CN115338542B - Monocrystalline silicon with hydrophobic functional surface and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of laser micromachining, and relates to monocrystalline silicon with a hydrophobic functional surface, and a preparation method and application thereof. The preparation method comprises the steps of carrying out laser-assisted water jet processing on the surface of monocrystalline silicon to form a micron-sized structure array on the surface of monocrystalline silicon; forming a nano structure on the surface of the micron-sized structure array by using a femtosecond laser to induce a low-frequency periodic surface structure, thereby forming a micro-nano double-scale layered structure on the surface of monocrystalline silicon; immersing monocrystalline silicon with a micro-nano double-scale layered structure on the surface into hydrophobic silane for silanization treatment, thus obtaining the silicon nitride; in the laser-assisted water jet processing, the water jet is placed in the laser along the scanning speed direction. The invention can make the monocrystalline silicon surface possess hydrophobicity or superhydrophobicity on the basis of forming a micro-nano double-scale layered structure on the monocrystalline silicon surface.

Description

A single crystal silicon with a hydrophobic functional surface and its preparation method and application

Technical Field

The invention belongs to the technical field of laser micro-machining, and relates to a single crystal silicon with a hydrophobic functional surface and a preparation method and application thereof.

Background technique

The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not be necessarily regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

Wettability is an important physical property that people study when a solid surface comes into contact with a liquid. Single-crystal silicon surfaces with good hydrophobicity have important applications in many fields such as optoelectronics, microelectronics, and biomedicine. For example, water droplets rolling on the surface of a silicon-based solar cell with good hydrophobicity can carry away pollutants such as dust accumulated on the surface, making the solar cell surface self-cleaning and improving the light absorption rate of the cell. In micro-electromechanical systems (MEMS), silicon-based surface microstructures with excellent hydrophobicity can effectively reduce adhesion (static friction) while increasing surface roughness, which is beneficial to improving production and service life.

In order to realize the hydrophobic self-cleaning function on the surface of materials, the existing methods used include vapor deposition, sol-gel method, hydrothermal synthesis method, electrospinning method, etc. However, these methods are limited in application due to the use of a large amount of chemicals, or cannot be applied on a large scale due to the high cost and complicated steps. Laser processing technology has the arbitrariness and controllability of processing structure, can realize programmed and large-area processing, and has the advantage of being environmentally friendly. The action mode of laser and material is usually manifested as thermal action, so the processing damage such as recast layer and heat-affected zone is relatively serious, making it difficult to make a hydrophobic structure on the surface of the material.

Summary of the invention

In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a single crystal silicon with a hydrophobic functional surface and a preparation method and application thereof, which can make the single crystal silicon surface hydrophobic or super hydrophobic on the basis of forming a micro-nano dual-scale layered structure on the single crystal silicon surface.

In order to achieve the above object, the technical solution of the present invention is:

On the one hand, a method for preparing single crystal silicon with a hydrophobic functional surface comprises the following steps: performing laser-assisted water jet processing on the surface of the single crystal silicon to form a micron-scale structure array on the surface of the single crystal silicon; inducing a low-frequency periodic surface structure by a femtosecond laser to form a nanostructure on the surface of the micron-scale structure array, thereby forming a micro-nano dual-scale layered structure on the surface of the single crystal silicon; immersing the single crystal silicon with the micro-nano dual-scale layered structure on the surface into hydrophobic silane for silanization treatment to obtain a hydrophobic functional surface; wherein, in the laser-assisted water jet processing, the water jet is placed behind the laser in the scanning speed direction.

In the laser-assisted water jet processing of the present invention, the water jet is placed after the laser in the direction of the scanning speed. After the area of the single crystal silicon to be processed is softened by laser heating, it is sheared and removed by the water jet in the plastic mode, thereby greatly reducing the recast layer and heat-affected zone generated by the laser processing. Then, the micron-level surface structure can be quickly prepared by laser-assisted water jet processing technology. On the basis of the micron-level structure, a low-frequency periodic surface structure is induced by femtosecond laser, so that a hierarchical structure functional surface with micro-nano dual scales can be quickly and controllably constructed on the surface of the micron-level structure array. Finally, after further treatment with hydrophobic silane, the surface of the single crystal silicon can be made hydrophobic, or even super-hydrophobic.

On the other hand, a single crystal silicon having a hydrophobic functional surface is obtained by the above preparation method.

