A method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with reflow

Abstract

The present invention discloses a method for manufacturing a three-dimensional microstructure by combining a heterogeneous material filling mold with a reflux method, comprising the following steps: preparing a PDMS negative mold; pouring two or more mobile phase materials into the PDMS negative mold in steps, curing, and then demoulding to obtain a heterogeneous positive mold structure containing two or more materials; heating the obtained heterogeneous positive mold structure and / or exposing it to a steam environment, reflowing one or more materials in the heterogeneous positive mold structure, and adjusting the degree of deformation of each material, and obtaining; the steam in the steam environment is formed by the volatilization of a solvent that can dissolve one or more materials in the heterogeneous positive mold structure. The method of the present invention can flexibly control the mold size, material properties and processing parameters, and manufacture 3D microstructures with high curvature, curved surface-non-curved surface composite 3D microstructures and multi-curvature complex curved surface microstructures, which is conducive to the development of new microfluidic devices and micro-nano optical devices, and adapts to different application requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of micro-machining, and in particular relates to a method for manufacturing a three-dimensional microstructure by combining a reverse mold with filling a heterogeneous material and reflow. Background Art

[0002] In recent years, with the development of micromachining technology, researchers have proposed various microstructure forming methods, mainly including photolithography, laser micromachining, hot embossing, injection molding, 3D printing and CNC engraving. Although these processing technologies can produce microstructures with high precision, they generally have great limitations in the flexibility of microstructure production. Generally, they can only process microstructures with regular shapes, that is, the microstructures have neat and clear edges and corners, and their 3D surfaces are usually rectangular or polyhedral. With the further expansion of the application of micromachining technology, it is becoming more and more important to produce microstructures or microdevices with complex three-dimensional curved surface features. In order to realize the production of microstructures with curved surface features, two main technologies have been developed in recent years: one is the grayscale photomask technology, which uses a photomask with a grayscale gradient distribution for exposure, so that the photoresist is exposed to different degrees of cross-linking or dissolution due to the action of ultraviolet light of different intensities, thereby producing a microstructure with curved surface features; the other is the photoresist reflow technology, which uses the increased fluidity of some positive photoresists when the baking temperature is higher than the glass transition temperature, so that the microstructures with neat corners formed by photolithography are formed into microstructures with smooth surfaces through reflow. Recently, researchers have further expanded the conventional photoresist reflow technology, and have produced artificial compound eye devices with complex three-dimensional curved surface structures by making multi-layer positive photoresist microstructures and combining them with photoresist reflow technology.

[0003] However, the above two technologies have great limitations in practical applications. Grayscale photomask technology requires expensive, high-resolution grayscale photomasks, which are complex to process and have high costs. In photoresist reflow technology, positive photoresists are usually used, and their spin coating thickness is often small (single spin coating thickness <50μm), which limits the height of the microstructure that can be produced. In addition, the positive photoresist material itself is often susceptible to acid, alkali or organic reagent corrosion, and its application range is limited. In particular, these technologies are powerless in the production of highly complex 3D microstructures, such as high-curvature 3D microstructures (such as spherical microstructures), curved-non-curved composite 3D microstructures, and complex curved surface microstructures. Therefore, it is urgent to develop new process methods to produce new devices with complex three-dimensional microstructures, such as cell culture chips with integrated spherical microcavity arrays, spherical microlenses, bionic compound eye systems, etc., to meet the development needs of micro-nano biological analysis technology and micro-nano optical technology. Summary of the invention

[0004] In view of the above-mentioned prior art, the present invention provides a method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with a reflow process, so as to overcome the limitation that the traditional micro-machining technology cannot manufacture complex three-dimensional microstructures with integrated curved surface features.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: to provide a method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with a reflow, comprising the following steps:

[0006] (1) preparing a PDMS negative mold;

[0007] (2) pouring two or more mobile phase materials into the PDMS female mold step by step, curing the mold, and then demolding to obtain a heterogeneous male mold structure containing two or more materials;

[0008] (3) heating the obtained heterogeneous positive mold structure and / or exposing it to a steam environment, reflowing one or several materials in the heterogeneous positive mold structure, and adjusting the deformation degree of each material, thereby obtaining the obtained structure; the steam in the steam environment is formed by the volatilization of a solvent that can dissolve one or several materials in the heterogeneous positive mold structure.

