystals and transition metal carbide single crystals. However, due to differences in melting point and reactivity with other materials constituting the electron source (particularly the metal tube that holds the single crystal), there are some differences in the processing temperature and the assembly process of the electron source, and these will be explained as appropriate.

[0033] As shown in Figure 4, large single crystals 4 of hexaborides and transition metal carbides can be grown by melt (liquid phase) crystal growth using, for example, the floating zone method. The single crystals 4 are several millimeters in diameter and several millimeters to several tens of millimeters in length, grown along the

[0100] crystal axis perpendicular to the (100) habit plane along which the crystal preferentially grows. These single crystals 4 are then cut and polished into square prisms with sides of several hundred micrometers, or cylindrical rods 5 with diameters of several hundred micrometers, or rods 5 with lengths of several millimeters. In this example, rods 5 were used that were square prisms with sides of 200 micrometers and lengths of 5 mm, or cylindrical rods 5 with diameters of 280 micrometers and lengths of 5 mm. The longitudinal direction of the rods 5 was the

[0100] orientation.

[0034] The crystal structure of the above-mentioned hexaboride single crystals and transition metal carbide single crystals is a simple cubic lattice of the cubic system as shown in Figures 2 and 3, and the (100) plane, (010) plane, (001) plane,

[0100] crystal axis,

[0010] crystal axis,

[0001] crystal axis, etc. are equivalent, and the effect is the same regardless of which plane or axis is used. Therefore, in the following explanation, {100} is used as an equivalent plane group, and {100} is used as an equivalent axis group. <100> The following explanation will be given using the notation "etc."

[0035] Next, a bonding method for holding a rod 5 of a hexaboride single crystal or a transition metal carbide single crystal and attaching a filament for heating will be described with reference to Figures 5 to 10. The electron source according to this embodiment has a structure in which a rod 5 of a hexaboride single crystal or a transition metal carbide is placed inside a metal tube 11 made of tantalum, niobium, or the like.

[0036] The material of the metal tube 11 used to join the hexaboride single crystal or transition metal carbide single crystal rod 5 is a high-melting-point metal such as tantalum or niobium, which has high ductility and is easy to draw into a minute metal tube 11 by tube drawing, and is also easy to machine into recesses, as described below. In this example, tantalum was used as an example to fabricate a minute metal tube 11 having an outer diameter of 500 μm, an inner diameter of 320 μm, a wall thickness of 90 μm, and a length of 5 mm.

[0037] Next, we will describe a method for joining a rod 5 of a transition metal carbide single crystal or a hexaboride single crystal using the metal tube 11. First, as shown in Figure 5, a guide pin 12 with a diameter of 300 μm and a length of 1 to 3 mm is inserted into the metal tube 11 using a pedestal 13, which is set up vertically. The guide pin 12 is inserted into the metal tube 11, and the metal tube 11 is then set up vertically relative to the pedestal 13. Next, when using a hexaboride single crystal, a paste 14 containing nanoparticles such as boron tetracarbide (B4C) with an average particle size of 0.01 to 0.1 μm and a carbon resin such as furan resin is filled into the metal tube 11 from above. Here, nanoparticles with an average particle size of 0.05 μm were used. On the other hand, when using a transition metal carbide single crystal, this filling step is not necessary because tantalum, niobium, or other metals do not react with the metal tube 11 at high temperatures.

[0038] Furthermore, a rod 5 of a hexaboride single crystal or a transition metal carbide single crystal is inserted from the top of the metal tube 11. A guide pin 12 can be used to control the length h by which the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal protrudes from the inside of the metal tube 11. In this embodiment, the protruding length h is set to be as long as 2 to 3 mm because one end of the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal is polished by electrolytic polishing, as will be described later with reference to FIGS.

[0039] Next, as shown in Figure 6, a rod 5 of a hexaboride single crystal or a transition metal carbide single crystal and a metal tube 11 are pressure-welded using a special tool developed by the present inventors from two orthogonal axes (four directions) in a plane perpendicular to the vertical direction of the rod 5. For simplicity of explanation, Figure 6 only shows the blade 15 of the pressure welding tool. The tip of the blade 15 of the pressure welding tool is provided with a pair of protrusions 150, one above the other, for forming recesses in the metal tube 11. The blade 15 of the pressure welding tool is brought close to the metal tube 11 with equal strokes from two orthogonal axes (four directions), and the protrusions 150 crush the outer periphery of the metal tube 11, forming multiple recesses 17 in the metal tube 11, as shown in Figure 7(c).

[0040] During this operation, the relative positions of the metal tube 11 and the rod 5 of the hexaboride single crystal or transition metal carbide single crystal are confirmed using a stereomicroscope 16, and the rotation axis of the rod 5 of the hexaboride single crystal or transition metal carbide single crystal is adjusted as appropriate so that each side of the square pillar-shaped rod 5 of the hexaboride single crystal or transition metal carbide single crystal is aligned with the stroke direction of the tool blade 15. This forms multiple recesses 17 from the outer periphery of the metal tube 11 to surround the central axis, and the bottom of each recess 17 is pressed against and comes into contact with the outer periphery of the rod 5 of the hexaboride single crystal or transition metal carbide single crystal, thereby automatically aligning the rod 5 with the central axis of the metal tube 11 and fixing it in place.

[0041] 7 is a schematic diagram of a rod 5 of a hexaboride single crystal or a transition metal carbide single crystal and a metal tube 11 joined by the method of this example. Fig. 7(a) shows a plan view of the joint as seen from the tip side of the rod 5, (b) shows a perspective view of the rod 5, and (c) shows a vertical cross section of the rod 5.

[0042] Using this joining method, the metal tube 11 and the rod 5 of hexaboride single crystal or transition metal carbide single crystal can be pressed evenly from two axes and four directions, resulting in a mechanically strong bond. Furthermore, by approaching the metal tube 11 with even strokes from two axes and four directions and crushing the outer periphery of the metal tube 11, the square-prism-shaped rod 5 of hexaboride single crystal or transition metal carbide single crystal can be automatically aligned and joined to the central axis of the metal tube 11, improving assembly accuracy and facilitating centering of the electron source, thereby improving yield. Furthermore, by joining at two points, top and bottom, in the axial direction, tilting of the rod 5 at the joint can be prevented, further improving centering accuracy.

