JP2004161503A - Gas purification method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas purification method capable of efficiently removing trace impurities contained in a waste gas from various processes using krypton or xenon and suitable for a pretreatment of a rare gas separation and recovery apparatus for continuously separating/recovering/recycleing a rare gas by being installed direct near a semiconductor manufacturing apparatus. <P>SOLUTION: In the removal of the trace impurities such as hydrogen, ammonia, steam or nitrogen oxides from a gaseous mixture consisting essentially of the rare gas and nitrogen, a reducing material removing process capable of converting hydrogen and ammonia to a gaseous mixture containing steam and nitrogen oxides by an oxidation reaction under the presence of oxygen or the nitrogen oxides, a denitration process capable of converting the nitrogen oxides and oxygen contained in the gaseous mixture after the reducing material removing process is finished to nitrogen and steam by a denitration catalytic reaction under the presence of oxygen and ammonia and a drying process capable of removing ammonia and steam in the gaseous mixture after the denitration process is finished are successively performed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas purification method, and in particular, has a reactivity such as hydrogen, ammonia, water vapor, or nitrogen oxide that hinders the operation when separating and recovering krypton and xenon, which are rare gases, from a gas mixture. A gas purification method used to remove trace impurities in advance, particularly in a process of manufacturing a semiconductor product, for example, a pretreatment of an apparatus for separating and recovering a rare gas in an exhaust gas discharged from a plasma processing apparatus. The present invention relates to an optimal method for removing the trace impurities.
[0002]
[Prior art]
For example, from a semiconductor manufacturing apparatus for manufacturing semiconductor products such as semiconductor integrated circuits, liquid crystal panels, solar cell panels, and magnetic disks, rare gases, especially krypton, xenon, and nitrogen are used as main components, and as trace impurities, , A gas mixture containing reactive substances such as hydrogen, ammonia, water vapor, and nitrogen oxides is discharged as exhaust gas. Therefore, in order to recover and reuse an expensive rare gas, these trace impurities must be removed from the exhaust gas without causing a loss of the rare gas.
[0003]
Various techniques have been proposed in the past to remove trace impurities as described above from the gas. However, all of these techniques involve only one type of component such as nitrogen oxides, hydrogen, and oxygen. Rare gas is recovered from a mixed gas that has a very low gas flow rate and contains many types of gases as impurities, such as gases discharged from various processes for semiconductor manufacturing. It is not a technology to do it. That is, in order to recover a rare gas from an exhaust gas of a semiconductor manufacturing apparatus, a technology for separating / removing / purifying trace impurities contained in the exhaust gas in a consistent form has not yet been established.
[0004]
A first step of removing fluorine when the impurity neon gas extracted from the KrF excimer laser oscillator of the semiconductor manufacturing apparatus contains fluorine, krypton, nitrogen, oxygen, carbon monoxide, carbon dioxide and water. A second step of removing carbon dioxide and moisture by adsorption after removing oxygen with a metal oxide catalyst, a third step of removing krypton by low-temperature adsorption, and removing nitrogen and carbon monoxide by further low-temperature adsorption A method of purifying neon by sequentially performing the fourth step has been proposed (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP 2001-232134 A (Page 1, FIG. 1)
[0006]
[Problems to be solved by the invention]
However, the above-mentioned method uses large amounts of low-temperature adsorption, requires large-scale equipment to obtain low temperatures, is a laborious and costly process, and is suitable for industrial gas manufacturers to carry out in-house. Despite this process, it is a process that separates and recovers rare gases in the exhaust gas discharged from the equipment at the semiconductor factory and in the immediate vicinity of the semiconductor manufacturing equipment, and reuses them. Is difficult to use.
[0007]
As described above, the conventional various techniques can be used in the immediate vicinity of a semiconductor manufacturing apparatus, and can appropriately remove two or more types of impurity components contained in gas discharged from various semiconductor manufacturing processes. There was a problem that there was no way. In particular, various removal means have been studied depending on the types of impurity components contained in the exhaust gas. However, a plurality of impurities can be efficiently removed from a gas mixture containing a plurality of them, and the loss of a rare gas can be suppressed. A process that can be reused at a rate has not been established. In addition, when the adsorption step is used in multiple stages, there remains a problem that the cost of equipment increases and the loss of rare gas slightly increases.
[0008]
Therefore, the present invention can remove trace impurities such as hydrogen, ammonia, water vapor, and nitrogen oxides contained in a gas mixture containing a rare gas and nitrogen as main components at low cost and with high efficiency, and in particular, semiconductors. In manufacturing equipment, it can be applied to exhaust gas from various processes of oxidation, nitridation and oxynitridation using expensive krypton and xenon.In addition, it can be installed immediately adjacent to semiconductor manufacturing equipment to continuously separate rare gases from exhaust gas. It is an object of the present invention to provide a gas purification method capable of realizing a small system that can be collected and reused.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the gas purification method of the present invention comprises, as a first configuration, a rare gas and nitrogen as main components, and at least one of hydrogen, ammonia, water vapor, and nitrogen oxide as trace impurities. A gas purification method for removing said trace impurities from a gas mixture, comprising removing a reducing substance capable of converting hydrogen and ammonia into a gas mixture containing water vapor by an oxidation reaction in the presence of at least one of oxygen and nitrogen oxides. A denitration step capable of converting nitrogen oxides and oxygen contained in the gas mixture after the reducing substance removal step to nitrogen and water vapor by a denitration catalyst reaction in the presence of ammonia, and terminating the denitration step Drying step capable of removing ammonia and water vapor in the gas mixture.
