JP4950763B2 - Plasma generator - Google Patents

Description

  The present invention relates to semiconductor manufacturing technology such as PFC (perfluorofluorocarbons) contained in exhaust gas discharged from a semiconductor manufacturing apparatus or a flat display manufacturing apparatus that performs a chemical vapor deposition (CVD) process or an etching process. The present invention relates to a plasma generating apparatus used for decomposing a gas having a high warming potential or a toxic gas.

In addition to inert gases such as Ar, Kr, Xe, He, and N ₂ , CF ₄ , C ₂ F ₄ , C ₂ F ₆ , C ₃ F ₈ , and C ₄ are included in the exhaust gas discharged from the semiconductor manufacturing apparatus. A wide variety of fluoride gases such as F ₆ , C ₄ F ₈ , C ₅ F ₈ , COF ₂ , HF, SiF ₄ , NF ₃ and SF ₆ are included.
These fluoride gases are supplied as raw materials to a semiconductor manufacturing apparatus, and there are components that are discharged out of the system without being consumed, and components that are by-produced by a reaction in the semiconductor manufacturing apparatus. May be discharged at a rate of several L / min.
If these fluoride gases are released into the atmosphere without being treated, they may cause pollution, pollution, and other human damage, as well as ozone destruction and global warming. Therefore, a highly efficient decomposition process is desired.

As treatment methods widely used for the purpose of removing the fluoride gas component from such exhaust gas, there are a combustion treatment method, a thermal decomposition treatment method, a dry adsorption removal method, a supercritical water decomposition treatment method and a plasma decomposition treatment method. Can be mentioned.
The combustion treatment method has the problem that NOx and SOx are contained in the exhaust gas, and the thermal decomposition treatment method has the problem that CF ₄ cannot be decomposed unless the temperature is raised to 1000 ° C. or higher. The problem is how to treat these agents.
In addition, since none of the three methods can achieve a removal efficiency of 95% or more, it is difficult to apply to future high-efficiency processing. Further, the supercritical water treatment method has a problem that the apparatus becomes large.

In view of these drawbacks, plasma decomposition and removal methods have been actively studied, particularly from the viewpoint that high-efficiency removal of 95% or more is possible. Plasma decomposition and removal methods are roughly classified into an atmospheric pressure plasma method and a reduced pressure plasma method.
In the atmospheric pressure plasma method, collisions between particles become intense, so the gas temperature is high and molecules in the plasma tend to decompose, but at the same time, unstable fluorine and carbon components after decomposition recombine at the plasma generator outlet. Probability is high and recombination PFC, mainly CF _4, is easily formed. Therefore, it is difficult for the atmospheric pressure plasma method to make the removal efficiency 99% or more.

On the other hand, in the low-pressure plasma, radicals generated by the plasma generator are not easily deactivated, and thus can be removed by a reaction agent or the like before the recombination PFC is generated.
For example, the present applicant has developed a PFC removal apparatus in which a PFC is plasma-decomposed in a reduced pressure atmosphere and reacted with a calcium oxide agent in a reduced pressure atmosphere in Patent Document 1, and CF ₄ can be removed with a removal efficiency of 99.99%. Indicated.

As a low-pressure plasma method for treating exhaust gas from a semiconductor manufacturing apparatus, a spiral coil is wound around the outer periphery of a cylindrical reaction vessel made of an insulating material into which exhaust gas is introduced, and high-frequency power is applied to this coil so that it enters the cylindrical reaction vessel. A method for generating a high frequency inductively coupled plasma has been developed.
In high frequency inductively coupled plasma, ions or electrons are reciprocated by an electromagnetic field that repeats reversal at high speed, and the plasma is maintained by collision between moving particles. Therefore, the coil can be installed outside the discharge region. .

In addition, since the coil is installed outside the discharge region, there is an advantage that the coil is not corroded or consumed by highly active radicals and ions excited by plasma.
Furthermore, by forming a spiral coil with a hollow pipe through which cooling water can flow, or by winding a thin coil around the gap between the main coils, power loss and plasma ignition power can be reduced, and the durability of the coil and chamber can be reduced. It is proposed that improvement can be achieved (see, for example, Patent Documents 2 and 3).

