Method for homoepitaxial growth of hexagonal diamond through chemical vapor deposition

Abstract

The invention discloses a method for homoepitaxial growth of hexagonal diamond through chemical vapor deposition. The method comprises the steps of seed crystal preparation and pretreatment, preparation of a metal mask, preparation of hexagonal diamond nanorods, growth of hexagonal diamond single crystals or thin films through a chemical vapor deposition method and the like. According to the method, the treatment mode that the metal mask is prepared for the seed crystal to protect the (100) crystal face and the (100) step face is obtained through plasma etching after the nanorod is prepared is adopted for the first time, and pure hexagonal diamond can be obtained in the follow-up growth process; and a chemical vapor deposition method for growing high-quality hexagonal diamond single crystals and films on self-made (100) hexagonal diamond seeds is proposed for the first time, so that the defects of preparing hexagonal diamonds by a high-temperature and high-pressure method are effectively overcome.

Description

Technical Field

[0001] The invention relates to the technical field of diamond preparation, and in particular to a method for growing hexagonal diamond by homoepitaxial chemical vapor deposition. Background Art

[0002] As a common and stable element, carbon is widely present in inorganic and organic substances in various forms and structures. Various carbon elements and compounds play a huge role in different fields due to their different structural characteristics. Usually, the carbon family is divided into two categories according to the structural characteristics: crystalline carbon and amorphous carbon (amorphous carbon). Among crystalline carbons, diamond has attracted attention due to its excellent performance. The latest research shows that diamond is expected to become an excellent candidate material for semiconductor devices, quantum precision detection and quantum computing. All carbon atoms in diamond are in the form of sp 3 Connected by covalent bonds, each carbon atom has four nearest neighbor atoms at equal distances (0.154nm). The special structure makes diamond the hardest substance in nature (Young's modulus 1200Gpa). In addition, diamond has good thermal conductivity (25W / cm·K), a wide band gap (5.5ev), a small dielectric constant (5.7) and stable chemical properties. Based on the stacking method of carbon atoms, the configuration of chemical bonds, bond lengths and structural units, diamond can be divided into cubic diamond and hexagonal diamond. At present, cubic diamond has a relatively mature preparation technology. However, hexagonal diamond has a special structure and poor stability, and its preparation method needs to be developed.

[0003] Hexagonal diamond has some unique advantages over cubic diamond. In the past, people once believed that cubic diamond was the hardest material in nature, but with the discovery of natural hexagonal diamond, people speculated that hexagonal diamond may have higher strength and hardness than cubic diamond, so hexagonal diamond has broad application prospects. The unit cell parameters of hexagonal diamond are a=251pm, c=412pm, c / a=1.64. This structure causes slight deformation of its unit cell, which may affect its physical properties, such as thermal conductivity and optical properties. Hexagonal diamond is more stable than cubic diamond at high temperatures, which makes it have potential application advantages in high temperature environments. Hexagonal diamond is transparent to visible light and infrared radiation and has a high refractive index (2.11~2.12), which makes it potentially useful in optical applications.

[0004] At present, meteorites are the only source of natural hexagonal diamonds. Recent studies have found that hexagonal diamonds can be synthesized under high temperature and high pressure using a six-sided top press. However, the high temperature and high pressure synthesis of hexagonal diamonds has strict environmental requirements and requires very high temperature and pressure. Although the six-sided top press can synthesize hexagonal diamonds, due to the high temperature and high pressure requirements, the sample is very small and the process is expensive. Although the two-sided top press effectively solves the problem of product defects, the preparation process still needs to be under high temperature and high pressure conditions, has strict environmental requirements, and the product size is small.

[0005] At present, the technology of artificial synthesis of hexagonal diamond still has the disadvantages of harsh preparation conditions, low product purity, and limited product size, which are specifically manifested as follows. In terms of preparation conditions, the existing methods for preparing hexagonal diamonds all require high temperature and high pressure. Usually, the preparation of hexagonal diamonds under high temperature and high pressure requires a temperature of 1000-1800°C and a pressure of 15-50Gpa. On the one hand, excessively high temperature and pressure increase the difficulty of equipment preparation and maintenance, and on the other hand, increase costs, making it difficult to achieve mass production. In terms of product purity, since the high temperature and high pressure method for preparing hexagonal diamonds is to transform graphite into hexagonal diamonds, graphite that has not undergone phase change may still be retained in the sample, thus affecting the performance of the material. In terms of product size, hexagonal diamonds are prepared by the existing top press high temperature and high pressure method. Due to the limitations of preparation conditions, the diameter of the product obtained is 2-10 mm, and the smaller size limits the application of hexagonal diamonds.

