JPH04184899A - Plasma generation device - Google Patents

Abstract

PURPOSE:To introduce a high power mu-wave and prolong an antenna life by cooling an antenna with a refrigerant circulating in the inside, refrigerating a casing with a cooling block, and effectively cooling inner and outer peripheries of a vacuum sealing member. CONSTITUTION:A mu-wave is propagated between a casing 22 and an antenna 23, and passes through a ceramic vacuum seal 27 to be emitted in a discharge tube 21 from the antenna 23. ECR is generated in a magnetic field of a magnet 29, and ion beams are drawn out from formed plasma with a drawing-out electrode 30. Electrons (e) are intercepted with a plate 26 to protect a sealing member 27 from a direct hit. The antenna 23 is cooled with water W, circulating in the inside, from the inside via, a joining part Q, and a joining part P with the casing 22 is effeciently cooled with a block 28 in an outer periphery, preventing temperature rise and breaking of the seal 27. This constitution normally operates the whole vacuum system for a long time, enabling introduction of a 1kw or more mu-wave and considerable prolongation of an antenna life with length of the discharge tube 21, an antenna protruded quantity in the discharge tube, and the plate 26 diameter suitably selected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plasma generation device. In particular, the present invention relates to a plasma generation device that generates plasma by using microwaves.

[Prior Art and its Problems] A method of generating plasma by electron cyclotron resonance using microwaves is known.

As an apparatus of this type, Japanese Patent Application Laid-Open No. 61-269900 discloses a plasma generating apparatus as shown in FIGS. 3 and 4. That is, in the figure, a magnetron (1), which is a microwave generator, and a rectangular waveguide (
2). A tubular antenna (8) extends from the inner surface of this waveguide (2), and this antenna penetrates through an opening (4) provided in the tube wall opposite to the tube wall where the antenna is installed. It extends outward from the waveguide (2). A cylindrical magnetic field generator (5) whose central axis coincides with this antenna (8) is provided. This magnetic field generator (5) consists of a plurality of ferrite rod-shaped magnets (6) arranged in a cylindrical shape so that the magnetic poles on the central axis side alternate. The magnetic field strength generated by the magnetic field generator (5) is less than the resonant magnetic field strength (magnetic field strength that satisfies the condition for generating II-ion cyclotron resonance B = ωm/e: m = mass of electron, e = charge of electron) on the central axis. The magnetic field strength is greater than the resonant magnetic field strength at positions away from the central axis. The opening provided in the waveguide (2) is sealed by a ceramic vacuum seal part (7) that surrounds the antenna (8) with a space, and the outer periphery of the magnetic field generator (5). The surface is covered by an outer wall (8) which is a discharge tube, and the inside of the outer wall (8) can be maintained in a high vacuum state. Waveguide (
A matching box (9) is provided at the end of 1). This matching box is adjusted so that the microwave emitted from the magnetron m is fully utilized to generate plasma and the reflected wave becomes O.

In the plasma generator configured in this way, plasma is generated as follows. Magnetron (1)
) is transmitted through the waveguide (2), reaches the antenna (8), and is emitted from the antenna (8) into a space maintained in a high vacuum state. The emitted microwaves propagate further into the magnetic field of the resonant magnetic field strength, where the energy is consumed to cause electron cyclotron resonance and generate plasma. The generated plasma is diffused along the central axis of the magnetic field generator (5).

Although heat is generated along with the generation of plasma, damage to the device due to heat generation can be prevented by flowing a cooling medium from the antenna into the waveguide (2). ” is disclosed.

The microwave antenna (3) shown in Figure 3 generates plasma by emitting microwaves to the discharge tube (8) through a ceramic vacuum seal (7). Accidents have occurred in which the vacuum seal portion (7) is damaged due to such factors, resulting in the failure of the entire vacuum system.

