Electron gun, 3D additive manufacturing device and electron microscope

Abstract

To simplify the protective circuit of a voltage power supply for ion reflectors.SOLUTION: An electron gun 200 comprises: a cathode 101 that discharges thermal electrons upon heating; a Wehnelt 102 in which a first opening is formed along the center axis at the tip of the cathode, and which converges a thermal electron passing through the first opening by the extraction voltage that is applied at a lower potential than the cathode; an ion reflector 103 in which a second opening is formed along the center axis, and which enables the thermal electron extracted from the cathode to pass through the second opening as an electron beam by an applied ion reflector voltage; a voltage power supply 108 for ion reflectors that applies an ion reflector voltage to the ion reflector; and an electrical discharge device 110 that is installed to the ion reflector.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an electron gun, a three-dimensional additive manufacturing apparatus, and an electron microscope. [Background technology]

[0002] Electron microscopes and 3D additive manufacturing devices that use electron sources such as thermionic electrons as their light source are equipped with electron beam columns. In electron microscopes, an electron beam is irradiated onto a sample, and an image is obtained from the secondary electrons and transmitted electrons generated from the sample's surface. In 3D additive manufacturing devices, a current on the order of mA is irradiated onto metal powder (powder sample) spread on a powder bed, and an object is created by stacking layers of molten metal powder.

[0003] In various conventional devices using an electron gun that emits an electron beam, the emission of the electron beam ionizes metal powder and residual gas in a chamber below the electron beam, and most of the ions are positive ions. These positive ions collide with a cathode, causing ion bombardment, which damages the cathode. Therefore, a technology for preventing ion bombardment has been disclosed (see Patent Document 1).

[0004] In the technology disclosed in Patent Document 1, a positive voltage is applied to the ion reflector (anode) by an ion reflector voltage power supply to prevent positive ions from rising. The potential barrier of the ion reflector to which a positive voltage is applied prevents positive ions from reaching above the ion reflector. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-61153 Summary of the Invention [Problem to be solved by the invention]

[0006] In electron guns, discharges can occur due to the accelerating voltage power supply that applies a negative potential to the cathode, or the electron beam spreading from the cathode can hit the ion reflector (anode). In these cases, currents generated by the discharge of the accelerating voltage power supply or the electron beam hitting the ion reflector (anode) can flow into the ion reflector voltage power supply, causing the ion reflector voltage power supply to malfunction. To protect the ion reflector voltage power supply, a protection circuit is sometimes used to block the flowing current. However, if the current that the protection circuit blocks is large, the configuration of the protection circuit becomes complex, and the installation area for the protection circuit becomes large.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to simplify the protection circuit of the voltage power supply for the ion reflector. [Means for solving the problem]

[0008] The present invention includes a cathode that emits thermoelectrons when heated, a Wehnelt having a first opening formed along the central axis of the tip of the cathode and focusing the thermoelectrons passing through the first opening by an extraction voltage applied at a potential lower than that of the cathode, an ion reflector having a second opening formed along the central axis and causing the thermoelectrons extracted from the cathode to pass through the second opening as an electron beam by an applied ion reflector voltage, an ion reflector voltage power supply that applies the ion reflector voltage to the ion reflector, and a discharge device installed on the ion reflector. [Effects of the Invention]

[0009] According to the present invention having the above configuration, the protection circuit for the voltage power supply for the ion reflector can be simplified. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an enlarged view showing an example of the configuration of a conventional electron gun. [Figure 2] FIG. 1 is a schematic diagram showing an example of the configuration of an electron beam column of an electron microscope. [Figure 3] FIG. 1 is a schematic diagram showing an example of the configuration of an electron beam column of a three-dimensional additive manufacturing apparatus. [Figure 4] FIG. 2 is a block diagram showing an example of the hardware configuration of a control unit of the electron gun. [Figure 5] FIG. 1 is a diagram showing an example of the configuration of a conventional field emission electron gun. [Figure 6] 1 is a diagram showing an example of the configuration of a field emission electron gun according to a first embodiment of the present invention. [Figure 7] 3A to 3C are diagrams for explaining the effects of the field emission electron gun according to the first embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing an example of the configuration of a field emission electron gun according to a second embodiment of the present invention. [Figure 9] 10A and 10B are diagrams for explaining an example of the configuration of a field emission electron gun according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention has been made to solve the above-mentioned problems. Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functions or configurations are designated by the same reference numerals, and redundant description will be omitted.

