Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Patent
1997-02-13
1998-01-27
Straub, Gary P.
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
423531, 422161, C01B 1774, C01B 1790
Patent
active
057119287
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase of international application PCT/JP96/01649, filed Jun. 17, 1996 which designated the U.S.
TECHNICAL FIELD
The present invention relates to a process for producing high-purity sulfuric acid which is suitably usable for a semiconductor device-fabricating process. More specifically, the present invention relates to a process for producing high-purity sulfuric acid, from which metal constituents and sulfurous acid gas (sulfur dioxide, SO.sub.2) as impurities have highly been removed.
BACKGROUND ART
In the processes for fabricating semiconductor devices, inorganic chemicals such as alkalies and acids, and organic solvents such as alcohols and ketones are used for the purpose of etching, cleaning or washing, peeling operations, etc., for wafers (inclusive of various states of wafers appearing in the course of processing thereof into devices; in the same meaning in the description appearing hereinafter). As the large-scale integrated circuits (LSIs) to be fabricated through these semiconductor device-fabricating processes are caused to have a higher density and a larger scale of integration, various kinds of contaminations come to affect the yield, quality and reliability of the resultant products of the semiconductor devices. Accordingly, the chemicals per se to be used in the semiconductor-fabricating processes have also been required to contain smaller amounts of impurities and to have a purity as high as possible.
In general, the semiconductor-fabricating processes include many element techniques (such as oxidation, film growth, and etching), and they also require cleaning (or washing) operations for the purpose of linking or connecting these element techniques, i.e., operations for removing various kinds of contaminations produced by the processing based on the respective elemental techniques, by use of physical and/or chemical means. Accordingly, in the semiconductor-fabricating processes, "cleaning" is a most fundamental and essential technique.
In the semiconductor-fabricating processes, sulfuric acid is sometimes used as a component constituting a cleaning liquid for cleaning silicon wafers, e.g., for the purpose of resist stripping, or for the purpose of removing organic contamination or a (minor) metal contamination by oxidation, etc. However, when a metal constituent as an impurity is present in the above sulfuric acid, there can be posed some problems such that the electric characteristics of the above silicon wafer are deteriorated, and the performances of the resultant device are deteriorated. Further, when sulfurous acid gas as an impurity is present in such sulfuric acid, problems similar to those as described above can be posed. Accordingly, the sulfuric acid to be used in the semiconductor-fabricating process is required to have a low metal constituent concentration as well as a low sulfurous acid gas concentration. However, a process for producing of such high-purity sulfuric acid which can provide a product satisfying the above-mentioned requirements and can also be conducted efficiently from an industrial point of view has never been found yet.
An object of the present invention is to provide a process for producing high-purity sulfuric acid from which metal constituents and sulfurous acid gas as impurities have highly been removed.
DISCLOSURE OF INVENTION
As a result of earnest study, the present inventor has found that the combination of a specific liquid temperature at the inlet port of a circulating pump and the liquid transport conducted by such a circulating pump may effectively suppress an increase in the level of metal impurities contained in the resultant sulfuric acid, and that such a combination is extremely effective in achieving the above object.
The process for producing high-purity sulfuric acid according to the present invention is based on the above discovery and comprises:
an absorption step of causing water to contact sulfuric acid anhydride in a gaseous state which may possibly contain sulfurous acid gas as an impurity, so
REFERENCES:
patent: 2730431 (1956-01-01), Haltmeier
patent: 5164049 (1992-11-01), Clark et al.
patent: 5194239 (1993-03-01), Masseling et al.
patent: 5198206 (1993-03-01), Schoubye
Straub Gary P.
Sumitomo Chemical Company Limited
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