Polyamide-coated filter membranes, filters, and methods

Abstract

To provide a novel and improved filter in the field of microelectronics device processing.SOLUTION: A coated filter membrane comprises: a porous polymeric filter layer comprising a polyolefin; and a crosslinked polyamide film at least partially coating the surface of the porous filter layer, wherein the coated filter membrane has a bubble point in a range from 2 to 400 psi, measured using HFE 7200, at a temperature of 20-25°C.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The following description relates to a filter membrane comprising a porous polymer filter layer coated with a layer containing a crosslinked polyamide polymer; methods of making the coated filter membrane, filter components and filters; and methods of using the coated filter membrane, filter components and filters to filter fluids such as liquid chemicals and remove unwanted substances from the fluids.

Background Art

[0002] Filter membranes and filter products used to remove unwanted substances from the flow of useful fluids are essential tools in modern industries. Useful fluids processed using filters include water, liquid industrial solvents and process fluids, industrial gases used in manufacturing or processing (e.g., in semiconductor fabrication), and liquids having medical or pharmaceutical applications. Unwanted substances removed from the fluids include impurities and contaminants such as particles, microorganisms and dissolved chemical species. Specific examples of filter applications include use in the pharmaceutical industry to remove particles and bacteria from therapeutic fluids, use in microelectronics and semiconductor processing, and use to treat ultra-high purity aqueous and organic solvent solutions for water purification methods.

[0003] To perform the filtering function, filter products include a filter membrane that is responsible for removing unwanted substances. The filter membrane may be in the form of a flat sheet that may be wound (e.g., spirally) or pleated as required. Alternatively, the filter membrane may be in the form of hollow fibers. The filter membrane may be housed in a housing such that the fluid being filtered needs to pass through the filter membrane before entering the inlet of the filter and passing through the outlet of the filter.

[0004] Filter membranes may be constructed from porous structures with average pore sizes that can be selected based on the application of the filter, i.e., the type of filtration performed by the filter. Typical pore sizes range from microns to submicrons, such as approximately 0.001 microns to approximately 10 microns. Membranes with an average pore size of approximately 0.001 to 0.05 microns are generally classified as ultrafiltration membranes. Membranes with pore sizes between approximately 0.05 and 10 microns are generally classified as microporous membranes.

[0005] Porous polymer films, including those made from various fluoropolymers, polyolefins, and nylon materials such as nylon 6 and nylon 66, are common types of filter membranes. Nylon filters are commercially used to filter solvent materials for photolithography methods in semiconductor fabrication. These methods require solvents of extremely high purity and must be filtered using highly efficient filtration systems. Filters made from nylon with controlled small pore sizes can be prepared, which may be effective for these applications. However, the liquids used in microelectronics and semiconductor processing can be acidic. Furthermore, some nylons are polymerized using metal catalysts such as magnesium. When such types of nylon in filter membranes are exposed to acidic liquids, the metal (e.g., magnesium) is more likely to be extracted from the nylon into the acidic fluid being filtered, in which case the metal is considered an impurity. In addition, nylon designed to be inert and solvent-resistant is not necessarily soluble in a wide range of solvents. This limits the options for preparing nylon filter membranes or filter membrane coatings. For these reasons at least, there is a continuing need for new and improved filters, including nylon-containing filters, in the field of filtration. [Overview of the project]

[0006] In the field of microelectronic device fabrication, methods are needed to maintain steady improvements in fabrication materials and the parallel steady improvements in the performance of microelectronic devices (e.g., speed and reliability). Opportunities to improve microelectronic device fabrication exist in all aspects of manufacturing methods, including methods and systems for filtering liquid materials.

[0007] In microelectronic device fabrication, a wide range of different types of liquid materials are used as processing solvents, cleaning agents, and other processing solutions. Most, if not all, of these materials are used at extremely high levels of purity. For example, liquid materials (e.g., solvents) used in photolithography of microelectronic devices must be of extremely high purity. Specific examples of liquids used in microelectronic device fabrication include spin-on-glass (SOG) technology, back-surface anti-reflective coating (BARC) methods, and processing solutions for photolithography. Some of these liquid materials are acidic. To provide these liquid materials at high levels of purity for use in microelectronic device fabrication, filtering systems must be highly effective at removing various contaminants and impurities from the liquid and must be stable (i.e., do not degrade or introduce contaminants) in the presence of the filtered liquid material (e.g., acidic material).

[0008] Many important considerations must be taken into account to provide filter systems with increasing effectiveness in complex applications such as microelectronics fabrication. Nylon materials (commonly known as polyamides) are used as porous filter membranes, as coatings for porous filter membranes, or both. Nylon is used as a filter membrane to filter various liquid materials involved in the fabrication of microelectronic devices, but as microelectronic device fabrication methods are constantly evolving, improvements are needed to make it effective or optimal.

[0009] For example, metal ions may be used as catalysts in the preparation of certain types of nylon materials, and may be present in very small amounts in the finished nylon filter material. Even such low levels of metal in nylon filters can be problematic when using the filters in microelectronic device fabrication because the metal may be extracted from the nylon filter material by acidic liquids. The extracted metal becomes an impurity in the liquid. Separately, nylon has variability in its ability to be fabricated into filter films. While nylon is designed to be stable and chemically resistant, this means that nylon may not be soluble in a wide range of solvents. Some nylons are soluble in certain types of solvents, such as acidic solvents (e.g., formic acid) and ionic solvents (e.g., calcium chloride). However, each of these solvents has its drawbacks. Formic acid can be difficult to handle, and calcium chloride may leave amounts of impurities in the nylon coating that are unacceptable for use as filters in microelectronic device fabrication at the tip node.

[0010] As described herein, the applicant has determined that it is possible to effectively coat certain types of polyamide onto porous polymer filter layers to produce coated filter films that exhibit useful or advantageous filtration performance when filtering contaminants or impurities from liquid fluids. For example, coated filter films can be used to remove contaminants from liquid materials, including acidic liquids, used in the fabrication of microelectronic devices, and to produce filtered liquid materials with extremely high levels of purity.

[0011] The purity level of the processed liquid and the associated performance of the filter membrane can be measured using a variety of different techniques. In one quantitative measurement, the effectiveness of the filter material can be evaluated by testing its effectiveness in removing known types and amounts of substances, such as dissolved metals or metal particles, e.g., "problem" substances, e.g., gold. The coated filter membranes described herein are highly effective in removing these types of problem particles and, for example, may be at least as effective as current or prior filter membranes based on these tests.

[0012] In other measurements, the effectiveness of a filter film may be measured in terms of its performance in a specific application, such as filtering fluids used in the fabrication of microelectronics or semiconductor devices. The effectiveness of the filter film may be measured in terms of performance, for example, by measuring the level of defects present in the microelectronics or semiconductor devices prepared using the fluid. For example, the effectiveness of a filter film can be evaluated by counting the number of defects, such as "bridge defects," present in the microelectronics or semiconductor devices prepared using the liquid processing solution that is processed (i.e., filtered) using the filter film. A lower number of defects in the device indicates a higher level of effectiveness of the filter film.

