Abstract
A multi-level microfluidic device is provided. The device includes a silicon wafer substrate and a stack of layers arranged on the silicon wafer substrate. The stack comprises a plurality of fluidic silicon layers, wherein each fluidic silicon layer includes a microfluidic structure at least one intermediate layer. The at least one intermediate layer is arranged between two fluidic silicon layers, and a fluid inlet and a fluid outlet in fluid connection with at least one of the fluidic silicon layers. Each layer in the stack is formed by deposition or growth. Methods for manufacturing microfluidic devices is also provided.
Claims
1. A method of manufacturing a microfluidic device, comprising the steps of: a) forming a first layer of a first material on a substrate; b) forming a first pattern in the first layer; c) forming a first conformal layer on the first layer, wherein the first conformal layer conforms to the first pattern in the first layer; d) forming a second layer of the first material on the first conformal layer; e) forming a second pattern in the second layer; f) forming a second conformal layer on the second layer, wherein the second conformal layer conforms to the second pattern in the second layer; and g) removing the first and second layers of the first material with chemical etching, wherein the first and second layers of the first material are sacrificial layers and wherein the first and second conformal layers are inert to the chemical etching.
2. The method according to claim 1, wherein the steps a), c), d), and f) are performed by deposition or growth.
3. The method according to claim 2, wherein the deposition is chemical vapor deposition or physical vapor deposition.
4. The method according to claim 2, wherein the growth is selected from epitaxial, layer-by-layer, joint islands, layer-plus-island, and isolated islands growth modes.
5. The method according to claim 1, wherein the first conformal layer comprises a material that is inert to hydrofluoric acid etching.
6. The method according to claim 1, wherein the second conformal layer comprises a material that is inert to hydrofluoric acid etching.
7. The method according to claim 1, wherein the first conformal layer and/or second conformal layer comprises a silicon layer.
8. The method according to claim 1, wherein the first sacrificial layer and the second sacrificial layer are dielectric layers.
9. The method according to claim 1, wherein the first and second conformal layers are made of (polycrystalline) silicon, silicon carbide, or silicon nitride.
10. The method according to claim 1, wherein step (g) is performed by hydrofluoric acid etching.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The above, as well as additional objects, features and advantages of the present disclosure, 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.
(2) FIG. 1 is a schematic illustration in a cross-sectional view of a representative microfluidic device according to an example of the present disclosure.
(3) FIG. 2 is a schematic illustration in a cross-sectional view of a representative microfluidic device according to an example of the present disclosure.
(4) FIGS. 3a to 3h show a schematic illustration of an example method according to the second aspect. FIG. 3a shows the first step 321 of forming a sacrificial layer 302 on a substrate 301. FIG. 3b shows the second step 322 of forming a first pattern 303 in the first sacrificial layer 302. FIG. 3c shows the step 323 of forming a first conformal layer 305a on the first sacrificial layer 302. FIG. 3d shows the subsequent steps 324, 325 of forming a second sacrificial layer 306 on top of the first conformal layer and forming a second pattern 307 in the second sacrificial layer. FIG. 3e shows the step of forming 326 a second conformal layer 305b on top of the second patterned 306 sacrificial layer. FIG. 3f shows the stack after steps of forming 327 a third sacrificial layer, forming 328 a pattern in the third sacrificial layer, and forming 329 a third conformal layer 310 such that it fills the space between the formed pattern. FIG. 3g shows the step of forming 330 a fluid inlet 308 and a fluid outlet 309. FIG. 3h shows the step 331 of removing the sacrificial layers to form a multi-level microfluidic device.
(5) FIGS. 4a to 4f show a schematic illustration of an example method according to the third aspect. FIG. 4a shows the first step 421 of providing a first silicon-based layer 402 on a substrate 401. FIG. 4b shows the step 422 of forming a first pattern 403 in the first silicon-based layer 402. FIG. 4c shows the step 423 of forming a first non-conformal layer 405a on the first silicon-based layer. FIG. 4d shows the subsequent step 424 of forming a second silicon-based layer 406 on the first non-conformal layer 405a and the step 425 of forming a pattern 407 in the second silicon-based layer. FIG. 4e shows the step 426 of forming a second non-conformal layer 405b on the second silicon-based layer 406. FIG. 4f shows the step 427 of forming a fluid inlet 408 and a fluid outlet 409 in fluid communication with each other.
