JP2598435B2 - Exhaust gas discharge treatment equipment - Google Patents

Description

The present invention relates to an apparatus for detoxifying exhaust gas by discharge plasma. More specifically, thin film forming technology using vacuum, for example, various chemical vapor deposition methods, that is, reduced pressure CV
D method (Chemical Vapor Deposition), plasma CVD method,
Exhaust gas discharge treatment equipment that detoxifies the reactive gas discharged in the photo-CVD method or plasma etching method from a small amount to a large amount on an industrial scale of semiconductor manufacturing under vacuum decompression by plasma treatment. About.

[Related Art] Reactive gas used in various CVD methods and plasma etching for forming a thin film using a vacuum is not necessarily consumed in a CVD chamber or an etching chamber when the thin film is formed. In some cases, residual or by-product gas was generated. In the process of forming a thin film, the source gas may be directly discharged from the pump without going through CVD or etching. Many of these reactive gases are untreated and can be released into the atmosphere, cause combustion or explosion, or are toxic. ing.

Conventionally, as a method for detoxifying these reactive gases, dilution with a large excess of inert gas, chemical treatment by catalytic reaction, wet absorption and adsorption removal, dry adsorption removal, and the like have been used. All of these methods are performed under normal pressure after the vacuum pump is discharged, and not only have the drawbacks of high equipment costs and operating costs, but also cannot ensure safety if attention is paid to maintenance. Have been reported as some accidents.

On the other hand, as a technique belonging to another system, an exhaust gas treatment method using discharge (discharge treatment method) has been proposed. These are characterized in that the gas to be treated is treated under reduced pressure in vacuum before the gas to be treated is discharged from the pump to the outside of the system.

For example, Japanese Unexamined Patent Publication No. 51-129868 discloses that a waste gas containing a toxic substance and an oxidizing agent are brought into contact with each other in a space where plasma is generated to convert the toxic substance into a stable compound. A method of removing is disclosed. Also, Japanese Patent Application Laid-Open No. 58-6231 discloses a waste gas treatment device which is disposed between a reaction tank for discharging reactive waste gas and a discharge device and decomposes and discharges waste gas by discharge. I have. However, in these discharge treatment methods, the load range capable of maintaining the plasma required for detoxifying the waste gas to a predetermined concentration is naturally limited, and a stable plasma state is maintained against a large load change, particularly, a pressure change. However, there is a problem that the applicable range of the exhaust gas treatment device must be limited.

Furthermore, recently, in the discharge treatment method, a method of using a plasma with a superimposed magnetic field in order to enable load fluctuation tracking (magnetic field superposition method) has been proposed (JSPS Plasma Electronics Research Group, January 1986). ). In the magnetic field superposition method, the direction of the electric field formed by the electrodes is approximately 45 °.
By applying a DC or AC magnetic field at an angle of about 135 °, the turning radius of the electrons in the plasma is reduced, and the electrons can turn between the electrodes. It has the characteristic that a stable discharge can be maintained underneath.