[0009] The heterogeneous positive mold structure is heated or exposed to a solvent vapor environment that can dissolve one of the materials, and the heating temperature and time or the saturated pressure and exposure time of the solvent vapor are controlled to cause one or several of the structural materials to reflux, so that the local microstructure composed of these materials forms a curved shape due to surface tension. Since different materials have different glass transition temperatures or the same solvent has different solubilities for different materials, the degree of deformation of each material is adjusted by controlling the heating temperature and time of the heterogeneous positive mold structure or controlling the saturated pressure and time of its exposure to the solvent vapor, thereby obtaining a microstructure with a complex three-dimensional shape that cannot be prepared by traditional micro-machining technology.

[0010] Based on the above technical solution, the present invention can also be improved as follows.

[0011] Furthermore, the PDMS negative mold structure in step (1) is prepared by the following method: using photolithography technology, laser processing technology, 3D printing technology or CNC engraving technology to make a master mold, and then pouring and molding to obtain the master mold.

[0012] Furthermore, before pouring and filling in step (2), the PDMS female mold is degassed in a vacuum environment of 5 to 15 kPa for at least 20 minutes.

[0013] Furthermore, in step (2), the mobile phase material is a photoresist solution and a polystyrene solution and / or a two-component epoxy adhesive, and its kinematic viscosity is less than 300 St.

[0014] Furthermore, in step (2), the difference in glass transition temperature between the two or more mobile phase materials is greater than 10°C.

[0015] Furthermore, the curing in step (2) is heating cross-linking curing, room temperature cross-linking curing, light radiation cross-linking curing or heating volatilization-cooling curing.

[0016] Furthermore, the heating temperature in step (3) is not less than 25°C.

[0017] Furthermore, in step (3), the steam environment is a saturated gas pressure environment of the solvent.

[0018] Furthermore, the material reflux in step (2) is repeated several times.

[0019] The beneficial effects of the present invention are as follows: by flexibly adjusting the mold size, material properties and processing parameters, 3D microstructures with high curvature (such as spherical microstructures), curved-non-curved composite 3D microstructures and multi-curvature complex curved microstructures can be produced, which is helpful to realize the development of new microfluidic devices and micro-nano optical devices, adapt to different application requirements, and is expected to promote the development of microfluidic technology and micro-nano optical technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the process of preparing a spherical microlens structure based on the method;

[0021] Figure 2 This is a micrograph of a spherical micromirror structure prepared based on the method;

[0022] Figure 3 A schematic diagram of the process of preparing a funnel-shaped micro-through-hole array chip based on the method;

[0023] Figure 4 Schematic diagram of the process of preparing a bionic compound eye structure based on this method. DETAILED DESCRIPTION

[0024] The specific implementation modes of the present invention are described in detail below with reference to the embodiments.

[0025] Example 1

[0026] Spherical microlens structures (such as SU-8 and epoxy glue) are made by filling and reflowing two heterogeneous materials. Figure 1 The specific steps are:

[0027] (1) Preparation of master mold: First, a master mold is made by photolithography process. The specific process is as follows: SU-8 3050 negative photoresist is spin-coated on a clean 4-inch silicon wafer (500 rpm, 12 s; 1000 rpm, 40 s) and allowed to stand for 2-3 h; after pre-baking (95°C, 30 min), exposure (3 min 0 s), post-baking (93.5°C, 5 min), natural cooling and development (PGEMA, 8 min), hard baking (170°C, 30 min), and the silicon wafer is cooled, the master mold with a cylindrical structure is completed.

[0028] (2) Preparation of PDMS negative mold: The negative mold structure was made by PDMS casting. The specific process was as follows: PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1, stirred evenly, and placed in a vacuum container for evacuation and degassing (1 h). The degassing PDMS was taken out and poured on the master mold. After standing for 15 min, it was moved to a hot plate for heating and curing (80 °C, 2 h). After cooling, the cured PDMS was peeled off from the mold and the excess PDMS was cut off with a scalpel to obtain a PDMS negative mold structure with a cylindrical microcavity.