[0012] <Example of conventional electron gun configuration> First, an example of the configuration of a conventional electron gun will be described with reference to Fig. 1. Fig. 1 is an enlarged view showing an example of the configuration of a thermionic electron type electron gun 11.

[0013] The electron gun 11 includes a control unit (not shown in FIG. 1) having the same functions as the control unit 10 shown in FIG. 2 described later and the control unit 30 shown in FIG. 3 described later, a cathode 20, a grid (Wehnelt) 21, and an anode (ion reflector) 22, as well as a gun chamber 51, a vacuum pipe 52, insulators 53 and 54, a liner tube 55, a grid voltage power supply (extraction voltage power supply) 23, an acceleration voltage power supply 24, an anode voltage power supply (voltage power supply for ion reflector) 25, and a cathode heating power supply 27.

[0014] Gun chamber 51 is formed with cathode 20, grid 21, and anode 22 inside. Vacuum pipe 52 is attached to one side of gun chamber 51 and connected to a vacuum pump (not shown). When the vacuum pump is operated, air inside gun chamber 51 is discharged through vacuum pipe 52, and gun chamber 51 becomes almost vacuum. However, a small amount of gas remains inside gun chamber 51.

[0015] The insulators 53 and 54 are both made of a non-conductive material and have insulating properties. Two current introduction terminals 20a connected to the cathode 20 and one current introduction terminal 21b connected to the grid 21 pass through the insulator 53, and are configured so that the cathode 20 and the grid 21 do not come into contact with the gun chamber 51. The two current introduction terminals 20a connected to the cathode 20 are each connected to the positive and negative poles of a cathode heating power supply 27 via conductors outside the gun chamber 51. The PG heater 20b, energized by the two current introduction terminals 20a, heats the cathode 20. The current introduction terminal 21b connected to the grid 21 is connected to the negative pole of a grid voltage power supply 23 via conductors outside the gun chamber 51. A negative voltage is commonly applied to the cathode 20 and the grid 21 by the accelerating voltage power supply 24.

[0016] The insulator 54 holds the anode 22 so that the anode 22 does not come into contact with the gun chamber 51. The anode 22 is connected to the positive pole of an external anode voltage power supply 25 through a conductor that extends into the gun chamber 51.

[0017] The liner tube 55 is a cylinder provided in the passage of the electron beam B (see FIGS. 2 and 3 described later) emitted from the cathode 20. The liner tube 55 functions as a vacuum partition for placing, outside of a vacuum, the electron optical system 12, which includes, for example, the gun alignment 13, the focusing lens 14, and the objective lens 15 shown in FIG. 2 described later. The liner tube 55 is maintained at, for example, a reference potential (ground potential). Since the liner tube 55 and the anode 22 are not in contact with each other, the anode 22 is maintained at a positive potential by the anode voltage power supply 25. The electron beam B emitted from the cathode 20 passes through the liner tube 55 and is irradiated onto the sample placed on the stage 16.

[0018] Because the electron beam column is configured in this manner, positive ions generated in the gun chamber 51 and the electron beam column are attracted to the liner tube 55, which is at ground potential. Furthermore, because the energy of the positive ions is at most about 100 eV, when a positive voltage of about 60 V to 1 kV is applied to the anode 22, most of the positive ions cannot overcome the potential barrier of the anode 22 and are taken in by the anode 22. For this reason, the positive ions do not reach the accelerating electric field with the cathode 20, which is located above the anode 22.

