Single crystal diamond and preparation method and application thereof

Abstract

The invention relates to a single crystal diamond and a preparation method and application thereof. The preparation method comprises the following steps: performing etching treatment on a diamond seed crystal; then introducing a carbon source, hydrogen and chlorine, and carrying out deposition growth of the monocrystal diamond; after deposition growth is finished, post-treatment is conducted, and the single crystal diamond is obtained. Chlorine and hydrogen are introduced in the chemical vapor deposition process at the same time, selective growth of a diamond phase can be promoted, chlorine can help to reduce formation of non-diamond carbon (such as graphite), and therefore the quality and the growth speed of diamond single crystals are improved, and the dislocation density is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to a single crystal diamond and a preparation method and application thereof. Background Art

[0002] Diamond has excellent optical, thermal, electrical and mechanical properties and is an ideal wide bandgap semiconductor material that can be used in optics, medicine, detectors and semiconductors.

[0003] The output of natural diamonds is limited, and the main methods for preparing artificial diamonds are the high temperature and high pressure method (HPHT method) and the MPCVD method (microwave plasma chemical vapor deposition method). The impurity control and product size of the high temperature and high pressure method (HPHT method) are not advantageous, so the main method for preparing single crystal diamonds for semiconductor materials is the microwave plasma chemical vapor deposition method. The main problem of this method is that the grown single crystal diamond has a high dislocation density and a low growth rate.

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

[0005] CN115726030A discloses a method for preparing single crystal diamond, including selecting seed crystals with similar height for pickling treatment, preparing a substrate table and coating a carbon film on the upper surface thereof, placing the pickled seed crystals on the coated substrate table, and then performing microwave etching and mixed gas growth of methane, carbon dioxide, argon, and nitrogen. The technical defect is that although this method improves the temperature distribution on the seed crystal and promotes the flatness of the growth surface, it is still a challenge to maintain consistency and control production costs in the process of mass production of high-quality and high-flatness single crystal diamonds.

[0006] CN116163015A A method for synthesizing single crystal diamond based on microwave plasma chemical vapor deposition technology, which mainly uses microwave plasma chemical deposition method to introduce hydrogen to etch straw, produce high-concentration carbon source gas as the carbon source for synthesizing diamond, and carry a small amount of oxygen source gas and nitrogen source gas, which can make the macroscopic surface of the synthesized diamond smoother, reduce the growth defects on the growth surface, and improve the crystal quality of diamond. At the same time, the design of the special structure of the support frame in the microwave plasma chemical deposition device can make the provided microwave electric field concentrated on the single crystal diamond substrate on the support frame, effectively promoting the high-speed growth of diamond. However, there are some technical defects in this preparation method: the carbon source utilization rate is low, resulting in a large amount of waste of high-purity hydrogen; at the same time, due to the extremely high control requirements for temperature and gas ratio during microwave plasma chemical vapor deposition, any slight deviation may lead to a decrease in the quality of diamond crystals, including crystal defects and uneven growth rate. In addition, this method may require complex equipment and precise operation, increasing the preparation cost and technical difficulty.

[0007] The existing technology has the defects of high dislocation density and low growth rate of single crystal diamond. Therefore, how to reduce the dislocation density of diamond and improve the growth efficiency has become a problem that needs to be solved urgently. Summary of the invention

[0008] In order to solve the above technical problems, the present invention aims to provide a single crystal diamond and a preparation method and use thereof. In the preparation method of single crystal diamond of the present invention, chlorine gas is used together with hydrogen gas during chemical vapor deposition to promote the selective growth of diamond phase. Chlorine gas can help reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality of diamond single crystal.

[0009] To achieve this object, the present invention adopts the following technical solutions:

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

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

[0012] The present invention can promote the selective growth of diamond phase by simultaneously introducing chlorine and hydrogen during chemical vapor deposition. 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.

[0013] Chlorine has a high reactivity to non-diamond structures (such as graphite and amorphous carbon), but it reacts slowly to carbon in diamond structures. Therefore, during the chemical vapor deposition of single-crystal diamond, chlorine atoms can quickly react with non-diamond carbon structures to form volatile chlorinated carbon compounds, thereby effectively removing non-diamond carbon, but without affecting the diamond phase structure, thus improving the growth quality of single-crystal diamond. Chlorine can also help remove impurities and contaminants on the surface, providing a cleaner surface for diamond growth. This not only helps to improve the quality of diamond, but also reduces the graphite phase nucleation sites that may be induced by the presence of 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. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] Preferably, the flow ratio of the carbon source, hydrogen and chlorine is (10-20):(300-400):(1-5), for example, it can be 10:300:110:350:110:400:1, 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, and other values ​​not listed within the numerical range are also applicable.