A third aspect is the application of single crystal silicon with a hydrophobic functional surface in the optoelectronics field, the microelectronics field and/or the biomedical field.

The beneficial effects of the present invention are:

The present invention firstly adopts the method of laser-assisted water jet processing to overcome the serious processing damage problems such as surface recasting layer and thermal cracks in traditional laser texturing. At the same time, through laser-assisted water jet processing and femtosecond laser-induced low-frequency periodic surface structure processing, not only the problem of low removal efficiency of femtosecond laser is solved, but also a hierarchical structure functional surface with micro-nano dual scales can be quickly and controllably constructed on the surface of single crystal silicon. Finally, it is further treated with hydrophobic silane to make the surface of single crystal silicon hydrophobic or super hydrophobic.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

FIG1 is a schematic diagram of the processing flow of laser-assisted water jet combined with femtosecond laser to prepare a micro-nano dual-scale single-crystal silicon hydrophobic functional surface in an embodiment of the present invention, (a) single-crystal silicon wafer to be processed (b) schematic diagram of laser-assisted water jet processing (c) laser-assisted water jet scanning path of matrix and V-groove array (d) matrix structure and V-groove array prepared by laser-assisted water jet (e) schematic diagram of femtosecond laser processing (f) micro-nano dual-scale structure surface prepared after femtosecond laser processing;

FIG2 is a laser scanning microscope image of a micron-scale structure array obtained by laser-assisted water jet processing in an embodiment of the present invention, (a) the micron-scale matrix structure of Example 1, (b) the micron-scale V-groove array of Example 2, and (c) the micron-scale V-groove array of Example 3;

FIG3 is a scanning electron microscope image of the surface of the micro-nano dual-scale matrix structure prepared in Example 1 of the present invention;

FIG4 is a scanning electron microscope image of the surface of the micro-nano dual-scale V-groove array structure prepared in Example 2 of the present invention;

FIG. 5 is a scanning electron microscope image of the surface of the micro-nano dual-scale V-groove array structure prepared in Example 3 of the present invention.

Detailed ways

It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and/or combinations thereof.

In view of the serious processing damage such as surface recast layer and thermal cracks in traditional laser texturing and the low removal efficiency of femtosecond laser, which makes it impossible to produce a micro-nano dual-scale hydrophobic functional surface on the surface of single crystal silicon, the present invention proposes a single crystal silicon with a hydrophobic functional surface and its preparation method and application.

A typical embodiment of the present invention provides a method for preparing single crystal silicon with a hydrophobic functional surface, wherein laser-assisted water jet processing is performed on the surface of the single crystal silicon, so that a micron-scale structure array is formed on the surface of the single crystal silicon; a nanostructure is formed on the surface of the micron-scale structure array by inducing a low-frequency periodic surface structure through a femtosecond laser, thereby forming a micro-nano dual-scale layered structure on the surface of the single crystal silicon; the single crystal silicon with the micro-nano dual-scale layered structure on the surface is immersed in hydrophobic silane for silanization treatment, thereby obtaining a hydrophobic functional surface. In the laser-assisted water jet processing, the water jet is placed behind the laser in the scanning speed direction.

First, laser-assisted water jet technology is used to process micron-scale structure arrays on the surface of single-crystal silicon. A micron-scale matrix structure can be obtained by scanning in mutually perpendicular directions through the laser-assisted water jet processing device, or a micron-scale array structure can be obtained by scanning in parallel in a certain direction. Laser-assisted water jet processing technology can controllably adjust the depth, width and spacing of microgrooves in the micron-scale structure array by adjusting the laser power, pulse width, pulse repetition frequency, water jet pressure, jet offset distance, water jet nozzle target distance, water jet impact angle, scanning speed, scanning spacing and other process parameters.

Afterwards, a femtosecond laser is used to induce a low-frequency periodic surface structure near the ablation threshold on the surface of the obtained micron-scale structure array. The central wavelength of the femtosecond laser is 800nm, the pulse width is 35fs, the repetition frequency is 1kHz, and the adjustable process parameters include energy density, defocus (positive when the objective lens is away from the single crystal silicon surface to be processed, and negative when it is away from the objective lens), scanning speed, size and direction, etc. By controlling the above process parameters, the morphology of the periodic surface structure generated on the micron-scale structure surface can be adjusted.

The femtosecond laser used is a Gaussian beam, and the distribution of its laser intensity along the radial direction r and the propagation direction z is shown in equations (1) to (2).

