Electron gun

Abstract

An electronic gun comprises an electronic gun chamber, an upper cover flange fixed to the electronic gun chamber, a movable seat and a deformation sleeve which are arranged on the upper cover flange in a penetrating mode, and an emission assembly which penetrates through the deformation sleeve and is fixed to the movable seat, one end of the deformation sleeve is fixed to the movable seat in a sealed mode, and the other end of the deformation sleeve is fixed to the upper cover flange in a sealed mode. The emission assembly comprises an emission source located in the electron gun chamber, a supporting table face facing the movable base in the axial direction is arranged in the upper cover flange, an opening structure is arranged at the position, corresponding to the movable base, of the upper cover flange, and the opening structure is used for providing a path for inserting or removing the adjusting gasket between the supporting table face and the movable base. The fine adjustment of the axial position of the emission source can be realized by inserting or removing the adjusting gasket between the supporting table top and the movable seat through the matching of the supporting table top and the opening structure, the emission parameters (such as emission current angular density, virtual element size and the like) of the electron gun can be controlled, and the service life of the electron gun can be prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of scanning electron microscopes, and in particular to an electron gun. Background Art

[0002] Scanning Electron Microscope (SEM), also known as SEM, is a microscopic analysis device that uses various physical signals stimulated by a focused electron beam scanning the sample surface to modulate imaging. Compared with traditional optical imaging, SEM can provide nanometer or even sub-nanometer resolution, and plays an indispensable role in defect detection and dimensional measurement in the production process of semiconductor devices. Among them, the electron gun is one of the key components of the SEM, and its main function is to emit an electron beam with a certain energy. The adjustability of the electron gun structure has a crucial influence on the emission parameters of the electron gun. However, the structural adjustability of the relevant electron gun is poor, which limits the optimization of the performance of the electron gun. Summary of the invention

[0003] The main technical problem solved by the present invention is to provide an electron gun to improve the adjustability of the electron gun structure.

[0004] In one embodiment, an electron gun is provided, comprising: Electron gun room; An upper cover flange is fixed to the electron gun chamber; A sealing assembly is arranged through the upper cover flange, and the sealing assembly includes a movable seat and a deformable sleeve; in the axial direction of the upper cover flange, one end of the deformable sleeve is sealed and fixed to the movable seat, and the other end of the deformable sleeve is sealed and fixed to the upper cover flange; An emission component, passing through the deformable sleeve and fixed to the movable seat, wherein the emission component comprises an emission source arranged inside the electron gun chamber; Among them, a support table is provided inside the upper cover flange, and the support table faces the movable seat in the axial direction. An opening structure is provided at the position of the upper cover flange corresponding to the movable seat; the opening structure is used to provide a path for inserting or removing an adjustment gasket between the support table and the movable seat, so as to adjust the position of the emission source in the axial direction by disassembling and assembling the adjustment gasket.

[0005] In one embodiment, the upper cover flange has a connecting sleeve portion and a sealing sleeve portion, the connecting sleeve portion and the sealing sleeve portion are coaxially connected in the axial direction, the supporting table is formed at the junction of the connecting sleeve portion and the sealing sleeve portion, and the other end of the deformation sleeve is sealed and fixed to an end of the sealing sleeve portion away from the connecting sleeve portion; Among them, the end face of the connecting sleeve away from one end of the sealing sleeve is a flange end face, and the opening structure includes a plurality of first grooves; the first grooves penetrate the flange end face and extend along the axial direction to connect with the supporting table surface.

[0006] In one embodiment, a plurality of second grooves are provided on the support table, and the plurality of second grooves and the plurality of first grooves are arranged alternately in a circumferential direction, and the second grooves are used to position a corresponding one of the adjustment gaskets between the support table and the movable seat; wherein the circumferential direction is a direction around the axial direction.

[0007] In one embodiment, the projection shapes of the second groove and the adjusting gasket in the plane where the supporting table is located are the same; and / or the number of the first groove and the number of the second groove are both set to four.

[0008] In one embodiment, the electron gun further comprises a plurality of fastening adjustment members, wherein the fastening adjustment members are connected to the connecting sleeve, and the plurality of fastening adjustment members and the plurality of first grooves are alternately arranged in a circumferential direction; the fastening adjustment members are used to abut against the movable seat in a radial direction to adjust the position of the emission source in the radial direction; wherein the circumferential direction is a direction around the axial direction, and the radial direction is a direction perpendicular to the axial direction.

[0009] In one embodiment, an observation window is provided on a side wall of the electron gun chamber in a radial direction, and the observation window is used to observe the interior of the electron gun chamber; wherein the radial direction is a direction perpendicular to the axial direction.

[0010] In one embodiment, the electron gun further comprises the adjusting gasket, and the adjusting gasket is arranged between the supporting table and the movable seat.

[0011] In one embodiment, the projection contour line of the adjusting gasket in the plane where the supporting table is located includes an inner arc segment, a first straight line segment, an outer arc segment and a second straight line segment connected end to end, and the inner arc segment and the outer arc segment are cocentric; Wherein, the adjacent inner arc segments, the first straight line segments, the outer arc segments and the second straight line segments are connected by chamfered corners, and / or the central angle between the inner arc segment and the outer arc segment is less than or equal to 45°.

[0012] In one embodiment, the electron gun further comprises an extraction electrode; the extraction electrode is arranged inside the electron gun chamber and is used to induce the emission source to emit electrons; the extraction electrode has a first through hole penetrating along the axial direction, and the first through hole is spaced opposite to the emission source in the axial direction; wherein: The radius of the first through hole is between 0.07 mm and 0.5 mm, and / or the width of the extraction pole in the axial direction is between 0.3 mm and 0.5 mm, and / or the distance between the extraction pole and the emission source in the axial direction is between 0.1 mm and 0.7 mm.

[0013] In one embodiment, the electron gun further comprises an anode; the anode is fixedly disposed inside the electron gun chamber for accelerating electrons emitted by the emission source; the extraction electrode is insulated and fixed to the anode, and the extraction electrode is located between the anode and the emission source in the axial direction.

[0014] In one embodiment, the extraction electrode has a front end surface and a rear end surface, the front end surface is the surface of the extraction electrode facing the emission source in the axial direction, and the central axis of the first through hole is perpendicular to the plane where the front end surface is located; the rear end surface is the surface of the extraction electrode facing the anode in the axial direction, and the rear end surface is a conical surface surrounding the first through hole.

