Diamond thick film and preparation method thereof

Abstract

The invention provides a diamond thick film and a preparation method thereof, and the preparation method comprises the following steps: (1) electrifying and heating the surface of a substrate by using a hot filament, introducing a methane and hydrogen mixed gas with the methane volume content of 2-8%, and depositing diamond on the surface of the substrate; (2) after the single deposition thickness of the diamond reaches 50-150 microns, stopping introducing the methane, and maintaining for 0.5-20 hours in a hydrogen atmosphere; (3) introducing a methane and hydrogen mixed gas with the methane volume content of 2-8%, and continuously depositing the diamond; (4) after the single deposition thickness of the diamond reaches 50-150 microns, stopping introducing the methane, and maintaining for 0.5-20 hours in the hydrogen atmosphere; and (5) according to the required thickness of the diamond thick film, the step (3) and the step (4) are repeated, the diamond thick film is obtained, and the thickness is 600-2500 microns. According to the method, the diamond phase content in the diamond thick film is increased, and the mechanical and thermal properties of the diamond thick film are improved.

Description

Technical Field

[0001] The present application relates to the field of material technology, and in particular to a diamond thick film and a preparation method thereof. Background Art

[0002] Diamond has a series of excellent properties such as high hardness, high wear resistance, high thermal conductivity, high transmittance in a wide spectral range, and good insulation. It has great application value in the fields of precision machining, chip thermal management, extreme environment optical windows, high-power semiconductor devices, etc. The preparation of large-size diamonds depends on the rapid development of CVD (chemical vapor deposition) technology. In the diamond CVD deposition system, the gas is excited by excitation sources such as microwaves, radio frequencies, high-temperature filaments, and DC arcs, and diamonds are deposited and grown on the surface of the substrate.

[0003] Among the different diamond CVD preparation methods, HFCVD (hot filament chemical vapor deposition) is widely used in the preparation of large-area diamond self-supporting thick films due to its advantages such as simple equipment, low cost, easy expansion of deposition area, and relatively fast growth rate. Its products are used in various types of grinding tools and chip thermal management.

[0004] HFCVD diamond preparation uses high-temperature hot filaments (Ta, W, Re, etc.) as excitation sources to stimulate hydrogen and methane gases to obtain active H atoms and carbon-containing groups (such as CH3, C2H4 groups, etc.), which grow on the surface of the deposition substrate. The role of active H atoms is to promote the deposition of diamond phase and etch non-diamond phase. Its deposition mechanism is similar to other CVD diamond deposition systems, the difference lies in the different excitation sources.

[0005] A major problem with HFCVD diamond deposition is that the excitation efficiency of the hot filament is not high enough, resulting in insufficient H atom concentration, so that there is always a certain amount of non-diamond phase in the deposited diamond film. The presence of non-diamond phase has an adverse effect on the quality of the diamond film, and will reduce a series of indicators such as wear resistance, thermal conductivity, and hardness of the diamond film. In addition, due to the different thermal expansion properties of non-diamond phases (such as graphite and amorphous carbon) and diamond, stress cracking may occur during the cooling process, and defects such as cracks and pits may occur during the processing process.

[0006] In order to reduce the non-diamond phase content in HFCVD diamond thick films and improve the mechanical and thermal properties, there are two feasible means in the prior art:

[0007] 1. Increase the filament temperature. Increasing the filament temperature can improve the excitation efficiency of active groups, thereby reducing the non-diamond phase content. However, in large-area HFCVD diamond deposition systems, increasing the filament power will significantly increase production costs. Data shows that under conventional deposition conditions, if the atomic hydrogen concentration increases by 10%, the filament power may need to increase by 50%, and the resulting increase in electricity costs will reach 25%;

[0008] 2. Reduce methane concentration. Reducing methane concentration can increase the proportion of active H atoms and improve the quality of diamond membranes. However, reducing methane concentration will reduce the membrane deposition rate and affect the membrane production efficiency. Typical thickness products will significantly increase electricity costs due to reduced methane concentration and slower deposition rate.

