A method for preparing high-precision three-dimensional silicon structure

Abstract

The invention discloses a method for preparing a high-precision three-dimensional silicon structure, comprising the following steps: (1) establishing a 3D model of a silicon structure to be printed and planning a printing path by software, and printing the model in a two-photon polymerization 3D printer using TPL photoresist to obtain an initial POSS model; (2) immersing the obtained model in propylene glycol methyl ether acetate to remove unpolymerized photoresist, taking the model out and then immersing it in isopropyl alcohol to remove the propylene glycol methyl ether acetate to obtain a POSS model; (3) sintering the POSS model in a high-temperature air atmosphere to remove organic components in the POSS model to obtain a silicon dioxide model; and (4) subjecting the silicon dioxide model and magnesium powder to a reduction reaction in a high-temperature argon atmosphere to reduce the silicon dioxide to silicon to obtain a silicon structure with submicron precision.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-precision three-dimensional silicon structure. Background Art

[0002] 3D printing is a new manufacturing technology developed in the 1980s. This process does not require molds; a virtual model can be designed directly using software, and then a physical model is directly obtained through a layer-by-layer additive process within the printing device. The principle of 3D printing based on photocuring is as follows: liquid 3D photoresist rapidly undergoes photopolymerization under light of a certain wavelength and intensity, causing its molecular weight to increase dramatically, transforming from a liquid to a solid state. After removing the excess liquid photoresist, the remaining solid portion is the resulting physical model. This technology not only has the ability to process arbitrarily complex structures, but also offers advantages over traditional manufacturing methods such as rapid prototyping, high design freedom, and material conservation. Two-photon polymerization 3D printing (TPL) is one of the most precise printing technologies, capable of achieving submicron resolution. This high manufacturing precision and mold-free design freedom make TPL printing technology an ideal choice for rapidly preparing tiny objects with precise structures.

[0003] However, the development of TPL printing is constrained by several factors, such as a limited selection of photoresists. Currently, most models produced using TPL printing are made from organic materials such as photosensitive resins and hydrogels. Reports and applications of TPL printing for inorganic models are limited. Silicon is the primary material for semiconductor devices. Modern electronic devices, such as computers, smartphones, and tablets, rely on silicon-based integrated circuits. Sensors and actuators in microelectromechanical systems (MEMS), widely used in automotive, medical, and consumer electronics, also rely on high-precision silicon structures. Therefore, silicon materials are of great significance to industrial development. Currently, methods for fabricating submicron silicon structures are complex, primarily using photolithography, etching, and chemical vapor deposition. Photolithography, the most common method, uses light to define patterns on silicon wafers. High-resolution photolithography techniques, such as deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography, can achieve submicron and nanometer resolution. Etching methods include dry and wet etching. Using plasma to etch the material allows for highly anisotropic etching, making it suitable for fabricating structures with vertical sidewalls. Chemical etching is suitable for fabricating larger silicon structures, but is significantly limited in resolution and aspect ratio. Chemical vapor deposition (CVD) deposits thin films on silicon wafers, followed by photolithography and etching processes to create fine structures. These methods often rely on large equipment, involve numerous steps, and are time- and financially expensive, making them unsuitable for the rapid fabrication of three-dimensional micro- and nanostructures in silicon. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for preparing high-precision three-dimensional silicon structures, which can quickly prepare silicon structures with submicron precision.

[0005] Technical solution: The method for preparing a high-precision three-dimensional silicon structure according to the present invention comprises the following steps:

[0006] (1) Using software to build a 3D model of the silicon structure to be printed and plan the printing path, use TPL photoresist to print it in a two-photon polymerization 3D printer (printed onto a quartz substrate) to obtain a high-precision initial POSS model;

[0007] (2) soaking the obtained model in propylene glycol methyl ether acetate until the unpolymerized photoresist is completely washed away, taking it out and then soaking it in isopropyl alcohol until the propylene glycol methyl ether acetate is completely washed away to obtain a POSS model;

[0008] (3) the POSS model is placed in a high-temperature air atmosphere and sintered to remove the organic components in the POSS model. During the sintering process, the entirety of the POSS model undergoes isotropic shrinkage to obtain a high-precision silicon dioxide model.

[0009] (4) The silica model and magnesium powder are subjected to a reduction reaction in a high-temperature argon atmosphere to reduce the silica to silicon, thereby obtaining a silicon structure with submicron line spacing and characteristic size (in Example 1, the spacing between two adjacent lines in the structure is equivalent to the resolution of the display screen, and the characteristic size refers to the width of the lines in the structure, which is equivalent to the pixel size).

