JP2907345B2 - Source gas excitation method in plasma torch - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for exciting a source gas in a plasma torch.

[Prior Art] For example, a plasma generating gas such as argon or a mixed gas of the same and a raw material is injected from one end or halfway of a plasma torch, and a high-frequency heating coil or a microwave cavity or the like is injected into this gas flow path. A plasma generation unit is provided to bring these gases into a plasma state. The generated plasma is blown out from the tip of the plasma torch, and is provided for a required use.

In a conventional plasma torch, a high-frequency electromagnetic field generated from a plasma generating unit such as a high-frequency heating coil or a microwave cavity is directly applied to a gas. Normally, a gas at room temperature is electrically neutral and the applied electromagnetic field is Not ionized enough to absorb energy. For this reason, in a conventional plasma torch, an electrode is provided in a gas flow path so that high-frequency electromagnetic field energy applied at the time of plasma generation can be absorbed, and an equalizing gas is weakly ionized by a method such as arc discharge at the electrode. I was

[Problems to be Solved by the Invention] However, if an electrode is provided in the gas flow path, there is a problem that the mixing of the electrode material into the plasma is inevitable.

Further, in the conventional plasma torch, when the plasma is sustained, the plasma temperature decreases when the gas flow rate increases, and the charged particles generated in the plasma are not sufficiently ionized by the newly supplied gas. There is a problem that the plasma flame flows out and becomes unstable and disappears. To prevent this as much as possible, besides exciting the gas and generating plasma, it is necessary to supply an excessive amount of high-frequency energy to maintain the plasma, which inevitably increases power consumption. There is.

An object of the present invention is to provide a method for exciting a source gas in a plasma torch capable of preventing the electrode material from being mixed into the plasma and stably forming the plasma.

[Means for Solving the Problems] The means of the present invention for achieving the above object will be described. The method for exciting a source gas in a plasma torch according to the present invention is characterized in that the source gas supplied into the plasma torch generates plasma. Before arriving at the portion, the material gas is irradiated with laser light to excite it in advance.

[Operation] The raw material gas irradiated with the laser in the plasma torch is
It is excited and partially ionized. When the raw material gas reaches the plasma generation part, the partially ionized electrons or ions absorb energy and excite the surrounding neutral gas to generate plasma.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. In the drawing, reference numeral 1 denotes a quartz plasma torch having a double structure so that a housing having an inner diameter of about 35 mm and a length of about 130 mm can be water-cooled, and 2A denotes cooling water for supplying cooling water into the housing of the plasma torch 1. An inlet, 2B is an outlet of cooling water from the housing of the plasma torch 1, 3 is a source gas supply pipe for supplying a source gas such as oxygen and SiCl _{4 to the} plasma torch 4, and 4 is a source gas supply pipe in the plasma torch 1. 3 is a cap-shaped source gas discharge section for discharging a source gas from the tip, 5 is a plasma gas supply pipe for supplying plasma gas into the plasma torch 1, 6 is a CO ₂ laser in the source gas in the source gas discharge section 4. A hollow cylindrical laser light input port for irradiating light, 7 is a seal portion to which a sealing gas is supplied so that impurities in the atmosphere do not enter the laser light input port 6 from the outside, and 8 is a plasma torch. A plasma generation unit formed in the plasma torch 1 by a high-frequency heating coil 9 provided on the outer periphery of the tip of the plasma generator 1, 10 is a weakly ionized gas formed in the source gas discharge unit 4, and 11 is a plasma generation unit 8. Plasma flame.

A source gas such as O ₂ or SiCl _{4 is} supplied from a source gas supply pipe 3 to a source gas discharge unit 4 in the plasma torch 1. Immediately after being emitted from the source gas emission unit 4, these source gases are continuously irradiated with CO ₂ laser light from the laser light incidence port 6, absorb the energy thereof, are partially ionized, and are partially ionized. It becomes 10. Since the laser beam input port 6 for irradiating the source gas emission section 4 with laser light has a hollow cylindrical shape, it is possible to prevent the laser beam from being absorbed and scattered before the source gas is irradiated. The weakly ionized gas flows into the plasma generation unit 8.

On the other hand, a plasma gas (for example, Ar, O ₂ or a mixed gas thereof) is supplied from a plasma gas supply pipe 5 to a plasma torch 1.
After cooling the wall surface of the raw material gas discharging portion 4
It is partially mixed with the weakly ionized gas 10 just below the laser beam irradiation area. The plasma gas and the source gas in a weakly ionized state are turned into a plasma flame 11 by the energy of the high-frequency electromagnetic field supplied from the high-frequency heating coil 9 in the plasma generation unit 8, blown out from the plasma torch 1, and discharged on the sample downstream of the plasma torch 1. The reaction product is deposited on the substrate. For example, a glass film with few impurities can be formed over a long time on a basic surface on a plane.

[Effects of the Invention] As described above, in the method of exciting a source gas in a plasma torch according to the present invention, before the source gas supplied into the plasma torch reaches the plasma generation unit, the source gas is irradiated with laser light. Since it is excited in advance, there is no need to arrange an electrode in the gas flow path, the electrode material is not mixed into the plasma, and the concentration of metal impurities in the reaction product is kept at a lower level than before, Plasma flame can be kept stable for a long time. Further, according to the present invention, high-frequency energy may be applied only in an amount necessary for causing a desired reaction, and power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of a plasma torch according to the present invention. 1 ... plasma torch, 3 ... source gas supply pipe, 4 ...
Source gas discharge section, 5: Plasma gas supply pipe, 6: Laser beam input port, 7: Seal section, 8: Plasma generation section, 9: High frequency heating coil, 10: Weakly ionized gas, 11
...... Plasma flame.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05H 1/26 B23K 10/00

Claims (1)

(57) [Claims] 1. A method of exciting a source gas in a plasma torch, wherein the source gas supplied to the plasma torch is irradiated with a laser beam to excite the source gas before the source gas reaches a plasma generation unit.