Patent Application
20130139690
1. Field of the Invention
The present invention relates to an exhaust gas treatment system that separates and recovers monosilane from a mixed gas, containing monosilane, discharged from a semiconductor fabrication equipment so as to recycle monosilane.
2. Description of the Related Art
Unused monosilane is contained in exhaust gas discharged from a semiconductor fabrication equipment, in particular a plasma CVD apparatus. Recycling monosilane by separating and recovering it therefrom enhances the utilization efficiency of monosilane, so that the reduction in gas utilities' cost can be expected.
In view of the above purpose, a method is reported where monosilane discharged from the semiconductor fabrication equipment is recycled. In this method, fine particles in exhaust gas is trapped by a filter provided at a subsequent stage and a gas containing monosilane that has passed through the filter is circulated in a chamber. Thus, the purity of monosilane is not very high and impurities are considered to be contained in a fabricated semiconductor (see References (1) and (2)).
Purge nitrogen in a dry pump provided at a stage subsequent to a plasma CVD apparatus is mixed in the exhaust gas discharged from a conventional solar cell manufacturing equipment functioning as the plasma CVD apparatus. In this case, the following had been reported. That is, when monosilane gas containing nitrogen is reused by circulating it in the solar cell manufacturing equipment, nitrogen is mixed into a solar cell manufactured and therefore the performance is degraded (see References (4) and (5)).
In view of the above, an attempt was made to separate nitrogen from monosilane and vice versa. This requires large-scale facilities such as rectifiers, which in turn is problematic in terms of offsetting the cost incurred (see Reference (3)).
The present invention has been made to solve problems as described above, and a purpose thereof is to provide an exhaust gas treatment system and its technology capable of suppressing the mixture of impurities into a semiconductor fabrication equipment while monosilane contained in exhaust gas discharged from the semiconductor fabrication equipment is efficiently separated and recovered so as to be reused.
In order to resolve the above-described problems, an exhaust gas treatment system according to one embodiment of the present invention is an exhaust gas treatment system for recovering monosilane from a mixed gas containing at least hydrogen and monosilane discharged from a semiconductor fabrication equipment, and the system includes: a pump unit configured to release the mixed gas discharged from the semiconductor fabrication equipment; and a silane gas treatment unit configured to separate and recover monosilane from the mixed gas so as to be recycled in the semiconductor fabrication equipment, wherein argon is used as a purge gas introduced into the pump unit.
According to this embodiment, monosilane discharged from a semiconductor fabrication equipment is separated and recovered so as to be recycled in the semiconductor fabrication equipment. Thus the utilization efficiency of monosilane can be improved and the operating cost can be reduced.
Since argon is used as the purge gas of the pump unit, the concentration of impurities in monosilane recovered can be reduced. Further, argon used is separated and recovered and then circulated in the pump unit so as to be reused. Thus the utilization efficiency of purge gas can be enhanced and the operating cost can be reduced.
Furthermore, a system is constructed as a production line of solar cells such that gas discharged only when an i (intrinsic) layer is fabricated is recovered and treated. Thus, the targeted gas can be efficiently separated and recovered.
Embodiments will now be described by way of examples only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures in which:
Hereinbelow, the embodiments of the present invention will be described with reference to the accompanying drawings. Note that the identical components are given the identical reference numerals in all accompanying Figures and the repeated description thereof will be omitted as appropriate.
The semiconductor fabrication equipment 1 is not limited to any particular equipment. For example, a plasma CVD apparatus for forming a film by thin-film silicon used for a solar cell may be used as the semiconductor fabrication equipment 1.
The composition of the mixed gas discharged from the semiconductor fabrication equipment 1 is not limited to any particular ones but may contain monosilane, hydrogen, and a small amount of impurities, for instance. The small amount of impurities may be a high-order silane having plural silicons, such as disilane or trisilane, CH4, PH3, and B2H6 (whose content rate in the mixed gas is in a range of 0.0001 to 1% each) and the like. It is desirable that only a semiconductor fabrication equipment 1 into which various dopant gases such as CH4, PH3, and B2H6 are not introduced be connected to the exhaust gas treatment system 200 of the present embodiment.
The pump unit 2 suctions the mixed gas discharged from the semiconductor fabrication equipment 1, and sends out the mixed gas to the silane gas treatment unit 20 provided at a stage subsequent to the pump unit 2. The type of a pump used is not limited to any particular one but a dry pump generally and oftentimes works well for the semiconductor fabrication equipment 1. The dry pump needs to introduce a purge gas for the purposes of, for instance, maintaining airtightness, preventing unnecessary deposited material, preventing the corrosion inside a pump, and improving exhaust capability. The purge gas used in the present embodiment is not limited to any particular ones as long as the following three conditions are met. The three conditions are: that the purge gas does not react with monosilane, that it does not operate as a dopant even if it is mixed with a process gas, and that it has a gas density enough to normally operate the pump. And the purge gas having such properties may be a noble gas other than helium (e.g., neon, argon, krypton, and xenon). In light of cost performance, argon is most preferable among those. Though the amount of gas introduced is not limited to any particular amount, it may generally be 10 to 50 NL/minute per pump.
Also, a filter 2a may be provided at a stage prior to and/or subsequent to a pump 2b. If, in particular, a relatively large amount of fine particles such as a high-order silane are present, it is preferable that the filter 2a be provided. The filter 2a is a fine particle capturing filter that selectively removes the fine particles, such as a high-order silane, contained in the mixed gas. Though not limited to any particular one, the filter to be used may be a filter of vortex type or the like.
Further, the semiconductor fabrication equipment 1 sometimes undergoes chemical cleaning in order to remove the deposited material, inside a chamber, resulting from the film formation. In general, the chemical cleaning is done such that, in order to remove a silicon thin film deposited in the chamber, a plasma treatment is conducted while a gas such as NF3 and F2 is being introduced. Since, however, such a gas has a combustion enhancing property, it is necessary to prevent the gas from contacting an inflammable gas such as hydrogen and monosilane. Thus, it is preferable that a switching valve 2c be provided at a stage subsequent to the pump 2b. With this configuration, an operation mode is switched to an combustion-enhancing gas treatment system when exhaust gas comes out as a result of the chemical cleaning, thereby preventing such exhaust gas from being mixed into a treatment line of a silane-based gas. It is to be noted here that the switching valve 2c may be provided with a built-in mechanism for realizing the aforementioned operation. Also, when the combustion-enhancing gas is to be released to atmosphere, it is desirable that the combustion-enhancing gas be diluted with an inert gas such as nitrogen.
The silane gas treatment unit 20 allows the mixed gas to pass therethrough and separates the mixed gas into monosilane, contained in the mixed gas, and primary-constituent mixed gas, excluding monosilane, such as hydrogen and argon (hereinafter also referred to as “hydrogen/noble gas-rich gas” containing a high proportion of hydrogen and purge gas). A method for separating the mixed gas is not limited to any particular methods as long as the mixed gas can be separated into monosilane and the primary-constituent mixed gas excluding monosilane. For example, such a method may be an adsorption separation method using adsorbents, a membrane separation method using a membrane separation module, or a cryogenic separation method where the mixed gas is separated through distillation or partial condensation utilizing the difference in temperature when the mixed gas is cooled to a low temperature so as to be liquefied and condensed.
The carrier gas supplied to the heating unit 21 may be an inert gas such as hydrogen, argon, or helium, for instance. The carrier gas is heated to 40 to 200° C. and then fed to each of the adsorption towers 22a to 22c.
The adsorption towers 22a to 22c according to the present embodiment are filled with adsorbents capable of adsorbing monosilane more efficiently than hydrogen, nitrogen, and argon. The absorbent like this is not limited to any particular one insofar as it conforms to the aforementioned purpose and may be activated carbon, silica gel, alumina gel, and zeolite such as 3A, 4A, 5A and 13X, for instance. The adsorption towers 22a to 22c may each have a structure, such as an electric furnace, which allows the temperature to be kept constant on the outside thereof. The temperature can be adjusted based on a detection result of a temperature detector (not shown) that is inserted inside the adsorption towers 22a to 22c. Also, a plurality of temperature detectors inserted thereinto allow an adsorption band to be kept track of so as to observe and grasp adsorption behavior. Differential pressures of the adsorption towers 22a to 22c are monitored by measuring the internal pressures of the adsorption towers 22a to 22c by a plurality of pressure sensors (not shown), so that the respective powdering conditions of the adsorbents can be grasped as well.
