Field emission electron source, method for manufacturing same, and electron beam apparatus using same

Abstract

The present invention improves the ratio of the emission angle current density to the total current of a field emission electron source in which the (100) plane of a hexaboride single crystal or a transition metal carbide single crystal is used as an electron emission surface, and improves the current stability. In the 1t of the electron source; 100 gt; a tip of a needle tip of an axial hexaboride single crystal or a transition metal carbide single crystal forms a top facet of a first (100) plane surrounded by a side facet, fine crystals having a top facet of a second (100) plane are formed in a plane of the top facet of the first (100) plane, and electrons are mainly emitted from the top facet of the second (100) plane. The side small surfaces are composed of at least four {n11} surfaces and at least four {n10} surfaces in which n is an integer of 1, 2, and 3, and the total area of the side small surfaces of the {n11} surfaces is greater than the total area of the side small surfaces of the {n10} surfaces.

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 Art

[0002] Electron microscopes have a spatial resolution that exceeds the optical limit and can observe nanometer to pm-level microstructures and analyze their composition. Therefore, they are widely used in engineering fields such as materials, physics, medicine, biology, electricity, and mechanics. Among electron microscopes, there is a scanning electron microscope (SEM) as a device that can easily observe the surface of a sample.

[0003] As electron sources used in electron beam devices such as scanning electron microscopes, there are thermal electron sources (TE), field emission electron sources (FE), and Schottky emission electron sources (SE). Among these electron sources, the field emission electron source (FE) can emit electron beams with the best monochromaticity and high brightness, so it can reduce the chromatic aberration of the electron optical system and is used as an electron source for scanning electron microscopes with high spatial resolution. The W needle tip is widely used in the field emission electron source. The W needle tip uses the {310} crystal plane of tungsten to make the tip of the needle-shaped electrode (needle tip) pointed.

[0004] Figure 1 Energy diagram showing the emission principle of field emission electron source. By concentrating the external electric field F at the tip of the W needle to apply a high electric field, the electrons e in the W needle tip are emitted into the vacuum through the effectively thinned energy barrier in quantum mechanics. Since it can work at room temperature, the energy half-value full width ΔE of the electrons e is FE In addition, since a high-density electron beam is emitted from the narrow electron-emitting surface at the tip of the very sharp needle, the brightness is as high as 10 8 (A / cm 2 sr) characteristics.

[0005] In order to further narrow the energy half-value width ΔE of the field emission electron source and increase the brightness B, it is also proposed to use LaB with a work function Φ lower than W. 6 Field emission electron sources made of hexaboride nanowires (e.g., Patent Document 1). Since the work function barrier is lower than W, electrons can be transmitted through a lower electric field for field emission, which can further reduce the energy half-value full width ΔE. FE .

[0006] The inventors have developed and disclosed a cold field emission electron source (CFE) using CeB fabricated by a conventional floating zone method. 6 The front end of the hexaboride single crystal is shaped into a hemispherical shape by electrolytic grinding, electric field evaporation, etc., and further heated at 700-1400°C to form CeB with low work function. 6 {310} crystal plane, and field emission is performed at room temperature (Patent Document 2). Compared with the existing W field emission electron source, the field emission electron source of the hexaboride single crystal has better monochromaticity and can also reduce the radiation angle current density J Ω (μA / sr) to the radiation angle current density J Ω The ratio of (μA / sr) to the total current It (μA) J Ω / It is 6 to 13 (1 / sr) or more. According to the present invention, the chromatic aberration of a scanning electron microscope under a low acceleration voltage can be improved, and the observation of the extreme surface of a sample and the observation of light element materials such as carbon compounds with high spatial resolution can be achieved. In addition, the size of a hexaboride single crystal produced by a floating zone method or the like is about 0.1 mm to several mm, so it can be assembled into an electron source by hand or by machinery, and has the advantage of being cheap, simple and having a high yield compared to an electron source using nanowires with a diameter of about tens to hundreds of nm.

[0007] Furthermore, the inventors conducted research and found that in the hexaboride single crystal <100> A small facet of the (100) plane is formed at the top of the needle tip of the hexaboride single crystal with an axis. When the field-emission electrons from the (100) plane are detected, the emission current has a higher stability than that from the {310} plane. The main reason for this is that the work function of the (100) plane is slightly higher than that of the {310} plane, and it is not easily affected by the work function changes caused by the adsorbed gas. In addition, since the atomic surface density is higher than that of the {310} plane, the structure is stable, and the vibration of atoms is also suppressed. By heating, it is easy to form a flat and large small facet, and the electric field concentration is reduced. Furthermore, the local work function changes caused by gas adsorption and desorption during electric field electron emission are averaged within the large small facet, and the overall change becomes smaller. Therefore, in <100> The front end of the hexaboride single crystal needle tip of the axis forms a small facet of the (100) plane, which can improve the current stability when detecting the electron beam emitted from the (100) plane.

[0008] However, the high work function and the reduced electric field concentration indicate that the (100) plane is less likely to emit electrons than the {310} plane. In addition, electrons emitted from the {310} plane formed on the side of the needle tip around the (100) plane are uselessly emitted outside the optical axis of the electron microscope. Therefore, there is a radiation angle current density J ΩThe problem is that the ratio of (μA / sr) to the total current It (μA) is significantly reduced to less than 1 (1 / sr).

[0009] If the total current It (μA) is too much, the electrons emitted uselessly outside the optical axis will come into contact with the extraction electrodes in the electron microscope, and an electron beam will be generated from the electrode surface to stimulate the desorption of the gas. The electron beam will be incident on and adsorbed on the surface of the field emission electron source, causing the work function to change and damaging the current stability.

[0010] Therefore, the inventors have conducted in-depth research on the improvement method, and the result is disclosed: <100> The tip of the hexaboride single crystal needle of the hexaboride single crystal has a top facet of the (100) face surrounded by side facets consisting of at least four {n11} faces with high work functions and at least four {n10} faces with low work functions, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces, thereby reducing unnecessary emission current from the side facets and reducing the radiation angle current density J of the probe current taken out from the electron emission part of the top (100) face of the electron source of the needle of the hexaboride single crystal. Ω The ratio of (μA / sr) to the total current It (μA) emitted from the electron source is improved to 2.6 to 4 (1 / sr), making it possible to realize a stable electron source with less current fluctuation than before (Patent Document 3).

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: Japanese Patent No. 05660564

[0014] Patent Document 2: Japanese Patent No. 06694515

[0015] Patent Document 3: International Publication No. 2022 / 064557 Summary of the invention

[0016] Problems to be solved by the invention

[0017] In the background technology, as mentioned above, CeB is used 6 When detecting field emission electrons from the (100) plane, the emission current is more stable than that from the {310} plane. By increasing the radiation angle current density J Ω The ratio of (μA / sr) to the total current It (μA) J Ω / It, can further improve the stability. In addition, the inventors further studied the results of CeB 6In transition metal carbide single crystals such as HfC, ZrC, and TiC, which have a lower work function than W and a similar cubic crystal structure, if field-emission electrons from the (100) plane are detected, the emission current stability is higher than that from the {310} plane. The field emission electron source using these low work function materials increases the emission angle current density J Ω The ratio of (μA / sr) to the total current It (μA) J Ω / It, the more the generation of electron beam-stimulated desorbed gas can be suppressed, the higher the stability. Ω / It is expected to further improve and develop new technology to suppress gas adsorption to the electron emission surface.

[0018] The object of the present invention is to solve the above-mentioned problems by using a method of utilizing a stable electron beam emitted from a local area of ​​an electron emission surface having a desired shape with little influence of gas adsorption and stable time variation, thereby suppressing the mixing of unstable electron beams emitted from outside the emission surface, thereby providing a field emission electron source of hexaboride single crystal and transition metal carbide single crystal having both monochromaticity and long-term stability of emission current, and providing an electron beam device such as an electron microscope that requires high resolution and long-term stability and can be used for various purposes.

[0019] Means for solving problems

[0020] In order to solve the above problems, the present invention uses a field emission electron source, which is characterized in that <100> At the front end of the needle tip of the hexaboride single crystal or the transition metal carbide single crystal of the axis, a top facet of the first (100) face surrounded by side facets is formed, and the side facets are composed of at least 4 {n11} faces and at least 4 {n10} faces, which are integers of n=1, 2, 3, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces, and further a tiny crystal having a top facet of the second (100) face is formed within the surface of the top facet of the first (100) face, and electrons are emitted from the top facet of the second (100) face.

[0021] Here, LaB is used as a hexaboride single crystal. 6 and CeB 6 The single crystal with HfC, ZrC and TiC as the main component, as the transition metal carbide single crystal, has a low work function, high heat resistance, and a cubic crystal structure required for forming the tiny crystal with the top small face of the second (100) face at the front end of the above-mentioned needle tip, and is a material suitable for the present invention.

[0022] In addition, the top facet of the above-mentioned second (100) surface is smaller than the top facet of the first (100) surface, and the ratio of one side of the top facet of the first (100) surface to one side of the top facet of the second (100) surface is 0.05 to 0.35. In addition, the side surface of the microcrystal forming the top facet of the second (100) surface is also a cubic shape formed by the {100} face group, or the side surface is a trapezoidal shape formed by the {111} face group, and one side of the top facet of the second (100) surface is in the range of 10 to 60 nm. In addition, the height of the microcrystal is more than 0.7 times of one side of the top facet of the second (100) surface, thereby effectively solving the problem.