[0010] Wherein, in step (1), during the printing process, the laser power is 5 to 50 mW / cm 2 , the printing speed is 300~15000μm / s.

[0011] Wherein, in step (1), the 3D printer is a two-photon laser direct writing 3D printer, and the light source of the printing device excites the photoinitiator. Under the action of the free radicals generated by the photoinitiator, a photopolymerization reaction rapidly occurs between the propyl acryloyloxy groups on the periphery of the POSS, and the molecular weight increases sharply from liquid to solid, thereby generating a solid POSS model, in which the silicon oxygen core of the POSS is also included.

[0012] Wherein, in step (1), the TPL photoresist is composed of the following components in parts by weight: 75 to 99 parts of POSS with a photocurable substituent, 0 to 20 parts of a diluent, and 1 to 5 parts of a photoinitiator.

[0013] The POSS with a photocurable substituent is octaacryloxypropyl POSS; the diluent is polyethylene glycol diacrylate; and the photoinitiator is 4,4′-bis(diethylamino)benzophenone.

[0014] The preparation method of TPL photoresist is as follows: POSS with a photocurable substituent, a diluent and a photoinitiator are mixed in a formulated amount, stirred evenly under light-proof conditions at room temperature to 50°C, to obtain TPL photoresist, and stored in a light-proof environment at 4°C.

[0015] Wherein, in step (2), the mixture is immersed in propylene glycol methyl ether acetate for 10 to 15 minutes and immersed in isopropyl alcohol for 10 to 15 minutes.

[0016] Wherein, in step (3), the sintering temperature is 700-800° C., and the sintering time is 2-2.5 hours.

[0017] The heating rate is 2-10°C / min, and the cooling rate is 2-10°C / min to room temperature.

[0018] Wherein, in step (4), the mixing mass ratio of the silica model to the magnesium powder is 1:10 to 15. The silica model and magnesium powder of not less than ten times the mass are placed in a sealed stainless steel sample boat for reduction reaction.

[0019] Wherein, in step (4), the temperature of the reduction reaction is 650-700° C., and the reaction time is 4-5 h.

[0020] The heating rate is 2-5°C / min, and the cooling rate is 5-6°C / min to room temperature.

[0021] The photoresist used in the present invention is mainly composed of POSS with photocurable substituents, which can form a hybrid model of polymerized organic-inorganic components under the action of free radicals generated by a photoinitiator. After obtaining the primary POSS model, the organic part is removed through high-temperature treatment, and the entire model will undergo isotropic contraction to obtain a silicon dioxide structure. After a magnesium thermal reduction reaction, a silicon structure that is isotropically contracted again is obtained, thereby achieving the purpose of high-precision 3D printing of silicon structures.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the method of the present invention uses cage-type polysilsesquioxane (POSS) with polymerizable substituents as the main component of the photoresist, uses two-photon laser direct writing (TPL)

[0023] 3D printing technology is used to create a high-precision POSS model. The organic components are then removed through high-temperature treatment to produce a silica structure. Finally, a magnesium-thermal reduction reaction is performed to obtain the desired submicron-level silicon structure. Compared to traditional etching processes, this method can rapidly create silicon structures with submicron precision, enabling the rapid and high-precision fabrication of arbitrarily complex silicon structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the method of the present invention;

[0025] Figure 2 This is a model diagram of the silicon structure to be printed in Example 1;

[0026] Figure 3 The scanning electron microscope images of the structures obtained at various stages of the method in Example 1 are shown;

[0027] Figure 4 EDS elemental analysis of the samples obtained at various stages of the method in Example 1;

[0028] Figure 5 XPS elemental chemical state analysis of the silicon dioxide structure and silicon structure before and after magnesium thermal reduction treatment in the method of Example 1; A) Si chemical state; B) O chemical state; C) Mg chemical state; D) C chemical state;

[0029] Figure 6 This is a model diagram of the silicon structure to be printed in Example 2 and the submicron precision silicon hollow spherical structure obtained after printing;

[0030] Figure 7 This is the modeling diagram of the silicon structure to be printed in Example 3 and the submicron precision diatom-shaped structure obtained after printing. DETAILED DESCRIPTION

[0031] Example 1

[0032] The method for preparing a high-precision three-dimensional silicon structure of the present invention comprises the following steps:

[0033] The target model is a line structure with a line period of 1.2μm and a feature size of 120nm. The modeling software is used to design a line structure with a lateral period of 2μm, such as Figure 2 shown.

[0034] (1) Preparation of TPL photoresist: 99 parts by weight of octaacryloxypropyl POSS and 1 part of 4,4′-bis(diethylamino)benzophenone were mixed, heated to 40° C. in a light-proof environment using a constant temperature magnetic stirring device and stirred until a uniform state was achieved, thereby preparing a TPL photoresist for use;

[0035] (2) Printing was performed using the TPL photoresist prepared in step (1) in a two-photon polymerization 3D printer (model: Nanoscribe Photonic Professional GT) with a laser power of 20 mW / cm 2 , the printing speed is 3000 μm / s, and the initial model is obtained;

[0036] (3) The obtained model was immersed in propylene glycol methyl ether acetate and taken out after 10 minutes; then immersed in isopropyl alcohol and taken out after 10 minutes, and the excess photoresist was removed to obtain a POSS line structure with a line period of 1.94 μm and a line width of 223 nm. Figure 3 As shown in A;

[0037] (4) The POSS line structure was sintered in an air atmosphere, heated at a rate of 5°C / min, maintained at 700°C for 2h, and then cooled to room temperature at a rate of 5°C / min to obtain a proportionally reduced silicon dioxide line structure with a line period of 1.16μm and a line width of 118nm. Figure 3 As shown in B;

[0038] (5) The obtained silicon dioxide line structure sample and excess magnesium powder (the mixing mass ratio of silicon dioxide line structure and magnesium powder is 1:10) are placed in a sealed stainless steel sample boat for magnesium thermal reduction. The reaction atmosphere is argon gas, the heating rate is 2°C / min, and after reaching 650°C, it is maintained for 4 hours, and then cooled to room temperature at 5°C / min. Submicron precision silicon line structure is obtained, with a line spacing of 1.02μm and a feature size of 105nm. Figure 3 As shown in C, the requirements of the target model are met.

[0039] like Figure 4 As shown, the POSS structure, silica structure and silicon structure obtained in Example 1 were subjected to EDS elemental analysis. The results showed that after sintering and magnesium thermal reduction treatment, carbon and oxygen elements were removed, proving that a structure composed of silicon was successfully obtained.

[0040] like Figure 5 As shown, XPS elemental chemical state analysis of the silica structure and silicon structure was performed. Figure A shows that the chemical state of Si before magnesium thermal reduction belongs to SiO2 (103.5eV), and it is converted into Si element (99.4eV) after the reduction reaction; Figure B shows that the chemical state of O before magnesium thermal reduction belongs to SiO2 (532.9eV), and the O intensity decreases significantly after the reduction reaction; Figure C shows that after magnesium thermal reduction, no Mg residue was detected on the surface of the product (Mg metal, Mg oxide 1303-1304.5eV); Figure D shows trace C residue or external contamination (CC peak 284.8eV).

[0041] Comparative Example 1

[0042] The target model is a line structure with a line period of 1.2μm and a feature size of 120nm. The modeling software is used to design a line structure with a lateral period of 2μm, such as Figure 2 shown.

[0043] (1) Preparation of TPL photoresist: 99 parts by weight of octaacryloxypropyl POSS and 1 part of 4,4′-bis(diethylamino)benzophenone were mixed, heated to 40° C. in a light-proof environment using a constant temperature magnetic stirring device and stirred until a uniform state was achieved, thereby preparing a TPL photoresist for use;

[0044] (2) Print the TPL photoresist prepared in step (1) in a two-photon polymerization 3D printer (model: Nanoscribe Photonic Professional GT) with a laser power of 30 mW / cm 2 , the printing speed is 3000 μm / s, and the initial model is obtained;

[0045] (3) The obtained model was immersed in propylene glycol methyl ether acetate and taken out after 10 minutes; then immersed in isopropyl alcohol and taken out after 10 minutes to remove the excess photoresist, thereby obtaining a POSS line structure with a line period of 1.97 μm and a line width of 358 nm;

[0046] (4) The POSS line structure was sintered in an air atmosphere, heated at a rate of 5°C / min, maintained at 700°C for 2 h, and then cooled to room temperature at a rate of 5°C / min to obtain a proportionally scaled silica line structure with a line period of 1.17 μm and a line width of 192 nm;

[0047] (5) The obtained silica line structure sample and excess magnesium powder (the mixing mass ratio of silica line structure and magnesium powder is 1:10) were placed in a sealed stainless steel sample boat for magnesium thermal reduction. The reaction atmosphere was argon, the heating rate was 2°C / min, and after reaching 650°C, it was maintained for 4 hours, and then cooled to room temperature at 5°C / min to obtain a submicron precision silicon line structure with a line spacing of 1.08μm and a feature size of 167nm.