[Problems to be Solved by the Invention] As described above, the discharge treatment method is characterized in that the gas to be treated can be treated under vacuum decompression before the gas is discharged out of the system by a pump. Since the discharge processing device is disposed between the various CVD devices and the etching device and the evacuation pump, in order for this to be practically practical, the discharge processing device should be easily incorporated between such devices. It is required to be as small and energy-saving as possible. To realize this, it is necessary to not only submit the basic concept of simply superimposing and applying a magnetic field to follow load fluctuations, but also to set the optimum configuration and dimensions of the electrodes that generate plasma as an actual device. However, the absolute amount of the exhaust gas discharged from semiconductor improvement is extremely large, and 50
It is not unusual to exceed 0sccm. Generally, there is usually a limit in the amount of the gas to be treated that can be detoxified by the plasma composed of a pair of electrodes.
In order to detoxify such a large amount of gas to be treated, a combination of a plurality of plasmas is required. In this case, a major problem that we have found is that the gas composition in each of the plasmas constituting the exhaust gas treatment system is different, so that the discharge characteristics inevitably behave differently for each plasma. According to the findings experimentally found by the present inventors, for example, in the case of a monosilane gas, the behavior is such that the discharge sustaining voltage increases as the concentration of monosilane in the plasma increases. This means that, for example, when a plurality of electrode pairs are connected in series, as the process proceeds, the gas composition passing through each electrode changes, and the discharge characteristics change significantly. Therefore, fine discharge control for each plasma is required in order to carry out the target processing. In order to perform the control, it is one method to install a separate power supply for each plasma. However, not only does the problem such as enormous equipment and power supply cost increase, but control becomes complicated. It does not necessarily provide a practical form. Therefore, a method for controlling a plurality of plasmas with one power supply is required. However, the above-mentioned prior art does not provide any knowledge on these points, and therefore, there is no actual exhaust gas treatment apparatus that can be put to practical use.

The present inventors have aimed at realizing a discharge processing apparatus that is sufficiently small and energy-saving to be put to practical use,
As a result of diligently studying to solve the above problems, the discharge treatment device is composed of a plurality of pairs of electrodes, and a variable impedance resistor or reactance is connected between one power supply and each cathode or anode, respectively. To control the discharge state by adjusting the voltage applied to each electrode pair, that is, by installing an impedance adjustment circuit between each electrode and the power supply, the control can be performed with one power supply. The present inventors have found that the desired detoxification treatment can be realized even for a large amount of gas to be treated, and have completed the present invention.

[Means for Solving the Problems] That is, according to the present invention, a discharge vessel configured by providing at least a pair of electrodes including a cathode and an anode in a tubular container having a gas inlet and a gas outlet, and the electrode In an exhaust gas discharge treatment apparatus including at least one DC or AC power supply connected to the discharge tube and a gas flow path formed in the discharge tube, a plurality of electrode pairs including the cathode and the anode are provided, and the plurality of electrodes are disposed. An exhaust gas discharge treatment device, wherein an impedance variable or fixed resistor or reactance is connected between each of the cathode or anode constituting the pair and the DC or AC power source, respectively.
Is provided.

 Hereinafter, the present invention will be described in detail.

The target gas to be treated in the present invention is a gas or a vapor that is used in a CVD method or a plasma etching method and may cause some disaster or pollution if released into the atmosphere without treatment. In particular, it is a gas that cannot be easily implemented by a conventional chemical treatment method such as a catalytic reaction or absorption / adsorption. For example, silane-based gases such as monosilane, disilane, and trisilane (these are decomposed into silicon or hydrogenated amorphous silicon and hydrogen by the discharge treatment according to the present invention);
Alkylsilane-based gases such as dimethylsilane (also decomposed into hydrogenated amorphous silicon carbide and hydrogen); Germanic gases (also decomposed into hydrogenated amorphous germane and hydrogen); chlorosilane-based gases; fluorosilane-based gases, etc. No. In addition, the present invention can also be applied to a borane-based gas such as diborane; an alkylborane-based gas such as trimethylboron; and a phosphine-based gas. In these cases, by adding oxygen or the like,
More effective processing is possible. Of course, the gas that can be applied is not limited to the above gases, and may be a mixture thereof, or a gas diluted with hydrogen, nitrogen, and an inert gas.

An exhaust gas discharge treatment apparatus to which the present invention is applied basically has a discharge tube configured by providing at least a pair of electrodes including a cathode and an anode in a tubular container having a gas inlet and a gas outlet. An exhaust gas discharge treatment device including at least one DC or AC power supply connected to the electrode and a gas flow passage formed in the discharge tube,
Any device may be used, and it can be suitably applied to any of the devices described above or used in other known discharge treatment methods. The present invention can also be suitably applied to an exhaust gas apparatus using at least one pair of a cathode pair and an anode pair proposed in another application filed on December 1, 1987 by the present inventors.

