JPH0334364B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a processing device for removing SiO ₂ dust generated in a semiconductor manufacturing process, particularly in a CVD process.

[Prior art and its problems]

The so-called CVD (Chemical Vapor
Deposition). CVD is thermal decomposition in the gas phase,
Single crystal semiconductors and insulating films (SiO ₂ , Si 3 N 4 , SiO 2 , Si ₃ N ₄ ,
This is a method of growing Al ₂ O ₃ , etc.).

SiO ₂ films are formed by thermal decomposition of silane (SiH ₄ ). Silane gas is introduced into a reaction tube together with a carrier gas, and SiO ₂ is formed through a thermal decomposition reaction, and this is grown on a substrate.

A part of the SiO ₂ produced in the reaction tube adheres to and grows on the substrate, but the excess SiO ₂ is diffused into the atmosphere together with the carrier gas.

SiO ₂ produced by CVD and released into the atmosphere
Since it is a fine dust of less than 30 microns and is not particularly harmful and there are no legal regulations, it has traditionally been dispersed into the atmosphere as is.

However, needless to say, the fact that there are no legal regulations does not mean that it is okay to disperse dust into the atmosphere; it is inherently undesirable to disperse dust into the atmosphere, and if it is left as it is, ,
It is clear that as the productivity of semiconductor devices increases, new dust pollution problems will eventually arise.

The reaction formula of CVD is as follows.

SiH ₄ +PH ₃ +O ₂ Ar base――――――――→ SiO ₂ +P ₂ O ₅ +
H ₂ O where SiH ₄ , PH ₃ and O ₂ are all gases,
SiH ₄ is pyrophoric and PH ₃ is harmful to living organisms. Therefore, the unreacted process gases are diffused into the atmosphere as they are, so there is no guarantee that the emissions are necessarily safe.

In addition, the reaction products SiO ₂ and P ₂ O ₅ are both white dust, and P ₂ O ₅ is hydrophilic and absorbs moisture in the system and becomes sticky. The abundance ratio of SiO ₂ and P ₂ O ₅ is about 9:1, and in any case, it is an important problem to effectively collect the overwhelmingly large amount of SiO ₂ released.

However, due to the stickiness of P ₂ O ₅ , filters, cyclone separators, etc. cannot effectively remove SiO ₂ , and SiO ₂ cannot be treated by washing with water because of its hydrophobic nature.

Incidentally, it is generally known that silicon compounds, as a unique property thereof, easily dissolve even in extremely dilute alkalis by producing silicate ions.

Therefore, in principle, SiO ₂ can also be treated by a wet method using an alkali as an absorbing liquid. However, in practice, a leaking tray tower (wet bubbling tower) is used to remove the gas discharged from the CVD reaction system.
Gas containing fine dust of SiO ₂ is blown into the tower,
When it came into contact with alkaline liquid, it not only had almost no effect, but white dust adhered to the blades and dampers of the blower that transports the air, making the blower inoperable, making it seem impossible to dispose of SiO ₂ dust. I was disappointed.

[Explanation of purpose and principle of the invention]

Therefore, the inventor discovered that the
We investigated the properties of SiO ₂ dust, and since it has an apparent hydrophobicity and a small particle size density, we created an extremely fine mist of alkaline solution and created a solution for this mist.
It was discovered that the SiO ₂ dust could be dissolved in the alkaline solution by violently colliding with the SiO ₂ dust and agitating it, and the SiO ₂ dust could be conveniently agitated during pneumatic transport by using a blower. Therefore, if alkaline liquid is spouted towards the blades of this blower, the impact force caused by the rotation of the blades will turn the alkaline liquid into a mist, allowing SiO ₂ to come into effective contact with this mist, and at the same time cleaning the blades.
Adhesion of SiO ₂ powder can be prevented.

Therefore, if a mist separator is installed after the blower and connected to the wet cleaning tower,
The functions of each stage are differentiated to effectively promote the reaction between the alkaline solution and SiO ₂ and to clean the reaction mist, making it possible to treat SiO ₂ dust, which was previously thought to be a nuisance.

[Structure of the invention]

That is, the present invention is an apparatus for cleaning SiO ₂ dust contained in exhaust gas by wet processing, in which an alkaline liquid jet nozzle is opened toward the blade of a blower that pumps exhaust gas into a wet cleaning tower, and the exhaust gas is The SiO ₂ dust contained in it is transported by air,
The SiO ₂ dust can be easily processed by bringing it into sufficient contact with alkaline liquid mist, promoting the reaction with a mist separator, and thoroughly cleaning with the alkaline liquid supplied into the wet cleaning tower. This is a SiO ₂ dust processing equipment that is characterized by:

[Description of Examples]

Embodiments of the present invention will be described below with reference to the drawings.

