Filament, emitter, and electron gun

Abstract

A filament that is used in an electron gun has grooves that extend along the length direction of the filament on the side surfaces of the filament.

Description

Filament, emitter, and electron gun

[0001] This invention relates to a filament, an emitter, and an electron gun.

[0002] Electron sources used in scanning electron microscopes (SEMs) and the like are well known.

[0003] Patent Document 1 describes an electron source aimed at providing an electron source that emits a stable electron beam even when subjected to external vibrations. The electron source comprises an insulating insulator, two conductive terminals spaced apart on the insulating insulator, a long filament stretched between the conductive terminals, and a needle-shaped cathode having an electron-emitting part attached to the filament. The electron source has a cross-sectional shape perpendicular to the axial direction of the filament, with a long direction and a short direction, the maximum length in the long direction being 1.5 times or more and 5 times or less the maximum length in the short direction, and the filament is stretched such that the long direction of the cross-sectional shape of the filament is ±10° or less with respect to the normal of the plane formed by three points: the two positions where the filament and the conductive terminals are attached, and the position of the cathode.

[0004] International Publication No. 2009 / 044871

[0005] The present invention provides a filament that can improve the accuracy of electron irradiation when used in an electron gun.

[0006] In other words, the present invention provides the following filament, emitter, and electron gun.

[0007] [1] A filament used in an electron gun, wherein the side surface of the filament has a groove extending along the length of the filament. [2] The filament according to [1], wherein, in a cross section perpendicular to the length of the filament, the direction in which the width of the filament is greatest is defined as the first direction, and the maximum width of the filament in a second direction perpendicular to the first direction is smaller than the maximum width of the filament in the first direction. [3] The filament according to [2], wherein the ratio of the maximum width of the filament in the first direction to the maximum width of the filament in the second direction is 1.5 or more and 5.0 or less. [4] The cross-sectional area of ​​the filament is 0.025 mm² ２A filament according to any one of [1] to [3] below. [5] A filament according to any one of [1] to [4] wherein the cross-sectional shape perpendicular to the length direction of the filament is polygonal. [6] A filament according to any one of [1] to [4] wherein the cross-sectional shape perpendicular to the length direction of the filament is elliptical. [7] An emitter comprising: a filament according to any one of [1] to [6]; a needle connected to the filament and emitting electrons from its tip; and a pair of electrodes connected to the filament and arranged to be spaced apart when projected onto a reference plane perpendicular to the Z direction in which the needle extends. [8] The emitter according to [7] wherein, in a cross-section parallel to the reference plane and passing through the connection portion between the filament and the pair of electrodes, the direction in which the width of the filament is maximum is defined as the third direction, and when the plane passing through the connection portion between the filament and the pair of electrodes and the tip of the needle is defined as plane S, the angle between the third direction and plane S is greater than 0 degrees and less than or equal to 90 degrees. [9] The emitter according to [8], wherein the angle between the third direction and the surface S is 80 degrees or more and 90 degrees or less.

[10] The emitter according to any one of [7] to [9], wherein the length of the filament between one end of the filament and the connection portion between the filament and the needle is 2 mm or more.

[11] The emitter according to any one of [7] to

[10] , wherein the filament comprises a first filament connecting one of the electrodes and the needle, and a second filament connecting the other electrode and the needle.

[12] An electron gun comprising the emitter according to any one of [7] to

[11] .

[0008] According to the present invention, a filament can be provided that can improve the electron irradiation accuracy when used in an electron gun.

[0009] This is a schematic perspective view showing a side view and a cross-section perpendicular to the longitudinal direction of a filament according to one embodiment. This is an example of an SEM image of the side view of the filament. This is a schematic perspective view showing a side view and a cross-section perpendicular to the longitudinal direction of a filament according to another embodiment. This is a schematic diagram of the emitter according to this embodiment. This is a schematic top view of the emitter according to this embodiment from the direction in which the needle extends. This is a schematic cross-sectional view of the electron gun according to this embodiment.

