JPH01309300A - Microwave plasma generator - Google Patents

Abstract

PURPOSE:To make it possible to generate a large dia. plasma being stable in high temp. and density efficiently by combining plasma and surface wave by a gap at a cylindrical coaxial wave guide, in microwave power by supplying large power stably without using a coaxial cable. CONSTITUTION:A microwave transmission circuit is mode-converted from an angular wave guide 40 and the like to a cylindrical coaxial wave guide 50, while a metal end plate 70, having an inner dia. opening 72 of which dia. is substantially the same as that of a cylindrical cavity 53 provided at an inner conduction body 51 around which a cylindrical outer conduction body 52 is arranged being elongated than the body 51, is set at a distance position (d) (gap) on the body spaced from an end of the body 51. A discharge pipe 80 is disposed at least through the opening 72 from the inside of cavity 53 of the body 51 and plasma is generated in the pipe 80 by use of microwave electric field generated at the gap. It is thus possible to feed large power with low loss and stability without using a coaxial cable in transmitting microwave power. Further, it is possible to generate stable large dia. plasma with high temp. and density.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to plastic equipment for etching, deposition, etc., and particularly to a plasma generating apparatus using microwave power suitable for these equipment.

[Conventional technology]

Regarding plasma generation devices using conventional microwave power, see (1) Review Scientific Instruments, 36.3 (1965), pp. 294 to 298 (Rev, Sci. Instrument, 36.3). (1965) 294-
298), (2) I.E.E. Transactions of Plasma Science. PS-3, 2 (1975) pp. 55-59 (I
E E E Trans, Plasma 5ci
ence. PS-3, 2 (1975) 55-59). (3) Review Scientific Instruments, 39.11 (1968) pp. 295-2
p. 97 (Rev, Sci, Instrum, 39.11 C1968) 295-297). (4) Review of Scientific Instruments, 41.10 (1970) pp. 1431-1433 (Rev, Sci. Instrum, 41,10 (1970) 1431
-1433), and (5) Japanese Journal of Applied Physics. Vol, 16. No. 11 (1977) No. 199
Pages 3 to 1998 (Jpn, J, Appl,
Phys. 16.11 (1977) 1993-1998).

[Problem to be solved by the invention]

The above-mentioned prior art documents (1) to (3) use coaxial cables to transmit microwave power, so they do not take into account the issue of increasing power, and they do not take into account issues such as stability at high power. There were problems with increasing the density of the plasma and increasing the diameter. On the other hand, the above-mentioned prior art documents (4) to (5) do not give sufficient consideration to aspects such as microwave utilization efficiency and radial distribution of plasma, and there are problems with plasma generation efficiency and its uniformity. there were. An object of the present invention is to provide a microwave plasma generator that solves the above problems and efficiently generates stable large-diameter plasma at high temperature and high density.

[Means to solve the problem]

The above purpose is to convert the mode of a microwave transmission circuit from, for example, a rectangular waveguide 40 to a circular coaxial waveguide 50, as shown in FIG. 52 is longer than the inner conductor 51 of the circular coaxial waveguide 50, and the metal end plate 70 has an open lower portion 2 with an inner diameter comparable to the inner diameter of the cylindrical cavity 53 provided in the inner conductor 51. The discharge tube 80 is attached to the outer conductor 52 at a distance d from the tip of the inner conductor 51 (gap portion).
is installed through the open lower 2 from at least inside the cylindrical cavity 53 of the inner conductor 51, and the discharge tube 80 is installed using the microwave electric field (surface wave) generated in the gap portion.
This is achieved by generating plasma within the

