Diamond-based boron nitride film and preparation method thereof

Abstract

The invention discloses a diamond-based boron nitride film and a preparation method thereof, and relates to the technical field of semiconductor epitaxial materials.The preparation method comprises the steps that a single crystal diamond substrate is sequentially subjected to polishing and cleaning pretreatment; performing luminance build-up cleaning treatment on the cavity, and raising the temperature in the cavity to a growth temperature; performing glow build-up activation treatment on the surface of the pretreated monocrystal diamond substrate; carrying out auxiliary glow-build-up activation treatment on the surface of the monocrystal diamond substrate after glow-build-up activation; growing a boron nitride film on the surface of the monocrystal diamond substrate after surface treatment; cooling the growth temperature to room temperature to obtain a cooled diamond-based boron nitride film; and carrying out annealing treatment on the cooled diamond-based boron nitride film to obtain the finally prepared diamond-based boron nitride film. According to the method, the key requirements of low interface damage, high nucleation activity, stress controllable release and the like can be met at the same time.

Description

Technical Field

[0001] This invention relates to the field of semiconductor epitaxial materials technology, specifically to a diamond-based boron nitride thin film and its preparation method. Background Technology

[0002] Diamond and boron nitride (BN) are both ultrawide bandgap semiconductor materials. Diamond has a bandgap of 5.5 eV, while boron nitride has a bandgap between 5.5 and 6.4 eV depending on its crystal form (such as hexagonal, cubic, etc.). Both have extremely high thermal conductivity (among the top known solid materials), extremely high mechanical hardness, high breakdown characteristics, and extremely strong high temperature resistance and radiation resistance. The ultrawide bandgap and high conduction / valence band shift of hexagonal boron nitride (h-BN) enable it to effectively confine charge carriers in diamond, allowing for the formation of two-dimensional hole-gas p-type devices that are superior to those of hydrogen / silicon-terminated diamond. Cubic boron nitride (c-BN) and diamond have extremely high crystal symmetry and very small lattice mismatch (1.3%). Their band alignment can form high-performance heterojunctions. Utilizing the n-type doping potential of c-BN can overcome the long-standing limitations in the fabrication of diamond n-type devices. The combination of diamond and boron nitride has the potential to achieve higher power and faster heat dissipation, thereby achieving higher power density and efficiency. Furthermore, the combination of boron nitride and diamond can realize solar-blind deep ultraviolet detectors with high signal-to-noise ratios. In quantum technology, h-BN itself contains quantum emitters, and its combination with diamond nitrogen-vacancy (NV) color centers holds promise for constructing hybrid quantum systems. It can also serve as an ideal optical cladding, helping to protect the coherence of qubits in diamond NV color centers. The combined advantages of both materials can be utilized for quantum sensing and quantum computing applications. Therefore, diamond-based boron nitride material systems will be of great significance in the development of high-performance radio frequency and power semiconductor devices, photodetectors, and quantum technologies.

[0003] Currently, the technology for preparing large-size diamonds is more mature and less expensive than that for preparing boron nitride. Epitaxial growth of boron nitride on diamond has become the preferred technical solution for developing diamond-based boron nitride material systems.

[0004] However, the performance advantages of diamond-based boron nitride materials are highly dependent on the quality of material growth. In particular, the quality control of the diamond interface before boron nitride growth has a significant impact on the performance of this composite material. How to control the orderliness of the interface chemical bonds, suppress the formation of amorphous layers, and obtain an interface with atomically clean and low-stress ideal band arrangement has become an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a diamond-based boron nitride thin film and its preparation method.

[0006] The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a diamond-based boron nitride thin film, comprising: Single-crystal diamond substrates were selected; The single-crystal diamond substrate is pretreated by polishing and cleaning in sequence to obtain a pretreated single-crystal diamond substrate; At room temperature, the cavity containing the pretreated single-crystal diamond substrate is subjected to a smoldering cleaning process using argon and nitrogen in sequence. Then, the temperature inside the cavity is raised to the growth temperature in a nitrogen atmosphere. The growth temperature is the temperature required to grow a boron nitride thin film. Under the growth temperature conditions, the surface of the pretreated single-crystal diamond substrate is subjected to smoldering activation treatment using argon gas to obtain a smoldering activated single-crystal diamond substrate. Nitrogen gas is introduced while maintaining the ignition treatment conditions. Nitrogen gas is used to assist the ignition activation treatment on the surface of the ignition activated single crystal diamond substrate. After the nitrogen ignition is stabilized, the argon gas is turned off to complete the interface pre-nitriding and the construction of nitrogen-related active sites, and a surface-treated single crystal diamond substrate is obtained. Under the growth temperature conditions, a boron nitride film is grown on the surface of the surface-treated single-crystal diamond substrate to obtain a diamond-based boron nitride film. In a nitrogen atmosphere, the growth temperature is cooled to room temperature to obtain a cooled diamond-based boron nitride film. The diamond-based boron nitride film after cooling is annealed by heating to the annealing temperature in a nitrogen atmosphere to obtain the final diamond-based boron nitride film.