[0019] Furthermore, even if part of the electron beam B emitted from the cathode 20 hits the anode 22, fewer secondary electrons are generated from the anode 22. Furthermore, low-energy secondary electrons generated from the anode 22 are captured by the anode 22 to which a positive voltage is applied, and are less likely to be emitted above the anode 22. This reduces the amount of ions generated between the cathode 20 and the anode 22, thereby suppressing ion bombardment of the cathode 20.

[0020] <Configuration example of an electron microscope> Next, an example of the configuration of an electron microscope will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing an example of the configuration of an electron beam column of an electron microscope 1. The electron microscope 1 comprises the electron gun 11, electron optical system 12, and stage 16 shown in Fig. 1. The electron optical system 12 also comprises a gun alignment 13, a focusing lens 14, and an objective lens 15. In addition, although not shown, the electron microscope 1 is also configured with a deflection coil for scanning the electron beam B, a stigma coil for astigmatism correction, and the like.

[0021] The cathode 20 is heated by a cathode current supplied by a cathode heating power supply 27 (see FIG. 1) for heating the cathode 20, and emits thermal electrons.

[0022] The grid 21 has a first opening 21a formed along the central axis C of the tip of the cathode 20. The grid 21 focuses the thermoelectrons passing through the first opening 21a by a grid voltage applied thereto that is lower in potential than the cathode 20.

[0023] A second opening 22a is formed in the anode 22 along the central axis C. The anode 22 extracts thermoelectrons from the cathode 20 by an anode voltage applied from an anode voltage power supply 25, and causes the thermoelectrons to pass through the second opening 22a as an electron beam B.

[0024] The control unit 10 then applies a positive anode voltage from the anode voltage power supply 25 to the anode 22. The control unit 10 also controls the operations of the grid voltage power supply (extraction voltage power supply) 23, acceleration voltage power supply 24, anode voltage power supply (voltage power supply for ion reflector) 25, and electron optical system 12 in the electron microscope 1. The electron optical system 12 then scans the electron beam B over the sample placed on the stage 16.

[0025] Therefore, gun alignment 13 corrects mechanical axial misalignment within the device so that electron beam B passes through the centers of focusing lens 14 and objective lens 15. Focusing lens 14 crosses over electron beam B to restrict the irradiation range of electron beam B. In electron microscope 1, an aperture (not shown) adjusts the shape and opening angle of electron beam B. Objective lens 15 focuses electron beam B on the sample.

[0026] Some of the thermions emitted from the cathode 20 may hit the anode 22. When the thermions hit the anode 22, secondary electrons are generated from the anode 22. Most of the secondary electrons have an energy of approximately 100 eV or less, so the residual gas around them is easily ionized, and the ions collide with the cathode 20, causing ion bombardment.

[0027] <Configuration example of 3D additive manufacturing equipment> Next, an example of the configuration of a conventional three-dimensional additive manufacturing apparatus will be described with reference to Fig. 3. Fig. 3 is a schematic diagram showing an example of the configuration of an electron beam column of a three-dimensional additive manufacturing apparatus 2. The three-dimensional additive manufacturing apparatus 2 includes an electron gun 31, an electron optical system 32, and a powder supply system 33. The powder supply system 33 spreads a powder sample on a powder bed 37. The electron gun 31 generates an electron beam B, and the electron optical system 32 scans the electron beam B over the powder sample spread on the powder bed 37.

[0028] The electron gun 31 includes a control unit 30, a cathode 40, a grid (Wehnelt) 41, an anode (ion reflector) 42, a grid voltage power supply (extraction voltage power supply) 43, an acceleration voltage power supply 44, and an anode voltage power supply (voltage power supply for ion reflector) 45. The electron optical system 32 includes a gun alignment 34, a focusing lens 35, and an objective lens 36. The powder supply system 33 includes a powder bed 37.

[0029] The cathode 40 is heated by a cathode current supplied by a cathode heating power supply 27 (see FIG. 1) for heating the cathode 40, and emits thermoelectrons.

[0030] A first opening 41a is formed in the grid 41 along the central axis C of the tip of the cathode 40. The grid 41 focuses the thermoelectrons passing through the first opening 41a by a grid voltage that is applied at a lower potential than the cathode 40.

