JPH0554812A - Ion source - Google Patents

Abstract

PURPOSE:To reduce the maintainance and inspection work for an ion source by providing a plasma-generating electrode for high-frequency discharge. CONSTITUTION:A discharge chamber 1 is formed by a cylindrical side plate 2 and a side-plate blocking lid plate 3. A plasma-generating electrode 4 is provided at approximately the center of the chamber 1 in such a manner as passing the center of the lid plate 3. A radiation shield 22 is located immediately in front of the plasma electrode 8 of a take out electrode system 11 and a columnar space is defined by a radiation shield 5 located on the inner periphery of the chamber 1 and by an intermediate radiation shield 6. Plasma is generated within the space. A cathode filament 7 heats the plasma space. The side shield 5 and the intermediate shield 6 are at the same anode potential as the chamber 1. High-frequency power is fed among the chamber 1, the electrode 4 and the shields 5,6 and thereby high-frequency discharge is generated between the electrode 4 and each of the shields 6,5 and excites and converts a vapor into plasma.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to an ion source capable of functioning at elevated temperatures suitable for producing ion beams of high melting point materials.

[0002]

2. Description of the Related Art Conventionally, an ion source has been one in which a raw material gas introduced into a discharge chamber is converted into plasma by discharge and extracted as an ion beam by an extraction electrode. There is a gas inlet in either of the discharge chambers. The inside of the discharge chamber can be evacuated. Inside, there is a cathode filament which is heated by the filament power supply. This also serves as a cathode and the discharge chamber as an anode, during which a direct current arc discharge is generated. Thermionic electrons are emitted from the filament and are accelerated and collide with gas molecules, which are ionized to form plasma. A permanent magnet is provided on the outer periphery of the discharge chamber so that plasma is confined in the center of the discharge chamber. At the outlet of the discharge chamber, there is an extraction electrode which is a porous metal plate, and the plasma inside can be extracted as an ion beam. In the past, such a source of gas was used, so such an ion source was acceptable. However, as the use of ion sources has expanded, there has been a demand for ion beams such as metals having a high melting point. For example, Si, Al, Cr, P or the like.

Of course, it is possible to produce these ions by thermally decomposing a gas substance containing these substances as a compound as a raw material. In that case, various ions are generated, so mass spectrometry is required to extract only desired ions. When a large-diameter ion beam is desired, the mass spectrometer itself becomes large. There is also a demand for obtaining desired ions without mass spectrometry. In this case, a single metal solid must be used as the starting material. In the case of a solid raw material, there is a form in which a separately heated oven is heated and evaporated to be introduced into the discharge chamber. Alternatively, the crucible containing the raw material solid may be built in the discharge chamber. In any case, the inside of the discharge chamber will have an unprecedentedly high temperature. It is necessary to provide a radiation shield of Ta, W, etc. along the inner wall of the discharge chamber in order to maintain the high temperature.
Further, in order to heat the solid raw material to high heat, a filament having an anodic potential may be provided for resistance heating.

[0004]

FIG. 3 shows an example of a conventional ion source. This is Y. Inouchi, H .; Tanaka, H .; Inam
i, F. Fukumaru, and K.K. Matsun
aga: "High-current metalio"
n beam extraction from a
multispion source "Rev.
Sci. Instrum. 61 (1), Jan. 199
0, p538. A separate evaporation source is provided to vaporize the solid raw material. There is an anodic filament AF which is energized and heated. This heat heats the radiation shield RS to the temperature required to hold the metal vapor. There is a cathode filament CF, which serves as a cathode to generate an arc discharge with the discharge chamber. Since the cathode filament has a higher temperature than the conventional one and a large amount of thermoelectrons are generated, spatter is increased. There is also consumption due to reaction with metal vapor. Originally, the cathode filament is an elongated wire. For this reason, the consumption of cathode filament is more intense than in the past. Since the life of the cathode filament is short, the cathode filament must be replaced frequently, and maintenance and inspection is troublesome. It is an object of the present invention to provide an ion source for high melting point substances by eliminating the need for a cathode filament replacement and overcoming such difficulties and reducing maintenance work.