In the method for detoxifying exhaust gas using discharge plasma according to the present invention, the main treatment is performed by a dissociation reaction of gas molecules excited by inelastic collision with electrons in the plasma. It is desirable that the rate of the reaction be sufficiently large to achieve the desired processing, and the rate of the reaction is governed by the electron density, the cross section of the dissociation collision between electrons and gas molecules, and the energy distribution function of the electrons. . If a large amount of energy is input to the processing equipment from outside the system, the electron density will increase and the reaction rate will increase.However, if the amount to be processed is large, not only a huge amount of energy input is required but also arc discharge will occur. This makes it difficult to maintain a stable plasma state.

Such a problem is caused by disposing a plurality of electrode pairs including a cathode and an anode, connecting one end of each electrode pair to a gas inlet, and connecting the other end to a gas outlet, dispersing supply power, and applying the power to a pair of electrode pairs. This can be avoided by reducing the required power. The arrangement of the electrode pairs may be basically parallel or serial with respect to the gas flow path (gas flow direction). However, since the processing speed by the plasma is generally a primary reaction with respect to the concentration of the gas to be processed, the series of the electrode pairs may be arranged in series. It is more preferable to arrange the gas flow path and take a long gas flow path. FIGS. 1 and 2 show an example in which a plurality of pairs (here, two pairs) of such electrode pairs are arranged in series. FIG. 1 is a longitudinal sectional view, and FIG.
It is an A 'arrow cross-sectional view. The number of electrode assembly rows may be arbitrarily set depending on the processing amount, pressure, and supply power. At this time, an isolation wall 7 for blocking discharge is provided between the electrode sets arranged in series so as to ensure the independence of each plasma and prevent one plasma from sneaking into the other. Existence is an effective means for avoiding interaction between discharges. It is preferable to use an insulator such as polytetrafluoroethylene for the isolation wall, but this is not always the case depending on the configuration of the electrode set.

Furthermore, when a plurality of pairs of electrodes are arranged, the discharge characteristics of each pair of electrodes are different. Therefore, simply connecting the power supply and the cathode of each pair of electrodes in parallel results in a uniform voltage between both ends of each pair of electrodes. The current is deflected to the electrode pair that forms the plasma having the gas composition having a small sustaining voltage, and it becomes difficult to effectively treat the gas. Here, by connecting a circuit element for adjusting the impedance between the power supply and the cathode or anode of each electrode pair, the current flowing through each electrode pair is arbitrarily controlled, and effective exhaust gas treatment becomes possible.

A more specific example will be described with reference to the drawings.

FIG. 3 is a graph showing the relationship between discharge current I and discharge voltage V of plasmas A and B having different gas compositions. Thus, the electrode pair that forms the plasma having the characteristic of A is A, and the electrode pair that forms the plasma having the characteristic of B is B, and the electrode pairs A and B are controlled in parallel as shown in FIG. Then However, simply connecting to a power supply as shown in FIG. 4 naturally results in the same discharge voltage (V ₀ ) at both electrode pairs A and B, so that FIG. Plasma is X
A current and voltage of the point (I _A, V _0), also plasma electrode B are current-voltage point Y (I _B, V ₀₎ is operated. That is,
Because it is I _A> I _B, current flow polarized in plasma A, therefore, the current flowing through the plasma B is put away smaller,
Effective gas processing becomes difficult.

On the other hand, in the present invention, as shown in FIG. 6, for example, circuit elements R _A and R _B having variable impedance are connected between the electrode pairs A and B and the power supply, and the discharge voltage at each electrode pair is reduced. Each is set arbitrarily. For example, by individually adjusting R _A and R _B so that the discharge voltage at the electrode pair _A becomes V _A and the discharge voltage at the electrode pair B becomes V _B , as shown in FIG. Plasma A is X '
In this respect, the plasma B can be operated at the point Y 'at the same time, and the extreme bias current of the plasma A can be eliminated, and the electric energy in both plasmas can be made substantially equivalent.

