Apparatus for separating and removing a dangerous substance from an exhaust gas

In order to separate and remove a dangerous substance such as yellow phosphorus from exhaust gas generated in a semiconductor fabricating process by chemical vapor deposition, the exhaust gas is bathed in operating oil of a cooled oil tank of an oil-sealed rotary vacuum pump so that molecules of the yellow phosphorus or the like are caught by the cooled operating oil so as to be enveloped in the operating oil. Thus, a mixture operating oil of the substance and the operating oil is generated in the form of colloid. The mixture operating oil is passed through an oil filter of a filtration device so that the substance such as yellow phosphorus is precipitated by the filter and then the substance is removed. Meanwhile, the operating oil as a filtrate from which the substance has been filtered is cooled by an oil-temperature controller, and then returned to the oil-sealed rotary vacuum pump. Thus, the exhaust gas suctioned into the oil tank of the vacuum pump is ordinarily made contact with the cooled operating oil thereby enhancing the efficiency of separating the substance such as yellow phosphorus.

BACKGROUND OF THE INVENTION 
This invention relates to a method and apparatus of separating and removing 
a dangerous substance such as white phosphorus included in exhaust gas 
generated in a semiconductor fabricating process by chemical vapor 
deposition or the like. 
In general, a substance such as white phosphorus is included in exhaust gas 
generated in a semiconductor fabricating process by chemical vapor 
deposition. When the white phosphorus as a single substance is exposed to 
the air, it is combustible even at an ordinary temperature. Therefore, the 
work of removing the white phosphorus is usually dangerous and has invited 
many accidents. 
To remove a dangerous substance such as white phosphorus in exhaust gas, 
there has been known a conventional method in which a filter is disposed 
at a suitable position of an inlet pipe through which the exhaust gas 
flows and the dangerous substance such as white phosphorus is removed in 
such a manner as to be separated from the exhaust gas through the filter. 
Generally, the inlet pipe is small in diameter and therefore the exhaust 
gas flows rapidly through the inlet pipe. Accordingly, it is difficult to 
enhance the efficiency of separating white phosphorus or the like by means 
of the filter attached to the inlet pipe as in the above method. Further, 
even if the filter is arranged at plural positions of the inlet pipe, this 
only invites degradation of cost efficiency, and complete separation and 
removal of white phosphorus or the like is difficult and non-reliable. 
The present invention has been made in view of the foregoing problems. The 
present invention has its object of overcoming the defects of the prior 
technique, that is, when the substance such as white phosphorus included 
in exhaust gas in a semiconductor fabricating process by chemical vapor 
deposition is separated and removed, enhancing the efficiency of 
separating the substance from the gas by a simple mechanism and securing 
safety in separation and removal of the substance. 
SUMMERY OF THE INVENTION 
To attain the foregoing object, the present invention is composed by a 
combination of the following techniques: 
(a) conducting exhaust gas generated in a semiconductor fabricating process 
or the like to an oil-sealed rotary vacuum pump using incombustible 
operating oil; 
(b) cooling the incombustible operating oil in the oil-sealed rotary vacuum 
pump and bathing the exhaust gas into the cooled operating oil stored in 
an oil tank to separate a substance such as white phosphorus from the 
exhaust gas and mix the substance with the operating oil; 
(c) conducting the operating oil mixed with the substance to a filtration 
device having a filter by operation of a circulating pump to filter and 
precipitate the substance such as white phosphorus through the filter so 
that the substance is removed individually; 
(d) conducting the operating oil as a filtrate from which the substance has 
been removed to an oil-temperature control device having a temperature 
control element by operation of the circulating pump to cool the operating 
oil to a set temperature by the oil-temperature control device and then 
returning the operating oil to the oil-sealed rotary vacuum pump; and 
(e) by the returned operating oil, rapidly cooling the exhaust gas 
including vapor of high temperature conducted to the oil-sealed rotary 
vacuum pump so as to promote the action of separating the substance such 
as white phosphorus from the exhaust gas in the oil-sealed rotary vacuum 
pump. 
The above steps (a) to (e) are repeated in its order. 
Under the above construction of the present invention, the exhaust gas is 
first conducted to the oil-sealed rotary vacuum pump using the 
incombustible operating oil and forced into oil bathing in the oil tank 
having large area while rapidly cooled. During the oil bathing, the 
substance such as white phosphorus is separated from the exhaust gas by 
the operating oil which is slow in flow speed. At the time, since the 
operating oil is cooled, molecules of the substance such as white 
phosphorus are rapidly separated from the exhaust gas and caught by the 
operating oil so as to be enveloped therein thereby forming a colloid with 
the operating oil. As a result of this, the operating oil becomes a 
mixture operating oil including the substance. Further, the rest of the 
exhaust gas from which the substance has been separated is released 
outwardly from the oil-sealed rotary vacuum pump and retreated if 
necessary. 