[0007] In one embodiment of the present invention, a single-crystal diamond substrate is selected, comprising: A single-crystal diamond substrate with (111) crystal orientation was selected and prepared by microwave plasma chemical vapor deposition. In one embodiment of the present invention, the single-crystal diamond substrate is subjected to polishing and cleaning pretreatment sequentially to obtain a pretreated single-crystal diamond substrate, comprising: The surface of the single-crystal diamond substrate is subjected to chemical mechanical polishing or mechanical polishing to obtain a polished single-crystal diamond substrate; The polished single-crystal diamond substrate was immersed and cleaned with a piranha solution at 80~120℃ to remove surface organic contaminants, resulting in an immersed and cleaned single-crystal diamond substrate. The pretreated single-crystal diamond substrate was ultrasonically cleaned sequentially with acetone, ethanol and deionized water at room temperature to obtain the pretreated single-crystal diamond substrate. In one embodiment of the present invention, the cavity containing the pretreated single-crystal diamond substrate is subjected to a glow cleaning treatment using argon and nitrogen gas sequentially at room temperature, followed by raising the temperature within the cavity to the growth temperature in a nitrogen atmosphere, including: Argon gas is introduced into the cavity containing the pretreated single-crystal diamond substrate at room temperature to perform the first ignition cleaning of the internal environment of the cavity. After the first ignition cleaning is completed, the argon gas is turned off and nitrogen gas is introduced into the cavity to perform the second ignition cleaning of the internal environment of the cavity, until the second ignition cleaning of the cavity is completed. After the chamber is cleaned to ignite, it is subjected to a gradient heating process in a nitrogen atmosphere until it reaches the growth temperature, wherein the growth temperature is 700~800℃, the heating rate is 30~40℃ / min below 500℃, the heating rate is 10~20℃ / min in the 500~700℃ range, and the heating rate is 5~10℃ / min in the 700~800℃ range.

[0008] In one embodiment of the present invention, under the growth temperature conditions, the surface of the pretreated single-crystal diamond substrate is subjected to a glow activation treatment using argon gas to obtain a glow-activated single-crystal diamond substrate, comprising: Under the growth temperature conditions, argon gas with a flow rate of 80~100 sccm is introduced, and a substrate bias voltage of 150~340V is applied to the pretreated single-crystal diamond substrate to perform a spark activation treatment on the surface of the pretreated single-crystal diamond substrate, so that the surface of the pretreated single-crystal diamond substrate undergoes interfacial chemical activation and removal of intrinsic chemical bonds, thereby obtaining the spark activated single-crystal diamond substrate, wherein the spark activation treatment time is 30~60s. In one embodiment of the present invention, nitrogen gas is introduced while maintaining the ignition treatment conditions. Nitrogen gas is used to assist in the ignition activation treatment of the surface of the ignited single-crystal diamond substrate. After the nitrogen ignition stabilizes, the argon gas is turned off, completing the interface pre-nitriding and the construction of nitrogen-related active sites, resulting in a surface-treated single-crystal diamond substrate, comprising: While maintaining the ignition treatment conditions, nitrogen gas with a flow rate of 20-40 sccm is introduced into the argon ignition state, so that the nitrogen gas is excited to form active nitrogen species under the assistance of argon plasma, so as to perform auxiliary ignition activation treatment on the surface of the single crystal diamond substrate after ignition activation. After the nitrogen ignition stabilizes, the argon gas is turned off. After the auxiliary ignition activation treatment is completed, the single crystal diamond substrate with the completed surface treatment is obtained. The auxiliary ignition activation treatment time is about 60-180 s. In one embodiment of the present invention, under the growth temperature conditions, a boron nitride thin film is grown on the surface of the surface-treated single-crystal diamond substrate to obtain a diamond-based boron nitride thin film, comprising: Under the specified growth temperature conditions, a boron nitride thin film is grown on the surface of the surface-treated single-crystal diamond substrate using physical vapor deposition to obtain the diamond-based boron nitride thin film. The second growth temperature is 600~800℃, the growth power is 80~100W, the growth time is 5~10 hours, and a mixture of nitrogen and argon is introduced as the working atmosphere during the growth process. The nitrogen flow rate is 20~40 sccm, the argon flow rate is 40~80 sccm, the pressure is 30~60 mbar, and the substrate bias voltage is 150~340V. In one embodiment of the present invention, the growth temperature is cooled to room temperature in a nitrogen atmosphere to obtain a cooled diamond-based boron nitride film, comprising: In a nitrogen atmosphere, the growth temperature is cooled to room temperature at a cooling rate of 5~15℃ / min to obtain a cooled diamond-based boron nitride film. In one embodiment of the present invention, the diamond-based boron nitride film after cooling is annealed by heating to an annealing temperature in a nitrogen atmosphere to obtain the final prepared diamond-based boron nitride film, comprising: Under a nitrogen atmosphere, the nitrogen flow rate is maintained at 800~1000 sccm, and the temperature is increased to the annealing temperature of 900~1000℃ at a heating rate of 15~20℃ / min. The annealing temperature is then maintained for 20~30 min to anneal the cooled diamond-based boron nitride film. After annealing, the temperature is reduced to room temperature at a cooling rate of 5~15℃ / min to obtain the final diamond-based boron nitride film.

