An electron gun

Abstract

An electron gun comprises an electron gun chamber, a cover flange fixed to the electron gun chamber, a movable seat and a deformation sleeve penetrating the cover flange, and an emission assembly penetrating the deformation sleeve and fixed to the movable seat, wherein one end of the deformation sleeve is sealingly fixed to the movable seat and the other end is sealingly fixed to the cover flange, the emission assembly comprises an emission source located inside the electron gun chamber, the inside of the cover flange is provided with a support platform facing the movable seat in the axial direction, and the cover flange is provided with an opening structure corresponding to the position of the movable seat, the opening structure is used to provide a path for inserting or removing an adjusting gasket between the support platform and the movable seat. Through the cooperation of the support platform and the opening structure, fine adjustment of the axial position of the emission source can be realized by inserting or removing the adjusting gasket between the support platform and the movable seat, which is not only beneficial to control the emission parameters (such as emission current angular density, virtual element size, etc.) of the electron gun, but also can prolong the service life of the electron gun.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of scanning electron microscopes, in particular to an electron gun. BACKGROUND

[0002] Scanning Electron Microscope (SEM) is a kind of microanalysis device that uses various physical signals excited by focused electron beam scanning on the sample surface to modulate imaging; compared with traditional optical imaging, scanning electron microscope can provide nanometer or even sub-nanometer resolution, and plays an indispensable role in the fields of defect detection and size measurement in semiconductor device production process. The electron gun is one of the key components of the scanning electron microscope, 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 structure adjustability of the related electron gun is poor, which limits the optimization of the performance of the electron gun. SUMMARY

[0003] The technical problem solved by the present application 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:

[0005] An electron gun chamber;

[0006] An upper cover flange fixed to the electron gun chamber;

[0007] A sealing assembly arranged through the upper cover flange, the sealing assembly comprising a movable seat and a deformation sleeve; in the axial direction of the upper cover flange, one end of the deformation sleeve is sealingly fixed with the movable seat, and the other end of the deformation sleeve is sealingly fixed with the upper cover flange;

[0008] An emission assembly fixed to the movable seat through the deformation sleeve, the emission assembly comprising an emission source arranged inside the electron gun chamber;

[0009] Wherein, the inside of the upper cover flange is provided with a support platform, the support platform faces the movable seat in the axial direction, and the upper cover flange is provided with an opening structure corresponding to the part of the movable seat; the opening structure is used to provide a path for inserting or removing an adjusting gasket between the support platform and the movable seat, so as to adjust the position of the emission source in the axial direction by disassembling the adjusting gasket.

[0010] 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 support table is formed at the joint of the connecting sleeve portion and the sealing sleeve portion, and the other end of the deformation sleeve is sealingly fixed to one end of the sealing sleeve portion away from the connecting sleeve portion.

[0011] In one embodiment, the end surface of the connecting sleeve portion away from the sealing sleeve portion is a flange end surface, and the opening structure includes a plurality of first grooves; the first grooves pass through the flange end surface and extend to the support table along the axial direction.

[0012] 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 alternately arranged in a circumferential direction; the second grooves are used to position a corresponding one of the adjusting washers between the support table and the movable seat; wherein the circumferential direction is a direction around the axial direction.

[0013] In one embodiment, the second grooves and the adjusting washers have the same projection shape in the plane of the support table; and / or the number of the first grooves and the number of the second grooves are both four.

[0014] In one embodiment, the electron gun further includes a plurality of fastening adjusting members connected to the connecting sleeve portion, and the plurality of fastening adjusting members and the plurality of first grooves are alternately arranged in a circumferential direction; the fastening adjusting members are used to abut 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.

[0015] In one embodiment, the electron gun chamber is provided with an observation window on the side wall in the radial direction, and the observation window is used to observe the inside of the electron gun chamber; wherein the radial direction is a direction perpendicular to the axial direction.

[0016] In one embodiment, the electron gun further includes the adjusting washers, and the adjusting washers are arranged between the support table and the movable seat.

[0017] In one embodiment, the projection contour line of the adjusting washer in the plane of the support table includes an inner arc segment, a first straight line segment, an outer arc segment, and a second straight line segment connected in sequence, and the inner arc segment and the outer arc segment share a common center.

[0018] In one embodiment, the adjacent inner arc segment, first straight line segment, outer arc segment, and second straight line segment are connected by a rounded corner, and / or the central angle of the inner arc segment and the outer arc segment is less than or equal to 45°.

[0019] In one embodiment, the electron gun further comprises an extraction electrode; the extraction electrode is arranged inside the electron gun chamber and is configured to induce the emission of electrons from the emission source; the extraction electrode has a first through-hole penetrating along the axial direction, the first through-hole is spaced apart from the emission source along the axial direction; wherein:

[0020] The radius of the first through-hole is between 0.07mm and 0.5mm, and / or the width of the extraction electrode along the axial direction is between 0.3mm and 0.5mm, and / or the distance between the extraction electrode and the emission source along the axial direction is between 0.1mm and 0.7mm.

[0021] In one embodiment, the electron gun further comprises an anode; the anode is fixedly arranged inside the electron gun chamber and is configured to accelerate the electrons emitted from the emission source; the extraction electrode is fixedly arranged on the anode and is located between the anode and the emission source along the axial direction.

[0022] 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 along the axial direction, and the central axis of the first through-hole is perpendicular to the plane on which the front end surface lies; the rear end surface is the surface of the extraction electrode facing the anode along the axial direction, and the rear end surface is a conical surface surrounding the first through-hole.