[0010]
Further, the gas purification method of the present invention is characterized in that, as a second configuration, the gas mixture containing a rare gas and nitrogen as main components, and at least one of hydrogen, ammonia, water vapor, and nitrogen oxides as trace impurities, is used. In a gas purification method for removing trace impurities, a reducing substance removing step capable of converting hydrogen and ammonia into a gas mixture containing water vapor by an oxidation reaction in the presence of at least one of oxygen and nitrogen oxide; A denitration step capable of converting nitrogen oxides and oxygen contained in the gas mixture after the neutral substance removal step to nitrogen and water vapor by a denitration catalytic reaction in the presence of hydrogen, and a gas mixture after the denitration step. A hydrogen oxidation step capable of converting hydrogen to water vapor by a hydrogen oxidation reaction in the presence of oxygen, and water in the gas mixture after the hydrogen oxidation step. It is characterized in that it comprises a removable drying gas.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a system diagram showing one embodiment of a gas purification apparatus to which the first configuration is applied in the gas purification method of the present invention. This gas purification device is composed of a rare gas-containing exhaust gas discharged from the plasma oxidation step, the plasma nitridation step, and the plasma oxynitridation step, for example, krypton and nitrogen as main components, and nitrogen oxides, hydrogen, oxygen, ammonia, as trace impurities. Perform a pre-stage purification process when separating and recovering krypton from a gas mixture supposed to contain water vapor and the like, and at least among the trace impurities, obstacles in the separation and recovery operation in the final rare gas separation and recovery device For removing nitrogen oxides, hydrogen, ammonia and water vapor, and comprises an oxygen adding means 11, a reducing substance removing means 12, an ammonia adding means 13, a denitration means 14 and a drying means 15. A rare gas separation and recovery device 16 is provided at a stage subsequent to 15.
[0012]
The nitrogen oxides include nitrogen dioxide, nitric oxide, nitrous oxide and their ions, radicals, and the like. Ammonia, hydrogen, oxygen, water vapor, and the like exemplified also include these ions and radicals. Shall be included. Further, the rare gas-containing exhaust gas includes not only the gas discharged from the reactor of the semiconductor manufacturing apparatus, but also the gas entrained from pumps at the subsequent stage.
[0013]
The composition of a gas mixture (hereinafter, referred to as source gas) taken out of a semiconductor manufacturing apparatus and serving as a raw material for rare gas recovery is, for example, a plasma oxidation step, a plasma nitridation step, or a plasma manufacturing step in a semiconductor manufacturing process using krypton or xenon. In the case of the exhaust gas from the plasma oxynitriding process, the exhaust gas of the plasma oxidizing process mainly includes krypton and xenon, which are rare gases, nitrogen for purging (including nitrogen entrainment of a back purge pump), and a small amount of oxygen. , Water vapor, and sometimes hydrogen. The exhaust gas of the plasma nitriding process contains ammonia, hydrogen, and water vapor as trace components in addition to the rare gas and nitrogen. The exhaust gas in the plasma oxynitriding step contains nitrogen oxides in addition to the exhaust gas components in the plasma oxidizing step and the plasma nitriding step. Depending on the scale of the semiconductor device, the emission concentration of the impurity component from each reactor is 1 vol% or less for each nitrogen oxide, 2 vol% or less for hydrogen, 2 vol% or less for oxygen, 1 vol% or less for ammonia, A state containing 5% by volume or less can be assumed.
[0014]
The gas purifying apparatus shown in the first embodiment has a configuration that can cope with each of these semiconductor manufacturing steps. For example, when each step of oxidation, nitridation, and oxynitridation is performed by one semiconductor manufacturing apparatus and the exhaust gas is processed, or each step of oxidation, nitridation, and oxynitridation is performed by another semiconductor manufacturing apparatus, Can be dealt with collectively and exhausted, and even when only one of the steps of oxidation, nitridation, and oxynitridation is performed, the gas purification apparatus having this configuration can be installed.
[0015]
The source gas G1 is introduced from the source gas introduction path 21 through the buffer / steam removal container 22 and the heater 23 to the reducing substance removing means 12, and the reducing substance removing step is performed. The source gas introduction path 21 is provided with a source gas analyzer 24 and a source gas flow meter 25, and performs component analysis of the source gas and measurement of the amount of impurities. The amount of the source gas introduced is adjusted by the flow control valve 26.
[0016]
The oxygen adding means 11 removes oxygen, which is insufficient to convert a reducing substance such as ammonia or hydrogen in the raw material gas into nitrogen oxides, nitrogen, or water vapor by the oxidation reaction in the reducing substance removing means 12, into the raw material gas G1. The amount of oxygen G2 added is controlled according to the amount of reducing substance measured by the raw material gas analyzer 24 and the raw material gas flow meter 25. That is, the amount of oxygen G2 added from the oxygen adding means 11 is set so that the amount of oxygen in the raw material gas directed to the reducing substance removing means 12 is sufficient to convert the reducing substance. It is measured by an oxygen flow meter 28 provided in the passage 27 and adjusted by an oxygen flow control valve 29.
[0017]
The raw material gas G1 is heated to a reaction temperature set in advance by the heater 23 and introduced into the reducing substance removing means 12. The reducing substance removing means 12 is one in which a reaction tube (catalytic reaction tube) 30 is filled with an oxidation catalyst 31. For example, hydrogen or ammonia causes the following catalytic reaction in the presence of oxygen. Thereby, hydrogen and ammonia are converted into nitrogen oxides, nitrogen, and water vapor. Note that the catalytic reaction is mainly a reaction between hydrogen and oxygen and between ammonia and oxygen, but a secondary reaction from each reaction product also occurs at the same time.