  By the way, in the high frequency inductively coupled plasma, there is a problem that the load impedance of the plasma generating device that generates plasma greatly varies depending on the gas variation such as the type, concentration, flow rate, and pressure and before and after the plasma ignition. Must handle large variations in load impedance.

Usually, in order to match the output impedance of a power source that applies high-frequency power to the load impedance, a matching circuit is provided between the power source and the electrode, and a variable capacitance or variable inductance that is a component of the matching circuit is connected to a servo motor or the like. Adjust through the adjustment mechanism. A matching method using a frequency control circuit as a matching circuit has also been proposed (see, for example, Patent Document 4).
JP 2006-326553 A Japanese Patent Laid-Open No. 11-76740 JP 2002-210330 A JP 2004-8893 A

As described above, a spiral coil is wound around the outer periphery of a cylindrical container made of an insulating material as means for removing harmful gas components such as PFC contained in exhaust gas discharged from a semiconductor manufacturing apparatus with high efficiency of 99% or more. It is effective to generate a high-frequency inductively coupled plasma in a cylindrical reaction vessel in a reduced pressure atmosphere to decompose and remove PFC.
However, in order to treat exhaust gas that varies widely, it is necessary to provide a matching circuit between the high-frequency power source and the coil and match the output impedance of the power source to the load impedance. There is a problem of depending on the matching circuit.

More specifically, the impedance range that can be matched depends on the variable capacitance or the capacitance of the variable inductance, the matching resolution depends on the step resolution of the servo motor, and the matching response time depends on the operating speed of the motor.
That is, in order to perform matching over a wide range, it is necessary to provide a variable capacitance or variable inductance having a large adjustment range. However, if the performance of the servo motor is the same, the matching resolution is lowered and the stability of plasma discharge is lowered.

  On the other hand, in order to improve the alignment resolution, it is necessary to increase the step resolution of the servo motor. As a result, the alignment response time becomes long, and there arises a problem that the exhaust gas processing efficiency is lowered. Although a matching method using a frequency control circuit has been proposed, it is intended to increase the matching speed, and does not prevent a reduction in matching resolution due to an expanded matching range.

In addition, as described above, it was shown that CF ₄ can be removed with a removal efficiency of 99.99% in a PFC removal apparatus that causes PFC to be plasma decomposed in a reduced pressure atmosphere and reacts with the calcium oxide agent in the reduced pressure atmosphere. It is important to react with the reactants before the recombined PFC is formed. For this reason, it is required to extend the lifetime of the active species generated in the plasma, or to make the distance between the plasma generating apparatus and the calcium oxide agent close. On the other hand, when putting the above-described PFC removal apparatus into practical use, it may be difficult to dispose the plasma generation apparatus and the calcium oxide agent at a short distance due to the installation location of the apparatus.

  The present invention has been made in view of the above problems of the background art, and provides a plasma generation apparatus capable of performing plasma discharge under wider gas conditions and a plasma generation apparatus that improves the removal efficiency of harmful components such as PFC. The purpose is to do.

To solve this problem,
According to the first aspect of the present invention, a spiral coil is wound around a cylindrical reaction vessel having a gas inlet and a gas outlet, and a high frequency power from a high frequency power source is applied to electrodes formed at two locations of the spiral coil. A plasma generating device that generates plasma in a gas reaction vessel and decomposes harmful components in the gas introduced from the gas inlet,
The high frequency ranges from 1 to 100 MHz;
The total number of turns of the helical coil is greater than the number of turns between the two electrodes of the helical coil, and a part of the helical coil is located outside the electrode on the gas outlet side;
L / M is 0.3 or more, where L is the number of turns of the coil existing outside the electrode on the gas inlet side, and M is the number of turns of the coil between the two electrodes. It is.