[Effect 1] In other words, for example, to transmit microwave power from a microwave oscillator to a circular coaxial waveguide via a rectangular waveguide, high power is stably supplied to the plasma with low loss without using a coaxial cable. can. Furthermore, when the metal end plate 70 is provided, an electric field consisting of a Z-axis direction component Ez and a radial direction component Er as shown in FIG. The space formed between the metal end plate 70 (gap portion d
), the inside of the discharge tube 80 installed from the inside of the inner conductor 51 through the open lower 2 is filled with high temperature, high density, stable large diameter plasma, and various gases from low pressure to atmospheric pressure. can be generated efficiently. Example 1 An example of the present invention will be described below with reference to FIGS. 1 to 5. FIG. 1(a) schematically shows the main part configuration of the three-dimensional circuit of the microwave plasma generator according to the present invention, and FIG. 1(b) schematically shows the intensity distribution of the microwave electric field. Microwave power is transmitted from the rectangular waveguide 4o to at least the inner conductor 51 and the cylindrical outer conductor 5.
2, and a gap d provided at the tip of the inner conductor 51 causes the inner conductor 51 to
#! made of quartz etc. provided in 53 parts of the cylindrical cavity etc. It is absorbed by the plasma as a surface wave through the edge discharge tube 80. Here, the gap d is the metal end plate 7 provided between the tip of the inner conductor 51 and the cylindrical outer conductor 52.
0 and is configured to be variable using screws, spacers, etc. The metal end plate 70 is provided with an open lower portion 2 having an inner diameter comparable to that of the cylindrical cavity 53 of the inner conductor 51, and the metal choke 71 can be inserted as shown in FIG. It is recommended that the microwave be installed in the microwave to reduce microwave loss. Further, it is preferable that at least one of the inner and outer conductors 51 and 52 is forcedly air-cooled or water-cooled. Here, the diameters of the inner and outer conductors 51 and 52 and the discharge tube 8o can be arbitrarily set depending on the purpose of use. Furthermore, in order to efficiently absorb microwave power into the plasma, the characteristic impedance of a coaxial circuit is usually 50Ω, so the dimensions of the eight surfaces in the rectangular waveguide of the coaxial waveguide converter 50 are set from the standard size. small (thin)
However, it is preferable to reduce the ratio of the H-plane to the dimension to reduce the characteristic impedance of the waveguide, and to provide a 1/4 wavelength transformer on the input side of the waveguide to match the characteristic impedance of the coaxial section. Further, it is preferable to make the shape of the inner conductor 51 into a doorknob shape as shown in FIG. 5, or to make the short circuit part a regular size and provide a plunger 60 (variable type) so that matching can be achieved. Further, a magnetic field generator 90 (consisting of a coil, a permanent magnet, etc.) is provided outside the outer conductor 52, and a divergent type (beech type)
If plasma is generated by superimposing magnetic fields such as , multicusp type or mirror type under electron cyclotron resonance conditions or conditions around it, it is easier to obtain high temperature, high density (above the cutoff density) plasma even at low pressure. (Of course, it is possible to do so without applying any voltage.) On the other hand, plasma gases include H2, He, 021N21Ar,
Select Xe, CH4, SiH, NH, CF4゜SiF4 according to the purpose, 10-'Torr~760T
Operate within the range of orr. The sample gas may be introduced into the discharge tube 80, for example, from the tube end as shown in FIG. 1(A), but this is not particularly limited and may be determined depending on the purpose. Figure 1 (b) shows the radial component Er of the electric field strength distribution in the space of the gap 6 and the Z axis (microwave propagation direction).
directional component Ez. The characteristics of this plasma device are that the electric field is a surface wave in which Er and component Ez acid components coexist, and the components on the Z axis are both weak, while the outside becomes stronger, and these desires and the diffusion phenomenon of sample gas particles. phase, which acts to obtain a radially uniform plasma at low pressures. Also, at high pressures, as shown in Figures 4 and 5,
Donut-shaped plasma is obtained. Select the pressure depending on the purpose. Figure 2 shows another second embodiment of the present invention in which the microwave plasma generator shown in Figure 1 (a) is applied to a plasma reaction apparatus for etching, deposition, and the creation of new materials. A block diagram is shown. Here, 10 is a high voltage power supply (DC or pulse), 20 is a micro oscillator (magnetron or gyrotron, 1 to 100 GHz, 10
~5.0OOOW), 30 is an isolator (or uniline), 40 is a three-dimensional circuit (directional coupler, wattmeter, E-
H tuner etc.), 50 is a coaxial waveguide converter, 5
1 is an inner conductor, 52 is a cylindrical outer 24 body, 60 is a plunger, 70 is a metal end plate, 80 is a discharge tube, 90 is a magnetic field generator (optional), 100 is an exhaust bag ffi, 1
10 is a plasma gas (Ar, He, 02, etc.) introducer;
1.20 is the reaction gas (CH,, NH,, CF,, SiF
. A counterfeit analyzer, 180 a spectrometer, and 190 a microcomputer for automatically controlling (optimizing) each device including data 1':i processing. In this embodiment, the above-described gap portion d is configured to be variable by adjusting the metal end plate 70 using screws, spacers, or the like. Further, the diameter of the inner conductor 51 becomes thicker at the coaxial converter 50 portion (doorknob shape). With this configuration, 1. For example, when creating an oxide high-temperature superconducting thin film, oxygen (O2), which is a plasma gas, can be ionized at low pressure (10-'Torr or less), and the low-energy oxygen radicals generated at this time can be ionized. The metal atoms, for example, Ba, Y, C:u, introduced as reaction particles react physically and chemically with the metal atoms introduced as reaction particles, and a high-quality film is formed on the substrate on the sample stage 140 at a low temperature while being optimized by the microcomputer 190. Moreover, it can be produced in a short time. FIG. 3 shows another third embodiment of the invention. This embodiment shows an apparatus that extracts ions and neutral particles from plasma and performs surface modification and treatment of materials. Here, 50 is a circular coaxial waveguide, 51 is an inner conductor, 52 is a cylindrical outer conductor, 60 is a plunger, 70 is a metal end plate (various modifications are possible), 71 is a metal choke, 80 is a discharge tube, 90 is a magnetic field generator (optional), 1
