Easily stripped diamond film and preparation method thereof

Abstract

The invention discloses an easy-to-peel diamond film and a preparation method thereof. The preparation method comprises the following steps: selecting a silicon wafer with a smooth surface as a substrate; activating the surface of the silicon wafer with plasma; coating the surface of the activated silicon wafer with nano-diamond seed crystals; transferring the silicon wafer coated with the seed crystals into MPCVD equipment and diamond growth equipment, introducing a proper amount of nitrogen-containing gas in the process gas except hydrogen-containing gas and carbon-containing gas at the initial stage of growing a diamond film under the condition that the surface temperature of the silicon wafer is lower than 750 DEG C, then adjusting the cavity pressure, the microwave power and the gas formula, continuously heating to a temperature interval suitable for diamond growth, and cooling to room temperature to obtain the diamond film. And cooling and taking out the diamond film after the diamond film grows to a preset thickness. The diamond film grown by the method provided by the invention not only keeps complete and crack-free, but also ensures that the diamond film is completely stripped from the silicon wafer by a physical method, and the stripping surface of the diamond film is high in smoothness, so that the next industrial application is facilitated.

Description

Technical Field

[0001] The invention relates to the field of diamond films, and in particular to an easily strippable diamond film and a preparation method thereof. Background Art

[0002] Diamond has many excellent properties such as high thermal conductivity, high sound wave transmission speed, transparency, high hardness, corrosion resistance, etc., and its application range is very wide. Since the crystal structure of silicon wafers is similar to that of diamonds and the expansion coefficients are close, the existing large-size polycrystalline diamond films are basically grown epitaxially on silicon wafers using chemical vapor deposition equipment (CVD). After the diamond film is epitaxially grown, the silicon wafer is usually thinned first and then the substrate material is etched away by chemical treatment to obtain a complete single diamond film. In the process of thinning and chemically corroding silicon wafers, toxic or easily made chemicals such as hydrofluoric acid and nitric acid are often required, which is not only costly but also environmentally unfriendly. This limits the wider application of diamond film products, and it is necessary to find a better manufacturing method. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides an easily strippable diamond film and a preparation method thereof. The diamond film grown by the method of the present invention not only keeps the diamond film intact and free of cracks, but also ensures that the diamond film can be completely stripped from the silicon wafer by physical methods. The stripping surface of the diamond film has high smoothness, avoiding the high cost and environmental unfriendliness caused by chemically corroding the silicon substrate to manufacture diamond film products.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] First, the present invention provides a method for preparing an easily strippable diamond film, comprising the following steps:

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

[0007] Activate the silicon wafer surface with plasma;

[0008] Coating diamond seed crystals on the surface of the activated silicon wafer;

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

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

[0011] During the film growth stage, the process gases in the MPCVD equipment are adjusted to hydrogen and methane, with a mass flow ratio of hydrogen:methane of 500:1-30. The cavity pressure and microwave power are continued to be increased to maintain the substrate surface temperature at 750-850°C. When the diamond film grows to a predetermined thickness, it is cooled and taken out.

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

[0013] Furthermore, the plasma activation of the silicon wafer surface is: placing the silicon wafer in an MPCVD device (microwave plasma chemical vapor deposition device), using hydrogen plasma to activate the surface, the chamber pressure of the MPCVD device is 4-20 Torr, and the activation time is 0.1-20 min.

[0014] Furthermore, the diamond seed crystals are coated on the surface of the activated silicon wafer by first ultrasonically dispersing the diamond seed crystals in a mixed solution of DMSO, isopropanol and acetone to form a diamond dispersion, and then spin-coating the diamond dispersion on the surface of the silicon wafer by a spinner and spin-drying.

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

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

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

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

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

[0020] Furthermore, before adjusting the process gas in the MPCVD device to hydrogen and methane, the reaction chamber of the MPCVD device needs to be vacuumed.

