JPH0436726B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Application of the Invention) The present invention relates to an exhaust gas treatment device that can safely and continuously treat harmful exhaust gas containing a large amount of combustible gas, particularly silane gas, at low running costs. (Prior art and its problems) In recent years, in the semiconductor manufacturing process, so-called CVD, in which a chemically reactive gas is blown into a vacuum reaction chamber and a solid phase alloy film is deposited on a substrate under controlled conditions, has been introduced.
(chemical vapor deposition) process, a deposition process such as a process to form an epitaxial layer with the same crystallinity as the substrate material, and an etching process that intentionally etches a part of the substrate material. Processes such as those in which a reactive gas is introduced into a low-pressure vacuum, in other words, a process in which the gas is introduced onto a substrate and a predetermined reaction energy is applied to carry out a desired gas phase reaction, has become essential. . By the way, many of the CVD and etching processes in the gas phase are often carried out by introducing chemically active gases or gases harmful to the human body, either singly or in combination, as shown in Table 1. . It is also used as an etching gas, for example.
Even if they are safe under normal conditions, such as CF ₄ , NF ₃ , SF ₂ , etc., when exposed to reaction energy in the reaction chamber, some of them thermally decompose into active radicals, resulting in F ₂ , In some cases, gases that are converted into harmful gases such as HF and discharged outside the reaction chamber are used. Therefore, it is strongly required that the harmful gases discharged through the reaction process described above be treated so that their concentration is below the standard value set by law before being discharged into the atmosphere. Therefore, methods such as removal treatment using chemisorption, oxide treatment using combustion, neutralization, and dilution have been developed as means for this purpose. Among these methods, the chemical adsorption method adsorbs harmful gas molecules by passing exhaust gas through an adsorbent layer such as a molecular sieve, and when the maximum adsorption capacity of the adsorbent is reached, a new adsorption layer is immediately added. Switch to and process.

[Table] ** Self: Self-flammable Possible: Flammable Not:
Nonflammability Support: Combustion support The adsorption layer that adsorbs harmful gases is reused by desorbing the adsorbed gas and regenerating it.
In this method, the desorbed harmful gas must be finally reprocessed by a treatment method other than the adsorption method. Therefore, since the processing cost is high and the amount of harmful gas to be processed is limited to a relatively small amount, this method is suitable for small-scale laboratories and cannot be called an industrial method. In addition, the combustion method involves blowing a large amount of air into the gas exhausted from the reaction chamber, for example, using propane gas as a pilot ignition source, mixing it with propane gas and igniting it for forced combustion, and then During natural gas e.g. silicon epitaxial CVD process or amorphous silicon
As in the CVD process, a large amount of silane gas (SiH ₄ , Si ₂ H ₆ , Si ₃ H ₈ , SiH ₂ Cl ₂ ,
For example, if a gas containing SiHCl ₃ (e.g. SiHCl 3) is emitted, if it contains SiH ₄ , it is combusted by mixing with air, and most of the harmful gas is stabilized by the reaction in number [1] in Table 2. This is a method of converting the oxide SiO ₂ into a modified substance, and is often used as the safest and most reliable way to treat large amounts of exhaust gas. However, in a system such as this method in which the oxides of the exhaust gas are precipitated as fine solid powder, as the treatment continues, the exhaust gas from the reaction chamber a is guided to the combustion chamber b, as shown in Figure 1. Oxide powder e gradually accumulates on the inner wall surface of the gas introduction pipe c over a certain length including the combustion opening d, and finally the exhaust gas flows into the introduction pipe c.
The interior is completely filled with a large amount of oxide powder to create a closed state. For this reason, there is a fundamental danger that the gas pressure within the reaction chamber may increase, leading to an unexpected serious accident. Note that f is a high frequency power supply, and g
is a reaction gas supply cylinder, and h is a vacuum pump. Therefore, in exhaust gas treatment equipment using the combustion method, how to prevent the generated solid powder from accumulating in the combustion port or combustion chamber, or how well to remove it is an important factor that determines the reliability of the treatment equipment. It's summery. In addition, the neutralization treatment method converts exhaust gas containing harmful gases led from the reaction chamber into alkali containing NaOH, kOH, etc.

