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

Abstract

The purpose of the present invention is to stabilize the probe current of a charged particle source for a long period of time. In the charged particle source of the present disclosure, an emitter tip portion 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 disposed between the first flat surface and the second flat surface. A first distance between the second flat surfaces among the plurality of second flat surfaces, which are present at positions facing each other across the optical axis, is larger than an outer diameter of a boundary portion between the tip portion and the needle portion.

Description

Technical Field

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

[0002] An electron source is an example of a charged particle source. The electron source is mounted on an electron gun of an electron beam application device represented by a scanning electron microscope (SEM). Electron beams are emitted from the front end 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 fly out of the electron source surface, which is called the work function. When the electrons on the electron source surface exceed the work function by gaining energy, the electrons are emitted from the electron source surface.

[0003] There are many ways to emit electrons, including a thermal electron source that accelerates the emission of electrons excited by heating, and a field emission electron source that emits electrons by tunneling effect through the action of an electric field. The electron source of a thermal electron source is heated to a high temperature, so it is difficult for the surrounding gas molecules to adsorb. As a result, no layer of other molecules is formed on the surface of the electron source, so the work function of the electron source surface is constant and the stability of the emitted current is high. Therefore, in a working atmosphere of 10 -3 It can also be used under low vacuum of about Pa. However, in the case of a thermal electron source, the energy deviation of the emitted electrons is large. The electron emission with large energy dispersion produces large chromatic aberration when passing through the lens, which becomes a cause of low spatial resolution in the SEM optical system. On the other hand, the field emission electron source has the characteristic of small energy dispersion of the emitted electrons. As a result, the brightness becomes higher, which contributes to the high spatial resolution of the SEM. However, usually, the field emission electron source is used below room temperature, so due to the adsorption of the surrounding gas, the work function changes and the electron emission amount changes.

[0004] Thus, the emission of electrons is mainly determined by the temperature of the electron source and the electric field strength at the front end 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 take into account both the stability of the current of electron emission and high spatial resolution.

[0005] After SEM emits electrons from an electron source, it uses an electron beam that passes through multiple apertures to irradiate the sample, and can capture and observe nanoscale microstructures. This electron beam is called a probe current. SEM has a high spatial resolution, so it is used in the inspection of the manufacturing process of semiconductor devices. As a representative example of inspection, pattern defect inspection can be cited. In order to implement accurate defect inspection, it is expected that the contrast or brightness of the observed image is constant. If the probe current changes for each observed image, the brightness of the image changes, and automatic identification of defects becomes difficult. In this way, continuous operation under a long-term stable probe current is required in the inspection of semiconductor devices. In addition, in recent years, with the high integration of semiconductor patterns, it is necessary to use a large current probe for observation with high productivity.

[0006] The Schottky electron source has excellent stability, but during such long-term operation, the probe current amount fluctuates in an unstable state due to changes in the surface state that depend on the vacuum environment and the use conditions of the electron source (electron source temperature, electric field strength).

[0007] The prior art patent documents related to the present application focus on the fact that the shape of the electron source has a great contribution to the electric field acting on the electron source. The purpose and features of the prior art patent documents are introduced below.

[0008] In semiconductor device inspection equipment, in order to achieve high spatial resolution, the diameter of the light source must be reduced. When the radius of the irradiated probe current is set to the size of the image of the SEM optical system, the light source diameter is the radius of the light source at the position of the object plane. If the current is the same, it means that the smaller the light source, the higher the brightness and the higher the spatial resolution. Since the energy dispersion of the electrons of the probe current of a small current is small, the expansion of the light source diameter caused by chromatic aberration can be suppressed. However, the overall shape of the Schottky electron source changes during long-term operation, so that the electric field strength changes continuously. As a result, a decrease in emission current and a change in brightness occur.