[0015] In one embodiment, a projection contour line of the first through hole in a plane parallel to a central axis of the first through hole includes a first contour line and a second contour line, and the first contour line and the second contour line are symmetrical about the central axis; The first contour line and the second contour line are straight line segments, or the first contour line and the second contour line are arc segments that are bent in a direction away from the central axis.

[0016] In one embodiment, the emission source has a needle tip portion, and the surface of the needle tip portion includes a first surface, a second surface, a third surface and a fourth surface, the first surface is a circular plane structure perpendicular to the geometric center line of the emission source, the second surface is a cylindrical curved surface structure surrounding the geometric center line, the third surface is a chamfered arc surface structure connected to the first surface and the second surface, and the fourth surface is a conical curved surface structure connected to the second surface on the side away from the third surface.

[0017] The electron gun according to the above embodiment includes an electron gun chamber, an upper cover flange fixed to the electron gun chamber, a movable seat and a deformation sleeve penetrating the upper cover flange, and an emission assembly penetrating the deformation sleeve and fixed to the movable seat, wherein one end of the deformation sleeve is sealed and fixed to the movable seat, and the other end is sealed and fixed to the upper cover flange, and the emission assembly includes an emission source located inside the electron gun chamber, and the interior of the upper cover flange is provided with a support table facing the movable seat in the axial direction, and the upper cover flange is provided with an opening structure at a position corresponding to the movable seat, and the opening structure is used to provide a path for inserting or removing an adjustment gasket between the support table and the movable seat. Through the cooperation of the support table and the opening structure, the fine adjustment of the axial position of the emission source can be achieved by inserting or removing the adjustment gasket between the support table and the movable seat, which is not only conducive to controlling the emission parameters of the electron gun (such as the emission current angular density, the size of the virtual element, etc.), but also can prolong the service life of the electron gun. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a schematic diagram of the overall structural architecture of an electron gun according to an embodiment.

[0019] Figure 2 The figure is a schematic diagram of the structure of the upper cover flange in an electron gun according to an embodiment.

[0020] Figure 3 The figure is a schematic diagram of the cross-sectional structure of an upper cover flange in an electron gun in an axial direction according to an embodiment.

[0021] Figure 4 The figure is a schematic diagram of the planar structure of an upper cover flange in an electron gun according to an embodiment.

[0022] Figure 5 The figure is a schematic diagram of the outline structure of an adjusting gasket in an electron gun according to an embodiment.

[0023] Figure 6 It is a schematic diagram of an enlarged structure of the needle tip of the emission source in an electron gun of an embodiment.

[0024] Figure 7 The figure is a schematic diagram of the relative position relationship between the emission source and the extraction electrode in an electron gun according to an embodiment.

[0025] Figure 8 It is a perspective projection diagram of an extraction pole in an electron gun according to an embodiment.

[0026] Fig. 9 Schematic diagram of the cross-sectional structure of an extraction electrode in an electron gun according to an embodiment (I).

[0027] Fig.10 Schematic diagram of the cross-sectional structure of an extraction electrode in an electron gun according to an embodiment (II).

[0028] Fig.11It is a curve diagram of the simulated emission current angular density changing with the extraction pole center hole radius in one embodiment.

[0029] Fig.12 It is a curve diagram of the simulated virtual element size changing with the extraction pole center hole radius in an embodiment.

[0030] Fig.13 It is a curve diagram of the simulated emission current angular density changing with the distance from the extraction pole to the emission source in an embodiment.

[0031] Fig.14 It is a curve diagram of the simulated virtual element size changing with the distance from the extraction pole to the emission source in an embodiment.

[0032] In the figure: 10. electron gun chamber; 11. observation window; 12. magnetic shielding layer; 20. upper cover flange; 20a. support table; 20b. flange end face; 20c. first groove; 20d. second groove; 21. connecting sleeve; 22. sealing sleeve; 30. movable seat; 40. deformation sleeve; 50, emission source; 51a, first surface; 51b, second surface; 51c, third surface; 51d, fourth surface; 52, anode; 53, extraction electrode; 53a, first contour line; 53b, second contour line; 53c, rear end surface; 53d, front end surface; 54, suppression electrode; 55, high voltage electrode; 56, insulating structural member; 57, extraction aperture; 60, fastening adjustment member; 70, adjusting gasket; 70a, inner arc segment; 70b, first straight segment; 70c, outer arc segment; 70d, second straight segment; 80, fluorescent screen; 90, camera. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below by specific embodiments in conjunction with the accompanying drawings. Wherein similar elements in different embodiments adopt associated similar element numbers. In the following embodiments, many detailed descriptions are for making the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different situations, or can be replaced by other elements, materials, methods. In some cases, some operations related to the present application are not shown or described in the specification, this is to avoid the core part of the present application being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0034] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various implementations. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a required sequence, unless otherwise specified that a certain sequence must be followed.

[0035] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application, unless otherwise specified, include direct and indirect connections (couplings).

[0036] See also Figures 1 to 10 The embodiment of the present application provides an electron gun, such as a tungsten filament electron gun, a lanthanum hexaboride (LaB6) filament electron gun, a thermal field emission electron gun, a cold field emission electron gun, etc.; the electron gun includes an electron gun chamber 10, an upper cover flange 20, a sealing component, an adjustment component, an emission component and other functional components that exist as needed, which are described in detail below.

[0037] See also Figure 1 The electron gun chamber 10 may be a vacuum-insulated chamber structure made of non-magnetic 316L stainless steel, Permalloy, or other materials; for example, in the case of a thermoelectric field emission electron gun, the vacuum degree of the electron gun chamber 10 is greater than 1*10 -7 The upper cover flange 20 is mainly used as a structural connection carrier between the electron gun chamber 10 and the sealing component and the adjustment component. The upper cover flange 20 is fixed to the electron gun chamber 10 , for example, the upper cover flange 20 is passed through and fixed to the interface of the electron gun chamber 10 .

[0038] In order to explain the electron gun more clearly and in detail, three different directions are defined in this article based on the upper cover flange 20, namely, the axial direction, the radial direction and the circumferential direction; among which, the axial direction can be understood as the direction of the central axis of the upper cover flange 20, the radial direction can be understood as the direction perpendicular to the axial direction, and the circumferential direction can be understood as the direction around the axial direction.

