Heat exchange – Structural installation
Reexamination Certificate
1999-01-29
2002-05-28
Ford, John K. (Department: 3743)
Heat exchange
Structural installation
C165S900000, C165S921000, C165S054000, C062S310000, C062S314000, C062S095000, C096S266000
Reexamination Certificate
active
06394174
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a system and a method for reclaiming process water in a manufacturing plant and more particularly, relates to a system and a method for reclaiming process water from a cooling tower exhaust gas which contains at least 80% relative humidity by utilizing a heat exchanger equipped with cooling elements that are cooled by a flow of exhaust gas formed by a general exhaust and a scrubber exhaust from a semiconductor fabrication facility.
BACKGROUND OF THE INVENTION
In various semiconductor fabrication processes, the effluent gases from a process chamber must be treated before they can be released into a factory exhaust system and into the atmosphere. It is known that a large number of reactant gases and their reaction products utilized in semiconductor fabrication processes are highly flammable or highly toxic. The spent reactant gases that are discharged out of the process chamber may contain gases that have not been reacted or have been only partially reacted and therefore must be treated before they can be released into the atmosphere.
In a semiconductor fabrication facility, the treatment of the exhaust gases generated from the facility is an important aspect of the total fabrication processes. Various exhaust gases are produced in a semiconductor fabrication facility, these include general exhaust, scrubbed exhaust and solvent exhaust. For discharging the general exhaust and the solvent exhaust, a system typically includes ductworks, exhaust fans, by-passes, and stacks can be used. For handling the scrubbed exhaust, a scrubber must be used for treating the exhaust before they can be released into the atmosphere. A by-pass system can be provided which allows the drawing of outside air when the pressure at the suction side of the blower exceeds a preset value.
In a general exhaust system, heat dissipated by the process equipment is normally removed. The general exhaust therefore does not normally contain acids, caustics or solvents. In a solvent exhaust system, air containing solvents from the process equipment is removed. The devices utilized in the exhaust system therefore must be explosion-proof for safety reasons. In the scrubbed exhaust system, air containing acids, caustics and other harmful chemicals from the process chamber is removed. Various caustics in the exhaust gases such as ammonia, silane or other toxic gases must be treated by a scrubber before releasing into the atmosphere. A wet scrubber is normally used to remove acids and caustics in a process chamber exhaust by washing the air with a solvent such as water. City water is adequate for such purpose. The waste water from the scrubber is then sent to a neutralization plant in a waste treatment area of the fabrication facility. A dry scrubber can also be used to remove caustics substances from a process chamber exhaust by absorbing the substances into a scrubber material which is typically maintained at an elevated temperature. The scrubber material can then be replaced when it is saturated with the toxic substances.
The various exhaust systems are connected to process machines via ductworks. For instance, when exhausting from a metal etcher, a chemical vapor deposition chamber or a sputter, spent reactant gases and reaction by-products are normally discharged into a scrubbed exhaust system for treatment before the exhaust can be released into the atmosphere. A typical system for treating exhaust gases from a semiconductor process chamber such as an etcher is shown in FIG.
1
.
Referring initially to
FIG. 1
, wherein a semiconductor fabrication system
10
is shown. The fabrication system
10
consists of an etcher
12
, a vent exhaust
14
, a main booster pump
16
, a dry pump
22
, a nitrogen purge gas supply
24
and a wet scrubber
26
. Into the metal etcher
12
, carrier gases and etchant gases (not shown) are first fed into the chamber through various valve openings (not shown). An inert gas such as pure nitrogen is normally used either as a carrier gas for the etchant gases or as a purge gas when venting of the chamber to atmospheric pressure is needed. In a typical metal etching application, etchant gases such as Cl
2
and BCl
3
are used. In a batch-type metal etcher where a plurality of wafers, i.e., 16 wafers in a column type etcher, are etched in a typical etching process. In order to achieve an effective etching rate for a large number of wafers, a high concentration of etchant gas must be utilized in the etch chamber
12
. The exhaust gases discharged from the etcher
12
at the outlet port
18
therefore contains a high concentration of un-spent etchant gases and other etching reaction by-products. The vent exhaust
14
is provided for venting of the pure nitrogen used to purge out the etch chamber
12
after an etching reaction. The un-spent etchant gases are discharged out of the etching chamber
12
by the main booster pump
16
. A dry pump
22
is subsequently used to deliver the un-spent etchant gases into a wet scrubber
26
The pump exhaust system
30
which includes the main booster pump
16
, the dry pump
22
and the dry nitrogen source
24
are controlled by a series of valves (not shown). When the valves between the etcher
12
and the main booster pump
16
are opened, exhaust gases exit outlet port
18
and pass through the passageway
28
to enter into the main booster pump
16
. The main booster pump
16
acts as the front stage pump and the dry pump
22
acts as the back stage pump, which work together to provide a vacuum that is sufficiently high for the etch chamber
12
prior to an etching process. The exhaust gases exit the dry pump
22
through passageway
34
and enter the wet scrubber
26
through an inlet port
20
. During a normal etching process, chamber
12
is first evacuated by the operation of the main booster pump
16
and the dry pump
22
to a suitable vacuum for conducting the etching process. Etchant gases then enter into the chamber to commence the etching process on the wafers. A suitable chamber pressure is maintained during such etching process.
FIG. 2
is a schematic illustrating a detailed view of the exhaust gas conduit
34
and the wet scrubber
26
shown in FIG.
1
. It is seen that exhaust gases
38
delivered from the dry pump
22
enter inlet
42
of the exhaust gas conduit
34
. The exhaust gas conduit
34
is normally constructed of stainless steel such that it can be maintained at an elevated temperature of approximately 120° C. by heaters
44
to reduce the potential of particulate depositions in the conduit
34
. As the exhaust gases
38
enter the wet scrubber
26
through the inlet port
20
, the exhaust gases
38
are washed by a cleaning solvent
48
dispensed from a spray head
50
. The cleaning solvent
48
is first supplied from a solvent reservoir (not shown) through conduit
52
. A commonly used cleaning solvent for a wet scrubber is city water. After being scrubbed by the cleaning solvent
48
, the exhaust gases
38
exit the wet scrubber
26
through an exhaust outlet port
46
into a factory exhaust system (not shown). The spent cleaning solvent
38
is collected by the solvent collection device
54
and then transported through conduit
56
into a spent solvent collection tank
58
.
It should be noted that, in the application of a wet scrubber for a metal etcher, the spent water collected in the collection tank
58
is maintained at a pH value between about 6 and about 6.3. In other words, the spent city water is allowed to be slightly acidic after it is used to scrub the exhaust gases. The effectiveness of the wet scrubbing operation is maintained by continuously adding fresh city water to the spent water collection tank
58
and recirculating the water through the scrubbing process as long as the pH value of the spent water is between the values described above.
The exhaust gas
62
exiting the wet scrubber
26
through the exhaust outlet port
46
is normally directly fed into a factory exhaust system. The exhaust gas
62
is normally cooled by city water to a low t
Ford John K.
Taiwan Semiconductor Manufacturing Company Ltd
Tung Randy W.
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