Exhaust gas treatment system

An exhaust gas treatment system treats a mixed gas containing at least hydrogen and monosilane discharged from a semiconductor fabrication equipment. The exhaust gas treatment system includes a pump unit which emits the mixed gas discharged from the semiconductor fabrication equipment, a compressor which compresses the mixed gas emitted by the pump unit and sends the mixed gas to a rear stage, a gas accommodation unit which collects and accommodates the compressed mixed gas, a flow rate control unit which controls a flow rate of the mixed gas supplied from the gas accommodation unit, and a membrane separation unit which causes the hydrogen to selectively permeate therethrough and separates the monosilane and the hydrogen from the mixed gas. Accordingly, the exhaust gas treatment system may be stably operated in a state where a change in pressure of the mixed gas discharged from the semiconductor fabrication equipment is alleviated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas treatment system which treats a gas containing hydrogen and a silane gas discharged from a semiconductor fabrication equipment.

2. Description of the Related Art

An exhaust gas which is discharged from a semiconductor fabrication equipment, and particularly, a plasma CVD device that forms a film of thin-film silicon used in a solar cell contains monosilane that needs to be detoxified, hydrogen that does not need to be detoxified, and fine particles (high-order silane) in a mixed state. In an existing exhaust gas treatment device, fine particles are removed by a filter, nitrogen is added to a mixed gas (hydrogen/monosilane=2 to 100) containing remaining monosilane and hydrogen, and the resultant gas is treated by a detoxifying device. The addition amount of nitrogen is adjusted so that the concentration of monosilane becomes 2% or less from the viewpoint of the production of powder.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

In the existing exhaust gas treatment device, since the detoxifying treatment is performed on the mixed gas containing a small amount of monosilane which needs to be detoxified and a large amount of hydrogen which does not need to be detoxified, an instrument necessary for detoxifying the monosilane and further the exhaust gas treatment device increase in size. Further, in a case where the monosilane is detoxified by combustion, the consumption amount of an LPG gas for combustion increases, and the energy efficiency degrades. Further, since the pressure and the flow rate of the exhaust gas discharged from the semiconductor fabrication equipment drastically change due to the operation condition of the semiconductor fabrication equipment, it was difficult to stably operate the exhaust gas treatment device.

The invention is made in view of such circumstances, and it is an object of the invention to provide a technique of decreasing a size of a system which treats an exhaust gas discharged from a semiconductor fabrication equipment. It is another object of the invention to provide a technique of decreasing a size of a system which treats an exhaust gas discharged from a semiconductor fabrication equipment and of stably operating the system for a long period of time.

An embodiment of the present invention relates to an exhaust gas treatment system which treats a mixed gas containing at least hydrogen and monosilane discharged from a semiconductor fabrication equipment. The exhaust gas treatment system includes: a pump which emits the mixed gas discharged from the semiconductor fabrication equipment; a compressor which compresses the mixed gas emitted by the pump and sends the mixed gas to a rear stage; a gas accommodation unit which collects and accommodates the compressed mixed gas; a flow rate control unit which controls a flow rate of the mixed gas supplied from the gas accommodation unit; and a membrane separation unit which causes the hydrogen to selectively permeate therethrough and separates the monosilane and the hydrogen from the mixed gas.

According to the embodiment, since the mixed gas containing at least the hydrogen and the monosilane discharged from the semiconductor fabrication equipment is separated into the monosilane which needs to be detoxified and the hydrogen which does not need to be detoxified by the membrane separation unit and the hydrogen and the monosilane which are separated from the mixed gas are respectively treated, a treatment instrument may be decreased in size, and further the exhaust gas treatment system may be made to be compact.

According to another embodiment, an exhaust gas treatment system treats a mixed gas containing at least hydrogen and monosilane discharged from a semiconductor fabrication equipment, and the exhaust gas treatment system includes: a membrane separation unit which causes the hydrogen to selectively permeate therethrough and separates the monosilane and the hydrogen from the mixed gas; a hydrogen recovery rate acquisition unit which acquires information on a recovery rate of the hydrogen separated by the membrane separation unit and calculates the recovery rate of the hydrogen; and a pressure control unit which controls a permeation side pressure of the membrane separation unit in response to a change in hydrogen recovery rate.

The pressure control unit may change the permeation side pressure based on the following equation. The equation is expressed by ΔP=C1×ΔA, C1≧0.5. Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔP indicates a decrease amount (kPa) of the permeation side pressure.

Another embodiment of the invention relates to an exhaust gas treatment system. The exhaust gas treatment system treats a mixed gas containing at least hydrogen and monosilane discharged from a semiconductor fabrication equipment, and the exhaust gas treatment system includes: a membrane separation unit which causes the hydrogen to selectively permeate therethrough and separates the monosilane and the hydrogen from the mixed gas; a hydrogen recovery rate acquisition unit which acquires information on a recovery rate of the hydrogen separated by the membrane separation unit and calculates the recovery rate of the hydrogen; and a temperature control unit which controls a temperature of the mixed gas flowing into the membrane separation unit in response to a change in hydrogen recovery rate.

The temperature control unit may change the temperature of the mixed gas flowing into the membrane separation unit based on the following equation. The equation is expressed by ΔT=C2×ΔA, C2≧0.8. Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔT indicates an increase amount (° C.) of the temperature of the mixed gas.

The hydrogen recovery rate acquisition unit may include a mixed gas analysis unit which measures a flow rate of the mixed gas flowing and a concentration of the hydrogen and the monosilane into the membrane separation unit, and a permeation side gas analysis unit which measures a flow rate of a gas and a concentration of the hydrogen and the monosilane, the gas comprising the hydrogen, and the monosilane being separated while permeating the membrane separation unit.

Further, the hydrogen recovery rate acquisition unit may include: a flow rate control unit which controls a flow rate of the mixed gas flowing into the membrane separation unit; a mixed gas analysis unit which measures a concentration of the hydrogen and the monosilane in the mixed gas of which the flow rate is controlled; and a permeation side gas analysis unit which measures a flow rate of a gas and a concentration of the hydrogen and the monosilane, the gas comprising the hydrogen, and the monosilane being separated while permeating the membrane separation unit.

Still another embodiment of the invention relates to an exhaust gas treatment system which treats a mixed gas containing at least hydrogen and monosilane discharged from a semiconductor fabrication equipment. The exhaust gas treatment system is an exhaust gas treatment system which separates respective gases, by membrane separation, from a mixed gas containing at least hydrogen and monosilane discharged from a semiconductor fabrication equipment, the exhaust gas treatment system including: a gas addition unit which adds a third element gas to the mixed gas discharged from the semiconductor fabrication equipment; a membrane separation unit which causes the hydrogen to selectively permeate therethrough and separates the monosilane and the hydrogen from the mixed gas having the third element gas added thereto; and a hydrogen recovery rate acquisition unit which acquires a recovery rate of the hydrogen separated by the membrane separation unit, wherein the third element gas addition unit changes the addition amount of the third element gas according to the following equation.
ΔF=C1×ΔA, C1≧0.3  Equation (3-1)
Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔF indicates a decrease amount (L/min) of the addition amount of the third element gas.

The exhaust gas treatment system according to the above embodiment includes a pressure control unit which controls a permeation side pressure of the membrane separation unit, wherein the pressure control unit may change the permeation side pressure of the membrane separation device according to the following equation.
ΔP=C2×ΔA, C2≧0.5

Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔP indicates a decrease amount (kPa) of the permeation side pressure of the membrane separation device.

Further, the exhaust gas treatment system according to the above embodiment includes a temperature control unit which controls a temperature of the mixed gas, wherein the temperature control unit may change the temperature of the mixed gas according to the following equation.
ΔT=C3×ΔA, C3≧0.8

Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔT indicates an increase amount (° C.) of the temperature of the mixed gas.

The hydrogen recovery rate acquisition unit may include a mixed gas analysis unit which measures a flow rate of the mixed gas flowing into the membrane separation unit and a concentration of the hydrogen and the monosilane, and a permeation side gas analysis unit which measures a flow rate of a gas separated while permeating the membrane separation unit and a concentration of the hydrogen and the monosilane.

According to the invention, it is possible to decrease the size of a system which treats an exhaust gas discharged from a semiconductor fabrication equipment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the invention will be described by referring to the drawings. Furthermore, in all drawings, the same reference numerals will be given to the same components, and the description thereof will not be repeated.

FIG. 1is a system diagram illustrating a schematic example of an exhaust gas treatment system according to the embodiment.FIG. 2is a system diagram more specifically illustrating a configuration of the exhaust gas treatment system according to the embodiment.FIG. 3is a system diagram illustrating an example of data processing of the respective components of the exhaust gas treatment system according to the embodiment.

As illustrated inFIG. 1, an exhaust gas treatment system100according to the embodiment includes a compressor11which collects and compresses a mixed gas containing at least hydrogen and monosilane discharged from plural semiconductor fabrication equipments1through a pump unit2, a gas accommodation unit3which accommodates the mixed gas discharged from the compressor11, a flow rate control unit4which controls a flow rate of the mixed gas from the gas accommodation unit3, a membrane separation unit6which separates the monosilane and the hydrogen from the mixed gas, a hydrogen gas treatment unit7which treats the hydrogen separated by the membrane separation unit6, and a silane gas treatment unit8which treats the silane gas separated by the membrane separation unit6.

The semiconductor fabrication equipment1is not particularly limited, but a plasma CVD device or the like which forms a film by thin-film silicon used in a solar cell may be exemplified.

The composition of the mixed gas discharged from the semiconductor fabrication equipment1is not particularly limited, but for example, contained are monosilane which need to be detoxified, hydrogen which does not need to be detoxified, nitrogen, and a small amount of impurities. As the small amount of impurities, high-order silane including plural Si such as disilane or trisilane, PH3, and B2H6(which are respectively 0.001 to 1%) may be exemplified.

The pump unit2suctions the mixed gas discharged from the semiconductor fabrication equipment1, and sends the mixed gas to the compressor11of the rear stage. The type of pump to be used is not particularly limited, but a dry pump is used in the semiconductor fabrication equipment in many cases. The dry pump may introduce a purging gas for the purpose of maintaining air-tightness, preventing unnecessary deposited material, preventing the corrosion inside the pump, and improving the emission performance. The purging gas is not particularly limited, but an inert gas such as nitrogen or argon is used in many cases.

Further, even the introduction amount of the purging gas is not particularly limited, but in general, the introduction amount is 10 to 50 NL/min for each pump.

Further, as illustrated inFIG. 2, a filter2amay be provided at the front stage and/or the rear stage of a pump2b. In particular, when a comparatively large amount of fine particles such as high-order silane exist in the exhaust gas, it is desirable to provide the filter2a. The filter2ais a fine particle capturing filter which selectively removes fine particles such as high-order silane contained in the mixed gas. The filter to be used is not particularly limited, but a vortex filter or the like may be used.

Further, in the semiconductor fabrication equipment1, chemical cleaning may be performed so as to remove a deposited material produced inside a chamber due to the film forming. In the chemical cleaning, it is general to perform a plasma treatment under the introduction of a gas such as NF3or F2so as to remove a silicon thin film deposited in the chamber. However, since such a gas has a combustion supporting property, there is a need to prevent the gas from contacting a combustible gas such as hydrogen or monosilane, and hence it is desirable to provide a switching valve2cin rear of the pump2bas in a case ofFIG. 2. Accordingly, when the exhaust gas of the chemical cleaning comes out, a combustion supporting gas treatment system is selected, so that such an exhaust gas is prevented from being mixed with a treatment line of a silane gas. Furthermore, in the switching valve2c, such a mechanism may be built in the pump.