In Fig. 1, the apparatus of the present invention includes a circulating water tank 1 filled with alkaline liquid, a wet cleaning tower 2, a blower 3 that sucks gas from the exhaust system of the process and pumps it into the cleaning tower 2, and a mist filled with alkaline liquid. It consists of a separator 4 and an eliminator 6 connected to an exhaust duct 5 of the cleaning tower 2.

Figure 2 shows a flow sheet diagram. The cleaning tower 2, the blower 3, and the mist separator 4 are installed on the circulating water tank 1, and the bottom of the cleaning tower 2 is communicated with the inside of the circulating water tank 1.

Alkaline liquid is sent from the circulating water tank 1 to the blower 3 and the cleaning tower 2 via pumps 9 and 10 and pipes 7 and 8.

Figures 3A and 3B show the structure of the blower 3 used in the device of the present invention. That is, the casing 3 of the blower 3
A spray nozzle 12 is installed inside the air blower, facing the blades 11 of the blower. spray nozzle 1
Reference numeral 2 has a mechanism for ejecting liquid from the gas suction side in the direction of rotation of the blades 11, forming a reaction chamber between the alkali liquid mist and the SiO ₂ dust within the casing 3a. Note that the liquid feeding pipe 7 is connected to the spray nozzle 12 .

Although the type of the blower is not limited in the present invention, a turbo centrifugal blower is preferred since it is necessary to atomize the liquid. A suitable blower is the Fan Scrubber manufactured by Nakajima Seisakusho Co., Ltd.

FIG. 4 shows the structure of the cleaning tower 2 and the mist separator 4.

First, once the dust collected in the mist from the blower 3 passes completely through the alkaline liquid through the mist separator 4, the reaction occurs in a completely different manner than inside the blower 3 in the previous stage. promoted. The cleaning tower 2 is installed above the mist separator 4. At least one perforated plate leakage shelf 13 is installed at regular intervals in the cleaning tower 2, and a liquid sprinkler pipe 14 is installed above the leakage shelf 13. This liquid sprinkler pipe 14 is connected to the liquid sending pipe 8 .

In the case of the present invention, most of the SiO ₂ dust contained in the exhaust gas is collected in mist in the blower 3 and mist separator 4 in the previous stage, so it is recommended to absorb the dust again in the cleaning tower 2. Not what I intended. In short, any material can be used as long as it can wash away the mist that has reacted with SiO ₂ . However, a mere mist separator alone is insufficient. In order to suppress the release of the mist generated in the previous stage and to remove SiO ₂ dust that has not been adsorbed by the mist, a large amount of liquid is supplied to the cleaning tower 2 and passed across the flow path of the exhaust gas containing the mist. It is necessary to form a liquid film or a liquid layer and allow the liquid to pass through it.

An example of the cleaning tower 2 suitable for this purpose is the Moretana tower manufactured by Fuji Kasui Kogyo Co., Ltd. and used in the CMT series exhaust gas treatment equipment. This Moretana tower was developed primarily for the purpose of treating exhaust gases (HCl, H ₂ SO ₄ , HFetc), but SiO ₂
As long as the dust is adsorbed in alkaline mist in advance, SiO ₂ can be removed by cleaning the mist.
The reaction between the alkali and the alkali is effectively promoted and can be effectively used in the apparatus of the present invention. Exhaust duct 5 connected to the top part of cleaning tower 2 in FIGS. 1 and 2
is connected to the eliminator 6, and a return pipe 15 to the circulating water tank 1 is provided in the vertical part before the connection.

Furthermore, for eliminator 6, return piping 16 to circulating water tank 1 and 2 times/day (timer setting)
A liquid supply pipe 17 is provided for supplying industrial water at a rate of .

In the embodiment, the water tank 1 is filled with alkaline liquid, and the alkaline liquid is transferred to the blower 3 by the pumps 9 and 10.
and the inside of the cleaning tower 2, and the operation of the blower 3 is started. The alkaline liquid ejected from the spray nozzle 12 in the blower 3 is struck by the rotating blades 11, accelerated in the circumferential direction by the wind force, and dispersed as a fine mist.

