Octagonal polycrystalline diamond and preparation method thereof

Abstract

The invention provides an octagonal polycrystalline diamond and a preparation method thereof, and relates to the technical field of MPCVD deposition. The preparation method of the octagonal polycrystalline diamond comprises the following steps: placing diamond fine powder on a substrate, and forming nucleation points on the surface of the substrate through pressurized grinding; the substrate loaded with the nucleation points is put into equipment for primary deposition, and a nanocrystalline diamond film is obtained; and then the deposition table is lifted for secondary deposition, a secondary deposition diamond film is obtained, the octagonal polycrystalline diamond is taken down from the secondary deposition diamond film, and the octagonal polycrystalline diamond is obtained. According to the preparation method, the nucleation points are generated on the surface of the substrate by using the pressurized grinding method, and then the eight-edge polycrystalline diamond is successfully prepared finally by regulating and controlling the plasma components, the plasma temperature and the plasma distribution in the vertical direction, and the prepared eight-edge polycrystalline diamond is wide in application range.

Description

Technical Field

[0001] The invention relates to the technical field of MPCVD deposition, and in particular to an octagonal polycrystalline diamond and a preparation method thereof. Background Art

[0002] Diamond, as a material with extremely high hardness, excellent thermal conductivity and chemical stability, is widely used in cutting tools, wear-resistant coatings, semiconductor substrates, optical devices and other fields. However, natural diamond resources are limited and expensive, so the technology of artificial synthetic diamond film has become a research hotspot. Chemical vapor deposition (CVD) technology is one of the main methods for preparing diamond film. It decomposes carbon-containing gas on the surface of the substrate to deposit carbon atoms to form a diamond film.

[0003] In CVD technology, polycrystalline diamond film has gradually become the focus of research due to its high fracture toughness and moderate cost. Polycrystalline diamond film is composed of multiple diamond grains with different orientations, which are connected to form a continuous film during the growth process. Compared with single crystal diamond, polycrystalline diamond film has higher fracture toughness and is suitable for occasions that need to withstand complex stress.

[0004] In the existing CVD technology, although the growth of diamond grains can be influenced by regulating process parameters such as temperature, pressure, gas composition and flow rate, it is still a challenge to precisely control the morphology of the grains. This is because the growth of the grains is affected by multiple factors, and there are complex interactions between these factors.

[0005] It is difficult to obtain grains of specific shapes, such as octagonal structures, in the process of preparing diamond films using existing MPVCD technology. Summary of the invention

[0006] The present invention provides an octagonal polycrystalline diamond and a preparation method thereof, so as to overcome the technical problem that it is difficult to prepare the octagonal polycrystalline diamond in the prior art.

[0007] In order to achieve the above-mentioned invention object, the technical solution provided by the present invention is as follows:

[0008] An octagonal polycrystalline diamond is prepared by MPCVD deposition technology.

[0009] A method for preparing octagonal polycrystalline diamond comprises the following steps:

[0010] S1, placing diamond fine powder on a substrate, forming nucleation points on the substrate surface by pressurized grinding, and obtaining a substrate carrying nucleation points;

[0011] S2, placing the substrate carrying the nucleation points into a microwave plasma chemical vapor deposition device for primary deposition to obtain a nanocrystalline diamond film, wherein the thickness of the nanocrystalline diamond film is 500-800 μm, and the deposition gas during the primary deposition process is a mixed gas of hydrogen, methane and nitrogen, wherein the flow rate of methane is 0.3-8% of the hydrogen, and the flow rate of nitrogen is 0.2-5% of the hydrogen;

[0012] S3, raising the deposition platform, performing secondary deposition on the nanocrystalline diamond film to obtain a secondary deposited diamond film, wherein the secondary deposited diamond film has octagonal polycrystalline diamonds, and the gas flow rate, substrate temperature, deposition chamber pressure and microwave power during the secondary deposition are the same as those of the primary deposition;

[0013] S4. After the secondary deposition is completed, the octagonal polycrystalline diamond is separated from the secondary deposited diamond film, and the octagonal polycrystalline diamond is obtained after cleaning and drying.