[0018]
2H ₂ + O ₂ → 2H ₂ O
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O
2NH ₃ + 2O ₂ → N ₂ O + 3H ₂ O
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O
12NH ₃ + 21O ₂ → 12NO ₂ + 18H ₂ O
In addition, as the oxidation catalyst 31 used in the reducing substance removing means 12, a commercially available catalyst can be used. Further, the reaction temperature may be set to a suitable temperature according to operating conditions such as the type and amount of catalyst used, the concentration and flow rate of the reacting gas, and is usually 150 ° C. or higher, preferably about 300 ° C. Further, a heating means may be provided in the catalyst reaction tube 30 instead of the heater 23. Further, the reducing substance removing means 12 can remove a reducing substance such as ammonia by using nitrogen oxide instead of oxygen.
[0019]
The gas from which the reducing substance has been removed by the reducing substance removing means 12 (reducing substance removing gas) is sent from the catalytic reaction tube 30 to the denitration means 14 through the reducing substance removing gas path 32. The reducing substance removing gas path 32 is provided with a reducing substance removing gas analyzer 33 for analyzing the components of the reducing substance removing gas and a reducing substance removing gas flow meter 34 for measuring the flow rate. A predetermined amount of ammonia G3 is added to the reducing substance removing gas from the ammonia adding means 13 based on the amounts of oxygen and nitrogen oxides in the reduced substance removing gas thus obtained. The amount of added ammonia is determined to be an amount sufficient to reduce oxidizing substances such as oxygen and nitrogen oxides in the reducing substance-removing gas. It is adjusted by the ammonia flow control valve 37.
[0020]
The denitration means 14 is a reactor in which a denitration catalyst 39 is filled in a reaction tube (denitration reaction tube) 38. The reducing substance removal gas after the addition of ammonia is subjected to a denitration step by a reaction with the denitration catalyst 39, And nitrogen oxides react with ammonia to convert to steam and nitrogen. The reaction between nitrogen oxide and ammonia (denitration reaction) and the reaction between oxygen and ammonia in this denitration step are as follows. As the denitration catalyst 39 used in the denitration means 14, a generally known denitration catalyst can be appropriately selected and used.
[0021]
3N ₂ O + 2NH ₃ → 4N ₂ + 3H ₂ O
6NO + 4NH ₃ → 5N ₂ + 6H ₂ O
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O
3O ₂ + 4NH ₃ → 2N ₂ + 6H ₂ O
[0022]
The denitration gas from which oxygen and nitrogen oxides have been removed by the denitration means 14 passes through a denitration gas path 41, and in a cooler 42, the heat generated by condensation of the reaction heat and some of the water vapor and a part of the water dissolved in this moisture After the ammonia is removed and the gas composition is measured by the denitration gas analyzer 43, it is introduced into the drying means 15 to perform a drying step, and the water vapor and ammonia in the denitration gas are adsorbed and removed by the adsorbent.
[0023]
The water vapor here includes those discharged from the semiconductor manufacturing apparatus, those generated by the oxidation reaction in the reducing substance removing means 12, and those generated by the denitration reaction in the denitration means 14. Ammonia is the surplus amount of ammonia added from the ammonia adding means 13 reacting with nitrogen oxides and oxygen.
[0024]
The drying means 15 is of a two-cylinder switching type having a pair of drying cylinders (adsorption cylinders) 52a and 52b each filled with a desiccant (adsorbent) 51. Therefore, while one adsorption column is performing the adsorption step of adsorbing and removing water vapor and ammonia, the other adsorption column is performing a regeneration step of desorbing the adsorbed water vapor and ammonia from the adsorbent. As the adsorbent 51, for example, activated carbon, silica gel, various zeolites, or the like can be selected. Among such adsorbents, potassium ion-exchanged A-type zeolite has the property of hardly adsorbing rare gases while having the ability to adsorb water vapor and ammonia sufficiently. As a result, rare gas can be more efficiently recovered, and a recovery rate of 99% or more can be expected even if the loss during regeneration of the adsorption column is considered.
[0025]
In this drying means 15, when one adsorption cylinder 52a is performing the adsorption step, the adsorption inlet valve 53a and the adsorption outlet valve 54a corresponding to the adsorption cylinder 52a are opened, and the regeneration inlet valve 55a and the regeneration outlet valve 56a are Closed, the denitration gas from the denitration gas path 41 is introduced into the adsorption cylinder 52a through the adsorption inlet valve 53a, and the adsorbent 51 adsorbs and removes water vapor and ammonia to become a dry gas, which is dried through the adsorption outlet valve 54a. It is led to the gas path 57.
[0026]
In the other adsorption column 52b, the adsorption inlet valve 53b and the adsorption outlet valve 54b are closed, the regeneration inlet valve 55b and the regeneration outlet valve 56b are opened, and the regeneration gas W1 from the adsorbent regeneration gas passage 58 passes through the regeneration inlet valve 55b. The exhaust gas W2 that has been introduced into the adsorption cylinder 52b and has regenerated the adsorbent is discharged from the regeneration outlet valve 56b through the regeneration gas discharge path 59. The two adsorption cylinders are switched between an adsorption step and a regeneration step by switching between open and closed states of each valve at a preset timing, and continuously perform adsorption and removal of water vapor and ammonia. In addition, a detector for moisture and ammonia is provided at the outlet side of the adsorbent inside the adsorption column to detect the progress of the adsorption band of moisture and ammonia in the adsorbent, and this signal determines the process switching time, thereby completely adsorbing the adsorbent. Thus, the number of times of process switching can be reduced, the operating life of valves and the like can be extended, and the loss of rare gas generated when the process of the adsorption cylinder is switched can be reduced.