[0013] Polyamides may be coated onto a filter layer from a solvent using a solvent other than formic acid and calcium chloride, respectively, which are not optimal for processing nylon coatings on filters used in microelectronic device fabrication. The solvent (other than formic acid and calcium chloride) may be non-acidic, non-ionic, and preferably can be handled and processed by conventional methods. Propanol, which is commonly and conventionally handled in industrial applications, is one example of a solvent that can be used to dissolve the exemplary polyamides described. Propanol is non-acidic and does not introduce impurities into the coated polyamide at a level that would render the polyamide unsuitable for microelectronic device applications.

[0014] Polyamides can be coated by any useful method, such as immersion precipitation, and may be crosslinked after coating to increase the solvent resistance of the polyamides.

[0015] In one embodiment, the present invention relates to a coated filter film comprising a porous polymer filter layer and a non-porous crosslinked polyamide film coating on the surface of the porous filter layer.

[0016] In another aspect, the present invention relates to a method for preparing a coated filter film. The method comprises coating a polymer solution onto the surface of a porous filter film, wherein the polymer solution comprises a polyamide polymer, a solvent, and a free radical source material; solidifying the polyamide of the polymer solution on the surface; and crosslinking the polyamide. [Brief explanation of the drawing]

[0017] [Figure 1] This graph shows the dye-binding ability of various filter films. [Figure 2] This graph shows the dye-binding ability of various filter films. [Figure 3] This graph shows the dye-binding ability of various filter films. [Figure 4] This graph shows the dye-binding ability of various filter films. [Figure 5] This figure shows data regarding the amount of metal extracted from the filter film. [Figure 6] This figure shows data regarding the stability of polyamide coatings after exposure to low pH organic solvents. [Figure 7] This figure shows data regarding the stability of polyamide coatings after exposure to common photoresist solvents. [Figure 8] This figure shows data related to coatings using varying amounts of photoinitiator. [Figure 9]A figure showing data on the counting of defects in different filter membranes. [Figure 10] A figure showing data on the metal removal efficiency of different filter membranes.

Mode for Carrying Out the Invention

[0018] The following description relates to a coated filter membrane, a method for producing products such as a coated filter membrane, a filter component containing the coated filter membrane, and a filter, and a method for using a coated filter membrane, a filter component, or a filter.

[0019] The coated filter membrane described includes a porous polymer filter layer and a polymer film coating on one or more surfaces of the porous polymer filter layer. The polymer film coating is a film coating containing a crosslinked polyamide polymer. Polyamide is often used to form a solution from nylon before crosslinking, but it can be difficult to handle (formic acid), or when the obtained nylon is used in a filter for microelectronic device processing, it may produce unacceptable levels of residues or contaminants (calcium chloride), and it may be dissolved in at least one solvent different from formic acid and calcium chloride. In some embodiments, the polymer film coating may be porous, and in other embodiments, the polymer film coating may be non-porous.

[0020] The polyamide film coating may be a continuous or semi - continuous layer of a film containing polyamide provided on the surface of the porous polymer filter layer. Preferred coatings are considered to be substantially thin as a "film". In some embodiments, the polyamide may be porous, and in other embodiments, the polyamide film may be non - porous or substantially non - porous (e.g., containing no substantial amount of void space). The film may be continuous over all or semi - continuous over one or more surfaces of the porous polymer film layer, i.e., the film may be discontinuous but cover a substantial portion of the porous polymer film layer.

[0021] A polymer film coating containing cross - linked polyamide can be prepared by preparing a polymer solution containing a polyamide polymer (not cross - linked), disposing the polymer solution on the surface of the porous polymer filter layer, and cross - linking the polyamide. The polymer solution may be disposed on the surface of the polymer filter layer in a manner effective to place a desired useful amount of polyamide on the outer and inner surfaces of the porous polymer filter layer, for example, by precipitation coating. Thereafter, the polyamide polymer may be cross - linked by any effective method. The cross - linked polyamide may be dried so that a continuous or semi - continuous porous or non - porous film coating remains on the surface of the filter layer, and the film coating contains (comprises, consists of, or consists essentially of) the cross - linked polyamide polymer. The film coating may be present in a significant portion of the inner surface of the pores of the porous polymer filter layer and on the outer (macroscopic) surface of the porous polymer filter layer.

[0022] The film coating may contain materials other than crosslinked polyamide, but a useful and preferred example of the film coating does not require any other materials. The described polyamide-containing film coating, after being applied, crosslinked, and dried, may contain at least 50, 70, 85, 90, or 95 weight percent of crosslinked polyamide based on the total weight of the dried film coating. A film coating essentially consisting of a crosslinked polyamide coating is a film coating containing 5, 2, 1, or 0.5 weight percent or less of materials other than crosslinked polyamide.

[0023] Coated filter films may be useful for filtering liquids to remove unwanted substances (e.g., impurities or contaminants) from the liquid, producing high-purity liquids that can be used as materials for industrial processes. Industrial processes may be any that require high-purity liquid materials as input materials, and non-limiting examples of such processes include the preparation of microelectronic or semiconductor devices, a particular example of which is a method for filtering liquid processing materials (e.g., solvents or liquids containing solvents) used in semiconductor photolithography. Examples of contaminants present in processing liquids or solvents used to prepare microelectronic or semiconductor devices include metal ions dissolved in the liquid, solid particles suspended in the liquid, and gelling or solidifying materials present in the liquid (e.g., those generated during photolithography).

[0024] A coated filter membrane may be useful for removing dissolved or suspended contaminants or impurities (such as sieves) from a liquid flowing through the coated filter membrane, either by a sieving mechanism or a non-sieving mechanism, preferably a combination of both. A sieving mechanism is a filtration method that removes particles from a liquid flow by mechanically holding them on the surface of the filter membrane, where the filter membrane works to mechanically interfere with the movement of particles, holding them within the filter and mechanically preventing them from flowing through the filter. Typically, the particles may be larger than the pores of the filter. A "non-sieving" filtration mechanism is a filtration method in which the filter membrane holds suspended particles or dissolved substances contained in the liquid flowing through the filter membrane in a manner that is not limited to mechanical, including, for example, an electrostatic mechanism.

[0025] In the exemplary coated filter membranes described, the porous polymer filter layer may function to remove substances from the liquid flow passing through the coated filter membrane by a sieving mechanism, and the polymer film coating containing a polyamide polymer may function to remove substances from the liquid flow by a non-sieving mechanism.

[0026] The porous polymer filter layer of a coated filter membrane is used for filtering high-purity liquids and may be any of the useful general range and types of porous polymer filter materials. The porous polymer filter layer may be characterized by its chemical composition, general shape, and one or more of the following physical and performance features: pore size, porosity, bubble points, and thickness.