DETAILED DESCRIPTION OF THE DISCLOSURE
(6) FIG. 1 shows a schematic illustration of a microfluidic device 1 according to an example of the present disclosure. In the example shown therein, the device 1 comprises three fluidic silicon-based layers 103a-c, and two intermediate layers 105a-b. The intermediate layer 105a separates the fluidic silicon-based layers 103a and b, and the intermediate layer 105b separates the fluidic silicon-based layers 103b and c. The layers 103a-c and 105a-b make up a stack 102. The device may be further provided with a fluid inlet 107 and a fluid outlet 109. The fluid inlet 107 may be in fluid connection with the fluid outlet 109 and at least one of the fluidic silicon-based layers 103 a-c. The microfluidic device further comprises a substrate 101 onto which the stack 102 may be provided. In embodiments, the stack 102 further comprises a top layer (not shown) for sealing the microfluidic device. The top layer may be at least partially transparent and may be made from e.g. glass, Pyrex, and/or polymers.
(7) The substrate 101 may be a silicon substrate, usually a monocrystalline silicon wafer substrate. Such wafers are known.
(8) The fluidic silicon-based layers 103a-c may be made from a material comprising silicon, usually a silicon material inert to chemical etching by hydrofluoric acid (HF), such as, but not limited to, for example (polycrystalline) silicon, Si.sub.XN.sub.Y, and/or SiC. The fluidic silicon-based layers comprise a microfluidic structure adapted to transport minute volumes of fluid within the layer. In the present example, the microfluidic structure comprises fluidic channels which may contain different geometries: several other structures may be contemplated, including pillars, groves, channels and/or wells.
(9) In the example shown in FIG. 1, the intermediate layers 105a-b may be made of the same material as the fluidic silicon-based layers 103a-c. Thus, the intermediate layers 105a-b also comprise a silicon-based material, such as (polycrystalline) silicon, Si.sub.XN.sub.Y, and/or SiC.
(10) The layers have been provided by deposition or growth, such as by chemical vapor deposition or physical vapor deposition. Thus, the device 1 may be a multi-level microfluidic device which requires only one wafer substrate.
(11) The fluidic silicon-based layers 103 may be provided with one or several fluid interconnections 111, allowing for fluid transport between individual layers. The fluid interconnections may be vertical or nearly vertical channels that enables fluid communication between individual fluid silicon-based layers.
(12) In the embodiment shown in FIG. 1, a microfluidic device having three fluidic layers is shown. However, it would be readily understood that the number of fluidic layers could be two, or more
(13) FIG. 2 also shows a schematic illustration of a representative microfluidic device 2 according to an example of the present disclosure. In the example shown therein, the device 2 comprises three fluidic silicon-based layers 203a-c, and two intermediate layers 205a-b. The intermediate layer 205a separates the fluidic silicon-based layers 205a and b, and the intermediate layer 205b separates the fluidic silicon-based layers 203b and c. The layers 203a-c and 205a-b make up a stack 202. The device may be further provided with a fluid inlet 207 and a fluid outlet 209. The fluid inlet 207 may be in fluid connection with the fluid outlet 209 and at least one of the fluidic silicon-based layers 203a-c. The microfluidic device further comprises a substrate 201 onto which the stack 202 may be provided. In embodiments, the stack 202 may further comprises a top layer (not shown) for sealing the microfluidic device. In embodiments, the top layer may be at least partially transparent and may be made from e.g. glass, Pyrex, and/or polymers.
(14) The substrate 201 may be a silicon substrate such as a monocrystalline silicon wafer substrate. Such wafers are known.
(15) The fluidic silicon-based layers 203a-c may be made from a material comprising silicon, usually a silicon material inert to chemical etching by hydrofluoric acid (HF), such as, but not limited to, for example (polycrystalline) silicon, Si.sub.XN.sub.Y, and/or SiC. The fluidic silicon-based layers comprise a microfluidic structure adapted to transport minute volumes of fluid within the layer. In the present example, the microfluidic structure comprises pillars but several other structures may be contemplated, such as for example grooves, channels and/or wells.
(16) In the example shown in FIG. 2, the intermediate layers 205a-b may be made of a different material than the fluidic silicon-based layers 203a-b.
(17) The layers have been provided by deposition or growth, such as by chemical vapor deposition or physical vapor deposition. Thus, the device 2 may be a multi-level microfluidic device which requires only one wafer substrate.
(18) The fluidic silicon-based layers 203 may be provided with one or several fluid interconnections 211, allowing for fluid transport between individual layers. The fluid interconnections may be vertical or nearly vertical channels that enables fluid communication between individual fluid silicon layers.
(19) FIGS. 3a to 3h show a schematic illustration of an example method of manufacturing a multi-level microfluidic device disclosed in the second aspect of the present disclosure. In the embodiment shown in FIGS. 3a to 3h, the layers of the first material may be sacrificial layers, usually made of SiO.sub.2. FIG. 3a shows the first step 321 of forming a sacrificial layer 302 on a substrate 301. The substrate may be a monocrystalline silicon wafer. Herein, the term “sacrificial layer” denotes a layer that is used during the method but may be at least partially removed before the final product is achieved. The sacrificial layer may be a SiO.sub.2 layer. The sacrificial layer 302 may be formed on the substrate 301 by deposition or growth, such as by chemical vapor deposition or physical vapor deposition. The sacrificial layer may be formed such that it covers the surface of the substrate.