[0010] Embodiments of the present invention will be described below with reference to the drawings. In all drawings, similar components are denoted by the same reference numerals, and their descriptions are omitted as appropriate. Also, the drawings are schematic diagrams and do not correspond to actual dimensional ratios. For example, expressions indicating arrangement such as "in a certain direction," "along a certain direction," "parallel," and "orthogonal" include not only exact arrangements but also configurations where the arrangement is relatively displaced by tolerances or angles and distances that allow the same function to be achieved. In this specification, "A to B" indicating a numerical range means A or greater and B or less unless otherwise specified.

[0011] (Filament) Figure 1 is a schematic perspective view showing a side view and a cross-section perpendicular to the longitudinal direction of a filament according to one embodiment. Figure 2 is an example of an SEM image of the side view of the filament.

[0012] The filament 15 according to this embodiment is a filament used in an electron gun. As shown in Figures 1 and 2, the filament 15 has a groove 15a on its side surface that extends along the length of the filament 15.

[0013] The filament 15 used in the electron gun connects, for example, a needle that emits electrons from its tip to a pair of electrodes. External or internal vibrations of the electron gun may propagate to the filament 15, causing the filament 15 to vibrate. In this case, the needle connected to the filament 15 vibrates, and the direction in which the needle emits electrons changes, which may reduce the electron irradiation accuracy of the electron gun. According to the inventors' studies, the filament 15 in this embodiment has a groove 15a on its side surface that extends along the length of the filament 15, thereby improving the mechanical strength of the filament 15. In addition, the surface roughness of the side surface of the filament 15 is increased, which improves the stability of the bond with other members (e.g., needles) joined to the side surface of the filament 15. As a result, vibration of the filament 15 can be suppressed, and therefore the electron irradiation accuracy can be improved when used in an electron gun. In addition, it is possible to suppress the other members (e.g., needles) joined to the side surface of the filament 15 from falling off the filament 15.

[0014] The groove 15a of the filament 15 does not have to be perfectly parallel to the longitudinal direction of the filament 15. The angle between the groove 15a of the filament 15 and the longitudinal direction of the filament 15 may be 5 degrees or less, 3 degrees or less, 1 degree or less, or 0 degrees. The angle between the groove 15a of the filament 15 and the longitudinal direction of the filament 15 may change along the longitudinal direction of the filament 15.

[0015] In the embodiments shown in Figures 1 and 2, the filament 15 has a plurality of grooves 15a on its side surface that extend along the length of the filament 15. The plurality of grooves 15a may be distributed across the entire side surface of the filament 15.

[0016] The cross-sectional shape of the groove 15a in a cross-section perpendicular to the length direction of the filament 15 may be a polygon such as a triangle or a quadrilateral. In this case, "polygon" includes not only strictly polygons but also polygons with rounded corners (corner radius). In this embodiment, the cross-sectional shape of the groove 15a is determined by observing a cross-section perpendicular to the length direction of the filament 15 using a scanning electron microscope (SEM).

[0017] In a cross-section perpendicular to the length of the filament 15, the depth of the groove 15a is preferably 0.1 μm to 5.0 μm, more preferably 0.2 μm to 3.0 μm, and even more preferably 0.3 μm to 2.0 μm. By setting the depth of the groove 15a to be greater than or equal to the lower limit, the surface roughness of the side surface of the filament 15 is increased, thereby further improving the stability of the bond with other members (e.g., needles) joined to the side surface of the filament 15, and preventing other members (e.g., needles) joined to the side surface of the filament 15 from falling off the filament 15. Furthermore, by setting the depth of the groove 15a to be less than or equal to the upper limit, the mechanical strength of the filament 15 can be further improved, making the filament 15 less prone to breakage. In this embodiment, a cross-section perpendicular to the length of the filament 15 is observed using a laser microscope, and the average value obtained by measuring five cross-sections is taken as the depth of the groove 15a.