[0031] A second opening 42a is formed in the anode 42 along the central axis C. Then, the anode 42 causes thermions extracted from the cathode 40 to pass as an electron beam B through the second opening 42a due to an anode voltage applied from an anode voltage power supply 45.

[0032] The control unit 30 applies a positive anode voltage from the anode voltage power supply 45 to the anode 42. The control unit 30 controls the operations of the grid voltage power supply (extraction voltage power supply) 43, the acceleration voltage power supply 44, the anode voltage power supply (voltage power supply for ion reflector) 45, the electron optical system 32, and the powder supply system 33 in the three-dimensional additive manufacturing apparatus 2.

[0033] The grid voltage power supply (extraction voltage power supply) 43 applies a grid voltage of lower potential to the grid 41 than the cathode 40, and draws the thermoelectrons from the cathode 40 to the grid 41. The acceleration voltage power supply 44 applies a negative voltage to both the cathode 40 and the grid 41, and accelerates the thermoelectrons emitted from the cathode 40. The anode voltage power supply (ion reflector voltage power supply) 45 applies a positive voltage to the anode 42.

[0034] The electron gun 31 included in the three-dimensional additive manufacturing apparatus 2 has the same configuration as the electron gun 11 included in the electron microscope 1 shown in Fig. 1. Therefore, detailed explanations of exemplary configurations of the electron gun 31 and electron beam column of the three-dimensional additive manufacturing apparatus 2 will be omitted.

[0035] Next, an example of the hardware configuration of the control unit 10 of the electron gun 11 shown in Fig. 2 and the control unit 30 of the electron gun 31 shown in Fig. 3 will be described with reference to Fig. 4. Fig. 4 is a block diagram showing an example of the hardware configuration of the control units of the electron gun 11 and the electron gun 31. Note that the control unit 10 provided in the electron gun 11 operates in the same manner as the control unit 30 in the electron gun 31, and therefore, the configuration of the control unit 30 will be described below as an example, and a duplicated description of the control unit 10 will be omitted.

[0036] The control unit 30 is an example of an information processing device, and includes a CPU (Central Processing Unit) 61, a ROM (Read Only Memory) 62, a RAM (Random Access Memory) 63, and the bus 64, which are all connected to the bus 64. The control unit 30 further includes a display device 65, an input device 66, a non-volatile storage 67, and a network interface 68.

[0037] The CPU 61 reads out program code of software that realizes each function according to this embodiment from the ROM 62, loads it into the RAM 63, and executes it. Variables, parameters, etc. generated during the calculation processing of the CPU 61 are temporarily written to the RAM 63, and these variables, parameters, etc. are read out by the CPU 61 as appropriate. However, an MPU (Micro Processing Unit) may be used instead of the CPU 61. The CPU 61 controls the operation of the grid voltage power supply (extraction voltage power supply) 23, the acceleration voltage power supply 24, and the anode voltage power supply (ion reflector voltage power supply) 25 shown in FIG. 1, or the grid voltage power supply (extraction voltage power supply) 43, the acceleration voltage power supply 44, and the anode voltage power supply (ion reflector voltage power supply) 45 shown in FIG. 3, to obtain a desired electron beam B.

[0038] The display device 65 is, for example, a liquid crystal display monitor, and displays to the user the results of the processing performed by the control unit 30. For example, the display device 65 provided in the electron microscope 1 displays the measurement results and images of the sample, and the display device 65 provided in the 3D additive manufacturing apparatus 2 displays the modeling results of each layer manufactured by additive manufacturing. The input device 66 is, for example, a keyboard, a mouse, etc., and allows the user to input predetermined operations and give instructions.

[0039] The nonvolatile storage 67 may be, for example, a hard disk drive (HDD), a solid state drive (SSD), a flexible disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, or a nonvolatile memory. The nonvolatile storage 67 stores an operating system (OS), various parameters, and programs for operating the control unit 30. The ROM 62 and the nonvolatile storage 67 permanently store programs, data, and the like required for the CPU 61 to operate, and are used as an example of a computer-readable, non-transitory recording medium that stores a program executed by the control unit 30.

