WO2006116865A1

WO2006116865A1 - Method of making micromolds

Info

Publication number: WO2006116865A1
Application number: PCT/CA2006/000699
Authority: WO
Inventors: Christophe Py; Karim Faid
Original assignee: National Research Council Of Canada
Priority date: 2005-05-05
Filing date: 2006-05-03
Publication date: 2006-11-09

Abstract

In a method of making a three dimensional microfluidics mold for the fabrication of microstructures on a substrate. Two or more masters are micromachined to create features in their surface thereof. The two or more masters or their complementary replicates are brought together in combination to form a cavity, and a curable mold-forming liquid into the cavity to make the microfluidics mold or a precursor thereof.

Description

METHOD OF MAKING MICROMOLDS FIELD OF THE INVENTION

[0001] This invention relates to the field of microfabrication, and in particular to a method of making three dimensional microstructures.

BACKGROUND OF THE INVENTION

[0002] Microstructures are required for many applications, such as the fabrication of sensors in the chemical, pharmaceutical and biotechnical industries, displays, optical devices, or chips in the electronics industry. Different techniques have been tried in the fabrication of such structures.

[0003] Soft lithography methods, pioneered in the 90s'by Whitesides (Xia, Angew. Chem. Int. Ed. 37, 550-575 (1998)), achieve very high resolution lithography using processes that are, in principle, as simple as stamping. The stamps or molds are usually made of Poly Dimethyl Siloxane derivatives (PDMS, known commercially as Silicone) and their features are obtained by replication of master molds fabricated by conventional microfabrication methods. The elastomeric and non-sticking properties of PDMS make the molds ideal for printing processes, such as the age-old inking-and-stamping process, but with submicron resolution. An alternative process is microchannel printing, where grooves are formed in the PDMS stamp: when the stamp is pressed in conformal contact with a substrate, the grooves form closed channels that can be filled with a given solution. The solution either wets the substrate to form a thin layer, or is cured or cross-linked to keep the 3D shape of the channel. PDMS or harder materials have also been used for embossing of polymers, and many other derivative methods have been reported.

[0004] Soft-lithography methods are particularly interesting in the area of organic semiconductor science: organic materials are typically not adapted to conventional lithographic methods, but soft-lithography methods can form polymers into patterned devices very simply. For example, optically-pumped lasers have been obtained by embossing highly photoluminescent polymers into distributed feedback gratings; patterned screens have been obtained by printing thin layers or monolayers on an electrode, either to form an insulator between that electrode and the active organic layers, or as an etching mask to pattern that electrode; pixelated PLED displays have been obtained by embossing electroluminescent polymers; conductive polymers have been directly printed on plastic to form flexible polymer electronics. Roll-to-roll printing, often cited as a possible breakthrough method of producing low-cost organic devices, has been demonstrated at the prototype level.

[0005] Chemical patterning, or the printing of chemically-active layers or self-assembled monolayers on flat surfaces, can also be used to fabricate sensors for the chemical, pharmaceutical and biotechnological industries. The space-resolved chemical fictionalization of the surface of a wafer can be used for the selective adsorption of chemical or biological species, the presence, the nature of which (or the activity, in case of living cells) can be detected, identified or monitored by sensors fabricated under the surface of that wafer. For example, in- vitro living cells will preferentially bond to hydrophilic than hydrophobic surfaces, so chemically patterning hydrophilic pads on an hydrophobic surfaces results in controlled positioning of the cells, for example on top of electrodes monitoring their electrophysiological activity (Faid, Biomedical Microdevices, 2005.

[0006] While soft-lithography printing methods have no inherent resolution limitation, practically speaking, their applications are limited to simple devices because of the difficulty of alignment to existing features. Multilayer organic devices can only be obtained by retrofitting conventional aligners to soft-lithography techniques (not commercially available at the present time), but mosaic patterns (side-by-side) need not be printed sequentially as in conventional microfabrication techniques.

[0007] 3D microfluidics has been reported whereby microfluidic channels are fabricated on sheets of Si, glass of PDMS, then holes are drilled through them, and the sheets are assembled and fused. This type of mechanism is however not conducive to high-resolution and is generally limited to mm-size features.

