KR20190071265A - Catalytic removal method of NOx and N2O from semiconductor exhausted gas with various pollutants - Google Patents

Abstract

The present invention relates to a catalyst removal method for reducing nitrogen oxide and nitrous oxide in exhaust gas emitted from semiconductor and display manufacturing processes. More particularly, the present invention relates to a removal method in which a pretreatment process and a catalyst process are combined in the presence of various pollutants (acid gas, dust, etc.) contained in the exhaust gas. Through a system in which a wet scrubber and a dust collector are connected in series with a reduction catalyst reactor or decomposition catalyst reactor, and a nitrogen oxide and nitrous oxide removal method using the system, various contaminants can be reduced to maintain catalyst durability and minimize process troubles, thereby providing an integrated treatment process of the exhaust gas.

Description

Technical Field [0001] The present invention relates to a catalyst removal method of NOx and N2O in a semiconductor manufacturing process exhaust gas containing various pollutants,

TECHNICAL FIELD The present invention relates to a catalyst removing method for reducing nitrogen oxide and nitrous oxide in exhaust gas emitted from a semiconductor and a display manufacturing process. More particularly, the present invention relates to a method for removing various pollutants (acid gas, dust, etc.) In which a pre-treatment process and a catalytic process are combined.

As global warming causes serious problems of climate change, interest in greenhouse gases is increasing worldwide. In general, greenhouse gases are classified into non-CO2 greenhouse gases including carbon dioxide and CH4, N2O, PFCs, HFCs, and SF6. N2O gas has a global warming index (GWP) have.

Recently, the use of N ₂ O has been rapidly increasing in the process of manufacturing electronic products such as displays. In general, a semiconductor device is formed by forming a semiconductor film, a conductive film, or an insulating film on a semiconductor substrate, and repeating etching and deposition processes according to the design structure of the semiconductor device. The plasma facility used in the process of forming a thin film and the etching process in the process of manufacturing such a semiconductor device is an essential core facility, which is widely used in a semiconductor manufacturing process, and the same plasma etching equipment is used in a display device such as a liquid crystal display.

In the etching process using the plasma facility, a semiconductor substrate on which a thin film with a predetermined thickness is deposited is loaded into a plasma etching chamber, a reactive gas is supplied to the etching chamber, a high frequency power source is applied to the etching chamber, State. The deposited thin film on the semiconductor substrate is etched by the reactive gas in the plasma state. At this time, by forming the unetched barrier layer selectively on the thin film by the reactive gas in the plasma state, the deposited thin film can be etched in a desired shape and structure. In this plasma process, a perfluorocompound (PFC) such as NF ₃ is used as an etch or a reactive gas. When these reactive gases are discharged after the process, they contain many contaminants such as nitrous oxide.

Particularly, the PFC is a gas widely used as a chamber cleaning agent in an etchant and a chemical vapor deposition process of a semiconductor etching process. Examples of the PFC used in this application include CF ₄ , CHF ₃ , CH ₂ F ₂ , C ₂ F ₄ , C ₂ F ₆ , C ₃ F ₆ , C ₃ F, C ₄ F ₈ , C ₄ F ₁₀ , NF ₃ , SF ₆ and the like can be used and PFC can be used as a cleaning agent, an etching agent, a solvent, a reaction raw material or the like instead of a chloro-fluorocarbon (CFC) A catalyst for decomposing and decomposing a perfluorinated compound in an exhaust gas and a method for decomposing and decomposing a perfluorinated compound in an exhaust gas using the catalyst have been studied in the related art 2004-0024775 published March 22, 2004).

In addition, nitrogen and oxygen contained in the PFC are decomposed at high temperatures and thus a large amount of harmful nitrogen oxides (thermal NOx) can be generated. In addition, dust and acid gas are very likely to be generated in the etching and deposition processes Therefore, it is present in a high concentration in the exhaust gas.