[0039] See also Figures 1 to 3The sealing assembly includes a movable seat 30 and a deformable sleeve 40 which are sequentially arranged through the upper cover flange 20 in the axial direction; wherein the deformable sleeve 40 is a sleeve structure which can be deformed when subjected to force, for example, the deformable sleeve 40 can adopt a bellows structure which can be telescopically deformed in the axial direction and oscillatingly deformed in the radial direction; the movable seat 30 is located on a side closer to the outside of the electron gun chamber 10 than the deformable sleeve 40, one end of the deformable sleeve 40 in the axial direction is sealed and fixed to the movable seat 30 (for example, welded and sealed), and the other end of the deformable sleeve 40 in the axial direction is sealed and fixed to the upper cover flange 20 (for example, welded and sealed).

[0040] On the one hand, a sealing structural connection relationship is established between the electron gun chamber 10 and the sealing component by the upper cover flange 20 to ensure the vacuum sealing of the electron gun chamber 10; on the other hand, by utilizing the characteristic that the deformable sleeve 40 can deform when subjected to force, a non-rigid connection relationship can be established between the upper cover flange 20 and the movable seat 30 to provide support for the movable seat 30 to move relative to the upper cover flange 20 and the electron gun chamber 10 (for example, axial movement, radial movement, etc.).

[0041] See also Figure 1 The emission assembly is arranged through the deformation sleeve 40, and the emission assembly is fixedly connected to the movable seat 30, so that the emission assembly can move synchronously with the movable seat 30; the emission assembly includes an emission source 51 arranged inside the electron gun chamber 10, and the emission source 51 can be understood as the cathode or filament of the electron gun, which is mainly used to generate electrons. It can be understood that in different types of electron guns, the electron gun chamber 10 is also provided with relevant functional components that cooperate with the emission source 51 to realize the electron gun's function of emitting electron beams.

[0042] For example, see Figure 1 and Figure 7 The electron gun is a thermal field emission type electron gun, which also includes a high-voltage electrode 55. An anode 52, an extraction electrode 53 and a suppression electrode 54 are arranged in the electron gun chamber 10; wherein the anode 52 and the emission source 51 are arranged opposite to each other in the axial direction, and are mainly used to accelerate the electrons emitted by the emission source 51; the extraction electrode 53 is arranged between the emission source 51 and the anode 52 in the axial direction, and is mainly used to provide a high-voltage electric field for the electron emission surface of the emission source 51 to induce the emission source 51 to emit electrons.

[0043] The suppression electrode 54 is located on the opposite side of the extraction electrode 53 relative to the electron emission surface of the emission source 51. It can also be understood that the electron emission surface of the emission source 51 is located between the suppression electrode 54 and the extraction electrode 53 in the axial direction. The suppression electrode 54 is mainly used to suppress unnecessary electron emission, such as suppressing electrons emitted from other surfaces of the emission source 51 except the electron emission surface.

[0044] The high-voltage electrode 55 is mainly used to connect an external power supply to apply voltage to the emission source 51, the anode 52, the extraction electrode 53 and the suppression electrode 54; for example, the high-voltage electrode 55 can be divided into four or five routes to feed high voltage, one or two routes to feed 2A heating current to the emission source 51, one route to feed -300V voltage to the suppression electrode 54, one route to feed 3000V voltage to the extraction electrode 53, and one route to feed 9000V voltage to the anode 52.

[0045] In some embodiments, the functional component in the emission assembly fixedly connected to the movable seat 30 may be a high voltage electrode 55, and the emission source 51 and the suppressor 54 are fixedly connected to the high voltage electrode 55. In other embodiments, the emission source 51 and the suppressor 54 have a corresponding high voltage electrode 55, and another two-axis high voltage electrode 55 is arranged on the side wall of the electron gun chamber 10 in the radial direction, and the two-axis high voltage electrode 55 is used to feed voltage to the anode 52 and the extraction electrode 53.

[0046] For example, please combine Figure 1 and Figure 7 The electron gun is a tungsten filament electron gun or a lanthanum hexaboride electron gun, and an anode 52 and a grid (not shown in the figure) are arranged inside the electron gun chamber 10; the anode 52 and the emission source 51 are arranged opposite to each other in the axial direction, and are mainly used to accelerate the electrons emitted by the emission source 51; the grid is located between the emission source 51 and the anode 52 in the axial direction, and is mainly used to control the flow rate of the electron beam and reduce the divergence angle of the electron beam.

[0047] See also Figures 1 to 4 The adjustment component is mainly used to adjust the position of the emission source 51 by adjusting the position of the movable seat 30; the adjustment component includes a plurality of fastening adjustment members 60 evenly arranged in the circumferential direction, such as three, four or other larger numbers; the fastening adjustment member 60 is connected to the portion of the upper cover flange 20 corresponding to the movable seat 30, and is mainly used to abut the movable seat 30 in the radial direction to adjust the position of the emission source 51 in the radial direction (hereinafter referred to as the radial position). In specific implementation, the fastening adjustment member 60 can adopt a top screw structure screwed to the upper cover flange 20, a combined structure composed of screws and nuts, a micrometer head structure installed on the upper cover flange 20, etc.

[0048] Also, see Figure 2 and Figure 4A support table 20a is provided inside the upper cover flange 20, and the support table 20a faces the movable seat 30 in the axial direction; an opening structure is also provided at a position of the upper cover flange 20 corresponding to the movable seat 30, and the opening structure is mainly used to provide a path for inserting or removing the adjusting gasket 70 between the support table 20a and the movable seat 30, so as to adjust the position of the emission source 51 in the axial direction (hereinafter referred to as the axial position) by disassembling and assembling the adjusting gasket 70 between the support table 20a and the movable seat 30, thereby realizing the adjustment of the distance between the emission source 51 and the anode 52 (or the extraction electrode 53).

[0049] In one embodiment, see Figure 3 and Figure 4 The upper cover flange 20 has a connecting sleeve 21 and a sealing sleeve 22 coaxially connected in the axial direction; wherein the deformable sleeve 40 is arranged through the sealing sleeve 22, and the end of the sealing sleeve 22 away from the connecting sleeve 21 in the axial direction is sealed and fixed with the corresponding end of the deformable sleeve 40; the inner diameter of the connecting sleeve 21 is set to be larger than the inner diameter of the sealing sleeve 22, so that a step surface structure can be formed inside the upper cover flange 20 and at the junction of the connecting sleeve 21 and the sealing sleeve 22, and the step surface structure is the support table 20a. The movable seat 30 is restricted in the connecting sleeve 21 by the support table 20a, and the adjusting fastener 60 is set to penetrate the side wall of the connecting sleeve 21 in the radial direction.