[0027]
The dry gas from which nitrogen oxides, hydrogen, oxygen, water vapor, and ammonia, which are trace impurities in the exhaust gas, have been removed in this manner becomes a gas mixture whose gas composition is mainly composed of a rare gas and nitrogen. After the amount of impurities is confirmed by the dry gas analyzer 61 provided in the path 57, the impurities are introduced into the rare gas separation and recovery device 16. The rare gas separation / recovery device 16 performs a process of separating the rare gas and the gas other than the rare gas from the dry gas introduced from the dry gas path 57, and usually converts the rare gas to 99.99% or more. What is recovered after purifying to a purity is used. The rare gas separation process can be performed by various operations conventionally performed, for example, a cryogenic separation method using a refrigerant such as liquefied nitrogen, a difference in adsorption performance between a rare gas and a gas other than the rare gas. And a membrane separation method using a difference in membrane permeability, and these can be combined as necessary. The rare gas P1 separated by the rare gas separation and recovery device 16 is recovered as a product from the rare gas recovery path 62.
[0028]
Here, in the adsorption / desorption operation in the drying means 15, the adsorption step is performed at a relatively low temperature and the desorption (regeneration) step is performed at a relatively high temperature in order to more effectively perform adsorption and desorption of water vapor, ammonia, and the like. Is preferably carried out by a temperature fluctuation adsorption separation method. For example, it is set so that the adsorption step is performed at normal temperature (15 to 35 ° C.) and the regeneration step is performed at 200 to 300 ° C.
[0029]
That is, in the desorption operation in the former stage of the regeneration step, the heating switching valve 63 provided in the adsorbent regeneration gas path 58 is switched to the regeneration gas heater 64 side, and the regeneration gas W1 is heated to about 300 ° C. by the heater 64. Into the adsorption column during the regeneration process. After completion of the regeneration operation of the adsorption cylinder, the heating switching valve 63 is switched to the heater bypass side to introduce the regeneration gas at the same temperature, usually at normal temperature, into the adsorption cylinder in the regeneration step, and to cool the adsorbent, It can be prepared for the next adsorption step. In addition, heating means may be provided in each of the adsorption tubes 52a and 52b instead of the heater 64. In this case, the heating switching valve 63 can also be omitted.
[0030]
Further, when ammonia and nitrogen oxides coexist in the raw material gas, particularly when ammonia and nitrogen dioxide are contained, ammonium nitrate may be formed and precipitated by reacting in the route. Therefore, even when ammonia and nitrogen oxides coexist in the exhaust gas from the semiconductor manufacturing process, or when there is almost no ammonia in the exhaust gas (raw material gas), moisture condensed at room temperature due to the high water vapor concentration causes the pipe If there is a risk of clogging, a pipe heating means 65 is provided from the source gas introduction path 21 to the heater 23, and pipes and valves are set at 150 ° C. or higher, preferably 210 ° C. or higher, which is the thermal decomposition temperature of ammonium nitrate. By heating, the pipes and valves can be prevented from being blocked by ammonium nitrate or moisture.
[0031]
In the reducing substance removing step, the addition amount of oxygen G2 added to the raw material gas G1 is controlled based on the concentration of ammonia and hydrogen in the raw material gas (analyzer 24) and the amount of the raw material gas (flow meter 25). Can be adjusted by the flow rate control valve 29. However, the residual oxygen concentration (analyzer 33) in the reducing substance removing gas after the reducing substance removing step becomes a constant amount. Alternatively, the flow control valve 29 can be controlled. Further, depending on the operating conditions, the flow meter 28 can be controlled to add a constant flow rate of oxygen.
[0032]
The amount of oxygen G2 added can be calculated from the theoretical amount of oxygen based on the amounts of ammonia and hydrogen and the chemical reaction formula. However, in order to completely remove ammonia and hydrogen, the amount of oxygen G2 is more than the theoretical amount. It is necessary to control to add oxygen. However, since the surplus oxygen is to be removed in the subsequent equipment, it is preferable to keep the amount of addition to a necessary minimum. It is also possible to estimate the corresponding exhaust gas composition based on the gas composition and flow rate used in the semiconductor manufacturing apparatus and the reaction conditions, and to control the amount of added oxygen based on the estimated amounts of ammonia and hydrogen. In this case, although an estimation error occurs, it is necessary to add oxygen in a relatively excessive amount, but there is an advantage that analysis is not required and the method is simple.
[0033]
Similarly to the control of the addition amount of oxygen G2, the control of the addition amount of ammonia G3 added in the denitration step is performed by controlling the concentration of oxygen and nitrogen oxide (analyzer 33) and the amount of gas (flow meter) 34), the amount of ammonia necessary for the reduction of nitrogen oxides and oxygen may be obtained, and the flow rate control valve 37 may be adjusted based on this. However, the residual ammonia concentration in the denitration gas after the denitration step (the analyzer 43 ) May be controlled to be constant. Further, depending on the operating conditions, the flow rate adjusting valve 37 can be controlled to add a constant flow rate of ammonia. Further, it is also possible to estimate the amount of oxygen or nitrogen oxide generated or remaining by the reducing substance removing means, and to control the amount of ammonia G3 added based on the estimated amount.