(2) That is, the vacuum seal part (7) becomes high temperature due to dielectric loss in the ceramic seal part due to charged particles from the plasma and microwaves, and is thermally deformed and damaged due to the high temperature of the joint part with the metal part. This is the waveguide section (2
) and the discharge tube section (8) by flowing a cooling medium, this problem cannot be prevented (although this publication does not specifically specify what the medium is, it is likely to be air due to its structure). ). In particular, when high-power microwaves exceeding 700 watts are introduced, the frequency of failure increases.

■Especially in the case of an ion source for extracting an ion beam, an extraction electrode (10) is provided, and the electrons that come out near this are accelerated and flow back toward the discharge tube (8). The ceramic vacuum seal part (7) was directly hit and damaged.

[Points to be solved by the invention] The present invention was made in view of the above problems, and prevents damage to the vacuum seal portion made of dielectric material, and allows constant introduction of microwaves of high power exceeding 700 watts. The purpose of the present invention is to provide a plasma generation device that can perform the following steps.

[Means for solving the problem 1 The above object is to provide a discharge tube whose interior is kept in a high vacuum, a magnetic field strength on the central axis is less than the resonant magnetic field strength, and a magnetic field strength at a position away from the central axis. a cylindrical magnetic field generating device that forms a magnetic field in the discharge tube in which the magnetic field is greater than or equal to the resonance magnetic field strength; a cylindrical casing having one end fixed to the wall of the discharge tube concentrically with the central axis of the discharge tube; a tubular antenna disposed concentrically inside the cylindrical casing and protruding a predetermined length from the one end of the cylindrical casing into the discharge tube; and an inner wall surface of the cylindrical casing. an annular vacuum sealing member made of a dielectric material and airtightly fixed to an outer wall surface of the antenna; a cooling medium circulating means for circulating a cooling medium within the tubular antenna; and a cooling medium circulation means corresponding to the vacuum sealing member. This is achieved by a plasma generation device comprising an annular cooling block attached to an outer wall surface of a cylindrical casing, so that microwaves are transmitted through a space between the cylindrical casing and the antenna. .

[Function 1: The antenna is cooled by the cooling medium circulating inside it, and the outer cylindrical casing is cooled by a cooling block, so the antenna should be fitted between the cylindrical casing and the antenna to correspond to this block. The outer and inner peripheral parts of the attached vacuum seal member are efficiently cooled, and a large temperature rise due to microwave power loss in the plasma, dielectric, and conductor is prevented. Therefore, the vacuum seal member is cooled to operate normally over a long period of time.

Therefore, it is also possible to introduce microwaves with a high power of 1 W, and the life of the antenna can be greatly extended.

[Example] Hereinafter, a plasma generator according to an example of the present invention will be described with reference to FIG. 1.

In Figure 1, the plasma generator as a whole is (20)
The cylindrical discharge tube (21) shown by is constructed in the same way as the conventional one, and its interior is kept under high vacuum. This prevents contamination of the inner circumferential wall by plasma.) This is constructed in the same manner as the third section of the conventional example, and has a large number of magnetic poles extending in the axial direction, with a large number of N poles and S poles. The arrangement is fixed by changing the arrangement alternately.Also, the discharge tube (21
) One end of a cylindrical casing (22) is fixed to the open end f21a) formed in the side wall of the casing (22), and a tubular antenna (23) as a double pipe is installed concentrically inside this casing (22).
is disposed and protrudes a predetermined amount into the discharge tube (21), and a circular flat plate (26) is fixed to one end protruding into the discharge tube (21).

The antenna (23) has a double tube structure, but the outer tube (23)
An inner tube (25) is arranged concentrically with the inner tube (4).
Water W circulates between the space Δ in 25) and the space Δ between the outer tube (24) and the inner tube (25) as shown by the arrow. Note that a drive unit for circulating this water is not shown.

