Single crystal diamond and method of manufacture and use thereof

Abstract

The present application relates to a kind of single crystal diamond and its preparation method and purposes, the preparation method includes the following steps: etching treatment diamond seed crystal;Then pass into carbon source, hydrogen and chlorine, carry out the deposition growth of single crystal diamond;After deposition growth, post-processing is carried out, and the single crystal diamond is obtained.The present application can promote the selective growth of diamond phase by introducing chlorine and hydrogen simultaneously in chemical vapor deposition process, chlorine can help reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality and growth rate of diamond single crystal, reducing dislocation density.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a single-crystal diamond, its preparation method, and its uses. Background Technology

[0002] Diamond possesses excellent optical, thermal, electrical, and mechanical properties, making it an ideal wide-bandgap semiconductor material applicable to fields such as optics, medicine, detectors, and semiconductors.

[0003] Natural diamond production is limited, and the main methods for preparing synthetic diamonds are high-temperature high-pressure (HPHT) and MPCVD (microwave plasma chemical vapor deposition). The high-temperature high-pressure (HPHT) method is not advantageous in terms of impurity control and product size. Therefore, the main method for preparing single-crystal diamonds for semiconductor materials is the microwave plasma chemical vapor deposition method. The main problem with this method is that the grown single-crystal diamonds have high dislocation density and low growth rate.

[0004] CN113186597A discloses a low-cost, large-size, high-quality single-crystal diamond, its preparation method, and its applications. The specific method involves chemical vapor deposition (CVD), which improves the quality of diamond crystals by optimizing growth conditions. The technical drawbacks include a relatively slow growth rate and potential stress control and crystal defect issues during the preparation of large-size diamonds, which may affect the photoelectric properties and mechanical strength of the diamond.

[0005] CN115726030A discloses a method for preparing single-crystal diamond, including selecting seed crystals with similar heights for acid etching, preparing a substrate stage and depositing a carbon film on its surface, placing the acid-etched seed crystal into the coated substrate stage, and then performing microwave etching and growth using a mixed gas of methane, carbon dioxide, argon, and nitrogen. The technical drawback is that, although this method improves the temperature distribution on the seed crystal and promotes a smooth growth surface, maintaining consistency and controlling production costs remain challenges in the mass production of high-quality, high-smoothness single-crystal diamond.

[0006] CN116163015A describes a method for synthesizing single-crystal diamond based on microwave plasma chemical vapor deposition (PCCVD). This method primarily utilizes PCCVD to etch straw with hydrogen gas, generating a high-concentration carbon source gas as the carbon source for diamond synthesis, along with small amounts of oxygen and nitrogen source gases. This results in a smoother macroscopic surface of the synthesized diamond, reducing growth defects and improving crystal quality. Simultaneously, the specially designed support structure in the PCCVD apparatus concentrates the provided microwave electric field onto the single-crystal diamond substrate, effectively promoting high-speed diamond growth. However, this method has several technical drawbacks: low carbon source utilization, resulting in a significant waste of high-purity hydrogen; and the extremely high precision required for temperature and gas ratio control during PCCVD means that even minor deviations can lead to a decrease in diamond crystal quality, including crystal defects and uneven growth rates. Furthermore, this method may require complex equipment and precise operation, increasing preparation costs and technical difficulty.

[0007] Existing technologies suffer from high dislocation density and low growth rate in single-crystal diamond. Therefore, how to reduce the dislocation density of diamond and improve its growth efficiency has become an urgent problem to be solved. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a single-crystal diamond, its preparation method, and its applications. In the preparation method of the single-crystal diamond described in this invention, chlorine and hydrogen are used together during the chemical vapor deposition process to promote the selective growth of the diamond phase. Chlorine can help reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality of the diamond single crystal.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing single-crystal diamond, the method comprising the following steps:

[0011] The diamond seed crystal is etched; then carbon source, hydrogen and chlorine are introduced to deposit and grow single crystal diamond; after the deposition and growth are completed, post-processing is performed to obtain the single crystal diamond.

[0012] This invention promotes the selective growth of the diamond phase by simultaneously introducing chlorine and hydrogen during chemical vapor deposition. Chlorine helps reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality and growth rate of diamond single crystals and reducing dislocation density.