[0029] (3) Heterogeneous material filling mold: A heterogeneous positive mold structure is made by two-step pouring filling. The specific process is as follows: first, the PDMS negative mold prepared in step (2) is degassed in a 10 kPa vacuum for 2 h ( Figure 1 a), then cast SU-8 photoresist (solute content 70%) diluted with cyclopentanone on the PDMS negative mold under light-proof conditions ( Figure 1 b), after standing for 30 min, use a blade to scrape off the excess SU-8 photoresist on the surface of the PDMS negative mold ( Figure 1 c), and the PDMS negative mold filled with SU-8 photoresist was transferred to a hot plate and baked at 95°C for 12 h. Due to the evaporation of the solvent, the volume of the SU-8 photoresist filled in the microcavity shrank and was deposited at the bottom of the microcavity ( Figure 1 d); After cooling, pour the mixed two-component epoxy glue ( Figure 1 e), and cover with a glass slide, let it stand for 30 minutes, then transfer it to a hot plate and heat it at 95°C for 1 hour to further promote the cross-linking and curing of the epoxy glue ( Figure 1 f); After cooling, peel off the PDMS female mold ( Figure 1 g), a heterogeneous positive mold structure consisting of two materials, SU-8 and epoxy glue, was obtained.

[0030] (4) Reflow of heterogeneous positive mold structure: SU-8 is thermally reflowed to form a spherical microlens structure. The specific process is as follows: the heterogeneous positive mold structure prepared in step (3) is placed in an oven and heated at 70°C for 10 min (Note: the glass transition temperature of uncrosslinked SU-8 photoresist is 55°C). The viscosity of the uncrosslinked SU-8 photoresist is greatly reduced due to heating, which increases its fluidity. Based on the principle of minimum energy, the SU-8 photoresist flowing under the action of surface tension forms a spherical shape, while the epoxy glue as the base structure maintains its original shape ( Figure 1 h); after cooling to room temperature (<30°C), SU-8 returns to a solid state (i.e., glassy state), and then is exposed to ultraviolet light and baked at 85°C for 1 hour to complete the cross-linking of SU-8 ( Figure 1 i), a spherical microlens structure with good physical and chemical stability was obtained ( Figure 2 ).

[0031] Example 2

[0032] The funnel-shaped micro-through hole array filter membrane (such as SU-8 photoresist, polystyrene and epoxy glue) was made by filling, reflowing and reverse molding. Figure 3 The specific steps are:

[0033] (1) Preparation of master mold: First, a master mold is made by photolithography process. The specific process is as follows: SU-8 3050 negative photoresist is spin-coated on a clean 4-inch silicon wafer (500rpm, 12s; 3000rpm, 30s), and allowed to stand for 2-3h; after pre-baking (95℃, 30min), exposure (3min40s), and post-baking (93.5℃, 5min); after natural cooling, a layer of SU-83050 negative photoresist is spin-coated again on the first layer of photoresist (500rpm, 12s; 3000rpm, 30s), and allowed to stand for 2-3h; after pre-baking (95℃, 30min), exposure (3min40s), post-baking (93.5℃, 5min), development (PGEMA, 8min), hard baking (170℃, 30min), and the silicon wafer is cooled, the master mold with a stepped cylindrical structure is completed.

[0034] (2) Preparation of PDMS negative mold: The negative mold structure was made by PDMS casting. The specific process was as follows: PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1, stirred evenly, and placed in a vacuum container for evacuation and degassing (1 h). The degassing PDMS was taken out and poured on the master mold. After standing for 15 min, it was moved to a hot plate for heating and curing (80 °C, 2 h). After cooling, the cured PDMS was peeled off from the mold and the excess PDMS was cut off with a scalpel to obtain a PDMS negative mold structure with a stepped cylindrical microcavity.

[0035] (3) Heterogeneous material filling mold: A heterogeneous positive mold structure is made by three steps of pouring and filling. The specific process is as follows: first, the PDMS negative mold prepared in step (2) is degassed in a 15 kPa vacuum for 0.5 h ( Figure 3 a), then cast SU-8 photoresist (solute content 10%) diluted with cyclopentanone on the PDMS negative mold under light-proof conditions ( Figure 3 b), after standing for 30 min, use a blade to scrape off the excess SU-8 photoresist on the surface of the PDMS negative mold ( Figure 3 c), and the PDMS negative mold filled with SU-8 photoresist was transferred to a hot plate and baked at 95°C for 24 h. Due to the evaporation of the solvent, the volume of the SU-8 photoresist filled in the microcavity shrank and was deposited in the lower microcavity structure ( Figure 3 d); after cooling, UV exposure and baking at 85°C for 1 hour to complete the cross-linking of SU-8; then, a polystyrene solution (25 wt%) prepared based on gamma-martinolactone solvent was poured on the surface of the PDMS female mold ( Figure 3 e), scrape off the excess polystyrene solution on the surface of the PDMS negative mold with a blade, and transfer the mold to a hot plate to remove the solvent by two steps of thermal drying (4h@95℃, 12h@150℃) ( Figure 3 f); After cooling naturally to room temperature, pour the mixed two-component epoxy glue ( Figure 3 g), and covered with a glass slide, left to stand for 30 min, then transferred to a hot plate and heated at 95 °C for 1 h to further promote the cross-linking and curing of the epoxy glue ( Figure 3 h); after cooling, the PDMS female mold is peeled off to obtain a heterogeneous male mold structure composed of three materials: SU-8, polystyrene and epoxy glue ( Figure 3 i).

