JP2005116312A - Microwave plasma generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave plasma generator preventing a gas to increase the output of a negative ion beam from adhering to the wall of a wave guide, efficiently generating a negative ion, and restraining a vacuum window from being broken by suppressing generation of discharge in the wave guide. <P>SOLUTION: A square cylinder-shaped thin plate conductor 16 is installed in the vicinity of the inner wall of the wave guide 4 apart from the wall, and the gas to increase the output of the negative ion beam is prevented from adhering to the wall by keeping this square cylinder-shaped thin plate conductor 16 at higher temperatures than that of the discharge vessel 1. The square cylinder-shaped thin plate conductor 16 is heated by using power of an electron jumping out of plasma, and a electric heater. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a microwave plasma generator used as a plasma source of a processing plasma apparatus such as a large ion source used for heating fusion plasma, a plasma dry etching apparatus, or a plasma vapor deposition apparatus.

Conventionally, a microwave plasma generator is used for an ion source of a neutral particle injection superheater for nuclear fusion, a plasma dry etching apparatus used in a semiconductor manufacturing apparatus, or a plasma source of a plasma vapor deposition apparatus. ing.
In particular, a waveguide is used in a plasma generator that generates plasma by introducing a high-power microwave of several hundred W or more into a discharge vessel.

  In addition, when used in a hydrogen negative ion source that generates negative ions of hydrogen or deuterium, it may be configured to introduce cesium gas into the discharge vessel in order to efficiently generate negative ions. is there.

Hereinafter, a conventional example of a hydrogen negative ion source which is one of microwave plasma generators will be described with reference to the drawings.
In FIG. 5, reference numeral 1 denotes a discharge vessel, and a microwave MW is introduced into the discharge vessel 1 through one of the flanges 2 of the discharge vessel 1 through a vacuum window 3 disposed midway from the microwave generator 20. A rectangular waveguide 4 is connected.

As the material of the vacuum window 3, alumina ceramics that is transparent to the passage of microwaves is used.
A permanent magnet 5 is disposed on the outer surface of the discharge vessel 1 and forms a magnetic field in the discharge vessel 1.
Further, the discharge vessel 1 is filled with a predetermined discharge gas, and discharge is generated by the interaction between the microwave MW and the magnetic field to form plasma.

Reference numeral 6 denotes a gas introduction pipe for supplying vaporized cesium gas. Cesium gas is a substance having the lowest ionization voltage, and negative ions of hydrogen or deuterium can be efficiently generated by mixing vaporized cesium gas into hydrogen plasma.
The other flange 7 of the discharge vessel 1 is provided with a plurality of extraction electrodes 8 for extracting ions in the plasma.

A voltage having a predetermined value is applied between the extraction electrodes 8 from the acceleration power source 10 via the insulating material 9 in order to accelerate the ion beam IB to a predetermined energy.
Reference numerals 11 and 12 denote bias power sources for applying a bias voltage between the discharge vessel 1 and the extraction electrode 8 and between the discharge vessel 1 and the waveguide 4.

FIG. 6 is a cross-sectional view along the axial direction of the hydrogen negative ion source shown in FIG. The extraction electrode 8 has a number of extraction holes 13 through which the accelerated ion beam IB passes.
By the way, in plasma generators using microwave discharge, there are many examples in which alumina ceramics that are vacuum windows 3 are directly installed on the flange 2. In such a configuration, the vacuum window 3 is exposed to the heat of plasma or the impact of plasma particles, and in some cases, the alumina ceramics may be damaged. Therefore, there is a problem that the density of plasma to be generated is limited and high density plasma cannot be generated.

  In the hydrogen negative ion source shown in FIG. 5, the reason why the bent waveguide 4 is installed is a measure for protecting the vacuum window material. The vacuum window 3 is formed by H corner or E corner to generate plasma. It is placed at a position where it does not look directly (see, for example, Patent Document 1).

  However, when only this H corner or E corner is disposed, the plasma in the discharge vessel 1 may enter the inside of the waveguide 4. If plasma is present in the waveguide 4, a part of the microwave MW traveling through the vacuum window 3 is reflected near the plasma surface. For this reason, the microwave MW could not be efficiently introduced into the discharge vessel 1.

