Charged particle source, charged particle gun, charged particle beam device

Abstract

The purpose of the present disclosure is to stabilize the probe current of a charged particle source over long periods of time. In a charged particle source according to the present disclosure, an emitter tip has a first flat surface perpendicular to an optical axis, a plurality of second flat surfaces parallel to the optical axis, and a plurality of third flat surfaces each disposed between the first flat surface and a second flat surface. Among the plurality of second flat surfaces, a first distance between second flat surfaces located at positions facing each other across the optical axis is greater than the outer diameter of the boundary portion between the tip and a needle.

Description

[Technical Field]

[0001] The present disclosure relates to a charged particle source that emits charged particles. [Background technology]

[0002] An electron source is an example of a charged particle source. Electron sources are mounted on the electron gun of electron beam application devices such as scanning electron microscopes (SEMs). Electron beams are emitted from the tip of the electron source. The energy difference between the vacuum level and the metal Fermi level of the electron source is the energy required for electrons to escape from the surface of the electron source, and is called the work function. When electrons on the surface of the electron source gain energy and exceed the work function, they are emitted from the surface of the electron source.

[0003] There are several ways to emit electrons, including thermionic electron sources, which accelerate and emit electrons excited by heating, and field emission electron sources, which emit electrons by the tunneling effect caused by the action of an electric field. Thermionic electron sources are heated to a high temperature, so they are less likely to adsorb surrounding gas molecules. This prevents the formation of a layer of other molecules on the surface of the electron source, making the work function of the electron source surface constant and resulting in high stability of the emitted current. Therefore, the operating atmosphere is 10 -3 They can be used even in low vacuums of around 100 Pa. However, with thermionic electron sources, the energy of the emitted electrons varies greatly. Electron emissions with this large energy dispersion result in large chromatic aberration when passing through a lens, which is one of the causes of low spatial resolution in SEM optical systems. On the other hand, field emission electron sources are characterized by small energy dispersion of the emitted electrons. This increases brightness and contributes to the high spatial resolution of SEMs. However, because field emission electron sources are typically used at temperatures below room temperature, the work function changes due to the adsorption of surrounding gases, causing fluctuations in the amount of electrons emitted.

[0004] In this way, the main parameters for electron emission are the temperature of the electron source and the electric field strength at the tip of the electron source. Among electron sources, there is a thermal field emission electron source (Schottky electron source) that uses both heat and electric field, and is used as an electron source that can achieve both stability of the emitted electron current and high spatial resolution.

[0005] SEM emits electrons from an electron source, then passes through multiple apertures before reaching the sample, using the electron beam to image and observe nanometer-order microstructures. This electron beam is called the probe current. SEM has high spatial resolution, so it is used in inspections of semiconductor device manufacturing processes. A typical example of such inspection is pattern defect inspection, and to perform accurate defect inspection, it is desirable for the contrast and brightness of the observed image to be consistent. If the probe current amount changes for each observed image, the image brightness will change, making automatic defect detection difficult. As such, semiconductor device inspection requires continuous operation with a stable probe current over long periods of time. Furthermore, with the recent increase in semiconductor pattern integration, high-throughput observation using a high-current probe is required.

[0006] Although Schottky electron sources are highly stable, during such long-term operation, the probe current fluctuates and becomes unstable due to changes in the surface condition, which depend on the vacuum environment and the operating conditions of the electron source (temperature and electric field strength of the electron source).

[0007] Prior patent documents related to the present application focus on the fact that the shape of the electron source significantly contributes to the electric field acting on the electron source. The objectives and features of the prior patent documents are introduced below.

[0008] In semiconductor device inspection equipment, a small source diameter is necessary to achieve high spatial resolution. The source diameter is the radius of the light source at the object plane when the radius of the irradiated probe current is taken as the image size of the SEM optical system. For the same current, a smaller light source results in higher brightness and higher spatial resolution. A small probe current has a small electron energy dispersion, which can suppress the expansion of the source diameter due to chromatic aberration. However, with long-term operation, the overall shape of the Schottky electron source changes, causing continuous changes in the electric field strength. This results in a reduction in emission current and changes in brightness.