[0018] The length of one groove 15a may be 10 μm or more and 10,000 μm or less, 20 μm or more and 5,000 μm or less, or 30 μm or more and 3,000 μm or less. In this embodiment, the side surface of the filament 15 is observed using a scanning electron microscope (SEM), and the average value obtained by measuring three side surfaces is taken as the length of one groove 15a.

[0019] On the side surface of the filament 15, the number of grooves 15a per unit length is preferably 0.03 grooves / μm or more and 2.00 grooves / μm or less, more preferably 0.04 grooves / μm or more and 1.50 grooves / μm or less, and even more preferably 0.05 grooves / μm or more and 1.00 grooves / μm or less. By setting the number of grooves 15a per unit length to be above the lower limit, the stability of the bond with other members (e.g., needles) joined to the side surface of the filament 15 can be further improved, and the detachment of other members (e.g., needles) from the filament 15 can be suppressed. Furthermore, by setting the number of grooves 15a per unit length to be below the upper limit, the mechanical strength of the filament 15 can be further improved, and the filament 15 becomes less prone to breakage. In this embodiment, the number of grooves 15a per unit length is obtained by the following method. A cross section perpendicular to the length direction of the filament 15 is observed using a laser microscope, and the length of the outer edge of the cross section and the number of grooves 15a observed in the cross section are measured. The average value obtained from measuring the five cross-sections is taken as the number per unit length of groove 15a.

[0020] As shown in Figure 1, in a cross-section perpendicular to the length of the filament 15, the direction in which the width d of the filament 15 is maximum is defined as the first direction, and the direction perpendicular to the first direction is defined as the second direction. In this embodiment, the maximum width d of the filament 15 in the second direction is defined as the second direction. ２ Preferably, the maximum width d of the filament 15 in the first direction. １ It is smaller than [the specified value]. According to the inventors' studies, by using such a filament 15 and arranging the filament 15 in a predetermined direction relative to the electron gun, vibration of the filament 15 can be further suppressed. Therefore, when used in an electron gun, the electron irradiation accuracy can be further improved. The detailed configuration of the electron gun will be described later.

[0021] The maximum width d of the filament 15 in the second direction ２ The maximum width d of the filament 15 in the first direction relative to this. １ The ratio (d １ / d ２ ) is preferably greater than 1.0 and less than or equal to 5.0, more preferably between 1.5 and 5.0, and even more preferably between 2.0 and 4.0. d１ / d ２ By setting it to exceed the above lower limit value or be equal to or higher than the above lower limit value, the vibration of the filament 15 can be further suppressed. Therefore, when used in an electron gun, the electron irradiation accuracy can be further improved. Also, d １ / d ２ By setting it to be equal to or lower than the above upper limit value, the radiation loss during heating when used in an electron gun can be suppressed. Therefore, an increase in the current required for heating can be suppressed.

[0022] As shown in FIG. 1, the cross-sectional shape perpendicular to the length direction of the filament 15 may be polygonal. In this case, the "polygon" includes not only a strict polygon but also a polygon with rounded corners (with a corner R).

[0023] FIG. 3 is a schematic perspective view showing the side surface of the filament according to another embodiment and a cross-section perpendicular to the length direction. As shown in FIG. 3, the cross-sectional shape perpendicular to the length direction of the filament 15 may be elliptical. In this case, the "ellipse" includes not only a strict ellipse but also a slightly deformed ellipse. Note that the cross-sectional shape perpendicular to the length direction of the filament 15 may be a perfect circle.