[0040] For example, a network interface card (NIC) or the like is used as the network interface 68. Various data can be transmitted and received between the 3D additive manufacturing apparatus 2 and the control unit 30, for example, via a local area network (LAN) or dedicated line connected to a terminal of the NIC.

[0041] The control unit 30 included in the electron gun 31 described above controls the anode voltage power supply 45 to apply a positive voltage to the anode 42. This allows the anode 42 to capture secondary electrons. The anode 42 also functions like a conventional ion reflector, repelling positive ions generated by ionization of residual gas below the anode 42 with the anode potential and preventing the positive ions from reaching the cathode 40. The anode 42 is also made of titanium (Ti), which suppresses the generation of secondary electrons. This allows the anode 42 to suppress the generation of secondary electrons that promote ionization between the cathode 40 and the anode 42, thereby reducing damage to the cathode 40 caused by ion bombardment.

[0042] <Configuration example of a field emission electron gun> Next, an example of the configuration of an electron gun of a conventional field-emission SEM (FE-SEM: Field-Emission Scanning Electron Microscope) will be described with reference to Fig. 5. Fig. 5 is a diagram showing an example of the configuration of a field-emission electron gun. As shown in Fig. 5, the electron gun 100 includes a cathode 101, a Wehnelt (grid) 102, an ion reflector (anode) 103, a column frame (liner tube) 104, a cathode heating power supply 105, an extraction voltage power supply 106, an acceleration voltage power supply 107, and an ion reflector voltage power supply 108. The electron gun 100 also includes a control unit (not shown).

[0043] A control unit (not shown) controls the operations of the cathode heating power supply 105, extraction voltage power supply 106, acceleration voltage power supply 107, and ion reflector voltage power supply 108. This control unit has the same configuration and function as the control unit 30 described in FIG.

[0044] The cathode 101 is heated by a cathode current supplied by a cathode heating power supply 105 to heat the cathode 101, thereby emitting thermoelectrons. The cathode 101 is a component made of a single crystal wire such as tungsten that has been sharpened by electrolytic polishing or the like. A Wehnelt 102 is disposed relative to the cathode 101. The Wehnelt 102 has a first opening formed along the central axis of the tip of the cathode 101, and focuses thermoelectrons passing through the first opening by applying an extraction voltage with a lower potential than the cathode 101. The ion reflector 103 also has a second opening formed along the central axis of the tip of the cathode 101, and the applied ion reflector voltage causes thermoelectrons extracted from the cathode 101 to pass through the second opening as an electron beam.

[0045] A positive voltage (extraction voltage) of several kV is applied to the Wehnelt 102 by an extraction voltage power supply 106, and electrons are extracted from the cathode 101 and focused.

[0046] The ion reflector 103 is disposed below the Wehnelt 102. As described above, the ion reflector 103 has a second opening formed along the central axis of the tip of the cathode 101. The ion reflector 103 passes electrons extracted from the cathode 101 as an electron beam through the second opening due to the applied ion reflector voltage. In addition, a positive ion reflector voltage (approximately 60 V to 100 V) is applied to the ion reflector 103 by the ion reflector voltage power supply 108, so that the potential barrier of the ion reflector 103 prevents positive ions from reaching above the ion reflector 103.

[0047] The column frame 104 is a liner tube (see the liner tube 55 in FIG. 1), and is maintained at a reference potential (ground potential), and induces discharge and inflow current between the column frame 104 and the ion reflector 103 .

[0048] In a field emission SEM, when electron emission becomes unstable due to gas or the like adsorbed to the tip of the cathode 101, the tip of the cathode 101 is cleaned by heating the cathode 101 and performing a flushing process on the cathode 101.

[0049] Here, the flushing process is a process in which the cathode heating power supply 105 heats the tip of the cathode 101. At this time, a control unit (not shown) applies a positive anode voltage from the ion reflector voltage power supply 108 to the ion reflector 103, and causes the cathode heating power supply 105 to energize the cathode 101, thereby performing the flushing process. The flushing process causes adsorbed gas to be desorbed from the tip of the cathode 101, and the cathode 101 is purified.

