JPS60195855A - Large capacity ion source - Google Patents

Abstract

PURPOSE:To extract an ion beam with high efficiency from an ion with large mass by providing an extraction electrode with apertures or slits for a number of ion beam extraction within the range containing an area with the strength of a magnetic field exceeding a specific value that is opposed to the magnetic pole of a permanent magnet installed on the wall surface of a container. CONSTITUTION:A number of permanent magnets 22 are provided on the outer circumference of a plasma generation container 21. DC voltage is applied between a cathode made of tungusten filament and the plasma generation container 21 that is used additionally as an anode electrode. Gas such as argon gas 25 introduced from a gas induction port 24 is ionized by the low pressure arc discharge and an ion beam is extracted from produced plasma by the beam extraction electrode system of a plasma electrode 26, acceleration electrode 27, and deceleration electrode 28. The electrode with aperture or slits for ion beam extraction is provided within the range containing an are exceeding at least 40 Gauss as the strength of a magnetic field that is opposed to the permanent magnets.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an ion source that generates ions to be implanted into or to process the surface of a fixed material such as a metal, and in particular, relates to an ion source that generates ions for implanting or processing the surface of a fixed material such as a metal, and particularly for obtaining a large current ion beam. Regarding large capacity ion sources.

[Background of the invention]

Conventionally, various ions with an energy of about 20 keV to 100 keV are injected into a solid surface, and used as an ion source to improve the wear resistance of the solid surface or to create a thin film on the surface.
Various ion sources such as Duo Plasmatron have been developed and have been put into practical use mainly for semiconductors, but the output ion beam current is small, about IOmA or less, and 1017 to 1010 ions/d are produced on solid metal surfaces. In order to inject a large amount, it has the disadvantage that it requires a very long processing time, such as continuous use for more than one day.

Recently, a large-capacity ion source as shown in FIG. 1 has been developed and used for a hydrogen-di-deuterium ion beam for heating experiments of fusion fence plasma.

In Figure 1, hydrogen gas is introduced into the plasma generation vessel 2 through the gas inlet 1, and a DC voltage is applied between the cathode 3 made of tungsten filament and the plasma generation vessel 2, which also serves as an anode electrode for arc discharge. This causes arc discharge, ionizes hydrogen gas, and creates plasma. From this plasma, plasma m pole 4. Accelerating electrode5. A hydrogen ion beam is extracted through a large number of apertures or slits with a diameter of about 4 nn formed in the deceleration electrode 6. In order to efficiently confine the hydrogen ion plasma, a large number of permanent magnets 7 are attached so that the north and south poles alternate as shown in FIGS. 1 and 2 (,). FIG. 2(b) shows the distribution of the magnetic field strength in the direction of arrow H-II of the ion source in FIG. 1.

In the ion source for nuclear fusion, as shown in Figure 2(b),
For an inner diameter of 150I, the range where a uniform hydrogen plasma can be produced is a plasma density of ±10%. The area where the aperture is located is 8 meters in diameter (less than 1 meter).On the other hand, in applications that extract ion beams of nitrogen, argon, etc. with a mass of 10 or more, the uniform area of the plasma is approximately three times larger in area than that for hydrogen ions. Because of this phenomenon, if an ion beam of nitrogen or the like is produced using the ion source structure shown in FIG. 1, the arc utilization rate, ion beam output, etc. will be greatly reduced.

[Purpose of the invention]

An object of the present invention is to provide a large-capacity ion source suitable for extracting an ion beam with high efficiency for ions having a large mass such as nitrogen or argon.

[Summary of the invention]

FIG. 1 shows an ion source developed for the lightest mass ions, such as hydrogen and deuterium.

