JPH0480723B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [3-1 Field of Industrial Application] The present invention relates to a waste gas treatment device. More specifically, the present invention applies to plasma processing used in the semiconductor industry, such as plasma etching or chemical vapor deposition (CVD).
Waste gas treatment including discharge tubes that perform plasma discharge on gases or vapors in order to detoxify gases or vapors that may cause some kind of pollution if released untreated into the atmosphere in the Deposition method. Regarding equipment. The discharge tube used in the present invention is approximately 10 ^-7
It operates in a wide pressure range from mmHg to about 10 mmHg and can achieve the above detoxification treatment with high efficiency.

[3-2 Prior Art] For example, in the case of manufacturing amorphous silicon solar cells, the raw material silane or disilane is used as it is or diluted with an appropriate gas and decomposed by plasma CVD in a reaction tank to produce amorphous silicon. It becomes a thin film. At this time, the unreacted raw material gas is discharged into the atmosphere by a pump together with the decomposition product hydrogen. Immediately before plasma CVD starts or ends, raw material gas may be discharged without undergoing any reaction in order to adjust the reaction and ensure product uniformity. In addition, phosphine or diborane may be mixed with the raw material gas to form a pn junction. Since all of these gases are toxic, the exhaust gases from pumps have traditionally been treated using chemical methods.

In addition to chemical treatments, electrical treatment methods and treatment devices have also been proposed. For example, JP-A No. 51-
No. 129868 discloses that by bringing a waste gas containing a toxic substance and an oxidizing agent into contact with each other in a space where plasma is generated, the toxic substance is converted into a stable compound, and this compound is removed from the waste gas. Disclosed is a method for treating characteristic waste gas. Furthermore, in Japanese Patent Application Laid-open No. 58-6231, a device is disposed between a reaction tank for discharging reactive waste gas and a discharge device, and the reactive waste gas is decomposed by plasma discharge and discharged by the discharge device. A waste gas treatment device has been proposed that is characterized by:

[3-3 Problems to be solved by the invention] In chemical processing methods, the processing equipment may be larger than the manufacturing equipment, and the plasma
Processing equipment may be required for each device such as CVD or plasma etching, so a small, simple, and effective processing method is desired. On the other hand, the conventional electrical processing method becomes extremely expensive if the same power source used for the plasma reaction tank is used. On the other hand, if cheap direct current or alternating current is used, there will be no discharge at all at pressures below 10 ^-2 mmHg, making it impossible to operate the waste gas treatment device electrically.

[3-4 Means and operation for solving the problems] As a result of intensive research to overcome the drawbacks of electrical waste gas treatment methods, the present inventor found that the electric field and magnetic field in the discharge tube are at an angle of about 45° to about 135°. We have found that if a magnetic field application device is installed so that the electric and magnetic fields intersect, and the waste gas is passed through a space where the electric and magnetic fields intersect, the plasma reaction will proceed efficiently even at a trace concentration of waste gas, and extremely efficient waste gas treatment will be possible. The present invention has been made based on this new knowledge.

That is, according to the present invention, at least one pair of electrodes is provided in a tubular container having a gas inlet and a gas outlet, and the gas inlet and the gas outlet are connected to the discharge tube and the gas outlet through a gas circulation space. In a waste gas treatment device that includes a DC or AC power supply connected to an electrode, the direction of the electric field formed by the electrode in the gas flow space is about 45° to about A magnetic field applying device for applying direct current or alternating current magnetic fields that intersect at an angle of 135° is attached to the discharge tube, and at least the surface of the vessel wall that intersects with the magnetic field lines of the discharge tube container is made of an insulator. A waste gas treatment device is provided.

