JP7736627B2 - Electron gun, 3D additive manufacturing device and electron microscope - Google Patents

Description

The present invention relates to an electron gun, a three-dimensional additive manufacturing device, and an electron microscope.

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 an electron microscope, 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 a 3D additive manufacturing device, a current on the order of mA is irradiated onto metal powder (powder sample) spread across a powder bed, and an object is created by stacking layers of molten metal powder.

In various conventional devices using electron guns that emit electron beams, the emission of the electron beam ionizes metal powder and residual gas in the chamber below the electron beam, with most of the ions being positive ions. These positive ions collide with the cathode, causing ion bombardment, which in turn damages the cathode. Therefore, technology to prevent ion bombardment has been disclosed (see Patent Document 1).

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.

Japanese Patent Application Laid-Open No. 2021-61153

In electron guns, discharges can occur due to the accelerating voltage power supply applying a negative potential to the cathode, or the electron beam spreading from the cathode can hit the ion reflector (anode). In these cases, current 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 protection circuit configuration becomes complex, and the installation area for the protection circuit becomes large.

The present invention was made to solve the above problems, and its object is to simplify the protection circuit for the voltage power supply for the ion reflector.

The present invention comprises 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 in the ion reflector.

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.

FIG. 1 is an enlarged view showing an example of the configuration of a conventional electron gun. FIG. 1 is a schematic diagram showing an example of the configuration of an electron beam column of an electron microscope. FIG. 1 is a schematic diagram illustrating an example of the configuration of an electron beam column of a three-dimensional additive manufacturing apparatus. FIG. 2 is a block diagram showing an example of the hardware configuration of a control unit of the electron gun. FIG. 1 is a diagram showing an example of the configuration of a conventional field emission electron gun. 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; 5A and 5B are diagrams for explaining the effect of the field emission electron gun according to the first embodiment of the present invention. 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. 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.

The present invention has been made to solve the above-mentioned problems. Below, an embodiment of the present invention will be described with reference to the accompanying drawings. In this specification and drawings, components having substantially the same function or configuration are designated by the same reference numerals, and redundant description will be omitted.

<Example of a 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 type electron gun 11.

The electron gun 11 includes a control unit (not shown in FIG. 1) with the same functions as the control unit 10 shown in FIG. 2 and the control unit 30 shown in FIG. 3, as well as a cathode 20, a grid (Wehnelt) 21, and an anode (ion reflector) 22. In addition, the electron gun 11 also includes 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 (ion reflector voltage power supply) 25, and a cathode heating power supply 27.

The gun chamber 51 is formed with a cathode 20, a grid 21, and an anode 22 inside. A vacuum pipe 52 is attached to one side of the gun chamber 51 and connected to a vacuum pump (not shown). When the vacuum pump is operated, the air inside the gun chamber 51 is exhausted through the vacuum pipe 52, creating a nearly vacuum state inside the gun chamber 51. However, a small amount of gas remains inside the gun chamber 51.

The insulators 53 and 54 are both made of a non-conductive material and are insulating. 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, preventing the cathode 20 and grid 21 from coming into contact with the gun chamber 51. The two current introduction terminals 20a connected to the cathode 20 are connected to the positive and negative poles of the 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 the grid voltage power supply 23 via conductors outside the gun chamber 51. A negative voltage is commonly applied to the cathode 20 and grid 21 by the acceleration voltage power supply 24.

The insulator 54 holds the anode 22 so that it does not come into contact with the gun chamber 51. The anode 22 is connected to the positive terminal of the external anode voltage power supply 25 via a conductor that extends into the gun chamber 51.

The liner tube 55 is a cylinder provided in the path of the electron beam B (see Figures 2 and 3 described below) emitted from the cathode 20. The liner tube 55 functions as a vacuum partition for placing the electron optical system 12, which includes the gun alignment 13, focusing lens 14, and objective lens 15 shown in Figure 2 described below, outside the vacuum. 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.

Because the electron beam column is configured in this way, 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 maximum energy of positive ions is approximately 100 eV, when a positive voltage of approximately 60 V to 1 kV is applied to the anode 22, most positive ions are unable to overcome the potential barrier of the anode 22 and are instead captured by the anode 22. As a result, positive ions do not reach the accelerating electric field with the cathode 20, which is located above the anode 22.

In addition, 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. 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 anode 22, suppressing ion bombardment of the cathode 20.