(20) In the embodiment shown in FIG. 2, a microfluidic device having three fluidic layers is shown. However, it would be readily understood that the number of fluidic layers could be two, or more.
(21) FIG. 3b shows the second step 322 of forming a first pattern 303 in the first sacrificial layer 302. The first pattern may be formed by photolithography and dry etching, which are known techniques. The etchant should be capable of etching a pattern in the sacrificial layer, but not capable of etching the conformal layer. The first pattern 303 may have many different shapes and forms, but may in principle be used as a template for the subsequent forming of a first conformal layer shown in FIG. 3c.
(22) FIG. 3c shows the step 323 of forming a first conformal layer 305a on the first sacrificial layer 302. As can be seen in FIG. 3c, the first conformal layer conforms to the shape of the pattern 303 in the sacrificial layer. When forming the conformal layer 305a, the conformal layer will conform to the shape of the pattern 303. Thus, the conformal layer fills the spaces made by the pattern. The conformal layer 305a may further extend above the space between the pattern 303 to form a layer on top of the patterned sacrificial layer. Herein, the conformal layer comprises silicon and may be selected from for example silicon, (poly)crystalline silicon, Si.sub.XN.sub.Y, and/or SiC. In embodiments, the conformal layer may be formed by deposition or growth. During deposition, the conformity of a layer to an underlying pattern can be tuned by selecting deposition parameters such as temperature and pressure.
(23) The conformal layer extending above the pattern in the sacrificial layer can be removed by a step of polishing and/or etching. In some examples, the conformal layer on top of the patterned sacrificial layer may be removed completely, except for the parts of the first conformal layers that may be positioned in between the first pattern, and a further conformal layer is formed on top of the patterned sacrificial layer using deposition or growth. This may be useful in examples where a very smooth surface is desired.
(24) FIG. 3d shows the subsequent steps 324, 325 of forming a second sacrificial layer 306 on top of the first conformal layer and forming a second pattern 307 in the second sacrificial layer. The second pattern may be identical to the first pattern. The second pattern may also differ from the first pattern. In embodiments, the second pattern may be formed using photolithography and dry etching. The etchant should be capable of etching a pattern in the sacrificial layer, but not capable of etching the conformal layer.
(25) FIG. 3e shows the step of forming 326 a second conformal layer 305b on top of the second patterned 306 sacrificial layer. After formation, the second conformal layer may extend above the pattern in the sacrificial layer. The conformal layer extending above the pattern may then be removed, and a new conformal layer may be deposited on top to achieve a desired thickness of the conformal layer.
(26) The steps of forming a sacrificial layer, forming a pattern in the sacrificial layer and forming a conformal layer on top of the sacrificial layer may be repeated in that order to form a desired number of layers of the stack.
(27) FIG. 3f shows the stack after steps of forming 327 a third sacrificial layer, forming 328 a pattern in the third sacrificial layer, and forming 329 a third conformal layer 310 such that it fills the space between the formed pattern. FIG. 3f shows the stack after a desired number of layers has been formed. In the example shown in FIG. 3f, the number of fluidic silicon layers may be three, but the present disclosure relates to any number of fluidic silicon layers equal to or above two.
(28) FIG. 3g shows the step of forming 330 a fluid inlet 308 and a fluid outlet 309. The fluid inlet 308 and the fluid outlet 309 should be in fluid communication with each other. Further optional steps include forming fluid interconnections that connects a first fluidic layer with another fluidic layer.
(29) FIG. 3h shows the step 331 of removing the sacrificial layers to form a multi-level microfluidic device. After removal, the stack may be formed by the materials deposited as conformal layers 305a-c.
(30) The step of removing the sacrificial layer may be typically performed by chemical etching using hydrofluoric acid. The hydrofluoric acid may be flushed into the device through the inlet. Thus, the sacrificial layer may be made of a material susceptible to chemical etching using hydrofluoric acid. Such materials include SiO.sub.2.
(31) Further optional steps include providing a final capping to the microfluidic device. In embodiments, the final capping may be transparent and may comprise for example a polymer or a glass. The step of providing a final capping may be performed before or after step 331.