[0009] Secondly, the present invention also provides a diamond-based boron nitride thin film, wherein the diamond-based boron nitride thin film is the final diamond-based boron nitride thin film obtained by the preparation method described in any of the above embodiments.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention introduces a nitrogen-assisted ignition pretreatment step into a single-crystal diamond substrate before boron nitride film growth. This controlled plasma activation and slight nitriding treatment of the single-crystal diamond substrate surface, without boron nitride deposition, preferentially promotes the formation of CN chemical bonds at the interface. Because this interface modification process introduces stable nitrogen-related active sites to the single-crystal diamond substrate surface in the early nucleation stage, it improves the interfacial chemical compatibility between diamond and boron nitride, thus providing favorable conditions for the subsequent stable adsorption of B atoms and the orderly construction of BN covalent bonds. This promotes uniform nucleation and continuous growth of the boron nitride film, alleviates the problem of nitrogen vacancy enrichment caused by insufficient local nitrogen supply in the initial growth stage, and effectively improves the crystal integrity and interface quality of the boron nitride film.

[0011] 2. This invention employs a stepwise substrate pretreatment method, first performing argon ignition activation followed by nitrogen-assisted ignition, to effectively remove adsorbed contaminants from the surface of single-crystal diamond substrates without relying on strong plasma etching or high-energy processing conditions. Since argon ignition primarily serves for surface cleaning and atomic rearrangement, while nitrogen-assisted ignition mainly involves surface chemical activation with the participation of low-energy reactive nitrogen species, this method enhances the chemical reactivity and interfacial bonding ability of the single-crystal diamond substrate surface without introducing significant lattice damage. This effectively suppresses the formation of amorphous layers and provides favorable conditions for constructing a cleaner and more stable diamond-boron nitride heterojunction interface. 3. This invention introduces a stepwise plasma interface pretreatment method before the growth of boron nitride thin films. By precisely controlling the nucleation conditions and interfacial chemical state on the single-crystal diamond substrate surface, the boron nitride thin film achieves a high and uniform nucleation density in the early stages of growth, and enhances the interfacial bonding stability between the boron nitride thin film and the single-crystal diamond substrate. Due to the more uniform nucleation distribution and more continuous interfacial bonding, the internal stress generated during the growth and cooling of the boron nitride thin film can be uniformly dispersed and gradually released over a larger area, thereby reducing the risk of cracking and local delamination caused by stress concentration. This facilitates the stable fabrication of thicker and larger-sized diamond-based boron nitride thin films, providing a reliable material basis for subsequent device processing and large-scale applications.