[0023] In one embodiment, the projection profile of the first through-hole in a plane parallel to the central axis of the first through-hole comprises a first profile line and a second profile line, the first profile line and the second profile line are symmetrical about the central axis;

[0024] Wherein, the first profile line and the second profile line are straight line segments, or the first profile line and the second profile line are arc line segments curved away from the central axis.

[0025] In one embodiment, the emission source has a needle tip part, and the surface of the needle tip part comprises a first surface, a second surface, a third surface and a fourth surface; the first surface is a circular planar 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 rounded corner arc surface structure connecting between the first surface and the second surface; and the fourth surface is a conical curved surface structure connecting on the side of the second surface away from the third surface.

[0026] The electron gun according to the above embodiment comprises 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 sealingly fixed to the movable seat, and the other end is sealingly fixed to the upper cover flange, the emission assembly comprises an emission source located inside the electron gun chamber, the inside of the upper cover flange is provided with a support platform facing the movable seat in the axial direction, and the part of the upper cover flange corresponding to the movable seat is provided with an opening structure for providing a path for inserting or removing the adjusting gasket between the support platform and the movable seat. By inserting or removing the adjusting gasket between the support platform and the movable seat, the axial position of the emission source can be finely adjusted, which is beneficial to control the emission parameters (such as emission current angular density, virtual element size, etc.) of the electron gun and prolong the service life of the electron gun. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The schematic diagram of the overall structure of the electron gun of an embodiment.

[0028] Figure 2 The schematic diagram of the structure of the upper cover flange of an embodiment of the electron gun.

[0029] Figure 3 The schematic diagram of the cross-sectional structure of the upper cover flange in the axial direction of an embodiment of the electron gun.

[0030] Figure 4 The schematic diagram of the planar structure of the upper cover flange of an embodiment of the electron gun.

[0031] Figure 5 The schematic diagram of the contour structure of the adjusting gasket of an embodiment of the electron gun.

[0032] Figure 6 The enlarged schematic diagram of the structure of the needle tip part of the emission source of an embodiment of the electron gun.

[0033] Figure 7 The schematic diagram of the relative position relationship between the emission source and the extraction electrode of an embodiment of the electron gun.

[0034] Figure 8 The schematic diagram of the projection perspective of the extraction electrode of an embodiment of the electron gun.

[0035] Figure 9 The schematic diagram of the cross-sectional structure of the extraction electrode of an embodiment of the electron gun (I).

[0036] Figure 10 The schematic diagram of the cross-sectional structure of the extraction electrode of an embodiment of the electron gun (II).

[0037] Figure 11A graph showing the simulated variation of the emission current angular density with the extraction pole central hole radius in one embodiment.

[0038] Figure 12 A graph showing the simulated variation of the virtual electron size with the extraction pole central hole radius in one embodiment.

[0039] Figure 13 A graph showing the simulated variation of the emission current angular density with the distance from the extraction pole to the emission source in one embodiment.

[0040] Figure 14 A graph showing the simulated variation of the virtual electron size with the distance from the extraction pole to the emission source in one embodiment.

[0041] In the drawings:

[0042] 10, electron gun chamber; 11, viewing window; 12, magnetic shielding layer; 20, upper cover flange; 20a, support table; 20b, flange end surface; 20c, first groove; 20d, second groove; 21, connecting sleeve portion; 22, sealing sleeve portion; 30, movable seat; 40, deformation sleeve;

[0043] 50, emission source; 51a, first surface; 51b, second surface; 51c, third surface; 51d, fourth surface; 52, anode; 53, extraction pole; 53a, first profile line; 53b, second profile line; 53c, rear end surface; 53d, front end surface; 54, suppression pole; 55, high voltage electrode; 56, insulating structural member; 57, extraction diaphragm;

[0044] 60, fastening adjusting member; 70, adjusting gasket; 70a, inner side circular arc segment; 70b, first straight line segment; 70c, outer side circular arc segment; 70d, second straight line segment; 80, fluorescent screen; 90, camera. DETAILED DESCRIPTION

[0045] The application will be further described in details below with specific embodiments and with reference to the drawings. In different embodiments, similar elements are designated by similar reference numerals. In the following embodiments, many details are described in order to make the application better understood. However, one skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials, methods. In some cases, some operations related to the application are not shown or described in the specification in order to avoid the core part of the application being overwhelmed by too much description, and it is not necessary to describe these related operations in details for one skilled in the art according to the description in the specification and the general technical knowledge in the art.

[0046] In addition, features described in the specification, operations or characteristics can be combined in any appropriate manner in various embodiments. Meanwhile, the steps or actions in the method description can also be sequentially changed or adjusted in a manner that can be apparent 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 do not mean that the sequence is necessary, unless otherwise stated that a certain sequence must be followed.

[0047] The serial numbers of components in this paper, such as "first", "second", etc., are only used to distinguish the described objects, and do not have any order or technical meaning. The "connection" and "coupling" in this application include direct and indirect connection (coupling) unless otherwise specified.

[0048] Please refer to Figures 1 to 10 The embodiments of the present application provide an electron gun, such as a tungsten filament electron gun, a lanthanum hexaboride (LaB6) filament electron gun, a hot 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 assembly, an adjusting assembly, an emitting assembly, and other functional components as needed, which will be described in detail below.

