KR102016751B1 - 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 oxides and nitrous oxides in exhaust gases emitted from semiconductor and display manufacturing processes, and more particularly, to remove various pollutants (acid gases, dusts, etc.) contained in exhaust gases. The present invention relates to a removal method in which a pretreatment process and a catalyst process are combined in the presence of the present invention, and a wet scrubber and a dust collector are connected in series with a reduction catalyst reactor or a decomposition catalyst reactor, and the durability of the catalyst through nitrogen oxide and nitrous oxide removal methods using such a system. It is an advantage to provide an integrated treatment process of exhaust gas that can reduce various pollutants in order to keep the process and minimize process troubles.

Description

Catalytic removal method of NOx and N2O from semiconductor exhausted gas with various pollutants}

The present invention relates to a catalyst removal method for reducing nitrogen oxides and nitrous oxides in exhaust gases emitted from semiconductor and display manufacturing processes, and more particularly, to remove various pollutants (acid gases, dusts, etc.) contained in exhaust gases. The present invention relates to a removal method in which a pretreatment process and a catalytic process are combined in the presence.

As the problem of climate change caused by global warming is getting serious, interest in greenhouse gases is increasing worldwide. In general, greenhouse gases are divided into carbon dioxide and non-CO2 greenhouse gases including CH4, N2O, PFCs, HFCs, SF6, etc. N2O gas has a very high global warming index (GWP) of 310 times compared to CO2. have.

Recently, the amount of N ₂ O is rapidly increasing in the process of manufacturing electronic products such as displays. In general, a semiconductor device forms a semiconductor film, a conductive film, or an insulating film on a semiconductor substrate, and the various types of films are manufactured by repeating etching and deposition processes according to the design structure of the semiconductor device. In the semiconductor device manufacturing process, the plasma equipment used for the thin film formation process and the etching process is an essential core equipment, and is widely used in the semiconductor manufacturing process, and the same plasma etching equipment is used in display devices such as liquid crystal displays.

In the etching process using the plasma apparatus, the semiconductor substrate on which a thin film having a predetermined thickness is deposited is loaded into a plasma etching chamber, and then a reaction gas is supplied to the etching chamber, and a high frequency power is applied to the etching chamber to plasma the reaction gas. To be in a state. The deposited thin film on the semiconductor substrate is etched by the reaction gas in the plasma state. At this time, by selectively forming a barrier layer not etched by the reaction gas in the plasma state on the thin film, the deposited thin film can be etched in a desired shape and structure. In such a plasma process, a perfluorine compound (PFC) such as NF ₃ is used as an etching or reaction gas, and when these reaction gases are discharged after the process, they include many pollutants such as nitrous oxide.

In particular, the PFC is a gas widely used as an etchant in a semiconductor etching process and a chamber cleaner in a chemical vapor deposition process. PFCs used for this purpose 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 may be used, and even in the case of a semiconductor process, PFC may be used for the purpose of a cleaner, an etchant, a solvent, a reaction material, or the like by replacing chloro-fluorocarbon (CFC), which is conventionally used. It can be included in the exhaust gas discharged from the manufacturing process and the workplace, the catalyst for the decomposition and removal of perfluorinated compound in the exhaust gas and the method of decomposing and removing the perfluorinated compound in the exhaust gas using the prior art has been studied. 2004-0024775: published March 22, 2004).

In addition, nitrogen and oxygen included in the PFC react with each other at high temperature to generate a large amount of harmful nitrogen oxides (thermal NOx), as well as a lot of dust and acid gases in the etching and deposition process. As a result, they are present at high concentrations in the exhaust gas.

Therefore, in order to apply a catalyst removal method that reduces nitrogen oxides and nitrous oxide in exhaust gases emitted from semiconductor and display manufacturing facilities, unlike catalyst exhaust gas in chemical and combustion / incineration processes, it is necessary to maintain catalyst durability and minimize process troubles. This requires an integrated treatment process that can reduce various contaminants.