[0034]
FIG. 2 is a system diagram showing one embodiment of a gas purification apparatus to which the second configuration is applied in the gas purification method of the present invention. This gas purification device is a rare gas-containing exhaust gas discharged from the above-described plasma oxidation step, plasma nitridation step, plasma oxynitridation step, for example, krypton and nitrogen, and nitrogen oxides, hydrogen, Performs a pre-stage purification process when krypton is separated and recovered from a gas mixture assumed to contain oxygen, ammonia, water vapor, etc., and at least, among the trace impurities, separation and recovery in a final rare gas separation and recovery device It removes nitrogen oxides, hydrogen, ammonia, and water vapor that are obstacles to the operation. The first oxygen addition means 111, the reducing substance removing means 112, the hydrogen addition means 113, the denitration means 114, the second oxygen addition means 115, a hydrogen oxidizing means 116 and a drying means 117, and a rare gas separation and recovery device 118 is provided at a stage subsequent to the drying means 117. To have.
[0035]
The nitrogen oxides include nitrogen dioxide, nitrogen monoxide, dinitrogen monoxide and their ions, radicals, and the like, similarly to the first embodiment, and include ammonia, hydrogen, oxygen, water vapor, and the like. Etc. also include these ions and radicals. Further, the rare gas-containing exhaust gas includes not only the gas discharged from the reactor of the semiconductor manufacturing apparatus, but also the gas entrained from pumps at the subsequent stage.
[0036]
The composition of the gas mixture (source gas G1) which is taken out of the semiconductor manufacturing apparatus and becomes a raw material for rare gas recovery is also the same as in the first embodiment. For example, in a semiconductor manufacturing process using krypton or xenon, In the case of exhaust gas from the plasma oxidation step, the plasma nitridation step, and the plasma oxynitridation step, the exhaust gas of the plasma oxidation step is mainly krypton or xenon, which is a rare gas, and nitrogen for purging (including entrainment of nitrogen in a back purge pump). In addition, it contains trace amounts of oxygen, water vapor, and sometimes hydrogen. The exhaust gas of the plasma nitriding process contains ammonia, hydrogen, and water vapor as trace components in addition to the rare gas and nitrogen. The exhaust gas in the plasma oxynitriding step contains nitrogen oxides in addition to the exhaust gas components in the plasma oxidizing step and the plasma nitriding step. Depending on the scale of the semiconductor device, the emission concentration of the impurity component from each reactor is 1 vol% or less for each nitrogen oxide, 2 vol% or less for hydrogen, 2 vol% or less for oxygen, 1 vol% or less for ammonia, A state containing 5% by volume or less can be assumed.
[0037]
The gas purifying apparatus shown in the second embodiment also has a configuration capable of coping with each of these semiconductor manufacturing steps. For example, when each step of oxidation, nitridation, and oxynitridation is performed by one semiconductor manufacturing apparatus and the exhaust gas is processed, or each step of oxidation, nitridation, and oxynitridation is performed by another semiconductor manufacturing apparatus, Can be dealt with collectively and exhausted, and even when only one of the steps of oxidation, nitridation, and oxynitridation is performed, the gas purification apparatus having this configuration can be installed.
[0038]
The source gas G11 is introduced from the source gas introduction path 121 through the buffer / steam removal container 122 and the heater 123 to the reducing substance removing means 112, and the reducing substance removing step is performed. The source gas introduction path 121 is provided with a source gas analyzer 124 and a source gas flow meter 125, and performs component analysis of the source gas and measurement of the amount of impurities. The amount of the source gas introduced is adjusted by the flow control valve 126.
[0039]
The first oxygen adding means 111 converts oxygen, which is insufficient to convert a reducing substance such as ammonia or hydrogen in the raw material gas into nitrogen oxides, nitrogen, and water vapor by the oxidation reaction in the reducing substance removing means 112, as a raw material. The amount of oxygen G12 to be added to the gas G11 is controlled according to the amount of reducing substance measured by the raw material gas analyzer 124 and the raw material gas flow meter 125. That is, the amount of oxygen G12 added from the first oxygen adding means 111 is set so that the amount of oxygen in the raw material gas directed to the reducing substance removing means 112 is sufficient to convert the reducing substance, It is measured by an oxygen flow meter 128 provided in the oxygen addition path 127 and adjusted by an oxygen flow control valve 129.
[0040]
The raw material gas G11 is heated to a reaction temperature set in advance by the heater 123 and introduced into the reducing substance removing means 112. The reducing substance removing means 112 is a catalyst reaction tube 130 filled with an oxidation catalyst 131. For example, hydrogen or ammonia is converted into nitrogen oxide, nitrogen, Converted to steam.
[0041]
2H ₂ + O ₂ → 2H ₂ O
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O
2NH ₃ + 2O ₂ → N ₂ O + 3H ₂ O
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O
12NH ₃ + 21O ₂ → 12NO ₂ + 18H ₂ O
[0042]
In addition, as the oxidation catalyst 131 used in the reducing substance removing means 112, a commercially available catalyst can be used. Further, the reaction temperature may be set to a suitable temperature according to operating conditions such as the type and amount of catalyst used, the concentration and flow rate of the reacting gas, and is usually 150 ° C. or higher, preferably about 300 ° C. Further, a heating unit may be provided in the catalyst reaction tube 130 instead of the heater 123.
