Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2000-05-31
2002-04-30
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S397000
Reexamination Certificate
active
06379796
ABSTRACT:
TECHNICAL FIELD
This invention relates to hollow fiber membranes for the degassing of chemical liquids and, more particularly, to composite hollow fiber membranes for the degassing of chemical liquids for use in semiconductor fabrication processes (e.g., photoresist solutions, developing solutions, and chemical liquids for use in a spin-on-glass process), inks for ink-jet printers, liquid crystals and organic solvents.
BACKGROUND ART
With respect to high-purity water for use in semiconductor fabrication, water drained from boilers, and the water supply lines of buildings, raw water containing dissolved oxygen in a saturated state tends to be responsible for oxidation. Accordingly, Japanese Patent Laid-Open No. 169303/'91 discloses a technique for reducing the dissolved oxygen concentration by removing dissolved oxygen from such raw water with the aid of a hollow fiber membrane. In this patent, there is used a three-layer composite hollow fiber membrane in which a homogeneous film consisting of a thin silicone rubber film, silicone-polycarbonate copolymer, poly(4-methylpentene-1), perfluoroalkyl polymer or segmented polyurethane is interposed between porous films.
Water-containing chemical liquids include semiconductor developing solutions, inks for ink-jet printers, alcohol-water mixtures and the like. In the case of such chemical liquids, they are sometimes used at a temperature lower than 30° C. so that their gas solubilities may be reduced to the utmost. The reasons why this method of use is employed are that, since water tends to have lower gas solubilities than organic solvent over a wide temperature range, the use of a water-based solution is suitable for the purpose of reducing dissolved gas concentrations, and that the gas solubilities become lower as the temperature of the solution is reduced.
However, when the method described in the aforementioned patent is applied to water-containing chemical liquids, the following problems arise. In the case of a hollow fiber membrane in which a thin silicone rubber film, silicone-polycarbonate copolymer, perfluoroalkyl polymer or segmented polyurethane is used as the homogeneous film, it has not only high oxygen and nitrogen permeation fluxes, but also a high water vapor permeation flux. Consequently, during the course of degassing, condensation causes waterdrops to be formed on the opposite surface of the membrane. This is the same situation as the leakage of raw water to the opposide surface. Moreover, the membrane swells severely with alcohols, ethers, ketones and esters contained in chemical liquids, so that the thin film may be broken or a large amount of solvent vapor may be discharged to the secondary side (or evacuated side) of the membrane. In the case of a hollow fiber membrane using poly(4-methylpentene-1), this membrane material has its glass transition region in the vicinity of 30° C. and hence becomes brittle in water having a temperature lower than 30° C. Consequently, the membrane tends to be broken by the action of external pressure and cause the leakage of raw water to the opposite surface.
In semiconductor fabrication processes, defects such as processing spots may be produced owing to gas bubbles introduced into the supplied chemical liquids. For example, in the lithographic process in which a thin film overlying a semiconductor wafer is patterned by coating with a photoresist solution, exposure to light through a pattern-bearing mask, development and etching, troubles such as poor patterning due to processing spots may be developed when the semiconductor wafer is spin-coated with a photoresist solution or developing solution having gas bubbles introduced thereinto. Moreover, when gas bubbles are introduced into the washing fluid used in the washing operations of the lithographic process, washing spots may be produced.
The cause for the introduction of gas bubbles is believed to be as follows. A chemical liquid is delivered to a discharge nozzle with the aid of nitrogen gas. When the chemical liquid is discharged from the nozzle, the pressure applied to the chemical liquid is returned to atmospheric pressure. As a result, the dissolved gas present therein becomes supersaturated and this supersaturated fraction forms gas bubbles. The formation of gas bubbles can be minimized by reducing the dissolved gas concentration in the chemical liquid delivery step according to a technique such as membrane degassing.
As techniques for removing dissolved gases from chemical liquids by use of a membrane, the following methods have been known.
(1) a method for removing dissolved nitrogen from a chemical liquid by use of a porous hollow fiber membrane having intercommunicating pores from the inner surface to the outer surface (Japanese Patent Laid-Open Nos. 243306/'96, 94447/'97, 7936/'97, 199607/'89 and 7915/'89; Japanese Patent Publication Nos. 57478/'93 and 45282/'93; and the like).
(2) a method for removing dissolved nitrogen from a chemical liquid by use of a heterogeneous hollow fiber membrane in which a homogeneous thin film layer (i.e., a thin film layer free of intercommunicating pores) is disposed on the surface and supported by a porous substrate layer formed from the same polymer as the homogeneous thin film layer (Japanese Patent Laid-Open Nos. 94447/'97, 187629/'97 and 278897/'94; and the like).
(3) a method for removing dissolved nitrogen from a chemical liquid by use of a non-porous (homogeneous) tubular membrane prepared by forming a tetrafluoroethylene resin having excellent solvent resistance into tubes (Japanese Patent Laid-Open Nos. 153675/'97, 243306/'97, 7936/'97, 267149/'93, 31804/'95, 57008/'97 and 124875/'96; Japanese Utility Model Laid-Open No. 9160/'90; and the like).
(4) a method for removing dissolved nitrogen from a chemical liquid by use of a two-layer composite hollow fiber membrane comprising a homogeneous thin film laminated onto a porous substrate layer (Japanese Utility Model Laid-Open No. 91601/'90; and Japanese Patent Laid-Open Nos. 243306/'97, 94447/'97 and 68007/'89).
(5) a method for removing dissolved nitrogen from a chemical liquid by use of a three-layer composite hollow fiber membrane prepared by interposing a non-porous film comprising a fluororesin between porous substrate layers comprising a fluororesin, and adhesive-bonding the layers with together to form an integral structure (Japanese Patent Laid-Open No. 63007/'89).
However, in the method (1), successful degassing cannot be achieved if the membrane material is highly wettable by the chemical liquid. Specifically, when the liquid being treated is fed to the primary side of the membrane, the liquid being treated penetrates into the pores and leaks out to the secondary side (i.e., the opposite side) of the membrane. This phenomenon is noticeable especially when the chemical liquid comprises a chemical liquid for use with semiconductors or an ink for ink-jet printers.
In the method (2), it is difficult to disturb the crystalline orientation of the homogeneous thin film layer perfectly in the spinning step, so that an ordered structure based on crystalline orientation is created to some extent. As a result, intercommunicating pores tend to be formed in the homogeneous thin film layer during the course of the drawing step for forming a porous layer. Moreover, during handling of the prepared membrane, mechanical rubbing tends to produce pinholes in the homogeneous thin film layer. With this membrane, therefore, successful degassing cannot be achieved because the liquid being treated penetrates into the pores of the porous layer and then leaks out through the pores or pinholes of the homogeneous thin film layer. Such leakage of the chemical liquid is noticeable especially when the chemical liquid comprises a chemical liquid for use with semiconductors or an ink for ink-jet printers.
In the method (3), not only the membrane material has a low nitrogen permeability coefficient, but also the tubes used for degassin
Fukushima Noriaki
Uenishi Masamoto
Fitch Even Tabin & Flannery
Gray J. M.
Kelly Cynthia H.
Mitsubishi Rayon Co. Ltd.
LandOfFree
Composite hollow fiber membrane does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite hollow fiber membrane, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite hollow fiber membrane will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2903153