Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Halogenous component
Reexamination Certificate
2001-01-29
2002-07-09
Anthony, Joseph D. (Department: 1714)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Halogenous component
C423S242100, C588S249000, C588S249000, C252S181700
Reexamination Certificate
active
06416726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for decomposing nitrogen fluoride or sulfur fluoride and a decomposing reagent used therefor.
In the present specification, the nitrogen fluoride designates a compound which comprises fluorine and nitrogen as essential constituent elements and which easily volatilizes. A typical example of nitrogen fluoride is nitrogen trifluoride (NF
3
). Sulfur fluoride designates a compound which comprises fluorine and sulfur as essential constituent elements and which easily volatilizes. A typical example of sulfur fluoride is sulfur hexafluoride (SF
6
). “A compound which easily volatilizes” herein denotes a compound which is a gas at room temperature and normal pressure, or a compound which is a liquid at room temperature but which forms a gas mixture containing at least 0.01% by volume of the compound as a vapor it an inert gas is co-present.
2. Description of the Related Art
Since nitrogen fluoride and sulfur fluoride defined above are thermally stable, they are used, for example, as gases for etching or cleaning in processes for manufacturing semiconductor devices. However, nitrogen fluoride and sulfur fluoride are substances which are suspected to have an influence on global warming because they have a large global warming potential (GWP) value and remain in the atmosphere without decomposition when released in the air, and it is said that they are preferably decomposed after use. Accordingly, decomposition of used nitrogen fluoride and sulfur fluoride into nontoxic substances is required.
A combustion decomposition method, a reagent decomposition method, a catalytic decomposition method, and the like have heretofore been proposed as technologies for decomposing nitrogen fluoride.
Decomposition of nitrogen fluoride by the combustion method unavoidably forms by-product NO
x
. The combustion method, therefore, requires removal of the by-product and an additional treatment of the fluorine component. Accordingly, the combustion method is not efficient from the standpoint of recovering the fluorine component. The proposed reagent decomposition methods and catalytic decomposition methods require special treating conditions to increase the decomposition efficiency, and special treatment is required for recovery of the fluorine component formed by the decomposition. Accordingly, the decomposition operation in situ where nitrogen fluoride is used (generation source of a nitrogen fluoride gas) cannot be simply conducted.
Furthermore, no method for efficiently and completely decomposing sulfur fluoride such as sulfur hexafluoride (SF
6
) into nontoxic substances has ever been known.
An object of the present invention is, therefore, to provide a method for decomposing nitrogen fluoride or sulfur fluoride, which allows decomposition of nitrogen fluoride or sulfur fluoride at a high efficiency by a simple operation and efficient recovery of decomposed fluorine, and to provide a decomposing reagent therefor.
SUMMARY OF THE INVENTION
The above object is solved in accordance with the present invention by providing a method for decomposing nitrogen fluoride or sulfur fluoride comprising contacting at least one of nitrogen fluoride and sulfur fluoride gases with a solid reagent containing elemental carbon and one or more of the alkaline earth metal elements.
More specifically, nitrogen fluoride can be decomposed by contacting a nitrogen fluoride gas with the reagent as mentioned above at a temperature of 200° C. or more. In the decomposition, formation of by-product carbon fluoride can be inhibited by contacting the nitrogen fluoride gas with the reagent at a temperature of 200 to 450° C. or at a temperature of not less than 700° C. Moreover, formation of by-product nitrogen oxide can be inhibited by contacting the nitrogen fluoride gas with the reagent at a temperature of 350° C. or more.
Furthermore, when the reagent mentioned above further contains an alkali metal element, a nitrogen fluoride gas can be similarly decomposed at a contact temperature of 200° C. or more. Moreover, formation of by-product carbon fluoride can be inhibited by contacting the nitrogen fluoride gas with the reagent at a temperature of 200 to 450° C. or at a temperature of not less than 700° C. Furthermore, formation of by-product nitrogen oxide can be inhibited at the contact temperature of 250° C. or more, lower than the lower limit of the contact temperature in the above case where the reagent does not contain an alkali metal element.
Similarly, sulfur fluoride can be decomposed by contacting a sulfur fluoride gas with a solid reagent containing elemental carbon and an alkaline earth metal element at a contact temperature of 300° C. or more. In the decomposition, formation of by-product sulfur oxide such as SO
2
can be inhibited by contacting the sulfur fluoride gas with the reagent at a temperature of 450° C. or more.
Furthermore, a sulfur fluoride gas can be similarly decomposed at a contact temperature of 300° C. or more when the reagent further contains an alkali metal element. In addition, in this case, formation of by-product sulfur oxide can be inhibited at a temperature lower than in the case where the reagent does not contain an alkali metal element. More concretely, formation of by-product SO
2
can be inhibited from a temperature of 350° C. or more.
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XP-002093101 (JP 5-15740A) Database WPI, Section Ch, Week 9309, Derwent Publications Ltd. Jan. 26, 1993.
Atobe Hitoshi
Ito Kazuto
Izumikawa Chiaki
Kaneko Toraichi
Tezuka Kazumasa
Anthony Joseph D.
Showa Denko K.K.
Sughrue & Mion, PLLC
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