阅读说明：本技术 一种自组装三维微纳结构的制备方法 (Preparation method of self-assembled three-dimensional micro-nano structure ) 是由 梁飞燕 童欣 王九鑫 何智恒 耿可佳 赵毅婕 于 2019-12-31 设计创作，主要内容包括：本发明公开了一种自组装三维微纳结构的制备方法,属于自组装技术领域。所述方法包括：表面预处理；旋涂SU-8光刻胶；前烘；对准和曝光；后烘；显影；二次匀胶；前烘；二次曝光；后烘；二次显影；转移及自组装,得到自组装三维微纳结构。本发明优化了光刻与显影等微电子工艺,利用SU-8负性光刻胶和SPR-220正性光刻胶成功制备了二维平面结构,且利用热力作为驱动力对二维微纳结构实施了自组装,制备了自组装三维微纳结构,为后续二维材料的自组装提供了平台。(The invention discloses a preparation method of a self-assembled three-dimensional micro-nano structure, and belongs to the technical field of self-assembly. The method comprises the following steps: surface pretreatment; spin-coating SU-8 photoresist; pre-baking; aligning and exposing; postbaking; developing; secondary glue homogenizing; pre-baking; carrying out secondary exposure; postbaking; carrying out secondary development; and transferring and self-assembling to obtain the self-assembled three-dimensional micro-nano structure. According to the invention, microelectronic processes such as photoetching and developing are optimized, the two-dimensional planar structure is successfully prepared by using the SU-8 negative photoresist and the SPR-220 positive photoresist, self-assembly is carried out on the two-dimensional micro-nano structure by using heat as a driving force, the self-assembled three-dimensional micro-nano structure is prepared, and a platform is provided for the self-assembly of a subsequent two-dimensional material.)

1. A preparation method of a self-assembled three-dimensional micro-nano structure is characterized by comprising the following steps:

surface pretreatment: cutting the round and complete silicon wafer into 2 multiplied by 2cm silicon wafers by using a laser scribing machine; plating copper on the surface of the silicon wafer, wherein the thickness of the film is 300nm, and cleaning the surface of the silicon wafer by using an ultrasonic cleaning machine;

spin coating SU-8 photoresist: placing a cleaned silicon wafer on dust-free paper, clamping the edge of the silicon wafer by using tweezers, placing the silicon wafer on a rotating table of a spin coater, opening an air valve to suck and fix the silicon wafer, sucking a preset amount of SU-8 photoresist by using a disposable suction tube to coat the surface of the silicon wafer, covering a cover plate of the spin coater, and starting spin coating after setting the rotating speed;

pre-baking: transferring the silicon wafer after the glue homogenizing is finished to dust-free paper, and baking the silicon wafer on a hot plate for 15 minutes, wherein the temperature is set to 95 ℃;

alignment and exposure: carrying out alignment exposure on the silicon wafer through an ultraviolet photoetching machine, and overlaying photoetching patterns on the silicon wafer together to build a two-dimensional micro-nano structure;

post-baking: the drying time is 15min, and the temperature is set to 95 ℃;

and (3) developing: placing the silicon wafer in SU-8 developer, and slightly shaking the container;

secondary glue homogenizing: cleaning the residual developing solution on the surface of the developed silicon wafer, and then spin-coating a layer of SPR-220 positive photoresist on the surface of the silicon wafer;

pre-baking: pre-baking the silicon wafer subjected to the secondary glue homogenizing on a hot plate for 30s at the temperature of 60 ℃, and standing the silicon wafer at room temperature for 3h after the pre-baking is finished;

and (3) secondary exposure: carrying out secondary exposure on the silicon wafer;

post-baking: the drying time is 15min, and the temperature is set to 95 ℃;

and (3) secondary development: carrying out secondary development on the silicon wafer, and slightly shaking the container;

and transferring and self-assembling to obtain the self-assembled three-dimensional micro-nano structure.

2. The method of claim 1, wherein the silicon wafer surface is plated with copper with a film thickness of 300nm, and cleaning the silicon wafer surface by using an ultrasonic cleaning machine comprises:

and (3) coating by using a high-vacuum magnetron sputtering coating machine, and then respectively ultrasonically cleaning the silicon wafer for 15 minutes by using acetone and absolute ethyl alcohol.