[0050] In addition, since the tip of the cathode 101 is heated during the flashing process, the shape of the tip of the cathode 101 may change at the atomic level depending on the temperature during the process, and the opening angle of the electron emission of the electron beam B emitted from the cathode 101 may increase, as shown in Fig. 5. In such a case, the expanded electron beam B may hit the ion reflector 103, causing a current due to the expanded electron beam B to flow into the ion reflector voltage power supply 108, which may cause a malfunction of the ion reflector voltage power supply 108. In addition, a discharge current from the accelerating voltage power supply 107 may also flow into the ion reflector voltage power supply 108.

[0051] <Configuration example of electron gun according to the first embodiment> Next, a configuration example of the electron gun according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing a configuration example of an electron gun 200 according to this embodiment. The electron gun 200 shown in Fig. 6 further includes a protection circuit 109 and a discharge device 110 in addition to the configuration of the electron gun 100 shown in Fig. 5.

[0052] The protection circuit 109 is a low-pass filter circuit provided between the ion reflector 103 and the ion reflector voltage power supply 108, and is composed of a capacitor 109a and a varistor diode 109b. The capacitor 109a and the varistor diode 109b are connected in parallel, with one end connected between the ion reflector 103 and the positive terminal of the ion reflector voltage power supply 108, and the other end connected to the negative terminal of the ion reflector voltage power supply 108. The protection circuit 109 blocks current flowing from the ion reflector 103 to the ion reflector voltage power supply 108, i.e., the current due to the above-mentioned expanded electron beam B and the discharge current due to the acceleration voltage power supply 107. Specifically, the protection circuit 109 blocks the current flowing from the ion reflector 103 to the ion reflector voltage power supply 108 when the current exceeds a predetermined threshold. This predetermined threshold is determined by the attenuation coefficient of the protection circuit 109 (low-pass filter circuit). That is, when a current (excessive current) that exceeds an allowable current amount (predetermined threshold) flows, the protection circuit 109 cuts off this current.

[0053] The discharge device 110 is made of a metal or the like that can induce a current, and is disposed between the ion reflector 103 and the column frame 104 while being connected to the ion reflector 103. The discharge device 110 induces a discharge between the ion reflector 103 and the column frame 104, and attracts the inflowing current to the column frame 104. By providing the discharge device 110, most of the current flowing into the ion reflector 103 is attracted to the column frame 104, so that the current flowing into the ion reflector voltage power supply 108 is significantly reduced, to the point where it barely flows. For this reason, the protection circuit 109 is simply configured with a capacitor 109a and a varistor diode 109b. The effect of the electron gun 200 will be described in detail with reference to FIG. 7.

[0054] 7 is a diagram for explaining the effect of the electron gun 200. The electron gun 300 shown in FIG. 7 does not include a discharge device. Furthermore, the components other than the protection circuit are the same as those of the electron gun 200 shown in FIG.

[0055] 7, the protection circuit 111 of the electron gun 300 is provided between the ion reflector 103 and the ion reflector voltage power supply 108, and is a low-pass filter circuit composed of an inductor 111a, a diode 111b, a resistor 111c, a capacitor 111d, and a capacitor 111e. The capacitor 111d and the diode 111b are connected in parallel, with one end connected between the positive terminal of the ion reflector voltage power supply 108 and one end of the inductor 111a, and the other end connected to the negative terminal of the ion reflector voltage power supply 108. The resistor 111c and the capacitor 111e are connected in parallel, with one end connected between the other end of the inductor 111a and the ion reflector 103, and the other end connected to the negative terminal of the ion reflector voltage power supply 108. Similar to the protection circuit 109, the protection circuit 111 cuts off the current flowing from the ion reflector 103 to the voltage power supply 108 for the ion reflector.

