High aspect ratio micro-nano needle tip array based on self-assembled mask and preparation method thereof

Abstract

This invention discloses a high aspect ratio micro / nano tip array based on a self-assembled mask and its fabrication method. The fabrication method includes: forming closely packed self-assembled microspheres on a silicon wafer surface to obtain a self-assembled mask; etching the self-assembled mask using ICP etching to obtain a patterned mask; etching the patterned mask using ICP etching to obtain a micro / nano tip array containing the mask; and removing the mask to obtain the micro / nano tip array. This invention enables the fabrication of large-area, flexibly tunable high aspect ratio micro / nano tip arrays with high efficiency and low cost.

Description

Technical Field

[0001] This invention relates to a high aspect ratio micro / nano needle tip array based on a self-assembled mask and its fabrication method, belonging to the field of micro / nano fabrication technology. Background Technology

[0002] Current micro-nano fabrication technologies mainly utilize techniques such as photolithography, wet etching, dry etching, and electrolytic deposition to process and manufacture materials at the micrometer and nanometer scales. However, the fabrication of existing micro / nano needle arrays often suffers from complex processes and high costs.

[0003] CN115793414B discloses a method for fabricating high aspect ratio microstructures with adjustable height. The method includes the following steps: First, a layer of photoresist is spin-coated onto a substrate at low speed; then, non-uniform grayscale exposure and development are performed using a laser direct-write device; subsequently, a first etching is performed on the multi-level photoresist pillars, with the etching time and depth selected according to the proportion of the multi-level structure; then, oxygen plasma is used to remove the residual photoresist after etching the first-level structure; then, the second-level structure is etched; subsequently, the residual photoresist on the upper layer of the second-level structure is removed; and so on, cyclically repeating the etching and photoresist removal process until the top layer of the last-level structure is completely removed. This method employs photolithography, which has high requirements for the fabrication environment, and uses a two-step Bosch-tapering process, resulting in drawbacks such as cumbersome technology and unstable processing results.

[0004] CN116119604A discloses a method and device for fabricating a high-density silicon microneedle array. The method includes the following steps: providing a silicon substrate and fabricating a negative photoresist layer on the silicon substrate; patterning the negative photoresist layer; fabricating a corresponding positive photoresist layer on the patterned negative photoresist layer; reflowing the fabricated positive photoresist layer to obtain a positive reflow photoresist layer; dry etching the silicon substrate using the positive reflow photoresist layer and the patterned negative photoresist layer to form the desired silicon microneedle array after etching, wherein the silicon microneedle array includes microneedles distributed on the silicon substrate, each microneedle including a needle body portion distributed on the silicon substrate and a needle head located on the needle body portion; and removing the positive reflow photoresist layer and the patterned negative photoresist layer. This method requires first using patterned negative photoresist as a preliminary mask, then using a reflow process with positive photoresist to generate an arc-shaped mask. After etching, the photoresist still needs to be removed. The process is complicated and the stability is difficult to control.

[0005] CN109173039B discloses a method for fabricating an inverted funnel-shaped silicon-based solid microneedle array. The method includes the following steps: 1) depositing a front-side silicon nitride protective film and a back-side silicon nitride protective film on a single-crystal silicon wafer; 2) spin-coating photoresist onto the front-side silicon nitride protective film and performing photolithography, the photoresist forming an array of circular masking films; 3) dry etching away the front-side silicon nitride protective film exposed outside the masking films to expose the single-crystal silicon wafer; 4) using an inductively coupled plasma etching system and employing the Bosch deep silicon etching process, anisotropically etching the single-crystal silicon wafer to etch an array of cylinders on the single-crystal silicon wafer; 5) removing the masking films from the single-crystal silicon wafer; 6) using an acidic etchant to perform isotropic wet etching on the single-crystal silicon wafer to obtain the microneedle array. This method requires first using patterned photoresist as a mask, generating a micropillar array through the Bosch process, and finally forming a needle-tip array by wet etching. The process is cumbersome and the process stability is difficult to control.

