JPH07130493A - Method and device for cooling microwave discharge tube - Google Patents

Abstract

PURPOSE:To establish a method of effectively cooling those parts of a microwave discharge tube which run temperature. CONSTITUTION:Microwaves emitted by a microwave oscillator 6 are introduced into a cavity resonator 1 via coaxial waveguide tubes 3, 4, and electric discharge is generated by the electric field due to microwaves. A refrigerant is introduced into this resonator 1 through the inner conductor 4 of the coaxial waveguide tubes 3, 4 coupled with the resonator 1 so as to cool the tubes 3, 4 serving as a microwave transmission path, the resonator 1, and a discharge tube 13 installed therein.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for cooling a microwave discharge tube which is excited by an electromagnetic wave in the microwave region, and is applicable to a plasma chemical vapor deposition apparatus such as a diamond thin film apparatus and a laser oscillator. You can

[0002]

2. Description of the Related Art A conventional diamond thin film manufacturing apparatus is shown in FIG.
Will be described with reference to. FIG. 3 is a front view showing the configuration of a conventional diamond thin film manufacturing apparatus. As shown in the figure,
The discharge tube 13 penetrates the waveguide 7 from above and below and is fixed by a sleeve 12, one end of the waveguide 7 is connected to the microwave oscillator 6, and a plunger 17 is attached to the other end.

A sample table 8 on which a substrate 9 such as a silicon wafer is placed is fixed inside the discharge tube 1, the upper end of which is connected to a sample gas supply source (not shown), and the lower end thereof is not shown. It is connected to the exhaust pipe. Therefore, when the microwave output from the microwave oscillator 6 propagates through the waveguide 7 and is introduced into the discharge tube 13, the mixed gas of methane and hydrogen flowing into the discharge tube 13 as the sample gas is microwave. The discharge thin film is formed on the substrate 9 by the plasma generated by the discharge excitation by the electric field.

[0004]

In the conventional diamond thin film manufacturing apparatus described above, the diamond thin film forming rate increases as the sample gas pressure in the discharge tube 13 increases, but the temperature of the discharge tube 13 increases accordingly. However, there is a drawback that microwave discharge for a long time cannot be performed.

Therefore, in order to cool the discharge tube 13, a hole is formed in the cavity resonator to the extent that microwaves do not leak, and air cooling is performed through this hole, so that there is a disadvantage of low efficiency. The reality is that the antenna of the waveguide coupling part cannot be effectively cooled.

Furthermore, when microwaves are introduced into the cavity resonator by an antenna attached to the coupling portion between the microwave coaxial waveguide and the cavity resonator, the electric field strength inside the cavity resonator is the same as that around the antenna. Since the portion is strong, the discharge tube near the antenna becomes particularly hot due to the strong discharge excitation of the gas near the antenna. Further, there is a problem that the coaxial waveguide is also heated by the reflected microwaves due to the variation of discharge plasma characteristics (load). The present invention has been made in view of the above prior art, and an object of the present invention is to provide a method and apparatus for efficiently cooling a heating part such as a discharge tube, an inner wall of a cavity resonator, an antenna, and a coaxial waveguide. .

[0007]

The structure of the present invention which achieves such an object is to introduce the microwave output from a microwave oscillator into a cavity resonator by using a coaxial waveguide, and to discharge by the electric field thereof. In the device for generating, by circulating a refrigerant such as air, nitrogen gas or liquid nitrogen in the inner conductor in the inner conductor and the outer conductor forming the coaxial waveguide, and introducing the refrigerant into the cavity resonator, Discharge tube,
The inner wall of the cavity resonator, the antenna, and the coaxial waveguide can be efficiently cooled.

[0008]

By supplying a coolant to the inner conductor of the coaxial waveguide, the tube wall of the inner conductor can be cooled, and the antenna at the coupling portion between the coaxial waveguide and the cavity resonator can be cooled. The discharge tube can be cooled by blowing the refrigerant ejected from the discharge tube around the antenna.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. [Embodiment 1] FIG. 1 shows an embodiment of the present invention. In this example, the present invention is applied to the production of a diamond thin film.

As shown in the figure, a cylindrical cavity resonator 1
Sleeves 12 penetrate through the upper and lower surfaces of (inner diameter 90 mm, length 100 mm), and discharge tubes 13 are inserted and installed inside the cylindrical cavity resonator 1 in close contact with the sleeves 12. . Inside the discharge tube 13, a substrate (silicon wafer) 9 for depositing a diamond thin film
And a sample table 8 therefor.

The discharge tube 13 has its upper end connected to the sample gas supply source 10 and its lower end connected to the exhaust pipe 11,
Mixed gas of hydrogen and 5% methane is 10To as sample gas
rr and flow rate of 1000 ml / min. A coaxial waveguide including an outer conductor 4 and an inner conductor 3 is connected to the cylindrical cavity resonator 1. The coaxial waveguide is a coaxial waveguide converter 2
And the microwave oscillator 6 through the rectangular waveguide 7.