3. The method of claim 1, wherein starting spin coating after the setting the rotational speed comprises: and respectively adopting low rotating speed of 500r/min for 3s, high rotating speed of 2000r/min for 30s and homogenizing for one time.

4. The method according to claim 1, wherein the exposure time for the alignment exposure of the silicon wafer by the uv lithography machine is 25 s.

5. The method according to claim 1, wherein the developing time for placing the silicon wafer in the SU-8 developing solution is 2.5 min.

6. The method of claim 1, wherein the spin coating parameters for spin coating a layer of SPR-220 positive photoresist on the surface of the silicon wafer are as follows: the low rotating speed is 500r/min and the time is 3s, the high rotating speed is 1000r/min and the time is 15s, and the glue is homogenized twice.

7. The method of claim 1, wherein the exposure time for the second exposure of the silicon wafer is 120 s.

8. The method according to claim 1, wherein the developing time for the secondary development of the silicon wafer is 6 min.

9. The method according to claim 1, wherein the transferring and self-assembling to obtain a self-assembled three-dimensional micro-nano structure comprises:

removing the copper film by using a copper etching solution to enable the micro-nano structure to be separated from the silicon wafer and float on the liquid surface, then cleaning the micro-nano structure in deionized water for 3-4 times to remove the copper etching solution, and then transferring the micro-nano structure to dust-free paper;

and placing the self-supporting two-dimensional structure on a hot plate, and carrying out thermally-driven self-assembly to obtain the self-assembled three-dimensional micro-nano structure.

Technical Field

The invention relates to the technical field of self-assembly, in particular to a preparation method of a self-assembled three-dimensional micro-nano structure.

Background

Self-assembly refers to the process of pre-existing composition, spontaneous formation of organized structures from random states, and the goal of controlling this process can be achieved by appropriate design of the components, changing the environment and the driving force. The application of the micro-nano structure self-assembly technology is significant to the life of people, the micro structure can be built on the ultra-fine layer by utilizing the micro-nano structure self-assembly technology, the controllability of the assembly process is gradually improved, the more complicated micro structure can be built, and the method has great application potential in the fields of metamaterial sensors, biomedicine, electromagnetism and the like.

At present, the technology of micro-nano structure self-assembly is rapidly developing, and methods for driving self-assembly such as surface tension driven self-assembly, magnetic force driven self-assembly, volume expansion driven assembly, differential thermal expansion driven self-assembly, thin film stress driven self-assembly, shape memory driven self-assembly and the like exist in the prior art, but a method for preparing a three-dimensional micro-nano structure by combining a microelectronic photoetching process and thermal force driven triggering self-assembly is not related.

Disclosure of Invention

In order to solve the problems in the prior art, the embodiment of the invention provides a preparation method of a self-assembled three-dimensional micro-nano structure, which comprises the following steps:

surface pretreatment: cutting the round and complete silicon wafer into 2 multiplied by 2cm silicon wafers by using a laser scribing machine; plating copper on the surface of the silicon wafer, wherein the thickness of the film is 300nm, and cleaning the surface of the silicon wafer by using an ultrasonic cleaning machine;

spin coating SU-8 photoresist: placing a cleaned silicon wafer on dust-free paper, clamping the edge of the silicon wafer by using tweezers, placing the silicon wafer on a rotating table of a spin coater, opening an air valve to suck and fix the silicon wafer, sucking a preset amount of SU-8 photoresist by using a disposable suction tube to coat the surface of the silicon wafer, covering a cover plate of the spin coater, and starting spin coating after setting the rotating speed;

pre-baking: transferring the silicon wafer after the glue homogenizing is finished to dust-free paper, and baking the silicon wafer on a hot plate for 15 minutes, wherein the temperature is set to 95 ℃;

alignment and exposure: carrying out alignment exposure on the silicon wafer through an ultraviolet photoetching machine, and overlaying photoetching patterns on the silicon wafer together to build a two-dimensional micro-nano structure;