[0006] CN115285931A discloses a method for preparing a conical silicon-based solid microneedle array. The method includes: (1) selecting a single-polished single-crystal silicon wafer, wherein the single-polished single-crystal silicon wafer includes a polished surface and a second surface opposite to each other, depositing a silicon nitride protective film on the polished surface and the second surface respectively, and depositing an aluminum protective film on the silicon nitride protective film on the polished surface by magnetron sputtering; (2) transferring the mask pattern to the aluminum protective film on the polished surface by photolithography; (3) etching the aluminum protective film and etching the silicon nitride protective film on the polished surface; (4) performing anisotropic etching on the polished surface of the silicon wafer after step (3) to obtain a cylindrical array structure; (5) performing isotropic wet etching on the silicon wafer after step (4) to etch a radially controllable conical array structure, wherein the etching solution is placed in an ice-water mixture tank; (6) cleaning the silicon wafer after step (5) to remove residual acid etching solution on the silicon wafer. This method employs a two-step process of masking and Bosch-tapering, which has problems such as cumbersome process flow and difficulty in controlling process stability.

[0007] It can be seen that existing technologies for fabricating micro / nano tip arrays typically begin with the generation of a patterned mask using positive or negative photoresist through photolithography. This is followed by etching to create a micrometer- or nanometer-scale cylindrical array, and then anisotropic wet etching to form the tip array. Existing technologies suffer from at least the following problems: complex process steps, high cost, difficulty in parameter control, significant fluctuations in interface composition and etching solution parameters due to wet etching, high environmental requirements, and high safety risks; difficulty in controlling the tip array morphology, making it more suitable for fabricating tip arrays of hundreds of micrometers but less suitable for fabricating nanometer- to several-micrometer-scale microtip arrays; difficulty in parameter adjustment, requiring extensive parameter optimization to fabricate tip arrays of different structures and sizes; and difficulty in achieving efficient and rapid fabrication of large-scale structures, limiting the industrial application of micro / nano tip arrays in practical devices. Summary of the Invention

[0008] To address at least one of the aforementioned technical problems, the present invention aims to provide a high aspect ratio micro / nano needle array based on a self-assembled mask and its fabrication method. The present invention enables the fabrication of large-area, flexibly tunable high aspect ratio micro / nano needle arrays with high efficiency and low cost.

[0009] To achieve the above objectives, the first aspect of the present invention provides a method for fabricating a high aspect ratio micro / nano needle tip array based on a self-assembled mask, comprising the following steps:

[0010] S1: Forming closely packed self-assembled microspheres on the surface of a silicon wafer to obtain a self-assembled mask;

[0011] S2: The self-assembled mask is etched using ICP etching to obtain a patterned mask;

[0012] S3: The patterned mask is etched using ICP etching to obtain a micro / nano needle array containing the mask;

[0013] S4: Remove the mask from the micro / nano needle array containing the mask to obtain the high aspect ratio micro / nano needle array based on the self-assembled mask.

[0014] According to a specific embodiment of the present invention, preferably, step S1 includes: extracting the dispersion of microspheres using a syringe; placing ultrapure water in a container; connecting one end of the syringe to an injection pump and the other end to a flexible tube, and aligning the flexible tube with the surface of the ultrapure water in the container; injecting the dispersion of microspheres into the surface of the ultrapure water in the container using the injection pump, syringe, and flexible tube; immersing a gel containing sodium dodecyl sulfate into the ultrapure water from one side edge of the liquid surface for 1-60 seconds, so that the microspheres on the liquid surface form a closely packed structure; placing a silicon wafer below the liquid surface, and then tilting it upwards at an angle greater than 0° and less than 60° to the liquid surface, transferring the closely packed self-assembled microspheres to the surface of the silicon wafer; and after drying, obtaining the self-assembled mask.

[0015] According to a specific embodiment of the present invention, preferably, in step S1, the microspheres include one or a combination of several of the following: polystyrene microspheres, silica microspheres, polymethyl methacrylate microspheres, and polyvinyl alcohol microspheres.

