An easily peelable diamond film and its preparation method

Abstract

This invention discloses an easily peelable diamond film and its preparation method, comprising the following steps: selecting a smooth silicon wafer as a substrate; activating the silicon wafer surface with plasma; coating the activated silicon wafer surface with nanodiamond seed crystals; transferring the seed-coated silicon wafer into an MPCVD diamond growth apparatus; in the initial stage of diamond film growth, the silicon wafer surface temperature is below 750°C; in addition to hydrogen and carbon-containing gases, an appropriate amount of nitrogen-containing gas is introduced into the process gas; then, the cavity pressure, microwave power, and gas formulation are adjusted, and the temperature is further increased to a suitable range for diamond growth; after the diamond film grows to a predetermined thickness, it is cooled and removed. The diamond film grown by this method maintains the integrity of the diamond film without cracks, and ensures that the diamond film can be completely peeled off from the silicon wafer by physical methods, with a high degree of smoothness on the peeling surface, facilitating subsequent industrial applications.

Description

Technical Field

[0001] This invention relates to the field of diamond films, and more particularly to an easily peelable diamond film and its preparation method. Background Technology

[0002] Diamond possesses numerous superior properties, including high thermal conductivity, high acoustic velocity, transparency, high hardness, and corrosion resistance, leading to a wide range of applications. Because silicon wafers have a similar crystal structure and a similar coefficient of thermal expansion, most large-size polycrystalline diamond films are epitaxially grown on silicon wafers using chemical vapor deposition (CVD). After epitaxy, the silicon wafer is typically thinned, and the substrate material is then etched away using chemical methods to obtain a complete, monolithic diamond film. However, the thinning and chemical etching processes often require toxic or easily manufactured chemicals such as hydrofluoric acid and nitric acid, resulting in high costs and environmental pollution. This limits the wider application of diamond film products, necessitating the search for superior manufacturing methods. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides an easily peelable diamond film and its preparation method. The diamond film grown by this method maintains the integrity of the diamond film without cracks, and ensures that the diamond film can be completely peeled off from the silicon wafer by physical methods. Furthermore, the peelable surface of the diamond film has high smoothness, avoiding the high cost and environmentally unfriendly problems caused by chemically etching the silicon substrate to manufacture diamond film products.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] Firstly, this invention provides a method for preparing an easily peelable diamond film, comprising the following steps:

[0006] A smooth silicon wafer is selected as the substrate;

[0007] Activating the surface of a silicon wafer with plasma;

[0008] Diamond seed crystals are coated onto the surface of the activated silicon wafer;

[0009] The silicon wafer coated with seed crystals is transferred into the MPCVD diamond growth equipment to grow a diamond thin film, specifically including:

[0010] In the nucleation and film formation stage, the silicon wafer coated with seed crystals is placed in an MPCVD device, hydrogen gas is introduced, the cavity pressure and microwave power are increased, and plasma is excited. When the substrate surface temperature reaches 550℃, methane and nitrogen gas are introduced. The mass flow rate ratio of hydrogen:methane:nitrogen gas is 500:10-100:1-30, the nucleation temperature is 550-650℃, and the nucleation time is 3-30 min.

[0011] During the thin film growth stage, the process gases in the MPCVD equipment are adjusted to hydrogen and methane, with a hydrogen:methane mass flow rate ratio of 500:1-30. The cavity pressure and microwave power are continuously increased to maintain the substrate surface temperature at 750-850℃. After the diamond film grows to the predetermined thickness, it is cooled down and removed.

[0012] Furthermore, a smooth silicon wafer is selected as the substrate, and at least one side of the silicon wafer is polished, with the surface roughness Rms of the polished surface being <10nm within a 30μm*30μm measurement area.

[0013] Furthermore, the plasma activation of the silicon wafer surface is as follows: the silicon wafer is placed in an MPCVD (microwave plasma chemical vapor deposition) device, and surface activation is performed using hydrogen plasma. The cavity pressure of the MPCVD device is 4-20 Torr, and the activation time is 0.1-20 min.