In the invention according to claim 2, when the number of turns of the coil existing outside the electrode on the gas outlet side is N and the number of turns of the coil between the two electrodes is M, N / M is 0.5 or more. The plasma generating apparatus according to claim 1 .

The invention according to claim 3 is the plasma generating apparatus according to claim 2 , wherein the N / M is 1.1 or less .

The invention according to claim 4 is the plasma generating apparatus according to any one of claims 1 to 3 , wherein the L / M is 3.2 or less .
The invention according to claim 5 is the plasma generating apparatus according to any one of claims 1 to 4, wherein the spiral coil is a prismatic hollow pipe.
The invention according to claim 6 is characterized in that an insulating and heat-resistant filling is filled in a gap between the cylindrical reactor and the helical coil. The plasma generation apparatus according to item 1.

In the present invention, a part of the spiral coil exists outside the two power supply electrodes formed on the spiral coil. And if there is a part of the coil outside the electrode on the gas inlet side, it is possible to reduce the burden on the matching circuit. As a result, the matching gas conditions when using the same matching circuit can be reduced. It is possible to spread.
In addition, when a part of the coil exists outside the electrode on the gas outlet side, the PFC decomposition efficiency can be improved.

FIG. 1 shows an example of a plasma generating apparatus according to the present invention.
The plasma generating apparatus of this example includes a cylindrical reaction vessel 1 made of an insulating material such as alumina or quartz, a spiral coil 2 made of a conductive material wound around the outer peripheral surface of the cylindrical reaction vessel 1, and the spiral A high-frequency power source 3 for supplying high-frequency power to the coil 2 and a matching unit 4 for matching the output impedance of the high-frequency power source 3 with the load impedance of the spiral coil 2 are mainly configured. The shape of the reaction vessel may be a rectangular tube other than a cylindrical shape.

Both ends of the cylindrical reaction vessel 1 are provided with a gas inlet 1a for introducing exhaust gas from a semiconductor manufacturing apparatus and the like, and an exhaust pump for discharging the gas after plasma processing while making the inside of the cylindrical reaction vessel 1 have a reduced pressure atmosphere. It is a gas outlet 1b connected to the.
The spiral coil 2 has electrodes formed at two locations thereof, and the electrode on the gas inlet 1a side serves as a feeding electrode 5 for applying high-frequency power through the matching unit 4, The electrode on the gas outlet side is a ground electrode 6 for allowing the applied high frequency power to flow out.

  In this plasma generation apparatus, plasma is generated by reversing the electromagnetic field at high speed by supplying high frequency power to the spiral coil 2 installed outside the discharge region (reaction vessel internal space). Therefore, the frequency of the high-frequency power of the high-frequency power source 3 is important because the moving distance of electrons and ions and the ease of ionization are determined by the reversal speed, that is, the frequency of the electromagnetic field.

  For example, a high frequency power supply is commercially available in a frequency range of 0.1 to 2450 MHz, but the ionization effect is low in the order of 0.1 MHz, and it is difficult to supply power with a conductor due to the skin effect in the order of 1000 MHz. It is better to select the frequency. In particular, at present, it is advantageous in terms of price and physical distribution to select a high-frequency power source having a frequency of 2 MHz, 13.56 MHz, and 60 MHz with many commercial products, but it is not limited to these from the viewpoint of plasma generation.

  The matching unit 4 has a matching circuit for matching impedances of the high-frequency power source 3 and the helical coil 1 serving as a load. The matching unit 4 varies greatly depending on gas variations such as composition, concentration, flow rate, pressure, etc., and before and after plasma ignition. It corresponds to the load impedance.

  The matching circuit is composed of a combination of a capacitor and an inductance, and adjusts a variable capacitance or a variable inductance, which is a component, via an adjustment mechanism such as a servo motor. Although it is called a π-type matching circuit or an L-type matching circuit depending on how the components are arranged, the present invention is not limited to any of them and can be combined. In addition, in order to omit the servo motor, it is possible to use a circuit that is composed only of electronic components and adjusts the frequency.

