JP2007258093A - Microwave plasma generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a larger area and the unformization, suppress the density jump involved in the increased microwave power and achieve the thermal stability of plasma discharge. <P>SOLUTION: A microwave plasma generator is equipped with a microwave source to generate excited microwaves, a plasma gas source, a vacuum vessel to generate plasma whose gas is supplied from the plasma gas source, a waveguide to introduce microwaves for excitement to the vessel, and a cylindrical cavity resonator 1 to form a cavity for resonance composed of a first conductor plate 4 installed on the waveguide and a second conductor plate 3 arranged opposite to the first conductor plate 4 and emitting microwaves into the vacuum vessel. A plurality of openings 5 are provided in the second conductor plate 3, including the center part thereof, of the cylindrical cavity resonator 1, and a quartz plate 2 is disposed in the each opening 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a microwave including a microwave source for generating excitation microwaves, a plasma gas source, a vacuum vessel for generating plasma to which gas is supplied from the plasma gas source, and a microwave launcher having a cavity resonator structure. The present invention relates to a wave plasma generator and is intended to generate high-density plasma uniformly over a large area. Such microwave plasma generators have a wide range of application fields such as semiconductor process fields, giant process fields such as liquid crystal panels, surface treatment processes in paper manufacturing, and surface function treatments in the textile industry. .

The demand for large-area plasma devices is required in liquid crystal panels and semiconductor processes, but problems remain such as the low density of parallel plate plasmas using high frequencies currently used. Plasma devices using microwaves have some advantages for the process, such as high density and low electron temperature, but on the other hand, as the area increases, the quartz plate or alumina plate used as the vacuum window becomes thicker. Cost and maintenance problems remain, such as the need for a large-area window plate. Further, in surface wave plasma, density jumps accompanying a decrease in mode jumps are a problem of operability.
In large-area plasma processes, plasma devices using parallel plate structure high-frequency (RF, 13.56 MHz) are used. However, the plasma density is low, and the electron temperature is high, so the dissociation is promoted excessively. There are many points that should be improved as processing plasma. For this reason, attempts have been made to generate large-area plasma, but it is still under development. For example, in the development of a plasma generator using microwaves, the size of a quartz plate necessary for a vacuum seal generally increases as the area increases.
In microwave-excited plasma, it has been pointed out that a density jump occurs in which the density jumps discontinuously as the microwave power increases.

JP 2004-200113 A A. Ogino et al, Jpn. J. Appl. Phys. Vol44 (2005) L352

FIG. 11 shows a conventional plasma generating apparatus, in which a microwave source for generating excitation microwaves is driven, and excitation microwaves are introduced into a vacuum vessel 21 for plasma generation through a coaxial waveguide 23. . Further, plasma gas is supplied from a plasma gas source (not shown). The parallel plate launcher 22 includes a first conductor plate 22, a quartz plate 26, and a second conductor plate 27 attached to the outer conductor 24 of the coaxial waveguide 23. The coaxial waveguide center conductor 25 passes through the hole 28 of the quartz plate 26.
The quartz plate 26 disposed between the first conductor plate 22 and the second conductor plate 27 constitutes a parallel plate launcher 22 that forms a resonant cavity.

Under such circumstances, the density jump with the increase in microwave power is suppressed, the area is increased and the area is made uniform, the thermal stability of the plasma discharge is increased, and the surface area wave and the volume volume wave plasma are increased. Is to try to generate.
In other words, by dividing the vacuum window that is required in accordance with the increase in the area of the plasma device and reducing the area, the maintenance of the device becomes easier in terms of cost and equipment. It is possible to improve the efficiency of plasma generation by disposing it at a location where the electric field strength is high.

  In the present invention, that is, by dividing the vacuum window that is required in accordance with the increase in the area of the plasma apparatus and reducing the area, the maintenance of the apparatus is facilitated in terms of cost and the installation of the quartz window with a further reduced area. By arranging the position at a place where the electric field strength in the resonance mode is strong, it is possible to improve the efficiency of plasma generation.

  Constructed as in the present invention, the introduction of a microwave launcher can realize a plasma with a plasma discharge region of 50 cm in diameter, and can generate a plasma having a plasma density characteristic that increases linearly as the microwave power increases. it can. There is an advantage that the vacuum window can be made small regardless of the diameter of the apparatus, and the cost performance and apparatus maintenance can be greatly improved.