A detailed description is now given of a method for separating monosilane using adsorbents. A carrier gas such as hydrogen that is heated to about 40 to 200° C. by the heating unit 21 is introduced to each of the adsorption towers 22a to 22c filled with adsorbents. The carrier gas is discharged by the vacuum pump 27 until the pressure reaches −0.1 MPaG to −0.09 MPaG. The pressure is maintained in this condition for about 1 to 100 hours. Then the respective temperatures of the adsorption towers 22a to 22c are cooled down to predetermined temperatures (an adsorbent pretreatment). Then, upon the introduction of a mixed gas whose temperature is 0 to 100° C. and whose pressure is −0.01 MPaG to 1.0 MPaG into the adsorption towers 22a to 22c, monosilane contained in the mixed gas is adsorbed to the absorbents filled inside the adsorption towers 22a to 22c. As a result, a gas whose monosilane concentration is 1.0% or below is discharged from the adsorption towers 22a to 22c in an early stage of the introduction of the mixed gas. In the light of energy efficiency, it is preferred that the mixed gas whose temperature is 30 to 40° C. and whose pressure is −0.01 MPaG to 2.0 MPaG be introduced into the adsorption towers 22a to 22c.
In so doing, the adsorption-desorption switching three-way valves 25a to 25c are controlled such that exhaust passages of the adsorption towers 22a to 22c communicate with the noble gas treatment unit 30. The gas analysis unit 26 conducts composition analysis of the mixed gas discharged from the absorbents by the use of a Fourier transform infrared spectrometer (FT-IR) and an on-line gas chromatography (GC). And when monosilane of a predetermined concentration is detected thereby, the adsorption-desorption switching three-way valves 25a to 25c shut off the passages between the adsorption towers 22a to 22c and the noble gas treatment unit 30.
At this time, monosilane is being adsorbed onto the absorbents. Thus, the silane gas treatment unit 20 according to the present embodiment desorbs the adsorbed monosilane by a temperature swing adsorption (TSA) process, for instance. More specifically, heating the adsorption towers 22a to 22c to about 40 to 120° C. by the electric furnace causes monosilane to be desorbed from the adsorbents. As a result, the gas discharged from the adsorption towers 22a to 22c substantially contains monosilane in a high concentration. Thus, the adsorption-desorption switching three-way valves 25a to 25c are controlled such that the exhaust passages of the adsorption towers 22a to 22c communicate with the semiconductor fabrication equipment 1. Also, monosilane adsorbed by a pressure swing adsorption (PSA) can be desorbed as well. More specifically, depressurizing the adsorption towers 22a to 22c down to −0.1 MPaG to −0.05 MPaG by the vacuum pump 27 causes monosilane to be desorbed from the adsorbents. As a result, the gas discharged from the adsorption towers 22a to 22c substantially contains monosilane in a high concentration. Thus, the adsorption-desorption switching three-way valves 25a to 25c are controlled such that the exhaust passages of the adsorption towers 22a to 22c communicate with the semiconductor fabrication equipment 1.
As described above, for the TSA process the silane gas treatment unit 20 controls the timings with which the mixed gas is introduced and the adsorption towers are heated, whereas for the PSA process the silane gas treatment unit 20 controls the timings with which the mixed gas is introduced and the adsorption towers are depressurized. Thereby, the monosilane gas alone can be separated from the mixed gas and then the thus separated monosilane gas can be sent to the semiconductor fabrication equipment 1 at a high concentration so as to be circulated thereinto. Also, the adsorption towers into which the mixed gas or carrier gas is introduced are switched sequentially by using the adsorption-desorption switching valves 23a to 23c and 24a to 24c. This enables the adsorption and desorption of monosilane in the mixed gas to be continuously carried out without any interruption. In other words, when the adsorption switching valve 23a is opened while the other valves are closed and when the adsorption-desorption switching three-way valve 25a is switched to a noble gas treatment unit 30 side, the mixed gas flows into the adsorption tower 22a only and monosilane in the mixed gas is adsorbed. Thus a gas with a reduced monosilane concentration can be obtained at the noble gas treatment unit 30. The adsorption is carried out for a predetermined length of time. Then the adsorption switching valve 23b is opened while the other valves are closed, and the adsorption-desorption switching three-way valve 25b is switched to the noble gas treatment unit 30 side. This delivers the mixed gas to the adsorption tower 22b where monosilane in the mixed gas is adsorbed, so that a gas with a reduced monosilane concentration can be continuously obtained at the noble gas treatment unit 30 side. In parallel with the aforementioned processing, the adsorption-desorption switching three-way valve 25a is switched to a semiconductor fabrication equipment 1 side and then monosilane adsorbed onto the adsorption tower 22a is desorbed through the above-described PSA or TSA process. This allows a gas containing monosilane in a high concentration to be circulated on the semiconductor fabrication equipment 1 side. Repeating these operations alternately for each adsorption tower allows a predetermined gas to be uninterruptedly supplied to the noble gas treatment unit 30 side and the semiconductor fabrication equipment 1 side.
The noble gas treatment unit 30 is not limited to any particular one as long as it can have the mixed gas, composed mainly of hydrogen and argon separated from monosilane by the silane gas treatment unit 20, pass therethrough and then can separate hydrogen from argon and vice versa. For example, the noble gas treatment unit 30 as used herein may be a adsorption-separation means using adsorbents, a membrane separation means using a membrane separation module, or a cryogenic separation means where the mixed gas is separated through distillation or partial condensation utilizing the difference in temperature when the mixed gas is cooled to a low temperature so as to be liquefied and condensed.
The material used for the dense layer may be polyimide, polysiloxane, polysilazane, acrylonitrile, polyester, cellulose polymer, polysulfone, polyalkylene glycol, polyethylene, polybutadiene, polystyrene, polyvinylhalide, polyvinylidene halide, polycarbonate, and block copolymers having repeating units of any of the preceding components, for instance.
The material used for the base material may be an inorganic material such as glass, ceramic, and sintered metal and a porous organic material, for instance. The porous organic material as used herein may be polyether, polyacrylonitrile, polyether, poly(arylene oxide), polyether ketone, polysulfide, polyethylene, polypropylene, polybutene, polyvinyl, and the like.
The flow rate, the pressure, and the temperature of the mixed gas supplied to the membrane separation apparatus 32 are not particularly limited. Also, the concentration of argon gas in the mixed gas, the non-permeation-side pressure and the permeation-side pressure of the membrane separation apparatus 32 are not particularly limited. For example, the flow rate may be 5 NL/min to 500 NL/min relative to the capacity of 1 L of the membrane separation apparatus 32, and may preferably be 10 NL/min to 100 NL/min. The pressure may preferably be −90 kPaG to 1.0 MPaG. The temperature may preferably be about −20° C. to 100° C. The concentration of argon gas in the mixed gas may preferably be 50 vol % or below. The non-permeation-side pressure of the membrane separation apparatus 32 may preferably be −90 kPaG to 1.0 MPaG. The permeation-side pressure may preferably be −100 kPaG to 0.9 MPaG.
Here, the capacity of the membrane separation apparatus 32 indicates the volume of a portion of the membrane separation apparatus 32 where the separation membrane in the separation apparatus 32 is filled in a sufficiently dense manner.
When the membrane separation unit is operated at a temperature, other than a room temperature, which serves as the temperature of the mixed gas supplied to the membrane separation apparatus 32, a temperature control unit 31 as shown in
The temperature control unit 31 is not particularly limited as long as it has a function of cooling or heating the mixed gas and it may be an electric heater, various heat exchangers, or the like, for instance. The mixed gas that has been cooled or heated by the temperature control unit 31 is supplied to the membrane separation apparatus 32.
Hydrogen gas separated by the membrane separation apparatus 32 is sent to a hydrogen gas treatment unit 40, whereas high-concentration argon is sent to the pump 2b. In the hydrogen gas treatment unit 40, the hydrogen recovered may simply be used for a combustion treatment or as fuel. Or the hydrogen gas treatment unit 40 may be configured such that the hydrogen recovered is diluted with nitrogen, air, or the like to an explosion limit or below and then the hydrogen diluted therewith is released to the outside. When the hydrogen recovered is to be diluted therewith, it is preferable for safety that the concentration of hydrogen be diluted to an explosion lower limit or below (e.g., 4 vol % or below). As a method for diluting hydrogen therewith, the hydrogen recovered is preferably diluted with nitrogen by a nitrogen manufacturing apparatus using a membrane separation method or PSA method. This method of diluting the hydrogen with nitrogen is economically inexpensive. The gas diluted therewith may be discharged to the outside by a blower. Also, a hydrogen gas purification unit may be provided where hydrogen can be purified and reused. The hydrogen purified may be used as raw materials for a fuel cell. How hydrogen is to be processed can be determined from a result obtained when the purity of recovered hydrogen is measured by a gas analysis unit 34a.
