Method for preparing polymer micro-nano structure by utilizing micro / nano photo-thermal photoetching

Abstract

The invention belongs to the technical field of polymer micro-nano structures, and particularly relates to a method for preparing a polymer micro-nano structure by utilizing micro / nano photo-thermal photoetching. The method comprises the following steps of: spin-coating or adhering a polymer with thermal response characteristics such as thermal crosslinking, thermal phase change or thermal phase separation and assembly on a mask plate by using the mask plate with a prefabricated nano structure; the method comprises the following steps of: inducing changes such as thermocuring, microphase separation molecule assembly, dissociation and the like of a polymer by adopting a light or laser projection technology and the like on the basis of micro-nano-scale photo-thermal hot spots generated by a local plasma resonance mechanism under illumination, so that polymer micro-nano structures such as micro / nano stripes or balls and the like are quickly formed, and finally micro-nano photoetching is realized. The polymer micro-nano structure prepared by the method has the characteristic size of more than ten nanometers to micrometers, and the spatial arrangement mode is adjustable. The method is not limited by optical diffraction limit, the photoetching feature size directly depends on the size of the prefabricated structure on the mask, cross-scale photoetching can be realized, and the technological process is greatly simplified.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer micro-nano structure preparation, and specifically relates to a method for preparing a polymer micro-nano structure. Background Art

[0002] Photolithography is widely used in the manufacture of microelectronic chips and micro-nanostructure optical / electrical devices. In the development of photolithography, researchers have proposed various photolithography schemes. For example, the more common mask photolithography. Among them, there are ultraviolet photolithography that relies on photomasks and single-photon absorption solubility changes, and nanoimprint photolithography that relies on physical contact imprint templates and light, heat, etc. to cure photoresists. This type of photolithography is a micro / nanostructure engraving process that combines low cost and high efficiency, but the expensive mask makes it difficult to customize personalized micro / nanostructures in small batches. Based on this, people have invented a direct-write maskless photolithography technology, which mainly includes high-energy beam (electron beam, laser, etc.) photolithography and probe (thermal probe, near-field probe) photolithography. This type of photolithography technology can realize arbitrary customization of high-resolution graphic structures and has extremely high degrees of freedom. However, its disadvantages are low photolithography efficiency and difficulty in achieving large-area photolithography.

[0003] In addition, there is a plasma near-field enhanced photothermal lithography using a nanometal structure template. This lithography is based on some materials that are easy to solidify or phase change when heated. Micro / nanoscale photothermal hot spots are generated by using mechanisms such as SPP formed at the nanometal structure under laser irradiation. The hot spots are used to perform thermal curing, phase separation assembly, dissociation and other changes on the thermosensitive material, thereby realizing micro / nanoscale lithography. Compared with conventional lithography, this lithography technology has unique advantages. For example, it can break through the optical diffraction limit; the lithographic feature size is no longer subject to the optical diffraction limit, but depends on the size of the thermally induced structural change area, and the size of this area is not only constrained by the light spot, but also further subject to multiple constraints such as thermally induced phase change threshold, thermally induced nonlinearity and thermal diffusion. Cross-scale lithography can be achieved by regulating thermal diffusion or performing corresponding light field shaping. In addition, the process flow of photothermal lithography is also greatly simplified, without the need for intermediate substances such as photocrosslinking agents, and no curing, pre-baking and post-baking are required during the lithography process. In addition, the nanometal structure template can be reused many times, greatly saving the cost of lithography. Finally, photothermal lithography does not have high requirements for the optical wavelength, and can achieve wide-band photothermal lithography. Therefore, near-field enhanced nanophotothermal lithography technology has great application value and potential for the manufacture of polymer micro / nanostructures. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing polymer micro-nano structures by using micro / nano photothermal lithography, which can realize cross-scale lithography, simplify the process flow and reduce the lithography cost.