[0006] In order to improve the shortcomings of the current technology for preparing hexagonal diamond, the present invention proposes to prepare hexagonal diamond by chemical vapor deposition. Chemical vapor deposition (CVD) is a technology commonly used in materials science and semiconductor industry, mainly used to manufacture thin films, nanomaterials and other high-performance materials. Its principle is to use a single substance or compound containing the element of the material to be deposited to react on the surface of the substrate to obtain high-quality single crystals or thin films. According to the different activation methods of the elements to be deposited, the chemical vapor deposition method can be divided into: hot wire method (HF-CVD), combustion flame method (CF-CVD), microwave plasma chemical vapor deposition method (MP-CVD), electron cyclotron resonance microwave plasma chemical vapor deposition method (ECR-MPCVD), radio frequency chemical vapor deposition method (RF-CVD), direct current chemical vapor deposition method (DC-CVD), direct current assisted plasma chemical vapor deposition method (DC-PACVD), direct current arc plasma jet chemical vapor deposition method (DCArc Plasma Jet CVD) and laser chemical vapor deposition method (LCVD).

[0007] The process of synthesizing diamond by CVD includes the following basic steps: (1) gaseous hydrocarbons are introduced into the CVD reaction chamber; (2) these hydrocarbons are decomposed into free radicals (C x H y ); (3) After mutual collision and reaction, the free radicals eventually contact the substrate surface; (4) The free radicals are adsorbed on the substrate surface; (5) The adsorbed free radicals decompose, and the released active carbon atoms diffuse and then form hexagonal diamonds; (6) Inactive substances (such as hydrogen) desorbed from the surface will form hydrogen molecules or other by-products, which will be carried away and removed by the airflow.

[0008] Each CVD has its own unique advantages. HF-CVD has low cost and convenient operation for preparing hexagonal diamond. The product size is not limited, and a large area of ​​hexagonal diamond film can be obtained. CF-CVD has fast speed, simple equipment, low cost, and can prepare hexagonal diamond under normal pressure. MP-CVD can effectively control the thickness and uniformity of the product. The prepared hexagonal diamond has high purity, high quality, no pollution, and high stability. Large-area thin film products can also be obtained. ECR-MPCVD further improves the plasma density, and the deposition pressure is low. It can maintain high-density discharge at low pressure with low ion energy to achieve large-area uniform deposition of hexagonal diamond. RF-CVD has high process stability and good product quality for preparing hexagonal diamond. DC-CVD has fast growth, high quality, and good uniformity for preparing hexagonal diamond. DC-PACVD combines the advantages of direct current and plasma assistance, with fast deposition rate and good film quality. It is suitable for deposition at a relatively low temperature and is substrate-friendly. DC Arc Plasma Jet CVD uses the energy generated by arc discharge to highly ionize the gas, thereby obtaining high-density plasma active groups. It has a large deposition area and a fast deposition speed, and has the largest linear growth rate among many preparation methods. LCVD can selectively undergo photochemical reactions, which can reduce the temperature of depositing single crystals or thin films, and the laser has a high energy density. Through various chemical vapor deposition methods, ideal hexagonal diamond products can be grown on hexagonal diamond seeds, which has a huge value space. Summary of the invention

[0009] In order to solve the problems of harsh conditions for preparing hexagonal diamond under high temperature and high pressure, low product purity and small product size, the present invention provides a method for growing hexagonal diamond by homoepitaxial growth of hexagonal diamond by chemical vapor deposition, and for the first time grows high-quality hexagonal diamond single crystals and thin films on homemade hexagonal diamond seeds by chemical vapor deposition.

[0010] In the natural state, graphite is stable and hexagonal diamond is metastable, so there is a large amount of graphite in nature. The preparation of hexagonal diamond by high temperature and high pressure method is to transform graphite into hexagonal diamond under special conditions (high temperature and high pressure). Because there is a high potential barrier between graphite and hexagonal diamond, once one phase is formed, it is difficult to transform into another phase. Therefore, very high temperature and pressure are required to make the two phases transform. Compared with the preparation of hexagonal diamond by high temperature and high pressure method, CVD can effectively reduce the temperature and pressure required in the preparation process. Because CVD does not transform from graphite phase to hexagonal diamond, but a chemical reaction occurs between the substrate surface and the gas phase hydrocarbon groups to continuously generate sp 3 The process of hybridization of saturated carbon structure. In this process, the appropriate amount of H can inhibit the formation of graphite or other crystals, and finally obtain pure hexagonal diamond.

[0011] Recent studies have shown that not all crystal faces can be used to grow large hexagonal diamonds. For example, cubic diamonds are easily grown on the (001) face of hexagonal diamonds. Theoretical studies have shown that the (100) crystal face of hexagonal diamonds and its step faces have the lowest energy, so hexagonal diamonds grow in a direction perpendicular to the (100) face. To prepare pure hexagonal diamonds, it is necessary to ensure that the crystal faces exposed by the seed crystals are (100) and (100) step faces, and avoid exposing the (001) crystal face.

[0012] Based on the above theory, the present invention adopts for the first time a processing method of preparing a mask for the seed crystal to protect the (100) crystal plane, preparing nanorods and then plasma etching to obtain the (100) step surface, ensuring that the crystal planes exposed by the seed crystal are the (100) and (100) step surfaces, avoiding the growth of cubic diamonds on the (001) plane, which is conducive to obtaining pure hexagonal diamonds in the subsequent growth process.

