JPH0521193A - High-frequency plasma device - Google Patents

Abstract

PURPOSE:To heat a material evenly from the upper stream to the downstream of the plasma by providing one side electrode at the upper stream side and at the downstream side of a high-frequency plasma torch respectively, and adding a system connected to a plasma power source which is independent from a high-frequency plasma power source. CONSTITUTION:A high-frequency coil 1 is positioned outside a plasma confinement tube 2, lets flow a high-frequency current fed from a high-frequency power source, and induces an induction current in the plasma by this high-frequency current. This current flows to the surface of the plasma near the high-frequency coil 1, and the plasma is heats by the Joule heating. As a result, an energy is thrown in to the midstream of the plasma through a nozzle. An upper stream side electrode 4 is formed of copper or brass. At the downstream side of the plasma torch, one side electrode 5 is provided. The electrode 4 at the upper stream side and the electrode 5 at the downstream side of the plasma torch which are independent from a power source 3 are connected. A vacuum container 7 is preferable to be insulated from the electrode 5 electrically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductively coupled high frequency plasma device.

[0002]

2. Description of the Related Art Inductively coupled high frequency plasma (hereinafter referred to as high frequency plasma) is used in fields such as ultrafine particle synthesis, thermal spraying, vapor deposition, and chloride oxidation. The high-frequency plasma has features that the volume of the plasma is larger than that of the direct-current plasma and the flow velocity of the plasma is slow. Therefore, in the high frequency plasma, there is an advantage that the residence time of the supplied material is long. On the other hand, the high-frequency plasma has a hydrodynamic characteristic that the flow reverses upstream near the central axis of the upstream part of the high-frequency plasma coil due to this principle. When a raw material such as gas or powder is blown into this backflow portion, there is a drawback that the plasma becomes unstable.

To overcome this drawback, improvements have been made to high frequency plasma torches. The first method is to control the flow in the high-frequency plasma torch and insert a water-cooling nozzle for supplying raw material into the plasma, and supply the raw material from this nozzle. A schematic diagram of this device is shown in FIG. 2 (Japanese Patent Laid-Open No. 63-58799). The second method is to install an auxiliary plasma torch upstream of the high frequency plasma torch. The one that installs a direct current non-transfer type plasma torch as an auxiliary plasma torch is called a hybrid plasma and was developed in the oldest. FIG. 3 shows a schematic view of an apparatus in which a single DC non-transfer type plasma torch 8 is installed (JP-A-55-32317). FIG. 4 shows an apparatus in which a plurality of DC non-transfer type plasma torches 8 are installed (Japanese Patent Laid-Open No. 63-22184).
2). A method of installing a separate high-frequency plasma torch (Japanese Patent Laid-Open No. 61-161138) as an auxiliary plasma torch has also been developed.

There is another drawback in the material process using the high frequency plasma in addition to the above-mentioned drawbacks. Since the high-frequency plasma has a low flow velocity, the raw material heated in the upstream portion and the middle-stream portion of the plasma is cooled by radiative cooling while long staying in the downstream portion of the plasma. That is, it is difficult to take out the material while being heated appropriately. The improvements described above are aimed at the plasma flow and temperature distribution in the upstream part of the high-frequency plasma. Therefore, the first drawback has been improved. However, regarding the second drawback, although the temperature distribution in the upstream part is improved, the temperature distribution in the downstream part is not improved.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, it is an object of the present invention to provide a high frequency plasma device which uniformly heats a material in the upstream portion, the middle flow portion and the downstream portion of plasma.

[0006]

As a result of various experiments and studies conducted by the inventor of the present invention, the present invention has been achieved. With the high-frequency plasma alone, the material is heated only in the midstream portion. When the auxiliary plasma is installed, the temperature distribution is improved only in the installed part. Then, the method of heating the upstream part and the downstream part simultaneously was examined. In the transfer-type arc plasma, heating is performed in the plasma flame as well, but the vicinity of the anode and the cathode is intensively heated. This is because the potential drop is large near the anode and the cathode due to the anode fall and the cathode fall. By arranging the anode and cathode of this transfer arc at the upstream and downstream parts of the high-frequency plasma, it is possible to not only heat the high-frequency plasma flame but also heat the upstream and downstream parts in a focused manner. The present invention has been reached.

That is, according to the present invention, in a high frequency plasma apparatus, one electrode is provided on the upstream side of the high frequency plasma torch, the other electrode is provided on the downstream side of the high frequency plasma torch, and both electrodes are independent from the high frequency plasma power source. The high-frequency plasma device is characterized by adding a system connected to the plasma power source.