【table】

[Table] Exhaust gas and alkaline hydrolysis are performed using a method called jet cleaning, in which the exhaust gas is thoroughly mixed with the exhaust gas by showering with aqueous lysate solution or submerged in a film of alkaline aqueous solution many times, and then mixed with rapid water flow in a violently turbulent flow. Mix thoroughly with the aqueous solution. For example, as shown in Table 3, harmful gases contained in exhaust gas are converted into water-soluble substances through hydrolysis reactions,
Turns into sludge floating in water.

[Table] The wastewater containing these substances is then passed through a sedimentation tank, an acid-alkali neutralization tank, a CaCO ₃ mixing tank, and a solid-liquid separation process to ensure that the hazardous substances in the final wastewater are below the specified value before being discharged as industrial wastewater. . In addition, sludge separated by mixing precipitated solids with CaCO ₃ is treated as industrial waste by a specialist company, and treatment using this neutralization method is only used as the above-mentioned harmful gas abatement equipment. Rather, it is used as the final stage for general exhaust gas and industrial waste water. Moreover, since this method can be connected to existing industrial wastewater treatment equipment, it is possible to reduce the scale of the equipment attached to the reaction apparatus, so it is usually widely used. However, with this neutralization method, the chemical reaction that eliminates the harmful substances occurs only through contact reaction between the harmful substances in the gas exhausted from the reaction chamber and the alkaline aqueous solution used for hydrolysis treatment. It is difficult to continuously treat this gas to below the specified value for a long period of time. The dilution method mixes a source containing a small amount of harmful substances with a large amount of inert _N2 gas, air, or water. This method dilutes the concentration to below the specified value and then discharges it, and it is a device that does not itself have a detoxification reaction.The devices using each of the above methods vary depending on the nature, amount, exhaust environment, etc. of the exhaust gas. used alone or in combination. For example, the silicon epitaxial CVD mentioned above
When gas containing a large amount of silane gas is exhausted from the reaction chamber side, such as in the process or amorphous silicon CVD process, most of the gas is self-combustible, as shown in Table 1, and can be combusted simply by mixing with air. In the case of silane gas, which is made into harmless SiO ₂ powder and rendered harmless by a good hydrolysis reaction with an alkaline aqueous solution, a combustion method is used, and the remaining harmful silane gas that has not been rendered harmless is converted into an alkaline aqueous solution. A combination with a device for neutralizing with an aqueous solution is used. (Object of the Invention) The present invention aims to combust exhaust gas containing a gas that reacts with air to produce solid fine powder, particularly exhaust gas containing silane gas, which is a self-combustible gas, using the produced fine powder as in the conventional apparatus described above. To provide a treatment facility capable of continuously removing high concentration harmful gases for a long period of time safely, reliably, and at low running cost without clogging the mouth or combustion chamber.
Next, the details will be explained using the drawings. (Means and effects of the present invention for solving the problems) The present invention is characterized by the following points. One is to extend the length of the pipe from the opening at the end of the gas introduction pipe, which is provided to guide the exhaust gas from the reaction chamber into the combustion chamber, over a length or longer where there is a possibility that the produced solid fine powder may be deposited. A large number of shower outlets for washing water are installed in the wall. By continuing to flow washing water from here during the treatment, the fine solid powder is washed away to prevent it from depositing on the inner wall surface of the tube. Also the second
is characterized in that by using an alkaline aqueous solution that undergoes a hydrolysis reaction with silane gas instead of washing water as necessary, the harmful gas caused by combustion is rendered harmless and further rendered harmless. It is something to do. Next, the present invention will be specifically explained using examples. FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the main part thereof. In the figure, 1 is a reaction chamber, and there is a high-frequency power supply 2 for supplying reaction energy.