[0027] The shape may be a planar sheet stretched to a length and width dimension, with thickness defining two opposing main surfaces separated by a third dimension. The sheet may preferably have a relatively uniform thickness across the length and width dimension. An alternative shape may be a hollow fiber, which may include a length and a substantially uniform thickness stretching between the inner and outer diameters.

[0028] A wide variety of polymers are available for forming porous polymer filter layers (e.g., membranes), and some specific examples include non-fluorinated polymers such as polyolefins, polyhaloolefins, polyesters, polyimides, polyetherimides, polysulfones, polyethersulfones, and polycarbonates, as well as fluoropolymers and other common and specific types of useful polymers.

[0029] Suitable polyolefins include, for example, polyethylene (e.g., ultra-high molecular weight polyethylene (UPE)), polypropylene, alpha-polyolefins, poly-3-methyl-1-butene, poly-4-methyl-1-butene, and copolymers of ethylene, propylene, 3-methyl-1-butene or 4-methyl-1-butene with each other or with trace amounts of other olefins; exemplary polyhaloolefins include polytetrafluoroethylene, polyvinylidene fluoride, and copolymers thereof with other fluorinated or non-fluorinated monomers. Exemplary polyesters include polyethylene terephthalate and polybutylene terephthalate, and related copolymers.

[0030] In some embodiments, the porous polymer filter layer does not need to be fluorinated or perfluorinated and may contain only non-fluorinated polymers essentially made from non-fluorinated monomers. Exemplary filter layers may contain, consist of, or essentially consist of polyolefins such as polyethylene (e.g., UPE). Preferred polymer filter layers in the present invention contain, consist of, or essentially consist of non-fluorinated polymer materials. Porous polymer filter layers essentially made from non-fluorinated materials may contain less than 0.5, 0.1, or 0.01 weight percent of fluorine. Porous polymer filter layers essentially made from polyolefins, e.g., polyethylene, may be derived from monomers containing at least 99, 99.5, or 99.0 weight percent of polyolefin (e.g., polyethylene) monomers.

[0031] Porous polymer filters of any composition may be optionally treated, for example, with plasma, to enhance their adhesion or filtering properties.

[0032] In some embodiments, the filter layer is made from a non-nylon polymer such as polyolefin, e.g., polyethylene, e.g., ultra-high molecular weight polyethylene (UPE). Nylon is often prepared using a metal catalyst such as magnesium. Magnesium present in the filter layer may be potentially extracted when used in the filtration of certain types of liquids, such as acidic liquids. In some embodiments, the filter layer may be made from a non-nylon polymer to avoid the presence of such extractable metals. According to a useful example of the present invention, the coated filter membrane may include (or be, or essentially be) a non-nylon porous polymer filter layer coated with the described crosslinked polyamide (e.g., polyolefin, e.g., UPE filter membrane). The metal (e.g., magnesium) content of the polyamide-coated non-nylon (e.g., UPE) porous polymer filter layer is substantially lower than the metal (e.g., magnesium) content of an equivalent nylon filter layer. The porous polymer filter layer (e.g., polyolefin, e.g., UPE filter membrane) may be made of a non-nylon polymer or may be essentially made of one; a porous polymer filter layer essentially made of a non-nylon polymer is a filter membrane containing a non-nylon polymer such as polyolefin (e.g., polyethylene, polypropylene, UPE, etc.) in an amount of 5, 2, 1, or 0.5 weight percent or less of nylon based on the total weight of the filter membrane, for example, in an amount of at least 95, 98, 99, or 99.5 weight percent of polyolefin (e.g., polyethylene, polypropylene, UPE, etc.) based on the total weight of the porous polymer filter layer.

[0033] An exemplary porous polymer filter layer may have pores of a size (average pore diameter) that can be considered either a microporous filter membrane or an ultrafiltration membrane. Microporous membranes may have an average pore diameter in the range of about 0.05 microns to about 10 microns, and the pore diameter is selected based on one or more factors, including the particle size or type of impurities to be removed, pressure and pressure drop requirements, and viscosity requirements of the liquid being processed by the filter. Ultrafiltration membranes may have an average pore diameter in the range of 0.001 microns to about 0.05 microns. The pore diameter is often reported as the average pore diameter of the porous material, which can be measured by known techniques such as mercury porosimetry (MP), scanning electron microscopy (SEM), liquid displacement spectroscopy (LLDP), or atomic force microscopy (AFM).

[0034] Bubble points are also a known feature of porous membranes. In the bubble point test method, a sample of a porous polymer filter layer is moistened by immersion in a liquid with a known surface tension, and gas pressure is applied to one side of the sample. The gas pressure is gradually increased. The minimum pressure at which the gas flows through the sample is called the bubble point. According to this specification, useful or preferred examples of useful bubble points for porous polymer filter layers may be in the range of 2 to 400 psi, for example, 20 to 200 psi, measured using an HFE7200 at a temperature of 20 to 25°C.

[0035] The porous polymer filter layers described herein may have any porosity that allows the porous polymer filter layer to be effective as described herein for filtering a flow of liquid to produce a highly pure filtered liquid material. Exemplary porous polymer filter layers may have relatively high porosity, e.g., porosity of at least 50, 60, 70, 80, 85, 90, 95, or 98 percent, e.g., porosity in the range of 50, 60, 70, 80, or 85 to 90, 95, or 98 percent. As used herein, and in the field of porous materials, the “porosity” (sometimes referred to as void fraction) of a porous material is a measure of the void (i.e., “empty”) space of an object as a percentage of its total volume, and is calculated as the volume fraction of the voids of an object relative to its total volume. An object with zero percent porosity is completely solid.

[0036] The porous polymer filter layer described may be in the form of a sheet or hollow fiber having any useful thickness, for example, in the range of 5 to 100 microns, or for example, 20 to 50 microns.

[0037] According to this specification, the physical properties of a coated filter film are substantially determined by, and equivalent to or nearly equivalent to, the corresponding physical properties of a porous polymer filter layer. The porous polymer filter layer may be selected based on physical properties including bubble points, porosity, pore size, and thickness. After coating with a non-porous film coating containing a crosslinked polyamide polymer as described, these physical properties may still be substantially the same or nearly the same for the coated filter film.

[0038] The coated filter membrane includes the polyamide film coating described, for example, a continuous or semi-continuous film coating on the surface of a porous polymer filter layer. The polyamide film coating is effective as a filtering component of the coated filter membrane and includes crosslinked polyamides that improve the filtering performance (e.g., filtering effectiveness or retention) of the coated filter membrane by acting as a non-sieve filter medium. The polyamide may be selected for its filtering effectiveness and its processability. With respect to processability, preferred polyamides can be effectively (and preferably efficiently) placed on the surface of the porous polymer filter layer by a useful coating method before crosslinking, and then crosslinked to improve the solvent resistance of the polyamide.