Therefore, the microwave having a frequency of 2.45 GHz generated by the microwave oscillator 6 passes through the rectangular waveguide 7 and the coaxial waveguide converter 2 and then the inner conductor 4 and the outer conductor 3 of the coaxial waveguide. And is introduced into the cylindrical cavity resonator 1.
Furthermore, since the inner conductor 4 is coupled to the cylindrical cavity resonator 1 as a loop antenna, a microwave electric field is formed inside the cylindrical cavity resonator 1.

Further, a Teflon plate 5 is interposed between the inner conductor 4 and the outer conductor 3 of the coaxial waveguide, and one end of the inner conductor 4 penetrates the coaxial waveguide converter 2 to circulate the refrigerant. It is connected to the pump 14. Therefore, CFCs discharged as a refrigerant from the refrigerant circulation pump 14 are introduced into the cylindrical cavity resonator 1 through the inner conductor 4. By flowing Freon in the inner conductor 4 of the coaxial waveguide in this way, the tube wall of the inner conductor 4 can be cooled and the antenna at the coupling portion between the coaxial waveguide and the cylindrical cavity resonator 1 can be cooled. In addition, the CFCs ejected from the inner conductor 4 are discharged from the discharge tube 13 near the antenna.
The discharge tube 13 can also be cooled by being blown onto.

A pipe connecting the cylindrical cavity resonator 1 to the refrigerant circulation pump 14 is provided so that the CFCs that have cooled the discharge tube 13 and the like circulate to the refrigerant circulation pump 14. Table 1 shows the measurement results of the thin film produced after discharging for 1 hour by the cooling device for the microwave discharge tube of the present embodiment having the above-mentioned configuration, in comparison with the prior art.

[0015]

[Table 1]

As can be seen from this table, in the present invention, the microwave power can be increased as compared with the prior art, and plasma can be generated in a larger space than in the prior art.
As a result, the reaction of methane necessary for diamond synthesis can be sufficiently controlled, and thus the film formation rate was improved as shown in Table 1.

[Second Embodiment] FIG. 2 shows another embodiment of the present invention. In this embodiment, nitrogen gas is used as the refrigerant instead of CFC. That is, one end of the inner conductor 4 penetrates the coaxial waveguide converter 2 and is connected to the gas compressor 15, and the other end thereof is connected to the discharge tube 13 in the cylindrical cavity resonator 1.
Is formed as a gas ejection nozzle 16 at a position facing each other. Therefore, the nitrogen gas discharged from the gas compressor 15 as a refrigerant is introduced into the cylindrical cavity resonator 1 through the inner conductor 4, and the nitrogen gas ejected from the gas ejection nozzle 16 locally discharges the discharge tube 13 near the substrate. Therefore, the amount of microwave energy injected into the discharge plasma can be increased.

Table 1 shows the experimental results of diamond synthesis of this example. As shown in this table, it can be seen that the same effect as in Example 1 is obtained as compared with the conventional technique.
This example is not limited to the synthesis of diamond, and since the discharge conditions can be diversified by changing the nozzle shape for ejecting the coolant or making the ejection pulse, it is possible to change the film quality of the thin film to be produced. it can.

[0019]

As described above in detail with reference to the embodiments, according to the cooling function of the present invention, the discharge tube and the like are cooled by the refrigerant in the microwave discharge device, so that it is possible to operate under various pressure conditions. The discharge can be maintained stably for a long time, and since the temperature of the antenna for introducing the microwave into the cavity resonator and the waveguide are constant, the operation performance can be stabilized.

[Brief description of drawings]

FIG. 1 is a front view of a diamond thin film manufacturing apparatus according to an embodiment of the present invention.

FIG. 2 is a front view of a diamond thin film manufacturing apparatus according to another embodiment of the present invention.

FIG. 3 is a front view showing a conventional manufacturing apparatus.

[Explanation of symbols]

 1 cylindrical cavity resonator 2 coaxial waveguide converter 3 outer conductor 4 inner conductor 5 Teflon plate 6 microwave oscillator 7 rectangular waveguide 8 sample stage 9 substrate 10 sample gas supply source 11 exhaust pipe 12 sleeve 13 discharge Pipe 14 Refrigerant circulation pump 15 Gas compressor 16 Gas injection nozzle 17 Plunger

Claims (3)

[Claims] 1. A device for introducing a microwave output from a microwave oscillator into a cavity resonator through a coaxial waveguide to generate a discharge by an electric field of the microwave,
The coaxial waveguide, the cavity resonator, and the cavity resonance, which guide the refrigerant into the cavity resonator through the inner conductor of the coaxial waveguide coupled to the cavity resonator and serve as a microwave transmission path. A method of cooling a microwave discharge tube, characterized in that the discharge tube installed inside the vessel is cooled. 2. The microwave discharge tube according to claim 1, wherein an inner conductor of a coaxial waveguide is coupled to the antenna for introducing microwaves to the cavity resonator to form a refrigerant outlet port. Cooling system. 3. A nozzle structure is formed so that the discharge port of the refrigerant from the inner conductor of the coaxial waveguide coupled to the antenna is concentrated on the discharge tube installed in the cavity resonator. The cooling device for a microwave discharge tube according to claim 2.