[0014] Preferably, the frequency of the initial deposition in S2 is 2.45 GHz, the microwave power of the initial deposition is 1 kW-15 kW, and the flow rate of the hydrogen is 200-800 sccm.

[0015] Preferably, the frequency of the initial deposition in S2 is 915 MHz, the microwave power of the initial deposition is 1 kW-120 kW, and the flow rate of the hydrogen is 1-10 slm.

[0016] Preferably, the temperature of the initial deposition in S2 is 800-1000°C.

[0017] Preferably, the deposition chamber pressure of the initial deposition in S2 is 2-40 kPa.

[0018] Preferably, the deposition platform in S3 is raised by 5 mm-10 mm.

[0019] Preferably, the growth parameters of the central grains during the secondary deposition process are α It is 2.25-3, and the growth parameter α is the ratio of the growth rates of the {100} facet and the {111} facet in diamond.

[0020] Preferably, the secondary deposition time in S3 is 100-300 hours.

[0021] In the preparation method of the present invention, the substrate is a circular substrate with a thickness of 0.5-2 cm, and the substrate material can be silicon, sapphire, graphite, molybdenum, etc. The substrate needs to be pre-treated, and a certain amount of diamond fine powder is added to the surface of the substrate. After pressure grinding, a certain number of nucleation points appear on the surface of the substrate.

[0022] The preparation of octagonal polycrystalline diamond by MPCVD technology is completed through two depositions, forming a nanocrystalline diamond film through the first deposition and forming an octagonal polycrystalline diamond through the second deposition.

[0023] The flow rates of hydrogen, methane and nitrogen during the primary and secondary deposition processes will affect the growth and final morphology of the grains, but the main effect is on nitrogen. Increasing the gas flow rates of hydrogen and methane usually leads to faster growth. Hydrogen and methane usually do not cause significant changes in the state of the polycrystalline diamond film, so it is sufficient to control the gas flow rates of hydrogen and methane within an appropriate range. However, the effect of nitrogen is different. Nitrogen has a more obvious effect on polycrystalline diamond film. Adding a small amount of nitrogen can significantly increase the growth rate of the polycrystalline diamond film. Excessive addition may even damage the growth quality of the polycrystalline diamond film, thereby changing the morphological characteristics of the polycrystalline diamond film. The addition of nitrogen can not only accelerate the deposition rate, but also change the morphological characteristics of polycrystalline diamond. Too high a nitrogen flow rate will cause the crystal quality of the polycrystalline diamond film to deteriorate, while too low a nitrogen flow rate will have little effect on the deposition of the diamond film. Both too high and too low a nitrogen flow rate will affect the morphology of the polycrystalline diamond film, thereby inhibiting the production of octagonal polycrystalline diamond. Therefore, the nitrogen flow rate needs to be controlled within an appropriate range.

[0024] After the initial deposition, a nanocrystalline diamond film is obtained. The height of the deposition platform is then increased, and the deposition temperature is increased accordingly. The nanocrystalline diamond is wrapped by the plasma. Under the action of the plasma, the nanocrystalline diamond continues to grow, and the outer ring contour gradually becomes larger. The enlargement of the outer ring mainly includes the growth of diamond crystals and the growth of octagonal polycrystalline diamonds. The middle part is the growth of diamond crystals, and the outer ring is the growth of octagonal polycrystalline diamonds. The octagonal polycrystalline diamonds are attached to the growth of diamond crystals. The octagonal polycrystalline diamonds grow on the outer crystal plane of the diamond crystals and grow at the same time as the diamond crystals under the influence of plasma. The growth contour is also consistent with the diamond crystals, accompanied by gradual thickening. Due to the increase in deposition temperature, the deposition time becomes shorter, and the outer ring contour at the upper end gradually shrinks until a diamond {100} face or peak appears on the top. The deposition is completed and an octagonal polycrystalline diamond is obtained.