[0050] For ease of description, the end face of the connecting sleeve 21 away from the end of the sealing sleeve 22 in the axial direction is defined as the flange end face 20b; wherein, the opening structure includes a plurality of first grooves 20c, the first grooves 20c penetrate the flange end face 20b and extend in the axial direction to connect with the support table 20a, and the plurality of first grooves 20c and the plurality of fastening and adjusting members 60 are evenly and alternately arranged in the circumferential direction. For example, four first grooves 20c are arranged in the connecting sleeve 21 in the form of a 90° angle between two of them, and a fastening and adjusting member 60 is provided at the portion of the connecting sleeve 21 between two adjacent first grooves 20c.

[0051] The first groove 20c extending in the axial direction can guide the adjusting gasket 70 during the process of disassembling and assembling the adjusting gasket 70, so as to facilitate the disassembly and assembly of the adjusting gasket 70 outside the electron gun chamber 10; meanwhile, it is also beneficial to the integrity of the outer contour structure of the upper cover flange 20 (specifically, the connecting sleeve portion 21).

[0052] In other embodiments, the upper cover flange 20 may also adopt other suitable structural structures, for example, the opening structure includes a notch structure arranged along the radial direction through the connecting sleeve 21, and the number of notch structures can be set to one or more; for example, under the premise of ensuring that the emission source 51 and the anode 52 (or the extraction electrode 53) are centrally assembled in the electron gun chamber 10, the connecting sleeve 21 and the fastening adjustment member 60 may be omitted; that is, as long as the adjustment gasket 70 can be inserted or removed between the support table 20a and the movable seat 30 with the help of the opening structure; all these will not be elaborated here.

[0053] First, by tightening the adjustment member 60 against the movable seat 30 in the radial direction, the radial position (or the position in the XY plane) of the emission source 51 can be adjusted, so as to accurately align the emission source 51 with the anode 52 (or the extraction electrode 53) to ensure the collimation of the electron beam emitted by the electron gun. And by inserting or removing the adjustment gasket 70 between the support table 20a and the movable seat 30 through the opening structure (specifically, the first groove 20c), the axial position (or the position in the Z-axis direction) of the emission source 51 can be accurately adjusted to achieve the adjustment of the distance between the emission source 51 and the anode 52 (or the extraction electrode 53).

[0054] As a result, the adjustability of the electron gun structure is effectively improved, so that the electron gun has the ability to finely adjust the position of the emission source 51 relative to the anode 52 (or the extraction electrode 53) in multiple dimensions such as X, Y, and Z, which is beneficial to the precise adjustment and control of the emission parameters of the electron gun (such as the emission current angular density, the size of the imaginary element, etc.) under a specific emission voltage, and provides support for optimizing the signal-to-noise ratio and minimum resolution of the image collected by the scanning electron microscope, and extending the service life of the electron gun.

[0055] Secondly, there is no need to perform hole opening processing on the movable seat 30, the upper cover flange 20, the high-voltage electrode 55 and other components, and the opening structure (such as the first groove 20c) can be used to provide path support for the disassembly and assembly of the adjusting gasket 70. On the one hand, the risk of leakage and discharge in the electron gun chamber 10 can be reduced; on the other hand, with the help of the adjusting gasket 70 as an adjusting element for the axial position of the emission source 51, the force-bearing area of ​​the upper cover flange 20 can be effectively increased and the pressure of the upper cover flange 20 in the axial direction can be reduced, which is beneficial to reduce the risk of leakage at the sealing connection between the upper cover flange 20 and the deformation sleeve 40; at the same time, the adjusting gasket 70 can also provide a more stable structural support for the movable seat 30 (together with the emission assembly), providing support for enhancing the overall structural stability of the electron gun.

[0056] Third, by inserting different thicknesses or different numbers of adjusting gaskets 70 between the support table 20a and the movable seat 30, the precision of the axial position adjustment of the emission source 51 can be ensured, and the position can be finely adjusted or fine-tuned; for example, the thickness of the adjusting gasket 70 in the axial direction is 0.05mm. In a certain specific case, when the adjusting gasket 70 is not inserted, the spacing between the emission source 51 and the extraction pole 53 in the axial direction is about 0.1mm. By inserting different numbers of adjusting gaskets 70 in the form of stacking in the axial direction between the support table 20a and the movable seat 30, the spacing between the emission source 51 and the extraction pole 53 can be gradually increased from 0.1mm to 0.05mm. In this way, the axial position of the emission source 51 can be finely adjusted or fine-tuned in the micrometer level conveniently and flexibly.

[0057] It should be noted that the description of the adjustment gasket 70 is introduced in the embodiment of the present application only for understanding the structural structure, implementation principle and functional effect of the electron gun, and does not mean that the adjustment gasket 70 must be a component of the electron gun.

[0058] In some embodiments, the adjusting gasket 70 is a component of the electron gun, and is detachably disposed between the supporting table 20 a and the movable seat 30 . The axial position of the emission source 51 can be fine-tuned by increasing or decreasing the number or thickness of the adjusting gasket 70 .

[0059] In other embodiments, the adjustment gasket 70 is not a component of the electron gun, but a consumable or spare part used in conjunction with the electron gun; for example, when the axial position of the emission source 51 needs to be adjusted, the adjustment gasket 70 is inserted and supported between the support table 20a and the movable seat 30 through the opening structure.

[0060] In one embodiment, see Figure 4 Combined with Figure 2 and Figure 3 A second groove 20d is provided on the support table 20a, and the second groove 20d is used to position a corresponding adjustment gasket 70 on the support table 20a, so that the adjustment gasket 70 can be stably supported between the support table 20a and the movable seat 30, thereby achieving the purpose of stably limiting the axial position of the emission source 51; the number of the second grooves 20d is the same as the number of the first grooves 20c, for example, the number of both is two, three, four or other greater numbers; multiple second grooves 20d and multiple first grooves 20c are alternately arranged in the circumferential direction, for example, four second grooves 20d and four first grooves 20c are alternately arranged in the circumferential direction, and the angle between two adjacent second grooves 20d in the circumferential direction is 90°.

