JPH02265150A - Sheet plasma ion and electron source by uramoto method - Google Patents

Abstract

PURPOSE:To generate an ion beam with high electric current density by supplying He gas from an ion source, an electron source, and a discharging cathode side and O2 gas from an anode side. CONSTITUTION:A porous first drawing out electrode 24 which has a large surface area and is to be mounted on a sheet plasma side plane and a first electrode 27 which is for drawing out an ion beam from a linear plasma source are kept positive voltage against an anode 13 and when high positive voltage is applied to a second drawing out electrode 25 with a large surface area and a second drawing out electrode 28, electrons are accelerated. In this case, the anode side becomes a linear electron source and generates plane-like electron beam. Meanwhile, the side plane of a sheet plasma becomes a plane-like electron source and the accelerated electrons are curved by a magnetic field and form an electron flow focusing in vertical direction to a horizontal plane. To generate ion source of O2 which is especially important and chemically active gas, O2 gas is supplied from the anode side 20 and basic electric discharge is maintained by supplying He gas from the cathode side. By this method, aimed oxygen ion source with large current and high electric current density is achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION A method of modifying the surface of a material by ion beam irradiation has recently become increasingly important. However, it is nearly impossible to uniformly modify the surface of a large-area material at high speed with an ion beam (linear) accelerated from a point-like ion source.

As a new attempt, we have developed a method in which an ion beam (area type) accelerated from a long linear ion source is used to irradiate the material and move the material at a constant speed. One possible method is to irradiate the material surface with an ion beam (volume type). From this point of view, the development of long linear or large area ion sources with -like high density is required first. Sheet plasma easily meets this requirement. That is, it is paper-like plasma that is wide and thin. If the paper-like surface is used, it becomes a planar ion source (electron source), and if the paper-like tip is used, it becomes a long linear ion source (electron source). If this sheet plasma is to be generated by a DC discharge, an important issue to keep in mind is that the hot cathode of the discharge is protected from physical damage (ion backflow collisions and thermal lifetime of the cathode material), and that it is protected from chemical damage. It must also be protected from chemically active gases (when used as an ion source of oxygen, for example). Thus, the method of generating sheet plasma by direct discharge between an anode and an elongated hot cathode is not suitable for industrialization because the cathode is neither physically nor chemically protected. Instead, insert an intermediate electrode between the anode and cathode,
The cathode area is around I Torr, and the anode area is 1O-3Torr.
A pressure gradient type discharge that maintains the temperature around rr is considered. In this pressure gradient type discharge, damage to the cathode due to ion backflow collisions from the anode region can be avoided because the mean free path of ions in the cathode region is extremely short. This principle also
It is also applied when an inert gas (Ar, He, etc.) is flowed from the cathode side to maintain a basic discharge, and a chemically active gas (02, N2, etc.) is introduced to the anode side to create an ion source. That is, the pressure of the inert gas in the cathode region is 1 lower than that in the anode region.
Since it is about 0.03 times higher, chemical damage to the cathode due to chemically active gas on the anode side can be avoided.

Now, the problem here is the intermediate electrode that constitutes the pressure gradient type discharge. Considering that sheet plasma is generated by electric discharge, common sense would require an intermediate electrode with a slit-shaped window as shown in Figures 1 and 2, and the cathode would also have an elongated shape. At this time, attention must be paid to the exhaust conductance of the intermediate electrode. For example, if you want to generate a sheet plasma with a width of 20 cm, experience shows that 20 cm
A slit window of 0.5 cm requires an intermediate electrode about 3 cm long. The exhaust conductance of the slit window is about 200 l/sec (relative to Ar), and if the cathode side is kept at I Torr and the anode side is kept at 10' Torr, a gas flow rate of 200 Torr4/see will be from the cathode side. 2 x 105/! on the anode side!
A pump with a pumping speed of /sec is required. This speed is extremely high and cannot be realized with general vacuum equipment. As a result, the pressure gradient type discharge having this slit-type intermediate electrode has the following serious drawbacks. ■Gas efficiency is extremely poor. ■Poor discharge efficiency (discharge current is difficult to pass through the intermediate electrode). ■It is difficult for the plasma density in the middle of the sheet plasma to be uniform. ■A simple and long-life discharge cathode (Patent Application No. 54-057395) cannot be used.