Publication No. 2004-0024775 (published March 22, 2004)

The present invention relates to a catalyst removal method for reducing nitrogen oxides and nitrous oxides in exhaust gases emitted from semiconductor and display manufacturing processes. The present invention relates to nitrogen present with various contaminants (acid gases, dust, etc.) contained in exhaust gases. In order to effectively reduce oxides and nitrous oxide, there is provided a removal method combining a pretreatment process and a catalytic process.

The method for removing nitrous oxide using a catalyst from the exhaust gas discharged from the semiconductor process according to an embodiment of the present invention for solving the problems of the background technology described above and the problem to be solved in the present invention, the exhaust Supplying a gas to the wet scrubber; Supplying the exhaust gas passing through the wet scrubber to an electric dust collector; And a third step of supplying the exhaust gas passing through the electrostatic precipitator to a reduction catalyst reactor, wherein the reduction catalyst reactor is supplied with ammonia as a reducing agent.

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

The ammonia reducing agent reduces N 2 O and NO x to nitrogen and oxygen at a temperature of 350 to 400 ° C., and supplies it to a reduction catalyst reactor at a molar flow rate of 0.8 to 1.4 times the total mole flow rate of N 2 O and NO x contained in the exhaust gas. More preferably.

According to another embodiment of the present invention, a method for removing nitrous oxide using a catalyst from exhaust gas discharged from a semiconductor process includes: a first step of supplying the exhaust gas to a wet scrubber; Supplying the exhaust gas passing through the wet scrubber to an electric dust collector; And a third step of supplying the exhaust gas passing through the electrostatic precipitator to the decomposition catalyst reactor, wherein the wet scrubber is supplied with ozone.

In the wet scrubber, the acid gas is collected using a basic solution, NOx is converted to NO2 by ozone supplied, and then reacted with sodium sulfide (Na ₂ S) to be further supplied to reduce the amount. Moisture particles aggregate and are removed by electrical charge.

The decomposition catalyst reactor preferably includes a decomposition catalyst obtained by impregnating a rhodium nitrate aqueous solution with a carrier made of an Al 2 O 3 -CeZr composite oxide.

Another embodiment of the present invention includes a method for removing nitrous oxide from the exhaust gas discharged from the semiconductor process, the first step of measuring the concentration of nitrous oxide (N ₂ O) in the 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 using a reaction system in which a wet scrubber, a dust collector, and a reduction catalyst reactor are connected in series, and the nitrous oxide measured in the first step is 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 catalyst reactor are connected in series.

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

1 is a block diagram showing an N ₂ O / NO x integrated treatment step including a pretreatment step, (A) shows a reduction catalyst step, and (B) shows a decomposition catalyst step.
2 is a specific result of the N ₂ O / NOx conversion rate according to the space velocity (10,000h-1, 15,000h-1, 20,000h-1, open symbol is NO, closed symbol means N ₂ O box).
3 is a result of measuring the NOx conversion rate by ozone injection in the wet reduction device.
4 is a result of measuring the N ₂ O conversion rate before and after ozone injection.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to ordinary or dictionary meanings, but should be construed as meanings and concepts corresponding to the technical spirit of the present invention.

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

Throughout this specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless otherwise stated.

Terms such as "first" and "second" are intended to distinguish one component from another component, and the scope of rights should not be limited by these terms. For example, the first component may be named the second component, and similarly, the second component may also be named the first component.

The exhaust gas of the semiconductor process contains hundreds to thousands of μg / m3 of dust and tens of ppm of acidic gases, depending on the process, and several hundred ppm of N ₂ O and NOx are emitted in an uneven manner. Due to the nature of the semiconductor process, the emission concentrations of these pollutants are very variable, and the composition of the pollutants also varies widely.

Contaminants which have the greatest influence on the catalytic process in the composition of these exhaust gases include acid gases and dusts, which do not directly cause problems in the catalytic process in the short term. Activity is inferior and may act as a major factor causing troubles in various processes.

As such, the selection of a pretreatment process for removing various pollutants is very important in the pollutant reduction process for semiconductor exhaust gases.