The compressor11is not particularly limited, but a diaphragm type 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, and the like may be exemplified. Among these, the diaphragm type compressor is more desirable.

The operation condition of the compressor11is not particularly limited, but it is desirable to operate the compressor so that the temperature of the compressed mixed gas becomes 200° C. or less which is a decomposition temperature of monosilane. That is, when it is supposed that the mixed gas discharged from the pump unit2is compressed from normal pressure, it is desirable to operate the compressor so that the compression ratio becomes 4.4 or less.

The compressor configuration used in the compressor11is not particularly limited, but in order to stably operate the compressor even when the flow rate of the mixed gas supplied to the compressor changes, it is desirable to have a configuration in which inverters are provided in parallel or a spill-back type configuration in which the mixed gas once compressed by the compressor is returned to the suction side of the compressor again.

The gas accommodation unit3is used to collect the mixed gas discharged from the plural semiconductor fabrication equipments1through the pump unit2in a tank having a sufficient capacity or the like, and is used to average a change in flow rate and pressure of the mixed gas discharged from the respective semiconductor fabrication equipments1and to circulate the mixed gas with the constant flow rate and the constant pressure to the membrane separation unit6at all times. Further, a function of removing fine particles contained in the mixed gas may be provided by devising a structure.

The size of the tank used in the gas accommodation unit3is not particularly limited, but it is desirable that the size is equal to or larger than the sum of the maximum flow rates of the gases supplied to the respective semiconductor fabrication equipments1.

The pressure inside the tank used in the gas accommodation unit3is not particularly limited, but it is desirable that the pressure is 1 MPaG at maximum.

Further, when the operation of the equipment starts, it is desirable that the exhaust gas or the purging gas of the pump is supplied from the compressor11to the gas accommodation unit3and is accumulated in the gas accommodation unit3while the outlet valve of the gas accommodation unit3is closed. Accordingly, even when the flow rate of the exhaust gas of the semiconductor fabrication equipment largely changes, it is possible to maintain a pressure sufficient for maintaining the supply flow rate to the separation equipment to be constant and to increase the amount of a gas which may be accommodated in the gas accommodation unit3. Accordingly, it is possible to decrease the volume of the gas accommodation unit. Further, when a sufficient pressure is accumulated, the non-permeation side pressure of the membrane separation device may be set to be high, which is advantageous in operation due to a sufficient differential pressure with respect to the permeation side.

The flow rate control unit4is used to control the flow rate and the pressure of the mixed gas collected in the gas accommodation unit3so that the flow rate and the pressure become constant. The control method thereof is not particularly limited, but it is desirable that the control method is not influenced by a change in pressure of the mixed gas supplied to the flow rate control unit4, for example, a mass flow controller or the like may be exemplified. Further, even as for the pressure, the necessary pressure may be ensured by selecting the operation condition of the compressor11.

The membrane separation unit6includes at least a membrane separation device6band a permeation side pressure control unit6cand/or a non-permeation side pressure control unit6das illustrated inFIG. 2. The membrane separation device6bis a membrane through which hydrogen selectively permeate. There is no particular limitation if metal elements, for example, palladium, nickel, and the like reacting with monosilane are not contained as a main element, and various semipermeable membranes may be exemplified. The semipermeable membrane includes, for example, a dense layer through which hydrogen selectively permeates and a porous base material which supports the dense layer. As the shape of the semipermeable membrane, a flat membrane, a spiral membrane, and a hollow fiber membrane may be exemplified. Among these, the hollow fiber membrane is more desirable.

As the material used in the base material, an inorganic material such as glass, ceramic, and sintered metal and a porous organic material may be exemplified. As the porous organic material, polyether, polyacrylonitrile, polyether, poly (arylene oxide), polyetherketone, polysulfide, polyethylene, polypropylene, polybutene, polyvinyl, and the like may be exemplified.

The flow rate, the pressure, and the temperature of the mixed gas supplied to the membrane separation device6b, the concentration of the monosilane gas, and the non-permeation side pressure and the permeation side pressure of the membrane separation device6bare not particularly limited. For example, as the flow rate, the flow rate is 5 NL/min to 500 NL/min with respect to the capacity of 1 L of the membrane separation device, and is desirably 10 NL/min to 100 NL/min. As the pressure, −90 kPaG to 1.0 MPaG is desirable. As the temperature, about −20° C. to 100° C. is desirable. As the concentration of the monosilane gas, 30 vol % or less, desirably 20 vol % or less, more desirably, 10 vol % or less is desirable. As the non-permeation side pressure of the membrane separation device6b, −90 kPaG to 0.85 MPaG is desirable. As the permeation side pressure, −100 kPaG to 0.9 MPaG is desirable.

Here, the capacity of the membrane separation device indicates the volume of the portion in which the separation membrane is sufficiently charged inside the membrane separation device.

Further, when the operation is performed at a temperature other than a room temperature as the temperature of the mixed gas supplied to the membrane separation device6b, there is a need to provide a temperature control unit6aillustrated inFIG. 2.

The temperature control unit6ais not particularly limited if a function of cooling or heating the mixed gas is provided, but an electric heater, various heat exchangers, or the like may be exemplified. The mixed gas which is cooled or heated by the temperature control unit6ais supplied to the membrane separation device6b.

In fact, the membrane separation conditions are closely concerned with each other. For example, in a case of the membrane separation capacity of 1 L, the supply flow rate to the membrane separation device is desirably 20 NL/min to 50 NL/min, the concentration of the monosilane gas is desirably 10 vol % or less, the temperature is desirably 10° C. to 40° C., the non-permeation side pressure of the membrane separation device is desirably the atmospheric pressure or more, and the permeation side pressure is desirably −100 kPaG to −60 kPaG.

The respective gases separated by the membrane separation device6bare sent to the hydrogen gas treatment unit7and the silane gas treatment unit8. In the hydrogen gas treatment unit7, the simply collected hydrogen is used for a combustion treatment or fuel. For example, as illustrated inFIG. 2, the hydrogen may be diluted by a dilution unit7bby nitrogen, air, or the like so as to be an explosion limit or less and may be discharged to the outside. Further, at the dilution time, it is desirable to dilute the hydrogen so that the concentration of the hydrogen becomes an explosion lower limit or less (4 vol % or less) from the viewpoint of safety. The dilution rate of the dilution unit7bis not particularly limited if at least the concentration of monosilane satisfies 5 ppmv or less. When the dilution rate is controlled based on a measurement result of a permeation side gas analysis unit6e, the dilution rate may be effectively controlled without any consumption. The separated gas which is diluted by the dilution unit7bis discharged to the outside by a blower7c. Further, in order to reduce the concentration of monosilane in the collected gas, a mechanism (not illustrated) may be further provided which selectively detoxifies the monosilane. A detoxifying agent which selectively performs a detoxifying treatment is not particularly limited, but an oxidizing agent, an adsorbing agent, or the like may be exemplified. Further, as illustrated inFIG. 4, a hydrogen gas purification unit7amay be provided so that hydrogen is purified and used again.

Further, in the silane gas treatment unit8, for example, as illustrated inFIG. 2, monosilane as a toxic gas is diluted by a dilution unit8bin accordance with the specification of the device of a detoxifying unit8cas a detoxifying device so as to be a predetermined concentration, and is introduced into the detoxifying unit8c, so that the monosilane is detoxified to be an allowable concentration or less and is discharged to the outside by the blower8d. Furthermore, a silane gas purification unit8amay be provided so that the monosilane is purified and used again.

In the exhaust gas treatment system according to the embodiment, various additional instruments illustrated inFIGS. 2 and 3may be further provided.

For example, as illustrated inFIG. 2, a gas analysis unit5may be provided so as to measure the concentration of the element gas of the mixed gas of which the flow rate is controlled to be constant by the flow rate control unit4, and particularly, the concentration of the hydrogen and the monosilane in the gas. In the gas analysis unit5, the method thereof is not particularly limited if at least the concentration of the hydrogen and the monosilane in the mixed gas may be measured. For example, an FT-IR with a gas circulation type sample cell, an on-line type gas chromatograph, or the like may be exemplified.

Further, as illustrated inFIG. 2or3, in order to adjust the concentration of the monosilane in the mixed gas, a third element gas addition unit10may be provided before and after the gas analysis unit5, and a third element gas may be added to the mixed gas by a predetermined amount. The third element gas to be added is not particularly limited if the gas does not abruptly react with the element gas such as the monosilane in the mixed gas, but for example, nitrogen, argon, hydrogen, helium, xenon, a hydrocarbon gas having a carbon number of 1 to 4, and the like may be exemplified. When the third element gas addition unit10is provided, it is desirable to provide the gas analysis unit5before and after the third element gas addition unit so as to measure the concentration of the hydrogen and the monosilane in the mixed gas before and after the addition of the third element gas.

Further, as illustrated inFIG. 2, in order to measure the flow rate of each gas separated by the membrane separation unit6and the concentration of the element thereof, a permeation side gas analysis unit6eand a non-permeation side gas analysis unit6fmay be provided. For example, in the hydrogen gas treatment unit7, the flow rate of the permeation side gas of the membrane separation device6band the concentration of the hydrogen and the monosilane in the gas are measured. Accordingly, the dilution rate of the dilution unit7bwhen emitting the collected hydrogen gas into the atmosphere may be controlled based on the measurement result so that the concentration of the monosilane becomes an allowable concentration (5 ppmv or less). In the dilution unit7b, in order to safely emit the collected hydrogen into the atmosphere, nitrogen, air, or the like may be added thereto so that the concentration of the monosilane becomes the allowable concentration or less and the concentration of the hydrogen becomes the explosion lower limit (4 vol % or less).

Furthermore, as for the permeation side gas which is discharged from the permeation side of the membrane separation device6b, the flow rate and the concentration of the hydrogen and the monosilane thereof are measured by the permeation side gas analysis unit6e. Further, the permeation side pressure control unit6cis used to control the permeation side pressure of the membrane separation device6b. The recovery rate (the hydrogen recovery rate) of the hydrogen gas may be calculated by combining the measurement result which can be obtained with the measurement result of the flow rate of the mixed gas which is supplied to the membrane separation device6band is not yet separated and the concentration of the hydrogen and the monosilane thereof. Here, the hydrogen recovery rate is defined by the following equation (1-1).
Hydrogen recovery rate(%)=100×((A/100)×B))/((C/100)×D).  Equation (1-1)

Here, A indicates the concentration of the hydrogen (permeation side hydrogen concentration) (vol %) of the permeation side gas, B indicates the flow rate of the permeation side gas (permeation side total gas flow rate) (L/min), C indicates the concentration of the hydrogen (supply side hydrogen concentration) (vol %) of the mixed gas supplied to the membrane separation device, and D indicates the flow rate (supply side total gas flow rate) (L/min) of the mixed gas supplied to the membrane separation device.

The degradation state of the membrane separation device6bmay be recognized by monitoring the hydrogen recovery rate. For example, the operation may be performed while maintaining the high hydrogen recovery rate at all times by controlling the temperature of the mixed gas supplied to the membrane separation device6b, the non-permeation side pressure of the membrane separation device6b, the permeation side pressure thereof, or the addition amount of the third element gas with degradation in the hydrogen recovery rate. At this time, as for the decrease amount of the hydrogen recovery rate, it is desirable to control the temperature of the mixed gas supplied to the membrane separation device6b, the permeation side pressure of the membrane separation device6b, and the addition amount of the third element gas so as to satisfy the following equation (1-2) to equation (1-4).
ΔP=C1×ΔA, C1≧0.5  Equation (1-2)

Here, ΔP indicates a permeation side pressure decrease amount (kPa), and ΔA indicates a decrease rate (%) of the hydrogen recovery rate.
ΔT=C2×ΔA, C2≧0.8  Equation (1-3)

Here, ΔT indicates a temperature increase amount (° C.), and ΔA indicates a decrease rate (%) of the hydrogen recovery rate.
ΔF=C3×ΔA, C3≧0.3  Equation (1-4)

Here, ΔF indicates a decrease amount (L/min) of the third element gas addition amount, and ΔA indicates a decrease rate (%) of the hydrogen recovery rate.