The high-concentration argon separated by the membrane separation apparatus 32 can be circulated by the pump 2b so as to be reused. In so doing, whether or not the high-concentration argon is to be reused may be determined based on a result obtained when the purity of recovered argon is measured by a gas analysis unit 34b provided at a non-permeation side. Depending on the purity of high-concentration argon gas circulated by the pump 2b, a mechanism by which to circulate only the purge gas in the pump may be provided. More specifically, if high-concentration argon gas whose content of hydrogen is 4.0 vol % or above is to be circulated, it will be desirable that this high-concentration argon gas be circulated as the purge gas only in the pump 2b. In this case, the sealing argon gas fed to the pump 2b is preferably fresh argon from a compressed gas cylinder. If the high-concentration argon gas is to be circulated as the purge gas only in the pump 2b, there may be provided a mechanism wherein the argon gas can be recovered further efficiently by selecting an operating condition of the membrane separation apparatus 32. Also, there may be provided a mechanism for controlling the amount of noble gas supplied from the compressed gas cylinder relative to the amount of circulated argon so that the purge gas (pump feeding gas) supplied to the pump 2b can be supplied steadily without fluctuations in the amount supplied thereto. Also, as will be discussed later, an accumulator 9a may be provided at a midway point of a circulation line led to a pump, so that the supply pressure to the pump can be kept constant.
In the exhaust gas treatment system according to the present embodiment, other various supplemental facilities as shown in
The exhaust gas treatment system as illustrated in
A compression unit 3 is not particular limited and may be a diaphragm compressor, a centrifugal compressor, an axial flow compressor, a reciprocating compressor, a twin-screw compressor, a single-screw compressor, a scroll compressor, a rotary compressor or the like. Among these compressors, a diaphragm compressor is highly preferred.
The operating condition of the gas compression unit 3 is not particularly limited and the compression unit 3 is preferably operated such that the temperature of the mixed gas after compression is 200° C., which is a decomposition temperature of monosilane, or below. That is, when, for example, the mixed gas discharged from the pump unit 2 is compressed from an ordinary pressure, the compressor is preferably operated at a compression ratio of 4.4 or below. If there are thermally unstable impurities, such as B2H6, in the mixed gas, the temperature of the mixed gas after compression will be preferably 100° C. or below for the purpose of decomposing such impurities. That is, when, for example, the mixed gas discharged from the pump unit 2 is compressed from an ordinary pressure, the compressor is preferably operated at a compression ratio of 2.0 or above.
The structure of a compressor used for the gas compression unit 3 is not particularly limited. In order to stably operate the compressor even when the flow rate of the mixed gas fed to the compressor varies, the gas compression unit 3 is preferably configured such that both a compressor and an inverter are provided or the gas compression unit 3 is preferably configured by the use of a spill-back method where the mixed gas once compressed by the compressor is returned to a suction side of compressor.
A gas container 4 collects the mixed gas discharged from a plurality of semiconductor fabrication equipment 1 through the pump units 2 in a tank or the like having a sufficient capacity. Thereby, the gas container 4 can average variations in the flow rate and the pressure of the mixed gas discharged from the respective semiconductor fabrication equipment 1 and can constantly deliver the mixed gas having a constant flow rate and a constant pressure to the silane gas treatment unit 20 provided at a stage subsequent to the gas container 4. Also, a function of removing fine particles contained in the mixed gas may be added by devising the structure of the exhaust gas treatment system.
Though not particularly limited, the size of the tank used for the gas container 4 may preferably be set to at least a value corresponding to the sum of maximal flow rates of gases supplied to the respective semiconductor fabrication equipment 1.
Though not particularly limited, the pressure inside the tank used for the gas container 4 may be accumulated at a maximum of 10 MPaG. It may preferably be accumulated up to 5.0 MPaG or more preferably be accumulated up to 1 MPaG.
At the start-up of the system, it is preferable that while an outlet valve of the gas container 4 is being closed, the purge gas in a pump or the exhaust gas be supplied to the gas container 4 from the gas compression unit 3 so as to be accumulated in the gas container 4. This can maintain a pressure enough to mitigate adverse changes in the supply flow rate of gas supplied to the respective separation apparatuses provided at stages subsequent to the gas container 4, in the event that the exhaust gas flow rate of the semiconductor fabrication equipment varies greatly. At the same time, the amount of gas that can be held in the gas container 4 can be increased and therefore the volume of the gas container can be reduced. Further, accumulation of sufficient pressure allows the separation efficiency at each of the separation apparatuses, which is operationally advantageous.
A flow rate control unit 5 controls the flow rate and the pressure of the mixed gas gathered in the gas container 4 so that the flow rate and the pressure thereof are constant. Though not particularly limited, a method for controlling the flow rate and the pressure thereof may preferably be one that is not affected by a change in the pressure of the mixed gas supplied to the flow rate control unit 5. Such a method may be one using a mass flow controller, for instance. Also, as for the pressure, a necessary pressure can be ensured by selecting an operating condition of the gas compression unit 3.
A boosting unit 7 is used to introduce a gas composed mainly of monosilane separated by the silane gas treatment unit 20 into a silane gas purification unit 50 described later and is used to boost the pressure up to a certain pressure level in order to circulate monosilane in the semiconductor fabrication equipment 1. The boosting unit 7 as used herein is not particularly limited insofar as it attains the aforementioned purpose and may preferably be one having the same features and requisites as that of the above-described gas compression unit 3.
The silane gas purification unit 50 is configured such that it has a first purification unit 60 therewithin. A second purification unit 70 may be further provided at a stage subsequent to the first purification unit 60.
The absorbent used in the adsorption towers 62a to 62c (72a to 72c) is not particularly limited as long as it can selectively adsorb the impurities, such as phosphine, diborane and disilane, contained in the mixed gas composed mainly of monosilane. Such adsorbent may be activated carbon, silica gel, alumina gel, and zeolite such as 3A, 4A, 5A and 13X, for instance. Type-A zeolite, which is ion-exchanged with magnesium and manganese, and zeolite with a mordenite-type framework are more preferable.
The adsorption towers 62a to 62c (72a to 72c) may each have a structure, such as an electric furnace, which allows the temperature to be kept constant on the outside thereof. The temperature can be adjusted based on a detection result of a temperature detector (not shown) that is inserted inside the adsorption towers 62a to 62c (72a to 72c). Also, a plurality of temperature detectors inserted thereinto allow an adsorption band to be kept track of so as to observe adsorption behavior. Differential pressures of the adsorption towers 62a to 62c (72a to 72c) are monitored by measuring the internal pressures of the adsorption towers 62a to 62c (72a to 72c) by a plurality of pressure sensors (not shown), so that the respective powdering conditions of the adsorbents can be grasped as well.
The type of carrier gas fed to the heating unit 61 (71) may be an inert gas such as nitrogen, hydrogen, and argon, for instance. The carrier gas is heated to 40 to 200° C. and then fed to each of the adsorption towers 62a to 62c (72a to 72c).
An operation of the first purification unit 60 and the second purification unit 70 is as follows. A carrier gas such as hydrogen that is heated to about 40 to 200° C. by the heating unit 61 (71) is first introduced to each of the adsorption towers 62a to 62c (72a to 72c). Then the carrier gas is discharged by the vacuum pump 66 (76) until the pressure reaches −0.1 MPaG to −0.09 MPaG. The pressure is maintained in this condition for about 1 to 100 hours. Then the respective temperatures of the adsorption towers 62a to 62c (72a to 72c) are cooled down to predetermined temperatures (an adsorbent pretreatment). Then, upon the introduction of a mixed gas whose temperature is 0 to 100° C. and whose pressure is −0.01 MPaG to 5.0 MPaG into the adsorption towers 62a to 62c (72a to 72c), phosphine, diborane, disilane and the like contained in the mixed gas are adsorbed to the absorbents. As a result, a gas whose total concentration of phosphine, diborane, disilane and the like is 1000 ppm or below, preferably 100 ppm or below, or more preferably 10 ppm or below is discharged from the adsorption towers 62a to 62c (72a to 72c) in an early stage of the introduction of the mixed gas. In the light of energy efficiency, it is preferred that the mixed gas whose temperature is 30 to 40° C. and whose pressure is −0.01 MPaG to 1.0 MPaG be introduced into the adsorption towers 62a to 62c (72a to 72c).