Therefore, in order to apply a catalyst removal method for reducing nitrogen oxides and nitrous oxide in the exhaust gas emitted from the semiconductor and display manufacturing enterprises, unlike the exhaust gas of the chemical and combustion / incineration processes, it is necessary to maintain the durability of the catalyst and minimize the process trouble Therefore, an integrated treatment process capable of reducing various pollutants is required.

Published Japanese Patent Application No. 2004-0024775 (published March 22, 2004)

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst removal method for reducing nitrogen oxide and nitrous oxide in an exhaust gas emitted from a semiconductor and a display manufacturing process, A pretreatment process for effectively reducing oxides and nitrous oxide, and a removal method combined with a catalytic process.

A method for removing nitrous oxide from a exhaust gas discharged from a semiconductor process using a catalyst according to an embodiment of the present invention, which solves the problems of the prior art and the problems to be solved by the present invention, A first step of supplying the gas to the wet scrubber; A second step of supplying exhaust gas having passed through the wet scrubber to the electrostatic precipitator; And a third step of supplying exhaust gas passing through the electrostatic precipitator to a reduction catalyst reactor, wherein ammonia is supplied as a reducing agent to the reduction catalyst reactor.

In the wet scrubber, acidic gas is collected using a basic solution, and in the electrostatic precipitator, water particles are agglomerated and removed through electric charge, and the reduction catalyst reactor preferably includes a zeolite catalyst impregnated with iron ions Do.

The ammonia reducing agent reduces N2O and NOx to nitrogen and oxygen at a temperature of 350 to 400 ° C, and supplies the reduced amount to a reducing catalyst reactor at a molar flow rate of 0.8 to 1.4 times the total molar flow rate of N2O and NOx contained in the exhaust gas .

According to another aspect of the present invention, there is provided a method for removing nitrous oxide from an exhaust gas discharged from a semiconductor process using a catalyst, the method comprising: a first step of supplying the exhaust gas to a wet scrubber; A second step of supplying exhaust gas having passed through the wet scrubber to the electrostatic precipitator; And a third step of supplying exhaust gas passing through the electrostatic precipitator to a decomposition catalytic reactor, wherein the ozone is supplied to the wet scrubber.

In the wet scrubber, using the basic solution acidic gas are collected, and then the NOx is converted to NO2 by the ozone to be supplied, is reduced by reaction with added sodium sulfide (Na ₂ S) supplied to the, in the electrostatic precipitator Water particles are aggregated and removed through electrical charge.

It is preferable that the decomposition catalytic reactor includes a decomposition catalyst obtained by impregnating a support made of an Al2O3-CeZr composite oxide with an aqueous solution of rhodium nitrate.

In another embodiment of the present invention, there is a method of removing nitrous oxide from exhaust gas discharged from a semiconductor process, comprising the steps of: measuring the concentration of nitrous oxide (N ₂ O) in a semiconductor process exhaust gas; And when the concentration of nitrous oxide measured in the first step is less than 200 ppm, the exhaust gas is removed by using a reaction system in which a wet scrubber, a dust collector and a reduction catalyst reactor are connected in series, When the concentration of nitrogen is more than 200 ppm, it is preferable to remove the exhaust gas using a reaction system in which a wet scrubber, a dust collector and a decomposition catalytic reactor are connected in series.

It is possible to effectively reduce nitrogen oxides and nitrous oxide present in various pollutants (acidic gas, dust, etc.) contained in the exhaust gas according to the present invention, and that the wet scrubber and the dust collector are connected in series with the reduction catalytic reactor or the decomposition catalytic reactor The system is able to provide an integrated treatment process of exhaust gas that can reduce various pollutants in order to maintain the durability of the catalyst and to minimize the process trouble through the nitrogen oxide and nitrous oxide removal method using such a system have.

1 is a block diagram showing a N ₂ O / NOx integrated treatment process including a pretreatment process, wherein (A) shows a reduction catalyst process and (B) shows a decomposition catalyst process.
Fig. 2 shows the results of specific N ₂ O / NO x conversion rates depending on the space velocity (10,000 h-1, 15,000 h-1, and 20,000 h-1, open symbol means NO and closed symbol means N ₂ O box).
3 shows the results of measurement of NOx conversion by ozone injection in a wet reduction apparatus.
4 shows the results of measurement of the conversion of N ₂ O before and after ozone injection.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the description, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and should be construed in accordance with the technical concept of the present invention.