Further, for example, in the silane gas treatment unit8, the flow rate of the non-permeation side gas of the membrane separation device6band the concentration of the hydrogen and the monosilane in the gas are measured. Accordingly, the dilution rate of the dilution unit8bwhen detoxifying the collected monosilane gas using the detoxifying unit8cmay be controlled based on the measurement result so that the concentration of the monosilane becomes the allowable concentration (for example, about 2 vol %) or less of the detoxifying device.

Furthermore, the above-described control is performed by using a calculation control unit30illustrated inFIG. 3. Further, the calculation control unit30may control the flow rate of the mixed gas using the flow rate control unit4based on the flow rate of the controlled mixed gas, the measurement result of the concentration of the monosilane in the mixed gas obtained by the gas analysis unit5, and the capacity of the membrane separation device.

Further, the calculation control unit30may calculate the hydrogen recovery rate based on the flow rate value of the mixed gas obtained by the flow rate control unit4, the measurement result of the concentration of the monosilane in the mixed gas obtained by the gas analysis unit5, and the measurement result of the flow rate of the permeation side gas and the concentration of the monosilane in the permeation side gas obtained by the permeation side gas analysis unit6e.

The calculation control unit30may control the temperature of the mixed gas supplied to the membrane separation device6b, the non-permeation side pressure of the membrane separation device6b, the permeation side pressure thereof, and the addition amount of the third element gas with respect to the decrease amount of the calculated hydrogen recovery rate.

Further, the calculation control unit30may determine how the operation condition of the hydrogen gas purification unit7ais or whether the collected hydrogen gas will be used again based on the measurement result of the flow rate of the permeation side gas and the concentration of the hydrogen and the monosilane in the permeation side gas obtained by the permeation side gas analysis unit6e. When the calculation control unit30determines that the collected hydrogen gas will not be used again, the calculation control unit may control the dilution rate of the dilution unit7bof the hydrogen gas treatment unit7so that the concentration of the monosilane becomes the allowable concentration (5 ppmv or less).

Further, the calculation control unit30may determine how the operation condition of the silane gas purification unit8ais or whether the collected monosilane is used again based on the measurement result of the flow rate of the non-permeation side gas and the concentration of the hydrogen and the monosilane in the non-permeation side gas obtained by the non-permeation side gas analysis unit6f. When the calculation control unit30determines that the collected monosilane will not be used again, the calculation control unit may control the dilution rate of the dilution unit8bof the silane gas treatment unit8so that the concentration of the monosilane becomes the allowable concentration (for example, about 2 vol %) or less of the detoxifying device. Further, a valve may be provided at the rear stage of the non-permeation side gas analysis unit6fso as to switch a line directed to the detoxifying unit8cand a line directed to the semiconductor fabrication equipment1for the purpose of reuse.

According to the exhaust gas treatment system, even when the flow rate and the pressure of the mixed gas discharged from the semiconductor fabrication equipment change, the operation may be stably performed without a back pressure which influences the pump emitting the mixed gas discharged from the semiconductor fabrication equipment while the pressure and the flow rate of the mixed gas supplied to the membrane separation unit are maintained to be constant.

Hereinafter, the embodiment will be described in detail based on Example, but the embodiment is not limited to the example.

FIG. 4is a system diagram illustrating a configuration of an exhaust gas treatment system according to Example 1-1. As illustrated inFIG. 4, the exhaust gas treatment system according to the first embodiment is connected to three thin-film silicon solar cell manufacturing CVD devices which is one of the semiconductor fabrication equipments1. The exhaust gas treatment system suctions the mixed gas discharged from the plural PE-CVD devices12together with nitrogen introduced from the outside by a dry pump13acorresponding to each device, and sends the resultant gas toward the compressor26through the filter14. Furthermore, a switching valve33is provided behind the dry pump13a. Accordingly, when the exhaust gas of the chemical cleaning comes out, a combustion supporting gas treatment system is selected, so that such an exhaust gas is prevented from being mixed with a treatment line of a silane gas.

As the compressor26, a compressor is selected which may be operated at the compression ratio of 4. In a state where an accumulation valve32is closed, each purging nitrogen of the pump flows at the flow rate of 30 NL/min, so that the pressure of a hermetic tank15(capacity: 5 m3) increases to 0.3 MPaG. Subsequently, the accumulation valve32is opened so that the supply of a gas to a mass flow controller16starts and the respective PE-CVD devices12are operated so as to be late by 4 minutes. The operations of the respective PE-CVD devices12are performed on the condition illustrated in Table 1. The gas flow rate is controlled at 151.5 NL/min by the mass flow controller16, the temperature is adjusted to be 40° C. by a heat exchanger18, and then the result is supplied to a membrane separation module20(a polyimide hollow fiber membrane with a capacity of 2.4 L). At this time, the pressure is adjusted to be −98 kPaG by a permeation side back pressure valve21a. Further, the pressure is adjusted to be 0.1 MPaG by a non-permeation side back pressure valve21b. The composition and the flow rate of the exhaust gas of the compressor at this time are illustrated in Table 2. The concentration of SiH4of the separated permeation side gas is 0.019 vol %, and the hydrogen recovery rate is 90.9%, which is constant regardless of a change in exhaust gas flow rate.

Furthermore, a flowmeter22aand an analysis device17aillustrated inFIG. 4are used to measure the flow rate of the mixed gas discharged from the PE-CVD device12and the concentration of the hydrogen and the monosilane in the mixed gas. Regarding the mixed gas of which the flow rate or the pressure is controlled at a predetermined value by the mass flow controller16, the concentration of the hydrogen and the monosilane is measured by the analysis device17b, and the mixed gas flows into the membrane separation module20while the temperature is controlled by the functions of the heat exchanger18and a circulation constant temperature reservoir19. Flowmeters22band22care respectively provided at the rear stage of the permeation side and the non-permeation side of the membrane separation module20.

In the exhaust gas treatment system illustrated inFIG. 4, the permeation side gas of the membrane separation module passes through the flowmeter22band an analysis device17c, so that the flow rate of the permeation side gas and the concentration of the hydrogen and the monosilane in the permeation side gas are measured. The permeation side gas which is suctioned by the dry pump13bis diluted by nitrogen appropriately based on the measurement result and is emitted to the atmosphere by a blower25a. On the other hand, the non-permeation side separated gas of the membrane separation module20passes through the flowmeter22cand an analysis device17d, so that the flow rate of the non-permeation side gas and the concentration of the hydrogen and the monosilane in the non-permeation side gas are measured. The non-permeation side gas is diluted by nitrogen appropriately based on the measurement result and is combusted and detoxified by a combustion detoxifying device23. The gas which is combusted and discharged by the combustion detoxifying device23is supplied to a bag filter24by a blower25bso as to remove foreign matter such as particles produced by the combustion, and is emitted to the atmosphere by a blower25c.

The same operation is performed as in Example 1-1 except that the non-permeation side back pressure valve21bis opened by using the membrane separation module20having a membrane separation capacity of 4.8 L so that the non-permeation side pressure becomes a normal pressure, the permeation side pressure is adjusted to −70 kPa, and the temperature of the supply gas is set to 80° C. As a result, the concentration of SiH4of the separated permeation side gas is 0.052 vol %, and the hydrogen recovery rate is 63.3%, which is constant regardless of a change in exhaust gas flow rate.

FIG. 5is a diagram illustrating a monitored result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value) when the exhaust gas treatment system is operated so as to satisfy the equation (1-2) (C1=0.5) in a state where the condition of Example 1-2 is set as an initial condition except that the pressure is adjusted to 50 kPaG by a non-permeation side back pressure valve21b. Furthermore, the number of years in use (corresponding value) is a value which is obtained by converting the operation time of the acceleration test into the number of real years. The accelerated degradation test was performed so that the total flow rate of the supplied mixed gas is set to 50 times that of the normal test and the supplied monosilane gas concentration and the supplied nitrogen gas concentration are constant. From this result, it is found that the exhaust gas treatment system may be operated for a long period of time while maintaining the hydrogen recovery rate by operating the exhaust gas treatment system so as to satisfy the equation (1-2).

FIG. 6is a diagram illustrating a monitored result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value) when the exhaust gas treatment system is operated so as to satisfy the equation (1-3) (C2=1.0) in a state where the condition of Example 1-1 is set as an initial condition. From this result, it is found that the exhaust gas treatment system may be operated for a long period of time while maintaining the hydrogen recovery rate by operating the exhaust gas treatment system so as to satisfy the equation (1-3).

FIG. 7is a diagram illustrating a monitored result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value) when the exhaust gas treatment system is operated so as to satisfy the equation (1-4) (C3=1.0) in a state where an initial condition is set as in Example 1-1 except that nitrogen of 30 NL/min is added in a third element gas addition unit10using a membrane separation module having a membrane separation capacity of 3.0 L. From this result, it is found that the exhaust gas treatment system may be operated for a long period of time while maintaining the hydrogen recovery rate by operating the exhaust gas treatment system so as to satisfy the equation (1-4).

COMPARATIVE EXAMPLE 1-1

FIG. 8is a system diagram illustrating a configuration of an exhaust gas treatment system according to Comparative example 1-1. The exhaust gas treatment system according to Comparative example 1-1 illustrated inFIG. 8is not provided with the compressor, the hermetic tank, the accumulation valve, and the mass flow controller. The CVD device is connected to the exhaust gas treatment system, the operation of the exhaust gas treatment system is performed on the same condition as that of Example 1-1, and a changing exhaust gas is directly circulated to the membrane separation device. As a result, the concentration of SiH4of the separated permeation side gas and the hydrogen recovery rate change as illustrated in Table 3 in response to a change in exhaust gas flow rate. Further, the concentration of SiH4of the permeation side gas increases to 0.044 vol % at maximum, and the dilution rate for the emission to the atmosphere needs to be 2.3 times that of Example 1-1.

COMPARATIVE EXAMPLE 1-2

The operation is performed with the same configuration and the same condition as those of Comparative example 1-1 except that the membrane separation capacity of the exhaust gas treatment system is set to 1.2 L. As a result, the concentration of SiH4of the permeation side gas may be decreased as illustrated in Table 3, but the hydrogen recovery rate decreases.

COMPARATIVE EXAMPLE 1-3

FIG. 9is a diagram illustrating a monitored result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value) when the exhaust gas treatment system is operated so as not to satisfy the equation (1-2) (C1=0.1) in a state where the condition of Example 1-1 is set as an initial condition. From this result, it is found that the hydrogen recovery rate decreases in a short period of time when the exhaust gas treatment system is operated so as not to satisfy the equation (1-2).

COMPARATIVE EXAMPLE 1-4

FIG. 10is a diagram illustrating a monitored result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value) when the exhaust gas treatment system is operated so as not to satisfy the equation (1-3) (C2=0.25) in a state where the condition of Example 1-2 is set as an initial condition. From this result, it is found that the hydrogen recovery rate decreases in a short period of time when the exhaust gas treatment system is operated so as not to satisfy the equation (1-3).

