Single crystal diamond wafer and preparation method and application thereof

Abstract

The invention relates to a single crystal diamond wafer and a preparation method and application thereof, the preparation method comprises the following steps: (1) epitaxially growing second silicon carbide on a first silicon carbide substrate to form a second silicon carbide layer to obtain a first composite wafer; the crystal structure of the second silicon carbide is consistent with that of the single crystal diamond; (2) performing heat treatment and first laser treatment on the first composite wafer to remove silicon atoms in the second silicon carbide layer and form a crystal defect layer to obtain a second composite wafer; and (3) in mixed gas, carrying out in-situ deposition of carbon atoms on the crystal defect layer, and then removing the first silicon carbide substrate to obtain the monocrystal diamond wafer, the mixed gas comprises a carbon-containing reaction gas. According to the preparation method provided by the invention, the preparation of the large-size and high-performance single crystal diamond wafer is realized through the mutual cooperation of all processes.

Description

Technical Field

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

[0002] In recent years, new application scenarios such as super-fast charging of electric vehicles, ultra-high voltage power transmission and transformation, and large-scale energy storage have emerged continuously. The physicochemical properties of third-generation semiconductors are no longer sufficient to meet higher performance requirements. Fourth-generation ultra-wide bandgap semiconductor materials have begun to attract widespread attention due to their superior physicochemical properties, especially their bandgap far exceeding that of third-generation semiconductors, and have broad application potential in fields such as power electronics, radio frequency electronics, and deep ultraviolet optoelectronic devices. Among the candidate materials for fourth-generation semiconductors, diamond single crystal is hailed as the "ultimate semiconductor material" due to its excellent carrier mobility, thermal conductivity, dielectric breakdown strength, and ultra-wide bandgap and optical transparency from infrared to deep ultraviolet.

[0003] As a core material for fourth-generation semiconductors, diamond semiconductors possess characteristics such as ultra-wide bandgap, high breakdown field strength, and high carrier saturation drift velocity. Diamond is also one of the best thermally conductive materials in nature, with a thermal conductivity far exceeding that of traditional heat dissipation materials, effectively reducing the temperature of electronic devices. Furthermore, diamond exhibits excellent mechanical properties and chemical stability, ensuring long-term stable operation of devices. These characteristics make diamond substrates potentially suitable for developing high-temperature, high-frequency, and high-power semiconductor devices, overcoming technical bottlenecks such as self-heating and avalanche breakdown.

[0004] Despite the many advantages that make diamond a popular candidate for fourth-generation semiconductor materials, the technology for preparing diamond wafers is still immature, especially the technology for preparing high-performance single-crystal diamond wafers.

[0005] Currently, polycrystalline diamond can be prepared using the traditional high-temperature and high-pressure method, and then polycrystalline diamond wafers can be obtained by subsequent machining. For example, the prior art CN118767804A discloses a method for preparing high thermal conductivity polycrystalline diamond under high temperature and high pressure, including: mixing raw carbon source and catalyst, molding them under pressure using a mold, and assembling them together with pre-fabricated assembly components to form an integral synthetic block; placing the integral synthetic block in a quasi-static high-pressure device and subjecting it to high-temperature and high-pressure treatment under a pre-set synthesis pressure program to achieve epitaxial growth of diamond; then crushing the integral synthetic block to peel off polycrystalline diamond sheet samples; and removing the catalyst from the polycrystalline diamond sheet samples to obtain high thermal conductivity polycrystalline diamond sheets. This prior art uses different forms of carbon source as raw materials, and under high temperature and high pressure conditions, the carbon source is directly converted into polycrystalline diamond through the action of a catalyst.

[0006] However, due to the extreme hardness of diamond, machining polycrystalline diamond wafers is very difficult, and the largest polycrystalline diamond wafer that can be fabricated using traditional processes is no larger than 4 inches. Single-crystal diamond films can be fabricated on heterogeneous substrates such as silicon and silicon carbide using chemical vapor deposition, but currently, the size of single-crystal diamond wafers that can be fabricated using this process is no larger than 1 inch, far from meeting the industry's demand for high-performance, large-size wafers.

[0007] Therefore, providing a method for preparing high-performance, large-size single-crystal diamond wafers is a technical problem that urgently needs to be solved. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a single-crystal diamond wafer, its preparation method, and its applications. The single-crystal diamond wafer preparation method provided by the present invention grows a second silicon carbide layer with a crystal structure consistent with that of single-crystal diamond using epitaxial growth. Furthermore, it designs heat treatment, laser processing, and in-situ carbon atom deposition processes to promote homogeneous deposition, thereby achieving the preparation of large-size and high-performance single-crystal diamond wafers.

[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 a single-crystal diamond wafer, the method comprising the following steps:

[0011] (1) A second silicon carbide layer is epitaxially grown on the surface of a first silicon carbide substrate to obtain a first composite wafer; the crystal structure of the second silicon carbide is consistent with the crystal structure of single crystal diamond.

[0012] (2) The first composite wafer is subjected to heat treatment and first laser treatment to remove silicon atoms in the second silicon carbide layer and form a crystal defect layer on the surface of the first silicon carbide substrate to obtain the second composite wafer.

[0013] (3) In a mixed gas, carbon atoms are deposited in situ on the crystal defect layer in the second composite wafer, and then the first silicon carbide substrate is removed to obtain the single crystal diamond wafer; the mixed gas includes a carbon-containing reactive gas.

[0014] The present invention provides a method for preparing single-crystal diamond wafers. A second silicon carbide layer with the same crystal structure as the desired single-crystal diamond is epitaxially grown on the surface of a first silicon carbide substrate, forming a first composite wafer. Then, under heat treatment and a first laser treatment, silicon atoms in the second silicon carbide layer on the first composite wafer evaporate first, leaving carbon atoms in the second silicon carbide layer, forming a crystal defect layer in the second composite wafer. Subsequently, in a mixed gas containing carbon-containing reactive gases, carbon atoms in the mixed gas are deposited in situ on the crystal defect layer, filling the vacancies of the evaporated silicon atoms, thereby forming a single-crystal diamond wafer. This invention grows a second silicon carbide layer with the same crystal structure as single-crystal diamond through epitaxial growth. Furthermore, the designed heat treatment, laser treatment, and in-situ carbon atom deposition processes enable homogeneous deposition, which is beneficial for preparing large-size and high-performance single-crystal diamond wafers.

[0015] Preferably, in step (1), the size of the first silicon carbide substrate is 4 inches or more, such as 4 inches, 6 inches or 8 inches.

[0016] In this invention, the "size of the first silicon carbide substrate" refers to the maximum width on the surface of the first silicon carbide substrate.

[0017] Preferably, the first silicon carbide substrate is pretreated before the epitaxial growth of the second silicon carbide.