[0016] According to a specific embodiment of the present invention, preferably, in step S1, the diameter of the microspheres is 50 nm-10 μm.

[0017] According to a specific embodiment of the present invention, preferably, in step S1, the injection rate of the dispersion of the microspheres into the surface of the ultrapure water in the container is 10-500 μL / min.

[0018] According to a specific embodiment of the present invention, preferably, in step S1, the closely packed self-assembled microspheres formed on the surface of the silicon wafer are monolayer microspheres.

[0019] According to a specific embodiment of the present invention, preferably, in step S2, the conditions for etching the self-assembled mask by ICP etching include: upper electrode power of 30-500W, lower electrode power of 5-100W, pressure of 1-50Pa, etching gas of Ar and / or O2, etching gas flow rate of 10-150sccm, and etching time of 30-300s.

[0020] According to a specific embodiment of the present invention, preferably, in step S3, the conditions for etching the patterned mask using ICP etching include: an upper electrode power of 100-1500W, a lower electrode power of 5-50W, a pressure of 1-50Pa, using C4F8 gas as the passivation gas and SF6 gas as the etching gas, alternating between the two for several cycles. More preferably, in a single cycle, the C4F8 gas flow rate is 10-200 sccm, the passivation time is 5-50 s, the SF6 gas flow rate is 10-200 sccm, and the etching time is 5-50 s. More preferably, the number of cycles is 10-300.

[0021] According to a specific embodiment of the present invention, preferably, step S4 includes: immersing the mask-containing micro / nano needle array in ultrapure water for ultrasonic cleaning to remove the mask, thereby obtaining the high aspect ratio micro / nano needle array based on the self-assembled mask.

[0022] A second aspect of the present invention provides a high aspect ratio micro / nano needle tip array based on a self-assembled mask, which is prepared by the above-described preparation method.

[0023] According to a specific embodiment of the present invention, preferably, the aspect ratio of the high aspect ratio micro / nano needle array based on the self-assembled mask is 1:5 to 10:1.

[0024] According to a specific embodiment of the present invention, preferably, the diameter of the tip of the needle in the high aspect ratio micro / nano needle array based on the self-assembled mask is 10-30 nm, and the diameter of the bottom of the needle is 50 nm-5 μm.

[0025] According to a specific embodiment of the present invention, preferably, the spacing between the bottom ends of two adjacent tips in the high aspect ratio micro / nano tip array based on the self-assembled mask is 100nm-10μm.

[0026] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0027] This invention studies the self-assembly technology of microspheres, enabling rapid fabrication of large-area silicon wafer surface masks. The mask size can be flexibly adjusted according to processing requirements, eliminating the need for photolithography, reducing environmental requirements, and lowering costs. Building upon this, this invention achieves rapid fabrication of high aspect ratio micro / nano tip arrays in a single step by using only the Bosch process and adjusting ICP process parameters to simultaneously form a tilt angle during downward etching. The microneedle height can be flexibly adjusted as needed, and the processing technology remains stable. This invention overcomes the problems of cumbersome process flows, numerous process steps, and high fabrication costs associated with existing technologies. It avoids the two-step Bosch-tapering process and the technical paths of fabricating patterned photoresist masks, dry etching, and wet etching. It offers numerous advantages such as low process cost, easy parameter adjustment, high flexibility, high processing efficiency, and stable processing results. Therefore, this invention can fabricate large-area, flexibly controllable high aspect ratio micro / nano tip arrays with high efficiency, speed, and low cost. The high aspect ratio micro / nano needle tip array prepared by this invention can be widely used in optical devices, energy absorption and storage devices, hydrophilic and hydrophobic surface manipulation, droplet transport, biosensors, bioengineering and biomanufacturing, and has key technological transformation value. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the microsphere self-assembly system in Example 1.

[0029] Figure 2 This is an electron microscope image of the self-assembled mask arrangement in Example 1.

[0030] Figure 3 This is a flowchart illustrating steps S2 and S3 in Examples 1-3.