[0039] To provide the desired processability, the preferred polyamide can be dissolved in a solvent to form a polymer solution which may be coated on the surface of the porous polymer filter layer in a desired amount, and then precipitated from the polymer solution onto the surface of the porous polymer filter layer; that is, the preferred polyamide can be dissolved in a solvent and precipitated onto the surface of the porous polymer filter layer. The amount and arrangement of the polyamide material coated on the surface should be sufficient to allow the polyamide to improve the filtering performance of the porous polymer filter membrane, but should not cause any unacceptable adverse effects with respect to the flow or filtering properties of the porous polymer filter membrane, for example, by significantly reducing the ability of a liquid to flow through the porous polymer filter membrane when used as a filter.

[0040] The crosslinked polyamide may be effective in acting as a filter material as described herein, and is preferably a pre-crosslinked form that can be provided as a coating for a porous polymer film coating by useful coating techniques, for example, preferably by precipitation coating from a copolymer solution in which the polyamide is dissolved (before crosslinking) in a solvent as described herein.

[0041] Polyamides are a well-known class of polymers, including nylon. Chemically, polyamides are considered polymers containing multiple repeating carbon-based organic polymer backbone units separated by repeating amide bonds. The term “polyamide” refers to polymers derived from two or more reactive monomer compounds having repeating amide groups (e.g., polyamide “copolymers” and “ternary copolymers”), as well as blends of two or more different such polyamides.

[0042] Polyamides can be prepared by reacting monomers or reactive raw materials containing combinable functional groups to form a polymer backbone having repeating amide bonds. Therefore, examples of monomers and reactive materials useful for preparing polyamides include diamine monomers and dicarboxylic acid monomers. Exemplary polyamides include copolymers and ternary copolymers prepared by polymerizing combinations of two or three diamine and dicarboxylic acid monomers.

[0043] Useful monomers, such as diamines or dicarboxylic acids, may be linear in shape, comprising a saturated linear hydrocarbon compound and two functional groups, for example, two amines or two carboxylic acid groups. These compounds react to form linear (e.g., aliphatic) units of a polyamide skeleton. Other useful monomers may be compounds comprising two functional groups (e.g., amines or carboxylic acid groups) bonded to a non-linear compound, such as an aromatic compound or a saturated cyclic or bicyclic compound. These compounds react to form non-linear units of a polyamide skeleton, for example, cyclic or polycyclic units.

[0044] In some embodiments, the polyamides herein, useful for film coating of coated filter films, may contain linear and nonlinear skeletal units, for example, by reacting linear and nonlinear monomers to produce polyamides having skeletal units containing linear and nonlinear skeletal units. Nonlinear skeletal units may preferably be effective in increasing the ability of the non-crosslinked polyamide to dissolve in a desired solvent and form the polymer solution described.

[0045] Some specific, detailed, non-limiting examples of linear compounds (monomers) that may be useful in preparing the polyamides described herein include caprolactam, hexamethylenediamine adipate, and combinations thereof. A detailed, non-limiting example of non-linear compounds (monomers) that may be useful in preparing the polyamides described herein is 4,4-diamino-dicyclohexylmethane adipate. These exemplary monomers should not be construed as limiting the types of monomers or reactive materials that can be used to prepare the useful polyamides described herein. Other linear monomers (e.g., linear diamines and linear dicarboxylic acid groups) are also useful in preparing the polyamides described herein, as are other non-linear monomers (e.g., diamines and dicarboxylic acid compounds containing a cyclic six-membered saturated ring structure (e.g., a divalent cycloalkylene residue) or two linked cyclic six-membered saturated ring structures (e.g., a divalent dicycloalkylene residue)).

[0046] The polyamides described may preferably be made from repeating amide groups separated by a combination of linear and non-linear skeletal units that makes the polyamide solvent-processable in a desired solvent described different from formic acid and calcium chloride, or that enables such processing. A polyamide is considered solvent-processable if it can dissolve in a solvent before crosslinking and form a polymer solution that may be applied as a coating to a porous polymer filter layer. Preferably, the polyamide is completely soluble in the solvent in an amount sufficient to form a polymer solution useful for coating, for example, by immersion precipitation.

[0047] Polyamides, like certain polyamides and nylons, do not need to be melt-processable, for example, thermoplastic, which means that polyamides can repeatedly move between a liquefied (molten) state and a solid state without substantially degrading.

[0048] It is known that various polyamides can be solvent-treated using certain types of solvents, such as some acidic solvents (e.g., formic acid) and certain ionic solvents (e.g., calcium chloride). For example, some nylons, such as nylon 66, are soluble in formic acid and calcium chloride, but are generally not soluble in other organic materials. However, formic acid can be difficult to handle. Also, calcium chloride is not a preferred solvent for preparing nylon materials for filters used to filter high-purity liquids, such as those used in semiconductor processing, because the nylon material coated from calcium chloride will consequently contain unacceptable levels of impurities.

[0049] Preferred non-crosslinked polyamide materials herein may be solvent-treated with solvents other than formic acid and calcium chloride. More generally, certain useful and preferred non-crosslinked polyamides may be soluble in a variety of non-acidic solvents, such as organic solvents (optionally containing water), which, unlike formic acid and calcium chloride, are easier to handle than formic acid and do not result in the presence of unwanted residues on the coated polyamide when used in filters for processing high-purity materials.

[0050] The useful or preferred non-crosslinked polyamides herein may be soluble in at least one alternative solvent, namely, a solvent that is different from formic acid and different from calcium chloride, and preferably free of formic acid or calcium chloride (for example, it may be made from or essentially made from such a solvent). A solvent essentially made from a solvent different from formic acid and calcium chloride means one or a combination of a solvent different from formic acid and calcium chloride, and water as needed, and a solvent containing 5, 2, 1, or 0.5 weight percent or less of formic acid or calcium chloride.

[0051] Examples of alternative solvents include a variety of organic, non-acidic, and non-ionic solvents commonly used, handled, and processed in various industrial and commercial processes, which can be used to dissolve non-crosslinked polyamides and form polyamide coatings free from unacceptable amounts of solvent residue. The solvent is useful and sufficient in amount to dissolve the non-crosslinked polyamide, enabling it to serve as a vehicle for coating a desired amount of non-crosslinked polyamide onto a substrate, for example, onto a porous polymer filter layer, by the immersion precipitation coating method.

[0052] Unlike formic acid and calcium chloride, preferred solvents in the present invention include lower aliphatic alcohols (e.g., C1-C3, C4, C5, or C6 aliphatic alcohols) such as methanol, ethanol, propanol, butanol, and isopropanol, and chlorinated hydrocarbons. The useful or preferred non-crosslinked polyamides herein are soluble in one or a combination of these solvents, optionally combined with water, to such an extent that the non-crosslinked polyamide can be coated onto a porous polymer filter layer from the solvent as described herein. Certain preferred non-crosslinked polyamides in the present invention are soluble in a solvent consisting of or essentially derived from propanol and optional water, for example, optionally made from propanol alone combined with water at a weight of 20 percent or less of the total weight of the solvent.