[0049] Please refer to Figure 1 The electron gun chamber 10 can be a vacuum insulated chamber structure made of non-magnetic 316L stainless steel, permalloy, etc. For example, for a thermionic field emission electron gun, the vacuum degree of the electron gun chamber 10 is greater than 1*10 -7 Pa. The upper cover flange 20 is mainly used as a structural connection carrier between the electron gun chamber 10 and the sealing assembly and the adjusting assembly. The upper cover flange 20 is fixed to the electron gun chamber 10, for example, the upper cover flange 20 is provided through and fixed to the interface of the electron gun chamber 10.

[0050] In order to more clearly and specifically describe the electron gun, the upper cover flange 20 is defined as three different directions in this paper, namely the axial direction, the radial direction and the circumferential direction. 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.

[0051] Please refer to Figures 1 to 3The sealing assembly comprises a movable seat 30 and a deformation sleeve 40 arranged in sequence along the axial direction through the upper cover flange 20; wherein the deformation sleeve 40 is a sleeve structure capable of deforming under stress, for example, the deformation sleeve 40 can adopt a bellows structure capable of expanding and contracting in the axial direction and swinging in the radial direction; the movable seat 30 is located closer to the outside of the electron gun chamber 10 than the deformation sleeve 40, one end of the deformation sleeve 40 in the axial direction is sealingly fixed (such as welded sealing) with the movable seat 30, and the other end of the deformation sleeve 40 in the axial direction is sealingly fixed (such as welded sealing) with the upper cover flange 20.

[0052] On the one hand, the sealing structure connection relationship between the upper cover flange 20 and the sealing assembly is established to ensure the vacuum sealing of the electron gun chamber 10; on the other hand, by using the characteristic that the deformation sleeve 40 can deform under stress, a non-rigid connection relationship can be established between the upper cover flange 20 and the movable seat 30 to provide support for the position movement (such as axial movement, radial movement, etc.) of the movable seat 30 relative to the upper cover flange 20 and the electron gun chamber 10.

[0053] Please refer to Figure 1 The emission assembly is arranged through the deformation sleeve 40, and the emission assembly is fixedly connected with the movable seat 30, so that the emission assembly can move synchronously with the movable seat 30; the emission assembly comprises an emission source 51 arranged inside the electron gun chamber 10, which can be understood as a cathode or a filament of an electron gun, mainly used for generating electrons. It can be understood that in different types of electron guns, the electron gun chamber 10 also has related functional components cooperating with the emission source 51 to realize the function of emitting electron beams.

[0054] Exemplarily, please refer to Figure 1 and Figure 7 The electron gun is a hot field emission type electron gun, which also comprises a high-voltage electrode 55, and the electron gun chamber 10 is provided with an anode 52, an extraction electrode 53 and a suppression electrode 54; wherein the anode 52 is arranged in opposite relation to the emission source 51 in the axial direction, mainly used for accelerating 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, mainly used for providing a high-voltage electric field for the electron emission surface of the emission source 51 to induce the emission of electrons by the emission source 51.

[0055] 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, which can also be understood as 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, and the suppression electrode 54 is mainly used for suppressing the emission of electrons by surfaces other than the electron emission surface of the emission source 51.

[0056] The high-voltage electrode 55 is mainly used for connecting external power supply to apply voltage to the emission source 51, the anode 52, the extraction electrode 53 and the suppressor 54; for example, the high-voltage electrode 55 can be divided into four or five paths to feed high voltage, one or two paths to feed 2A heating current to the emission source 51, one path to feed -300V voltage to the suppressor 54, one path to feed 3000V voltage to the extraction electrode 53, and one path to feed 9000V voltage to the anode 52.

[0057] In some embodiments, the functional component fixedly connected with the movable seat 30 in the emission assembly can be the high-voltage electrode 55, and the emission source 51 and the suppressor 54 are fixedly connected with the high-voltage electrode 55. In other embodiments, the emission source 51 and the suppressor 54 correspond to one high-voltage electrode 55, and another two-axial high-voltage electrode 55 is arranged on the side wall of the electron gun chamber 10 in the radial direction, which is used to feed voltage to the anode 52 and the extraction electrode 53.

[0058] Exemplarily, please refer to Figure 1 and Figure 7 , the electron gun is a tungsten filament electron gun or a lanthanum hexaboride electron gun, and the inside of the electron gun chamber 10 is provided with the anode 52 and the grid (not shown in the figure); wherein the anode 52 is arranged opposite to the emission source 51 in the axial direction, and is mainly used for accelerating 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 for controlling the flow of the electron beam and reducing the divergence angle of the electron beam.

[0059] Please refer to Figures 1 to 4 , the adjusting assembly is mainly used for adjusting the position of the emission source 51 by adjusting the position of the movable seat 30; the adjusting assembly includes a plurality of fastening adjusting members 60 arranged uniformly in the circumferential direction, for example, three, four or more; the fastening adjusting member 60 is connected to the part of the upper cover flange 20 corresponding to the movable seat 30, and is mainly used for abutting against 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 radial position). In specific implementation, the fastening adjusting member 60 can adopt a structure including but not limited to a top screw structure screwed to the upper cover flange 20, a combined structure composed of a screw and a nut, a differential head structure installed on the upper cover flange 20, etc.

[0060] Meanwhile, please refer to Figure 2 and Figure 4The inner part of the upper cover flange 20 is provided with a support platform 20a, which faces the movable seat 30 in the axial direction; and an opening structure is also provided at the part of the upper cover flange 20 corresponding to the movable seat 30, which is mainly used to provide a path for inserting or removing the adjusting gasket 70 between the support platform 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 axial position) by disassembling and assembling the adjusting gasket 70 between the support platform 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).