Examples Hereinafter, embodiments of a microwave plasma generating apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 shows an overall schematic diagram of a large-diameter microwave plasma apparatus according to the present invention.
In FIG. 1, 7 is a microwave oscillator, 8 is an isolator, and 9 is an EH tuner. The microwave plasma generator is made of cylindrical stainless steel having an inner diameter of 550 (1). Using a magnetron oscillator with a maximum output of 3 kW, a microwave is introduced into the vacuum vessel using the rectangular waveguide 14. Microwaves radiated through the slot antenna 15 cut on the lower surface of the waveguide 14 are distributed as resonance modes in the cylindrical resonator 1 attached to the lower portion of the slot antenna 15. In a cylindrical resonator with an inner diameter of 550 mm and a depth of 40 mm, the TM330 mode satisfies the resonance condition when the inside is air and the microwave frequency is 2.45 GHz. For this reason, in this plasma generator, the quartz plate 2 is used as a vacuum window on the lower surface of the portion where the electric field strength is strong, and one piece is arranged at the center and six pieces around it. Reference numeral 10 denotes plasma, and reference numeral 11 denotes a stage, which includes a stage movable unit 13. Reference numeral 12 denotes an air cooling fan, and a turbo molecular pump 16 is provided in the vacuum vessel via a gate valve 17.

FIG. 2 is a cross-sectional view and a top view of a cylindrical cavity resonator of the microwave plasma generator according to the present invention.
In FIG. 2, a microwave source for generating excitation microwaves is driven, and excitation microwaves are introduced into a vacuum vessel for plasma generation through a waveguide, and plasma gas is supplied from a plasma gas source (not shown). It is configured as follows. The resonator 1 is placed on the body 6, and the quartz plate 2 is mounted and held on the conductor plate 3. The quartz plate 2 is airtightly held and fixed to the conductor plate 3 by an O-ring.

  In the resonator part of FIG. 2, the quartz plate 2 has a diameter of 140 mm and a thickness of 13 mm. When the device diameter is further increased, the arrangement and the number of the opening holes 5 are set by calculating the resonator mode corresponding to the size of the diameter.

When the device is enlarged, the quartz plate is arranged in accordance with the electromagnetic field distribution in the resonance mode determined by the device size (diameter). The diameter should be determined to satisfy the number of modes. For example, since in the case of a device with a diameter of 50cm it is to just TM ₃₃ mode (first 3 azimuthal mode number m = 3, 3 number of radial mode after n = 3), azimuthally 3 × 2 = 6 quartz, which is twice as much as m, is arranged at the center.

In a resonator with a diameter of 500 mm, one quartz plate with a diameter of 140 mm and a thickness of 13 mm is installed in the center and six in the periphery, so that microwaves can pass through the quartz plate from the location where the electric field of TM ₃₃₀ mode is strong. It was introduced into a vacuum vessel and a uniform plasma was generated.

  FIG. 10 shows an example of the arrangement of dielectric plates provided on the conductor plate 3 in another embodiment of the present invention.

  A quartz plate is installed in a place with a strong electromagnetic field intensity distribution using a cavity resonator, which enables efficient microwave introduction, and because the area of the quartz plate is small, a cup with the generated plasma is available. The ring can be held weak. For this reason, there exists an advantage which can suppress the mode jump at the time of the increase in microwave power.

  FIG. 3 shows the result of radial distribution of ion saturation current (plasma electron density) measured using a Langmuir probe. Here, the ion saturation current is substantially proportional to the plasma electron density when the electron temperature is constant, and FIG. 3 shows an approximate spatial distribution of the electron density. The probe is located 35cm downstream from the top plate on which the quartz plate is installed. The plasma was generated with a microwave power of 1 kW, an Ar gas flow rate of 200 sccm, oxygen 25 sccm, and nitrogen 100 sccm mixed gas at a pressure of 30 mTorr. The plasma density distribution has a peak at the center, but the full width at half maximum is about 50 cm in diameter.

  FIG. 4 shows changes in microwave power and ion saturation current (plasma electron density) when the microwave incident power is changed. The position of the probe is r = 0 cm. As can be seen from FIG. 4, the plasma density changes linearly with the increase of the microwave power, and no density jump as in the conventional surface wave plasma apparatus is observed (Non-Patent Document 2 I. Ghanashev, M Nagatsu, et al, Jpn. J. Appl. Phys. 36, (1997) 4704). In various plasma treatments, it is necessary to continuously change the plasma density with the incident power as shown in Fig. 4, and this result satisfies the condition.

I. Ghanashev, M. Nagatsu, et al, Jpn. J. Appl. Phys. 36, (1997) 4704.

  Next, as an application of the present plasma apparatus, an etching apparatus for a large area semiconductor process, a carbon nanomaterial production apparatus such as nanocrystalline diamond or carbon nanotube, a plasma source for various functional thin film production, and the like can be cited. In this case, so-called surface-wave plasma (SWP), which generates high-density plasma near the top of the device, is suitable, and surface-wave plasma is generated by increasing the microwave power and gas pressure used. can do. On the other hand, in the case of generating plasma inside a vessel away from the top plate of the vacuum vessel, so-called volume-wave plasma (VWP) is used. For example, plasma sterilization of resin-packed medical equipment or internal sterilization of PET bottle containers, confidential coating of inner walls, sterilization of fibers, etc. requires that plasma be generated inside the object, and volume wave plasma should be used. Can be achieved. Such internal processing is difficult with surface wave plasma using down-streaming.