When exhaust gas containing SiO ₂ dust is introduced from the exhaust system of the CVD equipment, the amount of SiO 2 contained in the gas is
The SiO ₂ dust is uniformly mixed with the alkaline liquid mist generated in the casing 3a by the strong stirring force generated by the rotation of the blades 11, and the alkali liquid (NaOH, NaCO ₃ etc.) mist and SiO ₂ dust come into contact with each other. Therefore, SiO ₂ is easily dissolved by the reaction of SiO ₂ +2NaOH→Na ₂ SiO ₃ +H ₂ O or SiO ₂ +Na ₂ CO ₃ →Na ₂ SiO ₃ +CO ₂ . This reaction progresses more easily as the alkaline liquid mist becomes finer, and it will not separate from the mist thereafter.

Through the above reaction, the sodium ions in the alkaline solution are changed into a mist of soluble silicate (Na ₂ SiO ₃ ), which is sent into the mist separator 4 . Inside the mist separator 4 is a balancing pipe 1.
8 is constantly filled with alkaline liquid, and here the reaction is promoted in a completely different manner than in the blower 3 or the washing tower 2. The mist that has absorbed so-called dust will pass through the alkaline solution once, and extremely large mist will be collected here.

The mist not collected by the mist separator is sent into the cleaning tower 2. Alkaline liquid is constantly supplied into the cleaning tower 2, and a liquid film or liquid layer is formed on the leakage shelf 13 of each stage, so the mist and exhaust gas are removed by the wind force of the blower 3 into a liquid layer or a liquid layer. By passing through it, the mist comes into contact with the alkaline liquid, and the mist is absorbed into the liquid film or layer. The alkaline liquid falls onto the leak shelf 13 due to its own weight and is absorbed by the liquid in the water tank 1. The exhaust gas from which the mist has been removed flows out from the cleaning tower 2, is separated into gas and liquid by the eliminator 6, and then diffused into the atmosphere.

As described above, the present invention forms a reaction chamber in the casing of a blower by contacting SiO ₂ with a fine mist of alkaline solution, and
By stirring and mixing SiO ₂ dust with alkaline liquid mist in a blower, the reaction between the alkaline liquid and SiO ₂ can be easily carried out.No special stirring or mixing means are required, and a spray nozzle is provided. By using a blower and a mist separator, the reaction can be carried out during air transport, and the mixture can be immediately fed into the washing tower.

〔Effect of the invention〕

Therefore, according to the present invention, using equipment similar to conventionally known flue gas desulfurization equipment, dust removal equipment, denitrification equipment, etc., it is possible to easily remove SiO ₂ dust, which has been difficult to treat by wet methods. This makes it possible to prevent dust pollution caused by SiO ₂ . Looking at the dust collection rate of SiO ₂ ,
At most 20 to 30 using a single fan or a single cleaning tower
%, whereas the device of the present invention can actually collect 99.5%.

Furthermore, according to the present invention, since SiO ₂ is recovered in the form of Na ₂ SiO ₃ , it is possible to reuse this if necessary.

Furthermore, harmful components contained in the exhaust gas from the CVD equipment can be removed at the same time, and the inside of the blower is constantly cleaned with alkaline liquid, so there is no chance of dust adhering to the rotating blades and making the blower inoperable. .

As described above, according to the present invention, by combining existing equipment, it is possible to achieve an effect that exceeds the ability of each equipment alone, and it is possible to extremely easily process SiO ₂ dust, which has been considered difficult in the past. It is effective.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an embodiment of the device of the present invention;
Fig. 2 is a flow sheet diagram of the device of the present invention, Fig. 3 A is a sectional view of the blower used in the present invention, B is a side view,
FIG. 4 is a longitudinal sectional view of the cleaning tower and the mist separator. 1... Circulating water tank, 2... Wet cleaning tower, 3... Blower, 3a... Casing, 4... Mist separator, 11... Vane, 12... Spray nozzle.

Claims (1)

[Scope of Claims] 1. A device that collects SiO ₂ dust contained in exhaust gas by wet processing, which absorbs gas containing SiO ₂ dust from an exhaust system in a manufacturing process and also contains fine alkaline liquid inside. It is filled with a blower that mainly controls the contact reaction function between SiO ₂ and alkaline liquid while generating mist, and alkaline liquid that passes the exhaust gas sent from the blower.
A liquid film or liquid layer is formed inside the gas flow path by a mist separator that controls the function of promoting the reaction between SiO ₂ and the alkaline liquid, and the alkaline liquid that is constantly supplied. 1. A SiO ₂ dust processing device characterized by having a combination with a wet cleaning tower that controls the function of cleaning and removing mist that has reacted with SiO ₂ in the pumped exhaust gas.