[0036] (4) Heterogeneous mold reflow: The integrated curved surface complex microstructure is formed by dissolving and reflowing polystyrene. The specific process is as follows: the heterogeneous positive mold prepared in step (3) and the glass dish containing gamma-martinol solvent are placed in a closed drying dish and left to stand for 30 minutes. Since the volatilized gamma-martinol solvent dissolves the polystyrene, the fluidity of the polystyrene microstructure increases. Based on the principle of minimum energy, the polystyrene flowing under the action of surface tension forms a hemispherical curved surface structure, while the cross-linked SU-8 and epoxy adhesive structure parts remain in their original shape ( Figure 3 j); After the mold is transferred to the air, the gamma-martinolactone solvent evaporates, and the polystyrene returns to a solid state, thereby obtaining a heterogeneous positive mold structure with an inverted funnel-shaped structure.

[0037] (5) Inverted molding to make a funnel-shaped micro-through hole array filter membrane: A funnel-shaped micro-through hole array filter membrane is made by PDMS casting inverted molding. The specific process is as follows: PDMS prepolymer and curing agent are mixed at a mass ratio of 10:1, stirred evenly, placed in a vacuum container to evacuate and remove bubbles (1 hour), and the defoamed PDMS is taken out and cast on the inverted funnel-shaped heterogeneous positive mold made in step (4) ( Figure 3 k), and a glass slide with polyvinyl alcohol (PVA) was placed on the PDMS, and a 2kg weight was placed on the glass slide. After standing for 1 hour, it was moved to a hot plate for heating and curing (80°C, 2h) ( Figure 3 l), after cooling, remove the glass slide and peel the PDMS / PVA composite film from the mold ( Figure 3 m), and remove the PVA support layer by water-soluble method ( Figure 3 n), thereby obtaining a filter membrane having a funnel-shaped micro-through hole array ( Figure 3 o), which can be applied to the rapid and efficient enrichment of circulating tumor cells.

[0038] Example 3

[0039] The bionic compound eye structure (such as SU-8 and polystyrene) was made by filling and reflowing two heterogeneous materials. Figure 3 The specific steps are:

[0040] (1) Preparation of master mold: First, a master mold is made by photolithography process. The specific process is as follows: SU-8 3050 negative photoresist is spin-coated on a clean 4-inch silicon wafer (500rpm, 12s; 1000rpm, 40s), and allowed to stand for 2-3h; after pre-baking (95℃, 30min), exposure (3min40s), and post-baking (93.5℃, 5min); after natural cooling, a layer of SU-83010 negative photoresist is spin-coated again on the first layer of photoresist (500rpm, 12s; 3000rpm, 40s), and allowed to stand for 2-3h; after pre-baking (95℃, 30min), exposure (3min40s), post-baking (93.5℃, 5min), development (PGEMA, 8min), hard baking (170℃, 30min), and the silicon wafer is cooled, the master mold with a multi-level cylindrical array structure is completed.

[0041] (2) Preparation of PDMS negative mold: The negative mold structure was made by PDMS casting. The specific process was as follows: PDMS prepolymer and curing agent were mixed in a mass ratio of 10:1, stirred evenly, and placed in a vacuum container for evacuation and degassing (1 h). The degassing PDMS was taken out and cast on the master mold. After standing for 15 min, it was moved to a hot plate for heating and curing (80 °C, 2 h). After cooling, the cured PDMS was peeled off from the mold and the excess PDMS was cut off with a scalpel to obtain a PDMS negative mold structure with a multi-level cylindrical microcavity array.