[0009] Patent document 1 aims to overcome the problem of the stability of the current and proposes the following shape of the electron source. The charged particle source including the thermal electron source of Patent document 1 has an emission surface as the surface that emits the most electrons, a first side surface adjacent to the emission surface, and a second side surface. In addition, an edge surface is formed between the first side surface and the second side surface. The width of the edge surface is 20% to 40% of the width of the emission surface.

[0010] This shape can be expected to maintain the shape even under the working condition of applying a low electric field in a small current probe current. However, as mentioned above, the demand for high-productivity inspection based on a large current probe current is also strong, requiring high spatial resolution. In the case of using an electron source at high temperature and high electric field in order to use a large current, the expansion of the light source diameter caused by chromatic aberration becomes dominant. As another means, the probe current can be increased by adjusting the optical magnification. This expands the intake of emitted electrons from the vicinity of the optical axis orthogonal to the center of the emission surface to the portion away from the axis through the shadow.

[0011] It is believed that the charged particle source of patent document 1 has a needle shape as a whole, and a front end portion described in each figure of the document is formed at the front end of the needle. The front end portion shape in the document is formed in a manner that the end of the side surface 113 is adjacent to the side of the needle portion. In the case where the front end portion is rapidly switched from the face to the needle shape, the farther the emitted electrons are, the more the equipotential surface is deformed. As a result, energy dispersion becomes larger, which becomes the reason for the expansion of the light source diameter.

[0012] The purpose of patent document 2 is that even when the probe current is a high current, the energy dispersion of the emitted electrons is small and the light source diameter is small. As mentioned above, when a high current is obtained, the energy dispersion increases and the light source diameter tends to expand. According to the technology recorded in patent document 2, by making the electric field acting on the surface of the electron source front end uniform over a wide range, the energy dispersion when taking in a high current can be suppressed.

[0013] Therefore, when the electron source front end is a spherical surface as in Patent Document 2, the equipotential lines near the electron source front end also become spherical surfaces, so the energy dispersion of the emitted electrons can be suppressed to the maximum extent in terms of calculation. However, in reality, the spherical surface is composed of multiple steps, which contributes to current instability.

[0014] Prior art literature

[0015] Patent Literature

[0016] Patent Document 1: Japanese Patent Application Publication No. 2017-157558

[0017] Patent document 2: WO2020115825A1 Summary of the invention

[0018] Problems to be solved by the invention

[0019] The atoms constituting the Schottky electron source move due to the free energy generated by heating. As a result, the tip of the needle-shaped electron source expands in diameter in a rounded manner. The movement of the atoms is defined as diffusion.

[0020] In particular, when comparing the front ends of electron sources of the same diameter, the closer the shape is to a sphere, the higher the free energy is, and the easier it is for atoms forming the electron source to diffuse. As a result, the shape of the {100} plane, which is the electron emission surface, changes over time in the crystal plane at the front end of the electron source.

[0021] As in the charged particle source of Patent Document 2, when the aperture is large and the front end surface is close to a spherical shape, there is a tendency that the {100} plane has a step shape of two or more levels. The step collapses from the end of the {100} plane due to the aforementioned diffusion, and the step moves toward the center. The movement of the step and the diffusion of atoms vary according to the balance between the temperature of the electron source and the strength of the electric field acting on the front end of the electron source to extract electrons.

[0022] The step portion of the electron source is composed of a surface other than the {100} surface that is the electron emission surface, and it is difficult to emit electrons. The step moves within the {100} surface of the front end, so the probe current becomes unstable every time the step passes. In addition, due to these effects, the radius of the front end of the electron source has been expanding for a long time, and the electric field strength changes according to the change of shape. As a result, the front end of the electron source continues to diffuse, so it is believed that the probe current is always unstable.

[0023] When the tip of the electron source is close to a spherical surface, high spatial resolution can be expected, but it is very difficult to maintain the balance between heat and electric field, and the probe current may become unstable periodically. Electron sources used for inspection and length measurement in scanning electron microscopes need to maintain a stable electron emission amount from the tip {100} surface for a long time.