[0009] Therefore, existing technical means are not suitable for large-scale production of HFCVD diamond thick film quality improvement. Summary of the invention

[0010] The purpose of this application is to provide a diamond thick film and a preparation method thereof, so as to reduce the non-diamond phase content in the diamond thick film and improve the mechanical and thermal properties of the diamond thick film. The specific technical scheme is as follows:

[0011] The first aspect of the present application provides a method for preparing a diamond thick film, which comprises the following steps:

[0012] (1) A hot filament is electrically heated on the surface of the substrate, the temperature of the hot filament is 2000°C to 2400°C, the ambient pressure is 30 Torr to 60 Torr, the temperature of the substrate is 700°C to 1000°C, the distance between the substrate and the hot filament is 1 mm to 10 mm, and then a mixed gas of methane (CH4) and hydrogen (H2) with a methane volume content of 2% to 8% is introduced to deposit diamond on the surface of the substrate;

[0013] (2) After the single deposition thickness of the diamond reaches 50 μm to 150 μm, stop introducing the methane and maintain the atmosphere under a single hydrogen atmosphere for 0.5 h to 20 h;

[0014] (3) introducing a methane and hydrogen mixed gas having a methane volume content of 2% to 8% to continue depositing the diamond;

[0015] (4) After the single deposition thickness of the diamond reaches 50 μm to 150 μm, the introduction of methane is stopped, and the hydrogen atmosphere is maintained for 0.5 h to 20 h;

[0016] (5) According to the desired thickness of the diamond thick film, repeat the steps (3) and (4) to obtain the diamond thick film, wherein the thickness of the diamond thick film is 600 μm to 2500 μm.

[0017] In some embodiments of the present application, in step (2) and step (4), the single hydrogen atmosphere is maintained for 1 h to 10 h.

[0018] In some embodiments of the present application, the deposition rate of the diamond is 1.4 μm / h to 10 μm / h.

[0019] In some embodiments of the present application, in step (1), the substrate is selected from at least one of Si, graphite, Mo, W, SiO2, tungsten carbide, silicon carbide, and Si3N4.

[0020] In some embodiments of the present application, in step (1), the hot filament is selected from at least one of a tungsten filament, a rhenium filament, and a tantalum filament.

[0021] The second aspect of the present application provides a diamond thick film prepared according to the preparation method provided in the first aspect of the present application.

[0022] In some embodiments of the present application, in a Raman spectrum test, based on the Raman peak area of ​​the diamond thick film, the diamond phase Raman peak area accounts for 85% to 95%.

[0023] In some embodiments of the present application, the wear ratio of the diamond thick film is 500,000 to 1,000,000.

[0024] In some embodiments of the present application, the thermal conductivity of the diamond thick film is 1000 W / (m·K) to 1800 W / (m·K).

[0025] The present application provides a diamond thick film and a preparation method thereof. The method reduces the content of non-diamond phase in the diamond film and increases the content of diamond phase in the diamond thick film by targeted etching of a diamond film with a single deposition thickness of 50μm~150μm, thereby improving the mechanical and thermal properties of the diamond thick film. At the same time, during the time when the methane is stopped, the diamond thick film is no longer deposited. At this time, the deposited diaphragm can be stress-relaxed under high temperature, reducing the cracking ratio of the diamond thick film caused by stress, thereby improving the production yield of the diamond thick film. At the same time, the method intermittently closes the methane to retain hydrogen, and the increased pure hydrogen atmosphere time is shorter than the growth time of conventional HFCVD diamonds. The increased electricity cost and reduced production efficiency are within a controllable range, avoiding the cost increase caused by the conventional method of increasing the filament temperature and the reduced production efficiency caused by reducing the methane concentration. Furthermore, the method avoids the re-exploration of process conditions and is a universal process suitable for the preparation of HFCVD and other CVD diamond films. The diamond thick film provided in the present application has a higher diamond phase content, and better mechanical properties and thermal properties. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0027] HFCVD is widely used in the preparation of large-area self-supporting diamond thick films due to its advantages such as simple equipment, low cost, easy expansion of deposition area, and relatively fast growth rate. However, a certain amount of non-diamond phase exists in the prepared diamond thick film, which affects the mechanical and thermal properties of the diamond thick film. Based on this, the present application provides a diamond thick film and a preparation method thereof to increase the diamond phase content in the diamond thick film, thereby improving its mechanical and thermal properties.