■The width of the sheet plasma cannot be adjusted externally. No discharge in 0 weak magnetic field. Therefore, a sheet plasma having this slit-type intermediate electrode is not suitable for a linear or planar ion source (electron source) for general industrial use.

Therefore, in this invention, we developed a simple and highly efficient sheet plasma generation method called pressure gradient discharge and driftwood method (patent application 57-
060634) was combined to solve the above drawbacks of the slit type. First, the cathode and the intermediate electrode are cylindrical plasma (0,7
(around cmφ) can be used as is. In this way, the intermediate electrode is a simple one with a center hole of 0.7 cmφ and a length of about 3 cm, and its exhaust conductance is 1.5.
1! .

/5ec (relative to Ar). The cylindrical discharge plasma flow that has passed through this intermediate electrode is easily transformed into sheet plasma by two permanent magnets placed on both sides (the generation method of the patent application). Considering the degree of vacuum in this state, even if the cathode side is kept at I Torr, the anode side (10-3 Torr) is 1.5 x 10
A general exhaust pump of 37 sec may be installed (flow rate: 1.5 Torrl/5 ec).

That is, the problems of gas efficiency and pumping are easily solved.Secondly, since the cylindrical plasma is axially symmetrical with respect to the magnetic field, the discharge plasma flow passes through the intermediate electrode efficiently and does not deteriorate the discharge force efficiency. It is also very advantageous to be able to use a simple and long-life cathode.

In addition, there is an automatic correction function that makes the plasma density uniform within the sheet width, and it can also be used in a weak magnetic field (25 Gauss or more), so it is possible to generate linear or planar ion sources (electron sources). Become easy and efficient. The cathode is physical (patent application 54-
As mentioned above, the use of a cathode made of 057395 provides even more complete protection due to its longer thermal life and protection from chemical damage.

The ion source of this invention can be either linear or planar. Since the linear ion source is formed near the slit anode (13) in FIG. 3, high-density plasma can be used. Therefore, a high current density ion beam can be generated. The width of this ion beam is determined by the width of the plasma (currently, a width of 40 cm is easily achieved as an example). On the other hand, a planar ion source uses the side surface of the sheet plasma, 24.25 in Figure 3, so the maximum area is determined by sheet width x sheet length (40 cm x 50 cm).
cm is easily realized). In the case of this sheet shape, the plasma density is considerably lower (by a fraction) than in the linear shape, but it is stable because it is a low electron temperature plasma (the electron temperature suddenly becomes low at a small distance from the center of the sheet). Available for It is natural that the sides can be used linearly.

The above description mainly assumes application to a driftwood sheet plasma ion source, but in Figure 3, if 24.27 is kept at a positive potential with respect to the anode (13) and 25.28 is given a higher positive potential, electrons will be generated. can be accelerated. In this case, the anode side becomes a linear electron source and forms a planar electron beam. On the other hand, the side surface of the sheet plasma becomes a planar electron source, and the accelerated electrons are bent by the magnetic field, forming an electron stream that is focused in the direction perpendicular to the plane of the paper as shown in FIG. Therefore, even low energy (1 to 2 KeV) can be used as a large current of electrons (several amperes or more). This opens the door to new applications not available with conventional electron beams.

Recently, oxygen ion sources have become increasingly important in connection with research on superconductivity. However, at present, a stable oxygen ion source with high current and high current density has not yet been realized.