[0043] Furthermore, when a hexaboride single crystal is used, paste 14, a mixture of boron tetracarbide (B4C) nanoparticles and a carbon resin such as furan resin, flexibly deforms during pressure welding, filling the gap between the deformed metal tube 11 and the hexaboride single crystal rod 5 without leaving any gaps. Because paste 14 uses small nanoparticles with an average particle size of 0.1 μm or less, the hexaboride single crystal rod 5 is not damaged or broken during pressure welding, improving the yield of the pressure welding process. The reason for setting the average particle size of the nanoparticles at 0.01 μm or more is that if the average particle size is too small, the apparent volume of the B4C powder increases, making it difficult to mix the paste, and the nanoparticles themselves are difficult to manufacture, resulting in high costs.

[0044] After the metal tube 11 is pressure-welded to the rod 5 of the hexaboride single crystal or transition metal carbide single crystal, the dotted line portion 11-1 of the metal tube 11 where the guide pin 12 was inserted is no longer needed. Therefore, the metal tube 11 is removed from the guide pin 12 and then cut with a cutter to reduce the heat capacity of the metal tube 11. In the case of the hexaboride single crystal, the paste 14 is then hardened by heating in the air, and then carbonized by heating at a high temperature of 1000°C or higher in a vacuum for several hours. This prevents degassing from the paste 14 and forms a reaction barrier layer that prevents reaction at high temperatures between the metal tube 11, such as tantalum, and the hexaboride single crystal rod 5.

[0045] 8, a filament 18 made of tungsten or the like is directly spot-welded to a metal tube 11 to which a rod 5 made of a hexaboride single crystal or a transition metal carbide single crystal is joined. Furthermore, both ends of the filament 18 are spot-welded to a pair of electrodes 20 fixed to a stem 19 to form a structure 1001 that serves as the prototype of the electron source. Since the structure 1001 is formed by joining metals together, a strong bond can be easily obtained by spot welding.

[0046] A specific example of the welding process for forming this structure 1001 will be described with reference to Fig. 9. When directly spot welding a filament 18 made of tungsten or the like to a metal tube 11 to which a rod 5 made of a hexaboride single crystal or a transition metal carbide single crystal is joined, an alignment jig 21 as shown in Fig. 9(a) is used. First, the filament 18 made of tungsten or the like is accurately aligned to the metal tube 11 using an alignment jig 21-1, and then the metal tube 11 and the filament 18 are spot welded together.

[0047] 9(b), the metal tube 11 to which the filament 18 is spot-welded and the stem 19 are accurately aligned using an alignment jig 21-2, and the filament 18 and the pair of electrodes 20 fixed to the stem 19 are spot-welded to form the structure 1001. In this way, by using the alignment jigs 21-1 and 21-2, at the stage of assembling the structure 1001, the central axes of the metal tube 11 and the rod 5 of the hexaboride single crystal or transition metal carbide single crystal are aligned with the centers of the pair of electrodes 20 fixed to the stem 19, so that the structure 1001 can be centered with high precision.

[0048] In the above examples, rods 5 of hexaboride single crystals or transition metal carbide single crystals cut into a rectangular prism shape were used as components of the structure 1001. The hexaboride single crystal or transition metal carbide single crystal rod 5 may also be machined into a cylinder as shown in FIG. 4 . FIG. 10 shows an example in which a cylindrical hexaboride single crystal or transition metal carbide single crystal rod 5-1 is used. To join the cylindrical hexaboride single crystal or transition metal carbide single crystal rod 5-1 to the metal tube 11, pressure welding can be performed using a special tool developed in this example from three equally spaced axes and three directions in a plane perpendicular to the vertical direction of the hexaboride single crystal or transition metal carbide single crystal rod 5-1. In particular, in the case of the transition metal carbide single crystal rod 5, pressure welding can be performed without using paste 14. Therefore, it is preferable to machine the rod 5 into a cylinder similar in shape to the inner diameter of the metal tube 11, as this facilitates pressure welding.

[0049] 10(a) is a plan view of the joint as seen from the tip side of the rod 5-1, (b) is a perspective view of the rod 5-1, and (c) is a vertical cross-sectional view of the rod 5-1. Figures 10(b) and 10(c) show the state after cutting off the portion corresponding to the portion 11-1 that becomes unnecessary after pressure welding of the rod 5 made of the hexaboride single crystal or transition metal carbide single crystal of the metal tube 11 described in Figure 6.

[0050] Furthermore, as in the case of the quadrangular prism-shaped rod 5 of the hexaboride single crystal or transition metal carbide single crystal described with reference to Figures 6 and 7, it is of course also possible to join the metal tube 11 and the cylindrical rod 5-1 of the hexaboride single crystal or transition metal carbide single crystal by pressure welding from two axes and four directions.

[0051] Next, in structure 1001, the tip of the portion of rod 5 of hexaboride single crystal or transition metal carbide single crystal protruding from metal tube 11 is reduced in diameter into a cone shape by electrolytic polishing. Electrolytic polishing is performed by dipping the tip of rod 5 of hexaboride single crystal or transition metal carbide single crystal assembled as shown in Fig. 11 into electrolyte 22 such as nitric acid contained in container 25, and applying voltage from AC or DC power supply 24 between it and ring-shaped counter electrode 23 made of platinum or the like.

[0052] When a rod 5 of a hexaboride single crystal or a transition metal carbide single crystal is immersed in an electrolyte (electrolytic polishing solution) 22, as shown in Figure 12, a meniscus forms on the liquid surface, and the polishing rate is slow at the liquid surface and fast at the submerged portion. As electrolytic polishing progresses and the polishing area of ​​the rod 5 of a hexaboride single crystal or a transition metal carbide single crystal immersed in the electrolyte 22 decreases, the electrolytic current decreases. When the electric field current decreases to a certain level (cutoff current), the power supply 24 is turned off, and the tip 6 can be machined into a tapered tip, as shown by the dotted line in Figure 12. The longitudinal direction of the tip 6 is oriented in the

[0100] direction.