[0016] In the present invention, the flow rate ratio of the carbon source, hydrogen and chlorine is further controlled to be (10-20):(300-400):(1-5), wherein the role of hydrogen is to help activate chlorine molecules, so that chlorine atoms are more likely to react with non-diamond carbon, thereby enhancing the overall etching effect, and at the same time being able to 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 effect on the diamond phase. A suitable ratio is maintained between the two to further improve the quality of the diamond single crystal. If the content of chlorine is too much, the diamond surface is over-etched, which may cause more defects; if the content of chlorine is too little, the etching effect is not obvious, the non-diamond phase structure increases, and surface defects are caused.

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

[0018] Preferably, the mixed gas includes hydrogen and chlorine in a flow ratio of (95-99):(5-1), for example, it can be 95:5, 96:4, 97:3, 98:2 or 99:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] The present invention introduces chlorine as an etchant during the seed crystal etching process, which can be used to remove unnecessary carbon layers or defective areas, thereby improving the surface quality and flatness of the diamond.

[0020] As an etchant, chlorine has high selectivity for diamond carbon structures (such as graphite phase) and can effectively remove the graphite phase while having little effect on the diamond phase. At the same time, chlorine can react with non-diamond carbon in the growth process to generate volatile chlorides, thereby reducing the accumulation of graphite and improving the quality of diamond single crystals. Compared with common oxygen etchants, oxygen will not only etch the non-diamond carbon phase, but also etch the diamond itself to a certain extent, which may bring more defects to the diamond surface, reduce the quality, and also cause damage to the diamond layer or a decrease in the 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 chlorine atoms more likely to react with non-diamond carbon, thereby enhancing the overall etching effect. On the other hand, chlorine provides a cleaner growth environment for diamond by selectively removing non-diamond carbon. 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°C-1000°C, for example, it can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the etching pressure is 90 mbar-120 mbar, for example, 90 mbar, 100 mbar, 110 mbar or 120 mbar, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] Preferably, the etching time is 30 min-2 h, for example, 30 min, 1 h, 1.5 h or 2 h, but is not limited to the listed values, and other values ​​not listed within the numerical 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 comprises any one of methane, acetylene, propane, butane, carbon monoxide or carbon dioxide or a combination of at least two thereof. Typical but non-limiting combinations include a combination of methane and acetylene, a combination of methane and carbon monoxide, a combination of methane and propane, preferably methane.

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

[0029] Preferably, the pressure during the 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 numerical range are also applicable.

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

[0031] Preferably, the post-treatment is to perform reduction treatment on the surface of the single crystal diamond under vacuum.

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

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

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

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

[0036] Preferably, the post-treatment time is 1 h-3 h, for example, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

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

[0039] (2) Etching the diamond seed crystal: placing the diamond seed crystal in a microwave plasma chemical vapor growth device, evacuating the device, introducing hydrogen and chlorine at a flow ratio of (95-99):(5-1), the mixed gas absorbing microwave energy to generate mixed plasma, and etching the diamond seed crystal with the mixed plasma at 600° C.-1000° C. and a pressure of 90 mbar-120 mbar for 30 min-2 h;

[0040] (3) Preparation of single crystal diamond growth: A carbon source, hydrogen and chlorine are introduced into a microwave plasma device at a flow rate ratio of (10-20):(300-400):(1-5), and single crystal diamond is deposited and grown on the etched diamond seed crystal at 800°C-1200°C and a pressure of 100mbar-200mbar, and the deposition growth time is greater than 100h;

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

[0042] In a second aspect, the present invention provides a single crystal diamond prepared by the preparation method according to the first aspect, wherein the dislocation density of the single crystal diamond is 50-230 / mm 2 .

[0043] The single crystal diamond prepared by the present invention has lower dislocation density and higher growth quality.

[0044] In a third aspect, the present invention provides a use of the 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 the present invention has a lower dislocation density and is an ideal wide bandgap semiconductor material, and can be applied to the fields of optics, medicine, detectors, semiconductors, etc.

[0046] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists 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) 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 and growth rate of diamond single crystals and reducing dislocation density.

[0049] (2) The single crystal diamond prepared by the present invention has a lower dislocation density and is an ideal wide bandgap semiconductor material, which can be used in the fields of optics, medicine, detectors and semiconductors. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below by specific implementation methods. However, the following examples are only 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 shall be subject to the claims.