In order to create an ion source of oxygen (0°), which is a particularly important chemically active gas, by using this invention, as shown in Figure 3, 02 gas is flowed from the anode side 20, and the basic discharge is from the cathode side. It may be maintained by flowing He gas. The ionization voltage of He gas is 24.5V, which is twice as high as the 12.2V of 0° gas, and the ionization efficiency of He gas is around 1 ion pair/cm at maximum, which is about 10 ion pairs/cm at maximum for 02 gas. cm
It is 1/10 compared to . That is, He gas has a 10 to 20 times smaller ionizing effect than 0° gas at the same gas pressure. Thus, the plasma density on the anode side of the 02 gas is
It is easy to make the plasma density significantly higher than that of He gas (carrier gas and inert gas). Also, since He+ ions in He gas have a small mass, ions in 02 gas (O
It also becomes easier to separate it from the yen O+). Based on this principle, if large current discharge is performed while protecting the cathode, the desired large current and large current density oxygen ion source can be achieved.

[Brief explanation of drawings]

FIG. 1 of the drawings is a configuration diagram of a pressure gradient type discharge sheet plasma generation device using a slit type intermediate electrode, and FIG. 2 is a conceptual diagram of a cross section of the slit type intermediate electrode and a cross section of the sheet plasma. In addition, Figure 3 of the drawings is a configuration diagram of the driftwood type pressure gradient type discharge sheet plasma generation device, and Figure 4
The figure is a conceptual diagram of the cross section of the discharge anode and the sheet plasma. In the drawing, 1 is an elongated discharge cathode, 2 is a slit-type intermediate electrode, 3 is a discharge anode, 4 is a basic discharge gas (flowing from the cathode side), 5 is a sheet plasma (indicates the width direction), 6 is a discharge power source, 7 indicates the uniform magnetic field along the discharge, 8 indicates the exhaust pump, 9 indicates the cross section of the slit-type intermediate electrode (2), 10 indicates the slit-shaped window, 1
1 shows a cross section of the sheet plasma (5). In addition, 12 is a simple and long-life discharge cathode (patent application 54-057395).
), 13 is a discharge anode with a slit, and 14 is the first intermediate electrode for pressure gradient discharge, which is repurposed from one for cylindrical plasma (a hole with a diameter of 0.7 cm and a length of about 3 cm is drilled in the center). 15 is the second intermediate electrode for pressure gradient discharge, which is also a repurposed one for cylindrical plasma (a hole of 1.5 cm diameter and about 4 cm length is drilled in the center).
, 16 is a basic discharge body introduced from the cathode side, 17 is an air-core coil for generating a uniform magnetic field along the discharge plasma, and 18 is a pair of permanent magnets (simple) for transforming the cylindrical plasma into sheet plasma. Highly efficient sheet plasma generation (patent application 57-060634), 19 is a driftwood type sheet plasma (having a large width perpendicular to the plane of the paper), 20 is an additional gas introduced from the anode side, 21 is a discharge power source, 22
23 indicates an exhaust pump on the side of the sheet plasma, 23 indicates an exhaust pump for gas flowing out from the anode of the sheet plasma, and 24 indicates a porous, large-area extraction first electrode placed on the side of the sheet plasma, which pumps the ion beam. When the anode (
13) is biased to a negative potential when using an electron beam, and biased to a positive potential when using an electron beam; 25 is a large-area extraction second electrode; negative when using an ion beam and positive when using an electron beam; An electrode to which a voltage is applied, 26 an ion beam or an electron beam that is accelerated into a volume (bending perpendicular to the plane of the paper due to the magnetic field), and 27 an ion beam from a linear plasma source as shown in FIG. The first electrode for extracting the beam, and the anode (1) for ion beams.
3), an electrode that is biased to a negative potential and a positive potential when an electron beam is used; 28 is a second extraction electrode; an electrode to which a negative accelerating voltage is applied when an ion beam is used and a positive accelerating voltage is applied when an electron beam is used; 29; 30 shows the cross section of the anode (13), 31 shows the slit of the anode, and 32 shows the linear cross section of the sheet plasma.

Claims (1)

[Claims] Linear or planar (1) ion source, (2) electron source, using pressure gradient gas discharge and a simple and highly efficient sheet plasma generation method (Patent Application No. 57-060634). (3) An oxygen ion source that flows He gas from the cathode side of the discharge and O_2 gas from the anode side.