Biocompatible, high aspect ratio porous membranes

Abstract

The present invention provides a method for manufacturing a semiconductor device having a desired thermal expansion coefficient and a large surface area (e.g., approximately 4000 mm 2 The porous membrane 102 may be fabricated according to an exemplary process of lithographically patterning a photoresist 104, then developing and etching the photoresist 104. In one embodiment, the etch barrier layer is selected from materials that do not react with or introduce metals or other contaminants into the membrane layer 102.

Description

[Background technology]

[0001] Porous membranes are used in a variety of biological filtration processes. The membranes are made of a thin layer of polymeric material with holes drilled into it. One type of such material is made by a process called track-etch, shown in Figure 1. Track-etch materials are made using an electron gun. Electrons are directed at the membrane under vacuum conditions. The electrons drill holes in the membrane, making it porous. Due to the random nature of the process, the resulting holes are randomly distributed on the membrane surface. The process can result in larger pores than intended due to overlapping holes.

[0002] Photolithography has been used to fabricate membrane materials. U.S. Patent No. 7,784,619, inventor Jacobsen and patentee Baxter International, describes a photolithographic method for fabricating membranes. In such a process, conventional semiconductor fabrication methods are used to create a membrane with the desired array of holes.

[0003] The inventors have realized that standard methods for semiconductor manufacturing fail to provide large surface area films with desirable properties. It is difficult to produce large surface area films that result in a flat surface. One problem is the tendency of the film material to roll up after removal from the support. Another problem is film contamination from hard mask layers required to create high aspect ratio holes in the film. In some applications, it may be desirable to produce films that are free of metal contaminants. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 7,784,619 Summary of the Invention [Problem to be solved by the invention]

[0005] Accordingly, the present invention aims to improve microporous membranes and methods for their manufacture. [Means for solving the problem]

[0006] In one aspect, the invention includes a porous membrane for liquid filtration, the porous membrane comprising a polymeric membrane layer, the polymeric membrane layer having an average pore size in the range of 1 to 100 μm, a pore size standard deviation of 0.7 μm or less, and a deviation factor of 0.2 or less. 2 It is desirable for the pore size distribution to be large, such as 0.3 μm or less. In one embodiment of the present invention, the pore size distribution has a standard deviation in the range of 0.15 to 0.7 μm, more preferably 0.15 to 0.40 μm, or 0.15 to 0.30 μm.

[0007] The polymeric membrane can be made of a variety of polymers, including, for example, polyimide, polyamide, polycarbonate, polyetherimide, polyetherketone, polyurethane, synthetic polymers, low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon, Teflon (polytetrafluoroethylene), thermoplastic polyurethane (TPU), polyethylene, acrylate polymers, acrylate monomers, acrylate elastomers, etc. In a preferred embodiment, the polymeric material is polyimide.

[0008] In another aspect, the present invention relates to a method for making a porous membrane for liquid filtration, the method comprising: (a) depositing a photoresist layer on a top surface of a substrate, the substrate comprising a support layer, a polymer layer, and a hard mask layer, the polymer layer having a thickness of 5 to 25 μm, and the support layer and polymer layer having thermal expansion coefficients matched to within ±25% of each other; (b) exposing the photoresist to a light pattern; (c) developing the photoresist layer to provide a first opening pattern in the photoresist layer that exposes portions of the hard mask layer; (d) etching the exposed portions of the hard mask layer to provide a first opening pattern in the hard mask layer that exposes portions of the underlying polymer layer; (e) removing the photoresist; (f) etching the polymer layer through the openings in the hard mask layer to provide a third opening pattern in the polymer layer; (g) removing the hard mask layer; and (h) removing the polymer layer from the support layer, thereby providing a porous membrane, wherein the pore size of the porous membrane is determined by the light pattern, and the membrane has a pore size of 4000 mm. 2 It has a surface area of ​​more than 10 ...

[0009] In another aspect, the present invention relates to a porous membrane, the porous membrane having a pore size of 4000 mm. 2 The porous film has a continuous surface area of ​​100 μm or more, a thickness of 5 to 25 μm, and an opening pattern, the average aspect ratio of the openings being in the range of 0.5:1 to 20:1, and the polymer does not contain detectable amounts of hard mask material or reaction products of the hard mask layer and the polymer, or the amount present is so small that it has no biological effect, meaning that it is not toxic to cells, etc. In one embodiment, the porous film has the ability to be planarized with a deviation ratio of 0.2 or less.