[0008]

The present invention will be described in detail below. This will be described with reference to FIG. The high frequency plasma apparatus of the present invention shown in FIG. 1 is an apparatus which has an anode in the upstream part of the high frequency plasma torch and a cathode in the downstream part of the high frequency plasma torch and is connected to a direct current plasma power supply independent of the high frequency power supply. ..

The high frequency plasma torch comprises a high frequency coil 1 through which a high frequency current flows and a plasma confinement tube 2 for confining plasma. The plasma confinement tube 2 is made of an insulator, is not induced by high frequencies and prevents the plasma from discharging into the coil. The high frequency coil 1 is located outside the plasma confinement tube 2, and a high frequency current supplied from a high frequency power source 3 is flown to induce an induction current in the plasma. The induced current flows to the plasma surface in the vicinity of the high frequency coil 1, and the Joule heat heats the plasma. Therefore,
In the high-frequency plasma, energy is dropped in the plasma midstream portion near the high-frequency coil.

A nozzle for supplying gas is installed upstream of the high frequency plasma torch and supplies gas to the plasma. The high frequency plasma torch upstream electrode 4 must be made of a conductor such as copper or brass. Further, the high frequency plasma torch upstream electrode 4 needs to be sufficiently cooled. The other electrode 5 is installed downstream of the high frequency plasma torch. When the high frequency plasma device is applied to the film forming process, the substrate holder or the substrate can be used as the electrode. It is also possible to form the electrode into an annular shape and install it directly below the high-frequency plasma torch so that the plasma flame blows through from the center of the electrode.

A plasma power source 6 independent of the high frequency plasma power source 3 is connected to the high frequency plasma torch upstream electrode 4 and the high frequency plasma torch downstream electrode 5. Although a DC power supply is used as the independent power supply 6, an AC power supply or a high frequency power supply may be used. When the independent power source 6 is a DC power source, the polarity of the electrodes is arbitrary. That is, the upstream electrode 4 may be a cathode and the downstream electrode 5 may be an anode, or the upstream electrode 4 may be an anode and the downstream electrode 5 may be a cathode.

The vacuum vessel 7 is preferably electrically insulated from the downstream electrode 5. That is, when the vacuum container 7 and the downstream electrode 5 are electrically connected, the transitional arc discharges not by the downstream electrode 5 but by the part immediately downstream of the high frequency plasma torch of the vacuum container 7 as an electrode. Examples of the present invention will be shown below.

[0013]

【Example】

Example 1 Using the apparatus of the present invention shown in FIG. 1, the downstream electrode 5, that is, the substrate 5-1 placed on the substrate holder 5-2 was heated to measure the temperature. The temperature of the substrate 5-1 was measured with a thermocouple. The procedure is as follows. The vacuum container 7 is evacuated. 40 l / min of argon is supplied from the nozzle to the upstream part of the high frequency plasma torch. The high frequency plasma power supply 3 is operated to ignite plasma. When the vacuum container 7 reaches the atmospheric pressure, the vacuum container 7 is opened to the atmosphere. At this time, the anode output condition in the high frequency power supply is an anode voltage of 5 kV and an anode current of 5 A. Therefore, the anode output is 25 kW. After that, the independent power source 6 is operated to superimpose the transfer type arc on the high frequency plasma. At this time, the upstream electrode 4 was used as an anode, and the substrate 5-1 and the substrate holder 5-2 which were the downstream electrodes 5 were used as cathodes. The operating conditions of the independent power source 6 are an output voltage of 40 V and an output current of 40 A, depending on the substrate position, and an electric power of 1.6 kW, which is 1/10 or less of the output of the high frequency power source. For comparison, an experiment in which the independent power source 6 was not operated was also conducted. The output of the high frequency power supply at this time was also set to 25 kW.

The temperature measured by the thermocouple rises and becomes constant over time. The temperature that has become constant is defined as the ultimate temperature. The temperature reached by the high frequency + transfer arc plasma and the temperature reached only by the high frequency plasma by the apparatus of the present invention were measured at various substrate distances. The substrate distance means the distance from the high frequency plasma torch exit to the substrate.

Table 1 shows the results. When the 1.6kW transfer type arc is superposed, the reached temperature is higher than that when only high-frequency plasma is used. Further, for comparison, the ultimate temperature was measured when the output of the high frequency plasma power source was set to 26.6 kW and when the 4 kW non-transfer type arc plasma was superimposed on the 25 kW high frequency plasma. This result is also shown in Table 1.
As shown in Fig. 5, the reached temperature is higher when the transfer type arc is superposed than in the case where only the high frequency plasma is used or when the non-transfer type arc is superposed. That is, the superposition of the transfer type arc efficiently heats the downstream portion of the plasma, so that the temperature reached by the substrate increases.

