JP5176051B2 - Plasma generator and diamond generation method - Google Patents

Description

The present invention relates to a plasma generating apparatus and a plasma generating method for generating high energy plasma.

Patent Document 1 describes a plasma processing apparatus that generates plasma using argon gas. In this plasma processing apparatus, a dielectric layer is provided on the surface of a metal substrate having a plurality of through-holes, and a plurality of the dielectric layers are overlapped, and a counter electrode is formed by arranging them in parallel to the first electrode portion. The first electrode supply means and the second gas supply means for supplying an inert gas having a pressure close to the atmospheric pressure to the through hole and the gap, and the surface treatment gas or the reactive gas in the gap. A third gas supply means for supplying, a first power source for generating a plasma in the through hole by applying a voltage between the metal substrates, and applying a voltage between the first electrode part and the second electrode part. And a second power source for generating plasma in the gap.

In Patent Literature 2 , (1) a polymer base material is subjected to a CVD plasma treatment using a methane-argon mixed gas to form a carbon interlayer film, and (2) a carbon interlayer film is formed. A method is described that includes a step of subjecting a polymer substrate to a CVD plasma treatment using a hydrocarbon-containing gas to form a diamond-like carbon film.

In a normal plasma generation method, plasma is generated by reducing the pressure using a vacuum vessel. Since it is difficult to create and use a large vacuum container, the size of the substrate that can be used is limited when a film is formed on the substrate.

Patent Document 1 describes that plasma treatment can be performed under atmospheric pressure. However, in the plasma processing apparatus and the plasma processing method described in Patent Document 1, it is necessary to repeat plasma ignition by applying a DC voltage between the electrodes. Further, since it is a direct current glow discharge, the energy of plasma is low and diamond cannot be synthesized.

In the plasma method described in Patent Document 2, an alternating current having a relatively low frequency of 13 MHz is used. As described in paragraph 0011 of Patent Document 2, it is understood that the gas pressure is maintained at about 10 to 150 Pa (more preferably about 13 to 135 Pa), and the operation is performed at a considerably low pressure. Therefore, it is difficult to use a large member. Moreover, the energy of the plasma is low, and it seems that diamond can not be generated even though a diamond-like carbon film can be formed.

An object of the present invention is to provide a plasma generation apparatus and a plasma generation method that can be carried out at a relatively high pressure. It is another object of the present invention to provide a plasma generation method capable of generating high energy plasma capable of generating diamond.

In order to solve the above problems, a plasma generator according to the present invention includes a reaction vessel, a first gas supply device that supplies argon gas to the reaction vessel, and a second gas supply device that supplies a gas containing hydrocarbons. And a third gas supply device for supplying hydrogen and a microwave introduction device for introducing a microwave having a frequency of 1 GHz or more into the reaction vessel, the microwave introduction device has an electrode that is a coaxial line, The electrode has an electrode body part and an insulator covering the periphery of the electrode body part, so that plasma is generated only at the electrode tip, and plasma is generated using only argon gas at a pressure of 800 to 1013 hPa. While maintaining, hydrocarbons and hydrogen are introduced into the plasma . The microwave introduction device has an annular cavity resonator surrounded by a metal wall, and the cavity resonator is preferably provided with a liquid metal introduction port.

The plasma generation method according to the present invention supplies a gas containing argon gas to a reaction vessel, introduces a microwave having a frequency of 1 GHz or more into the reaction vessel, generates plasma, and maintains the generated plasma in the reaction vessel. A gas containing a hydrocarbon is supplied.

Furthermore, in the method for producing diamond according to the present invention, a substrate is installed in a reaction vessel, argon gas is supplied to the reaction vessel, and the electrode is a coaxial line having an electrode main body covered with an insulator around the reaction vessel. Introducing microwaves of the above frequency, generating plasma only at the electrode tip using argon gas at a pressure of 800 to 1013 hPa, and supplying gas containing hydrocarbons and hydrogen to the reaction vessel while maintaining the generated plasma Then, diamond is generated on the substrate.

The plasma generation apparatus and the plasma generation method according to the present invention of the present invention have the effect that plasma can be generated and maintained at a pressure close to atmospheric pressure or under atmospheric pressure. Therefore, it can be implemented easily. Moreover, it is easy to enlarge the reaction vessel, and a film forming process can be performed on a large member. Further, since high-energy plasma is generated, diamond can be generated.

The best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing a plasma generator.

