Cleaning and liquid contact with solids – Apparatus – With heating – cooling or heat exchange means
Reexamination Certificate
2001-11-07
2004-08-31
Stinson, Frankie L. (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
With heating, cooling or heat exchange means
C134S111000, C134S182000, C134S902000
Reexamination Certificate
active
06782901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a sulfuric acid recycle apparatus, which can be suitably applied, e.g., to a recycle apparatus for recycling sulfuric acid which is used for a wafer process in a semiconductor fabricating process.
2. Related Art
A large quantity of wafer cleaning fluid prepared by mixing sulfuric acid with hydrogen peroxide solution has been conventionally used in a semiconductor fabricating process for exfoliating resist applied to a wafer and for removing an organic matter stuck to the surface of the wafer. Upon completion of a wafer cleaning process, the wafer cleaning fluid becomes wasted fluid (hereinafter referred to as a wafer cleaning waste fluid), and the wafer cleaning waste fluid is lowered in concentration owing to water which is produced by decomposition of hydrogen peroxide solution, and hence it is difficult to be recycled. Further, since a wasting cost and a collecting cost of the wafer cleaning waste fluid are cheap, wafer cleaning waste fluid is wasted as it is.
However, considering the occurrence of today's environmental problem which is caused by using a large quantity of such a wafer cleaning fluid and by repetitively wasting such a wafer cleaning waste fluid, a wasting process of the wafer cleaning waste fluid is not preferable in view of countermeasures against environmental protection even if a wasting cost thereof is cheap.
Further, since sulfuric acid per se is a powerful chemical of strong acidity, it cannot be wasted as it is, but need be wasted after a neutralization process and cohesion and precipitation processes are applied thereto. Under such circumstances, there is a problem that a large quantity of chemicals are required for effecting waste process of sulfuric acid.
Accordingly, it is a very important problem to reduce an amount of wasted sulfuric acid in view of countermeasures against environmental protection, and there has been desired development of techniques for concentrating sulfuric acid which is lowered in concentration upon completion of a wafer cleaning process to prepare sulfuric acid so as to be recycled for the same purpose.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a sulfuric acid recycle apparatus capable of concentrating sulfuric acid, which is lowered in concentration upon completion of a wafer cleaning process, to a level to be recycled.
It is a first aspect of the invention to provide a sulfuric acid recycle apparatus for recycling sulfuric acid in a wafer cleaning fluid prepared by mixing sulfuric acid with hydrogen peroxide solution wherein the apparatus comprises a reaction bath having two openings formed of at least an introduction port and a discharge port for obtaining concentrated sulfuric acid by concentrating sulfuric acid in a wafer cleaning waste fluid introduced from the introduction port upon completion of a wafer cleaning process, then discharging the concentrated sulfuric acid from the discharge port, and a wafer processing bath for processing wafers, and a supply unit for supplying the concentrated sulfuric acid to the wafer processing bath.
That is, the sulfuric acid recycle apparatus of the invention removes residual hydrogen peroxide solution from the wafer cleaning waste fluid, or water and the like which are produced by decomposition of hydrogen peroxide solution, thereby concentrating sulfuric acid, and returning the concentrated sulfuric acid again to the wafer processing bath so as to recycle sulfuric acid in the wafer cleaning process.
The reaction bath of the invention may have a construction capable of storing the wafer cleaning waste fluid temporarily therein at the time of concentration process, and having corrosion resistance against sulfuric acid and hydrogen peroxide solution under concentration conditions. The reaction bath may be made of e.g., quarts glass.
For the supply unit for supplying concentrated sulfuric acid to the wafer processing bath, e.g., a pump serving as a unit for supplying a fluid owing to the difference in pressure may be used. In this case, although the concentrated sulfuric acid can be directly supplied from the reaction bath to the wafer processing bath, it is preferable to provide a cooling bath between the reaction bath and the wafer processing bath considering a case where the sulfuric acid is heated when it is concentrated, or a case where the concentrated sulfuric acid has a high temperature. For the pump of this type, a rotary pump, a diaphragm pump, and various other pumps may be used.
According to the invention, the sulfuric acid recycle apparatus includes the reaction bath for concentrating the sulfuric acid in the wafer cleaning waste fluid and the supply unit for supplying the thus obtained concentrated sulfuric acid to the wafer processing bath. Accordingly, water in the wafer cleaning waste fluid and hydrogen peroxide solution can be concentrated and removed, and the thus obtained concentrated sulfuric acid can be supplied to the wafer processing bath to be recycled again for use in a wafer cleaning process. Further, it is possible to continuously effect a series of processes comprising a wafer cleaning process, a concentration process of sulfuric acid in the wafer cleaning waste fluid and a recycling step of concentrated sulfuric acid, which is very efficient. As a result, a cost involving in wafer cleaning process can be reduced.
With the sulfuric acid recycle apparatus having the foregoing construction, heating units for heating the wafer cleaning waste fluid is provided in the reaction bath and a gas discharge port
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for discharging a gas produced from the wafer cleaning waste fluid when it is heated by the heating unit, wherein a suction unit for sucking the gas is connected to the gas discharge port.
That is, although vapor is produced from water in the wafer cleaning waste fluid or the hydrogen peroxide solution when sulfuric acid is heated or concentrated, such a gas is not released to the outside owing to a natural diffusion but it is positively sucked and removed from the gas discharge port
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formed in the reaction bath, thereby quickly concentrating sulfuric acid.
For the heating unit, it may be formed of any type if it can heat the wafer cleaning waste fluid in the reaction bath, and a heating method and the like is not limited to a particular one. That is, it may be a unit capable of heating the reaction bath from the outside or a unit capable of heating the reaction bath from the inside thereof. Particularly, if the heating unit is a type capable of directly heating the wafer cleaning waste fluid, the wafer cleaning waste fluid can be heated efficiently and concentration of sulfuric acid can be effected quickly. For such heating units, a unit having a heater made of, e.g., a tantalum and tungsten which is covered with quarts glass at the periphery thereof may be employed.
Further, for the suction unit, an aspirator and the like serving as a unit for sucking a gas utilizing decompression may be employed. If such an aspirator is employed, the reaction bath can be decompressed, thereby lowering a boiling point of water and that of hydrogen peroxide solution so as to accelerate the removal of water and hydrogen peroxide solution.
It is preferable to provide in the reaction bath a plurality of partition plates for changing an advancing direction of wafer cleaning waste fluid, and an inclination plate disposed at the portion closer to the gas discharge port rather than the partition plates for allowing concentrated sulfuric acid to flow along the surface thereof.
It is preferable to allow the wafer cleaning waste fluid to flow toward the gas discharge port provided in the reaction bath while the wafer cleaning fluid is vertically circulated by convection when a plurality of partition plates are disposed in the reaction bath. That is, when three pieces of partition plates are used, a first partition plate positioned at the introduction port side of the reaction bath is disposed to be remote from the bottom surface of the reaction bath, and a second
Fujii Seiichi
Yasuda Okimitsu
Flynn ,Thiel, Boutell & Tanis, P.C.
Perrin Joseph
Stinson Frankie L.
Suntec System Co., Ltd.
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