JPH04162331A - Cold cathode type sheet-shaped ion beam generator - Google Patents

Abstract

PURPOSE:To relief bad influence of cathode sputter particles by installing separated rod-shaped cathodes off an ion beam leading-out axis inside an anode. CONSTITUTION:An anode is constructed by a cylinder package provided with an interdicting port 11 for gas to be ionized and a slit 14 for taking out ions, sheet-shaped positive ion beams are taken out by ion leading-out electrodes 22, 23 having minus potential are provided in the vicinity of the slit 14. Inside the anode 10, at least two rod-shaped cathodes 30, 40 having the same potential are installed off the leading-out axis for ion beams along the longitudinal direction of the anode 10. Cathode sputter particles are therefore ionized and probabilities that these particles pass through the slit 14 of the anode 10 or stick onto the electrodes near the slit 14 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cold cathode ion source for generating a sheet-shaped positive ion beam.

[Prior Art] Sheet-shaped ion beams have high utility value, and it is particularly desired to develop a device that generates a sheet-shaped beam of oxygen pressure ions. However, in the case of a hot cathode type ion source, the cathode is not only spattered by the bombardment of oxygen pressure ions, but also is violently oxidized due to the high cathode temperature, causing severe damage to the cathode in a short period of time. occurs. In other words, the life of the cathode was short, and it was necessary to frequently replace it.

From the viewpoint of long-term stable use, a cold cathode ion source that does not use a hot cathode is extremely useful. As a cold cathode type sheet-like ion beam generator, the anode is a cylindrical envelope equipped with an inlet for the gas to be ionized and a slit for taking out the ions. It is conceivable to arrange a rod-shaped cathode and provide an ion extraction electrode with a negative potential near the slit.

When such a configuration is employed, a discharge occurs between the two electrodes when the gas pressure within the anode, the distance between the anode and the cathode, and the potential applied to the picture electrode are appropriate.

Some of the positive ions generated by this discharge bombard the cathode, and secondary electrons are emitted from the cathode. Similarly, the radiation accompanying the discharge causes photoelectrons to be emitted from the cathode. These electrons are accelerated toward the inner surface of the envelope, which is the anode, and collide with gas molecules along the way, ionizing them. Therefore, the discharge continues and plasma is generated between the anode and the cathode. An ion extraction electrode extracts a sheet-shaped positive ion beam from this plasma through a slit. In particular, by devising the shape and structure of the anode and ion extraction electrode near the slit for extracting positive ions, the discharge region can be localized around the ion beam extraction axis, thereby improving ion extraction efficiency. .

[Problems to be Solved by the Invention] Generally, in the case of a cold cathode ion source, positive ion bombardment or radiation irradiation is continuously applied to the cathode as described above in order to sustain the discharge for plasma generation. Secondary electrons must be continuously emitted from the cathode. In other words, cathode sputtering due to positive ion bombardment is an unavoidable problem.

Moreover, in the above-mentioned cold cathode sheet-like ion beam generator, the cathode is placed on the central axis inside the anode, so the positive ion bombardment is particularly important when localizing the discharge area around the ion beam extraction axis. It concentrates on the cathode surface on the axis. The particles sputtered from this cathode surface are -
Not only does this cause a problem in that the neutral parts are ionized and mixed into the desired ion beam, but also neutral parts are diluted and deposited on the electrode in the vicinity of the slit, causing insulation deterioration.

The present invention has been made in view of the above points, and is a cold cathode type in which the negative effects of cathode sputtered particles are alleviated by paying consideration to the geometric arrangement of the cathode, anode, and ion extraction electrode and the applied voltage. An object of the present invention is to provide a sheet-like ion beam generator.

[Means for Solving the Problems] A cold cathode sheet-like ion beam generator according to the present invention includes a cylindrical envelope provided with an inlet for a gas to be ionized and a slit for taking out ions. is an anode, and a sheet-shaped positive ion beam is extracted by an ion extraction electrode with a negative potential provided near the slit. It is characterized by being arranged along the longitudinal direction and off the ion beam extraction axis.

In order to improve the plasma density and increase the ion current, a permanent electromagnet is placed inside each cathode so as to generate a magnetic flux having a component perpendicular to the electric field on the cathode surface. In order to increase the component of leakage magnetic flux due to this permanent magnet in the direction perpendicular to the electric field on the cathode surface, the permanent magnets inside each cathode are divided and arranged in the longitudinal direction of the cathode so that the polarities are alternately arranged. If necessary, a spacer made of a non-magnetic material is inserted between the divided magnet pieces. In addition, the permanent magnets inside each cathode are arranged in sections in a direction perpendicular to the longitudinal direction of the cathode so that the polarities are arranged alternately, and spacers made of a non-magnetic material are inserted between the divided magnet pieces as necessary. is also effective.