00 is an exhaust device, 110 is an introduction device for sample gas, carrier gas, etc., 120 is an introduction device for sample gas, reaction gas, etc.
130 is a reaction chamber, 140 is a sample stage, 150 is a temperature controller, 180 is a spectrometer, and 200 is an ion extractor. Note that the ion extractor 200 can also be configured as an electron or neutral particle (atom or radical) extractor. With this configuration, a large-diameter, uniform, and high-density sample gas or carrier gas plasma can be generated. Then, for example, using the ion extractor 200, a large-diameter, uniform, high-density ion beam is extracted from the plasma, and the surface treatment or surface modification of the substrate set on the sample stage 140 is performed in a short time and at low temperature. be able to. It is also possible to sputter a target with the ion beam and deposit target material onto the substrate. Furthermore, surface treatment etc. can be performed using the above-mentioned neutral particles. FIG. 4 shows the basic configuration of a fourth embodiment of the present invention applied to the analysis of trace elements in the biological field and the like. Here, 300 is a microwave generation system, which includes a microwave oscillator such as Magne 1 to Ron, a high voltage power supply, a microwave power meter, an E-H (or stub) tuner, and the like. 400 is a microwave plasma generation system. Based on FIG. 1(a), it consists of a circular coaxial waveguide, an inner conductor, a metal end plate, a discharge tube, etc. as shown in FIG. Reference numeral 500 denotes a sample gas introduction system, which includes a sample, a carrier gas, a nebulizer, and the like. 600 is a measurement/analysis system, which includes a spectrometer, a mass spectrometer, and the like. 70
0 is a control system consisting of a microcomputer, etc. 70
0 is a control system consisting of a microcomputer, etc., and performs data organization and optimal control of this device. The operating pressure in this embodiment is basically atmospheric pressure since a large amount of power can be stably supplied, and the diameter of the discharge tube etc. may be smaller than in the second and third embodiments. FIG. 5 shows details of an embodiment of the plasma generation system 400 in the embodiment shown in FIG. 4 of the present invention. Here, 50 is a flat 4-wave tube made of copper or aluminum (inner dimensions: 8.6DIIllX 109.2nu
51 is an inner conductor made of copper or the like (the coaxial converting part is shaped like a truncated cone (for example, the bottom diameter is 40 mm, the top diameter is 1 mm) as shown in the figure.
5 mm, height 30 mm), and the upper part of the shaft has a cylindrical cavity 53 (diameter, e.g. 4 to 1 mm) for passing the discharge tube 80.
2mff1) is provided. Reference numeral 52 denotes a cylindrical outer conductor made of copper or the like, and a disc-shaped end plate 7 made of copper or the like.
0 is installation. The end plate 70 is provided with an open lower portion 2 having an inner diameter approximately equal to the inner diameter of the cylindrical cavity 53 provided in the inner conductor 51, and the thickness of the periphery thereof is concentrically thinner than that of the outer periphery. Yes (thickness ≧0.11I
I11). Furthermore, a gap d (0.5 to 20 mm) between the tip of the inner conductor 51 and the end plate 70
) is configured to be adjustable. Reference numeral 80 denotes a discharge tube (inner diameter: e.g. 4 to 10 nm) made of quartz or the like, one end of which is open, and the other end so that plasma gas 501 (He, N, Ar, etc.) can be supplied from the radial direction. A branch pipe 81 is provided. Further, an inner tube 82 made of quartz or the like is provided coaxially from the other end of the discharge tube 80, and a nebulizer (
A carrier gas (same type as the plasma gas 501) or the like 500 is introduced together with the sample through a gas (not shown). 5
Reference numeral 10 denotes a cooling system for cooling the discharge tube 80, the inner conductor 51, etc., and a coolant 502 (for example, air or water may be used. In this case, a water outlet is provided, and the inner conductor 51 and a configuration configured to cool the discharge tube 80). With this configuration, the discharge tube 8
0, the inner conductor 51, and the metal end plate 70 can be efficiently cooled. 9+00 indicates diffused plasma, and '7)01 indicates donut-shaped high temperature plasma. Note that the shape and size of the discharge tube 8o and the inner conductor 51 are not limited. ,≦2K
W) is the inner conductor 51 and the metal end plate 7.
The electric field is concentrated in the 8th part of the gap 0, and an electric field distribution as shown in FIG. 1(b) is obtained. Therefore, the plasma gas 501 introduced from the branch pipe 81 is ionized, and a doughnut-shaped high-temperature plasma %01 is generated inside the discharge tube 8o. When the sample 500 to be analyzed is introduced from the inner tube 82 into the center of the doughnut-shaped high temperature plasma-01, the sample efficiently undergoes atomization → excitation → ionization without diffusing to the periphery. . When the light generated at this time is introduced into the spectrometer 600 and the ions are introduced into the mass spectrometer 600 via an ion sampling interface system (not shown), high frequency (for example, 27 MH
z) Quantitative analysis can be performed with higher sensitivity than when using induced plasma. Note that a solution can also be directly analyzed as a sample, and there are no particular restrictions on the sample, including organic substances and halogens. In addition, the plasma gas also includes He, N2.
Ar, etc. can be used, and there are no particular limitations. In addition, the microwave plasma generation device of the present invention can be applied to any device using plasma. Further, plasma can also be generated in a pulsed manner. [Effects of the Invention] According to the present invention, since microwave power is coupled between the plasma and the surface wave in the gap d provided in the circular coaxial waveguide, a large power can be stably supplied without using a coaxial cable. Moreover, since it can be efficiently absorbed into plasma, high-temperature, high-density plasma can be generated for various gases depending on the purpose, over a wide range from low pressure (about 10'' Torr) to high pressure (atmospheric pressure). effective. Furthermore, by superimposing an external magnetic field, high-density plasma with a cutoff density or higher can be generated for various gases. Therefore, the plasma of the present invention has the advantage that it can be applied to etching, deposition, creation of new materials, surface processing and modification, etc., and can also be widely used as a light emission source, ion source, etc. in elemental analysis.