[0031] Figure 4 This is a morphology diagram of the micro / nano needle tip array in Example 1.

[0032] Figure 5 This is a morphology diagram of the micro / nano needle tip array in Example 2.

[0033] Figure 6 This is a morphology diagram of the micro / nano needle tip array in Example 3.

[0034] Explanation of icon numbers:

[0035] 1-Syne; 2-Injection pump; 3-Tube; 4-Container. Detailed Implementation

[0036] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will now be described in detail below, but this should not be construed as limiting the scope of the invention.

[0037] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0039] According to a specific embodiment of the first aspect of the present invention, the present invention provides a method for fabricating a high aspect ratio micro / nano needle tip array based on a self-assembled mask, comprising the following steps:

[0040] S1: Forming closely packed self-assembled microspheres on the surface of a silicon wafer to obtain a self-assembled mask;

[0041] S2: The self-assembled mask is etched using ICP etching to obtain a patterned mask;

[0042] S3: The patterned mask is etched using ICP etching to obtain a micro / nano needle array containing the mask;

[0043] S4: Remove the mask from the micro / nano needle array containing the mask to obtain the high aspect ratio micro / nano needle array based on the self-assembled mask.

[0044] In some embodiments, the silicon wafer may be a silicon wafer with a (100) crystal plane or a silicon wafer with a (111) crystal plane.

[0045] In some embodiments, the preparation method further includes step S0 before step S1: pretreatment of the silicon wafer, the pretreatment including cleaning and heat treatment. The cleaning may be ultrasonic cleaning in an organic solvent, such as, but not limited to, acetone. The time, power, and frequency of the ultrasonic cleaning can be conventionally adjusted by those skilled in the art. After ultrasonic cleaning, contaminants on the surface of the silicon wafer can be removed. The heat treatment temperature can be 200°C, and the time can be 1-10 minutes. The heat treatment can be performed using a hot plate. After heat treatment, organic impurities on the surface of the silicon wafer can be removed.

[0046] In some embodiments, step S1 includes: extracting a dispersion of microspheres using a syringe; placing ultrapure water in a container; connecting one end of the syringe to an injection pump and the other end to a flexible tube, with the flexible tube overlapping the surface of the ultrapure water in the container; injecting the dispersion of microspheres into the surface of the ultrapure water in the container using the injection pump, syringe, and flexible tube; immersing a gel containing sodium dodecyl sulfate into the ultrapure water from one side edge of the liquid surface for 1-60 seconds, causing the microspheres on the liquid surface to form a closely packed structure; placing a silicon wafer below the liquid surface, then tilting it upwards at an angle greater than 0° and less than 60° to the liquid surface, transferring the closely packed self-assembled microspheres to the surface of the silicon wafer; and after drying, obtaining the self-assembled mask.

[0047] In some embodiments, in step S1, the microspheres include one or a combination of several of the following: polystyrene microspheres, silica microspheres, polymethyl methacrylate microspheres, and polyvinyl alcohol microspheres. More preferably, the diameter of the microspheres is 50 nm to 10 μm.

[0048] In some embodiments, in step S1, the solvent in the dispersion of the microspheres is, for example, but not limited to, one or a combination of several of dimethyl sulfoxide (DMSO), alcohol, anhydrous ethanol, and isopropanol. The concentration of the microspheres in the dispersion of the microspheres can be 1 × 10⁻⁶. 6 cells / ml up to 1×10 10 per ml.

[0049] In some embodiments, in step S1, the dispersion of the microspheres is obtained by dispersing the microspheres in a solvent using an ultrasonic method. The duration, power, and frequency of the ultrasonication can be conventionally adjusted by those skilled in the art.

[0050] In some embodiments, in step S1, the injection rate of the dispersion of the microspheres into the surface of the ultrapure water in the container is 10-500 μL / min.

[0051] In some embodiments, in step S1, the closely packed self-assembled microspheres formed on the surface of the silicon wafer are monolayer microspheres.

[0052] In some embodiments, in step S1, the gel containing sodium dodecyl sulfate only needs to be completely immersed in ultrapure water, and there is no special limitation on its amount.