[0024] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to stabilize the probe current of a charged particle source for a long period of time.

[0025] Solutions to Solve Problems

[0026] In the charged particle source disclosed in the present invention, the front end portion of the emitter has: a first flat surface, which is perpendicular to the optical axis; a plurality of second flat surfaces, which are parallel to the optical axis; and a plurality of third flat surfaces, which are arranged between the first flat surface and the second flat surface, and a first distance between the second flat surfaces among the plurality of second flat surfaces that are located at positions opposite to each other across the optical axis is larger than the outer diameter of the boundary portion between the front end portion and the needle portion.

[0027] Effects of the Invention

[0028] The charged particle source of the present disclosure can easily maintain a stable shape. As with the front end, the shape of the {100} plane is stable and the shape of the front end can be more firmly maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 An overall view of the electron source according to Embodiment 1 is shown.

[0030] Figure 2 This is an enlarged view of the vicinity of the tip of the needle 101 of the electron source.

[0031] Figure 3 This is an enlarged view of the front end shape of the charged particle source according to the second embodiment.

[0032] Figure 4 Deformation of the electron source front end caused by the diffusion of tungsten atoms.

[0033] Figure 5 This is an enlarged view of the front end shape of the charged particle source according to the third embodiment.

[0034] Figure 6 This is a configuration diagram of a charged particle beam device 600 according to a fourth embodiment.

[0035] Figure 7 This is a configuration diagram of a charged particle beam device according to the fifth embodiment. DETAILED DESCRIPTION

[0036] <Implementation 1: Basic Principle>

[0037] The following first describes the basic principle of the embodiment of the present disclosure, and then describes the specific structure of the embodiment. The radius of the electron source is defined as r, and the radius of the electron source that increases per unit time due to thermal diffusion is defined as dr / dt. If the time change of the radius when an electric field is applied in addition to the heating of the electron source is defined as (dr / dt) F , it can be expressed by the following formula. Where F represents the electric field applied to the front end of the electron source, and ν represents the surface tension acting on the surface of the electron source: (dr / dt) F =(1-F 2 r / 8πν)dr / dt.

[0038] By applying (1-F 2 The electric field of F above r / 8πν) = 0 can suppress the deformation caused by diffusion. When the front end shape is spherical, it has the advantage of being able to act uniformly in a large range, but when electrons are emitted under the condition of balanced destruction, diffusion occurs in the entire range of the front end of the electron source.

[0039] In order to prevent the curvature from changing within the widest possible range, it is effective to have a shape with a neck and a front end close to a sphere. This allows the curvature of the front end related to the probe current to be constant. However, by not being a complete sphere but having a portion with a local change in curvature, the front end shape can be maintained for a long time.

[0040] Therefore, the charged particle source disclosed in the present invention has a constriction near the front end of the needle-shaped structure represented by single crystal tungsten, and the front end has a polyhedral front end from the constriction. The polyhedron has a {100} face on the upper surface and the four sides. With the {100} face on the upper surface as the center, there is an inclined surface of a {110} face inclined 45° from the upper surface between the {100} face on the side surface. As a result, a strong electric field can be formed locally around the {100} face, close to (1-F 2 r / 8πν)=0. In addition, since the front end is a constricted and regular polyhedron-like shape, the side 4 directions also have a shape similar to the front end, and the same crystal growth is observed in all directions. That is, by setting the charged particle source with the bottom and side surfaces of the front end as rotationally symmetric crystal planes, the above effect can be obtained.

[0041] <Implementation 1: Structure of Charged Particle Source>

[0042] Figure 1 This is a general view of an electron source according to Embodiment 1 of the present disclosure. In Embodiment 1, a structural example of a Schottky electron source formed of tungsten will be described as a representative charged particle source.