[0023] In addition, the top facet of the first (100) surface has a multi-level structure with a side of less than 1.5 μm and less than 4 levels, thereby suppressing the surface diffusion of the adsorbed gas from the tip side wall toward the electron emission surface, and effectively solving the problem.

[0024] As a method for manufacturing an electron source for solving the above-mentioned problems, in the present invention, <100> The front end portion of a rod of a hexaboride single crystal or a transition metal carbide single crystal is electrolytically ground to form a needle tip whose front end portion is shaped into a cone. By heating the needle tip and applying a strong electric field with positive polarity to the needle tip, a top facet of a first (100) face surrounded by side facets is formed at the front end of the needle tip. The side facets are composed of at least 4 {n11} faces of integers of n=1, 2, 3 and at least 4 {n10} faces, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces. Then, the electric field is mainly reduced, thereby forming a microcrystal having a top facet of a second (100) face in the top facet of the first (100) face at the front end of the needle tip, thereby solving the problem.

[0025] Furthermore, in order to solve the above-mentioned problems, in the present invention, in an electron beam device including an electron source, a sample stage for placing a sample, and an electron optical system for focusing electrons emitted from the electron source into a beam and irradiating the beam to the sample on the sample stage, <100> The front end of the needle tip of the hexaboride single crystal, transition metal carbide single crystal, or transition metal carbide single crystal of the axis forms a top facet of the first (100) face surrounded by side facets, and then a needle tip of a tiny crystal having a top facet of the second (100) face is formed within the surface of the top facet of the first (100) face to form a field emission electron source. The side facets are composed of at least 4 {n11} faces, which are at least integers of n=1, 2, 3, and at least 4 {n10} faces, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces.

[0026] Effects of the Invention

[0027] According to the present invention, it is possible to provide a new field emission electron source having both monochromaticity and long-term stability of emission current, and an electron beam device such as an electron microscope equipped with the field emission electron source and usable for various applications requiring high resolution and long-term stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an energy diagram showing the operating principle of a field emission electron source used in electron beam devices such as electron microscopes.

[0029] Figure 2 This is a perspective view showing the crystal structure (unit cell) of the hexaboride single crystal used in the electron source of Example 1.

[0030] Figure 3 This is a perspective view showing the crystal structure (unit cell) of a transition metal carbide single crystal used in the electron source of Example 1.

[0031] Figure 4 This is a schematic diagram of the state where a quadrangular prism or cylindrical rod is cut out along the

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

[100] crystal axis in Example 1.

[0032] Figure 5 This is a perspective view showing a state in which the metal tube and the rod of the hexaboride single crystal or the transition metal carbide single crystal of Example 1 are mounted on an assembly table.

[0033] Figure 6 This is a stereoscopic diagram illustrating the positional relationship between the metal tube, the crimping tool, and the stereoscopic microscope for mounting the rod of the hexaboride single crystal or the transition metal carbide single crystal on an assembly table, which illustrates the method for joining the metal tube and the rod of the hexaboride single crystal or the transition metal carbide single crystal of Example 1.

[0034] Figure 7 The figures illustrate the bonding structure of the metal tube of Example 1 and the tetrahedral prism rod of the hexaboride single crystal and the transition metal carbide single crystal, wherein (a) is a top view, (b) is a stereoscopic view, and (c) is a front cross-sectional view.

[0035] Figure 8 This is a front view of a structure serving as a prototype of the electron source for explaining the assembly structure of the electron source of Example 1.

[0036] Fig. 9 The figures illustrate the alignment fixture used during assembly of the electron source of Example 1, wherein (a) is a stereoscopic view of the metal tube, the filament, and the alignment fixture for aligning their positions, and (b) is a stereoscopic view of the metal tube, the tube holder, and the alignment fixture for aligning their positions after the filament is spot-welded.

[0037] Fig.10It is a figure which illustrates another example of the joining structure of the metal tube of Example 1 and the cylindrical rod of the hexaboride single crystal and the transition metal carbide single crystal, (a) is a top view, (b) is a stereoscopic view, and (c) is a front cross-sectional view.

[0038] Fig.11 This is a front cross-sectional view showing a state where the electron source structure is immersed in an electrolytic polishing liquid, for explaining a step of sharpening the rod tip of the electron source of Example 1 by electrolytic polishing to produce a needle tip.

[0039] Fig.12 This is a front cross-sectional view of a hexaboride needle tip, a transition metal carbide single crystal, and an electrolytic polishing liquid, illustrating the principle of manufacturing a needle tip by electrolytic polishing the front end of the rod of the electron source of Example 1.

[0040] Fig.13 This is a front view of the electron source of the hexaboride single crystal and the transition metal carbide single crystal of Example 1.

[0041] Fig.14 The figures show the process of forming the electron emission surface at the front end of the needle tip of Example 2 and Example 3, (a) is a stereoscopic diagram showing the shape of the front end of the needle tip after electrolytic polishing, (b) is a stereoscopic diagram showing the shape of the front end of the needle tip after the first stage of thermoelectric field treatment, and (c) is a stereoscopic diagram showing the shape of the front end of the needle tip after the second stage of thermoelectric field treatment.

[0042] Fig.15 The figures show the process condition range of the manufacturing method of Example 2, (a) shows the process condition range of the first stage of the thermoelectric field treatment, and (b) shows the process condition range of the second stage of the thermoelectric field treatment.

[0043] Fig.16 It is a cross-sectional view of the front end of the needle tip, showing the mechanism of forming a tiny crystal having a top small face of a second (100) face within a top small face of a first (100) face in the manufacturing method of Examples 2 and 3, (a) is a cross-sectional view illustrating the state of the top small face when the first stage of thermoelectric field treatment is performed, and (b) is a cross-sectional view illustrating the state of the top small face when the second stage of thermoelectric field treatment is performed.

[0044] Fig.17 The figures show the process condition range of the manufacturing method of Example 3, (a) is a figure showing the process condition range of the first stage of the thermoelectric field treatment, and (b) is a figure showing the process condition range of the second stage of the thermoelectric field treatment.

[0045] Fig.18These are field emission microscope observation images of the needle tip of the transition metal carbide single crystal using HfC in Example 4, (a) is a field emission microscope observation image of the field emission of the needle tip after the first stage of heat treatment, and (b) is a field emission microscope observation image of the field emission of the needle tip after the second stage of heat treatment.

[0046] Fig.19 In the field emission electron source of the transition metal carbide single crystal using HfC in Example 4, the radiation angle current density J relative to the total current It (μA) was measured in the case where only the top small face of the first (100) face was formed and in the case where the microcrystal with the top small face of the second (100) face was formed. Ω (μA / sr) curve.

[0047] Fig. 20 The radiation angle current density J is compared between the case where only the top facet of the first (100) plane is formed in the field emission electron source of the transition metal carbide single crystal of HfC in Example 4 and the case where the microcrystal having the top facet of the second (100) plane is formed. Ω (μA / sr) stability curve.

[0048] Fig.21 is a graph showing the change of the electron emission characteristics of the field emission electron source based on the size (length of one side) of the microcrystal with the top small face of the second (100) face of Example 5, (a) is a graph showing the change of the electric field intensity at the center of the tip tip, and (b) is a graph showing the radiation angle current density J Ω (c) is a graph showing the change in light source diameter.

[0049] Fig. 22 is a graph showing the change of the electron emission characteristics of the field emission electron source based on the ratio of the height of the microcrystal to the length of one side of the top small face of the second (100) surface in Example 5, (a) is a graph showing the change of the electric field intensity at the center of the tip tip, and (b) is a graph showing the radiation angular current density J Ω A graph showing the change in (μA / sr).

[0050] Fig.23The results of studying the relationship between the case where one side of the top facet of the first (100) face of Example 5 is 170 nm and the case where one side is 340 nm are shown. (a) is a graph showing the change in the electric field intensity at the center of the tip tip based on the size (one side length) of the microcrystal having the top facet of the second (100) face, (b) is a graph showing the change in the electric field intensity ratio relative to the ratio of the length of one side of the top facet of the second (100) face to the length of one side of the top facet of the first (100) face, and (c) is a graph showing the radiation angular current density J relative to the ratio of the length of one side of the top facet of the second (100) face to the length of one side of the top facet of the first (100) face. Ω (μA / sr) changes.

[0051] Fig.24 This is a three-dimensional image of the needle tip of Example 6, which is made of a multi-level structure with a first top (100) small surface at the front end of the needle tip.

[0052] Fig.25 It is a schematic cross-sectional view of the electron beam apparatus of Example 7 (a scanning electron microscope equipped with a field emission electron source using a hexaboride single crystal and a transition metal carbide needle tip of the present invention). DETAILED DESCRIPTION

[0053] In the following description, the crystal plane and crystal orientation are expressed in accordance with the Miller index. A single plane is designated by (), and an equivalent face group is designated by {}. A crystal axis direction is designated by [], and an equivalent axis direction is designated by <>.

[0054] As a result of intensive research by the inventors, a method for implementing the invention uses the following field emission electron source, which is characterized in that <100> The tip of the needle tip of the hexaboride single crystal or transition metal carbide single crystal of the axis forms a top facet of the first (100) face surrounded by side facets, wherein the side facets are composed of at least 4 {n11} faces and at least 4 {n10} faces, which are integers of n=1, 2, and 3, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces, and further a microcrystal having a top facet of the second (100) face is formed within the surface of the top facet of the first (100) face, and electrons are emitted from the top facet of the second (100) face. The reason for this is described below.