  FIG. 2 shows an example of the matching unit 4. The matching unit 4 of this example has a matching circuit composed of two variable capacitors 4a and 4b. A first variable capacitor 4a is connected between the high-frequency power source 3 and the feeding electrode 5, and this first A second variable capacitor 4b is connected between one end of one variable capacitor 4a and ground, and the capacity of each variable capacitor 4a, 4b can be varied by an actuator such as a servo motor (not shown). It has become.

The material of the spiral coil 1 and the electrodes 5 and 6 is preferably a highly conductive material such as copper or aluminum, but is not limited thereto.
Since the skin effect increases as the frequency of the output high frequency of the high frequency power supply 3 increases, the current is transmitted only through the surface layer of the spiral coil 1, the substantial resistance increases and the power loss increases. The coil 1 itself may be easily deteriorated by heat generation.

  As a countermeasure, in this example, the spiral coil 2 is constituted by a hollow pipe, and cooling water is allowed to pass therethrough. It is also effective to apply silver plating to the surfaces of the spiral coil 2 and the electrodes 5 and 6 in order to prevent the deterioration. As the hollow pipe constituting the spiral coil 2, a cylindrical one or a prismatic one can be used.

Further, the gap between the cylindrical reaction vessel 1 and the helical coil 2 can be filled with a filler. By filling the packing, the cooling effect of the cooling water passing through the inside of the spiral coil 2 made of a hollow pipe is efficiently reflected in the cylindrical reaction vessel 1 and cooled, and the temperature of the cylindrical reaction vessel 1 due to plasma discharge is cooled. The rise and thermal strain can be reduced, which is effective for improving the durability of the cylindrical reaction vessel 1.
Examples of the filling material include silicone resins, but other materials may be used as long as they are highly insulating and heat resistant.

Of the helical coil 1, the number of turns of a coil (hereinafter referred to as “main part”) positioned between both electrodes 5 and 6 determines the inductance of the main part together with the coil radius and the length between both electrodes 5 and 6. This factor is calculated and determined from the frequency of the high-frequency power used and the impedance design of the main part.
In the prior art, a spiral coil having the number of turns determined by this calculation is wound, and electrodes are provided at both ends of the spiral coil to apply high-frequency power, but another coil is provided outside the main part. It has been found that it is preferable to arrange them.

  FIG. 3 shows an example of the spiral coil 2 in an enlarged manner. The helical coil 2 in this example is composed of three parts along the axial direction of the cylindrical reaction vessel 1, and the part between the feeding electrode 5 and the ground electrode 6 is the main part M and the part as described above. The portion on the gas introduction port 1a side with respect to the power supply electrode 5 is defined as the introduction port side portion L, and the portion on the gas outlet port 1b side with respect to the ground electrode 6 is defined as the discharge port side portion N.

The number of turns M of the main part M is the number of turns determined by the calculation method. Further, the winding numbers L and N of the inlet side L and the outlet side N are L ≧ 0 and N ≧ 0 (however, when either L or N is 0, the other is It is necessary that either one of these two portions L and N is present.
Furthermore, the winding number L of the introduction port side L is 0.5 times or more of the winding number M of the main part M, and the winding number N of the outlet port side part N is 0. 0 of the winding number M of the main part M. It is preferable to be 3 times or more. The upper limit values of the number of windings M and N are determined by the length of the cylindrical reaction vessel 1 which is the main part of the plasma generation apparatus, but in general, both are set to 15 times or less of M.

  When the introduction port side portion L exists, an effect of applying a voltage higher than the power supply voltage to the coil end on the gas introduction port 1a side is obtained. For this reason, the effect of pre-exciting the gas before reaching the main part M is obtained. It has been confirmed that the effect is obtained when the ratio of the number of turns L of the inlet side L and the number of turns M of the main part M is L / M> 0. However, the upper limit is determined from the size of the plasma generating apparatus.