[0013] In addition, in theory, the size of hexagonal diamond prepared by CVD is not limited. By controlling the various parameters of CVD, as long as enough time is provided, the hexagonal diamond single crystal or polycrystalline thin film product of the ideal size can be obtained. However, CVD technology has its own advantages and disadvantages. By controlling various parameters, existing CVD can be used to prepare hexagonal diamond single crystals and thin films. For example, the most common MP-CVD has the advantages of controllable product thickness and uniformity, high product purity and high quality, no pollution, high stability, and large deposition area. However, the product generation rate is very low when preparing large-area thin films.

[0014] In order to improve the shortcoming that MP-CVD has a slow speed in preparing hexagonal diamond, the present invention also creatively proposes to introduce a laser source parallel to the substrate in the MP-CVD device to accelerate the photolysis of the precursor. When preparing hexagonal diamond by MP-CVD, microwaves provide energy to decompose the gas-phase precursor, and the various groups and atoms obtained diffuse to the substrate at a long distance and slow speed, resulting in a slow deposition speed. Therefore, a laser source parallel to the substrate is introduced for irradiation, and part of the energy of the laser beam is used to fully decompose the gas-phase precursor, and part is absorbed by the decomposed groups to accelerate the diffusion of groups and atoms. The introduction of a parallel laser source is conducive to reducing the deposition temperature and accelerating the deposition speed. The thermal stress of the prepared film is small, melting and recrystallization are not easy to occur during the deposition process, and the prepared film has good uniformity.

[0015] Based on this, the present invention provides the following technical solutions:

[0016] A first aspect of the present invention provides a method for growing hexagonal diamond by homoepitaxial chemical vapor deposition, comprising the following steps:

[0017] Step S1, seed preparation and pretreatment:

[0018] Using hexagonal diamond seeds prepared in a double-sided top press chamber as a substrate, the seeds are first subjected to chemical mechanical polishing (CMP) to remove most of the defects and impurities on the surface of the seeds; the polished seeds are first soaked in acid, and then ultrasonically treated in acetone, ethanol and deionized water for 30 to 60 minutes in sequence to obtain hexagonal diamond seeds;

[0019] Step S2: preparing a metal mask:

[0020] The hexagonal diamond seeds obtained in step S1 are deposited using a magnetron sputtering deposition system; the vacuum degree in the deposition chamber is controlled, argon gas is introduced and the gas pressure is controlled, and the power is adjusted to obtain a metal nickel film; and then heat treatment is performed using nitrogen, i.e., the sample with the deposited nickel film is placed in an atmosphere tube furnace for annealing treatment, the annealing temperature is maintained, and nitrogen is introduced after the annealing is completed to allow it to cool naturally.

[0021] Step S3, preparing hexagonal diamond nanorods:

[0022] The hexagonal diamond seeds covered with the nickel mask obtained in step S2 are etched using an inductively coupled plasma (ICP) etching device, and oxygen is introduced to etch the hexagonal diamond seeds to obtain hexagonal diamond nanorods; after the etching is completed, the remaining impurities and nickel particles are washed away with acid; then, a vacuum is evacuated, hydrogen is introduced and the temperature is maintained, and the hexagonal diamond nanorods are etched with hydrogen to expose the (100) step surface;

[0023] Step S4, growing hexagonal diamond single crystal or thin film by chemical vapor deposition:

[0024] The hexagonal diamond nanorods obtained in step S3 are deposited on a deposition device using a chemical vapor deposition method to grow a hexagonal diamond single crystal or a thin film to obtain hexagonal diamond.

[0025] Furthermore, in step S2, the vacuum degree in the deposition chamber is controlled to be 1.0×10 -5 Pa, introduce argon gas with a flow rate of 30-40 sccm, control the gas pressure to 2Pa, and adjust the power to 45-60W.

[0026] Furthermore, in step S2, the hexagonal diamond seeds are deposited using a magnetron sputtering deposition system for 35 to 40 seconds to obtain a nickel film with a thickness of 5 to 6 nm; the sample with the deposited nickel film is placed in an atmosphere tube furnace for annealing, the annealing temperature is maintained at 700 to 750° C., and annealing is performed for 10 to 20 minutes.

[0027] Furthermore, in step S3, the RF / ICP power of the inductively coupled plasma etching equipment is adjusted to 100 / 800 W, the volume flow rate of oxygen is controlled to 25-30 sccm, the pressure is 25 m-Torr, and the etching time is 15-20 min to obtain hexagonal diamond nanorods with a height of 180-220 nm.

[0028] Furthermore, in step S3, the vacuum is evacuated to less than 0.1 Pa, hydrogen is introduced at a flow rate of 300 to 350 sccm, and the temperature is maintained at 700 to 750°C.

[0029] Furthermore, the chemical vapor deposition method in step S4 includes a hot wire method, a combustion flame method, a microwave plasma chemical vapor deposition method, an electron cyclotron resonance microwave plasma chemical vapor deposition method, a radio frequency chemical vapor deposition method, a direct current chemical vapor deposition method, a direct current assisted plasma chemical vapor deposition method, a direct current arc plasma jet chemical vapor deposition method and a laser chemical vapor deposition method.