[0061] Exemplarily, the depth of the second groove 20d in the axial direction is 0.01 mm, and the thickness of the adjusting gasket 70 in the axial direction is 0.05 mm, so that a portion of the adjusting gasket 70 can be accommodated by the second groove 20d, while achieving position restriction of the adjusting gasket 70, ensuring that the adjusting gasket 70 and other adjusting gaskets 70 subsequently inserted and stacked on the adjusting gasket 70 can be stably supported between the support table 20a and the movable seat 30.

[0062] On the one hand, by staggering the second groove 20d and the first groove 20c in the circumferential direction, it is not only possible to ensure that the adjusting gasket 70 can be stably inserted and supported between the support table 20a and the movable seat 30, so that the adjusting gasket 70 is in full contact with the upper cover flange 20 and the movable seat 30, but also to prevent the adjusting gasket 70 from accidentally moving into the first groove 20c and affecting the axial position of the emission source 51. In addition, by utilizing the alternating arrangement relationship between the first groove 20c and the second groove 20d, the adjusting gasket 70 can be conveniently and quickly disassembled and assembled from different positions of the upper cover flange 20, thereby improving the flexibility of adjusting the axial position of the emission source 51.

[0063] On the other hand, by utilizing a plurality of second grooves 20d to restrict the corresponding adjustment gaskets 70 to different positions of the support table 20a in the circumferential direction, the adjustment gaskets 70 can be evenly distributed between the support table 20a and the movable seat 30. This not only improves the force balance between the upper cover flange 20 and the movable seat 30, but also ensures that the movable seat 30 together with the emission source 51 can only move or change position relative to the upper cover flange 20 along the axial direction by inserting or removing the adjustment gasket 70, so as to ensure the collimation of the axial position adjustment of the emission source 51.

[0064] In other embodiments, the number of first grooves 20c may also be less than the number of second grooves 20d. For example, two first grooves 20c are arranged on the upper cover flange 20, and the two second grooves 20d are symmetrically arranged about a radial direction. A second groove 20d is arranged on both sides of each first groove 20c in the circumferential direction on the support table 20a, that is, four second grooves 20d are arranged on the support table 20a; in this way, the corresponding two or two groups of adjustment gaskets 70 can be inserted into two different positions of the support table 20 through one first groove 20c.

[0065] Of course, in some embodiments, the second groove 20d may be omitted, as long as the adjustment gasket 70 can be evenly and stably inserted and supported between the support table 20a and the movable seat 30 in the circumferential direction.

[0066] In one embodiment, see Figure 4 and Figure 5The projection shapes of the second groove 20d and the adjusting gasket 70 in the plane where the supporting table 20a is located are the same. By utilizing the shape matching relationship between the second groove 20d and the adjusting gasket 70, the adjusting gasket 70 can be stably positioned and restricted to avoid position displacement of the adjusting gasket 70 on the supporting table 20a, and it is beneficial to fully utilize the structural space of the upper cover flange 20.

[0067] For example, four second grooves 20d are provided on the support table 20a, that is, four or four groups of adjustment pads 70 can be inserted between the support table 20a and the movable seat 30; at this time, the adjustment pad 70 can adopt an arc-shaped sheet structure; for details, please refer to Figure 5 The projection contour line of the adjustment gasket 70 in the plane where the support table 20a is located includes an inner arc segment 70a, a first straight line segment 70b, an outer arc segment 70c and a second straight line segment 70d which are connected in sequence end to end; wherein, the inner arc segment 70a and the outer arc segment 70c are cocentric, and the central angle between the inner arc segment 70a and the outer arc segment 70c is 45°.

[0068] Therefore, an arc-shaped adjusting gasket 70 is adopted, and the central angle of the arc segment of the adjusting gasket 70 is limited. On the one hand, the number of the second grooves 20d and their alternating arrangement in the circumferential direction can be adapted, so that the adjusting gasket 70 can fully utilize the structural space between two adjacent first grooves 20c in the upper cover flange 20, increase the contact area between the adjusting gasket 70 and the upper cover flange 20 and the movable seat 30, and thus provide a more stable and balanced axial support for the movable seat 30.

[0069] On the other hand, in the process of rotating and moving the adjusting gasket 70 through the first groove 20c to the second groove 20d, the curvature matching relationship between the inner arc segment 70a of the adjusting gasket 70 and the outer circumferential surface of the movable seat 30 or between the outer arc segment 70c and the inner circumferential surface of the connecting sleeve 21 can be utilized to guide the adjusting gasket 70, so that the adjusting gasket 70 can smoothly and accurately reach the position corresponding to the second groove 20d, thereby realizing precise assembly of the adjusting gasket 70.

[0070] In other embodiments, the adjusting gasket 70 (together with the second groove 20d) may also adopt other suitable geometric shapes; for example, the adjusting gasket 70 is an arc-shaped sheet structure, and the central angle of the inner arc segment 70a and the outer arc segment 70c is less than 45°; for another example, the adjusting gasket 70 adopts a rectangular sheet structure, etc. All these will not be elaborated here.

[0071] For some examples, see Figure 5The adjacent inner arc segments 70a, the first straight segment 70b, the outer arc segment 70c and the second straight segment 70d in the adjusting gasket 70 are connected with rounded corners, so as to avoid the formation of sharp edges on the surface of the adjusting gasket 70 and provide support for smooth rotation, movement and disassembly of the adjusting gasket 70.

[0072] In one embodiment, see Figure 6 The contour shape of the emitting source 51 is roughly a needle-shaped structure, which has a needle tip portion and a needle body portion coaxially connected along the geometric center line L1 of the emitting source 51; wherein, the surface of the needle tip portion includes a first surface 51a, a second surface 51b, a third surface 51c and a fourth surface 51d, the first surface 51a is a circular plane structure perpendicular to the geometric center line L1, the second surface 51b is a cylindrical curved surface structure surrounding the geometric center line L1, the third surface 51c is a chamfered arc surface structure connected between the first surface 51a and the second surface 51b, and the fourth surface 51d is a conical curved surface structure connected between the second surface 51b and the surface of the needle body, that is, the fourth surface 51d is a conical curved surface structure connected to the second surface 51b away from the third surface 51c.