  In order to solve the above problems, in the hydrogen negative ion source shown in FIGS. 5 and 6, an insulating material is disposed between the discharge vessel 1 and the waveguide 4, and further the waveguide is supplied by the DC bias power source 12. 4 has a higher potential than the discharge vessel 1.

When the waveguide 4 is set to a higher potential than the discharge vessel 1, an electrostatic barrier is formed against ions in the plasma, and the entrance of the plasma into the waveguide 4 is suppressed. Therefore, a high-power microwave can be easily input to the discharge vessel 1.
JP-A-7-85993

On the other hand, in the field of nuclear fusion, with the progress of technological development, a high-power hydrogen negative ion source has been required.
An effective means of increasing the output of the negative ion beam is to add vaporized cesium gas into the hydrogen plasma.

  As described above, cesium gas is a substance having the lowest ionization voltage, which facilitates low-pressure discharge and is suitable as an electron supply source, and can efficiently convert atomic hydrogen into negative ions. Therefore, cesium gas is often used in large negative ion sources.

  Cesium has a melting point of 28.5 ° C., is heated in an appropriate oven, vaporized, and supplied to the discharge vessel 1. In the discharge vessel 1, the added cesium gas is ionized in the discharge plasma, while adhering to the wall of the discharge vessel 1 and the surface of the extraction electrode 8 to form a thin cesium layer. The hydrogen atoms colliding with the cesium layer are converted into negative ions when they leave, and efficient negative ion generation is performed.

  However, although cesium is a substance that is easily vaporized, it has a boiling point of 670 ° C., and therefore liquefies and easily adheres to places where the temperature is low. The discharge vessel 1 is always superheated by the heat of the discharge plasma, but the temperature of the waveguide 4 is lower than that of the discharge vessel because it is not heated. Therefore, cesium adheres also to the inner wall of the waveguide 4.

  When cesium gas adheres to the wall of the waveguide 4, the utilization efficiency of cesium decreases. In addition, when the pressure of the hydrogen gas supplied for some reason or the microwave power passing through the waveguide 4 fluctuates, a discharge may occur in the waveguide 4 in rare cases.

When a discharge occurs in the waveguide 4, not only microwave reflection occurs as described above, but also the vacuum window 3 may be destroyed depending on the state of the discharge.
As described above, in the negative ion source using the waveguide 4, prevention of cesium adhesion to the inner wall of the waveguide 4 is a big problem.

  The present invention has been made to solve the above-described problems. The gas that increases the output of the negative ion beam to the waveguide wall is prevented from adhering, and negative ions can be efficiently generated and guided. An object of the present invention is to obtain a microwave plasma generator that suppresses the occurrence of discharge in a wave tube and suppresses the destruction of a vacuum window.

  In order to achieve the above object, the invention described in claim 1 is a discharge vessel in which a gas to be discharged is filled and a plasma is formed in a reduced pressure, and a microwave is introduced into the discharge vessel and A waveguide that can be set to a temperature relatively higher than the temperature, a magnetic field forming means that forms a magnetic field inside the discharge vessel, and a gas introducer that supplies a gas that increases the output of a negative ion beam to the discharge vessel It is provided with.

  The invention according to claim 4 is a discharge vessel in which a gas to be discharged is filled and plasma is formed in a reduced pressure, and a microwave is introduced into the discharge vessel, and the inside is separated from the inner wall thereof. A waveguide having a thin plate-like electric conductor plate, a magnetic field forming means for forming a magnetic field inside the discharge vessel, and a gas introducing device for supplying a gas for increasing the output of a negative ion beam to the discharge vessel. It is characterized by that.

  According to the microwave plasma generation apparatus of the present invention, the adhesion of gas that increases the output of the negative ion beam to the waveguide wall can be prevented, negative ions can be generated efficiently, and the discharge in the waveguide can be performed. Generation | occurrence | production can be suppressed and destruction of a vacuum window can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the embodiment, the same parts as those in the conventional microwave plasma generator shown in FIGS. 5 and 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 1 is a diagram showing a first embodiment of the present invention. A hydrogen negative ion source which is one of microwave plasma generators will be described as an example as in the conventional example shown in FIGS.
In FIG. 1, the discharge vessel 1 has a substantially cylindrical shape with a diameter of 15 cm and an axial length of 15 cm. A flange 4A formed at one end of the waveguide 4 is connected to the flange 2 of the microwave introduction hole formed at one end of the discharge vessel 1 through an insulating material 9a.