The adsorption-desorption switching three-way valves 65a to 65c are controlled such that exhaust passages of the adsorption towers 62a to 62c in the first purification unit 60 communicate with the second purification unit 70. Also, the adsorption-desorption switching three-way valves 75a to 75c are controlled such that exhaust passages of the adsorption towers 72a to 72c in the second purification unit 70 communicate with a gas analysis unit 6e. Then a Fourier transform infrared spectrometer (FT-IR) and an on-line gas chromatography (GC) in the gas analysis unit 6e conduct composition analysis of phosphine, diborane, disilane and the like. And when phosphine, diborane, disilane and the like of predetermined concentrations are detected by the gas analysis unit 6e, the adsorption-desorption switching three-way valves 65a to 65c (75a to 75c) shut off the passages communicating with the second purification unit 70 (the gas analysis unit 6e).
Phosphine, diborane, disilane and the like adsorbed to the first purification unit 60 and/or the second purification unit 70 can be now desorbed through the TSA process or PSA process, for instance. More specifically, heating the adsorption towers 62a to 62c (72a to 72c) to about 40 to 120° C. by the electric furnace causes phosphine, diborane, disilane and the like to be desorbed from the adsorbents, when the TSA process is employed. Also, more specifically, depressurizing the adsorption towers 62a to 62c (72a to 72c) down to −0.1 MPaG to −0.05 MPaG causes phosphine, diborane, disilane and the like to be desorbed from the adsorbents, when the PSA process is employed. As a result, the gas discharged from the adsorption towers 62a to 62c (72a to 72c) substantially contains phosphine, diborane, disilane and the like in a high concentration. The gas containing phosphine, diborane, disilane and the like in a high concentration communicates with the exhaust passages and is treated appropriately and safely by a mixed gas treatment unit 8.
The mixed gas treatment unit 8 is an apparatus for detoxifying or abating monosilane, phosphine, diborane, disilane and the like, which are toxic gases. Also, the mixed gas treatment 8 is provided with a structure in which such toxic gases are diluted with noble gas to a predetermined concentration level and are then introduced into an detoxification unit or abatement unit where such gasses as monosilane, phosphine, diborane and disilane are detoxified or abated to an allowable concentration level or below and then discharged outside.
Gas analysis units 6a to 6f may be provided to measure the component of gas communicated to the silane gas treatment unit 20 from the flow rate control unit 5 as well as the component concentration of high-concentration monosilane gas and high-concentration argon separated by and discharged from the silane gas purification unit 50 and the noble gas treatment unit 30. A method for the measurement employed by the gas analysis units 6a and 6f is not particularly limited as long as at least the concentration of monosilane and the concentration of argon in the mixed gas can be measured. For example, such a method may be one using an FT-IR with a gas circulation type sample cell, an on-line type gas chromatograph, or the like.
If the concentration of argon and the concentration of monosilane measured by the gas analysis units 6c and 6e are less than predetermined concentration levels, a mechanism may be provided supplementarily where argon and monosilane are sent to the monosilane detoxification unit (not shown) and a noble gas exhaust unit (not shown), without being circulated in the semiconductor fabrication equipment 1 and the bump unit 2, respectively, so that they can be treated safely and appropriately.
The accumulators 9a and 9b have argon and monosilane, recovered by the noble gas treatment unit 30 and the silane gas purification unit 50, circulated in the pump unit 2 and the semiconductor fabrication equipment 1 at constant pressure. The accumulators 9a and 9b as used herein are not particularly limited insofar as they attain the aforementioned purpose. And the pressure to be accumulated in the accumulators 9a and 9b must be lower than the pressure of gas supplied to the accumulators 9a and 9b and higher than the pressure with which the differential pressure of a flow rate control apparatus of the semiconductor fabrication equipment 1 can be obtained. If no such a range of pressures can be obtained, a boosting apparatus (not shown) will be preferably provided at a stage prior to the accumulators in order to raise the supply pressure to the accumulators 9a and 9b. The boosting apparatus as used herein may preferably be one further having the same features and requisites as those of the above-described gas compression unit 3. The pressure to be accumulated in the accumulators 9a and 9b is not limited to a particular value insofar as it serves the aforementioned purpose and may preferably be 0.05 MPaG to 10 MPaG or more preferably 0.1 MPaG to 0.5 MPaG.
A detailed description is given hereunder of the present embodiment based on exemplary embodiments or examples but the present embodiment is not limited to these exemplary embodiments only.
A compressor capable of being operated at the compression ratio of 4 is selected as the compressor 82a. While an outlet valve (not shown) of a pressurized tank 83a (capacity: 1 m3) is closed, argon is delivered to each dry pump 81b as purge gas at the flow rate of 10 NL/min, so that the pressure of the pressurized tank 83 is boosted up to 0.5 MPaG. Then the outlet valve of the pressurized tank 83 is opened and the supply of gas to a mass flow controller 84a starts. Also, the respective thin-film silicon solar cell CVD apparatuses 80 start their operations such that the start of operation of each of the three thin-film silicon solar cell CVD apparatuses 80 lags each other by four minutes. The gas flow rate is controlled at 20 NL/min by the mass flow controller 84a and is supplied to an adsorption tower 101a of the silane gas treatment unit 20 (with activated carbon filled, as adsorbent, with a volume of 21.6 L). The gas, whose flow rate has been controlled at a constant value by the mass flow controller 84a, undergoes gas composition analysis, and the pressure of the adsorption tower 101a is controlled at 0.4 MPaG by a back pressure valve 107. Before the start of operation, each of adsorption towers 101a to 101c is heated to 200° C. and the pretreatment is carried out for four hours while hydrogen is delivered at a rate of 10 NL/min. Then it is cooled down to a room temperature and is then controlled at a predetermined adsorption temperature (e.g., 30° C.). The temperature of the gas that has passed through the adsorption tower 101a is adjusted at 30° C. by a temperature regulator 90 before the gas is introduced into a membrane separation module 91 (polyimide hollow fiber membrane with a volume of 1.2 L). A vacuum pump 93 is connected at a permeation side of the membrane separation module 91, and the permeation-side pressure of the membrane separation module 91 is adjusted to −0.1 MPaG at a permeation-side back pressure valve 92a. The flow rate and the composition of a gas on the permeation side are measured by GC (gas chromatogram) and FT-IR in a gas analysis unit 85c. The non-permeation-side pressure of the membrane separation module 91 is controlled to 0.4 MPaG at a non-permeation-side back pressure valve 92b. The flow rate and the composition of a gas on the non-permeation side are measured by a flowmeter 94b and the GC (gas chromatogram) and FT-IR in the gas analysis unit 85c. After the operation for one hour, the adsorption tower 101a closes adsorption switching valves 102a and 103a and opens adsorption switching valves 102b and 103b. Thereby, the operation is switched to an adsorption tower 101b so as to continue the operation. At the same time, both a desorption switching valve 104a and a carrier gas introduction switching valve 105a are opened so as to deliver hydrogen at a rate of 10 NL/min. Also, the pressure is reduced to −0.09 MPaG by a vacuum pump 106 over a period of one hour. As a result, components adsorbed to the adsorption tower 101a are removed. The flow rate and the composition of the desorbed gas are measured by a flowmeter 108a and a gas analysis unit 85b. The operating conditions and results are gathered in Table 1 and Table 2.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiment 1-1 excepting the flow rate of the mass flow controller 84a and the gas composition. The operating conditions and results are gathered in Table 1 and Table 2.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 1-1 to 1-3 excepting that zeolite is used as absorbent. The operating conditions and results are gathered in Table 1 and Table 2.
The exhaust gas treatment system is operated, similarly to the exemplary embodiments 1-1 to 1-3, using the membrane separation as shown in
The exhaust gas treatment system is operated, similarly to the exemplary embodiments 1-1 to 1-3, using the cryogenic separation as shown in
In order that n-type membranes are produced by one of the three thin-film silicon solar cell CVD apparatus 80 and p-type type membranes are produced by another one thereof, PH3 and B2H6 are introduced thereinto, respectively, and the exhaust gas treatment system is operated similarly to the exemplary embodiments 1-1 to 1-6 excepting that a silane gas purification unit 50 is provided.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 1-1 to 1-15 excepting that N2 is used as the purge gas. The operating conditions and results are gathered in Table 3 and Table 4.
Using SiH4 recovered in the exemplary embodiments 1-1, 1-4, 1-22 and 1-25 and the comparative examples 1-1 and 1-4, a-Si solar cells are made according to a routine method so as to conduct a characteristic evaluation of them. The results are gathered in Table 5.