[0053] In some embodiments, in step S1, the gel containing sodium dodecyl sulfate may include sodium dodecyl sulfate polyacrylamide gel. This sodium dodecyl sulfate polyacrylamide gel can be prepared using conventional methods in the art, and the present invention does not impose any particular limitations on it. Specifically, the preparation method of the sodium dodecyl sulfate polyacrylamide gel may include the following steps: reacting a mixture of acrylamide, a crosslinking agent, a accelerator, an initiator, sodium dodecyl sulfate, and water to obtain a sodium dodecyl sulfate polyacrylamide gel. The crosslinking agent includes N,N'-methylenebisacrylamide, the accelerator includes N,N,N',N'-tetramethylethylenediamine, and the initiator includes ammonium persulfate or a redox initiator system containing ammonium persulfate. The amounts of acrylamide, crosslinking agent, accelerator, initiator, sodium dodecyl sulfate, and water can be conventionally adjusted in the art. The reaction can be carried out in a mold at a temperature of 20-30°C for 1-20 hours. After the reaction is complete, conventional drying can be performed. This invention uses a gel containing sodium dodecyl sulfate, which is immersed in ultrapure water. The resulting surface tension gradient drives the movement of microspheres on the liquid surface, causing the microspheres to form a tightly packed, monolayer structure.

[0054] In some embodiments, in step S1, the volume of the dispersion of the microspheres, the cross-sectional area of ​​the container, and the volume of the ultrapure water therein can be flexibly adjusted according to actual conditions (e.g., the area of ​​the silicon wafer).

[0055] In some embodiments, the conditions for etching the self-assembled mask by ICP etching in step S2 include: upper electrode power of 30-500W, lower electrode power of 5-100W, pressure of 1-50Pa, etching gas of Ar and / or O2, etching gas flow rate of 10-150sccm, and etching time of 30-300s.

[0056] In some embodiments, the conditions for etching the patterned mask using ICP etching in step S3 include: an upper electrode power of 100-1500W, a lower electrode power of 5-50W, a pressure of 1-50Pa, using C4F8 gas as the passivation gas and SF6 gas as the etching gas, alternating between the two for several cycles. Preferably, in a single cycle, the C4F8 gas flow rate is 10-200 sccm, the passivation time is 5-50 s, the SF6 gas flow rate is 10-200 sccm, and the etching time is 5-50 s. Preferably, the number of cycles is 10-300.

[0057] In some embodiments, step S4 includes: immersing the mask-containing micro / nano needle tip array in ultrapure water for ultrasonic cleaning to remove the mask, thereby obtaining the high aspect ratio micro / nano needle tip array based on the self-assembled mask. The time, power, and frequency of the ultrasonic cleaning can be conventionally adjusted by those skilled in the art.

[0058] In some embodiments, the fabrication method can fabricate a large-area array of high aspect ratio micro / nano needle tips based on a self-assembled mask, wherein the large area ranges from 1 cm. 2 -1000cm 2 .

[0059] According to a specific embodiment of the second aspect of the present invention, the present invention provides a high aspect ratio micro / nano needle tip array based on a self-assembled mask, which is prepared by the above-described preparation method.

[0060] In some embodiments, the aspect ratio of the high aspect ratio micro / nano needle array based on the self-assembled mask is 1:5 to 10:1.

[0061] In some embodiments, the tip diameter of the needle in the high aspect ratio micro / nano needle array based on the self-assembled mask is 10-30 nm, and the bottom diameter of the needle is 50 nm-5 μm.

[0062] In some embodiments, the spacing between the bottom ends of two adjacent tips in the high aspect ratio micro / nano tip array based on the self-assembled mask is 100 nm-10 μm.

[0063] The technical solutions of the present invention are specifically illustrated by the following embodiments, but the present invention is not limited to these embodiments. Of course, various modifications can be made within the scope of the key points of the present invention.

