Patent Grant
7022164
In this age of increased air pollution, the removal of chemicals from the air we breathe is a concern of everyone. In addition, in the fabrication electronic materials and of devices such as semiconductors, there is a requirement for uncontaminated air of high quality.
Gas phase filtration is commonly accomplished using activated carbon manufactured in various ways. One approach uses a carbon/adhesive slurry to glue the carbon to the substrate. The adhesive decreases carbon performance by forming a film on its surface.
A second approach involves carbonizing an organic based web by heating, followed by carbon activation. This material is expensive and has relatively low adsorption capacity.
A third approach involves forming a slurry of carbon powders and fibers into sheets by a process analogous to a wet papermaking process. This material has a medium-to-high cost, and has an undesirable high pressure drop. Moreover, chemically impregnated carbon particles cannot be efficiently used in conjunction with an aqueous process, as the aqueous nature of the process either washes away the chemical used to impregnate the carbon, or reacts undesirably with the impregnating or active chemical groups thereby rendering it inoperative. In general, however, filter materials which do not incorporate chemically active groups perform far less effectively than those which do include chemically active groups.
None of these approaches fully achieve the desired properties which provide a clean, cost effective, high efficiency, low pressure drop, adsorptive composite.
The present invention comprises a clean, cost effective, high efficiency, low pressure drop, adsorptive, filter comprising a high surface area, highly acidic chemically impregnated adsorbent. A preferred embodiment of the invention can employ a non-woven composite material having acidic functional groups that bind to airborne bases. The invention can be used in lithography systems which employ materials that are sensitive to impurities, such as molecular bases present in the air circulating through semiconductor wafer processing equipment. A large number of bases including ammonia, NMP, triethylamine pyridine, and others, can be maintained at concentrations below 2 ppb in a tool cluster filtered with the present invention. The invention also includes methods for forming the filter comprising, for example, the dry application of an active adsorbent to a non-woven carrier material, which is then heated and calendered with cover sheets.
In a preferred embodiment of this invention the non-woven carrier materials can be polyester non-wovens, and the adsorbent can include sulfonated divinyl benzene styrene copolymer. Another preferred embodiment employs carboxylic functional groups. The acidic groups have a least 1 milliequivalent/gram acidity level or higher and preferably at least 4.0 milliequivalents/gram or higher. The polymers used are porous, preferably having a pore size in the range of 50–400 angstroms and a surface area of 20 m2/g or higher.
The dry processing of a non-woven polyester batting allows for even distribution of adsorbent particles throughout the depth of the polyester batting. This provides an increased bed depth at a very low pressure drop, which is highly desirable since a twofold increase in depth can increase the filter's breakthrough time (time to failure) fourfold when using these thin fabric based sulfonic beds.
Thus, the invention provides a clean, cost effective, high efficiency, low pressure drop, adsorptive non-woven filter composite, and a method for forming said composite. The novel filter composite is particularly useful for the removal of base contaminants in an air stream, which contaminants can be gaseous or vaporous. Particulates will also be removed if greater than the pore size of the filter. The filter has a service life of at least 12 months with a pressure drop to reduce power consumption and minimize impact on the systems operation. For example, a high pressure drop filter can require a longer time for a lithography system to equilibrate the temperature and humidity after filter replacement.
In an alternative embodiment, the filter uses both sulfonated divinyl benzene styrene copolymer and an activated carbon as the adsorbent. Activated carbon is discussed in greater detail in U.S. Pat. No. 5,582,865 title “Non-Woven Filter Composite”, issued Dec. 10, 1996 with Rezuke, et al., as inventors. The entire contents of this patent is incorporated herein by reference. The filter in this preferred embodiment has two (or more) layers, one of activated carbon and one of sulfonated divinyl benzene styrene copolymer beads. Additionally, two or more materials can be mixed to provide the filter system of the present invention.