The plasma generator 1 has a reaction vessel 2. A gas inlet 3 for introducing gas into the reaction vessel 2 and a gas outlet 4 for discharging gas are provided. Moreover, the plasma generator 1 has two or more gas supply devices. In this example, in addition to the first gas supply device 5 for supplying argon gas and the second gas supply device 6 for supplying methane gas, which is a hydrocarbon, a third gas supply device for supplying hydrogen. 7 is provided. The gas supply devices 5, 6, and 7 include control valves 5a, 6a, and 7a, respectively, and are configured to switch between gas supply and cutoff. The first gas supply device 5, the second gas supply device 6, and the third gas supply device 7 are connected to a buffer tank 8, and each gas reacts via the gas inlet after entering the buffer tank 8. It is supplied to the container 2. A rotary pump 9 is connected to the gas outlet 4.

The plasma generator 1 further includes a microwave introduction device 10 that introduces a microwave having a frequency of 1 GHz or more into the reaction vessel 2. In this example, a microwave of 2.45 GHz is used. The microwave introduction device 10 includes an electrode 11 and a cavity resonator 12.

FIG. 2 is an exploded view showing the configuration of the electrode 11. The electrode body 13 is made of copper. In order to generate plasma only at the electrode tip, the periphery of the electrode body 13 is covered with a fluororesin 14 that is an insulator. The electrode 11 is heated when power is introduced. When the temperature of copper reaches 300 ° C. or higher, atomic hydrogen in a plasma state enters the copper, generates heat in the process of becoming hydrogen molecules, and damages the electrode body 13. Therefore, an aluminum cap 15 that does not react with the atomic hydrogen is put on the electrode body 13 so that the electrode main body 13 and the atomic hydrogen are not in direct contact with each other at the tip of the electrode. The electrode body 13 is hollow and has a cooling hole. Since the high-frequency current flows only on the metal surface due to the skin effect, there is no electromagnetic effect unless the shape of the electrode surface is changed.

In order to stably generate plasma at the electrode tip, the upper end position of the fluororesin 14 was lowered to a portion not affected by heat and the following was performed. The electrode 11 of this example is designed so that the fluororesin exists as an insulator to the tip so that there is no impedance change as a coaxial line. When impedance mismatch occurs in the coaxial line due to the change in the upper end position of the fluororesin 14, heat generation and wavelength change in that portion, and the maximum place of the electric field moves from the tip of the electrode 11, and plasma ignition at the tip can be performed. Disappear. Therefore, using the fact that the value of dielectric constant of quartz is larger than that of fluororesin, quartz tube 16 is inserted into the cut-out portion, the impedance in the space is matched with fluororesin 14, and fluororesin exists up to the tip. It was made to be in the same state as it is. This dimension is obtained from the characteristic impedance equation of the tri-dielectric coaxial cylindrical capacitor, and the inner diameter of the quartz tube 16 is 4.2 mm and the outer diameter is 6.2 mm. As a result, impedance matching can be achieved, and plasma can be stably generated at the tip of the electrode. Therefore, the outer diameter and inner diameter of the quartz tube 16 are determined so that the characteristic impedance of the three dielectric coaxial cylindrical capacitor is Z ₀ = 29.3Ω so that no impedance mismatch exists in the coaxial line.

A resonance circuit for supplying a high voltage to the electrode 11 will be described. FIG. 3 is a circuit diagram showing a resonance circuit for supplying a high voltage. Such a resonance circuit is constituted by a semi-coaxial cavity resonator having a low skin resistance. FIG. 4 is a schematic view showing a plasma generator including the semi-coaxial cavity resonator 12. The cavity resonator 12 has an annular cavity surrounded by a metal wall, and the center part is a capacitive part. The electrode 11 is drawn out from the capacitance part of the cavity resonator, and plasma is generated ahead of it. In order to efficiently supply microwave power to the plasma without reflection, it is necessary to match impedances. Since power is supplied to the resonator through a coaxial cable having a characteristic impedance of 50Ω, in FIG. 3, the impedance Zin on the cavity resonator 12 and reaction vessel 2 side is matched to 50 + 0j (Ω). However, the plasma impedance is unknown, and a circuit adjustment mechanism is provided for impedance matching with an arbitrary plasma impedance. Here, the inductance L and the division ratio k can be adjusted when plasma is generated.

FIG. 5 is an enlarged cross-sectional view showing details of the cavity resonator 12. The cavity resonator 12 is provided with a liquid metal inlet 17. Liquid metal such as mercury can be injected into the cavity resonator 12 from the liquid metal inlet 17, but here, gallium heated to 30 ° C. or higher to be in a liquid state because it is not toxic and highly safe. use. L is changed by changing the length of the coaxial part of the semi-coaxial cavity resonator. As shown in FIG. 5, the bottom surface of the cavity resonator is filled with liquid gallium (hatched portion). A part of the electric circuit is constituted by the surface of the liquid gallium, and L is changed by adjusting the height h of the surface.

Next, adjustment of the division ratio k will be described. FIG. 6 is a sectional view showing a mechanism for adjusting the division ratio k. The electric power supplied from the lower part of FIG. 6 is supplied to the wall inside the resonator by a copper plate 18 having a thickness of 100 μm. The wall is capacitively coupled through a ceramic pipe 19. The division ratio k can be changed by pulling the ceramic pipe 19 out of the resonator and moving it with the micrometer head 20.