[0042] (3) Heterogeneous material filling mold: A heterogeneous positive mold structure (such as Figure 4 The specific process is as follows: first, the PDMS negative mold prepared in step (2) is degassed in a 5 kPa vacuum for 2 h ( Figure 4 a), then cast SU-8 photoresist (solute content 5%) diluted with cyclopentanone on the PDMS negative mold under light-proof conditions ( Figure 4 b), after standing for 30 min, the PDMS negative mold filled with SU-8 photoresist was transferred to a hot plate and baked at 95 °C for 12 h. Due to the evaporation of the solvent, the volume of the SU-8 photoresist filled in the microcavity shrank and was deposited at the bottom of the microcavity ( Figure 4 c); after cooling, a frame-shaped PDMS sheet is reversibly bonded to the surface of the PDMS female mold to form a liquid storage fence, and a polystyrene solution (25wt%) prepared based on gamma-martinolactone solvent is poured into the fence ( Figure 4 d), and the mold was transferred to a hot plate and the solvent was removed by two-step thermal drying (4h@95℃, 12h@150℃) ( Figure 4 e); After cooling naturally to room temperature, the PDMS fence and the female mold were peeled off to obtain a heterogeneous multi-level cylindrical array male mold structure composed of SU-8 and polystyrene ( Figure 4 f).

[0043] (4) Heterogeneous mold reflow: The bionic compound eye structure is formed by step-by-step thermal reflow of SU-8 and polystyrene. The specific process is as follows: the heterogeneous positive mold prepared in step (3) is pasted on a glass slide and placed in an oven at 70°C for 5 min. The viscosity of the uncrosslinked SU-8 photoresist on the upper layer is greatly reduced due to heating, resulting in fluidity. The SU-8 photoresist flowing under the action of surface tension forms a hemispherical curved surface shape, while the lower polystyrene structure basically maintains its original shape (Note: the glass transition temperature of polystyrene is ≈100°C) ( Figure 4 g); after cooling, it was exposed to UV light and baked at 110°C for 1 hour to complete the cross-linking of SU-8 ( Figure 4 h), and on the other hand, the thermal reflow of polystyrene is realized, so that the bottom polystyrene structure forms a spherical crown-shaped curved surface structure under the action of surface tension. After cooling, a bionic compound eye with a multi-level convex curved surface structure is obtained ( Figure 4 i).

[0044] Although the specific implementation of the present invention is described in detail in conjunction with the embodiments, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with reflow, characterized in that: The following steps are involved: (1) Preparation of PDMS negative mold; (2) pouring two or more mobile phase materials into the PDMS female mold step by step, curing the mold, and then demolding to obtain a heterogeneous male mold structure containing two or more materials; (3) heating the obtained heterogeneous positive mold structure and / or exposing it to a steam environment, reflowing one or more materials in the heterogeneous positive mold structure, and adjusting the degree of deformation of each material, thereby obtaining a product; wherein the steam in the steam environment is formed by the volatilization of a solvent that can dissolve the one or more materials in the heterogeneous positive mold structure; Wherein, the mobile phase material is a photoresist solution and a polystyrene solution and / or a two-component epoxy adhesive, and its kinematic viscosity is less than 300St; The photoresist solution is SU-8 photoresist.

2. The method for manufacturing a three-dimensional microstructure by combining heterogeneous material filling and reverse molding with reflow according to claim 1, characterized in that: The PDMS negative mold structure in step (1) is prepared by the following method: using photolithography technology, laser processing technology, 3D printing technology or CNC engraving technology to make a master mold, and then pouring and molding to obtain the master mold.

3. The method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with reflow according to claim 1, characterized in that: Before pouring and filling in step (2), the PDMS negative mold is degassed in a vacuum environment of 5-15 kPa for at least 20 minutes.

4. The method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with reflow according to claim 1, characterized in that: The difference in glass transition temperature between the two or more mobile phase materials in step (2) is greater than 10°C.

5. The method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with reflow according to claim 1, characterized in that: The curing in step (2) is heating cross-linking curing, room temperature cross-linking curing, light radiation cross-linking curing or heating volatilization-cooling curing.

6. The method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with reflow according to claim 1, characterized in that: The heating temperature in step (3) is not less than 25°C.

7. The method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with reflow according to claim 1, characterized in that: The steam environment in step (3) is a saturated gas pressure environment of the solvent.

8. The method for manufacturing a three-dimensional microstructure by filling a heterogeneous material with a mold and combining it with reflow according to claim 1, characterized in that: The material reflux in step (3) is repeated several times.

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