(32) When the sacrificial layers have been removed, a microfluidic device comprising a substrate and a stack comprising a plurality of fluid silicon-based layers and at least one intermediate layer, wherein the intermediate layer may be arranged between two fluidic silicon layers, may be formed. Fluidic silicon-based layers and intermediate layer(s) may be provided in an alternating fashion such that the fluidic silicon layers may be separated by an intermediate layer.
(33) The method described in relation to the FIGS. 3a to 3h could equally well be inverted. Stated differently, in another embodiment of the second aspect the layer structure is inverted as compared to the layer structure of FIGS. 3a to 3h. Thus, the first layer 302 may also be a first silicon-based layer, the pattern 303 may be formed in the first silicon-based layer, and wherein a sacrificial conformal layer may be a first conformal layer 305a, the first sacrificial conformal layer conforms to the shape of the pattern 303 in the silicon-based layer and so on in an alternating fashion until the desired number of levels have been deposited. Thereafter, the sacrificial conformal layer may be removed to form a microfluidic device according to the first aspect of the present disclosure.
(34) In the embodiment shown in FIGS. 3a to 3h, a microfluidic device having three fluidic layers may be formed. However, it would be readily understood that the number of fluidic layers could be two, or more. The method according to the second aspect may be highly scalable.
(35) In the second aspect, one of the first material and the material of the structural layer may be a silicon-based material, such as for example (polycrystalline) silicon, SiC, or Si.sub.xN.sub.y. The other material may then be an oxide material, such as SiO.sub.2, used to form the sacrificial layers.
(36) FIGS. 4a to 4h shows a schematic illustration of an example method of manufacturing a multi-level microfluidic device disclosed in the third aspect of the present disclosure.
(37) FIG. 4a shows the first step 421 of providing a first silicon-based layer 402 on a substrate 401. The silicon-based layer may be formed by means of deposition or growth, such as by chemical vapor deposition or physical vapor deposition. The first silicon-based layer comprises silicon. The first silicon-based layer may be for example (polycrystalline) silicon, silicon nitride, or silicon carbide. The substrate may be a monocrystalline silicon wafer. The first silicon-based layer may be formed such that it covers the substrate material.
(38) FIG. 4b shows the step 422 of forming a first pattern 403 in the first silicon-based layer 402. The pattern may be a pattern adapted to act as a microfluidic structure. The pattern may include different geometries, such as pillars, channels, grooves, wells or the like. The pattern may be formed by photolithographic masking followed by physical and/or chemical etching.
(39) FIG. 4c shows the step 423 of forming a first non-conformal layer 405a on the first silicon-based layer. Herein, the term “non-conformal layer” denotes a layer which during deposition does not conform to the shape of the underlying layer. Herein, the non-conformal layer may be deposited (or grown) such that it does not conform to the shape of the pattern formed in the first silicon-based layer. Instead of conforming to the shape of the pattern in the first silicon-based layer, it may be provided as an intermediate layer intended for separating the first patterned silicon-based layer from a subsequent patterned silicon-based layer. The non-conformal layer may comprise a dielectric material, such as a silicon oxide. A non-conformal deposition or growth can be provided by tuning the parameters during formation.
(40) FIG. 4d shows the subsequent step 424 of forming a second silicon-based layer 406 on the first non-conformal layer 405a and the step 425 of forming a pattern 407 in the second silicon-based layer. The steps 424 and 425 may be performed in the same or a similar manner as the step 421-423, using the same types of materials. However, the second pattern may in some examples differ from the first pattern.
(41) FIG. 4e shows the step 426 of forming a second non-conformal layer 405b on the second silicon-based layer 406. The second non-conformal layer may be formed in the same or similar manner as the first non-conformal layer. In some embodiments, the second non-conformal layer may also be a final capping that may be made of a transparent material such as a glass or a transparent polymer.
(42) FIG. 4f shows the step 427 of forming a fluid inlet 408 and a fluid outlet 409 in fluid communication with each other. The fluid inlet 408 and the fluid outlet 409 may further be in fluid connection communication with at least one of the patterned silicon-based layers. FIG. 4f further shows the optional step 427 of forming a third silicon-based layer 410 on top of the second non-conformal layer 405b and the optional step of forming a third pattern 411 in the third silicon-based layer.
(43) Further optional steps include forming a final capping on top of the third patterned silicon-based layer. It is readily understood that the method may include further steps to form further patterned silicon-based layers and non-conformal layers in an alternating manner.
(44) In some examples, the method further comprises the step of forming a fluid interconnection between silicon-based layers. This may be performed by forming a hole in at least one non-conformal layer.
(45) In the embodiment shown in FIGS. 4a to 4f, a microfluidic device having three fluidic layers may be formed. However, it would be readily understood that the number of layers could also be two, or higher. The method according to the second aspect is highly scalable.
(46) The disclosure 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 disclosure, as defined by the appended claims.