The outer tube (24) of the antenna (23) and the cylindrical casing (
A vacuum seal member (22) made of ceramic is provided between the
7) is fitted and fixed. That is, as shown by joints P and Q, it is hermetically joined to the inner wall of the casing (22) and the outer wall of the tubular antenna (23). Further, an annular cooling block (28) is fitted onto the outer wall surface of the casing (22) at a portion corresponding to the vacuum seal member (27).

Further, according to this embodiment, an extraction electrode (30) is attached to one end of the discharge tube (21). Discharge tube (21)
The length in the axial direction of the antenna (23) is 1.5 mm (e is the wavelength of the introduced microwave), the diameter of the flat plate (26) is l/4λ, and the length of the antenna (23) into the discharge tube (21) is The protrusion amount is 3/
4 λ is set.

The plasma generator according to the embodiment of the present invention is constructed as described above, and its operation will be explained next.

In Figure 1, the microwaves generated by the magnetron located on the right side are transmitted through the casing (22) and the antenna (2).
3) as shown by the arrow (32),
It passes through the ceramic vacuum seal member (27) and is emitted into the discharge tube (21) by the action of the antenna (23) as shown by the arrow (31). It propagates into a magnetic field with a microwave resonance magnetic field strength formed by a large number of magnets (29), where it causes electron cyclotrosi resonance 1EcR1, and its energy is consumed for plasma generation. Further, an ion beam is extracted from the plasma thus formed with an extraction amount of 1fi f30+, and in this case, the extraction electrode (3G) functions as an ion source.

At this time, the electrons [e] flow toward the vacuum seal member (27) as shown by the arrow, but they are blocked by the flat plate (26), and these electrons do not directly hit the vacuum seal member (27). .

Furthermore, even if heat is applied to the vacuum seal member (27) due to dielectric loss in the vacuum seal member (27) or energy loss due to eddy currents generated in the cylindrical casing (22), the cooling of the inner and outer circumferential portions , that is, the antenna (23
) is cooled from the inner periphery via the joint Q by the cooling water circulating inside the cooling block (28
), the joint P with the casing (22) is efficiently cooled, so the temperature of the vacuum seal member (27) does not rise, and damage to this seal, which conventionally occurs, is prevented.

This ensures that the entire vacuum system as shown in FIG. 1 operates normally over a long period of time. Further, according to this embodiment, the axial length of the discharge tube (21) serving as the cavity is 1.
The amount of protrusion of the antenna (23) into the discharge tube (21) is 374 mm, and the diameter of the flat plate (26) is 174 mm (wavelength =
1221)1)1)), microwaves are efficiently absorbed by the plasma, and in this example, microwaves of IKw or more can be introduced.
The lifespan of 3) was 10 times longer than the conventional lifespan despite the fact that several discharges occurred at the extraction electrode (30) and there was a backflow of electrons. In other words, it was maintenance free for about half a year.

FIG. 2 shows a plasma generator according to a second embodiment of the present invention, but parts corresponding to those in the first embodiment are designated by the same reference numerals, and detailed explanation thereof will be omitted.

That is, in this embodiment, a block plate (33) made of a dielectric material is further provided in the vicinity of the open end (21al). This block plate (33) is fitted into the tubular antenna (23). When metal ions are generated within (21), they also fly toward the vacuum seal member (27), but according to this embodiment, the opening degree of the open end 121a) is sufficiently small. Although the amount of attached metal ions is small,
Note that if the amount of this adhesion gradually increases, the microwaves will be blocked, making it impossible to transmit the microwaves into the discharge tube (21). Or the amount of transmission becomes very small. In order to cope with this, in this embodiment, a block plate (33) made of a dielectric material is arranged close to the opening end (21al).Thereby, metal ions flying from the discharge tube (21) are removed from the block plate (33). (33), and is prevented from adhering to the vacuum seal member (27).Thus, even if metal ions are generated, the plasma generator of this embodiment can perform the prescribed action for a long period of time. However, if a metal film is still attached to the vacuum seal member (27) and this shows a microwave shielding effect, RF at a frequency of about 13.56 MH, for example, can be easily applied to the antenna (23). As a result, plasma is generated around the vacuum sealing member (27), and the ions collide with the surface of the vacuum sealing member (271, that is, sputtering), thereby detaching and removing attached metal ions. Therefore, the microwave shielding effect caused by the metal ions attached to the vacuum seal member (27) is returned to zero.