[0016]

[Table 1]

(Embodiment 2) It was confirmed that the effect of the transfer type arc shown in Embodiment 1 can be seen in the case of reverse polarity and alternating current. In Example 1, the downstream electrode 5 was used as a cathode, but the reached temperature was measured when the downstream electrode 5 was an anode and the upstream electrode 4 was a cathode, and when the independent power source 6 was an AC power source. The output of the independent power supply was adjusted to 1.6kW. The frequency when the AC power supply is used is 50 Hz. The substrate distance was 100 mm.

Table 2 shows the results. 25kW high frequency +
The reached temperatures in the case of the 1.6 kW transfer type arc are almost equal to each other, and are higher than the reached temperatures in the case of only the 26.6 kW high frequency shown in Table 1. That is, in any case, the effect of heating the high frequency plasma downstream part by the transfer arc was observed.

[0019]

[Table 2]

(Example 3) Thermal spraying was carried out using the high frequency plasma apparatus of the present invention shown in FIG. The procedure is as follows. The vacuum container 7 is evacuated. 40 l / min of argon is supplied from the nozzle to the upstream part of the high frequency plasma torch. The high frequency plasma power supply 3 is operated to ignite plasma. When the vacuum container 7 reaches the atmospheric pressure, the vacuum container 7 is opened to the atmosphere. The independent power source 6 is operated to superimpose the transfer type arc on the high frequency plasma. At this time, the upstream electrode 4 serves as an anode, and the downstream electrode 5 includes the substrate 5-1 and the substrate holder 5.
-2 was used as the cathode. Substrate 5-by the superposed plasma
After heating No. 1, powder was supplied from the upstream part of the plasma torch and sprayed. If the substrate 5-1 during thermal spraying is overheated, it is possible to stop the transfer arc before or during thermal spraying. However, in order to improve the temperature distribution in the plasma during spraying, it is necessary to operate the transfer arc and the independent power source 6 before and during spraying.

Particle sizes of 60-80, 80-100, 100
Thermal spraying was performed using Ti powder of 120 micron as a raw material, and the density of the sprayed coating was measured. Table 3 shows a comparison between the case of only the high frequency plasma, the case of superposing the direct current non-transfer type arc on the high frequency plasma, and the case of superposing the transfer type arc on the high frequency plasma as shown in the present invention.

[0022]

[Table 3]

From the above, when the apparatus of the present invention is used to perform thermal spraying by a method of superposing a transfer type arc on a high frequency plasma, a coating having a higher density than that of the high frequency plasma spraying method can be obtained with any raw material particle size. This is because the high-frequency plasma apparatus of the present invention uniformly heats the material in the upstream portion, the middle-flow portion, and the downstream portion, and in the high-frequency plasma spraying method, the heating in the middle-flow portion is the center of the high-frequency plasma + This is because in the non-transfer type arc, the heating is mainly performed in the upstream portion and the middle-flow portion, so that the material is cooled in the downstream portion.

[0024]

With the apparatus of the present invention, it is possible to generate high-frequency plasma that uniformly heats the material in the upstream portion, the midstream portion, and the downstream portion of the plasma. As a result, it becomes possible to industrially operate the high-frequency plasma, and it is extremely large that it contributes to industrial development.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a high-frequency plasma device of the present invention.

FIG. 2 is a front sectional view showing a conventional high-frequency plasma device.

FIG. 3 is a front sectional view showing an apparatus in which a conventional single DC non-transfer type plasma is installed upstream of a high frequency plasma torch.

FIG. 4 is a front sectional view showing an apparatus in which a plurality of conventional DC non-transfer type plasmas are installed in an upstream part of a high frequency plasma torch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... High frequency coil 2 ... Plasma confinement tube 3 ... High frequency power source 4 ... High frequency plasma torch upstream electrode 5 ... High frequency plasma torch downstream electrode 6 ... Transfer type arc power supply 7 ... Vacuum container 8 ... DC non-transfer type plasma torch 9 ... DC Power supply 10 ... Raw material supply nozzle

Claims (1)

Claim: What is claimed is: 1. In a high frequency plasma device, one electrode is provided on the upstream side of the high frequency plasma torch, and the other electrode is provided on the downstream side of the high frequency plasma torch. A high-frequency plasma device characterized in that a system connected to a plasma power source independent of the high-frequency plasma power source is added.