[0013] Chlorine exhibits high reactivity with non-diamond structures (such as graphite and amorphous carbon), but its reaction rate with carbon in diamond structures is relatively slow. Therefore, during single-crystal diamond chemical vapor deposition, chlorine atoms can rapidly react with non-diamond carbon structures to form volatile chlorinated carbon compounds, effectively removing non-diamond carbon without affecting the diamond phase structure, thus improving the growth quality of single-crystal diamond. Chlorine also helps remove impurities and contaminants from the surface, providing a cleaner surface for diamond growth. This not only contributes to improving diamond quality but also reduces the number of graphite phase nucleation sites that may be induced by impurities.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0015] Preferably, the flow rate ratio of the carbon source, hydrogen, and chlorine is (10-20):(300-400):(1-5), for example, it can be 10:300:1, 10:350:1, 10:400:1, 15:300:5, 15:350:4, 15:400:1, 20:300:1, 20:350:2, 20:400:2, 20:400:1, 20:400:3, 20:400:4, or 20:300:5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] In this invention, the flow ratio of carbon source, hydrogen, and chlorine is further controlled to (10-20):(300-400):(1-5). The role of hydrogen is to help activate chlorine molecules, making it easier for chlorine atoms to react with non-diamond carbon, thereby enhancing the overall etching effect. At the same time, it can stabilize the diamond surface, reduce its surface defects, and help maintain the stability of the diamond phase. The role of chlorine is etching, which can effectively remove the graphite phase while having little impact on the diamond phase. Maintaining an appropriate ratio between the two can maximize the quality of diamond single crystals. If the chlorine content is too high, the diamond surface will be over-etched, which may cause more defects. If the chlorine content is too low, the etching effect will be insignificant, the non-diamond phase structure will increase, and surface defects will be caused.

[0017] Preferably, the etching method includes: the etching process includes: under vacuum conditions, activating a mixed gas to etch the diamond seed crystal.

[0018] Preferably, the mixed gas comprises hydrogen and chlorine in a flow ratio of (95-99):(5-1), such as 95:5, 96:4, 97:3, 98:2 or 99:1, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] This invention introduces chlorine gas as an etchant during the seed crystal etching process, which can be used to remove unwanted carbon layers or defect areas, thereby improving the surface quality and smoothness of diamond.

[0020] Chlorine, as an etchant, exhibits high selectivity for the carbon structure of diamond (such as the graphite phase), effectively removing the graphite phase while having minimal impact on the diamond phase. Furthermore, chlorine can react with non-diamond carbon during growth to generate volatile chlorides, thereby reducing graphite accumulation and improving the quality of diamond single crystals. In contrast, oxygen etchants not only etch non-diamond carbon phases but also etch the diamond itself to some extent, potentially introducing more defects into the diamond surface, reducing quality, and leading to damage to the diamond layer or a decrease in growth rate.

[0021] When chlorine and hydrogen are used together, chlorine has an etching effect on non-diamond structures, while hydrogen itself has a certain etching ability, especially for the treatment of surface dangling bonds. At the same time, hydrogen can help activate chlorine molecules, making it easier for chlorine atoms to react with non-diamond carbon, thereby enhancing the overall etching effect. On the other hand, chlorine selectively removes non-diamond carbon, providing a cleaner growth environment for diamond, while hydrogen can stabilize the diamond surface, reduce its surface defects, and help maintain the stability of the diamond phase. The combination of the two results in a more stable diamond single crystal structure.

[0022] Preferably, the etching temperature is 600℃-1000℃, for example, it can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] Preferably, the etching pressure is 90mbar-120mbar, for example, it can be 90mbar, 100mbar, 110mbar or 120mbar, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the etching time is 30 min to 2 h, for example, it can be 30 min, 1 h, 1.5 h or 2 h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the purity of the hydrogen is 5N (99.999%) or 6N (99.9999%).

[0026] Preferably, the purity of the chlorine gas is 5N (99.999%) or 6N (99.9999%).

[0027] Preferably, the carbon source includes any one or a combination of at least two of methane, acetylene, propane, butane, carbon monoxide, or carbon dioxide. Typical but non-limiting combinations include combinations of methane and acetylene, methane and carbon monoxide, and methane and propane, with methane being the most preferred.