[0009] Patent Document 1 aims to overcome this current stability issue and proposes the following shape of an electron source. The charged particle source including the thermionic electron source of Patent Document 1 has an emission facet, which is the surface that emits most electrons, and first and second side facets adjacent to the emission facet. An edge facet is also formed between the first and second side facets. The width of the edge facet is 20% to 40% of the width of the emission facet.

[0010] This shape is expected to maintain its shape even under operating conditions where a low electric field is applied at a small probe current. However, as mentioned above, there is also a strong demand for high-throughput inspection using a large probe current, and it is necessary to achieve both high spatial resolution. When an electron source is used at high temperature and high electric field to use a large current, the expansion of the source diameter due to chromatic aberration becomes dominant. As an alternative, the probe current can be increased by adjusting the optical magnification. This expands the capture of emitted electrons passing through the grain from near the optical axis perpendicular to the center of the emitting facet to off-axis areas.

[0011] The charged particle source of Patent Document 1 has an overall needle shape, and the tip portion shown in each figure of the document is considered to be formed at the tip of the needle. The tip portion shape in the document is formed so that the end of the side facet 113 is adjacent to the side surface of the needle. When the tip portion suddenly changes from a facet to a needle shape like this, the more the emitted electrons are off-axis, the more distorted the equipotential surface becomes. This increases the energy dispersion, causing the source diameter to expand.

[0012] The objective of Patent Document 2 is to provide a small source diameter and small energy dispersion of emitted electrons even under conditions where the probe current is large. As mentioned above, when a large current is obtained, the energy dispersion increases and the source diameter tends to expand. The technology described in Patent Document 2 makes the electric field acting on the surface of the tip of the electron source uniform over a wide range, thereby suppressing the energy dispersion when a large current is taken in.

[0013] Therefore, when the tip of the electron source is spherical as in Patent Document 2, the equipotential lines near the tip of the electron source are also spherical, so that the energy dispersion of the emitted electrons can be suppressed as much as possible in theory. However, in reality, the spherical surface is made up of many steps, which contribute to current instability. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] JP 2017-157558 A [Patent Document 2] WO2020115825A1 Summary of the Invention [Problem to be solved by the invention]

[0015] The atoms that make up the Schottky electron source move due to the free energy generated by heating. This causes the needle-shaped electron source to expand in diameter, making the tip round. This movement of atoms is defined as diffusion.

[0016] In particular, when comparing the tips of electron sources of the same diameter, the closer the shape is to a sphere, the higher the free energy, making it easier for the atoms that make up the electron source to diffuse. This causes the shape of the {100} plane, the electron-emitting surface, to change over time at the crystal surface at the tip of the electron source.

[0017] In the case of a charged particle source with a large diameter and a tip surface that is nearly spherical, as in the case of the charged particle source of Patent Document 2, the {100} plane tends to have two or more steps. These steps collapse from the edge of the {100} plane due to the diffusion described above, and move toward the center. The movement of these steps and the diffusion of atoms change depending on the balance between the temperature of the electron source and the strength of the electric field acting on the tip of the electron source to extract electrons.

[0018] The step portion of this electron source is composed of surfaces other than the {100} plane, which is the electron emission surface, making it difficult for electrons to be emitted. This step moves within the {100} plane of the tip, causing the probe current to become unstable each time the step passes. Furthermore, these effects cause the radius of the electron source tip to expand over the long term, and the change in shape causes the electric field strength to change. This causes the electron source tip to continue to diffuse, which is thought to make the probe current constantly unstable.

[0019] When the tip shape of the electron source is close to spherical, high spatial resolution can be expected, but maintaining the balance between heat and electric field is extremely difficult, and the probe current may become periodically unstable. Electron sources used for inspection and length measurement in scanning electron microscopes and the like must maintain a stable electron emission rate from the tip {100} face for a long period of time.