Although the embodiments of the present invention have been described above, the present invention is of course not limited thereto (and various modifications can be made based on the technical idea of the present invention).

For example, in the above embodiment, the amount of protrusion of the antenna (23) into the discharge tube (21), the axial length of the second discharge tube (the second axial length, the diameter of the flat plate (26), etc.) Although the wavelength of the wave is set to a predetermined relationship, the effect of the present invention is not lost even if the relationship is not the predetermined value.

Furthermore, in the above embodiments, the extraction electrode (30) was used as an ion source, but of course the present invention can also be applied to a simple plasma generating device by omitting the extraction electrode.

Further, in the above embodiments, the antenna (23) was cooled by circulating water, but the antenna (23) is not limited to this, and may be cooled by flowing other media, such as oil.

Furthermore, in the above embodiment, one end of the antenna (23) is provided with a flat plate (
Although the vacuum sealing member (26) was installed to block the electrons heading toward February, the effect of the present invention will not be significantly lost even if the flat plate is omitted in some cases.

[Effects of the Invention] As described above, according to the plasma generator of the present invention, the life of the vacuum seal portion can be made much longer than in the past, and therefore maintenance-free can be achieved for a long period of time.

[Brief explanation of the drawing]

1 and 2 are side sectional views of main parts of plasma generating apparatuses according to first and second embodiments of the present invention, FIG. 3 is a side sectional view of a conventional plasma generating apparatus, and FIG. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3; In addition, in the figure, (20)... Plasma generator (21)
... Cylindrical discharge tube (22) ... Cylindrical casing (23) ... Tubular antenna (27) ... Vacuum seal member (29) ... Magnetic field generator fee Yasushio Saka 1st University Figure 2 Figure 3

Claims (6)

[Claims] (1) A discharge tube whose interior is kept in a high vacuum, and a magnetic field in which the magnetic field strength on the central axis is less than the resonant magnetic field strength and the magnetic field strength at a position away from the central axis is equal to or higher than the resonant magnetic field strength. A cylindrical magnetic field generator formed in a tube, a cylindrical casing having one end fixed to the tube wall of the discharge tube concentrically with the central axis of the discharge tube, and a cylindrical casing arranged concentrically inside the cylindrical casing. a tubular antenna arranged to protrude a predetermined length into the discharge tube from the one end of the cylindrical casing; and an airtight space between an inner wall surface of the cylindrical casing and an outer wall surface of the antenna. a fixed annular vacuum seal member made of a dielectric; a cooling medium circulation means for circulating a cooling medium within the tubular antenna; and an annular cooling block, the plasma generating device being configured to transmit microwaves through a space between the cylindrical casing and the antenna. (2) The plasma generating device according to claim 1, wherein a shielding plate is fixed to one end of the antenna inside the discharge tube so as to receive electrons flowing toward the vacuum sealing member. (3) The plasma generator according to claim 1 or 2, wherein the antenna is a double tube, and a cooling medium is circulated between an inner tube and an outer tube. (4) The length of the discharge tube in the axial direction is 1.5λ (λ is the wavelength of the transmitted microwave).
) The plasma generator according to any one of the above. (5) The protrusion length of the antenna inside the discharge tube is 3/4λ
The plasma generation device according to any one of claims (1) to (4). (6) The shielding plate is a circular flat plate, and its diameter is 1/
4. The plasma generating device according to any one of claims (1) to (5), wherein the plasma generator has a wavelength of 4λ.