[0056] In the electron gun 300, since no discharge device is provided, the current flowing from the ion reflector 103 to the voltage power supply 108 for the ion reflector is greater than the current flowing to the voltage power supply 108 for the ion reflector in the electron gun 200. Therefore, in order to block a higher current, the protection circuit 111 has a more complex configuration than the protection circuit 109 shown in FIG. 6, and the installation area of ​​the protection circuit 111 is also larger than that of the protection circuit 109.

[0057] The electron gun 200 of the present embodiment described above is applicable to an electron microscope (see FIG. 2) and a three-dimensional additive manufacturing apparatus (see FIG. 3).

[0058] [effect] As described above, in the electron gun 200 of this embodiment, the discharge device 110 connected to the ion reflector 103 is provided between the ion reflector 103 and the column frame 104. Therefore, most of the current flowing into the ion reflector voltage power supply 108 is attracted to the column frame 104 by the discharge device 110, and therefore the protection circuit 109 can be simply configured.

[0059] <Configuration example of electron gun according to the second embodiment> Next, the configuration of a field emission electron gun according to a second embodiment of the present invention will be described with reference to Fig. 8. Fig. 8 is a diagram showing an example of the configuration of a field emission electron gun according to the second embodiment. As can be seen from a comparison of the configuration of an electron gun 400 shown in Fig. 8 with that of the electron gun 200 shown in Fig. 6, the electron gun 400 further includes a current detection unit 112 in addition to the configuration of the electron gun 200.

[0060] The current detection unit 112 is configured by, for example, an ammeter, and detects the current flowing into the ion reflector voltage power supply 108. When the current detection unit 112 detects a current, it outputs information about the detected current to a control unit (not shown). Then, the control unit turns off the power to the cathode heating power supply 105 to safely stop the electron beam B. When the current detection unit 112 does not detect a current, it does not perform any operation.

[0061] Normally, by providing the protection circuit 109 and the discharge device 110, almost no current flows into the ion reflector voltage power supply 108. However, for example, when there is an extremely high demand for protection of the ion reflector voltage power supply 108, or when the protection circuit 109 or the discharge device 110 fails and does not operate, the current detection unit 112 is used as a backup protection means.

[0062] Furthermore, for example, in the electron gun 400, the protection circuit 109 may not be provided, and only the discharge device 110 and the current detection unit 112 may serve as means for protecting the voltage power supply 108 for the ion reflector.

[0063] The electron gun 400 of this embodiment described above is applicable to the electron microscope 1 (see FIG. 2) and the three-dimensional additive manufacturing apparatus 2 (see FIG. 3).

[0064] [effect] As described above, the electron gun 400 of this embodiment is provided with the current detection unit 112 that detects the current flowing into the ion reflector voltage power supply 108. Therefore, when there is an extremely high demand for protection of the ion reflector voltage power supply 108 or when the protection circuit 109 or the discharge device 110 fails and does not operate, the electron beam B can be safely stopped, and the safety of the protection of the ion reflector voltage power supply can be improved.

[0065] <Modification> The configurations of the electron gun according to each embodiment of the present invention have been described above, but the present invention is not limited to these, and various other modified embodiments can be adopted as long as they do not deviate from the gist of the present invention as set forth in the claims.

[0066] In the electron guns of the above embodiments, one discharge device 110 (see FIGS. 6 and 8) connected to the ion reflector 103 is provided between the ion reflector 103 and the column frame 104, but the present invention is not limited to this. For example, in order to completely draw the current on the ion reflector 103 to the column frame 104, multiple discharge devices may be provided on the ion reflector 103.

[0067] 9A and 9B are diagrams for explaining an example of the configuration of a field emission electron gun according to this modified example. Fig. 9 shows an image of the ion reflector 103, a discharge device installed on the ion reflector 103, and a voltage power supply 108 for the ion reflector when the ion reflector 103 is viewed along the irradiation direction of the electron beam B shown in Fig. 6. Fig. 9A shows an image when one discharge device 110 is installed. Fig. 9B shows an image when three discharge devices are installed.