[0010] In another aspect, the invention includes a method for making a porous membrane, the method comprising: (a) depositing a photoresist layer on an upper surface of a substrate, the substrate comprising a support layer, a polymer layer, and a hard mask layer, the polymer layer having a thickness of 5 to 25 μm, and the substrate having a surface area of ​​4000 mm 2(e) removing the photoresist; (f) providing a third opening pattern in the polymer layer by etching the polymer layer through the openings in the hard mask layer, wherein the average aspect ratio of the third opening pattern is in the range of 0.5:1 to 20:1; (g) removing the hard mask layer; (i) after removing the hard mask layer, the polymer layer has no detectable amount of hard mask material or reaction products of the hard mask layer and the polymer, or the amount of any reaction products is so small that it has no biological effect; and (h) removing the polymer layer from the support layer to provide a porous membrane, wherein the pore size of the porous membrane is determined by the light pattern, and the membrane has a pore size of 4000 mm or less. 2 The coefficient of thermal expansion (CTE) of the polymer layer and the coefficient of thermal expansion (CTE) of the support layer can be controlled to be within ±15% of each other. More preferably, the CTEs are controlled to be within ±10% of each other. [Brief explanation of the drawings]

[0011] [Figure 1] 1 shows the surface of a porous membrane made by a track etch process. [Figure 2] 3 illustrates steps for fabricating a membrane according to one embodiment of the present invention. [Figure 3] 1 shows a photograph of a membrane according to one embodiment of the present invention. [Figure 4] 1 shows a scanning electron microscope image of a membrane according to one embodiment of the present invention. [Figure 5] This shows a polyimide film fabricated without controlling the CTE of the support layer and polymer layer. [Figure 6]1 shows a polyimide film fabricated in accordance with one embodiment of the present invention, in which the CTE of the support layer and the CTE of the polymer layer are controlled to be within 25% of each other. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention relates to the fabrication of polymeric membranes using photolithographic methods, where the membrane material is 4000 mm thick and can remain flat without curling or other deformation. 2 The surface area of ​​the substrate may be provided to have a continuous surface area of ​​at least 1000 nm.

[0013] The membranes of the present invention can be provided with any desired pore size and pore distribution while maintaining a continuous large surface area.

[0014] The process of the present invention allows for the production of biocompatible membranes and utilizes materials and methods that do not leave residual components in the processed polymeric material. For example, the etch mask is selected from materials that do not react with components of the polymer, such as carbon. Preventing such surface reactions is important for biological membranes that must not contaminate the material being filtered. The hard mask material and etching conditions can be selected to minimize the level of residual hard mask material found in the membrane. Residual material includes impurity elements from the hard mask material, such as aluminum and silicon. In one embodiment, the membrane comprises a biologically insignificant amount of residual hard mask material. In one embodiment, the amount of hard mask material on the surface of the polymer is preferably 0.15 μg / cm. 2 or less, more preferably 0.10 μg / cm 2 Below 0.01 μg / cm, most preferably 2 The following is the result.

[0015] 2, one exemplary process for fabricating a film of the present invention first includes providing a supporting base layer 100. Forming a film (polymer) layer 102 on the supporting layer 100. Forming a hard mask layer 103 on the polymer layer 102. Then, providing a photomask layer 104 on the hard mask layer 103.

[0016] The support substrate 100 can be made of, for example, glass. Other suitable materials include silicon and metal. The membrane layer 102 is a polymer layer. In a preferred embodiment of the present invention, the membrane layer 102 and the support substrate 100 have similar thermal expansion coefficients. The inventors have determined that matching the thermal expansion characteristics of the polymer layer 102 and the support substrate 100 allows the resulting membrane to resist deformation. This is a desirable property because a membrane that remains flat is easier to handle by the end user. One desirable material with a CTE similar to that of glass is polyimide. In one embodiment, polyimide is applied onto the substrate and cured, with the CTE of the cured polyimide material matching that of the glass. The inventors have determined that the greater the difference between the glass and the polymer membrane layer (e.g., polyimide), the greater the tendency for the polymer to become uneven when removed from the glass.