[0043] The electron source is composed of a needle portion 101 tapering toward the front end, a filament portion 102 bent into a V shape, and a zirconia portion 103. The vicinity of the root of the needle portion 101 is fixed to the filament portion 102 by welding. Zirconia is applied to the middle of the needle portion 101, and the needle portion 101 and the zirconia portion 103 are heated together by applying electricity to the filament portion 102 for heating.

[0044] Figure 2 This is an enlarged view of the vicinity of the tip of the needle 101 of the electron source. Figure 2 The upper part is a side view. Figure 2 The lower part is a bottom view (a view with the optical axis of the electron beam as the depth direction). If the central axis of the electron beam emitted from the front end of the electron source is defined as the optical axis 207, then the optical axis 207 is coaxial with the needle portion 101. Figure 2 As shown, the needle portion 101 has a constricted portion 201 with a width L1>L3 near the front end. As it moves from the constricted portion 201 toward the front end, the radius of the electron source temporarily increases. Thereafter, it becomes a shape like a polyhedron having multiple flat surfaces. The polyhedron portion 202 is defined from the constricted portion 201 to the front end. The constricted portion 201 is arranged at a position where a sphere circumscribed respectively to a surface perpendicular to the optical axis 207 (first flat surface 203) and a side surface parallel to the optical axis 207 intersects with the needle portion 101.

[0045] The polyhedral portion 202 has the following surfaces: a first flat surface 203 which is a surface perpendicular to the optical axis 207; second flat surfaces 204 and 205 which are surfaces horizontal 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 a {100} surface and a {110} surface which are 4-fold symmetrical about the optical axis 207. The second flat surface 204 ({100} surface) and the second flat surface 205 ({110} surface) are alternately arranged at intervals of 45°. The third flat surface 206 is arranged between the first flat surface 203 and the second flat surface 204 so as to be arranged in a straight line on the surface of the polyhedral portion 202.

[0046] The electron source in this embodiment is formed by processing a tungsten single crystal into a needle shape, and the optical axis direction is set to <100> The second flat surface 204 ({100} surface) has a longer width in the optical axis direction, and the second flat surface 205 ({110} surface) has a shorter width in the optical axis direction. The third flat surface 206 is composed of a {110} surface.

[0047] Regarding the second flat surface 204 ({100} surface), 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. Compared with the distance L2 in the optical axis direction from the first flat surface 203 to the position of the constricted portion 201, L2>r2. When the diameter of the constricted portion 201 is defined as L3, L1>L3>r1.

[0048] Zirconia from Figure 1 The zirconium oxide portion 103 diffuses toward the front end of the electron source to form a mixed layer with tungsten. As a result, the work function of the {100} surface is reduced, so electrons are emitted from the {100} surface. 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 to stably emit the probe current, it is necessary to stabilize the shape of the first flat surface 203 as the electron emission surface.

[0049] In the tungsten atoms constituting the electron source, surface tension with heat as a parameter acts, and the atoms diffuse in the direction where the radius becomes larger. As a result, the shape changes with the passage of time, the intensity of the electric field and the size of the crystal plane are not fixed, and the probe current becomes unstable. In contrast, the electron source in this embodiment has a constricted portion 201, and the constricted side and the front end side of the polyhedron portion 202 become symmetrical shapes, so diffusion occurs in the constricted portion 201 in the opposite direction. As a result, it is considered that there is an effect of suppressing the change in the size L1 of the polyhedron caused by diffusion.

[0050] As in the present embodiment, the crystal structure with rotational symmetry about the bottom and the side surface makes it easier to apply a uniform electric field from the first flat surface 203 to the side surface, compared with an electron source whose shape changes sharply from the electron emission surface to the needle shape, such as when the tip shape is a cone or a pyramid. As a result, it is easier to maintain the tip shape for a long time.

[0051] <Implementation Method 2>

[0052] Figure 3 FIG. 2 is an enlarged view of the front end shape of the charged particle source according to Embodiment 2 of the present disclosure. Figure 2 Likewise, Figure 3 The upper part is a side view. Figure 3 The lower part is a bottom view. In addition to the features of the first embodiment, the charged particle source of the second embodiment has the feature that the first flat surface 203 is in the shape of a quadrilateral. Figure 3 In the case of a quadrilateral as described above, changes in shape due to diffusion can be further suppressed compared to a circular shape.