[0061] In one embodiment, referring to Figure 3 and Figure 4 The upper cover flange 20 has a connecting sleeve part 21 and a sealing sleeve part 22 coaxially connected in the axial direction; wherein the deformation sleeve 40 is arranged through the sealing sleeve part 22, and the end of the sealing sleeve part 22 away from the connecting sleeve part 21 in the axial direction is sealingly fixed with the corresponding end of the deformation sleeve 40; the inner diameter of the connecting sleeve part 21 is larger than the inner diameter of the sealing sleeve part 22, so that a stepped surface structure, i.e. the support platform 20a, can be formed inside the upper cover flange 20 at the joint between the connecting sleeve part 21 and the sealing sleeve part 22. The movable seat 30 is limited in the connecting sleeve part 21 by the support platform 20a, and the adjusting fastener 60 is arranged through the side wall of the connecting sleeve part 21 in the radial direction.

[0062] For the convenience of description, the end face of the connecting sleeve part 21 away from the sealing sleeve part 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 pass through the flange end face 20b and extend to the joint with the support platform 20a in the axial direction, and the plurality of first grooves 20c and the plurality of fastening adjusting members 60 are uniformly and alternately arranged in the circumferential direction. For example, four first grooves 20c are arranged in the connecting sleeve part 21 with an angle of 90° between each other, and one fastening adjusting member 60 is arranged at the part of the connecting sleeve part 21 between the adjacent two first grooves 20c.

[0063] By arranging the first grooves 20c extending in the axial direction, the adjusting gasket 70 can be guided and oriented during the disassembly and assembly process, which facilitates the disassembly and assembly of the adjusting gasket 70 outside the electron gun chamber 10; at the same time, it is also beneficial to the integrity of the outer contour structure of the upper cover flange 20 (specifically the connecting sleeve part 21).

[0064] In other embodiments, the upper cover flange 20 can also adopt other suitable structural configurations, such as an open structure including a notch structure provided through the connecting sleeve 21 in the radial direction, and the number of notch structures can be 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 centered and assembled in the electron gun chamber 10, the connecting sleeve 21 and the fastening adjusting member 60 can also be omitted; that is, as long as the open structure can be used to insert or remove the adjusting gasket 70 between the support table 20a and the movable seat 30; and the like, which will not be described here.

[0065] First, by the fastening adjusting member 60 abutting the movable seat 30 from the radial direction, the radial position (or the position in the X-Y plane) of the emission source 51 can be adjusted to accurately center the emission source 51 and the anode 52 (or the extraction electrode 53), and ensure the collimation of the electron beam emitted by the electron gun. By the open 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 by inserting or removing the adjusting gasket 70 between the support table 20a and the movable seat 30, so as to adjust the distance between the emission source 51 and the anode 52 (or the extraction electrode 53).

[0066] Therefore, 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 precisely adjust and control the emission parameters (such as emission current angular density, virtual element size, etc.) of the electron gun under a certain emission voltage, and provides support for optimizing the signal-to-noise ratio and minimum resolution of the image collected by the scanning electron microscope, prolonging the service life of the electron gun, and the like.

[0067] Second, without the need for opening processing of the movable seat 30, the upper cover flange 20, the high-voltage electrode 55, and the like, the open structure (specifically, the first groove 20c) can provide path support for disassembling and adjusting the gasket 70. On the one hand, it can reduce the risk of gas leakage and discharge of the electron gun chamber 10; on the other hand, by using the adjusting gasket 70 as an adjusting element of the axial position of the emission source 51, the stress 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, thereby reducing the risk of gas 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 more stable structural support for the movable seat 30 (together with the emission assembly), thereby providing support for enhancing the structural stability of the electron gun as a whole.

[0068] Thirdly, by inserting the adjusting shims 70 with different thicknesses or different numbers between the support platform 20a and the movable seat 30, the axial position adjustment precision of the emission source 51 can be ensured, and the fine adjustment or micro-adjustment of the position can be realized; for example, the thickness of the adjusting shims 70 in the axial direction is 0.05 mm, and in some specific cases, the distance between the emission source 51 and the extraction electrode 53 in the axial direction is about 0.1 mm when the adjusting shims 70 are not inserted. By inserting the adjusting shims 70 with different numbers in the form of stacking in the axial direction between the support platform 20a and the movable seat 30, the distance between the emission source 51 and the extraction electrode 53 can be gradually increased from 0.1 mm to the order of 0.05 mm. In this way, the axial position of the emission source 51 can be conveniently and flexibly fine-adjusted or micro-adjusted to the order of microns.

[0069] It should be noted that the description of the adjusting shims 70 in the embodiments of the present application is only for the purpose of understanding the structure, implementation principle and functional effect of the electron gun, and does not mean that the adjusting shims 70 are necessarily a component of the electron gun.

[0070] In some embodiments, the adjusting shims 70 are a component of the electron gun, and the adjusting shims 70 are arranged in a detachable form between the support platform 20a and the movable seat 30. By increasing or decreasing the number or thickness of the adjusting shims 70, the axial position of the emission source 51 can be fine-adjusted or micro-adjusted.

[0071] In other embodiments, the adjusting shims 70 are not a component of the electron gun, but are consumables or spare parts used in cooperation with the electron gun; for example, when the axial position of the emission source 51 needs to be adjusted, the adjusting shims 70 are inserted and supported between the support platform 20a and the movable seat 30 through the opening structure.