A cylinder 3 for supplying a reaction gas, a vacuum pump system 4, and the like are connected, and silicon deposition processing is performed by, for example, a CVD method. 5 is an exhaust gas introduction pipe, and its connection part 4a with the vacuum pump 4
has a dilution gas introduction section 6, which prevents ignition and combustion of silane gas due to contact with air at the connection section. Also, the opening end 5a of the exhaust gas introduction pipe 5
For example, over a length of 50 cm over which the produced solid fine powder may be deposited, a large number of shower outlets 7a penetrating the inner wall as shown in FIG.
and a shower outlet 7 having a double pipe structure with outer wall pipes closed at both ends. Then, through the supply pipe 7b of washing water or an alkaline aqueous solution for washing, the exhaust gas introduction pipe 5 is supplied with the washing liquid supplied from a water source (not shown) or from the alkaline aqueous solution circulation pump 12 (described later) as indicated by a * mark in the figure. The inner wall surface is formed so that it can be constantly washed all around. 8 is a shower cleaning chamber which also serves as a combustion chamber, 9 is a combustion air intake provided on one side thereof, 10 is a damper for adjusting the amount of air intake, and the exhaust gas introduction pipe 5 is connected to the shower cleaning chamber 8. has an inclination to
It is fixed within the shower cleaning chamber 8 so that an air intake port 9 is formed around the periphery. The above-mentioned inclination prevents the cleaning water blown onto the inner wall surface of the exhaust gas introduction pipe 5 through the shower outlet 7a from flowing back into the vacuum pump 4 and further into the reaction chamber 1.
Also, the exhaust gas introduction pipe 5 is installed so that the tip opening 5a protrudes into the center of the shower cleaning chamber 8, and the pressure difference between the shower cleaning chamber 8 and the outside air is, for example, about 0.5 kg/cm ² or more. Next, select the exhaust capacity of the blower pump 20, which will be described later, and adjust the damper 10 to adjust the amount of air intake. The pressure inside the exhaust gas introduction pipe 5 is made to have a pressure difference of about 0.3 kg/cm ² or more with respect to that inside the shower cleaning chamber 8. Further, by locating the tip opening 5a of the exhaust gas introduction pipe 5 in the center of the shower cleaning chamber 8, untreated exhaust gas from the exhaust gas introduction pipe 5 can be thoroughly washed with the shower cleaning liquid. The conditions are such that the reaction in Table 2 [1] by combustion of silane gas, for example SiH ₄ , takes place. 11 is an alkaline aqueous solution tank installed at the bottom of the shower cleaning chamber, 12 is its circulation pump,
Reference numeral 13 denotes a shower nozzle, which is in a tank 11 containing an aqueous solution for cleaning by the shower nozzle 13 and a liquid for cleaning the inner wall surface of the exhaust gas introduction pipe 5.
The PH degree is always controlled by a PH meter 14. 15 is a duct, 16 is a gas cleaning packed tower, 17 is an alkaline aqueous solution tank provided at the bottom thereof, 18 is its circulation pump, 19 is a shower nozzle, 20 is a blower pump, 21 is an exhaust port, and tank 17 The PH level of the aqueous solution inside is constantly controlled by a PH meter 22. Then, the unreacted harmful silane gas that has not been completely treated by the combustion reaction described above is brought into contact with alkaline shower cleaning liquid, such as NaOH, from the shower nozzles 13 and 19 in the shower cleaning chamber 8 and the gas cleaning packed tower 16. For example, SiH ₄ gas is converted into a water-soluble substance by the hydrolysis reaction shown in [3] of Table 3, and the tank 11 is
and sludge to be sent to 17 and treated separately,
The treated air is discharged into the atmosphere from the exhaust port 21. (Effects of the Invention) In the apparatus of the embodiment configured as described above, the gas containing a large amount of self-combustible silane gas is evacuated from the reaction chamber 1 by the vacuum pump 4.