[0025] In the preparation method of the present invention, the substrate needs to be pre-treated, and the substrate surface is made to have nucleation ability through pressure grinding treatment, and the nucleation points on the substrate surface can promote nucleation. In the deposition process regulation, the flow rate of nitrogen is ensured. In the primary deposition, the deposition thickness of the nanocrystalline diamond film is ensured to be greater than 500μm. In the secondary deposition, by increasing the height of the deposition table, the plasma distribution and plasma temperature on the surface of the nanocrystalline diamond film will be changed, and the deposition environment of the nanocrystalline diamond film will change.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] The present invention first uses a pressurized grinding method to generate nucleation points on the substrate surface. In the primary deposition process, a nanocrystalline diamond film is prepared by adjusting process parameters. In the secondary deposition process, the deposition platform is raised to affect the plasma distribution and plasma temperature on the surface of the nanocrystalline diamond film, and a secondary deposition diamond film with octagonal polycrystalline diamond is deposited, and finally an octagonal polycrystalline diamond is successfully prepared. The prepared octagonal polycrystalline diamond has high hardness, stable physical and chemical properties, and special morphology. It can be used in engineering and biological fields, and can be used as a micro drill, biological electrode, and sewage detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The microstructure of the octagonal polycrystalline diamond prepared in Example 1;

[0029] Figure 2 is the Raman spectrum of the octagonal polycrystalline diamond prepared in Example 1;

[0030] Figure 3 is a microstructure diagram of the diamond film prepared in Comparative Example 1;

[0031] Figure 4 is a microstructure diagram of the diamond film prepared in Comparative Example 2;

[0032] Figure 5 is a microstructure diagram of the diamond film prepared in Comparative Example 3;

[0033] Figure 6 This is a microstructure diagram of the diamond film prepared in Comparative Example 4.

[0034] Figure 7 This is a microstructure diagram of the diamond film prepared in Comparative Example 5. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1

[0037] This embodiment provides an octagonal polycrystalline diamond, which is prepared by MPCVD deposition technology.

[0038] A method for preparing the octagonal polycrystalline diamond described in this embodiment comprises the following steps:

[0039] S1. A silicon wafer with a thickness of 1 cm and a diameter of 5 cm was selected as the substrate. Diamond fine powder with an average particle size of 10 μm was placed on the substrate. Nucleation points were formed on the substrate surface by pressurized grinding. The substrate silicon was cleaned with ethanol and acetone for 10 min respectively, and then dried.

[0040] S2, placing the substrate carrying the nucleation points into a microwave plasma chemical vapor deposition device for primary deposition, the deposition frequency is 2.45 GHz, the microwave power is 5 kW, the temperature is 900° C., the deposition chamber pressure is 10 kPa, the hydrogen flow rate is 300 sccm, the methane flow rate is 2% of the hydrogen, and the nitrogen flow rate is 0.5% of the hydrogen, to obtain a nanocrystalline diamond film, the thickness of the nanocrystalline diamond film is 600 μm;

[0041] S3, raising the deposition platform by 6 mm, and performing secondary deposition on the nanocrystalline diamond film, i.e., performing secondary growth of nanocrystalline diamond, and obtaining a secondary deposited diamond film after 200 h of deposition, wherein the gas flow rate, substrate temperature, deposition chamber pressure and microwave power during the secondary deposition are the same as those of the primary deposition, and the growth parameter α of the central grain during the secondary deposition is 2.6;

[0042] S4. After the secondary deposition is completed, the octagonal polycrystalline diamond is separated from the secondary deposited diamond film, and the octagonal polycrystalline diamond is obtained after cleaning and drying.

[0043] The microstructure of the octagonal polycrystalline diamond prepared in this embodiment is shown in FIG. Figure 1 It can be seen that the prepared octagonal polycrystalline diamond is an octagonal polycrystalline diamond with clear boundaries. Figure 2 This is the Raman spectrum analysis diagram.