[0072] In one embodiment, please refer to Figure 4 in combination with Figure 2 and Figure 3 The support platform 20a is provided with a second groove 20d for positioning a corresponding adjusting shim 70 on the support platform 20a, so that the adjusting shim 70 can be stably supported between the support platform 20a and the movable seat 30, thereby achieving the purpose of stably defining the axial position of the emission source 51. The number of the second grooves 20d is the same as that of the first grooves 20c, for example, both of them are two, three, four or more; the plurality of second grooves 20d and the plurality of 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 included angle between two adjacent second grooves 20d in the circumferential direction is 90°.

[0073] Exemplarily, the second groove 20d has a depth of 0.01 mm in the axial direction, and the adjusting gasket 70 has a thickness of 0.05 mm in the axial direction, so that a portion of the adjusting gasket 70 can be accommodated by the second groove 20d, while achieving the position limitation of the adjusting gasket 70, and 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 platform 20a and the movable seat 30.

[0074] On the one hand, by arranging the second groove 20d and the first groove 20c to be staggered in the circumferential direction, not only can the adjusting gasket 70 be stably inserted and supported between the support platform 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 the adjusting gasket 70 can be prevented from being accidentally moved into the first groove 20c to affect the axial position of the emission source 51. In addition, by using 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 directions of the upper cover flange 20, thereby improving the flexibility of the axial position adjustment of the emission source 51.

[0075] On the other hand, by using a plurality of second grooves 20d to limit the corresponding adjusting gaskets 70 at different positions of the support platform 20a in the circumferential direction, the adjusting gaskets 70 can be uniformly distributed between the support platform 20a and the movable seat 30, so that not only the balance of the force between the upper cover flange 20 and the movable seat 30 can be improved, but also by inserting or removing the adjusting gaskets 70, it can be ensured that the movable seat 30 together with the emission source 51 can only move or change position relative to the upper cover flange 20 in the axial direction, so as to ensure the collimation of the axial position adjustment of the emission source 51.

[0076] In other embodiments, the number of first grooves 20c can also be less than the number of second grooves 20d, for example, two first grooves 20c and two second grooves 20d are arranged symmetrically about a radial direction on the upper cover flange 20, and one second groove 20d is arranged on each side of the support platform 20a in the circumferential direction of each first groove 20c, that is, four second grooves 20d are arranged on the support platform 20a; so that two or two groups of adjusting gaskets 70 can be inserted into two different positions of the support platform 20 by one first groove 20c.

[0077] Of course, in some embodiments, the second groove 20d can also be omitted, as long as the adjusting gasket 70 can be uniformly and stably inserted and supported between the support platform 20a and the movable seat 30 in the circumferential direction.

[0078] In one embodiment, please refer to Figure 4 and Figure 5, the projection shape of the second groove 20d and the adjusting pad 70 in the plane where the support table 20a is located is the same, and the shape matching relationship between the second groove 20d and the adjusting pad 70 can be used to stably position and limit the adjusting pad 70, so as to avoid the position deviation of the adjusting pad 70 on the support table 20a, and facilitate the full use of the structural space of the upper cover flange 20.

[0079] Exemplarily, four second grooves 20d are arranged on the support table 20a, that is, four or four groups of adjusting pads 70 can be arranged between the support table 20a and the movable seat 30; at this time, the adjusting pad 70 can adopt an arc-shaped sheet structure; specifically, please refer to Figure 5 , the projection contour line of the adjusting pad 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 sequentially connected in a head-tail manner; wherein, the inner arc segment 70a and the outer arc segment 70c share a common center, and the central angle of the inner arc segment 70a and the outer arc segment 70c is 45°.

[0080] Therefore, the adjusting pad 70 with an arc-shaped structure is adopted, and the central angle of the arc segment of the adjusting pad 70 is limited. On the one hand, the number of the second grooves 20d and the alternate arrangement relationship thereof in the circumferential direction can be adapted, so that the adjusting pad 70 can fully utilize the structural space between adjacent two first grooves 20c in the upper cover flange 20, increase the contact area of the adjusting pad 70 with the upper cover flange 20 and the movable seat 30, and thus provide more stable and balanced axial support for the movable seat 30.

[0081] On the other hand, in the process of rotating and moving the adjusting pad 70 through the first groove 20c to the second groove 20d, the arc matching relationship between the inner arc segment 70a of the adjusting pad 70 and the outer peripheral surface of the movable seat 30 or between the outer arc segment 70c of the adjusting pad 70 and the inner peripheral surface of the connecting sleeve part 21 can be used to guide the adjusting pad 70, so that the adjusting pad 70 can smoothly and accurately reach the position corresponding to the second groove 20d, and the precise assembly of the adjusting pad 70 is realized.

[0082] In other embodiments, the adjusting pad 70 (together with the second groove 20d) can also adopt other suitable geometric shapes; for example, the adjusting pad 70 adopts 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 pad 70 adopts a rectangular sheet structure, etc. All of these will not be repeated here.

[0083] In some embodiments, please refer to Figure 5The chamfered corner between the adjacent inner arc segment 70a, the first straight segment 70b, the outer arc segment 70c and the second straight segment 70d in the adjusting gasket 70 is adjusted, so that relatively sharp edges on the surface of the adjusting gasket 70 are avoided, and smooth rotation movement and disassembly of the adjusting gasket 70 are supported.