From the above results, it is evident that use of argon as the purge gas prevents a dopant component from being mixed into monosilane recovered and therefore the adverse effect of the dopant component on the performance of the solar cells can be reduced. Also, use of adsorption separation as the silane gas treatment unit attains a higher monosilane recovery rate than when other separation methods are used at an equal or higher purity level. Furthermore, the hydrogen/argon mixed gas separated by the silane gas treatment unit is processed by the membrane separation apparatus, so that high-purity argon can be recovered with a higher recovery rate.
The silane gas treatment unit 20 allows the mixed gas to pass therethrough and separates the mixed gas into a monosilane-rich gas containing a high proportion of monosilane contained in the mixed gas and a hydrogen/noble gas-rich gas containing a high proportion of hydrogen and purge gas. A method for separating the mixed gas into a monosilane-rich gas and a hydrogen/noble gas-rich gas is not limited to any particular methods as long as the mixed gas can be separated into a gas composed primarily of monosilane and a mixed gas composed primarily of hydrogen and purge gas. For example, such a method may be an adsorption separation method using adsorbents.
In the present embodiment, the adsorption-desorption switching three-way valves 25a to 25c are controlled such that exhaust passages of the adsorption towers 22a to 22c communicate with the wet scrubber 204. The gas analysis unit 26 conducts composition analysis of the mixed gas discharged from the absorbents by the use of a Fourier transform infrared spectrometer (FT-IR) and an on-line gas chromatography (GC). And when monosilane of a predetermined concentration is detected thereby, the adsorption-desorption switching three-way valves 25a to 25c shut off the passages, between the adsorption towers 22a to 22c and the wet scrubber, by the adsorption-desorption switching three-way valves 25a to 25c.
Also, in the present embodiment, the exhaust passages of the adsorption towers 22a to 22c are connected to the silane gas purification unit 50 and, furthermore, the adsorption-desorption switching three-way valves 25a to 25c are controlled such that exhaust passages of the adsorption towers 22a to 22c communicate with and circulate in the semiconductor fabrication equipment 1.
As described above, for the TSA process the silane gas treatment unit 20 controls the timings with which the mixed gas is introduced and the adsorption towers are heated, whereas for the PSA process the silane gas treatment unit 20 controls the timings with which the mixed gas is introduced and the adsorption towers are depressurized. Thereby, the monosilane-rich gas can be separated and then the thus separated monosilane gas can be sent to the semiconductor fabrication equipment 1 at a high concentration so as to be circulated thereinto. Also, the adsorption towers into which the mixed gas or carrier gas is introduced are switched sequentially by using the adsorption-desorption switching valves 23a to 23c and 24a to 24c. This enables the adsorption and desorption of monosilane in the mixed gas to be continuously carried out without any interruption. In other words, when the adsorption switching valve 23a is opened while the other valves are closed and when the adsorption-desorption switching three-way valve 25a is switched to a wet scrubber 204 side, the mixed gas flows into the adsorption tower 22a only and monosilane in the mixed gas is mainly adsorbed. Thus a hydrogen/noble gas-rich gas with a reduced monosilane concentration can be obtained at the wet scrubber 204. The adsorption is carried out for a predetermined length of time. Then the adsorption switching valve 23b is opened while the other valves are closed, and the adsorption-desorption switching three-way valve 25b is switched to the wet scrubber 204 side. This delivers the mixed gas to the adsorption tower 22b where monosilane in the mixed gas is mainly adsorbed, so that a hydrogen/noble gas-rich gas whose monosilane concentration has been mainly reduced can be continuously obtained at the wet scrubber 204 side. In parallel with the aforementioned processing, the adsorption-desorption switching three-way valve 25a is switched to a silane gas purification unit 50 side so that the gas can be fed to the semiconductor fabrication equipment 1, and then monosilane mainly adsorbed onto the adsorption tower 22a is desorbed through the above-described PSA or TSA process. This allows a gas containing monosilane in a high concentration to be circulated on the semiconductor fabrication equipment 1 side. Repeating these operations alternately for each adsorption tower allows a predetermined gas to be uninterruptedly supplied to the wet scrubber 204 side and the silane gas purification 50 side.
The wet scrubber 204 is not limited to any particular one as long as impurities (mainly hydrides) in the hydrogen/noble gas-rich gas containing a high proportion of hydrogen and argon separated by the silane gas treatment unit 200 can be removed by having the impurities mainly composed of hydrides pass through water. The wet scrubber 204 may preferably be a water scrubber, provided with a rotary stirring structure, having a high contact efficiency, for instance. More preferably, the wet scrubber 204 may have a horizontal scrubber structure in order to relieve blockage caused by precipitates occurring in connection with the removal of the impurities.
The noble gas treatment unit 30 is not limited to any particular one as long as it can separate wet hydrogen and dry argon, whose water concentration is 20 ppm or below, from a “mixed gas” composed mainly of hydrogen, argon and moisture content. Here, the “mixed gas” is composed mainly of hydrogen, argon and moisture content obtained when a hydrogen/noble gas-rich gas mainly composed of hydrogen and argon separated from the monosilane-rich gas by the silane gas treatment unit 20 is passed through the wet scrubber 204 in order to remove the impurities contained in the hydrogen/noble gas-rich gas. The noble gas treatment unit 30 may be a membrane separation means using a membrane separation module, for instance. Though the structure of a membrane separation apparatus used in this case may be similar to that of the membrane separation apparatus 32 according to the first embodiment, a membrane used for the membrane separation 32 may preferably be one that allows hydrogen and moisture to be selectively passed through and one for which the coefficient of moisture is larger than that of hydrogen.
The structure of the silane purification unit 50 is similar to that of the first embodiment.
A detailed description is given hereunder of the present embodiment based on exemplary embodiments or examples but the present embodiment is not limited to these exemplary embodiments only.
A compressor capable of being operated at the compression ratio of 4 is selected as the compressor 82a. While an outlet valve (not shown) of a pressurized tank 83a (capacity: 1 m3) is closed, argon is delivered to each dry pump 81b as purge gas at the flow rate of 10 NL/min, so that the pressure of the pressurized tank 83a is boosted up to 0.5 MPaG. Then the outlet valve of the pressurized tank 83a is opened and the supply of gas to a mass flow controller 84a starts. Also, the respective thin-film silicon solar cell CVD apparatuses 80 start their operations such that the start of operation of each of the three thin-film silicon solar cell CVD apparatuses 80 lags each other by four minutes. The gas flow rate is controlled at 20 NL/min by the mass flow controller 84a and is supplied to an adsorption tower 101a of the silane gas treatment unit 20 (with activated carbon filled, as adsorbent, with a volume of 60 L). The gas, whose flow rate has been controlled at a constant value by the mass flow controller 84a, undergoes gas composition analysis, and the pressure of the adsorption tower 101a is controlled at 0.3 MPaG by a back pressure valve 107. Before the start of operation, each of adsorption towers 101a to 101c is heated to 200° C. and the pretreatment is carried out for four hours while hydrogen is delivered at a rate of 10 NL/min. Then it is cooled down to a room temperature and is then controlled at a predetermined adsorption temperature (e.g., 30° C.).
After the operation for one hour, the adsorption tower 101a closes adsorption switching valves 102a and 103a and opens adsorption switching valves 102b and 103b. Thereby, the operation is switched to an adsorption tower 101b so as to continue the operation. Simultaneously, a desorption switching valve 104a is opened and the pressure is reduced to −0.09 MPaG by a vacuum pump 106 over a period of one hour. As a result, components adsorbed to the adsorption tower 101a are removed. After the operation for one hour, the adsorption tower 101b closes the adsorption switching valves 102b and 103b and opens adsorption switching valves 102c and 103c. Thereby, the operation is switched to an adsorption tower 101c so as to continue the operation. Simultaneously, a desorption switching valve 104a is closed, a desorption switching valve 104b is opened, and the pressure is reduced to −0.09 MPaG by a vacuum pump 106 over a period of one hour. This removes the components adsorbed to the adsorption tower 101b. A cycle of three hours so far is now defined as one cycle. Now the adsorption tower in operation is returned from the adsorption tower 101c to the adsorption tower 101a and the adsorption tower for which the desorption is to be done is shifted from the adsorption tower 101b to the adsorption tower 101c. Then experiments from a second cycle and onward are conducted. The flow rate and the composition of each gas separated by the silane gas treatment unit 20 are measured by flowmeters 108a and 108b and gas analysis units 85b and 85c. The operating conditions are gathered in Table 6, and the separated gas components after the respective gases have been passed through the silane gas treatment unit are gathered in the Table 7 and Table 8.