[0051] In the following examples and comparative examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0052] Example 1

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

[0054] (1) cleaning the diamond seed crystal: placing the diamond seed crystal in aqua regia, heating it in a water bath at 70° C. and performing a first ultrasonic treatment for 30 min, then performing a second ultrasonic treatment for 30 min using ethanol and acetone, and performing a drying treatment; the aqua regia comprises a mixed solution of 36 mol % concentrated hydrochloric acid and 65 mol % concentrated nitric acid in a volume ratio of 3:1;

[0055] (2) Etching the diamond seed crystal: placing the diamond seed crystal in a microwave plasma chemical vapor growth device, evacuating the device, introducing hydrogen and chlorine at a flow ratio of 97:3, the mixed gas absorbs microwave energy to generate mixed plasma, and the mixed plasma etches the diamond seed crystal for 1 hour at 800° C. and a pressure of 100 mbar;

[0056] (3) Preparation of single crystal diamond growth: A carbon source, hydrogen and chlorine gas were introduced into a microwave plasma device at a flow rate ratio of 15:350:3, and single crystal diamond was deposited and grown on the etched diamond seed crystal at 1000°C and a pressure of 150 mbar for 150 hours;

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

[0058] Example 2

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

[0060] (1) cleaning the diamond seed crystal: placing the diamond seed crystal in aqua regia, heating it in a water bath at 60° C. and performing a first ultrasonic treatment for 40 min, then performing a second ultrasonic treatment for 40 min using ethanol and acetone, and performing a drying treatment; the aqua regia comprises a mixed solution of 36 mol % concentrated hydrochloric acid and 68 mol % concentrated nitric acid in a volume ratio of 3:1;

[0061] (2) Etching the diamond seed crystal: placing the diamond seed crystal in a microwave plasma chemical vapor growth device, evacuating the device, introducing hydrogen and chlorine at a flow ratio of 99:1, and the mixed gas absorbs microwave energy to generate mixed plasma. The mixed plasma etches the diamond seed crystal for 2 hours at 600° C. and a pressure of 90 mbar;

[0062] (3) Preparation of single crystal diamond growth: A carbon source, hydrogen and chlorine were introduced into a microwave plasma device at a flow ratio of 10:300:1, and single crystal diamond was deposited and grown on the etched diamond seed crystal at 800°C and a pressure of 100 mbar for 180 hours;

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

[0064] Example 3

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

[0066] (1) cleaning the diamond seed crystal: placing the diamond seed crystal in aqua regia, heating it in a water bath at 80° C. and performing a first ultrasonic treatment for 40 minutes, then performing a second ultrasonic treatment for 40 minutes using ethanol and / or acetone, and performing a drying treatment; the aqua regia comprises a mixed solution of 36 mol % concentrated hydrochloric acid and 68 mol % concentrated nitric acid in a volume ratio of 3:1;

[0067] (2) Etching the diamond seed crystal: placing the diamond seed crystal in a microwave plasma chemical vapor growth device, evacuating the device, introducing hydrogen and chlorine at a flow ratio of 95:5, the mixed gas absorbs microwave energy to generate mixed plasma, and the mixed plasma etches the diamond seed crystal for 30 minutes at 1000° C. and a pressure of 120 mbar;

[0068] (3) Preparation of single crystal diamond growth: A carbon source, hydrogen and chlorine gas were introduced into a microwave plasma device at a flow ratio of 18:400:5, and single crystal diamond was deposited and grown on the etched diamond seed crystal at 1200°C and a pressure of 200 mbar for 120 hours;

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

[0070] Example 4

[0071] This embodiment provides a method for preparing single crystal diamond, which is different from Embodiment 1 only in 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, which is different from Embodiment 1 only in 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, which differs from Embodiment 1 only in 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 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 diamond prepared in the embodiment and the comparative example 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) It can be seen from Examples 1 to 3 that the present invention can promote the selective growth of the diamond phase by simultaneously introducing chlorine and hydrogen during the microwave plasma chemical vapor deposition process. Chlorine can help reduce the formation of non-diamond carbon (such as graphite), thereby improving the quality of diamond single crystals.

[0085] (2) By comparing Example 1 with Example 4-Example 5, it can be seen that the present invention further controls the flow rate ratio of carbon source, hydrogen and chlorine to (10-20):(300-400):(1-5), wherein the effect of hydrogen makes chlorine atoms more likely to react with non-diamond carbon, thereby enhancing the overall etching effect, while being able to stabilize the diamond surface and reduce its surface defects. The role of chlorine is etching, which can effectively remove the graphite phase while having little effect on the diamond phase. A suitable ratio is maintained between the two to improve the quality of the diamond single crystal to a greater extent. If the chlorine content is too much, the etching is excessive, more surface defects are formed, and the dislocation density increases; if the chlorine content is too little, the etching effect is not ideal, the non-diamond phase structure increases, surface defects are formed, and the dislocation density increases.