[0053] Diffusion can be expressed as the surface free energy of tungsten atoms by the following equation: μ = Ω {νκ-(1 / 2)ε0F 2}. μ is the free energy, Ω is the volume of the tungsten atom, ν is the surface tension, κ is the local curvature, ε0 is the dielectric constant, and F is the electric field. Due to the gradient of free energy of the adjacent surface, atoms diffuse in the direction from high energy to low energy.

[0054] Figure 4 Deformation of the electron source front end caused by the diffusion of tungsten atoms. Figure 4 is a side view further enlarging the periphery of the first flat surface 203. When tungsten atoms diffuse according to the above formula, Figure 4 The tungsten atoms in the surface portion surrounded by the dotted line move toward the root direction away from the first flat surface 203 along the side. That is, the first flat surface 203 gradually narrows. As a result, a step is generated at the end of the first flat surface 203, as shown in the surface after diffusion drawn by the solid line. After the step is generated, the atoms continue to move from the end of the step, and the step becomes smaller toward the center. Due to the movement of the step in the first flat surface 203, the probe current becomes unstable. However, through the term (1 / 2)ε0F with the electric field as a parameter 2 Balanced with the surface tension term νκ, the movement of atoms can be stopped at this position.

[0055] When the shape of the first flat surface 203 is set to a quadrilateral as in the present embodiment, there are crystal planes adjacent to the first flat surface 203 constituting each side. The adjacent plane is the third flat surface 206 or the {112} plane existing 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 (refer to Figure 3 ), the inclination of the third flat surface 206 is 45° from the crystal structure relative to the first flat surface 203, and thus becomes an edge having an angle of α=180°-45°=135° or more. This becomes an edge portion with a small local curvature, which causes the suppression of surface tension caused by heat and the generation of a strong electric field, approaching a balanced direction.

[0056] The quadrilateral of the first flat surface 203 may be a strict quadrilateral or may have rounded corners and sides but be a quadrilateral as a whole. The actual α may have individual differences of about ±10° from the calculated value due to crystal structure strain and the like.

[0057] <Implementation Method 3>

[0058] Figure 5 FIG. 1 is an enlarged view of the front end shape of the charged particle source according to Embodiment 3 of the present disclosure. Figure 2 Likewise, Figure 5 The upper part is a side view. Figure 5 The lower section is a bottom view. Implementation 3 is a variation of Implementation 2. Figure 5 As shown, the width of the third flat surface 206 is defined as r3, and the width of the region between the third flat surfaces 206 represented by the {112} plane is defined as r4.

[0059] The first flat surface 203 is a quadrilateral, and the orientation of the corners thereof is such that the arrangement of the corners and sides is rotated by 45° according to the ratio between the width r3 of the third flat surface 206 surrounding the first flat surface 203 and r4 as the interval therebetween. In this embodiment, a configuration example is shown in which r3 ≤ r4 and the third flat surface 206 is arranged in the orientation of the corners of the quadrilateral (if a straight line connecting the center and the corner of the first flat surface 203 is extended, it intersects with the third flat surface 206).

[0060] like Figure 5As shown, the corner portion of the quadrilateral corresponding to the first flat surface 203 is consistent with the orientation of the third flat surface 206 present on the inclined surface at 90° intervals. The angle α of the edge at this time is an obtuse angle compared to Embodiment 2, which is approximately 145° or more. The sharper the edge, the stronger the electric field, and the more concentrated it acts on the edge portion. As a result, the intensity of the in-plane electric field of the first flat surface 203 is concentrated on the periphery, and a difference in the electric field intensity between the near-axial portion and the off-axial portion relative to the optical axis 207 is generated. As a result, energy dispersion becomes larger, and the radius of the light source is expanded due to the chromatic aberration of the lens. This is one of the main reasons for the degradation of resolution when used as a scanning electron microscope, and should be avoided as the performance of the electron source.

