Multilayer porous polymer membranes and related filters and methods

Abstract

The application relates to multilayer porous polymer membranes and related filters and methods. The present invention describes: a porous polymeric filtration membrane assembly comprising two polymeric filtration membranes in series, i.e. As part of the membrane assembly; a filter assembly and a filter product comprising two polymer filter membrane layers; methods of assembling the polymeric filtration membranes, the filter assemblies, and the filter products; and methods of using the polymer filtration membranes to remove particles from liquids, such as from semiconductor treatment liquid fluids.

Description

Technical Field

[0001] The following description relates to assemblies that include two polymer filtration membranes in series (i.e., as part of a membrane assembly); also to filter assemblies and filter products that include two polymer filtration membranes; also to methods of assembling polymer filtration membranes, filter assemblies, and filter products; and to methods of using polymer filtration membranes to remove particles from liquids such as semiconductor processing fluids. Background Art

[0002] Polymer filtration membranes are used to remove unwanted materials from fluids having a range of applications. The fluids include water, liquid industrial solvents and processing fluids, industrial gases for manufacturing or processing, and liquids having medical or pharmaceutical uses. Contaminants and impurities removed from the fluids include particulate contaminants, microorganisms, and dissolved chemical substances such as ionic species.

[0003] Two or more types of filtration membranes can be used together to remove different types of contaminants or impurities from a single liquid. A particular type of filtration membrane removes contaminants from a liquid via a sieving mechanism, by which contaminant particles larger than the pores of the membrane are mechanically prevented from passing through the membrane and are trapped within the membrane and cannot pass through the membrane. Other membranes act via non-sieving mechanisms, by which impurities smaller than the pores of the membrane are attracted to the membrane surface via chemical or electrostatic interactions and are retained within the membrane and do not escape from the membrane. By combining non-sieving membranes with sieving membranes, larger and smaller contaminants can be removed from liquids containing particles of different sizes.

[0004] Removing contaminants from liquids using filters is particularly important in the semiconductor processing industry, in which even the smallest impurities (sometimes in the nanoscale size range) can create defects in microelectronic devices. This is also true for many of the fluids used during semiconductor and microelectronic processing, one example being the photoresist solution used in lithography.

[0005] In a lithographic process, a photosensitive (or radiation-sensitive) photoresist solution is used to form a patterned coating on a surface. The photoresist solution is coated as a thin layer onto the surface of a substrate and a patterned mask is used to cover a portion of the coated surface. The unmasked areas of the photoresist solution are exposed to light. Then a solvent called a developer is applied to the surface of the photoresist solution. For a "positive photoresist", the portions of the photoresist that are exposed to light are degraded by the light and the developer dissolves the areas of the photoresist coating that were exposed to light, leaving a patterned coating where the mask was placed. For a "negative photoresist", the portions of the photoresist that are exposed to light are strengthened (polymerized or crosslinked) by the light, and the developer will only dissolve the unexposed, masked areas of the photoresist and leave a patterned coating in the areas not covered by the mask.

[0006] Conventional photoresist solutions can contain three different components: a polymer resin (a binder that provides physical properties such as adhesion, chemical resistance, etc.), a sensitizer (which has a photoactive compound), and a solvent. Unfortunately, the photoresist solution will also contain a certain amount of unwanted contaminant particles, which can be located on the surface of a semiconductor substrate and can create defects at the surface during subsequent processing. The contaminants can be particles or suspended or dissolved chemicals, and can have a range of sizes, including particles of nanoscale size.

[0007] The semiconductor manufacturing industry continues to require continuously improved filtration technologies, including effectively removing a high percentage of different types and sizes of contaminants from liquids such as photoresist solutions. SUMMARY OF THE INVENTION

[0008] Described below are filter assemblies, products, and methods using a first polymeric filter membrane referred to as an "open" membrane and a second polymeric filter membrane referred to as a "tight" membrane. The first (open) polymeric filter membrane has an average relatively large pore size and a lower bubble point compared to the second polymeric filter membrane, which has relatively smaller pores and a higher bubble point. The first or "open" polymeric filter membrane also has a relatively larger thickness compared to the smaller thickness of the second or "tight" polymeric filter membrane.

[0009] The polymeric filter membranes are used to remove contaminants from a liquid stream passing through the membranes, for example by first passing the liquid through the first (open) polymeric filter membrane and then through the second (tight) polymeric filter membrane.

[0010] According to an exemplary method and membrane, and without limiting the present description, the first (open) polymeric filtration membrane can be a polyolefin membrane prepared by a phase inversion technique, and the second (tight) polymeric filtration membrane can be a polyolefin membrane prepared by a stretching technique. Generally, the phase inversion polyolefin filtration membrane has a greater thickness and a more complex microporous structure than the stretched polyolefin filtration membrane, and the phase inversion polyolefin filtration membrane can exhibit retention ability and a greater retention capacity for a relatively wide range of different sized particles.

[0011] It is difficult to fabricate a polymeric filtration membrane with a smaller pore size without causing a significant loss in the flow rate of the membrane. The stretched polyolefin filtration membrane can be very thin (e.g., having a thickness of less than 10 microns while also having a relatively small pore size) and can achieve a useful combination of a very tight (small) pore size and a good flow rate. However, the thinner stretched membrane has a smaller retention capacity because there is limited effective surface area and less space within the thinner membrane.

[0012] According to the examples described herein, a first (open) polymeric filtration membrane that can be prepared by a phase inversion method and a second (tight) polymeric filtration membrane that can be prepared by a stretching method can be used in series to remove contaminants from a liquid. The open polymeric filtration membrane can remove relatively large sized contaminants from a liquid containing both larger and smaller sized contaminants. The tight polymeric filtration membrane can remove relatively smaller sized particles or dissolved contaminants that can pass through the first (upstream) polymeric filtration membrane. The combination of the two polymeric filtration membranes effectively removes different types and sizes of contaminants from the liquid passing through the first and second polymeric filtration membranes, including particulate contaminants that can be relatively large in size and dissolved or suspended chemical molecules that can be relatively small in size.

[0013] In one aspect, the present description relates to a method of filtering a semiconductor processing liquid. The method includes: passing the liquid through a first polymeric filtration membrane having an average bubble point of less than 120 pounds per square inch as measured using ethoxy-nonafluorobutane (HFE7200) and a thickness of at least 20 microns; and passing the liquid through a second polymeric filtration membrane having an average bubble point of greater than 120 pounds per square inch as measured using ethoxy-nonafluorobutane (HFE7200) and a thickness of less than 20 microns.

[0014] According to another aspect, the present description relates to a filter product for removing contaminants from a semiconductor processing fluid. The filter product comprises: a first polymeric filter membrane having an average bubble point of less than 120 pounds per square inch, as measured using ethoxy-nonafluorobutane (HFE7200), and a thickness of at least 20 microns; and a second polymeric filter membrane having an average bubble point of greater than 120 pounds per square inch, as measured using ethoxy-nonafluorobutane (HFE7200), and a thickness of less than 20 microns. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An example of an assembly showing a first (open) polymeric filter membrane and a second (tight) polymeric filter membrane in series is shown.