In the present invention, a method using two catalytic processes is proposed, and as shown in the N2O / NOx integrated treatment process including the pretreatment process shown in FIG. 1 (a), reduction of N2O and NOx simultaneously using a reducing agent is performed. After the NOx is first removed by the wet reduction in the catalytic process and the wet scrubber, it can be divided into a decomposition catalyst process using an N 2 O decomposition catalyst.

Each of these processes uses a different catalyst, but it is also possible to have a combined parallel operation, which is selectively operated according to the concentration of the exhaust gas supplied as needed. More specifically, for example, nitrogen monoxide and nitrous oxide in the semiconductor process exhaust gas ( After the concentration of NO / N ₂ O) is measured in advance, when the measured concentration of nitrous oxide is less than 200 ppm, the reduction catalyst process of FIG. 1 (a) is carried out. It may be a method of treatment through the decomposition catalyst process shown in Figure 1 (b).

In the present invention, in order to block the problems caused by acidic gas in advance to maintain catalyst durability and to prevent catalyst clogging due to dust, both the aforementioned reduction catalyst process and the decomposition catalyst process are wet scrubbers equipped with electrostatic precipitators. Will be used in common. For the collection of acidic gas, it is preferable to use a basic solution such as sodium hydroxide (NaOH, etc.) and maintain the pH in the range of 10-11.

In addition, the role of the electrostatic precipitator here serves to further remove contaminants that are not completely removed from the wet scrubber, and to aggregate 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 reduction catalyst, after the exhaust gas passes through the wet scrubber and the dust collector, the acid gas and the dust are removed and fed to the (reduction) catalyst reactor. In the catalytic reactor, an ammonia reducing agent is supplied, and a 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 a ratio of the sum of the number of moles of N 2 O and NO x 0.8 to 1.4, preferably in the range of 1.0 to 1.2, the concentration of N 2 O and NO x contained in the exhaust gas is constant In the case of no emissions, it is also possible to control the supply of reducing agent by measuring or monitoring the N2O and NOx concentrations in front of the integrated treatment process.

In the case of an integrated treatment process using a decomposition catalyst, the pretreatment process is almost 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 N2O decomposition are severely degraded due to NO, and the continuous exposure to high concentrations of NOx causes poisoning that does not restore the initial catalytic activity. Exhaust gases should be kept at a minimum of 30 ppm.

Therefore, in the wet reduction process of this invention, NOx in waste gas is removed beforehand by reaction of following formula (1) and (2). As confirmed by Equation (1), the ozone (O3) radicals generated through the ozone generator are first supplied to the wet scrubber to convert all the NO contained in the exhaust gas to NO2, and the converted NO2 is additionally supplied with sodium sulfide It is reduced through reaction with (Na ₂ S) (see Formula (2)).

NO + O ₃ → NO ₂ + O ₂ Formula (1)

2NO ₂ + Na ₂ S → N ₂ + Na ₂ SO ₄ Formula (2)

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

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 cracking catalytic reactor operates in the range of 350 to 400 ° C., and the more the NOx amount is minimized, the lower the reaction temperature can be.

[ Production Example  1] Preparation of Reduction Catalyst

The N ₂ O / NOx simultaneous reduction catalyst used as a reduction catalyst in the present invention is a zeolite catalyst impregnated with iron ions, and is subjected to water pretreatment by supplying water vapor to a zeolite in a nitrogen atmosphere for 0.1 to 2 hours, followed by water pretreatment. The zeolite was impregnated with iron ions using iron nitrate hydrate (Fe (NO ₃ ) ₃ 9H ₂ O), dried in air at a temperature of 100-120 ° C. for 5 to 24 hours, and then 400-600 ° C. It was prepared through a step of firing for 1 to 5 hours at a temperature of.

[ Production Example  2] Preparation of Decomposition Catalyst

To prepare a Ce-Zr composite oxide, an aqueous solution of cerium nitrate (Cerium nitrate) and an aqueous solution of zirconium nitrate (Zirconyl nitrate) are mixed to a stoichiometric ratio and then stirred. Thereafter, the pH of the mixed and stirred aqueous solution is adjusted to 8.0 to 12.0 to undergo a coprecipitation step to form a precipitate. At this time, the pH is adjusted by using a basic solution. As the basic solution, NH 4 OH, NaOH, and the like may be used, and ammonia was used in this preparation.