[0030] Furthermore, the hot filament method in step S4 includes the following steps: methane and hydrogen are introduced into the reaction chamber, the filament temperature in the reaction chamber is controlled at 2500°C, the substrate temperature is controlled at 700-900°C, the deposition pressure is controlled at 2.5Kpa, and a hexagonal diamond single crystal or thin film is formed on the substrate to obtain hexagonal diamond.

[0031] Furthermore, the combustion flame method in step S4 includes the following steps: using an oxygen-acetylene flame combustion method for deposition, the oxygen-acetylene flame temperature is 2000-3550K, the volume ratio of oxygen-acetylene is 0.85:1, and a hexagonal diamond single crystal or thin film is deposited on a hexagonal diamond substrate to obtain hexagonal diamond.

[0032] Furthermore, the DC arc plasma jet chemical vapor deposition method in step S4 includes the following steps: using a 100kW high-power DC Arc Plasma Jet CVD device, introducing a gas source containing argon, hydrogen, and methane, and using the high-temperature plasma generated by DC arc discharge to dissociate the gas source, the gas expands due to heat and is ejected from the anode nozzle to form an arc plasma column, the plasma temperature inside the arc plasma column reaches above 4000°C, and after the plasma is gradually cooled, hexagonal diamond single crystals or thin films are deposited on the substrate to obtain hexagonal diamond.

[0033] Furthermore, the microwave plasma chemical vapor deposition method in step S4 introduces a parallel laser source, comprising the following steps: using an MP-CVD device with a frequency of 2.45 GHz, introducing methane and hydrogen, wherein the purity of the methane and hydrogen is 5N, wherein the methane concentration is 4% to 8%, controlling the deposition pressure to be 15 to 25 Kpa, controlling the temperature in the reaction chamber to be 600 to 700° C., and simultaneously turning on a super-Gaussian distribution continuous laser source with a wavelength of 532 nm, and setting the laser power to 40 W / cm 2 The laser source is parallel to the substrate, irradiating the free radicals, the substrate temperature is controlled at 600-800°C, and hexagonal diamond single crystals or thin films are deposited on the substrate to obtain hexagonal diamond.

[0034] The second aspect of the present invention provides hexagonal diamond prepared by the above-mentioned method of chemical vapor deposition homoepitaxial growth of hexagonal diamond.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention proposes for the first time to grow high-quality hexagonal diamond single crystals and thin films on homemade (100) hexagonal diamond seeds by CVD, which effectively improves the shortcomings of high-temperature and high-pressure methods for preparing hexagonal diamond. The existing high-temperature and high-pressure methods for preparing hexagonal diamonds are of low purity, small size, and require high temperature and pressure. The preparation of hexagonal diamond by CVD is not a phase change process of graphite, which effectively reduces the temperature and pressure required in the preparation process. CVD does not require a catalyst, so the purity of hexagonal diamond prepared by CVD is relatively high. By accurately controlling various parameters and providing sufficient time, hexagonal diamond single crystals or polycrystalline thin film products of ideal size can be obtained.

[0037] 2. Compared with the traditional method for preparing hexagonal diamond, the present invention adopts for the first time a treatment method in which a metal mask is prepared on the seed crystal to protect the (100) crystal plane, and plasma etching is performed to obtain the (100) step surface after the nanorods are prepared, thereby ensuring that the crystal plane exposed by the seed crystal is the (100) and (100) step surfaces, which is conducive to obtaining pure hexagonal diamond in the subsequent growth process.

[0038] 3. This technology uses CVD to prepare hexagonal diamond single crystals and thin films on a hexagonal diamond substrate. It effectively makes up for the shortcomings of the existing high temperature and high pressure method for preparing hexagonal diamond, and on the basis of the existing MP-CVD technology, introduces a laser source parallel to the substrate to accelerate the photolysis of the precursor. The gas phase precursor is first decomposed using a microwave source to obtain various carbon-containing groups and various atoms. These groups and atoms are then irradiated by the laser source introduced parallel to the substrate. The irradiated groups and atoms absorb photons, accelerate diffusion, increase the deposition rate, and further improve the growth rate and quality of hexagonal diamond. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of the method for homoepitaxial growth of hexagonal diamond by chemical vapor deposition in Example 1 of the present invention.

[0040] Figure 2 Schematic diagram of the method for homoepitaxial growth of hexagonal diamond by chemical vapor deposition in Example 1 of the present invention.

[0041] Figure 3 Schematic diagram of the structure of the existing MP-CVD device in Example 6 of the present invention.

[0042] Figure 4 Schematic diagram of the structure of the MP-CVD device that introduces a parallel laser source in Example 6 of the present invention. DETAILED DESCRIPTION

[0043] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention. The following is a description of the principles and features of the present invention, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0044] Example 1: Method for growing hexagonal diamond by homoepitaxial chemical vapor deposition

[0045] This embodiment is used to provide a method for growing hexagonal diamond by chemical vapor deposition homoepitaxially according to the present invention. Figure 1 and Figure 2 They are respectively a flow chart and a schematic diagram of the preparation method of the present invention. As shown in the figures, the preparation method of the present invention comprises the following steps.