[0043]
The gas from which the reducing substance has been removed by the reducing substance removing means 112 (reducing substance removing gas) is sent from the catalytic reaction column 130 to the denitration means 114 through the reducing substance removing gas path 132. The reducing substance removing gas path 132 is provided with a reducing substance removing gas analyzer 133 for analyzing the components of the reducing substance removing gas, and the oxygen and nitrogen oxidation in the reducing substance removing gas measured here is measured. A predetermined amount of hydrogen G13 is added to the reducing substance removing gas from the hydrogenation means 113 based on the amount of the substance. The amount of hydrogen added is determined so as to be sufficient to reduce oxidizing substances such as oxygen and nitrogen oxides in the reducing substance removing gas, and a hydrogen flow meter 136 provided in the hydrogenation path 135 is provided. And a hydrogen flow control valve 137.
[0044]
The denitration means 114 is a reaction tube (denitration reaction tube) 138 filled with a denitration catalyst 139, and the reducing substance removal gas after hydrogenation is subjected to a denitration step by a reaction with the denitration catalyst 139, And nitrogen oxides react with hydrogen to convert to steam and nitrogen. The reaction between nitrogen oxide and hydrogen in this denitration step (denitration reaction) and the reaction between oxygen and hydrogen are as follows. As the denitration catalyst 139 used in the denitration means 114, a generally known denitration catalyst can be appropriately selected and used.
[0045]
2NO + 2H ₂ → N ₂ + 2H ₂ O
2NO + 4H ₂ → N ₂ + 4H ₂ O
N ₂ O + H ₂ → N ₂ + H ₂ O
O ₂ + 2H ₂ → 2H ₂ O
[0046]
In such a denitration reaction, when hydrogen is used as a reducing substance, it is necessary to consider safety aspects. For example, the concentration of hydrogen gas to be added should be kept below the explosion limit, or the composition of exhaust gas from semiconductor manufacturing equipment should be adjusted to the concentration of hydrogen gas. It is also necessary to devise a composition that does not explode and keep the composition from exploding. It is also desirable to prepare sintered metal on both sides of the denitration reaction tube 138 and take measures against explosion. This is the same for other catalytic reactions.
[0047]
The denitration gas from which oxygen and nitrogen oxides have been removed by the denitration means 114 passes through a denitration gas path 141 and is sent to a hydrogen oxidizing means 116, where a hydrogen oxidation step for removing hydrogen is performed. The denitration gas path 141 is provided with a denitration gas analyzer 142 for analyzing the components of the denitration gas and a denitration gas flow meter 143 for measuring the flow rate. Based on the hydrogen amount in the denitration gas measured here, A predetermined amount of oxygen G14 is added to the denitration gas from the second oxygen adding means 115. The addition amount of the oxygen G14 is determined to be an amount sufficient to reduce the hydrogen in the denitration gas, and is adjusted by the oxygen flow meter 144 and the oxygen flow control valve 145 provided in the second oxygen addition path 115. You.
[0048]
The hydrogen oxidizing means 116 is a device in which a reaction tube (hydrogen reaction tube) 146 is filled with a hydrogen oxidizing catalyst 147, and the denitration gas after oxygen addition is subjected to a hydrogen removing step by a reaction with the hydrogen oxidizing catalyst 147. Hydrogen and oxygen react to generate water vapor. As the hydrogen oxidation catalyst 147 used in the hydrogen oxidation means 116, a generally known hydrogen oxidation catalyst can be appropriately selected and used.
[0049]
The dehydrogenated gas from which hydrogen has been removed by the hydrogen oxidizing means 116 passes through a dehydrogenation gas path 148, and the heat generated by the reaction heat and partial condensation of water vapor is removed by a cooler 149. After the gas composition is measured in step (a), the gas is introduced into the drying means 117 to perform a drying step, and the water vapor in the dehydrogenated gas is adsorbed and removed by the adsorbent. The water vapor here is discharged from the semiconductor manufacturing apparatus, generated by the oxidation reaction in the reducing substance removing means 112 and the hydrogen oxidizing means 116, and generated by the denitration reaction in the denitrating means 114. Is included.
[0050]
The drying means 117 is of a two-cylinder switching type having a pair of adsorption cylinders (drying cylinders) 152a and 152b each filled with an adsorbent (drying agent) 151. Therefore, while one of the drying cylinders is performing the drying step of adsorbing and removing water vapor, the other drying cylinder is performing a regeneration step of desorbing the adsorbed water vapor from the desiccant. As the desiccant 151, for example, activated carbon, silica gel, various zeolites and the like can be selected. However, a potassium ion-exchanged A-type zeolite which has sufficient ability to adsorb water vapor and hardly adsorbs rare gas is desiccant. By adopting as, the rare gas can be recovered more efficiently, and a recovery rate of 99% or more can be expected even if the loss during regeneration of the drying cylinder is considered.
[0051]
In this drying means 117, when one of the drying cylinders 152a is performing a drying process, the drying inlet valve 153a and the drying outlet valve 154a corresponding to the drying cylinder 152a are opened, and the regeneration inlet valve 155a and the regeneration outlet valve 156a are It is closed, and the dehydrogenated gas from the dehydrogenated gas path 148 is introduced into the drying cylinder 152a through the drying inlet valve 153a, and the vapor is adsorbed and removed by the desiccant 151 to become the drying gas, which is dried through the drying outlet valve 154a. It is led to a gas path 157.
[0052]
In the other drying cylinder 152b, the drying inlet valve 153b and the drying outlet valve 154b are closed, the regeneration inlet valve 155b and the regeneration outlet valve 156b are opened, and the regeneration gas W11 from the desiccant regeneration gas path 158 passes through the regeneration inlet valve 155b. The exhaust gas W12 that has been introduced into the drying cylinder 152b to regenerate the desiccant is discharged from the regeneration outlet valve 156b through the regeneration gas discharge path 159. The two drying cylinders are switched between a drying step and a regeneration step by switching between open and closed states of each valve at a preset timing, and continuously perform adsorption removal of water vapor. In addition, a moisture detector is provided at the outlet side of the desiccant inside the drying cylinder to detect the progress of the adsorption band of moisture in the desiccant, and the signal is used to determine the process switching time, so that the desiccant is completely utilized. The number of times of the process switching can be reduced, the service life of the operating part such as a valve can be extended, and the loss of rare gas generated when the process of the drying cylinder is switched can be reduced.