[0044] Example 2

[0045] This embodiment provides an octagonal polycrystalline diamond, which is prepared by MPCVD deposition technology.

[0046] A method for preparing the octagonal polycrystalline diamond described in this embodiment comprises the following steps:

[0047] S1. A silicon wafer with a thickness of 1 cm and a diameter of 5 cm was selected as the substrate. Diamond fine powder with an average particle size of 13 μm was placed on the substrate. Nucleation points were formed on the substrate surface by pressurized grinding. The substrate silicon was cleaned with ethanol and acetone for 10 min respectively, and then dried.

[0048] S2, placing the substrate carrying the nucleation points into a microwave plasma chemical vapor deposition device for primary deposition, the deposition frequency is 2.45 GHz, the microwave power is 15 kW, the temperature is 800° C., the deposition chamber pressure is 40 kPa, the flow rate of hydrogen is 800 sccm, the flow rate of methane is 8% of the hydrogen, and the flow rate of nitrogen is 5% of the hydrogen, to obtain a nanocrystalline diamond film, the thickness of the nanocrystalline diamond film is 800 μm;

[0049] S3, raising the deposition platform by 10 mm, performing secondary deposition on the nanocrystalline diamond film for 300 h to obtain a secondary deposited diamond film, wherein the gas flow rate, substrate temperature, deposition chamber pressure and microwave power during the secondary deposition are the same as those of the primary deposition, and the growth parameters of the central grains during the secondary deposition are α is 3;

[0050] S4. After the secondary deposition is completed, the octagonal polycrystalline diamond is separated from the secondary deposited diamond film, and the octagonal polycrystalline diamond is obtained after cleaning and drying.

[0051] The microstructure of the octagonal polycrystalline diamond prepared in this example is similar to that in Example 1.

[0052] Example 3

[0053] This embodiment provides an octagonal polycrystalline diamond, which is prepared by MPCVD deposition technology.

[0054] A method for preparing the octagonal polycrystalline diamond described in this embodiment comprises the following steps:

[0055] 51. A silicon wafer with a thickness of 1 cm and a diameter of 5 cm was selected as the substrate. Diamond fine powder with an average particle size of 15 μm was placed on the substrate. Nucleation points were formed on the surface of the substrate by pressurized grinding. The substrate silicon was cleaned with ethanol and acetone for 10 min respectively and dried.

[0056] S2, placing the substrate carrying the nucleation points into a microwave plasma chemical vapor deposition device for primary deposition, the deposition frequency is 915 MHz, the microwave power of the primary deposition is 1 kW, the deposition temperature is 1000° C., the deposition chamber pressure is 2 kPa, the hydrogen flow rate is 1 slm, the methane flow rate is 0.3% of the hydrogen, and the nitrogen flow rate is 0.2% of the hydrogen, to obtain a nanocrystalline diamond film, the thickness of the nanocrystalline diamond film is 500 μm;

[0057] S3, raising the deposition platform by 5 mm, performing secondary deposition on the nanocrystalline diamond film for 100 h to obtain a secondary deposited diamond film, wherein the gas flow rate, substrate temperature, deposition chamber pressure and microwave power during the secondary deposition are the same as those of the primary deposition, and the growth parameter α of the central grain during the secondary deposition is 2.25;

[0058] S4. After the secondary deposition is completed, the octagonal polycrystalline diamond is separated from the secondary deposited diamond film, and the octagonal polycrystalline diamond is obtained after cleaning and drying.

[0059] The microstructure of the octagonal polycrystalline diamond prepared in this example is similar to that in Example 1.

[0060] Example 4

[0061] This embodiment provides an octagonal polycrystalline diamond, which is prepared by MPCVD deposition technology.