[0046] Step S1: Seed preparation and pretreatment

[0047] In the preparation of high-quality hexagonal diamonds, the selection of seed crystals is particularly important. There are two types of seed crystals to choose from: homogeneous and heterogeneous. From the perspective of the substrate, if you want to obtain high-quality hexagonal diamonds, it is best to use homogeneous seed crystals. Because the homogeneous substrate matches the lattice of the material to be deposited, the internal stress is small, and the probability of producing various defects such as vacancies and dislocations is small. Therefore, in the present invention, a hexagonal diamond seed crystal with a diameter of about 5 mm prepared in the pressure chamber of a two-sided top press is used as a substrate. The specific preparation method has been detailed in the patent disclosure document "A Technology for Preparing Hexagonal Diamonds", and the patent publication number is CN117085595A.

[0048] In order to prevent the poor quality of hexagonal diamond grown by CVD due to defects inside and on the surface of the seed crystal, in this embodiment, the seed crystal needs to be pretreated. The specific steps are as follows: first, the seed crystal is subjected to chemical mechanical polishing to remove most of the defects and impurities on the surface of the seed crystal; the polished seed crystal is first soaked in acid, and then ultrasonically treated in acetone, ethanol and deionized water for 30 to 60 minutes in sequence to obtain a hexagonal diamond seed.

[0049] Step S2: preparing a metal mask

[0050] After obtaining the hexagonal diamond seeds, in order to protect part of the hexagonal diamond (100) surface during subsequent etching, a JGP-450B magnetron sputtering deposition system was used to deposit metal nickel on the substrate surface. The specific steps were as follows: the vacuum degree of the deposition chamber was controlled to 1.0×10 -5 Pa, argon gas with a flow rate of 30-40 sccm is introduced to control the gas pressure to 2Pa, and the power is adjusted to 45-50W; the above deposition system is used to deposit on the hexagonal diamond seed obtained in step S1 for about 35-40s to obtain a nickel film with a thickness of 5-6nm; then nitrogen is used for heat treatment, that is, the sample with the deposited nickel film is placed in an atmosphere tube furnace for annealing; the annealing temperature is maintained at 700-750℃, and annealing is performed for 10-20min. After annealing, nitrogen is introduced to allow it to cool naturally, and the nickel will automatically become nickel particles of about 150nm due to surface tension. The hexagonal diamond surface covered with nickel particles will not be etched later, so the (100) surface of part of the hexagonal diamond seed can be protected.

[0051] Step S3: Preparation of hexagonal diamond nanorods

[0052] After obtaining the hexagonal diamond seed covered with a nickel mask, an inductively coupled plasma etching device is used for etching, and the specific steps are as follows: adjust the RF / ICP power to 100 / 800W, control the volume flow rate of oxygen to 25-30sccm, and the pressure to 25m-Torr. The hexagonal diamond seed covered with a nickel mask obtained in step S2 is etched using the above etching device, and the etching time is 15-20min, and a hexagonal diamond nanorod with a height of 180-220nm can be obtained; after etching, the residual impurities and nickel particles are washed away with acid.

[0053] Then, the vacuum is evacuated to less than 0.1 Pa, and hydrogen gas with a flow rate of 300-350 sccm is introduced, and the temperature is maintained at 700-750°C; the hexagonal diamond nanorods with a size of 180-220 nm are etched with hydrogen gas to expose the (100) step surface, because only on the (100) and (100) step surfaces of the hexagonal diamond seed can relatively pure and high-quality hexagonal diamonds be grown.

[0054] In this embodiment, the height of the hexagonal diamond nanorods is special. If the height of the nanorods is not within the range of 180 to 220 nm, the complete (100) step surface will not be exposed after the subsequent hydrogen etching, and the edge of the crystal surface will have defects and poor quality. After further growth of hexagonal diamond by CVD, the surface roughness is high and the quality is poor. Therefore, the oxygen etching time must be strictly controlled to control the height of the hexagonal diamond nanorods to about 200 nm to obtain a complete, high-quality (100) step surface.

[0055] Step S4: growing hexagonal diamond single crystal or thin film by CVD method

[0056] Use hot wire method (HF-CVD), combustion flame method (CF-CVD), microwave plasma chemical vapor deposition method (MP-CVD), electron cyclotron resonance microwave plasma chemical vapor deposition method (ECR-MPCVD), radio frequency chemical vapor deposition method (RF-CVD), direct current chemical vapor deposition method (DC-CVD), direct current assisted plasma chemical vapor deposition method (DC-PACVD), direct current arc plasma jet chemical vapor deposition method (DC Arc Plasma Jet CVD) or laser chemical vapor deposition method (LCVD), on the corresponding deposition equipment, the hexagonal diamond nanorods obtained in step S3 are deposited to grow hexagonal diamond single crystals or thin films to obtain the hexagonal diamond of the present invention. The specific method is shown in the following embodiments.