[0053] The electron source is assembled through the above steps. Figure 13 shows the structure of the fabricated field emission electron source 100. A rod 5 of hexaboride single crystal or transition metal carbide single crystal with a tip 6 reduced in diameter by electropolishing is held in a metal tube 11, which is welded to a filament 18 and then to an electrode 20 on a stem 19. The outer periphery of the metal tube is provided with multiple recesses in at least two axial directions surrounding the central axis, with the bottoms of each recess contacting the outer periphery of the rod 5 of hexaboride single crystal or transition metal carbide single crystal placed inside. This structure provides a strong and reliable bond that prevents the rod 5 of hexaboride single crystal or transition metal carbide single crystal from falling off even when heated at high temperatures. When using a hexaboride single crystal, it reacts with the metal tube 11, such as tantalum or niobium, at high temperatures, so a paste 14 made of a mixture of boron tetracarbide nanoparticles with an average particle size of 0.01 to 0.1 μm and carbon resin was filled between the metal tube 11 and the hexaboride single crystal rod 5, and then hardened and carbonized to achieve a highly heat-resistant bond. On the other hand, in the case of a transition metal carbide single crystal, it does not react with the metal tube 11, such as tantalum or niobium, at high temperatures, so this step was not performed. [Example]

[0054] In Example 2, a process for forming an electron emission surface of the present invention on the tip 6 of the field emission electron source 100 made of a hexaboride single crystal fabricated in Example 1 will be described. The case of a field emission electron source 100 made of a transition metal carbide will be described in Example 3.

[0055] Figure 14 is a diagram showing the process of forming the electron emission surface at the tip end of Examples 2 and 3. Figure 14(a) is a perspective view showing the tip end shape after electrolytic polishing, Figure 14(b) is a perspective view showing the tip end shape after the first-stage thermal field treatment, and Figure 14(c) is a perspective view showing the tip end shape after the second-stage thermal field treatment. Figure 15 is a diagram showing the process condition ranges for the manufacturing method of Example 2, where Figure 15(a) shows the process condition range for the first-stage thermal field treatment and Figure 15(b) shows the process condition range for the second-stage thermal field treatment.

[0056] First, as a first-stage process, a field emission electron source 100 made of a hexaboride single crystal having a tip 6 formed at the tip by electrolytic polishing as shown in FIG. 14(a) and a longitudinal direction of which is oriented in the

[0100] direction is set in a vacuum chamber (not shown), and as shown in FIG. 14(b), <100> At tip 6 of the axial hexaboride single crystal, a first (100) top facet 42 is formed, surrounded by side facets 41, each of which is composed of at least four {n11} planes, where n is an integer of 1, 2, or 3, and at least four {n10} planes, and the total area of ​​the side facets of the {n11} planes is greater than the total area of ​​the side facets of {n10}. Because the {n11} planes of hexaboride single crystals have a higher work function than the {n10} planes, by making the total area of ​​the side facets of the {n11} planes greater than the total area of ​​the side facets of {n10}, it is possible to reduce unnecessary current emitted off the optical axis from side facets 41.

[0057] The feature of this manufacturing method is that, as shown in the process region 151 of FIG. 15(a), the tip 6 is heated at 1500 to 1700° C. in a vacuum, and 1 to 4.5×10 9The first stage of the thermal electric field treatment involves applying an electric field of 1000 V / m. The effects of heating and electric field application in the first stage of the thermal electric field treatment will be specifically described below with reference to FIG.

[0058] First, we will explain the effect of heating in the first stage of thermal field processing. The hexaboride single crystal rod 5 is a high-melting-point material (LaB6: 2210°C, CeB6: 2190°C). When heated to 700-1400°C in a vacuum, atomic migration on the surface causes a restructuring of the crystal planes, particularly at the tip 6, as shown in process region 152. In this case, the (100) plane tends to grow at the top of the tip 6 and the {n10}>{n11} plane tends to grow on the sides. When heated further to 1500°C or higher, as in process region 153, evaporation from the surface gradually progresses, destroying the surface crystal structure. At temperatures above 1700°C in process region 154, evaporation becomes even more pronounced.

[0059] Therefore, heating at 1500-1700 °C mainly plays the role of evaporation, and no electric field is applied to the tip 6 of the hexaboride single crystal, or 1 × 10 9 When heated under a weak electric field of 100 V / m or less, the tip 6 narrows while maintaining a shape similar to the shape created by electropolishing, as in process region 153. Furthermore, when heated to 1700°C or higher, as in region 154, evaporation becomes intense, making it difficult to maintain a shape similar to the shape created by electropolishing.

[0060] Next, the effect of the electric field applied to the tip 6 in the first stage of thermal electric field treatment will be explained. This has two effects. First, the first effect will be explained below.

[0061] In this embodiment, as described above, evaporation of the surface of the tip 6 occurs simply by heating the process region 153 to 1500 to 1700°C, but field evaporation also occurs by applying a positive polarity electric field to the tip 6. A feature of field evaporation is that, unlike evaporation caused by heating alone, the pointed portion of the tip 6 evaporates preferentially, so the tip of the tip 6 is processed into a shape that is close to a hemisphere as a whole.

[0062] Next, we will explain the second effect. Generally, when a strong electric field is applied to a heated tip 6, atomic diffusion occurs on the surface due to electrostatic force, and a crystal plane with a high atomic density grows large and builds up. This is known to occur in the case of ZrO / W(100) tips used for Schottky electron emitters, for example.

[0063] As a result of extensive research by the present inventors, <100> At the tip of the hexaboride single crystal of the axis, 1 to 4.5 × 10 9 We found that applying a strong electric field of 100 V / m caused a buildup in which a (100) plane was formed on the top of tip 6. We also found that the electric field that caused the buildup did not depend on polarity, and that the (100) plane could be built up using either a positive or negative electric field.

[0064] However, if an electric field with a negative polarity is applied to the tip, the above-mentioned field evaporation effect will not occur, and a large amount of electrons will be emitted from the tip of a hexaboride single crystal when a high temperature and high electric field are applied, which will result in the generation of electron beam stimulated desorption gas, reducing the degree of vacuum and raising the risk of the tip being damaged by discharge.Therefore, in the manufacturing method of this embodiment, it is preferable to apply an electric field with a positive polarity.

[0065] In addition, as in process area 155, 4.5 × 10 9 If an electric field stronger than V / m is applied, the effect of field evaporation becomes too strong, and the tip of tip 6 is processed into a hemispherical shape.