Throughout this specification, when a member is "on " another member, this includes not only when the member is in contact with another member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "including" an element, it is understood that it may include other elements as well, without departing from the other elements unless specifically stated otherwise.

The terms "first "," second ", and the like are intended to distinguish one element from another, and the scope of the right should not be limited by these terms. For example, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

The exhaust gas of a semiconductor process, and is to be included back-to thousands ㎍ / m3 dust, acidic gases of several tens ppm in accordance with the process, the discharge of hundreds of ppm N ₂ O and NOx is not certain. Due to the nature of the semiconductor process, the emission concentrations of these contaminants are very variable, and the composition of contaminants is also very diverse.

Among the composition of the exhaust gas, the pollutants that have the greatest influence on the catalytic process include acid gas and dust. Although it does not directly cause short-term problems in the catalytic process, if the long- The activity decreases, and it also acts as a main factor causing various process troubles.

In this way, it is very important to select the pretreatment process to remove various pollutants in the pollutant abatement process for semiconductor exhaust gas.

The present invention proposes a method of using two catalytic processes. As shown in the N2O / NOx integrated treatment process including the pretreatment process shown in FIG. 1 (a), reduction with simultaneous reduction of N2O and NOx using a reducing agent It can be classified into a catalytic process and a decomposition catalytic process using a N2O decomposition catalyst after first removing NOx by wet reduction in a wet scrubber.

These processes use different catalysts respectively, but it is also possible to perform complex parallel operation selectively operating according to the concentration of the exhaust gas supplied as needed. More specifically, for example, nitrogen monoxide and nitrous oxide NO / N ₂ O) is measured in advance, the reduction catalyst process of FIG. 1 (a) is carried out when the concentration of nitrous oxide measured is less than 200 ppm, and when the concentration of nitrous oxide is more than 200 ppm, And the decomposing catalyst process shown in Fig. 1 (b).

In the present invention, in order to maintain the catalyst durability by preventing the problem caused by the acid gas in advance and to prevent the clogging of the catalyst by the dust, the wet scrubber equipped with the electrostatic precipitator Are commonly used. It is preferable that a basic solution such as sodium hydroxide (NaOH or the like) is used and the pH is maintained in the range of 10 to 11 for trapping the acid gas.

Here, the role of the electrostatic precipitator is to additionally remove contaminants that have not been completely removed from the wet scrubber, and perform the function of agglomerating the moisture particles through electric charge so that moisture is not excessively contained in the exhaust gas.

In the case of an integrated treatment process using a reducing catalyst, after the exhaust gas passes through the wet scrubber and the dust collector, the acid gas and dust are removed and supplied (reduced) to the catalytic reactor. In the catalytic reactor, an ammonia reducing agent is supplied, and the reduction reaction proceeds at a reaction temperature of 350 to 400 ° C to reduce N 2 O and NO x to nitrogen and oxygen.

The ammonia reducing agent may be supplied in the range of 0.8 to 1.4, preferably 1.0 to 1.2, and the concentration of N2O and NOx contained in the exhaust gas may be constant It is also possible to control the supply amount of the reducing agent by measuring or monitoring the N2O and NOx concentrations in the front end of the integrated treatment process.

In the case of the integrated treatment process using the decomposition catalyst, the pretreatment process is substantially the same as the reduction catalyst process described above, but further includes a wet reduction process for removing NOx from the wet scrubber.

This is because most of the catalysts used for the decomposition of N2O are very severely deteriorated by NO, and when they are continuously exposed to a high concentration of NOx, the poisoning phenomenon that does not recover the initial catalytic activity occurs. The NOx concentration should be maintained within a minimum of 30 ppm.