[0028] The first aspect of the present application provides a method for preparing a diamond thick film, which comprises the following steps:

[0029] (1) A hot filament is electrically heated on the substrate surface, the temperature of the hot filament is between 2000°C and 2400°C, the ambient pressure is between 30 Torr and 60 Torr, the substrate temperature is between 700°C and 1000°C, the distance between the substrate and the hot filament is between 1 mm and 10 mm, and then a methane and hydrogen mixed gas with a methane volume content of 2% to 8% is introduced to deposit diamond on the substrate surface;

[0030] (2) After the single deposition thickness of diamond reaches 50 μm~150 μm, stop introducing methane and maintain it in a separate hydrogen atmosphere for 0.5 h~20 h;

[0031] (3) A methane and hydrogen mixture with a methane volume content of 2% to 8% is introduced to continue depositing diamonds;

[0032] (4) After the single deposition thickness of diamond reaches 50 μm~150 μm, stop introducing methane and maintain it in a separate hydrogen atmosphere for 0.5 h~20 h;

[0033] (5) According to the desired thickness of the diamond thick film, repeat the steps (3) and (4) to obtain the diamond thick film, wherein the thickness of the diamond thick film is 600 μm to 2500 μm.

[0034] For example, in step (1) and step (3), the volume content of methane in the CH4 and H2 mixed gas introduced can be 2%, 4%, 6%, 8% or a range consisting of any two of these values. If the volume content of methane in the CH4 and H2 mixed gas introduced is less than 2%, the methane concentration is too low, which will reduce the deposition rate of the diamond thick film and affect the production efficiency; if the volume content of methane is greater than 8%, the hydrogen concentration is too low, and it is difficult to fully etch the non-diamond phase formed in the diamond thick film deposition process, thereby reducing the quality of the diamond thick film. When the single deposition thickness of diamond is too thick, for example, greater than 150μm, it is difficult for hydrogen atoms to effectively penetrate and etch the non-diamond phase; when the single deposition thickness of diamond is too thin, for example, less than 50μm, turning off methane for etching will increase the production cost. For example, the single deposition thickness of diamond in step (2) and step (4) can be 50 μm, 70 μm, 80 μm, 95 μm, 110 μm, 120 μm, 140 μm, 150 μm, or a range consisting of any two of these values; the maintenance time in a single hydrogen atmosphere can be 0.5 h, 1 h, 2 h, 4 h, 5 h, 6.5 h, 7 h, 9 h, 10 h, 12 h, 13.5 h, 15 h, 16 h, 18 h, 19 h, 20 h, or a range consisting of any two of these values. After the single deposition thickness of the diamond thick film is controlled within the above range, the methane is turned off, and the time for the single hydrogen introduction is controlled within the above range, so that hydrogen atoms can effectively penetrate into the diamond thick film to etch the non-diamond phase, thereby improving the quality of the diamond thick film without increasing the production cost. Finally, a diamond thick film with a thickness of 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, 1800 μm, 2000 μm, 2500 μm or a range consisting of any two of these values ​​can be obtained.

[0035] In general, the method for preparing a thick diamond film provided by the present application is to turn off the methane after a single deposition of diamond reaches a certain thickness. At this time, part of the energy originally used to activate the methane is completely converted to activate the hydrogen, so that the concentration of hydrogen atoms in the system is greatly increased, and the non-diamond phase previously deposited and generated is etched; at the same time, since the thickness of a single deposition is controlled within the range of 50μm~150μm, the active hydrogen atoms can penetrate into the interior of the thick diamond film for the etching process, avoiding the deposition thickness being too thick to be deeply etched; in the subsequent deposition process of restoring the methane supply, the small amount of pores generated by the etching of the non-diamond phase are refilled with the diamond phase, and since there is no need to perform the nucleation process again, the diamond phase will continue to grow on the generated diamond. In repeating the above process many times, the non-diamond phase in each layer of the deposited film is etched, which increases the content of the diamond phase, so that the properties of the deposited thick diamond film are closer to the intrinsic properties of diamond, and the quality of the thick diamond film is improved.