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

[0022] The present invention selects a silicon wafer with a smooth surface as a substrate material, activates the surface of the silicon wafer with plasma, and then coats the surface of the silicon wafer with nano-diamond seed crystals, and then puts the silicon wafer into a device for growing diamond by a vapor deposition method to grow a diamond film. In the initial stage of growing a diamond film, that is, when the surface temperature of the silicon wafer 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, and then the cavity pressure, microwave power and gas formula are adjusted, and the temperature continues to rise to a temperature range suitable for diamond growth. When the diamond film grows to a predetermined thickness, the growth of the diamond film is completed, and the temperature is lowered and taken out.

[0023] The adhesion between the diamond film grown by the method of the present invention and the silicon wafer is adjusted by the substrate surface morphology, seed crystal concentration, the timing and concentration of nitrogen introduced during the nucleation and film growth process, which can not only keep the diamond film intact and free of cracks, but also ensure that the diamond film is completely peeled off from the silicon wafer by physical methods (using mechanical force), and the peeling surface of the diamond film is highly smooth, which is convenient for the next industrial application. The diamond film grown by the method of the present invention avoids the high cost and environmental unfriendly problems caused by chemically corroding silicon substrates to manufacture diamond film products, reduces the manufacturing cost of large-area diamond films and protects the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the process flow diagram of the present invention. DETAILED DESCRIPTION

[0025] In order 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, rather than limiting the claims of the present invention.

[0026] Embodiment 1:

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

[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 and surface activated using hydrogen plasma. The activation process used a chamber pressure of 15 Torr and a time of 3 minutes.

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

[0030] Then the single crystal silicon wafer coated with seed crystal is put into MPCVD equipment again to grow diamond film. It is divided into two stages. The first stage is called nucleation film formation stage, when the substrate surface temperature is lower than 750℃, and the second stage is called film growth stage, when the substrate surface temperature is higher than 750℃. Specifically:

[0031] 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 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 mass flow ratio of hydrogen to methane of 490:9. The cavity pressure and microwave power of the MPCVD equipment were further increased, the substrate surface temperature reached 850°C, the cavity pressure was 100 Torr, and the diamond film was grown stably. When the diamond film grew to a predetermined thickness of 10μm, the growth of the diamond film was completed, and the film was cooled and taken out.

[0033] The silicon substrate with the diamond film grown on it was taken out from the MPCVD device, and the silicon substrate in the diamond film was fixed by a vacuum suction cup. A roller with a diameter of 10 cm and a tape on the surface was used to roll over the surface of the diamond film, so that the diamond film adhered to the tape and was peeled off from the silicon substrate, obtaining a polycrystalline diamond film with a diameter of 2 inches, a thickness of 10 μm, and a peeling surface roughness of less than 1 nm.

[0034] Embodiment 2:

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

[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 and surface activated 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 less than 10nm are ultrasonically dispersed in a mixed solution of DMSO, isopropanol and acetone (DMSO:IPA:acetone=5:3:2, volume ratio) to form a 0.1wt% nano-diamond dispersion; after activation, the single crystal silicon wafer is taken out, and the nano-diamond dispersion is spin-coated on the surface of the single crystal silicon wafer by a spinner and then dried.

[0038] Then the single crystal silicon wafer coated with seed crystal is put into MPCVD equipment again to grow diamond film. It is divided into two stages. The first stage is called nucleation film formation stage, when the substrate surface temperature is lower than 750℃, and the second stage is called film growth stage, when the substrate surface temperature is higher than 750℃. 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, and then hydrogen, methane and oxygen are introduced. The mass flow ratio of hydrogen: methane: oxygen is 500: 1-30: 1-10. The MPCVD equipment cavity pressure and microwave power are continued to increase. The substrate surface temperature reaches 850°C, the cavity pressure is 100 Torr, and the diamond film is grown stably. When the diamond film grows to the predetermined thickness of 10μm, the growth of the diamond film is completed, and the temperature is reduced and taken out.