<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 includes the electron gun 11, electron optical system 12, and stage 16 shown in Fig. 1. The electron optical system 12 also includes a gun alignment 13, a focusing lens 14, and an objective lens 15. Although not shown, the electron microscope 1 also includes a deflection coil for scanning the electron beam B, a stigma coil for astigmatism correction, and the like.

The cathode 20 is heated by the cathode current supplied by the cathode heating power supply 27 (see Figure 1) to heat the cathode 20, causing it to emit thermoelectrons.

A first opening 21a is formed in the grid 21 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 applying a grid voltage with a lower potential than the cathode 20.

A second opening 22a is formed in the anode 22 along the central axis C. The anode 22 extracts thermoelectrons from the cathode 20 using the anode voltage applied from the anode voltage power supply 25, and passes them through the second opening 22a as an electron beam B.

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 operation of the grid voltage power supply (extraction voltage power supply) 23, acceleration voltage power supply 24, anode voltage power supply (ion reflector voltage power supply) 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.

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

Some of the thermions emitted from the cathode 20 may strike the anode 22. When the thermions strike 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 in the vicinity is easily ionized, and these ions collide with the cathode 20, causing ion bombardment.

<Configuration example of a 3D additive manufacturing device>
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.

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.

The cathode 40 is heated by the cathode current supplied by the cathode heating power supply 27 (see Figure 1) to heat the cathode 40, causing it to emit thermoelectrons.

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 applying a grid voltage that is lower in potential than the cathode 40.

A second opening 42a is formed in the anode 42 along the central axis C. The anode 42 then passes the thermoelectrons extracted from the cathode 40 as an electron beam B through the second opening 42a due to the anode voltage applied from the anode voltage power supply 45.

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 operation of the grid voltage power supply (extraction voltage power supply) 43, acceleration voltage power supply 44, anode voltage power supply (ion reflector voltage power supply) 45, electron optical system 32, and powder supply system 33 in the 3D additive manufacturing device 2.

The grid voltage power supply (extraction voltage power supply) 43 applies a grid voltage to the grid 41 that is lower in potential than the cathode 40, drawing 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, accelerating 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.

The electron gun 31 provided in the 3D additive manufacturing device 2 also has a configuration similar to the electron gun 11 provided 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 3D additive manufacturing device 2 will be omitted.

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 electron gun 31. Note that the control unit 10 provided in the electron gun 11 operates in the same way as the control unit 30 in the electron gun 31, so the following description will use the configuration of the control unit 30 as an example, and redundant description of the control unit 10 will be omitted.

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 a bus 64, all of which are connected to the bus 64. Furthermore, the control unit 30 includes a display device 65, an input device 66, non-volatile storage 67, and a network interface 68.

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

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

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

The network interface 68 may be, for example, a network interface card (NIC). Various types of data can be sent and received between the 3D additive manufacturing device 2 and the control unit 30 via a local area network (LAN) or dedicated line connected to the NIC terminal.

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. Furthermore, the anode 42 functions like a conventional ion reflector by using the anode potential to repel positive ions generated by ionization of residual gas below the anode 42 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 anode 42, thereby reducing damage to the cathode 40 caused by ion bombardment.

<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).

A control unit (not shown) controls the operation 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 functions as the control unit 30 described in Figure 4.

The cathode 101 is heated by a cathode current supplied by the cathode heating power supply 105 to heat the cathode 101, 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 other techniques. A Wehnelt 102 is positioned 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.

A voltage of several kV (extraction voltage) is applied to the Wehnelt 102 by the extraction voltage power supply 106, extracting and focusing electrons from the cathode 101.

The ion reflector 103 is positioned 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 causes electrons extracted from the cathode 101 to pass through the second opening as an electron beam 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 the potential barrier of the ion reflector 103 prevents positive ions from reaching above the ion reflector 103.

The column frame 104 is a liner tube (see liner tube 55 in Figure 1) that is maintained at a reference potential (ground potential) and induces discharge and inflow current between it and the ion reflector 103.

In a field emission SEM, when electron emission becomes unstable due to gas or other substances 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.

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, the control unit (not shown) applies a positive anode voltage from the ion reflector voltage power supply 108 to the ion reflector 103, and energizes the cathode 101 with the cathode heating power supply 105 to perform the flushing process. The flushing process causes adsorbed gas to desorb from the tip of the cathode 101, cleaning the cathode 101.

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 as shown in Figure 5, the opening angle of the electron emission of the electron beam B emitted from the cathode 101 may increase. In such a case, the expanded electron beam B may hit the ion reflector 103, causing the current from the expanded electron beam B to flow into the ion reflector voltage power supply 108, potentially causing a malfunction of the ion reflector voltage power supply 108. In addition, the discharge current from the acceleration voltage power supply 107 may flow into the ion reflector voltage power supply 108.