[0018] Preferably, the pretreatment includes polishing and cleaning performed sequentially.

[0019] Preferably, the polishing method includes chemical mechanical polishing.

[0020] Preferably, the surface smoothness of the polished first silicon carbide substrate is at the atomic level.

[0021] In this invention, the specific flatness of the surface of the polished first silicon carbide substrate is not specifically limited, as long as the flatness reaches the atomic level. Those skilled in the art can select the specific flatness as needed.

[0022] Preferably, the method for epitaxial growth of the second silicon carbide in step (1) includes chemical vapor deposition.

[0023] Preferably, the raw materials used for epitaxial growth of the second silicon carbide in step (1) include a carbon source and a silicon source.

[0024] Preferably, the carbon source includes methane.

[0025] Preferably, the silicon source includes silane or trichlorosilane.

[0026] Preferably, the molar ratio of the carbon source to the silicon source is 1:(0.8-1.8), such as 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7 or 1:1.8, etc.

[0027] In this invention, when silane is used as the silicon source, the molar ratio of the carbon source to the silicon source is 1:(0.8-1.2); when trichlorosilane is used as the silicon source, the molar ratio of the carbon source to the silicon source is 1:(1.2-1.8). The reasoning is as follows: Silane (SiH4) is a highly reactive silicon source, and when combined with the carbon source methane (CH4), it more easily forms a high-quality 3C-SiC epitaxial layer, with the best effect achieved when the stoichiometric ratio with the carbon source is close to 1:1. Trichlorosilane (SiHCl3), on the other hand, has lower reactivity. When mixed with the carbon source methane (CH4), it generates HCl, inhibiting rapid deposition. Therefore, it is necessary to increase the molar ratio of the silicon source to the carbon source to compensate for the reaction efficiency. A suitable high Si / C ratio helps improve interface quality and deposition rate.

[0028] Preferably, the carrier gas used in the epitaxial growth process in step (1) includes hydrogen.

[0029] Preferably, the epitaxial growth temperature in step (1) is 1400-1700℃, such as 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, 1650℃ or 1700℃.

[0030] Preferably, the thickness of the first silicon carbide substrate in step (1) is 400-750 μm, such as 400 μm, 450 μm, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm or 750 μm.

[0031] In this invention, the larger the size of the first silicon carbide substrate, the greater its thickness should be to prevent deformation or breakage of the composite wafer during subsequent high-temperature epitaxy and laser processing. Exemplarily, but not limitingly, when using a 4-inch first silicon carbide substrate, the thickness of the first silicon carbide substrate is preferably 450±50 μm; when using an 8-inch first silicon carbide substrate, the thickness of the first silicon carbide substrate is preferably 700±50 μm.

[0032] Preferably, the thickness of the second silicon carbide layer formed in step (1) is 5-10 nm, such as 5.0 nm, 5.5 nm, 6.0 nm, 6.5 nm, 7.0 nm, 7.5 nm, 8.0 nm, 8.5 nm, 9.0 nm, 9.5 nm or 10.0 nm.

[0033] Preferably, in step (1), the crystal structure of the first silicon carbide in the first silicon carbide substrate includes either the 4H crystal form or the 6H crystal form.

[0034] Preferably, the crystal structure of the second silicon carbide in the second silicon carbide layer formed in step (1) includes the 3C crystal form.

[0035] The second silicon carbide (3C-SiC) of the 3C crystal form used in this invention has the same crystal structure as the single-crystal diamond of the target product, both being cubic crystal systems. Therefore, a single-crystal diamond wafer can be obtained by removing silicon atoms from 3C-SiC and then depositing carbon atoms in situ. However, it is not yet possible to achieve stable industrial production of 3C-SiC with a size of 4 inches or larger. Therefore, it is necessary to select 4H or 6H crystal form silicon carbide with a large-size structure as a substrate, and epitaxially grow a larger size of 3C-SiC on its surface. On this basis, silicon removal and in-situ carbon atom deposition are performed on 3C-SiC to achieve a large-size single-crystal diamond wafer.

[0036] Preferably, the heat treatment in step (2) includes a first heat treatment and a second heat treatment.

[0037] Preferably, step (2) of performing heat treatment and first laser treatment on the first composite wafer includes: performing a first heat treatment on the first composite wafer, and then, under a second heat treatment condition, simultaneously using a first laser to heat the surface of the second silicon carbide layer in the first composite wafer, causing silicon atoms in the second silicon carbide layer to evaporate and form a crystal defect layer.

[0038] In this invention, the processing instrument used in the first laser processing and the wavelength of the first laser are not specifically limited. The only requirement is to ensure that silicon atoms in the second silicon carbide layer evaporate first during the second heat treatment and the first laser processing, while retaining carbon atoms in the second silicon carbide layer. Those skilled in the art can select specific laser processing instruments and set specific laser wavelengths as needed. Exemplarily, but not limitingly, the first laser processing can use an Nd:YAG laser with a wavelength of 1064 nm to achieve rapid evaporation of silicon atoms in the second silicon carbide layer.

[0039] In this invention, step (2) of the second heat treatment performed simultaneously with the first laser treatment process can be set to the same temperature conditions as the first heat treatment. Furthermore, the first heat treatment and the second heat treatment are continuous process operations. For example, the first composite wafer is first subjected to a preheating process of the first heat treatment for 30-60 minutes, and then the second heat treatment is performed at the same temperature. At the same time, the second silicon carbide layer in the first composite wafer is subjected to the first laser treatment during the second heat treatment process.

[0040] The purpose of the second heat treatment: During the first laser processing, the first composite wafer needs to undergo a second heat treatment process simultaneously to avoid a rapid increase in the local temperature of the wafer surface during the first laser processing of the first composite wafer, which would result in an excessive temperature difference on the surface of the first composite wafer, leading to cracking of the diamond wafer finally prepared.

[0041] Preferably, the temperature set for the first heat treatment is 800-1100℃, such as 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃ or 1100℃.

[0042] Preferably, the first heat treatment is performed under vacuum conditions.

[0043] Preferably, the holding time of the first heat treatment is 30-60 minutes, such as 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, or 60 minutes.

[0044] Preferably, the power of the first laser is 50-150W, such as 50W, 60W, 70W, 80W, 90W, 100W, 110W, 120W, 130W, 140W or 150W.

[0045] Preferably, the pulse width of the first laser is 10-30ns, such as 10ns, 15ns, 20ns, 25ns, or 30ns.

[0046] Preferably, the pulse frequency of the first laser is 20-50kHz, such as 20kHz, 25kHz, 30kHz, 35kHz, 40kHz, 45kHz or 50kHz.

[0047] Preferably, the focal diameter of the first laser is 50-100μm, such as 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm or 100μm.