COMPARATIVE EXAMPLE 1-5

FIG. 11is a diagram illustrating a monitored result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value) when the exhaust gas treatment system is operated so as not to satisfy the equation (1-4) (C3=0.2) in a state where the initial condition is set as in Example 1-1 except that nitrogen of 30 NL/min is added by the third element gas addition unit10using the membrane separation module having a membrane separation capacity of 3.0 L. From this result, it is found that the hydrogen recovery rate decreases in a short period of time when the exhaust gas treatment system is operated so as not to satisfy the equation (1-4).

FIGS. 12 and 13are system diagrams illustrating a schematic example of an exhaust gas treatment system according to the embodiment.FIG. 14is a system diagram illustrating an example of data processing of the respective components of the exhaust gas treatment system according to the second embodiment. As illustrated inFIG. 12, an exhaust gas treatment system1100according to the embodiment includes a mixed gas analysis unit1003which measures a flow rate and a concentration of hydrogen and monosilane of a mixed gas containing at least the hydrogen and the monosilane discharged from a semiconductor fabrication equipment1001through a pump1002, a membrane separation unit1004which separates the monosilane and hydrogen from the mixed gas, a permeation side pressure control unit1005which controls a permeation side pressure of a membrane separation unit1004, a permeation side gas analysis unit1006which measures a flow rate and a concentration of the hydrogen and the monosilane of the permeation side gas separated by the membrane separation unit1004, a hydrogen gas treatment unit1007which treats the hydrogen separated by the membrane separation unit1004, and a silane gas treatment unit1008which treats the monosilane separated by the membrane separation unit1004.

The semiconductor fabrication equipment1001is not particularly limited, but a plasma CVD device or the like which forms a film by thin-film silicon used in a solar cell may be exemplified.

The composition of the mixed gas discharged from the semiconductor fabrication equipment1001is not particularly limited, but for example, contained are monosilane which needs to be detoxified, hydrogen which does not need to be detoxified, nitrogen, argon, and a small amount of impurities. As the small amount of impurities, high-order silane including plural Si such as disilane or trisilane, PH3, and B2H6(which are respectively 0.001 to 1%) may be exemplified.

The pump unit1002suctions the mixed gas discharged from the semiconductor fabrication equipment1001, and sends the mixed gas to the mixed gas analysis unit1003of the rear stage. The type of pump to be used is not particularly limited, but a dry pump is used in the semiconductor fabrication equipment in many cases. The dry pump may introduce a purging gas for the purpose of maintaining air-tightness, preventing unnecessary deposited material, preventing the corrosion inside the pump, and improving the emission performance. The purging gas is not particularly limited, but an inert gas such as nitrogen or argon is used in many cases. Further, even the introduction amount of the purging gas is not particularly limited, but in general, the introduction amount is 10 to 50 NL/min for each pump.

Further, as illustrated inFIG. 13, a filter1002amay be provided at the front stage and/or the rear stage of a pump1002b. In particular, when a comparatively large amount of fine particles such as high-order silane exist in the exhaust gas, it is desirable to provide the filter1002a. The filter1002ais a fine particle capturing filter which selectively removes fine particles such as high-order silane contained in the mixed gas. The filter to be used is not particularly limited, but a vortex filter or the like may be used.

Further, in the semiconductor fabrication equipment1001, chemical cleaning may be performed so as to remove a deposited material produced inside a chamber due to the film forming. In the chemical cleaning, it is general to perform a plasma treatment under the introduction of a gas such as NF3or F2so as to remove a silicon thin film deposited in the chamber. However, since such a gas has a combustion supporting property, there is a need to prevent the gas from contacting a combustible gas such as hydrogen or monosilane, and hence it is desirable to install a switching valve1002cin rear of the pump1002bas in a case ofFIG. 13. Accordingly, when the exhaust gas of the chemical cleaning comes out, a combustion supporting gas treatment system is selected, so that such an exhaust gas is prevented from being mixed with a treatment line of a silane gas. Furthermore, in the switching valve1002c, such a mechanism may be built in the pump.

The mixed gas analysis unit1003and the permeation side gas analysis unit1006are one of the hydrogen recovery rate acquisition units, and are provided so as to measure at least the flow rates of the mixed gas and the permeation side gas separated by the membrane separation unit and the concentration of the hydrogen and the monosilane of the permeation side gas. In the gas analysis units, the method is not particularly limited if the flow rate of the gas and the concentration of the hydrogen and the monosilane may be measured. For example, a general dry type or wet type flowmeter may be used for the flow rate. Further, in the measurement of the concentration of the hydrogen and the monosilane, an FT-IR with a gas circulation type sample cell, an on-line type gas chromatograph, or the like may be used.

From the measurement result, the recovery rate (the hydrogen recovery rate) of the hydrogen gas may be calculated according to Equation (2-1).
Hydrogen recovery rate(%)=100×((A/100)×B))/((C/100)×D)  Equation (2-1)

Here, A indicates the concentration of the hydrogen (permeation side hydrogen concentration) (vol %) of the permeation side gas, B indicates the flow rate of the permeation side gas (permeation side total gas flow rate) (L/min), C indicates the concentration of the hydrogen (supply side hydrogen concentration) (vol %) of the mixed gas supplied to the membrane separation device, and D indicates the flow rate (supply side total gas flow rate) (L/min) of the mixed gas supplied to the membrane separation device.

As illustrated inFIG. 13, the membrane separation unit1004includes a temperature control unit1004awhich controls a temperature of the mixed gas supplied to a membrane separation device1004band the membrane separation device1004b.

The temperature control unit1004ais not particularly limited if a function of cooling or heating the mixed gas is provided, but an electric heater, various heat exchangers, or the like may be exemplified.

The membrane separation device1004bis a membrane through which hydrogen selectively permeates. There is no particular limitation if metal elements, for example, palladium, nickel, and the like reacting with monosilane are not contained as a main element, and various semipermeable membranes may be exemplified. The semipermeable membrane includes, for example, a dense layer through which hydrogen selectively permeates and a porous base material which supports the dense layer. As the shape of the semipermeable membrane, a flat membrane, a spiral membrane, and a hollow fiber membrane may be exemplified. Among these, the hollow fiber membrane is more desirable.

As the material used in the base material, an inorganic material such as glass, ceramic, and sintered metal and a porous organic material may be exemplified. As the porous organic material, polyether, polyacrylonitrile, polyether, poly (arylene oxide), polyetherketone, polysulfide, polyethylene, polypropylene, polybutene, polyvinyl, and the like may be exemplified.

Next, the permeation side pressure control unit1005and a non-permeation side pressure control unit1012are used to respectively control the permeation side pressure and the non-permeation side pressure of the membrane separation device1004b. When the pressure of the mixed gas supplied to the membrane separation device1004bis low so as to be about the atmospheric pressure, a pressure control device such as a back pressure valve and a dry pump causing the permeation side of the membrane separation device1004bto be a vacuum of the atmospheric pressure or less are provided in the permeation side pressure control unit1005so as to ensure a sufficient differential pressure with respect to a supply pressure and to control the permeation side pressure at a constant value. When the pressure of the mixed gas supplied to the membrane separation device1004bis sufficiently high (a pressure increasing unit is provided in the flow rate control unit), the permeation side pressure control unit1005and the non-permeation side pressure control unit1012are respectively provided with a device such as a back pressure valve which maintains a constant pressure, and the non-permeation side pressure and the permeation side pressure of the membrane separation device1004bare controlled at a constant value.

The flow rate, the pressure, and the temperature of the mixed gas supplied to the membrane separation device1004b, the concentration of the monosilane gas, and the non-permeation side pressure and the permeation side pressure of the membrane separation device1004bare not particularly limited. For example, as the flow rate, the flow rate is 5 NL/min to 500 NL/min with respect to the capacity of 1 L of the membrane separation device, and is desirably 10 NL/min to 100 NL/min. As the pressure, −90 kPaG to 1.0 MPaG is desirable. As the temperature, about −20° C. to 100° C. is desirable. As the concentration of the monosilane gas, 30 vol % or less, desirably 20 vol % or less, more desirably, 10 vol % or less is desirable. As the non-permeation side pressure of the membrane separation device1004b, −90 kPaG to 0.85 MPaG is desirable. As the permeation side pressure, −100 kPaG to 0.9 MPaG is desirable.

Here, the capacity of the membrane separation device indicates the volume of the portion in which the separation membrane is sufficiently charged inside the membrane separation device.

In fact, the membrane separation conditions are closely concerned with each other. For example, in a case of the membrane separation capacity of 1 L, the supply flow rate to the membrane separation device is desirably 20 NL/min to 50 NL/min, the concentration of the monosilane gas is desirably 10 vol % or less, the pressure is desirably the atmospheric pressure or more, the temperature is desirably 10° C. to 40° C., the permeation side pressure of the membrane separation device is desirably −100 kPaG to −60 kPaG.

The respective gases separated by the membrane separation device1004bare sent to the hydrogen gas treatment unit1007and the silane gas treatment unit1008. In the hydrogen gas treatment unit1007, the simply collected hydrogen is used for a combustion treatment or fuel. For example, as illustrated inFIG. 13, the separated gas may be diluted by a dilution unit1007bby nitrogen, air, or the like so that the concentration of the monosilane in the collected gas becomes the allowable concentration or less (5 ppmv or less) and may be discharged to the outside. Further, at the dilution time, it is desirable to dilute the hydrogen so that the concentration of the hydrogen becomes an explosion lower limit or less (4 vol % or less) from the viewpoint of safety. The dilution rate of the dilution unit1007bis not particularly limited if at least the concentration of monosilane satisfies 5 ppmv or less. When the dilution rate is controlled based on a measurement result of a permeation side gas analysis unit1006, the dilution rate may be effectively controlled without any consumption. The separated gas which is diluted by the dilution unit1007bis discharged to the outside by a blower1007c. Further, in order to reduce the concentration of monosilane in the collected gas, a mechanism (not illustrated) may be further provided which selectively detoxifies the monosilane. A detoxifying agent which selectively performs a detoxifying treatment is not particularly limited, but an oxidizing agent, an adsorbing agent, or the like may be exemplified. Further, a hydrogen gas purification unit1007amay be provided so that the hydrogen is purified and used again.

Further, in the silane gas treatment unit1008, for example, monosilane as a toxic gas is diluted by a dilution unit1008bin accordance with the specification of the device of a detoxifying unit1008cas a detoxifying device so as to be a predetermined concentration, and is introduced into the detoxifying unit1008c, so that the monosilane is detoxified to be an allowable concentration or less and is discharged to the outside by the blower1008d. Furthermore, a silane gas purification unit1008amay be provided so that the monosilane is purified and used again.

Further, in the exhaust gas treatment system according to the embodiment, a non-permeation side gas analysis unit1013is provided so as to measure the flow rate of the non-permeation side monosilane rich gas separated by the membrane separation device1004b, the concentration of the monosilane, and the like, which may be reflected to the operation condition of the silane gas treatment unit1008of the rear stage.

For example, when the collected monosilane is detoxified and emitted by the silane gas treatment unit1008, there is a need to dilute the collected monosilane to become a predetermined concentration in accordance with the specification of the detoxifying device. However, when there is data of the non-permeation side gas analysis unit at this time, it is possible to prevent the monosilane from being uselessly diluted too much or prevent a problem occurring in the detoxifying device due to the insufficient dilution.

Further, when the silane gas treatment unit1008is provided with the silane gas purification unit1008aand the monosilane gas is purified and used again, the non-permeation side gas analysis unit1013may be used to analyze a small amount of impurities in the collected monosilane by a gas chromatograph or the like other than the flow rate and the concentration of the monosilane. With such a configuration, when the condition of the optimal purification treatment is selected or the amount of impurities is too large, the purification treatment is not performed and the detoxifying treatment may be selected. At this time, it is desirable to provide a valve at the rear stage of the gas analysis unit so as to switch the detoxifying unit and the reuse line.