[0066] In the first stage of the thermal field treatment (process region 151) of this embodiment, the effect of the thermal field evaporation and the effect of the build-up are appropriately combined, <100> At the tip 6 of the hexaboride single crystal shaft, a first (100) top facet 42 was formed, surrounded by side facets 41, consisting of at least four {n11} planes (where n = 1, 2, or 3) and at least four {n10} planes, with the total area of ​​the {n11} side facets > the total area of ​​the {n10} side facets. This is because the thermal field evaporation effect reduces the sharp edges of the {n10} planes compared to the overall surface curvature of the tip 6, making them less likely to grow. Furthermore, the build-up effect promotes the growth of the (100) plane at the top of the tip 6 and the {n11} planes, especially the {111} high-density crystal planes, on the sides surrounding it. This is the effect of the first thermal field treatment of the present invention.

[0067] In the present invention, a second thermal field treatment is subsequently performed to form a microcrystal having a second (100) plane top facet 43 within the (100) plane top facet 42, as shown in Figure 14(c). Here, the microcrystal forming the second (100) plane top facet has a cubic shape with its side faces also formed by {100} planes, or a trapezoidal shape with its side faces formed by {111} planes.

[0068] Specifically, as shown in the process region 156 of FIG. 15(b), after the first (100) top facet 42 is formed by the first-stage thermal electric field treatment, the heating temperature is lowered to 1300 to 1500°C, and the positive electric field is reduced to less than half, 1 to 2.25 × 10 9 The heating temperature was reduced to 1300-1500°C in order to suppress the evaporation of CeB6, and the electric field was reduced to less than half in order to weaken the build-up effect.

[0069] Figure 16 shows cross-sectional views of the structural changes that occur at the end surface of the first (100) apical facet 42 of the tip 6 during the first-stage thermal field treatment in Figure 15(a) and the second-stage thermal field treatment in Figure 15(b). The buildup occurs when, as shown in Figure 16(a), the amount of atomic diffusion toward the tip 6 due to the electrostatic force of the electric field F exceeds the amount of atomic diffusion toward the tip 6 due to the temperature T. This promotes atomic diffusion toward the apex of the tip 6, promoting the growth of the (100) plane at the apex and the side facets 41, particularly the {111} plane, of high-density crystal planes on the surrounding sides. Lowering the electric field F from this state, as in the second-stage thermal field treatment in Figure 15(b), reduces the amount of atomic diffusion on the surface toward the tip 6. In this case, when the amount of atomic diffusion on the surface toward the bottom of the tip 6 due to the temperature T becomes dominant, as shown in Figure 16(b), the end face of the first (100) facet 42 at the top of the tip 6 collapses, a step occurs in the (100) plane, and a microcrystal with a second top facet 43 of a (100) plane is formed within the first top facet 42. In this example, the temperature was also lowered to suppress the evaporation of CeB6, but lowering the temperature T too much also reduces the amount of atomic diffusion on the surface toward the bottom of the tip 6, so lowering it below 1300°C is not recommended.

[0070] That is, the manufacturing method of the field emission electron source 100 can be summarized as follows: A high electric field with a positive polarity is applied to the tip 6 of a single crystal of hexaboride or transition metal carbide with its longitudinal direction oriented in the

[0100] direction at a high temperature, causing atoms to migrate toward the tip 6's tip end, resulting in a buildup and the formation of a first (100) top facet 42. Then, by reducing the electric field applied to the tip 6, a microcrystal having a second (100) top facet 43 grows within the first (100) top facet 42.

[0071] Although this embodiment is an example of CeB6, the same process can be applied to LaB6, which has almost the same thermal and chemical properties, such as melting point.

[0072] The above two-stage thermal field treatment <100> At the tip 6 of a hexaboride single crystal of CeB6, LaB6, etc., with the longitudinal axis oriented in the

[0100] direction, a first (100) top facet 42 is formed, which is composed of at least four {n11} planes, where n = 1, 2, or 3, and at least four {n10} planes, and is surrounded by side facets such that the total area of ​​the side facets of the {n11} planes > {n10}, and further, a microcrystal is formed which has a second (100) top facet 43 within the first (100) top facet 42. [Example]

[0073] In this example, the process of forming an electron emission surface on the tip of a transition metal carbide single crystal such as HfC, ZrC, or TiC will be described using Figures 14, 16, and 17. The melting points of transition metal carbide single crystals are significantly higher than those of hexaboride single crystals (HfC: 3890°C, ZrC: 3532°C, TiC: 3170°C, LaB6: 2210°C, CeB6: 2190°C) and their vapor pressures are also very low. Therefore, the process temperature and evaporation effect differ from those in Example 1, but the basic process concept is the same.

[0074] FIG. 17 is a diagram showing the process condition ranges for the manufacturing method of Example 3, where (a) of FIG. 17 shows the process condition range for the first stage of thermal electric field treatment, and (b) of FIG. 17 shows the process condition range for the second stage of thermal electric field treatment.

[0075] First, as a first thermal electric field treatment, a field emission electron source 100 of a transition metal carbide single crystal, the tip of which has been electrolytically polished to form a tip 6 at the tip as shown in FIG. 14(a), is set in a vacuum chamber (not shown), and as shown in the process region 161 of FIG. 17(a), the tip 6 is heated at 1500 to 1800°C in a vacuum, and 3 to 6 × 10 9An electric field of V / m is applied. <100> A tip 40 of the axial transition metal carbide is formed with a first (100) top facet 42 surrounded by side facets 41, each of which is composed of at least four {n11} planes, where n = 1, 2, or 3, and at least four {n10} planes, and the total area of ​​the side facets of the {n11} planes is greater than the total area of ​​the side facets of {n10}. Because the {n11} planes of the transition metal carbide single crystal also have a higher work function than the {n10} planes, it is possible to reduce unnecessary current emitted off the optical axis from the side facets 41 by making the total area of ​​the side facets of the {n11} planes greater than the total area of ​​the side facets of {n10}.

[0076] As shown in process region 162, when heated to 1500-1800°C in a vacuum, the surface atomic migration causes the reconstruction of the crystal planes, especially of the tip 6 at the tip end. In this case, the (100) plane tends to grow on the top of the tip 6, and the {n10}>{n11} plane tends to grow on the side. As shown in process region 163, when heated to 1500-1800°C in a vacuum, the crystal planes of 6×10 9 If an electric field stronger than V / m is applied, the effect of field evaporation becomes too strong, and the tip of tip 6 is processed into a hemispherical shape.