In this coprecipitation step, it is very important to control the pH. If the pH is less than 8.0 or more than 12.0, precipitation of chemical bonds does not occur or there is a problem in crystal growth. In this preparation example, the pH was adjusted to 10.0 using ammonia.

In the manufacturing process of the Ce-Zr composite oxide, the ratio of Ce and Zr was 2: 1 to adjust the molar ratio of the precursor metal, and the initial concentration of each precursor aqueous solution was adjusted to maintain the molar ratio.

When the co-precipitation step is completed and precipitation occurs, the precipitate prepared through the co-precipitation step, that is, Ce-Zr composite oxide, is recovered through plural times washing and filtration.

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

Ce-Zr composite oxide, which was dried and calcined, was uniformly mixed with γ-Al 2 O 3 to prepare a carrier for the decomposition catalyst. The alumina used in the preparation of the carrier is in the form of γ-Al2O3, and the powder of γ-Al2O3 can be simply mixed with Ce-Zr composite oxide, but the Ce-Zr composite oxide is boehmite (Boehmite, AlO (OH)). It is also possible to prepare the carrier by mixing with the sol and then drying and calcining.

During the preparation of such a carrier, the amount of Ce-Zr composite oxide mixed with alumina or boehmite sol was maintained in the range of about 10 wt% to prepare a carrier, and the alumina / Ce-Zr composite oxide carrier was impregnated with an aqueous solution of rhodium nitrate. To prepare a decomposition catalyst.

At this time, the amount of the rhodium nitrate solution supported is preferably controlled to maintain the amount of rhodium, which is a metal impregnated in the catalyst, to 1.0wt%. After the rhodium nitrate solution is impregnated, the drying and firing steps are performed. At this time, the drying and firing conditions are the same as the drying and firing conditions carried out in the previous Ce-Zr composite oxide manufacturing process, after drying for about 24 hours at about 100 ℃, firing was performed at about 550 ℃ for about 4 hours. .

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

N2O and NOx concentrations were adjusted to form in the range of 800 ~ 1,000ppm and 200 ~ 300ppm, respectively, acidic gas (HF, HCl) was supplied in the range of several tens of ppm. In addition, dust was combusted by adjusting the flow rate of the silane so that dust concentrations of about 300 µg / m3 were formed in the exhaust gas.

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

In the catalytic reactor in which the decomposition catalytic process is performed, an ozone generator is connected to a wet scrubber for removing NOx, and an aqueous sodium hydroxide solution for removing acid gas and an aqueous sodium sulfide solution as a wet reducing agent are installed periodically.

[ Example  One]

The composition of the simulated exhaust gas was carried out under the condition of 12% O2 by operating the plasma combustion system, and the dust and NOx concentrations formed by the combustion of silane were about 300 µg / m ³ and 320 ppm, respectively. In addition, in order to create an acid gas atmosphere, HF was injected at about 35 ppm, HCl was injected at about 48 ppm, and N 2 O was supplied at a concentration of 850 ppm.

Table 1 below summarizes the results of confirming the acid gas and dust removal performance by measuring the concentration of the front (In) and the rear (Out) of the wet scrubber. As shown in Table 1 below, the acid gas showed a removal performance of almost 95 to 100%, and the dust concentration was found to be about 95% or more removed.

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 [㎍ / ㎥] 310 295 15 12

[ Example  2]

After mounting the reduction catalyst prepared in Preparation Example 1 in the catalytic reactor, the characteristics of simultaneous reduction of NOx and N ₂ O with respect to the exhaust gas of Example 1 passed through a wet scrubber.

The ammonia reducing agent was supplied in the same mole number as the sum of the NO x and N 2 O molar ratios, and the experiment was performed according to the temperature for each space velocity, and the results are shown in FIG.