[0005] The method for preparing polymer micro-nano structures by micro / nano photothermal lithography provided by the present invention comprises the following specific steps:

[0006] (1) Using nano-patterning technology (such as electron beam lithography, laser nano-lithography, ultraviolet lithography, nano-imprinting, etc.), a nanostructure array of metal or other photothermal conversion media is produced on a substrate (such as a silicon wafer substrate or other semiconductor or dielectric substrate, etc.) as a reusable nano-mask (such as Figure 2 );

[0007] (2) Spin coating or laminating a polymer with thermal response properties (such as thermal curing or thermal phase separation assembly) on a nanomask, and using light or laser projection or direct writing technology to generate micro-nanoscale photothermal hotspots (such as Figure 3 ), inducing changes such as thermal curing, microphase separation molecular assembly or dissociation of the polymer, thereby quickly forming a periodic polymer micro-nano structure and ultimately realizing micro-nano lithography.

[0008] In the present invention, the substrate is a silicon wafer or other semiconductor or dielectric materials.

[0009] In the present invention, the substrate is cut into a size of 1.2 cm × 1.5 cm. Figure 2 shown.

[0010] In the present invention, the nano-patterning technology includes electron beam lithography, laser nano-lithography, ultraviolet lithography, nano-imprinting and the like.

[0011] In the present invention, the micro / nano mask in step (1) is a micro / nano round hole mask, or a micro / nano line mask. The diameter of the round holes in the micro / nano round hole mask is 50nm to 15μm, and the distance between two adjacent round holes is 100nm to 6μm; the line width in the micro / nano line mask is 1 to 2μm, and the distance between adjacent lines is 1.5 to 15μm. The micro / nano structure corresponding to step (2) is a micro / nano sphere, or a micro / nano stripe.

[0012] In the present invention, the polymer having thermal response characteristics includes a thermosetting polymer or a thermally induced phase separation polymer, etc. The thermosetting polymer includes a thermal cross-linking material and a thermal phase change material;

[0013] Specifically, the polymer includes but is not limited to PDMS, block copolymer (PS-b-PMMA), silk fibroin and other thermally induced phase separation materials.

[0014] In the present invention, the micro / nano structure array on the micro / nano mask is nano balls (particles), lines, etc., with a size arbitrarily adjustable between 50nm and 15μm, and the spacing between them is 100nm to 15μm.

[0015] In the present invention, when spin coating the polymer, firstly, a slow spin coating at a rotation speed of 300-500 rpm is used for 0.5-1 min, and then a fast spin coating at a rotation speed of 1000-3000 rpm is used for 1-5 min to ensure that the polymer is evenly covered on the substrate.

[0016] In the present invention, the laser wavelength is 532nm or 980nm; when the laser is a continuous laser, the laser spot can be a Gaussian circular spot with a spot diameter of 10 to 50μm, a laser power of 2 to 20W, and a scanning speed of 10 to 1000um / s.

[0017] In the present invention, the laser wavelength is 532nm or 980nm; when the laser is a nanosecond laser, the laser spot can be a Gaussian circular spot with a spot diameter of 10 to 50μm, a laser power of 100 to 500mW, a scanning speed of 250 to 1000nm / s, a laser pulse width of 100 to 200ns, and a laser repetition frequency of 100 to 300KHz.

[0018] In the present invention, in addition to using laser as a heat source, a high-intensity light source such as a halogen lamp can also be used; the power of the light source is 500-1000W.

[0019] The polymer micro-nano structure prepared by the present invention has a characteristic size ranging from tens of nanometers to tens of micrometers, has strong repeatability, and the spatial arrangement is freely adjustable. A variety of structures can be customized according to needs, and it has high flexibility, high precision and wide adaptability.

[0020] Further:

[0021] (i) For thermosetting polymers:

[0022] When the micron mask is a micro / nano circular hole mask:

[0023] (1) A neatly arranged microsphere structure is produced on a thermally cross-linked material (e.g., PDMS), wherein the diameter of the microsphere is 10 to 15 μm and the distance between adjacent microspheres is 3 to 6 μm. Figure 4 );

[0024] (2) Produce neatly arranged nanosphere structures on thermal phase change materials (e.g., silk fibroin), with the diameter of the nanospheres being about 50 to 200 nm and the distance between adjacent nanospheres being 100 to 150 nm. Figure 7 ).