[0008] It is known to make 3 D molds can of assembled pseudo molds, which are either surface machined masters, or replicates of surface machined masters. They are generally made of an elastomer. However, since there is no commercially method of assembling them with sufficient precision, the assembled 3D molds can only be made with relatively low resolution [0009] These prior art techniques are discussed generally in the following references: Jo, "Three-dimensional micro-channel fabrication in PDMS elastomer", J. Microelectromechanical Systems 9(1) 2000; MEMS handbook / edited by Mohamed Gad-el-Hak, Boca Raton, FL : CRC Press, 2001; Chiu, "Patterned deposition of cells and proteins onto surfaces by using 3D microfluidic systems", PNAS 97(6), 2408, 2000; Juncker, "Soft and rigid two-level microfluidic networks for patterning surfaces", JMicromech. and Microeng. 11, 532, 2001; Wu, "Fabrication of complex three- dimensional microchannel systems in PDMS", JACS. 125 (2), 554-559, 2003; Liu, "Development of integrated microfluidic system for genetic analysis", J. Microlitho., Microfab. Microsyst., 2(4) 340-355, 2003; Romanato, X-ray lithography for 3D microfluidic applications, Microelec. Eng. 73-74 Special Iss. SI : 870-875, 2004; Kang, "Development of an assembly- free process based on virtual environment for fabricating 3D microfluidic systems using microstereolithography technology, J. Manufact. Science and Eng. Trans, of the ASME. 126 (4) : 766-771, 2004; Hinder, "Compositional mapping of SAM derivatized within microfluidics networks", Langmuir 18(S); 3151-3158, 2002; Thiebaud, "PDMS device for patterned application of microfluids to neuronal cells arranged by microcontact printing", Biosens. and Bioelec. 17, 87, 2002.

SUMMARY OF THE INVENTION

[0010] hi one aspect the invention the invention provides a method of making a three dimensional microfluidics mold for the fabrication of microstructures on a substrate, comprising micromachining two or more masters to create features in a surface thereof; bringing said two or more of said masters or their complementary replicates together in combination to form a cavity; and introducing a curable mold- forming liquid into said cavity to make said microfluidics mold or a precursor thereof.

[0011] The microfluids mold can also be considered as a form of microstamp that is applied to the surface on which the microstructure is to be formed. Unlike the prior art the present invention permits the fabrication of relatively complex three dimensional microstructures to high resolution because at least a part of the mold, or all of it, is itself formed by molding. This enables much more complex three dimensional molds to be made than is possible by simply bringing together surface machined parts, or their replicates. Also, in practice some features are easier to make than their complementary features, and curable liquids, such as PDMS, not present the same sticking problems can be used to make the final mold, especially if the final mold has features or is made of a material that would be hard to peel off from silicon.

[0012] The curable liquid is typically an organic polymer such as poly dimethyl siloxane, or a derivative thereof. This resulting mold permits the mass production of high resolution three dimensional microstructures on a surface, such as the surface of a silicon substrate.

[0013] In accordance with another aspect the invention provides a microfluidics mold comprising a mold body and a mold cavity, and wherein said mold body or a precursor thereof is a unitary part of polymeric material molded in a cavity defined by two or more micromachined masters or replicates thereof.

[0014] The molded precursor acts like a master if it is reused to make a subsequent mold. An aspect of the invention is therefore that masters, or their replicates, can be assembled and the microcavities between those molds filled with a liquid that is then cured to form a true three-dimensional mold, rather than creating pseudo-3D molds separately then assembling them as in the prior art. Masters, by contrast, can be assembled with higher resolution so the resulting 3D mold formed by embodiments of the present invention can attain higher resolution than the prior art.

[0015] The micromachining may involve patterning substrates, for example, silicon substrates and then forming the mold by bringing together either the patterned substrates directly, or complementary replicas of the substrates made by flowing a curable liquid over the patterned substrate.

[0016] The masters can be microfabricated by conventional bulk or surface micromaching to have surface features. The masters can be based on Si, glass or other suitable substrates and the features can be machined in the bulk of the substrate or patterned in photoresists (e.g. SU8, a very high-aspect ratio photosensitive epoxy well known in the field of MEMs, and distributed in North America by the company Microchem) or other polymeric or inorganic materials which are compatible with microfabrication techniques and have sufficient structural integrity for replication.

[0017] The masters, or their replicates in PDMS or other materials (one may be transparent to facilitate alignment) are aligned in a conventional aligner retrofitted for that special use, and contacted such that some of the surface features are in contact with each other. The empty space between the masters is filled with a filler material (for example, UV, heat or containing a curing agent, and again PDMS can be used) and cured. The top master is removed, forming a mold with vertical connections between the top and the bottom where the surface features were in contact. The process can be repeated as many times as needed to form a sophisticated three dimensional microfluidic chip with high-resolution.

[0018] In an aspect of the invention there is provided a high-resolution 3D process, carried by aligning micro-machined masters or their replicates under an aligner and then filling the space with a curable polymer such as PDMS to form a 3D mold or a precursor thereof.

[0019] The resulting mold or stamp can be used for the parallel and self-aligned printing of mosaic patterns. The use of a stamp is desirable because the mosaic patterns are printed in one single step, and it does not require any alignment between layers, since it is built in the mold. Since the alignment steps are critically time-consuming and have a large impact on yield in any microfabrication process, this is an important consideration.

[0020] Molds in accordance with the invention can be used to carry out the parallel printing of electroluminescent color displays. Additionally, the high-resolution 3D molding method can be applied to form various cost-effective microfluidic assays for biological chips. For example, it is useful in the development of synthetic neural networks and their integration with electrophysiological monitoring systems. In a synthetic neural network, cells have to be close enough for neurites to grow in between them and communication to take place. A suitable chip can be fabricated in PDMS by the proposed 3D molding process.

[0021] In an embodiment of the invention there is provided a method of making a three- dimensional ("3D") microfluidics mold, said method comprising obtaining a first master or replicate thereof having surface features; obtaining a second master or replicate thereof having surface features adapted to align to the surface feature of the first master, such that when the two masters are aligned surface features of the first master touch surface features of the second master; aligning the first and second masters as described in step; and filling the empty space between the two aligned masters with a suitable curable liquid; curing the liquid, and removing at least one of the masters to expose a mold or a precursor thereof made of the cured liquid. [0022] In another embodiment of the invention there is provided a method of fabricating a 3D microfluidics structure comprising the steps of obtaining masters which are microfabricated by conventional bulk or surface micromaching to have surface features, the masters being based on Si, glass or other suitable substrates and wherein the features can be machined in the bulk of the substrate or patterned in photoresists (e.g. SU8, a very high- aspect ratio photosensitive epoxy well known in the field of MEMs) or other polymeric or inorganic materials; making a complementary replicate in a rigid material of one or more than one of the masters by applying a layer of material such as a thick polymer on the substrate, cross linking it, or curing it, and peeling it off; aligning the masters, and/or their complementary replicates in a conventional aligner retrofitted for that special use, and contacted such that some of the surface features are touching; filling the empty space between the aligned complementary replicates and/or masters with a filler material (for example, UV, heat or containing a curing agent, and again PDMS can be used) and cured; removing at least one of the masters and or the complementary replicates and forming a mold where the surface features were touching; and repeating the process as many times as needed to form a sophisticated 3D microfluidic chip with a high-resolution.

[0023] In another embodiment of the invention there is provided a method of making a three-dimensional ("3D") microfluidics structure, said method comprising obtaining a first master having surface features; obtaining a second master having surface features and being complementary to the first master, such that when the two masters are aligned surface features the first master touch surface features of the second master; aligning the first and second masters as described in step (b); filling the empty space between the two aligned masters with a suitable material; and removing the first and the second master to leave behind a structure.

[0024] In some instances it will be desired to obtain at least one master produced using a Si or glass substrate. In some instances at least one master may be formed by bulk machining of and/or photo resist patterning on the substrate.

[0025] In some instances one or more replicas of a master is made and the replica is used in steps c, d and e instead of the master, hi some instances it will be desirable to employ a transparent master (or a transparent replica of a master) to facilitate alignment. [0026] In some instances the surface features are features whose extension away from the wafer is significant compared to its lateral extent, such that by aligning several such features and filling the space in between, a self-supported mold can eventually be obtained.

[0027] In some instances the surface feature are indentation into the wafer such that when filled with filling material it creates a complement replicate and becomes an extension away from the wafer which is significant compared to its lateral extent, such that by aligning several such features and filling the space in between, a self-supported mold can eventually be obtained.

[0028] In some instances it will be desirable to choose surface features of the 1^st and 2^nd master such that the resulting product is self supporting.

[0029] In some instances the surface features include inverted pyramids, towers, walls and channels.

[0030] In some instances the master is covered by a non sticking layer before it is filled with the filling material.

[0031] In yet another embodiment of the invention there is provided a method of making a 3D stamp, comprising the steps of; obtaining a substrate; making a first master by etching inverted pyramids in said substrate; obtaining a second substrate; making a second master by etching elongated channel in said second substrate; obtaining a third substrate; making a third master by etching a reservoir in said third substrate; making complementary replicates of first, second and third masters; aligning said first and second complementary replicates such that said pyramids align with said elongated channels; filing the empty space with said filling material to create a first structure; removing said first master; aligning said third complementary replicate with said first structure such that the reservoir will flow into said elongated channels; and filling the empty space with said filling material to create a stamp.

[0032] In a still further embodiment of the invention there is provided a method of making a PDMS neurochip comprising the steps of obtaining a substrate; making a first master by etching inverted pyramids in said substrate; making a first complementary replicate of the first master; obtaining a second substrate; making a second master by patterning towers and walls in said second substrate; aligning said comlementary replicate with said towers; filing the empty space with said filling material to make a first structure; removing said first and second master; making a second complementary replicate of said second master; and aligning said second complementary replicate with said first structure to create said neurochip.

[0033] The invention also provides a method of producing a patterned substrate, said method comprising obtaining a film on a first side of a substantially inert backing; creating microholes in the film; bonding the second side of the backing to a carrier; obtaining a mask in the first side of the backing and creating windows in the thin film mask, said windows being aligned so as to connect to a microhole; etching the backing through the windows in the mask, to create an inverted pyramid structure resulting in a membrane including the micro-hole; obtaining a second chip defining channels; bonding the second chip to the backing such that a channel is positioned over a microhole in substantially sealing engagement; releasing the backing from the carrier; applying a pattern region on the first side of the membrane in alignment with micro-holes such that a micro-hole is located at the bottom of a well and the well is connected to other wells via trenches; and optionally coating the resulting product with a bio-compatible, electrically insulating plastic so as not to plug the micro-hole, and polylysine or another suitable thin- film to promote the implantation of different types of cells.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: -

[0035] Figure 1 is a perspective view of part a prior art color display;

[0036] Figure 2 illustrates the steps in the fabrication of a color display using a mold made in accordance with an embodiment of the invention;

[0037] Figure 3 is a schemactic illustration of the application of electroluminescent polymer through a single funnel network;

[0038] Figure 4 is a schematic view of a mold with three funnel networks for the respective primary colors of the display;

[0039] Figure 5 shows the steps involved in making a mold according to a first embodiment of the invention; [0040] Figure 6 is a micrograph showing the funnels and channels; [0041] Figure 7 shows a synthetic cell/network interface;

[0042] Figure 8 shows the steps involved in making a mold according to a second embodiment of the invention; and

[0043] Figure 9 shows the steps of making the mold in accordance with the second embodiment in plan view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Figure 1 shows a typical color flat-panel display display, which comprises bars 11 , 12, and 13 of electroluminescent material representing the three primary colours (blue, red and green, represented here by different grey levels) on a substrate 10. The three primary colors are arranged in sequence. A color pixel is the result of the combination of those 3 color sub-pixels addressed by independent electrical means. Any color of the visible spectrum can be displayed by modulating the light output of the primary colors.

[0045] The portion of the flat-panel color display is made with a microfluidics mold or stamp as shown in Figure 2. The stamp with internal cavities forming channels 21 complementary to the bars 11, 12, and 13 is applied to the surface of the silicon substrate 10. The channels are then filled with a curable electroluminescent material in liquid form, which is then allowed to cure to form the bars 11, 12, and 13.

[0046] Figure 3 shows the funnels 30 through which the liquid flows into the channels 21. The layout of the mold is shown in more detail in Figure 4. Three sets of funnels 30, 31, and 32 are provided corresponding to the three primary colors. The funnels open at their narrow end into channels which form the color bars 12, 13, 14, and at their wide end into reservoirs 40, 41, 42, which contain the curable electrolumiscent liquid used to make the color bars. It will be noted that the sets of funnels are offset and the funnels of each set supply every third channel, so that, for example, the funnels 30 might supply the red bars, the funnels 31 might supply the green bars, and the funnels 32 might supply the blue bars. In accordance with an embodiment of the invention the mold is itself made out of a molded material formed from surface machined mold components. [0047] To make a color display, blue, green and red solvated electroluminescent polymer (represented here by different shades of grey) are poured through funnels and distributed to every third channel. The polymers are filled from the top reservoir from which the channels are fed through the funnels. The excess fluids are pulled from the end of the channels by natural as assisted flow. In this way, it is possible to carry out the parallel printing of color PLED displays. In theory there is no limit to how many different chemicals could be printed in parallel, though patterning resolution will be a limiting factor.

[0048] The microfluidics mold shown in Figure 2 can also print chemical agents imparting different surface properties on the substrate. This allows, for example, the selective implantation of different types of cells on a chip, resulting in a multi-cell network chip. It could also be used for the selective recognition of different types of chemical or biological species for multi-analyte detectors.

Example 1

[0049] To produce a mold of the type shown in Figure 4, the process illustrated in Figure 5 is carried out. First (step a) an SiO₂ thin film mask is first deposited on the surface of a first Si substrate with a (100) crystalline orientation to create three arrays of windows about 900 μm square in the thin film mask with a 1.2mm pitch. Each array is laterally shifted by 400μm with respect to the next and with a vertical pitch of lcm.

[0050] The first Si substrate is etched (step b) in a KOH solution to reveal (111) crystalline facets creating inverted pyramid with a square bottom approximately 300μm in size.

[0051] An SiO₂ thin film mask (step c) is formed on the surface of a second Si substrate to create an array of elongated windows with a 300μm width and separated by lOOμm, for a pitch of 400μm. Channels are etched in the Si substrate through the windows by either KOH or other wet or dry echting methods known in the art.

[0052] An SiO₂ thin film mask is deposited on the surface of a third Si substrate with a (100) crystalline orientation to create three large square windows in the thin film mask, with a vertical pitch of lcm. Deep reservoirs are then etched (step d) through the windows using KOH. [0053] The features of the first and second Si substrates are replicated (step e) by applying a thick coat of a PDMS prepolymer to each substrate, and then curing it, typically by cross-linking, and peeling off the PDMS replicate, thereby creating pyramids in the replicate of the first Si substrate and walls in the replicate of the second Si substrate corresponding to the channels. Optionally, anti-stick treatments can be applied to the two PDMS replicates.

[0054] The two PDMS replicates are then aligned such that each wall is in contact with the narrow base of the pyramid, every third wall being aligned with a pyramid from the same array, approaching the two replicates until the narrow base of each pyramid is in contact with one wall, filling the space in between the two replicates with a PDMS prepolymer, curing the PDMS, thereby creating in a PDMS-I thick layer a first interim mold comprising an array of channels, each connected to a funnel, every third channel being connected to a funnel from the same array. The first Si substrate replicate is then peeled off from the PDMS-I thick layer.

[0055] The features of the third Si substrate are replicated in complementary form by applying a thick coat of a PDMS prepolymer, curing it and peeling off the PDMS replicate to obtain three large mesas. Optionally anti-stick treatments are applied to this PDMS replicate but not to the thick layer PDMS-I . This third Si PDMS substrate replicate is then aligned to the PDMS-I replicate and second Si substrate replicate assembly to form a second interim mold such that each array of funnels is in contact with only one mesa and no fluid can penetrate the funnels. The empty space between the third Si substrate replicate and the PDMS-I thick layer is filled with a PDMS prepolymer, which is then cured to form a second thick layer PDMS-2 bonded to the first thick layer PDMS-I (step f).

[0056] Finally, the third Si substrate replicate (step g) is peeled from the top and the second Si substrate replicate is peeled from the bottom to form the final microfiuidics stamp or mold.

[0057] The mold can then be applied on a substrate where forming strips of polymers of three different primary colors is desirable as shown in Figure 2. The three reservoirs are filled each with a polymer of a different primary color. The polymers will flow from each reservoir to every third channel through the funnels and the excess will flow out of the end of the channels, either by natural flow or by being pumped by external means.

[0058] Figure 6 is a micrograph showing the channels and funnels. Example 2

[0059] This second example is a process flow for the fabrication of a synthetic cell shown in Figure 7 for a network/chip interface of the type disclosed in the US patent no. 601,568,220, IPSO, May 6, 2004, Geoff Mealing, NRC. This technique adapts molding to an aligner so as to allow 3D features formed on wafers by conventional micromachining (and in some cases by replication) to be assembled and contacted, and the space in between them to be filled with a curable polymer. The method has been demonstrated with epoxy glues and PDMS as the materials of the final 3D mold, but the use of other materials within the skill of one skilled in the art is also contemplated.

[0060] In this technique, illustrated in Figure 8, a SiN thin film mask 40 (step a) is formed on the surface of a Si wafer 41 with a (100) crystalline orientation to create (preferably about 75-125 μm), more preferably about 100 μm square windows in the thin film mask, with a 200μm pitch. The Si wafer 41 is etched with a KOH solution to reveal (111) crystalline facets 42 creating an inverted pyramid (step b).The complementary feature of a pyramid is the formed in steps c(i) and C(ii) by applying a thick polymer 44, on top of the Si wafer and curing it, for example by cross-linking, then peeling it off the Si wafer.

[0061] A tower-and-wall pattern with a 200 μm pitch step (d) in Figure 8 and step (d) in Figure 9 is created on a second substrate, for example, using an SU8 photoresist on a Si wafer patterned by conventional optical lithography. Optionally, anti-stick treatments can be applied to the two patterned substrates. This tower-and-wall pattern 45, 46 also shown in Figure 9 (step d) creates a complementary well 48 and trench 49 pattern in the final mold.

[0062] The tower-and-wall pattern is aligned with the pyramid pattern (step e) and the space between filled with a curable polymer 51. The contact area between the apex of the pyramids and the towers form, in complementary molding, a microhole 50, the size of which can be controlled by the elasticity of the materials employed and the pressure applied.

[0063] The polymer is cured and the two substrates are removed to obtain a PDMS chip defining channels 46 with a 200 μm pitch. The PDMS chip 52 is then inverted and fused to an Si chip 53 (step g) such that a channel is positioned over a microhole 50 in substantially sealing engagement with the funnels facing the microchannels 57. The entire chip is optionally coated with parylene and/or polylysine or other thin-films known to promote the implantation of different types of cells.

[0064] Table III sets out steps for the production and fusing of two PDMS chips. Table III

Steps al SiN Plasma Enhanced Chemical Vapor Deposition, 1 μm. a2 I Litho 1 , defining 100 square openings b Si etch, KOH, 80C.

Replicate channels in PDMS to obtain self-standing PDMS film (lmm thick) with pyramids on top. Bond PDMS film to glass substrate.

Litho 2 in SU8-50 on Si wafer to define towers and walls. el j Align Si wafer with replicate obtained in C, and contact with controlled force so apex of pyramids are flattened on SU8-50 to 3-5 μm squares e2 Fill space with PDMS;

Cure; peel Si wafer and PDMS replicate obtained in C

gl Litho 3 in SU8-50 on second Si wafer to walls as complement of channels. g2 Replicate channels in PDMS to obtain self-standing PDMS film (lmm thick) with channels on top.

Spin PDMS thin film (5-10 μm) on PDMS replicate obtained in step G Align replicate obtained in G with replicate obtained in F; cure PDMS. [0065] Wells and trenches are conducive to selected implantation of neurons and directed growth of neurites (picture above is actual pattern with 20μm square wells, 3μm wide trenches, all being 70μm deep). Micro-hole (black dot) membranes (dotted outline) have been described in the literature as allowing monitoring the electrophysiological activity of ion channels in neurons. Subterranean microfluidics channels (grey) will allow both recording this activity and delivering drug to the cell to allow chemical patch-clamping.