post-baking: the drying time is 15min, and the temperature is set to 95 ℃;

and (3) developing: placing the silicon wafer in SU-8 developer, and slightly shaking the container;

secondary glue homogenizing: cleaning the residual developing solution on the surface of the developed silicon wafer, and then spin-coating a layer of SPR-220 positive photoresist on the surface of the silicon wafer;

pre-baking: pre-baking the silicon wafer subjected to the secondary glue homogenizing on a hot plate for 30s at the temperature of 60 ℃, and standing the silicon wafer at room temperature for 3h after the pre-baking is finished;

and (3) secondary exposure: carrying out secondary exposure on the silicon wafer;

post-baking: the drying time is 15min, and the temperature is set to 95 ℃;

and (3) secondary development: carrying out secondary development on the silicon wafer, and slightly shaking the container;

and transferring and self-assembling to obtain the self-assembled three-dimensional micro-nano structure.

Optionally, plating copper on the surface of the silicon wafer, wherein the thickness of the film is 300nm, and cleaning the surface of the silicon wafer by using an ultrasonic cleaning machine comprises:

and (3) coating by using a high-vacuum magnetron sputtering coating machine, and then respectively ultrasonically cleaning the silicon wafer for 15 minutes by using acetone and absolute ethyl alcohol.

Optionally, the starting of spin coating after the setting of the rotation speed includes: and respectively adopting low rotating speed of 500r/min for 3s, high rotating speed of 2000r/min for 30s and homogenizing for one time.

Optionally, the exposure time for performing alignment exposure on the silicon wafer by using the ultraviolet lithography machine is 25 s.

Optionally, the developing time of placing the silicon wafer in the SU-8 developing solution is 2.5 min.

Optionally, the spin coating parameters of spin coating a layer of SPR-220 positive photoresist on the surface of the silicon wafer are as follows: the low rotating speed is 500r/min and the time is 3s, the high rotating speed is 1000r/min and the time is 15s, and the glue is homogenized twice.

Optionally, the exposure time for performing the second exposure on the silicon wafer is 120 s.

Optionally, the developing time for performing the secondary development on the silicon wafer is 6 min.

Optionally, the transferring and self-assembling to obtain a self-assembled three-dimensional micro-nano structure includes:

removing the copper film by using a copper etching solution to enable the micro-nano structure to be separated from the silicon wafer and float on the liquid surface, then cleaning the micro-nano structure in deionized water for 3-4 times to remove the copper etching solution, and then transferring the micro-nano structure to dust-free paper;

and placing the self-supporting two-dimensional structure on a hot plate, and carrying out thermally-driven self-assembly to obtain the self-assembled three-dimensional micro-nano structure.

The technical scheme provided by the embodiment of the invention has the following beneficial effects:

it is worth to say that, in the invention, a copper film with the thickness of 300nm is plated on a silicon plate by using a magnetron sputtering film plating method, the copper film is etched immediately, so that a micro plane structure built on the copper film can be transferred to a paper substrate, and a built two-dimensional microstructure is composed of SU-8 photoresist and SPR-220 photoresist, wherein the SU-8 photoresist is used as a panel, and the SPR-220 photoresist is used as a hinge for connecting two adjacent panels. When the microstructure is transferred from the silicon chip to the paper substrate and heated to the melting point of the hinge material, the surface tension generated by the melting of the hinge can pull the panel up, thereby completing the folding action and realizing the self-assembly of the two-dimensional structure to the three-dimensional structure.

In addition, the invention optimizes the micro-electronic processes such as photoetching and developing, successfully prepares the two-dimensional planar structure by using the SU-8 negative photoresist and the SPR-220 positive photoresist, respectively determines the settings of key process parameters such as spin coating parameters, exposure time, developing time and the like of the SU-8 photoresist and the SPR-220 photoresist in the experimental process according to the test result, and implements self-assembly on the two-dimensional micro-nano structure by using heat as a driving force. Therefore, the self-assembled three-dimensional micro-nano structure is prepared by micro-electronic processes such as spin coating, photoetching and etching and assisted by a self-assembly technology, and a platform is provided for the self-assembly of the subsequent two-dimensional material.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a simple flow chart of a method for preparing a self-assembled three-dimensional micro-nano structure according to an embodiment of the invention;

fig. 2 is a complete flow chart of a method for preparing a self-assembled three-dimensional micro-nano structure according to an embodiment of the present invention;

fig. 3 is a schematic diagram of thermally driven self-assembly of a micro-nano structure according to an embodiment of the present invention;

fig. 4 is an optical microscope image of two-dimensional micro-nano structures with different exposure times according to an embodiment of the present invention;