[0061] In the second and third embodiments, the ratio between the width r3 of the third flat surface 206 and the width r4 of the region headed by {112} between the third flat surfaces is not particularly limited. The electric field applied to the edge portion is optimized by changing the ratio of the size of the surface around the first flat surface 203 according to the electron emission conditions of the electron source. In this way, the stabilization of the probe current brought about by the stabilization of the first flat surface 203 and the state of small energy dispersion of electrons, which is the main cause of chromatic aberration, can be taken into account.

[0062] <Implementation Method 4>

[0063] Figure 6 1 is a block diagram of a charged particle beam device 600 according to Embodiment 4 of the present disclosure. The charged particle beam device 600 is equipped with any of the electron sources 601 according to Embodiments 1 to 3, and can be applied as a scanning electron microscope.

[0064] The charged particle beam device 600 has an extraction electrode 602 in a manner opposite to the electron source 601 directly below. By applying a voltage to the extraction electrode 602, electrons are extracted from the electron source 601. The electron source 601 and the extraction electrode 602 can constitute an electron gun (charged particle gun). A focusing lens 603 is provided in the middle section of the charged particle beam device 600, and an electron beam 605 passes and converges. The current amount of the radiated electron beam 605 is adjusted by the focusing lens 603. An objective lens 604 is provided in the lower section to focus the electron beam 605 toward the sample 606.

[0065] <Implementation method 5>

[0066] Figure 7 It is a structural diagram of a charged particle beam device according to Embodiment 5 of the present disclosure. Figure 7 The figure shows the periphery of the electron source 601. In this embodiment, in addition to the structure described in the fourth embodiment, an auxiliary electrode 701 is added between the electron source 601 and the extraction electrode 602 to make the shape of the tip of the electron source 601 uniform. The other structures are the same as those of the fourth embodiment.

[0067] In order to maintain the front end shape of the electron source 601, it is necessary to balance the surface tension based on temperature and the electric field. The electron source 601 is a polyhedron with a necking, which not only needs to maintain the shape in the axial direction, but also needs to maintain the shape in all directions of the side. In addition, the second flat surface 204 emits electrons in a large number in the same manner as the first flat surface 203, so it is necessary to make the electric field of the effect uniform. However, according to the order of the first flat surface 203, the third flat surface 206, and the second flat surface 204, the more away from the extraction electrode 602, the weaker the electric field acted on the electron source by the extraction electrode 602. Therefore, in the present embodiment, an auxiliary electrode 701 is provided to apply an electric field from the second flat surface 204 away from the extraction electrode 602 to the necking portion 201.

[0068] The auxiliary electrode 701 is a structure combined with the extraction electrode 602, and is electrically equipotential with the extraction voltage. In order to reduce the deviation of the electric field on the root side of the polyhedron portion 202 acting on the front end of the electron source, the auxiliary electrode 701 is arranged on the root side closer to the front end. 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 front end of the electron source. In this way, a uniform extraction voltage can be applied to the entire front end of the electron source. The shape of the electron source 601 of embodiments 1 to 3 has a neck, so that the bottom surface and the side surface are symmetrical, so by making the electric field uniform, the effect of maintaining the shape of the electron source can be obtained.

[0069] This embodiment also includes the 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 according to the individual differences in the shape of the actual electron source and the electrode. Feedback is applied to the control of the voltage applied to the auxiliary electrode 701 according to the amount of current flowing to each electrode, especially the amount of current emitted from the second flat surface 204 ({100} surface). In this way, a uniform electric field centered on the front end of the electron source, which cannot be adjusted in a single electrode, can be obtained.