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

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

[0088] (5) It can be seen from Example 1 and Comparative Example 1 that the present invention can promote the selective growth of diamond phase by simultaneously introducing chlorine and hydrogen during microwave plasma chemical vapor deposition, and 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 the crystal growth process, the dislocation density of the prepared single crystal diamond is higher.

[0089] In summary, the present invention can promote the selective growth of diamond phase by simultaneously introducing chlorine and hydrogen during the microwave plasma chemical vapor deposition process. 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 is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing single crystal diamond, characterized in that: The preparation method comprises the following steps: The diamond seed crystal is etched; then a carbon source, hydrogen and chlorine are introduced to perform deposition growth of single crystal diamond; after the deposition growth is completed, post-treatment is performed to obtain the single crystal diamond.

2. The preparation method according to claim 1, characterized in that: The flow ratio of the carbon source, hydrogen and chlorine when introduced is (10-20):(300-400):(1-5).

3. The preparation method according to claim 1 or 2, characterized in that: The etching process comprises: exciting a mixed gas under vacuum conditions to etch the diamond seed crystal; Preferably, the mixed gas comprises hydrogen and chlorine in a flow ratio of (95-99):(5-1).

4. The preparation method according to any one of claims 1 to 3, characterized in that The etching temperature is 600°C-1000°C; Preferably, the etching pressure is 90mbar-120mbar; Preferably, the etching time is 30 min-2 h.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The carbon source includes any one of methane, acetylene, propane, butane, carbon monoxide or carbon dioxide, or a combination of at least two thereof, preferably methane.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The temperature during the deposition growth is 800°C-1200°C; Preferably, the pressure during the deposition growth is 100 mbar-200 mbar; Preferably, the deposition growth time is greater than 100 hours; Preferably, the post-treatment is to perform reduction treatment on the surface of the single crystal diamond under vacuum; Preferably, the flow rate of hydrogen used in the post-treatment process is 50sccm-200sccm; Preferably, the post-treatment temperature is 500°C-1000°C; Preferably, the post-treatment time is 1 h-3 h.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The step of cleaning the diamond seed crystal is also included before etching; Preferably, the specific steps of cleaning include: placing the diamond seed crystal in aqua regia, heating in a water bath at 60°C-80°C and performing a first ultrasonic treatment for 10min-40min, then performing a second ultrasonic treatment with an organic solvent for 10min-40min, and performing a drying treatment; Preferably, the organic solvent comprises ethanol and / or acetone; Preferably, the aqua regia comprises a mixed solution of concentrated hydrochloric acid with a concentration of 36 mol%-38 mol% and concentrated nitric acid with a concentration of 65 mol%-68 mol% in a volume ratio of 3:

1.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (1) Cleaning the diamond seed crystal: placing the diamond seed crystal in aqua regia, heating in a water bath at 60° C.-80° C. and performing a first ultrasonic treatment for 10 min-40 min, then performing a second ultrasonic treatment for 10 min-40 min using ethanol and / or acetone, and performing a drying treatment; the aqua regia comprises a mixed solution of concentrated hydrochloric acid with a concentration of 36 mol%-38 mol% and concentrated nitric acid with a concentration of 65 mol%-68 mol% in a volume ratio of 3:1; (2) Etching the diamond seed crystal: placing the diamond seed crystal in a microwave plasma chemical vapor growth device, evacuating the device, introducing hydrogen and chlorine at a flow ratio of (95-99):(5-1), the mixed gas absorbing microwave energy to generate mixed plasma, and etching the diamond seed crystal with the mixed plasma at 600° C.-1000° C. and a pressure of 90 mbar-120 mbar for 30 min-2 h; (3) Preparation of single crystal diamond growth: A carbon source, hydrogen and chlorine are introduced into a microwave plasma device at a flow rate ratio of (10-20):(300-400):(1-5), and single crystal diamond is deposited and grown on the etched diamond seed crystal at 800°C-1200°C and a pressure of 100mbar-200mbar, and the deposition growth time is greater than 100h; (4) Hydrogen reduction treatment: After the growth is completed, the single crystal diamond is treated with hydrogen at a flow rate of 50 sccm-200 sccm at 500° C.-1000° C. for 1 h-3 h to obtain the single crystal diamond.

9. A single crystal diamond, characterized in that: The single crystal diamond is prepared according to the preparation method according to any one of claims 1 to 8, and the dislocation density of the single crystal diamond is 50-230 / mm 2 .

10. Use of the single crystal diamond according to claim 9, characterized in that: The single crystal diamond is used in the fields of optics, medicine, detectors and semiconductor devices.