[0048] Preferably, the scanning speed of the first laser is 500-2000 mm / s, such as 500 mm / s, 600 mm / s, 700 mm / s, 800 mm / s, 900 mm / s, 1000 mm / s, 1100 mm / s, 1200 mm / s, 1300 mm / s, 1400 mm / s, 1500 mm / s, 1600 mm / s, 1700 mm / s, 1800 mm / s, 1900 mm / s, or 2000 mm / s.

[0049] Preferably, the first laser processing uses either a single-beam laser system or a multi-beam laser system, preferably a multi-beam laser system, such as a 2-beam laser system, a 4-beam laser system, a 6-beam laser system, or an 8-beam laser system, and more preferably a 4-beam laser system.

[0050] The present invention employs a multi-beam laser system, particularly a 4-beam laser system for parallel processing, in the first laser processing stage. This ensures high scanning efficiency without being too complex to implement due to the structure of the multi-beam laser system.

[0051] Preferably, the temperature set for the second heat treatment is 800-1100℃, such as 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃ or 1100℃.

[0052] In this invention, the “set temperature” for the first heat treatment and the second heat treatment refers to the set temperature of the equipment used to perform the first heat treatment and the second heat treatment.

[0053] The present invention regulates the temperature of the first and second heat treatment settings in two ways: first, it can enhance the thermal activation of the material surface, increase silicon atom migration and surface desorption rate; second, it can enhance the laser absorption rate of the material and avoid the generation of thermal stress cracks.

[0054] Preferably, the second heat treatment is performed under vacuum conditions.

[0055] Preferably, during the simultaneous second heat treatment and the first laser treatment, the local temperature of the surface of the second silicon carbide layer in the first composite wafer is 2400-3600℃, such as 2400℃, 2500℃, 2600℃, 2700℃, 2800℃, 2900℃, 3000℃, 3100℃, 3200℃, 3300℃, 3400℃, 3500℃, or 3600℃.

[0056] In this invention, the "local temperature of the surface of the second silicon carbide layer" refers to the temperature of the surface of the second silicon carbide layer when it is laser-treated under the conditions of the second heat treatment.

[0057] In this invention, the surface of the second silicon carbide layer is heated by laser scanning. Under the conditions of the second heat treatment, the temperature of the laser-treated surface of the second silicon carbide layer is raised to a specific temperature range. This temperature range is maintained above the temperature at which silicon atoms evaporate and below the temperature at which carbon atoms sublimate. Within this stable range, the temperature can be as high as possible so that the silicon atoms in the second silicon carbide layer evaporate rapidly, but the sublimation of carbon atoms is avoided, and carbon atoms are retained.

[0058] During the simultaneous second heat treatment and first laser treatment, the present invention can use an infrared temperature measuring device to monitor the surface temperature of the second silicon carbide layer in real time, ensuring that the surface temperature does not exceed the sublimation temperature of carbon atoms.

[0059] Preferably, the time for simultaneously performing the second heat treatment and the first laser treatment is 20-100s, such as 20s, 30s, 40s, 50s, 60s, 70s, 80s, 90s or 100s.

[0060] Preferably, in the mixed gas of step (3), the concentration of the carbon-containing reaction gas is 1-5 vol%, for example, 1 vol%, 2 vol%, 3 vol%, 4 vol%, or 5 vol%.

[0061] Preferably, the carbon-containing reaction gas in step (3) includes methane.

[0062] Preferably, the mixed gas in step (3) further includes a carrier gas.

[0063] Preferably, in the mixed gas in step (3), the carrier gas includes hydrogen.

[0064] Preferably, during the in-situ deposition of carbon atoms in step (3), a second laser is used to irradiate the mixed gas, and carbon atoms are decomposed in the reaction gas of the mixed gas for in-situ deposition on the crystal defect layer.

[0065] In this invention, the laser equipment used for the second laser processing and the wavelength of the second laser are not specifically limited, as long as the second laser can decompose carbon atoms from the carbon-containing reaction gas under irradiation of the mixed gas. Those skilled in the art can select the appropriate equipment as needed. Exemplarily, but not limitingly, the second laser can be a CO2 laser with a wavelength of 10.6 μm, to achieve the decomposition of carbon atoms from the carbon-containing reaction gas under irradiation of the mixed gas.

[0066] In this invention, the beam of the second laser used for the second laser processing is not specifically limited, including but not limited to a single-beam laser system, a two-beam laser system or a four-beam laser system, and those skilled in the art can choose according to their needs.

[0067] Preferably, in the in-situ deposition of carbon atoms in step (3), the temperature is set to 800-1100℃, such as 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃ or 1100℃.

[0068] This invention uses laser irradiation to decompose carbon-containing reactive gases in the mixed gas. During this process, the in-situ deposition equipment can be set to a lower temperature to achieve low-temperature in-situ deposition on crystal defect layers, while avoiding the graphitization of deposited carbon.

[0069] Preferably, in the in-situ deposition of carbon atoms in step (3), the pressure is set to 1-10 kPa, such as 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa or 10 kPa.

[0070] Preferably, after the in-situ deposition of carbon atoms in step (3) and before removing the first silicon carbide substrate, carbon atom deposition is further performed on the surface of the layer structure obtained after the in-situ deposition of carbon atoms.

[0071] In this invention, after the in-situ deposition of carbon atoms, carbon atom deposition continues. The carbon atoms decomposed from the carbon-containing reactive gas are first deposited in situ to fill the silicon atom vacancies in the crystal defect layer. After the vacancies in the crystal defect layer are completely filled with carbon atoms, a single-crystal diamond layer is formed. The grown single-crystal diamond layer serves as a new substrate, and carbon atom deposition continues on its surface to obtain a single-crystal diamond layer with gradually increasing thickness, thereby forming a single-crystal diamond wafer with a relatively thick thickness and a large size.

[0072] Preferably, during the continued deposition of carbon atoms, the temperature is set to 800-1100℃, such as 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, or 1100℃.

[0073] Preferably, during the continued deposition of carbon atoms, the pressure is set to 1-10 kPa, such as 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa or 10 kPa.

[0074] In this invention, the "set temperature" and "set pressure" in the carbon atom deposition process refer to the temperature and pressure set by the deposition equipment during the deposition process.

[0075] Preferably, the total time for the in-situ deposition of carbon atoms and the continued deposition of carbon atoms is 50-200 hours, such as 50 hours, 75 hours, 100 hours, 125 hours, 150 hours, 175 hours or 200 hours.

[0076] Preferably, step (3) involves removing the first silicon carbide substrate by chemical mechanical polishing.

[0077] Preferably, after removing the first silicon carbide substrate in step (3), the edges of the remaining components are also polished.