[0005]

SUMMARY OF THE INVENTION The ion source of the present invention is a discharge chamber which can be evacuated to a vacuum to excite a gas substance into plasma by causing an electric discharge inside, and a radiation provided along the inner wall of the discharge chamber. A shield, a magnet provided on the outer periphery of the discharge chamber for confining plasma, an extraction electrode system made of a porous metal plate provided at the outlet of the discharge chamber, and provided inside the discharge chamber and insulated from the discharge chamber. A plasma generating electrode and a high frequency power supply for supplying high frequency power between the discharge chamber and the plasma generating electrode are included, and a high frequency discharge is generated between the discharge chamber and the plasma generating electrode to excite neutral particle vapor and thereby generate plasma. The extraction electrode is characterized as being extracted as an ion beam. In other words, there is no cathode filament, and a new plasma generating electrode is installed inside the discharge chamber in addition to this. Then, a high frequency discharge is generated between the plasma generating electrode and the discharge chamber. Further, instead of providing the plasma generating electrode, one radiation shield may be used as an electrode to cause high frequency discharge between this and the discharge chamber. Further, in order to generate the metal vapor, an evaporation source may be provided separately from the ion source, or a crucible containing a solid raw material may be placed in the ion source.

[0006]

In the conventional ion source, the cathode filament is energized to generate thermoelectrons, and a direct current is caused to flow between the cathode filament and the wall of the discharge chamber to form a direct current arc discharge. When targeting high melting point materials, the temperature of the cathode filament is as high as 2800 ° C to 3000 ° C. However, in the case of the present invention, no cathode filament exists. Instead, there is a plasma generating electrode for high frequency discharge. This is not a filament and does not generate heat by itself. Therefore, the temperature rises to about the same level as the surrounding radiation shield. That is, it is about 1800 ° C. Moreover, the plasma generating electrode does not need to be linear like a filament to increase the resistance value and can be a plate having a large area. Since it has a lower temperature and a larger volume, it has a longer life and consumes less than conventional cathode filaments.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. The discharge chamber 1 is a container that can be evacuated to a vacuum, and is formed by a cylindrical side plate 2 and a lid plate 3 that closes one of the side plates.
A plasma generating electrode 4 is provided almost in the center of the discharge chamber 1 so as to penetrate the center of the lid plate 3. Ta or W is provided on the inner circumference of the side plate 2.
A thin cylindrical cylindrical radiation shield 5 is provided. Further, a disk-shaped radiation shield 6 which is perpendicular to the axial direction is provided at a position slightly closer to the lid plate 3 than the center of the discharge chamber. Several anodic filaments 7 project at right angles from the cover plate 3. This is an anode potential and serves as a heater for heating the inside of the discharge chamber. Although it is a heater made of a thin wire such as tungsten, it is not consumed because it is not subjected to sputtering by ions in the plasma because it has an anode potential. These plasma generating electrode 4 and anode filament 7 penetrate a radiation shield 6 parallel to the cover plate. An extraction electrode system 1 including a plasma electrode 8 which is a porous electrode plate, an extraction electrode 9, and a ground electrode 10 on the side opposite to the cover plate 3 of the discharge chamber 1.
1 is provided. These are for extracting plasma as an ion beam from the ion source. Several magnets 12 are provided on the outer circumference of the discharge chamber 1. This prevents the plasma from contacting the wall surface of the discharge chamber 1 by forming a cusp magnetic field. The magnetizing direction is the radial direction, and the magnetizing directions are arranged to be reversed between the adjacent magnets. A high frequency power supply 13 is connected between the plasma electrode 4 and the discharge chamber 1.
This is for applying a high frequency electric field between the plasma generating electrode 4 and the discharge chamber 1 to cause a high frequency discharge.

In this example, an evaporation source 14 is provided outside the discharge chamber 1 and heats a solid having a high melting point to form vapor. The evaporation source 14 has a crucible 15 for containing a solid material, a heater 16 and an oven 17. These are surrounded by a mantle tube 18. The raw material is heated by the heater 16 to form steam. Some radiation shields are provided to block heat exchange with the outside. The evaporation source 14 and the discharge chamber 1 are connected by a connecting pipe 19. The route through which the steam passes is the radiation
It is a feed pipe 20 surrounded by a rud. There is a region surrounded by the insulator 21 at the tip of the ion source, and the tip is connected to various processing devices.

There is a radiation shield 22 immediately before the plasma electrode 8 of the extraction electrode system 11, and a cylindrical space is formed by the radiation shield 5 at the inner circumference of the discharge chamber 1 and the intermediate radiation shield 6. Partitioned. Plasma is generated inside this. The anode filament 7 and the plasma generating electrode 4 are inside the plasma space. The cathode filament generates radiant heat to heat the plasma space. The radiation shield 5 on the side surface and the radiation shield 6 in the middle have the same anode potential as the discharge chamber 1. Since high frequency power is supplied between the discharge chamber 1 and the plasma generation electrode 4, the plasma generation electrode 4 and the radiation shield are connected.
A high-frequency discharge is generated between the contacts 6 and 5, and this excites vapor to form plasma. The frequency and power of the high frequency power source should be appropriately selected depending on the size and material of the ion source. For example, one with 13 MHz and 1 kW can be used. The plasma is extracted as an ion beam by the extraction electrode system 11.