[0077] The reason why the tip 6 has the same structure as that of a hexaboride single crystal is that a transition metal single crystal is a compound with the same cubic crystal structure as a hexaboride single crystal, and the geometric relationship between the side facet 41 and the top facet 42, which stabilize the surface energy when built up, is similar. However, due to differences in melting points, it is necessary to apply a higher temperature and a higher electric field than to the tip of a hexaboride single crystal.

[0078] Next, in this embodiment, as a second thermal electric field treatment, the positive electric field is reduced to 1 to 3×10, which is less than half the normal value, while heating at 1500 to 1800° C. as shown in the process region 164 of FIG. 17(b). 9The electric field F was lowered to 100 V / m. As a result, the amount of atoms diffusing downward from the tip 6 due to the temperature T exceeded the amount of atoms diffusing on the surface toward the tip of the tip 6 due to the electrostatic force of the electric field F, causing the end face of the first (100) top facet 42 to collapse, creating a step in the (100) plane, and forming a microcrystal with a second (100) top facet 43 within the first top facet 42. [Example]

[0079] In this example, the electron emission characteristics of a field emission electron source fabricated according to the present invention are described. Here, we explain an example of a field emission electron source using HfC, a transition metal carbide single crystal, in which the first top (100) facet 42 is a square with dimensions of 170 nm length × 170 nm width, and the second top (100) facet 43 is made up of microcrystals with dimensions of 50 nm length × 50 nm width × 50 nm height.

[0080] Although not described in this example, when a field emission electron source made of a single crystal of another transition metal carbide such as ZrC is used, or when a field emission electron source made of a single crystal of a hexaboride such as CeB6 is used, it is possible to obtain substantially the same characteristics, although there are some differences.

[0081] First, Figure 18(a) shows a field emission microscope (FEM) image from the HfC field emission electron source fabricated through the process up to the first thermal electric field treatment in Figure 17(a), and Figure 18(b) shows an FEM image of the HfC field emission electron source fabricated through the process up to the second thermal electric field treatment in Figure 17(b).

[0082] As shown in the FEM image in Figure 18(a), the tip 6 fabricated by the first thermal electric field treatment step in Figure 17(a) has a large, flat facet 42 on the first apex (100) plane of the tip 6, which makes it difficult for an electric field to be applied, resulting in a relatively small amount of emitted current and a dark image.On the other hand, the surrounding {n10} facets (n = 1 to 3) such as {310}{210}{110} are pointed and tend to concentrate the electric field, resulting in a relatively large amount of emitted current and a bright image.

[0083] On the other hand, as shown in the FEM image of Fig. 18(b), the tip fabricated by performing the steps up to the second thermal field treatment in Fig. 17(b) appears relatively bright in the center because the electric field is concentrated on the (100) plane of the second top facet 43, which is formed of microcrystals formed within the plane of the first (100) top facet 42. On the other hand, the underlying first top (100) facet 42 and the surrounding side facets from the {n10} plane appear dark due to a relatively reduced electric field strength.

[0084] FIG. 19 shows the radial angular current density J per total current It (μA) of the tip 6 in FIG. 18(a) on which only the first (100) facet 42 is formed, and the tip 6 in FIG. 18(b) on which a microcrystal having the second (100) facet 43 of the present invention is formed. Ω The line 1900 shows the angular current density J per total current It (μA) of the tip 6 of the field emission electron source having only the first (100) facet 42. Ω (μA / sr). Line 1901 is the radial current density J per total current It (μA) of the tip 6 of the field emission electron source having a microcrystal of the second (100) facet 43. Ω (μA / sr). The tip 6 of the present invention has a J Ω / It is enhanced by about 4 times more than 12, and a large radiation angular current density J is obtained with a small total current It (μA). Ω (μA / sr) can be obtained.

[0085] FIG. 20 shows the angular current density J of the field emission electron source in FIG. 18(a) in which only the first top (100) facet 42 is formed, and the field emission electron source in FIG. 18(b) in which a microcrystal having the second top (100) facet 43 of the present invention is formed. Ω The results are compared for the stability of the angular current density J (μA / sr) of the tip 6 of the field emission electron source having only the first (100) facet 42. Ω (μA / sr), and the line 2001 represents the angular current density J of the field emission electron source in which a microcrystal having a second top (100) facet 43 is formed.Ω (μA / sr) is shown.

[0086] The tip formed with only the first top (100) facet 42 is J. Ω The initial value of the current (μA / sr) was set to 14 μA / sr, and the field emission electron source in which the microcrystals having the second (100) facet 43 were formed was set to twice that, 28 μA / sr. The field emission electron source in which only the first top (100) facet 42 was formed had noise in the emission current, as shown by line 2000, and the noise increased over time, and the emission current also decreased. In contrast, the field emission electron source in which the microcrystals having the second (100) facet 43 were formed had noise in the emission current, as shown by line 2001. Ω Even though the initial value of (μA / sr) was set to twice as high, there was almost no current noise and the current was stable with no decrease.

[0087] One of the reasons for this is that the field emission electron source in which the microcrystals having the second top (100) facet 43 are formed has a larger J than the field emission electron source in which only the first top (100) facet 42 is formed. Ω / It is four times larger, so J is twice as large. Ω (μA / sr), only half the total current It (μA) is required, and the amount of electron-beam-stimulated desorption gas generated from the electrode is halved. This halves the amount of electron-beam-stimulated desorption gas incident on the second top (100) facet 43.

[0088] However, this alone cannot explain the large difference in stability. Therefore, the second reason is that the microcrystalline steps that form the second apex (100) facet 43 act as a diffusion barrier or a trap site for the adsorbed gas when the gas adsorbed on the sidewall of the tip 6 diffuses toward the apex of the tip 6, making it difficult for the adsorbed gas to reach the second apex (100) facet 43.

[0089] In this way, when the field emission electron source of the present invention is used, the J Ω / It>12(1 / sr) is obtained, and the radial current density J required for electron microscopes is obtained with a small total current It (μA). Ω Specifically, with a very small total current It (μA) of 0.7 to 2 μA, a J of 10 to 25 μA / sr, which is normally required for electron microscopes, can be obtained. Ω (μA / sr) can be obtained. In addition, under the condition of a total current It = 10 μA, which is typical in a normal electron microscope, a large beam angular current density J of 100 μA / sr or more can be obtained. Ω (μA / sr) can be obtained, which makes it possible to respond to high-speed elemental analysis that requires a large beam angular current density, for example. [Example]

[0090] The size of the microcrystals (defined here as the length of one side of the (100) facet of the microcrystals) can be controlled by the electric field, temperature, and holding time applied in the second thermal field treatment of Examples 2 and 3. Therefore, in this Example, we investigated the change in electron emission characteristics depending on the size of the microcrystals formed within facet 42 of the first top (100) plane, and will explain the results of determining the optimal microcrystal size and height, and the relationship between the size of facet 42 of the first top (100) plane and the size of facet 43 of the second top (100) plane.

