Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Organic component
Reexamination Certificate
2000-04-05
2001-08-28
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Organic component
C423S242200, C423S243010, C423S245200
Reexamination Certificate
active
06280696
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and apparatus for treating an exhaust gas and more particularly, relates to a method and apparatus for treating an exhaust gas from a semiconductor fabrication machine by a wet scrubbing process wherein ozone gas is pumped into a spent water reservoir to caused an oxidation reaction of the volatile organic compounds dissolved in the spent water.
BACKGROUND OF THE INVENTION
In semiconductor fabrication processes, effluent or exhaust gas from a process chamber must be treated chemically or physically before they can be released into a factory exhaust system and subsequently into the atmosphere. A large number of reactant gases utilized in the semiconductor fabrication processes and their reaction products are either highly flammable, toxic or foul-smelling. Some of the spent reactant gases exhausted out of a process chamber may contain gases that have not been reacted or have been partially reacted and therefore must be chemically treated before they can be released into the atmosphere. Gas treatment units such as gas reactor columns are frequently used for such purpose of converting toxic gases into non-toxic gases.
While a gas reactor column can be a hot bed reactor that treats a wide variety of gases in a single cartridge without creating additional effluent disposal problems, a simpler method of treating exhaust gases is the use of an absorption unit that functions on the principle of gas absorption into a porous substance without chemical reactions taken place. This type of physical absorption process can be carried out by using a bed of porous substance such as activated carbon for absorbing certain components in exhaust gases. Specifically, those of low boiling temperature and of foul-smelling.
For instance, in the exhaust gas exiting a photoresist stripper chamber, various toxic and foul-smelling gases are present. Typically, a photoresist solvent of ACT®-690 is used in a photoresist stripper chamber. Various high boiling temperature gases such as dimethyl sulfoxide (DMSO, C
2
H
6
SO), N-methyl pyrolidone (NMP, C
2
H
9
NO), methyl ethyl alcohol (MEA, C
2
H
7
NO) and various foul-smelling gases such as dimethyl sulfide (C
2
H
6
S), dimethyl disulfide (C
2
H
6
S
2
) and residual solvents such as isopropyl alcohol (IPA) and acetone are present in the exhaust gas. These major components are shown in FIG.
1
. While the low boiling temperature gases, i.e., those having a boiling temperature of less than 100° C. such as dimethyl sulfide, dimethyl disulfide, IPA and acetone can be successfully removed by an absorption apparatus filled with activated carbon as the absorption substance, the high boiling temperature gases such as DMSO, NMP and MEA carimot be effectively removed in the absorption apparatus. The total percentage of toxic, high boiling temperature gases removed from the exhaust gas therefore is poor and unacceptable when the exhaust gas is only treated by an absorption apparatus.
The following examples 1~3 illustrate results of the photoresist stripper chamber exhaust gas being treated by a conventional absorption method.
EXAMPLE 1
The exhaust gas from a photoresist stripper chamber is treated which contains 8~200 ppm dimethyl sulfoxide, 21~250 ppm 2-aminoethanol, 1~20 ppm N-methyl pyrolidone, 21 ppm ethylene glycol, 0.5~10 ppm dithiolethylene glycol, 0.5~3 ppm dimethyl sulfide and 20~150 ppm isopropyl alcohol.
The flow rate of the exhaust gas exiting the chamber is 2,000~4,000 m
3
/hr which is kept at a temperature of about 45° C. The exhaust gas is first cooled by a coil-type cooling apparatus to approximately 14° C., and then fed directly into an absorption apparatus which contains activated carbon. The exhaust gas exiting the absorption apparatus was analyzed to show a removal efficiency of 70.1~78.3% at an energy usage rate of 72,000 k cal/hr. The efficiency is therefore not satisfactory since toxic components in the exhaust gas are allowed to escape into the atmosphere.
EXAMPLE 2
The content of the exhaust gas is similar to that shown in Example 1. The exhaust gas is directly fed to an absorption apparatus containing activated carbon for an absorption treatment. The exhaust gas exiting the absorption apparatus was determined at a removal efficiency of about 65.3~80.0%. However, foul-smell was detected after the absorption apparatus was used only for 3 days, and the activated carbon had to be replaced after 7 days due to excessive condensation in the carbon.
EXAMPLE 3
In this third example, as shown in
FIG. 2
, an absorption apparatus
10
is utilized which consists of an absorption wheel
12
, a heat exchanger
14
, a preheat furnace
16
and a burner
18
. The VOC absorption
20
is first received from a semiconductor fabrication apparatus, which typically contains about 6.0 Kg/hr VOC exhaust at room temperature, the VOC exhaust
20
is fed into a rotating absorption wheel
12
to absorb the VOC content in the exhaust by activated elements such as aluminum oxide or molecular sieve. The treated exhaust gas is then divided into two exhaust gas flows
22
,
24
at a ratio of flow volume at about 9:1. Therefore, a majority of the treated waste gas
22
which amounts to about 0.23 Kg/hr is released to the atmosphere. The smaller amount. i.e. about 10%, of the treated exhaust gas is then used for regeneration of the activate chemicals on the absorption wheel
12
by first combining with a high temperature gas through the heat exchanger
14
achieving a gas flow
26
having a temperature at about 180° C. The high temperature treated exhaust gas
26
is then flown into the absorption wheel
12
in an opposite direction to remove the VOC coated on the active absorption elements on the absorption wheel
12
. A treated exhaust gas
28
, which contains about 5.77 Kg/hr VOC then exits the absorption wheel
12
and is sent to a preheat furnace
16
for preheating and then into a burner
18
for burning of the VOC content. The high temperature exhaust gas
32
after the burner
18
achieve a temperature of about 760° C. is then sent into the preheat furnace
16
to supply heat to the furnace. After a heat exchanging process
34
, the gas exits the preheat furnace
16
and enters the heat exchanger
14
for release into the atmosphere with a low VOC content of about 0.06 Kg/hr.
In the conventional setup in
FIG. 2
, the high temperature exhaust gas
26
sent from the heat exchanger
14
into the absorption wheel
12
frequently is not hot enough for removing the VOC content coated on the active elements in the wheel, particularly when difficult to remove VOC compounds such as DMSO, MEA and NMP are involved. Once the active elements on the absorption wheel
12
is covered with VOC, the absorption efficiency of the wheel is greatly reduced such that wheel
12
is no longer capable of absorbing VOC materials. The conventional absorption wheel apparatus
10
is therefore not efficient in treating exhaust gases that contain high boiling point volatile organic compounds.
It is therefore an object of the present invention to provide a method for removing high boiling volatile organic compounds from an exhaust gas that does not have the drawbacks or shortcomings or the conventional methods.
It is another object of the present invention to provide a method for removing high boiling point volatile organic compounds from an exhaust gas that does not require the use of an absorption apparatus.
It is a further object of the present invention to provide a method for removing high boiling point organic compounds from an exhaust gas that utilizes a wet scrubbing apparatus.
It is still another object of the present invention to provide a method for removing high boiling point organic compounds from an exhaust gas by treating spent water that contains volatile organic compounds by an oxidation agent.
It is another further object of the present invention to provide a method for removing high boiling point volatile organic compounds from an exhaust gas by using a wet scrubbing equipment and by treating spent water that
Hsiang Ta-Tien
Hsu Hua-Ching
Griffin Steven P.
Medina Maribel
Taiwan Semiconductor Manufacturing Company Ltd
Tung & Associates
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