JPH02273443A - Multistage acceleration type charged particle beam source - Google Patents

Abstract

PURPOSE:To enhance the discharge resisting property and magnetic shield property of the invention stated in the title by providing first and second shield electrodes and providing a division resistance for applying acceleration voltage with partial pressure therebetween. CONSTITUTION:Charged particle beams drawn out from an electron beam source 1 are accelerated by the plural accelerating electrodes 11 of a multistage accelerating tube 2. Outside the tube 2 are provided a first shield electrode 12 kept in the same electric potential as that of each electrode 11 and a second shield electrode 13 kept in the same electric potential and located on the outside of the electrode 12, and a division electrode 28 for applying acceleration voltage to the electrode 11 is provided between the electrodes 12, 13 so that the potential distribution of the pipe 2 and that of the resistance 28 are uniformed, and also, an insulating bar 20 i.e., a metallic member is disposed in a position corresponding to the electric potential of the electrode 11 in phase with the cycle of division of the pipe 2, and acceleration voltage of each stage is applied thereto so that the potential distribution of the bar 20 is also uniformed. As a result, the invention has its high pressure resisting property improved so that its discharge resisting property is enhanced and also that its magnetic shield effect is further increased.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to improvement of a multi-stage accelerated charged particle beam source, and in particular,
The present invention relates to an improved structure suitable for a multi-stage acceleration type charged particle beam source having a high acceleration voltage of 00 to 300 kV, for example, a multi-stage acceleration field emission type electron gun.

[Conventional technology]

A conventional multi-stage accelerated charged particle beam source is, for example, disclosed in Japanese Patent Application Laid-open No. 1983-
, +-17534, an accelerating electrode is provided at each inner stage of a multistage accelerating tube, a shield electrode is provided at each outer stage, and an accelerating voltage is applied to each stage between the multistage accelerating tube wall and the shield electrode. A dividing resistor was installed for dividing the voltage. Generally, the accelerating electrode and shielding electrode are made of a metal with high magnetic permeability, and play the role of relaxing the potential distribution on the wall of the multistage accelerating tube and shielding from external magnetic fields. [Problem to be solved by the invention] In this type of multistage accelerated charged particle beam source, the part where high voltage discharge is most likely to occur is the part where the insulating cylindrical member of each stage of the multistage acceleration tube is connected to the acceleration electrode. This is the joint with the metal spacer installed between each insulating cylindrical member. The electric field strength in this part is determined by the shape of the joint and the shape and arrangement of the accelerating electrode and the shield electrode, but the most basic thing is not to concentrate the electric field in that part. In the above-mentioned conventional technology, dividing resistors and insulating rods connected to the charged particle source were installed between the multistage accelerating tube wall and the seal 1 electrode. Since the potential distribution becomes non-uniform due to the divided resistors, there is a limit to relaxing the electric field strength at the junction. Furthermore, for the same reason, there is a limit to the effectiveness of shielding external magnetic fields. In particular, as the accelerating voltage becomes higher, it is necessary to perfect the high voltage discharge and magnetic shielding, but the conventional technology is no longer able to adequately meet this requirement. Therefore, an object of the present invention is to further improve the discharge resistance characteristics and magnetic shielding characteristics of a multistage accelerated charged particle beam source.