In general, there is a theory that plasma loss is proportional to 5/B, where M is the mass of the ions and B is the strength of the magnetic field on the inner wall of the plasma container. It was predicted that the structure shown in FIG. 1 would have too large a plasma loss and would be impractical. However, when we experimented by creating plasma using the magnetic field shown in Figure 1, we found that even ions like argon, which have a mass 40 times that of hydrogen, can create plasma with the same efficiency as hydrogen. It was discovered through experiments that the range of hydrogen is much wider than that of hydrogen. Therefore, an ion source with the same structure as an ion source for hydrogen can only utilize a part of the uniform plasma generated for heavy ions, and the beam output will be significantly small. It was necessary to do so.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 3 and 4. A large number of permanent magnets 2 are placed around the outer periphery of the plasma generation container 21.
2, and a cathode 2 made of tungsten ficimene 1.
A DC voltage is applied between W1 and the plasma generating container 21 which also serves as an anode electrode, and gas such as argon gas 25 introduced from the gas inlet 24 is heated to W1 by low-pressure arc discharge.
The plasma electrode 26. With the beam extraction electrode system of the accelerating electrode 27 and decelerating electrode 28,
Take out the ion beam. The plasma generation container 21 is made of stainless steel and has an inner diameter of 150 m, an outer diameter of 156 + n + a, and a depth of 165 m, and is magnetized in the height direction on the outer periphery of the cylindrical surface with a height of 25 ytm r + I] 8 mm + length of 15.
16 rows of permanent magnets with 0+nm residual magnetization of 8500 Gauss,
The N and S poles are arranged so as to alternately touch the outer periphery of the cylindrical surface. Further, the bottom surface of the plasma generation container 21 has a height of 25n.
Two permanent magnets each with a length of 120 m and a length of 40 strokes are arranged at approximately equal intervals, with N and S poles alternating on the outside bottom of the cylinder.

At this time, the distribution of magnetic field strength is il
The determined values are shown in FIG. Furthermore, FIG. 4 shows the density distribution of argon plasma.

Uniform argon plasma has a diameter of 130m+n, that is, on the IV-TV arrow line in Figure 2, it can be found in areas where the magnetic field strength is 40 Gauss or more, and covers an area about three times that of hydrogen plasma. Recognize.

The number of ions produced by arc power] kW is also
It was also confirmed through experiments that the efficiency is as high as or higher than that of hydrogen. Therefore, the beam extraction aperture of the beam extraction electrode system such as the plasma electrode 26 is also provided in a range of 130 m in diameter, and a beam output three times that of a conventional ion source for nuclear fusion can be obtained. On the other hand, when obtaining the same beam output as in FIG. 1, the plasma generation vessel can be made compact and the filament power, arc power, etc. can be reduced to 1/3 pA degree.

The ion source shown in FIG. 3 has a structure in which the N pole and multipole of a permanent magnet are alternately electrified.

Since the leakage magnetic field to the extraction electrode etc. can be made very small, the divergence angle of the beam 11 is small even at a low acceleration voltage of about 200 to 5 ooo v, and it is easy to increase the diameter, so it is suitable for ion milling and ion beam sputtering. It has a wide range of uses such as , reactive etching, etc.

〔Effect of the invention〕

According to the present invention, since plasma can be used effectively, it is possible to obtain an ion beam output approximately twice that of the conventional method with the same external shape and the same arc power as the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional ion source, and FIG. 2(a) is a cross-sectional view of a conventional ion source. (b) is a characteristic diagram showing the distribution of magnetic field strength along the II-n arrow line in FIG. 1, FIG. 3 is a cross-sectional view of one embodiment of the present invention, and FIG. It is a characteristic diagram showing the magnetic field distribution and plasma density on the -IV arrow line. 4.26...Plasma electrode, 5,27...Acceleration electrode. 1st day also 2 Kasumi (CL) (b) Invitation 3 (2) Ki 4

Claims (1)

[Scope of Claims] 1. A plasma generation chamber is formed by a plasma generation chamber having a multi-pig permanent magnet whose magnetic poles face the rear surface of the container and whose polarities are alternately combined, and a plasma generation chamber is provided within the plasma generation chamber, The mass number of ions when ionized in the plasma generation chamber by causing an arc discharge using sis particles is 10.
In an ion source that includes a filament that serves as a cathode that ionizes the neutral gas to generate ions, and a plurality of extraction poles that extract the generated ions as an ion beam. A large number of ion beam extraction apertures or extraction ffi poles with slits are installed in a range including a region where the strength of the magnetic field facing the magnetic pole of the permanent magnet installed on the wall of the container exceeds at least 40 Gauss. A large-capacity ion source characterized by: