A METHOD FOR PRODUCING A BLOOD FILTER AND A BLOOD FILTER

Abstract

A method for producing a blood filter, the blood filter being a filter for filtering blood, the method comprising providing a first layer; providing a block copolymer layer above the first layer; converting the block copolymer layer to a mask by selectively removing domains of the block copolymer layer; etching pores through the first layer in regions exposed by the mask; wherein a pore size is below 20 nm, the pore size preferably being 6.6 nm or smaller.

Claims

1. A method for producing a blood filter, the blood filter being a filter for filtering blood, the method comprising providing a first layer; providing a block copolymer layer above the first layer; converting the block copolymer layer to a mask by selectively removing domains of the block copolymer layer; etching pores through the first layer in regions exposed by the mask; wherein a pore size is below 20 nm, the pore size preferably being 6.6 nm or smaller.

2. The method according to claim 1, further comprising providing a substrate before providing the first layer, such that the first layer is provided above the substrate; forming a channel through the substrate, the channel being configured to provide fluid communication between a first and a second end of the channel, the first end of the channel being directly below the etched pores of the first layer, whereby components of blood pass both the pores and the channel, when the blood filter is in use.

3. The method according to claim 2, wherein the channel extends through the substrate in a direction orthogonal to the first layer, and wherein the second end of the channel is arranged at a bottom side of the substrate; or the channel extends along an interface between the substrate and the first layer, and wherein the second end of the channel is arranged at an opening in the first layer.

4. The method according to claim 1, further comprising: removing the mask; and forming a polymer brush layer above the first layer after removal of the mask, the polymer brush layer being a polymer layer comprising a plurality of polymer chains wherein each polymer chain is attached to an underlying layer at one end of the polymer chain.

5. The method according to claim 4, further comprising: providing an oxide layer above the first layer before providing the block copolymer layer; and wherein the polymer brush layer is formed above the oxide layer such that the polymer chains of the polymer brush layer are attached to the first layer by the oxide layer.

6. The method according to claim 1, further comprising: depositing a film on inner surfaces of the pores of the first layer; or oxidizing inner surfaces of the pores of the first layer.

7. The method according to claim 1, wherein the block copolymer layer comprises vertical cylindrical domains, each vertical cylindrical domain being a cylindrical domain with an orientation perpendicular to the first layer; and wherein the block copolymer layer is converted to a mask by selectively removing the vertical cylindrical domains of the block copolymer layer, whereby the pores of the first layer comprise a plurality of round holes.

8. The method according to claim 1, wherein the block copolymer layer comprises lamella domains or horizontal cylindrical domains, each horizontal cylindrical domain being a cylindrical domain with an orientation parallel with the first layer; and wherein the block copolymer layer is converted to a mask by selectively removing the lamella domains or horizontal cylindrical domains of the block copolymer layer, whereby the pores of the first layer comprise a plurality of slits.

9. The method according to claim 1, the method further comprising shaping the pores of the first layer such that the pores taper.

10. The method according to claim 1, wherein a fill-factor of the pores is at least 40%, the fill-factor of the pores being open pore area per area unit of the first layer.

11. The method according to claim 1, wherein the first layer is 20 nm to 2000 nm thick.

12. The method according to claim 1, wherein the substrate comprises one or more integrated circuits.

13. The method according to claim 1, wherein the block copolymer layer comprises: polystyrene-polymethylmethacrylate block copolymers, and/or polylactic acid-polyvinylpyridine block copolymers, and/or polyethylene oxide-polydimethylsiloxane block copolymers.

14. The method according to claim 1, wherein the block copolymer layer comprises block copolymers with a molecular weight below 30 kg/mol.

15. A blood filter for filtering blood, the blood filter comprising: a first layer; pores extending through the first layer, wherein a pore size is below 20 nm, the pore size preferably being 6.6 nm; wherein the pores of the first layer comprises a plurality of round holes and wherein the plurality of round holes are arranged as a first lattice in a first region of the first layer and as a second lattice in a second region of the first layer, the first and second lattice having same periodicity but different orientations, or wherein the pores of the first layer comprises a plurality of slits, and wherein each slit of the plurality of slits extends along a curved path across a surface of the first layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0124] The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.

[0125] FIG. 1 illustrates a flowchart of a method

[0126] FIGS. 2A-D illustrate production of round hole pores

[0127] FIGS. 3A-D illustrate production of slit pores

[0128] FIGS. 4A-B illustrate a filter with a vertical channel

[0129] FIGS. 5A-B illustrate a filter with a horizontal channel

[0130] FIG. 6 illustrates tapered round hole pores

[0131] FIG. 7 illustrates tapered slit pores

[0132] FIGS. 8A-B illustrate pore shrinking using a polymer brush layer

[0133] FIG. 9 illustrates pore shrinking using a film on inner surfaces of pores

[0134] FIG. 10 illustrates pore shrinking using oxidized inner surfaces of pores

[0135] FIG. 11 illustrates a flowchart of a method

[0136] FIGS. 12A-G illustrate steps of a method

[0137] FIG. 13 illustrates a filter

[0138] FIG. 14 illustrates a filter

DETAILED DESCRIPTION

[0139] In cooperation with attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to a preferable embodiment, being not used to limit the claimed scope. This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0140] In the following, methods for producing filters and filters will be discussed. The filters discussed may be used as blood filters.

[0141] FIG. 1 illustrates a flowchart of a method 100 for producing a filter 1. The method 100 may be used to produce a filter 1 with pores 32 in the shape of round holes 50 or in the shape of slits 60. The method 100 illustrated in FIG. 1 will hereinafter be discussed together with FIGS. 2A-D and FIGS. 3A-D. FIGS. 2A-D illustrate cut-outs of the filter 1 during the production of round hole pores 32, 50. FIGS. 3A-D illustrate cut-outs of the filter 1 during the production of slit pores 32, 60.

[0142] The method 100 comprises the optional step of providing S101 a substrate 10. The method 100 comprises the steps of providing S102 a first layer 30, e.g. above the substrate 10, and providing S104 a block copolymer layer 40 above the first layer 30.

[0143] In the following, the method will be described as the first layer 30 being provided on a substrate 10. However, it should be understood that the method may also be applied in situations where a substrate 10 is not used.

[0144] The substrate 10 may e.g. be a stack comprising a wafer 12 and an oxide layer 14 on top of the wafer 12. The first layer 30 may comprise a semiconductor, an oxide or a nitride, e.g. Si, SiO.sub.2, Si.sub.3N.sub.4. The block copolymer layer 40 may comprise polystyrene-polymethylmethacrylate (polystyrene-PMMA) block copolymers, and/or polylactic acid-polyvinylpyridine block copolymers, and/or polyethylene oxide-polydimethylsiloxane block copolymers.

[0145] FIG. 2A illustrates a cut-out of a filter 1 (during production) after a BCP layer 40 has been provided. The BCP layer 40 in FIG. 2A comprises vertical cylindrical domains 45. Such vertical cylindrical domains 45 may be formed e.g. when the BCP layer 40 comprises polystyrene-b-PMMA which has been baked at 250? C. The vertical cylindrical domains 45 may be configured to have diameter smaller than 100 nm, such as smaller than 20 nm. The vertical cylindrical domains 45 may be configured to have a fill-factor of at least 40%.

[0146] FIG. 3A illustrates a cut-out of a filter 1 (during production) after a BCP layer 40 has been provided. The BCP layer 40 in FIG. 2A comprises lamella domains 46. Such lamella domains 46 may be formed e.g. when the BCP layer 40 comprises polystyrene-b-PMMA which has been baked at 250? C. The lamella domains 46 may be configured to have a width smaller than 100 nm, such as smaller than 20 nm. The lamella domains 46 may be configured to have a fill-factor of at least 40%. As understood by the skilled person, the lamella domains 46 may be replaced by horizontal cylindrical domains.

[0147] The method 100 further comprises the step of converting S106 the block copolymer layer 40 to a mask 48 by selectively removing domains of the block copolymer layer 40.

[0148] FIG. 2B illustrates a cut-out of a filter 1 (during production) after the vertical cylindrical domains 45 have been removed. Thus, a mask 48 is formed where the first layer 30 may be exposed in the regions where the vertical cylindrical domains 45 previously were. Vertical cylindrical domains 45 of PMMA may be selectively removed from a polystyrene surrounding by a wet etch of acid acetic.

[0149] FIG. 3B illustrates a cut-out of a filter 1 (during production) after the lamella domains 46 have been removed. Thus, a mask 48 is formed where the first layer 30 may be exposed in the regions where the lamella domains 46 previously were. Lamella domains 46 of PMMA may be selectively removed from a polystyrene surrounding by a wet etch of acid acetic.

[0150] The method 100 further comprises the step of etching S108 pores 32 through the first layer 30 in regions exposed by the mask 48. For example, the pores may be formed by dry etching.

[0151] FIG. 2C illustrates a cut-out of a filter 1 (during production) after etching S108 of pores 32 through the first layer 30. The pores 32 herein have the shape of round holes 50. The pores 32 may have the same shape as the previous vertical cylindrical domains 45. FIG. 2D illustrates the round hole pores 32, 50 after removal of the mask 48.

[0152] FIG. 3C illustrates a cut-out of a filter 1 (during production) after etching S108 of pores 32 through the first layer 30. The pores 32 herein have the shape of slits 60. The pores 32 may have the same shape as the previous lamella domains 46. FIG. 3D illustrates the slit pores 32, 50 after removal of the mask 48. A close-up view of the slit pores 32, 50 is also presented in FIG. 3D.

[0153] The method 100 may further comprise the optional step of forming S114 a channel 20 through the substrate 10, the channel 20 being configured to provide fluid communication between a first 21 and a second 22 end of the channel 20, the first end 21 of the channel 20 being directly below the etched pores 32 of the first layer 30.

[0154] The channel 20 may extend through the substrate 10 in a direction orthogonal to the first layer 30, wherein the second end 22 of the channel 20 is arranged at a bottom side of the substrate 10. Such a channel may be termed a vertical channel. As an alternative, the channel 20 may extend along an interface between the substrate 10 and the first layer 30, wherein the second end 22 of the channel 20 is arranged at an opening 26 in the first layer. Such a channel 20 may be termed a horizontal channel.

[0155] FIG. 4A illustrates a perspective view of a cross-section of a filter 1 with a vertical channel. FIG. 4B illustrates a perspective view of the same cross-section of the filter 1 of FIG. 4A, seen from the bottom side.

[0156] FIG. 5A illustrates a top view of a filter 1 with a horizontal channel. FIG. 5B illustrates a perspective view of a cross-section of the filter 1 of FIG. 5A. The cross-section being along the A-A line in FIG. 5A.

[0157] A vertical channel, such as the one in FIGS. 4A-B, may be formed by backside etching of the substrate. Dry etching may be used, e.g. deep reactive ion etching. Alternatively, or additionally, wet etching may be used, e.g. wet etching with potassium hydroxide KOH. Alternatively, or additionally, laser ablation may be used. In FIGS. 4A-B there is a support 92 for the membrane. The support may comprise a part of the substrate 10. Thus, the method may comprise forming a support 92 for the membrane. Thus, formation of the channel may be configured to leave part of the substrate 10 below the membrane such that a support 92 for the membrane is formed.

[0158] A horizontal channel, such as the one in FIGS. 5A-B, may be formed in a buried oxide layer (BOX layer) arranged below the first layer 30. The BOX layer may herein be an oxide layer 14 which is part of the substrate 10, as illustrated in FIG. 5B. The opening 26 in the first layer 30 may be formed next to the pores 32 of the first layer 30, e.g. at a distance from the pores 32 of the first layer 30. The opening 26 in the first layer 30 may be formed at a distance from the membrane.

[0159] The horizontal channel may then be formed by etching, e.g. wet etching, the horizontal channel between the opening in the first layer and the pores of the first layer. Thus, the horizontal channel may extend underneath, and in parallel with, the first layer, as illustrated in FIGS. 5A-B. Etch fluid may herein pass through the pores 32 and/or the opening 26 in the first layer 30 to form the horizontal channel. The dimensions and/or direction of the channel 20 may be controlled by e.g. doping selective etching. For example, in FIGS. 5A-B the BOX layer 14 in the region between the pores 32 and the opening 26 may be doped differently from the rest of the BOX layer 14 such that the etch selectively etches this region.

[0160] According to an embodiment, a protective layer may be deposited on the first layer 30 on a frontside of the filter 1 during etching from the backside.

[0161] The method 100 may further comprise the optional step of shaping S109 the pores 32 of the first layer 30 such that the pores 32 taper. FIG. 6 illustrates tapered round hole pores 32, 50 in a cut-out of a filter 1 (during production). FIG. 7 illustrates tapered slit pores 32, 60 in a cut-out of a filter 1 (during production). A close-up view of one of the slit pores 32, 60 is also presented in FIG. 7.

[0162] The tapered pores 32 may, as illustrated, be wider at the top side of the first layer 30 than at the bottom side of the first layer 30. Thus, the diameter of a round hole pore 32, 50 may be larger at the top side of the first layer 30 than at the bottom side of the first layer 30. Similarly, the width of a slit pore 32, 60 may be larger at the top side of the first layer 30 than at the bottom side of the first layer 30.

[0163] Pores 32 of the first layer 30 may be shaped S109 to taper by undercut etching such that an undercut under the mask is formed. Undercut etching may be achieved by use of an isotropic etch.

[0164] The method 100 may comprise the optional step of shrinking the pores 32. In the following, three different ways to shrink the pores 32 will be discussed: pore shrinking using a polymer brush layer 70, pore shrinking using a film 80 on inner surfaces of the pores 32, and pore shrinking using oxidated inner surfaces 82 of the pores. FIG. 11 illustrates a flow chart of a method 100 comprising optional steps for shrinking the pores.

[0165] FIG. 8A-B schematically illustrates how pores 32 may be shrunk using a polymer brush layer 70. FIG. 8A is a cross-sectional view of a filter 1 (during production, before forming the channel 20). FIG. 8B is a top view of the same filter 1. The polymer brush layer 70 comprises a plurality of polymer chains 72 wherein each polymer chain is attached to an underlying layer at one end of the polymer chain 72, as seen in FIG. 8A. Further, in FIG. 8A the polymer chains 72 are attached to an oxide layer 74, the oxide layer 74 being arranged on top of the first layer 30. As seen in FIG. 8A-B, polymer chains 72 in the vicinity of a pore 32 may extend, with the unattached end, over the edge of the pore 32. This may happen around the circumference of the pore 32. Thereby the pore size may be reduced. As seen in FIG. 11 the method may comprise the optional steps of removing S111 the mask 48 and thereafter forming S113 a polymer brush layer 70 above the first layer 30. If the polymer brush layer 70 is to be attached to an oxide layer 74, the method 100 may further comprise the step of providing S103 an oxide layer 74 above the first layer 30 before providing the BCP layer 40.

[0166] To exemplify the above: An oxide layer 74 of e.g. silicon oxide, e.g. 200 nm thick silicon oxide, may be provided on top of the first layer 30 before providing the BCP layer 40. After etching of the pores 30 and removal of the mask 48, a polymer brush layer 70 may be spin coated or polymerized on top of the oxide layer 74 such that the polymer chains 72 attach to the oxide layer 74. In accordance with the above, the oxide layer 74 may function as a hardmask during etching of the underlying layer, it may further increase the nanopore aspect ratio, and it may further act as a binding surface for the polymer brush layer 70.

[0167] FIG. 9 schematically illustrates how pores 32 may be shrunk using a film 80 on inner surfaces of pores 32. FIG. 9 is a cross-sectional view of a filter 1 (during production, before forming the channel 20). The illustrated film 80 conformally coats the surface of the first layer 30, including the inner surfaces of the pores 32. The film 80 may be deposited by atomic layer deposition (ALD) and/or chemical vapor deposition and/or self-assembly of monolayers and/or metal ion infusion using polymer brushes and/or sputtering. The film 80 may be deposited before or after the formation of the channel 20. If the film 80 is deposited before the formation of the channel 20, parts of the film 80 at the bottom of the pores 32 may be removed by etching. In accordance with the above, and as seen in FIG. 11, the method may comprise the optional step of depositing S115 a film 80 on inner surfaces of the pores 32 of the first layer 30.