[0036] In the present application, the single deposition thickness of diamond in step (2) and the single deposition thickness of diamond in step (4) can be the same or different; the maintenance time of the single hydrogen atmosphere in step (2) and the maintenance time of the single hydrogen atmosphere in step (4) can be the same or different; as long as it is within the scope of the present application and can achieve the purpose of the present application.

[0037] In some embodiments of the present application, in step (2) and step (4), the hydrogen atmosphere is maintained for 1 h to 10 h. For example, the maintenance time in the hydrogen atmosphere can be 1 h, 2 h, 3 h, 4.5 h, 6 h, 8 h, 9 h, 10 h or a range consisting of any two of the values. The time for the above-mentioned single hydrogen introduction is related to the single deposition thickness of the diamond. When the deposition thickness is thin, less time is required, and when the deposition thickness is thick, longer time is required. Controlling the time for the single hydrogen introduction within the above range can fully etch the non-diamond phase produced in the diamond deposition, improve the quality of the diamond thick film, and at the same time, relative to commonly used technical means (such as increasing the filament temperature and reducing the methane concentration), it can improve production efficiency and reduce production costs.

[0038] In some embodiments of the present application, the deposition rate of diamond is 1.4 μm / h to 10 μm / h. For example, the deposition rate of diamond can be 1.4 μm / h, 2 μm / h, 3 μm / h, 4 μm / h, 5 μm / h, 6 μm / h, 8 μm / h, 10 μm / h, or a range consisting of any two of these values. By controlling the deposition rate of diamond within the above range, the increase of non-diamond defects in the film caused by too fast a deposition rate can be reduced, while at the same time overcoming the problem of reduced production efficiency and increased production costs caused by a slow deposition rate.

[0039] In some embodiments of the present application, in step (1), the substrate is selected from at least one of Si, graphite, Mo, W, SiO2, tungsten carbide, silicon carbide, and Si3N4. The above-mentioned types of substrates have good chemical stability and mechanical properties, can resist chemical reactions that may occur in reaction gases and high temperature environments, and have good nucleation properties, providing good conditions for the growth of diamond thick films.

[0040] In some embodiments of the present application, in step (1), the hot filament is selected from at least one of tungsten filament, rhenium filament and tantalum filament. The above-mentioned hot filaments have the advantages of high melting point, good chemical stability, suitable thermal electron emission performance and high thermal conductivity, which is conducive to the dissociation of reaction gas, reduces the generation of impurities during the deposition process, and improves the quality of diamond thick film.

[0041] The second aspect of the present application provides a diamond thick film prepared according to the preparation method provided in the first aspect of the present application.

[0042] In some embodiments of the present application, in the Raman spectrum test, based on the diamond thick film Raman peak area, the diamond phase Raman peak area accounts for 85% to 95%. For example, the diamond phase Raman peak area can account for 85%, 87%, 89%, 91%, 93%, 95% or a range consisting of any two values ​​therein. The diamond thick film Raman peak area is the sum of the diamond phase Raman peak area and the non-diamond phase Raman peak area. By regulating the proportion of the diamond phase Raman peak area within the above range, it is beneficial to improve the hardness and wear resistance of the diamond thick film, increase the thermal conductivity of the diamond thick film, etc., thereby expanding the application range of the diamond thick film and improving the quality of the diamond thick film.

[0043] In some embodiments of the present application, the wear ratio of the diamond thick film is 500,000 to 1,000,000. For example, the wear ratio of the diamond thick film is 500,000, 550,000, 600,000, 640,000, 680,000, 730,000, 800,000, 860,000, 900,000, 950,000, 1,000,000, or a range consisting of any two of these values. The above-mentioned diamond thick film exhibits a high wear ratio and has good mechanical properties.