FIG. 1 shows an example of the basic structure of a discharge tube that constitutes the main part of this waste gas treatment device. Plasma processing such as plasma etching or
Gases or vapors that may cause some kind of pollution if released into the atmosphere untreated in the CVD method, such as silane gases (silane, disilane, trisilane, etc.), borane gases (diborane, etc.), phosphine gases Gases or vapors such as diabetic silicone and its derivatives or organic metals, which are discharged during the manufacture of semiconductor devices, are introduced into the discharge tube through the gas inlet 4. The introduced gas or vapor reaches the gas circulation space 10. In the gas flow space 10, a direct current or alternating current magnetic field 6 is applied which intersects the direction of the electric field formed by at least one pair of electrodes 1 and 2 connected to a direct current or alternating current power source at an angle of about 45 degrees to about 135 degrees. When the gas or vapor is introduced into the space where the electric and magnetic fields intersect, a discharge occurs. This discharge occurs over a wide pressure range from about 10 ^-7 mmHg to about 10 mmHg. Due to this discharge, the above gas or vapor is turned into plasma, and the next reaction takes place. Silane turns into silicone and hydrogen, diborane turns into boron and hydrogen, in the presence of oxygen it turns into boron oxide and hydrogen, phosphine turns into phosphorus oxide and water in the presence of oxygen, silicone fluoride turns into silicone and calcium fluoride, Organometallics change into water, carbon dioxide, and metal oxides in the presence of oxygen. Generated hydrogen, water vapor, carbon dioxide gas, etc. are discharged from the gas outlet 5 as safe gas or steam. Solid products such as silicone, boron, boron oxide, boron nitride, and phosphorus oxide are deposited within the discharge tube, particularly near the electrodes or on the inner walls. When the atmospheric pressure is low, it is deposited on the inside of the vessel wall 3 on both sides of the cathode, but when the atmospheric pressure is high and a glow is formed on the outside of the anode, it is also deposited on the vessel wall near the glow. Also, when the gas flow rate is increased, much more deposition is observed on the downstream side of the gas flow than on the upstream side of the plasma region. This indicates that radicals generated within the plasma are carried downstream and deposited under the influence of air currents. The deposited solid product can usually be removed from the tube using known means. For example, the easiest method is to cover the electrode surface with a metal foil such as aluminum foil and cover the other parts with an insulating film, and replace these as appropriate. It is also possible to construct the discharge tube so that it can be easily disassembled and to disassemble and clean it at appropriate intervals. Furthermore, it is also possible to apply mechanical vibration to the outer wall of the discharge tube and the electrodes to cause the solid products to fall downward and collect and remove them outside the space near the discharge. In order to facilitate cleaning inside the pipe, the inner wall surface may be covered with a vinyl film and the film may be replaced as appropriate. By the above-described method, gases or vapors which may cause some pollution if released into the atmosphere while still being treated are rendered harmless.

The tubular container used in the present invention does not need to be cylindrical as seen in ordinary discharge tubes, but can have an arbitrary cross section,
For example, containers of triangular or rectangular cross section can also be used. The electric field may be of any magnitude as long as it starts a discharge. This value varies widely depending on the type of gas to be treated, gas pressure, electrode spacing, etc. It only needs to be large enough to generate plasma. The potential between the electrodes to obtain the preferred electric field magnitude is typically about 10V or higher. Any DC power source, single-phase AC power source, or multi-phase AC power source can be used.From the standpoint of performing a plasma reaction continuously, that is, from the standpoint of avoiding the possibility of gas being discharged untreated, a DC power source or a multi-phase AC power source can be used. Preferably, a polyphase AC power source is used. Although the spacing between the electrodes is not critical, it is generally preferable that the spacing between the electrodes be larger than the radius of gyration r of electrons determined by the following equation using the magnetic flux density B.

However, V: kinetic energy of the electron perpendicular to the magnetic field (electron volt) m: weight of the electron e: charge of the electron The magnitude of the required magnetic field varies depending on the electrode spacing and applied voltage. The magnetic flux density B may be one that satisfies the following formula.

However, d: electrode spacing V, m, e: as described above.

The magnitude of the magnetic field is generally preferably several Gauss or more, and more preferably in the practical range of about 100 to about 500 Gauss. The magnetic field applying device may be an electromagnet or a permanent magnet. Any of a DC magnetic field application device, a single-phase AC magnetic field application device, and a multi-phase AC magnetic field application device can be used, but from the standpoint of performing a plasma reaction continuously, in other words, it is possible for gas to be discharged untreated. It is preferable to use a direct current magnetic field applying device or a multiphase alternating current magnetic field applying device from the viewpoint of avoiding problems. In the present invention, at least the surface of the portion of the wall of the discharge tube that intersects with the lines of magnetic force is made of an insulator. If the part of the vessel wall that intersects with the magnetic field lines is conductive, the loss of electrons will increase and the efficiency of waste gas treatment will decrease. In one preferred embodiment of the present invention, the wall of the discharge tube is made of a conductive material and also serves as an electrode, and the portion that intersects with the lines of magnetic force is covered with an insulating film.
Further, a gas to be treated can be made to coexist with a gas to be treated, such as oxygen or nitrogen, which stabilizes the discharge and/or facilitates the separation of solid substances generated as the gas becomes plasma. For this purpose,
Preferably, the discharge vessel is provided with an additional gas inlet.

Plasma is a state of ionization caused by electrical discharge, and the temperature of plasma varies depending on the gas pressure, type of gas, etc. Plasma energy starts from 1eV
It is in the range of about 10eV. The time during which the gas or vapor introduced through the gas inlet undergoes a plasma reaction under the action of the intersecting electric and magnetic fields varies depending on the gas flow rate and discharge power. That is, if the discharge power is increased, this time can be shortened, and if the discharge power is kept constant and the flow rate is increased, this time needs to be lengthened. The relationship between flow rate and discharge current is shown in FIG. The time period typically ranges from about 0.01 seconds to about 5 minutes. An example of the gas density of plasma is shown in FIG. This depends on the size of the device. In general, there is a proportionality law in discharge, and if the product pd of gas pressure p and inter-electrode distance d is constant, the discharge state will be similar. Therefore, if p is made smaller, d can be made larger.