In order to improve the focusing ability of the ion beam, a permanent magnet is embedded in the anode end portion constituting the slit, and this permanent magnet generates a magnetic flux having a component parallel to the ion beam extraction axis in the anode slit.

In order to further increase the ion current, a positive potential repeller electrode is provided inside the anode on the opposite side of the cathode from the slit.

[Function] In the cold cathode sheet-like ion beam generator according to the present invention, each of the divided rod-shaped cathodes is disposed inside the anode with the ion beam extraction shaft removed, so that the cathode sputtered particles are not ionized. This reduces the probability that the particles will pass through the slit of the anode or be deposited on the electrode near the slit.

If a permanent magnet is placed inside each cathode to generate a magnetic flux with a component perpendicular to the electric field on the cathode surface, the secondary electrons emitted from the cathode will be accelerated by the electric field and will receive force from the magnetic field. make a spiral movement. Therefore, the effective orbital length of the secondary electrons increases, the probability of collision with gas molecules increases, and the plasma density increases.

If the permanent magnet inside each cathode is divided in the longitudinal direction of the cathode and the divided magnet pieces are arranged so that the polarity is reversed with a non-magnetic spacer in between, leakage with a large cathode longitudinal component perpendicular to the electric field on the cathode surface can be avoided. Magnetic flux is obtained. If the permanent magnet inside each cathode is divided in a direction perpendicular to the longitudinal direction of the cathode, and the divided magnet pieces are arranged so that the polarity is reversed with a non-magnetic spacer in between, the electric field on the surface of the cathode and the longitudinal direction of the cathode can be A leakage magnetic flux with a large component orthogonal to both is obtained.

It is difficult to effectively and inexpensively realize these magnetic field distributions using electromagnets.

By embedding a permanent magnet in the anode end of the slit and generating a magnetic flux in the anode slit with a component parallel to the ion beam extraction axis, a spiral motion of the electrons toward the anode is generated. This not only improves the ionization efficiency, but also makes the magnetic flux distribution along the ion beam extraction axis a compressive magnetic flux, making it easier for positive ions to be focused at the slit.

If a repeller electrode with a positive potential is provided inside the anode on the side opposite to the slit with respect to the cathode, positive ions will efficiently head toward the slit of the anode, increasing the ion current.

Embodiment FIG. 1 is a sectional view of a cold cathode sheet-like ion beam generator according to an embodiment of the present invention, and FIG.
It is an A sectional view.

This device 2 uses a cylindrical envelope as an anode 10. The anode 10 has an inlet 11 for the gas to be ionized.
is provided. Further, the envelope constituting this anode 10 is provided with an inwardly bent portion 12.13, and a slit 14 extending in the longitudinal direction of the anode 10 is formed between both bent portions 12.13. ing. At the tip of the anode end bent portion 12.13 that constitutes the anode slit 14 in this way, there is a permanent magnet 15.18 extending in the longitudinal direction of the slit.
are buried so that the same poles face each other.

An ion extraction electrode 22.23 is attached to both bent portions 12.13 of the anode 10 via an insulator 20.21, and the slit 24 of this ion extraction electrode 22.23 overlaps the slit 14 of the anode IO. It will be done. While a positive potential is applied to the anode IO, a negative potential is applied to the ion extraction electrode 22.23, and as will be explained later, the plasma generated inside the anode 10 is extracted through the slit 14.24. A sheet-like positive ion beam is extracted along the axis 25.

Inside the anode 10, two rod-shaped cathodes 30 and 40, both of which are held at zero potential, are arranged along the longitudinal direction of the anode 10.
Moreover, they are arranged so as to face each other with the ion beam extraction shaft 25 removed.

Both cathodes 30.40 each have a shell with a rectangular cross section, the opposing front faces 31.41 are slightly inclined toward the slit 14 side of the anode IO, and the side faces 32.42 are slightly directed inward. Inside each cathode 30.40 is a front surface 31.41.
Permanent magnets are divided and arranged so as to extend in the longitudinal direction of the cathode on the side, and water cooling pipes 33 and 43 are placed on the back side along the permanent magnets.
is placed. The permanent magnet inside each cathode 30.40 is
The cathode is not only divided into many parts in the longitudinal direction (see FIG. 2), but also divided into two in the direction perpendicular to this (see FIG. 1).

As shown in FIG. 1, each cathode 30.40 is divided into two permanent magnet pieces 34a, 3 in a direction perpendicular to the longitudinal direction of the cathode.
411; 44a, 44b are arranged with different polarities in each cathode 30.40, and a spacer 51.81 made of a non-magnetic material is inserted between adjacent magnet pieces. both cathodes 3
The relationship between the permanent magnet pieces 34a and 44a between 0.40 and 3
In the relationship between 4b and 44b, the same poles are opposite.