[0016] Figure 2 An example of a filter product showing a first (open) polymeric filter membrane and a second (tight) polymeric filter membrane is shown.

[0017] Figure 3 An example of a filter product showing a first (open) polymeric filter membrane and a second (tight) polymeric filter membrane contained within a filter housing is shown.

[0018] Figure 4 And 5 Retention rate data showing the described polymeric filter membrane assembly and a comparative polymeric filter membrane are shown.

[0019] The figures are schematic and not necessarily drawn to scale. DETAILED DESCRIPTION

[0020] Described below are: polymeric filter membranes (or more simply "membranes", "filter membranes", etc., as used herein); assemblies containing two or more polymeric filter membranes including a "first" (or "open") polymeric filter membrane and a "second" (or "tight") polymeric filter membrane; filter products containing a first polymeric filter membrane and a second polymeric filter membrane; and related methods of using polymeric filter membrane assemblies and filter products, particularly methods for removing contaminants from semiconductor processing liquids. Herein, the first polymeric filter membrane is sometimes referred to as the "first membrane" or "open membrane", and the second polymeric filter membrane is sometimes referred to as the "second membrane" or "tight membrane".

[0021] The described filter product and filtration method use an arrangement of two different polymeric filter membranes, i.e., at least two different "membranes" or "membrane layers" arranged in series to perform the filtration step. This arrangement may sometimes be referred to as a "stacked" arrangement or a "multilayer membrane assembly", which includes two different polymeric filter membranes and may optionally include additional filter membranes or support layers. The polymeric filter membranes may be assembled into a laminated composite membrane, where the first polymeric filter membrane is joined to the second polymeric filter membrane by lamination (without using a separate adhesive), or the polymeric filter membranes may be unattached, i.e., non-laminated.

[0022] The first polymeric filter membrane or "open membrane" is adapted to remove relatively large-sized contaminants from a liquid containing contaminants in a relatively large and small size range. The open membrane has pores with a relatively large pore size compared to the smaller pores of the tight membrane. The tight membrane may have pores with a relatively small size and a relatively small thickness compared to the larger thickness of the open membrane. The combination of the two polymeric filter membranes effectively removes different types of particles from the liquid passing through both the first polymeric filter membrane and the second polymeric filter membrane, including relatively large-sized particulate contaminants and relatively small-sized dissolved or suspended chemical molecules. The tight membrane is adapted to remove and collect relatively small-sized particles or dissolved contaminants that can pass through the open membrane.

[0023] According to an exemplary method and filter assembly, a liquid may be caused to first flow through the open membrane having a larger thickness and larger pores, and then flow through the tight membrane having a smaller thickness and smaller pores. An assembly comprising a combination of an open upstream polymeric filter membrane and a tight downstream polymeric filter membrane can be used to remove a range of different-sized contaminants from a liquid. Desirably, compared to the amount of contaminants removed by filtering the liquid using only the tight membrane and the amount of contaminants removed by filtering the liquid using only the open membrane, the assembly comprising both the open membrane and the tight membrane can effectively remove a greater amount (higher percentage) of contaminants (e.g., contaminants of a specific size) from the liquid. The performance of the polymeric filter membrane in removing contaminants of a specific size can be measured in terms of "retention rate" and can be evaluated by a retention rate test of removing standard particles (or "test particles") from a sample liquid having a known particle concentration under controlled conditions.

[0024] According to certain specific membrane assemblies and methods, a membrane assembly comprising at least one open membrane and at least one tight membrane can be used to remove contaminants of various sizes from a liquid containing contaminants. The liquid can be any type of liquid that is significantly purer but contains contaminants of a certain range of sizes that are desired to be filtered. Examples of such liquids include various types of liquids used in the processing of semiconductor or microelectronic devices, which are referred to herein as "semiconductor processing fluids". Semiconductor processing fluids include liquids that are used as or contain one or more of the following: water or organic solvents such as isopropyl alcohol (and many other organic and inorganic chemicals, including organic solvents and organic or inorganic acids and bases, see below); reaction materials such as reaction monomers, oligomers or polymers, including but not limited to the types used in photosensitive materials such as photoresist solutions; cleaning solutions; acids or bases; and others. A specific example of a semiconductor processing fluid is a "photoresist solution" that contains a polymer resin, a sensitizer (which has a photoactive compound), and a solvent.

[0025] Each of the open polymer membrane and the tight polymer membrane has two opposing surfaces or opposing "sides" and a membrane thickness between the two opposing surfaces. The pores of the polymer filtration membrane are located throughout the thickness of the membrane to allow liquid to flow through the thickness of the membrane from one side of the membrane to and through the opposite side of the membrane. This type of membrane is sometimes referred to as an "open pore" membrane.

[0026] The open pore membrane can be in the form of a thin film or sheet of a porous polymer material having a relatively uniform thickness and an open pore structure that includes a polymer matrix defining a large number of open "units" or "pores". The open units can be referred to as openings, pores, channels or passageways, which are mostly interconnected between adjacent units to allow fluid to flow through the thickness of the membrane from one side of the membrane to the other side. The passageways can provide tortuous tunnels or paths through which the liquid to be filtered must pass. Contaminants in the liquid passing through the polymer filtration membrane in the form of particles or dissolved or suspended molecular chemicals are trapped by the membrane or are trapped within the membrane based on size (i.e., "screening" mechanism) or based on chemical or electrostatic attraction between the membrane surface and the contaminants (i.e., "non-screening" mechanism).

[0027] The polymeric filtration membrane can be made of a polymeric material or combination of polymeric materials known to be useful for making open-porous membranes and can be described in terms of physical properties such as, for example, thickness, morphology, pore size, porosity, etc. Examples of useful polymeric materials include polyolefins such as polyethylene (PE) (which includes polyethylene of various molecular weights such as ultra-high molecular weight polyethylene (UPE) and includes homopolymers, copolymers, and mixtures), and polypropylene (PP) (which also includes its copolymers and mixtures). Other polymers useful for forming the polymeric filtration membrane include polyethers such as polyetheretherketone (PEEK), polysulfone, polyamide (e.g., nylon), fluoropolymers (including fluorinated and perfluorinated polymers), polyesters (e.g., polyethylene terephthalate), and other types of polymers and copolymers known to be useful for preparing polymeric filtration membranes.

[0028] The term "polyethylene" refers to a polymer having a linear molecular structure that is partially or substantially composed of repeating -CH2-CH2- units. Polyethylene can be made by reacting a monomer composition containing monomers, including ethylene monomers, consisting of or substantially consisting of ethylene monomers. Thus, a polyethylene polymer can be a polyethylene homopolymer prepared by reacting monomers consisting of or substantially consisting of ethylene monomers. Alternatively, a polyethylene polymer can be a polyethylene copolymer prepared by reacting a combination of ethylene and non-ethylene monomers, the combination of ethylene and non-ethylene monomers including ethylene monomers and one or more additional types of monomers (e.g., another α-olefin monomer such as an alkene such as butene, hexene, or octene or combinations thereof), consisting of or substantially consisting of ethylene monomers and one or more additional types of monomers. For a polyethylene copolymer, the amount of ethylene monomers used to produce the copolymer relative to the non-ethylene monomers can be any useful amount, such as an amount of ethylene monomers of at least 50, 60, 70, 80, or 90 (weight)% of the total weight of all monomers (ethylene monomers and non-ethylene monomers) in the monomer composition used to prepare the ethylene copolymer.