[0062] A method for preparing the octagonal polycrystalline diamond described in this embodiment comprises the following steps:

[0063] S1. A silicon wafer with a thickness of 1 cm and a diameter of 5 cm was selected as the substrate. Diamond fine powder with an average particle size of 15 μm was placed on the substrate. Nucleation points were formed on the substrate surface by pressurized grinding. The substrate silicon was cleaned with ethanol and acetone for 10 min respectively, and then dried.

[0064] S2, placing the substrate carrying the nucleation points into a microwave plasma chemical vapor deposition device for primary deposition, the deposition frequency is 915 MHz, the microwave power of the primary deposition is 120 kW, the deposition temperature is 800° C., the deposition chamber pressure is 40 kPa, the hydrogen flow rate is 10 slm, the methane flow rate is 8% of the hydrogen, and the nitrogen flow rate is 5% of the hydrogen, to obtain a nanocrystalline diamond film, the thickness of the nanocrystalline diamond film is 800 μm;

[0065] S3, raising the deposition platform by 10 mm, performing secondary deposition on the nanocrystalline diamond film for 300 h to obtain a secondary deposited diamond film, wherein the gas flow rate, substrate temperature, deposition chamber pressure and microwave power during the secondary deposition are the same as those of the primary deposition, and the growth parameter α of the central grain during the secondary deposition is 3;

[0066] S4. After the secondary deposition is completed, the octagonal polycrystalline diamond is separated from the secondary deposited diamond film, and the octagonal polycrystalline diamond is obtained after cleaning and drying.

[0067] The microstructure of the octagonal polycrystalline diamond prepared in this example is similar to that in Example 1.

[0068] Example 5

[0069] This embodiment provides an octagonal polycrystalline diamond, which is prepared by MPCVD deposition technology.

[0070] A method for preparing the octagonal polycrystalline diamond described in this embodiment comprises the following steps:

[0071] S1. A silicon wafer with a thickness of 1 cm and a diameter of 5 cm was selected as the substrate. Diamond fine powder with an average particle size of 15 μm was placed on the substrate. Nucleation points were formed on the substrate surface by pressurized grinding. The substrate silicon was cleaned with ethanol and acetone for 10 min respectively, and then dried.

[0072] S2, placing the substrate carrying the nucleation points into a microwave plasma chemical vapor deposition device for primary deposition, the deposition frequency is 915 MHz, the microwave power of the primary deposition is 10 kW, the deposition temperature is 900° C., the deposition chamber pressure is 10 kPa, the hydrogen flow rate is 3 slm, the methane flow rate is 5% of the hydrogen, and the nitrogen flow rate is 2% of the hydrogen, to obtain a nanocrystalline diamond film, the thickness of the nanocrystalline diamond film is 700 μm;

[0073] S3, raising the deposition platform by 5 mm, performing secondary deposition on the nanocrystalline diamond film for 200 h to obtain a secondary deposited diamond film, wherein the gas flow rate, substrate temperature, deposition chamber pressure and microwave power during the secondary deposition are the same as those of the primary deposition, and the growth parameters of the central grains during the secondary deposition are α is 2.5;

[0074] S4. After the secondary deposition is completed, the octagonal polycrystalline diamond is separated from the secondary deposited diamond film, and the octagonal polycrystalline diamond is obtained after cleaning and drying.

[0075] The microstructure of the octagonal polycrystalline diamond prepared in this example is similar to that in Example 1.

[0076] Comparative Example 1

[0077] This comparative example is similar to Example 1, except that the flow rate of nitrogen in this comparative example is 0.1% of the flow rate of hydrogen. The microstructure of the diamond film prepared in this comparative example is shown in FIG. Figure 3 As shown, it can be seen that the grains on the prepared diamond film do not have an octagonal polycrystalline structure.

[0078] Comparative Example 2

[0079] This comparative example is similar to Example 1, except that the flow rate of nitrogen in this comparative example is 8% of the flow rate of hydrogen. The microstructure of the diamond film prepared in this comparative example is shown in FIG. Figure 4As shown, it can be seen that the grains on the prepared diamond film do not have an octagonal polycrystalline structure.