In the plasma generator 1, a substrate attachment portion 21 is provided in the reaction vessel 2. A substrate such as silicon can be attached to the substrate attachment portion 21, and a film such as a diamond film can be formed on the surface thereof.

Next, examples of the present invention will be described. In this example, the present invention is applied to diamond production. As the plasma generator 1, the one shown in FIGS. 1 to 6 is used.

Silicon is used for the substrate to be used. Further, as a pretreatment, scratching is performed about 20 times with a diamond powder of about 6 μm, and ultrasonic cleaning is performed. A substrate is attached to the substrate attachment portion 21.

First, argon gas is supplied into the reaction vessel 2 from the first gas supply device 5. Plasma is generated using only an argon gas flow rate of 100 sccm at a pressure of 800 to 1013 hPa, and the pressure is increased to 1013 hPa while maintaining the plasma, and methane is supplied from the second gas supply device 6 and hydrogen is buffered from the third gas supply device 7. The mixed gas is introduced into the reaction vessel 2. The mixed gas is guided from the side so that it can be sufficiently supplied to the plasma. The pressure in the reaction vessel 2 is adjusted by an exhaust valve while exhausting with a rotary pump.

As generation conditions in this example, the pressure is 1013 hPa, the mixed gas used is changed in CH ₄ flow rate to 2.8 sccm, hydrogen flow rate to 100 sccm, and argon gas flow rate to 0 to 100 sccm. The substrate temperature was set to around 870 ° C., and the input power was changed from 100 to 200 W in order to maintain the temperature, and the generation time was set to 0.5 to 1 hour.

In this way, diamond could be generated on the substrate. FIG. 7 is a scanning electron micrograph of the diamond film, and FIG. 8 is an enlarged photograph thereof. It is observed that diamond is generated in a ring shape on the substrate. FIG. 9 is a graph showing the analysis result of the film generated on the substrate by laser Raman spectroscopy. The laser Raman spectroscopic analysis result also showed a diamond at 1333 cm ⁻¹ , confirming that it was diamond.

INDUSTRIAL APPLICABILITY The present invention can be used as a plasma generator and a plasma generation method that can generate plasma under atmospheric pressure or a pressure close thereto. Since a vacuum vessel is not required, there is no restriction on the size of the reaction vessel, and a large apparatus can be easily produced. Therefore, plasma processing can be performed on a large member. It can generate high-energy plasma and can be used to generate diamond.

It is a conceptual diagram which shows a plasma generator. It is an exploded view which shows the structure of an electrode. It is a circuit diagram which shows a resonance circuit. It is the schematic of the plasma generator containing a semi-coaxial type cavity resonator. It is an expanded sectional view which shows the detail of a cavity resonator. It is sectional drawing which shows the adjustment mechanism of the division ratio k. It is a scanning electron micrograph of a diamond film. It is a scanning electron micrograph (enlarged photograph) of a diamond film. It is a graph which shows the analysis result by a laser Raman spectroscopy.

Explanation of symbols

1. 1. Plasma generator 2. Reaction vessel 3. Gas inlet 4 4. Gas discharge port First gas supply device 6. Second gas supply device 7. Third gas supply device 10. Microwave introduction device 11. Electrode 12. Cavity resonator 17. Liquid metal inlet 21. Board mounting part

Claims (4)

A reaction vessel, a first gas supply device for supplying argon gas to the reaction vessel, a second gas supply device for supplying a gas containing hydrocarbons, a third gas supply device for supplying hydrogen, and a reaction vessel A microwave introducing device that introduces a microwave having a frequency of 1 GHz or more has an electrode that is a coaxial line, and the electrode has an electrode body and an insulator that covers the periphery of the electrode body. Plasma generation is performed by generating plasma only at the electrode tip, generating plasma using only argon gas at a pressure of 800 to 1013 hPa, and introducing hydrocarbons and hydrogen into the plasma while maintaining the plasma. apparatus. The plasma generating apparatus according to claim 1, wherein the electrode main body is made of copper, and an aluminum cap is provided on the electrode main body at the tip of the electrode. The plasma generating apparatus according to claim 1, wherein the electrode main body is hollow. A substrate is installed in the reaction vessel, argon gas is supplied to the reaction vessel, and a microwave having a frequency of 1 GHz or more is introduced into the reaction vessel by an electrode that is a coaxial line having an electrode body portion covered with an insulator around the periphery, Generation of diamond that generates a diamond on the substrate by generating a plasma only at the electrode tip using only argon gas at a pressure of 800 to 1013 hPa and supplying the gas containing hydrocarbon and hydrogen to the reaction vessel while maintaining the generated plasma. Method.