[0053] Therefore, useful or preferred solvents may, may be, or essentially be, a solvent containing one or a combination of the following, further optionally combined with a certain amount of water: lower aliphatic alcohols such as methanol, ethanol, propanol, butanol, and isopropanol; and one or more chlorinated hydrocarbons. The solvent may optionally contain a certain amount of water, for example, up to about 20, 10, or 5 percent water.

[0054] A solvent essentially consisting of a specific solvent or combination of solvents (including an amount of water as needed) is a solvent containing a specific solvent or combination of solvents, and one or more different materials (e.g., solvents) in amounts of 5, 2, 1, or 0.5 weight percent or less from the specific solvent. A solvent essentially consisting of one or a combination of lower aliphatic alcohols such as methanol, ethanol, propanol, butanol, isopropanol, chlorinated hydrocarbons, or combinations thereof, including optional water, is a solvent containing one or a combination of these solvents, optional water, and any other materials in amounts of 5, 2, 1, or 0.5 weight percent or less.

[0055] Depending on the solvent, heating may be used to enable or promote the dissolution of the non-crosslinked polyamide into the solvent. For example, in the absence of heating, the non-crosslinked polyamide may take a long time or even several days to dissolve completely in the solvent as described. For example, heating the solvent to a temperature in the range of 60-80°C shortens this time. Preferably, heating allows the described non-crosslinked polyamide to dissolve completely in the solvent in a few hours (e.g., 2, 4, or 6 hours) or less (e.g., less than 40, 30, 20, or 10 minutes).

[0056] According to some embodiments of the polyamides and methods herein, a polyamide can be dissolved in a solvent to form a polymer solution which may be applied to a porous polymer filter layer by immersion precipitation, followed by a step of crosslinking the polyamide. A typical method includes one or more steps: forming or providing a polymer solution containing an uncrosslinked polyamide dissolved in a solvent (including an optional amount of water, as described herein formic acid-free and calcium chloride-free solvents) together with a free radical source material; applying the polymer solution to a porous polymer filter layer; precipitating (solidifying) the polyamide from the polymer solution onto the porous polymer filter layer; crosslinking the polyamide coated on the porous polymer filter layer; and drying the polyamide.

[0057] The process of precipitating a polymer from a polymer solution onto a filter layer, also known as immersion precipitation or phase inversion, is a generally known method for placing a polymer film on a substrate. In this technique, when applied to the polyamide and polymer solutions of this specification, a polymer solution containing polyamide may be coated onto a porous polymer filter layer, and the polyamide in the polymer solution may be precipitated from the polymer solution onto the porous polymer filter layer by contacting the polymer solution-coated filter layer with a coagulation solution containing a non-solvent such as an aqueous liquid (e.g., by immersing the coated filter layer in a coagulation bath). The polymer (i.e., non-crosslinked polyamide) precipitates from the polymer solution onto the surface of the film layer coated with the polymer solution due to the exchange of solvent and non-solvent that occurs when the polymer solution is exposed to the coagulation solution. The polymer must be soluble in the solvent of the polymer solution and must precipitate or coagulate upon contact with the non-solvent of the coagulation solution (e.g., an aqueous liquid).

[0058] The polymer solution contains any effective amount of solvent, dissolved polyamide, and free radical source material. An exemplary polymer solution may contain, up to about 10 or 20, e.g., 0.5 to 8 or 0.5 to 5 or 3 weight percent of polyamide, up to about 5, e.g., 0.5 to 6 or 1 to 5 weight percent of free radical source material, with the remainder being the solvent (e.g., an organic solvent as described herein, combined with an optional amount of water).

[0059] Exemplary polymer solutions do not require, and may omit, acidic solvents such as formic acid and ionic solvents such as calcium chloride. Preferred solvents may be propanol containing optional water, but other non-acidic, non-basic, and non-ionic solvents, including the exemplary solvents described herein, may be used alone or in combination with propanol.

[0060] A polymer solution may contain, be composed of, or be essentially composed of polyamide, free radical source material, and solvent (e.g., those described and illustrated herein). A polymer solution essentially composed of polyamide, free radical source material, and solvent (e.g., those described and illustrated herein) refers to a polymer solution containing at least 95, 98, 99, or 99.5 weight percent of polyamide, free radical source material, and solvent (e.g., those described and illustrated herein), as well as any other material in amounts of 0.5, 1, 2, or 5 weight percent or less.

[0061] After the polyamide has precipitated on the surface of the filter layer, the polyamide may be crosslinked to increase its solvent resistance. The crosslinked polyamide is one in which the polymer chains of the polyamide composition (e.g., coated and precipitated polyamide) are chemically crosslinked with each other; thus, at least one polyamide chain is crosslinked (chemically bonded) with at least one other polyamide chain at at least one position, where optionally, a single polyamide chain and multiple bonds exist between one, two or more other polyamide chains.

[0062] Crosslinking can be induced by any useful mechanism, a preferred method being exposure of the coated polyamide material to a free radical source material and a radiation source such as ultraviolet (UV) radiation. Useful examples of free radical source materials are well known and include photoinitiators such as benzoin, benzoin ethyl ether, benzophenone, benzophenone derivatives, diarykoxyacetophelnones such as Michler ketone, alpha-hydroxyketone, benzyl dimethyl ketal, isopropylthioxanthanum, diethoxyacetophenone, substituted benzoins such as acetophenone, benzyl, peroxides and other derivatives (substituted forms), and mixtures thereof. A preferred example of a free radical source material is benzophenone. This or another free radical source material may be used in combination.

[0063] Optionally, if desired, the polymer solution may contain one or more additional polyfunctional compounds, such as polyfunctional compounds, that increase the level of crosslinking between the polyamide chains of the polymer solution. Crosslinking agents are not required, and exemplary polymer solutions do not require the presence of polyfunctional crosslinking agents in addition to the polyamide polymer, and may be omitted.

[0064] The method used to induce crosslinking of polyamides may be any method useful in producing crosslinked polyamides with increased solvent resistance compared to uncrosslinked polyamides. Methods other than the use of UV radiation and free radical sources, such as the use of e-beam radiation, may be useful.

[0065] The described crosslinked polymers, which are coated onto a porous polymer filter as part of a coated filter film, can be characterized with respect to the dye-binding ability of the crosslinked polymer. In particular, charged dyes may be bound to the surface of the crosslinked polymer. The amount of dye that can be bound to the crosslinked polymer may be quantitatively measured by spectroscopy based on the difference in the measured film absorption readings at the dye absorption frequency obtained before and after coating with the crosslinked polyamide. The dye-binding ability may be evaluated using negatively charged dyes or positively charged dyes.