Therefore, in the wet reduction process of the present invention, NOx in the exhaust gas is removed in advance through the reactions of the following formulas (1) and (2). As shown in Equation (1), the ozone (O3) radicals generated through the ozone generator are first supplied to the wet scrubber to convert NO contained in the exhaust gas into NO2, and the converted NO2 is converted into sodium sulfide (Na ₂ S) (see equation (2)).

NO + O ₃ ? NO ₂ + O ₂ ????? (1)

2NO ₂ + Na ₂ S? N ₂ + Na ₂ SO ₄ ????? (2)

The sodium sulfide can be dissolved in a wet scrubber aqueous solution and sprayed, and the NOx is reduced through a contact reaction with NO2. Therefore, in the wet reduction process according to the present invention, it is necessary to control the amount of supplied ozone and the amount of supplied sodium sulfide by measuring or monitoring the reduced NOx concentration. Particularly, in the case of sodium sulfide, It is also possible to do.

The exhaust gas after passing through the wet scrubber contains little NOx and other contaminants and is fed to a catalytic reactor with a cracking catalyst. The decomposition catalytic reactor operates at a reaction temperature in the range of 350 to 400 ° C., and the lower the amount of NOx, the lower the reaction temperature.

[ Manufacturing example  1] Preparation of reduction catalyst

In the present invention, the simultaneous reduction catalyst for N ₂ O / NO x used as a reduction catalyst is a zeolite catalyst impregnated with iron ions. After steam pretreatment is performed by supplying water vapor to the zeolite in a nitrogen atmosphere for 0.1 to 2 hours, (Fe (NO ₃ ) ₃ 9H ₂ O) is impregnated with iron ions and dried in air at a temperature of 100 to 120 ° C for 5 to 24 hours, followed by drying at 400 to 600 ° C ≪ / RTI > for 1 to 5 hours.

[ Manufacturing example  2] Preparation of decomposition catalyst

To prepare the Ce-Zr composite oxide, an aqueous solution of cerium nitrate and an aqueous solution of zirconyl nitrate are mixed in the stoichiometric ratio and stirred. Thereafter, the pH of the mixed and stirred aqueous solution is adjusted to 8.0 to 12.0, followed by coprecipitation to form a precipitate. At this time, the pH is adjusted by using a basic solution. NH4OH, NaOH and the like can be used as the basic solution, and ammonia was used in the present example.

When pH is less than 8.0 or more than 12.0, precipitation due to chemical bonding does not occur or there is a problem in crystal growth. Therefore, the pH range is adjusted to a range of 8.0 to 12.0 In the present example, the pH was adjusted to 10.0 using ammonia.

In the course of the preparation of the Ce-Zr complex oxide, the molar ratio of the precursor metal was adjusted to 2: 1 ratio of Ce to Zr, and the initial concentration of each precursor aqueous solution was adjusted to maintain this molar ratio.

When the precipitation occurred after completion of the coprecipitation step, the precipitate produced through the coprecipitation step, that is, the Ce-Zr complex oxide was recovered by washing and filtering a plurality of times.

The recovered Ce-Zr complex oxide was dried at 100 ° C. for 24 hours or more to remove excess water and calcined at 550 ° C. for 4 hours.

The carrier of the decomposition catalyst was prepared by uniformly mixing Ce-Zr complex oxide with γ-Al2O3 after drying and calcination. The alumina used in the preparation of the support may be a mixture of Ce-Zr complex oxide and Boehmite, AlO (OH) 2, It is also possible to prepare a carrier by mixing with a sol, followed by drying and firing.

The carrier was prepared by maintaining the amount of the Ce-Zr complex oxide mixed with alumina or boehmite sol in the range of about 10 wt% in the course of the production of the support. The prepared alumina / Ce- Zr complex oxide carrier was impregnated with an aqueous solution of rhodium nitrate To prepare a decomposition catalyst.

The amount of the rhodium nitrate solution to be supported at this time is preferably adjusted so that the amount of rhodium as a metal impregnated in the catalyst is maintained at 1.0 wt%, and the solution is impregnated with an aqueous solution of rhodium nitrate, followed by drying and firing. The drying and firing conditions were the same as those of the drying and calcination performed in the previous Ce-Zr complex oxide production process. After drying for about 24 hours at about 100 ° C., firing was performed at about 550 ° C. for about 4 hours .