Further, when the operation condition of the semiconductor fabrication equipment, and particularly, the flow rate or the pressure largely changes or when the exhaust gases of plural semiconductor fabrication equipments having different operation conditions are collectively treated, as illustrated inFIG. 13, it is desirable to provide a compressor1009, a gas accommodation unit1010, and a flow rate control unit1011so as to control the flow rate of the mixed gas supplied to the membrane separation unit1004at a constant value.

The compressor1009is not particularly limited, but a diaphragm type 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, and the like may be exemplified. Among these, the diaphragm type compressor is more desirable.

The operation condition of the compressor1009is not particularly limited, but it is desirable to perform the operation so that the temperature of the compressed mixed gas becomes equal to or lower than 200° C. which is a decomposition temperature of monosilane. That is, when it is supposed that the mixed gas discharged from the pump unit1002is compressed from normal pressure, it is desirable to operate the compressor so that the compression ratio becomes equal to or lower than 4.4.

The compressor configuration used in the compressor1009is not particularly limited, but in order to stably operate the compressor even when the flow rate of the mixed gas supplied to the compressor changes, it is desirable to have a configuration in which inverters are provided in parallel or a spill-back type configuration in which the mixed gas once compressed by the compressor is returned to the suction side of the compressor again.

The gas accommodation unit1010is used to collect the mixed gas in a tank or the like having a sufficient capacity when the flow rate or the pressure of the mixed gas discharged from the semiconductor fabrication equipment1001through the pump unit1002is not stable or the exhaust gases from the plural semiconductor fabrication equipments1001is collectively treated. Accordingly, a change in flow rate and pressure of the mixed gas discharged from the respective semiconductor fabrication equipments1001is averaged, and the mixed gas having a constant flow rate and a constant pressure at all times is circulated to the membrane separation unit1004. Further, a function of removing fine particles contained in the mixed gas may be provided by devising a structure.

The size of the tank used in the gas accommodation unit1010is not particularly limited. However, in a case of one semiconductor fabrication equipment, it is desirable that the size of the tank is the maximum flow rate of the equipment. Then, in a case where plural semiconductor fabrication equipments are collectively treated, it is desirable that the size of the tank is equal to or more than the sum of the maximum flow rates of the gases supplied to the respective semiconductor fabrication equipments.

The pressure inside the tank used in the gas accommodation unit1010is not particularly limited, but it is desirable that the pressure is 1 MPaG at maximum.

Further, when the operation of the equipment starts, it is desirable that the exhaust gas is supplied from the compressor1009to the gas accommodation unit1010and is accumulated in the gas accommodation unit1010while the outlet valve of the gas accommodation unit1010is closed. Accordingly, even when the flow rate of the exhaust gas of the semiconductor fabrication equipment largely changes, it is possible to maintain a pressure sufficient for maintaining the supply flow rate to the separation device to be constant and to increase the amount of a gas which may be accommodated in the gas accommodation unit1010. Accordingly, it is possible to decrease the volume of the gas accommodation unit. Further, when a sufficient pressure is accumulated, the non-permeation side pressure of the membrane separation device may be set to be high, which is advantageous in operation due to a sufficient differential pressure with respect to the permeation side pressure.

The flow rate control unit1011is used to control the flow rate of the mixed gas at a constant value. The control method is not particularly limited, but it is desirable that the control method is not influenced by a change in pressure of the mixed gas supplied to the flow rate control unit1011, for example, a mass flow controller or the like may be exemplified.

In the embodiment, the degradation state of the membrane separation device1004bmay be recognized by monitoring the hydrogen recovery rate calculated by the hydrogen recovery rate acquisition unit. Accordingly, the operation may be performed while maintaining the high hydrogen recovery rate at all times by controlling the permeation side pressure of the membrane separation device1004bor the temperature of the mixed gas supplied to the membrane separation device1004baccording to the following equation (2-2) and equation (2-3) with the degradation in the hydrogen recovery rate.

Furthermore, as the control method, a control of satisfying only the equation (2-2) or the equation (2-3) and a control of satisfying both the equation (2-2) and the equation (2-3) may be adopted. Further, when the operation is performed in accordance with the control, the hydrogen recovery rate may be 60% or more and the concentration of the monosilane of the permeation side gas may be 1.0% or less.
ΔP=C1×ΔA, C1≧0.5  Equation (2-2)

Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔP indicates a pressure decrease amount (kPa) from the permeation side pressure of the membrane separation device4b.
ΔT=C2×ΔA, C2≧0.8  Equation (2-3)

Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔT indicates a temperature increase amount (° C.) of the mixed gas.

Furthermore, the above-described control is performed by using a calculation control unit1030illustrated inFIG. 14. Further, the calculation control unit1030may control the flow rate of the mixed gas using the flow rate control unit1011based on the flow rate of the controlled mixed gas, the measurement result of the concentration of the hydrogen and the monosilane in the mixed gas obtained by the mixed gas analysis unit1003and the capacity of the membrane separation device.

Further, the calculation control unit1030may calculate the hydrogen recovery rate based on the flow rate value of the mixed gas obtained by the flow rate control unit1011, the measurement result of the concentration of the hydrogen and the monosilane in the mixed gas obtained by the mixed gas analysis unit1003, and the measurement result of the flow rate of the permeation side gas and the concentration of the hydrogen and the monosilane in the permeation side gas obtained by the permeation side gas analysis unit1006.

The calculation control unit1030may control the temperature of the mixed gas supplied to the membrane separation device104bor the non-permeation side pressure and the permeation side pressure of the membrane separation device104bwith respect to the decrease amount of the calculated hydrogen recovery rate.

Further, the calculation control unit1030may determine how the operation condition of the hydrogen gas purification unit is or whether the collected hydrogen gas will be used again based on the measurement result of the flow rate of the permeation side gas and the concentration of the hydrogen and the monosilane in the permeation side gas obtained by the permeation side gas analysis unit1006. When the calculation control unit1030determines that the collected hydrogen gas will not be used again, the calculation control unit may control the dilution rate of the dilution unit1007bof the hydrogen gas treatment unit1007so that the concentration of the monosilane becomes the allowable concentration (5 ppmv or less).

Further, the calculation control unit1030may determine how the operation condition of the monosilane purification unit is or whether the collected monosilane will be used again based on the measurement result of the flow rate of the non-permeation side gas and the concentration of the hydrogen and the monosilane in the non-permeation side gas obtained by the non-permeation side gas analysis unit1013. When the calculation control unit1030determines that the collected monosilane will not be used again, the calculation control unit may control the dilution rate of the dilution unit1008bof the silane gas treatment unit1008so that the concentration of the monosilane becomes the allowable concentration (for example, about 2 vol %) or less of the detoxifying device.

According to the exhaust gas treatment system of the second embodiment, the mixed gas containing at least the hydrogen and the monosilane is separated by the membrane separation device1004binto the monosilane which needs to be detoxified and the hydrogen which does not need to be detoxified. Since the hydrogen and the monosilane which are separated from the mixed gas are respectively treated by the hydrogen gas treatment unit1007and the silane gas treatment unit1008, the treatment instrument may be decreased in size, and further the exhaust gas treatment system may be made to be compact.

Further, it is possible to efficiently treat the exhaust gas which is discharged from plural semiconductor fabrication equipments, for example, plural plasma CVD devices which form a film of thin-film silicon used in the solar cell. Further, the degradation in the performance of separating the mixed gas with the degradation in the membrane separation device may be suppressed by selecting an appropriate operation condition, and the high separation performance may be maintained for a long period of time.

Hereinafter, the embodiment will be described in detail based on Example, but the embodiment is not limited to the example.

FIG. 15is a system diagram illustrating a configuration of an exhaust gas treatment system according to Example 2. As illustrated inFIG. 15, the exhaust gas treatment system according to the second embodiment is connected to three thin-film silicon solar cell manufacturing CVD devices which is one of the semiconductor fabrication equipments1001. The exhaust gas treatment system1100suctions the mixed gas discharged from the plural PE-CVD devices1014together with nitrogen introduced from the outside by a dry pump1015acorresponding to each device, and sends the resultant gas toward the compressor1017through the filter1016. Furthermore, a switching valve (not illustrated) may be provided behind the dry pump1015a. Accordingly, when the exhaust gas of the chemical cleaning comes out, a combustion supporting gas treatment system is selected, so that such an exhaust gas is prevented from being mixed with a treatment line of a silane gas.

As the compressor1017, a compressor is selected which may be operated at the compression ratio of 4. In a state where an accumulation valve1032is closed, the purging nitrogen of the dry pump1015aflows at the flow rate of 30 NL/min, so that the pressure of the hermetic tank1018(capacity: 5 m3) increases to 0.3 MPaG. Subsequently, the accumulation valve1032is opened so that the supply of the gas to a mass flow controller1019starts and the respective PE-CVD devices1014are operated so as to be late by 4 minutes. The gas flow rate is controlled by the mass flow controller1019, the temperature is adjusted to a predetermined temperature by a heat exchanger1021, and then the result is supplied to a membrane separation device1023(polyimide hollow fiber membrane). At this time, the permeation side pressure is adjusted to be a predetermined pressure by a permeation side back pressure valve1025a. Further, the pressure is adjusted to be a normal pressure by the non-permeation side back pressure valve1025b. Further, after the operation of the PE-CVD device starts, the amount of the purging nitrogen of the dry pump1015ais adjusted to be a predetermined flow rate.

An analysis device1020ais used to measure the concentration of the hydrogen and the monosilane in the mixed gas, and includes an FT-IR device with a gas cell and an on-line gas chromatograph (GC) device. As for the mixed gas of which the flow rate or the pressure is controlled to be a predetermined value by the mass flow controller1019, the concentration of the hydrogen and the monosilane is measured by the analysis device1020a. Subsequently, the temperature of the mixed gas is controlled by the functions of the heat exchanger1021and a circulation constant temperature reservoir1022, and the mixed gas flows into the membrane separation device1023. Flowmeters1024aand1024bare respectively provided at the rear stage of the permeation side and the non-permeation side of the membrane separation device1023.

In the exhaust gas treatment system illustrated inFIG. 15, the permeation side separated gas of the membrane separation device1023passes through the flowmeter1024aand the analysis device1020b, so that the flow rate and the concentration of the hydrogen and the monosilane are measured. The permeation side separated gas is diluted by nitrogen appropriately based on the measurement result, and is emitted into the atmosphere by the dry pump1015b. On the other hand, the non-permeation side separated gas of the membrane separation device1023passes through the flowmeter1024band the analysis device1020c, so that the flow rate and the concentration of the monosilane are detected, and the non-permeation side separated gas is combusted and detoxified by the combustion detoxifying device1026. As for the gas which is combusted and discharged by the combustion detoxifying device1026, foreign matter such as particles produced by the combustion are removed by a bag filter1027, and the gas is emitted into the atmosphere by the blower1028.

The exhaust gas treatment system with a configuration illustrated inFIG. 15is connected to the thin-film silicon solar cell CVD device, and a change over time in hydrogen gas recovery rate is monitored while the operation is continued with several patterns of the flow rate and the concentration of the monosilane. Regarding a change in hydrogen gas recovery rate, a change in hydrogen recovery rate is measured by changing the temperature of the temperature control unit and the permeation side pressure of the membrane separation device. The result is illustrated inFIGS. 16 to 19.