[0055] As disclosed by the inventors in Patent Document 3, a field emission electron source using the (100) plane has a higher emission current stability than a field emission electron source using the (310) plane, but the radiation angle current density J ΩThe problem is that the ratio of (μA / sr) to the total current It (μA) is low. As a solution, it is necessary to reduce the electron emission from the periphery other than the small facet of the top (100) face. Therefore, by developing a new manufacturing method, <100> The tip of the single crystal needle tip of the axis is formed with a top facet of the (100) face surrounded by side facets consisting of at least 4 {n11} faces of integers of n=1, 2, 3 and at least 4 {n10} faces, and an electron source needle tip is successfully manufactured in which the total area of ​​the side facets of the {n11} face with a high work function is greater than the total area of ​​the side facets of the {n10} face with a low work function, and the radiation angular current density J is reduced to Ω (μA / sr) relative to the total current It (μA) Ω / It increased to 2.6~4.

[0056] However, in this structure, the facet of the top (100) surface is also a flat structure. Although the area is reduced, the {n10} facets such as the {310} facets of the side facets adjacent to the top (100) facet are sharp, so the electric field is easily concentrated, making it difficult to J Ω / It is further improved.

[0057] Therefore, in an embodiment of the present invention, by further improving the manufacturing method of Patent Document 3, it was found that by forming a top facet of a first (100) face surrounded by side facets such that the total area of ​​the side facets of the {n11} facets is greater than the total area of ​​the side facets of the {n10} facets, and then forming a microcrystal having a top facet of a second (100) face within the top facet of the first (100) face, the electric field is concentrated on the top facet of the second (100) face, the electron emission from the highly stable (100) face is increased, and the electric field applied to the side facet {n10} face is relatively weakened, thereby suppressing the emission of unnecessary off-axis current and further improving J. Ω / It.

[0058] Hereinafter, the present invention will be described by way of embodiments with reference to the accompanying drawings. In the embodiments of the electron beam device, a scanning electron microscope (SEM) is used as an example for description, but the present invention is not limited thereto and can be applied to electron beam devices including a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), an electron beam exposure device, an electron beam 3D printer, an X-ray tube, etc. In addition, in the following drawings, in order to facilitate the understanding of the structure of the invention, the scale of each structure is appropriately changed.

[0059] Example 1

[0060] In Example 1, using Figures 2 to 13 The structure of the field emission electron source (hereinafter sometimes referred to as the electron source) of the present invention and its assembly method are described. The method for forming the top facets of the first and second (100) surfaces of the tip tip, which is a feature of the present invention, is described in Example 2 and later.

[0061] First, as the material of the electron source of the present invention, a rare earth hexaboride single crystal or a transition metal carbide single crystal is used. Specifically, lanthanide elements La, Ce, Pr, Nd, Sm, Eu, Gd, etc. can be used as the hexaboride single crystal, and LaB 6 , CeB 6 , PrB 6 、NdB 6 、SmB 6 ,EuB 6 , GdB 6 Equivalent chemical formula. Figure 2 Schematic diagram of the unit cell 200 is shown. The unit cell 200 has a cubic crystal structure in which a block of six boron atoms 2 is located at the body center of a simple cubic lattice of metal atoms 1. These materials are generally suitable as high melting point (e.g. LaB 6 :2483K、CeB 6 : 2463K), materials for electron sources with low vapor pressure, high hardness, resistance to ion impact and lower work function than W (such as LaB 6 , CeB 6 : about 2.6eV<W: about 4.3eV). Among them, LaB 6 , CeB 6 It is a material that is particularly widely used as a thermal electron source. As a hexaboride single crystal, LaB can be effectively used. 6 , CeB 6 A single crystal with a main component.

[0062] On the other hand, as the transition metal carbide single crystal, single crystals containing HfC, ZrC, and TiC as a main component can be used particularly effectively. Figure 3 A schematic diagram of the unit cell 201 is shown. The unit cell 201 has a cubic crystal structure in which metal atoms 1 and carbon atoms 3 are alternately arranged. These materials are suitable as materials for electron sources having a higher melting point than hexaboride single crystals (e.g., HfC: 4163K, ZrC: 3805K, TiC: 3443K), a lower vapor pressure, a higher hardness, and a lower work function than W (e.g., HfC, ZrC, TiC: about 3.3 eV).

[0063] In this embodiment, the CeB hexaboride single crystal is mainly used. 6 The following is an example of a transition metal carbide single crystal HfC. CeB 6 In rare earth hexaboride single crystals, there are f electrons with strong energy localization and high state density just below the Fermi level, and the electron density for supplying emission current is high, which is particularly suitable as a material for making hexaboride single crystals for field emission electron sources. On the other hand, HfC is a material with the highest melting point among transition metal carbide single crystals, making it particularly suitable.

[0064] In hexaboride single crystals and transition metal carbide single crystals, the manufacturing method of the present invention is roughly the same, but due to differences in melting point, reactivity with other materials that constitute the electron source (especially the metal tube that holds the single crystal), etc., there are some differences in the processing temperature and the assembly process of the electron source, which are appropriately explained.

[0065] like Figure 4 As shown, hexaboride single crystals and transition metal carbide single crystals can be grown by, for example, melt (liquid phase) crystal growth using a floating zone method, and can produce large single crystals 4 having a diameter of several mm and a length of several mm to several 10 mm, which grow in the

[100] crystal axis direction perpendicular to the (100) plane of the crystal trace surface where the crystal grows preferentially. The single crystal 4 is cut into a square prism with a side of several 100 μm, or a cylinder with a diameter of several 100 μm and a length of several mm by cutting or grinding for use. In this embodiment, a square prism with a side of 200 μm and a length of 5 mm or a cylinder with a diameter of 280 μm and a length of 5 mm is used. The length direction of the rod 5 is the

[100] direction.

[0066] In addition, the crystal structures of the above-mentioned hexaboride single crystal and transition metal carbide single crystal are as follows: Figure 2 and Figure 3 The figure shows a simple cubic lattice of a cubic crystal system. The (100) plane is equivalent to the (010) plane, the (001) plane, the

[100] crystal axis is equivalent to the

[010] crystal axis, the

[001] crystal axis, etc., and the effect is the same regardless of which plane or axis direction is used. Therefore, in the following description, the equivalent plane group is marked as {100}, etc., and the equivalent axis group is marked as <100> etc. for explanation.

[0067] Next, use Figures 5 to 10 The electron source of this embodiment has a structure in which the hexaboride single crystal or transition metal carbide rod 5 is arranged inside a metal tube 11 such as tantalum or niobium.

[0068] The material of the metal tube 11 used for joining with the rod 5 of the hexaboride single crystal or transition metal carbide single crystal is preferably a high melting point metal such as tantalum, niobium, etc., and is rich in ductility, and is easy to make a tiny metal tube 11 by drawing a tube, and is also easy to process the concave portion described later. In this embodiment, tantalum is used as an example, and a tiny metal tube 11 with an outer diameter of Φ500μm, an inner diameter of Φ320μm, a wall thickness of 90μm, and a length of 5mm is made.

[0069] Next, a method for joining the rod 5 of the transition metal carbide single crystal or hexaboride single crystal using the above-mentioned metal tube 11 is described. Figure 5 As shown in FIG. 1 , a base 13 is used to vertically raise a guide pin 12 having a diameter of 300 μm and a length of 1 to 3 mm that enters the inner diameter of the metal tube 11. The guide pin 12 is inserted into the metal tube 11 so that the metal tube 11 is vertically raised relative to the base 13. Next, in the case of using a hexaboride single crystal, a mixture of tetraboron carbide B having an average particle size of 0.01 to 0.1 μm is added. 4 The paste 14 of nanoparticles such as C and carbon resins such as furan resin is filled into the metal tube 11 from the top. Here, nanoparticles with an average particle size of 0.05 μm are used. On the other hand, in the case of transition metal carbide single crystals, they do not react with the metal tube 11 such as tantalum and niobium at high temperatures, so this filling process is not required.

[0070] Then, the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal is inserted from the upper part of the metal tube 11. The length h of the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal protruding from the inside of the metal tube 11 can be controlled by the guide pin 12. Figure 11-12 As will be described later, since the tip of one side of the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal is cut by electrolytic grinding, the protruding length h is increased to 2 to 3 mm.

[0071] Then, if Figure 6 As shown, the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal and the metal tube 11 are pressed together from two orthogonal axes and four directions in a plane perpendicular to the vertical direction of the rod 5 using a special tool developed by the inventor. Figure 6 In order to simplify the description, only the blade 15 of the crimping tool is shown. A pair of protrusions 150 for forming recesses in the metal tube 11 are provided at the front end of the blade 15 of the crimping tool. The blade 15 of the crimping tool is brought close to the metal tube 11 from the two-axis and four-axis directions with equal strokes, and the protrusions 150 are used to press the outer periphery of the metal tube 11, thereby forming a plurality of recesses on the metal tube 11. Figure 7 The recess 17 shown in (c).