[Brief explanation of the drawing]

Figure 1 (A) shows the main configuration of the microwave plasma generator according to the present invention, Figure 1 (B) shows the electric field strength distribution in the gap, and Figure 2 shows the application of the present invention to a plasma reactor. Fig. 3 is a block diagram of an embodiment showing an ion source of the present invention and its application to a process;
FIG. 4 is a block diagram of an embodiment showing the application of the present invention to an analytical instrument, and FIG. 5 is a block diagram showing details of the microwave plasma generation system 400 in FIG. 4. 10... High voltage power supply, 20... Microwave oscillator, 5
o... Circular coaxial waveguide, 51... Cylindrical inner conductor, 5
2... Cylindrical outer conductor, 70... Metal end plate, 71... Metal choke, 80... Discharge tube, 9
0... Magnetic field generator, 100... Exhaust device, 110.
...Gas introduction device, 120...Reaction gas introduction device. 130...Reaction chamber, 140...Sample stage, 190...
・Microcomputer, 200...Ion extractor,
300...Microwave generation system, 400...Microwave plasma generation system, 500...Gas introduction system, 600...
...Measurement and analysis system, '7) O#...Doughnut-shaped plasma. Q force ゛ insertion (q −he hehe (~raNki to % Chikuchi (heber l + ζ \ ~ ?ρρ, 11%: My 70; anti-generation tree ρρ: My 7ri 2 艷fu 0 Last Z season (1st doubt fρρ
: Kotobeo dried 1 ＼ soup sheep Western dish not included

Claims (1)

[Claims] 1. A circular coaxial waveguide consisting of a cylindrical outer conductor and an inner conductor having a cylindrical cavity, for introducing microwave power from one end, and the other end of the circular coaxial waveguide. a metal end plate provided at the tip of the cylindrical outer conductor and having an opening with an inner diameter comparable to the inner diameter of the cylindrical cavity of the inner conductor; and the inner conductor is shorter than the cylindrical outer conductor. The gap formed between the tip of the inner conductor and the metal end plate, and the cylindrical shape of the inner conductor in order to form plasma of the substance to be turned into plasma by the microwave electric field generated in the gap. A microwave plasma generation device comprising a discharge tube provided from inside a cavity through the gap portion and the opening. 2. The microwave plasma generator according to item 1, in which the gap length of the gap portion can be varied. 3. The microwave plasma generator according to item 1 or 2, wherein the discharge tube includes an inlet for introducing the substance to be turned into plasma and an opening for utilizing the plasma. 4. The microwave plasma generation device according to any one of items 1 to 3, including a magnetic field applying means provided around the gap portion to superimpose an external magnetic field on the microwave electric field.