[0017] In one embodiment, the polyimide has a CTE of 3 ppm / °C at a thickness of 20 μm from 50°C to 200°C, and the glass has a CTE of 3.2 ppm / °C from 50°C to 200°C. As noted above, the CTE of the polymer and the CTE of the support layer are preferably within ±25% of each other, more preferably within ±15% of each other, and most preferably within ±10% of each other. For example, the CTE of the glass described above is approximately 7% higher than the CTE of the polyimide layer.

[0018] Suitable materials for the membrane layer 102 include polyimide, polyamide, polycarbonate, polyetherimide, polyetherketone, polyurethane, synthetic polymer, low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon, Teflon (polytetrafluoroethylene), thermoplastic polyurethane (TPU), polyethylene, acrylate polymer, acrylate monomer, and acrylate elastomer. Coating of the membrane layer 102 onto the support 100 can be performed using spin coating, spray coating, meniscus coating, slot-die coating, dip coating, extrusion coating, or lamination (attaching an adhesive to a substrate). Curing of the membrane layer 102 can be performed using thermal curing, UV (ultraviolet) curing, or a combination of both.

[0019] The hard mask layer 103 is typically an inorganic material that can be selectively etched relative to polymeric materials such as the membrane layer and photomask layer. The inorganic layer is preferably made of a material that does not react in any way with the membrane layer 102. For example, aluminum is a well-known etch mask layer, but Al can react with the polyimide of the membrane layer to form Al-C. This is undesirable because any metal contaminants tend to make the membrane incompatible for bioprocessing applications. Preferably, the hard mask layer is made of an aluminum alloy that reacts little or not at all with the polymer of the underlying membrane layer 102. Deposition of the hard mask layer 103 can be performed using physical vapor deposition, evaporation, chemical vapor deposition, and / or spray coating.

[0020] Suitable hard mask materials include inorganic materials, organic materials, and multilayers of inorganic and organic materials. More specifically, hard mask materials include metals, insulators, semiconductors, photoresists, inorganic materials, organic materials, multilayer films, or combinations thereof. In certain embodiments, the hard mask can include hydrogenated amorphous SiN (SiN:H) or hydrogenated amorphous SiO (SiO:H). Deposition of the hard mask can be performed using physical vapor deposition, evaporation, chemical vapor deposition, spray coating, plating, lamination, spin coating, meniscus coating, slot-die coating, dip coating, or extrusion coating.

[0021] Photoresist layer 104 is preferably a photoresist material that can be exposed and patterned using lithography techniques commonly used in semiconductor and flat panel display manufacturing. The photoresist material can be either a positive or negative photoresist. The photoresist material is typically deposited to a desired thickness using a spin-on method and then cured. The photoresist is then exposed to a light pattern that defines the pattern of the photoresist material upon development of the photoresist. Positive photoresist leaves material in areas not exposed to light and is removed upon development. Negative photoresist is the opposite. Specifically, negative photoresist leaves material in areas exposed to light and is removed upon development.

[0022] The structure shown in Figure 2(a) shows a cross-section of the support 100, membrane layer 102, hard mask layer 103, and photoresist layer 104. The material can either be applied during patterning or pre-applied and subsequently patterned. The overall shape is not particularly important and can be disk-shaped, square, or rectangular. Figure 3 shows a disk-shaped membrane on a support structure. Using the present invention, a 4000mm 2 Large area porous membranes such as those having surface areas of 1000 .mu.m or more can be provided.

[0023] The first step in fabricating a film from the structure of FIG. 2(a) is to provide a patterned photoresist layer 104 by exposing the surface of the photoresist to a light pattern and developing the photoresist to leave the photoresist pattern shown in FIG. 2(b). The location of the light exposure depends on whether a positive or a screw photoresist is used. The photoresist 104 in FIG. 2(b) includes an opening 101 in the photoresist layer. The opening 101 in the photoresist layer 104 is formed during development after exposing the photoresist layer 104 to the light pattern.

[0024] After the formation of the opening 101, the hard mask 103 is etched at the location of the opening 101 to form the hard mask opening 106 shown in FIG. 2(c). Etching of the hard mask 103 can be performed using one or more of wet chemical etching, plasma etching, non-reactive sputtering, or a combination of these techniques. In one embodiment, the hard mask layer is etched using a combination of acetic acid, phosphoric acid, nitric acid, and water. In one embodiment, the hard mask layer is etched with ammonium fluoride (NHF) and hydrofluoric acid (HF). In another embodiment, the hard mask layer can be removed using laser ablation. Etching is often performed at high temperatures. As mentioned above, it is desirable to select a material for the hard mask layer that does not react with the polymer of the underlying membrane layer 102 at temperatures during processing, such as etching of the hard mask layer 103.