The fire did not ignite at the connection between the vacuum pump 4 and the exhaust gas inlet pipe 5, and it came into contact with a large amount of air from the air intake port 9 for the first time in the double pipe section 7 (see Figure 3) where the shower outlet 7a was provided. Inert N ₂ gas, the amount of which is adjusted so that combustion is started, is mixed by the dilution gas introduction section 6 and sent into the exhaust gas introduction pipe 5. On the other hand, the exhaust gas introduction pipe 5 mentioned above
Due to the differential pressure between the inside of the shower cleaning chamber 8 and the inside of the shower cleaning chamber 8, some of the air from the air intake port 9 is transferred from the tip opening 5a of the exhaust gas introduction pipe 5 to the vacuum pump 4 side by 20 to 30 cm, for example.
flow backwards. Therefore, if the exhausted self-combustible silane gas is, for example, SiH ₄ , it will spontaneously ignite upon contact with the air in the double pipe structure 7 including the open end 5a of the exhaust gas introduction pipe 5 and cause the second gas to ignite. The reaction represented by the reaction formula in Table 1 occurs. Therefore, if this is left as it is, powdered SiO ₂ will adhere to the inner wall surface of the exhaust gas introduction pipe 5 near the open end 5a. Especially reaction chamber 1
In the silicon epitaxial CVD process where a large amount of silane gas is flowed from the side, and the amorphous silicon CVD process, a large amount of SiO ₂ powder is deposited.
Finally, the cross section of the open end 5a of the exhaust gas introduction pipe 5 is closed, and the reaction chamber 1 is closed as described above.
This results in extremely dangerous consequences such as increasing the pressure of the reaction gas in the vacuum pump 4 or increasing the back pressure of the vacuum pump 4 and reducing the exhaust capacity. However, in the present invention, as described above, the double shower outlet 7a is provided with a length of approximately 50 cm from the open end 5a of the exhaust gas introduction pipe 5, that is, the length of the backflow of air from the shower cleaning chamber 8. Pipe structure part 7
is provided, and the cleaning liquid is continuously flowed onto the inner wall surface of the exhaust gas introduction pipe 5 while the silane gas is being exhausted, thereby performing shower cleaning. For this reason, the combustion reaction produced
The fine SiO ₂ powder is washed away without giving it time to adhere to the tube wall. Therefore, by appropriately selecting the amount of cleaning liquid blown out from the shower outlet 7a provided in the double pipe structure 7, oxide solids such as SiO ₂ can be continuously generated even at high concentrations. Even in this state, the cross section of the tip opening 5a of the exhaust gas introduction pipe 5 can be reliably prevented from being blocked. Therefore, harmful exhaust gas can be safely and reliably treated without any fear of accidents or problems caused by blockage. In addition, the treatment is not limited to the combustion reaction as in the embodiment apparatus, but the treatment is performed in combination with the hydrolysis reaction, and as a shower cleaning liquid used in the double pipe structure 7 in the combustion reaction treatment process, By using the alkaline aqueous solution produced by the circulation pump 12 used for hydrolysis reaction treatment, harmful gases can be efficiently chemically removed without increasing running costs or complicating treatment equipment and management. It can be processed safely and reliably by turning it into the most stable and harmless substance.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the conventional device, Figures 2 and 3
The figure is an example of an apparatus for implementing the present invention and an explanatory diagram of its essential parts.

Claims (1)

[Scope of Claims] 1. An exhaust gas treatment device that transports exhaust gas containing naturally occurring toxic gases to a combustion chamber through an exhaust gas introduction pipe, mixes it with air, and burns it to treat it as an oxide. A shower outlet for cleaning liquid is provided on the inner wall surface from the tip opening of the introduction pipe to a length where oxides may be deposited.
An exhaust gas treatment device characterized in that the deposition of the oxides is thereby continuously prevented. 2. An exhaust gas treatment device according to claim 1, characterized in that an alkaline aqueous solution that hydrolyzes harmful gas components and converts them into harmless substances is used as the cleaning liquid for the shower outlet.