[0066] In some embodiments, a filter film coated with a crosslinked polyamide may have a greater dye-binding capacity for positively charged dyes, negatively charged dyes, or both, when evaluated using the same exercise or test conditions, than equivalent filters made from or coated with certain previously used polyamides, such as nylon 6 or nylon 66. The described coated filter film may have a dye-binding capacity for methylene blue dye at a rate of at least 0.2 micrograms (μg / mg) per milligram of filter film, for example, 0.5 or 1.0 μg / mg; alternatively or further, the described coated filter film may have a dye-binding capacity for Ponceau S dye at a rate of at least 0.2 micrograms (μg / mg) per milligram of filter film, for example, 0.05, 0.25, 0.5 or 0.6 μg / mg.

[0067] In some embodiments, a filter membrane coated with the crosslinked polyamide disclosed herein has a diameter of 47 mm and a thickness of 55 microns. When the sample is immersed in 15 ml of 0.1 N HCl solution (hydrochloric acid) for 24 hours, the amount of magnesium (Mg) extracted is 1.0 ng / cm³. 2 (nanograms / square centimeter), 0.9 ng / cm 2 , 0.8 ng / cm 2 , 0.7 ng / cm 2 , 0.6 ng / cm 2 , 0.5 ng / cm2 or 0.4 ng / cm 2 It contains less than [amount]. The amount of Mg is measured by inductively coupled plasma mass spectrometry (ICP-MS). The crosslinked polyamide film coating on the porous polymer filter may optionally be treated, for example, by plasma treatment, to enhance its filtering properties.

[0068] As part of the desired coating properties of the polyamide, the crosslinked and dried polyamide film coating should not unacceptably close the pores of the porous film layer, for example, it should not cause an unacceptable change in the flow properties of the porous polymer filter layer of the coated filter membrane. The flow rate and velocity of the liquid passing through the coated film membrane (i.e., the porous polymer film coating after the polyamide film coating has been placed on the porous polymer film layer) should be sufficient and acceptable for the coated film membrane to function as a commercial filter membrane. In a preferred example of a method that can provide the coating described, the polyamide may be coated onto the porous polymer filter layer by applying a polymer solution containing (non-crosslinked) polyamide dissolved in a solvent onto the surface of the porous polymer filter layer, thereby allowing the (non-crosslinked) polyamide to precipitate (solidify) from the polymer solution onto the surface of the filter layer. The precipitated (non-crosslinked) polyamide covers the surface of the porous polymer filter layer in an amount that allows the coated polyamide to function effectively as a non-sieve filter material without significantly blocking the openings of the porous filter membrane after crosslinking and drying, i.e., without reducing the flow through the membrane by more than 30, 20, 10, or 5 percent (based on flow velocity, or as a 5, 10, 20, or 30 percent increase in flow time).

[0069] The filter membranes, or filters or filter components containing filter membranes, described herein may be useful in methods for filtering liquid chemical materials to purify or remove unwanted substances from them, particularly in industrial processes requiring the input of chemical materials of extremely high purity, to produce extremely pure liquid chemical materials. Generally, the liquid chemical material may be any of the various useful commercial materials, or any liquid chemical material useful or used for any industrial or commercial application. Specific examples of the filters described herein may be used to filter liquid solvents or other processing solutions used in semiconductor or microelectronics fabrication applications, or to purify useful liquid chemical materials, for example, in semiconductor photolithography methods. Some specific, non-limiting examples of solvents that may be filtered using the described filter membranes include n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethyl acetate (2EEA), xylene, cyclohexanone, ethyl lactate, methyl isobutylcarbinol (MIBC), methyl isobutyl ketone (MIBK), isoamyl acetate, undecane, propylene glycol methyl ether (PGME), and propylene glycol monomethyl ether acetate (PGMEA).

[0070] For usefulness in filtering liquid chemical materials, such as solvents, the described cross-linked polyamides must be resistant to the liquid chemical material being filtered, for example, substantially resistant to degradation in the presence of these liquids. Preferred cross-linked polyamide materials are resistant to the liquid chemical material being filtered (e.g., solvent or acid) and are effective in processing liquid chemical materials by filtration to produce liquid chemical materials with extremely low levels of impurities such as dissolved metals and extremely low levels of suspended particles or other impurities or contaminants.

[0071] The coated filter membrane may be contained within a larger filter structure, such as a filter or filter cartridge used in a filtering system. The filtering system, for example, places the coated filter membrane as part of a filter or filter cartridge in a flow path for a liquid chemical material, allowing the coated filter membrane to flow through the liquid chemical material so that it can remove impurities and contaminants. The filter or filter cartridge structure may include one or more additional materials and structures that support the coated filter membrane within the filter, allowing the fluid to flow from the filter inlet through the coated membrane to the filter outlet, thereby passing through the coated filter membrane as it passes through the filter. The coated filter membrane supported by the filter structure may be in any useful shape, such as a pleated cylinder, a cylindrical pad, one or more unpleated (flat) cylindrical sheets, or a pleated sheet.

[0072] An example of a filter structure including a coated filter membrane in the form of a pleated cylinder can be prepared to include the following components, all of which may but may not be included in the filter structure: a rigid or semi-rigid core supporting the pleated cylindrical coated filter membrane at the internal opening of the pleated cylindrical coated filter membrane; a rigid or semi-rigid cage supporting or enclosing the exterior of the pleated cylindrical coated filter membrane outside the filter membrane; optional tipping or "packs" located at each of the two opposing ends of the pleated cylindrical coated filter membrane; and a filter housing including an inlet and an outlet. The filter housing may be of any useful desired size, shape and material, and may preferably be made from a suitable polymer material. [Examples]

[0073] Porosimetry Bubble Point Porosimetry and bubble point testing measure the pressure required to force air through the moist pores of a membrane. Bubble point testing is a well-known method for determining the pore size of a membrane.

[0074] Flow velocity measurement The flow rate of isopropanol (IPA) was determined by cutting the membrane into 47 mm discs, moistening them with IPA, and then placing the discs in a filter holder equipped with a reservoir to hold the volume of IPA. The reservoir was connected to a pressure regulator. IPA was flowed through the membrane under a differential pressure of 14.2 psi (pounds per square inch). After equilibrium was achieved, the time required for 10 ml of IPA to flow through the membrane was recorded.

[0075] Example 1 This example describes the preparation of a 14 wt% polyamide stock solution. In a round-bottom flask equipped with a stirring bar and condenser, 14 grams of Ultramid1C (BASF) resin were added to a mixture of 1-propanol (Sigma) / DI water in 86 g of water. The mixture was prepared by mixing 20 ml of DI water with 80 ml of 1-propanol. The mixture was heated under reflux for 10 hours until all the resin was dissolved. The resulting solution was clear and contained no undissolved solids.

[0076] Example 2 This example describes the preparation of a polyamide coating solution.