2 is a result of measuring the N ₂ O / NOx conversion rate in the reduction catalyst reactor according to the space velocity, the space rate 10,000 ~ 15,000h ^-1 shows a conversion rate of more than 90% at a temperature of 370 ℃ or more, the reaction temperature is As the temperature approached 400 ° C., the catalytic activity was converted to 100%.

When the space velocity increased to 20,000 h ^{- 1} , a decrease in activity of about 20% was observed. However, when the reaction temperature reaches 400 ° C, the decrease in conversion was reduced, indicating a conversion rate of 90% or more.

In addition, the NOx exhibited a high catalytic efficiency (i.e., conversion rate) of almost 100% regardless of the space velocity in the measured reaction temperature range.

[ Example  3]

After the decomposition catalyst prepared in Preparation Example 2 was attached to the catalytic reactor, the N 2 O reduction characteristics of the exhaust gas passed through the wet scrubber were observed.

In the case of using a decomposition catalytic reactor, 30 g / h of ozone was supplied to a wet scrubber as a pretreatment apparatus through an ozone generator, and NOx was previously reduced in a wet scrubber.

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

Figure 4 shows the results of observing the N ₂ O conversion rate of the decomposition catalyst process in the case of not performing the removal of NOx (O3 0g / h) and when the removal of NOx by performing ozone (O3 30g / h) Shown.

In the case of using a decomposition catalyst, when the ozone is not supplied to remove NOx, the activity of the catalyst tended to be very low, and the conversion was about 70% lower even at the reaction temperature of 400 ° C. However, when NOx was removed in advance through ozone injection, it showed 20 ~ 40% activity improvement in the entire reaction temperature range of 350 ~ 400 ℃, and the conversion rate was over 90% at the temperature above 390 ℃. I could secure it.

The present invention is not limited to the above-described specific embodiments and descriptions, and various modifications can be made by those skilled in the art without departing from the gist of the present invention claimed in the claims. Such variations are within the protection scope of the present invention.

Claims (10)

delete delete delete delete delete Supplying exhaust gas to the wet scrubber;
Supplying the exhaust gas passing through the wet scrubber to an electric dust collector; And
And a third step of supplying the exhaust gas passing through the electrostatic precipitator to the decomposition catalyst reactor.
The wet scrubber is supplied with ozone,
The decomposition catalyst reactor includes a decomposition catalyst obtained by impregnating a rhodium nitrate aqueous solution into a carrier made of an Al 2 O 3 -CeZr composite oxide, to remove nitrous oxide using a catalyst from an exhaust gas discharged from a semiconductor process. Way.
The method of claim 6,
In the wet scrubber, the acidic gas is collected using a basic solution,
NO is converted into NO ₂ by the supplied ozone, and then reacted with sodium sulfide (Na ₂ S) to be further reduced to reduce the nitrous oxide using a catalyst from the exhaust gas discharged from the semiconductor process. How to remove.
The method of claim 6,
In the electrostatic precipitator, a method of removing nitrous oxide using a catalyst from the exhaust gas discharged from the semiconductor process, characterized in that the water particles are aggregated to remove through electrical charge.
delete In the method for removing nitrous oxide from the exhaust gas discharged from the semiconductor process,
A first step of measuring concentrations of nitrogen monoxide and nitrous oxide in the semiconductor process exhaust gas; And
When the concentration of nitrous oxide measured in the first step is less than 200ppm, the exhaust gas is treated by a reduction catalytic reaction method, and when the concentration of nitrous oxide measured in the first step is more than 200ppm, the exhaust gas To process by any one of claims 6 to 8;
The reduction catalytic reaction method, the first step of supplying the exhaust gas to the wet scrubber; Supplying the exhaust gas passing through the wet scrubber to an electric dust collector; And a third step of supplying exhaust gas passing through the electrostatic precipitator to a reduction catalyst reactor.
The ammonia is supplied to the reduction catalyst reactor as a reducing agent, the method for removing nitrous oxide using a catalyst from the exhaust gas discharged from the semiconductor process.