Patent Application
20240082782
The present invention relates to a treatment device suitable for an abatement process of a hardly decomposable semiconductor manufacturing exhaust gas including perfluoro compounds (PFCs), N2O, and the like.
In a manufacturing process for a semiconductor device or a liquid crystal display, gases of various kinds of fluorine compounds are used as a cleaning gas, an etching gas, and the like. Such fluorine compounds are referred to as “PFCs”, and typical examples thereof include: perfluorocarbons such as CF4, C2F6, C3F8, C4F8, and C5F8; hydrofluorocarbons such as CHF3; and inorganic fluorine-containing compounds such as SF6 and NF3. In the manufacturing process for a semiconductor device, etc., as a material gas for producing a nitride film, N2O (nitrous oxide) and the like are used. Various kinds of PFCs, N2O, and the like used in the manufacturing process for a semiconductor device or a liquid crystal display are exhausted as an exhaust gas together with N2, Ar, and the like used as, for example, a carrier gas and a purge gas. Throughout the present description, this exhaust gas is referred to as “semiconductor manufacturing exhaust gas”, or simply referred to as “exhaust gas”. In addition, a manufacturing process for a semiconductor device and a manufacturing process for a liquid crystal display are collectively referred to as “semiconductor manufacturing process”.
Here, a proportion of PFCs, N2O, and the like in the entire exhaust gas is small compared to that of other gases such as N2 and Ar. However, the global warming potential (GWP) of PFCs, N2O, and the like is as large as several thousands to several tens of thousands of times that of CO2, and the atmospheric lifetime thereof is also as long as several thousands to several tens of thousands of years compared to that of CO2. Therefore, devastating effects are caused, even if a small amount of the gas is discharged to the atmosphere. Furthermore, perfluorocarbons represented by CF4 and C2F6 are stable when it comes to a C—F bond (a bond energy thereof is as large as 130 kcal/mol), and thus decomposition thereof is known to not be easy. Accordingly, various technologies have been developed to abate used PFCs, N2O, and the like from an exhaust gas.
As a technology for abating the exhaust gas that includes hardly decomposable PFCs, N2O, and the like, Patent Literature 1 (Japanese Laid-Open Patent Publication No. 2002-188810) below discloses an exhaust gas treatment device in which dust and the like included in a noxious exhaust gas is eliminated by an inlet scrubber, then the exhaust gas is thermally decomposed in an exhaust gas treatment tower provided with an electric heater, and the decomposed gas is abated through gas-liquid contact in a wet outlet scrubber, for example.
However, the above conventional art has the following problems. Specifically, when PFCs in an exhaust gas contain hardly decomposable CF4 as a main component, an electric heater has to be used at a very high temperature, for example, 1500° C. or more. However, the use in such a temperature range is close to the limit in terms of the physical property of the heating element material of the electric heater, and thus there is a problem that it is difficult to continuously operate the electric heater for a long time.
“The 2030 Agenda for Sustainable Development” was adopted in the United Nations Summit in September 2015. After that, various discussions and investigations about, for example, efficient use of energy in future have been conducted. Under these circumstances, also, regarding the above conventional exhaust gas treatment device that includes an electric heater and that consumes a relatively large amount of power as energy during heating, it is easily estimated that the needs for high efficiency and energy saving brought about by such high efficiency are growing.
Therefore, a main object of the present invention is to provide a treatment device for semiconductor manufacturing exhaust gas that can more efficiently utilize electric power energy and can remarkably improve efficiency of abating a semiconductor manufacturing exhaust gas containing CF4, which is the most hardly decomposable PFC, as a main component, while maintaining advantages of the conventional exhaust gas treatment device using an electric heater as they are.