[0041] The silicon substrate with the diamond film grown on it was taken out from the MPCVD device, and the silicon substrate in the diamond film was fixed by a vacuum suction cup. A roller with a diameter of 10 cm and a tape on the surface was used to roll over the surface of the diamond film, so that the diamond film adhered to the tape and was peeled off from the silicon substrate, obtaining a polycrystalline diamond film with a diameter of 2 inches, a thickness of 10 μm, and a peeling surface roughness of less than 0.5 nm.

[0042] According to the disclosure of the above description, those skilled in the art to which the present invention belongs may also 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 scope of protection of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing an easily strippable diamond film, characterized in that: The steps include: A silicon wafer with a smooth surface is selected as the substrate; Activate the silicon wafer surface with plasma; Coating diamond seed crystals on the surface of the activated silicon wafer; The seed-coated silicon wafer is transferred into the diamond growth equipment of the MPCVD equipment to grow a diamond film, specifically including: In the nucleation and film formation stage, the silicon wafer coated with the seed crystal is placed in the MPCVD equipment, hydrogen is introduced, the cavity pressure and microwave power are increased, and the plasma is excited. When the substrate surface temperature reaches 550°C, methane and nitrogen are introduced, and the mass flow ratio of hydrogen: methane: nitrogen is 500:10-100:1-30, the nucleation temperature is 550-650°C, and the nucleation time is 3-30min; During the film growth stage, the process gases in the MPCVD equipment are adjusted to hydrogen and methane, with a mass flow ratio of hydrogen:methane of 500:1-30. The cavity pressure and microwave power are continued to be increased to maintain the substrate surface temperature at 750-850°C. When the diamond film grows to a predetermined thickness, it is cooled and taken out.

2. The method for preparing an easily strippable diamond film according to claim 1, wherein: A silicon wafer with a smooth surface is selected as the substrate, and at least one side of the silicon wafer is polished, and the surface roughness Rms of the polished surface within a 30 μm*30 μm measurement area is less than 10 nm.

3. The method for preparing an easily strippable diamond film according to claim 1, characterized in that: The method of using plasma to activate the surface of the silicon wafer is as follows: placing the silicon wafer in an MPCVD device and using hydrogen plasma to activate the surface. The chamber pressure of the MPCVD device is 4-20 Torr and the activation time is 0.1-20 min.

4. The method for preparing an easily strippable diamond film according to claim 1, wherein: The diamond seed crystals are coated on the surface of the activated silicon wafer by first ultrasonically dispersing the diamond seed crystals in a mixed solution of DMSO, isopropanol and acetone to form a diamond dispersion, and then spin-coating the diamond dispersion on the surface of the silicon wafer by a spinner and spin-drying.

5. The method for preparing an easily strippable diamond film according to claim 4, characterized in that: The average particle size of the diamond seed crystal is less than 100 nm, and the mass fraction of the diamond seed crystal in the diamond dispersion is 0.01-5%.

6. The method for preparing an easily strippable diamond film according to claim 1, characterized in that: In the nucleation and film forming stage, in the process gas, the molar ratio of carbon element: hydrogen element is 0.5%<1.2%, and the molar ratio of nitrogen element: hydrogen element is 0.1%<0.4%.

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

8. The method for preparing an easily strippable diamond film according to claim 1, characterized in that: During the film growth stage, the process gases in the MPCVD equipment are adjusted to hydrogen, methane and oxygen, and the mass flow ratio of hydrogen: methane: oxygen is 500: 1-30: 1-10. The cavity pressure and microwave power are continuously increased to maintain the substrate surface temperature at 750-850°C. When the diamond film grows to a predetermined thickness, the growth of the diamond film is completed, and the film is cooled and taken out.

9. The method for preparing an easily strippable diamond film according to claim 1, characterized in that: Before adjusting the process gas in the MPCVD device to hydrogen and methane, the reaction chamber of the MPCVD device is also vacuumed.

10. A diamond film, characterized in that: The film is prepared by the method for preparing an easily strippable diamond film as claimed in any one of claims 1 to 9.

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