[0073] In a specific implementation, the diameter of the circular planar structure corresponding to the first surface 51a can be about one-third of the radius of the cylindrical curved surface structure corresponding to the second surface 51b, and the surface of the needle body can be covered with a film layer (such as a zirconium oxide coating, a zirconium silicide coating, etc.) to protect the emission source 51; of course, the emission source 51 can also use carbon nanotubes.

[0074] Therefore, by setting the top surface of the needle tip to a geometric shape in which a circular plane structure, a chamfered arc surface structure and a cylindrical curved surface structure are connected, the surface of the emission source 51 can have a greater field strength, which is beneficial to improving the electron emission efficiency and making the emission source 51 have a higher brightness; at the same time, utilizing the second surface 51b of the cylindrical curved surface structure is beneficial to slowing down the consumption of the surface film layer of the emission source 51, thereby increasing the service life of the emission source 51.

[0075] In one embodiment, see Figure 1 and Figure 7 Combined with Figure 6The electron gun provided in the embodiment of the present application is a thermal field emission type electron gun. As mentioned above, the electron gun further includes an anode 52, an extraction electrode 53 and a suppression electrode 54; wherein the anode 52 is fixedly arranged inside the electron gun chamber 10, the extraction electrode 53 is located between the anode 52 and the emission source 51 in the axial direction, and the extraction electrode 53 is insulated and fixed to the anode 52 to ensure that the extraction electrode 53 and the emission source 51 are spaced opposite to each other in the axial direction. The suppression electrode 54 is located on the opposite side of the extraction electrode 53 relative to the emission source 51 (specifically, the first surface 51a) in the axial direction. For example, the spacing between the suppression electrode 54 and the emission source 51 (specifically, the first surface 51a) in the axial direction is between 0.1mm and 0.4mm.

[0076] More specifically, the extraction electrode 53 has a first through hole (i.e., the center hole of the extraction electrode 53, not marked in the figure) that penetrates in the axial direction, the extraction electrode 53 is insulated and fixed to the anode 52, and the first through hole is spaced and opposite to the emission source 51 (specifically, the first surface 51a) in the axial direction. The extraction electrode 53 can be fixedly connected to the anode 52 through a columnar or spherical insulating structure 56. For example, the material of the insulating structure 56 can be alumina ceramic, polyetheretherketone, etc.

[0077] See also Fig.11 and Fig.12 , under the premise that the voltage of the extraction electrode 53, the width H1 of the extraction electrode 53 in the axial direction, and the distance D1 between the extraction electrode 53 and the emission source 51 (specifically, the first surface 51a) in the axial direction remain unchanged, Fig.11 shows a curve of the emission current angular density of the electron gun as the radius R1 of the first through hole changes, Fig.12 A curve showing the change of the virtual element size of the electron gun with the radius R1 of the first through hole is shown.

[0078] from Fig.11 It can be seen that when the radius R1 of the first through hole is reduced from 0.5mm to 0.07mm, the emission current angular density increases from 50uA / Sr to 120uA / Sr; in terms of segmentation, when the radius R1 of the first through hole is reduced from 0.5mm to 0.2mm, the emission current angular density increases from 50uA / Sr to 100uA / Sr, and the increase rate is fast; and when the radius R1 of the first through hole is reduced from 0.2mm to 0.07mm, the emission current angular density increases from 100uA / Sr to 120uA / Sr, and the increase rate slows down. Fig.12 It can be seen that when the radius R1 of the first through hole decreases from 0.5 mm to 0.2 mm, the virtual element size decreases from 41 nm to 36 nm; and when the radius R1 of the first through hole decreases from 0.2 mm to 0.07 mm, the virtual element size is basically stable at about 36 nm.

[0079] Therefore, in some embodiments, taking into account the influence of the radius R1 of the first through hole on the angular density of the emission current and the size of the imaginary element, the radius of the first through hole of the extraction electrode 53 can be between 0.07 mm and 0.5 mm. That is to say, according to actual needs (such as the overall performance requirements of the electron gun), the radius of the first through hole can be selected within the range of 0.07 mm to 0.5 mm.

[0080] See also Fig.13 and Fig.14 , under the premise that the voltage of the extraction pole 53, the width H1 of the extraction pole 53 in the axial direction, and the radius R1 of the first through hole remain unchanged, Fig.13 FIG. 4 shows a curve showing the variation of the emission current angular density of the electron gun with the distance D1 between the extraction electrode 53 and the emission source 51. Fig.14 The curve showing the change of the virtual element size of the electron gun with the distance D1 is shown.

[0081] from Fig.13 It can be seen that when the spacing D1 decreases from 0.7mm to 0.1mm, the emission current angular density increases from 20uA / Sr to 200uA / Sr; in terms of segmentation, when the spacing D1 decreases from 0.7mm to 0.3mm, the emission current angular density increases from 20uA / Sr to 50uA / Sr, and the increase rate is slow; when the spacing D1 decreases from 0.3mm to 0.1mm, the emission current angular density increases from 50uA / Sr to 200uA / Sr, and the increase rate is fast. Fig.14 It can be seen that when the spacing D1 decreases from 0.7mm to 0.1mm, the size of the virtual element decreases from 50nm to 32nm; in terms of segmentation, when the spacing D1 decreases from 0.7mm to 0.2mm, the size of the virtual element decreases faster; when the spacing decreases from 0.2mm to 0.1mm, the size of the virtual element decreases slower.

[0082] Therefore, in some embodiments, the distance D1 between the extraction pole 53 and the emission source 51 in the axial direction can be between 0.1 mm and 0.7 mm, so that the distance D1 can be adjusted to a required distance range or a suitable distance value by inserting or removing the adjustment gasket 70 between the support table 20a and the movable seat 30; wherein, based on the selection of the thickness dimension of the adjustment gasket 70 in the axial direction, the adjustment accuracy of the distance D1 can be controlled to the micron level, for example, the 50 micron level.

[0083] It should be noted that those skilled in the art should understand that, for a scanning electron microscope using an electron gun, the angular density of the emission current mainly affects the signal-to-noise ratio of the image collected by the scanning electron microscope, while the size of the virtual element mainly affects the imaging resolution of the centering.

[0084] For some examples, see Figure 7The width H1 of the extraction pole 53 in the axial direction can be controlled within the range of 0.3 mm to 0.5 mm, which is beneficial to the processing and manufacturing of the extraction pole 53 from an engineering perspective and to the coordination between functional components such as the extraction pole 53 and the emission source 51.

