Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
2000-07-20
2002-11-19
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S170000, C422S171000, C422S172000, C422S174000, C422S182000
Reexamination Certificate
active
06482367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for removing harmful components in an exhaust gas derived during manufacturing an electronic circuit element such as a semiconductor device or a liquid crystal device, particularly during a cleaning or etching process. Further, the present invention relates to an apparatus that is applicable to remove harmful components in a gas generated during the process of smelting aluminum.
2. Description of the Prior Art
In a semiconductor manufacturing apparatus such as a CVD apparatus, a gas for deposition (such as SiH
4
, Si
2
H
6
, SiH
2
Cl
2
, TEOS, PH
3
, B
2
H
6
, NH
3
, N
2
O, or the like) is used in forming various thin films, and a cleaning gas (such as NF
3
, C
2
F
6
, CF
4
, SF
6
, or the like) is usually used for cleaning the inside of the semiconductor manufacturing apparatus after completing the deposition process.
These gases inherently have various dangerous factors such as flammability, explosiveness, corrosiveness, poisonousness, and the like. Therefore, it is required to remove(detoxify) harmful components in these gases using a harm-removing apparatus equipped, for example, with a means for oxidizing and heating the gases before they are released into atmospheric air.
In the semiconductor manufacturing apparatus such as a CVD apparatus, complex decomposition reactions occur in the gases that are being used, so that new decomposition products (such as F
2
, HF, and SiOx) are generated as a result and these decomposition products are discharged together with the undecomposed deposit gas and the cleaning gas.
In the semiconductor manufacturing process, a semiconductor manufacturing apparatus such as a CVD apparatus generally operates as follows: deposition using a deposition gas such as SiH
4
(toxic to a human body and explosive)→purging of residual SiH
4
gas from the CVD chamber using nitrogen→cleaning the CVD chamber using a cleaning gas such as C
2
F
6
(harmless to a human body though exhibiting a greenhouse effect)→purging of the cleaning gas from the CVD chamber using nitrogen→repeating this cycle.
Here, one group of said gases to be used for cleaning of a CVD chamber is what is known as PFC gases. PFC is an abbreviation for “perfluorocarbon” or “perfluoride compound”. Representative examples of PFC are CF
4
, CHF
3
, and said C
2
F
6
. If the term “compound” is used instead of “carbon”, PFC will further include fluorine compounds that do not contain carbon, such as NF
3
, SF
6
, and SF
4
.
The purpose of the present invention is to establish a technique for removal of the former PFC gases, which technique has not yet reached an applicable level for use in a removal device or a removal method. Naturally, however, the technique of the present invention is also applicable for removal of all the PFC gases including the latter PFC gases.
The PFC gases as represented by CF
4
and C
2
F
6
are non-flammable and toxicity of the gases themselves on human beings is unknown. At least, acute and subacute toxicities are not known. However, since the compounds themselves are stable, they remain unchanged and stay for a long period of time if they are released to an ambient atmosphere. It is reported that the life span until consumption in the atmosphere is 50,000 years in the case of CF
4
, and 10,000 years in the case of C
2
F
6
.
Further, the global warming factor (relative to CO
2
) is 4,400 in the case of CF
4
and 6,200 in the case of C
2
F
6
(after 20 years have passed), which involves a problem that cannot be left aside in considering the earth environment. Therefore, it is eagerly desired to establish a means for removing the PFC gases as represented by CF
4
and C
2
F
6
.
However, the former PFC gases, i.e. the compounds as represented by CF
4
, CHF
3
, and C
2
F
6
, have a stable C—F bond (having a bonding energy as large as 130 kcal/mol) and are not easily decomposed, so that it is extremely difficult to remove them by simple thermal oxidation decomposition.
For example, in the case of C
2
F
6
, the decomposition proceeds by a cut in the C—C bond, so that C
2
F
6
, can be removed by limiting the processing flow rate to be less than 250 liters/min at a processing temperature of 1000° C. However, in the case of CF
4
, it is necessary to cut the C—F bond that has the largest bonding energy, so that a temperature of 1400° C. is required even with the above-mentioned flow rate. In addition, even by the above method, it is difficult to remove more than 80% of the total gas.
Further, if an electric heater is to be used, attainment of a high temperature atmosphere of more than 1400° C. is an upper limit also from the view point of materials for the heater, so that a long-term usage is almost impossible. Moreover, maintaining the temperature of the entire apparatus is also difficult and, in combination with a thermal insulating material, the total volume of the apparatus will be large and it will not be a compact apparatus. What is more important is that the thermal energy cost will be excessively high.
Here, in this field, the following new method has been proposed. International Publication Number WO94/05399#Method of Decomposing Gaseous Halocarbon# reports that coexistence of O
2
makes it possible to decompose and remove, for example, CF
4
at a temperature of 600 to 700° C. However, a detailed follow-up experiment of the contents of the publication turned out to be a complete failure in removal under this condition.
Also, an attempt is made to positively introduce H
2
gas to pyrolyze PFC. However, it requires a high processing temperature and, besides, it may not be suitable for use from the view point of safety, since the H
2
gas is flammable and explosive.
SUMMARY OF THE INVENTION
The present invention is intended to develop a harm-removing apparatus capable of decomposing and removing PFC components at a high removal ratio at a temperature as low as possible (with thermal energy consumed at an amount as small as possible). In other words, the present invention provides a method and an apparatus for removing PFC components at a low temperature, removing the derived fluorine components by separately washing or fixing them, and releasing the other components into the atmospheric air basically as CO
2
and H
2
O. The essence of a PFC removing method according to the present invention is bellow:
The method of the present invention mixes at least one of a hydrocarbon gas and NH
3
gas with an exhaust gas containing a perfluorocarbon or a perfluorocompound and thermally decomposes the mixed gas in a non-oxidizing atmosphere at a temperature (600-1300° C.) lower than the temperature at which the conventional apparatus and method performs thermal decomposition.
The term “non-oxidizing atmosphere” herein used will be described later in detail, but means, in a word, an atmosphere free of oxygen in decomposing of the exhaust gas.
When the exhaust gas is washed with water prior to the thermal decomposition, it is possible not only to remove soluble components, dust and the like in the exhaust gas as discharged from manufacturing equipment prior to the thermal decomposition but also to allow the exhaust gas to be incorporated with water content so as to cause the perfluorocarbon or perfluorocompound contained in the exhaust gas to be thermally hydrolyzed.
Where the hydrocarbon gas is mixed excessively, the gas thermally decomposed comes to contain unreacted hydrocarbon gas and soot resulting from the decomposition reaction. Such unreacted hydrocarbon gas and the soot are removed by burning in the next step. Therefore, the term “flammable components” used herein is meant to include an excess of the hydrocarbon gas and soot.
For instance, in the case of thermal decomposition of CF
4
and C
2
F
6
using C
3
H
8
in a non-oxidizing atmosphere, the decomposition proceeds as follows:
C
3
H
8
→
3
C+
8
H (radicals) . . . decomposition at the gas decomposer room;
CF
4
+
4
H (radicals)→C+
4
HF . . . decomposition at the g
Kanken Techno Co., Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Hien
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