[0078] As a preferred embodiment of the present invention, the method for preparing the single-crystal diamond wafer includes the following steps:

[0079] S1. A first silicon carbide substrate with a thickness of 400-750μm is polished by chemical mechanical polishing to make the surface smoothness of the polished first silicon carbide substrate atomic level. The polished first silicon carbide substrate is then cleaned to remove impurities and oxides from the surface of the first silicon carbide substrate, resulting in a pretreated first silicon carbide substrate.

[0080] The first silicon carbide in the first silicon carbide substrate has a crystal structure including either 4H or 6H crystal forms; the size of the first silicon carbide substrate is 4 inches or more.

[0081] S2. Using carbon and silicon sources with a molar ratio of 1:(0.8-1.8) as raw materials and hydrogen as carrier gas, a second silicon carbide is epitaxially grown on the surface of one side of the pretreated first silicon carbide substrate by chemical vapor deposition. The epitaxial growth temperature is 1400-1700℃, forming a second silicon carbide layer with a thickness of 5-10nm, to obtain a first composite wafer; the crystal structure of the second silicon carbide in the second silicon carbide layer includes the 3C crystal form.

[0082] S3. The first composite wafer undergoes a first heat treatment in a vacuum environment at a temperature of 800-1100℃ for 30-60 minutes. Then, a second heat treatment is performed in the vacuum environment at the same temperature. Simultaneously, a first laser is used to heat the surface of the second silicon carbide layer in the first composite wafer. The first laser has a power of 50-150W, a pulse width of 10-30ns, a pulse frequency of 20-50kHz, a focal diameter of 50-100μm, and a scanning speed of 500-2000mm / s. The first laser processing employs either a single-beam laser system or a multi-beam laser system. During the simultaneous second heat treatment and the first laser processing, the local surface temperature of the second silicon carbide layer in the first composite wafer is 2400-3600℃, and the duration of the simultaneous second heat treatment and the first laser processing is 20-100s. During the simultaneous second heat treatment and the first laser processing, silicon atoms in the second silicon carbide layer evaporate to remove silicon atoms from the second silicon carbide layer, forming a crystal defect layer on the surface of the first silicon carbide substrate, thereby obtaining the second composite wafer.

[0083] S4. A mixed gas is formed using methane as the reactant gas and hydrogen as the carrier gas, wherein the concentration of the reactant gas in the mixed gas is 1-5 vol%. The mixed gas is irradiated with a second laser to decompose carbon atoms in the reactant gas of the mixed gas. Carbon atoms are deposited in situ on the crystal defect layer in the second composite wafer. Then, carbon atoms are deposited on the surface of the layer structure obtained after the in-situ deposition of carbon atoms to obtain a third composite wafer. The temperature set during the in-situ deposition of carbon atoms and the continued deposition of carbon atoms are independently selected from 800-1100°C, and the pressure is independently selected from 1-10 kPa. The total time for the in-situ deposition of carbon atoms and the continued deposition of carbon atoms is 50-200 h. Then, the first silicon carbide substrate in the third composite wafer is removed by chemical mechanical polishing, and the edges of the remaining components are polished to obtain the single crystal diamond wafer.

[0084] In a second aspect, the present invention provides a single-crystal diamond wafer, which is prepared by the preparation method described in the first aspect.

[0085] The single-crystal diamond wafer provided by this invention is prepared by a specific method and has the advantages of large size and excellent performance.

[0086] Preferably, the thickness of the single-crystal diamond wafer is 10-100μm, such as 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm.

[0087] Preferably, the size of the single-crystal diamond wafer is 4 inches or more.

[0088] In this invention, "the size of the single-crystal diamond wafer" refers to the maximum width of the surface of the single-crystal diamond wafer, which is the size of the single-crystal diamond wafer.

[0089] Thirdly, the present invention provides a single-crystal diamond wafer according to the second aspect, the single-crystal diamond wafer being used in the fields of semiconductors, optics, quantum technology or machining.

[0090] The single-crystal diamond wafer provided by this invention can be applied to any field that can be conceived by those skilled in the art.

[0091] Compared with the prior art, the present invention has at least the following beneficial effects:

[0092] The present invention provides a method for preparing single-crystal diamond wafers. A second silicon carbide layer with the same crystal structure as the desired single-crystal diamond is epitaxially grown on the surface of a first silicon carbide substrate, forming a first composite wafer. Then, under heat treatment and a first laser treatment, silicon atoms in the second silicon carbide layer on the first composite wafer evaporate first, leaving carbon atoms in the second silicon carbide layer, forming a crystal defect layer in the second composite wafer. Subsequently, in a mixed gas containing carbon-containing reactive gases, carbon atoms in the mixed gas are deposited in situ on the crystal defect layer, filling the vacancies of the evaporated silicon atoms, thereby forming a single-crystal diamond wafer. This invention grows a second silicon carbide layer with the same crystal structure as single-crystal diamond through epitaxial growth. Furthermore, the designed heat treatment, laser treatment, and in-situ carbon atom deposition processes enable homogeneous deposition, which is beneficial for preparing large-size and high-performance single-crystal diamond wafers. Attached Figure Description

[0093] Figure 1 This is a schematic diagram of the crystal structure of the 4H-SiC substrate provided in Example 1.

[0094] Figure 2 This is a partially enlarged schematic diagram of the crystal structure of the 4H-SiC substrate provided in Example 1.

[0095] Figure 3 This is a schematic diagram of the crystal structure of the first composite wafer provided in Example 1.

[0096] Figure 4 This is a partially enlarged schematic diagram of the crystal structure of the first composite wafer provided in Example 1.

[0097] Figure 5 This is a schematic diagram of the crystal structure of the second composite wafer provided in Example 1.

[0098] Figure 6 This is a partially enlarged schematic diagram of the crystal structure of the second composite wafer provided in Example 1.

[0099] Figure 7 This is a schematic diagram of the crystal structure of the third composite wafer provided in Example 1.

[0100] Figure 8 This is a partially enlarged schematic diagram of the crystal structure of the third composite wafer provided in Example 1.

[0101] Figure 9 This is a schematic diagram of the crystal structure of the 6H-SiC substrate provided in Example 3.

[0102] Figure 10 This is a partially enlarged schematic diagram of the crystal structure of the 6H-SiC substrate provided in Example 3.

[0103] Figure 11 This is a schematic diagram of the crystal structure of the first composite wafer provided in Example 3.

[0104] Figure 12 This is a partially enlarged schematic diagram of the crystal structure of the first composite wafer provided in Example 3.

[0105] Figure 13 This is a schematic diagram of the crystal structure of the second composite wafer provided in Example 3.

[0106] Figure 14 This is a partially enlarged schematic diagram of the crystal structure of the second composite wafer provided in Example 3.

[0107] Figure 15 This is a schematic diagram of the crystal structure of the third composite wafer provided in Example 3.