[0064] Example 1

[0065] S0: Pre-processing of silicon wafers

[0066] A sample with a thickness of 500 μm and an area of ​​6.25 cm² was selected.2 The (100) crystal plane silicon wafer square cut piece was placed in acetone and ultrasonically cleaned for 3 min; then it was placed on a hot plate and baked at 200℃ for 5 min to obtain the pretreated silicon wafer.

[0067] S1: Fabrication of large-area self-assembled masks

[0068] The process is carried out using a microsphere self-assembly system, such as Figure 1 As shown, the system includes: a needle 1, an infusion pump 2 connected to one end of the needle 1, a flexible tube 3 connected to the other end of the needle 1, and a container 4; the container 4 is an open cylindrical container, which can be made of plastic, and its cross-sectional diameter is 15cm; it should be noted that... Figure 1 Other conventional components, such as stands and displays, are also shown in the illustration, but the present invention does not impose any special limitations on these components.

[0069] Polystyrene (PS) microspheres with a diameter of 900 nm were added to an ethanol / water mixture and ultrasonically dispersed for 10 min to obtain 200 μL of polystyrene microsphere dispersion, in which the concentration of polystyrene microspheres was 1 × 10⁻⁶. 9 pcs / ml;

[0070] The dispersion of polystyrene microspheres was drawn using syringe 1; 200 ml of ultrapure water was placed in a container; one end of syringe 1 was connected to syringe pump 2, and the other end was connected to tubing 3. After the surface of the ultrapure water stabilized, tubing 3 was placed over the surface of the ultrapure water in container 4. The dispersion of polystyrene microspheres was injected into the surface of the ultrapure water in container 4 at a rate of 200 μL / min using syringe pump 2, syringe 1, and tubing 3 to ensure uniform dispersion; a gel containing sodium dodecyl sulfate was immersed in the ultrapure water for 10 seconds on one side, and the volume of the gel containing sodium dodecyl sulfate was approximately 5 cm³. 3 The preparation method is as described above, which involves forming a tightly packed, monolayer structure of polystyrene microspheres on the surface of ultrapure water; immersing a pretreated silicon wafer (with the (100) crystal face facing upward) at an angle below the liquid surface, and then removing it at a 30° angle upwards to transfer the tightly packed, monolayer self-assembled polystyrene microspheres to the surface of the silicon wafer; after standing and drying, the self-assembled mask is obtained; the arrangement of the self-assembled mask is as follows. Figure 2 As shown, polystyrene microspheres are formed in a tightly packed, monolayer structure on the surface of the pretreated silicon wafer.

[0071] S2: Fabrication of patterned masks

[0072] like Figure 3As shown, the self-assembled mask was etched using an ICP device (SINTECH_SI500). The etching conditions included: upper electrode power of 200W, lower electrode power of 50W, pressure of 3Pa, etching gas of O2, etching gas flow rate of 40sccm, and etching time of 40s, resulting in a patterned mask.

[0073] S3: Fabrication of micro / nano needle tip arrays

[0074] like Figure 3 As shown, the patterned mask was etched using an ICP device (SINTECH_SI500). The etching conditions included: an upper electrode power of 500W, a lower electrode power of 15W, a pressure of 7Pa, and C4F8 gas as the passivation gas and SF6 gas as the etching gas, which were alternately cycled. In a single cycle, the C4F8 gas flow rate was 100 sccm, the passivation time was 12s, the SF6 gas flow rate was 15 sccm, and the etching time was 9s. After 100 cycles, a micro / nano needle tip array containing the mask was obtained.

[0075] S4: Mask Removal

[0076] The masked micro / nano needle array was immersed in ultrapure water and ultrasonically cleaned for 3 minutes to remove the mask, resulting in a high aspect ratio micro / nano needle array based on a self-assembled mask.

[0077] Electron microscopy examination revealed that, for example Figure 4 As shown, the micro / nano needle tip array has an aspect ratio of 6:1, a tip diameter of 10 nm, a tip diameter of 500 nm, and a spacing of 900 nm between the tips of two adjacent needle tips.