[0072] During the operation, the positional relationship between the metal tube 11 and the rod 5 of the hexaboride single crystal or transition metal carbide single crystal is confirmed by a stereoscopic microscope 16, and the rotation axis of the rod 5 of the hexaboride single crystal or transition metal carbide single crystal is appropriately adjusted so that the side surfaces of the rod 5 of the hexaboride single crystal or transition metal carbide single crystal in the shape of a quadrangular prism are aligned with the stroke direction of the tool blade 15. Thus, a plurality of recesses 17 are formed in a manner of surrounding the central axis from the outer periphery of the metal tube 11, and the bottom of each recess 17 is pressed and contacted with the outer peripheral surface of the rod 5 of the hexaboride single crystal or transition metal carbide single crystal, thereby automatically aligning the rod 5 of the hexaboride single crystal or transition metal carbide single crystal with the central axis of the metal tube 11 and fixing it.

[0073] Figure 7 It is a schematic diagram of a rod 5 and a metal tube 11 of a hexaboride single crystal and a transition metal carbide single crystal joined by the method of this embodiment. Figure 7 (a) is a plan view of the joint portion viewed from the front end side of the rod 5 , (b) is a perspective view of the rod 5 , and (c) is a cross-sectional view of the rod 5 in the vertical direction.

[0074] When this joining method is used, the metal tube 11 and the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal can be pressed evenly from two axes and four directions to obtain a mechanically strong joint. In addition, since the metal tube 11 is approached from two axes and four directions with an even stroke and is flattened from the outer periphery of the metal tube 11, the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal in the shape of a quadrangular prism can be automatically arranged on the central axis of the metal tube 11 and joined, and the assembly accuracy is improved, so the axial alignment of the electron source becomes easy and the yield rate is also improved. Moreover, by joining at the upper and lower positions in the axial direction, the rod 5 can be prevented from tilting at the joint portion, which has the effect of further improving the accuracy of the axial alignment.

[0075] In addition, when using hexaboride single crystal, boron tetracarbide B is mixed during pressure bonding. 4 The paste 14 of carbon resin such as carbon nanoparticles and furan resin is deformed flexibly to fill the gap between the deformed metal tube 11 and the hexaboride single crystal rod 5 without gap. As the paste 14, small nanoparticles with an average particle size of 0.1 μm or less are used, so that the hexaboride single crystal rod 5 will not be damaged and broken during crimping, and the yield rate in the crimping process can be improved. In addition, the average particle size of the nanoparticles is set to 0.01 μm or more because if the average particle size is too small, B 4 The apparent volume of the C powder increases, making it difficult to mix the paste, and the production of the nanoparticles themselves becomes difficult, resulting in an increase in cost.

[0076] After the metal tube 11 is crimped to the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal, the dotted line portion 11-1 in which the guide pin 12 is inserted in the metal tube 11 is no longer needed, so after the metal tube 11 is removed from the guide pin 12, it is cut with a cutter to reduce the heat capacity of the metal tube 11. Then, in the case of the hexaboride single crystal, after the paste 14 is cured by heating in the atmosphere, it is heated at a high temperature of 1000°C or more in a vacuum for several hours to carbonize the paste 14. In this way, degassing from the paste 14 can be eliminated, and a reaction barrier layer can be formed to prevent the reaction at high temperature between the metal tube 11 of tantalum or the like and the rod 5 of the hexaboride single crystal.

[0077] Then, if Figure 8 As shown in the figure, a filament 18 of tungsten or the like is spot welded directly to a metal tube 11 of a rod 5 to which a hexaboride single crystal or a transition metal carbide single crystal is bonded. Furthermore, both ends of the filament 18 are welded to a pair of electrodes 20 fixed to a stem 19, thereby forming a structure 1001 as a prototype of an electron source. The structure 1001 is formed by bonding metals to each other, so that a strong bond can be easily obtained by spot welding.

[0078] use Fig. 9 A specific example of the welding process for forming the structure 1001 is described below. When spot welding the filament 18 of tungsten or the like is directly performed on the metal tube 11 of the rod 5 joined with the hexaboride single crystal or the transition metal carbide single crystal, a welding method such as Fig. 9 First, the filament 18 made of tungsten or the like and the metal tube 11 are accurately aligned using the positioning jig 21 - 1 , and the metal tube 11 and the filament 18 are spot welded.

[0079] Then, if Fig. 9 As shown in (b), the metal tube 11 with the filament 18 spot-welded thereto is accurately aligned with the tube holder 19 using the alignment jig 21-2, and the filament 18 is spot-welded to a pair of electrodes 20 fixed to the tube holder 19 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 the transition metal carbide single crystal are aligned with the center of the pair of electrodes 20 fixed to the tube holder 19, so that the structure 1001 can be axially aligned with high precision.

[0080] In the above embodiment, the rod 5 of hexaboride single crystal or transition metal carbide single crystal cut into a quadrangular prism shape is used as a component of the structure 1001. The rod 5 of hexaboride single crystal or transition metal carbide single crystal can be as follows: Figure 4 As shown, it is processed into a cylinder. Fig.10This is an example of using a cylindrical hexaboride single crystal or transition metal carbide single crystal rod 5-1. When joining the cylindrical hexaboride single crystal or transition metal carbide single crystal rod 5-1 to the metal tube 11, it is sufficient to press-fit at least from three equally spaced axes and three directions in a plane perpendicular to the plumb direction of the hexaboride single crystal or transition metal carbide single crystal rod 5-1 using a special tool developed in this embodiment. In particular, in the case of the transition metal carbide single crystal rod 5, it is possible to press-fit without using the paste 14, so it is easier to press-fit a cylindrical rod that is processed into a shape similar to the inner diameter of the metal tube 11, and is therefore preferred.

[0081] Fig.10 (a) shows a top view of the joint portion viewed from the front end side of the rod 5-1, (b) shows a three-dimensional view of the rod 5-1, and (c) shows a cross-sectional view of the rod 5-1 in the vertical direction. Fig.10 In (b) and (c), it is shown that the equivalent Figure 6 The state in which the portion 11-1 of the rod 5 of the hexaboride single crystal and the transition metal carbide single crystal of the metal tube 11 described above is cut off after the unnecessary portion 11-1 after crimping.

[0082] In addition, with the use of Figure 6 and Figure 7 Similarly to the case of the tetrahedral rod 5 of single crystal hexaboride or transition metal carbide, it is of course possible to join the metal tube 11 to the cylindrical rod 5-1 of single crystal hexaboride or transition metal carbide from two axes and four directions.

[0083] Next, in the structure 1001, the tip of the portion of the hexaboride single crystal or transition metal carbide single crystal rod 5 extending from the metal tube 11 is reduced in diameter into a conical shape by electrolytic grinding. Fig.11 As shown, the front end portion of the assembled hexaboride single crystal or transition metal carbide single crystal rod 5 is immersed in an electrolyte 22 such as nitric acid placed in a container 25, and a voltage is applied from an AC or DC power supply 24 between an opposing electrode 23 formed in a ring shape and made of platinum or the like, thereby performing electrolytic grinding.

[0084] like Fig.12 As shown, when the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal is immersed in the electrolyte (electrolytic polishing liquid) 22, a curved liquid surface is formed on the liquid surface, and the polishing speed of the liquid surface part is slow, and the polishing speed of the liquid part is fast. As the electrolytic polishing proceeds, the polishing area of ​​the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal in the part immersed in the electrolyte 22 becomes smaller, and the electrolytic current decays accordingly. If the power supply 24 is cut off when the electric field current decays to a certain level (cut-off current), as shown in FIG. Fig.12 As shown by the dotted line, it can be processed into a needle tip 6 with a tapered tip. The long side direction of the needle tip 6 is the

[100] direction.

[0085] Through the above steps, the assembly of the electron source is completed. Fig.13 The structure of the manufactured field emission electron source 100 is shown. The rod 5 of the hexaboride single crystal or the transition metal carbide single crystal having the needle tip 6 whose diameter is reduced by electrolytic grinding is held by the metal tube 11, and the metal tube 11 is welded to the filament 18, and further welded to the electrode 20 of the tube holder 19. Then, a plurality of recesses are provided on the outer periphery of the metal tube in a manner surrounding the central axis from at least two axial directions, and the bottom of each of the plurality of recesses is in contact with the outer periphery of the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal arranged inside. Thus, a strong and reliable bonding structure is formed in which the rod 5 of the hexaboride single crystal or the transition metal carbide single crystal will not fall off even when heated at a high temperature. In addition, when using a hexaboride single crystal, since it reacts with the metal tube 11 of tantalum, niobium, etc. at high temperature, a paste 14 of a mixture of nanoparticles of boron tetracarbide with an average particle size of 0.01 to 0.1 μm and a carbon resin is filled between the metal tube 11 and the hexaboride single crystal rod 5, and the paste is solidified and further carbonized to perform high heat-resistant bonding. On the other hand, in the case of a transition metal carbide single crystal, since it does not react with the metal tube 11 of tantalum, niobium, etc. at high temperature, this step is not performed.

[0086] Example 2

[0087] In Example 2, a process for forming the electron emission surface of the present invention by the tip 6 at the front end of the field emission electron source 100 of the hexaboride single crystal produced in Example 1 is described. The field emission electron source 100 of transition metal carbide is described in Example 3.