[0025] When the micron mask is a micron line mask:

[0026] (1) Produce neatly arranged micro / nano line structures on thermal cross-linking materials (e.g., PDMS), where the width of the micro / nano lines is 1-2 μm and the spacing between adjacent lines is 1.5-2 μm. Figure 5 ).

[0027] (2) Produce neatly arranged micrometer line structures on thermal phase change materials (e.g., silk fibroin), with a micrometer line width of about 1 to 2 μm and a spacing of 12 to 15 μm between adjacent lines (e.g., Figure 6 ).

[0028] (ii) For thermally induced phase separation polymers, when only light or laser is used for projection or scanning without using a prefabricated nanomask, the nanostructures fabricated on thermally induced phase separation materials (e.g., block copolymers) do not have good periodicity and regularity, and are specifically manifested as randomly distributed nano-fingerprint morphology (e.g., Figure 8 ), the spacing between fingerprint lines is 15-20nm, and the width of the lines is 8-10nm;

[0029] (1) When using a prefabricated micron-line mask, a neatly arranged nano-stripe structure is produced inside the lines of the mask, with a spacing of 15 to 20 nm between the stripes and a stripe width of 8 to 10 nm. Fig. 9 ).

[0030] (2) When using a prefabricated micrometer circular hole mask, a neatly arranged nanometer circular hole structure is manufactured inside the circular holes of the mask, with a spacing of 15 to 20 nm between the holes and a diameter of 8 to 10 nm. Fig.10 ).

[0031] In the present invention, for thermally cured or dissociated polymers such as PDMS or silk fibroin, a developer is used to remove the exposed or unexposed areas to obtain the remaining micro-nano structure; for polymers such as thermally processed microphase separation molecular assemblies such as block copolymers, after their phase separation is completed, oxygen plasma etching is used to remove one phase, leaving the other phase of micro-nano polymer, thereby forming a micro-nano structure.

[0032] In the present invention, for polymers such as block copolymers and other thermally produced microphase separation molecular assemblies, when a prefabricated mask is not used, photothermal technology can only produce randomly distributed nano-fingerprint structures on the block copolymers; while when a micron line or circular hole structure is used as a mask, this technology can be used to produce neatly arranged nano-stripes or circular hole structures inside the micron lines or circular holes.

[0033] In summary, the present invention uses a mask with a prefabricated nanostructure (reusable) to spin-coat or laminate a polymer with thermal response characteristics such as thermal crosslinking, thermal phase change or thermal phase separation assembly on the mask. Using light or laser projection or direct writing technology, based on the micro-nanoscale photothermal hot spots generated by the local plasma resonance mechanism under illumination, the polymer is induced to undergo thermal curing, microphase separation molecular assembly, dissociation and other changes, thereby quickly forming highly regular micro / nano stripes, and even structures such as spheres, and finally realizing micro-nano lithography. The polymer micro-nano structure prepared by the present invention has a characteristic size that can be arbitrarily adjusted between 50nm and 15μm, and the spatial arrangement can be arbitrarily designed. Applicable polymers include but are not limited to PDMS, silk fibroin, block copolymers (PS-b-PMMA) and other thermally induced physical and chemical change materials. Compared with conventional lithography, this lithography technology has unique advantages. For example, it is no longer limited by the optical diffraction limit; the lithography feature size directly depends on the size of the prefabricated structure on the mask, and cross-scale lithography can be achieved. In addition, the process flow of photothermal lithography is greatly simplified, and no intermediate substances such as photocrosslinking agents are required. There is no need for curing, pre-baking and post-baking during the lithography process. The prefabricated mask can be reused many times, which greatly saves the cost of lithography. On the other hand, photothermal lithography based on the localized plasma resonance mechanism does not have high requirements for the optical band, and can achieve wide-band photothermal lithography. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the method for preparing polymer micro-nano structures by using micro / nano photothermal lithography of the present invention.

[0035] Figure 2 This is a physical picture of the initial substrate prepared in the present invention.