FIGS. 16 to 21are graphs illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the pressure.FIGS. 16 and 17are graphs illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the pressure on the condition that the purging nitrogen of the pump is not introduced.FIGS. 18 to 21are graphs illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the pressure on the condition that the purging nitrogen of the pump is introduced by 10 mL/min. For comparison,FIGS. 16,18, and20illustrate the operation result when the equation (2-2) is satisfied (C1=1.0), andFIGS. 17,19, and21illustrate the operation result when the equation (2-2) is not satisfied (C1=0.1). The initial condition of the test is illustrated in Table 4. The operation result illustrated inFIGS. 16 and 17is obtained when the operation is performed with the respective conditions of a pressure change test (1) illustrated in Table 4. The operation result illustrated inFIGS. 18 and 19is obtained when the operation is performed with the respective conditions of a pressure change test (2) illustrated in Table 4. The operation result illustrated inFIGS. 20 and 21is obtained when the operation is performed with the respective conditions of a pressure change test (3) illustrated in Table 4.

Table 5 to Table 7 illustrate a total result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value). The result of Table 5 is illustrated inFIG. 16(C1=1.0) andFIG. 17(C1=0.1). The result of Table 6 is illustrated inFIG. 18(C1=1.0) andFIG. 19(C1=0.1). The result of Table 7 is illustrated inFIG. 20(C1=1.0) andFIG. 21(C1=0.1). Furthermore, the number of years in use (corresponding value) is a value which is obtained by converting the operation time of the acceleration test into the number of real years. The accelerated degradation test was performed so that the total flow rate of the supplied mixed gas is set to 50 times that of the normal test and the supplied monosilane gas concentration and the supplied nitrogen gas concentration are constant. The method of the accelerated degradation test is further written in Table 5 to Table 7. In the exhaust gas treatment system according to Example 2, whenever the hydrogen gas recovery rate decreases by about 10%, it is controlled that the permeation side pressure decreases by about 10 kPa in a case of C1=1.0 and decreases by about 1 kPa in a case of C1=0.1. From this result, it is found that the exhaust gas treatment system may be operated for a long period of time while maintaining a high hydrogen recovery rate when the exhaust gas treatment system is operated so as to satisfy the equation (2-2). Furthermore, desirably, the value of C1may be 0.5 or more.

FIGS. 22 to 27are graphs illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the temperature.FIGS. 22 and 23are graphs illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the pressure on the condition that the purging nitrogen of the pump is not introduced.FIGS. 24 to 27are graphs illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the pressure on the condition that the purging nitrogen of the pump is introduced by 10 NL/min. For comparison,FIGS. 22,24, and26illustrate the operation result when the equation (2-3) is satisfied (C2=1.0), andFIGS. 23,25, and27illustrate the operation result when the equation (2-3) is not satisfied (C2=0.25). The initial condition of the test is illustrated in Table 4. The operation result illustrated inFIGS. 22 and 23is obtained when the operation is performed with the respective conditions of a temperature change test (1) illustrated in Table 4. The operation result illustrated inFIGS. 24 and 25is obtained when the operation is performed with the respective conditions of a temperature change test (2) illustrated in Table 4. The operation result illustrated inFIGS. 26 and 27is obtained when the operation is performed with the respective conditions of a temperature change test (3) illustrated in Table 4.

Table 8 to Table 10 illustrate the total result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value). The result of Table 8 is illustrated inFIG. 22(C2=1.0) andFIG. 23(C2=0.25). The result of Table 9 is illustrated inFIG. 24(C2=1.0) andFIG. 25(C2=0.25). The result of Table 10 is illustrated inFIG. 26(C2=1.0) andFIG. 27(C2=0.25). Furthermore, the number of years in use (corresponding value) is a value which is obtained by converting the operation time of the acceleration test into the number of real years. The accelerated degradation test was performed so that the total flow rate of the supplied mixed gas is set to 50 times that of the normal test and the supplied monosilane gas concentration and the supplied nitrogen gas concentration are constant. The method of the accelerated degradation test is further written in Table 8 to Table 10. In the exhaust gas treatment system according to Example 2, whenever the hydrogen gas recovery rate decreases by about 10%, it is controlled that the operation temperature (the temperature of the mixed gas) increases by about 10° C. in a case of C2=1.0 and increases by about 2.5° C. in a case of C2=0.25. From this result, it is found that the exhaust gas treatment system may be operated for a long period of time while maintaining a high hydrogen recovery rate when the exhaust gas treatment system is operated so as to satisfy the equation (2-3). Furthermore, desirably, the value of C2may be 0.8 or more.

FIG. 28is a schematic diagram illustrating a configuration of an exhaust gas treatment system according to a third embodiment.FIG. 29is a system diagram more specifically illustrating a configuration of the exhaust gas treatment system according to the embodiment.FIG. 30is a system diagram illustrating an example of data processing of the respective components of the exhaust gas treatment system according to the embodiment. As illustrated inFIG. 31, an exhaust gas treatment system.2100according to the third embodiment includes at least a third element gas addition unit2003which controls an addition amount of a third element gas added to a mixed gas containing at least hydrogen and monosilane discharged from a semiconductor fabrication equipment2001through the pump unit2002, a mixed gas analysis unit2004which measures the total flow rate of the mixed gas and the concentration of the hydrogen and the monosilane in the mixed gas, a membrane separation unit2005which separates the monosilane and the hydrogen from the mixed gas, a permeation side gas analysis unit2006which measures the flow rate of the gas separated by the membrane separation unit2005and the concentration of the hydrogen and the monosilane, a hydrogen gas treatment unit2007which treats the hydrogen separated by the membrane separation unit2005, and a silane gas treatment unit2008which treats the monosilane separated by the membrane separation device.

The semiconductor fabrication equipment2001is not particularly limited, but a plasma CVD device or the like which forms a film by thin-film silicon used in a solar cell may be exemplified.

The composition of the mixed gas discharged from the semiconductor fabrication equipment2001is not particularly limited, but for example, contained are monosilane which need to be detoxified, hydrogen which does not need to be detoxified, nitrogen, and a small amount of impurities. As the small amount of impurities, high-order silane including plural Si such as disilane or trisilane, PH3, B2H6(which are respectively 0.001 to 1%), and nitrogen may be exemplified.

The pump unit2002suctions the mixed gas discharged from the semiconductor fabrication equipment2001, and sends the mixed gas to the mixed gas analysis unit2004of the rear stage. The type of pump to be used is not particularly limited, but a dry pump is used in the semiconductor fabrication equipment in many cases. The dry pump may introduce a purging gas for the purpose of maintaining air-tightness, preventing unnecessary deposited material, preventing the corrosion inside the pump, and improving the emission performance. The purging gas is not particularly limited, but an inert gas such as nitrogen or argon is used in many cases. Further, even the introduction amount of the purging gas is not particularly limited, but in general, the introduction amount is 10 to 50 NL/min for each pump.

Further, as illustrated inFIG. 29, a filter2002amay be provided at the front stage and/or the rear stage of a pump2002b. In particular, when a comparatively large amount of fine particles such as high-order silane exist in the exhaust gas, it is desirable to provide the filter2002a. The filter2002ais a fine particle capturing filter which selectively removes fine particles such as high-order silane contained in the mixed gas. The filter to be used is not particularly limited, but a vortex filter or the like may be used.

Further, in the semiconductor fabrication equipment2001, chemical cleaning may be performed so as to remove a deposited material produced inside a chamber due to the film forming. In the chemical cleaning, it is general to perform a plasma treatment under the introduction of a gas such as NF3or F2so as to remove a silicon thin film deposited in the chamber. However, since such a gas has a combustion supporting property, there is a need to prevent the gas from contacting a combustible gas such as hydrogen or monosilane, and hence it is desirable to provide a switching valve2002cin rear of the pump2002bas in a case ofFIG. 29. Accordingly, when the exhaust gas of the chemical cleaning comes out, a combustion supporting gas treatment system is selected, so that such an exhaust gas is prevented from being mixed with a treatment line of a silane gas. Furthermore, in the switching valve, such a mechanism may be built in the pump.

The third element gas addition unit2003is provided so as to adjust the concentration of the monosilane in the mixed gas by adding a predetermined amount of a third element gas to the mixed gas. The third element gas to be added is not particularly limited if the gas does not abruptly react with the element gas such as the monosilane in the mixed gas, but for example, nitrogen, argon, hydrogen, helium, xenon, a hydrocarbon gas having a carbon number of 1 to 4, and the like may be exemplified.

The mixed gas analysis unit2004and the permeation side gas analysis unit2006are one of the hydrogen recovery rate acquisition units, and are provided so as to measure at least the flow rates of the mixed gas and the permeation side gas separated by the membrane separation unit and the concentration of the hydrogen and the monosilane. In the gas analysis units, the method is not particularly limited if the flow rate of the gas and the concentration of the hydrogen and the monosilane may be measured. For example, a general dry type or wet type flowmeter may be used for the flow rate. Further, in the measurement of the concentration of the hydrogen and the monosilane, an FT-IR with a gas circulation type sample cell, an on-line type gas chromatograph, or the like may be used.

From the measurement result, the recovery rate (the hydrogen recovery rate) of the hydrogen gas may be calculated according to Equation (3-4).
Hydrogen recovery rate(%)=100×(A/100×B))/(C/100×D)  Equation (3-4)

Here, A indicates the concentration of the hydrogen (permeation side hydrogen concentration) (vol %) of the permeation side gas, B indicates the flow rate of the permeation side gas (permeation side total gas flow rate) (L/min), C indicates the concentration of the hydrogen (supply side hydrogen concentration) (vol %) of the mixed gas supplied to the membrane separation device, and D indicates the flow rate (supply side total gas flow rate) (L/min) of the mixed gas supplied to the membrane separation device.

As illustrated inFIG. 29, the membrane separation unit2005includes a temperature control unit2005awhich controls the temperature of the mixed gas supplied to a membrane separation device2005b, the membrane separation device2005b, a permeation side pressure control unit2005cand/or a non-permeation side pressure control unit5d.

The temperature control unit2005ais not particularly limited if a function of cooling or heating the mixed gas is provided, but an electric heater, various heat exchangers, or the like may be exemplified. The membrane separation device2005bis a membrane through which hydrogen selectively permeate. There is no particular limitation if metal elements, for example, palladium, nickel, and the like reacting with monosilane are not contained as a main element, and various semipermeable membranes may be exemplified. The semipermeable membrane includes, for example, a dense layer through which hydrogen selectively permeates and a porous base material which supports the dense layer. As the shape of the semipermeable membrane, a flat membrane, a spiral membrane, and a hollow fiber membrane may be exemplified. Among these, the hollow fiber membrane is more desirable.

As the material used in the base material, an inorganic material such as glass, ceramic, and sintered metal and a porous organic material may be exemplified. As the porous organic material, polyether, polyacrylonitrile, polyether, poly (arylene oxide), polyetherketone, polysulfide, polyethylene, polypropylene, polybutene, polyvinyl, and the like may be exemplified.

Next, a permeation side pressure control unit2005cand a non-permeation side pressure control unit2005dare used to respectively control the permeation side pressure and the non-permeation side pressure of the membrane separation device2005b. When the pressure of the mixed gas supplied to the membrane separation device5bis low so as to be about the atmospheric pressure, a pressure control device such as a back pressure valve and a dry pump causing the permeation side of the membrane separation device to be a vacuum of the atmospheric pressure or less are provided in the permeation side pressure control unit2005cso as to ensure a sufficient differential pressure with respect to a supply pressure and to control the permeation side pressure at a constant value. When the pressure of the mixed gas supplied to the membrane separation device2005bis sufficiently high (a pressure increasing unit is provided in the flow rate control unit), the permeation side pressure control unit and the non-permeation side pressure control unit are respectively provided with a device such as a back pressure valve which maintains a constant pressure, and the non-permeation side pressure and the permeation side pressure of the membrane separation device are controlled at a constant value.