[0066] The inverted pyramids can be bulk micro-machined in Si, and then replicated a first time. Independently, a pattern of towers and walls patterns (ie, the complement of wells and trenches) would be fabricated in SU8 on a Si or glass chip or etched in its bulk. Those two patterns are then be aligned and contacted and the void filled with PDMS or another curable polymer. PDMS is elastomeric and reports have suggested that small apertures may collapse. However, the 3D molding process has been successful with harder UV curable epoxies such 1191 -M epoxy provided by Dymax Corp. and commonly used as a medical device adhesive that shouldn't have that issue. In that case, the towers and walls pattern would have to be treated (e.g. thin PDMS film) to avoid sticking.

[0067] A third pattern is fabricated in SU8 on a Si or glass chip or etched in its bulk with the complement of microfluidic channels features, then replicated in PDMS or another curable polymer. The two parts are then aligned and fused.

Claims

1. A method of making a three dimensional micro fluidics mold for the fabrication of microstructures on a substrate, comprising: micromachining two or more masters to create surface features thereon; bringing said two or more of said masters or their complementary replicates together in combination to form a cavity; and introducing a curable mold-forming liquid into said cavity to make said microfluidics mold or a precursor thereof.

2. A method as claimed in claim 1 , wherein said two or more masters or their complementary replicates are aligned so that machined surface features of the respectve masters or their complementary replicates are in contact.

3. A method as claimed in claim 1, wherein said curable mold-forming liquid is an organic polymer.

4. A method as claimed in claim 3, wherein said organic polymer is poly dimethyl siloxane, or a derivative thereof.

5. A method as claimed in claim 1 , wherein said at least one master is micromachined by surface etching.

6. A method as claimed in any one of claims 1 to 5, wherein at least one of the components brought together to form the cavity is complementary replicate of one of the masters, and wherein the complementary replicate is made by flowing a curable liquid into the surface features of its corresponding master.

7. A method as claimed in claim 6, wherein the curable liquid used to make said replicate is an organic polymer.

8. A method as claimed in claim 7, wherein said organic polymer used to make said complementary replicates is poly dimethyl siloxane, or a derivative thereof.

9. A method as claimed in claim 1 , creating complementary replicates from said at least two masters, bringing said complementary replicates together in alignment to create said cavity, flowing curable liquid into said cavity, and curing said liquid to create said microfluidics mold.

10. A method as claimed in claim 1, comprising : patterning first, second, and third masters; creating complementary first, second, and third complementary replicates of said respective patterned first, second, and third masters; bringing said first and second replicates together in alignment to form a first cavity; flowing curable liquid into said first cavity to create a mold precursor; bringing said mold precursor together with the replicate of said third master to form a second cavity; and flowing curable liquid into said cavity mold to create said microfluidics mold.

11. A method as claimed in claim 12, wherein said first master is patterned to form a set of arrays of pyramid cavities therein, each array being offset relative to the other arrays.

12. A method as claimed in claim 11, wherein said pyramid cavities are formed by masking a silicon substrate with a (100) crystalline orientation, and etching with etch solution to reveal (111) crystalline facets.

13. A method as claimed in claim 12, wherein said second master is patterned to form a plurality of channels therein, and the narrow tips of the pyramids of the replicate of the second master are brought into alignment with walls in the replicate of the second master complementary to the channels in the second master.

14. A method as claimed in claim 13, wherein said third master is patterned to form an array of deep reservoirs, and mesas in the replicate of said third master complementary to said deep reservoirs are brought into alignment with each array of funnels formed in the first interim mold by the pyramids in the replicate of the first master complementary to the pyramid cavities in the first master.

15. A method as claimed in claim 1, comprising: creating a complementary replicate of a first master; bringing the complementary replicate of the first master together with a second master for form a first cavity; introducing curable liquid into the first cavity to create a precursor of the mold; creating a complementary replicate of a third master; and fusing the complementary replicate of the third master with the precursor to create the microfluidics mold.

16. A method as claimed in claim 15, comprising forming pyramidal cavities in said first master such that pyramids are formed on the complementary replicate of the first master; creating an array of towers in said second master; and contacting the apices of the pyramids with the towers whereby the precursor comprises an array of pyramidal funnels leading to respective wells complementary to the towers in the second master.

17. A method as claimed in claim 16, wherein said towers are interconnected by walls, which create complementary trenches in the precursor.