  FIG. 5 shows the relationship between the discharge transition boundary of the surface wave plasma (SWP) and the volume wave plasma (VWP), the gas pressure, and the incident microwave power when argon gas is used.

FIG. 6 shows the discharge transition boundary between surface wave plasma (SWP) and volume wave plasma (VWP), gas pressure, and incident microwave power when oxygen, nitrogen, and oxygen-nitrogen mixed gas (simulating air) are used. Showing the relationship.
Plot the boundary of discharge transition of surface wave plasma (SWP) and volume wave plasma (VWP) when using oxygen, nitrogen or nitrogen-oxygen mixed gas (ratio that simulates air) against pressure and incident power Yes.

FIG. 7 shows a photograph and a conceptual diagram when a biomarker (biological indicator) used for verification of medical sterilization using volume wave plasma is placed on a stage in a container. The bioindicator used was a glassine wrapping paper in which 10 ⁴ , 10 ⁵ , 10 ⁶ , 10 ⁷ , and 10 ⁸ Bacillus Atrophaeus bacteria were embedded in a strip made of cellulose fiber. What was sealed with was used.

  FIG. 8 shows the relationship between the plasma irradiation time and the temperature on the stage (CW microwave 2 kW, pressure 50 mTorr, z = 40 cm), and the measurement result of the petri dish temperature on the stage in continuous wave (CW) microwave discharge. Is shown. Here, the measurement result of the thermo label at the position where the microwave power is 2 kW and the downstream z = 40 cm is shown. As a result, the temperature of the petri dish surface placed on the stage increases monotonously with the plasma discharge time. For this reason, when the plastic wrapping paper is irradiated with plasma, it is necessary to set the discharge time to about 5 minutes and take off time for temperature reduction.

Next, the result of using this apparatus for plasma sterilization is shown. FIG. 9 shows the results of a sterilization experiment using CW microwave plasma.
○ indicates that it was killed, and ● indicates that it was not killed.
This shows whether biomarkers can be sterilized when irradiated with oxygen plasma using continuous wave microwaves. The biomarker is used as it is without opening the packaging of glassine paper. Experimental results show that all samples from 10 ⁴ to 10 ⁸ have been killed. The temperature on the petri dish is about 95 degrees at maximum, but it is lower than the temperature at which bacteria are used for dry heat sterilization, which is about 160 degrees. Bacteria are said to continue to survive even at temperatures of about 100 degrees.
Furthermore, in this experiment, as a result of performing an experiment in a gas simulating air in which oxygen and nitrogen are mixed, good sterilization characteristics are obtained, and a microwave discharge plasma sterilizer using air can be realized.

In the embodiment of the sterilizer, the microwave power is 2 to 2.5 kW with a CW output, the instantaneous power is a maximum of 4 kW, and the average power is 2 kW in the pulse oscillation operation. The gas pressure was used at 4 Pa to 30 Pa.
When used for etching, the power was the same as described above, and the pressure was used from 2 Pa to 13 Pa. When used for CVD, the pressure was used from 5 Pa to 150 Pa.

  The net on-time of the plasma is 20 minutes for sterilizing the inside of the wrapping paper and 5 minutes for sterilizing the unwrapped surface. When there is a thermal problem, the on time is set to 30 seconds to 5 minutes and the off time is set to the same level. Plasma discharge is performed by placing an object to be sterilized on the stage of the apparatus.

As for the number of quartz plates shown in FIG. 2, the conductor plate 3 is provided with seven opening holes including the central portion.
The quartz plate 2 has a diameter of 140 mm and a thickness of 13 mm. The inner diameter of the body 6 is 550 mm.

  In the present invention, by adopting the above-described configuration, a uniform distribution can be obtained within a predetermined incident power range. Moreover, it increased almost monotonously with increasing incident power, and no density jump was observed.