[0029] The term "polypropylene" refers to a polymer having a molecular structure that is partially or substantially composed of repeating -CH-CH(CH3)- units. Polypropylene can be made by reacting a monomer composition containing monomers, said monomers including propylene monomers, consisting of or substantially consisting of propylene monomers. Thus, a polypropylene polymer can be a polypropylene homopolymer prepared by reacting monomers consisting of or substantially consisting of propylene monomers. Alternatively, a polypropylene polymer can be a polypropylene copolymer prepared by reacting a combination of propylene and non-propylene monomers, said combination of propylene and non-propylene monomers containing propylene monomers and one or more additional types of monomers (e.g., another α-olefin monomer, such as an alkene, such as ethylene, butene, hexene, or octane, or a combination thereof), consisting of or substantially consisting of propylene monomers and one or more additional types of monomers. For a polypropylene copolymer, the amount of propylene monomers used to produce the copolymer relative to the non-propylene monomers can be any useful amount, such as an amount of propylene monomers that is at least 50, 60, 70, 80, or 90 (weight)% of the total weight of all monomers (propylene monomers and non-propylene monomers) in the monomer composition used to prepare the propylene copolymer.

[0030] As used herein, a composition (e.g., a polymer composition) described as "substantially consisting of" a particular ingredient or a combination of specified ingredients is a composition that contains said ingredient or combination of specified ingredients and no more than a small or insignificant amount of other materials (e.g., no more than 3, 2, 1, 0.5, 0.1, or 0.05 weight% of any other ingredient or combination of ingredients).

[0031] For example, a polymer prepared from a monomer "substantially consisting of" an olefin, ethylene, or propylene monomer is a polymer prepared from an olefin monomer, ethylene monomer, or propylene monomer, respectively, and no more than a small or insignificant amount of other monomer materials (e.g., no more than 3, 2, 1, 0.5, 0.1, or 0.05 weight% of any other monomer).

[0032] As another example, a polymer composition or polymer film described as "substantially consisting of" a polyolefin, polyethylene, or polypropylene is a polymer composition or polymer film that contains, respectively, a polyolefin (including copolymers), polyethylene (including copolymers), or polypropylene (including copolymers) and no more than a small or insignificant amount of different types of polymers (e.g., no more than 3, 2, 1, 0.5, 0.1, or 0.05 weight% of any other type of polymer).

[0033] An exemplary assembly of polymer filtration membranes can include two polymer filtration membranes arranged in series to allow a liquid to first flow through a first (upstream) polymer filtration membrane described as an open membrane and then through a second (downstream) polymer filtration membrane described as a tight membrane. The first (open) polymer filtration membrane is relatively thick compared to the second (tight) polymer filtration membrane and has pores of relatively larger size compared to the second polymer filtration membrane.

[0034] The first (open) polymer filtration membrane can be made of any useful polymer, such as polyolefins (e.g., polypropylene, polyethylene, or copolymers thereof), polyetheretherketone (PEEK), polysulfone, polyamide (e.g., nylon), fluoropolymers (including fluorinated and perfluorinated polymers), polyesters (e.g., polyethylene terephthalate), and other types of polymers and copolymers that can form an open polymer filtration membrane. According to the exemplary membrane assembly, the first polymer filtration membrane can have a relatively greater thickness compared to the second membrane, a relatively greater pore size (average) compared to the second polymer filtration membrane, a relatively higher measured "flow time" compared to the second polymer filtration membrane, and a lower bubble point compared to the second polymer filtration membrane.

[0035] The first polymer filtration membrane can be a type of open cast membrane that can be used as a polymer filtration membrane (e.g., a polymer filtration membrane that can be used to remove contaminants from semiconductor processing liquids). The first polymer filtration membrane has several physical properties (e.g., pore size, porosity, and bubble point) and filtration properties (e.g., retention rate and flow time or flow rate) that allow the first polymer filtration membrane to be used alone as a polymer filtration membrane to remove unwanted contaminants from a liquid stream or to be used in combination with a second (tight) polymer filtration membrane as part of a filtration membrane assembly.

[0036] Useful first polymer filtration membranes can be of the types sometimes described as ultraporous membranes, nanoporous membranes, microporous membranes, etc. These polymer filtration membranes typically effectively remove undesirable contaminants (e.g., particulate materials or dissolved chemical substances or both) from a liquid stream. A useful average pore size can be selected based on one or more factors including: fluid flow rate, pressure, pressure drop considerations, viscosity considerations, the quantity and type of contaminants in the liquid to be filtered (e.g., dissolved metal ions or particulate contaminants in the liquid). Examples of useful first polymer filtration membranes include various membranes that are commercially available and known to be useful in microfiltration applications, including polymer filtration membranes considered to be microporous, ultraporous or nanoporous. Exemplary first polymer filtration membranes can have an average pore size in the range from about 0.001 microns to about 5 microns or 10 microns (1 nanometer to about 5,000 nanometers or 10,000 nanometers (nm)), e.g., from 0.01 microns to 0.8 microns (from 10 nanometers to 800 nanometers).

[0037] Useful or preferred first polymer filtration membranes can be considered to have a relatively uniform pore size and a degree of pore symmetry, or can have a relatively non-uniform pore size and a degree of pore asymmetry. The polymer filtration membranes can be isotropic or anisotropic (in terms of pore size), symmetric or asymmetric, "skinned" or "unskinned", or combinations thereof. Polymer filtration membranes having pores of substantially uniform size that are uniformly distributed throughout the membrane thickness are typically referred to as "isotropic" or "homogeneous". In contrast, anisotropic (also referred to as "asymmetric") membranes can be considered to have a morphology in which there is a pore size gradient across the membrane. For example, an anisotropic or asymmetric membrane can have a porous structure that has relatively large pores on one membrane surface and relatively small pores on the other membrane surface, where the pore structure varies along the thickness of the membrane. The term "asymmetric" is typically used interchangeably with the term "anisotropic".

[0038] The first polymer filtration membrane can be in the form of a sheet having a relatively uniform thickness (e.g., a thickness in the range from 20 microns to 300 microns, e.g., from 30 microns or 50 microns to 150 microns, 200 microns or 250 microns).