[0108] Figure 16 This is a partially enlarged schematic diagram of the crystal structure of the third composite wafer provided in Example 3.

[0109] Among them, 1, 4H-SiC substrate; 2, 3C-silicon carbide layer; 3, crystal defect layer; 4, single crystal diamond wafer; 5, 6H-SiC substrate. Detailed Implementation

[0110] The technical solution of the present invention will be further described below with reference to the accompanying drawings and 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.

[0111] Example 1

[0112] This embodiment provides a method for preparing a single-crystal diamond wafer, the specific steps of which are as follows:

[0113] S1. A 4-inch 4H-SiC substrate 1 with a thickness of 400 μm was polished using chemical mechanical polishing (CMP). This resulted in an atomically smooth surface. The polished 4H-SiC substrate 1 was then cleaned to remove impurities and oxides from its surface, yielding a pretreated 4H-SiC substrate 1. Its crystal structure is shown in the schematic diagram below. Figure 1 As shown, a partially enlarged schematic diagram of the crystal structure is as follows: Figure 2 As shown, 4H-SiC is stacked in an ABCB configuration.

[0114] S2. Using methane and silane in a molar ratio of 1:1 as raw materials and hydrogen as the carrier gas, 3C-silicon carbide is epitaxially grown on one side of the pretreated 4H-SiC substrate 1 obtained in step S1 using chemical vapor deposition. The epitaxial growth temperature is 1500℃, forming a 6nm thick 3C-silicon carbide layer 2, thus obtaining the first composite wafer. Its crystal structure schematic diagram is shown below. Figure 3 As shown, a partially enlarged schematic diagram of the crystal structure is as follows: Figure 4 As shown, the 3C-SiC in the 3C-silicon carbide layer 2 is stacked in an ABC configuration.

[0115] S3. The first composite wafer obtained in step S2 is subjected to a first heat treatment in a vacuum environment. The temperature of the first heat treatment is set at 900℃, and the holding time is 50 minutes. Then, a second heat treatment is performed at the set temperature of 900℃ in a vacuum environment. Simultaneously, a first laser emitted from an Nd:YAG laser is used to heat the surface of the 3C-silicon carbide layer 2 in the first composite wafer, maintaining the local temperature on the surface of the 3C-silicon carbide layer 2 during laser treatment at 3000±4℃. The time for both the second heat treatment and the first laser heating is... The first laser treatment lasted 50 seconds. Its wavelength was 1064 nm, power was 100 W, pulse width was 20 ns, pulse frequency was 30 kHz, focal diameter was 75 μm, and scanning speed was 1000 mm / s. The first laser treatment employed a four-beam laser system for parallel processing. Under simultaneous second heat treatment and first laser treatment, silicon atoms in the 3C-silicon carbide layer 2 were completely evaporated, removing the silicon atoms from the 3C-silicon carbide layer 2. This resulted in the formation of a crystal defect layer 3 on the surface of the 4H-SiC substrate 1, yielding the second composite wafer. A schematic diagram of its crystal structure is shown below. Figure 5 As shown, a partially enlarged schematic diagram of the crystal structure is as follows: Figure 6 As shown.

[0116] S4. A mixed gas is formed using methane as the reactant gas and hydrogen as the carrier gas. The concentration of methane in the mixed gas is 3 vol%. A second laser emitted from a CO2 laser is used to irradiate the mixed gas, activating the methane gas and causing it to decompose into carbon atoms. Carbon atoms are then deposited in situ on the crystal defect layer 3 of the second composite wafer obtained in step S3. Next, carbon atom deposition continues on the surface of the layer structure obtained after the in-situ carbon atom deposition, resulting in a third composite wafer. A schematic diagram of its crystal structure is shown below. Figure 7 As shown, a partially enlarged schematic diagram of the crystal structure is as follows: Figure 8As shown, during the in-situ carbon atom deposition and the continued carbon atom deposition process, the wavelength of the second laser was 10.6 μm, the temperature for both the in-situ and continued carbon atom deposition was 900 °C, the pressure was 4 kPa, and the total time for both was 120 h. Then, chemical mechanical polishing was used to remove the 4H-SiC substrate 1 from the third composite wafer, and the edges of the remaining components were polished to obtain a single crystal diamond wafer 4 with a thickness of 54 μm and a size of 4 inches. The single crystal diamond wafer 4 was also stacked in an ABC configuration.

[0117] Example 2

[0118] This embodiment provides a method for preparing a single-crystal diamond wafer, the specific steps of which are as follows:

[0119] S1. A 6-inch 4H-SiC substrate is polished using chemical mechanical polishing. The thickness of the 4H-SiC substrate is 600μm, so that the surface smoothness of the polished 4H-SiC substrate is at the atomic level. The polished 4H-SiC substrate is then cleaned to remove impurities and oxides from the substrate surface, resulting in a pretreated 4H-SiC substrate.

[0120] S2. Using methane and trichlorosilane in a molar ratio of 1:1.5 as raw materials and hydrogen as carrier gas, 3C-silicon carbide is epitaxially grown on one side of the pretreated 4H-SiC substrate obtained in step S1 by chemical vapor deposition. The epitaxial growth temperature is 1400℃, forming a 3C-silicon carbide layer with a thickness of 5nm, thus obtaining the first composite wafer.

[0121] S3. The first composite wafer obtained in step S2 is subjected to a first heat treatment in a vacuum environment. The temperature of the first heat treatment is set at 800℃ and the holding time is 60min. Then, a second heat treatment is performed at the set temperature of 800℃ in a vacuum environment. At the same time, the surface of the 3C-silicon carbide layer in the first composite wafer is heated by the first laser emitted by the Nd:YAG laser. The local temperature on the surface of the 3C-silicon carbide layer during laser treatment is maintained at 2410±3℃. The time for the second heat treatment and the first laser heating is 100s. The wavelength of the first laser is 1064nm, the power is 50W, the pulse width is 10ns, the pulse frequency is 20kHz, the focal diameter is 50μm, and the scanning speed is 500mm / s. The first laser treatment is performed in parallel by a four-beam laser system. Under the simultaneous second heat treatment and the first laser treatment, the silicon atoms in the 3C-silicon carbide layer are completely evaporated to remove the silicon atoms in the 3C-silicon carbide layer, forming a crystal defect layer on the surface of the 4H-SiC substrate, thus obtaining the second composite wafer.