[0084] In one embodiment, referring to Figure 6 The profile of the emission source 51 is approximately needle-shaped, which has a needle tip part and a needle body part coaxially connected along a geometric center line L1 of the emission source 51; wherein the surface of the needle tip part 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 planar 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 corner arc surface structure connected between the first surface 51a and the second surface 51b, and the fourth surface 51d is a tapered curved surface structure connected between the second surface 51b and the surface of the needle body part, that is, the fourth surface 51d is a tapered curved surface structure connected on the side of the second surface 51b away from the third surface 51c.

[0085] In 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 part can be covered with a film layer (such as a zirconium oxide plating layer, a zirconium silicide plating layer, etc.) to protect the emission source 51; of course, the emission source 51 can also use carbon nanotubes.

[0086] Therefore, by setting the top surface of the needle tip part as a geometric shape with a circular planar structure, a chamfered corner arc surface structure and a cylindrical curved surface structure connected, the surface of the emission source 51 can have greater field strength, which is conducive to improving the electron emission efficiency and making the emission source 51 have higher brightness; at the same time, using the second surface 51b of the cylindrical curved surface structure is conducive to slowing down the consumption of the film layer on the surface of the emission source 51, thereby improving the service life of the emission source 51.

[0087] In one embodiment, referring to Figure 1 and Figure 7 and combining Figure 6The electron gun provided by the embodiments of the present application is a hot field emission type electron gun. As described above, the electron gun further comprises an anode 52, an extraction electrode 53 and a suppression electrode 54. 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 is fixedly insulated to the anode 52, so as to ensure that the extraction electrode 53 and the emission source 51 are spaced apart 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 distance between the suppression electrode 54 and the emission source 51 (specifically, the first surface 51a) in the axial direction is between 0.1 mm and 0.4 mm.

[0088] More specifically, the extraction electrode 53 has a first through hole (i.e., the central hole of the extraction electrode 53, not labeled in the figure) penetrating in the axial direction. The extraction electrode 53 is fixedly insulated to the anode 52. The first through hole is spaced apart from 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 structural member 56. For example, the material of the insulating structural member 56 can be alumina ceramic, polyether ether ketone, etc.

[0089] It can be seen from Figure 11 and Figure 12 that, 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, Figure 11 a curve showing the variation of the emission current angular density of the electron gun with the radius R1 of the first through hole is shown, Figure 12 and a curve showing the variation of the virtual element size of the electron gun with the radius R1 of the first through hole is shown.

[0090] It can be seen from Figure 11 that, when the radius R1 of the first through hole decreases from 0.5 mm to 0.07 mm, the emission current angular density increases from 50 uA / Sr to 120 uA / Sr. In terms of segments, when the radius R1 of the first through hole decreases from 0.5 mm to 0.2 mm, the emission current angular density increases from 50 uA / Sr to 100 uA / Sr, and the increasing speed is relatively fast. When the radius R1 of the first through hole decreases from 0.2 mm to 0.07 mm, the emission current angular density increases from 100 uA / Sr to 120 uA / Sr, and the increasing speed is relatively slow. Figure 12 It can be seen from Figure 12 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. 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.

[0091] Therefore, in some embodiments, the radius of the first through hole of the extraction electrode 53 can be between 0.07mm and 0.5mm, considering the influence of the radius R1 of the first through hole on the emission current angular density and the virtual element size. That is, the radius of the first through hole can be selected within the range of 0.07mm to 0.5mm according to actual needs (e.g., overall performance requirements of the electron gun).

[0092] Please refer to Figure 13 and Figure 14 , 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 radius R1 of the first through hole remain unchanged, Figure 13 a curve showing the emission current angular density of the electron gun as the distance D1 between the extraction electrode 53 and the emission source 51 changes is shown, Figure 14 a curve showing the virtual element size of the electron gun as the distance D1 changes is shown.

[0093] From Figure 13 it can be seen that when the distance D1 decreases from 0.7mm to 0.1mm, the emission current angular density increases from 20uA / Sr to 200uA / Sr; in terms of segments, when the distance D1 decreases from 0.7mm to 0.3mm, the emission current angular density increases from 20uA / Sr to 50uA / Sr at a slower rate; when the distance D1 decreases from 0.3mm to 0.1mm, the emission current angular density increases from 50uA / Sr to 200uA / Sr at a faster rate. From Figure 14 it can be seen that when the distance D1 decreases from 0.7mm to 0.1mm, the virtual element size decreases from 50nm to 32nm; in terms of segments, when the distance D1 decreases from 0.7mm to 0.2mm, the virtual element size decreases at a faster rate; when the distance D1 decreases from 0.2mm to 0.1mm, the virtual element size decreases at a slower rate.

[0094] Therefore, in some embodiments, the distance D1 between the extraction electrode 53 and the emission source 51 in the axial direction can be between 0.1mm and 0.7mm, so that the distance D1 can be adjusted to a desired distance range or a suitable distance value by inserting or removing the adjusting gasket 70 between the support mesa 20a and the movable seat 30; wherein based on the selection of the thickness dimension of the adjusting gasket 70 in the axial direction, the adjustment accuracy of the distance D1 can be controlled to the order of microns, for example, the order of 50 microns.

[0095] It should be noted that those skilled in the art should understand that, in terms of a scanning electron microscope to which the electron gun is applied, the emission current angular density mainly affects the signal-to-noise ratio of the image collected by the scanning electron microscope, and the virtual element size mainly affects the imaging resolution in the center.