[0080] Comparative Example 3

[0081] This comparative example is similar to Example 1, except that the height of the deposition platform is not increased during the secondary deposition process in this comparative example. The microstructure of the diamond film prepared in this comparative example is shown in FIG. Figure 5 As shown, it can be seen that the grains on the prepared diamond film only have an octagonal polycrystalline prototype structure, not a complete octagonal polycrystalline structure.

[0082] Comparative Example 4

[0083] This comparative example is similar to Example 1, except that the height of the deposition platform during the secondary deposition in this comparative example is 15 mm. The microstructure of the diamond film prepared in this comparative example is shown in FIG. Figure 6 As shown, it can be seen that the grains on the prepared diamond film are embryonic octagonal polycrystalline diamonds and large polycrystalline diamonds. Due to the extremely uneven distribution of plasma, some nanocrystalline diamonds rapidly increase in size, and some nanocrystalline diamonds are transformed into octagonal polycrystalline diamond embryonic forms. As shown in the figure, the polycrystalline diamond on the left is larger in size, which is quite different from the octagonal polycrystalline diamond embryonic form.

[0084] Comparative Example 5

[0085] This comparative example is similar to Example 1, except that the secondary deposition time in this comparative example is 80 hours. The microstructure of the diamond film prepared in this comparative example is shown in FIG. Figure 7 As shown, it can be seen that the grains on the prepared diamond film do not have an octagonal polycrystalline structure.

[0086] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An octagonal polycrystalline diamond, characterized in that: The octagonal polycrystalline diamond is prepared by MPCVD deposition technology.

2. A method for preparing the octagonal polycrystalline diamond according to claim 1, characterized in that: The following steps are involved: S1, placing diamond fine powder on a substrate, forming nucleation points on the substrate surface by pressurized grinding, and obtaining a substrate carrying nucleation points; S2, placing the substrate carrying the nucleation points into a microwave plasma chemical vapor deposition device for primary deposition to obtain a nanocrystalline diamond film, wherein the thickness of the nanocrystalline diamond film is 500-800 μm, and the deposition gas during the primary deposition process is a mixed gas of hydrogen, methane and nitrogen, wherein the flow rate of methane is 0.3-8% of the hydrogen, and the flow rate of nitrogen is 0.2-5% of the hydrogen; S3, raising the deposition platform, performing secondary deposition on the nanocrystalline diamond film to obtain a secondary deposited diamond film, wherein the secondary deposited diamond film has octagonal polycrystalline diamonds, and the gas flow rate, substrate temperature, deposition chamber pressure and microwave power during the secondary deposition are the same as those of the primary deposition; S4. After the secondary deposition is completed, the octagonal polycrystalline diamond is separated from the secondary deposited diamond film, and the octagonal polycrystalline diamond is obtained after cleaning and drying.

3. The preparation method according to claim 2, characterized in that: The frequency of the initial deposition in S2 is 2.45 GHz, the microwave power of the initial deposition is 1 kW-15 kW, and the flow rate of the hydrogen is 200-800 sccm.

4. The preparation method according to claim 2, characterized in that: The frequency of the initial deposition in S2 is 915 MHz, the microwave power of the initial deposition is 1 kW-120 kW, and the flow rate of the hydrogen is 1-10 slm.

5. The preparation method according to claim 2, characterized in that: The temperature of the initial deposition in S2 is 800-1000°C.

6. The preparation method according to claim 2, characterized in that: The deposition chamber pressure of the initial deposition in S2 is 2-40 kPa.

7. The preparation method according to claim 2, characterized in that: The deposition platform in S3 is raised by 5 mm to 10 mm.

8. The preparation method according to claim 2, characterized in that: During the secondary deposition process, the growth parameter α of the central grain is 2.25-3.

9. The preparation method according to claim 2, characterized in that: The time of the secondary deposition in S3 is 100-300 hours.

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