[0025] It should be understood that the hard mask layer is important for providing a mask for later etching openings in the membrane layer 102. While several hard mask materials are known, many existing hard mask materials react with carbon in the underlying membrane layer 102. For example, the inventors have observed that when aluminum is used as a hard mask on a polyimide film, Al—C forms in the membrane layer. This reaction occurs in part due to the high temperatures to which the substrate is exposed during fabrication. For these reasons, it is desirable to use hard mask materials that are free of potential metal contaminants, such as the aforementioned SiN and SiH.

[0026] After patterning the hard mask layer 103 to form the opening 106, the photoresist may be removed using a solvent such as NMP (N-methylpyrrolidone), and then the membrane layer 102 may be patterned to form the opening 107. The patterning of the membrane layer 102 through the hard mask opening 106 is shown in FIG. 2( e). This is an etching process designed to selectively remove the polymer membrane layer within the hard mask opening 106. The etching method may include wet chemical etching, plasma etching, non-reactive sputtering, or a combination of these techniques. In particular, the material must be etched sufficiently to expose the underlying support layer 100 through the membrane layer opening 107.

[0027] After patterning membrane layer 102 to form membrane layer opening 107, hard mask layer 103 is preferably removed, as shown in Figure 2(f). Removal of hard mask layer 103 is preferably performed in a manner that is selective to membrane layer 102.

[0028] After removal of the hard mask layer 103, the patterned membrane layer 102 shown in Figure 2(g) is separated from the support layer 100. Separation of the membrane layer 102 can be performed using mechanical separation, laser separation, solution-based separation, thermal separation, or a combination of these techniques.

[0029] The support layer and membrane layer are selected to have sufficient adhesion to withstand processing while allowing for separation of the layers after patterning. In one embodiment, the support 100 is made of glass and the membrane layer 102 is a polyimide. In a preferred embodiment, the support 100 and membrane 102 are selected to have similar coefficients of thermal expansion. The inventors have found that matching the CTE of the support 100 and the CTE of the membrane layer 102 is important to provide a flat membrane upon peeling from the support. If the CTEs are not matched, the membrane will tend to curl upon peeling, which is undesirable.

[0030] The membrane 102 can be separated from the support 100 using mechanical processes or a combination of chemical and mechanical processes. For example, the membrane can be peeled off using a laser lift-off (LLO) method. Alternatively or additionally, the membrane can include a de-bonding layer (DBL) between the membrane 102 and the support layer 100. In a preferred embodiment, the membrane layer 102 and the support layer 100 are selected so that they are easily separable without the use of LLO or DBL.

[0031] FIG. 4 shows a scanning electron microscope image of a film according to one embodiment of the present invention. The lithographic methods described herein can be used to create regular patterns of pores. While desired patterns are possible, one advantage of using lithographic methods is that they avoid problems with pore overlap due to random processes. Furthermore, in one embodiment, pore shapes that are symmetrical with respect to the x-y direction can be reproduced uniformly across the thickness of the film along the z direction. For example, pore shapes that are symmetrical with respect to the x-y direction can be extruded along the z direction with or without a draft angle. This can be used to avoid complex pore shapes or threefold symmetry in the z direction (i.e., gyroid shapes) that can naturally occur when a suitable hard mask is not available.

[0032] In one embodiment, the pores are designed to have diameters in the range of 1 to 100 μm, preferably 1 to 10 μm, more preferably 3 to 7 μm, and most preferably approximately 5 μm. The membrane thickness and pore diameter determine the maximum aspect ratio. The membrane thickness is often in the range of 5 to 25 μm. The aspect ratio can be in the range of 0.5:1 to 20:1, preferably 1:1 to 10:1, more preferably 2:1 to 5:1, and most preferably approximately 3:1. In one aspect, the present invention can produce membranes with low variability in the distribution of pore sizes of desired sizes. In one aspect, the variability can be characterized as the pore size standard deviation. The pore size standard deviation is preferably 0.70 μm or less, more preferably 0.50 μm or less, and even more preferably 0.30 μm or less. In other embodiments, the standard deviation of the pore size may be in the range of 0.1 to 0.5 μm, preferably in the range of 0.15 to 0.4 μm, and more preferably in the range of 0.15 to 0.3 μm. Table 1 shows the pore size and standard deviation of the membrane according to the present invention.