[0096] In some embodiments, please refer to Figure 7The width H1 of the extraction pole 53 in the axial direction can be controlled in the range of 0.3mm-0.5mm, which is beneficial for machining the extraction pole 53 from the engineering point of view and realizing the cooperation between the extraction pole 53 and the functional components such as the emission source 51.

[0097] In some embodiments, the extraction pole 53 can also be fixedly arranged relative to the emission source 51, so that vibration noise is not introduced, and by inserting or removing the adjusting gasket 70 between the support table 20a and the movable seat 30, fine adjustment of the distance between the extraction pole 53 (together with the emission source 51) and the anode 52 can be realized, so that the electron gun can meet different application requirements.

[0098] In one embodiment, referring to Figure 1 The electron gun chamber 10 is provided with an observation window 11 on the side wall in the radial direction; for example, the observation window 11 can adopt a standard CF vacuum flange interface, and the material of the observation window 11 can be hard glass, sapphire, quartz, etc. By means of the observation window 11, the internal situation of the electron gun chamber 10 can be observed under the cooperation of an observation device such as an optical microscope.

[0099] 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 pole 53) can be observed through the observation window 11.

[0100] For another example, if the inside of the electron gun chamber 10 discharges and sparks due to charge accumulation, the specific discharge position can also be observed and determined through the observation window 11.

[0101] 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, so as to avoid damage to the components caused by the collision between the extraction pole 53 and the emission source 51.

[0102] It is considered that in addition to the position and size parameters of the extraction pole 53, the geometric shape of the extraction pole 53 (specifically the first through hole) also has a very important influence on the emission parameters of the electron gun.

[0103] In some embodiments, the first through hole can also adopt a variable-diameter arc-shaped hole structure; specifically, referring to Figure 8In a plane parallel to the central axis L2 of the first through hole, the projected contour lines of the first through hole include a first contour line 53a and a second contour line 53b. The first contour line 53a and the second contour line 53b are symmetrical about the central axis L2 (it can be understood that the distance between the first contour line 53a and the second contour line 53b is equivalent to the diameter of the first through hole), and the first contour line 53a and the second contour line 53b are arc segments curved away from the central axis L2. Since the first through hole of the variable-diameter arc-shaped hole structure has no sharp edges, it not only helps to increase the emission current angular density and reduce the probability of discharge in the emission source 51, but also facilitates polishing.

[0104] In some embodiments, please refer to Figure 7 and Figure 8 The first through hole adopts a straight hole structure with equal diameter, 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 electrode 53 adopts a straight hole structure with equal diameter, which is beneficial to the processing and manufacturing of the extraction electrode 53.

[0105] In other embodiments, the extraction electrode 53 may also adopt other suitable geometries to meet different application needs. For example, please refer to... Figure 9 The extraction electrode 53 has a front surface 53d and a rear surface 53c. The front surface 53d can be understood as the surface of the extraction electrode 53 facing the emission source 51 in the axial direction. The front surface 53d is a planar structure surrounding the first through hole, that is, the central axis L2 is perpendicular to the plane containing the front surface 53d. The rear surface 53c can be understood as the surface of the extraction electrode 53 facing the anode 52 in the axial direction. The rear surface 53c is a conical surface surrounding the first through hole. In this way, the conical structure of the rear surface 53c can reflect the secondary electrons emitted by the anode 52, preventing the secondary electrons from hitting the emission source 51.

[0106] In some embodiments, please refer to Figure 10 The extraction electrode 53 has an extraction aperture 57 at one end facing the emission source 51 in the axial direction (e.g., the end where the front surface 53d is located). The extraction aperture 57 has a second through hole that is coaxially connected to the first through hole. For example, the material of the extraction aperture 57 can be a platinum-iridium alloy or molybdenum, and the wall of the second through hole can be plated with a noble metal layer to prevent oxidation.

[0107] By using the extraction aperture 57, the surface field strength of the emission source 51 can be increased, the electron emission efficiency can be improved, the divergence angle of the electron beam can be limited, stray electrons can be blocked, the beam spot size can be controlled, and the energy broadening of the electron beam can be suppressed. Thus, without changing the voltage of the extraction electrode 53, the emission current density can be increased and the energy dispersion can be reduced.

[0108] In some embodiments, referring to Figure 1 The electron gun further comprises a fluorescent screen 80 arranged on the 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 mounted on the electron gun chamber 10 by means of the flange to ensure the vacuum sealing of the electron gun chamber 10.

[0109] The electron beam can be imaged by means of the fluorescent screen 80, and the size and shape of the electron spot presented by the fluorescent screen 80 can reflect the characteristics of the size and shape of the incident electron beam, thereby providing support for adjusting the position of the emission source 51. For example, the fluorescent screen 80 can be a YAG or YAP single crystal scintillator screen, or a fluorescent powder screen, so that the fluorescent screen 80 has a high electron detection efficiency; the surface of the fluorescent screen 80 can be coated with a film (for example, an aluminum film) to increase the electron detection efficiency and reduce stray light.

[0110] Specifically, taking the extraction electrode 53 fixedly insulated on the anode 52 as an example, first, it is ensured 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 observing the electron spot on the fluorescent screen 80 (for example, by means of a camera 90 or the like), the radial position (i.e., the position in the X-Y plane) of the emission source 51 can be adjusted by means of the fastening adjusting member 60 to ensure that the electron spot is located at the center of the fluorescent screen 80, that is, the centering of the emission source 51 with the extraction electrode 53 (together with the anode 52) is completed, and the collimation adjustment of the electron gun is realized.