[0077] A solution was prepared containing 2 g of benzophenone (Sigma), 28.57 g of the stock solution prepared in Example 1, and 69.43 g of a propanol:water mixture (80:20 Vol%). After mixing for 30 minutes, the benzophenone was completely dissolved.

[0078] Example 3 This embodiment demonstrates the coating of a UPE film with polyamide.

[0079] A 47 mm UPE disc (average HFE bubble point 99 psi) was moistened with the coating solution described in Example 2 for 10 seconds. The disc was removed and placed between 1 mil polyethylene sheets. A rubber roller was rolled over the polyethylene / disc / polyethylene sandwich laid flat on a table to remove excess solution. The UPE film was removed from the sandwich and immediately placed in deionized (DI) water, swirled for 2 minutes to wash and allow the coating solution to settle on the surface of the porous disc. The disc was removed and again placed between 1 mil polyethylene sheets. A rubber roller was rolled over the polyethylene / disc / polyethylene sandwich laid flat on a table to remove excess water. The polyethylene sandwich was then secured to a transport device with tape, and the device transported the assembly into a Fusion Systems broadband UV exposure apparatus emitting wavelengths from 200 nm to 600 nm. The exposure time was controlled by the speed at which the assembly moved through the UV apparatus. In this example, the assembly moved through the UV chamber at 8 feet per minute. After exiting the UV apparatus, the film was removed from the sandwich and immediately placed in a 60 wt% isopropanol solution containing 2.5 wt% HCl, and washed by swirling for 12 hours. The coated film disc was then washed again by swirling in a 100% isopropanol solution for another hour. Following this washing procedure, the film was dried on a holder in an oven operating at 50°C for 10 minutes.

[0080] The average flow rate of isopropanol in the six coated membrane disc samples was 5.1 ml / min. The average flow rate in the three uncoated membrane samples tested was 6.2 ml / min. The average HFE bubble point in the six coated membrane disc samples was 96 psi.

[0081] Example 4 This example demonstrates the methylene blue dye binding ability of a UPE disc prepared in the manner described in Example 3. This example further demonstrates that, when carried out using the coating solution of Example 2, the process of Example 3 yields a UPE film capable of binding to a positively charged dye.

[0082] Three water-moistened 47 mm coated disc membranes from Example 3 were placed in a beaker containing 50 ml of 0.00075 wt% methylene blue dye (Sigma) adjusted to pH 10 with 10 M sodium hydroxide. The beaker was covered, and the coated membrane discs were immersed for 2 hours with continuous mixing at room temperature. The discs were then removed, and the absorbance of the dye solution was measured using a Cary spectrophotometer (Agilent Technologies) operating at 664 nm. The membranes were rinsed with water and immersed in 50 ml of 100% isopropanol for 30 minutes. This step desorbs all dye molecules that have nonspecifically bound to the membrane surface. Nonspecific adsorption refers to dye molecules that do not bind to the coated membrane surface by electrostatic interactions. The membrane discs were then removed, and the absorbance of the isopropanol solution was measured using a Cary spectrophotometer (Agilent Technologies) operating at 656 nm.

[0083] Using the slopes of the calibration curves shown in Figures 1 and 2, absorbance data of the dye solution before and after immersion of the film, and absorbance data of the isopropanol solution, were converted to the mass of methylene blue dye bound to the film per unit mass of film. The dye was cationic and bound to the negatively charged groups imparted to the film by the polyamide coating with an average dye-binding capacity of 1.4 μg / mg. In contrast, the average dye-binding capacity of the uncoated UPE film was 0.1 μg / mg under similar experimental conditions.

[0084] Example 5 This example demonstrates the Ponceau S dye binding ability of a UPE disc prepared in the manner described in Example 3. This example further demonstrates that, when carried out using the coating solution of Example 2, the process of Example 3 yields a UPE film capable of binding to negatively charged dyes.

[0085] Three water-moistened 47 mm coated disc membranes from Example 3 were placed in a beaker containing 50 ml of 0.002 wt% Ponceau S dye (Sigma) solution. The beaker was covered, and the coated membrane discs were immersed for 2 hours with continuous mixing at room temperature. The discs were then removed, and the absorbance of the dye solution was measured using a Cary spectrophotometer (Agilent Technologies) operating at 518 nm. The membranes were rinsed with water and immersed in 50 ml of 100% isopropanol for 30 minutes. This step desorbed all dye molecules nonspecifically bound to the membrane surface. The membrane discs were then removed, and the absorbance of the isopropanol solution was measured using a Cary spectrophotometer (Agilent Technologies) operating at 501 nm.

[0086] Using the slopes of the calibration curves shown in Figures 3 and 4, absorbance data of the dye solution before and after immersion of the film, and absorbance data of the isopropanol solution, were converted to the mass of dye bound to the film per unit mass of film. The dye was anionic and bound to the positively charged groups imparted to the film by the polyamide coating with an average dye-binding capacity of 0.75 μg / mg. In contrast, the average dye-binding capacity of the uncoated UPE film was 0.05 μg / mg under similar experimental conditions.

[0087] Example 6 This example demonstrates the ability of nylon 6,6 membranes to bind methylene blue and Ponceau S dyes.

[0088] A single water-moistened 47 mm section of a nylon 6,6 membrane with an average HFE bubble point greater than 100 psi was immersed in 50 ml of either methylene blue or Ponceau S dye solution as described in Examples 4 and 5. The membrane bound to methylene blue with an average dye-binding capacity of 5.4 μg / mg and to Ponceau S with an average dye-binding capacity of 4.3 μg / mg.

[0089] Example 7 This example demonstrates the ability of nylon 6 membranes to bind methylene blue and Ponceau S dyes.

[0090] A single water-moistened 47 mm section of a nylon 6 membrane with an average HFE bubble point of 62 psi was immersed in 50 ml of either methylene blue or Ponceau S dye solution as described in Examples 4 and 5. The membrane bound to methylene blue with an average dye-binding capacity of 1.4 μg / mg and to Ponceau S with an average dye-binding capacity of 10.7 μg / mg.

[0091] Example 8 This embodiment demonstrates that polyamide-coated UPE membranes are cleaner than nylon 6 membranes with respect to metals extractable in low pH solutions.

[0092] A 47 mm disc of nylon 6 film and a 47 mm disc of the film prepared in Example 3 were extracted with 0.1 N HCl. The amount of extracted metal was quantified using ICP-MS. As shown in Figure 5, 40 ng / cm² of Mg was extracted from the nylon 6 film compared to 0.4 ng / cm² from the polyamide-coated UPE film. The total metal extracted from nylon 6 and the polyamide-coated UPE film was 90 ng / cm² and 33 ng / cm², respectively.

[0093] Example 9 This embodiment demonstrates that polyamide-coated UPE films are stable in low-pH organic solvents.