[0088] Fig.14 1 and 2 are diagrams showing the process of forming the electron emission surface at the tip end of Example 2 and Example 3. Fig.14 (a) is a perspective view showing the shape of the tip of the needle after electrolytic polishing. Fig.14 (b) is a perspective view showing the shape of the tip of the needle after the first stage of the thermoelectric field treatment. Fig.14 (c) is a perspective view showing the shape of the tip of the needle tip after the second stage of the thermoelectric field treatment. Fig.15 is a diagram showing the range of process conditions for the manufacturing method of Example 2, Fig.15 (a) is a diagram showing the process condition range of the first stage of the thermoelectric field treatment, Fig.15 (b) is a diagram showing the process condition range of the second stage thermoelectric field treatment.

[0089] First, as the first stage of the process, Fig.14The field emission electron source 100 of the hexaboride single crystal whose front end is electrolytically polished to form a needle tip 6 with a longitudinal direction of

[100] orientation at the front end is set in a vacuum chamber not shown in the figure, as shown in FIG. Fig.14 As shown in (b), <100> A top facet 42 of a first (100) face surrounded by side facets 41 is formed on the needle tip 6 of the hexaboride single crystal of the optical axis, and the side facets 41 are composed of at least 4 {n11} faces of integers of n=1, 2, 3 and at least 4 {n10} faces, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces. The work function of the {n11} faces of the hexaboride single crystal is higher than that of {n10}, and therefore, by making the total area of ​​the side facets of the {n11} faces greater than the total area of ​​the side facets of the {n10} faces, it is possible to reduce the unnecessary current emitted from the side facets 41 to the outside of the optical axis.

[0090] The manufacturing method is characterized in that Fig.15 As shown in the process area 151 of (a), the needle tip 6 is heated at 1500 to 1700° C. in a vacuum while applying 1 to 4.5×10 9 Thermoelectric field treatment with an electric field of V / m. Fig.15 (a) The effects of heating and electric field application in the first stage of the thermoelectric field treatment are specifically described.

[0091] First, the effect of heating in the first stage of the thermoelectric field treatment will be described. The hexaboride single crystal rod 5 is a high melting point material (LaB 6 :2210℃,CeB 6 :2190℃), but if heated to 700~1400℃ in vacuum, the crystal plane of the tip 6 at the front end is reconstructed by the movement of atoms on the surface, as shown in process area 152. In this case, there is a tendency for the (100) plane to grow at the top of the tip 6 and the {n10}>{n11} plane to grow on the side. Furthermore, when heated to above 1500℃ as in process area 153, evaporation from the surface gradually proceeds, the crystal structure of the surface is destroyed, and evaporation becomes more significant above 1700℃ in process area 154.

[0092] Therefore, heating at 1500-1700°C mainly plays the role of evaporation. When no electric field is applied to the needle tip 6 of the hexaboride single crystal, or when the electric field is 1×10 9 When heating is performed under a weak electric field of less than V / m, the needle tip 6 becomes thinner while maintaining a shape similar to that produced by electrolytic polishing, as in process region 153. Furthermore, when heating is performed to 1700° C. or higher, as in region 154, evaporation becomes intense, and it becomes difficult to maintain a shape similar to that produced by electrolytic polishing.

[0093] Next, the effect of the electric field applied to the needle tip 6 in the first stage of the thermoelectric field treatment will be described. This has two effects. First, the first effect will be described below.

[0094] In this embodiment, as described above, evaporation of the surface of the needle tip 6 is caused only by heating the process area 153 at 1500 to 1700°C, but electric field evaporation is also caused by applying an electric field that makes the needle tip 6 positive. The characteristics of electric field evaporation are different from evaporation by heating alone, and the tip of the needle tip 6 evaporates preferentially, so the front end of the needle tip 6 is processed into a shape that is generally close to a hemispherical shape.

[0095] In general, in a ZrO / W (100) tip for a Schottky electron source, when a strong electric field is applied to the heated tip 6, surface atoms diffuse due to electrostatic force, and crystal planes with high atomic density grow and accumulate in large quantities.

[0096] The inventors have conducted in-depth research and found that even if <100> In the needle tip of the hexaboride single crystal of the axis, if the needle tip 6 heated to 1500-1700°C as in the process area 151 is subjected to 1-4.5×10 9 A strong electric field of 100 V / m will also cause (100) face accumulation at the top of the needle tip 6. It can also be seen that the electric field that causes accumulation has no polarity dependence, and both positive and negative electric fields can cause (100) face accumulation.

[0097] However, when an electric field is applied to make the needle tip negatively polarized, the above-mentioned electric field evaporation effect does not occur, and a large amount of electron emission occurs from the needle tip of the hexaboride single crystal at a high temperature and with a high electric field applied. As a result, there is a risk of reduced vacuum due to the generation of desorbed gas stimulated by the electron beam, and discharge damage to the needle tip. Therefore, in the manufacturing method of this embodiment, it is preferred that the electric field applied be of positive polarity.

[0098] In addition, when a ratio of 4.5×10 9 When the electric field is stronger than V / m, the effect of electric field evaporation is too strong, and the front end of the needle tip 6 is processed into a hemispherical shape.

[0099] In the first stage of the thermoelectric field treatment (process area 151) of this embodiment, by appropriately combining the effect of the thermoelectric field evaporation and the effect of the deposition, it is possible to <100> A top facet 42 of the first (100) face surrounded by side facets 41 is formed on the needle tip 6 at the front end of the hexaboride single crystal of the axis, and the side facets 41 are composed of at least 4 {n11} faces of integers of n=1, 2, and 3 and at least 4 {n10} faces, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces. This is because, by the effect of thermoelectric field evaporation, the parts that are sharper than the overall curvature of the surface of the needle tip 6, such as the {n10} faces, are cut and difficult to grow, and, by the effect of accumulation, the growth of the (100) face is promoted at the top of the needle tip 6, and the growth of the {n11} faces is promoted on the sides surrounding the (100) faces, and in particular, the growth of the high-density crystal face of {111} is promoted. This is the effect of the first stage of thermoelectric field treatment of the present invention.

[0100] In the present invention, if Fig.14 As shown in (c), by newly performing the second stage of thermoelectric field treatment after this step, a microcrystal having a second top facet 43 with a (100) plane is formed within the surface of the top facet 42 of the above-mentioned (100) face. Here, the microcrystal forming the top facet of the second (100) face is a cubic shape whose side surface is also formed by the {100} face group, or a trapezoidal shape whose side surface is formed by the {111} face group.

[0101] Specifically, Fig.15 As shown in the process area 156 of (b), after the first (100) top facet 42 is formed by the first stage of the thermoelectric field treatment, the heating temperature is reduced to 1300°C to 1500°C, and the positive polarity electric field is also reduced to less than half of 1 to 2.25×10 9 V / m. The heating temperature is lowered to 1300-1500°C to suppress CeB 6 The purpose of reducing the electric field to less than half is to weaken the effect of accumulation.

[0102] Fig.16 The cross-sectional view shows Fig.15 (a) The first stage of thermoelectric field treatment and Fig.15 The structural changes that occur on the end surface of the first (100) top facet 42 of the needle tip 6 during the second stage of the thermoelectric field treatment of (b). Fig.16As shown in (a), the amount of atomic diffusion toward the front end of the needle tip 6 based on the electrostatic force of the electric field F is greater than the amount of atomic diffusion toward the bottom of the needle tip 6 based on the temperature T, and atomic diffusion toward the top of the needle tip 6 is promoted, and the (100) plane is promoted at the top, and the growth of the side facet 41 of the high-density crystal plane of the {111} plane is particularly promoted on the side surrounding the (100) plane, thereby causing accumulation. When starting from this state as shown in Fig.15 When the electric field F is reduced as in the second stage of the thermoelectric field treatment of (b), the amount of atomic diffusion toward the surface of the tip 6 is reduced. At this time, when the amount of atomic diffusion toward the surface below the tip 6 based on the temperature T is dominant, as shown in FIG. Fig.16 As shown in (b), the end face of the first (100) facet 42 of the top of the needle tip 6 is deformed, a step difference is generated in the (100) face, and a micro crystal of the second top facet 43 having a (100) plane is formed in the first top facet 42. In this embodiment, in order to suppress CeB 6 However, if the temperature T is too low, the amount of atoms diffusing toward the surface below the needle tip 6 will also decrease. Therefore, it is not preferable to lower the temperature to below 1300°C.

[0103] That is, the manufacturing method of the field emission electron source 100 can be summarized as follows. A high electric field is applied at a high temperature to a single crystal tip 6 of hexaboride or transition metal carbide with the long side direction in the

[100] orientation, which makes the tip 6 positively polarized, thereby causing accumulation due to the movement of atoms toward the front end of the tip 6 to form a top facet 42 of the first (100) surface. Then, by reducing the electric field applied to the tip 6, a microcrystal having a top facet 43 of the second (100) surface is grown within the surface of the top facet 42 of the first (100) surface.

[0104] In addition, this embodiment is CeB 6 For example, LaB has similar thermal and chemical properties such as melting point. 6 The same process can also be applied.

[0105] Through the above two-stage thermoelectric field treatment, <100> CeB of the axis 6 , LaB 6 A top face 42 of a first (100) face surrounded by side facets is formed on the needle tip 6 of a hexaboride single crystal with an equilongated direction in the

[100] orientation, and then a tiny crystal having a top face 43 of a second (100) face is formed within the surface of the top face 42 of the first (100) face, wherein the side facets are composed of at least 4 {n11} faces of integers n=1, 2, 3 and at least 4 {n10} faces, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces.