[0036] Figure 3 The invention describes that, near the preset micro-nano structure, the local electromagnetic field distribution is enhanced based on the local plasma resonance mechanism under illumination and the photothermal hotspot phenomenon induced by it, which induces changes such as thermal curing of the polymer, microphase separation molecular assembly, and dissociation at the hotspot, ultimately realizing micro-nano lithography.

[0037] Figure 4 The invention relates to a micron sphere mask and a micron sphere array manufactured on a thermal cross-linking material (eg, PDMS) using photothermal lithography technology.

[0038] Figure 5 The invention relates to a micron line mask and a micron line array manufactured on a thermal cross-linking material (eg, PDMS) using a photothermal lithography technique.

[0039] Figure 6The invention relates to a micrometer line mask and a micrometer line array manufactured on a thermal phase change material (eg, silk fibroin) by using a photothermal lithography technique.

[0040] Figure 7 The invention relates to a nanosphere mask plate and a nanosphere array manufactured on a thermal phase change material (eg, silk fibroin) using photothermal lithography technology.

[0041] Figure 8 The randomly arranged nano-fingerprint structure is directly manufactured on a thermally induced phase separation material (eg, a block copolymer) by utilizing photothermal method without using a mask in the present invention.

[0042] Fig. 9 The invention relates to a nano-stripe mask and a nano-stripe structure manufactured on a thermally induced phase separation material (eg, a block copolymer) by using a photothermal lithography technique.

[0043] Fig.10 The invention relates to a nanosphere mask plate and a nanosphere array manufactured on a thermally induced phase separation material (eg, a block copolymer) by using a photothermal lithography technique. DETAILED DESCRIPTION

[0044] The present invention is further described below by way of embodiments in conjunction with the accompanying drawings.

[0045] The method for preparing polymer micro / nano structures by using micro / nano photothermal lithography provided by the present invention can be divided into a method for preparing micro / nano structures for thermally cured polymers using a prefabricated micro / nano mask, and a method for preparing micro / nano structures for thermally induced phase separation polymers using a prefabricated micro / nano mask.

[0046] (I) A method for preparing a micro / nano structure for a thermally cured polymer using a prefabricated micro / nano mask, the specific steps being:

[0047] Step S1: pre-treating the substrate by immersing it in an isopropanol solution for ultrasonic cleaning for 5 minutes, and then etching the substrate with oxygen plasma for 20 seconds to enhance the adhesion of the polymer on the substrate;

[0048] Step S2: using nanopatterning technology to produce a nanostructure array of metal or other photothermal conversion media on a substrate as a reusable nanomask;

[0049] Step S3: Spin-coating a polymer with thermal curing properties (e.g., PDMS, silk fibroin) uniformly on a substrate having a nanostructure array of metal or other photothermal conversion media, or attaching a nanostructure template to the aforementioned thermal responsive polymer films;

[0050] Step S4: Projecting or scanning a light or laser of a specific wavelength onto the polymer film in contact with the nano-photothermal mask;

[0051] Step S5: Based on the micro-nanoscale photothermal hotspots (such as Figure 3 As shown), inducing the aforementioned polymer to undergo thermal curing (e.g., thermal crosslinking or thermal phase change, etc.), thereby forming a micro-nano structure;

[0052] Step S6: Use a developer to remove the unexposed area and retain the thermally cured polymer, thereby finally achieving micro-nano lithography.

[0053] (ii) A method for preparing micro / nano structures of thermally induced phase separation polymers using a prefabricated micro / nano mask, the specific steps being:

[0054] Step S1: pre-treating the substrate by immersing it in an isopropanol solution for ultrasonic cleaning for 5 minutes, and then etching the substrate with oxygen plasma for 20 seconds to enhance the adhesion of the polymer on the substrate;

[0055] Step S2: using a patterning technique to fabricate a nanostructure array of metal or other photothermal conversion media on a substrate as a reusable nanomask;

[0056] Step S3: evenly spin-coating a polymer having a thermally induced microphase separation property (e.g., a block copolymer) on a substrate having a nanostructure array of a metal or other photothermal conversion medium, or attaching a nanostructure template to the aforementioned thermally responsive polymer film;

[0057] Step S4: Projecting or scanning a light or laser of a specific wavelength onto the polymer film in contact with the nano-photothermal mask;

[0058] Step S5: Based on the micro-nanoscale photothermal hotspots (such as Figure 3 As shown), inducing thermally induced microphase separation of the aforementioned polymer, thereby forming a nanostructure;

[0059] Step S6: using oxygen plasma etching to remove one phase of the polymer that has completed phase separation, and retaining the other phase of the polymer, to achieve nanolithography.