[0057] Step S5: Product analysis and evaluation

[0058] The surface morphology of the hexagonal diamond single crystal or thin film obtained in step S4 can be observed by optical microscope and scanning electron microscope to determine the grain size, orientation and other information of the hexagonal diamond; strain, lattice structure, vibration mode and other information can be analyzed by Raman spectrum and infrared spectrum; defect state and impurity and other characteristics can be analyzed by photoluminescence spectrum; and hexagonal diamond can be qualitatively and quantitatively analyzed by X-ray diffraction. All the above analysis methods prove that high-quality hexagonal diamond single crystal or thin film can be prepared by CVD, and the preparation environment required is not as harsh as the high temperature and high pressure method, and the obtained product has higher purity and is not limited in size.

[0059] It is worth noting that hexagonal diamond cannot be prepared by using hexagonal diamond as a substrate. This technology proposes to expose the (100) and (100) step surfaces on the basis of existing hexagonal diamond to prepare hexagonal diamond. In the process of preparing hexagonal diamond, only the (100) crystal plane and the (100) step surface can grow hexagonal diamond, and the (001) crystal plane will grow cubic diamond. This technology adopts the pre-treatment method of preparing a metal nickel mask and plasma etching to prepare hexagonal diamond nanorods. By preparing a nickel mask, the (100) surface of the substrate can be effectively protected, and by plasma etching, the (100) step surface can be effectively exposed. Both types of crystal planes have good surface quality and provide a good substrate for the subsequent growth of hexagonal diamond.

[0060] Example 2: Growth of hexagonal diamond single crystal or thin film by hot wire method (HF-CVD)

[0061] This embodiment is used to provide a method for growing a hexagonal diamond single crystal or thin film by the HF-CVD method in Example 1, and the specific method is as follows. Methane and hydrogen are introduced into a reaction chamber, the filament temperature in the reaction chamber is controlled at about 2500°C, the substrate temperature is controlled at 700-900°C, and the deposition pressure is controlled at 2.5KPa; the carbon-containing gas is activated into CH3 groups and H atoms by the hot filament, and then deposited on the hexagonal diamond substrate obtained in step S3 of Example 1 to obtain the hexagonal diamond single crystal or thin film of this embodiment.

[0062] Example 3: Growth of hexagonal diamond single crystal or thin film by combustion flame method (CF-CVD)

[0063] This embodiment is used to provide a method for growing a hexagonal diamond single crystal or thin film by the CF-CVD method in Example 1. The specific method is as follows. Hexagonal diamond is deposited by an oxygen-acetylene flame (reducing flame) combustion method. The temperature of the oxygen-acetylene flame reaches 2000-3550K. The volume ratio of oxygen-acetylene is 0.85:1. The hexagonal diamond is deposited on the hexagonal diamond substrate obtained in step S3 of Example 1 to obtain the hexagonal diamond single crystal or thin film of the present invention. In this embodiment, the higher flame temperature can cause the carbon-containing gas (taking methane as an example) and hydrogen to dissociate, and then hexagonal diamond is grown on the substrate.

[0064] Example 4: Growth of hexagonal diamond single crystal or thin film by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD), radio frequency chemical vapor deposition (RF-CVD), direct current chemical vapor deposition (DC-CVD), direct current assisted plasma chemical vapor deposition (DC-PACVD), laser chemical vapor deposition (LCVD)

[0065] This embodiment is used to provide a method for growing hexagonal diamond single crystals or thin films by the ECR-MPCVD, RF-CVD, DC-CVD, DC-PACVD and LCVD methods in Embodiment 1. The specific method is as follows.

[0066] For the ECR-MPCVD method, an ECR-MPCVD device with a frequency of 2.45 GHz is used to deposit on the hexagonal diamond substrate obtained in step S3 of Example 1 at a pressure of 0.5 Kpa and a temperature of 600-900°C to obtain the hexagonal diamond of the present invention.

[0067] For the RF-CVD method, a RF-CVD device with a frequency of 13.56 MHz and a maximum power of 1 kW was used, and methane and hydrogen were introduced, and the vacuum degree was controlled at 10 -5 Pa, the substrate temperature is controlled at about 700° C., and deposited on the hexagonal diamond substrate obtained in step S3 of Example 1 to obtain the hexagonal diamond of the present invention.

[0068] For the DC-CVD method, a DC-CVD device with a 45kW high-stable DC glow discharge power supply is used, hydrogen (purity of 99.9%), methane (purity of 99.99%), nitrogen (purity of 99.9%) and argon (purity of 99.9%) are introduced, the deposition temperature is controlled to be 800° C., and deposition is performed on the hexagonal diamond substrate obtained in step S3 of Example 1 to obtain the hexagonal diamond of the present invention.

[0069] For the DC-PACVD method, a mixed gas of methane and hydrogen is introduced. The volume ratio of methane to hydrogen is 5% to 12%, the gas flow rate is 400 sccm, and the chamber pressure is 100 to 130 Torr. The discharge voltage and discharge current are 840 to 910 V and 90 to 110 A, respectively. The substrate temperature is controlled at 600 to 900° C., and the hexagonal diamond substrate obtained in step S3 of Example 1 is deposited to obtain the hexagonal diamond of the present invention.