[0033] [Table 1]

[0034] These results are based on 15 measurement points on each 100mm x 150mm sheet. Some areas with smaller pores were observed, which may indicate debris blocking the pores. The presence of larger pores appears to be due to defects in the mask. During production, mask defects can be addressed by replacing the mask.

[0035] The membranes of the present invention have pore size distributions that allow reliable separation of materials based on size. Membrane retention was determined by testing the membrane with a suspension of uniform particles (polystyrene microspheres) of known size and concentration and quantifying the particles that were able to pass through the membrane (particles downstream of the membrane). The polystyrene beads used in this test were unfunctionalized and undyed. Three bead size distributions were tested: nominal sizes of 6 μm, 10 μm, and 12 μm. The comparison membrane was a GE Healthcare TEM Nucleopore membrane with a nominal pore size of 10 μm. The membranes of the present invention used in this test had a precise size of 10.3 μm ± 0.2 μm (statistical evaluation based on SEM micrographs). As shown in Table 2, the membranes of the present invention exhibited a significantly lower standard deviation of the average retention compared to commercially available track-etched membranes, demonstrating the reliability of the membranes of the present invention in terms of pore size reproducibility.

[0036] [Table 2]

[0037] The porous membranes of the present invention have the desirable property of not curling up after being peeled from the support. This characteristic becomes more important as the surface area of ​​the membranes produced increases. For example, a membrane with a surface area of ​​4000 mm 2 In these cases, the inventors have observed that the membrane tends to curl after peeling from the support. Previous attempts to develop porous membranes using photolithography / etching have used polymer layers with variable thermal expansion coefficients, which are difficult to fabricate without curling upon peeling, especially when large surface areas are required. These limitations severely limit the size of the membrane's surface area.

[0038] The desired level of flat deviation, i.e., the deviation ratio calculated as the ratio of the maximum deviation from the plane when the membrane is self-supporting divided by the length of the membrane across the plane, is 0.2 or less. Figure 5 shows a membrane with a deviation value of 0.22, calculated as the curl at 10 mm divided by the maximum diameter of 47 mm. This level of deviation is due to uncontrolled CTE between the substrate and polymer layer, resulting in a curled film upon separation of the polymer layers. Figure 6 shows a membrane according to one embodiment of the present invention with a deviation ratio of 0.04, i.e., a deviation of 1 mm or less for a 25 mm diameter.

[0039] Jurkat cells (human lymphoma) were cultured in RPMI medium supplemented with fetal bovine serum and a combination of antibiotics (streptomycin and penicillin) and passaged twice before use in experiments. Cells were cultured alone (control) and in the presence of GE Healthcare's TEM Nucleopore and membranes of the present invention for a total of 7 days and monitored periodically to maintain exponential growth (direct control of cell number). Cell viability for all groups (control, TrackEtch, and membranes of the present invention) was quantitatively determined on days 1 and 7 using a Nucleocounter 200 (Chemometec) and a dedicated VialCassette, as shown in Table 3.

[0040] [Table 3]

[0041] The results showed that there was no difference in viability of Jurkat cells cultured in the presence of the membrane compared to the control, ie, no cytotoxicity.

[0042] Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. All references, including U.S. and foreign patent documents, are specifically incorporated herein by reference in their entirety. The specification and examples are exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

Claims

1. A porous membrane (102) comprising a polymer layer, said polymer layer having a thickness of 4000 mm ２ a thickness of 5 to 25 μm, and a pattern of openings etched through the thickness of the polymer layer using a hard mask (104), the openings having an average aspect ratio in the range of 0.5:1 to 20:1, the porous film (102) comprising 0.15 μg / cm or less of residual hard mask material on or within the polymer layer, the residual hard mask material comprising at least elemental aluminum or elemental silicon.

2. 10. The porous membrane (102) of claim 1, wherein the surface of the porous membrane (102) has a deviation ratio of 0.2 or less.

3. 3. The porous membrane (102) of claim 1 or 2, wherein the standard deviation of pore diameters of the porous membrane (102) is 0.3 μm or less.

4. The porous membrane (102) according to any one of claims 1 to 3, wherein the pore size standard deviation of the porous membrane (102) is in the range of 0.15 to 0.40 μm.