[0024] The cross-sectional area of the filament 15 is preferably 0.005 mm ２ or more and 0.025 mm ２ or less, more preferably 0.008 mm ２ or more and 0.020 mm ２ or less. By setting the cross-sectional area of the filament 15 to be equal to or more than the above lower limit value, the vibration of the filament 15 can be further suppressed. Therefore, when used in an electron gun, the electron irradiation accuracy can be further improved. Also, when used in an electron gun, the filament 15 electrically connects a needle that emits electrons from the tip and an electrode. By setting the cross-sectional area of the filament 15 to be equal to or less than the above upper limit value, a thermal gradient occurs between the needle and the electrode when used in an electron gun, so heating can be performed with an appropriate current.

[0025] The filament 15 preferably contains a transition metal such as tungsten, more preferably at least one selected from the group consisting of tungsten, tantalum, rhenium, and molybdenum, and even more preferably tungsten. This ensures that when used in an electron gun, it exhibits sufficient electron emission characteristics even after electron emission has occurred for a certain period of time. When the entire filament 15 is considered to be 100% by mass, the content of the above components may be, for example, 50% by mass or more, 90% by mass or more, or 99% by mass or more.

[0026] The filament 15 preferably contains potassium in addition to the transition metal, or contains rhenium as the transition metal. This ensures that when used in an electron gun, it exhibits sufficient electron emission characteristics even after electron emission has occurred for a certain period of time. Furthermore, when rhenium is included as the transition metal, the filament 15 preferably contains tungsten and rhenium. When rhenium is included as the transition metal, the rhenium content in the filament 15 may be, for example, 2% by mass or more and 27% by mass or less. When potassium is added as a raw material in addition to the transition metal, the potassium content in the filament 15 may be, for example, 50 ppm or more and 100 ppm or less.

[0027] (Method for manufacturing a filament) The filament 15 according to this embodiment can be manufactured, for example, by appropriately adjusting the metal composition of the raw material containing a transition metal, sintering the raw material under appropriate conditions to obtain a metal bar, and then processing the bar into a linear shape by drawing. According to the inventors' studies, it is believed that in the process of stretching and processing the bar, the crystal structure of the metal changes, and grooves 15a extending along the length of the filament 15 are formed on the side surface of the filament 15.

[0028] According to the inventors' studies, it is believed that in the drawing process, processing the bar material while heating it at a temperature of, for example, 1200K to 1500K can facilitate the production of a filament 15 having grooves 15a. The heating time may be, for example, 100 hours to 500 hours.

[0029] According to the studies of the present inventors, it is considered that by adding potassium in addition to a transition metal as a raw material or by including rhenium as a transition metal, it becomes easier to manufacture the filament 15 having the groove 15a. When adding potassium in addition to a transition metal as a raw material, the content of potassium in the raw material may be, for example, 50 ppm or more and 100 ppm or less. When including rhenium as a transition metal, the content of rhenium in the raw material may be, for example, 2% by mass or more and 27% by mass or less.

[0030] (Emitter) FIG. 4 is a schematic view of the emitter according to the present embodiment. As shown in FIG. 4, the emitter 10 according to the present embodiment includes a filament 15, a needle 11, and a pair of electrodes 30. The needle 11 is connected to the filament 15 and emits electrons from the tip 11a. The pair of electrodes 30 is connected to the filament 15 and is arranged so as to be spaced apart when projected onto a reference plane perpendicular to the Z direction in which the needle 11 extends. Hereinafter, the direction in which the pair of electrodes 30 is arranged is the X direction, the direction in which the needle 11 extends is the Z direction, the direction perpendicular to the X direction and the Z direction is the Y direction, and the plane perpendicular to the Z direction is the reference plane. That is, the reference plane is a plane parallel to the XY plane.

[0031] As shown in FIG. 4, the pair of electrodes 30 includes one electrode 31 and the other electrode 33. The one electrode 31 and the other electrode 33 are arranged so as to be spaced apart in the X direction.

[0032] The emitter 10 according to the present embodiment includes at least one filament 15. In the embodiment shown in FIG. 4, the emitter 10 includes a single filament 15. In the embodiment shown in FIG. 4, the filament 15 has a shape in which the center of the linear filament is bent in a V shape.