[Means for Solving the Problem 1] The above purpose is to provide a first shield electrode made of a high magnetic permeability metal on the outer periphery of each stage of the multistage accelerator tube, and a first shield electrode made of a metal with high permeability on the outside of each membrane of the electrode. This is achieved by providing a second shield electrode made of magnetic metal, and installing a dividing resistor, an insulating rod, etc. between the first seal electrode and the second shield electrode. Further, the insulating rod has a structure in which metal members are arranged at positions corresponding to each accelerating electrode potential in accordance with the division period of the multistage accelerating tube, and accelerating voltages of each stage corresponding to each of the metal members are applied. By making the potential distribution uniform along the insulating rod, the withstand voltage characteristics of the insulating rod can be greatly improved. [Function] The potential distribution on the surface and inside of the insulating member of the multistage acceleration tube is determined by the shape and arrangement of the acceleration electrode inside the multistage acceleration tube and the shield electrode on the outside. In order to effectively prevent high voltage discharge, it is important to prevent electric field concentration at the joint between the insulating cylindrical member and the metal spacer in each stage of the multistage accelerator tube. To achieve this, (1) make the potential distribution uniform in the circumferential direction, (2) bring the accelerating electrode and the shield electrode close together, and (3) bring the end of the surface electrode and the above-mentioned joint together. Increasing the distance between the two is effective. In the present invention, in order to realize the above (1) and (2), a substantially concentric first shield electrode is arranged around the outer periphery of each stage of the multi-stage accelerator tube, and dividing resistors or insulating rods are arranged outside of the first shield electrode. Established. Furthermore, in order to equalize the electric field disturbed by the dividing resistors, insulating rods, etc., second shield electrodes were provided at each stage outside of the dividing resistors, insulating rods, etc. If high magnetic permeability metal is used for these first and second shield electrodes, the magnetic shielding effect will be even better than before, and the shielding performance will be improved. Countermeasures are needed. Furthermore, as the accelerating voltage increases, the length required to insulate the high voltage also needs to increase in proportion to the voltage. However, it is necessary to improve the shielding performance almost in proportion to the length. By using the present invention, it is possible to solve all the problems in terms of shielding measures and discharge prevention measures that accompany the increase in voltage. [Example] Hereinafter, an example of the present invention will be described with reference to FIG. This embodiment concerns a multi-stage acceleration field emission type electron gun. A multi-stage accelerator tube 2 and a flange 4 are mounted on the mirror body 3 to form a vacuum vessel. This interior is evacuated from the mirror body side, and an atmosphere of insulating gas such as freon exists between the multistage accelerator tube 2 and the Si housing 33. A field emission electron beam source 1- is attached to the flank T', and an extraction electrode J- is mounted opposite to the field emission electron beam source 1-.
0 is set. Further, an accelerating electrode 11 is attached to the inside of each stage of the multistage accelerating tube, and a first shield electrode 12 and a second shield electrode 13 are attached to the outside. A dividing resistor 28 and an insulating rod 20 are attached between the first shield electrode 12 and the second seal 1-complete connection 13. Activate the electron beam source. The extraction power supply 30 supplies a voltage of 3 to 6 kV between the field emission electron beam source and the extraction electrode to cause field emission. The accelerating voltage generated by the accelerating power supply 31 is applied to the field emission electron beam source, and at the same time is dividedly applied to each stage of the multistage accelerating tube by the dividing resistor 28. The field-emitted electron beam passes through an electrode hole provided in the extraction electrode ]O, and is accelerated to a predetermined energy by each accelerating electrode. Thereafter, it reaches the sample through an irradiation system such as a deflection coil and a focusing I-nons (not shown). The axis alignment of the electron beam is performed by rotating the insulating rod 20 by the drive mechanism 25, further converting the rotational movement into a translational movement by the fine movement mechanism 26, and moving the fine movement plate 5. According to this embodiment, by installing the single-divided resistor 28 and the insulating rod 20 between the first shield electrode and the second shield electrode, the multistage accelerator tube 2, the divided resistor 28, and the insulating rod 2
In both cases, the discharge resistance characteristics were improved. FIG. 2 shows another embodiment of the present invention. The basic structure is the same as the first embodiment shown above, but the structure of the insulating rod 20 is brought into contact with the division period of the multi-stage acceleration tube 2 and the division period 1.2.13. Thereby, the discharge resistance characteristics of the insulating rod 20 were further improved. Note that, although the second embodiment has been shown using a field emission type electron gun as an example, it goes without saying that the present invention is applicable to charged particle sources in general, including ordinary electron guns and ion sources. Effects of the Invention According to the present invention, it is possible to make the potential distribution of both the single-divided resistor of the multistage accelerator tube and the insulating rod more uniform and smooth, thereby improving high voltage resistance characteristics. At the same time, since the magnetic shielding effect is further increased, the magnetic shielding effect is also improved.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are both longitudinal sectional views showing the structure of a multi-stage acceleration field emission type electron gun, which is an embodiment of the present invention. ]...Field emission electron beam source, 2...Multi-stage accelerator tube, 3...Mirror body, 4...Flange, 5...Micro-motion plate, 10-Archive electrode, ]1...Acceleration electrode, 12 First shield electrode, 13
...Second shield electrode, 20. Insulating rod, 21.. Insulating member, 22. Metal member, 25. Drive mechanism, 26.. Fine movement mechanism, 28. Division resistor, 30. Bowing power source, 31.. - Acceleration power source. Flushing power supply, 33...Insulating housing. 1

Claims (1)

[Claims] 1. A charged particle beam source, a multistage acceleration tube having therein at least two or more accelerating electrodes for accelerating the charged particle beam extracted from the charged particle beam source, and the multistage acceleration tube. In a multi-stage accelerated charged particle beam source having a dividing resistor for applying an accelerating voltage to the accelerating electrode in a divided manner on the outside of the tube,
A first shield electrode held at the same potential as each accelerating electrode is provided at each stage on the outside of the multistage accelerating tube, and a second shield electrode held at the same potential outside the first shield electrode. A multistage accelerated charged particle beam source, characterized in that the dividing resistor is installed between a first shield electrode and a second shield electrode. 2. In the multistage acceleration charged particle beam source according to item 1, an insulating rod is further provided outside the multistage acceleration tube along the longitudinal direction of the multistage acceleration tube and connected to the charged particle beam source side. A multistage accelerated charged particle source characterized in that the insulating rod is also installed between the first shield electrode and the second shield electrode. 3. In the multi-stage accelerated charged particle beam source according to item 2, the insulating rod has a metal member at the acceleration electrode potential position of each stage of the multi-stage acceleration tube, and the metal members correspond to each other. A multi-stage accelerated charged particle beam source, characterized in that the first shield electrode and the second shield electrode are brought into contact with each other. 4. A multi-stage accelerator tube having a vacuum-resistant structure, an electron beam source inside the multi-stage accelerator tube, an extraction electrode for emitting an electric field from the electron beam source, and an electron beam emitted from the electrode hole of the extraction electrode. It has at least two or more accelerating electrodes for acceleration, and a dividing resistor for applying an accelerating voltage to the accelerating electrodes in divided parts is located outside the multi-stage accelerating tube, and the electron beam source is located on the electron beam axis. In a multi-stage acceleration field emission electron gun having an axis alignment mechanism, each stage on the outside of the multi-stage acceleration tube includes a first shield electrode made of a high magnetic permeability metal held at the same potential as each acceleration electrode; It has a second shield electrode made of high magnetic permeability metal that is approximately concentric with the shield electrode and held at the same potential as the shield electrode, and the dividing resistor and the driving shaft of the alignment mechanism are connected between the first shield electrode and the second shield electrode. A multi-stage acceleration field emission type electron gun characterized by being installed between the electrodes. 5. In the apparatus according to item 4, the alignment mechanism drive shaft has metal members disposed at the same period as the division period of the multistage accelerator tube, and the metal members correspond to the first or second shields. A multi-stage acceleration field emission type electron gun characterized by an insulating rod having a structure that makes contact with an electrode.