5. The porous membrane (102) according to any one of claims 1 to 4, wherein the pore size standard deviation of the porous membrane (102) is in the range of 0.15 to 0.30 μm.

6. 6. The porous membrane (102) of any one of claims 1 to 5, wherein the polymer layer is selected from polyimide, polyamide, polycarbonate, polyetherimide, polyetherketone, polyurethane, synthetic polymer, low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon, polytetrafluoroethylene, thermoplastic polyurethane (TPU), polyethylene, acrylate polymer, or acrylate elastomer.

7. The porous membrane (102) of any one of claims 1 to 6, wherein the polymer layer is a polyimide.

8. 8. The porous membrane (102) of any one of claims 1 to 7, wherein the porous membrane (102) has undetectable or biologically insignificant levels of metal contaminants.

9. The porous membrane (102) of any one of claims 1 to 8, wherein the pores of the porous membrane (102) have an aspect ratio of 0.5:1 to 20:

1.

10. A method for producing a porous membrane (102), comprising: (a) depositing a photoresist layer on an upper surface of a substrate comprising a support layer, a polymer layer, and a hard mask layer, wherein the polymer layer has a thickness of 5-25 μm, and the substrate has a surface area of ​​4000 mm ２ and wherein the hard mask layer and the polymer layer do not form a reaction layer at the interface. (b) exposing the photoresist layer to a light pattern; (c) developing the photoresist layer to provide a first opening pattern in the photoresist layer that exposes portions of the hard mask layer; (d) etching the exposed portions of the hard mask layer to provide a second pattern of openings in the hard mask layer that expose portions of the underlying polymer layer; (e) removing the photoresist layer; (f) providing a third opening pattern in the polymer layer by etching the polymer layer through the openings in the hard mask layer, wherein the third opening pattern has an average aspect ratio in the range of 0.5:1 to 20:1; (g) removing the hard mask layer, wherein the polymer layer after removal of the hard mask layer does not have a detectable amount of hard mask material or reaction products of the hard mask layer and the polymer layer; (h) removing the polymer layer from the support layer to provide a porous membrane; The pore size of the porous membrane (102) is determined by the light pattern, and the porous membrane is 4000 mm ２ The method has a surface area of ​​at least

11. The method of claim 10 , wherein the support layer and the polymer layer have coefficients of thermal expansion that are matched to within ±15% of each other.

12. 12. The method of claim 10 or 11, wherein the support layer and the polymer layer have coefficients of thermal expansion that are matched to within ±10% of each other.

13. The porous membrane (102) is 4000 mm ２ 13. The method of any one of claims 10 to 12, wherein the surface area is equal to or greater than 1000 nm.

14. The porous membrane (102) is 0.1 m ２ 14. The method of any one of claims 10 to 13, wherein the surface area is greater than or equal to 1000 nm.

15. 15. The method of any one of claims 10 to 14, wherein the porous membrane (102) is selected from polyimide, polyamide, polycarbonate, polyetherimide, polyetherketone, polyurethane, synthetic polymer, low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon, polytetrafluoroethylene, thermoplastic polyurethane (TPU), polyethylene, acrylate polymer, or acrylate elastomer.

16. The method of any one of claims 10 to 15, wherein the porous membrane (102) comprises polyimide.

17. 17. The method of any one of claims 10 to 16, wherein the porous membrane (102) has undetectable or biologically insignificant levels of metal contaminants.

18. The method of any one of claims 10 to 17, wherein the pores of the porous membrane (102) have an aspect ratio of 0.5:1 to 20:

1.

19. 4000mm ２ a porous film (102) comprising a polyimide having a continuous surface area of ​​1000 nm or more, a thickness of 5 to 25 μm, and an opening pattern, wherein the openings of the opening pattern have an average aspect ratio in the range of 0.5:1 to 20:1, and the polyimide has no detectable amount of reaction products of the hard mask material or hard mask layer with a polymer, or has 0.15 μg / cm 2 or less of reaction products of the hard mask material or hard mask layer with a polymer; The porous film (102) is a porous film in which the hard mask material contains at least one element, aluminum or silicon, and the reaction product is Al—C.

20. 20. The porous membrane (102) of claim 19, wherein the porous membrane (102) has a pore size standard deviation of 0.3 μm or less.

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