[0028] Preferably, the temperature during deposition and growth is 800℃-1200℃, for example, it can be 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0029] Preferably, the pressure during deposition growth is 100 mbar-200 mbar, for example, it can be 100 mbar, 110 mbar, 120 mbar, 130 mbar, 140 mbar, 150 mbar, 160 mbar, 170 mbar, 180 mbar, 190 mbar or 200 mbar, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0030] Preferably, the deposition growth time is greater than 100 hours, for example, it can be 100 hours, 110 hours, 120 hours, 130 hours, 140 hours, 150 hours, 160 hours, 170 hours, 180 hours, 190 hours or 200 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the post-processing involves reducing the surface of the single-crystal diamond under vacuum conditions.

[0032] Preferably, the flow rate of hydrogen used in the post-treatment process is 50 sccm-200 sccm, for example, it can be 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm, 100 sccm, 110 sccm, 120 sccm, 130 sccm, 140 sccm, 150 sccm, 160 sccm, 170 sccm, 180 sccm, 190 sccm or 200 sccm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0033] This invention uses hydrogen to post-treat diamond. Pure hydrogen gas flows over the diamond surface and reacts with chlorine to generate HCl gas, which is then discharged from the system with the gas flow. This method can not only effectively remove chlorine, but also repair some surface defects caused by unpaired carbon atoms.

[0034] During the post-processing of single-crystal diamond, when pure hydrogen gas (H2) flows over the diamond surface containing chlorine (Cl), the hydrogen reacts with chlorine atoms on or near the surface to produce hydrogen chloride (HCl). It can also react with chlorine compounds adsorbed on the diamond surface, removing chlorine while ensuring a more thorough cleaning. Hydrogen gas also has etching capabilities, effectively removing unwanted phase structures, resulting in a purer and smoother diamond surface. Unpaired carbon atoms (dangling bonds) may exist on the diamond surface, which can cause surface defects or affect electrical properties. Hydrogen gas can combine with these dangling bonds to form stable CH bonds, thereby reducing surface defects.

[0035] Preferably, the post-processing temperature is 500℃-1000℃, for example, it can be 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃ or 1000℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0036] Preferably, the post-processing time is 1-3 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0038] (1) Cleaning the diamond seed crystal: Place the diamond seed crystal in aqua regia, heat it in a water bath at 60℃-80℃ while performing a first ultrasonic treatment for 10min-40min, then perform a second ultrasonic treatment with ethanol and / or acetone for 10min-40min, and then perform a drying treatment; the aqua regia is a mixed solution of concentrated hydrochloric acid with a concentration of 36mol%-38mol% and concentrated nitric acid with a concentration of 65mol%-68mol% in a volume ratio of 3:1.

[0039] (2) Etching the diamond seed crystal: The diamond seed crystal is placed in a microwave plasma chemical vapor deposition equipment. The equipment is evacuated and hydrogen and chlorine are introduced at a flow ratio of (95-99):(5-1). The mixed gas absorbs microwave energy and generates mixed plasma. Under the conditions of 600℃-1000℃ and pressure of 90mbar-120mbar, the mixed plasma etches the diamond seed crystal for 30min-2h.

[0040] (3) Growth and preparation of single crystal diamond: Carbon source, hydrogen and chlorine are introduced into microwave plasma equipment at a flow ratio of (10-20):(300-400):(1-5). Single crystal diamond is deposited and grown on the diamond seed crystal after etching at 800℃-1200℃ and pressure of 100mbar-200mbar. The deposition and growth time is greater than 100h.

[0041] (4) Hydrogen reduction treatment: After growth, the single crystal diamond is treated with hydrogen at a flow rate of 50 sccm-200 sccm for 1-3 hours at 500℃-1000℃ to obtain the single crystal diamond.

[0042] Secondly, the present invention provides a single-crystal diamond prepared by the preparation method described in the first aspect, wherein the dislocation density of the single-crystal diamond is 50-230 dislocations / mm. 2 .

[0043] The single-crystal diamond prepared by this invention has a lower dislocation density and higher growth quality.

[0044] Thirdly, the present invention provides an application of single-crystal diamond as described in the second aspect, wherein the single-crystal diamond is used in the fields of optics, medicine, detectors and semiconductor devices.

[0045] The single-crystal diamond prepared by this invention has a lower dislocation density and is an ideal wide-bandgap semiconductor material that can be applied in fields such as optics, medicine, detectors and semiconductors.