[0020] The present disclosure has been made in view of the above-mentioned problems, and has an object to stabilize the probe current of a charged particle source over a long period of time. [Means for solving the problem]

[0021] In the charged particle source according to the present disclosure, the emitter tip has a first flat surface perpendicular to the optical axis, a plurality of second flat surfaces parallel to the optical axis, and a plurality of third flat surfaces arranged between the first flat surface and the second flat surfaces, and a first distance between the second flat surfaces, which are positioned opposite each other across the optical axis, is greater than the outer diameter of the boundary between the tip and the needle portion. [Effects of the Invention]

[0022] The charged particle source according to the present disclosure can easily maintain a stable shape. The shape of the {100} plane is stable in the four side directions as well as the tip, making it possible to more firmly maintain the shape of the tip. [Brief explanation of the drawings]

[0023] [Figure 1] 1 shows an overall view of an electron source according to a first embodiment. [Figure 2] 1 is an enlarged view of the vicinity of the tip of a needle part 101 of an electron source. [Figure 3] 10 is an enlarged view of the tip shape of the charged particle source according to the second embodiment. FIG. [Figure 4] Deformation of the electron source tip due to diffusion of tungsten atoms is shown. [Figure 5] FIG. 10 is an enlarged view of the tip shape of the charged particle source according to the third embodiment. [Figure 6] FIG. 6 is a configuration diagram of a charged particle beam device 600 according to a fourth embodiment. [Figure 7] FIG. 10 is a configuration diagram of a charged particle beam device according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] <Embodiment 1: Basic Principle> The basic principles of the embodiments of the present disclosure will be described below, followed by a specific configuration of the embodiments. The radius of the electron source is defined as r, and the increase in the radius of the electron source per unit time due to thermal diffusion is defined as dr / dt. The change in radius over time when an electric field is applied in addition to heating the electron source is expressed as (dr / dt)F If we define it as follows, it can be expressed by the following equation: where F is the electric field applied to the tip of the electron source, and ν is the surface tension acting on the surface of the electron source: (dr / dt) F =(1-F 2 r / 8πν)dr / dt.

[0025] (1-F 2 It is possible to suppress deformation due to diffusion by applying an electric field of F or greater where r / 8πν) = 0. A spherical tip has the advantage of being able to apply a uniform electric field over a wide area, but if electrons are emitted under unbalanced conditions, diffusion will occur throughout the entire tip of the electron source.

[0026] In order to keep the curvature of the tip of the electron source constant over as wide a range as possible, it is effective to have a shape that is close to a sphere with a constriction. This allows the curvature of the leading edge related to the probe current to be constant. However, by having a portion where the curvature changes locally rather than being a perfect sphere, the tip shape can be maintained for a long period of time.

[0027] Therefore, the charged particle source according to the present disclosure has a constriction near the tip of a needle-like material, typically single-crystal tungsten, and a polyhedron-shaped tip portion beyond the constriction. This polyhedron has {100} planes on the top and four sides. The {100} plane on the top is the center, and between the {100} plane on the side, there is a {110} plane inclined at 45° from the top. This creates a strong electric field locally around the {100} plane, and (1-F 2 The value of r / 8πν can be brought close to 0. In addition, because the tip shape is constricted and close to a regular polyhedron, the four side surfaces also have a similar shape to the tip, and similar crystal growth is observed in all directions. In other words, the above effects can be achieved by making the bottom and side surfaces of the tip a charged particle source composed of rotationally symmetric crystal planes.

[0028] <First Embodiment: Configuration of Charged Particle Source> 1 shows an overall view of an electron source according to a first embodiment of the present disclosure. In this first embodiment, a configuration example of a Schottky electron source made of tungsten will be described as a typical charged particle source.

[0029] The electron source is composed of a needle part 101 that tapers towards the tip, a V-shaped bent filament part 102, and a zirconia part 103. The base of the needle part 101 is fixed to the filament part 102 by welding. Zirconia is applied to the middle of the needle part 101, and by applying electricity and heating the filament part 102, both the needle part 101 and the zirconia part 103 are heated.