[0122] S4. A mixed gas is formed using methane as the reactant gas and hydrogen as the carrier gas. The concentration of the reactant gas in the mixed gas is 1 vol%. The mixed gas is irradiated with a second laser emitted by a CO2 laser to activate the methane gas in the mixed gas. Carbon atoms are decomposed in the methane gas and deposited in situ on the crystal defect layer of the second composite wafer obtained in step S3. Then, carbon atoms are deposited on the surface of the layer structure obtained after the in-situ carbon atom deposition to obtain a third composite wafer. During the in-situ carbon atom deposition and the continued carbon atom deposition, the wavelength of the second laser is 10.6 μm, the temperature set for the in-situ carbon atom deposition and the continued carbon atom deposition is 800 °C, the pressure is 1 kPa, and the total time for the in-situ carbon atom deposition and the continued carbon atom deposition is 200 h. Then, the 4H-SiC substrate 1 in the third composite wafer is removed by chemical mechanical polishing, and the edges of the remaining components are polished to obtain a single crystal diamond wafer with a thickness of 40 μm and a size of 6 inches.

[0123] Example 3

[0124] This embodiment provides a method for preparing a single-crystal diamond wafer, the specific steps of which are as follows:

[0125] S1. An 8-inch 6H-SiC substrate 1 was polished using chemical mechanical polishing. The thickness of the 6H-SiC substrate 1 was 750 μm, resulting in an atomic-level surface smoothness. The polished 6H-SiC substrate 1 was then cleaned to remove impurities and oxides from its surface, yielding a pretreated 6H-SiC substrate 1. Its crystal structure diagram is shown below. Figure 9 As shown, a partially enlarged schematic diagram of the crystal structure is as follows: Figure 10 As shown, 6H-SiC is stacked in an ABCACB configuration.

[0126] S2. Using methane and trichlorosilane in a molar ratio of 1:1.8 as raw materials and hydrogen as the carrier gas, 3C-silicon carbide is epitaxially grown on one side of the pretreated 6H-SiC substrate 1 obtained in step S1 using chemical vapor deposition. The epitaxial growth temperature is 1700℃, forming a 10nm thick 3C-silicon carbide layer 2, thus obtaining the first composite wafer. Its crystal structure schematic diagram is shown below. Figure 11 As shown, a partially enlarged schematic diagram of the crystal structure is as follows: Figure 12 As shown, the 3C-SiC in the 3C-silicon carbide layer 2 is stacked in an ABC configuration.

[0127] S3. The first composite wafer obtained in step S2 is subjected to a first heat treatment in a vacuum environment. The temperature of the first heat treatment is set at 1100℃, and the holding time is 30 minutes. Then, a second heat treatment is performed at the set temperature of 1100℃ in a vacuum environment. At the same time, the surface of the 3C-silicon carbide layer 2 in the first composite wafer is heated by the first laser emitted by the Nd:YAG laser. The local temperature on the surface of the 3C-silicon carbide layer 2 during laser treatment is maintained at 3590±5℃. The time for the second heat treatment and the first laser heating are simultaneously... The first laser treatment lasts for 20 seconds. Its wavelength is 1064 nm, power is 150 W, pulse width is 30 ns, pulse frequency is 50 kHz, focal diameter is 100 μm, and scanning speed is 2000 mm / s. The first laser treatment uses a four-beam laser system for parallel processing. Under simultaneous second heat treatment and first laser treatment, silicon atoms in the 3C-silicon carbide layer 2 are completely evaporated to remove silicon atoms from the 3C-silicon carbide layer 2, forming a crystal defect layer 3 on the surface of the 6H-SiC substrate 1, resulting in the second composite wafer. A schematic diagram of its crystal structure is shown below. Figure 13 As shown, a partially enlarged schematic diagram of the crystal structure is as follows: Figure 14 As shown.

[0128] S4. A mixture of methane as the reactant gas and hydrogen as the carrier gas is formed, with a reactant gas concentration of 5 vol%. The mixture is irradiated with a second laser emitted from a CO2 laser to activate the methane gas, causing it to decompose and release carbon atoms. Carbon atoms are then deposited in situ on the crystal defect layer 3 of the second composite wafer obtained in step S3. Next, carbon atom deposition continues on the surface of the resulting layer structure to obtain a third composite wafer, the crystal structure of which is shown in the schematic diagram below. Figure 15 As shown, a partially enlarged schematic diagram of the crystal structure is as follows: Figure 16 As shown, during the in-situ carbon atom deposition and the continued carbon atom deposition process, the wavelength of the second laser was 10.6 μm, the temperature for both the in-situ and continued carbon atom deposition was 1100 °C, the pressure was 10 kPa, and the total time for both was 50 h. Then, the 6H-SiC substrate 1 in the third composite wafer was removed by chemical mechanical polishing, and the edges of the remaining components were polished to obtain a single crystal diamond wafer 4 with a thickness of 35 μm and a size of 8 inches. The single crystal diamond wafer 4 was also stacked in an ABC configuration.

[0129] Example 4

[0130] The difference between this embodiment and Embodiment 1 is as follows: the temperature of both the first and second heat treatments in step S3 is 800℃; the methane gas concentration used in step S4 is 2 vol%, the pressure during carbon atom deposition is 1 kPa, the temperature set for both in-situ carbon atom deposition and continued deposition is 800℃, and the total time for both in-situ and continued carbon atom deposition is 50 h; correspondingly, the thickness of the single-crystal diamond wafer obtained is 10 μm. All other aspects are the same as in Embodiment 1.

[0131] Example 5

[0132] The difference between this embodiment and Embodiment 1 is as follows: the temperature of the first and second heat treatments in step S3 is 1050℃; the methane gas concentration used in step S4 is 5 vol%, the pressure during carbon atom deposition is 6 kPa, the temperature set for both in-situ carbon atom deposition and continued deposition is 1050℃, and the total time for in-situ carbon atom deposition and continued carbon atom deposition is 150 h; correspondingly, the thickness of the prepared single-crystal diamond wafer is 100 μm. All other aspects are the same as in Embodiment 1.

[0133] Example 6

[0134] The only difference between this embodiment and Embodiment 1 is that step S1, which involves polishing and cleaning the 4H-SiC substrate, is omitted. All other aspects are the same as in Embodiment 1.

[0135] Example 7

[0136] The only difference between this embodiment and Embodiment 1 is that the thickness of the 3C-silicon carbide layer formed by epitaxial growth in step S2 is 3 nm. All other aspects are the same as in Embodiment 1.

[0137] Example 8

[0138] The only difference between this embodiment and Embodiment 1 is that the thickness of the 3C-silicon carbide layer formed by epitaxial growth in step S2 is 12 nm. All other aspects are the same as in Embodiment 1.

[0139] Example 9

[0140] The difference between this embodiment and Embodiment 1 is only that: during the second heat treatment in step S3, a first laser emitted from an Nd:YAG laser is used to heat the surface of the 3C-silicon carbide layer in the first composite wafer. The wavelength of the first laser is 1064 nm, the power is 30 W, the pulse width is 10 ns, the pulse frequency is 20 kHz, and the focal diameter is 50 μm. The local temperature on the surface of the 3C-silicon carbide layer during laser treatment is maintained at 2200 ± 3 °C. The rest is the same as in Embodiment 1.