[0068] As shown in FIG. 9, the ion reflector 103 is round, and a hole in the center of the ion reflector 103 is a second opening through which the electron beam B passes. An ion reflector voltage power supply 108 is connected to the ion reflector 103. When only one discharge device 110 is installed on the ion reflector 103, it may be installed at any position on the ion reflector 103, as shown in FIG. 9(A). When multiple (e.g., three) discharge devices 110a to 110c are installed on the ion reflector 103, the multiple (e.g., three) discharge devices 110a to 110c are installed in a dispersed manner on the ion reflector 103, as shown in FIG. 9(B). As an example of a dispersed arrangement, the angles with respect to the center point of the ion reflector 103 are set to equal angles, such as 120 degrees. This makes it easier to completely attract the current dispersed on the ion reflector 103 to the ion reflector 103. Furthermore, even if one discharge device (for example, discharge device 110a) is damaged, the other discharge devices (for example, discharge devices 110b and 110c) can discharge to the column frame 104.

[0069] When two discharge devices 110 are distributed on the ion reflector 103, the angles with respect to the center point of the ion reflector 103 are set to be equal angles, such as 180 degrees. In this way, multiple discharge devices 110 may be arranged at equal angles according to the number of discharge devices 110 to be installed on the ion reflector 103. [Explanation of symbols]

[0070] 1...electron microscope, 2...three-dimensional additive manufacturing device, 11,31,100,200,300,400...electron gun, 12,32...electron optical system, 13,34...gun alignment, 14,35...focusing lens, 15,36...objective lens, 16...stage, 18,108...voltage power supply for ion reflector, 19,103...ion reflector, 20,40,101...cathode, 20a,21b...current introduction terminal, 20b...PG heater, 21,41...grid, 21a,41a...first opening, 22,42...anode, 22a,42a...second opening, 23,43...grid voltage power supply, 24,44,107...accelerating voltage power supply, 25,45...anode voltage power supply, 27,105...cathode Heating power supply, 30...controller, 33...powder supply system, 37...powder bed, 51...gun chamber, 52...vacuum drawing pipe, 53, 54...insulator, 55...liner tube, 61...CPU, 62...ROM, 63...RAM, 64...bus, 65...display device, 66...input device, 67...non-volatile storage, 68...network interface, 102...Wehnelt, 104...column frame, 106...extraction voltage power supply, 109, 110, 111...protection circuit, 109a, 111d, 111e...capacitor, 109b...varistor diode, 110...discharge device, 111a...inductor, 111b...diode, 111c...resistor, 112...current detection unit

Claims

1. a cathode that is heated to emit thermions; a Wehnelt, a first opening formed along a central axis of the tip of the cathode, which focuses the thermoelectrons passing through the first opening by an extraction voltage applied at a potential lower than that of the cathode; an ion reflector having a second opening formed along the central axis, the ion reflector allowing the thermoelectrons extracted from the cathode to pass through the second opening as an electron beam in response to an applied ion reflector voltage; an ion reflector voltage power supply that applies the ion reflector voltage to the ion reflector; a discharge device installed on the ion reflector. Electron gun.

2. One or more discharge devices are installed in the ion reflector, and the one or more discharge devices discharge to a column frame maintained at ground potential.

2. The electron gun according to claim 1.

3. A protection circuit is provided to cut off excessive current flowing into the ion reflector.

2. The electron gun according to claim 1.

4. The protection circuit is a low-pass filter circuit composed of a capacitor and a varistor diode.

4. The electron gun according to claim 3.

5. a current detection unit that detects a current flowing into the ion reflector; When the current detection unit detects the current, the power source for heating the cathode is turned off.

2. The electron gun according to claim 1.

6. an electron gun according to any one of claims 1 to 5; A powder bed on which powder samples are spread, a powder supply system for spreading the powder sample on the powder bed; an electron optical system that scans the electron beam over the powder sample spread on the powder bed; 3D additive manufacturing device.

7. an electron gun according to any one of claims 1 to 5; a stage on which a sample is placed; an electron optical system that scans the sample placed on the stage with the electron beam; Electron microscope.

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