After a gas containing large amounts of hydrogen and argon, which are separated by the silane gas treatment unit 20 and then sent to the gas analysis unit 85b, has been passed through a water scrubber 1000, the gas is now sent to the noble gas treatment unit 30. The temperature of the gas is adjusted at 30° C. by the temperature regulator 90 of the noble gas treatment unit 30 before the gas is introduced into a membrane separation module 91 (polyimide hollow fiber membrane with a volume of 0.6 L). A vacuum pump 93 is connected at a permeation side of the membrane separation module 91, and the permeation-side pressure of the membrane separation module 91 is adjusted to −0.1 MPaG at a permeation-side back pressure valve 92a. The non-permeation-side pressure of the membrane separation module 91 is controlled to 0.1 MPaG at a non-permeation-side back pressure valve 92b. The flow rate and the composition of a gas on the non-permeation side are measured by a flowmeter 94b and the GC (gas chromatogram) and FT-IR in a gas analysis unit 85e. The results analyzed by the gas analysis unit 85e are gathered in Table 9. Table 9 also shows the results of comparative examples 2-1 to 2-6 where the gas discharged from the gas analysis unit 85b is fed to the noble gas treatment unit 30 by bypassing the water scrubber 1000.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiment 2-1 excepting the flow rates of the mass flow controllers 84a and 84b and the gas composition. The experiments are conducted under conditions where the flow rate of the mass flow controller 84b is 2.5 NL/min in the exemplary embodiment 202 and 0.5 NL/min in the exemplary embodiment 2-3.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 2-1 to 2-3 excepting that zeolite 13X (80 L) is used.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 2-1 to 2-6 excepting that the gas having passed through the gas analysis unit 85b in the exemplary embodiments 2-1 to 2-6 is fed to the noble gas treatment unit 30 by bypassing the water scrubber 1000 (no such a bypass line is depicted in
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 2-1 to 2-6 excepting that N2 is used as the purge gas. Analysis results of the gas analysis unit 85f under such conditions are gathered in Table 11.
Using SiH4 recovered in the exemplary embodiments 2-1 to 2-6 and the comparative examples 2-7 to 2-12, a-Si solar cells are made according to a routine method so as to conduct a characteristic evaluation of them. The results are gathered in Table 12.
From the above results, it is evident that use of argon as the purge gas prevents a dopant component from being mixed into monosilane recovered and therefore the adverse effect of the dopant component on the performance of the solar cells can be reduced. Also, the hydrogen/noble gas-rich gas separated by the silane gas treatment unit is made to pass through the water scrubber. Thus high-purity argon gas where the hydrides such as diborane and disilane have been removed can be recovered and recycled.
The pump unit 2 suctions the mixed gas discharged from the semiconductor fabrication equipment 1, and sends out the mixed gas to the gas compression unit 3 provided at a stage subsequent to the pump unit 2.
The structure of a compressor used for the gas compression unit 3 is not particularly limited. In order to stably operate the compressor even when the flow rate of the mixed gas fed to the compressor varies, the gas compression unit 3 is preferably configured such that both a compressor and an inverter are provided or the gas compression unit 3 is preferably configured by the use of a spill-back method where the mixed gas once compressed by the compressor is returned to a suction side of compressor.
The operating condition of the compressor used for the gas compression unit 3 is preferably operated such that the temperature of the compress gas to be fed to subsequent stages is 70 to 250° C. or preferably 100 to 200° C. That is, when, for example, the mixed gas discharged from the pump unit 2 is compressed from an ordinary pressure, the compressor is preferably operated at a compression ratio of 10 or below or more preferably a compression ratio of 6 or below.
In order to achieve a desired pressure, the gas compression unit 3 may be configured such that a plurality of compressors are placed in series to each other. In such a case, for the purpose of enhancing the compression efficiency, it is preferable that an after-cooler 3b (or an inner-cooler 3d) is each provided subsequent to each of a plurality of compressors. And it is preferable that the temperature of the mixed gas is cooled down to −50° C. to 50° C. or more preferably to 0° C. to 30° C. each time and then the thus cooled mixed gas is fed to a next compressor.
The gas container 4 collects the mixed gas discharged from a plurality of semiconductor fabrication equipment 1 through the gas compression units in a tank or the like having a sufficient capacity. Thereby, the gas container 4 can average variations in the flow rate and the pressure of the mixed gas discharged from the respective semiconductor fabrication equipment 1 and can constantly deliver the mixed gas having a constant flow rate and a constant pressure to the silane gas treatment unit 20 provided at a stage subsequent to the gas container 4. The gas container 4 may be provided with a structure by which to deliver the gas to a subsequent stage at a constant flow rate. Also, a function of removing fine particles contained in the mixed gas may be added by devising the structure of the exhaust gas treatment system.
Though not particularly limited, the size of the tank used for the gas container 4 may preferably be set to at least a value corresponding a maximal flow rate of gas supplied to the semiconductor fabrication equipment 1.
Though not particularly limited, the pressure inside the tank used for the gas container 4 may be accumulated at a maximum of 10 MPaG. It may preferably be accumulated up to 5.0 MPaG or more preferably be accumulated up to 1 MPaG.
At the start-up of the system, it is preferable that while the outlet valve of the gas container 4 is being closed, the purge gas in a pump or the mixed gas be supplied to the gas container 4 from the gas compression unit 3 so as to be accumulated in the gas container 4. This can maintain a pressure enough to mitigate adverse changes in the supply flow rate of gas supplied to the respective subsequent separation apparatuses, in the event that the exhaust gas flow rate of the semiconductor fabrication equipment varies greatly. At the same time, the amount of gas that can be held in the gas container 4 can be increased and therefore the volume of the gas container 4 can be reduced. Further, accumulation of sufficient pressure allows the separation efficiency at each of the separation apparatuses, which is operationally advantageous.
For the TSA process the silane gas treatment unit 20 controls the timings with which the mixed gas is introduced and the adsorbents are heated, whereas for the PSA process the silane gas treatment unit 20 controls the timings with which the mixed gas is introduced and the adsorbents are depressurized is depressurized. Thereby, the monosilane gas alone can be separated from the mixed gas and then the thus separated monosilane gas can be sent to the silane gas purification unit 50 at a high concentration so as to be circulated into the semiconductor fabrication equipment 1. Also, the adsorbents into which the mixed gas or carrier gas is introduced are switched sequentially by using the valves 23a to 23c and 24a to 24c. This enables the adsorption and desorption of monosilane in the mixed gas to be continuously carried out without any interruption. In other words, when the valve 23a is opened while the other valves are closed and when the three-way valve 25a is switched to a noble gas treatment unit 30 side, the mixed gas flows into the adsorption tower 22a only and monosilane in the mixed gas is adsorbed. Thus a gas with a reduced monosilane concentration can be obtained at the noble gas treatment unit 30. The adsorption is carried out for a predetermined length of time. Then the valve 23b is opened while the other valves are closed, and the three-way valve 25b is switched to the noble gas treatment unit 30 side. This delivers the mixed gas to the adsorption tower 22b where monosilane in the mixed gas is adsorbed, so that a gas with a reduced monosilane concentration can be continuously obtained at the noble gas treatment unit 30 side. In parallel with the aforementioned processing, the three-way valve 25a is switched to a semiconductor fabrication equipment 1 side and then monosilane adsorbed onto the adsorption tower 22a is desorbed through the above-described PSA or TSA process. This allows a gas containing monosilane in a high concentration to be circulated on the semiconductor fabrication equipment 1 side. Repeating these operations alternately for each adsorbent allows a predetermined gas to be uninterruptedly supplied to the noble gas treatment unit 30 side and the silane gas purification unit 50 side.
The structure of the noble gas treatment unit 30 is similar to that of the first embodiment.
The noble gas treatment unit 30 is not limited to the membrane separation means and the adsorption-separation means alone as long as the mixed gas can be separated into monosilane and other components excluding monosilane. For example, the noble gas treatment unit 30 as used herein may be an adsorption-separation means using adsorbents or a cryogenic separation means where the mixed gas is separated through distillation or partial condensation utilizing the difference in temperature when the mixed gas is cooled to a low temperature so as to be liquefied and condensed.
Note that the structure of the silane purification unit 50 is similar to that of the first embodiment.