  The other end of the waveguide 4 is connected to a microwave power source (not shown) that generates a microwave of 2.45 GHz, for example. Microwaves from the microwave power source pass through the waveguide 4 and are introduced into the discharge vessel 1.

Further, on the outer wall surface of the cylindrical portion of the discharge vessel 1, two annular permanent magnets 5 made of Sm-Co as magnetic field forming means are formed in the vicinity of the flange flanges 2 and 7 formed at both ends of the discharge vessel 1. It is arranged.
Since the pair of permanent magnets 5 are magnetized in opposite directions in the radial direction, the lines of magnetic force largely project toward the central axis in the discharge vessel 1.

Hydrogen gas is introduced into the discharge vessel 1 from a gas inlet (not shown), and can be maintained at a predetermined pressure of 0.1 Pa by an exhaust device (not shown).
The microwave supplied from the waveguide 4 discharges hydrogen gas by the interaction with the magnetic field to generate plasma.

After the hydrogen plasma is generated, a gas that increases the output of the negative ion beam vaporized from an inlet (not shown) is added to the hydrogen plasma in the discharge vessel 1. Hydrogen negative ions are efficiently generated by adding a gas that increases the output of the negative ion beam.
In addition, an extraction electrode 8 is attached to the flange 7 of the discharge vessel 1 via a plurality of insulating rings 9b.

In the extraction electrode 8, a large number of ion extraction holes 13 are formed in the central portion so that the axial direction of the discharge vessel 1 is the ion extraction direction.
A predetermined voltage for extracting and accelerating ions is applied to the extraction electrode 8, and the generated negative hydrogen ions are accelerated while passing through the through-hole 13 and extracted outside the ion source.

The waveguide 4 is positively biased with respect to the discharge vessel 1 as described above, and plasma movement in the direction of the waveguide 4 is prevented by an electrostatic barrier.
A bias voltage is applied between the discharge vessel 1 and the extraction electrode 8 in order to adjust the operation of the ion source.

A heating heater 15 is disposed along the outer wall of the waveguide 4, and the waveguide 4 can be maintained at a temperature relatively higher than that of the discharge chamber 1. The gas that increases the output of the negative ion beam tends to adhere to the wall of the discharge chamber 1 where the temperature is relatively low.
Reference numeral 14 in FIG. 1 denotes a cooling pipe for passing cooling water, and adjusts the temperature of the waveguide in combination with the heater 15.

  As described above, according to the present embodiment, the temperature of the waveguide 4 connected to the discharge vessel 1 can be set to a temperature relatively higher than that of the discharge vessel 1, so that the output of the negative ion beam to the waveguide wall can be reduced. Adhesion of increasing gas can be prevented, negative ions can be generated efficiently, and discharge in the waveguide 4 can be prevented.

Next, a second embodiment of the present invention will be described with reference to FIG.
In the present embodiment, a configuration is such that a thin rectangular tube-shaped conductor 16 is supported inside the waveguide 4 along a tube wall via a support 17 that reduces heat transfer.

However, the inner dimension of the rectangular tube-shaped conductor 16 is set to a dimension that does not hinder the propagation of microwaves passing through the conductor.
The rectangular tube-shaped conductor 16 and the waveguide 4 can be set to have the same potential.

As described above, between the discharge vessel 1 and the waveguide 4, the DC bias power source 12 biases the waveguide 4 so as to have a higher potential than the discharge vessel 1, thereby suppressing plasma movement.
For this reason, electrons in the plasma are accelerated in the direction of the waveguide 4. Also in the case of the first embodiment, electrons collide with the waveguide 4 and heat the tube wall, but the temperature rise is not large because of the large heat capacity and exposure to the atmosphere.