[0033] In another embodiment, the emitter 10 includes a plurality of filaments 15. The filament 15 may include, for example, a first filament connecting one electrode 31 and the needle 11, and a second filament connecting the other electrode 33 and the needle 11.

[0034] The length of the filament 15 between one end of the filament 15 and the connection portion between the filament 15 and the needle 11 is preferably 2 mm to 10 mm, more preferably 3 mm to 8 mm, and even more preferably 4 mm to 6 mm. By setting the length of the filament 15 to below the above upper limit, vibration of the filament 15 can be further suppressed, thereby improving the electron irradiation accuracy when used in an electron gun. Furthermore, by setting the length of the filament 15 to above the above lower limit, a thermal gradient is created between the needle 11 and the electrode 30, allowing heating to be performed with an appropriate current.

[0035] In the embodiment shown in Figure 4, the needle 11 is connected to the filament 15 at its base end 11b, which is the end opposite to the tip 11a that emits electrons. The tip 11a of the needle 11 may be pointed or tapered.

[0036] The length of the needle 11 is preferably 100 μm or more and 5000 μm or less, more preferably 500 μm or more and 3000 μm or less, and even more preferably 1000 μm or more and 2000 μm or less. By setting the length of the needle 11 to be above the lower limit, the electron irradiation accuracy can be further improved when used in an electron gun. Also, by setting the length of the needle 11 to be below the upper limit, the generation of emission noise can be suppressed when used in an electron gun.

[0037] Needle 11 may include, for example, at least one selected from the group consisting of iridium, tungsten, tantalum, rhenium, molybdenum, and lanthanides. Lanthanides may include, for example, at least one selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Needle 11 may include, for example, compounds containing iridium and lanthanides such as iridium-cerium compounds and iridium-lanthanum compounds, single crystals of tungsten such as W(100) and W(310), and LaB ６ and CeB ６It may also contain at least one selected from the group consisting of lanthanides such as borides and HfC. The needle 11 is preferably Ir ２ Ce, Ir ３ Ce, Ir ７ Ce ２ , and Ir ５ It contains iridium cerium compounds such as Ce, and more preferably Ir ２ Ce and Ir ７ Ce ２ It includes at least one selected from the group consisting of the following. This ensures that when used in an electron gun, it exhibits sufficient electron emission characteristics even after electron emission has occurred for a certain period of time.

[0038] The emitter 10 may be equipped with a diffusion source (not shown) on the outer circumference of the central part of the needle 11. The material of the diffusion source may be, for example, an oxide of a metallic element selected from the group consisting of Ca, Sr, Ba, Sc, Y, La, Ti, Zr, Hf, and lanthanides.

[0039] Figure 5 is a schematic top view of the emitter needle according to this embodiment, taken from the direction in which the needle extends.

[0040] In the embodiment shown in Figure 5, one electrode 31 is connected to the filament 15 on one side in the Y direction, and the other electrode 33 is connected to the filament 15 on the other side in the Y direction. According to our research, by connecting one electrode 31 and the other electrode 33 to the filament 15 in this way, vibration of the filament 15 can be further suppressed. Therefore, when used in an electron gun, the electron irradiation accuracy can be further improved.

[0041] The third direction is defined as the direction in which the width of the filament 15 is maximized in a cross-section parallel to the reference plane, passing through the connection portion between the filament 15 and the pair of electrodes 30. The plane passing through the connection portion between the filament 15 and the pair of electrodes 30 and the tip 11a of the needle 11 is defined as plane S. The angle between the third direction and plane S is preferably greater than 0 degrees and 90 degrees or less, more preferably 80 degrees or more and 90 degrees or less, even more preferably 85 degrees or more and 90 degrees or less, and even more preferably 90 degrees.