[0141] Example 10

[0142] The difference between this embodiment and Embodiment 1 is only that: during the second heat treatment in step S3, a first laser emitted from an Nd:YAG laser is used to heat the surface of the 3C-silicon carbide layer in the first composite wafer. The wavelength of the first laser is 1064 nm, the power is 180 W, the pulse width is 30 ns, the pulse frequency is 50 kHz, and the focal diameter is 100 μm. The local temperature on the surface of the 3C-silicon carbide layer during laser treatment is maintained at 3800 ± 7 °C. All other aspects are the same as in Embodiment 1.

[0143] Example 11

[0144] The only difference between this embodiment and Embodiment 1 is that the temperature set for both the in-situ deposition of carbon atoms in step S4 and the continued deposition is 700°C. All other aspects are the same as in Embodiment 1.

[0145] Example 12

[0146] The only difference between this embodiment and Embodiment 1 is that the temperature set for both the in-situ deposition of carbon atoms in step S4 and the continued deposition is 1200°C. All other aspects are the same as in Embodiment 1.

[0147] Example 13

[0148] The only difference between this embodiment and Embodiment 1 is that the concentration of methane in the mixed gas in step S4 is 10 vol%. The rest is the same as in Embodiment 1.

[0149] Comparative Example 1

[0150] The only difference between this comparative example and Example 1 is that step S3 omits the first and second heat treatment processes. All other aspects are the same as in Example 1.

[0151] Comparative Example 2

[0152] The only difference between this comparative example and Example 1 is that the epitaxial growth process of the 3C-silicon carbide layer in step S2 is omitted, and the first heat treatment is directly performed on the 4H-SiC substrate, while the second heat treatment and the first laser treatment are performed simultaneously on its surface. All other aspects are the same as in Example 1.

[0153] Performance testing: The thermal conductivity, dislocation density, and carrier mobility of the products obtained by the preparation methods provided in Examples 1-13 and Comparative Examples 1-2 were tested. The specific testing process is as follows:

[0154] (1) Thermal conductivity: The thermal conductivity of the products prepared in Examples 1-13 and Comparative Examples 1-2 was measured using the laser flare method. The specific operation was as follows: the front side of the product was irradiated with a laser pulse, and the temperature rise curve of the back side was recorded by an infrared detector. The thermal diffusivity (α) was calculated by fitting the curve, combined with the specific heat capacity (C).p From density (ρ), we obtain thermal conductivity (κ): κ = α·C p ·ρ

[0155] (2) Dislocation density: The surface defects of the products prepared in Examples 1-13 and Comparative Examples 1-2 were detected by scanning the surface of the products with a laser beam using a laser scattering instrument.

[0156] (3) Carrier mobility: The carrier mobility of the products prepared in Examples 1-13 and Comparative Examples 1-2 was determined by the van der Burg method combined with the Hall effect, with reference to ASTM F76 standard.

[0157] The test results are shown in Table 1.

[0158] Table 1

[0159]

[0160] The test results show that:

[0161] (1) As can be seen from Examples 1 to 5, the method for preparing single-crystal diamond wafers provided by the present invention grows a second silicon carbide layer with the same crystal structure as single-crystal diamond by epitaxial growth, and designs heat treatment, laser treatment and in-situ deposition process of carbon atoms to promote homogeneous deposition. Furthermore, a large-size first silicon carbide substrate is selected to realize the preparation of large-size and high-performance single-crystal diamond wafers.

[0162] (2) By comparing Example 1 and Example 6, it can be seen that the preparation method provided by the present invention pre-treats the 4H-SiC substrate, improves the flatness of the substrate surface by chemical mechanical polishing, and removes impurities and oxides from the substrate surface by cleaning, which can improve the performance of the prepared single crystal diamond wafer. However, if the pre-treatment process of step S1 is omitted, the thermal conductivity and carrier mobility of the prepared product will decrease, and the dislocation density will increase.

[0163] (3) By comparing Example 1 with Examples 7 and 8, it can be seen that in this invention, if the thickness of the epitaxially grown 3C-silicon carbide layer is too thin, some carbon atoms will volatilize during the laser silicon removal process, affecting the uniformity of subsequent in-situ deposition and thus affecting the performance of the final product. If the thickness of the epitaxially grown 3C-silicon carbide layer is too thick, silicon atoms will not volatilize completely during the laser silicon removal process, affecting the uniformity of subsequent in-situ deposition and forming local heterogeneous deposition, thus resulting in a deterioration in the performance of the final product.

[0164] (4) By comparing Example 1 with Examples 9 and 10, it can be seen that in this invention, if the heating temperature of the 3C-silicon carbide layer is too low, it is not enough to allow the silicon atoms in the 3C-silicon carbide layer to evaporate effectively, and the silicon atoms in the 3C-silicon carbide layer cannot be effectively removed, resulting in a decrease in the performance of the prepared product; if the heating temperature of the 3C-silicon carbide layer is too high, it will cause the carbon atoms in the 3C-silicon carbide layer to sublimate and cause the 3C-silicon carbide layer to undergo a phase transition, resulting in poor performance of the prepared product.

[0165] (5) By comparing Example 1 with Examples 11 and 12, it can be seen that in this invention, if the temperature of in-situ deposition of carbon atoms is too low, effective deposition of carbon atoms will not be achieved, resulting in a decrease in the performance of the prepared product; if the temperature of in-situ deposition of carbon atoms is too high, the deposited carbon will be graphitized, affecting the performance of the obtained product.

[0166] (6) By comparing Example 1 and Example 13, it can be seen that if the concentration of the reactant gas in the mixed gas is too high, too many carbon atoms will be deposited on the surface of the second composite wafer, resulting in a shell, or even forming impurities such as carbon black that adhere to the material surface, affecting the performance of the final product.

[0167] (7) By comparing Example 1 with Comparative Example 1, it can be seen that if the first heat treatment process and the second heat treatment process in step S3 are omitted in this invention, the omission of the first heat treatment process will cause the substrate temperature to be lower than the ambient temperature. The thermal stress cannot be released during the first laser treatment, causing the layer structure of the laser treatment to warp or microcrack. Then, if the second heat treatment process is omitted, it will cause the 3C-silicon carbide to break, making it impossible to prepare a single crystal diamond wafer, or even to prepare a product with a complete structure.

[0168] (8) By comparing Example 1 and Comparative Example 2, it can be seen that if the epitaxial growth process of the 3C-silicon carbide layer is omitted and subsequent processes are carried out directly on the surface of the 4H-SiC substrate, it will be impossible to achieve the deposition of homogeneous substrate and the preparation of large-size high-performance single-crystal diamond wafers.