[0014] Furthermore, the process of coating the activated silicon wafer surface with diamond seed crystals involves: first, ultrasonically dispersing the diamond seed crystals in a mixed solution of DMSO, isopropanol, and acetone to form a diamond dispersion; then, spin-coating the diamond dispersion onto the surface of the silicon wafer using a spin coater and then spin-drying it.

[0015] Furthermore, the average particle size of the diamond seed crystal is less than 100 nm, and the mass fraction of the diamond dispersion is 0.01-5%.

[0016] Furthermore, in the nucleation and film formation stage, the process gas contains: 0.5% < molar ratio of carbon to hydrogen < 1.2%, and 0.1% < molar ratio of nitrogen to hydrogen < 0.4%.

[0017] Furthermore, during the nucleation and film formation stage, the cavity pressure of the MPCVD equipment is 30-70 Torr;

[0018] During the film growth stage, the chamber pressure of the MPCVD equipment is 50-150 Torr, and the growth thickness of the diamond film is controlled between 0.01-200 μm.

[0019] Furthermore, during the thin film growth stage, the process gases in the MPCVD equipment are adjusted to be hydrogen, methane, and oxygen, with a hydrogen:methane:oxygen mass flow rate ratio of 500:1-30:1-10. The cavity pressure and microwave power are continuously increased to maintain the substrate surface temperature at 750-850°C. After the diamond film grows to the predetermined thickness, the diamond film growth is completed, and the film is cooled down and removed.

[0020] Furthermore, before adjusting the process gases in the MPCVD equipment to hydrogen and methane, the reaction chamber of the MPCVD equipment needs to be evacuated.

[0021] Secondly, the present invention also provides an easily peelable diamond film, which is prepared by the method described above for preparing an easily peelable diamond film.

[0022] This invention selects a smooth silicon wafer as the substrate material, activates the silicon wafer surface with plasma, then coats the silicon wafer surface with nanodiamond seed crystals, and then places the silicon wafer into an apparatus for growing diamond using a vapor deposition method to grow a diamond film. In the initial stage of diamond film growth, that is, within the stage where the silicon wafer surface temperature rises from room temperature to below 750°C, in addition to hydrogen and carbon-containing gases, an appropriate amount of nitrogen-containing gas is introduced into the process gas. Then, the cavity pressure, microwave power, and gas formulation are adjusted, and the temperature is further increased to the suitable temperature range for diamond growth. When the diamond film grows to the predetermined thickness, the diamond film growth is completed, and the wafer is cooled and removed.

[0023] The adhesion between the diamond film grown by the method of this invention and the silicon wafer can be adjusted by the substrate surface morphology, seed crystal concentration, and the timing and concentration of nitrogen gas introduced during the nucleation and film growth process. This ensures that the diamond film remains intact and crack-free, while also guaranteeing complete peeling of the diamond film from the silicon wafer using physical methods (mechanical force). Furthermore, the peeled surface of the diamond film has high smoothness, facilitating subsequent industrial applications. The diamond film grown by this method avoids the high cost and environmentally unfriendly problems caused by chemically etching silicon substrates to manufacture diamond film products, reducing the manufacturing cost of large-area diamond films and protecting the environment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0025] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0026] Example 1:

[0027] A single-crystal silicon wafer with a diameter of 2 inches and a thickness of 1 mm and a (100) crystal orientation was selected as the substrate material. The surface roughness Rms of the silicon wafer in the 30x30 micrometer measurement area was <0.2 nm.

[0028] The single-crystal silicon wafer was placed in a microwave plasma chemical vapor deposition (MPCVD) device with a microwave frequency of 2.45 GHz to activate the surface using hydrogen plasma. The activation process used a cavity pressure of 15 Torr and a time of 3 minutes.

[0029] First, diamond seed crystals with a particle size of less than 10 nm are ultrasonically dispersed in a mixed solution of DMSO, isopropanol and acetone (DMSO:IPA:acetone = 5:3:2, volume ratio) to form a 0.1 wt% nano-diamond dispersion. After activation, the single crystal silicon wafer is taken out, and then the nano-diamond dispersion is spin-coated onto the surface of the single crystal silicon wafer using a spin coater and then dried.

