JPS61153937A - Electron beam generator - Google Patents

Abstract

PURPOSE:To prevent occurrence of anode point by arranging an electrode for shaping the plasma potential distribution near to the second accelerating electrode at the plasma region side thereby uniforming the plasma potential on the surface of second accelerating electrode. CONSTITUTION:An electron beam generator is constituted by containing first and second accelerating electrodes 1, 2, plasma potential distribution shaping electrode 3 and cathode 4 in a plasma container 5. Discharge is produced between the cathode 4 and the second accelerating electrode 2 to produce plasma thus to emit an electron beam 7 into an ion production container 8 and to produce ions which are used to eliminate the potential barrier produced in the vicinity of the opening 9 of second accelerating electrode 2 by space charges. While the third electrode 3 will correct distorsion of the plasma potential distribution thus to prevent occurrence of anode point. Consequently, discharge between the accelerating electrodes 1, 2 is prevented resulting in stable electron acceleration.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electron beam generator.

(Prior art) In conventional electron beam generators, a negative potential barrier (space charge) is created in front of the cathode, and of the electrons emitted from the cathode surface, only the electrons that can overcome this barrier are accelerated (space charge limited). The beam current can be increased by increasing the accelerating voltage, but this increases both the beam current and the kinetic energy of the electrons at the same time, and these cannot be controlled independently. The beam current is also about IA even at an accelerating voltage of 2 to 3 KV, and it has been difficult to increase it much more than this. In an electron beam generator that solves the problems of conventional electron beam generators, two accelerating electrodes are provided. are defined in order.

In the electron beam generator configured in this way,
A large current electron beam can be obtained as follows. When an accelerating voltage is applied between the two accelerating electrodes, electrons generated in the plasma region are attracted to the first accelerating electrode provided between the electron beam accelerating region and the ion generating region and rush into the ion producing region. The ion generation region is filled with an inert gas, and when electrons accelerated in the electron beam acceleration region enter the ion generation region, ions are generated by collision between the electrons and atoms of the inert gas. These ions are accelerated in the opposite direction to the electrons by a second accelerating electrode disposed between the plasma region and the electron beam acceleration region, and mix with space charges formed near the opening of the second accelerating electrode. This lowers the potential barrier and allows electrons to be emitted without being limited by space charge. Therefore, in an electron beam generator that uses plasma as a cathode and has an ion generation region that removes the influence of space charges, it is possible to control energy and current independently, and generate a large beam with desired energy. It becomes possible to obtain a current electron beam.

(Problems to be Solved by the Invention) In the electron beam generation device that uses the plasma region described above as a cathode, the following problems occur when the anode electrode for generating plasma is also used as the second accelerating electrode. It was found that this occurs. Plasma is the second
If the spatial distribution is uniform near the accelerating electrode, an equipotential surface will be created parallel to the electrode surface, and in order to extract electrons from the plasma source, the potential of the first accelerating electrode will be kept positive with respect to the plasma potential. Electrons uniformly flow into the first accelerating electrode surface. However, when the discharge current between the cathode electrode and the anode electrode is increased in an attempt to increase the current of the electron beam, a small number of spots called anode spots are generated on the surface of the second accelerating electrode, which is the anode electrode. This anode point is accompanied by a spherical high plasma density area at the top.

Most of the electron current is concentrated at the anode point. When this phenomenon occurs, a discharge occurs between the first and second accelerating electrodes,
Not only will it not be possible to obtain good electron acceleration, but it will also lead to damage to the electrode. The occurrence of an anode point indicates that the equipotential surface in the plasma near the surface of the second accelerating electrode is not parallel to the electrode surface and has a large distortion so that the electron current is concentrated at one point. It is most important for this type of electron beam generator to suppress the generation of anode spots by eliminating distortion of the equipotential surface in the plasma near the surface of the second accelerating electrode.

(Means for solving the problem) The above problem is caused by the fact that the ion generation region, the first accelerating electrode, the electron beam accelerating region, the second accelerating electrode, and the plasma region used as the above-mentioned cathode are provided in this order. The above-mentioned electron beam generator is characterized in that a plasma potential distribution shaping electrode is disposed in the plasma region close to the second accelerating electrode, thereby preventing disturbances in the plasma potential, that is, generation of anode spots.

The plasma potential distribution shaping electrode is installed equidistantly from the second accelerating electrode, keeping a distance shorter than the diameter of the plasma accompanying the anode point generated near the second accelerating electrode. This electrode is made of a highly conductive material, but MO
It is preferably formed from a high melting point metal such as. Further, as this electrode, a metal mesh or a metal plate having an opening can be used.