In another preferred embodiment a synthetic carbon material, such as that described in U.S. Pat. No. 5,834,114, entitled “Coated absorbent fibers”, issued Nov. 10, 1998 with Economy, et al., as inventors, the contents of which are incorporated herein by reference, can be coated with the materials of the present invention to provide a porous acidic filter in accordance with the invention.
A detection system and method of use for determining when the filter needs to be replaced by detecting base contaminants in air is described in U.S. Pat. No. 6,207,460 entitled “Detection of Base Contaminants in Gas Samples”, issued Mar. 27, 2001 with Oleg Kishkovich, et al as inventors. Also U.S. Pat. No. 6,096,267 entitled “Detecting of Base Contaminants”, filed issued Aug. 1, 2000 with Oleg Kishkovich, et al as inventors and U.S. Pat. No. 6,296,806 entitled “Protection of Semiconductor Fabrication and Similar Sensitive Processes”, issued Oct. 2, 2001 with Oleg Kishkovich, et al as inventors can also be used with the present invention. These patents disclose the protection of a DUV lithography processes using chemically amplified photoresists which are sensitive to amines in the air. These patents are incorporated in the present application in their entirety by reference.
A preferred embodiment of a method of fabricating a filter element having large surface area and the desired flow characteristics involves the use of a powdered material that is deposited in sequential layers one on top of the other. Following the deposit of each layer of powdered material, a binder material is delivered onto each layer of powdered material using a printing technique in accordance with a computer model of the three dimensional filter element being formed. Following the sequential application of all of the required powder layers and binder material to form the part in question, the unbound powder is appropriately removed, resulting in the formation of the desired three dimensional filter element. This technique provides for the fabrication of complex unitary or composite filter elements having high surface area that are formed with a very high degree of resolution.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Referring to
The structure of
The composite 16, can be contained within any suitable container or frame work for installation in an intended position for filtering operation, typically in the form of a removable or replaceable filter element. For many purposes, it is preferable to increase the surface area of the filter material exposed to an incident air flow, and for this purpose the composite can be pleated to provide the increased surface area.
One embodiment is shown in
An alternative embodiment is shown in
A further embodiment is shown in
In a preferred embodiment, adsorbent particles are evenly distributed throughout the non-woven or fiber matrix or polyester batting. An example of an adsorbent particle includes but is not limited to sulfonated divinyl benzene styrene copolymer.
In a preferred embodiment, the ion exchange strongly acidic preliminary catalyst has the important properties including a particle size of between 0.3 and 1.2 mm, a porosity of approximately 0.30 ml/g, and an average pore diameter of 250 Å. The catalyst preferably has a higher porosity of up to 300 ml/g, or higher. In addition in a preferred embodiment has the properties of concentration of acid site of approximately 1.8 meq/ml and surface area of 45 m2/g. One such catalyst is sold under the trade name AMBERLYST®15 DRY or AMERLYST®035DRY by Rohm and Haas.
Overall, the dry processing of the fiber matrix, which includes the combination of the fluidized bed sulfonated divinyl benzene styrene copolymer deposition process, the inherent stratification of the batting's density, and the even distribution of the sulfonated divinyl benzene styrene copolymer particles as well as stratification of the sulfonated divinyl benzene styrene copolymer particle size, allows for a fabric architecture having an increased bed depth at a very low pressure drop, which is highly desirable due to its high first pass efficiency coupled with its low operating costs.
The term “efficiency” as employed herein is defined by the formula X−Y/X wherein X is the upstream concentration of pollutant, and Y is the downstream concentration of pollutant.
It is recognized that the filter can have a mix of an activated carbon and the preliminary catalyst material discussed above. This combination has sufficient porosity and strongly acidic groups to provide east permanent removal of medium and strong basis and sufficient retention of weak bases form the airborne base contaminants. The filter can also include a porous polymer material.
The filter as described is employed in filtering the air in environments such as semiconductor fabrication systems where there is a requirement for uncontaminated air of high quality.
Referring to
The adsorbent particles 60 distributed in the matrix 62 are then heated, preferable using two zones 68, 70 of infrared energy at different wavelengths. The batting 62 is heated to an overall average temperature of between 250° and 350° F.