Then, by operation of the circulating pump, the mixture operating oil is 
conducted to the filtration device. The substance such as white phosphorus 
included in the mixture operating oil is filtered and precipitated through 
the filter so as to be removed in an appropriate manner. Accordingly, the 
substance such as white phosphorus can be separated and removed in safety. 
The operating oil as a filtrate from which the substance has been removed 
is conducted to the oil-temperature control device having the temperature 
control element by operation of the circulating pump, cooled to a set 
temperature by the temperature control element and then returned to the 
oil-sealed rotary vacuum pump. By the cooled operating oil, the operating 
oil in the vacuum pump is rapidly cooled and regulated in temperature, so 
that the temperature at the oil bathing of the exhaust gas just after the 
exhaust gas is suctioned into the vacuum pump is regulated. As a result of 
the temperature regulation, the substance such as white phosphorus is 
separated from the exhaust gas and mixed with the operating oil with 
efficiency and the safety of the work using the filtration device is 
improved. 
Accordingly, the present invention has many effects on industrial 
utilization, e.g., effects that the mechanism of the apparatus is simple, 
the mechanism of separating the substance such as white phosphorus can be 
connected in common to different kinds of apparatus in chemical vapor 
deposition and the like and the apparatus is convenient to operate and can 
be provided at low cost.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Description is made below about preferred embodiments of the present 
invention with reference to the drawings. 
First Embodiment 
FIG. 1 shows a first embodiment in which a separation and removal apparatus 
of the present invention is applied to a separation and removal apparatus 
for white phosphorus or the like. The separation and removal apparatus is 
composed so as to safely and effectively remove impurities generated from 
an unnecessary reactive gas such as phosphin PH.sub.3 in a process room 
after chemical vapor deposition in a semiconductor fabricating process, 
e.g., impurities such as vaporous white phosphorus generated by thermal 
decomposition of phosphin. 
Reference numeral 1 is a process room for fabricating semiconductors by 
chemical vapor deposition. The process room 1 is connected, through an 
inlet pipe 2, to an oil-sealed rotary vacuum pump 3 to be driven by a 
motor 3a. The vacuum pump 3 has an oil tank (not shown) for storing 
incombustible operating oil such as fluorinated oil which is composed of 
three kinds of atoms, i.e., carbon, fluoride and oxygen. By operation of 
the vacuum pump 3, gas exhausted from the process room 1 is suctioned into 
the vacuum pump 3 through the inlet pipe 2 and led into the oil tank of 
the vacuum pump 3. Thus, white phosphorus or the like contained in the 
exhaust gas is bathed into the operating oil. During the oil bathing, 
molecules of white phosphorus or the like are separated from the exhaust 
gas in such a manner as to be enveloped in the operating oil, thereby 
generating a mixture operating oil mixed with the molecules of white 
phosphorus or the like and formed into colloid. 
The oil-sealed rotary vacuum pump 3 is connected to a filtration device 5 
through a pipe 4. The filtration device 5 is connected to an 
oil-temperature control device 7 through a conductive pipe 6. The 
oil-temperature control device 7 is connected to the vacuum pump 3 through 
a return pipe 9. On the way of the pipe 4, there is provided a circulating 
pump 11 to be driven by a motor 10. The circulating pump 11 circulates the 
operating oil among the vacuum pump 3, the filtration device 5 and the 
oil-temperature control device 7. 
The filtration device 5 has a cartridge-type oil filter F, which is 
exchangeable, receives the mixture operating oil generated in the vacuum 
pump 3 by operation of the circulating pump 11, and filters and 
precipitates white phosphorus or the like through the oil filter F. The 
oil filter F is exchanged when necessary. At this time, white phosphorus 
or the like filtered and precipitated is removed with the oil filter F. 
The operating oil from which white phosphorus or the like has been 
precipitated by the filtration device 5, is conducted to the 
oil-temperature control device 7 through the conductive pipe 6 by 
operation of the circulating pump 11. The oil-temperature control device 7 
has a temperature control element 8. The temperature control element 8 
controls so that the operating oil conducted to the oil-temperature 
control device 7 cools down to a set temperature. The operating oil cooled 
through the oil-temperature control device 7 is returned to the oil-sealed 
rotary vacuum pump 3 through the return pipe 9, thereby mixing with 
operating oil in the vacuum pump 3. 