In order to achieve the above object, the present invention is directed to a treatment device 10 for semiconductor manufacturing exhaust gas having the following configuration, for example, as shown in
Specifically, the treatment device 10 includes: an inlet scrubber 12 for washing, with liquid, an exhaust gas E exhausted through a semiconductor manufacturing process; a gas treatment furnace 14 for thermally decomposing the exhaust gas E that has passed through the inlet scrubber 12; and an outlet scrubber 16 for washing, with liquid, the exhaust gas E thermally decomposed by the gas treatment furnace 14. Among these, the gas treatment furnace 14 includes: an outer cylinder 18 having a sealed cylindrical main body 18a that includes a gas treatment space 18b formed therein and a gas introduction port 18c drilled in a bottom thereof; an inner cylinder 20 that extends across the gas treatment space 18b such that one end thereof is mounted to the bottom inside the main body 18a so as to enclose the gas introduction port 18c and another end thereof is opened and located at a position close to a ceiling surface of the main body 18a; and an electric heater 22 that is hung from a ceiling 18d of the main body 18a and that has a heating element 22a having a long bar shape placed in an internal space of the inner cylinder 20. In front of the gas introduction port 18c, a decrease part 24 for decreasing, at once, an inner diameter of a passage for the exhaust gas E that has passed through the inlet scrubber 12, to a diameter not greater than a diameter of the gas introduction port 18c is provided. Furthermore, in front of the gas introduction port 18c, reducing gas supply means 26 for supplying a predetermined amount of reducing gas G toward the exhaust gas E is provided in the vicinity of an end on an upstream side in an exhaust gas flowing direction of the decrease part 24.
The present invention exhibits, for example, the following effects.
When the reducing gas G, which is supplied from the reducing gas supply means 26 to the exhaust gas E washed with liquid that has passed through the inlet scrubber 12, passes through the decrease part 24, a flow speed thereof is increased and, at the same time, the contact opportunity thereof with PFCs, N2O, and the like, which are abatement (thermal decomposition) target components in the exhaust gas E, increases. Subsequently, the exhaust gas E and the reducing gas G supplied into the gas treatment furnace 14 through the gas introduction port 18c while having the increased flow speed collide with the heating element 22a of the electric heater 22 placed in the inner cylinder 20 to produce turbulent flow, thereby further increasing the contact opportunity of the reducing gas G with PFCs, N2O, and the like in the exhaust gas E. The action of the radicalized reducing gas G is enhanced by being heated in this state, so that PFCs, N2O, and the like in the exhaust gas E are thermally decomposed very efficiently. The high-temperature exhaust gas E thermally decomposed as above is to flow down outside the inner cylinder 20. At this time, a heat-insulating effect can be exerted so as to prevent the temperature inside the inner cylinder 20 from being lowered.
With the above-described synergistic action, 99.9% or more of CF4, which is the most hardly decomposable PFC, can be decomposed at a heating temperature lower than before, for example, 1250° C. to 1350° C.
In the present invention, when the exhaust gas E contains PFCs, a flow rate of the reducing gas G to be supplied by the reducing gas supply means 26 is preferably at a proportion of 0.1 to 5 parts by volume with respect to 100 parts by volume of a flow rate of the exhaust gas E to be supplied to the gas treatment furnace 14.
If the flow rate of the reducing gas G to be supplied is less than 0.1 parts by volume with respect to 100 parts by volume of the flow rate of the exhaust gas E to be supplied to the gas treatment furnace 14, the addition effect of the reducing gas G is not sufficiently exerted. On the contrary, if the flow rate of the reducing gas G to be supplied is more than 5 parts by volume with respect to 100 parts by volume of the flow rate of the exhaust gas E to be supplied to the gas treatment furnace 14, the addition effect of the reducing gas G is sufficiently exerted but the effect peaks, resulting in wastefully burning the reducing gas G. Thus, a proportion of the reducing gas G that is added to the exhaust gas E to be supplied to the gas treatment furnace 14 is set within the above range, whereby a thermal decomposition efficiency of PFCs in the exhaust gas E due to addition of the reducing gas G can be maximized.
In the present invention, the reducing gas G is preferably hydrogen or ammonia.
In this case, the amount of carbon dioxide to be discharged to the atmosphere after thermal decomposition of the exhaust gas E can be reduced. When an abatement-target component in the exhaust gas E contains N2O, the amount of NOx (nitrogen oxide) to be discharged after thermal decomposition of the N2O can be remarkably reduced.
According to the present invention, a treatment device for semiconductor manufacturing exhaust gas that can more efficiently utilize electric power energy and can remarkably improve efficiency of abating a semiconductor manufacturing exhaust gas containing CF4, which is the most hardly decomposable PFC, as a main component, while maintaining advantages of the conventional exhaust gas treatment device using an electric heater as they are, can be provided.