  In the second embodiment, the electrons collide with the rectangular tube-shaped conductor 16. The rectangular tube-shaped conductor 16 is a thin plate and is heated to a high temperature because heat transfer with the wall of the waveguide 4 is small. The plate thickness of the rectangular tube-shaped conductor 16 and the support 17 are adjusted by the colliding electron power so that the rectangular tube-shaped conductor 16 has a relatively higher temperature than the wall of the discharge vessel 1.

  Thus, also in this embodiment, since the temperature of the waveguide 4 connected to the discharge vessel 1 can be set relatively higher than that of the discharge vessel 1, it is possible to prevent cesium from adhering to the waveguide wall, and negative ions Can be efficiently generated, and the occurrence of discharge in the waveguide 4 can be prevented.

Next, a third embodiment of the present invention will be described with reference to FIG.
In FIG. 3, the discharge vessel 1 and the waveguide 4 are set to the same potential, and the rectangular tube conductor 16 is set to a positive potential with respect to the waveguide 4. Reference numeral 18 denotes a support made of alumina ceramics. In the first and second embodiments, the discharge vessel 1 and the waveguide 4 have different potentials. For this reason, microwave power supplies, bias power supplies, waveguides, cables, and other structures installed at high potentials must be insulated according to their potentials.
In contrast, in FIG. 3, since the discharge vessel 1 and the waveguide 4 have the same potential, the configuration of the high potential portion is facilitated.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
In the second and third embodiments of the present invention, the power of electrons ejected from the plasma is used for heating the rectangular tube-shaped conductor 16. However, there are times when it is desired to change the temperature of the rectangular tubular conductor 16 during operation of the ion source.

  FIG. 4 shows an embodiment for such a purpose. A cooling pipe 14 and a heater 15 are provided around a rectangular tube-shaped conductor 16 as shown. By using the cooling pipe 14 and the heater 15 together, the temperature of the rectangular tube-shaped conductor 16 can be arbitrarily set regardless of the electron power.

Sectional drawing which shows the 1st Embodiment of this invention. Sectional drawing which shows the 2nd Embodiment of this invention. Sectional drawing which shows the 3rd Embodiment of this invention. Sectional drawing which shows the 4th Embodiment of this invention. The perspective view which shows the conventional microwave plasma generator. Sectional drawing which shows the conventional microwave plasma generator.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Discharge container, 3 ... Vacuum window, 4 ... Waveguide, 5 ... Permanent magnet, 8 ... Extraction electrode, 9 ... Insulating material, 10 ... Acceleration power supply, 11, 12 ... Bias power supply, 13 ... Extraction hole, 14 ... Cooling tube, 15 ... heater, 16 ... rectangular tube conductor, 17, 18 ... support, 20 ... microwave generator, MW ... microwave, IB ... ion beam.

Claims (7)

  A discharge vessel filled with a gas to be discharged and in which a plasma is formed, and a waveguide capable of setting a temperature relatively higher than the temperature of the discharge vessel while introducing a microwave into the discharge vessel; A microwave plasma generating apparatus comprising: a magnetic field forming means for forming a magnetic field inside the discharge vessel; and a gas introducing device for supplying a gas for increasing the output of a negative ion beam to the discharge vessel.   2. The microwave plasma generator according to claim 1, further comprising heating means for heating the waveguide.   The microwave plasma generator according to claim 2, wherein the discharge vessel and the waveguide can be set to different potentials.   A discharge vessel filled with a gas to be discharged and a plasma is formed inside the pressure-reduced interior, and a microwave was introduced into the discharge vessel, and a thin plate-like electric conductor plate was installed in the interior away from the inner wall. A microwave plasma comprising: a waveguide; a magnetic field forming means for forming a magnetic field inside the discharge vessel; and a gas introducer for supplying a gas for increasing the output of a negative ion beam to the discharge vessel. Generator.   The microwave according to claim 4, wherein the discharge vessel and the waveguide can be set to different potentials, and the waveguide and the thin electric conductor plate can be set to the same potential. Plasma generator.   5. The discharge vessel and the waveguide can be set to the same potential, and the waveguide and the thin electric conductor plate can be set to different potentials. Microwave plasma generator. 5. The microwave plasma generator according to claim 4, further comprising heating means for heating the thin plate-like electric conductor plate.

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