As shown in FIG. 2, in each cathode 30, 40, permanent magnet pieces 34a, 35a are divided into many pieces in the longitudinal direction of the cathode.

36a, . . .; 44a, 45a, 46a, .
, 53.54°..., 62. B3.64. ... has been inserted. Permanent magnet piece 34 between both cathodes 30°40
Relationship between a and 44a, relationship between 35a and 45a, 36a
In the relationship between and 46a (the same applies hereinafter), the same poles are opposite to each other. The same applies to the relationship between the permanent magnet pieces 34b and 44b between the cathodes 30 and 40.

Further, an arcuate repeller electrode 70 having a positive potential is provided inside the anode IO in order to reflect or reverse positive ions flowing toward the opposite side of the slit 14 with respect to the cathode 30.40.

In the cold cathode sheet-like ion beam generator 2 according to the present embodiment described above, a space P including the front faces 31, 41 of both cathodes 30, 40 and the vicinity of the slit 14 inside the anode 10 is a space where plasma is generated. From this plasma, a sheet-shaped positive ion beam is extracted through the slab (14.24). Moreover, the cathode 30.
40 are placed inside the anode IO with the ion beam extraction shaft 25 removed, so that the sputtered particles of the cathode 30.40 generated by positive ion bombardment are transferred to the slit 14.2.
The probability of passing through 4 is reduced. Therefore, mixing of sputtered particles into the obtained ion beam is suppressed. Further, insulation deterioration due to deposition of sputtered particles inside the device, such as between the anode 10 and the ion extraction electrodes 22 and 23, is also alleviated.

Now, in the plasma space P, the leakage magnetic flux of the permanent magnet pieces 34a, 34b, -; 44a, 44b, - in the cathode 30.40 and the permanent magnet 15.16 in the anode bending part 12.13 is distributed. .

Permanent magnet pieces 34a, 34b, - in cathode 30.40;
44a.

44b, . . . generate leakage magnetic flux having a component orthogonal to the surface electric field of the cathode 30, 40. Therefore, the secondary electrons emitted from the cathode front face 31, 41 receive forces from both the electric field and the magnetic field and undergo a spiral motion, increasing the effective length of the orbit.
The probability of collision ionization with gas molecules introduced from the inlet 11 increases, and the plasma density increases. Moreover, both cathodes 30□
The permanent magnets in 40 are divided and arranged so that their polarities are alternately arranged in both the longitudinal direction of the cathode and the direction perpendicular thereto, and spacers 51 and 52 made of a non-magnetic material are placed between these divided magnet pieces. , 5L54. ..., 81.6
Since 2,63°64, . . . are inserted, the leakage magnetic flux component perpendicular to the electric field increases, and the probability of ionization due to collision with gas molecules increases.

Permanent magnet 15°I embedded in the anode bending part 12.13
B not only generates a magnetic flux protruding between the cathode 30.40 and the anode bend 12.13, but also the anode slit 1.
4, a concentrated magnetic flux is generated parallel to the ion beam extraction axis 25. Cathode 30.40 and anode bent portion 12.
13 has a large component perpendicular to the electric field in the plasma space P, causing the electrons to draw a spiral trajectory and promoting ionization upon collision with gas molecules. Since the magnetic flux in the anode slit 14 passes through the narrow gap between the permanent magnet pieces 15 and 1 G, the component along the ion beam extraction axis 25 becomes large. Therefore, the magnetic flux near the anode slit 14 has a compressed magnetic flux distribution for the positive ions to be extracted, focuses the positive ions on the extraction shaft 25, and increases the ion current to be extracted.

There is a slit 1 in the positive ions generated in the plasma space P.
4.24, there is one that travels in the opposite direction and passes through the gap of 30° and 40° between both cathodes. When the repeller electrode 70 is not provided, some of the positive ions that have passed through the gap between the cathodes 3rj and 40 collide with the anode 10 or are reflected. However, since it is decelerated by the anode lO, this anode I
The kinetic energy upon collision with O is small. Some positive ions reverse their direction of movement midway and are accelerated toward the cathode 30.40 again. These positive ions are transferred to the cathode 30
．． It collides with the side 32.42 of 40 and cannot be used effectively. However, as shown in FIG.
When a higher potential than the anode 10 is applied to the repeller electrode 70, positive ions can be efficiently reflected or reversed and used effectively, and the ion current extracted increases.

For example, if Ar gas is introduced so that the gas pressure inside the anode IO is 1.33X10-2 Pa, and the dimensions of the slit 14.24 are 50 mm in length and 0.5 mm in width, approximately 5
An ionic current of mA is obtained. In this way, a large ion current can be obtained even at low gas pressures.