[0030] FIG. 2 is an enlarged view of the vicinity of the tip of the needle portion 101 of the electron source. The upper part of FIG. 2 is a side view, and the lower part of FIG. 2 is a bottom view (with the optical axis of the electron beam in the depth direction). If the central axis of the electron beam emitted from the tip of the electron source is defined as optical axis 207, then optical axis 207 is coaxial with the needle portion 101. The needle portion 101 has a constricted portion 201 near the tip, with width L1 > L3, as shown in FIG. 2. The radius of the electron source temporarily increases from the constricted portion 201 toward the tip. Thereafter, it assumes a polyhedron-like shape with multiple flat surfaces. The portion from the constricted portion 201 to the tip is defined as a polyhedron portion 202. The constricted portion 201 is located at a position where a sphere circumscribing a plane perpendicular to the optical axis 207 (first flat surface 203) and a sphere circumscribing a side surface parallel to the optical axis 207 intersects with the needle portion 101.

[0031] The polyhedron portion 202 has the following surfaces: a first flat surface 203 that is perpendicular to the optical axis 207; second flat surfaces 204 and 205 that are parallel to the optical axis 207; and a third flat surface 206 between the first flat surface 203 and the second flat surface 204. The second flat surface is composed of {100} and {110} planes that are four-fold symmetric about the optical axis 207. The second flat surface 204 ({100} plane) and the second flat surface 205 ({110} plane) are alternately arranged at 45° intervals. The third flat surface 206 is arranged in a straight line on the surface of the polyhedron portion 202 between the first flat surface 203 and the second flat surface 204.

[0032] The electron source in this embodiment is obtained by processing a single crystal of tungsten into a needle shape, and the optical axis direction is <100>. When the width is longer in the optical axis direction, it is the second flat surface 204 ({100} plane), and when it is shorter in the optical axis direction, it is the second flat surface 205 ({110} plane). The third flat surface 206 is composed of the {110} plane.

[0033] Regarding the second flat surface 204 ({100} plane), when the width in the direction perpendicular to the optical axis 207 is defined as r1 and the width in the direction parallel to the optical axis is defined as r2, r1 < r2. When compared with the distance L2 in the optical axis direction from the first flat surface 203 to the constricted portion 201 position, L2 > r2. When the diameter of the constricted portion 201 is L3, L1 > L3 > r1.

[0034] Zirconia diffuses from the zirconia portion 103 in FIG. 1 toward the tip of the electron source, forming a mixed layer with tungsten. As a result, the work function of the {100} plane decreases, and electrons are emitted from the {100} plane. In particular, the electrons emitted from the {100} of the first flat surface 203 are used as the probe current of the scanning electron microscope. In order for the probe current to be stably emitted, the shape of the first flat surface 203, which is the electron emission surface, needs to be stable.

[0035] In the tungsten atoms constituting the electron source, surface tension with heat as a parameter acts, and atoms diffuse in the direction of increasing radius. As a result, the shape changes over time, the electric field strength and the size of the crystal plane do not become constant, and the probe current becomes unstable. On the other hand, the electron source in this embodiment has a constricted portion 201, and the constricted side and the tip side of the polyhedral portion 202 have a symmetric shape. Therefore, diffusion occurs in the opposite direction in the constricted portion 201. It is considered that this has the effect of suppressing the change in the dimension L1 of the polyhedron due to diffusion.

[0036] In the present embodiment, a crystal structure that is rotationally symmetric with respect to the bottom and side surfaces allows a uniform electric field to be applied from the first flat surface 203 to the side surfaces, compared to electron sources whose tip shape changes suddenly from the electron emission surface to a needle shape, such as when the tip shape is a cone or pyramid. This makes it easy to maintain the tip shape for a long period of time.

[0037] <Embodiment 2> 3 is an enlarged view of the tip shape of a charged particle source according to a second embodiment of the present disclosure. As in FIG. 2, the upper part of FIG. 3 is a side view, and the lower part of FIG. 3 is a bottom view. In addition to the features of the first embodiment, the charged particle source according to the second embodiment is characterized in that the first flat surface 203 has a rectangular shape. When the first flat surface 203 is rectangular as shown in FIG. 3, changes in shape due to diffusion can be more effectively suppressed compared to when the first flat surface 203 is circular.

[0038] Diffusion can be expressed as the surface free energy of tungsten atoms by the following equation: μ = Ω{νκ-(1 / 2)ε0F 2} where μ is the free energy, Ω is the volume of a tungsten atom, ν is the surface tension, κ is the local curvature, ε0 is the dielectric constant, and F is the electric field. The free energy gradient between adjacent surfaces causes atoms to diffuse from higher energy potentials to lower energy potentials.

[0039] FIG. 4 shows the deformation of the electron source tip due to the diffusion of tungsten atoms. FIG. 4 is a side view further enlarged around the first flat surface 203. When tungsten atoms diffuse according to the above formula, the tungsten atoms in the surface area enclosed by the dotted line in FIG. 4 move along the side toward the base, away from the first flat surface 203. In other words, the first flat surface 203 gradually narrows. This causes a step to appear at the edge of the first flat surface 203, as shown in the surface after diffusion depicted by the solid line. Even after the step appears, atoms continue to move from the edge of the step, causing the step to become smaller toward the center. This movement of the step within the first flat surface 203 makes the probe current unstable. However, the term (1 / 2)ε0F, which uses the electric field as a parameter, 2However, by balancing with the surface tension term νκ, it is possible to stop the movement of the atoms at that position.

[0040] When the shape of the first flat surface 203 is quadrilateral as in this embodiment, there are crystal planes adjacent to the first flat surface 203 that form each side. These adjacent planes are the third flat surface 206 or the {112} planes that exist between the third flat surfaces 206. If the angle formed by the four sides of the quadrilateral of the first flat surface 203 and the adjacent plane is defined as α (see FIG. 3), the third flat surface 206 is inclined at 45° relative to the first flat surface 203 from the crystal structure, resulting in an edge with an angle of α = 180° - 45° = 135° or more. This results in an edge with a small curvature locally, which suppresses surface tension due to heat and generates a strong electric field, approaching a balanced direction.

[0041] The quadrangular shape of first flat surface 203 includes not only a strict quadrangle but also a quadrangle having rounded corners and sides but an overall quadrangle shape. Note that the actual α may vary by about ±10° from the calculated value due to distortion of the crystal structure, etc.

[0042] <Third Embodiment> 5 is an enlarged view of the tip shape of a charged particle source according to embodiment 3 of the present disclosure. As in FIG. 2, the upper part of FIG. 5 is a side view, and the lower part of FIG. 5 is a bottom view. Embodiment 3 is a modification of embodiment 2, and as shown in FIG. 5, the width of the third flat surface 206 is defined as r3, and the width of the region between each third flat surface 206, represented by the {112} plane, is defined as r4.

[0043] The first flat surface 203 is quadrilateral, and the orientation of the corners and sides is rotated by 45° depending on the ratio between the width r3 of the third flat surface 206 surrounding the first flat surface 203 and the spacing r4. In this embodiment, r3≦r4, and the third flat surface 206 is arranged in the orientation of the quadrilateral corners (when the line connecting the center of the first flat surface 203 and the corner is extended, it intersects with the third flat surface 206).

[0044] As shown in Figure 5, the corners of the square of the first flat surface 203 are aligned with the third flat surfaces 206, which are located on the inclined surface at 90° intervals. The edge angle α in this case is more obtuse than in the second embodiment, approximately 145° or greater. The sharper the edge, the stronger the electric field concentrated at the edge. This causes the electric field strength to concentrate on the periphery within the first flat surface 203, resulting in a difference in electric field strength between the paraxial portion and the off-axis portion with respect to the optical axis 207. This increases energy dispersion, and the source radius increases due to chromatic aberration of the lens. This is one of the causes of resolution degradation when used in a scanning electron microscope and should be avoided in terms of electron source performance.

[0045] In the second and third embodiments, there is no particular limitation on the ratio between the width r3 of the third flat surface 206 and the width r4 of the region between the third flat surfaces, including the {112}. The electric field applied to the edge portion is optimized by changing the ratio of the surface sizes around the first flat surface 203 according to the electron emission conditions of the electron source. This makes it possible to achieve both a stable probe current due to the stabilization of the first flat surface 203 and a small state of electron energy dispersion, which is a cause of chromatic aberration.

[0046] <Fourth Embodiment> 6 is a configuration diagram of a charged particle beam device 600 according to a fourth embodiment of the present disclosure. The charged particle beam device 600 is equipped with an electron source 601 according to any one of the first to third embodiments and can be used as a scanning electron microscope.

[0047] The charged particle beam device 600 has an extraction electrode 602 directly below and facing an electron source 601. Electrons are extracted from the electron source 601 by applying a voltage to the extraction electrode 602. The electron source 601 and extraction electrode 602 can form an electron gun (charged particle gun). A condenser lens 603 is provided in the middle of the charged particle beam device 600, through which an electron beam 605 passes and is focused. The condenser lens 603 adjusts the amount of current of the emitted electron beam 605. An objective lens 604 is provided in the lower stage, and focuses the electron beam 605 toward a sample 606.

[0048] <Fifth Embodiment> 7 is a configuration diagram of a charged particle beam device according to a fifth embodiment of the present disclosure. FIG. 7 shows the periphery of an electron source 601. In this embodiment, in addition to the configuration described in the fourth embodiment, an auxiliary electrode 701 is added between the electron source 601 and the extraction electrode 602 to make the tip shape of the electron source 601 uniform. The other configurations are the same as those of the fourth embodiment.

[0049] To maintain the tip shape of the electron source 601, a balance between the surface tension due to temperature and the electric field is required. The electron source 601 has a polyhedral shape with a constriction, and it is necessary to maintain the shape not only in the axial direction but also in all lateral directions. Furthermore, the second flat surface 204, like the first flat surface 203, emits a large amount of electrons, so it is necessary to make the electric field acting on it uniform. However, the electric field acting on the electron source by the extraction electrode 602 becomes weaker with increasing distance from the extraction electrode 602, in the order of the first flat surface 203, the third flat surface 206, and the second flat surface 204. Therefore, in this embodiment, an auxiliary electrode 701 is provided to apply an electric field from the second flat surface 204, which is farther from the extraction electrode 602, to the constriction 201.

[0050] The auxiliary electrode 701 is structured to be combined with the extraction electrode 602, and is electrically equipotential with the extraction voltage. In order to reduce variations in the electric field acting on the base side of the polyhedron portion 202 at the tip of the electron source, the auxiliary electrode 701 is arranged closer to the base than the tip. Furthermore, in order to make the electric field uniform, the ends of the extraction electrode 602 and the auxiliary electrode 701 are arranged on a spherical surface centered on the tip of the electron source. This makes it possible to apply a uniform extraction voltage across the entire tip of the electron source. Since the electron source 601 in each of the first to third embodiments has a constricted shape, the bottom and side surfaces are symmetrical, and this effect of making the electric field uniform can be used to maintain the shape of the electron source.

[0051] This embodiment also includes a case where the extraction electrode 602 and the auxiliary electrode 701 are electrically insulated from each other and have different potentials. In this case, the auxiliary electrode 701 can be modulated with a voltage different from that of the extraction electrode 602, depending on individual differences in the shapes of the actual electron sources and electrodes. The amount of current flowing through each electrode, particularly the amount of current emitted from the second flat surface 204 ({100} plane), is fed back to control the voltage applied to the auxiliary electrode 701. This allows for a uniform electric field centered on the tip of the electron source, which cannot be adjusted with a single electrode.