Where I is the laser intensity, z is the distance from the laser waist in the beam propagation direction, r is the distance from the center of the spot in the radial direction, P is the beam power, λ is the laser wavelength, and _ω0 is the beam waist radius.

As known from equations (1) and (2), the laser intensity of a Gaussian beam is maximum at the beam waist (i.e., z=0), and decreases as |z| increases, that is, the laser intensity gradually decreases as the defocus amount increases in the positive or negative direction.

The research results show that near the ablation threshold, laser-induced surface periodic structures will appear on the surface of the material. When a femtosecond laser is used to scan the surface of the micron-scale structure with an energy density near the ablation threshold, the laser intensity injected into the surface of the micron-scale structure by the femtosecond laser will change with the depth of different positions of the micron-scale structure, thereby inducing sub-wavelength structures (scaled at hundreds of nanometers) such as fine corrugated periodic structures and coarse corrugated periodic structures at different positions of the micron-scale structure. At the same time, by changing the laser energy density, defocus, scanning speed, etc., it is possible to control the sidewalls of the micron-scale structure to obtain corrugated structures of different periods and depths; by changing the direction of the scanning speed, different angles can be formed with the laser polarization direction, thereby obtaining different corrugation orientations. Combined with the micron-scale structure array obtained by laser-assisted water jet, a multi-level hierarchical structure can be obtained. After silanization treatment, the surface reaches the Cassie-Baxter state, increasing the contact angle between the droplet and the single-crystal silicon surface, thereby obtaining hydrophobicity or even super-hydrophobicity.

In some embodiments, a pulsed fiber laser emitting nanosecond laser light with a central wavelength of 1064 nm is used in laser-assisted water jet processing.

In some embodiments, the process of laser-assisted water jet machining includes the following steps:

Adjust the water jet impact angle, water jet offset distance, and nozzle target distance;

Adjust the water jet pressure;

Set laser pulse width, pulse repetition frequency, laser power, and scanning speed;

The scanning trajectory file is written according to the scanning direction and scanning spacing, and the processing program is run to complete the horizontal processing. Then the workpiece is automatically rotated to repeat the above operation to complete the vertical processing and construct a micron-level structure array.

In one or more embodiments, the water jet impact angle is 40° to 50°, the water jet offset distance is 0.4 to 0.6 mm, and the nozzle target distance is 0.4 to 0.6 mm.

In one or more embodiments, the water jet pressure is 6-10 MPa.

In one or more embodiments, the laser pulse width is 10 to 350 ns, the pulse repetition frequency is 20 to 1000 kHz, the laser power is 10 to 20 W, and the scanning speed is 1 to 3 mm/s.

In some embodiments, the central wavelength of the femtosecond laser is 800 nm, the pulse width is 35 fs, the repetition frequency is 1 kHz, and the femtosecond laser is a Gaussian beam.

In some embodiments, the process of femtosecond laser inducing low-frequency periodic surface structure comprises the following steps:

Set the laser power and repetition frequency according to the ablation threshold of the material;

Adjust the scanning direction, scanning speed and scanning spacing according to the processing trajectory to form a processing trajectory file;

Adjust the amount of defocus;

Run the processing trajectory file to complete automatic processing.

In one or more embodiments, the laser power is 2.91-7.10 μW.

In one or more embodiments, the scanning speed is 200-400 μm/s, and the scanning pitch is 38-78 μm.

In one or more embodiments, the defocus amount is +60 to +120 μm.

In some embodiments, the hydrophobic silane is perfluorodecyltriethoxysilane. The immersion time is 12 to 36 hours.

Another embodiment of the present invention provides a single crystal silicon having a hydrophobic functional surface, which is obtained by the above-mentioned preparation method.

In some embodiments, the surface water contact angle is 130° to 153°.

A third embodiment of the present invention provides an application of single crystal silicon having a hydrophobic functional surface in the optoelectronics field, the microelectronics field and/or the biomedical field.

Specifically, the application in the preparation of silicon-based solar cells or micro-electromechanical systems.

In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

Example 1

As shown in FIG1 , the method for preparing a single-crystal silicon micro-nano dual-scale anti-reflection velvet surface includes the following steps:

1. Laser-assisted water jet processing to prepare micron-scale matrix structure arrays, using a laser with a wavelength of 1064nm. The specific steps are as follows:

(1) Adjust the water jet impact angle to 42°, the water jet offset distance to 0.5 mm, and the nozzle target distance to 0.4 mm.