[0078] Example 2

[0079] The silicon wafers used were pretreated as described in Example 1;

[0080] S1: Fabrication of large-area self-assembled masks

[0081] Polystyrene (PS) microspheres with a diameter of 1200 nm were added to an ethanol / water mixture and ultrasonically dispersed for 10 min to obtain 200 μL of polystyrene microsphere dispersion, in which the concentration of polystyrene microspheres was 1 × 10⁻⁶. 9 The number of units per ml; the remaining preparation steps of the self-assembled mask are the same as in Example 1;

[0082] S2: Fabrication of patterned masks

[0083] like Figure 3As shown, the self-assembled mask was etched using an ICP device (SINTECH_SI500). The etching conditions included: upper electrode power of 200W, lower electrode power of 50W, pressure of 3Pa, etching gas of O2, etching gas flow rate of 40sccm, and etching time of 40s, resulting in a patterned mask.

[0084] S3: Fabrication of micro / nano needle tip arrays

[0085] like Figure 3 As shown, the patterned mask was etched using an ICP device (SINTECH_SI500). The etching conditions included: an upper electrode power of 500W, a lower electrode power of 15W, a pressure of 7Pa, and C4F8 gas as the passivation gas and SF6 gas as the etching gas, which were alternately cycled. In a single cycle, the C4F8 gas flow rate was 100 sccm, the passivation time was 11s, the SF6 gas flow rate was 15 sccm, and the etching time was 10s. After 80 cycles, a micro / nano needle tip array containing the mask was obtained.

[0086] S4: Mask Removal

[0087] The masked micro / nano needle array was immersed in ultrapure water and ultrasonically cleaned for 3 minutes to remove the mask, resulting in a high aspect ratio micro / nano needle array based on a self-assembled mask.

[0088] Electron microscopy examination revealed that, for example Figure 5 As shown, the micro / nano needle tip array has an aspect ratio of 4:1, a tip diameter of 10 nm, a tip diameter of 500 nm, and a spacing of 900 nm between the tips of two adjacent needle tips.

[0089] Example 3

[0090] The silicon wafers used were pretreated as described in Example 1;

[0091] S1: Fabrication of large-area self-assembled masks

[0092] Polystyrene (PS) microspheres with a diameter of 1500 nm were added to an ethanol / water mixture and ultrasonically dispersed for 10 min to obtain 200 μL of polystyrene microsphere dispersion, in which the concentration of polystyrene microspheres was 1 × 10⁻⁶. 9 The number of units per ml; the remaining preparation steps of the self-assembled mask are the same as in Example 1;

[0093] S2: Fabrication of patterned masks

[0094] like Figure 3As shown, the self-assembled mask was etched using an ICP device (SINTECH_SI500). The etching conditions included: upper electrode power of 200W, lower electrode power of 50W, pressure of 3Pa, etching gas of O2, etching gas flow rate of 40sccm, and etching time of 40s, resulting in a patterned mask.

[0095] S3: Fabrication of micro / nano needle tip arrays

[0096] like Figure 3 As shown, the patterned mask was etched using an ICP device (SINTECH_SI500). The etching conditions included: an upper electrode power of 500W, a lower electrode power of 15W, a pressure of 7Pa, and C4F8 gas as the passivation gas and SF6 gas as the etching gas, which were alternately cycled. In a single cycle, the C4F8 gas flow rate was 100 sccm, the passivation time was 10s, the SF6 gas flow rate was 15 sccm, and the etching time was 10s. After 60 cycles, a micro / nano needle tip array containing the mask was obtained.

[0097] S4: Mask Removal

[0098] The masked micro / nano needle array was immersed in ultrapure water and ultrasonically cleaned for 3 minutes to remove the mask, resulting in a high aspect ratio micro / nano needle array based on a self-assembled mask.

[0099] Electron microscopy examination revealed that, for example Figure 6 As shown, the micro / nano needle tip array has an aspect ratio of 3:1, a tip diameter of 10 nm, a tip diameter of 500 nm, and a spacing of 900 nm between the tips of two adjacent needle tips.