The flow rate, the pressure, and the temperature of the mixed gas supplied to the membrane separation device2005b, the concentration of the monosilane gas, the addition amount of the third element gas, and the non-permeation side pressure and the permeation side pressure of the membrane separation device2005bare not particularly limited. For example, as the flow rate, the flow rate is 5 NL/min to 500 NL/min with respect to the capacity of 1 L of the membrane separation device, and is desirably 10 NL/min to 100 NL/min. As the pressure, −90 kPaG to 1.0 MPaG is desirable. As the temperature, about −20° C. to 100° C. is desirable. As the concentration of the monosilane gas, 30 vol % or less, desirably 20 vol % or less, more desirably, 10 vol % or less is desirable. As the addition amount of the third element gas, 1 to 100 NL/min is desirable, and desirably, 1 to 50 NL/min is desirable. As the non-permeation side pressure of the membrane separation device5b, −90 kPaG to 0.85 MPaG is desirable. As the permeation side pressure, −100 kPaG to 0.9 MPaG is desirable. Here, the capacity of the membrane separation device indicates the volume of the portion in which the separation membrane is sufficiently charged inside the membrane separation device.

In fact, the membrane separation conditions are closely concerned with each other. For example, in a case of the membrane separation capacity of 1 L, the supply flow rate to the membrane separation device is desirably 20 NL/min to 50 NL/min, the concentration of the monosilane gas is desirably 10 vol % or less, the pressure is desirably the atmospheric pressure or more, the temperature is desirably 10° C. to 40° C., the addition amount of the third element gas is desirably 1 to 10 NL/min, and the permeation side pressure of the membrane separation device is desirably −100 kPaG to −60 kPaG.

The respective gases separated by the membrane separation device2005bare sent to the hydrogen gas treatment unit2007and the silane gas treatment unit2008. In the hydrogen gas treatment unit2007, the simply collected hydrogen is used for fuel. For example, as illustrated inFIG. 29, the separated gas may be diluted by nitrogen, air, or the like in a dilution unit2007bso that the concentration of the monosilane in the collected gas becomes the allowable concentration or less (5 ppmv or less), and may be emitted to the outside. Further, at the dilution time, it is desirable to dilute the hydrogen so that the concentration of the hydrogen becomes an explosion lower limit or less (4 vol % or less) from the viewpoint of safety. The dilution rate of the dilution unit2007bis not particularly limited if at least the concentration of the monosilane satisfies 5 ppmv or less. When the dilution rate is controlled based on a measurement result of the permeation side gas analysis unit, the dilution rate may be effectively controlled without any consumption. The separated gas which is diluted by the dilution unit2007bis discharged to the outside by a blower2007c. Further, in order to reduce the concentration of the monosilane in the collected gas, a mechanism (not illustrated) may be further provided which selectively detoxifies the monosilane. A detoxifying agent which selectively performs a detoxifying treatment is not particularly limited, but an oxidizing agent, an adsorbing agent, or the like may be exemplified. Further, a hydrogen gas purification unit2007amay be provided so that the hydrogen is purified and used again.

Further, in the silane gas treatment unit2008, for example, monosilane as a toxic gas is diluted by a dilution unit2008bin accordance with the specification of the device of a detoxifying unit2008cas a detoxifying device so as to be a predetermined concentration, and is introduced into the detoxifying unit2008c, so that the monosilane is detoxified to be an allowable concentration or less and is discharged to the outside by the blower2008d. Furthermore, a silane gas purification unit2008amay be provided so that the monosilane is purified and used again.

Further, in the exhaust gas treatment system2100according to the embodiment, a non-permeation side gas analysis unit2012is provided so as to measure the flow rate of the non-permeation side monosilane rich gas separated by the membrane separation device2005b, the concentration of the monosilane, and the like, which may be reflected to the operation condition of the silane gas treatment unit2008of the rear stage.

For example, when the collected monosilane is detoxified and emitted by the silane gas treatment unit2008, there is a need to dilute the collected monosilane to become a predetermined concentration in accordance with the specification of the detoxifying device. However, when there is data of the non-permeation side gas analysis unit at this time, it is possible to prevent the monosilane from being uselessly diluted too much or prevent a problem occurring in the detoxifying device due to the insufficient dilution.

Further, when the silane gas treatment unit2008is provided with the silane gas purification unit2008aand the monosilane gas is purified and used again, the non-permeation side gas analysis unit2012may be used to analyze a small amount of impurities in the collected monosilane by a gas chromatograph or the like other than the flow rate and the concentration of the monosilane. When the condition of the optimal purification treatment is selected or the amount of impurities is too large, the purification treatment is not performed and the detoxifying treatment may be selected. At this time, it is desirable to provide a valve at the rear stage of the gas analysis unit so as to switch the detoxifying unit and the reuse line.

Further, when the operation condition of the semiconductor fabrication equipment, and particularly, the flow rate or the pressure largely changes or when the exhaust gases of plural semiconductor fabrication equipments having different operation conditions are collectively treated, as illustrated inFIG. 29, it is desirable to provide a compressor2009, a gas accommodation unit2010, and a flow rate control unit2011so as to control the flow rate of the mixed gas supplied to the membrane separation unit2005at a constant value.

The compressor2009is not particularly limited, but a diaphragm type 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, and the like may be exemplified. Among these, the diaphragm type compressor is more desirable.

The operation condition of the compressor2009is not particularly limited, but it is desirable to perform the operation so that the temperature of the compressed mixed gas becomes equal to or lower than 200° C. which is a decomposition temperature of monosilane. That is, when it is supposed that the mixed gas discharged from the pump unit2002is compressed from normal pressure, it is desirable to operate the compressor so that the compression ratio becomes equal to or lower than 4.4.

The compressor configuration used in the compressor2009is not particularly limited, but in order to stably operate the compressor even when the flow rate of the mixed gas supplied to the compressor changes, it is desirable to have a configuration in which inverters are provided in parallel or a spill-back type configuration in which the mixed gas once compressed by the compressor is returned to the suction side of the compressor again.

The gas accommodation unit2010is used to collect the mixed gas in a tank or the like having a sufficient capacity when the flow rate or the pressure of the mixed gas discharged from the semiconductor fabrication equipment2001through the pump unit2002is not stable or the exhaust gases from the plural semiconductor fabrication equipments2001is collectively treated. Accordingly, a change in flow rate and pressure of the mixed gas discharged from the respective semiconductor fabrication equipments2001is averaged, and the mixed gas having a constant flow rate and a constant pressure at all times is circulated to the membrane separation unit2005. Further, a function of removing fine particles contained in the mixed gas may be provided by devising a structure.

The size of the tank used in the gas accommodation unit2010is not particularly limited. However, in a case of one semiconductor fabrication equipment, it is desirable that the size of the tank is the maximum flow rate of the equipment. Then, in a case where plural semiconductor fabrication equipments are collectively treated, it is desirable that the size of the tank is equal to or more than the sum of the maximum flow rates of the gases supplied to the respective semiconductor fabrication equipments.

The pressure inside the tank used in the gas accommodation unit2010is not particularly limited, but it is desirable that the pressure is 1 MPaG at maximum. Further, when the operation of the equipment starts, it is desirable that the exhaust gas is supplied from the compressor2009to the gas accommodation unit2010and is accumulated in the gas accommodation unit2010while the outlet valve of the gas accommodation unit2010is closed. Accordingly, even when the flow rate of the exhaust gas of the semiconductor fabrication equipment largely changes, it is possible to maintain a pressure sufficient for maintaining the supply flow rate to the separation device to be constant and to increase the amount of a gas which may be accommodated in the gas accommodation unit2010. Accordingly, it is possible to decrease the volume of the gas accommodation unit. Further, when a sufficient pressure is accumulated, the non-permeation side pressure of the membrane separation device may be set to be high, which is advantageous in operation due to a sufficient differential pressure with respect to the permeation side.

The flow rate control unit2011is used to control the flow rate of the mixed gas at a constant value. The control method is not particularly limited, but it is desirable that the control method is not influenced by a change in pressure of the mixed gas supplied to the flow rate control unit2011, for example, a mass flow controller or the like may be exemplified.

According to the exhaust gas treatment system2100of the embodiment, the degradation state of the membrane separation device2006bmay be recognized by monitoring the hydrogen recovery rate calculated by the hydrogen recovery rate acquisition unit. Accordingly, the operation may be performed while maintaining the high hydrogen recovery rate at all times by controlling the addition amount of the third element gas, the temperature of the mixed gas supplied to the membrane separation device2006b, or the permeation side pressure of the membrane separation device according to the following equations (3-1) to (3-3) with the degradation in the hydrogen recovery rate.

Furthermore, as the control method, a control of satisfying only the equation (3-1), a control of satisfying one of the equation (3-1), the equation (3-2), and the equation (3-3), and a control of satisfying all of the equation (3-1) to the equation (3-3) may be adopted. Further, when the operation is performed by the control, the hydrogen recovery rate may become 60% or more and the concentration of the monosilane of the permeation side gas may become 1.0% or less.
ΔF=C1×ΔA, C1≧0.3  Equation (3-1)

Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔF indicates a decrease amount (L/min) of the addition amount of the third element gas.
ΔP=C2×ΔA, C2≧0.5  Equation (3-2)

Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔP indicates a pressure decrease amount (kPa) from the permeation side pressure of the membrane separation device5b.
ΔT=C3×ΔA, C3≧0.8  Equation (3-3)

Here, ΔA indicates a decrease rate (%) of the hydrogen recovery rate, and ΔT indicates a temperature increase amount (° C.) of the mixed gas.

Furthermore, the above-described control is performed by using a calculation control unit2030illustrated inFIG. 30. Further, the calculation control unit2030may control the flow rate of the mixed gas using the flow rate control unit2011based on the flow rate of the controlled mixed gas, the measurement result of the concentration of the monosilane in the mixed gas obtained by the mixed gas analysis unit2004, and the capacity of the membrane separation device.

Further, the calculation control unit2030may calculate the hydrogen recovery rate based on the flow rate value of the mixed gas obtained by the flow rate control unit2011, the measurement result of the concentration of the monosilane in the mixed gas obtained by the mixed gas analysis unit2004, and the measurement result of the flow rate of the permeation side gas and the concentration of the monosilane in the permeation side gas obtained by the permeation side gas analysis unit2006.

The calculation control unit2030may control the temperature of the mixed gas supplied to the membrane separation unit2005, the non-permeation side pressure and the permeation side pressure of the membrane separation unit2005, and the addition amount of the third element gas with respect to the decrease amount of the calculated hydrogen recovery rate.

Further, the calculation control unit2030may determine how the operation condition of the hydrogen gas purification unit is or whether the collected hydrogen gas will be used again based on the measurement result of the flow rate of the permeation side gas and the concentration of the monosilane in the permeation side gas obtained by the permeation side gas analysis unit2006. When the calculation control unit2030determines that the collected hydrogen gas will not be used again, the calculation control unit may control the dilution rate of the dilution unit2007bof the hydrogen gas treatment unit2007so that the concentration of the monosilane becomes the allowable concentration (5 ppmv or less).