[0106] Example 3

[0107] Next, in this embodiment, use Fig.14 and Fig.16 , Fig.17 The process of forming an electron emission surface at the tip end of a transition metal carbide single crystal such as HfC, ZrC, and TiC is described. The melting point of a transition metal carbide single crystal is significantly higher than that of a hexaboride single crystal (HfC: 3890°C, ZrC: 3532°C, TiC: 3170°C, LaB 6 :2210℃、CeB 6 : 2190°C), the vapor pressure is also very low, so the process temperature and evaporation effect are different from those in Example 1, but the basic process idea is the same.

[0108] Fig.17 is a diagram showing the range of process conditions for the manufacturing method of Example 3, Fig.17 (a) is a diagram showing the process condition range of the first stage of the thermoelectric field treatment, Fig.17 (b) is a diagram showing the process condition range of the second stage thermoelectric field treatment.

[0109] First, as the first thermoelectric field treatment, similarly to the case of the hexaboride single crystal, Fig.14 The field emission electron source 100 of the transition metal carbide single crystal having a tip 6 formed at the front end thereof after electrolytic grinding is performed as shown in (a) is set in a vacuum chamber not shown in the figure. Fig.17 As shown in the process area 161 of (a), the needle tip 6 is heated at 1500 to 1800° C. in a vacuum while applying 3 to 6×10 9 V / m electric field. <100> A top facet 42 of a first (100) face surrounded by side facets 41 is formed on the needle tip 40 of the transition metal carbide of the optical axis, and the side facets 41 are composed of at least 4 {n11} faces and at least 4 {n10} faces, which are integers of n=1, 2, and 3, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces. Since the work function of the {n11} faces of the transition metal carbide single crystal is also higher than the work function of the {n10} faces, by setting the total area of ​​the side facets of the {n11} faces to be greater than the total area of ​​the side facets of the {n10} faces, it is possible to reduce unnecessary current emitted from the side facets 41 to the outside of the optical axis.

[0110] As shown in process region 162, when heating to 1500-1800°C in vacuum, the surface atoms move, especially the crystal plane of the tip 6 at the front end is reconstructed. In this case, there is a tendency for the (100) plane to grow at the top of the tip 6 and for the {n10}>{n11} plane to grow at the side. As shown in process region 163, heating to 1500-1800°C in vacuum and applying a ratio of 6×10 9 When the electric field is stronger than V / m, the effect of electric field evaporation is too strong, and the front end of the needle tip 6 is processed into a hemispherical shape.

[0111] The reason why the tip 6 has the same front end structure as that of the hexaboride single crystal is that the transition metal single crystal is a compound having the same cubic crystal structure as that of the hexaboride single crystal, and the geometric relationship between the side facets 41 and the top facets 42 that stabilize the surface energy during stacking is similar. However, reflecting the difference in melting point, etc., it is necessary to apply a higher temperature and a higher electric field than that of the hexaboride single crystal tip.

[0112] Next, in this embodiment, as the second thermoelectric field treatment, Fig.17 As shown in the process area 164 of (b), the heating is performed while maintaining the temperature at 1500 to 1800°C, and the positive electric field is reduced to less than half of 1 to 3×10 9 V / m. As a result, the amount of atomic diffusion toward the bottom of the needle tip 6 based on the temperature T is greater than the amount of atomic diffusion toward the surface of the front end of the needle tip 6 based on the electrostatic force of the electric field F, and the end face of the top face 42 of the first (100) surface is deformed, and a step difference is generated in the (100) surface, so that a micro crystal having a second top face 43 with a (100) plane can be formed in the surface of the first top face 42.

[0113] Example 4

[0114] In this embodiment, the electron emission characteristics of the field emission electron source made in the present invention are described. Here, an example of a field emission electron source using HfC, a transition metal carbide single crystal, is described, wherein the first top (100) face 42 of the transition metal carbide single crystal is a square shape of 170 nm in length × 170 nm in width, and the size of the microcrystal constituting the second top (100) face 43 is a cubic shape of 50 nm in length × 50 nm in width × 50 nm in height.

[0115] Although not described in this embodiment, in the case of a field emission electron source using a single crystal of a transition metal carbide such as ZrC, or using CeB 6 In the case of a field emission electron source of a hexaboride single crystal, although there are some differences, substantially the same characteristics can be obtained.

[0116] first, Fig.18(a) indicates that it comes from Fig.17 A field emission microscope image (FEM: Field Emission Microscope image) of the field emission electron source of HfC produced in the steps up to the first thermoelectric field treatment in (a), Fig.18 (b) means in Fig.17 (b) is a FEM image of the field emission electron source of HfC produced in the steps up to the second thermoelectric field treatment.

[0117] exist Fig.17 The needle tip 6 produced in the first thermoelectric field treatment step (a) is as follows Fig.18 As shown in the FEM image (a), the small face 42 of the first top (100) surface of the needle tip 6 is large and flat, so it is difficult to apply an electric field, and the emission current is relatively small and dark. On the other hand, the surrounding {310}{210}{110} and other {n10} small faces (n=1-3) are sharp, and the electric field is easily concentrated, so the emission current is relatively large and bright.

[0118] On the other hand, proceed to Fig.17 The needle tip manufactured by the process of the second thermoelectric field treatment of (b) is as follows Fig.18 As shown in the FEM image (b), the electric field is concentrated on the (100) surface of the second top facet 43 formed by the microcrystals formed in the surface of the top facet 42 of the first (100) surface, so the center of the needle tip becomes relatively bright. On the other hand, the electric field intensity of the facet 42 of the first top (100) surface that becomes the base and the side facets from the {n10} surface around it are relatively reduced and darkened.

[0119] Fig.19 Yes Fig.18 (a) The needle tip 6 is formed with only the first (100) facet 42 and Fig.18 (b) The radiation angle current density J per total current It (μA) of the needle tip 6 of the present invention formed with a microcrystal having a second (100) facet 43 Ω Line 1900 is the radiation angle 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 Line 1901 is the radiation angle current density J per total current It (μA) of the tip 6 of the field emission electron source of the micro crystal having the second (100) facet 43. Ω (μA / sr). The needle tip 6 of the present invention is shown as line 1901, and it can be seen that J Ω / It is increased to about 4 times above 12, and a large radiation angle current density J is obtained with a small total current It (μA) Ω (μA / sr).

[0120] Fig. 20 It is only formed Fig.18 The field emission electron source of the small face 42 of the first top (100) surface of (a) and the Fig.18 The radiation angle current density J of the field emission electron source of the microcrystal having the small face 43 of the second top (100) face of the present invention (b) Ω Line 2000 represents the radiation angle current density J of the tip 6 of the field emission electron source having only the first (100) facet 42. Ω (μA / sr), line 2001 represents the radiation angular current density J of the field emission electron source of the microcrystal formed with the small face 43 having the second top (100) plane. Ω (μA / sr).

[0121] The needle tip having only the facet 42 formed with the first top (100) face will Ω The initial value of (μA / sr) is set to 14μA / sr, and the field emission electron source formed with a micro crystal having a second (100) face 43 is set to twice that, i.e., 28μA / sr. The field emission electron source formed with only the face 42 of the first top (100) face, as shown by line 2000, has noise in the emission current, which increases over time and reduces the emission current. In contrast, as shown by line 2001, the field emission electron source formed with a micro crystal having a second (100) face 43 has a low emission current, although J is set to 28μA / sr. Ω The initial value of (μA / sr) was set twice as high, but there was almost no current noise and the current did not decrease but remained stable.

[0122] One of the reasons is that the field emission electron source having the small face 43 of the second top (100) surface has a higher J than the field emission electron source having only the small face 42 of the first top (100) surface. Ω / It is 4 times, so even if there are 2 times J Ω (μA / sr), half of the total current It (μA) is sufficient, and the electron beam generated from the electrode stimulates the degassing gas to be halved. As a result, the electron beam incident on the small face 43 of the second top (100) surface stimulates the degassing gas to be halved.

[0123] However, this alone cannot explain the large difference in stability. Therefore, as a second reason, it is believed that the step difference of the tiny crystals forming the small face 43 of the second top (100) becomes a diffusion barrier and a capture point for the adsorbed gas when the gas adsorbed on the side wall of the needle tip 6 diffuses toward the top of the needle tip 6, making it difficult for the adsorbed gas to reach the small face 43 of the second top (100) surface.

[0124] Thus, when the field emission electron source of the present invention is used, a J value four times or more can be obtained compared with the conventional field emission electron source. Ω / It>12(1 / sr), the radiation angle current density J required by the electron microscope can be obtained with a small total current It(μA) Ω Specifically, it is possible to obtain a J of 10 to 25 μA / sr, which is usually required in electron microscopy, with a very small total current It (μA) of It = 0.7 to 2 μA. Ω (μA / sr). In addition, under the condition of a total current It = 10 μA in a normal electron microscope, a large radiation angle current density J of 100 μA / sr or more can be obtained. Ω (μA / sr), for example, it can cope with the high-speed element analysis that requires a large radiation angle current density.

[0125] Example 5

[0126] The size of the microcrystal (here defined by the length of one side of the (100) facet of the microcrystal) can be controlled by the electric field, temperature, and holding time applied in the second thermoelectric field treatment of Example 2 and Example 3. Therefore, in this example, the change in electron emission characteristics caused by the size of the microcrystal formed within the facet 42 of the first top (100) face is investigated, and the results of finding the optimal microcrystal size, height, and the relationship between the size of the facet 42 of the first top (100) face and the size of the facet 43 of the second top (100) face are described.