[0085] In some embodiments, the extraction electrode 53 may also be fixed relative to the emission source 51. This not only avoids the introduction of vibration noise, but also enables fine adjustment of the distance between the extraction electrode 53 (together with the emission source 51) and the anode 52 by inserting or removing the adjustment gasket 70 between the support table 20a and the movable seat 30, so that the electron gun can meet different application requirements.

[0086] In one embodiment, see Figure 1 The electron gun chamber 10 is provided with an observation window 11 on the radial side wall; for example, the observation window 11 may adopt a standard CF vacuum flange interface, and the material of the observation window 11 may be hard glass, sapphire, quartz, etc. Through the observation window 11, the internal situation of the electron gun chamber 10 may be observed with the cooperation of an observation device such as an optical microscope.

[0087] For example, the position of the emission source 51 in the electron gun chamber 10 and the distance between the emission source 51 and the anode 52 (or the extraction electrode 53 ) can be observed through the observation window 11 .

[0088] For another example, if discharge and sparking occur inside the electron gun chamber 10 due to charge accumulation, the specific discharge position can be observed and determined through the observation window 11 .

[0089] For another example, during the process of disassembling and assembling the adjusting gasket 70 , the relative positions of the emission source 51 and other components can be observed in real time through the observation window 11 to avoid component damage caused by the extraction pole 53 and the like colliding with the emission source 51 .

[0090] It is considered that in addition to the position and size parameters of the extraction electrode 53 having an influence on the emission parameters of the electron gun, the geometric shape of the extraction electrode 53 (specifically, the first through hole) also has a very important influence on the emission parameters.

[0091] In some embodiments, the first through hole may also adopt a variable diameter arc hole structure; for details, please refer to Figure 8In a plane parallel to the central axis L2 of the first through hole, the projection contour of the first through hole includes a first contour 53a and a second contour 53b; wherein the first contour 53a and the second contour 53b are symmetrical about the central axis L2 (it can be understood that the spacing between the first contour 53a and the second contour 53b is equivalent to the diameter of the first through hole), and the first contour 53a and the second contour 53b are arc segments that bend in a direction away from the central axis L2. Since the first through hole of the variable diameter arc hole structure has no sharp edges, it is not only beneficial to increase the angular density of the emission current and reduce the probability of discharge of the emission source 51, but also easy to polish.

[0092] In some embodiments, please combine Figure 7 and Figure 8 The first through hole adopts an equal-diameter straight hole structure, that is, the first contour line 53a and the second contour line 53b are both straight line segments parallel to the central axis L2; ​​the first through hole of the extraction pole 53 adopts an equal-diameter straight hole structure, which is conducive to the processing and manufacturing of the extraction pole 53.

[0093] In other embodiments, the extraction pole 53 may also adopt other suitable geometric shapes to meet different application requirements. Fig. 9 , the extraction electrode 53 has a front surface 53d and a rear surface 53c; wherein, the front surface 53d can be understood as the surface of the extraction electrode 53 facing the emission source 51 in the axial direction, and the front surface 53d is a planar structure surrounding the first through hole, that is, the central axis L2 is perpendicular to the plane where the front surface 53d is located; the rear surface 53c can be understood as the surface of the extraction electrode 53 facing the anode 52 in the axial direction, and the rear surface 53c is a conical surface surrounding the first through hole. In this way, with the help of the conical surface structure of the rear surface 53c, the secondary electrons emitted by the anode 52 can be reflected to prevent the secondary electrons from hitting the emission source 51.

[0094] For some examples, see Fig.10 The extraction electrode 53 is provided with an extraction aperture 57 at one end (e.g., the end where the front end surface 53d is located) in the axial direction facing the emission source 51, and the extraction aperture 57 has a second through hole coaxially connected to the first through hole. Exemplarily, the material of the extraction aperture 57 can be a platinum-iridium alloy or molybdenum, and a precious metal layer that prevents oxidation can be plated on the hole wall of the second through hole.

[0095] The extraction aperture 57 can increase the surface field strength of the emission source 51, improve the electron emission efficiency, limit the divergence angle of the electron beam, block stray electrons, adjust the beam spot size, and suppress the energy broadening of the electron beam. In this way, the emission current density can be increased and the energy dispersion can be reduced without changing the voltage of the extraction electrode 53.

[0096] For some examples, see Figure 1 The electron gun further includes a fluorescent screen 80, which is disposed on a side of the electron gun chamber 10 opposite to the sealing assembly or the upper cover flange 20 in the axial direction; for example, the fluorescent screen 80 can be installed on the electron gun chamber 10 by means of a flange to ensure the vacuum sealing of the electron gun chamber 10.

[0097] The electron beam can be imaged by the fluorescent screen 80, and the size and shape of the electron spot presented by the fluorescent screen 80 can reflect the size and shape of the incident electron beam, so as to provide support for adjusting the position of the emission source 51. Exemplarily, the fluorescent screen 80 can be a YAG or YAP single crystal scintillator screen, or a phosphor screen, so that the fluorescent screen 80 has a higher electron detection efficiency; the surface of the fluorescent screen 80 can be coated (such as an aluminum film) to increase the electron detection efficiency and reduce stray light.

[0098] Specifically, taking the extraction electrode 53 being insulated and fixed to the anode 52 as an example, first ensure that the anode 52, the extraction electrode 53 and the fluorescent screen 80 are assembled at the center of the electron gun chamber 10; after the electron spot is observed on the fluorescent screen 80 (for example, by observing with the help of a camera 90, etc.), the radial position of the emission source 51 (that is, the position in the XY plane) can be adjusted by tightening the adjustment member 60 to ensure that the electron spot is located at the center of the fluorescent screen 80, that is, the alignment of the emission source 51 and the extraction electrode 53 (together with the anode 52) is completed, thereby achieving the collimation adjustment of the electron gun.

[0099] Subsequently, the assembly error between related components (for example, the assembly error between the extraction electrode 53, the anode 52 and the fluorescent screen 80) can be determined by adjusting the voltage of the extraction electrode 53 or the anode 52 and determining the influence of the voltage of the extraction electrode 53 or the anode 52 on the position of the electron spot.