Further, the calculation control unit2030may determine how the operation condition of the monosilane purification unit is or whether the collected monosilane will be used again based on the measurement result of the flow rate of the non-permeation side gas and the concentration of the monosilane in the non-permeation side gas obtained by the non-permeation side gas analysis unit2012. When the calculation control unit2030determines that the collected monosilane will not be used again, the calculation control unit may control the dilution rate of the dilution unit2008bof the silane gas treatment unit2008so that the concentration of the monosilane becomes the allowable concentration (for example, about 2 vol %) or less of the detoxifying device.

According to the exhaust gas treatment system of the third embodiment, the mixed gas containing at least the hydrogen and the monosilane is separated by the separation membrane into the monosilane which needs to be detoxified and the hydrogen which does not need to be detoxified. When the hydrogen and the monosilane separated from the mixed gas are respectively treated, a treatment instrument may be decreased in size, and further the exhaust gas treatment system may be made to be compact.

Further, the temperature may be controlled in a comparatively mild condition by adding the third element gas, whereby energy may be saved. The degradation in the separation performance with the degradation of the membrane separation device may be suppressed by controlling the addition amount of the third element gas, whereby the high separation performance may be maintained for a long period of time.

Accordingly, it is possible to decrease the size of the equipment which treats the exhaust gas discharged from the plasma CVD device that forms a film of thin-film silicon used in a solar cell. Further, it is possible to efficiently treat the exhaust gas discharged from the plasma CVD device that forms a film of thin-film silicon used in a solar cell.

Hereinafter, the embodiment will be described in detail based on Example, but the embodiment is not limited to the example.

FIG. 31is a system diagram illustrating a configuration of an exhaust gas treatment system of Example 3. As illustrated inFIG. 31, the exhaust gas treatment system according to the third embodiment is connected to three thin-film silicon solar cell manufacturing CVD devices which is one of the semiconductor fabrication equipments1. The exhaust gas treatment system2100suctions the mixed gas discharged from plural PE-CVD devices2013together with nitrogen introduced from the outside by a dry pump2014acorresponding to each device, and sends the result toward a compressor2016through a filter2015. Furthermore, a switching valve (not illustrated) may be provided behind the dry pump2014a. Accordingly, when the exhaust gas of the chemical cleaning comes out, a combustion supporting gas treatment system is selected, so that such an exhaust gas is prevented from being mixed with a treatment line of a silane gas.

As the compressor2016, a compressor is selected which may be operated at the compression ratio of 4. In a state where an accumulation valve2032is closed, the purging nitrogen of the dry pump2014aflows at the flow rate of 30 NL/min, so that the pressure of the hermetic tank2017(capacity: m3) increases to 0.3 MPaG. Subsequently, the accumulation valve2032is opened so that the supply of a gas to a mass flow controller2018starts and the respective PE-CVD devices2013are operated so as to be late by 4 minutes. The flow rate of the gas is controlled by the mass flow controller2018, and the temperature thereof is adjusted to a predetermined temperature by a heat exchanger2021, and then the gas is supplied to a membrane separation device2023(polyimide hollow fiber membrane). At this time, the permeation side pressure is adjusted to be a predetermined pressure by a permeation side back pressure valve2025a. Further, the pressure is adjusted to be a normal pressure by the non-permeation side back pressure valve2025b. Further, after the operation of the PE-CVD device starts, the amount of the purging nitrogen of the dry pump2014ais adjusted to be a predetermined flow rate.

An analysis device2019ais used to measure the concentration of the hydrogen and the monosilane in the mixed gas, and includes an FT-IR device with a gas cell and an on-line gas chromatograph (GC) device. As for the mixed gas of which the flow rate or the pressure is adjusted to be a predetermined value by the mass flow controller2018, the concentration of the hydrogen and the monosilane is measured by the analysis device2019a. After a predetermined amount of the third element gas is added by a third element gas addition unit2020, the temperature of the mixed gas having the third element gas added thereto is controlled by the functions of the heat exchanger2021and a circulation constant temperature reservoir2022, and the mixed gas flows into the membrane separation device2023. Flowmeters2024aand2024bare respectively provided at the rear stages of the permeation side and the non-permeation side of the membrane separation device2023.

In the exhaust gas treatment system illustrated inFIG. 31, the permeation side separated gas of the membrane separation device2023passes through the flowmeter2024aand an analysis device2019b, so that the flow rate and the concentration of the hydrogen and the monosilane are measured. The permeation side separated gas is diluted by nitrogen appropriately based on the measurement result, and is emitted into the atmosphere by the dry pump2014b. On the other hand, the non-permeation side separated gas of the membrane separation device2023passes through the flowmeter2024band the analysis device2019c, so that the flow rate and the concentration of the monosilane are detected, and the non-permeation side separated gas is combusted and detoxified by the combustion detoxifying device2026. As for the gas which is combusted and discharged by the combustion detoxifying device2026, foreign matter such as particles produced by the combustion are removed by a bag filter2027, and the gas is emitted into the atmosphere by the blower2028.

The exhaust gas treatment system with a configuration illustrated inFIG. 31is connected to the thin-film silicon solar cell CVD device, and a change over time in hydrogen gas recovery rate is monitored while the operation is continued with several patterns of the flow rate and the concentration of the monosilane.

FIG. 32Ais a graph illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the nitrogen addition amount so as to satisfy the equation (3-1) (C1=0.5) on the condition that the purging nitrogen of the pump is 0 NL/min. Further, for comparison,FIG. 32Billustrates the operation result when the equation (3-1) is not satisfied (C1=0.1) on the condition that the purging nitrogen of the pump is 0 NL/min. The initial condition of the test is illustrated in Table 11. Table 14 illustrates the total result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value). Further,FIG. 32Cis a graph illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the nitrogen addition amount so as to satisfy the equation (3-1) (C1=0.5) on the condition that the purging nitrogen of the pump is 10 NL/min. Further, for comparison,FIG. 32Dillustrates the operation result when the operation is performed so as not to satisfy the equation (3-1) (C1=0.1) on the condition that the purging nitrogen of the pump is 10 NL/min. The initial condition of the test is illustrated in Table 12. Table 15 illustrates the total result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value). Further,FIG. 32Eis a graph illustrating a change in hydrogen recovery rate when the operation is performed with the adjustment of the nitrogen addition amount so as to satisfy the equation (3-1) (C1=1.0) on the condition that the purging nitrogen of the pump is 50 NL/min. Further, for comparison,FIG. 32Fillustrates the operation result when the operation is performed so as not to satisfy the equation (3-1) (C1=0.1) on the condition that the purging nitrogen of the pump is 50 NL/min. The initial condition of the test is illustrated in Table 13. Table 16 illustrates the total result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value).

Furthermore, the number of years in use (corresponding value) is a value which is obtained by converting the operation time of the accelerated degradation test into the number of real years. The accelerated degradation test was performed so that the total flow rate of the supplied mixed gas is set to 50 times that of the normal test and the supplied monosilane gas concentration and the supplied nitrogen gas concentration are constant. The method of the accelerated degradation test is further written in Table 14, Table 15, and Table 16. From this result, it is found that the exhaust gas treatment system may be operated for a long period of time while maintaining the high hydrogen recovery rate by operating the exhaust gas treatment system so as to satisfy the equation (3-1).

FIGS. 33 to 37are graphs obtained by measuring a change in hydrogen recovery rate by changing the nitrogen addition amount supplied by the third element gas addition unit2020, the permeation side pressure of the membrane separation device, and the temperature of the temperature control unit with respect to a change in hydrogen gas recovery rate when the purging nitrogen of the pump is not introduced.FIG. 33illustrates the result when the operation is performed without the adjustment of the initial nitrogen addition amount.FIG. 34illustrates the result when the operation is performed so that the initial nitrogen addition amount satisfies the equation (3-1) (C1=0.3).FIG. 35illustrates the result when the operation is performed so that the initial nitrogen addition amount satisfies the equation (3-1) (C1=0.3) and the operation is performed so that the permeation side pressure of the membrane separation device satisfies the equation (3-1) (C2=1.0).FIG. 36illustrates the result when the operation is performed so that the initial nitrogen addition amount satisfies the equation (3-1) (C1=0.3) and the operation is performed so that the temperature of the temperature control unit satisfies the equation (3-2) (C3=2.0).FIG. 37illustrates the result when the operation is performed so that the initial nitrogen addition amount satisfies the equation (3-1) (C1=0.3), the operation is performed so that the permeation side pressure of the membrane separation device satisfies the equation (3-2) (C2=1.0), and then the operation is performed so that the temperature of the temperature control unit satisfies the equation (3-3) (C3=2.0). The initial condition of the test is illustrated in Table 17. Table 18 illustrates the total result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value). Furthermore, the number of years in use (corresponding value) is a value which is obtained by converting the operation time of the accelerated degradation test into the number of real years. The accelerated degradation test was performed so that the total flow rate of the supplied mixed gas is set to 50 times that of the normal test and the supplied monosilane gas concentration and the supplied nitrogen gas concentration are constant. The method of the accelerated degradation test is further written in Table 18. From this result, it is found that the exhaust gas treatment system may be operated for a long period of time while maintaining the high hydrogen recovery rate by operating the exhaust gas treatment system so that the nitrogen addition amount supplied by the third element gas addition unit, the permeation side pressure of the membrane separation device, and the temperature of the temperature control unit respectively satisfy the equation (3-1), the equation (3-2), and the equation (3-3).

FIGS. 38 to 42are graphs obtained by measuring a change in hydrogen recovery rate by changing the nitrogen addition amount supplied by the third element gas addition unit, the permeation side pressure of the membrane separation device, and the temperature of the temperature control unit with respect to a change in hydrogen gas recovery rate when the purging nitrogen of the pump is introduced by 10 NL/min.FIG. 38illustrates the result when the operation is performed without the adjustment of the initial nitrogen addition amount.FIG. 39illustrates the result when the operation is performed so that the initial nitrogen addition amount satisfies the equation (3-1) (C1=0.5).FIG. 40illustrates the result when the operation is performed so that the initial nitrogen addition amount satisfies the equation (3-1) (C1=0.5) and the operation is performed so that the permeation side pressure of the membrane separation device satisfies the equation (3-2) (C2=1.0).FIG. 41illustrates the result when the operation is performed so that the initial nitrogen addition amount satisfies the equation (3-1) (C1=0.5) and the operation is performed so that the temperature of the temperature control unit satisfies the equation (3-3) (C3=2.0).FIG. 42illustrates the result when the operation is performed so that the initial nitrogen addition amount satisfies the equation (3-1) (C1=0.5), the operation is performed so that the permeation side pressure of the membrane separation device satisfies the equation (3-2) (C2=1.0), and then the operation is performed so that the temperature of the temperature control unit satisfies the equation (3-3) (C3=2.0). The initial condition of the test is illustrated in Table 19. Table 20 illustrates the total result of a change in hydrogen recovery rate with respect to the number of years in use (corresponding value). Furthermore, the number of years in use (corresponding value) is a value which is obtained by converting the operation time of the accelerated degradation test into the number of real years. The accelerated degradation test was performed so that the total flow rate of the supplied mixed gas is set to 50 times that of the normal test and the supplied monosilane gas concentration and the supplied nitrogen gas concentration are constant. The method of the accelerated degradation test is further written in Table 20. From this result, it is found that the exhaust gas treatment system may be operated for a long period of time while maintaining the high hydrogen recovery rate by operating the exhaust gas treatment system so that the nitrogen addition amount supplied by the third element gas addition unit, the permeation side pressure of the membrane separation device, and the temperature of the temperature control unit respectively satisfy the equation (3-1), the equation (3-2), and the equation (3-3).

The invention is not limited to the above-described embodiments and examples, and various modifications such as a change in design may be made based on the knowledge of the person skilled in the art. Then, the modified embodiments are also included in the scope of the invention.