[0042] The inventors have found that the direction in which the filament 15 is most likely to vibrate is perpendicular to the surface S. As a result of further diligent investigation, the inventors have found that by bringing the angle between the third direction and the surface S closer to 90 degrees, the vibration of the filament 15 can be further suppressed. By setting the angle between the third direction and the surface S within the above range, the vibration of the filament 15 can be further suppressed. Therefore, when used in an electron gun, the electron irradiation accuracy can be further improved. In addition, according to the inventors' investigation, by having a groove 15a on the side surface of the filament 15 that extends along the length of the filament 15, the mechanical strength of the filament 15 is improved, and as a result, vibration of the filament 15 can be suppressed. Therefore, when used in an electron gun, the electron irradiation accuracy can be further improved.

[0043] The emitter 10 according to this embodiment may be a thermal field emission emitter (TFE) or a cold field emission emitter (CFE).

[0044] (Electron gun) Figure 6 is a schematic cross-sectional view of the electron gun according to this embodiment. For convenience, in Figure 6, both ends of the filament 15 are shown on the near side of the paper relative to the pair of electrodes 30.

[0045] The electron gun 100 according to this embodiment includes an emitter 10. In the embodiment shown in Figure 6, the electron gun 100 includes a suppressor 50 and a base 70.

[0046] In the embodiment shown in Figure 6, a portion of the needle 11, the filament 15, a portion of one electrode 31, a portion of the other electrode 33, and a portion of the base 70 are housed inside the suppressor 50.

[0047] The suppressor 50 has an opening 50a. Electrons emitted from the tip 11a of the needle 11 are configured to be emitted to the outside of the suppressor 50 through the opening 50a. In the embodiment shown in Figure 6, the tip 11a of the needle 11 protrudes to the outside of the suppressor 50 through the opening 50a.

[0048] The base 70 is made of an insulating material such as resin and ceramic. The base 70 is fixed to the suppressor 50. One electrode 31 and the other electrode 33 are fixed to the base 70. One electrode 31 and the other electrode 33 penetrate the base 70 in the Z direction.

[0049] The electron gun 100 according to this embodiment can be used in an electron beam apparatus. Examples of electron beam apparatus include X-ray generators, electron microscopes, semiconductor manufacturing equipment, analytical equipment, and processing equipment.

[0050] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention.

[0051] The present invention will be described in detail below with reference to the examples. However, the present invention is not limited in any way to the descriptions in these examples.

[0052] (Preparation of Filaments) For each example and comparative example, the filaments (made of tungsten) shown in Table 1 were prepared. In Example 1 and Comparative Example 1, the cross-sectional shape perpendicular to the length direction of the filament is a rectangle with a long side of 220 μm and a short side of 80 μm. In Example 2, the cross-sectional shape perpendicular to the length direction of the filament is a circle with a diameter of 150 μm. In Example 3 and Comparative Example 2, the cross-sectional shape perpendicular to the length direction of the filament is a circle with a diameter of 125 μm. Also, d １ / d ２ In a cross-section perpendicular to the length of the filament, the direction in which the width of the filament is maximum is defined as the first direction, and the direction perpendicular to the first direction is defined as the second direction. The maximum width d of the filament in the second direction is defined as the first direction. ２ The maximum width d of the filament in the first direction relative to this. １ This shows the ratio.

[0053] (Fabrication of the electron gun) The filament was bent into a V-shape, and each end of the filament was welded to a pair of electrodes fixed to an insulator. Next, a needle (a tungsten single crystal with a (100) crystal orientation) was welded to the top of the filament. The length of the filament between one end and the connection point between the filament and the needle was set to 5.6 mm. In a cross section parallel to a plane (reference plane) perpendicular to the direction in which the needle extends, passing through the connection point between the filament and the pair of electrodes, the direction in which the filament width is maximum was defined as the third direction. When the plane passing through the connection point between the filament and the pair of electrodes and the tip of the needle was defined as plane S, the angle between the third direction and plane S was set to 89 degrees. Next, the tip of the needle was electropolished to sharpen it, and a diffusion source (zirconium oxide) was formed on the outer circumference of the central part of the needle to obtain an emitter.