In the exhaust gas treatment system according to the present embodiment, other various supplemental facilities as shown in
A detailed description is given hereunder of the present embodiment based on exemplary embodiments or examples but the present embodiment is not limited to these exemplary embodiments only.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiment 3-1 excepting that a secondary gas temperature, when the mixed gas is compressed by the diaphragm compressor 363a, is adjusted at 200° C. and excepting that the temperature of the compressed mixed gas is adjusted at 40° C. by the pre-cooler 361 and the after-cooler 362 and the compressor is operated in a single stage. The operating conditions of the gas compression unit 300a and the flow rates and compositions of the gas analyzed by the gas analysis unit 85a are gathered in Table 13.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 3-1 and 3-2 excepting the flow rate of the mass flow controller 84a and the gas composition. The operating conditions of the gas compression unit 300a and the flow rates and compositions of the gas analyzed by the gas analysis unit 85a are gathered in Table 13.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 3-1 and 3-2 excepting that the secondary gas temperature, when the mixed gas is compressed by the diaphragm compressors 363a to 363e, is adjusted at 60° C. and excepting that the temperature of the compressed mixed gas is adjusted at 30° C. by the pre-cooler 361, the coolers 364a to 364d, and the after-cooler 362, and compression is performed in five stages. The operating conditions of the gas compression unit 300a and the flow rates and compositions of the gas analyzed by the gas analysis unit 85a are gathered in Table 14.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 3-1 and 3-2 excepting that the secondary gas temperature, when the mixed gas is compressed by the diaphragm compressor 363a, is adjusted at 300° C. The operating conditions of the gas compression unit 300a and the flow rates and compositions of the gas analyzed by the gas analysis unit 85a are gathered in Table 14.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 3-1 and 3-2 and the comparative examples 3-1 and 3-2 excepting the flow rate of the mass flow controller 84a and the gas composition. The operating conditions of the gas compression unit 300a and the flow rates and compositions of the gas analyzed by the gas analysis unit 85a are gathered in Table 14.
In order to recycle monosilane gas, various kinds of mixed gases in the exemplary embodiments 3-1 to 3-6 and the comparative examples 3-1 to 3-6 analyzed by the gas analysis unit 85a are supplied to the adsorption tower 101a (with activated carbon filled as adsorbent) of the silane gas treatment unit 20 employing an adsorption separation method as shown in
After the operation for one hour, the adsorption tower 101a closes the adsorption switching valves 102a and 103a and opens the adsorption switching valves 102b and 103b. Thereby, the operation is switched to the adsorption tower 101b so as to continue the operation. Simultaneously, the desorption switching valve 104a is opened and the pressure is reduced to −0.09 MPaG by the vacuum pump 106 over a period of one hour. As a result, components adsorbed to the adsorption tower 101a are removed. After the operation for one hour, the adsorption tower 101b closes the adsorption switching valves 102b and 103b and opens the adsorption switching valves 102c and 103c. Thereby, the operation is switched to the adsorption tower 101c so as to continue the operation. Simultaneously, the desorption switching valve 104a is closed, the desorption switching valve 104b is opened, and the pressure is reduced to −0.09 MPaG by the vacuum pump 106 over a period of one hour. A cycle of three hours so far is now defined as one cycle. Now the adsorption tower in operation is returned from the adsorption tower 101c to the adsorption tower 101a and the adsorption tower for which the desorption is to be done is shifted from the adsorption tower 101b to the adsorption tower 101c. Then experiments from a second cycle and onward are conducted. The mixed gas containing large amounts of hydrogen and argon, which are separated by the silane gas treatment unit 20 and then sent to the gas analysis unit 85b, is sent to the noble gas treatment unit 30. The temperature of the gas is adjusted at 30° C. by the temperature regulator 90 of the noble gas treatment unit 30 before the gas is introduced into the membrane separation module 91 (polyimide hollow fiber membrane with a volume of 0.6 L). Note that, in the exemplary embodiments 3-5 and 3-6 and the comparative examples 3-5 and 3-6, the experiments are conducted using the membrane separation module of 1.5 L in volume. The vacuum pump 93 is connected at a permeation side of the membrane separation module 91, and the permeation-side pressure of the membrane separation module 91 is adjusted to −0.1 MPaG at a permeation-side back pressure valve 92a. The non-permeation-side pressure of the membrane separation module 91 is controlled to 0.1 MPaG at a non-permeation-side back pressure valve 92b. The flow rate and the composition of a gas on the non-permeation side are measured by the flowmeter 94b and the GC (gas chromatogram) and FT-IR in the gas analysis unit 85e. The results analyzed by the gas analysis unit 85e are gathered in Table 15.
The pressure of the mixed gas discharged by the vacuum pump 106 of the silane gas treatment unit 20 is boosted by a compression unit 300b through an operation similar to that of the compression unit 300a. Then the temperature of the mixed gas is adjusted at 30° C. by the after-cooler 362 so as to be accumulated in the pressurized tank 83b (capacity: 1 m3). The flow rate of the mixed gas accumulated by the pressurized tank 83b is controlled at a constant of 2.0 NL/min by the mass flow controller 84b and is supplied to the silane gas purification unit 50. In the exemplary embodiments 3-1 and 3-2, the constant value is 2.0 NL/min. In the exemplary embodiments 3-3 and 3-4, the constant value is 2.5 NL/min. In the exemplary embodiments 3-5 and 3-6, the constant value is 0.5 NL/min.
From the above results, it is evident that since the compressors inside the gas compression unit are operated by controlling the temperature of secondary outburst gas in a range of 100 to 200° C., a hydrogenated impurity gas (e.g., diborane and disilane) excluding monosilane can be efficiently decomposed and therefore monosilane can be recovered with a high recovery rate. Also, the hydrogen/argon mixed gas, which has been separated by the monosilane treatment unit, is made to pass through the noble gas treatment unit, so that high-purity argon can be recovered with a high recovery rate.
Note that the structures of the gas compression unit 3, the gas container 4, the silane gas treatment unit 20, the wet scrubber 204, and the noble gas treatment unit 30 are similar to those of the first to third embodiments.
The material used for the dense layer may be polyimide, polysiloxane, polysilazane, acrylonitrile, polyester, cellulose polymer, polysulfone, polyalkylene glycol, polyethylene, polybutadiene, polystyrene, polyvinylhalide, polyvinylidene halide, polycarbonate, and block copolymers having repeating units of any of the preceding components, for instance.
The material used for the base material may be an inorganic material such as glass, ceramic, and sintered metal and a porous organic material, for instance. The porous organic material as used herein may be polyether, polyacrylonitrile, polyether, poly(arylene oxide), polyether ketone, polysulfide, polyethylene, polypropylene, polybutene, polyvinyl, and the like.
The flow rate, the pressure, and the temperature of the mixed gas supplied to the membrane separation apparatus 472 are not particularly limited. Also, the concentration of argon gas in the mixed gas, the non-permeation-side pressure and the permeation-side pressure of the membrane separation apparatus 472 are not particularly limited. For example, the flow rate may be 5 NL/min to 500 NL/min relative to the capacity of 1 L of the membrane separation apparatus 472, and may preferably be 10 NL/min to 100 NL/min. The pressure may preferably be −90 kPaG to 1.0 MPaG. The temperature may preferably be about −20° C. to 100° C. The non-permeation-side pressure of the membrane separation apparatus 472 may preferably be −90 kPaG to 1.0 MPaG. The permeation-side pressure may preferably be −100 kPaG to 0.9 MPaG.
When the membrane separation unit is operated at a temperature, other than a room temperature, which serves as the temperature of the mixed gas supplied to the membrane separation apparatus 472, a temperature control unit 471 as shown in
The temperature control unit 471 is not particularly limited as long as it has a function of cooling or heating the mixed gas and it may be an electric heater, various heat exchangers, or the like, for instance. The mixed gas that has been cooled or heated by the temperature control unit 471 is supplied to the membrane separation apparatus 472.
A gas mainly composed of moisture vapor and noble gas, excluding monosilane, separated by the membrane separation apparatus 472 is sent to the mixed gas treatment unit 8, whereas high-concentration monosilane is sent to the semiconductor fabrication equipment 1. In so doing, the mixed gas other than monosilane may be analyzed by a gas analysis unit 416a, so that the analysis result can be made use of in the setting of operating conditions. Also, the high-concentration monosilane may be analyzed by a gas analysis 416b, so that whether or not the high-concentration monosilane is to be recycled into the semiconductor fabrication equipment 1 can be determined.
The noble gas/silane separation unit 470 is not limited to the membrane separation means and the adsorption-separation means alone as long as the mixed gas can be separated into monosilane and other components excluding monosilane. For example, the noble gas/monosilane separation unit 470 as used herein may be an adsorption-separation means using adsorbents or a cryogenic separation means where the mixed gas is separated through distillation or partial condensation utilizing the difference in temperature when the mixed gas is cooled to a low temperature so as to be liquefied and condensed.
