Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – With means applying electromagnetic wave energy or...
Reexamination Certificate
2001-05-14
2003-09-16
Mayekar, Kishor (Department: 1753)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
With means applying electromagnetic wave energy or...
C422S121000, C422S122000
Reexamination Certificate
active
06620385
ABSTRACT:
BACKGROUND OF THE INVENTION
The disclosures of the Japanese Patent Applications Nos. Hei-8-235832 filed on the Aug. 20, 1996 and Hei-9-31441 filed on the Jan. 31, 1997 are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for purifying a gas containing contaminants. More specifically, the present invention relates to a method and an apparatus for purifying a gas by producing microparticles of the contaminants present in a gas and decomposing the resultant microparticles of contaminants with a photocatalyst for facilitating the removal thereof.
RELATED ART
It was considered satisfactory in semiconductor industries in the past to remove only solid particles such as dust from a gas such as air in a clean room. Methods for removing solid particles can be classified broadly into 2 categories: (1) mechanical filtration methods (e.g. HEPA (High Efficiency Particulate Air) filter); and (2) methods for trapping microparticles electrostatically (e.g. MESA filter). Methods included in the category (2) comprise charging microparticles electrically with a high electrical voltage and filtering the charged microparticles with an electrically conductive filter. Gaseous contaminants, however, cannot be removed by any method of either category.
Development of semiconductors of higher quality and finer precision has made it necessary to remove not only dust-like solid particles but also gaseous contaminants. Gaseous contaminants include: organic compounds including phthalic esters; organosilicon compounds including siloxane; acidic gases including sulfur oxides (SOx), nitrogen oxides (NOx), hydrogen chloride (HCl) and hydrogen fluoride (HF); as well as basic gases including NH
3
and amines. Amines may be included among organic compounds also. Anions such as NO
3
−
, NO
2
−
, SO
4
2−
, etc. have characteristics and exert adverse effects similar to acidic gases, and therefor, are considered as a member of acidic gases out of convenience. Likewise, cations such as NH
4
+
, etc. have characteristics and exert adverse effects similar to basic gases, and therefor, are considered as a member of basic gases for convenience.
Organic compounds or organosilicon compounds, when deposited onto the surface of a wafer (substrate), may have a negative effect on the affinity (drapability) of a substrate for a resist. Decreased affinity may exert a harmful influence on both the film thickness of a resist and the adhesion of a substrate to a resist (“Air Cleaning”, Vol. 33, No. 1, pp. 16-21, 1995). For example, SOx may bring about defective insulation in an oxide layer. NH
3
may produce ammonium salts that are responsible for the blooming (poor resolution) of a wafer (Realize Inc., “Saishin Gijyutsu Kozau, Shiryo-shu”, Oct. 29, 1996, pp. 15-25, 1996). For the aforementioned reasons, such gaseous contaminants may diminish the productivity (yield) of semiconductor products.
It was also considered satisfactory in the past to remove gaseous contaminants to a level of ppm. It has become required now to remove gaseous contaminants to a level of ppb. Among organic compounds, alkanes such as methane and the like are not so reactive as to exert an unfavorable influence on a semiconductor, and hence are not required to be removed to a level of ppb.
Removal of contaminants including organic compounds, especially gaseous organic compounds is described below in more detail.
Known methods for removing organic compounds include decomposition by combustion, catalytic decomposition, removal by adsorption, decomposition with O
3
and the like. These known methods, however, are not effective in removing organic compounds present in low concentrations in air for feeding a clean room.
In a clean room, contamination with organic compounds of an extremely slight concentration cannot be ignored. External organic compounds may be introduced into a clean room. For example, outdoor air is contaminated with organic compounds originating from exhaust gas of cars or those resulting from degassing of polymer products. On the other hand, internal organic compounds may be generated in a clean room. For example, polymer materials (e.g. polymeric plasticizers, releasers, antioxidants and the like) which are used for constructing a clean room are producers of organic gases (“Air Cleaning”, Vol. 33, No. 1, pp. 16-21, 1995). Synthetic polymers are used in packing materials, sealants, adhesives and wall-forming materials in a clean room. In addition, plastic containers are disposed in a clean room. These synthetic polymers may evolve a trace amount of organic gases. More particularly, sealants and the production units thereof may give off gaseous siloxane, and plastic containers may give off gaseous phthalic esters. It has recently been found that gas evolves also from polymer materials employed in a production unit. A process unit is partially or entirely surrounded by plastic plates which also produce organic gas. A variety of solvents (e.g. alcohols, ketones, etc., which are necessary for operations in a clean room are also a contamination source.
As stated above, a clean room is contaminated variously and heavily with not only organic compounds attributable to external air but also with organic compounds and organosilicon compounds that are generated internally.
In view of energy saving considerations, recycling of air in a clean room has become more frequent recently. In consequence, organic gases are progressively concentrated in a clean room, leading to heavier contamination of the base materials of a wafer and a substrate. These organic compounds are likely to deposit onto the bodies (e.g., starting materials and semi-fabricated products of a semiconductor wafer, a glass substrate, etc.) placed in a clean room, adversely affecting them.
A contact angle indicates a degree of contamination on a wafer substrate with organic compounds and organosilicon compounds. The contact angle refers to the angle formed by the water and the surface of a substrate when the surface is wet with water. The surface of a substrate, when covered with a hydrophobic (oily) substance, becomes more water-repellent and less wettable, hence the contact angle of water on the surface of a substrate becomes larger. In other words, when the contact angle is larger, the degree of contamination is higher. On the contrary, when the contact angle is smaller, the degree of contamination is lower.
When a substrate is contaminated with organic compounds and organosilicon compounds, its affinity (drapability) for a resist decreases, imparting an unfavorable influence on the resist and the film thickness or on the adhesion of the substrate to the resist, that may result in lower quality and a lower yield.
Techniques in the high-technology field have made remarkable progress in realizing semiconductor devices of a maximal precision and a minimal size. In consequence, it has become necessary for a clean room to be free from organic compounds normally present in the air of the level that had conventionally been able to be ignored (an extremely low concentration of the ppb level) [Preparatory Manuscripts for the 39th Meeting of the Applied Physical Society, p.86 (1992, Spring); “Air Cleaning”, Vol. 33, No. 1, pp. 16-21, (1995)], as well as gaseous contaminants including SO
2
, HF, NH
3
[“Ultra Clean Technology”, Vol. 6, pp. 29-35 (1994)]. Because, it has been revealed that the presence of these gaseous contaminants diminished remarkably the productivity (yield). The present invention is aiming to efficiently remove these gaseous contaminants.
The present inventors have proposed a method for removing hydrocarbons present in a gas comprising the steps of: irradiating the gas with an ultraviolet ray and/or a radiation ray so as to produce microparticles from the hydrocarbon; and trapping the resultant hydrocarbon microparticles with a filter or charging the hydrocarbon microparticles electrically with a photoelectron and trapping the resultant charged microparticles (Laid Open Japan
Ebara Corporation
Mayekar Kishor
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