[0053]
The dry gas from which nitrogen oxides, hydrogen, oxygen, water vapor, and ammonia, which are trace impurities in the exhaust gas, have been removed in this manner becomes a gas mixture whose gas composition is mainly composed of a rare gas and nitrogen. After the amount of impurities is confirmed by the dry gas analyzer 161 provided in the path 157, the impurities are introduced into the rare gas separation and recovery device 118, and a process for separating gases other than the rare gas is performed in the same manner as described above. The rare gas P11 purified and separated to a purity of 99.99% or more is recovered as a product from the rare gas recovery path 162.
[0054]
Note that the adsorption / desorption operation in the drying unit 117 can be performed in the same manner as the drying unit 15 in the first embodiment, and the desiccant regeneration step is performed by the heating switching provided in the adsorbent regeneration gas path 158. This can be performed by switching the valve 163 between the regeneration gas heater 164 side and the heater bypass side as the regeneration step proceeds. Also in this case, by using the means for heating the drying cylinder, the heating switching valve 163 and the regeneration gas heater 164 can be omitted.
[0055]
Further, as described in the first embodiment, when ammonia and nitrogen oxide coexist in the raw material gas or when the water vapor concentration is high, a pipe is provided from the raw material gas introduction path 121 to the heater 123. It is preferable to provide a heating means 165. Further, the addition amounts of the oxygen G12, the hydrogen G13, and the oxygen G14 added to the raw material gas G11 may be controlled based on the amounts of the components that react with the oxygen G12, the hydrogen G13, and the oxygen G14. A fixed amount may be used, or a fixed amount may be added.
[0056]
【Example】
Reducing substance removal process
A stainless steel reaction tube (17.5 mm inner diameter) was charged with 15 g of Pash catalyst DASH220D (0.5% palladium / alumina) manufactured by NE Chemcat Corporation as an oxidation catalyst. A heater was installed outside the reaction tube to control the temperature so that the reaction tube maintained 300 ° C. As a gas mixture to be treated (introduced gas), a gas having the same concentration of krypton and nitrogen as a base gas and a different concentration of ammonia and hydrogen to be removed was prepared.
[0057]
Then, oxygen was added to the introduced gas and introduced into the reaction tube at atmospheric pressure. The concentration of nitric oxide and nitrogen dioxide in the reaction tube outlet gas is detected by a chemiluminescence NOx meter, the concentration of nitrous oxide is detected by GC-MS, the concentration of hydrogen and oxygen is detected by GC-TCD, and the concentration of ammonia is detected. Each was measured by the tube method. As a result, it was found that under an excess of oxygen, ammonia and hydrogen in the outlet gas were below the measurement limit, whereas water vapor, nitrogen oxides and oxygen generated by the reaction were present.
[0058]
Denitration process
A stainless steel reaction tube (17.5 mm inner diameter) was charged with 15 g of Pash catalyst DASH220D (0.5% palladium / alumina) manufactured by NEC Chemcat Corporation as a denitration catalyst. A heater was installed outside the reaction tube to control the temperature so that the reaction tube maintained 300 ° C. As a gas mixture to be treated (introduced gas), a gas in which the concentrations of nitrogen oxides and oxygen to be removed were changed using an equivalent mixture of krypton and nitrogen as a base gas was prepared.
[0059]
Then, ammonia was added to the introduced gas and introduced into the reaction tube at atmospheric pressure. Further, in order to prevent nitrate precipitation, the piping of the introduced gas was kept at 210 ° C. or higher by piping heating means. The concentrations of nitric oxide and nitrogen dioxide in the outlet gas of the reaction tube were measured by a chemiluminescence NOx meter, the concentration of nitrous oxide was measured by GC-MS, and the oxygen concentration was measured by GC-TCD. As a result, it was found that the nitrogen oxide can be surely removed by setting the amount of addition of ammonia as a reducing substance to an appropriate amount in excess of the nitrogen oxide. It was also confirmed that nitrogen oxide and oxygen could be removed in the same manner even when hydrogen was added instead of ammonia.
[0060]
Hydrogen oxidation process
As a hydrogen oxidation catalyst, 30 g of Pd catalyst G74D (0.5% palladium / alumina) manufactured by Nissan Gardler Catalysts Co., Ltd. was charged into a stainless steel reaction tube (17.5 mm inner diameter). To this reaction tube, 0.6% by volume of oxygen gas with respect to a gas containing 1% by volume of hydrogen in an equivalent mixture of krypton and nitrogen was added, and introduced at atmospheric pressure at 2 L / min. The concentrations of hydrogen and oxygen in the sample were measured by GC-TCD. As a result, at the outlet of the reaction tube, the content of hydrogen was 0.1 ppm by volume or less, and the content of oxygen was 0.1% by volume. At this time, the initial temperature of the hydrogen oxidation column was 80 ° C., but the heat of reaction raised the outlet gas temperature to about 170 ° C.