[0039] The first polymer filtration membrane can have any porosity that will allow the polymer filtration membrane to be effective as described herein. Exemplary first polymer filtration membranes can have a relatively high porosity, for example, a porosity in the range from 40% to 80%. As used herein, the "porosity" (sometimes also referred to as void fraction) of a polymer filtration membrane is a measure of the percentage of void (i.e., "empty") space in the polymer filtration membrane that occupies the total volume of the polymer filtration membrane, and is calculated as the fraction of the void volume of the polymer filtration membrane to the total volume of the polymer filtration membrane. A body with zero percent porosity is completely solid.

[0040] Examples of polymer filtration membranes that can be used as the first polymer filtration membrane and have the described physical properties include polyolefin (e.g., polyethylene and polypropylene) membranes prepared by known methods, which include melt casting and phase inversion methods, where specific examples include thermally induced phase separation methods (TIPS), solvent evaporation induced phase separation (SEIPS), and nonsolvent induced phase separation.

[0041] The first polymer filtration membrane can be treated or coated by adding ionic groups (cationic or anionic groups) to the surface of the polymer filtration membrane to improve the removal of dissolved or suspended contaminants in a liquid by a non-sieving filtration mechanism.

[0042] The bubble point is a known property of a polymer filtration membrane and is related to the pore size of the polymer filtration membrane. A relatively high bubble point indicates that the pores of the polymer filtration membrane are relatively small and a relatively low bubble point indicates that the pore size of the polymer filtration membrane is relatively large. The bubble point measurement is based on the premise that for a specific fluid and pore size, with the polymer filtration membrane continuously wetted, the pressure required to force a bubble through the pores of the polymer filtration membrane is inversely proportional to the size of the pores. The porosity method bubble point test method measures the pressure required to push a gas (e.g., air) through the wet pores of the membrane. The bubble point test is a well-known method for determining or estimating the pore size of a membrane. Examples of useful average bubble points of the first polymer filtration membrane as described, measured using the test method described herein (using ethoxy-nonafluorobutane (HFE-7200) as the wetting solvent and a temperature of 22 °C), can be less than 130 psi, for example, in the range from 50 psi or 60 psi to 110 psi or 120 psi.

[0043] In combination with a desired bubble point and filtration performance (e.g., measured by the retention rate described herein), the first polymeric filtration membrane can exhibit a useful flow rate of liquid through the polymeric filtration membrane. The flow rate of liquid through the polymeric filtration membrane can be measured in terms of the flow rate or the flow time (which is the reciprocal of the flow rate). The first polymeric filtration membrane as described can have a useful or relatively low flow time, preferably in combination with a bubble point within the range described and good filtration performance (e.g., measured by a retention rate test). Useful examples of the first (open) polymeric filtration membrane can have a measured flow time of less than about 15,000 seconds or less than 13,000 seconds (e.g., less than 10,000 seconds, 5,000 seconds, or 1,000 seconds) when measured using isopropyl alcohol (IPA) as described herein.

[0044] The level of effectiveness of a polymeric filtration membrane in removing contaminants (including dissolved or suspended chemical molecules) from a liquid can be measured in one way as "retention rate". The retention rate related to the filtration performance of a polymeric filtration membrane generally refers to the total amount of one or more contaminants removed (when using the filter or under test conditions) from the liquid relative to the total amount of one or more contaminants present in the liquid before the liquid containing the contaminants passes through the polymeric filtration membrane. Thus, the "retention rate" value of a polymeric filtration membrane is a percentage, where a polymeric filtration membrane with a higher retention rate value (higher percentage) is relatively more effective in removing contaminants from the liquid, while a polymeric filtration membrane with a relatively lower retention rate value (lower percentage) is less effective in removing contaminants from the liquid.

[0045] As measured under test conditions, examples of the first (open) polymeric filtration membrane can exhibit a retention rate of more than 98% or 99% for a monolayer coverage of 1.0%; a retention rate of more than 97% or 98% for a monolayer coverage of 2.0; a retention rate of more than 98% or 99% for a monolayer coverage of 2.0; a retention rate of more than 95%, 96% or 97% for a monolayer coverage of 3.0; and a retention rate of more than 94% or 95% for a monolayer coverage of 4.0; each of the above is measured using the test method described herein. See Figure 5 。

[0046] The second polymer filtration membrane is thinner than the first polymer filtration membrane and has pores of a smaller size compared to the first polymer filtration membrane. The second polymer filtration membrane can be made of any useful polymer and can preferably be made of polyolefins (such as polypropylene, polyethylene (including its copolymers), or a mixture of two or more polyolefins or polyolefin copolymers). Specific examples of the second polymer filtration membrane can include polymers, consisting of polymers, or consisting essentially of polymers, where the polymers are polyolefins, such as polypropylene, polyethylene, or a mixture of polyethylene and polypropylene.

[0047] The second polymer filtration membrane of the assembly can consist of a single polymer filtration membrane or alternatively can comprise two or more “sub - layers,” in which case the second polymer filtration membrane can be regarded as a “multi - layer” membrane comprising two or more sub - layers. The second polymer filtration membrane can be in the form of a sheet having a relatively uniform thickness. The second polymer filtration membrane of the assembly consisting of a single filtration layer (single polymer filtration membrane) can have a thickness of less than 10 microns, 15 microns, or 20 microns, for example, can have a thickness in the range from 0.1 micron to 10 microns or from 0.2 micron to 5 microns. The second polymer filtration membrane comprising two or more sub - layers can comprise a number of sub - layers each having a thickness in these ranges and can have a total thickness in these ranges.

[0048] The second “tight” polymer filtration membrane has pores that are smaller than the pores of the first “open” polymer filtration membrane, and this will allow the second polymer filtration membrane to effectively function as the tight layer of the filter assembly as described, for example, to remove relatively small contaminants from a liquid that have not been removed by liquid flow through the first “open” polymer filtration membrane upstream of the second “tight” polymer filtration membrane. In some exemplary second polymer filtration membranes or exemplary sub - layers of the second membrane, the second polymer filtration membrane or its sub - layers can have an average pore size in the range from about 0.001 micron to about 0.1 micron (1 nanometer to about 500 (nm)), such as from 0.01 micron to 0.05 micron (from 10 nanometers to 50 nanometers) or from 0.001 micron to 0.005 micron (from 1 nanometer to 5 nanometers).

[0049] Examples of polymer filtration membranes that can be used as the second polymer filtration membrane and have the described physical properties can be prepared by known methods that prepare polyolefin membranes by any useful technique (e.g., extrusion, melt casting, or phase inversion techniques), followed by uniaxially or biaxially stretching the membrane to a reduced thickness. By one technique, a second polymer filtration membrane containing polyethylene (including copolymers), polypropylene (including copolymers), or mixtures thereof (including the polyethylene, polypropylene, or mixtures thereof, consisting essentially of the polyethylene, polypropylene, or mixtures thereof, or consisting of the polyethylene, polypropylene, or mixtures thereof) can be prepared by extruding a polymer (polyolefin) resin containing a diluent to form a polyolefin sheet and stretching the sheet, followed by extraction and annealing steps.

[0050] The second polymer filtration membrane can be treated or coated by adding ionic groups (cationic or anionic groups) to the surface of the membrane to improve the removal of dissolved or suspended contaminants in the liquid by a non-sieving filtration mechanism.