The usage of this waste gas treatment device is diverse. One specific example is shown in FIG. This waste gas treatment equipment 1
2 and 13 are plasma processing (plasma
CVD or plasma etching) reaction tank 1
1 and the exhaust pump 14. A switching valve 16,1 is provided to facilitate cleaning of the processing equipment.
7. It is also possible to arrange a cylinder 15 for supplying a gas that stabilizes the discharge and/or facilitates the splitting of the solid material produced by turning the gas into plasma.

In order to ensure that the plasma reaction takes place, the discharge tube used in the present invention has a gas inlet between opposing electrodes, or the outer wall of the gas transport or discharge tube is one electrode, and the inside Either provide a structure in which the gas flow path always passes between opposing electrodes by providing another pole, or have a structure in which the distance between the outer wall that is not an electrode and the outermost part of the electrode is one mean free path or less. It is preferable to design it as follows. Specific examples of the method of generating the necessary magnetic field and the shape of the electrodes in this waste gas treatment apparatus are shown in FIGS. 6 to 10. In the figure, 7 is a permanent magnet, 8 is an electromagnet, and 9 is an insulating film. The discharge tube can be quickly cleaned by depositing solid products on the insulating film and replacing it. When using alternating current for discharge, as illustrated in Figure 10, three-phase alternating current is used to ensure that there is no time when the current is zero in the processing equipment, thereby preventing insufficient processing. The release of gas is prevented.

[3-5 Effects of the Invention] According to the present invention, a small, simple, efficient, and economical waste gas treatment device is provided. The discharge tube used in the present invention can discharge even at low pressures of 10 ^-2 mmHg or less and can stimulate the plasma reaction of waste gas. Therefore, the waste gas treatment apparatus of the present invention can render even trace amounts of waste gas harmless extremely efficiently.

[3-6 Example] FIG. 4 shows the voltage/current characteristics when a magnetic field of 480 Gauss is applied to cause a discharge using the discharge tube shown in FIG. 2. It was confirmed that discharge occurred even when the flow rate of silane gas was sufficiently low. At this time, if the magnetic field is removed, the discharge cannot be maintained. The relationship between the flow rate of the gas to be treated and the required current is as shown in FIG. It was observed that amorphous silicon was deposited near the electrodes and on the inner wall of the vessel due to silane gas plasma treatment. In addition, confirmation that this treatment is complete can be made by observing the silane spectrum with a spectrometer (Nikon G-500), measuring the change point of the discharge characteristics, and checking whether the white powder of silicon oxide is no longer present in the gas released into the air. I decided to do it depending on whether or not it occurred.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the basic structure of a discharge tube used in this waste gas treatment apparatus, and FIG. 2 shows the structure and dimensions of the discharge tube used when testing the effectiveness of the present invention. FIG. 3 shows a method of using the waste gas treatment apparatus of the present invention. FIG. 4 shows the discharge characteristics of nitrogen and silane. FIG. 5 shows the relationship between throughput and required current.
FIGS. 6 to 10 show specific examples of this waste gas treatment apparatus. FIG. 10 shows a wiring method when three-phase alternating current is used for discharge. In each figure, reference numbers represent the following: 1, 2: electrode, 3: discharge tube wall, 4: gas inlet, 5: gas outlet, 6: magnetic field lines, 7: permanent magnet, 8: electromagnet, 9: insulating film, 10: gas circulation space, 11: plasma processing reaction tank, 12, 13: main waste gas treatment device, 14: exhaust pump, 15: gas supply cylinder, 16, 17: switching valve.

Claims (1)

[Scope of Claims] 1. A discharge tube and the electrode, in which at least one pair of electrodes is provided in a tubular container having a gas inlet and a gas outlet, the gas inlet and the gas outlet being connected by a gas circulation space. In a waste gas treatment device including a DC or AC power supply connected to the gas inlet, the direction of the electric field formed by the electrode in the gas flow space is approximately 45° to approximately 135 A magnetic field applying device for applying direct current or alternating current magnetic fields that intersect at an angle of . Waste gas treatment equipment. 2. The processing apparatus according to claim 1, wherein the electrodes are arranged at intervals larger than a radius of gyration r of electrons determined by the magnetic flux density B of the applied magnetic field. 3. The processing device according to claim 1 or 2, wherein the power source is a DC power source, and the magnetic field application device is a DC magnetic field application device. 4. The processing device according to claim 1 or 2, wherein the power source is a multiphase AC power source, and the magnetic field application device is a DC or multiphase AC magnetic field application device. 5. Claims 1 to 4, characterized in that the wall of the discharge tube also serves as an electrode and is made of a conductive material, and the inner surface of the wall is covered with an insulating film. The processing device according to any one of the above. 6. The vessel between the discharges has an additional gas inlet through which a gas is introduced which stabilizes the discharge and/or facilitates the separation of the solid material produced by the plasmaization of the gas. Claim 1 characterized in that it is configured as follows.
5. The processing device according to any one of items 5 to 5.