18. A method as claimed in claim 16, wherein the apices of the pyramids contact the towers in such a way that the microholes are formed between the pyramidal funnels and the corresponding cells.

19. A method as claimed in claim 18, wherein the replicate of the first master and the second master are brought together with sufficient pressure to form said microholes in the resulting precursor.

20. A method as claimed in claim 17 or 18, wherein the complementary replicate of the third master comprises recessed channels in communication with said respective cells.

21. A microfluidics mold comprising a mold body and a mold cavity, and wherein said mold body or a precursor thereof is a unitary part of polymeric material molded in a cavity defined by two or more micromachined masters or replicates thereof.

22. A microfluidics mold as claimed in claim 21 , wherein said polymeric material is poly dimethyl siloxane, or a derivative thereof.

23. A microfluidics mold as claimed in claim 22, wherein said body is of unitary form and comprises arrays of funnels leading to respective channels, the arrays of channels being in communication with respective reservoirs.

24. A microfluidics mold as claimed in claim 23, wherein the arrays of funnel are offset relative to each other, each array of funnels supplying respective sets of channels.

25. A microfluidics mold as claimed in claim 21, wherein the mold body comprises a precursor of unitary form fused to a replicate of a micromachined master.

26. A microfluidics mold as claimed in claim 25, wherein said mold body comprises an array of funnels leading through microholes to corresponding cells in communication with microchannels.

27. A method of making a three-dimensional ("3D") microfluidics mold, comprising obtaining a first master or replicate thereof having surface features; obtaining a second master or replicate thereof having surface features adapted to align to the surface feature of the first master, such that when the two masters are aligned surface features of the first master touch surface features of the second master; aligning the first and second masters as described in step; and filling the empty space between the two aligned masters with a suitable curable liquid; curing the liquid, and removing at least one of the masters to expose a mold or a precursor thereof made of the cured liquid.

28. A method of fabricating a 3D microfluidics structure comprising the steps of obtaining masters which are microfabricated by conventional bulk or surface micromaching to have surface features; making a complementary replicate in a rigid material of one or more than one of the masters by applying a layer of material such as a thick polymer on the substrate, curing it, and peeling it off; aligning the masters, and/or their complementary replicates, and contacted them such that some of the surface features are touching; filling the empty space between the aligned complementary replicates and/or masters with a curable filler material; curing the filler material; removing at least one of the masters and or the complementary replicates and forming a mold where the surface features were touching; and repeating the process as many times as needed to form a complex 3D microfluidic chip with a high-resolution.

29. A method as claimed in claim 28 wherein the masters are based on Si, glass or other suitable substrates and wherein the features are machined in the bulk of the substrate or patterned in photoresists or other polymeric or inorganic materials.

30. A method of making a 3D stamp, comprising the steps of; obtaining a substrate; making a first master by etching inverted pyramids in said substrate; obtaining a second substrate; making a second master by etching elongated channel in said second substrate; obtaining a third substrate; making a third master by etching a reservoir in said third substrate; making complementary replicates of first, second and third masters; aligning said first and second complementary replicates such that said pyramids align with said elongated channels; filing the empty space with a curable filler material to create a first structure; removing said first master; aligning said third complementary replicate with said first structure such that the reservoir will flow into said elongated channels; and filling the empty space with said curable material to create a mold.

31. A method of producing a patterned substrate, said method comprising obtaining a film on a first side of a substantially inert backing; creating microholes in the film; bonding the second side of the backing to a carrier; obtaining a mask in the first side of the backing and creating windows in the thin film mask, said windows being aligned so as to connect to a microhole; etching the backing through the windows in the mask, to create an inverted pyramid structure resulting in a membrane including the micro-hole; obtaining a second chip defining channels; bonding the second chip to the backing such that a channel is positioned over a microhole in substantially sealing engagement; releasing the backing from the carrier; applying a pattern region on the first side of the membrane in alignment with micro-holes such that a micro-hole is located at the bottom of a well and the well is connected to other wells via trenches.

32. A method as claimed in claim 31, wherein the resulting product is coated with a bio-compatible, electrically insulating plastic so as not to plug the micro-hole, and polylysine or other suitable thin-film to promote the implantation of different types of cells.