(2) Adjust the water jet pressure to 8 MPa.

(3) Set the laser pulse width to 10 ns, the pulse repetition frequency to 1000 kHz, the laser power to 15 W, and the scanning speed to 3 mm/s.

(4) The scanning interval is selected as 40 μm. After the scanning trajectory file is written, the processing program is run to complete the horizontal processing in sequence. Then, the workpiece is automatically rotated 90° and the processing program is run to complete the vertical processing. The constructed micron-scale rectangular structure array is shown in Figure 2(a), where the microgroove depth is 7.2 μm and the width is 22.1 μm.

Second, based on the micron-scale rectangular structure array, a femtosecond laser is used to induce a surface periodic structure array near the ablation threshold. A femtosecond laser with a central wavelength of 800nm, a pulse width of 35fs, and a repetition frequency of 1kHz is used. The femtosecond laser is a Gaussian beam. The specific steps are as follows:

(1) The laser power is set to 2.91 μW near the ablation threshold of the material.

(2) Set the scanning speed to 200 μm/s, set the scanning interval to 54 μm, and generate the processing trajectory file.

(3) Adjust the defocus to +80μm.

(4) Run the processing trajectory file to complete the scan, and the uniform periodic structure morphology of the surface of the micron-scale matrix structure is obtained as shown in Figure 3. It can be seen that the surface of the micron structure is uniformly distributed with a low-frequency periodic surface structure perpendicular to the laser polarization E. After being immersed in perfluorodecyltriethoxysilane solution for 24 hours, the contact angle is measured by a contact angle meter and is 134°.

Example 2

As shown in FIG1 , the method for preparing a single-crystal silicon micro-nano dual-scale anti-reflection velvet surface includes the following steps:

1. Laser-assisted water jet processing to prepare micron-scale matrix structure arrays, using a laser with a wavelength of 1064nm. The specific steps are as follows:

(1) Adjust the water jet impact angle to 45°, the water jet offset distance to 0.6 mm, and the nozzle target distance to 0.6 mm.

(2) Adjust the water jet pressure to 6 MPa.

(3) Set the laser pulse width to 100 ns, the pulse repetition frequency to 144 kHz, the laser power to 20 W, and the scanning speed to 1 mm/s.

(4) The scanning pitch is selected as 40 μm, and after writing the scanning trajectory file, the processing program is run to complete the vertical processing. The constructed micron-scale V-groove structure array is shown in Figure 2(b), where the microgroove depth is 20.6 μm and the width is 37.5 μm.

Second, based on the micron-scale rectangular structure array, a femtosecond laser is used to induce a surface periodic structure array near the ablation threshold. A femtosecond laser with a central wavelength of 800nm, a pulse width of 35fs, and a repetition frequency of 1kHz is used. The femtosecond laser is a Gaussian beam. The specific steps are as follows:

(1) The laser power is set to 2.91 μW near the ablation threshold of the material.

(2) Set the scanning speed to 300 μm/s, set the scanning interval to 38 μm, and generate the processing trajectory file.

(3) Adjust the defocus to +60μm.

(4) Run the processing trajectory file to complete the scan. The uniform periodic structural morphology of the surface of the micron-scale matrix structure is shown in Figure 4. It can be seen that the surface of the micron structure is uniformly distributed with a low-frequency periodic surface structure perpendicular to the laser polarization E. After being immersed in perfluorodecyltriethoxysilane solution for 24 hours, the contact angle was measured by a contact angle meter and was 153°, which is super hydrophobic.

Example 3

As shown in FIG1 , the method for preparing a single-crystal silicon micro-nano dual-scale anti-reflection velvet surface includes the following steps:

1. Laser-assisted water jet processing to prepare micron-scale matrix structure arrays, using a laser with a wavelength of 1064nm. The specific steps are as follows:

(1) Adjust the water jet impact angle to 48°, the water jet offset distance to 0.4 mm, and the nozzle target distance to 0.5 mm.

(2) Adjust the water jet pressure to 10 MPa.

(2) Set the laser pulse width to 350 ns, the pulse repetition frequency to 100 kHz, the laser power to 10 W, and the scanning speed to 2 mm/s.

(3) The scanning interval is selected as 40 μm, and after writing the scanning trajectory file, the processing program is run to complete the vertical processing. The constructed micron-scale V-groove structure array is shown in Figure 2(c), where the microgroove depth is 10.6 μm and the width is 23.2 μm.