[0091] Figure 21 is a graph showing the change in the electron emission characteristics of the field emission electron source depending on the size (length of one side) of the microcrystal having the second (100) top facet of Example 5. Figure 21(a) is a graph showing the change in the electric field strength at the center of the tip, and Figure 21(b) is a graph showing the change in the radiation angular current density J Ω FIG. 21(c) is a graph showing the change in the light source diameter.

[0092] Figure 21 shows how the electric field strength at the center of the tip 6 (Figure 21(a)), the angular radiation current density (Figure 21(b)), and the light source diameter when used in an electron microscope (Figure 21(c)) change depending on the size of the cubic microcrystals that form the second (100) apex facet formed within the first apex (100) facet plane. Here, the size of the (100) plane within the first apex facet 42 is shown as 170 nm (a square shape measuring 170 nm long and 170 nm wide), the same as in Example 4. In Figures 21(a)-(c), the extraction voltage is set to 2 kV.

[0093] First, from the left end of FIG. 21(a), when there are no microcrystals and only the first (100) top facet 42 is formed, the electric field strength at the center of the tip 6 is about 1.5×10 9 V / m, whereas the electric field intensity at the center of the tip 6 of the second (100) top facet 43 increases as the size of the microcrystal of the second (100) top facet 43 increases, reaching 3.2 × 10 when the size of the microcrystal is 20 nm. 9 V / m and then gradually decreased.

[0094] In addition, the radiation angular current density J shown in Fig. 21(b) Ω The maximum current density (μA / sr) was 93 μA / sr when the size of the second (100) top facet 43 microcrystallites was 30 nm. Ω The reason for the slight difference in the size of the microcrystals at which the maximum (μA / sr) is obtained is that even if the electric field strength is strong, if the area of ​​the second top (100) facet 43, which serves as the electron emission surface, is small, the radiation angular current density J that can be extracted is small. Ω On the other hand, if the size of the second (100) top facet 43 microcrystals is too large, the electric field concentration becomes difficult, and the radiation angular current density J that can be extracted also decreases. Ω Therefore, there is an optimum range for the size of the microcrystals of the second (100) top facet 43.

[0095] Furthermore, Figure 21(c) shows how the source diameter of the field emission electron source changes with the size of the microcrystals on the second (100) top facet 43. The smaller the size of the microcrystals, the smaller the source diameter becomes, improving the resolution of the electron microscope. On the other hand, without the microcrystals on the second (100) top facet 43, electrons are emitted from the relatively large first top (100) facet 42, resulting in a larger source diameter.

[0096] From the above results, it is found that the size of the microcrystals of the second (100) top facet 43 should not be too small or too large. Specifically, it is found that the size of the J Ω = 20 μA / sr or more can be easily obtained, and the source diameter is small, 2 nm or less, in the range of 10 to 60 nm. Furthermore, if the size of the microcrystals is in the range of 20 to 40 nm, J is three times larger than that of conventional methods. Ω In particular, if the size of the microcrystals is 30 nm, J is about four times higher than that of conventional methods. Ω / It is preferable to obtain it.

[0097] The above study is for the case where the microcrystals of the second (100) top facet 43 are cubic. The height of the microcrystals may differ from the length of one side of the top (100) facet 43. Therefore, when the size of the microcrystals (defined here as the length of one side of the second top (100) facet 43) is 30 nm, which is the optimum size, as shown in Figure 21, how the electric field and the radial current density J change when the height of the microcrystals is changed. Ω FIG. 22 shows the results of investigating whether (μA / sr) changes.

[0098] 22A and 22B are graphs showing the change in the electron emission characteristics of the field emission electron source depending on the ratio of the height of the microcrystal to the length of one side of the top facet of the second (100) plane in Example 5. FIG. 22A is a graph showing the change in the electric field strength at the center of the tip, and FIG. 22B is a graph showing the change in the radiation angular current density J Ω 22(a) and 22(b), the extraction voltage is set to 2 kV.

[0099] As the height of the second (100) top facet 43 decreases relative to the size (length of one side) of the microcrystal, the electric field strength decreases as shown in FIG. 22(a), and the radial angular current density J Ω 22, it can be seen that in order to fully obtain the effect of electric field concentration by the microcrystals of the second (100) top facet 43, it is preferable that the height of the microcrystals of the second (100) top facet 43 be at least 0.7 times the size (length of one side) of the microcrystals.

[0100] Next, we will show the results of an investigation into the relationship between the size (length of one side) of the first (100) apex facet 42 of the base and the size (length of one side) of the second (100) apex facet 43, which serves as the electron emission surface. Figure 23 shows the results of an investigation into the relationship between the size (length of one side) of the first (100) apex facet of Example 5, when the size of one side of the first (100) apex facet is 170 nm and when it is 340 nm. Figure 23(a) shows the change in electric field strength at the center of the tip depending on the size (length of one side) of a microcrystal having a second (100) apex facet. Figure 23(b) shows the change in the electric field strength ratio depending on the ratio of the length of one side of the second (100) apex facet to the first (100) apex facet. Figure 23(c) shows the radiation angular current density J depending on the ratio of the length of one side of the second (100) apex facet to the first (100) apex facet. Ω 23(a)-(c) show the change in the extraction voltage (μA / sr).

[0101] 23(a) shows the dependence of the electric field strength on the size (side length) of the microcrystals of the first (100) apex facet 42 when the size (side length) is 170 nm (line 2301) and when the size (side length) of the first (100) apex facet 42 is twice as large, 340 nm (line 2302). As the size of the underlying first (100) apex facet 42 increases, electric field concentration becomes less likely even for the same microcrystal size, and the electric field strength decreases.