[0060] Example 1: For PDMS (thermal cross-linking material), a silicon wafer substrate is immersed in an isopropanol solution and cleaned by ultrasonic oscillation for 5 minutes, and then taken out and dried as a substrate. Figure 2 As shown. Using nano-patterning technologies such as electron beam lithography, laser nano-lithography, ultraviolet lithography, and nano-imprinting, micro-nanostructure arrays of different geometric shapes are produced on the substrate as a reusable nano-mask, such as Figure 4, the micron sphere or micron line structure mask shown in 5. Spin the PDMS solution at 500 rpm for 1 minute, and then use 1000 rpm for spin coating for 1 minute to evenly spin coat it on the silicon wafer substrate with the micro-nano structure array. After the PDMS film is prepared, it can also be directly attached to the aforementioned nano mask. Use a light source to perform photothermal radiation or scanning on the PDMS film with a preset micro-nano metal structure array. The hot spots brought about by the local plasma enhancement effect at the micro-nano structure array are used to induce thermal cross-linking and curing of PDMS, thereby quickly forming a highly regular micron sphere array or micron line array, as shown in the attached Figure 4 , as shown in 5.

[0061] Example 2: For silk fibroin (thermal phase change material), a silicon wafer substrate was immersed in an isopropanol solution and cleaned by ultrasonic oscillation for 5 minutes, and then taken out and dried as a substrate. Figure 2 As shown. Using nano-patterning technologies such as electron beam lithography, laser nano-lithography, ultraviolet lithography, and nano-imprinting, micro-nanostructure arrays of different geometric shapes are produced on the substrate as a reusable nano-mask, such as Figure 6 The micron line mask shown. The silk fibroin solution was rotated at 500 rpm for 1 min, and then spun at 1000 rpm for 5 min to evenly spin coat it onto the silicon wafer substrate with the micro-nano structure array. After the silk fibroin film is prepared, it can also be directly attached to the aforementioned nano mask. A light source is used to perform photothermal radiation or scanning on the silk fibroin film with a preset micro-nano metal structure array. The hot spots brought about by the localized plasma enhancement effect at the micro-nano structure array are used to induce the cross-linking and curing of the silk fibroin, thereby quickly forming a highly regular micron line array or nanosphere array, as shown in the attached Figure 6 , as shown in 7.

[0062] Example 3: For block copolymers (thermally induced phase separation materials), a silicon wafer substrate was immersed in an isopropanol solution and ultrasonically cleaned for 5 minutes, and then taken out and dried as a substrate. Figure 2 As shown. Using nano-patterning technologies such as electron beam lithography, laser nano-lithography, ultraviolet lithography, and nano-imprinting, micro-nanostructure arrays of different geometric shapes are produced on the substrate as a reusable nano-mask, such as Fig. 9 , micrometer lines and circular hole structure mask shown in 10. When no prefabricated nanomask is used and only light or laser is used for projection or scanning, the nanostructures fabricated on the block copolymer have a certain randomness, which is specifically manifested in the form of nano-fingerprints, as shown in the attached Figure 8 When the prefabricated micron line mask is introduced, a neatly arranged nano-stripe structure is created inside the lines of the mask through light or laser projection or scanning, as shown in the attached figure. Fig. 9When the prefabricated micrometer circular hole mask is used, a neatly arranged nanometer circular hole structure is produced inside the circular holes of the mask, as shown in the attached figure. Fig.10 shown.