This is because, when there is an electrode pair A that forms a plasma having a large sustaining voltage and an electrode pair B having a small voltage, a circuit element having a smaller impedance is provided between the power supply and the cathode or anode of the electrode pair A. By connecting a circuit element having a larger impedance between the power supply and the electrode pair B, the value of the current flowing through both electrode pairs can be controlled, and the amount of power consumed by both electrode pairs can be controlled. It means that.

In the case of a DC power supply, it is preferable that the circuit element employs a variable resistor. In the case of an AC power supply, a variable resistor or a variable reactance may be used, but a reactance is more preferable from the viewpoint of avoiding heat generation in the element. When the composition and the flow rate of the gas to be processed flowing through each electrode are fixed, it is not always necessary to use a circuit element having a variable capacity. May be selected and used. Further, even if the circuit elements are not necessarily controlled for all the electrode pairs, it is possible to achieve the object if at least one is provided, but in fact, for each electrode pair, It is preferable to connect a circuit element with a variable capacitance because the degree of freedom of operation is increased. Furthermore, it goes without saying that the capacitance of the circuit elements is preferably selected to minimize the power consumption in the elements.
Further, the connection position of the circuit element may be between the power supply and the cathode of each electrode pair or between the power supply and the anode.

Further, if desired, superimposing a magnetic field on the electric field formed by the electrodes can reduce the radius of gyration of electrons and maintain the plasma stably over a wide range of pressure conditions and gas composition conditions. This is an effective means, and it is particularly preferable that a magnetic field is applied at an angle of 45 ° to 135 ° with the direction of the electric field formed by the electrode. In this case, the magnetic field may be a DC magnetic field or an AC magnetic field, but a DC magnetic field is more preferable from the viewpoint of continuously performing the plasma reaction. A permanent magnet may be used as the DC magnetic field generator. Reference numeral 3 in FIGS. 1 and 2 denotes a magnetic field applying device provided for such a purpose. Incidentally, 9 is a yoke. The applied surface magnetic flux density is several gauss or more, preferably 100 to 10,000.
It is about Gaussian. The load condition employed in this case is about 0.1 mTorr to 10 Torr.

In the present invention, as described above, a plurality of electrode pairs are preferably arranged in series with respect to the flow direction of the gas to be treated, and a variable impedance circuit element is connected between the electrode pair and a power source, so that each electrode is By adjusting the discharge voltage applied to the pair, a single power supply controls a plurality of plasmas, so that effective treatment of exhaust gas is practiced.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 The apparatus shown in FIG. 1 was used. Width 20cm Length 30cm Thickness
Cathode 1 with a pair of 2mm stainless steel plates facing each other at 2cm intervals
A pair of stainless steel plates having a width of 1.5 cm, a length of 30 cm and a thickness of 2 mm were placed on both sides of the pair of cathodes in a direction perpendicular to the pair of cathodes through a polytetrafluoroethylene resin (trademark: Teflon) 4.
The anode 2 was opposed to each other at an interval of. The two sets of these electrode pairs are placed side by side in a stainless steel vacuum vessel 8 having a capacity of 2 liters having a 2-inch flange for gas introduction and gas derivation, with a Teflon resin plate as an isolation wall 7, and the first set of electrodes One end of the pair is connected to the gas outlet 6, and one end of the second pair of electrodes is connected to the gas outlet 6, so that the gas to be treated is the first.
After flowing in the length direction of the pair of electrode pairs, it flows out along the length direction of the second pair of electrode pairs. Furthermore, from the outside of the container, the surface magnetic flux density
A DC magnetic field was applied by a 500 gauss permanent magnet.