Hereinafter, an embodiment of a treatment device for semiconductor manufacturing exhaust gas, according to the present invention, will be described with reference to the drawing.
The inlet scrubber 12 is a wet scrubber that eliminates dust, water-soluble components, and the like contained in the exhaust gas E to be introduced into the gas treatment furnace 14. In the present embodiment, the inlet scrubber 12 includes a straight tube type scrubber body 12a, and a spray nozzle 12b that is installed in the vicinity of the top of the scrubber body 12a inside the scrubber body 12a and that sprays a chemical liquid such as water in an atomized state. The inlet scrubber 12 communicates with an exhaust gas generation source (not shown) such as a semiconductor manufacturing apparatus via an exhaust gas duct 28.
In addition, the inlet scrubber 12 is installed so as to stand on a chemical liquid tank 30 (see
In the present embodiment shown in
The gas treatment furnace 14 is a device that thermally decomposes PFCs, N2O, and the like in the exhaust gas E by using an electric heater 22, and generally includes an outer cylinder 18, an inner cylinder 20, and the electric heater 22.
The outer cylinder 18 or at least an inner surface thereof is made of a refractory material such as a castable refractory material, and has a sealed circular cylindrical main body 18a including a gas treatment space 18b formed therein. As shown in
Although the outer cylinder 18 is formed in a sealed circular cylindrical shape in the present embodiment, the shape of the outer cylinder 18 may be formed in any shape as long as the outer cylinder 18 has a cylindrical shape having both ends sealed, for example, a sealed quadrangular cylindrical shape or the like.
In the illustrated embodiment, the gas introduction port 18c is drilled at the center of the bottom of the main body 18a, and a gas exhaust port 18f for exhausting the exhaust gas E thermally decomposed in the gas treatment space 18b inside the main body 18a is drilled at a position close to the gas introduction port 18c in the bottom of the main body 18a.
The inner cylinder 20 is formed of a refractory material such as a castable refractory material, a metal material such as Hastelloy (registered trademark of Haynes International) or stainless steel, or the like, and is a circular cylindrical member having both ends opened in the longitudinal direction thereof. One end of the inner cylinder 20 in the longitudinal direction is mounted to the bottom inside the main body 18a of the outer cylinder 18 so as to enclose the gas introduction port 18c. The inner cylinder 20 extends across the gas treatment space 18b of the outer cylinder 18, and the other end thereof in the longitudinal direction is located at a position close to a ceiling surface of the main body 18a of the outer cylinder 18.
Although the inner cylinder 20 is formed in a circular cylindrical shape in the present embodiment, the shape of the inner cylinder 20 may be any shape as long as the inner cylinder 20 has a cylindrical shape having both ends opened, for example, a quadrangular cylindrical shape or the like.
The electric heater 22 is a heat source for heating the gas treatment space 18b inside the gas treatment furnace 14, and has a heating element 22a having a long bar shape. As the heating element 22a, an element that has corrosion resistance to HF (hydrogen fluoride) produced as a byproduct by thermally decomposing PFCs in the exhaust gas E to be treated, and can generate heat at high temperatures is used. Specifically, examples thereof include ceramic materials such as silicon carbide (SiC), molybdenum disilicide (MoSi2), and lanthanum chromite (LaCrO3), and materials formed by helically winding a metal wire such as a nichrome wire or Kanthal (registered trademark of Sandvik AB) wire, which is a heating resistor, inside a protective pipe made of ceramic such as alumina or metal such as Hastelloy (registered trademark of Haynes International).
The heating element 22a is inserted in an internal space of the main body 18a through the insertion opening 18e provided at a predetermined position in the ceiling 18d of the outer cylinder 4, whereby the electric heater 22 is detachably mounted. Accordingly, the electric heater 22 is hung from the ceiling 18d of the main body 18a of the outer cylinder 18, and the heating element 22a having a long bar shape is placed in the internal space of the inner cylinder 20.
Although not shown, temperature measurement means such as a thermocouple for detecting the temperature of the gas treatment space 18b is mounted in the gas treatment furnace 14 configured as above, for example, and temperature data (temperature signal) detected by the temperature measurement means is provided via a signal line to control means including a central processing unit (CPU), a memory, an input device, a display device, etc. A power supply unit, etc., which is not shown, is also connected to the control means.