FIG. 5 is a SU-8 photo-etching mask provided by an embodiment of the present invention;

fig. 6 is a schematic plan view of a two-dimensional micro-nano structure provided in an embodiment of the present invention;

fig. 7 is an optical microscope image of a two-dimensional micro-nano structure provided by an embodiment of the invention;

FIG. 8 is a block diagram of a lithographically formed panel provided by an embodiment of the present invention;

FIG. 9 is a graph of SU-8 photoresist topography at different development times provided by an embodiment of the present invention;

FIG. 10 is a schematic diagram of an SPR-220 photolithography mask provided by embodiments of the present invention;

FIG. 11 is a two-dimensional block diagram of the assembly of a self-supporting SU-8 panel and SPR-220 hinge that is not attached to a Si substrate according to embodiments of the present invention;

fig. 12 is a three-dimensional micro-nano structure diagram after self-assembly according to an embodiment of the present invention;

fig. 13 is a three-dimensional micro-nano structure diagram after another self-assembly according to an embodiment of the present invention;

FIG. 14 is an optical microscope image of the micro-nano structure self-assembly formed by the SU-8 panel and the SPR-220 hinge provided by the embodiment of the present invention;

FIG. 15 is a block diagram of a self-assembled structure of an SU-8 panel and an SPR-220 hinge according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a simple flow chart of a method for preparing a self-assembled three-dimensional micro-nano structure according to an embodiment of the invention; fig. 2 is a complete flow chart of a preparation method of a self-assembled three-dimensional micro-nano structure provided by the embodiment of the invention. Referring to fig. 1-2, the method includes:

it should be noted that the self-assembly of the micro-nano structure is a spontaneous process, and although the process is spontaneous, an external stimulus such as heat, pH, magnetic field, etc. is usually required to trigger the process. The self-assembly in the present invention is triggered by a thermal driving force. A simple and typical micro-nano self-assembled structure comprises two rigid panels and a hinge, wherein the hinge connected between the two panels is made of a material capable of responding to different stimuli (such as heat) and is accompanied by chemical or physical changes (such as melting) when the hinge is stimulated. When the physical properties of the hinge change, a driving force (e.g., surface tension) is typically generated spontaneously, causing movement of the panel connected to the hinge. As shown in fig. 3, the two rigid panels fold under heat, i.e., self-assemble.

Step 201: the round complete silicon wafer was cut into 2 x 2cm silicon wafers using a laser dicing saw.

It should be noted that the laser dicing machine can irradiate the high-intensity laser on the silicon wafer, and the laser can scribe a slight groove on the surface of the silicon wafer, so that the silicon wafer is easy to be manually divided. The cutting of the complete silicon wafer can increase the utilization rate of the silicon wafer and can not cause the waste of the photoresist and the developing solution.

Step 202: copper is plated on the surface of the silicon wafer, the thickness of the film is 300nm, and then the surface of the silicon wafer is cleaned by using an ultrasonic cleaning machine.

Specifically, a high vacuum magnetron sputtering coating machine is used for coating, and then acetone and absolute ethyl alcohol are used for respectively ultrasonically cleaning the silicon wafer for 15 minutes.

The sputtering process is a process in which incident ions undergo energy and momentum exchange through a series of collisions. Before formal sputtering begins, argon gas is filled into the cavity, electrons collide with argon atoms in the process of accelerating to fly to the silicon substrate under the action of an electric field to ionize a large amount of argon ions and electrons, the electrons continuously collide with the argon atoms in the process of flying to the substrate to generate more argon ions and electrons, the argon ions accelerate to bombard the target under the action of the electric field, a large amount of target atoms are sputtered, and neutral target atoms are deposited on the silicon substrate to form a film. The process conditions used in the process of sputtering the copper film in the invention are as follows: argon flow 10SCCM, reaction chamber pressure 1.0Pa, sputtering power 150W, and sputtering time 10 min.