In the present invention, a subsequent experiment was conducted using a simulated exhaust gas having a composition similar to the exhaust gas emitted from the actual electronic industry through a plasma combustion apparatus for burning silane (SiH 4) and an acid gas injection system. These simulated exhaust gases were used to evaluate the performance of each catalytic process according to the present invention.

The concentrations of N2O and NOx were controlled to be in the range of 800 ~ 1,000ppm and 200 ~ 300ppm respectively, and the acid gas (HF, HCl) was supplied in the range of several tens ppm. In addition, the dust was burned by regulating the flow rate of the silane to form a dust concentration of about 300 μg / m 3 in the exhaust gas.

The total flow rate of the simulated exhaust gas was maintained at 10 Nm ³ / hr. The exhaust gas was passed through the wet scrubber and the catalytic reactor sequentially, and the wet scrubber included the electrostatic precipitator at the downstream end.

In the case of a catalytic reactor in which a decomposition catalytic process is performed, an ozone generator is connected to a wet scrubber for removal of NOx, and an aqueous sodium hydroxide solution for acid gas removal and an aqueous sodium sulfide solution for wet oxidation are periodically supplied.

[ Example  One]

Composition of simulated exhaust gas, was conducted under the conditions of 12% O2 plasma to activate the combustion system, particulates and NOx concentration are formed from the combustion of silane was about 300 ㎍ / m ³ and out and 320ppm respectively. In addition, about 35 ppm of HF and about 48 ppm of HCl were added to provide an acidic gas atmosphere, and N 2 O was supplied at a concentration of 850 ppm.

Table 1 below shows the results of confirming the acid gas and dust removal performance by measuring the concentrations of the In and the Out of the wet scrubber. As shown in the following Table 1, the acidic gas showed a removal performance of about 95 to 100%, and the dust concentration was found to be removed by about 95% or more.

division In 1 time In 2 times Out 1 time Out 2 times HF [ppm] 34.57 37.24 0.068 0.086 HCl [ppm] 48.51 48.96 1.38 2.03 Si-based dust [/ / m 3] 310 295 15 12

[ Example  2]

Simultaneous reduction of NOx and N ₂ O was examined with respect to the exhaust gas of Example 1 through the wet scrubber after the reduction catalyst prepared in Preparation Example 1 was installed in a catalytic reactor.

The ammonia reducing agent was supplied at the same mole number as the sum of the NOx and N2O mole ratios, and the experiment was carried out according to the temperature by space velocity. The results are shown in Fig.

2 shows the results of measurement of the conversion of N ₂ O / NO x in the reduction catalytic reactor according to the space velocity. At a space velocity of 10,000 to 15,000 h ^-1 , the conversion was mostly 90% or higher at a temperature of 370 ° C or higher, The catalyst activity was found to be 100% as the temperature became closer to 400 ° C.

When the space velocity was increased to 20,000 h ^{- 1} , the activity decreased by about 20%, but when the reaction temperature reached 400 ° C, the conversion rate decreased and the conversion rate was 90% or more.

In the case of NOx, the catalytic efficiency (that is, the conversion ratio) was almost 100%, regardless of the space velocity, between the measured reaction temperature ranges.

[ Example  3]

After the decomposition catalyst prepared in the above-mentioned Production Example 2 was installed in a catalytic reactor, the N2O reduction characteristic of the exhaust gas passed through the wet scrubber was observed.

In the case of using a decomposition catalytic reactor, ozone of 30 g / h was supplied to a wet scrubber as a pretreatment device through an ozone generator to perform reduction treatment of NOx in the wet scrubber in advance.

Through wet reduction, NOx was removed at a conversion rate close to 100% (see FIG. 3), and the NOx concentration supplied to the catalytic reactor was found to be less than 10 ppm.