While the gas treatment furnace 14 configured as above is placed on the upper side of the chemical liquid tank 30, an upper end of a short pipe 24a having an inner diameter almost the same as that of the gas introduction port 18c is communicably connected to the gas introduction port 18c, and a lower end of the short pipe 24a is communicably connected to a region where the exhaust gas E having passed through the inlet scrubber 12 flows in the chemical liquid tank 30. Accordingly, the short pipe 24a functions as a “decrease part 24” for decreasing, at once, the inner diameter of the passage for the exhaust gas E that has passed through the inlet scrubber 12, to a diameter not greater than the diameter of the gas introduction port 18c.
In the vicinity of a part to which the short pipe 24a is connected in a ceiling of the chemical liquid tank 30, i.e., in the vicinity of an end on an upstream side in an exhaust gas flowing direction of the decrease part 24, reducing gas supply means 26 for supplying a predetermined amount of reducing gas G toward the exhaust gas E to be supplied into the gas treatment furnace 14 via the decrease part 24 is provided.
The reducing gas supply means 26 includes: a reducing gas supply pipe 26a having a tip that communicates with the internal space of the chemical liquid tank 30 in the vicinity of the part to which the short pipe 24a is connected in the ceiling of the chemical liquid tank 30, and a base end that is connected to a storage source 26c, such as a tank or a cylinder, for storing the reducing gas G; flow rate adjustment means 26b that is provided on the reducing gas supply pipe 26a and that adjusts the amount of the reducing gas G to be supplied into the chemical liquid tank 30; and the like.
Examples of the reducing gas G to be supplied by the reducing gas supply means 26 include hydrogen, carbon monoxide, ammonia, and hydrocarbon, and when hydrogen or ammonia is used as the reducing gas G among these, the amount of carbon dioxide to be discharged to the atmosphere after thermal decomposition of the exhaust gas E can be reduced. When an abatement-target component in the exhaust gas E contains N2O, the amount of NOx to be discharged after thermal decomposition of N2O can also be remarkably reduced by supplying hydrogen or ammonia the amount of which is almost the same as that of the N2O.
When a hydrocarbon such as CH4 (methane) is, for example, used as the reducing gas G, initial cost and running cost of the entire treatment device 10 for an exhaust gas containing PFCs can be reduced.
Here, when the exhaust gas E contains PFCs, a flow rate of the reducing gas G to be supplied from the reducing gas supply means 26 is, for example, 0.2 to 10 liters/minute with respect to a flow rate of the exhaust gas E to be supplied to the gas treatment furnace 14 being 200 liters/minute, and specifically, the flow rate of the reducing gas G is preferably at a proportion of 0.1 to 5 parts by volume with respect to 100 parts by volume of the flow rate of the exhaust gas E to be supplied to the gas treatment furnace 14, and more preferably within a range of 0.5 to 2.5 parts by volume.
When ammonia is used as the reducing gas G, urea or urea aqueous may be used as the supply source.
The outlet scrubber 16 is a wet scrubber that cools the thermally decomposed exhaust gas E that has passed through the gas treatment furnace 14 and that finally eliminates dust, water-soluble components, and the like produced as a byproduct through thermal decomposition, from the exhaust gas E. In the present embodiment, the outlet scrubber 16 includes: a straight tube type scrubber body 16a that communicates, via the exhaust pipe 34, with the gas exhaust port 18f provided in the bottom of the main body 18a of the gas treatment furnace 14; a plurality of perforated plates 16b (four perforated plates 16b in the present embodiment) installed so as to be spaced from each other in the vertical direction in the scrubber body 16a; and a downward-oriented spray nozzle 16c that is mounted right above the perforated plate 16b arranged at the top and sprays a chemical liquid such as water from the upper side in the direction opposite to the flowing direction of the exhaust gas E. The outlet scrubber 16 is installed so as to stand on the chemical liquid tank 30, so that the discharged water is delivered to the chemical liquid tank 30.