Since the plasma generating electrode is not a cathode and does not generate thermoelectrons, it has a relatively low temperature. As mentioned earlier, this is 1
It is about 800 ° C. Since it is possible to form a thick electrode plate with a large area, damage due to sputtering is small. On the contrary, since the plasma generating electrode is located in the high temperature plasma space surrounded by the radiation shield, metal vapor or the like will not be deposited on it. Even if it adheres temporarily, the temperature is high, so it evaporates again.
Therefore, the plasma generating electrode is always normal and does not wear out, so there is almost no need to replace it.

FIG. 2 shows another embodiment of the present invention. This is to divert one of the existing radiation shields 6 in the intermediate portion to the plasma generating electrode 24 instead of providing the independent plasma generating electrode 4. In this case, this radiation
The field and other radiation shields 6, 5 must be insulated. By doing so, one member can be saved and the structure can be simplified. Further, since the range where the discharge occurs becomes wider, there is an advantage that plasma generation becomes more active. Further, in this example, a crucible 26 containing the solid raw material 25 is placed inside the discharge chamber 1 without separately providing an evaporation source. The solid raw material becomes vapor due to the heat of the cathode filament 7. This has the advantage that the device is simplified because no evaporation source is required.

[0012]

The plasma generating electrode used in the present invention has a temperature lower than that of the cathode filament and it is not necessary to increase the resistance value, so that the structure can be geometrically resistant to heat. The ion source that uses a high melting point material as a plasma must be heated to a higher temperature. However, since the present invention does not use a cathode filament having a short life, the labor for maintenance and inspection is reduced and the maintenance becomes easier.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an ion source according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of an ion source according to another embodiment of the present invention.

FIG. 3 is a schematic sectional view of an ion source according to a conventional example.

[Explanation of symbols]

 1 Discharge Chamber 2 Side Plate 3 Lid Plate 4 Plasma Generation Electrode 5 Radiation Shield 6 Radiation Shield 7 Anode Filament 8 Plasma Electrode 9 Extraction Electrode 10 Grounding Electrode 11 Extraction Electrode System 12 Magnet 13 High Frequency Power Supply 14 Evaporation Source 15 Crucible 16 Heater 17 Oven 18 Overcoat 19 Communication Pipe 20 Feed Pipe 21 Insulator 22 Radiation Shield

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuhiro Matsuda 47 Umezu Takaunecho, Ukyo-ku, Kyoto City Nissin Electric Co., Ltd. (72) Inventor Yu Inouchi 47 Umezu Takaunecho, Ukyo-ku, Kyoto Nissin Electric Co., Ltd.

Claims (2)

[Claims] 1. A discharge chamber which can be evacuated to a vacuum to excite a gas substance into plasma by causing an electric discharge inside, a radiation shield provided along the inner wall of the discharge chamber, and an outer periphery of the discharge chamber. And a magnet for confining the plasma, an anode filament provided inside the discharge chamber, which is a heater having the same or substantially the same potential as the discharge chamber, and an extraction electrode made of a porous metal plate provided at the outlet of the discharge chamber. A system, a plasma generating electrode provided inside the discharge chamber and insulated from the discharge chamber, and a high-frequency power source for supplying high-frequency power between the discharge chamber and the plasma generating electrode, and between the discharge chamber and the plasma generating electrode. An ion source characterized in that a high frequency discharge is caused to excite a gas to generate a plasma, which is then extracted as an ion beam from an extraction electrode. 2. A discharge chamber which can be evacuated to a vacuum to excite a gas substance into plasma by causing an electric discharge inside, a radiation shield provided along the inner wall of the discharge chamber, and an outer periphery of the discharge chamber. And a magnet for confining the plasma, an anode filament provided inside the discharge chamber, which is a heater having the same or substantially the same potential as the discharge chamber, and an extraction electrode made of a porous metal plate provided at the outlet of the discharge chamber. High-frequency power is supplied between the discharge chamber and the radiation shield for electrodes, which has a large area and is insulated from the discharge chamber and other radiation shields provided inside the system and the discharge chamber. And a high-frequency power source for generating a high-frequency discharge between the discharge chamber and the radiation shield for electrodes to excite the gas to generate plasma, which is extracted as an ion beam from the extraction electrode. On source.