[0046] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] (1) By introducing chlorine and hydrogen simultaneously during microwave plasma chemical vapor deposition, the present invention can promote the selective growth of diamond phase. Chlorine can help reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality and growth rate of diamond single crystals and reducing dislocation density.

[0049] (2) The single-crystal diamond prepared by this invention has a lower dislocation density and is an ideal wide bandgap semiconductor material that can be applied to fields such as optics, medicine, detectors and semiconductors. Detailed Implementation

[0050] The technical solution of the present invention will be further illustrated below through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0051] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0052] Example 1

[0053] This embodiment provides a method for preparing single-crystal diamond, the method comprising the following steps:

[0054] (1) Cleaning the diamond seed crystal: Place the diamond seed crystal in aqua regia, heat it in a water bath at 70°C while performing a first ultrasonic treatment for 30 minutes, then perform a second ultrasonic treatment with ethanol and acetone for 30 minutes, and then perform a drying treatment; the aqua regia consists of a mixed solution of concentrated hydrochloric acid with a concentration of 36 mol% and concentrated nitric acid with a concentration of 65 mol% in a volume ratio of 3:1.

[0055] (2) Etching the diamond seed crystal: The diamond seed crystal is placed in a microwave plasma chemical vapor deposition equipment. The equipment is evacuated and hydrogen and chlorine are introduced at a flow ratio of 97:3. The mixed gas absorbs microwave energy and generates mixed plasma. Under the conditions of 800℃ and 100mbar, the mixed plasma etches the diamond seed crystal for 1 hour.

[0056] (3) Growth and preparation of single crystal diamond: Carbon source, hydrogen and chlorine are introduced into microwave plasma equipment at a flow ratio of 15:350:3. Single crystal diamond is deposited and grown on the diamond seed crystal after etching at 1000℃ and 150mbar for 150h.

[0057] (4) Hydrogen reduction treatment: After the growth is completed, the single crystal diamond is treated with hydrogen at a flow rate of 100 sccm at 700℃ for 2 hours to obtain the single crystal diamond.

[0058] Example 2

[0059] This embodiment provides a method for preparing single-crystal diamond, the method comprising the following steps:

[0060] (1) Cleaning the diamond seed crystal: The diamond seed crystal is placed in aqua regia, heated in a water bath at 60°C and subjected to a first ultrasonic treatment for 40 minutes, followed by a second ultrasonic treatment with ethanol and acetone for 40 minutes, and then dried; the aqua regia is a mixed solution of concentrated hydrochloric acid with a concentration of 36 mol% and concentrated nitric acid with a concentration of 68 mol% in a volume ratio of 3:1.

[0061] (2) Etching the diamond seed crystal: The diamond seed crystal is placed in a microwave plasma chemical vapor deposition equipment. The equipment is evacuated and hydrogen and chlorine are introduced at a flow ratio of 99:1. The mixed gas absorbs microwave energy and generates mixed plasma. Under the conditions of 600℃ and 90mbar, the mixed plasma etches the diamond seed crystal for 2 hours.

[0062] (3) Growth and preparation of single crystal diamond: Carbon source, hydrogen and chlorine are introduced into microwave plasma equipment at a flow ratio of 10:300:1. Single crystal diamond is deposited and grown on the diamond seed crystal after etching at 800℃ and 100mbar for 180h.

[0063] (4) Hydrogen reduction treatment: After the growth is completed, the single crystal diamond is treated with hydrogen at 500℃ and a flow rate of 50 sccm for 3 hours to obtain the single crystal diamond.

[0064] Example 3

[0065] This embodiment provides a method for preparing single-crystal diamond, the method comprising the following steps:

[0066] (1) Cleaning the diamond seed crystal: Place the diamond seed crystal in aqua regia, heat it in an 80°C water bath while performing a first ultrasonic treatment for 40 min, then perform a second ultrasonic treatment with ethanol and / or acetone for 40 min, and then perform a drying treatment; the aqua regia consists of a mixed solution of concentrated hydrochloric acid with a concentration of 36 mol% and concentrated nitric acid with a concentration of 68 mol% in a volume ratio of 3:1.