In addition, the permanent magnet pieces 34a, 34b in the cathode 30.40,
-; 44a, 44b, ... and anode bent portion 12.13
It is preferable to use, for example, cobalt samarium rare earth magnets as the permanent magnets 15 and 18 inside. However, the temperature of the cathode 30 tends to rise due to positive ion bombardment.
．． Water cooling pipes 33, 43 are provided inside the magnet 40 to suppress the temperature rise of the permanent magnet pieces 34a, 34b, -; 44a, 44b, -. The surface of the cathode 30.40 is suitably composed of a metal such as molybdenum, tantalum, or tungsten. Permanent magnet-16 in cathode 30.40 = stones 34a, 35a, 36a,...; 44a, 45
Non-magnetic spacers 52, 53, between a, 46a, .
54. ..., [i2.133,64. ... does not need to be provided.

[Effects of the Invention] As described above, in the cold cathode sheet-like ion beam generator according to the present invention, the divided rod-shaped cathodes are all disposed inside the anode with the ion beam extraction shaft removed, so that positive ions are generated. The probability that the cathode sputtered particles generated by the impact are ionized and pass through the anode slit or adhere to the electrode near the slit is reduced, and the adverse effects of the cathode sputtered particles are alleviated.

Furthermore, if a permanent magnet is placed inside each cathode to generate a magnetic flux with a component perpendicular to the electric field on the cathode surface, the effective trajectory length of the secondary electrons emitted from the cathode will increase, causing collisions with gas molecules. The type MIs rate increases and the plasma density increases. If the permanent magnet inside each cathode is divided in the longitudinal direction of the cathode or in a direction perpendicular to this direction, and the divided magnet pieces are arranged so that the polarity is reversed with a non-magnetic spacer in between, the electric field on the cathode surface can be reduced. A leakage magnetic flux with a large component orthogonal to the ion beam is obtained, and the ionization efficiency is increased.

By embedding a permanent magnet in the anode end of the slit and generating a magnetic flux in the anode slit with a component parallel to the ion beam extraction axis, a spiral motion of the electrons toward the anode is generated. This not only improves the ionization efficiency, but also causes positive ions to be focused near the ion beam extraction axis due to the effect of magnetic compression, increasing the current density of the extracted ion beam.

In addition, if a repeller electrode is provided inside the anode on the side opposite to the slit with respect to the cathode, and the shape, arrangement, and applied potential of this liberator electrode are appropriately selected, positive ions can be directed toward the slit of the anode efficiently. , the ionic current increases.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a cold cathode sheet-like ion beam generator according to an embodiment of the present invention, and FIG. 2 is a previous cross-sectional view taken along line A-A. Explanation of symbols 2...Ion beam generator, 10...Anode, 11
...Gas inlet, 12.13...Anode bending part, 14
...Slit, 15.16...Permanent magnet, 20.2
1... Insulator, 22.23... Ion extraction electrode, 2
4...Slit, 25...Ion beam extraction shaft, 3
[), 40... cathode, 33.43... water cooling pipe,
34a, 34b, 35a, 3Ga; 44a, 44b
, 45a, 40a --- Permanent magnet piece, 51, 52, 5
3.54; Of, 62.03. I34...Nonmagnetic spacer, 70...Libera electrode, P...Plasma space. Patent applicant: Hirano Mitsune, Co., Ltd.

Claims (1)

[Claims] 1. A cylindrical envelope provided with an inlet for a gas to be ionized and a slit for extracting ions is used as an anode, and an ion extraction electrode with a negative potential is provided near the slit. A device in which a sheet-like positive ion beam is extracted by a
A cold cathode sheet-like ion beam generator characterized in that each of the rod-like cathodes is arranged along the longitudinal direction of the anode and off the ion beam extraction axis. 2. The cold cathode sheet-like ion beam generator according to claim 1, wherein a permanent magnet is disposed inside each cathode so as to generate a magnetic flux having a component perpendicular to the electric field on the surface of the cathode. 3. The permanent magnets inside each cathode are divided in the longitudinal direction of the cathode so that their polarities are alternately arranged, and a spacer made of a non-magnetic material is inserted between the divided magnet pieces. cold cathode sheet-shaped ion beam generator. 4. The permanent magnets inside each cathode are arranged in sections in a direction perpendicular to the longitudinal direction of the cathode so that the polarities are arranged alternately, and a spacer made of a non-magnetic material is inserted between the divided magnet pieces. The cold cathode sheet-like ion beam generator according to claim 2 or 3. 5. A permanent magnet is embedded in the anode end constituting the slit so as to generate a magnetic flux having a component parallel to the ion beam extraction axis in the anode slit. The cold cathode sheet-like ion beam generator according to any one of the items. 6. Cold cathode sheet-like ion beam generation according to any one of claims 1 to 5, characterized in that a repeller electrode with a positive potential is provided inside the anode on the side opposite to the slit with respect to the cathode. Device.