Air filter

Details Air filter Air filter

2000-12-13

2002-10-29

Bushey, C. Scott (Department: 1724)

Gas separation

With means securing or retaining separating media

Unit or cohesive sheet-like media in flow line or frame

C055S524000

Reexamination Certificate

active

06471740

ABSTRACT:

TECHNICAL FIELD
The present invention concerns an air filter for use in a clean room used, for example, in factories or research laboratories relevant to the field of semiconductors, foodstuffs and biotechnology, a method of manufacturing thereof, a local facility and a clean room equipped with the air filter.
BACKGROUND ART
In clean rooms used heretofore, for example, in factories or research laboratories in the relevant field of semiconductors, foodstuffs, medicines and biotechnology, dry air filters for trapping air-born particles are disposed to air introduction paths and air passing there through is introduced into the clean room.
Air filters used at present in clean rooms include ULPA (abbreviation for
U
ltra Low
P
enetration
A
ir) using glass fibers for the filter medium and HEPA (abbreviation for
H
igh
E
fficiency
P
article
A
ir), and such filters are excellent filters in view of removal of dusts and, for example, ULPA filters can remove fine particles even of 0.1 &mgr;m. Further, non-glass type filters using fluoro resin or quartz fibers instead of the glass fibers for the filter medium have also been developed so as not to release inorganic substances from the air filters.
Recently, with the increase of integration degree of semiconductors, diffusing of gaseous organic substances as well as dusts in the clean room air have considered to be the cause of defects. That is, it has been pointed out that organic substances are adsorbed on the surface of semiconductor substrates (silicon wafers) in clean rooms, to deteriorate device characteristics (for example, Fujii, “Gaseous Contaminants and Current Situation for Countermeasure of Removal”, Air Cleaning, Vol. 32, No. 3, p 43 (1994), published from the Foundation of Japan Air Cleaning Society).
Further, it has been well-known that an n-type semiconductor is obtained by doping P (phosphorus) and a p-type semiconductor is obtained by doping B (boron, into a silicon wafer in semiconductor manufacturing steps but, if phosphorus compounds or boron compounds are present in the clean room air, these may possibly cause unnecessary doping, so that it is necessary to remove such ingredients from the clean room air.
The present invention has been accomplished to solve the problems described above and it is an object thereof to provide an air filter for trapping air-born particles that can eliminate the presence of gaseous organic substances, for example, in clean rooms, semiconductor production apparatus or the like, a method of manufacturing an air filter therefor, a treatment agent constituting the air filter, a method of manufacturing a filter medium, a clean room and a local facility such as a semiconductor production apparatus in which gaseous organic substances are not present, as well as a clean room and a local facility in which phosphorus compounds and boron compounds are not present.
DISCLOSURE OF THE INVENTION
The present inventors have made earnest studies for attaining the foregoing object and, as a result, have accomplished the present invention based on the finding that presence of gaseous organic substances in a clean room and a local facility such as a semiconductor production apparatus is mainly caused by air filters disposed to air introduction paths and gaskets intervened for attaching the air filters to openings, for example, of a ceiling.
That is, it has been found by the study of the present inventors that gaseous organic substances such as cyclosiloxanes, carboxylic acid esters, phosphoric acid esters, hydrocarbons, and phenols are released from the existent air filters described above and that such organic substances are released from treatment agents impregnated between each of fibers upon forming the fibers into a cloth-like filter medium (including a binder for binding fibers, a water repellent for improving dust trapping effect and a plasticizer or an antioxidant), silicone oils deposited to fibers in a case where the filter medium is glass fibers (this is a reinforcing material upon spinning glass fibers which serves also as a water repellent of the filter medium) and sealing materials for bonding a filter medium and a frame. Further, it has also been found that organic substances are detected at a high ratio also from rubber materials used so far as gaskets.
Specifically, it has been found that the ingredient of the conventional water repellent (non-silicone type) in the treatment agent is liquid paraffins (aliphatic hydrocarbon having 12 to 18 carbon atoms) which contain a plasticizer or an antioxidant of relatively low molecular weights Further, while the sealing material comprising a polyurethane or epoxy type resin as the main ingredient is used, it has been found that isocyanates of the main agent left after the curing reaction become organic contaminations in a case of a two component polyurethane resin, while amine compounds used as a curing agent become organic contaminations in a case of a two component epoxy resin. It has also been found that conventional sealing materials contain plasticizers and antioxidants of relatively low molecular weight.
Based on the findings described above, the present invention provides an air filter comprising a filter medium formed of fibers treated with a treatment agent into a cloth-like shape, a frame for containing the filter medium and a sealing material for tightly sealing a portion between the frame and the filter medium for trapping air-born particles, wherein at least one of the filter medium and the sealing material does not release gaseous organic substances during use.
Further, the present invention provides an air filter satisfying one of the following definitions (a)-(c) and (e)-(g) for the treatment agent and the sealing material.
(a) The main ingredient of a non-silicone type water repellent contained in the treatment agent is at least one of an aliphatic hydrocarbon having 20 carbon atoms or more and a higher alcohol having 18 carbon atoms or more.
(b) The main ingredient of the plasticizer contained in the treatment agent is at least one of carboxylic acid esters, polyester and epoxy type compound having 400 or more molecular weight.
(c) The main ingredient of the antioxidant contained in the treatment agent is a phenolic compound having 300 or more molecular weight.
(e) The main ingredient of the plasticizer contained in the sealing material is at least one of carboxylic acid esters, polyesters and epoxy type compounds having 400 or more molecular weight.
(f) The main ingredient of the antioxidant contained in the sealing material is a phenolic compound having 300 or more molecular weight.
(g) The main ingredient of the lubricant contained in the sealing material is at least one of an aliphatic hydrocarbon having 20 carbon atoms or more and a higher alcohol having 18 carbon atoms or more.
Further, the present invention provides a method of manufacturing an air filter which comprises selectively using the plasticizer and the antioxidant defined in (b), (c), (e) and (f) for the treatment agent and the sealing agent described above.
Now, if the main ingredient of the non-silicone type water repellent in (a) and the main ingredient of the lubricant in (g) are an aliphatic hydrocarbon having 19 carbon atoms or less and a higher alcohol having 17 carbon atoms or less, the gaseous substances are present in the clean room air being entrained by air passing through the air filter in a usual clean room, which is controlled at a temperature of 23° C. and at a humidity of 30-40% and in which the flow rate of air passing through the air filter is about 0.3 to 0.4 m/s, but such gaseous substances are not present in the clean room air when an aliphatic hydrocarbon having 20 carbon atoms or more and a higher alcohol 18 having carbon atoms or more is used.
Further, if the main ingredient of the plasticizer in (b) and (e) is dibutyl phthalate (molecular weight 278), dioctyl phthalate (molecular weight 391) or di-2-ethylhexyl adipate (molecular weight 371) having 400 or more molecular weight, the gaseous substances are present in the clean room air being

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