[0100] When the emission parameters of the electron gun need to be adjusted, the adjustment gasket 70 can be inserted or removed between the support table 20a and the movable seat 30 to adjust the emission parameters by adjusting the axial position of the emission source 51 (that is, the distance D1 between the emission source 51 and the extraction pole 53).

[0101] For some examples, see Figure 1 The electron gun chamber 10 is further provided with a magnetic shielding layer 12. For example, the material of the magnetic shielding layer 12 may be Permalloy. The emission source 51, the anode 52, the extraction electrode 53, the suppression electrode 54, etc. are all located in the space surrounded by the magnetic shielding layer 12. The magnetic shielding layer 12 can shield the influence of the external magnetic field on the electron beam.

[0102] The above specific examples are used to illustrate the present invention, which is only used to help understand the present invention and is not intended to limit the present invention. For those skilled in the art, according to the concept of the present invention, some simple deductions, modifications or substitutions can be made.

Claims

1. An electron gun, characterized in that: include: Electron gun room; An upper cover flange is fixed to the electron gun chamber; A sealing assembly is arranged through the upper cover flange, and the sealing assembly includes a movable seat and a deformable sleeve; in the axial direction of the upper cover flange, one end of the deformable sleeve is sealed and fixed to the movable seat, and the other end of the deformable sleeve is sealed and fixed to the upper cover flange; An emission component, passing through the deformable sleeve and fixed to the movable seat, wherein the emission component comprises an emission source arranged inside the electron gun chamber; Among them, a support table is provided inside the upper cover flange, and the support table faces the movable seat in the axial direction. An opening structure is provided at the position of the upper cover flange corresponding to the movable seat; the opening structure is used to provide a path for inserting or removing an adjustment gasket between the support table and the movable seat, so as to adjust the position of the emission source in the axial direction by disassembling and assembling the adjustment gasket.

2. The electron gun according to claim 1, characterized in that The upper cover flange comprises a connecting sleeve and a sealing sleeve, wherein the connecting sleeve is coaxially connected with the sealing sleeve in the axial direction, the supporting table is formed at the junction of the connecting sleeve and the sealing sleeve, and the other end of the deformable sleeve is sealed and fixed with an end of the sealing sleeve away from the connecting sleeve; Among them, the end face of the connecting sleeve away from one end of the sealing sleeve is a flange end face, and the opening structure includes a plurality of first grooves; the first grooves penetrate the flange end face and extend along the axial direction to connect with the supporting table surface.

3. The electron gun according to claim 2, characterized in that A plurality of second grooves are provided on the support table, and the plurality of second grooves and the plurality of first grooves are arranged alternately in a circumferential direction, and the second grooves are used to position a corresponding one of the adjustment gaskets between the support table and the movable seat; wherein the circumferential direction is a direction around the axial direction.

4. The electron gun according to claim 3, characterized in that The projection shapes of the second groove and the adjusting gasket in the plane where the supporting table is located are the same; and / or the number of the first groove and the number of the second groove are both set to four.

5. The electron gun according to claim 2, characterized in that The electron gun further comprises a plurality of fastening and adjusting members, wherein the fastening and adjusting members are connected to the connecting sleeve, and the plurality of fastening and adjusting members and the plurality of first grooves are alternately arranged in a circumferential direction; the fastening and adjusting members are used to abut against the movable seat in a radial direction to adjust the position of the emission source in the radial direction; wherein the circumferential direction is a direction around the axial direction, and the radial direction is a direction perpendicular to the axial direction.

6. The electron gun according to claim 1, characterized in that An observation window is provided on the side wall of the electron gun chamber in the radial direction, and the observation window is used to observe the interior of the electron gun chamber; wherein the radial direction is a direction perpendicular to the axial direction.

7. The electron gun according to any one of claims 1 to 6, characterized in that The electron gun further comprises the adjusting gasket, which is arranged between the supporting table and the movable seat.

8. The electron gun according to claim 7, characterized in that The projection contour line of the adjusting gasket in the plane where the supporting table is located includes an inner arc segment, a first straight line segment, an outer arc segment and a second straight line segment connected end to end in sequence, and the inner arc segment and the outer arc segment share a common center; Wherein, the adjacent inner arc segments, the first straight line segments, the outer arc segments and the second straight line segments are connected by chamfered corners, and / or the central angle between the inner arc segment and the outer arc segment is less than or equal to 45°.

9. The electron gun according to any one of claims 1 to 6, characterized in that The electron gun further comprises an extraction electrode; the extraction electrode is arranged inside the electron gun chamber, and is used to induce the emission source to emit electrons; the extraction electrode has a first through hole penetrating along the axial direction, and the first through hole is spaced opposite to the emission source in the axial direction; wherein: The radius of the first through hole is between 0.07 mm and 0.5 mm, and / or the width of the extraction pole in the axial direction is between 0.3 mm and 0.5 mm, and / or the distance between the extraction pole and the emission source in the axial direction is between 0.1 mm and 0.7 mm.

10. The electron gun according to claim 9, characterized in that The electron gun further comprises an anode which is fixedly arranged inside the electron gun chamber and used for accelerating the electrons emitted by the emission source. The extraction electrode is insulated and fixed to the anode and is located between the anode and the emission source in the axial direction.

11. The electron gun according to claim 10, characterized in that The extraction electrode has a front end surface and a rear end surface, the front end surface is the surface of the extraction electrode facing the emission source in the axial direction, and the central axis of the first through hole is perpendicular to the plane where the front end surface is located; the rear end surface is the surface of the extraction electrode facing the anode in the axial direction, and the rear end surface is a conical surface surrounding the first through hole.

12. The electron gun according to claim 9, characterized in that The projection contour line of the first through hole in a plane parallel to the central axis of the first through hole includes a first contour line and a second contour line, and the first contour line and the second contour line are symmetrical about the central axis; The first contour line and the second contour line are straight line segments, or the first contour line and the second contour line are arc segments that are bent in a direction away from the central axis.

13. The electron gun according to claim 9, characterized in that The emission source has a needle tip portion, and the surface of the needle tip portion includes a first surface, a second surface, a third surface and a fourth surface. The first surface is a circular plane structure perpendicular to the geometric center line of the emission source, the second surface is a cylindrical curved surface structure surrounding the geometric center line, the third surface is a chamfered arc surface structure connected between the first surface and the second surface, and the fourth surface is a conical curved surface structure connected to the second surface on a side away from the third surface.

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