It should be noted that the above cleaning process is very important, and aims to make the surface of the silicon wafer as clean as possible without contamination, enhance the adhesion between the photoresist and the silicon substrate, and ensure the uniformity and flatness of the surface after the spin coating is completed. If the wafer surface has too many contaminants, spin-on photoresist tends to cause micro-bubbles that can greatly affect the lithographic pattern.

Step 203: placing the cleaned silicon wafer on dust-free paper, clamping the edge of the silicon wafer by using tweezers, placing the silicon wafer on a rotating table of a spin coater, opening an air valve to suck and fix the silicon wafer, sucking a predetermined amount of SU-8 photoresist by using a disposable suction pipe, coating the surface of the silicon wafer, covering a cover plate of the spin coater, and starting spin coating after setting the rotating speed.

The spin coater used in the invention is a KW-4A type desk spin coater, the spin coater can uniformly spin-coat photoresist on the surface of a silicon wafer by high-speed rotation, and the spin coater is provided with a low-rotation-speed region and a high-rotation-speed region and can be used step by step. Specifically, the method adopts low rotating speed of 500r/min for 3s, high rotating speed of 2000r/min for 30s and glue homogenizing.

It should be noted that, through research and analysis on surface topography maps of SU-8 panels with different rotating speeds, it can be seen that when the rotating speed is 1500r/min, colored stripes appear on the surface of the two-dimensional panel structure under an optical microscope, and through research and analysis, it is considered that the colored stripes appear on the surface of the two-dimensional panel structure due to the uneven thickness, thick periphery and thin middle of the photoresist on the surface of the silicon wafer after photoresist uniformization is completed because the rotating speed is too low, so that in the invention, the rotating speed is adjusted from 1500r/min to 2000r/min, and when the rotating speed is 2000r/min, the SU-8 glue surface is flat and meets the requirements.

In addition, the purpose of setting the low rotating speed of 500r/min is to firstly approximately disperse the viscous SU-8 photoresist and then uniformly coat the surface of the silicon wafer with the photoresist at a high rotating speed.

Moreover, in the process of dripping the glue on the surface of the silicon wafer, white light irradiation is avoided as much as possible, and the generation of micro bubbles is reduced as much as possible.

Step 204: the silicon wafer after the completion of the spin coating was transferred to a dust-free paper and pre-baked on a hot plate for 15 minutes at a temperature of 95 ℃.

It should be noted that care should be taken to avoid white light irradiation during the pre-baking process, otherwise the photoresist will be denatured and agglomeration will easily occur during the baking process.

Step 205: and aligning and exposing the silicon wafer through an ultraviolet lithography machine, and overlaying the lithography patterns on the silicon wafer together to build a two-dimensional micro-nano structure, wherein the exposure time is 25 s.

Specifically, the silicon wafer is subjected to alignment by using an H94-27A type single-sided ultraviolet lithography machine. The type of photoetching machine is mainly applied to the development and production of medium and small-scale integrated circuits and semiconductor components, and is suitable for the alignment exposure of various substrates with the diameter of less than 153mm and the thickness of less than 5 mm. 365nm, 404nm and 435nm combined ultraviolet light is used in the exposure process, the exposure area is as large as phi 170mm, the exposure intensity is larger than 5mw/cm2, the exposure resolution is smaller than 2 mu m, various exposure modes such as hard contact, soft contact and micro-force contact can be realized, the alignment precision is smaller than 1 mu m, and the preparation requirement of a two-dimensional micron-submicron structure can be basically met.

It should be noted that different exposure times may affect the final experimental result, and fig. 4 is an optical microscope image of a two-dimensional micro-nano structure with different exposure times, where the exposure times from left to right are 120s and 25s, respectively. It can be observed that when the exposure time is 120s, the panel pitch is too small to meet the requirement; when the exposure time is properly decreased to 25s, the panel pitch is increased. The study and comparison show that the spacing between SU-8 panels is about 50 μm when the exposure time is 25s, which is satisfactory. Thus, the exposure time in this step is set to 25s in the present invention.