[0048] Compared with Example 1, the increased laser intensity resulted in an increase in the polymerization area, which widened the lines, resulting in an increase in feature size by approximately 59.04% and an increase in line spacing by approximately 5.88%. The accuracy decreased compared with Example 1 and did not meet the target model requirements.

[0049] Comparative Example 2

[0050] The target model is a line structure with a line period of 1.2μm and a feature size of 120nm. The modeling software is used to design a line structure with a lateral period of 2μm, such as Figure 2 shown.

[0051] (1) Preparation of TPL photoresist: 99 parts by weight of octaacryloxypropyl POSS and 1 part of 4,4′-bis(diethylamino)benzophenone were mixed, heated to 40° C. in a light-proof environment using a constant temperature magnetic stirring device and stirred until a uniform state was achieved, thereby preparing a TPL photoresist for use;

[0052] (2) Printing was performed using the TPL photoresist prepared in step (1) in a two-photon polymerization 3D printer (model: Nanoscribe Photonic Professional GT) with a laser power of 20 mW / cm 2 , the printing speed is 2500 μm / s, and the initial model is obtained;

[0053] (3) The obtained model was immersed in propylene glycol methyl ether acetate and taken out after 10 minutes; then immersed in isopropyl alcohol and taken out after 10 minutes to remove the excess photoresist, thereby obtaining a POSS line structure with a line period of 2.01 μm and a line width of 273 nm;

[0054] (4) The POSS line structure was sintered in an air atmosphere, heated at a rate of 5°C / min, maintained at 700°C for 2 h, and then cooled to room temperature at a rate of 5°C / min to obtain a proportionally scaled silica line structure with a line period of 1.21 μm and a line width of 144 nm;

[0055] (5) The obtained silica line structure sample and excess magnesium powder (the mixing mass ratio of silica line structure and magnesium powder is 1:10) are placed in a sealed stainless steel sample boat for magnesium thermal reduction. The reaction atmosphere is argon, the heating rate is 2°C / min, and after reaching 650°C, it is maintained for 4 hours, and then cooled to room temperature at 5°C / min to obtain a submicron precision silicon line structure with a line spacing of 1.05μm and a feature size of 130nm.

[0056] Compared with Example 1, the scanning speed is reduced, resulting in a decrease in the diffusion rate of free radicals. The free radical concentration per unit volume increases, resulting in an increase in the polymerization area, making the lines wider, resulting in a 27.45% increase in the feature size and an increase in the line spacing by approximately 2.94%. The accuracy is reduced compared with Example 1 and does not meet the target model requirements.

[0057] Example 2

[0058] The target model is a hollow spherical structure with a diameter of 30 μm and a characteristic size of 400 nm. The structure is designed using modeling software such as Figure 6 As shown in A.

[0059] (1) Preparation of TPL photoresist: 90 parts by weight of octamethacryloyloxypropyl POSS, 9 parts by weight of ethylene glycol dimethacrylate, and 1 part by weight of 4,4′-bis(diethylamino)benzophenone were mixed, heated to 40° C. in a light-proof environment using a constant temperature magnetic stirring device and stirred until a uniform state was achieved, thereby preparing a TPL photoresist for use;

[0060] (2) Print the TPL photoresist prepared in step (1) in a two-photon polymerization 3D printer (model: Nanoscribe Photonic Professional GT) with a laser power of 5 mW / cm 2 , the printing speed is 300 μm / s, and the initial model is obtained;

[0061] (3) The obtained model was immersed in propylene glycol methyl ether acetate and taken out after 10 minutes; then immersed in isopropyl alcohol and taken out after 10 minutes to remove the excess photoresist, thereby obtaining a POSS hollow spherical structure with a diameter of 40.76 μm and a characteristic size of 669 nm;

[0062] (4) The POSS hollow spherical structure was sintered in an air atmosphere, heated at a rate of 2°C / min, maintained at 700°C for 2 h, and then cooled to room temperature at a rate of 5°C / min to obtain a proportionally reduced hollow spherical structure with a diameter of 32.49 μm and a characteristic size of 434 nm;

[0063] (5) The obtained hollow spherical structure sample and excess magnesium powder (the mass ratio of the hollow spherical structure to magnesium powder is 1:10) are placed in a sealed stainless steel sample boat for magnesium thermal reduction. The reaction atmosphere is argon gas, the heating rate is 2 ° C / min, and after reaching 650 ° C, it is maintained for 4 h, and then cooled to room temperature at 5 ° C / min to obtain a submicron precision silicon hollow spherical structure with a diameter of 28.51 μm and a characteristic size of 382 nm. Figure 6 As shown in B, the requirements of the target model are met.