[0051] Useful or preferred second polymer filtration membranes (whether in a single layer form or multiple sub-layer forms) can have several physical properties (e.g., pore size, porosity, and bubble point) and filtration properties (e.g., retention rate and flow time or flow rate), which effectively allow the second polymer filtration membrane to be used alone as a polymer filtration membrane to remove undesirable contaminants from a liquid stream, or as part of an assembly of two or more polymer filtration membranes as described in combination with another polymer filtration membrane, the assembly comprising a first (open) polymer filtration membrane combined with a second (tight) polymer filtration membrane.

[0052] The bubble point of the second (tight) polymer filtration membrane of an assembly comprising a first (open) polymer filtration membrane and a second (tight) polymer filtration membrane (including the first (open) polymer filtration membrane and the second (tight) polymer filtration membrane, consisting essentially of the first (open) polymer filtration membrane and the second (tight) polymer filtration membrane, or consisting of the first (open) polymer filtration membrane and the second (tight) polymer filtration membrane) can preferably be greater than the bubble point of the first (open) polymer filtration membrane. Examples of useful bubble points of the second (tight) polymer filtration membrane as described, measured using the test methods described in the examples section herein, can be greater than 100 psi, e.g., in the range from 120 psi to 300 psi, e.g., in the range from 130 psi to 200 psi.

[0053] The second polymer filtration membrane can have any porosity that will allow the polymer filtration membrane to be effective when used as the second polymer filtration membrane described herein. Exemplary second polymer filtration membranes can have a relatively high porosity, such as a porosity in the range from 40% to 80%.

[0054] When measured separately, the second polymer filtration membrane can have a useful or relatively low flow time, preferably in combination with a relatively high bubble point and good filtration performance. The second polymer filtration membrane can have a flow time less than that of the first polymer filtration membrane used in conjunction with the second polymer filtration membrane. Exemplary second polymer filtration membranes can have a measured flow time of less than about 15,000 seconds or less than 11,000 seconds or less than 10,000 seconds, 9,000 seconds or 5,000 seconds or 1,000 seconds as measured using IPA as described below.

[0055] Exemplary second polymer filtration membranes can exhibit a retention of greater than 97% or 98% for a monolayer coverage of 1.0%; a retention of greater than 95% or 96% for a monolayer coverage of 2.0; a retention of greater than 96% or 97% for a monolayer coverage of 2.0; a retention of greater than 93% or 94% for a monolayer coverage of 3.0; and a retention of greater than 91% or 92% for a monolayer coverage of 4.0; each of which is measured at a useful flow rate through the membrane using the tests described in the Examples section. See Figure 4 .

[0056] A membrane assembly comprising a first polymer filtration membrane and a second polymer filtration membrane in series can have a total thickness of two polymer filtration membranes equal to the combined thickness of the first polymer filtration membrane and the second polymer filtration membrane, excluding any additional polymer filtration membranes, filter elements, or support layers that may be used in combination with the first polymer filtration membrane and the second polymer filtration membrane of the assembly. Exemplary thickness values for the membrane assembly can be comparable to the thickness of the first polymer filtration membrane of the assembly, such as in the range from 20 microns to 300 microns, such as from 30 microns or 50 microns to 150 microns, 200 microns or 250 microns.

[0057] Like each of the first polymer filtration membrane and the second polymer membrane that make up the membrane assembly, the assembly can also be evaluated with respect to the properties of the assembly (such as bubble point, retention, and flow time).

[0058] The bubble point of an assembly comprising a first polymeric filtration membrane and a second polymeric filtration membrane (including, consisting essentially of, or consisting of the first and second polymeric filtration membranes) may preferably be greater than the bubble point of the first (open) polymeric filtration membrane. According to an exemplary membrane assembly, the assembly may have a bubble point (average bubble point) comparable to the bubble point of the second (tight) polymeric filtration membrane of the assembly, e.g., an average bubble point within 10% of the average bubble point of the second (tight) membrane, measured in pounds per square inch. Exemplary average bubble points of the membrane assembly may be greater than 100 psi, e.g., in the range from 120 psi to 300 psi, e.g., in the range from 130 psi to 200 psi.

[0059] When measuring the retention rate of each of the first and second polymeric filtration membranes individually, the retention rate of an assembly comprising a first (open) polymeric filtration membrane and a second (tight) polymeric filtration membrane (including, consisting essentially of, or consisting of the first (open) and second (tight) polymeric filtration membranes) may be better compared to both the retention rate of the first (open) polymeric filtration membrane and the retention rate of the second (tight) polymeric filtration membrane. This may be demonstrated during the use of the membrane assembly to remove contaminants from a semiconductor processing fluid such as a photoresist solution, or may be demonstrated by testing under controlled conditions, e.g., by measuring the retention rate of test contaminants present in a test solution containing test particles of known concentration under controlled conditions. Examples of test particles are G25 particles made of polystyrene and having an average particle diameter from 3 nanometers to 25 nanometers. Other types and sizes of test particles may also be suitable for measuring the retention rate of the assembly and the retention rate of each polymeric filtration membrane individually.

[0060] An exemplary assembly comprising a single first polymeric filtration membrane and a single second polymeric filtration membrane (including, consisting essentially of, or consisting of the single first and single second polymeric filtration membranes) may exhibit a measured retention rate value of greater than 99% for a monolayer coverage of 1.0%; a retention rate of greater than 98% or 99% for a monolayer coverage of 2.0; a retention rate of greater than 98% for a monolayer coverage of 3.0; and a retention rate of greater than 98% for a monolayer coverage of 4.0; each of the above being measured using the tests described in the Examples section at a useful flow rate through the membrane. SeeFigure 4 and 5 。

[0061] A membrane assembly comprising a first polymeric filtration membrane and a second polymeric filtration membrane (including, consisting essentially of, or consisting of the first and second polymeric filtration membranes) can have a flow time comparable to either or both of the flow times of the first polymeric filtration membrane of the assembly or the second polymeric filtration membrane of the assembly when each is measured separately. The assembly can have a useful or relatively low flow time, preferably in combination with a relatively high bubble point and good filtration performance as described herein for membrane assemblies, for example. Exemplary membrane assemblies can have a measured flow time of less than 20,000 seconds measured using IPA as described herein.

[0062] A membrane assembly comprising at least a first (open) polymeric filtration membrane and a second (tight) polymeric filtration membrane can be incorporated into a filter product and used to filter liquids such as semiconductor processing liquids, for example. The assembly can comprise a first polymeric filtration membrane and a second polymeric filtration membrane arranged in series between an inlet and an outlet of the filter product. The assembly can comprise or can be used in conjunction with one or more additional membranes or support layers or support structures (such as a frame). In a preferred use, the first polymeric filtration membrane is upstream with respect to the liquid flow through the assembly and the second polymeric filtration membrane is downstream. The upstream side of the second polymeric filtration membrane faces the downstream side of the first polymeric filtration membrane. Liquid first flows through the first polymeric filtration membrane and then through the second polymeric filtration membrane.