  On the other hand, when the lead-out side portion N exists, when the plasma generated in the main portion M passes, a capacitive coupling element is induced between the plasma and the ground, and an effect of forming a weakly excited state is obtained. Although it has been confirmed that the effect is obtained at a ratio N / M> 0 of the number of turns N of the outlet port side N and the number of turns M of the main part M, the larger the effect, the greater the effect. However, the upper limit is determined from the size of the plasma generating apparatus.

In the plasma generation apparatus of the present invention, high frequency inductively coupled plasma is generated. In generating high frequency inductively coupled plasma, the gas pressure in the reaction vessel is an important factor that determines the collision frequency between particles.
In a low rare gas atmosphere at a pressure of 1 Pa or less, the probability of collision between ionized electrons and particles is too low, and it is difficult to generate stable plasma. On the other hand, if the pressure is too high, the run-up distance of electrons, that is, the collision energy and the ease of ionization are reduced.

Similar to Paschen's law for DC discharge, the discharge start voltage also depends on the pressure and the distance between the electrodes, and the discharge start voltage increases as the product of the pressure and the distance between the electrodes increases, that is, a high output power source is required. It becomes.
For the above reasons, the internal pressure of the cylindrical reaction vessel 1 is set to 0.1 to 50 Torr, more preferably 1 to 10 Torr. The exhaust capacity required for the exhaust pump is calculated from the exhaust gas flow rate and the set pressure in the container. A pump with an exhaust capacity excessive by several tens of percent and a conductance adjustment valve are provided to mitigate pressure fluctuations during flow rate fluctuations. It is effective.

Specific examples are shown below.
(Example 1 ... Example in which gas inlet side L is provided)
A cylindrical cylindrical vessel made of alumina having an inner diameter of 42 mm was used as the cylindrical reaction vessel, and a 1/4 inch copper hollow pipe was used as a spiral coil wound around the outer periphery of the side surface of the cylindrical vessel. Inside the copper hollow pipe, 15 ° C. water was flowed at 1.5 L / min.

  The spiral coil was provided with a power supply electrode and a ground electrode, the ground electrode was grounded, and the power supply electrode was connected to a 2 MHz high frequency power source via the L-type matching circuit shown in FIG. 2 to supply a high frequency power of 0.5 kW. The number of turns of the spiral coil was 10 for the main part M, and the number of turns for the gas inlet side L was 10 for Example A, 3 for Example B, and 0 for Comparative Example C. There is no gas outlet side N.

  Both ends of the cylindrical reaction vessel 1 were connected to SUS flanges, 1000 cc / min Ar was introduced from the gas inlet side, and exhausted by a vacuum exhaust pump from the gas outlet side. The conductance adjustment valve provided between the SUS flange of the gas outlet and the vacuum exhaust pump was operated to adjust the pressure in the cylindrical reaction vessel to a constant 1 Torr.

In discharging, the power source impedance and the load impedance were matched by independently controlling the capacities of the two variable capacitors of the L-type matching circuit shown in FIG. The combination of the capacities of the two variable capacitors determines the reflected power from the load, that is, the power supplied to the load, and determines the utilization efficiency of the power supplied from the high frequency power source.
In other words, this means that the two variable capacitor capacities are adjusted in order to increase the power supply utilization efficiency, but in order to obtain a stable discharge state, there are many combinations of capacitor capacities that can increase the power supply utilization efficiency. Is more preferable.

FIG. 4 shows a combination region of variable capacitor capacities that can achieve a utilization efficiency of 90% or more with respect to a supplied power of 0.5 kW, and illustrates the three coils shown in FIG. In addition, all the conditions other than the number of coil turns were compared and compared.
Using the spiral coil of Example A in which the number of turns of the main part is 10 and the number of turns of the gas inlet side is 10 is a region where the utilization efficiency with respect to the supplied power of 0.5 kW can be 90% or more is The capacity of the variable capacitor is in the range of 45 to 100%, and the capacity of the second variable capacitor is in the range of 0 to 80%.
This means that good results can be obtained in about one third of the adjustable region of the matching circuit.