In the outlet scrubber 16 of the present embodiment, unlike the above-described inlet scrubber 12, a new chemical liquid such as clean water is supplied to the spray nozzle 16c (see
An exhaust fan 36 for discharging the treated exhaust gas E to the atmosphere is connected at an outlet of the outlet scrubber 16.
Corrosion-resistant lining or coating is applied, using vinyl chloride, polyethylene, unsaturated polyester resin, fluororesin, or the like, to parts other than the gas treatment furnace 14 of the treatment device 10 for semiconductor manufacturing exhaust gas according to the present embodiment, to protect each part from corrosion due to corrosive components such as hydrofluoric acid contained in the exhaust gas E or produced by thermal decomposition of the exhaust gas E.
Further, when the exhaust gas E is abated using the treatment device 10 for semiconductor manufacturing exhaust gas configured as above, an operation switch (not shown) of the treatment device 10 is firstly turned on to operate the gas treatment furnace 14 and the electric heater 22, thereby starting heating the gas treatment space 18b in the gas treatment furnace 14.
When the temperature inside the gas treatment space 18b reaches a predetermined temperature, in a range of 800° C. to 1400° C., corresponding to the type of the exhaust gas E to be treated, the exhaust fan 36 operates to start introduction of the exhaust gas E into the treatment device 10. Then, the exhaust gas E passes through the inlet scrubber 12, the gas treatment furnace 14, and the outlet scrubber 16 in this order, to abate abatement-target components (i.e., PFCs, N2O, and the like) in the exhaust gas E. In addition, the control means, which is not shown, controls the amount of power to be supplied to the electric heater 22 of the gas treatment furnace 14 so as to maintain a predetermined temperature inside the gas treatment space 18b.
In the treatment device 10 for semiconductor manufacturing exhaust gas according to the present embodiment, when the reducing gas G, which is supplied from the reducing gas supply means 26 to the exhaust gas E washed with liquid that has passed through the inlet scrubber 12, passes through the decrease part 24, a flow speed thereof is increased and at the same time the contact opportunity thereof with PFCs, N2O, and the like, which are abatement (thermal decomposition) target components in the exhaust gas E, increases. Subsequently, the exhaust gas E and the reducing gas G supplied into the gas treatment furnace 14 through the gas introduction port 18c while having the increased flow speed collide with the heating element 22a of the electric heater 22 placed in the inner cylinder 20 to produce turbulent flow, thereby further increasing the contact opportunity of the reducing gas G with PFCs, N2O, and the like in the exhaust gas E. The action of the radicalized reducing gas G is enhanced by being heated in this state by the electric heater 22 in the inner cylinder 20, so that PFCs, N2O, and the like in the exhaust gas E are thermally decomposed very efficiently. The high-temperature exhaust gas E thermally decomposed as above is to flow down outside the inner cylinder 20. At this time, a heat-insulating effect can be exerted so as to prevent the temperature inside the inner cylinder 20 from being lowered.
With the above-described synergistic action, 99.9% or more of CF4, which is the most hardly decomposable PFC, can be decomposed at a heating temperature lower than before, for example, 1250° C. to 1350° C.
In the above-described embodiment, the gas introduction port 18c provided in the outer cylinder 18 of the gas treatment furnace 14 communicates, via the short pipe 24a, with the upper space where the exhaust gas E washed with liquid by the inlet scrubber 12 flows in the chemical liquid tank 30. However, instead of using the short pipe 24a, the gas introduction port 18c of the outer cylinder 18 and the upper space of the chemical liquid tank 30 may be directly connected. In this case, an edge itself, on the front side in the gas flowing direction, of the gas introduction port 18c of the outer cylinder 18 functions as the decrease part 24.
In the above-described embodiment, when the gas introduction port 18c of the gas treatment furnace 14 communicates, via the short pipe 24a, with the upper space (passage for the exhaust gas washed with liquid) of the chemical liquid tank 30, it is preferable that a heat exchanger (not shown) is provided between the short pipe 24a and the exhaust pipe 34, i.e., the exhaust heat of the exhaust gas E that flows through the exhaust pipe 34 is supplied to the exhaust gas E that flows through the short pipe 24a, to preheat the exhaust gas E. In this case, it is possible to more efficiently utilize energy.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/014176 | Apr 2021 | WO | international |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/016592 | 4/26/2021 | WO |