A variable resistor having a maximum of 5 kΩ was connected in series with each of the cathodes of both electrode pairs, and the resistor was connected to one constant power DC power supply. From the gas inlet, 100% monosilane gas was supplied at a flow rate of 200 sccm to form plasma on both electrode pairs. A voltage value between the cathode and anode of each of the electrode pairs of the therapy, that is, a discharge voltage value,
The current value flowing through the cathode, that is, the discharge current value
While measuring with an ammeter, the concentration of monosilane gas at the gas outlet was measured with a quadrupole mass spectrometer.

When the variable resistance connected to each electrode pair was adjusted such that the power consumption of both the first and second electrode pairs was 200 W, the monosilane gas concentration at the gas outlet was 1.2%. At this time, the discharge voltage of the first set is 1.1 kV, the flow of the discharge is 182 mA, and the value of the variable resistor is 0.756 kΩ.
The discharge voltage of the second set is 0.9 kV and the discharge current is 222 m
A, the value of the variable resistor was 1.52 kΩ.

Comparative Example 1 In Example 1, the variable resistance was eliminated, and both electrode pairs were directly connected to a power source to generate plasma under the same conditions. As a result, the discharge voltage of the first set was 0.9 kV, the discharge current was 167 mA, and the discharge voltage of the second set was 0.9 kV, but the discharge current was 389 mA. At this time, arc discharge frequently occurred in the first set of plasmas, and it was difficult to maintain a stable plasma state. Although the sum of the power consumption in both electrode pairs was 500 W, which was larger than that in Example 1, the monosilane gas concentration at the gas outlet was 4.3%, and it became clear that the treatment efficiency was greatly reduced.

[Effects of the Invention] According to the present invention, a flammable gas such as a monosilane gas discharged on an industrial scale in semiconductor manufacturing can be treated at a lower power consumption and a higher treatment rate by a discharge treatment method comprising a plurality of pairs of electrodes. It provides a way to make it happen, and its industrial applicability is extremely large in terms of pollution prevention and disaster prevention.

[Brief description of the drawings]

1 and 2 are sectional views showing an apparatus used in an embodiment of the present invention. FIG. 1 is a longitudinal sectional view, and FIG. 2 is a transverse sectional view taken along the line AA '. . FIGS. 3 and 5 are graphs showing the relationship between the discharge current and the discharge voltage of plasmas A and B, and FIGS. 4 and 6 are circuit diagrams including the electrode pairs and the power supply.

Claims (6)

(57) [Claims] 1. A discharge tube comprising a tubular container having a gas inlet and a gas outlet provided with at least a pair of electrodes comprising a cathode and an anode, and at least one DC or AC power supply connected to the electrodes. And a gas flow path formed in the discharge tube, wherein a plurality of electrode pairs each comprising the cathode and the anode are provided, and each of the cathode or anode constituting the plurality of electrode pairs is connected to the DC An exhaust gas discharge treatment device, wherein a variable impedance or fixed resistor or a reactance is connected to an AC power supply. 2. An exhaust gas discharge processing apparatus according to claim 1, wherein a discharge state is controlled by adjusting a discharge voltage applied to each electrode pair by adjusting each connected impedance. . 3. The method according to claim 1, wherein a plurality of pairs of electrodes are arranged in parallel with the gas flow path, and one end of each pair of electrodes is connected to a gas inlet and the other end is connected to a gas outlet. Exhaust gas discharge treatment equipment. 4. The discharge of exhaust gas according to claim 1, wherein a plurality of pairs of electrodes are arranged in series, and one end of the pair of electrodes is connected to a gas inlet and the other end is connected to a gas outlet. Processing equipment. 5. An exhaust gas discharge treatment apparatus according to claim 1, wherein a magnetic field is superimposed. 6. The direction of the electric field formed by the electrode and the angle of 45 ° to 135 °
The exhaust gas treatment apparatus according to claim 5, wherein a DC or AC magnetic field is applied at an angle of °.