[0044] In some embodiments of the present application, the thermal conductivity of the diamond thick film is 1000W / (m·K) to 1800 W / (m·K), for example, the thermal conductivity of the diamond thick film can be 1000W / (m·K), 1100W / (m·K), 1250W / (m·K), 1400W / (m·K), 1520W / (m·K), 1640W / (m·K), 1730W / (m·K), 1800W / (m·K) or a range consisting of any two of the values. The above diamond thick film exhibits a high thermal conductivity and has good thermal properties.

[0045] Example

[0046] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by mass.

[0047] Test methods and equipment:

[0048] Determination of diamond phase content:

[0049] The diamond thick films prepared in the examples and comparative examples were cut into samples of 1 cm×1 cm by laser cutting and the samples were analyzed by LabRam HR Evolution Raman spectrometer at a laser wavelength of 532 nm at 800-1800 cm -1 Raman spectrum test in wavenumber range. The Raman peak of the test data is fitted. The peak area of ​​the diamond thick film Raman peak is the sum of the peak area of ​​the diamond phase Raman peak and the peak area of ​​the non-diamond phase Raman peak. By calculating the ratio of the peak area of ​​the diamond phase Raman peak to the peak area of ​​the diamond thick film Raman peak, the diamond phase content is obtained, which is expressed as the proportion of the diamond phase Raman peak area.

[0050] Mechanical properties test:

[0051] The diamond thick films prepared in the examples and comparative examples were cut into φ6 mm disc samples by laser cutting. With reference to "JB-T 3235-2013 Polycrystalline Diamond Wear Ratio Determination Method", the diamond thick film samples were subjected to wear ratio tests on a JTYD-241 wear ratio tester to obtain sample wear ratio data.

[0052] Thermal performance test:

[0053] The diamond thick film prepared in the embodiment and the comparative example was prepared into a φ12.7 mm wafer sample by laser cutting. According to "ASTM E1461-13 (2022) Standard Test Method for Thermal Diffusivity by the Flash Method", the density of the sample was obtained by the Archimedes method, the specific heat of the sample was obtained by the STA 449F3 thermal analyzer using the sapphire method, and the thermal diffusion coefficient of the sample was obtained by the NETZSCH LFA 467 laser thermal conductivity meter. The three were multiplied to obtain the thermal conductivity value of the sample, i.e., the thermal conductivity coefficient.

[0054] Calculation of the increase in electricity costs:

[0055] Increase in electricity cost (%) = Increased electricity cost ratio × 50% × 100%. 50% refers to the electricity cost generated when the conventional preparation method is used to prepare the diamond thick film, which accounts for 50% of the total cost. The total cost includes electricity cost and material cost. This is a conventional technology in this field. Taking Comparative Example 3 as an example of the conventional preparation method, when the CH4 volume content is 4%, the electricity cost generated when the diamond thick film is prepared using the method of Comparative Example 3 accounts for 50% of the total cost. Comparative Example 3 uses the conventional preparation method of diamond thick film, and its electricity cost is used as the benchmark, so there is no increase in electricity cost.

[0056] The method of the present application is used to prepare a diamond thick film: the increased electricity cost ratio = the maintenance time of the hydrogen atmosphere alone / the time of passing the methane and hydrogen mixed gas to deposit the diamond thick film.

[0057] A diamond thick film is prepared by increasing the filament temperature: the preparation of the diamond thick film after increasing the filament temperature is shown in Comparative Example 4, and the preparation of the diamond thick film before increasing the filament temperature is shown in Comparative Example 3. Taking Comparative Example 3 as a benchmark, in Comparative Example 4, when the filament temperature is increased from 2200°C to 2600°C, the growth rate of the diamond thick film is increased from 4.3μm / h to 6.4μm / h, and the time for growing a 1000μm thick diamond thick film is reduced from 232.5h to 156h, and the power for maintaining the filament temperature at 2600°C is 2.3 times the power for maintaining the filament temperature at 2200°C. The energy consumption of producing a 1000μm thick diamond thick film in Comparative Example 4 = the power to maintain a filament temperature of 2600°C × the time to grow a 1000μm thick diamond thick film; the energy consumption of producing a 1000μm thick diamond thick film in Comparative Example 3 = the power to maintain a filament temperature of 2200°C × the time to grow a 1000μm thick diamond thick film; the increased electricity cost ratio of Comparative Example 4 = (energy consumption of producing a 1000μm thick diamond thick film in Comparative Example 4 / energy consumption of producing a 1000μm thick diamond thick film in Comparative Example 3) - 1 = (time to grow a 1000μm thick diamond thick film in Comparative Example 4 / time to grow a 1000μm thick diamond thick film in Comparative Example 3) × 2.3-1.