[0127] Fig.21 This is a graph showing changes in the electron emission characteristics of the field emission electron source of Example 5 caused by the size (length of one side) of the microcrystal having the top small facet of the second (100) plane. Fig.21 (a) is a graph showing the change in the electric field intensity at the center of the tip end. Fig.21 (b) represents the radiation angle current density J Ω (μA / sr) changes in the curve, Fig.21 (c) is a graph showing changes in the diameter of the light source.

[0128] exist Fig.21 The electric field strength at the center of the tip 6 is shown in FIG. Fig.21 (a)), radiation angle current density ( Fig.21 (b)) and the light source diameter when used in an electron microscope ( Fig.21(c)) varies depending on the size of the cubic microcrystals of the second (100) top facet formed in the first top (100) facet. In addition, here, the size of the (100) plane in the plane of the first top facet 42 is an example of 170nm (a square of 170nm in length and 170nm in width), which is the same as Example 4. In addition, in Fig.21 In (a) to (c), the extraction voltage is 2 kV.

[0129] First, from Fig.21 As can be seen from the left end of (a), the electric field intensity at the center of the tip 6 when there is no microcrystal but only the first (100) top facet 42 is about 1.5×10 9 V / m, on the other hand, the size of the microcrystal on the second (100) top face 43 becomes larger, and the electric field intensity at the front center of the needle tip 6 on the second (100) top face 43 increases, and the size of the microcrystal reaches 3.2×10 9 V / m, and then slowly decrease.

[0130] in addition, Fig.21 The radiation angle current density J shown in (b) Ω (μA / sr) is the largest at 93μA / sr when the size of the microcrystals on the second (100) top face 43 is 30nm. Electric field intensity and radiation angle current density J Ω The reason why the size of the microcrystal with the maximum (μA / sr) is slightly different is that even if the electric field strength is strong, if the area of ​​the small face 43 of the second top (100) face that becomes the electron emission face is small, the radiation angle current density J Ω On the other hand, if the size of the microcrystals of the second (100) top facet 43 is too large, the electric field is difficult to concentrate, and the extracted radiation angle current density J Ω Therefore, there is an optimal range for the size of the micro crystals of the second (100) top facet 43 .

[0131] also, Fig.21 (c) shows how the light source diameter of the field emission electron source changes according to the size of the tiny crystals of the second (100) top face 43. The smaller the size of the tiny crystals, the smaller the light source diameter, and the resolution of the electron microscope is improved. On the other hand, when there are no tiny crystals of the second (100) top face 43, electrons are emitted from the relatively large first top (100) face 42, so the light source diameter becomes larger.

[0132] According to the above results, the size of the micro crystals of the second (100) top facet 43 can be neither too small nor too large. Specifically, the J value commonly obtained in conventional field emission electron sources can be easily obtained.Ω = 20μA / sr or more, and the light source diameter is also reduced to 10nm to 60nm, which is less than 2nm. Furthermore, if the size of the microcrystal is in the range of 20nm to 40nm, J can be obtained more than three times that of the past. Ω In particular, if the size of the microcrystal is set to 30 nm, a J of about 4 times the conventional one can be obtained. Ω / It, therefore preferred.

[0133] The above study is based on the case where the microcrystals on the second (100) top face 43 are cubic in shape. The length of one side of the microcrystal relative to the face 43 on the top (100) face is sometimes different in height. Fig. 22 The survey shows that Fig.21 When the optimal size of the microcrystal (here, defined as the length of one side of the small face 43 of the second top (100) surface) is 30 nm, the electric field and the radiation angle current density J are changed when the height of the microcrystal changes. Ω The result of how (μA / sr) changes.

[0134] Fig. 22 is a graph showing changes in the electron emission characteristics of the field emission electron source of Example 5 based on the ratio of the height of the microcrystal to the length of one side of the top facet of the second (100) plane, Fig. 22 (a) is a graph showing the change in the electric field intensity at the center of the tip end. Fig. 22 (b) shows the radiation angle current density J Ω (μA / sr) changes. Fig. 22 (a) Fig. 22 In (b), the extraction voltage is 2 kV.

[0135] The size (length of one side) of the tiny crystals relative to the second (100) top facet 43 decreases with height, as shown in FIG. Fig. 22 As shown in (a), the electric field strength decreases, as Fig. 22 As shown in (b), the radiation angle current density J Ω (μA / sr) also decreases. Fig. 22 It can be seen that in order to fully obtain the electric field concentration effect generated by the microcrystals on the second (100) top face 43, the height of the microcrystals on the second (100) top face 43 is preferably at least 0.7 times the size of the microcrystals (the length of one side).

[0136] Next, the results of studying the relationship between the size (length of one side) of the small face 42 of the first (100) top of the substrate and the size (length of one side) of the small face 43 of the second top (100) surface that becomes the electron emission surface are shown. Fig.23 The results of studying the relationship when one side of the top facet of the first (100) plane in Example 5 is 170 nm and 340 nm are shown. Fig.23 (a) is a diagram showing changes in the electric field intensity at the center of the tip tip depending on the size (length of one side) of a microcrystal having a top facet of the second (100) plane. Fig.23 (b) is a graph showing a change in the electric field intensity ratio relative to the ratio of the length of a side of the top facet of the second (100) surface to the top facet of the first (100) surface. Fig.23 (c) shows the radiation angle current density J Ω (μA / sr) versus the ratio of the length of one side of the top facet of the second (100) surface to the length of one side of the top facet of the first (100) surface. Fig.23 In (a) to (c), the extraction voltage is 3 kV.

[0137] Fig.23 (a) shows the dependence of the electric field intensity of the needle tip 6 on the size (length of one side) of the microcrystal when the size (length of one side) of the first (100) top face 42 is 170nm (line 2301) and when the size (length of one side) of the first (100) top face 42 is 340nm (line 2302), which is twice the size. When the size of the first (100) top face 42 of the substrate becomes larger, it is difficult for the electric field to concentrate even with the same size of the microcrystal, so it is known that the electric field intensity decreases.

[0138] Fig.23 (b) shows the results of the study of the normalized electric field intensity relative to 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 represents the case where the size of the first (100) top facet 42 is 170nm, and line 2304 represents the case where the size of the first (100) top facet 42 is 340nm. The change in the electric field intensity ratio is roughly determined by the ratio of the size of the facet 42 of the first top (100) face to the size of the facet 43 of the second top (100) face of the microcrystal.

[0139] Fig.23 (c) shows the radiation angle current density J Ω(μA / sr) depends on 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 microcrystals of the facet 43 of the second top (100) facet. Line 2305 represents the case where the size of the first (100) top facet 42 is 170nm, and line 2306 represents the case where the size of the first (100) top facet 42 is 340nm. The cases where the lead-out voltage is 2kV when the first top facet 42 is 170nm and the lead-out voltage is 3.2kV ​​when the size of the facet 42 of the first top (100) facet is 340nm are compared. Thus, although the lead-out voltages are 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 of the facet 43 of the second top (100) facet is set to 0.05 to 0.35, the electric field concentration effect of the microcrystals of the facet 43 of the second top (100) facet can be effectively utilized. Furthermore, 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 0.1 to 0.25, a J value three times higher than that of the conventional value can be obtained. Ω / It(Radiation angle current density J Ω In addition, when the ratio of the size of the first (100) top facet 42 to the size of the microcrystal of the second top (100) facet 43 is 0.15 to 0.2, a J of about 4 times the conventional one can be obtained. Ω / It is particularly preferred.

[0140] The following points can be learned from the above results.

[0141] 1) The size (length of one side) of the minute crystals of the facet 43 of the second top (100) surface is preferably in the range of 10 to 60 nm, further preferably 20 to 40 nm, and particularly preferably 30 nm.

[0142] 2) It is appropriate that the height of the fine crystals of the small face 43 of the second top (100) surface is at least 0.7 times the vertical and horizontal dimensions (the length of one side) of the fine crystals.

[0143] 3) The ratio of the size (length of one side) of the tiny crystals of the small face 43 of the second top (100) surface to the size (length of one side) of the small face 42 of the first (100) top of the substrate is preferably in the range of 0.05 to 0.35, more preferably in the range of 0.1 to 0.25, and particularly preferably in the range of 0.15 to 0.2.

[0144] 4) The minute crystal forming the top facet 43 of the second (100) plane is in the shape of a cube whose side surfaces are also formed by the {100} face group or in the shape of a trapezoid whose side surfaces are formed by the {111} face group.

[0145] Example 6

[0146] In the above-mentioned embodiments 2 to 5, the case where the first top (100) facet 42 serving as the base is a single-stage structure is described. In fact, the first top (100) facet 42 may be manufactured in a multi-stage structure according to the electric field, temperature, and holding time applied in the second thermoelectric field treatment of embodiments 2 and 3. If the first top (100) facet 42 is configured as a multi-stage structure, the number of stages of the diffusion barrier for the adsorbed gas diffused from the side wall of the needle tip 6 increases, thereby further improving the stability of the emission current.

[0147] Fig.24 This is a three-dimensional image of the needle tip of Example 6, which is made of a multi-level structure with a first top (100) small surface at the front end of the needle tip.