[0030] The seed-coated single-crystal silicon wafer is then placed back into the MPCVD equipment to grow a diamond thin film. This process is divided into two stages: the first stage, called the nucleation stage, has a substrate surface temperature below 750°C; the second stage, called the thin film growth stage, has a substrate surface temperature above 750°C. Specifically:

[0031] In the first stage, after hydrogen is introduced into the equipment for ignition, the cavity pressure and microwave power are gradually increased. When the substrate surface temperature reaches 550°C, methane and nitrogen are introduced into the process gas. At this time, the mass flow ratio of hydrogen:methane:nitrogen is 45:4:1. When the substrate temperature reaches 650°C, it is maintained for 5 minutes, and the cavity pressure is maintained at 50 Torr.

[0032] In the second stage, the process gases in the MPCVD equipment were adjusted to hydrogen and methane, with a hydrogen:methane mass flow rate ratio of 490:9. The cavity pressure and microwave power of the MPCVD equipment were further increased until the substrate surface temperature reached 850°C and the cavity pressure reached 100 Torr, stabilizing the growth of the diamond film. When the diamond film grew to the predetermined thickness of 10 μm, the growth of the diamond film was completed, and it was cooled and removed.

[0033] The silicon substrate with the diamond film grown was removed from the MPCVD equipment. The silicon substrate in the diamond film was adsorbed and fixed by a vacuum chuck. A roller with tape attached to its surface was rolled over the diamond film with a diameter of 10 cm to adhere the diamond film to the tape and peel it off from the silicon substrate, resulting in a polycrystalline diamond film with a diameter of 2 inches, a thickness of 10 μm, and a surface roughness of less than 1 nm.

[0034] Example 2:

[0035] A single-crystal silicon wafer with a diameter of 2 inches and a thickness of 1 mm and a (100) crystal orientation was selected as the substrate material. The surface roughness Rms of the silicon wafer in the 30x30 micrometer measurement area was <0.2 nm.

[0036] The single-crystal silicon wafer was placed in a microwave plasma chemical vapor deposition (MPCVD) device with a microwave frequency of 2.45 GHz to activate the surface using hydrogen plasma. The activation process used a chamber pressure of 15 Torr and a time of 3 minutes.

[0037] First, diamond seed crystals with a particle size of less than 10 nm are ultrasonically dispersed in a mixed solution of DMSO, isopropanol and acetone (DMSO:IPA:acetone = 5:3:2, volume ratio) to form a 0.1 wt% nano-diamond dispersion. After activation, the single crystal silicon wafer is taken out, and then the nano-diamond dispersion is spin-coated onto the surface of the single crystal silicon wafer using a spin coater and then dried.

[0038] The seed-coated single-crystal silicon wafer is then placed back into the MPCVD equipment to grow a diamond thin film. This process is divided into two stages: the first stage, called the nucleation stage, has a substrate surface temperature below 750°C; the second stage, called the thin film growth stage, has a substrate surface temperature above 750°C. Specifically:

[0039] In the first stage, after hydrogen is introduced into the equipment to start the ignition, the cavity pressure and microwave power are gradually increased. When the substrate surface temperature reaches 550°C, methane and nitrogen are introduced into the process gas. At this time, the mass ratio of hydrogen:methane:nitrogen is 45:4:1. When the substrate temperature reaches 650°C, it is maintained for 5 minutes, and the cavity pressure is 50 Torr.

[0040] In the second stage, the MPCVD equipment is evacuated to remove nitrogen from the growth gas. Then, hydrogen, methane, and oxygen are introduced at a hydrogen:methane:oxygen mass flow rate ratio of 500:1-30:1-10. The cavity pressure and microwave power of the MPCVD equipment are further increased until the substrate surface temperature reaches 850°C and the cavity pressure reaches 100 Torr, stabilizing the growth of the diamond film. When the diamond film grows to the predetermined thickness of 10 μm, the growth of the diamond film is complete, and it is cooled and removed.