The electron beam generator of the present invention can be used for metal melting and vapor deposition in vacuum metallurgy, as well as for electron beam excitation laser oscillation equipment.

(Function) In the present invention, since the plasma potential distribution shaping electrode is provided, the potential of the spatial surface on which this electrode is placed is always kept at the same potential, so no distortion of the plasma potential distribution occurs. This prevents the formation of anode spots.

(Embodiment) The figure is a side sectional view of one embodiment of the present invention. A first accelerating electrode 1, a second accelerating electrode 2, and a plasma potential distribution shaping electrode 3 are provided in this order in a mutually insulated state,
This second accelerating electrode 2 also functions as an anode electrode that generates plasma by causing a discharge between it and the cathode electrode 4 . A discharge power source 1 is provided between the second accelerating electrode 2 and the cathode electrode 4.
When a voltage is applied by 2, a medium such as an inert gas filled in the plasma container 5 is ionized into electrons and ions to form plasma. This plasma is held in the plasma container 5, but when an acceleration voltage is applied between the first acceleration electrode l and the second acceleration electrode 2 by the acceleration power source 6, the electrons in the plasma container 5 are first accelerated. The electron beam is accelerated by the electrode 1 and emitted as an electron beam 7 outside the plasma container 5 .

An ion generation region filled with an inert gas or the like is also formed on the downstream side of the first accelerating electrode 1 by an ion generation container 8, and when the electron beam 7 flows into this ion generation region, ions are generated. . The generated ions are accelerated by the second accelerating electrode 2 in a direction opposite to that of the electrons, and the potential barrier due to the space charge formed near the opening 9 of the second accelerating electrode 2 is removed or reduced.

Furthermore, in the present invention, since the plasma potential distribution shaping electrode 3 is provided, distortion of the plasma potential that occurs when a discharge current is applied between the cathode electrode and the anode electrode is forcibly corrected, and the anode electrode The occurrence of dots is prevented. Therefore, even at a low accelerating voltage, it is possible to stably obtain a high current electron beam according to the plasma density in the plasma container, and damage to the accelerating electrode is prevented. The medium for generating electrons and ions is the inlet 1 of the plasma container 5.
It is preferable that the ion-generating container 8 flows in from 0 and is discharged from the outlet 11 of the ion-generating container 8, but it may be sealed to maintain the filled state.

The plasma potential distribution shaping electrode may have a completely floating potential, or may be given an appropriate potential from the outside.

In an electron beam generator having exactly the same configuration as shown in the figure except that no plasma potential distribution shaping electrode is provided, He is used as the medium, and the opening of the second accelerating electrode is shaped like a slit (width 0.5 mm, length 3 mm). cm ), plasma already begins to concentrate in a part of the slit-shaped opening at a discharge current of 100 mA, and the electron beam acceleration voltage also increases to 150 mA.
■The extent was the limit.

In contrast, in the illustrated electron beam generator of the present invention having an electrode for shaping plasma potential distribution, even if the discharge current is increased to 500 mA, the plasma is uniformly distributed over the entire slit-shaped opening, and the accelerating voltage 200
It was observed that the electron beam was accelerated throughout the slit without any problem even when V~300 .mu. was applied. The electron beam power density thus obtained is sufficient for various applications of electron beams (for example, excitation of gas lasers and annealing of semiconductors).

(Effects of the Invention) As explained in detail above, the electron beam generator of the present invention has the plasma potential distribution shaping electrode disposed close to the second accelerating electrode on the plasma region side, so that it is shared with the discharge anode electrode. The plasma potential on the surface of the second accelerating electrode is forcibly made uniform in the area where the potential distribution shaping electrode is arranged, and the generation of anode spots is prevented. Therefore, even if the discharge current increases, no anode point is generated, so the first
Further, no discharge occurs between the second accelerating electrodes, and electron acceleration is always performed stably. Further, the first and second accelerating electrodes are not damaged.

[Brief explanation of drawings]

The figure is a side sectional view of one embodiment of the present invention. 1...First accelerating electrode 2...Second accelerating electrode 3...Plasma potential distribution shaping electrode 4...
... Cathode electrode 5 ... Plasma container 6 ... Acceleration power source

Claims (1)

[Claims] A first accelerating electrode, a second accelerating electrode, and a plasma potential distribution shaping electrode are provided in this order, and are arranged on the plasma potential distribution shaping electrode side with respect to the second accelerating electrode and between the second accelerating electrode and the plasma potential distribution shaping electrode. An electron beam generating device comprising a cathode electrode that generates plasma by causing an electric discharge, and a plasma container that holds the generated plasma.