It should be noted that, in this step, the photolithography mask and the silicon wafer are aligned and exposed, that is, in this step, the photolithography mask needs to be used to leave a specific pattern on the silicon wafer during photolithography. Specifically, the photolithographic mask used in this step is: SU-8 lithography masks, as shown in FIG. 5.

In addition, when the photoetching mask is prepared, three two-dimensional structures with different sizes are prepared on the same photoetching mask, and the sizes are respectively as follows: the side length of the panel is 500 μm, the width of the hinge is 50 μm, and the length is 500 μm; 1000 μm, hinge width 100 μm, length 1000 μm; 200 μm, a hinge width of 20 μm and a length of 200 μm. The size of the selected photoetching mask plate is as follows: the panel side was 500 μm, the hinge width was 50 μm, and the length was 500 μm. Fig. 6 is a schematic plan view of a two-dimensional micro-nano structure, and referring to fig. 6, a white square part is a panel structure, and a black part is an hinge structure. Fig. 7 is an optical microscopic image of a two-dimensional micro-nano structure.

It is worth to say that the structure size of 500 μm is selected, the photoetching process and the self-assembly process under the size are mainly considered comprehensively, the too large size is selected, the photoetching is easier, but the self-assembly is more difficult due to gravity; if the size is too small, the difficulty of photolithography will increase accordingly.

Step 206: post-baking is carried out, the baking time is 15min, and the temperature is set to be 95 ℃.

Step 207: the silicon wafer is placed in SU-8 developer, and the container is gently shaken, and the developing time is 2.5 min.

Note that the container was gently shaken to make the development more thorough. After the development was completed, the SU-8 panel structure on the surface of the silicon wafer was clearly observed, as shown in FIG. 8.

In addition, fig. 9 is a surface topography diagram of SU-8 photoresist with different development times, which are 2.5min, 5min and 6min from left to right respectively. As can be seen from FIG. 9, the SU-8 photoresist has sharp and regular edges and a clear and flat pattern in accordance with the requirement at the development time of 2.5min, so that the development time of SU-8 is set to 2.5min in the present invention.

Step 208: cleaning the residual developing solution on the surface of the developed silicon wafer, and then spin-coating a layer of SPR-220 positive photoresist on the surface of the silicon wafer, wherein the spin-coating parameters are 500r/min at a low rotation speed for 3s, 1000r/min at a high rotation speed for 15s, and the photoresist is homogenized twice.

It should be noted that the photoresist used in the present invention includes two types, SU-8 negative photoresist and SPR-220 positive photoresist. SU-8 negative photoresist, the light receiving part is not easily dissolved, so the light part can be left during developing, and the unexposed part can be removed; SPR-220 positive photoresists have well soluble illuminated portions and unexposed portions that can be left behind during development. In addition, the SU-8 photoresist is hard after being heated and hardened, and is an ideal choice for rigid panels and supporting materials; SPR-220 photoresist was used as the hinge material (melting point about 100 ℃ C.). Therefore, in the invention, two times of glue homogenizing are required, SU-8 negative photoresist is used once, and SPR-220 positive photoresist is used for the second time.

Step 209: and pre-baking the silicon wafer subjected to the secondary glue homogenizing on a hot plate for 30s at the temperature of 60 ℃, and standing the silicon wafer at room temperature for 3h after the pre-baking is finished.

It should be noted that, because the SPR-220 photoresist is not easy to solidify, if the exposure is carried out under the condition that the SPR-220 photoresist is not completely solidified, the silicon wafer is adhered to the photoetching mask plate to cause pollution, and therefore, the silicon wafer needs to be placed still for 3 hours at room temperature.

Step 210: and carrying out secondary exposure on the silicon wafer, wherein the exposure time of the SPR-220 positive photoresist is 120 s.

It should be noted that, after the first exposure and development is completed, the SU-8 panel of the micro-nano structure is fixed, so the SPR-220 hinge pattern must be aligned with the built panel structure, and if the SPR-220 hinge pattern is misaligned, the microstructure cannot be built successfully.