[0102] Figure 23(b) shows the results of investigating the normalized electric field strength versus the ratio of the size (length of one side) of the first (100) top facet 42 to the size (length of one side) of the microcrystal of the second top facet 43. Line 2303 shows the case when the size of the first (100) top facet 42 is 170 nm, and line 2304 shows the case when the size of the first (100) top facet 42 is 340 nm. The change in the electric field strength ratio is determined almost entirely by the ratio of the size of the first top (100) plane facet 42 to the size of the second top (100) plane facet 43 of the microcrystal.

[0103] Figure 23(c) shows the radial current density J Ω 23 shows the dependence of the current (μA / sr) on the ratio of the size (side length) of the first (100) top facet 42 to the size (side length) of the microcrystallites of the second top (100) plane facet 43. Line 2305 shows the case where the size of the first (100) top facet 42 is 170 nm, and line 2306 shows the case where the size of the first (100) top facet 42 is 340 nm. A comparison was made between an extraction voltage of 2 kV when the first top facet 42 was 170 nm and an extraction voltage of 3.2 kV when the first top (100) plane facet 42 was 340 nm. Although the extraction voltage is different, it can be seen that if the ratio of the size of the first (100) top facet 42 to the size of the microcrystals on the second (100) top facet 43 is set to 0.05 to 0.35, the effect of electric field concentration by the microcrystals on the second (100) top facet 43 can be effectively utilized. Furthermore, if the ratio of the size of the first (100) top facet 42 to the size of the microcrystals on the second (100) top facet 43 is set to 0.1 to 0.25, the J can be increased by more than three times compared to the conventional method. Ω / It(radial angular current density J Ω In addition, if the ratio of the size of the first (100) top facet 42 to the size of the microcrystals of the second top (100) facet 43 is set to 0.15 to 0.2, the J is about four times larger than that of the conventional method. Ω / It is obtained and is particularly preferred.

[0104] From the above results, the following points were learned.

[0105] 1) The size (length of one side) of the minute crystals of facet 43 of the second top (100) plane is preferably in the range of 10 to 60 nm, more preferably 20 to 40 nm, and particularly preferably 30 nm.

[0106] 2) The height of the minute crystals on the facet 43 of the second top (100) plane is preferably 0.7 times or more the length and width (length of one side) of the minute crystals.

[0107] 3) The ratio of the size (length of one side) of the microcrystals of the second (100) apex facet 43 to the size (length of one side) of the first (100) apex facet 42 of the substrate is suitably in the range of 0.05 to 0.35, more suitably in the range of 0.1 to 0.25, and particularly suitably in the range of 0.15 to 0.2.

[0108] 4) The microcrystals forming the top facet 43 of the second (100) plane are either cubic in shape with sides also formed by {100} planes, or trapezoidal in shape with sides formed by {111} planes. [Example]

[0109] In the above Examples 2 to 5, the case where the first top (100) facet 42 serving as the base has one step has been described. In practice, it is possible to create a multi-step structure for the first top (100) facet 42 by adjusting the electric field, temperature, and holding time applied in the second thermal field treatment of Examples 2 and 3. If the first top (100) facet 42 has a multi-step structure, the number of steps of the diffusion barrier for the adsorbed gas diffusing along the sidewall of the tip 6 increases, which has the effect of further improving the stability of the emission current.

[0110] FIG. 24 is a perspective view of a tip in Example 6, in which the first apex (100) facet at the tip end is made to have a multi-stage structure.

[0111] 24 shows the structure of a field emission electron source having two stages of first top (100) facets 42. In this case, as in Example 5, the size (length of one side) of the microcrystals of the second top (100) facet 43 at the top is preferably in the range of 10 to 60 nm, more preferably 20 to 40 nm, and particularly preferably 30 nm, and the ratio of the size of the second (100) top facet 43 of the microcrystals at the top to the size of the underlying first (100) top facet 42 is preferably in the range of 0.05 to 0.35, more preferably 0.1 to 0.25, and particularly preferably 0.15 to 0.2.

[0112] This relationship remains the same even when the number of steps is increased; therefore, as the number of steps increases, the size of the bottom (100) facet 42 increases, resulting in a thicker tip 6 diameter. Specifically, even if the size of the microcrystals on the second (100) facet 43 is set to the smallest optimum range of 10 nm and the ratio of the size of the microcrystals on the second (100) facet 43 to the size of the first (100) facet 42 is set to the largest optimum range of 0.35, the diameter of the tip 6 exceeds 1.5 μm if there are five or more steps. In this case, the extraction voltage required to obtain field-emitted electrons becomes too high, making it difficult to operate in an electron microscope due to the limitations of the high-voltage power supply used in the electron microscope and the voltage resistance between the electrodes. Therefore, it is appropriate to limit the number of steps on the first (100) facet 42 to four or less. [Example]

[0113] Example 7 will be described with reference to Fig. 25. Fig. 25 is a schematic cross-sectional view of an electron beam apparatus (a scanning electron microscope equipped with a field emission electron source using a tip of the hexaboride single crystal or transition metal carbide of the present invention) according to Example 7.

[0114] Example 7 shows an example of a scanning electron microscope 1000 equipped with an electron source (field emission electron source) 100 that uses, as an electron emission surface, the facet 43 of the second apex (100) plane of the tip 6 of the HfC transition metal carbide single crystal evaluated in Example 4. Although not mentioned in this example, similar effects can be obtained when a hexaboride single crystal such as CeB6 is used.

[0115] 25 shows a schematic diagram of a scanning electron microscope 1000, which is an electron beam apparatus according to Example 7. A field emission electron source 100 is constantly heated by a constant current flowing from a heating power supply 103 controlled by a computer 101 and a controller 102, and a positive voltage is applied to an extraction electrode 105 by an extraction power supply 104 with respect to a tip 6 of the field emission electron source 100, thereby emitting electrons by field emission.

[0116] The emitted electron beam 106 is accelerated toward a grounded anode 108 by a negative high voltage applied by an acceleration power supply 107, and is focused by a first condenser lens 109, an aperture 110, a second condenser lens 111, an objective lens 112, and an astigmatism correction coil 113. The beam is scanned by a deflection scanning coil 114 and irradiated onto an observation area on a sample 115, and the generated secondary electrons are detected by a secondary electron detector 116. Although detectors other than the secondary electron detector are not shown, other detectors such as a backscattered electron detector and an elemental analyzer may also be used.

[0117] That is, the scanning electron microscope 1000 comprises a field emission electron source 100, a sample stage 117 on which a sample 115 is placed, and an electron optical system that focuses electrons emitted from the field emission electron source 100 into a beam and irradiates the sample 115 on the sample stage 117.