[0063] Reference Figure 1 , illustrates an assembly 100 of a first (open) polymeric filtration membrane 102 and a second (tight) polymeric filtration membrane 104 in series. The open polymeric filtration membrane 102 is upstream with respect to the liquid flow 110 into the upstream surface of the open polymeric filtration membrane 102. Liquid 110 (see arrow) flows into the first polymeric filtration membrane 102, which has a greater thickness and greater pore size compared to the second polymeric filtration membrane 104. Contaminants present in the liquid 110 are removed by the pores of the first (open) polymeric filtration membrane 102. After flowing through the polymeric membrane 102, the liquid flows into the second (tight) polymeric filtration membrane 104, which has a smaller thickness and relatively smaller sized pores. After the liquid 110 has passed through the first polymeric filtration membrane 102, smaller contaminants remaining in the liquid 110 can be removed by the second polymeric filtration membrane 104 by sieving or non-sieving mechanisms. The filtrate 112 (see arrow) passes through the downstream surface of the second polymeric filtration membrane 104.

[0064] Figure 1 The assembly 100 is shown to consist of a first polymeric filtration membrane 102 and a second polymeric filtration membrane 104, without additional filtration membranes or support membranes or structures, although not illustrated, which may be included during the use of the exemplary assembly 100. Further, the second polymeric filtration membrane 104 is illustrated as consisting of a single polymeric filtration membrane layer, but may optionally be made to include two or more sublayers, as described herein.

[0065] The polymeric filtration membranes 102 and 104 may be separated from each other (i.e., not attached), but are arranged such that the downstream surface of the first polymeric filtration membrane 102 faces or is adjacent to or contacts the upstream surface of the second polymeric filtration membrane 104. If desired but not required, the two polymeric filtration membranes may be attached at their opposing surfaces (the outlet surface of the first polymeric filtration membrane is attached to the inlet surface of the second polymeric filtration membrane) by a lamination step, by which the surfaces of the two polymeric filtration membranes are brought into contact with each other and caused to adhere together under high temperature and slight pressure. The temperature and pressure conditions of the optional lamination step are moderate to avoid significantly affecting the morphology and filtration performance properties (flow time, retention rate) of the first polymeric filtration membrane or the second polymeric filtration membrane. The lamination step may be performed without placing additional materials (such as adhesives) between the surfaces of the two polymeric filtration membranes.

[0066] The membrane assembly may be incorporated into a filter product, such as a filter cartridge (removable filter cartridge) that supports the membrane assembly within a liquid flow or a filter housing that includes any structure for supporting the membrane assembly to allow a liquid fluid to flow through the membrane assembly from the inlet side of the membrane assembly, through the membrane assembly, and out of the membrane assembly from the outlet side. The filter housing may include an inlet located on one side of the supported membrane assembly and an outlet located on a second side of the membrane assembly, the inlet allowing fluid to enter the housing and the outlet allowing fluid to leave the filter housing after passing through the membrane assembly when the membrane assembly is supported by the filter housing.

[0067] The terms "inlet" and "outlet" may refer to a defined opening or a defined conduit (tube, pipe, or their junctions) of a specific structure, such as a filter housing or a component of a filter housing (e.g., a support frame, a core, a cage, etc.), or may refer to a space ("inlet space" or "outlet space") located on either side of the membrane assembly when supported by the filter housing, the space accommodating the fluid flowing into or out of the membrane assembly. The terms "inlet" and "outlet" generally may refer to a space on either side of the membrane assembly, the space accommodating the fluid flowing into the membrane assembly, flowing through the membrane assembly, and flowing out of the membrane assembly when the membrane assembly is supported by the filter housing.

[0068] The filter housing contains a membrane assembly that is supported to allow fluid to pass through the membrane and can be a component of a larger filtration system that supplies filtered liquid chemicals to a tool or process for manufacturing microelectronic or semiconductor devices. The filter assembly or filter housing can include one or more of a variety of additional materials and structures that support the membrane assembly within the filter housing to facilitate fluid flow through the membrane assembly. The membrane assembly supported by the filter housing can be of any useful shape, such as a pleated cylinder, a cylindrical pad, one or more non-pleated (flat) cylindrical sheets, pleated sheets, and other shapes.

[0069] An example of a filter structure (e.g., a removable filter cartridge) that contains a membrane assembly can be in the form of a replaceable filter cartridge that includes a pleated cylindrical filter element that contains a membrane assembly with additional components, which can include one or more of the following: a rigid or semi-rigid core that supports the pleated membrane assembly at the inner side (inlet or outlet) of the pleated membrane assembly; a rigid or semi-rigid cage that supports or surrounds the outer side (outlet or inlet) of the membrane assembly at the outside of the pleated membrane assembly; and optional end pieces or "pucks" located at each of the two opposite ends of the pleated membrane assembly. The replaceable filter cartridge is considered to have an inlet on one side of the membrane assembly and an outlet on the opposite side of the membrane assembly; depending on the direction of liquid flow through the membrane assembly, the inlet or outlet can be on either side of the membrane.

[0070] As an example, Figure 2Disclosed is a filter product (replaceable filter element) 230, which includes a pleated cylindrical assembly (e.g., a filter element) 210 and end pieces 222, with other optional structural components not specifically shown. The cylindrical assembly 210 includes a membrane assembly 212 as described herein and is pleated. The end pieces 222 are attached (e.g., “encapsulated”) to one end of the cylindrical filter assembly 210. The end pieces 222 may preferably be made of a melt-processable polymeric material (e.g., a thermoplastic fluoropolymer). A core (not shown) may be placed at the internal opening or space (“inlet”) 224 of the pleated cylindrical assembly 210, and a cage (not shown) may be placed around the external opening or space (“outlet”) of the pleated cylindrical assembly 210. Thus, the filter element includes inlets and outlets (e.g., at the core, cage, or other support structures) on each of the inlet (upstream) side of the membrane and the outlet (downstream) side of the membrane assembly 212, where the positions of the inlets and outlets depend on the direction in which the liquid is caused to flow through the membrane assembly 212 when the filter element 230 is installed in a filter housing that may also have inlets and outlets. A second end piece (not shown) may be attached (“encapsulated”) to the second end of the pleated cylindrical assembly 230. Then, the resulting replaceable filter element 230 having two relatively encapsulated ends and optional core and cage may be placed into a larger filter housing that includes an upstream housing inlet for receiving liquid flowing into the filter membrane and a downstream housing outlet for discharging the liquid that has passed through the membrane assembly. The housing is configured such that a certain amount of liquid entering the housing at the housing inlet must pass through the membrane assembly 212 before leaving the filter housing at the housing outlet.

[0071] The components of the filter housing may have any useful and desired size, shape, and material, and may preferably be a fluorinated or non-fluorinated polymer, such as nylon, polyethylene, or a fluorinated polymer, such as poly(tetrafluoroethylene-co-perfluoro(alkyl vinyl ether)), perfluoroalkoxy alkane (PFA), perfluoromethyl alkoxy (MFA), or another suitable fluoropolymer (e.g., a perfluoropolymer).