Further, when the spiral coil of Example B in which the number of turns M of the main part M is 10 and the number of turns L of the gas inlet side part L is 3 is used, the utilization efficiency with respect to the supplied power of 0.5 kW can be 90% or more. The region exists in a range where the capacity of the first variable capacitor is 50 to 90% and the capacity of the second variable capacitor is 0 to 60%.
This means that good results can be obtained in about 1/7 of the adjustable region of the matching circuit.

On the other hand, when the spiral coil of Comparative Example C in which the number of turns M of the main part M is 10 and the number of turns L of the gas inlet side L is 0 is used, the utilization efficiency with respect to the supplied power of 0.5 kW is 90% or more. The region where the first variable capacitor has a capacity of 45 to 55% and the second variable capacitor has a capacity of 0 to 20% exists.
This means that only 1/50 or less of the adjustable region of the matching circuit can provide good results. This result means that if the capacitance of the variable capacitor is not finely adjusted instantaneously in response to fluctuations in load impedance due to fluctuations in gas conditions, the plasma will be deactivated, and the burden on the matching circuit is large. Means.

  That is, as described above, it can be said that the burden on the matching circuit can be reduced by using the coil in which the gas inlet side L is present. At the same time, it can be said that the ratio of the number of turns of the gas inlet side portion L to the number of turns of the main portion M is 0.3 or more in order to sufficiently obtain the effect of reducing the burden on the matching circuit.

Further, when the number of turns of the gas introduction part L is increased, there is a demerit that the plasma generating apparatus is enlarged. If the total length of the apparatus exceeds 2 m, it becomes difficult to carry it into the equipment area of the semiconductor manufacturing factory. Therefore, the length of the plasma part considering the front and rear piping must be within 1.5 m.
In the case of Example 1, since the length of the main part M corresponds to 100 mm, the ratio L / M of the number of turns of the gas inlet side L cannot be 15 or more. Even if it is assumed that the adjustable region of the matching circuit expands in proportion to the winding ratio L / M based on the results of Examples A and B and Comparative Example C, the matching circuit is saturated at a ratio of 3.2. Since the effect of the inlet side L is expected to gradually decrease, it can be determined that a sufficient effect can be obtained when the ratio L / M of the number of turns is 3.2 or less.

(Example 2 ... Example of providing gas outlet port side N)
A cylindrical cylindrical vessel made of alumina having an inner diameter of 42 mm was used as the cylindrical reaction vessel, and a 1/4 inch copper hollow pipe was used as a spiral coil wound around the outer periphery of the side surface of the cylindrical reaction vessel. Inside the copper hollow pipe, 15 ° C. water was flowed at 1.5 L / min.

The spiral coil was provided with a power feeding electrode and a ground electrode, the ground electrode was grounded, and the power feeding electrode was connected to a 2 MHz high frequency power source via an L-type matching circuit to supply 1.0 kW high frequency power.
As for the number of turns of the spiral coil, the number of turns between the two electrodes (main part) is 10 in common, and the number of turns on the gas outlet side is 11 in Example D, 7 in Example E, 4 in Comparative Example F, In Comparative Example G, the volume was 0.

Both ends of the cylindrical reaction vessel are connected to a SUS flange, and 460 cc / min Ar, 30 cc / min O ₂ and 10 cc / min CF ₄ are introduced from the gas inlet side, and vacuum is supplied from the gas outlet side. It exhausted with the exhaust pump. The conductance adjustment valve provided between the SUS flange of the gas outlet and the vacuum exhaust pump was operated to adjust the pressure in the alumina cylindrical container to a constant 3 Torr. Note that the CF ₄ gas decomposition efficiency of the plasma generator was evaluated by continuously measuring the CF ₄ concentration with a Fourier transform infrared spectrometer (FT-IR) installed downstream of the vacuum pump.