[0094] UPE-coated polyamide film samples were immersed in a 60 wt% isopropanol solution containing 3.5 wt% HCl for 9 days. The amount of polyamide on the film surface at time 0 and after immersion in the low pH organic solvent was determined in the form of peak ratios by ATR-FTIR ("ATR") spectroscopy. ATR measurements were performed using a Bruker Tensor27FTIR equipped with an ATR assembly containing germanium crystals. All spectra were recorded by scanning 32 times at a resolution of 4 cm⁻¹. The background was bare crystal. Peak areas at 1713 and / or 1496 cm⁻¹ (corresponding to amide stretching) were obtained using the OPUS data acquisition program, and the sum was divided by the total peak areas at 2918 and 2850 cm⁻¹ (corresponding to UHMWPE stretching) to obtain the amount of acrylamide monomer grafted onto the UHMWPE (ultra-high molecular weight polyethylene) surface. The UHMWPE signal is used as a conventional internal standard to normalize the difference in absolute absorbance intensity of the amide peak, which may be due to variations in the modification level between membrane disks.

[0095] As shown in Figure 6, the amount of polyamide coated on the film surface did not decrease after exposure to a low pH organic solvent. This suggests that the polyamide coating is stable in photoapplications such as BARC, ITC, and SOG, which are acidic.

[0096] Example 10 This embodiment demonstrates that polyamide-coated UPE films are stable in common photoresist solvents.

[0097] UPE-coated polyamide film samples were immersed in cyclohexanone, OK73, and ArF thinner (PGMEA 45-55%, HBM 35-45%, EL 5-15%) for 5 days. The amount of polyamide on the film surface at time 0 and after 5 days of immersion in the organic solvent was determined in the form of peak ratios by ATR-FTIR ("ATR") spectroscopy, as described in Example 8. As shown in Figure 7, the amount of polyamide coated on the film surface was essentially the same before and after immersion.

[0098] Example 11 In this example, the concentration of benzophenone in the coating formulation is compared.

[0099] 47 mm sections of UPE membranes (average HFE bubble point 80 psi) were coated with polyamide using 3 wt% Ultramid1C and 0.5, 1, or 2 wt% benzophenone concentrations according to the process described in Example 3. After exiting the UV apparatus, the membrane sections were removed from the polyethylene sheet sandwich and immediately placed in a Soxhlet extractor containing 100% isopropanol. Extraction was carried out for 24 hours. The amount of polyamide on the membrane surface at time 0 and after extraction with isopropanol was determined in the form of peak ratios by ATR-FTIR ("ATR") spectroscopy, as described in Example 8. As shown in Figure 8, the amount of polyamide coated on the membrane surface decreased by approximately 45%, 12%, and 2% at 0.5, 1, and 2 wt% benzophenone concentrations, respectively.

[0100] Example 12 This embodiment demonstrates that when a lithography solution is filtered using a filtration device containing a film coated according to the process described in Example 3 (UPE, average HFE bubble point 100 psi), the resulting wafer defect count is reduced.

[0101] The filter device was filled with TOK OK73 solvent (PGME:PGMEA 70:30) and flashed with 6 liters of solvent. Lithography was performed on an ASML 1970i and TEL LITHIUS Pro-Zi track coating development system at 1.35 NA. For defect testing, a mask with only the L45P100 pattern was used with full-field exposure. For pattern defect testing, PT-CAR AIM5484 (JSR) material coated on ARC-29SR-309 (BSI) was used. Bare silicon wafers were coated with PT-CAR (AIM5484) resist on ARC (ARC-29SR-309). The wafer was exposed to the mask characteristic L45P100 pattern with full-field exposure. Patterned wafers were measured with a KLA2925 using a standard recipe. Defects were re-verified and classified using a KLA eDR-7100.

[0102] As shown in Figure 9, the polyamide-coated UPE film exhibited the lowest defect count (best performance) at 6±1, compared to 9±1 and 20±1 for nylon 6 (average HFE bubble point 60 psi) and the UPE film (average HFE bubble point 100 psi), respectively.

[0103] Example 13 Examples of solvent filtration for the removal of metal contaminants UPE membranes (average HFE bubble point 80 psi) were coated with polyamide according to the process described in Example 3 and cut into 47 mm membrane sections. These membrane sections were prepared by washing several times with 10% HCl, immersing overnight in 10% HCl, and equilibrating with deionized water. One 47 mm membrane section for each sample was fixed to a clean PFA 47 mm Single Stage Filter Assembly (Savillex). The membrane and filter assembly were flushed with IPA, followed by a coating solvent. The coating solvent was PGMEA. CONOSTAN Oil Analysis Standard S-21 (SCP Science) was spiked into the coating solvent at a target concentration of 5 ppb for each metal. To determine the metal removal efficiency of the filtration, the corresponding 47 mm filter assembly containing each filter was passed through the metal-spiked coating solvent at 10 mL / min, and the filtrate was collected in 100 mL, 150 mL, and 200 mL clean PFA jars. The metal concentrations in the metal-spiked coating solvent and each filtrate sample were determined using ICP-MS.

[0104] The results are shown in Table 10 for total metal removal (%) and in Figure 10 for the removal % of individual metals (PGMEA) in 200 mL filtration, compared to nylon 6 membranes (average HFE bubble point 62 psi, adjusted with 0.35% HCl). The polyamide-coated UPE membrane has comparable metal removal efficiency to the nylon 6 membrane. However, the polyamide-coated UPE membrane shows improved removal of individual metals, at least Al, Ti, Cr, Mn, Fe, Ni, and Sn, compared to the nylon 6 membrane. TIFF0007900476000001.tif30170

Claims

1. A porous polymer filter layer containing polyolefin, and A cross-linked polyamide film that at least partially coats the surface of a porous filter layer. A coated filter film comprising, A coated filter film having bubble points ranging from 2 psi to 400 psi, measured using HFE7200 at a temperature of 20–25°C.

2. The coated filter film according to claim 1, wherein the bubble point is in the range of 50 psi to 150 psi.

3. The coated filter film according to claim 1, characterized in that it has a dye-binding ability to at least 0.2 micrograms of methylene blue dye per milligram of coated filter film.

4. The coated filter film according to claim 1, characterized in that it has a dye-binding ability to at least 0.2 micrograms of Ponceau S dye per milligram of coated filter film.

5. From a sample of a coated filter film having a diameter of 47 mm and a thickness of 55 microns, when the sample was immersed in 15 ml of 0.1 N HCl solution for 24 hours, the extracted magnesium was 1.0 ng / cm³. ２ The coated filter film according to claim 1, characterized in having less than [amount missing].

6. The coated filter film according to any one of claims 1 to 5, wherein the polyolefin is ultra-high molecular weight polyethylene.

7. A coated filter film according to any one of claims 1 to 5, wherein the crosslinked polyamide film comprises a copolymer of polyamide 6 and polyamide 6,6.

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