[0118] Electrons are emitted from a field-emission electron source 100 using the (100) plane of a HfC tip 6 as its electron emission surface. Because the work function of HfC is approximately 3.3 eV, lower than the 4.3 eV of a field-emission electron source using a W{310} plane, the emitted electrons have a narrow full width at half maximum and good monochromaticity. This reduces chromatic aberration in the objective lens 112 and allows a more focused electron beam 106 to be irradiated onto the sample 115. This allows for high-resolution scanning electron microscope images to be obtained. CeB6 also achieves a similar effect, albeit with an even narrower beam width, because its work function is approximately 2.6 eV, lower than the 4.3 eV of a field-emission electron source using a W{310} plane.

[0119] Furthermore, the field emission electron source 100 of the present invention emits electrons from the facet 43 of the second top (100) plane of the small-area microcrystal, which contributes to a small source diameter and improved resolution. Ω / It(radial angular current density J Ω The ratio of the total current It (μA / sr) to the total current It (μA) is more than four times higher, reducing the off-axis current and reducing the irradiation of unnecessary electrons on components around the electron source. Furthermore, the generation of electron-beam-stimulated desorption gas from the electrodes is suppressed, improving the stability of the field emission electron source 100. Furthermore, the microcrystalline steps act as a barrier to adsorbed gases diffusing along the sidewalls of the tip 6, delaying the arrival of adsorbed gases at the facet 43 of the second top (100) plane, further improving the stability of the field emission electron source 100. Therefore, the interval between flushing processes required for surface cleaning of the field emission electron source 100 can be extended, enabling stable measurements over long periods of time.

[0120] In addition, the field emission electron source 100 of the present invention is J Ω Because / It is more than four times higher than that of conventional electron sources, it is possible to produce a large beam angle current density. This is particularly effective when performing elemental analysis, where a large beam angle current density is necessary to shorten analysis time.

[0121] The above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0122] 1...metal atom, 2...boron atom, 3...carbon atom, 4...single crystal, 5...rod, 6...tip, 11...metal tube, 12...guide pin, 13...base, 14...paste, 15...blade, 16...stereomicroscope, 17...recess, 18...filament, 19...stem, 20...electrode, 21-1, 21-2...alignment jig, 22...electrolyte, 23...counter electrode, 24...power supply, 25...container, 41...side facet, 42...first top facet, 43...second top facet, 100...field emission electron source, 101...computer, 102...controller, 103...heating power supply, 104...extraction power supply, 105...extraction electrode, 106...electron beam, 107...acceleration power supply, 108...anode, 109...first condenser lens, 110...diaphragm, 111...second condenser lens , 112...objective lens, 113...astigmatism correction coil, 114...deflection scanning coil, 115...sample, 116...secondary electron detector, 117...sample stage, 150...protrusion, 151-156...process area of ​​tip of hexaboride single crystal, 161-165...process area of ​​tip of transition metal carbide single crystal, 200, 201...simple cubic lattice, 1000...scanning electron microscope, 1001...structure

Claims

1. <100> A field emission electron source comprising: a tip of a hexaboride single crystal or a transition metal carbide single crystal on an axis; a first (100) top facet surrounded by side facets, the side facets having at least four {n11} planes, where n is an integer of 1, 2, or 3, and at least four {n10} planes, and the total area of ​​the side facets of the {n11} planes > the total area of ​​the side facets of {n10}; and a microcrystal having a second (100) top facet within the first (100) top facet; and the source of electrons emitting mainly from the second (100) top facet.

2. 2. The field emission electron source according to claim 1, The hexaboride single crystal is LaB 6 or CeB 6 A field emission electron source characterized in that it is a single crystal mainly composed of

3. 2. The field emission electron source according to claim 1, A field emission electron source characterized in that the transition metal carbide single crystal is a single crystal containing HfC, ZrC or TiC as a main component.

4. 2. The field emission electron source according to claim 1, A field emission electron source, characterized in that the {n11} plane of the tip of the hexaboride single crystal or the transition metal carbide single crystal has a higher work function than the {n10} plane.

5. 2. The field emission electron source according to claim 1, a top facet of the second (100) plane of the microcrystallite is smaller than a top facet of the first (100) plane of the microcrystallite;

6. 2. The field emission electron source according to claim 1, The microcrystals are cubic in shape with a top and sides made up of {100} planes, or trapezoidal in shape with a top facet made up of a (100) plane and sides made up of {111} planes.

7. 2. The field emission electron source according to claim 1, a ratio of a side length of a top facet of the second (100) plane of the microcrystal to a side length of a top facet of the first (100) plane of the microcrystal is in the range of 0.05 to 0.

35.

8. 2. The field emission electron source according to claim 1, A field emission electron source, wherein the length of one side of the top facet of the second (100) plane of the microcrystal is in the range of 10 to 60 nm.

9. 2. The field emission electron source according to claim 1, A field emission electron source, wherein the height of the microcrystals is 0.7 times or more the length of one side of the top facet of the second (100) plane.

10. 2. The field emission electron source according to claim 1, A field emission electron source characterized in that the top facet of the first (100) plane has a multi-step structure with four or less steps.

11. A method for manufacturing a field emission electron source, comprising the steps of: applying a high electric field with positive polarity to a tip of a single crystal of hexaboride or transition metal carbide, the longitudinal direction of which is oriented in the [100] direction, at a high temperature; causing a buildup due to the migration of atoms toward the tip's tip end, forming a first (100) top facet; and then, by reducing the electric field applied to the tip, growing a microcrystal having a second (100) top facet within the plane of the first (100) top facet.

12. 1. An electron beam apparatus comprising: an electron source; a sample stage on which a sample is placed; and an electron optical system that converges electrons emitted from the electron source into a beam and irradiates the beam onto the sample on the sample stage, The electron source is <100> An electron beam device comprising: a tip of a hexaboride single crystal or a transition metal carbide single crystal of an axis; a first (100) top facet surrounded by side facets, the side facets having at least four {n11} planes, where n is an integer of 1, 2, or 3, and at least four {n10} planes, and the total area of ​​the side facets of the {n11} planes > the total area of ​​the side facets of {n10}; a microcrystal having a second (100) top facet within the first (100) top facet; and a field emission electron source for emitting electrons from the second (100) top facet.

Images