[0064] Example 3

[0065] The target model is a diatom-shaped structure with a size of 40*25*10μm and a feature size of 500nm. The structure is designed using modeling software such as Figure 7 As shown in A.

[0066] (1) Preparation of TPL photoresist: 90 parts by weight of octamethacryloxypropyl POSS, 9 parts of polyethylene glycol diacrylate, and 1 part of 4,4′-bis(diethylamino)benzophenone were mixed, heated to 40° C. in a light-proof environment using a constant temperature magnetic stirring device and stirred until a uniform state was achieved, thereby preparing a TPL photoresist for use;

[0067] (2) Print the TPL photoresist prepared in step (1) in a two-photon polymerization 3D printer (model: Nanoscribe Photonic Professional GT) with a laser power of 50 mW / cm 2 , the printing speed is 15000μm / s, and the initial model is obtained;

[0068] (3) The obtained model was immersed in propylene glycol methyl ether acetate and taken out after 15 minutes; then immersed in isopropyl alcohol and taken out after 15 minutes to remove the excess photoresist, thereby obtaining a POSS diatom-shaped structure with an overall size of approximately 60*40*15 μm;

[0069] (4) Sintering the POSS diatom-shaped structure in an air atmosphere, heating at a rate of 2°C / min, maintaining it at 700°C for 2 h, and then cooling it to room temperature at a rate of 5°C / min to obtain a proportionally reduced diatom-shaped silica structure;

[0070] (5) The obtained diatom-shaped silica structure sample and excess magnesium powder (the mixing mass ratio of the structure and magnesium powder is 1:15) are placed in a sealed stainless steel sample boat for magnesium thermal reduction. The reaction atmosphere is argon gas, the heating rate is 5°C / min, and after reaching 650°C, it is maintained for 5h, and then cooled to room temperature at 5°C / min to obtain a diatom-shaped structure with an overall size of approximately 38.52*24.42*9.58μm and a characteristic size of 482nm. Figure 7 As shown in B, the requirements of the target model are met.

Claims

1. A method for preparing a high-precision three-dimensional silicon structure, characterized in that: The steps include: (1) Using software to build a 3D model of the silicon structure to be printed and plan the printing path, and then use TPL photoresist to print it in a two-photon polymerization 3D printer to obtain the initial POSS model; The TPL photoresist is composed of the following components in parts by weight: 75-99 parts of POSS with a photocurable substituent, 0-20 parts of a diluent, and 1-5 parts of a photoinitiator; wherein the POSS with a photocurable substituent is octaacryloxypropyl POSS or octamethacryloxypropyl POSS; (2) soaking the obtained model in propylene glycol methyl ether acetate to remove the unpolymerized photoresist, taking it out and then soaking it in isopropyl alcohol to remove the propylene glycol methyl ether acetate to obtain a POSS model; (3) sintering the POSS model in a high-temperature air atmosphere to remove the organic components in the POSS model and obtain a silica model; the sintering temperature is 700-800 °C and the sintering time is 2-2.5 h; (4) The silica model and magnesium powder are subjected to a reduction reaction in a high-temperature argon atmosphere to reduce the silica to silicon, thereby obtaining a silicon structure with submicron precision; the reduction reaction temperature is 650~700℃, and the reaction time is 4~5h.

2. The preparation method according to claim 1, wherein: The diluent is polyethylene glycol diacrylate or ethylene glycol dimethacrylate; the photoinitiator is 4,4'-bis(diethylamino)benzophenone.

3. The preparation method according to claim 1, wherein: In step (1), during the printing process, the laser power is 5~50mW / cm 2 , printing speed is 300~15000μm / s.

4. The preparation method according to claim 1, wherein: In step (2), soak in propylene glycol methyl ether acetate for 10 to 15 minutes; soak in isopropyl alcohol for 10 to 15 minutes.

5. The preparation method according to claim 1, wherein: In step (3), the heating rate is 4-5°C / min; the cooling rate is 4-5°C / min to room temperature.

6. The preparation method according to claim 1, wherein: In step (4), the mixing mass ratio of the silica model and the magnesium powder is 1:10-15.

7. The preparation method according to claim 1, wherein: In step (4), the heating rate is 2-5°C / min; the cooling rate is 5-6°C / min to room temperature.

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