In the exhaust gas treatment system according to the present embodiment, other various supplemental facilities as shown in
The exhaust gas treatment system as illustrated in
A flow rate control unit 5 controls the flow rate and the pressure of the mixed gas gathered in the gas container 4 so that the flow rate and the pressure thereof are constant. Though not particularly limited, a method for controlling the flow rate and the pressure thereof may preferably be one that is not affected by a change in the pressure of the mixed gas supplied to the flow rate control unit 5. Such a method may be one using a mass flow controller, for instance. Also, as for the pressure, a necessary pressure can be ensured by selecting an operating condition of the gas compression unit 3.
A boosting unit 7 is used to introduce a gas composed mainly of monosilane separated by the silane gas treatment unit 20 into the silane gas purification unit 50 described later and is used to boost the pressure up to a certain pressure level in order to circulate monosilane in the semiconductor fabrication equipment 1. The boosting unit 7 as used herein is not particularly limited insofar as it attains the aforementioned purpose and may preferably be one having the same features and requisites as that of the above-described gas compression unit 3.
The mixed gas treatment unit 8 is an apparatus for detoxifying or abating monosilane, phosphine, diborane, disilane and the like, which are toxic gases. Also, the mixed gas treatment 8 is provided with a structure in which such toxic gases are diluted with noble gas to a predetermined concentration level and are then introduced into an detoxification unit or abatement unit where such gasses as monosilane, phosphine, diborane and disilane are detoxified or abated to an allowable concentration level or below and then released outside.
Gas analysis units 6a to 6g may be provided to measure the component of gas communicated to the silane gas treatment unit 20 from the flow rate control unit 5 as well as the component concentration of high-concentration monosilane gas and high-concentration argon separated by and discharged from the silane gas purification unit 50 and the noble gas treatment unit 30. A method for the measurement employed by the gas analysis units 6a to 6g is not particularly limited as long as at least the concentration of monosilane and the concentration of argon in the mixed gas can be measured. For example, such a method may be one using an FT-IR with a gas circulation type sample cell, an on-line type gas chromatograph, or the like.
If the concentration of argon and the concentration of monosilane measured by the gas analysis units 6g and 6c are less than predetermined concentration levels, a mechanism may be provided supplementarily where argon and monosilane are sent to the monosilane detoxification unit (not shown) and a noble gas exhaust unit (not shown), without being circulated in the semiconductor fabrication equipment 1 and the bump unit 2, respectively, so that they can be treated safely and appropriately.
The accumulators 9a and 9b have argon and monosilane, recovered by the noble gas treatment unit 30 and the silane gas purification unit 50, circulated in the pump unit 2 and the semiconductor fabrication equipment 1 at constant pressure. The accumulators 9a and 9b as used herein are not particularly limited insofar as they attain the aforementioned purpose. And the pressure to be accumulated in the accumulators 9a and 9b must be lower than the pressure of gas supplied to the accumulators 9a and 9b and higher than the pressure with which the differential pressure of a flow rate control apparatus of the semiconductor fabrication equipment 1 can be obtained. If no such a range of pressures can be obtained, a boosting apparatus (not shown) will be preferably provided at a stage prior to the accumulators in order to raise the supply pressure to the accumulators 9a and 9b. The boosting apparatus as used herein may preferably be one further having the same features and requisites as those of the above-described gas compression unit 3. The pressure to be accumulated in the accumulators 9a and 9b is not limited to a particular value insofar as it serves the aforementioned purpose and may preferably be 0.05 MPaG to 10 MPaG or more preferably 0.1 MPaG to 0.5 MPaG.
A detailed description is given hereunder of the present embodiment based on exemplary embodiments or examples but the present embodiment is not limited to these exemplary embodiments only.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiment 4-1 excepting that the secondary gas temperature, when the mixed gas is compressed by the diaphragm compressor 363a, is adjusted at 70° C. and excepting that the temperature of the compressed mixed gas is adjusted at 35° C. by the pre-cooler 361 and coolers 364 and the compressor is operated in four stages. The operating conditions of the gas compression unit 300a and the flow rates and compositions of the gas analyzed by the gas analysis unit 85a are gathered in Table 17.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 4-1 and 4-2 excepting the flow rate of the mass flow controller 84a and the gas composition. The operating conditions of the gas compression unit 300a and the flow rates and compositions of the gas analyzed by the gas analysis unit 85a are gathered in Table 13.
In order to recycle monosilane gas, various kinds of mixed gases in the exemplary embodiments 4-1 to 4-6 analyzed by the gas analysis unit 85a are supplied to the adsorption tower 101a (with activated carbon filled as adsorbent) of the silane gas treatment unit 20 employing an adsorption separation method as shown in
After the operation for one hour, the adsorption tower 101a closes the adsorption switching valves 102a and 103a and opens the adsorption switching valves 102b and 103b. Thereby, the operation is switched to the adsorption tower 101b so as to continue the operation. Simultaneously, the desorption switching valve 104a is opened and the pressure is reduced to −0.09 MPaG by the vacuum pump 106 over a period of one hour. As a result, components adsorbed to the adsorption tower 101a are desorbed. After the operation for one hour, the adsorption tower 101b closes the adsorption switching valves 102b and 103b and opens the adsorption switching valves 102c and 103c. Thereby, the operation is switched to the adsorption tower 101c so as to continue the operation. Simultaneously, the desorption switching valve 104a is closed, the desorption switching valve 104b is opened, and the pressure is reduced to −0.09 MPaG by the vacuum pump 106 over a period of one hour. A cycle of three hours so far is now defined as one cycle. Now the adsorption tower in operation is returned from the adsorption tower 101c to the adsorption tower 101a and the adsorption tower for which the desorption is to be done is shifted from the adsorption tower 101b to the adsorption tower 101c. Then experiments from a second cycle and onward are conducted. The mixed gas containing large amounts of hydrogen and argon, which are separated by the silane gas treatment unit 20 and then sent to the gas analysis unit 85b, passes through the water scrubber so as to remove the hydrides in the mixed gas. And the mixed gas where the hydrides have been removed by the water scrubber is now sent to the noble gas treatment unit 30. The temperature of the gas is adjusted at 30° C. by the temperature regulator 90 of the noble gas treatment unit 30 before the gas is introduced into the membrane separation module 91 (polyimide hollow fiber membrane with a volume of 0.6 L). A vacuum pump 94 is connected at a permeation side of the membrane separation module 91, and the permeation-side pressure of the membrane separation module 91 is adjusted to −0.1 MPaG at a permeation-side back pressure valve 92a. The non-permeation-side pressure of the membrane separation module 91 is controlled to 0.1 MPaG at a non-permeation-side back pressure valve 92b. The flow rate and the composition of a gas on the non-permeation side are measured by a flowmeter 93b and GC (gas chromatogram) and FT-IR in the gas analysis unit 85e. The results analyzed by the gas analysis unit 85e are gathered in Table 18.
The exhaust gas treatment system is operated under the same conditions as those of the exemplary embodiments 4-1 to 4-6 excepting that the mixed gas is fed to the analysis unit 85g by bypassing the noble gas/silane separation unit 470. The results concerning the flow rates and compositions of the mixed gas measured by the GC (gas chromatogram) and FT-IR in the gas analysis unit 85g are gathered in Table 20.
Using the mixed gas containing SiH4 recovered in the exemplary embodiments 4-1 to 4-6 and the comparative examples 4-1 to 4-6, a-Si solar cells are made according to a routine method so as to conduct a characteristic evaluation of them. The results show that although no change is found in the characteristics of the solar cells fabricated according to the exemplary embodiments 4-1 to 4-6, the characteristics thereof fabricated according to the comparative examples 4-1 to 4-6 are significantly degraded.
From the above results, it is evident that use of argon as the purge gas and installation of the noble gas/silane separation unit at a final stage of the monosilane recycling process prevent high-concentration argon from being mixed into monosilane recovered and therefore the adverse effect of the high-concentration argon on the performance of the solar cells can be reduced. Also, the mixed gas, containing a high proportion of hydrogen and argon separated by the silane separation unit, is made to pass through the water scrubber, so that the hydrogenated impurities can be removed. Also, the mixed gas that has passed through the water scrubber is further subjected to the separation treatment at the membrane separation apparatus, so that high-purity argon can be recovered with a higher recovery rate.
The present invention is not limited to the above-described embodiments only. It is understood that various modifications such as changes in design may be made based on the knowledge of those skilled in the art, and the embodiments added with such modifications are also within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-171980 | Jul 2010 | JP | national |
| 2011-078522 | Mar 2011 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2011/004329 | Jul 2011 | US |
| Child | 13754004 | US |