[0168] FIG. 10 schematically illustrates how pores 32 may be shrunk using oxidized inner surfaces 82 of pores 32. The inner surfaces of the pores may be oxidized during etching of the pores 32 or in a subsequent oxidation step. The inner surfaces of the pores 32 may be oxidized by thermal oxidation, e.g. by dry or wet thermal oxidation. In accordance with the above, and as seen in FIG. 11, the method may comprise the optional step of oxidizing S117 inner surfaces of the pores 32 of the first layer 30.

[0169] In the following an example of a production flow for a filter 1 with a vertical channel 20 is given. The production flow is illustrated by FIGS. 12A-G which show the filter (during production) in cross-sectional views.

[0170] A silicon wafer 12 with an oxide layer 14 on top forms the substrate 10. The silicon wafer may be 450-600 ?m thick. The oxide layer 14 may be e.g. 2000 nm thick. A first layer 30 of Si, polycrystalline Si, SiO.sub.2, Si.sub.3N.sub.4, or SiNx may be provided on top of the oxide layer 14, see FIG. 12A. The thickness of the first layer 30 may be e.g. 20-2000 nm, preferably 20-500 nm. As shown in FIG. 12B, a select area of the first layer 30 may be opened by conventional photolithography patterning of a hardmask 37, the hardmask 37 may comprise a dielectric (Al.sub.2O.sub.3) or metal (TaN, Ru etc.). This process can be achieved by dry or wet etch means.

[0171] As seen in FIG. 12C, a spin on carbon layer 38 and spin on glass layer 39 may be deposited, followed by a BCP layer 40. The BCP layer 40 may be baked to self-assemble into suitable domains. The domains may be vertical cylindrical domains 45 with a diameter smaller than 100 nm, such as smaller than 20 nm. The domains may be lamella domains 46 with a width smaller than 100 nm, such as smaller than 20 nm.

[0172] The BCP layer 40 may then be converted to a mask 48. The spin on carbon layer 38 and/or the spin on glass layer 39 may further be converted to part of the mask 48.

[0173] Selective dry etching may then be used to transfer the pattern of the mask 48 to the underlying first layer 30, as seen in FIG. 12D. The hardmask 37 may also be removed, as further seen in FIG. 12D.

[0174] Next, a backside resist 9 may be deposited and patterned with standard photolithography. The backside resist 9 may subsequently be developed after which dry etching leads to part of the channel 20 being formed, e.g. the part up to the oxide layer 14, see FIG. 12E. Part of the substrate 10 may be left to form a support 92 for the membrane.

[0175] The backside resist may subsequently be removed and supports 92 may be thinned down, e.g. to a height of 50-100 ?m, see FIG. 12F.

[0176] Finally, the exposed oxide layer 14 may be wet etched to release the first layer 30 which then forms the membrane layer in the released region.

[0177] According to an embodiment, the final release of the membrane can be achieved through wet etching (e.g., buffered hydrogen fluoride (HF)) or dry etching (e.g., plasma, vapor HF).

[0178] FIGS. 13 and 14 illustrate two different types of filters 1 which may be produced by the method 100.

[0179] FIG. 13 illustrates a perspective view of a cross-section of a filter 1 wherein the pores 32 of the first layer 30 comprise a plurality of round holes 50 and wherein the plurality of round holes 50 are arranged as a first lattice 51 in a first region 53 of the first layer 30 and as a second lattice 52 in a second region 54 of the first layer 30, the first 51 and second 52 lattice having same periodicity but different orientations. In the figure, grain boundaries between the different regions have been marked with lines, it should be understood that these lines are for illustrative purposes only.

[0180] FIG. 14 illustrates a perspective view of a cross-section of a filter 1 wherein the pores 32 of the first layer 30 comprise a plurality of slits 60, and wherein each slit of the plurality of slits 60 extends along a curved path across a surface of the first layer 30. A close-up view of the slit pores 32, 50 is also presented in FIG. 14.

[0181] In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.