[0148] Fig.24 The structural diagram of the field emission electron source is shown in the case where the first top (100) facet 42 is a 2-level case. In this case, as in Example 5, the size (length of one side) of the microcrystal as the second top (100) facet 43 at the top is preferably in the range of 10 to 60 nm, further preferably in the range of 20 to 40 nm, and particularly preferably in the range of 30 nm, and the ratio of the size of the second (100) top facet 43 of the top microcrystal to the size of the first (100) top facet 42 of the base is preferably in the range of 0.05 to 0.35, further preferably in the range of 0.1 to 0.25, and particularly preferably in the range of 0.15 to 0.2.

[0149] This relationship remains the same even if the number of levels increases. Therefore, as the number of levels increases, the size of the bottom-level top (100) facet 42 increases, and the diameter of the needle tip 6 becomes thicker. Specifically, even if the size of the microcrystals of the second top (100) facet 43 is set to 10 nm, which is the smallest within the optimal range, and the ratio of the size of the microcrystals of the second (100) top facet 43 to the size of the first (100) top facet 42 is set to 0.35, which is the largest, if it is set to 5 or more levels, the diameter of the needle tip 6 will exceed 1.5 μm. In this case, the extraction voltage required to obtain field-induced emission electrons becomes too high, and it is difficult to operate in the electron microscope due to the constraints of the high-voltage power supply used in the electron microscope and the voltage resistance limitations between the electrodes. Therefore, the number of levels of the first (100) top facet 42 is preferably 4 or less.

[0150] Example 7

[0151] use Fig.25 Example 7 is described. Fig.25 It is a schematic cross-sectional view of the electron beam apparatus of Example 7 (a scanning electron microscope equipped with a field emission electron source using a hexaboride single crystal and a transition metal carbide needle tip of the present invention).

[0152] In Example 7, an example of a scanning electron microscope 1000 equipped with an electron source (field emission electron source) 100 using the facet 43 of the second top (100) face of the needle tip 6 of the transition metal carbide single crystal of HfC evaluated in Example 4 as an electron emission face is shown. 6 The same effect can be obtained in the case of hexaboride single crystals.

[0153] Fig.25 A schematic diagram of a scanning electron microscope 1000 is shown as an electron beam device of Example 7. The field emission electron source 100 is always heated by a constant current flowing through a heating power source 103 controlled by a computer 101 and a controller 102, and a positive voltage is applied to the needle tip 6 of the field emission electron source 100 at an extraction electrode 105 by an extraction power source 104, thereby emitting electrons by field emission.

[0154] The emitted electron beam 106 is accelerated toward the grounded anode 108 by the negative high voltage applied by the acceleration power supply 107, and is converged by the first condensing lens 109, the aperture 110, the second condensing lens 111, the objective lens 112, and the astigmatism correction coil 113, and is scanned by the deflection scanning coil 114 to irradiate the observation area on the sample 115, and the generated secondary electrons are detected by the secondary electron detector 116. Detectors other than the secondary electron detector are not shown in the figure, but other than the secondary electron detector, a reflected electron detector, an element analyzer, etc. are also used.

[0155] That is, the scanning electron microscope 1000 includes 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 beam onto the sample 115 on the sample stage 117 .

[0156] Electrons are emitted from a field emission electron source 100 that uses the (100) surface of the HfC needle tip 6 as the electron emission surface. The work function of the HfC of the emitted electrons is about 3.3 eV, which is lower than the 4.3 eV of the field emission electron source using the W{310} surface, so the energy half-value full width is narrow and the monochromaticity is good. Therefore, the chromatic aberration in the objective lens 112, etc. is reduced, and the electron beam 106 that is further reduced can be irradiated to the sample 115. In this way, a high-resolution scanning electron microscope image can be obtained. When using CeB 6 In the case of , the work function is about 2.6 eV, which is lower than 4.3 eV of the field emission electron source using the W{310} plane, so the same effect can be obtained while being narrower.

[0157] In addition, the field emission electron source 100 of the present invention emits electrons from the small face 43 of the second top (100) face of the small crystal, so the diameter of the light source is small, which helps to improve the resolution. Ω / It(Radiation angle current density J Ω (ratio of μA / sr to total current It (μA)) is 4 times higher, which can reduce the current outside the optical axis, thereby reducing the irradiation of excess electrons to the components around the electron source. Furthermore, it is possible to suppress the electron beam generated from the electrode from stimulating the desorbed gas, thereby improving the stability of the field emission electron source 100. Furthermore, since the step difference of the tiny crystals becomes a barrier for the adsorbed gas that diffuses on the surface of the side wall of the needle tip 6, it is possible to delay the adsorbed gas from reaching the small face 43 of the second top (100) surface, thereby further improving the stability of the field emission electron source 100. Therefore, the operation interval of the rinsing treatment required for the surface cleaning of the field emission electron source 100 can be extended, and stable measurements can be performed for a long time.

[0158] In addition, the J of the field emission electron source 100 of the present invention is Ω / It is more than 4 times higher than that of conventional electron sources, so a large radiation angle current density can also be obtained. In particular, in the case of elemental analysis, a large radiation angle current density is necessary and effective in order to shorten the analysis time.

[0159] The above-mentioned embodiments are examples described in detail in order to explain the present invention in an easy-to-understand manner, and are not limited to all the structures described. In addition, a part of the structure of a certain embodiment may be replaced with the structure of another embodiment, and a structure of another embodiment may be added to the structure of a certain embodiment. In addition, with respect to a part of the structure of each embodiment, other structures may be added, deleted, or replaced.

[0160] Explanation of symbols

[0161] 1…metal atom, 2…boron atom, 3…carbon atom, 4…single crystal, 5…rod, 6…needle tip, 11…metal tube, 12…guide pin, 13…base, 14…paste, 15…blade, 16…stereoscopic microscope, 17…recess, 18…filament, 19…tube holder, 20…electrode, 21-1, 21-2…positioning fixture, 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…leading out Source, 105…extraction electrode, 106…electron beam, 107…acceleration power supply, 108…anode, 109…first focusing lens, 110…aperture, 111…second focusing lens, 112…objective lens, 113…aberration correction coil, 114…deflection scanning coil, 115…sample, 116…secondary electron detector, 117…sample stage, 150…protrusion, 151~156…processing area of ​​the needle tip of the hexaboride single crystal, 161~165…processing area of ​​the needle tip of the transition metal carbide single crystal, 200, 201…simple cubic lattice, 1000…scanning electron microscope, 1001…structure.

Claims

1. A field emission electron source, characterized in that: At the front end of the needle tip of the hexaboride single crystal or the transition metal carbide single crystal of the <100> axis, a top facet of a first (100) face surrounded by side facets is formed, and a tiny crystal having a top facet of a second (100) face is formed within the top facet of the first (100) face, and electrons are mainly emitted from the top facet of the second (100) face, wherein the side facets are composed of at least 4 {n11} faces, which are integers of n=1, 2, 3, and at least 4 {n10} faces, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces.

2. The field emission electron source according to claim 1, characterized in that: The hexaboride single crystal is a single crystal with LaB6 or CeB6 as a main component.

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

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

5. The field emission electron source according to claim 1, characterized in that: The top facet of the second (100) face of the minute crystal is smaller than the top facet of the first (100) face.

6. The field emission electron source according to claim 1, characterized in that: The minute crystals are in a cubic shape with the top and sides consisting of {100} faces, or in a trapezoidal shape with the top face being a (100) face and the sides consisting of {111} faces.

7. The field emission electron source according to claim 1, characterized in that: The ratio of the length of one side of the top facet of the second (100) plane of the minute crystal to the length of one side of the top facet of the first (100) plane is in the range of 0.05 to 0.

35.

8. The field emission electron source according to claim 1, characterized in that: The length of one side of the top facet of the second (100) plane of the minute crystal is in the range of 10 to 60 nm.

9. The field emission electron source according to claim 1, characterized in that: The height of the minute crystal is greater than or equal to 0.7 times the length of one side of the top facet of the second (100) plane.

10. The field emission electron source according to claim 1, characterized in that: The small facet on the top of the first (100) face is a multi-level structure of 4 or less levels.

11. A method for manufacturing a field emission electron source, characterized in that: For a single crystal needle tip of hexaboride or transition metal carbide with the long side direction in the [100] orientation, a high electric field with positive polarity is applied to the needle tip at high temperature, thereby causing accumulation due to the movement of atoms toward the front end of the needle tip to form a top small face of the first (100) face. The electric field applied to the needle tip is then reduced, thereby causing a tiny crystal with a top small face of the second (100) face to grow within the plane of the top small face of the first (100) face.

12. An electron beam device comprising: an electron source; a sample stage on which a sample is placed; and an electron optical system that focuses electrons emitted from the electron source into a beam and irradiates the beam onto the sample on the sample stage, characterized in that: The electron source forms a top facet of a first (100) face surrounded by side facets at the front end of the needle tip of a hexaboride single crystal or a transition metal carbide single crystal of the <100> axis, and forms a tiny crystal having a top facet of a second (100) face within the top facet of the first (100) face, and mainly emits electrons from the top facet of the second (100) face, wherein the side facets are composed of at least 4 {n11} faces of an integer of n=1, 2, 3 and at least 4 {n10} faces, and the total area of ​​the side facets of the {n11} faces is greater than the total area of ​​the side facets of the {n10} faces.

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