<Configuration example of electron gun according to first embodiment>
Next, an example of the configuration of the electron gun according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing an example of the configuration 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.

The protection circuit 109 is a low-pass filter circuit arranged 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 it exceeds a predetermined threshold. This predetermined threshold is determined by the attenuation coefficient of the protection circuit 109 (low-pass filter circuit). In other words, the protection circuit 109 cuts off current when a current (excessive current) that exceeds the allowable current amount (predetermined threshold) flows.

The discharge device 110 is made of a metal or other material capable of inducing a current, and is connected to the ion reflector 103 and disposed between the ion reflector 103 and the column frame 104. This 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, significantly reducing the current flowing into the ion reflector voltage power supply 108 and almost eliminating it. For this reason, the protection circuit 109 is simply configured with a capacitor 109a and a varistor diode 109b. The effects of the electron gun 200 will be explained in detail with reference to Figure 7.

Figure 7 is a diagram illustrating the effects of the electron gun 200. The electron gun 300 shown in Figure 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 Figure 6.

As shown in Figure 7, the protection circuit 111 of the electron gun 300 is a low-pass filter circuit provided between the ion reflector 103 and the ion reflector voltage power supply 108, and is composed of an inductor 111a, a diode 111b, a resistor 111c, a capacitor 111d, and a capacitor 111e. Capacitor 111d and diode 111b are connected in parallel, with one end connected between the positive pole of the ion reflector voltage power supply 108 and one end of inductor 111a, and the other end connected to the negative pole of the ion reflector voltage power supply 108. Resistor 111c and capacitor 111e are connected in parallel, with one end connected between the other end of inductor 111a and the ion reflector 103, and the other end connected to the negative pole of the ion reflector voltage power supply 108. Like the protection circuit 109, the protection circuit 111 cuts off the current flowing from the ion reflector 103 to the ion reflector voltage power supply 108.

Since the electron gun 300 does not have a discharge device, the current flowing from the ion reflector 103 to the ion reflector voltage power supply 108 is greater than the current flowing to the ion reflector voltage power supply 108 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.

The electron gun 200 of this embodiment described above can be applied to electron microscopes (see Figure 2) and three-dimensional additive manufacturing devices (see Figure 3).

[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.

<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 by comparing 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.

The current detection unit 112 is composed of, 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). The control unit then powers off the cathode heating power supply 105 to safely stop the electron beam B. If the current detection unit 112 does not detect a current, it does not take any action.

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

Also, 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 ion reflector voltage power supply 108.

The electron gun 400 of this embodiment described above can be applied to the electron microscope 1 (see Figure 2) and the three-dimensional additive manufacturing device 2 (see Figure 3).

[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.

<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.

In the electron guns of the above embodiments, an example has been described in which a single discharge device 110 (see Figures 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.

Figure 9 is a diagram illustrating an example configuration of a field emission electron gun according to this modified example. Figure 9 also illustrates an image of the ion reflector 103, the discharge device installed on the ion reflector 103, and the 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 Figure 6. Figure 9(A) illustrates an image when one discharge device 110 is installed. Figure 9(B) illustrates an image when three discharge devices are installed.

As shown in FIG. 9, the ion reflector 103 is round, and the 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-110c are installed on the ion reflector 103, the multiple (e.g., three) discharge devices 110a-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 (e.g., discharge device 110a) is damaged, other discharge devices (e.g., discharge devices 110b and 110c) can still discharge to the column frame 104.

When two discharge devices 110 are distributed on the ion reflector 103, the angles relative to the center point of the ion reflector 103 should be equal, such as 180 degrees. In this way, multiple discharge devices 110 can be arranged at equal angles according to the number of discharge devices 110 to be installed on the ion reflector 103.

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 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 (7)

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 disposed on the ion reflector. 2. The electron gun according to claim 1, wherein one or more discharge devices are provided in the ion reflector, and the one or more discharge devices discharge to a column frame maintained at a ground potential. The electron gun according to claim 1 , further comprising a protection circuit that blocks excessive current flowing into the ion reflector. 4. The electron gun according to claim 3, wherein the protection circuit is a low-pass filter circuit configured by a capacitor and a varistor diode. a current detection unit that detects a current flowing into the ion reflector;
2. The electron gun according to claim 1, wherein a power source for heating the cathode is turned off when the current detection unit detects the current. 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 powder sample spread on the powder bed with the electron beam. 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.