[0111] Subsequently, the assembly error between the relevant components (for example, the assembly error between the extraction electrode 53, the anode 52 and the fluorescent screen 80) can be judged by adjusting the voltage of the extraction electrode 53 or the anode 52 and judging the influence of the voltage of the extraction electrode 53 or the anode 52 on the position of the electron spot.

[0112] When it is necessary to regulate the emission parameters of the electron gun, the adjusting shims 70 can be inserted or removed between the support table 20a and the movable seat 30, and the axial position of the emission source 51 (i.e., the distance D1 between the emission source 51 and the extraction electrode 53) is adjusted to realize the adjustment of the emission parameters.

[0113] In some embodiments, referring to Figure 1 The interior of the electron gun chamber 10 is further provided with a magnetic shielding layer 12; for example, the material of the magnetic shielding layer 12 can be permalloy; the emission source 51, the anode 52, the extraction electrode 53, the suppression electrode 54 and the like are located in the space surrounded by the magnetic shielding layer 12. The magnetic shielding layer 12 can be used to shield the influence of external magnetic fields on the electron beam.

[0114] The above application of specific examples to illustrate the present invention, is only used to help understand the present invention, and does not limit the present invention. For the skilled in the art to which the present invention belongs, according to the idea of the present invention, several simple deductions, deformation or replacement can be made.

Claims

1. An electron gun, characterized in that, include: Electron gun chamber; The upper cover flange is fixed to the electron gun chamber; A sealing assembly is provided through the upper cover flange. The sealing assembly includes a movable seat and a deformation sleeve. In the axial direction of the upper cover flange, one end of the deformation sleeve is sealed and fixed to the movable seat, and the other end of the deformation sleeve is sealed and fixed to the upper cover flange. A launching assembly, which passes through the deformable sleeve and is fixed to the movable seat, includes a launching source disposed inside the electron gun chamber; The upper cover flange has a support platform inside, which faces the movable seat in the axial direction. The upper cover flange has an opening structure corresponding to the movable seat. The opening structure is used to provide a path for inserting or removing an adjusting shim between the support platform and the movable seat, so as to adjust the position of the transmitter in the axial direction by removing and installing the adjusting shim. 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 support platform is formed at the junction of the connecting sleeve portion and the sealing sleeve portion. The other end of the deformation sleeve is sealed and fixed to the end of the sealing sleeve portion away from the connecting sleeve portion.

2. The electron gun as described in claim 1, characterized in that, The end face of the connecting sleeve away from 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 support platform.

3. The electron gun as described in claim 2, characterized in that, The support platform is provided with a plurality of second grooves, which are arranged alternately with the plurality of first grooves in the circumferential direction. The second grooves are used to position a corresponding adjusting shim between the support platform and the movable seat; wherein, the circumferential direction is the direction around the axial direction.

4. The electron gun as described in claim 3, characterized in that, The second groove and the adjusting shim have the same projection shape in the plane of the support platform; and / or the number of the first groove and the second groove is set to four.

5. The electron gun as described in claim 2, characterized in that, The electron gun also includes multiple fastening adjustment components connected to the connecting sleeve. The multiple fastening adjustment components and the multiple first grooves are alternately arranged in the circumferential direction. The fastening adjustment components are used to abut against the movable seat in the radial direction to adjust the position of the emission source in the radial direction. The circumferential direction is the direction around the axial direction, and the radial direction is the direction perpendicular to the axial direction.

6. The electron gun as claimed in claim 1, characterized in that, The electron gun chamber has an observation window on its radial sidewall, which is used to observe the interior of the electron gun chamber; wherein, the radial direction is perpendicular to the axial direction.

7. The electron gun as described in any one of claims 1-6, characterized in that, The electron gun also includes the adjusting shim, which is disposed between the support platform and the movable seat.

8. The electron gun as described in claim 7, characterized in that, The projection outline of the adjusting shim on the plane of the support platform includes an inner arc segment, a first straight line segment, an outer arc segment, and a second straight line segment that are connected end to end, and the inner arc segment and the outer arc segment share the same center. Wherein, adjacent inner arc segments, the first straight line segment, the outer arc segment, and the second straight line segment are connected by rounded 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 as described in any one of claims 1-6, characterized in that, The electron gun further includes an extraction electrode; the extraction electrode is disposed inside the electron gun chamber and is used to induce the emission source to emit electrons; the extraction electrode has a first through hole extending along the axial direction, the first through hole being spaced apart from the emission source in the axial direction; wherein: The radius of the first through hole is between 0.07mm and 0.5mm, and / or the width of the extraction electrode in the axial direction is between 0.3mm and 0.5mm, and / or the distance between the extraction electrode and the emission source in the axial direction is between 0.1mm and 0.7mm.

10. The electron gun as claimed in claim 9, characterized in that, The electron gun also includes an anode; the anode is fixedly disposed inside the electron gun chamber and is used to accelerate the 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.

11. The electron gun as claimed in 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 tapered surface surrounding the first through hole.

12. The electron gun as claimed in claim 9, characterized in that, The projection contour 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. Wherein, 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 curve away from the central axis.

13. The electron gun as claimed in claim 9, characterized in that, The emission source has a needle tip, the surface of which includes a first surface, a second surface, a third surface and a fourth surface. The first surface is a circular planar 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 rounded arc surface structure connected between the first surface and the second surface. The fourth surface is a conical curved surface structure connected to the side of the second surface away from the third surface.

Images