Claims

1. A method for preparing polymer micro-nano structures using micro / nano photothermal lithography, characterized in that: The specific steps are: (1) Using nanopatterning technology, a nanostructure array of metal or other photothermal conversion media is produced on a substrate as a reusable micro / nano mask; (2) Spin-coat or laminate a polymer with thermal response properties onto a nanomask, and use light source or laser projection or direct writing technology to induce changes such as thermal curing, microphase separation molecular assembly or dissociation of the polymer based on the micro-nanoscale photothermal hotspots generated by the localized plasma resonance mechanism under illumination, thereby quickly forming a periodic polymer micro-nano structure and ultimately achieving micro-nano lithography.

2. The method according to claim 1, characterized in that: The micro / nano mask of the array structure is a micro / nano circular hole mask, or a micro / nano line mask; the diameter of the circular holes in the micro / nano circular hole mask is 50nm~15μm, and the distance between two adjacent circular holes is 100nm~6μm; the line width in the micron line mask is 1~2μm, and the distance between adjacent lines is 1.5~15μm; the corresponding micro / nano structure is a micro / nano sphere, or a micro / nano stripe.

3. The method according to claim 1, characterized in that: The substrate is a silicon wafer or a dielectric material; the substrate is cut into a size of 1.2 cm×1.5 cm; The nano-patterning technology is electron beam lithography, laser nano-lithography, ultraviolet lithography or nano-imprinting.

4. The method according to claim 1, characterized in that The polymer with thermal response characteristics includes heat-curing polymers and thermally induced phase separation polymers; heat-curing polymers include thermal cross-linking materials and thermal phase change materials.

5. The method according to claim 4, characterized in that The polymer is selected from PDMS, block copolymer (PS-b-PMMA), and silk fibroin.

6. The method according to claim 1, characterized in that When spin coating the polymer, first use a slow spin coating at a rotation speed of 300 to 500 rpm for 0.5 to 1 min, and then use a fast spin coating at a rotation speed of 1000 to 3000 rpm for 1 to 5 min to ensure that the polymer is evenly covered on the substrate.

7. The method according to claim 1, characterized in that The wavelength of the laser is 532nm or 980nm; When the laser is a continuous laser, the laser spot is a Gaussian circular spot, the spot diameter is 10-50μm, the laser power is 2-20W, and the scanning speed is 10-1000um / s; When the laser is a nanosecond laser, the laser spot is a Gaussian circular spot with a spot diameter of 10 to 50 μm, a laser power of 100 to 500 mW, a scanning speed of 250 to 1000 nm / s, a laser pulse width of 100 to 200 ns, and a laser repetition frequency of 100 to 300 KHz.

8. The method according to claim 1, characterized in that: The light source uses a halogen lamp, and the light source power is 500-1000W.

9. The method according to claim 1, characterized in that: (i) For thermosetting polymers: When the micron mask is a micro / nano circular hole mask: (1) Producing neatly arranged micron-sphere structures on thermally cross-linked materials, wherein the diameter of the micron-spheres is 10 to 15 μm and the distance between adjacent spheres is 3 to 6 μm; (2) Produce neatly arranged nanosphere structures on thermal phase change materials, with the diameter of the nanospheres being 50 to 200 nm and the distance between adjacent nanospheres being 100 to 150 nm; When the micron mask is a micron line mask: (1) Producing neatly arranged micro / nano line structures on thermal cross-linking materials, wherein the width of the micro / nano lines is 1 to 2 μm and the spacing between adjacent lines is 1.5 to 2 μm; (2) Produce neatly arranged micrometer line structures on thermal phase change materials, with the width of the micrometer lines being about 1 to 2 μm and the spacing between adjacent lines being 12 to 15 μm; (ii) For thermally induced phase separation polymers, (1) Using a micro / nano line mask, neatly arranged micro / nano stripe structures are produced inside the lines of the mask, with the spacing between stripes being 15 to 20 nm and the width of the stripes being 8 to 10 nm; (2) Using a micro / nano circular hole mask, a neatly arranged nano circular hole structure is produced inside the circular holes of the mask, with the spacing between the holes being 15 to 20 nm and the diameter of the circular holes being 8 to 10 nm.

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