4 shows the results of observing the conversion of N ₂ O in the decomposition catalytic process when no NOx removal was performed (O 3 0 g / h) and when NO x removal was performed by supplying ozone (O 3 30 g / h) Respectively.

In the case of the process using the decomposition catalyst, the activity of the catalyst tended to be very low when ozone was supplied and NOx was not removed, and the conversion was 70% lower even at the reaction temperature of 400 ° C. However, when NOx is removed in advance through ozone injection, it shows a 20 ~ 40% improvement in activity over the reaction temperature range of 350 ~ 400 ℃, and a conversion rate of more than 90% .

The present invention is not limited to the above-described specific embodiment and description, and various changes and modifications may be made by those skilled in the art without departing from the scope of the present invention as claimed in the claims. And such modifications are within the scope of protection of the present invention.

Claims (10)

A first step of supplying the exhaust gas to a wet scrubber;
A second step of supplying exhaust gas having passed through the wet scrubber to the electrostatic precipitator; And
And a third step of supplying the exhaust gas passing through the electrostatic precipitator to the reduction catalyst reactor,
Wherein ammonia is supplied as a reducing agent to the reduction catalyst reactor, wherein the catalyst is used to remove nitrous oxide from the exhaust gas discharged from the semiconductor process.
The method according to claim 1,
A method for removing nitrous oxide from a waste gas discharged from a semiconductor process using a catalyst, characterized in that in the wet scrubber, an acidic gas is collected using a basic solution.
The method according to claim 1,
A method for removing nitrous oxide from a exhaust gas discharged from a semiconductor process using a catalyst, wherein the electrostatic precipitator cools and removes water particles through an electric charge.
The method according to claim 1,
Wherein the reduction catalyst reactor comprises a zeolite catalyst impregnated with iron ions, wherein the catalyst is used to remove nitrous oxide from the exhaust gas discharged from the semiconductor process.
The method according to claim 1,
The ammonia reducing agent reduces N2O and NOx to nitrogen and oxygen at a temperature of 350 to 400 ° C, and supplies the reduced amount to a reducing catalyst reactor at a molar flow rate of 0.8 to 1.4 times the total molar flow rate of N2O and NOx contained in the exhaust gas And removing the nitrous oxide from the exhaust gas discharged from the semiconductor process using the catalyst.
A first step of supplying the exhaust gas to a wet scrubber;
A second step of supplying exhaust gas having passed through the wet scrubber to the electrostatic precipitator; And
And a third step of supplying the exhaust gas passing through the electrostatic precipitator to the decomposition catalytic reactor,
Wherein the wet scrubber is supplied with ozone, wherein the exhaust gas discharged from the semiconductor process is removed using a catalyst.
The method according to claim 6,
In the wet scrubber, acidic gas is collected using a basic solution,
After the NOx is converted to NO2 by the ozone to be supplied, to remove the nitrous oxide to the reaction with additional sodium sulfide (Na ₂ S) to be fed into a catalyst from the exhaust gas discharged from a semiconductor process, characterized in that the reduction How to.
The method according to claim 6,
A method for removing nitrous oxide from a exhaust gas discharged from a semiconductor process using a catalyst, wherein the electrostatic precipitator cools and removes water particles through an electric charge.
The method according to claim 6,
Characterized in that the decomposition catalytic reactor includes a decomposition catalyst obtained by impregnating a support made of an Al2O3-CeZr complex oxide with an aqueous solution of rhodium nitrate, and removing the nitrous oxide from the exhaust gas discharged from the semiconductor process Way.
A method for removing nitrous oxide from an exhaust gas discharged from a semiconductor process,
A first step of measuring a concentration of nitrogen monoxide and nitrous oxide (NO / N ₂ O) in a semiconductor process exhaust gas; And
Wherein when the concentration of nitrous oxide measured in the first step is less than 200 ppm, the exhaust gas is treated by the method of any one of claims 1 to 5,
Treating the exhaust gas with a method according to any one of claims 6 to 9 when the concentration of nitrous oxide measured in the first step exceeds 200 ppm. A method for removing nitrous oxide from a discharged exhaust gas using a catalyst.

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