[0067] (2) Etching the diamond seed crystal: The diamond seed crystal is placed in a microwave plasma chemical vapor deposition equipment. The equipment is evacuated and hydrogen and chlorine are introduced at a flow ratio of 95:5. The mixed gas absorbs microwave energy and generates mixed plasma. Under the conditions of 1000℃ and 120mbar, the mixed plasma etches the diamond seed crystal for 30 minutes.

[0068] (3) Growth and preparation of single crystal diamond: Carbon source, hydrogen and chlorine were introduced into the microwave plasma equipment at a flow ratio of 18:400:5. Single crystal diamond was deposited and grown on the diamond seed crystal after etching at 1200℃ and 200mbar for 120h.

[0069] (4) Hydrogen reduction treatment: After the growth is completed, the single crystal diamond is treated with hydrogen at a flow rate of 200 sccm at 1000℃ for 1 hour to obtain the single crystal diamond.

[0070] Example 4

[0071] This embodiment provides a method for preparing single-crystal diamond. The only difference from Embodiment 1 is that the flow ratio of methane, hydrogen and chlorine in step (3) is 15:350:0.05.

[0072] Example 5

[0073] This embodiment provides a method for preparing single-crystal diamond. The only difference from Embodiment 1 is that the flow ratio of methane, hydrogen and chlorine in step (3) is 15:350:7.

[0074] Example 6

[0075] This embodiment provides a method for preparing single-crystal diamond. The only difference from Embodiment 1 is that chlorine gas is not introduced during the etching process in step (2).

[0076] Example 7

[0077] This embodiment provides a method for preparing single-crystal diamond, which differs from Embodiment 1 only in that hydrogen gas is not introduced in step (4).

[0078] Comparative Example 1

[0079] This comparative example provides a method for preparing single-crystal diamond, which differs from Example 1 only in that chlorine gas is not introduced in step (3).

[0080] Test method: The dislocation density of the single-crystal diamonds prepared in the examples and comparative examples was tested using a transmission electron microscope. The test results are shown in Table 1 below.

[0081] Table 1

[0082] <![CDATA[Dislocation density (number / mm 2 )]]> Example 1 53 Example 2 55 Example 3 56 Example 4 85 Example 5 89 Example 6 230 Example 7 220 Comparative Example 1 260

[0083] The test results show that:

[0084] (1) As can be seen from Examples 1-3, the present invention can promote the selective growth of diamond phase by simultaneously introducing chlorine and hydrogen during microwave plasma chemical vapor deposition. Chlorine can help reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality of diamond single crystal.

[0085] (2) By comparing Example 1 with Examples 4-5, it can be seen that the present invention further controls the flow ratio of carbon source, hydrogen and chlorine to (10-20):(300-400):(1-5). The role of hydrogen is to make chlorine atoms more likely to react with non-diamond carbon, thereby enhancing the overall etching effect and stabilizing the diamond surface and reducing its surface defects. The role of chlorine is etching, which can effectively remove the graphite phase and has little effect on the diamond phase. Maintaining a suitable ratio between the two can improve the quality of diamond single crystal to a greater extent. If the chlorine content is too high, the etching will be over-etched, forming more surface defects and increasing the dislocation density. If the chlorine content is too low, the etching effect will be unsatisfactory, the non-diamond phase structure will increase, forming surface defects and increasing the dislocation density.

[0086] (3) By comparing Example 1 and Example 6, it can be seen that the present invention introduces chlorine gas as an etchant during the seed crystal etching process, which can be used to remove unwanted carbon layers or defect areas, thereby improving the surface quality and smoothness of diamond.

[0087] (4) By comparing Example 1 and Example 7, it can be seen that the present invention uses hydrogen to post-process diamond. When pure hydrogen flows over the diamond surface, it reacts with chlorine to generate HCl gas, which is then discharged out of the system with the gas flow. This method can not only effectively remove chlorine, but also repair some surface defects caused by unpaired carbon atoms.

[0088] (5) As can be seen from Example 1 and Comparative Example 1, the present invention can promote the selective growth of the diamond phase by simultaneously introducing chlorine and hydrogen during microwave plasma chemical vapor deposition. Chlorine can help reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality of diamond single crystals. When chlorine is not introduced during crystal growth, the dislocation density of the prepared single crystal diamond is higher.

[0089] In summary, this invention promotes the selective growth of the diamond phase by simultaneously introducing chlorine and hydrogen during microwave plasma chemical vapor deposition. Chlorine can help reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality of diamond single crystals.