[0070] For the LCVD method, hydrogen and methane are first introduced, and then a Nd:YAG pulse laser is used as a heat source for LCVD to directly act on the reaction gas. The laser interacts with the reaction gas molecules or the molecules on the substrate surface, and the gas molecules are activated by the energy of the laser to promote the chemical reaction, and then deposited on the hexagonal diamond substrate obtained in step S3 of Example 1 to obtain the hexagonal diamond of the present invention.

[0071] Example 5: Growth of hexagonal diamond single crystal or thin film by DC Arc Plasma Jet CVD

[0072] This embodiment is used to provide a method for growing hexagonal diamond single crystals or thin films by the DC Arc Plasma Jet CVD method in Example 1, and the specific method is as follows. A 100kW high-power DC Arc Plasma Jet CVD device is used, a gas source (a mixed gas such as argon, hydrogen, and methane) is introduced, and the high-temperature plasma generated by the DC arc discharge is used to dissociate the gas source. The gas expands due to heat and is ejected from the anode nozzle to form an arc plasma column, and the internal plasma temperature can reach more than 4000°C. These plasmas are gradually cooled and finally deposited on the hexagonal diamond substrate obtained in step S3 of Example 1 to obtain the hexagonal diamond of the present invention.

[0073] Example 6: Growth of hexagonal diamond single crystal or thin film by microwave plasma chemical vapor deposition (MP-CVD) using a parallel laser source

[0074] This embodiment is used to provide a method for growing hexagonal diamond single crystal or thin film by MP-CVD method in embodiment 1. The specific method is as follows. Use MP-CVD equipment with a frequency of 2.45 GHz, introduce methane and hydrogen, both of which have a purity of 5N, wherein the methane concentration is 4% to 8%, control the deposition pressure to 15 to 25 Kpa, control the temperature in the reaction chamber to 600 to 700°C, and simultaneously turn on the ultra-Gaussian distribution continuous laser source with a wavelength of 532 nm, and set the laser power to 40 W / cm 2 The laser source is parallel to the substrate, irradiating the free radicals, and the substrate temperature is controlled at 600-800° C. The free radicals are deposited on the hexagonal diamond substrate obtained in step S3 of Example 1 to obtain the hexagonal diamond of the present invention.

[0075] In this embodiment, the substrate temperature is slightly higher than the temperature in the reaction chamber, which can accelerate the deposition rate of hexagonal diamond on the one hand, and effectively prevent the hexagonal diamond from graphitizing or generating other diamond-like phases on the other hand.

[0076] in, Figure 3 This is a schematic diagram of an existing MP-CVD device. As shown in the figure, the MP-CVD device includes a deposition chamber, a sample stage, a substrate holder, a microwave source, etc., wherein an air inlet and an air outlet are respectively provided above and below the deposition chamber, the substrate holder is used to place the sample substrate, and a quartz window is provided on the air inlet. The microwave source transmits microwave energy to the reaction chamber through the quartz window, excites and ionizes the gas molecules, and generates plasma. The plasma is composed of high-energy particles (electrons, ions, free radicals, etc.). These particles have extremely high energy and can promote chemical reactions. The high-energy particles in the plasma react with the gas molecules to produce reactants (such as carbon, hydrogen and other elements), which form a thin film on the surface of the substrate. Under the excitation of the high-energy particles, the thin film on the substrate is gradually deposited and grown to obtain a deposition product.

[0077] Figure 4 This is a schematic diagram of the MP-CVD device of the present invention that introduces a parallel laser source. As shown in the figure, the traditional MP-CVD only relies on microwaves to decompose and accelerate the gas phase precursor during the diamond deposition process, while the present invention introduces a laser source on the basis of the traditional equipment, and can use microwaves and lasers to simultaneously accelerate the decomposition of the gas phase precursor and free radicals, so that the gas phase precursor is decomposed more thoroughly, the migration speed of the free radicals is accelerated, the deposition speed is increased, and the growth speed and quality of the hexagonal diamond of the present invention are further improved.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for growing hexagonal diamond by homoepitaxial chemical vapor deposition, characterized in that: The following steps are involved: Step S1, seed preparation and pretreatment: Using hexagonal diamond seeds prepared in a double-sided top press chamber as a substrate, the seeds are first subjected to chemical mechanical polishing to remove most of the defects and impurities on the surface of the seeds; the polished seeds are first soaked in acid, and then ultrasonically treated in acetone, ethanol and deionized water for 30 to 60 minutes in sequence to obtain hexagonal diamond seeds; Step S2: preparing a metal mask: The hexagonal diamond seeds obtained in step S1 are deposited using a magnetron sputtering deposition system; the vacuum degree in the deposition chamber is controlled, argon gas is introduced and the gas pressure is controlled, and the power is adjusted to obtain a metal nickel film; and then heat treatment is performed using nitrogen, i.e., the sample with the deposited nickel film is placed in an atmosphere tube furnace for annealing treatment, the annealing temperature is maintained, and nitrogen is introduced after the annealing is completed to allow it to cool naturally. Step S3, preparing hexagonal diamond nanorods: Using an inductively coupled plasma etching device to etch the hexagonal diamond seeds covered with the nickel mask obtained in step S2, and introducing oxygen to etch the hexagonal diamond seeds to obtain hexagonal diamond nanorods; After etching, the remaining impurities and nickel particles are cleaned with acid; then, the vacuum is evacuated, hydrogen is introduced and the temperature is maintained, and the hexagonal diamond nanorods are etched with hydrogen to expose the (100) step surface; Step S4, growing hexagonal diamond single crystal or thin film by chemical vapor deposition: The hexagonal diamond nanorods obtained in step S3 are deposited on a deposition device using a chemical vapor deposition method to grow a hexagonal diamond single crystal or a thin film to obtain hexagonal diamond.