The infrared energy causes the adsorbent particles to adhere to the batting at points where the particles contact the batting. This procedure avoids the necessity of raising the temperature of the entire batting to a point at, or near, the melting point of the polyester batting, which could cause the batting to melt and collapse thereby encasing the particles and destroying their chemical activity.
The batting 62 is then calendared using a pair of calender rolls 76,78. The first of these rolls 76 (Heated Steel Roller) can be temperature controlled which allows the heating and calendering steps to be carried out at a steady temperature of around 140°, and prevents overheating and subsequent melting of cover sheet and prevents over calendering of the fabric. The second roll, roll 78, is a rubber roll having a durometer that avoids crushing of the adsorbent particles.
In
The cover sheet (66 and 80) can have the following specifications: Polyester Non Woven 100% 2.25 Denier Fiber. The Binder consists of a Fiber Ratio of 55 g/45g. The thickness is 0.024 inches and the weight is 1.75 oz./yd2.
Furthermore, when the temperature controlled roller 76 is used, the pressure at which the batting is 2000 pounds across the 26 inch distance. Higher calendaring pressures can crush the particles particularly when those particles are activated carbon based, thereby forming dust, which cannot be retained in the filter composite and can consequently pass into the gas stream.
In addition, a synthetic non-woven cover sheet 80, which helps to maintain the sulfonated divinyl benzene styrene copolymer in the batting, may be calendared with the batting 62, as discussed above. After the filter is formed, gussets or spacers are placed in the filter. The filter is sealed into a metal box.
Optionally, the material may be conducted over an upper roller 84 to facilitate cooling the material prior to further processing. The method of manufacture for an activated carbon filter is described in detail in U.S. Pat. No. 5,582,865 titled “Non-Woven Filter Composite”. The entire contents of this patent is incorporated herein by reference.
While the above described method is a preferred method of creating the filter, it is recognized that other techniques can be used. Some of these techniques include those developed by Hoechst such as that described in U.S. Pat. No. 5,605,746, the entire contents of which is incorporated herein by reference or KX Media. The common feature in all these methods are the incorporation of a chemically active sorbent into a porous media structure.
A pleated filter structure 220 using the porous acidic polymer of the present invention is illustrated in
Considering service life data only, it appears that filter #3 performed best. However, if additional data is considered, the conclusion is not so simple. Pressure drop of filter #1 was 0.2″WC; for filter #2 was 0.3″WC; and for filter #3 was 1.0″WC. Filters #1 and #2 are very close to tool manufacturer's specifications, but #3 creates an excessive pressure drop that interferes with tool's proper ECU functioning. Excessive pressure drop is undesirable for multiple reasons. For example, it increases fan load and power consumption, reduces airflow through the tool and positive pressure inside the enclosure. Thus filter #1 made in accordance with the present invention provided a substantial improvement in service life while providing a pressure drop that is compatible with tool operation.
Another preferred embodiment of the invention involves the fabrication of high surface area filter elements using a three dimensional printing technique as described in U.S. Pat. No. 5,204,055, 5,340,656, and U.S. Pat. No. 5,387,380, the entire contents of these patents being incorporated herein by reference.
Such a method of fabrication of a filter element is illustrated in connection with
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
The present application is a divisional of U.S. patent application Ser. No. 10/178,424, filed on Jun. 24, 2002, now U.S. Pat. No. 6,610,128, issued on Aug. 26, 2003, which is a divisional of U.S. patent application No. 09/378,180, filed on Aug. 20, 1999, now U.S. Pat. No. 6,447,584, issued on Sep. 10, 2002, which claims the benefit of U.S. Provisional Patent Application No. 60/097,215, filed on Aug. 20, 1998, the entire teachings of which are incorporated herein by reference.
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| Number | Date | Country | |
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| Child | 10647656 | US | |
| Parent | 09378180 | Aug 1999 | US |
| Child | 10178424 | US |