[0070] <Regarding Modifications of the Present Disclosure>

[0071] In the above embodiments, an electron source is used as an example for the charged particle source, but the same effect can be obtained by using the present disclosure for other charged particle sources such as an ion source that generates ions. The present disclosure is not limited to the above embodiments, and includes various modifications. For example, regarding the zirconium oxide part of the electron source, the corresponding material is not limited to Zr, but also includes materials such as Ti, Sc, and Ba.

[0072] As an application example of the charged particle beam device of the present disclosure, the charged particle source of the present disclosure can be used not only for a scanning electron microscope as in the fourth embodiment but also for a focused ion beam device and an electron beam drawing device.

[0073] Explanation of symbols

[0074] 101—needle part, 102—filament part, 103—zirconium oxide part, 201—neck part, 202—polyhedron part, 203—first flat surface, 204—second flat surface ({100} surface), 205—second flat surface ({110} surface), 206—third flat surface, 207—optical axis, 601—electron source, 602—extraction electrode, 603—focusing lens, 604—objective lens, 605—electron beam, 606—sample, 701—auxiliary electrode.

Claims

1. A charged particle source, comprising an emitter for emitting charged particles from a front end, wherein the charged particle source is characterized in that: The transmitter has: a front end portion; and a needle portion having a shape that tapers toward the front end portion. The front end portion has: a first flat surface which is perpendicular to an optical axis which coincides with a crystal axis in the length direction of the charged particle source; a plurality of second flat surfaces parallel to the optical axis; and a plurality of third flat surfaces, which are arranged between the first flat surface and the second flat surface, The plurality of third flat surfaces are arranged in planes different from 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, among the plurality of second flat surfaces, that are located at positions opposing each other across the optical axis is greater than an outer diameter of a boundary portion between the tip portion and the needle portion.

2. The charged particle source according to claim 1, characterized in that: When a surface whose normal line is the direction in which the optical axis extends is a {100} surface, the first flat surface is the {100} surface.

3. The charged particle source according to claim 1, characterized in that: When a plane whose normal line is the direction in which the optical axis extends is a {100} plane, the plurality of second flat planes are composed of {100} planes and {110} planes.

4. The charged particle source according to claim 1, characterized in that: When a plane whose normal line is the direction in which the optical axis extends is a {100} plane, the third flat surface is a {110} plane.

5. The charged particle source according to claim 3, characterized in that: The second flat surface composed of a {100} plane has a maximum dimension in a direction in which the optical axis extends that is larger than a maximum dimension in a direction orthogonal to the optical axis.

6. The charged particle source according to claim 3, characterized in that: The plurality of second flat surfaces are composed of four {100} surfaces and four {110} surfaces.

7. The charged particle source according to claim 4, characterized in that: The third flat surface is composed of four {110} planes.

8. The charged particle source according to claim 1, characterized in that: The first flat surface is a quadrilateral.

9. The charged particle source according to claim 8, characterized in that: When the third flat surface is projected onto a plane including the first flat surface, four third flat surfaces are arranged on four straight lines respectively connecting the center and four corners of the first flat surface.

10. The charged particle source according to claim 1, characterized in that: The emitter is composed of a single crystal of tungsten. The needle portion is coated with zirconium oxide.

11. A charged particle gun, characterized in that: have: The charged particle source of claim 1; and an extraction electrode for extracting the charged particles from the charged particle source by applying an electric field to the charged particle source, The portion of the lead-out electrode closest to the distal end portion is arranged on a spherical surface centered on the distal end portion.

12. The charged particle gun according to claim 11, characterized in that The charged particle gun further includes an auxiliary electrode, a portion of the auxiliary electrode closest to the front end portion being arranged on the spherical surface. The auxiliary electrode causes an auxiliary electric field that reduces a deviation in an electric field applied by the extraction electrode to a boundary portion between the tip portion and the needle portion to act on the charged particle source.

13. A charged particle beam device, characterized in that: A charged particle source according to claim 1 is provided.

14. A charged particle beam device, characterized in that: A charged particle gun according to claim 11 is provided.

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