2. The method for growing hexagonal diamond by homoepitaxial chemical vapor deposition according to claim 1, characterized in that: In step S2, the vacuum degree in the deposition chamber is controlled to be 1.0×10 -5 Pa, introduce argon gas with a flow rate of 30-40 sccm, control the gas pressure to 2Pa, and adjust the power to 45-60W.

3. The method for growing hexagonal diamond by homoepitaxial chemical vapor deposition according to claim 1, characterized in that: In the step S2, the hexagonal diamond seeds are deposited using a magnetron sputtering deposition system for 35 to 40 seconds to obtain a nickel film with a thickness of 5 to 6 nm; the sample with the deposited nickel film is placed in an atmosphere tube furnace for annealing, the annealing temperature is maintained at 700 to 750° C., and the annealing is performed for 10 to 20 minutes.

4. The method for growing hexagonal diamond by homoepitaxial chemical vapor deposition according to claim 1, characterized in that: In step S3, the RF / ICP power of the inductively coupled plasma etching equipment is adjusted to 100 / 800 W, the volume flow rate of oxygen is controlled to 25-30 sccm, the pressure is 25 m-Torr, and the etching time is 15-20 min to obtain hexagonal diamond nanorods with a height of 180-220 nm.

5. The method for growing hexagonal diamond by homoepitaxial chemical vapor deposition according to claim 1, characterized in that: In the step S3, the vacuum is evacuated to less than 0.1 Pa, hydrogen gas is introduced at a flow rate of 300-350 sccm, and the temperature is maintained at 700-750°C.

6. The method for growing hexagonal diamond by homoepitaxial chemical vapor deposition according to claim 1, characterized in that: The chemical vapor deposition method in step S4 includes a hot wire method, a combustion flame method, a microwave plasma chemical vapor deposition method, an electron cyclotron resonance microwave plasma chemical vapor deposition method, a radio frequency chemical vapor deposition method, a direct current chemical vapor deposition method, a direct current assisted plasma chemical vapor deposition method, a direct current arc plasma jet chemical vapor deposition method and a laser chemical vapor deposition method.

7. The method for growing hexagonal diamond by homoepitaxial chemical vapor deposition according to claim 6, characterized in that: The hot wire method in step S4 comprises the following steps: introducing methane and hydrogen into a reaction chamber, controlling the filament temperature in the reaction chamber at 2500° C., controlling the substrate temperature at 700-900° C., controlling the deposition pressure at 2.5 KPa, forming a hexagonal diamond single crystal or thin film on the substrate, and obtaining hexagonal diamond; The combustion flame method in step S4 comprises the following steps: using an oxygen-acetylene flame combustion method for deposition, the oxygen-acetylene flame temperature is 2000-3550K, the volume ratio of oxygen-acetylene is 0.85:1, and a hexagonal diamond single crystal or thin film is deposited on a hexagonal diamond substrate to obtain hexagonal diamond.

8. The method for growing hexagonal diamond by homoepitaxial chemical vapor deposition according to claim 6, characterized in that: The DC arc plasma jet chemical vapor deposition method in step S4 comprises the following steps: using a 100kW high-power DC Arc Plasma Jet CVD device, introducing a gas source containing argon, hydrogen and methane, and utilizing the high-temperature plasma generated by DC arc discharge to dissociate the gas source, so that the gas expands due to heat and is ejected from the anode nozzle to form an arc plasma column, wherein the plasma temperature inside the arc plasma column reaches above 4000°C, and after the plasma is gradually cooled, a hexagonal diamond single crystal or thin film is deposited on a substrate to obtain hexagonal diamond.

9. The method for growing hexagonal diamond by homoepitaxial chemical vapor deposition according to claim 6, characterized in that: The microwave plasma chemical vapor deposition method in step S4 introduces a parallel laser source, comprising the following steps: using an MP-CVD device with a frequency of 2.45 GHz, introducing methane and hydrogen, wherein the purity of the methane and hydrogen is 5N, wherein the methane concentration is 4% to 8%, controlling the deposition pressure to be 15 to 25 Kpa, controlling the temperature in the reaction chamber to be 600 to 700° C., and simultaneously turning on a super-Gaussian distribution continuous laser source with a wavelength of 532 nm, and setting the laser power to 40 W / cm 2 The laser source is parallel to the substrate, irradiating the free radicals, the substrate temperature is controlled at 600-800°C, and hexagonal diamond single crystals or thin films are deposited on the substrate to obtain hexagonal diamond.

10. Hexagonal diamond prepared by the method for growing hexagonal diamond by homoepitaxial chemical vapor deposition as claimed in any one of the preceding claims.

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