[0061]
Drying process
60 g of zeolam A-3 (potassium ion-exchanged A-type zeolite (potassium A-type zeolite)) manufactured by Tosoh Corporation was filled as an adsorbent into a stainless steel adsorption cylinder having an inner diameter of 17.5 mm. A gas mixture obtained by adding 0.5% by volume of ammonia and 0.5% by volume of water vapor to a mixture of krypton and nitrogen as a base gas at a rate of 2 L / min at 25 ° C. was introduced into this adsorption column. The contents of ammonia and water were measured. As a result, over 3 hours or more from the start of the adsorption, the concentration in the outlet gas could be maintained at 1 ppm by volume of ammonia and at a dew point of -80 ° C or lower (1 ppm by volume of water). Furthermore, the process switching time in the pair of adsorption cylinders was set to 3 hours, the regeneration temperature was set to 300 ° C., the regeneration gas (nitrogen) was set to 0.25 L / min, and a repeated adsorption / regeneration test was performed. It was confirmed that there was no change in the adsorption capacity.
[0062]
Also, in addition to potassium A-type zeolite, equilibrium adsorption of krypton using sodium A-type zeolite (Zeolam A-4 manufactured by Tosoh Corporation) and sodium X-type zeolite (Zeolam F-9HA manufactured by Tosoh Corporation) The amount was measured. As a result, potassium A-type zeolite hardly adsorbs krypton, whereas sodium A-type zeolite and sodium X-type zeolite both adsorb krypton at a rate of 0.09 mol / kg (at 50 kPa, 25 ° C.). There was found.
[0063]
Since the krypton adsorbed by the adsorbent is discharged together with the regeneration gas in the regeneration step, it is possible to increase the krypton recovery rate by using a potassium A-type zeolite that does not adsorb krypton. . In the drying step in the second embodiment, it was confirmed that the use of the potassium A-type zeolite enables reliable adsorption and removal of water while suppressing the loss of krypton.
[0064]
【The invention's effect】
As described above, according to the present invention, noble gas, particularly expensive krypton or hydrogen contained in a gas mixture containing xenon and nitrogen as main components, ammonia, water vapor, trace amounts of nitrogen oxides, etc. Impurities can be efficiently separated and removed. In particular, even in various semiconductor processing steps, such as an oxidation step, a nitridation step, and an oxynitridation step, trace amounts of exhaust gas (gas mixture) containing a rare gas such as krypton or xenon after being used as an atmosphere gas. Impurity components can be reliably separated and removed, and the equipment cost and operation cost of the entire rare gas purification device can be reduced.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a first embodiment of a gas purification apparatus to which the present invention is applied.
FIG. 2 is a system diagram showing a second embodiment of a gas purification apparatus to which the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Oxygen adding means, 12 ... Reducing substance removing means, 13 ... Ammonia adding means, 14 ... Denitration means, 15 ... Drying means, 16 ... Rare gas separation and recovery device, 21 ... Source gas introduction path, 22 ... Buffer and moisture Removal container, 23: heater, 24: source gas analyzer, 25: source gas flow meter, 26: flow control valve, 27: oxygen addition path, 28: oxygen flow meter, 29: oxygen flow control valve, 30 ... Catalyst reaction tube, 31 ... Oxidation catalyst, 32 ... Reducing substance removing gas path, 33 ... Reducing substance removing gas analyzer, 34 ... Reducing substance removing gas flow meter, 35 ... Ammonia addition path, 36 ... Ammonia flow meter 37, ammonia flow control valve, 38, denitration reaction tube, 39, denitration catalyst, 41, denitration gas path, 42, cooler, 43, denitration gas analyzer, 51, adsorbent, 52a, 52b, adsorption tube, 57 ... dry Gas path, 58: adsorbent regeneration gas path, 59: regeneration gas discharge path, 61: dry gas analyzer, 62: rare gas recovery path, 63: heating switching valve, 64: regeneration gas heater, 65: pipe heating means Reference numerals 111, first oxygen adding means, 112, reducing substance removing means, 113, hydrogen adding means, 114, denitration means, 115, second oxygen adding means, 116, hydrogen oxidizing means, 117, drying means, 118, rare Gas separation and recovery equipment

Claims (2)

In a gas purification method for removing the trace impurities from a gas mixture containing at least one of hydrogen, ammonia, water vapor, and nitrogen oxides as a trace impurity, mainly containing a rare gas and nitrogen, hydrogen and ammonia are converted to oxygen and A reducing substance removing step capable of being converted into a gas mixture containing water vapor and nitrogen oxide by an oxidation reaction in the presence of at least one of the nitrogen oxides, and a reducing substance removal step comprising: A denitration step capable of converting nitrogen oxides and oxygen to be converted into nitrogen and steam by a denitration catalytic reaction in the presence of ammonia, and a drying step capable of removing ammonia and steam in the gas mixture after the denitration step. A gas purification method comprising: In a gas purification method for removing the trace impurities from a gas mixture containing at least one of hydrogen, ammonia, water vapor, and nitrogen oxides as a trace impurity, mainly containing a rare gas and nitrogen, hydrogen and ammonia are converted to oxygen and A reducing substance removing step capable of being converted into a gas mixture containing water vapor and nitrogen oxide by an oxidation reaction in the presence of at least one of the nitrogen oxides, and a reducing substance removal step comprising: A denitration step capable of converting nitrogen oxides and oxygen to nitrogen and water vapor by a denitration catalytic reaction in the presence of hydrogen, and converting the hydrogen in the gas mixture after the denitration step into a water vapor by a hydrogen oxidation reaction in the presence of oxygen. A hydrogen oxidation step that can be converted to water and a drying step that can remove water vapor in the gas mixture after the hydrogen oxidation step. Gas purification method characterized.

Images