In addition, in this step, the photolithography mask and the silicon wafer also need to be aligned for exposure, that is, in this step, the photolithography mask is also used to leave a specific pattern on the silicon wafer during photolithography. The photolithography mask used in this step is: SPR-220 lithography reticle is shown in detail in FIG. 10.

Step 211: post-baking is carried out, the baking time is 15min, and the temperature is set to be 95 ℃.

Step 212: and carrying out secondary development on the silicon wafer for 6min, and slightly shaking the container.

It should be noted that this step is to remove the excess SPR-220 photoresist, leaving the photo-etched hinge structure. Also, the container is gently shaken, and the development can be more thorough. As can be seen by observation, the two-dimensional structure formed by the SU-8 panel and the SPR-220 hinge has good alignment and clear separation.

Step 213: and removing the copper film by using a copper etching solution to enable the micro-nano structure to be separated from the silicon wafer and float on the liquid surface, then cleaning the micro-nano structure in deionized water for 3-4 times to fully remove the copper etching solution, and then transferring the micro-nano structure to dust-free paper.

It should be noted that after the micro-nano structure is built on the silicon wafer, the micro-nano structure still adheres to the copper film, and self-assembly cannot be performed, so that the structure needs to be transferred to heat the structure. FIG. 11 is a two-dimensional block diagram of the combination of a self-supporting SU-8 panel and SPR-220 hinges, not attached to a Si substrate.

Step 214: and placing the self-supporting two-dimensional structure on a hot plate, and carrying out thermally-driven self-assembly to obtain a self-assembled three-dimensional micro-nano structure.

Specifically, the three-dimensional micro-nano structure after self-assembly is shown in fig. 12 and 13.

It should be noted that fig. 14 is an optical microscope image of the micro-nano structure self-assembly formed by the SU-8 panel and the SPR-220 hinge, and after the self-assembly is finished, a white part is still in contact with the dust-free paper, and a gray part indicates that the panel is pulled up. As can be seen from the figure, the two-dimensional structure with different panel numbers can realize the heat-driven self-assembly, and the feasibility of the heat-driven three-dimensional self-assembly with different configurations is proved. Also, as shown in FIG. 15, (a-b) the heating temperature is 120 ℃, (c-d) the heating temperature is 130 ℃, (e-f) the heating temperature is 140 ℃, and as the heating temperature is increased from 120 ℃ to 130 ℃, the self-assembly angle is also increased from 15 ° of 120 ℃ to 28 °, but no significant increase in the self-assembly angle is observed when the heating temperature is increased to 140 ℃ or more, and it should be 140 ℃, the SPR-220 hinge is completely melted and the surface tension is balanced.

It is worth to say that, in the invention, a copper film with the thickness of 300nm is plated on a silicon plate by using a magnetron sputtering film plating method, the copper film is etched immediately, so that a micro plane structure built on the copper film can be transferred to a paper substrate, and a built two-dimensional microstructure is composed of SU-8 photoresist and SPR-220 photoresist, wherein the SU-8 photoresist is used as a panel, and the SPR-220 photoresist is used as a hinge for connecting two adjacent panels. When the microstructure is transferred from the silicon chip to the paper substrate and heated to the melting point of the hinge material, the surface tension generated by the melting of the hinge can pull the panel up, thereby completing the folding action and realizing the self-assembly of the two-dimensional structure to the three-dimensional structure.

In addition, the invention optimizes the micro-electronic processes such as photoetching and developing, successfully prepares the two-dimensional planar structure by using the SU-8 negative photoresist and the SPR-220 positive photoresist, respectively determines the settings of key process parameters such as spin coating parameters, exposure time, developing time and the like of the SU-8 photoresist and the SPR-220 photoresist in the experimental process according to the test result, and implements self-assembly on the two-dimensional micro-nano structure by using heat as a driving force. Therefore, the self-assembled three-dimensional micro-nano structure is prepared by micro-electronic processes such as spin coating, photoetching and etching and assisted by a self-assembly technology, and a platform is provided for the self-assembly of the subsequent two-dimensional material.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.