[0058] Preparation of diamond thick film by reducing methane concentration: the preparation of diamond thick film after reducing methane concentration is shown in Comparative Example 5, and the preparation of diamond thick film before reducing methane concentration is shown in Comparative Example 3. Taking Comparative Example 3 as a benchmark, in Comparative Example 5, when the methane concentration, i.e., the methane volume content, is reduced from 4% to 1.5%, the growth rate of diamond thick film is reduced from 4.3 μm / h to 0.7 μm / h, and the time for growing a 1000 μm thick diamond thick film is increased from 232.5 h to 1428.5 h. The proportion of increased electricity cost in Comparative Example 5 = (the time for growing a 1000 μm thick diamond thick film in Comparative Example 5 / the time for growing a 1000 μm thick diamond thick film in Comparative Example 3)-1.

[0059] Example 1

[0060] <Preparation of Diamond Thick Film>

[0061] (1) A tungsten wire was electrically heated on the substrate surface at a temperature of 2200°C, the ambient pressure was 45 Torr, tungsten carbide was used as the substrate, the substrate temperature was 800°C, the distance between the substrate and the tungsten wire was 5 mm, and then a CH4 and H2 mixed gas with a methane volume content of 4% was introduced to deposit diamond on the substrate surface at a deposition rate of 4.3 μm / h.

[0062] (2) After the diamond deposition thickness reaches 100 μm, the methane flow is stopped and maintained in a hydrogen atmosphere alone for 5 h.

[0063] (3) A mixed gas of CH4 and H2 with a methane volume content of 4% is then introduced to continue depositing diamond.

[0064] (4) After the single deposition thickness of diamond reaches 100 μm, the introduction of methane is stopped and maintained in a single hydrogen atmosphere for 5 h.

[0065] (5) Repeat steps (3) and (4) 9 times to obtain a diamond thick film with a thickness of 1000 μm.

[0066] Example 2 to Example 10

[0067] Except for adjusting the relevant parameters according to Table 1, the rest is the same as Example 1.

[0068] Comparative Example 1 to Comparative Example 2

[0069] Except for adjusting the relevant parameters according to Table 1, the rest is the same as Example 1.

[0070] Comparative Example 3

[0071] <Preparation of Diamond Thick Film>

[0072] The substrate surface was heated by a tungsten wire at a temperature of 2200°C and an ambient pressure of 45 Torr. Tungsten carbide was used as the substrate. The substrate temperature was 800°C and the distance between the substrate and the tungsten wire was 5 mm. Then a CH4 and H2 mixed gas with a methane volume content of 4% was introduced to deposit diamond on the substrate surface. The diamond deposition rate was 4.3μm / h. After 232.5h of deposition, a diamond thick film with a thickness of 1000μm was obtained.

[0073] Comparative Example 4

[0074] <Preparation of Diamond Thick Film>

[0075] The substrate surface was heated by a tungsten filament at a temperature of 2600°C. The pressure of the ambient vacuum chamber was 45 Torr. Tungsten carbide was used as the substrate. The substrate temperature was 800°C. The distance between the substrate and the tungsten filament was 5 mm. Then a CH4 and H2 mixed gas with a methane volume content of 4% was introduced to deposit diamond on the substrate surface. The diamond deposition rate was 6.4μm / h. After 156h of deposition, a diamond thick film with a thickness of 1000μm was obtained.