[0090] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing single-crystal diamond, characterized in that, The preparation method includes the following steps: The diamond seed crystal is etched; then carbon source, hydrogen and chlorine are introduced to deposit and grow single crystal diamond; after the deposition and growth are completed, post-processing is performed to obtain the single crystal diamond. The etching process includes: under vacuum conditions, activating a mixed gas to etch the diamond seed crystal; the mixed gas includes hydrogen and chlorine with a flow ratio of (95-99):(5-1); The flow rate ratio of the carbon source, hydrogen and chlorine is (10-20):(300-400):(1-5).

2. The preparation method according to claim 1, characterized in that, The etching temperature is 600℃-1000℃.

3. The preparation method according to claim 1, characterized in that... The etching pressure is 90 mbar-120 mbar.

4. The preparation method according to claim 1, characterized in that, The etching time is 30 min to 2 h.

5. The preparation method according to claim 1, characterized in that, The carbon source includes any one or a combination of at least two of methane, acetylene, propane, butane, carbon monoxide, or carbon dioxide.

6. The preparation method according to claim 5, characterized in that, The carbon source is methane.

7. The preparation method according to claim 1, characterized in that, The temperature during deposition and growth is 800℃-1200℃.

8. The preparation method according to claim 1, characterized in that, The pressure during deposition and growth is 100 mbar-200 mbar.

9. The preparation method according to claim 1, characterized in that, The deposition and growth time is greater than 100 hours.

10. The preparation method according to claim 1, characterized in that, The post-processing involves reducing the surface of the single-crystal diamond under vacuum conditions.

11. The preparation method according to claim 1, characterized in that, The flow rate of hydrogen used in the post-treatment process is 50 sccm-200 sccm.

12. The preparation method according to claim 10, characterized in that, The post-processing temperature is 500℃-1000℃.

13. The preparation method according to claim 10, characterized in that, The post-processing time is 1-3 hours.

14. The preparation method according to claim 1, characterized in that, The etching process also includes cleaning the diamond seed crystal.

15. The preparation method according to claim 14, characterized in that, The specific cleaning steps include: placing the diamond seed crystal in aqua regia, heating it in a water bath at 60℃-80℃ while simultaneously performing a first ultrasonic treatment for 10min-40min, followed by a second ultrasonic treatment with an organic solvent for 10min-40min, and then drying it.

16. The preparation method according to claim 15, characterized in that, The organic solvents include ethanol and / or acetone.

17. The preparation method according to claim 15, characterized in that, The aqua regia comprises a mixed solution of concentrated hydrochloric acid (36 mol%-38 mol%) and concentrated nitric acid (65 mol%-68 mol%) in a volume ratio of 3:

1.

18. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Cleaning the diamond seed crystal: Place the diamond seed crystal in aqua regia, heat it in a water bath at 60℃-80℃ while performing a first ultrasonic treatment for 10min-40min, then perform a second ultrasonic treatment with ethanol and / or acetone for 10min-40min, and then perform a drying treatment; the aqua regia is a mixed solution of concentrated hydrochloric acid with a volume ratio of 3:1 and a concentration of 36mol%-38mol% and concentrated nitric acid with a concentration of 65mol%-68mol%. (2) Etching the diamond seed crystal: The diamond seed crystal is placed in a microwave plasma chemical vapor deposition equipment. The equipment is evacuated and hydrogen and chlorine are introduced at a flow ratio of (95-99):(5-1). The mixed gas absorbs microwave energy and generates mixed plasma. Under the conditions of 600℃-1000℃ and pressure of 90mbar-120mbar, the mixed plasma etches the diamond seed crystal for 30min-2h. (3) Growth and preparation of single crystal diamond: Carbon source, hydrogen and chlorine are introduced into microwave plasma equipment at a flow ratio of (10-20):(300-400):(1-5). Single crystal diamond is deposited and grown on the diamond seed crystal after etching at 800℃-1200℃ and pressure of 100mbar-200mbar. The deposition and growth time is greater than 100h. (4) Hydrogen reduction treatment: After growth, the single crystal diamond is treated with hydrogen at a flow rate of 50 sccm-200 sccm for 1-3 hours at 500℃-1000℃ to obtain the single crystal diamond.