1 shows an overall schematic view of a large area microwave plasma apparatus according to the present invention. It is sectional drawing of the resonator part of the microwave plasma generator which concerns on this invention. The radial distribution of ion saturation current (plasma electron density) is shown. The relationship between microwave power and ion saturation current (plasma electron density) is shown. The relationship between the discharge transition boundary of surface wave plasma (SWP) and volume wave plasma (VWP), gas pressure, and incident microwave power when argon gas is used is shown. The relationship between the discharge transition boundary of the surface wave plasma (SWP) and the volume wave plasma (VWP), gas pressure, and incident microwave power when oxygen, nitrogen, and oxygen-nitrogen mixed gas (simulating air) is used is shown. A photograph of a biomarker placed on the stage is shown. The relationship between the plasma irradiation time and the temperature on the stage (CW microwave 2 kW, pressure 50 mTorr, z = 40 cm) is shown. The results of sterilization using CW microwave plasma (circle indicates death; ● indicates no death). The example of arrangement | positioning of the disk shaped dielectric material plate which concerns on this invention is shown. Sectional drawing of the principal part of the conventional microwave plasma generator is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Resonator 2 Quartz plate 3 2nd conductor 4 1st conductor 5 Opening hole 6 Trunk part 7 Microwave transmitter 8 Isolator 9 EH tuner 10 Plasma 11 Stage 12 Air-cooling fan 13 Stage movable part 14 Waveguide 15 Slot antenna 16 Turbo Molecular pump 17 Gate valve

Claims (15)

A microwave source for generating excitation microwaves;
A plasma gas source;
A vacuum vessel for plasma generation to which gas is supplied from the plasma gas source;
A waveguide for introducing a microwave for excitation into the container;
A first conductor plate mounted on the waveguide; and a second conductor plate disposed opposite to the first conductor plate, mounted with a dielectric and emitting microwaves into the vacuum vessel. A microwave plasma generator comprising a cavity resonator forming a resonance cavity, wherein the second conductor plate of the cavity resonator is provided with a plurality of opening holes including a central portion of the conductor plate, and the opening A microwave plasma generator characterized by mounting a dielectric plate in a hole. A microwave source for generating excitation microwaves;
A plasma gas source;
A vacuum vessel for plasma generation to which gas is supplied from the plasma gas source;
A waveguide for introducing a microwave for excitation into the container;
A first conductor plate mounted on the waveguide, and a second disk-shaped conductor plate disposed opposite to the first conductor plate, mounted with a dielectric, and emitting microwaves into the vacuum vessel. A microwave plasma generator comprising a cylindrical cavity resonator that forms a resonant cavity, and a plurality of aperture holes including a central portion of the conductor plate in the second disk-shaped conductor plate of the cylindrical cavity resonator And a disk-shaped dielectric plate is mounted in the opening hole. A microwave source for generating excitation microwaves;
A plasma gas source;
A vacuum vessel for plasma generation to which gas is supplied from the plasma gas source;
A rectangular waveguide for introducing a microwave for excitation into the container;
A slot antenna for introducing microwaves from the rectangular waveguide;
A first conductor plate mounted on the rectangular waveguide; a second disk-shaped conductor plate disposed opposite to the first conductor plate; mounted with a dielectric; and emitting microwaves into the vacuum vessel; A microwave plasma generator comprising a cylindrical cavity resonator forming a resonant cavity comprising: a plurality of openings including a central portion of the conductor plate in a second disk-shaped conductor plate of the cylindrical cavity resonator A microwave plasma generator characterized in that a hole is provided and a disk-shaped dielectric plate is mounted in the opening hole.   The microwave plasma generator according to any one of claims 1 to 3, wherein the dielectric plate is a quartz plate. The microwave plasma generator according to any one of claims 1 to 4, wherein the thickness of the quartz plate is 10 mm. The microwave plasma generator according to any one of claims 1 to 5, wherein an opening hole is provided at a central portion of the second conductor plate and a plurality of opening holes are provided around the opening hole. The microwave plasma generator according to any one of claims 1 to 6, wherein an opening hole is provided at a central portion of the second conductor plate and six opening holes are provided around the opening hole. The microwave plasma generator according to any one of claims 1 to 6, wherein an opening hole is provided in a central portion of the second conductor plate and ten opening holes are provided around the opening hole. . The microwave plasma generator according to any one of claims 1 to 8, wherein the plurality of opening holes are provided symmetrically about an axis. The microwave plasma generator according to any one of claims 1 to 9, wherein the opening hole has a diameter of 100 mm to 150 mm. The height of the cylindrical cavity is selected to be TMmnp mode (where m is the number of modes in the azimuth direction, n is the number of radial modes, and p is the number of axial modes). The microwave plasma generator according to any one of claims 1 to 10, wherein the microwave plasma generator is provided.   The microwave is converted from the waveguide, the microwave is supplied to the cavity resonator disposed inside the vacuum vessel, and high density plasma is generated uniformly in a large area. The microwave plasma generator of any one of these.   The microwave plasma generator according to any one of claims 1 to 12, wherein a uniform surface wave excited microwave plasma is generated below the cavity resonator.   The microwave plasma generation apparatus according to any one of claims 1 to 12, wherein a volume wave excitation microwave plasma that spreads across the entire lower portion of the cavity resonator is generated.   The microwave plasma generator according to claim 1, wherein the microwave source is a pulse discharge microwave.

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