Claims

1. A method for fabricating a high aspect ratio micro / nano needle tip array based on a self-assembled mask, comprising the following steps: S1: Forming closely packed self-assembled microspheres on the surface of a silicon wafer to obtain a self-assembled mask; S2: The self-assembled mask is etched using ICP etching to obtain a patterned mask; S3: The patterned mask is etched using ICP etching to obtain a micro / nano needle tip array containing the mask; wherein the conditions for etching the patterned mask using ICP etching include: upper electrode power of 100-1500W, lower electrode power of 5-50W, pressure of 1-50Pa, C4F8 gas as passivation gas and SF6 gas as etching gas, which are alternated for several cycles; in a single cycle, the C4F8 gas flow rate is 10-200 sccm, the passivation time is 5-50s, the SF6 gas flow rate is 10-200 sccm, and the etching time is 5-50s; the number of cycles is 10-300. S4: Remove the mask from the micro / nano needle array containing the mask to obtain the high aspect ratio micro / nano needle array based on the self-assembled mask.

2. The preparation method according to claim 1, wherein, Step S1 includes: extracting the dispersion of microspheres using a syringe; placing ultrapure water in a container; connecting one end of the syringe to an injection pump and the other end to a flexible tube, with the flexible tube overlapping the surface of the ultrapure water in the container; injecting the dispersion of microspheres into the surface of the ultrapure water in the container using the injection pump, syringe, and flexible tube; immersing a gel containing sodium dodecyl sulfate into the ultrapure water from one side edge of the liquid surface for 1-60 seconds, causing the microspheres on the liquid surface to form a closely packed structure; placing a silicon wafer below the liquid surface, then tilting it upwards at an angle greater than 0° and less than 60° to the liquid surface, transferring the closely packed self-assembled microspheres to the surface of the silicon wafer; and drying it to obtain the self-assembled mask.

3. The preparation method according to claim 1 or 2, wherein, In step S1, the microspheres include one or a combination of several of the following: polystyrene microspheres, silica microspheres, polymethyl methacrylate microspheres, and polyvinyl alcohol microspheres.

4. The preparation method according to claim 1 or 2, wherein, In step S1, the diameter of the microspheres is 50 nm-10 μm.

5. The preparation method according to claim 2, wherein, In step S1, the injection rate of the dispersion of the microspheres into the surface of the ultrapure water in the container is 10-500 μL / min.

6. The preparation method according to claim 1 or 2, wherein, In step S1, the closely packed self-assembled microspheres formed on the surface of the silicon wafer are monolayer microspheres.

7. The preparation method according to claim 1, wherein, In step S2, the conditions for etching the self-assembled mask using ICP etching include: upper electrode power of 30-500W, lower electrode power of 5-100W, pressure of 1-50Pa, etching gas of Ar and / or O2, etching gas flow rate of 10-150sccm, and etching time of 30-300s.

8. The preparation method according to claim 1, wherein, Step S4 includes: immersing the mask-containing micro / nano needle array in ultrapure water for ultrasonic cleaning to remove the mask, thereby obtaining the high aspect ratio micro / nano needle array based on the self-assembled mask.

9. A high aspect ratio micro / nano needle tip array based on a self-assembled mask, which is prepared by the preparation method according to any one of claims 1-8.

10. The high aspect ratio micro / nano needle tip array based on a self-assembled mask according to claim 9, wherein, The aspect ratio of the high aspect ratio micro / nano needle array based on the self-assembled mask is 1:5 to 10:

1.

11. The high aspect ratio micro / nano needle tip array based on self-assembled mask according to claim 9, wherein, The diameter of the tip of the high aspect ratio micro / nano needle array based on the self-assembled mask is 10-30 nm, and the diameter of the bottom of the needle tip is 50 nm-5 μm.

12. The high aspect ratio micro / nano needle tip array based on a self-assembled mask according to claim 9, wherein, The spacing between the bottom ends of two adjacent tips in the high aspect ratio micro / nano tip array based on the self-assembled mask is 100 nm-10 μm.

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