[0054] As shown in Figure 6, an emitter was placed inside a cylindrical suppressor having a circular opening. The emitter was positioned so that its tip protruded from the suppressor's opening. A power supply for heating the emitter was connected to a pair of electrodes to obtain an electron gun.

[0055] (Measurement of distance D) Vacuum chamber (Vacuum level: 1 × 10⁻⁶) －７ An electron gun was placed inside Pa), and a camera was positioned to capture an image of the needle from the direction in which the needle extends (Z direction).

[0056] Images of the needle were taken from the direction in which the needle extends (Z direction). Next, the emitter was flushed five times under the condition that the needle temperature was raised from 25°C to 1530°C in 1 minute, and then the heating was stopped immediately and allowed to cool naturally. Images were taken similarly after each flushing process. From each image, the initial position O of the needle tip before flushing and the position P of the needle tip after the nth flushing process were determined. ｎ The following was obtained. The distance D between the two furthest points out of the six obtained was measured.

[0057] Table 1 shows the distance D for each example and comparative example.

[0058]

[0059] In each embodiment, it was confirmed that the distance D was shorter compared to Comparative Examples 1 and 2. In other words, in each embodiment, the displacement of the tip 11a of the needle 11 was suppressed when the flushing process was repeated compared to Comparative Examples 1 and 2.

[0060] This application claims priority based on Japanese Patent Application No. 2024-209311, filed on 2 December 2024, and incorporates all of its disclosures herein.

[0061] 10 Emitter 11 Needle 11a Tip 11b Base 15 Filament 15a Groove 30 Electrode 31 One electrode 33 Other electrode 50 Suppressor 50a Aperture 70 Base 100 Electron gun

Claims

1. A filament used in an electron gun, wherein the side surface of the filament has a groove extending along the length of the filament.

2. The filament according to claim 1, wherein, in a cross-section perpendicular to the longitudinal direction of the filament, when the direction in which the width of the filament is greatest is defined as the first direction, the maximum width of the filament in the second direction perpendicular to the first direction is smaller than the maximum width of the filament in the first direction.

3. The filament according to claim 2, wherein the ratio of the maximum width of the filament in the first direction to the maximum width of the filament in the second direction is 1.5 or more and 5.0 or less.

4. The cross-sectional area of ​​the filament is 0.025 mm². ２ The filament according to any one of claims 1 to 3, which is as follows:

5. The filament according to any one of claims 1 to 3, wherein the cross-sectional shape perpendicular to the length direction of the filament is polygonal.

6. The filament according to any one of claims 1 to 3, wherein the cross-sectional shape perpendicular to the length direction of the filament is elliptical.

7. An emitter comprising: a filament according to any one of claims 1 to 3; a needle connected to the filament and emitting electrons from its tip; and a pair of electrodes connected to the filament and arranged to be spaced apart when projected onto a reference plane perpendicular to the Z direction in which the needle extends.

8. The emitter according to claim 7, wherein, in a cross-section parallel to the reference plane and passing through the connection portion between the filament and the pair of electrodes, the direction in which the width of the filament is maximum is defined as the third direction, and when the surface passing through the connection portion between the filament and the pair of electrodes and the tip of the needle is defined as surface S, the angle between the third direction and surface S is greater than 0 degrees and less than or equal to 90 degrees.

9. The emitter according to claim 8, wherein the angle between the third direction and the surface S is 80 degrees or more and 90 degrees or less.

10. The emitter according to claim 7, wherein the length of the filament between one end of the filament and the connection portion between the filament and the needle is 2 mm or more.

11. The emitter according to claim 7, wherein the filament comprises a first filament connecting one of the electrodes and the needle, and a second filament connecting the other electrode and the needle.

12. An electron gun comprising the emitter described in claim 7.

Images