Further, the oil-sealed rotary vacuum pump 3 is connected to an outlet pipe 
12. The rest of the exhaust gas, from which white phosphorus has been 
separated into the mixture operating oil during the oil bathing in the 
vacuum pump 3, is emitted out of the vacuum pump 3 through the outlet pipe 
12. The rest of the exhaust gas may be subjected to a re-treatment or a 
treatment on environmental hygiene if necessary. 
Next, description is made about a method of separating and removing white 
phosphorus or the like by using the separation and removal apparatus 
having the above construction. 
First, a flow of gas exhausted from the process room 1 in a semiconductor 
fabricating process by chemical vapor deposition, is conducted to the 
oil-sealed rotary vacuum pump 3. In the vacuum pump 3, white phosphorus or 
the like included in the exhaust gas is bathed into the operating oil in 
the oil tank of the vacuum pump 3. During the oil bathing, white 
phosphorus or the like is separated from the exhaust gas in such a manner 
that molecules of white phosphorus or the like are enveloped in the 
operating oil, thereby generating a mixture operating oil in the form of 
colloid. The rest of the exhaust gas, from which white phosphorus has been 
separated into the mixture operating oil by the oil bathing, is emitted 
out of the vacuum pump 3 through the outlet pipe 12. 
Next, the mixture operating oil generated in the oil-sealed rotary vacuum 
pump 3 is conducted to the filtration device 5 through the pipe 4 by 
operation of the circulating pump 11. In the filtration device 5, white 
phosphorus or the like in the mixture operating oil is filtered and 
precipitated by the oil filter F of the filtration device 5. The white 
phosphorus or the like is removed with the oil filter F whenever the oil 
filter F is exchanged by a new one. As mentioned above, since the white 
phosphorus or the like in the exhaust gas is first mixed with the 
operating oil and then the white phosphorus or the like is removed so as 
to be precipitated from the mixture operating oil by the oil filter F, the 
white phosphorus or the like can be safely removed as compared with the 
conventional method. 
Then, by operation of the circulating pump 11, the rest of the operating 
oil from which the white phosphorus or the like has been filtered and 
precipitated by the filtration device 5, is conducted to the 
oil-temperature control device 7 through the conductive pipe 6 and 
controlled to cool down to a set temperature by the temperature control 
element 8 of the oil-temperature control device 7. Thereafter, the rest of 
the operating oil cooled is returned to the oil-sealed rotary vacuum pump 
3 through the return pipe 9 thereby mixing with operating oil in the 
vacuum pump 3. 
The operating oil in the vacuum pump 3 is ordinarily heated by 
high-temperature exhaust gas introduced from the process room 1. In the 
above case, however, since the operating oil from the oil-temperature 
control device 7 is cooled, the operating oil in the vacuum pump 3 is 
cooled and regulated in temperature so as to be maintained at a set 
temperature where possible. Thus, since the exhaust gas is bathed into the 
operating oil cooled at any time in the vacuum pump 3, separation of white 
phosphorus or the like in the exhaust gas can be promoted at the oil 
bathing. 
At the time, the temperature of the operating oil in the oil-sealed rotary 
vacuum pump 3 is preferably set to within the range of 10.degree. to 
15.degree. C. in practice. In order to maintain the temperature of the 
operating oil in the vacuum pump 3 at within the range of 10.degree. to 
15.degree. C., the operating oil returned from the oil-temperature control 
device 7 is preferably set to the range of 0.degree. to 5.degree. C., 
though it also depends on the flow rate of the operating oil. 
In detail, practically, when the temperature of the operating oil in the 
vacuum pump 3 is below 10.degree. C., the action of separating white 
phosphorus or the like from the exhaust gas bathed into the operating oil 
is deteriorated and in addition the filtration efficiency is lowered 
because of low viscosity of the operating oil. This prevents the fluidity 
of the operating oil, thereby resulting in hardness of the smooth 
circulation of the operating oil. On the contrary, when the temperature of 
the operating oil is over 15.degree. C., the safety at the filtration and 
precipitation of white phosphorus or the like by the filtration device 5 
is lowered. Accordingly, when the temperature of the operating oil in the 
vacuum pump 3 is set to within the range of 10.degree. to 15.degree. C., 
the action of separating white phosphorus or the like by bathing the 
exhaust gas into the operating oil can be promoted, and the safety at the 
filtration and precipitation of white phosphorus or the like by the 
filtration device 5 can be secured. Further, since the viscosity of the 
operating oil is further effective on the filtering action, the fluidity 
of the operating oil cannot be prevented and the smooth circulation of the 
operating oil can be achieved. 