[0052] <Modifications of the present disclosure> In the above embodiments, an electron source has been described as an example of a charged particle source, but similar effects can be obtained by applying the present disclosure to other charged particle sources, such as an ion source that generates ions. The present disclosure is not limited to the above-described embodiments and includes various modifications. For example, the material applicable to the zirconia portion of the electron source is not limited to Zr but also includes materials such as Ti, Sc, and Ba.

[0053] As application examples of the charged particle beam device according to the present disclosure, the charged particle source according to the present disclosure can be used not only in a scanning electron microscope as in the fourth embodiment, but also in a focused ion beam device or an electron beam lithography device. [Explanation of symbols]

[0054] 101 Needle 102 Filament section 103 Zirconia section 201 Waist 202 Polyhedron part 203 1st flat surface 204 2nd flat surface ({100} surface) 205 2nd flat surface ({110} surface) 206 3rd flat surface 207 Optical axis 601 Electron source 602 Extraction electrode 603 Condenser Lens 604 Objective Lens 605 Electron Beam 606 samples 701 Auxiliary electrode

Claims

1. A charged particle source having an emitter that emits charged particles from a tip, The emitter has a tip portion and a needle portion tapered toward the tip portion, The tip portion is a first flat surface perpendicular to an optical axis aligned with a longitudinal crystal axis of the charged particle source; a plurality of second flat surfaces parallel to the optical axis; a plurality of third flat surfaces disposed between the first flat surface and the second flat surface; It has a polyhedral shape composed of the plurality of third flat surfaces are arranged in a plane different from any of a plane parallel to the first flat surface, a plane perpendicular to the first flat surface, a plane parallel to the second flat surface, and a plane perpendicular to the second flat surface; A first distance between the second flat surfaces that are positioned opposite each other across the optical axis is greater than an outer diameter of a boundary between the tip portion and the needle portion. A charged particle source comprising:

2. When a plane having a normal in the direction in which the optical axis extends is defined as a {100} plane, the first flat plane is a {100} plane.

2. The charged particle source according to claim 1, wherein:

3. When a plane having a normal in the direction in which the optical axis extends is defined as a {100} plane, the plurality of second flat planes are constituted by {100} planes and {110} planes.

2. The charged particle source according to claim 1, wherein:

4. When a plane having a normal line in the direction in which the optical axis extends is defined as a {100} plane, the third flat plane is a {110} plane.

2. The charged particle source according to claim 1, wherein:

5. The second flat surface constituted by the {100} plane has a maximum size in the direction of extension of the optical axis that is larger than a maximum size in the direction perpendicular to the optical axis.

4. The charged particle source according to claim 3, wherein the charged particle source comprises:

6. The plurality of second flat surfaces are composed of four {100} surfaces and four {110} surfaces.

4. The charged particle source according to claim 3, wherein the charged particle source comprises:

7. The third flat surface is composed of four {110} faces.

5. The charged particle source according to claim 4, wherein the charged particle source comprises:

8. 2. The charged particle source of claim 1, wherein said first flat surface is rectangular.

9. When the third flat surface is projected onto a plane including the first flat surface, the four third flat surfaces are disposed on four straight lines connecting the center of the first flat surface with the four corners, respectively.

9. The charged particle source of claim 8.

10. the emitter is made of a single crystal of tungsten, The needle portion is coated with zirconia.

2. The charged particle source according to claim 1, wherein:

11. 10. The charged particle source of claim 1 . an extraction electrode that extracts the charged particles from the charged particle source by applying an electric field to the charged particle source; Equipped with The portion of the extraction electrode closest to the tip is arranged on a spherical surface with the tip as the center. A charged particle gun characterized by:

12. the charged particle gun further includes an auxiliary electrode having a portion closest to the tip disposed on the spherical surface; The auxiliary electrode applies to the charged particle source an auxiliary electric field that reduces variations in the electric field that the extraction electrode applies to the boundary portion between the tip portion and the needle portion.

12. The charged particle gun according to claim 11, wherein the charged particle gun is a laser beam.

13. A charged particle beam device comprising the charged particle source according to claim 1.

14. A charged particle beam device comprising the charged particle gun according to claim 11.

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