[0072] Reference Figure 3, the filter product 250 includes a housing that internally houses a replaceable filter element 230. The filter product 250 includes a dual-component housing that includes a bowl 252 attached to a base 254 at an open end of the bowl 252. Optionally, the bowl may be removably engaged with the base 254 to allow the bowl 252 to be separated from the base 254, thereby allowing the removable filter element 230 to be placed into or removed from the interior of the housing. The assembled housing includes an inlet 256, an inlet space 260 located on an inner side of the filter element 230, an outlet space 262 between the filter element 230 and the bowl 252, and an outlet 258. The removable filter element 230 may be located inside the bowl 252, and the arrangement of the removable filter element allows liquid to flow into the inlet 256, into the inlet space 260, then through the filter assembly 212 of the filter element 230, into the outlet space 262, and then out of the filter product 250 through the outlet 258.

[0073] The membrane assemblies as described can be used in methods for filtering liquid chemicals to purify or remove unwanted materials (contaminants) from the liquid chemicals, especially in methods for producing high-purity liquid chemicals that can be used in industrial processes that require a liquid chemical input with a very high purity level. Generally, the liquid chemical can be any one of a variety of useful commercial liquid chemicals of a type useful in any industrial or commercial application. Specific examples of the membrane assemblies and filter products as described can be used to purify liquid chemicals used in semiconductor or microelectronics fabrication applications, such as for filtering liquid solvents or other processing solutions used in semiconductor lithography methods, wet etching or cleaning steps, methods for forming spin-on glass (SOG), backside anti-reflection coating (BARC) methods, etc.

[0074] Some specific non-limiting examples of solvents (including cleaning solutions) that can be filtered using the membrane assemblies as described include: n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethyl acetate (2EEA), xylene, cyclohexanone, ethyl lactate, methyl isobutyl carbinol (MIBC), methyl isobutyl ketone (MIBK), isoamyl acetate, undecane, propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), or mixtures of any of these, such as a mixture of PGME and PGMEA; or concentrated or diluted ammonium hydroxide, hydrogen peroxide, hydrochloric acid, HF, sulfuric acid, another peroxide solution, or combinations of these, such as a combination of ammonium hydroxide and hydrogen peroxide, or a combination of hydrochloric acid and hydrogen peroxide.

[0075] A more specific example of a semiconductor processing fluid is a "photoresist solution" which includes a polymeric resin, a sensitizer (also known as an "inhibitor" and which modulates the photochemical process), and a solvent.

[0076] Exemplary photoresist solutions include reactive curable polymeric resins which can be cured in the presence of electromagnetic radiation and in the presence of a sensitizer. The type of radiation can be: deep ultraviolet radiation, near ultraviolet radiation, electron beam radiation, x-ray radiation. Examples of specific reactive polymers known to be useful in photoresist solutions include polymethylmethacrylate (PMMA) resins, isoprene, polyalkyl aldehydes, diazonaphthoquinone (DNQ) resins, novolak resins (phenol-formaldehyde polymers), epoxy resins, non-stoichiometric thiol-ene (OSTE) polymeric resins, and hydrogen silsesquioxane (HSQ) resins. A variety of solvents and photosensitizers are known to be useful in photoresist solutions containing different types of curable polymeric resins. Each of the polymeric resin, the solvent, and the sensitizer can be used in a specific amount effective in a particular photoresist solution.

[0077] Examples of unwanted contaminants that can be present in photoresist solutions and that can desirably be removed by the filtration step using the membrane assemblies as described include particulate contaminants which can be reactive polymer particles, dissolved metal ions ("metals"), or other particulate or dissolved contaminants.

[0078] The terms "metal" and "metal ion" are used in a manner consistent with their use in the fields of chemistry and semiconductor processing and refer to molecular species containing metal ions, metal atoms, or metal complexes. Metal contaminants can be or can include neutral, negatively charged, or positively charged metal species. Some examples of specific metals or metal ions that can be removed from photoresist solutions include Na, K, Ca, Fe, Mg, Al, Cr, Ni, and Zn.

[0079] Particulate contaminants in photoresist solutions can include reactive monomers, oligomers, or polymerized polymers having a particle size in the range from 0.01 microns to 0.2 microns.

[0080] The membrane assemblies or the first or second membranes can be tested individually or together for retention, bubble point, and flow time according to the following test methods.

[0081] Retention rate test method using test particles

[0082] The effectiveness level of a polymeric filtration membrane or membrane assembly in removing unwanted substances (i.e., “contaminants”) from a liquid can be measured as “retention rate” in one way. The retention rate generally refers to the amount of contaminants removed from the liquid relative to the total amount of contaminants initially present in the liquid before passing the liquid containing contaminants through the membrane or membrane assembly. The “retention rate” value of a polymeric filtration membrane or membrane assembly is a percentage, where a polymeric filtration membrane with a higher retention rate value (higher percentage) is relatively more effective in removing contaminants from the liquid, while a polymeric filtration membrane with a relatively lower retention rate value (lower percentage) is relatively less effective in removing contaminants from the liquid.

[0083] The retention rate can be measured by measuring the number of test particles removed from a liquid stream using a polymeric filtration membrane or membrane assembly placed in the liquid stream. By one method, the retention rate can be measured by passing a sufficient amount of a test aqueous solution at a constant flow rate through a membrane containing 0.1% Triton X-100 and 8 ppb polystyrene particles (e.g., G25 circular polystyrene particles having a nominal diameter of 3 nm to 25 nm) to achieve 1% monolayer coverage of the membrane and collecting the permeate. The concentration of polystyrene particles in the permeate can be calculated based on the absorbance of the permeate. Then the particle retention rate is calculated using the following equation based on the particle concentrations in the feed and the filtrate:

[0084] Particle retention rate

[0086] Bubble point test method using HFE-7200

[0087] By a method of determining the bubble point of a polymeric filtration membrane, a sample of the polymeric filtration membrane is immersed in a liquid having a known surface tension and wetted by the liquid, and a gas pressure is applied to one side of the sample. The gas pressure is gradually increased. To measure the bubble point, a 47 mm polymeric filtration membrane disk is placed in a holder and a high permeability spunbond nonwoven fabric (PGI Corporation) is placed downstream as a support layer. Air is pressurized through the holder and measured as a function of pressure. Then a low surface tension fluid HFE-7200 (3M) is introduced to the downstream side to wet the membrane. Air is pressurized through the holder again and the air flow rate is measured as a function of pressure.

[0088] The minimum pressure at which gas flows through the sample is called the initial bubble point.

[0089] The pressure at which the ratio of the air flow rate of the wet membrane to the air flow rate of the dry membrane is 0.5 is called the average bubble point. If the membrane produces two different pressure values based on the side of the membrane facing the air, then the lower measured value is used as the average bubble point.