[0041] The silicon substrate with the diamond film grown was removed from the MPCVD equipment. The silicon substrate in the diamond film was adsorbed and fixed by a vacuum chuck. A roller with tape attached to its surface was rolled over the diamond film with a diameter of 10 cm to adhere the diamond film to the tape and peel it off from the silicon substrate, resulting in a polycrystalline diamond film with a diameter of 2 inches, a thickness of 10 μm, and a surface roughness of less than 0.5 nm.

[0042] Based on the disclosure in the foregoing specification, those skilled in the art can make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for preparing an easily peelable diamond film, characterized in that: Includes the following steps: A smooth silicon wafer is selected as the substrate. At least one side of the silicon wafer is polished, and the surface roughness Rms of the polished surface in a 30μm*30μm measurement area is <10nm. Activating the surface of a silicon wafer with plasma; Diamond seed crystals are coated on the activated silicon wafer surface. Specifically, diamond seed crystals with an average particle size of less than 100 nm are dispersed in a solution to form a diamond dispersion with a mass fraction of 0.01-5%. The diamond dispersion is then spin-coated onto the silicon wafer surface and spun dry. The silicon wafer coated with seed crystals is transferred into the MPCVD diamond growth equipment to grow a diamond thin film, specifically including: In the nucleation and film formation stage, the seed-coated silicon wafer is placed in an MPCVD device, hydrogen gas is introduced, the cavity pressure and microwave power are increased to excite plasma, and when the substrate surface temperature reaches 550℃, methane and nitrogen gas are introduced. The mass flow ratio of hydrogen:methane:nitrogen is 500:10-100:1-30, the nucleation temperature is 550-650℃, and the nucleation time is 3-30 min. In the process gases, the molar ratio of carbon to hydrogen is 0.5% < 1.2%, and the molar ratio of nitrogen to hydrogen is 0.1% < 0.4%. During the thin film growth stage, the process gases in the MPCVD equipment are adjusted to hydrogen and methane, with a hydrogen:methane mass flow rate ratio of 500:1-30. The cavity pressure and microwave power are continuously increased to maintain the substrate surface temperature at 750-850℃. After the diamond film grows to the predetermined thickness, it is cooled down and removed.

2. The method for preparing the easily peelable diamond film according to claim 1, characterized in that: The process of activating the silicon wafer surface with plasma involves placing the silicon wafer in an MPCVD device and activating the surface using hydrogen plasma. The chamber pressure of the MPCVD device is 4-20 Torr, and the activation time is 0.1-20 min.

3. The method for preparing the easily peelable diamond film according to claim 1, characterized in that: The process of coating diamond seed crystals onto the activated silicon wafer surface involves: first, ultrasonically dispersing the diamond seed crystals in a mixed solution of DMSO, isopropanol, and acetone to form a diamond dispersion; then, spin-coating the diamond dispersion onto the surface of the silicon wafer using a spin coater and then spin-drying it.

4. The method for preparing the easily peelable diamond film according to claim 1, characterized in that: During the nucleation and film formation stage, the cavity pressure of the MPCVD equipment is 30-70 Torr. During the film growth stage, the chamber pressure of the MPCVD equipment is 50-150 Torr, and the growth thickness of the diamond film is controlled between 0.01-200 μm.

5. The method for preparing the easily peelable diamond film according to claim 1, characterized in that: During the thin film growth stage, the process gases in the MPCVD equipment are adjusted to hydrogen, methane, and oxygen, with a hydrogen:methane:oxygen mass flow rate ratio of 500:1-30:1-10. The cavity pressure and microwave power are continuously increased to maintain the substrate surface temperature at 750-850°C. Once the diamond film has grown to the predetermined thickness, the diamond film growth is completed, and the film is cooled down and removed.

6. The method for preparing the easily peelable diamond film according to claim 1, characterized in that: Before adjusting the process gases in the MPCVD equipment to hydrogen and methane, the reaction chamber of the MPCVD equipment is also evacuated.

7. A diamond film, characterized in that, It is prepared by the method for preparing easily peelable diamond films as described in any one of claims 1 to 6.

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