FIG. 5 shows the influence of the number of coil turns at the gas outlet side N on the decomposition efficiency when CF ₄ gas is decomposed under the above conditions. All conditions except the number of coil turns were made common.
Using the coil of Example D in which the number of turns of the main part M is 10 and the number of turns of the gas outlet side N is 11 turns, CF ₄ of 10 cc / min is 99.9% higher at a power supply of 1.0 kW. It can be decomposed with efficiency. Further, when the coil of Example E in which the number of turns of the main part M is 10 and the number of turns of the gas outlet port side N is 7 is used, the supply power of 1.0 kW and 10 cc / min of CF ₄ is 99.8%. Can be decomposed with high efficiency.

On the other hand, the spiral coil of Comparative Example F in which the number of turns of the main part M is 10 and the number of turns of the gas outlet side N is 4 or the number of turns of the main part M is 10 and the number of turns of the gas outlet side N is When the spiral coil of Comparative Example G having zero turns is used, the decomposition efficiency when 10 cc / min of CF ₄ is decomposed with a supply power of 1.0 kW is less than 99.0%.

  Moreover, it turns out that decomposition | disassembly efficiency is improved by providing the gas outlet opening side part N from FIG. Furthermore, it can be seen that when the ratio N / M of the number of turns of the gas outlet port side N to the number of turns of the main part M is 0.5 or more, the decomposition efficiency is 99.0% or more. Since the atmospheric pressure plasma abatement apparatus currently used in the market is about 98 to 99%, it can be said that the turn ratio N / M for achieving a decomposition efficiency of 99.0% or more needs to be 0.5 or more.

On the other hand, when the ratio of the gas outlet side N is increased, there is a demerit that the plasma generator is enlarged. If the total length of the apparatus exceeds 2 m, it becomes difficult to carry it into the equipment area of the semiconductor manufacturing factory. Therefore, the length of the plasma part considering the front and rear piping must be within 1.5 m.
Since the length of the main part corresponds to 100 mm, the winding ratio N / M cannot be 15 or more. From the results of FIG. 5, it can be determined that the effect of expanding the winding ratio N / M is gradually reduced, and that a sufficient effect can be obtained when the winding ratio N / M is 1.1 or less.

It is a schematic block diagram which shows an example of the plasma production apparatus of this invention. It is drawing which shows the structure of the matching device used for the plasma production apparatus of this invention. It is a schematic block diagram which shows the example of the principal part of the plasma production apparatus of this invention. 3 is a graph showing the results of Example 1. 10 is a graph showing the results of Example 2.

Explanation of symbols

1 .... Cylindrical reaction vessel, 1a ... Gas inlet, 1b ... Gas outlet, 2 .... Spiral coil, 3. High frequency power supply, 4 .... Matching device, 5 .... Feed electrode, 6 .... Ground Electrode, M ... Main part, L ... Gas inlet side, N ... Gas outlet side

Claims (6)

A spiral coil is wound around a cylindrical reaction vessel having a gas inlet and a gas outlet, and plasma is generated in the cylindrical reaction vessel by applying high-frequency power from a high-frequency power source to electrodes formed at two locations of the helical coil. A plasma generating device that decomposes harmful components in the gas introduced from the gas inlet,
The high frequency ranges from 1 to 100 MHz;
The total number of turns of the helical coil is greater than the number of turns between the two electrodes of the helical coil, and a part of the helical coil is located outside the electrode on the gas outlet side;
L / M is 0.3 or more, where L is the number of turns of the coil existing outside the electrode on the gas inlet side, and M is the number of turns of the coil between the two electrodes. . The number of turns of the coil lying outside of the gas outlet side of the electrode is N, when the number of turns of the coil between the two electrodes was set to M, claim 1, N / M is equal to or not less than 0.5 the plasma generating apparatus according to. The plasma generation apparatus according to claim 2, wherein the N / M is 1.1 or less. The said L / M is 3.2 or less, The plasma generation apparatus of any one of Claim 1 thru | or 3 characterized by the above-mentioned. The plasma generating apparatus according to any one of claims 1 to 4, wherein the helical coil is a prismatic hollow pipe. The plasma generating apparatus according to any one of claims 1 to 5, wherein a gap between the cylindrical reactor and the spiral coil is filled with an insulative and heat-resistant filler.

Images