[0090] Flow time test method

[0091] The ease with which a liquid passes through a polymeric filtration membrane or membrane assembly (e.g., the flow rate of the liquid through the membrane or membrane assembly) can be evaluated as a measured "flow time", which is the reciprocal of the flow rate. The flow time can be defined as the time required for 500 milliliters of fluid (isopropyl alcohol in this case) to pass through a porous membrane or membrane assembly having a surface area of 13.8 cm 2 at 14.2 psi.

[0092] Example

[0093] Table 1 shows a comparison of the average bubble point, flow time, and thickness for two examples of a first (open) polymeric filtration membrane, a single example of a second (tight) polymeric filtration membrane, and an example of an assembly comprising the first (open) polymeric filtration membrane and the second (tight) polymeric filtration membrane.

[0094] Table 1

[0095]

[0096] Table 2

[0097]

[0098] Figure 4 and 5 The graphs of and show the particle retention data for the membranes and membrane assemblies of Tables 1 and 2, which were tested according to the retention test method described herein, using G25 PSL test particles at 8 parts per million in deionized water and 0.1% Triton X-100 surfactant.

[0099] Figure 4 Show the measured retention values for two different assemblies ("Assembly 1" and "Assembly 2") of a first (open) polymeric filtration membrane and a second (tight) polymeric membrane. Assembly 1 is a non-laminated assembly consisting of an open polymeric filtration membrane ("first layer") and a tight polymeric filtration membrane made of stretched UPE ("second layer"). Assembly 2 is a non-laminated assembly consisting of an open polymeric filtration membrane ("first layer") and a tight polymeric filtration membrane made of stretched UPE ("second layer"). For test particles at particle loads associated with monolayer values of 1.0, 2.0, 3.0, and 4.0, the measured retention for each of Assembly 1 and Assembly 2 is at least 98%.

[0100] Figure 4Also shown are the measured retention values for a dense polymeric filtration membrane that was tested separately and is a stretched UPE membrane (“Exemplary Dense Membrane 2”). For test particles at particle loadings associated with up to 1.5 monolayers, the measured retention of Exemplary Dense Membrane 2 is approximately 98%, and for higher particle loadings, the measured retention is less than 98%.

[0101] Figure 5 Shown are the measured retention values for Assembly 2 and those values are compared to the measured retention values of two different open polymeric filtration membranes (“Exemplary Open Membrane 3” and “Exemplary Open Membrane 4”). Exemplary Open Membrane 3 is a melt cast membrane. Exemplary Open Membrane 4 is a melt cast membrane.

[0102] For test particles at particle loadings associated with 1.0, 2.0, 3.0, and 4.0 monolayers, the measured retention of Assembly 2 is at least 98%.

[0103] For test particles at particle loadings associated with up to 1.5 or approximately 2.0 monolayers, the measured retention of Exemplary Open Membrane 3 is approximately 98%, and for higher particle loadings, the measured retention is less than 98%.

[0104] For test particles at particle loadings associated with up to approximately 2.5 monolayers, the measured retention of Exemplary Open Membrane 4 is approximately 98%, and for higher particle loadings, the measured retention is less than 98%.

Claims

1. A method of filtering a semiconductor processing liquid, the method comprising: passing the liquid through a first polymeric filtration membrane having: an average bubble point of less than 120 pounds per square inch measured using ethoxy nonafluorobutane (HFE7200), and a thickness of at least 20 microns; and passing the liquid through a second polymeric filtration membrane having: an average bubble point of greater than 120 pounds per square inch measured using ethoxy nonafluorobutane (HFE7200), and a thickness of less than 20 microns.

2. The method according to claim 1, wherein the method of passing the liquid through both the first polymeric filtration membrane and the second polymeric filtration membrane removes a greater amount of contaminants from the liquid compared to the methods of passing the liquid through the first polymeric filtration membrane alone and passing the liquid through the second polymeric filtration membrane alone.

3. The method according to claim 1, wherein the liquid is a photoresist solution, and the photoresist solution comprises: A polymer resin, a sensitizer, and a solvent.

4. The method according to claim 3, wherein the photoresist solution comprises metal contaminants.

5. The method according to claim 3, wherein the photoresist solution comprises contaminant particles having a particle size in the range from 0.01 microns to 0.2 microns.

6. The method according to claim 1, wherein the first polymeric filtration membrane is a melt-cast polyolefin membrane.

7. The method according to claim 1, wherein the first polymeric filtration membrane has a thickness in the range from 20 microns to 300 microns.

8. The method according to claim 1, wherein the second polymeric filtration membrane is a stretched polyolefin membrane.

9. The method according to claim 1, wherein the second polymeric filtration membrane has a thickness in the range from 0.1 microns to 10 microns.

10. A filter product for removing contaminants from a semiconductor processing fluid, the filter product comprising: a first polymeric filtration membrane having an average bubble point of less than 120 pounds per square inch measured using ethoxy nonafluorobutane (HFE7200), and a thickness of at least 20 microns; and a second polymeric filtration membrane having an average bubble point of greater than 120 pounds per square inch measured using ethoxy nonafluorobutane (HFE7200), and a thickness of less than 20 microns.

11. The filter product according to claim 10, wherein the first polymeric filtration membrane is a melt-cast polyolefin membrane.

12. The filter product according to claim 10, wherein the first polymeric filtration membrane has a thickness in the range from 20 microns to 300 microns.

13. The filter product according to claim 10, wherein the second polymeric filtration membrane is a stretched polyolefin membrane.

14. The filter product according to claim 10, wherein the second polymeric filtration membrane has a thickness in the range from 0.1 microns to 10 microns.

15. The filter product according to claim 10, which includes a frame, and the first polymeric filtration membrane and the second polymeric filtration membrane are supported by the frame.

16. The filter product according to claim 10, wherein the filter product is a replaceable filter element.

17. The filter product according to claim 10, wherein the filter product includes a housing, the housing including an inlet, an inlet space, an outlet, and an outlet space, adapted to allow a liquid to flow through the inlet into the inlet space, then flow through the first polymeric filtration membrane, then flow through the second polymeric filtration membrane, and then flow into the outlet space.

18. The filter product according to claim 10, wherein the filter product provides a better retention rate of G25 circular polystyrene particles compared to both the retention rate of the first polymeric filtration membrane alone and the retention rate of the second polymeric filtration membrane alone.

19. The filter product according to claim 10, wherein based on a 4.0% monolayer of G25 circular polystyrene particles having a nominal diameter of 5 nanometers to 15 nanometers, the filter product exhibits a measured retention rate of at least 98%.

20. The filter product according to claim 10, wherein based on a 3.0% monolayer of G25 circular polystyrene particles having a nominal diameter of 5 nanometers to 15 nanometers, the filter product exhibits a measured retention rate of at least 98%.

21. A semiconductor processing filtration system, comprising: The filter product according to claim 17, A semiconductor processing fluid source connected to the inlet, and A semiconductor processing device connected to the outlet.

22. The semiconductor processing filtration system according to claim 21, wherein the semiconductor processing fluid is a photoresist solution.

Images