Second Embodiment 
FIG. 2 shows a second embodiment of the present invention. In this 
embodiment, in order to maintain the operating oil in the oil-sealed 
rotary vacuum pump 3 at a set temperature, a flow rate of the operating 
oil to be returned from the oil-temperature control device 7 to the vacuum 
pump 3 is hold at a set value. 
In detail, there is provided at the oil-sealed rotary vacuum pump 3 an 
operating-oil temperature sensor 14 for sensing the temperature of the 
operating oil in the oil tank. Manual valves 15, 15 are provided in the 
conductive pipe 6 and the return pipe 9, respectively. 
The temperature of the operating oil is sensed by the operating-oil 
temperature sensor 14. Then, the openings of the manual valves 15, 15 are 
controlled to regulate the flow rate of the operating oil to be returned 
to the vacuum pump 3 in order that the temperature of the operating oil is 
at the set temperature, i.e., within the range of 10.degree. to 15.degree. 
C. Thus, the temperature of the operating oil in the vacuum pump 3 can be 
maintained at the set temperature. 
Third Embodiment 
FIGS. 3 and 4 show a third embodiment of the present invention. In this 
embodiment, the temperature of the operating oil in the oil-sealed rotary 
vacuum pump 3 is automatically maintained at the set temperature. 
In detail, a flow-rate control mechanism 17 is disposed in the return pipe 
9. The operating oil from the oil-temperature control device 7 is returned 
to the vacuum pump 3 through the return pipe 9 after the flow rate thereof 
is regulated by the flow-rate control mechanism 17, and then mixed with 
operating oil in the vacuum pump 3. In this case, respective manual valves 
15 are fully opened. The flow-rate control mechanism 17 is not necessarily 
disposed in the return pipe 9 and may be disposed in the pipe 4 or the 
conductive pipe 6. Essentially, the flow-rate control mechanism 17 can be 
disposed at any place on a circulation path where the operating oil in the 
vacuum pump 3 is returned to the vacuum pump 3 via the filtration device 5 
and the oil-temperature control device 7. 
As shown in FIG. 4, the flow-rate control mechanism 17 receives an electric 
control signal from a controller 16, and based on the signal operates so 
as to control the flow rate of the operating oil. The temperature control 
element 8 of the oil-temperature control device 7 also operates by 
receiving an electric control signal from the controller 16. There is 
inputted to the controller 16 an output signal from the operating-oil 
temperature sensor 14 of the oil-sealed rotary vacuum pump 3. Based on the 
temperature of the operating oil in the vacuum pump 3, which has been 
sensed by the operating-oil temperature sensor 14 of the vacuum pump 3, 
the controller 16 outputs control signals to the temperature control 
element 8 of the oil-temperature control device 7 and the flow-rate 
control mechanism 17 respectively, thereby regulating the temperature of 
the oil-temperature control device 7 at the set temperature and operating 
the flow-rate control mechanism 17 to regulate the flow rate of the 
operating oil at a necessary rate along the program. Further, the 
controller 16 regulates both the temperature and flow rate of the 
operating oil in such a manner as to be associated with each other thereby 
automatically maintaining the operating oil in the vacuum pump 3 at the 
set temperature. 
As mentioned above, according to the present embodiment, the temperature of 
the operating oil in the oil-sealed rotary vacuum pump 3 can be 
automatically controlled to maintain the set temperature. 
A separation and removal apparatus of the present invention may be so 
composed that, in addition to the construction of the third embodiment, a 
viscosity sensor (not shown) for sensing a viscosity of the operating oil 
is disposed in the filtration device 5, an output signal of the viscosity 
sensor is inputted to the controller 16 and the flow-rate control 
mechanism 17 and the temperature control element 8 are controlled based on 
the viscosity of the operating oil. Thus, the operating oil returned to 
the oil-sealed rotary vacuum pump 3 can be regulated so as to have a 
viscosity suitable for filtration and then circulated, thereby improving 
filtration efficiency of the operating oil. 
Further, in the controller 16, either the flow-rate control mechanism 17 or 
the temperature control element 8 of the oil-temperature control device 7 
may be controlled singly so that the operating oil in the oil-sealed 
rotary vacuum pump 3 is maintained at the set temperature. 
Furthermore, in the above embodiments, a dangerous substance is separated 
and removed from the exhaust gas generated in the semiconductor 
fabricating process. Besides the semiconductor fabricating process, a 
method of separating and removing a substance from exhaust gas and a 
separation and removal apparatus of the present invention can be applied 
to the case of separating and removing a dangerous substance from exhaust 
gas generated in processes other than the semiconductor fabricating 
process.