[0076] Comparative Example 5

[0077] <Preparation of Diamond Thick Film>

[0078] The substrate surface was heated by a tungsten wire at a temperature of 2200°C. The pressure of the vacuum chamber was 45 Torr. Tungsten carbide was used as the substrate. The substrate temperature was 800°C. The distance between the substrate and the tungsten wire was 5 mm. Then a CH4 and H2 mixed gas with a methane volume content of 1.5% was introduced to deposit diamond on the substrate surface. The diamond deposition rate was 0.7μm / h. After deposition for 1428.5 hours, a diamond thick film with a thickness of 1000μm was obtained.

[0079] Table 1

[0080] Note: “ / ” in Table 1 means no relevant parameters.

[0081] In Table 1, it can be seen from Examples 1 to 10 and Comparative Examples 1 to 5 that the diamond thick film prepared by the method provided in the present application has a high diamond phase content and exhibits excellent thermal and mechanical properties. It can be seen from Examples 1 to 10 and Comparative Examples 1 and 2 that by controlling the single diamond deposition thickness and the single hydrogen maintenance time within the scope of the present application, a diamond thick film with high diamond phase content and excellent thermal and mechanical properties can be prepared. It can be seen from Examples 2 and 3 and Examples 4 and 6 that when the volume content of methane introduced is the same and the single deposition thickness is the same, the increase in electricity cost increases with the increase in the maintenance time of the single hydrogen atmosphere. It can be seen from Examples 1 to 3, 4, and 6 that the maintenance time of the single hydrogen atmosphere is in the range of 1h~10h, and the prepared diamond thick film has excellent thermal and mechanical properties, while being able to take into account lower costs. According to calculations, the increase in electricity cost brought about by this method is less than that by increasing the filament temperature or reducing the methane concentration.

[0082] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a diamond thick film, comprising the following steps: (1) heating the substrate surface with a hot filament, wherein the temperature of the hot filament is 2000°C to 2400°C, the ambient pressure is 30 Torr to 60 Torr, the temperature of the substrate is 700°C to 1000°C, the distance between the substrate and the hot filament is 1 mm to 10 mm, and then introducing a methane and hydrogen mixed gas with a methane volume content of 2% to 8%, and depositing diamond on the substrate surface; (2) After the single deposition thickness of the diamond reaches 50 μm to 150 μm, stop introducing the methane and maintain the atmosphere under a single hydrogen atmosphere for 0.5 h to 20 h; (3) introducing a methane and hydrogen mixed gas having a methane volume content of 2% to 8% to continue depositing the diamond; (4) After the single deposition thickness of the diamond reaches 50 μm to 150 μm, the introduction of methane is stopped, and the hydrogen atmosphere is maintained for 0.5 h to 20 h; (5) According to the desired thickness of the diamond thick film, repeat the steps (3) and (4) to obtain the diamond thick film, wherein the thickness of the diamond thick film is 600 μm to 2500 μm.

2. The preparation method according to claim 1, wherein In the step (2) and the step (4), the single hydrogen atmosphere is maintained for 1 h to 10 h.

3. The preparation method according to claim 1, wherein The deposition rate of the diamond is 1.4 μm / h to 10 μm / h.

4. The preparation method according to claim 1, wherein In the step (1), the substrate is selected from at least one of Si, graphite, Mo, W, SiO2, tungsten carbide, silicon carbide, and Si3N4.

5. The preparation method according to claim 1, wherein In the step (1), the hot filament is selected from at least one of tungsten filament, rhenium filament and tantalum filament.

6. A diamond thick film obtained by the preparation method according to any one of claims 1 to 5.

7. The diamond thick film according to claim 6, wherein: In the Raman spectroscopy test, based on the Raman peak area of ​​the diamond thick film, the Raman peak area of ​​the diamond phase accounts for 85%~95%.

8. The diamond thick film according to claim 6, wherein: The wear ratio of the diamond thick film is 500,000 to 1,000,000.

9. The diamond thick film according to claim 6, wherein: The thermal conductivity of the diamond thick film is 1000W / (m·K) to 1800W / (m·K).

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