Second, based on the micron-scale rectangular structure array, a femtosecond laser is used to induce a surface periodic structure array near the ablation threshold. A femtosecond laser with a central wavelength of 800nm, a pulse width of 35fs, and a repetition frequency of 1kHz is used. The femtosecond laser is a Gaussian beam. The specific steps are as follows:

(1) The laser power is set to 7.10 μW near the ablation threshold of the material.

(2) Set the scanning speed to 400 μm/s, set the scanning interval to 78 μm, and generate the processing trajectory file.

(3) Adjust the defocus to +120μm.

(4) Run the processing trajectory file to complete the scan, and the uniform periodic structure morphology of the surface of the micron-scale matrix structure is obtained as shown in Figure 5. It can be seen that the surface of the micron structure is uniformly distributed with a low-frequency periodic surface structure perpendicular to the laser polarization E. After being immersed in perfluorodecyltriethoxysilane solution for 24 hours, the contact angle measured by the contact angle meter is 130°.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (8)

1. A method for preparing a single crystal silicon with a hydrophobic functional surface, characterized in that laser-assisted water jet processing is performed on the surface of the single crystal silicon, so that a micron-scale V-groove structure array is formed on the surface of the single crystal silicon; a nanostructure is formed on the surface of the micron-scale V-groove structure array by inducing a low-frequency periodic surface structure with a femtosecond laser, inducing a fine corrugation periodic structure and a coarse corrugation periodic structure, and changing the direction of the scanning speed to obtain different corrugation orientations, thereby forming a micro-nano dual-scale layered structure on the surface of the single crystal silicon; the single crystal silicon with the micro-nano dual-scale layered structure on the surface is immersed in hydrophobic silane for silanization treatment, and the single crystal silicon is obtained; wherein, in the laser-assisted water jet processing, the water jet is placed after the laser in the scanning speed direction; In laser-assisted water jet machining, a pulsed fiber laser emitting nanosecond laser light with a central wavelength of 1064 nm is used; The process of laser-assisted water jet machining includes the following steps: Adjust the water jet impact angle, water jet offset distance, and nozzle target distance; Adjust the water jet pressure; Set laser pulse width, pulse repetition frequency, laser power, and scanning speed; The scanning trajectory file is written according to the scanning direction and scanning spacing, and the processing program is run to complete the horizontal processing. Then the workpiece is automatically rotated and the above operation is repeated to complete the vertical processing, thus constructing a micron-level structure array. The water jet impact angle is 40°~50°, the water jet offset distance is 0.4~0.6 mm, and the nozzle target distance is 0.4~0.6 mm; The water jet pressure is 6~10 MPa; The laser pulse width is 10~350 ns, the pulse repetition frequency is 20~1000 kHz, the laser power is 10~20 W, and the scanning speed is 1~3 mm/s; The process of femtosecond laser-induced low-frequency periodic surface structure includes the following steps: Set the laser power and repetition frequency according to the ablation threshold of the material; Adjust the scanning direction, scanning speed and scanning spacing according to the processing trajectory to form a processing trajectory file; Adjust the amount of defocus; Run the processing trajectory file to complete automatic processing; Laser power is 2.91~7.10 µW; The scanning speed is 200~400 µm/s, and the scanning interval is 38~78 µm; The defocus range is +60~+120 µm. 2. The method for preparing a single crystal silicon with a hydrophobic functional surface as claimed in claim 1, characterized in that the central wavelength of the femtosecond laser is 800nm, the pulse width is 35fs, and the repetition frequency is 1kHz. 3. The method for preparing a single crystal silicon having a hydrophobic functional surface as claimed in claim 1, wherein the hydrophobic silane is perfluorodecyltriethoxysilane. 4. The method for preparing a single crystal silicon having a hydrophobic functional surface as claimed in claim 3, wherein the immersion time is 12 to 36 hours. 5. A single crystal silicon with a hydrophobic functional surface, characterized in that it is obtained by the preparation method of the single crystal silicon with a hydrophobic functional surface according to any one of claims 1 to 4. 6. The single crystal silicon with a hydrophobic functional surface as claimed in claim 5, characterized in that the water contact angle of the surface is 130°~153°. 7. Use of the single crystal silicon with a hydrophobic functional surface as claimed in claim 5 or 6 in the optoelectronic field, microelectronic field or biomedical field. 8. The use according to claim 7, characterized in that it is used in the preparation of silicon-based solar cells or micro-electromechanical systems.