[0169] In summary, the method for preparing a single-crystal diamond wafer provided by the present invention involves epitaxially growing a second silicon carbide layer on the surface of a first silicon carbide substrate, which has the same crystal structure as the single-crystal diamond to be prepared, to form a first composite wafer. Then, heat treatment is performed, specifically by first heating the substrate to a set temperature value to reach the ambient temperature for heat treatment, and then maintaining the substrate temperature at the ambient temperature for heat treatment. A first laser is used to cause the silicon atoms in the second silicon carbide layer on the first composite wafer to evaporate first, leaving carbon atoms in the second silicon carbide layer, forming a crystal defect layer in the second composite wafer. Subsequently, in a mixed gas containing carbon-containing reactive gases, carbon atoms in the mixed gas are deposited in situ on the crystal defect layer, filling the vacancies of the evaporated silicon atoms, thereby forming a single-crystal diamond wafer. This invention grows a second silicon carbide layer with the same crystal structure as single-crystal diamond using epitaxial growth. Furthermore, by designing heat treatment, laser treatment, and in-situ carbon atom deposition processes, homogeneous deposition can be achieved. In addition, the use of a large-size first silicon carbide substrate is beneficial for preparing large-size and high-performance single-crystal diamond wafers.

[0170] 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 a single-crystal diamond wafer, characterized in that, The preparation method includes the following steps: (1) A second silicon carbide layer is epitaxially grown on the surface of a first silicon carbide substrate to obtain a first composite wafer; the crystal structure of the second silicon carbide is consistent with the crystal structure of single crystal diamond. (2) The first composite wafer is subjected to heat treatment and first laser treatment to remove silicon atoms in the second silicon carbide layer and form a crystal defect layer on the surface of the first silicon carbide substrate to obtain the second composite wafer. (3) In a mixed gas, carbon atoms are deposited in situ on the crystal defect layer in the second composite wafer, and then the first silicon carbide substrate is removed to obtain the single crystal diamond wafer; the mixed gas includes a carbon-containing reactive gas.

2. The preparation method according to claim 1, characterized in that, Before the second silicon carbide is epitaxially grown, the first silicon carbide substrate is also pretreated; Preferably, the pretreatment includes polishing and cleaning performed sequentially; Preferably, the polishing method includes chemical mechanical polishing; Preferably, the surface smoothness of the polished first silicon carbide substrate is at the atomic level.

3. The preparation method according to claim 1 or 2, characterized in that, The method for epitaxially growing the second silicon carbide in step (1) includes chemical vapor deposition; Preferably, the raw materials used for the epitaxial growth of the second silicon carbide in step (1) include a carbon source and a silicon source; Preferably, the carbon source includes methane; Preferably, the silicon source includes silane or trichlorosilane; Preferably, the molar ratio of the carbon source to the silicon source is 1:(0.8-1.8); Preferably, the carrier gas used in the epitaxial growth process in step (1) includes hydrogen; Preferably, the epitaxial growth temperature in step (1) is 1400-1700℃.

4. The preparation method according to any one of claims 1-3, characterized in that, Step (1) The thickness of the first silicon carbide substrate is 400-750 μm; Preferably, the thickness of the second silicon carbide layer formed in step (1) is 5-10 nm; Preferably, in step (1), the crystal structure of the first silicon carbide in the first silicon carbide substrate includes either the 4H crystal form or the 6H crystal form; Preferably, the crystal structure of the second silicon carbide in the second silicon carbide layer formed in step (1) includes the 3C crystal form.

5. The preparation method according to any one of claims 1-4, characterized in that, Step (2) The process of heat treatment and first laser treatment of the first composite wafer includes: performing a first heat treatment on the first composite wafer, and then, under the second heat treatment conditions, simultaneously using a first laser to heat the surface of the second silicon carbide layer in the first composite wafer, causing silicon atoms in the second silicon carbide layer to evaporate and form a crystal defect layer; Preferably, the temperature set for the first heat treatment is 800-1100℃; Preferably, the first heat treatment is performed under vacuum conditions; Preferably, the holding time for the first heat treatment is 30-60 minutes; Preferably, the power of the first laser is 50-150W; Preferably, the pulse width of the first laser is 10-30 ns; Preferably, the pulse frequency of the first laser is 20-50 kHz; Preferably, the focal diameter of the first laser is 50-100 μm; Preferably, the scanning speed of the first laser is 500-2000 mm / s; Preferably, the first laser processing employs either a single-beam laser system or a multi-beam laser system, and more preferably a multi-beam laser system. Preferably, the temperature set for the second heat treatment is 800-1100℃; Preferably, the second heat treatment is performed under vacuum conditions; Preferably, during the simultaneous second heat treatment and the first laser treatment, the local temperature of the surface of the second silicon carbide layer in the first composite wafer is 2400-3600°C. Preferably, the time for simultaneously performing the second heat treatment and the first laser treatment is 20-100 seconds.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (3), the concentration of the carbon-containing reactive gas in the mixed gas is 1-5 vol%. Preferably, the carbon-containing reaction gas in step (3) includes methane; Preferably, the mixed gas in step (3) further includes a carrier gas; Preferably, in the mixed gas in step (3), the carrier gas includes hydrogen.

7. The preparation method according to any one of claims 1-6, characterized in that, In the in-situ deposition of carbon atoms in step (3), a second laser is used to irradiate the mixed gas, and carbon atoms are decomposed in the reaction gas of the mixed gas for in-situ deposition on the crystal defect layer. Preferably, the temperature is set at 800-1100℃ during the in-situ deposition of carbon atoms in step (3); Preferably, the pressure set during the in-situ deposition of carbon atoms in step (3) is 1-10 kPa; Preferably, after the in-situ deposition of carbon atoms in step (3) and before removing the first silicon carbide substrate, carbon atom deposition is further performed on the surface of the layer structure obtained after the in-situ deposition of carbon atoms. Preferably, during the continued deposition of the carbon atoms, the temperature is set to 800-1100°C; Preferably, the total time for the in-situ deposition of carbon atoms and the continued deposition of carbon atoms is 50-200 hours; Preferably, the method for removing the first silicon carbide substrate in step (3) includes chemical mechanical polishing; Preferably, after removing the first silicon carbide substrate in step (3), the edges of the remaining components are also polished.

8. A single-crystal diamond wafer, characterized in that, The single-crystal diamond wafer is prepared using the preparation method described in any one of claims 1-7.

9. The single-crystal diamond wafer according to claim 8, characterized in that, The thickness of the single-crystal diamond wafer is 10-100 μm; Preferably, the size of the single-crystal diamond wafer is 4 inches or more.

10. A single-crystal diamond wafer according to claim 8 or 9, characterized in that, The single-crystal diamond wafers are used in the fields of semiconductors, optics, quantum technology, or machining.

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