[0012] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0013] Figure 1 This is a schematic flowchart of a method for preparing a diamond-based boron nitride thin film provided by the present invention; Figure 2This is a schematic diagram comparing the interface state of diamond and boron nitride on a single-crystal diamond substrate after conventional polishing and cleaning, and on a single-crystal diamond substrate with surface treatment completed by the method provided in this invention. Figure 3 This is a three-dimensional atomic force microscope schematic diagram of the surface morphology of diamond and diamond-based boron nitride films obtained under different processing conditions, provided in the embodiments of the present invention. Figure 4 This is a scanning electron microscope comparison image of the surface morphology of boron nitride films grown on a single-crystal diamond substrate obtained by conventional polishing and cleaning methods and a single-crystal diamond substrate obtained by the method provided in this invention. Figure 5 This is a high-resolution transmission electron microscope comparison image of the interface between a boron nitride thin film grown on a single-crystal diamond substrate obtained by conventional polishing and cleaning methods and a single-crystal diamond substrate obtained by the method provided in this invention. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0015] Example 1 Based on current research findings, the following challenges remain in improving the performance and quality of diamond-based boron nitride: First, the surface condition of the diamond substrate not only affects the nucleation density and grain size distribution of boron nitride (BN) films, but also significantly influences the point defect structure within the BN film. In the early stages of BN film growth, insufficient chemical activity on the diamond surface, inadequate interfacial reactions, or limited local nitrogen source supply can easily introduce intrinsic point defects such as nitrogen vacancies into the BN film. Nitrogen vacancies, being a type of defect with low formation energy and high occurrence probability in BN materials, disrupt local BN covalent bond structures, introducing defect energy levels into the band structure. This not only reduces the crystallinity of the BN film, leading to the formation of a large amount of amorphous BN, but also adversely affects carrier transport characteristics, interfacial electrical properties, and device reliability. Especially in diamond / boron nitride heterostructures, N vacancies are more likely to accumulate in the initial nucleation region and near the interface, further weakening the interfacial bonding strength and exacerbating stress concentration at the interface.

[0016] Secondly, the cleaning process at the diamond interface can easily damage the diamond surface. The formation of amorphous layers and hybrid carbon leads to poor boron nitride growth quality, poor boron nitride crystal orientation at the interface, and easy enrichment of boron nitride in the amorphous layer. Under current technological conditions, the diamond surface is usually pretreated only by mechanical polishing, chemical cleaning, or strong plasma etching. Although this can reduce surface roughness or remove contaminants to some extent, it is often difficult to effectively improve the chemical reactivity of the diamond surface. It cannot provide sufficient nitrogen-related active sites for stable nucleation of boron nitride. In this case, the lack of stable and controllable nitrogen-related active sites near the interface in the early stage of boron nitride growth results in insufficient nitrogen supply, making it difficult to effectively suppress nitrogen vacancies in the boron nitride film, which tend to accumulate in the initial nucleation region and at the interface. To enhance surface reactivity, plasma etching or high-energy treatment can be used, but this can easily introduce lattice damage or new defects into the diamond surface. These defects may also evolve into new defect sources during subsequent boron nitride growth, which is detrimental to the control of nitrogen vacancies and the improvement of interface quality. In summary, while existing substrate pretreatment processes improve surface morphology, they still struggle to simultaneously meet multiple requirements such as enhanced nucleation activity, low interfacial damage, and nitrogen vacancy suppression.

[0017] Finally, the fabrication of large-size diamond-based boron nitride materials remains challenging. Interfacial stress continues to significantly impact material growth, and macroscopic defects such as film wrinkling are common. Existing diamond-based boron nitride materials can be prepared using a mechanical transfer method, where a separately grown boron nitride film is transferred onto diamond, followed by epitaxial growth. However, due to insufficient chemical bonding at the mechanical transfer interface, residual stress generated during film growth is difficult to release effectively, reaching levels on the order of GPa, thus inducing a high density of interfacial defects. Macroscopically, this typically manifests as a significant increase in film surface roughness (R0). q The method suffers from reduced crystal quality and film wrinkling issues when the film thickness exceeds 5nm, and cracking or localized peeling is prone to occur when the film thickness exceeds 100-200nm, severely affecting the performance and reliability of subsequent devices. More importantly, the above method is difficult to scale up efficiently, which is detrimental to the future development of low-cost diamond-based boron nitride materials.

[0018] Therefore, how to effectively regulate the diamond surface, enhance its chemical activity, and construct a surface environment conducive to nitrogen stability and interfacial reaction in the early stage of nucleation while avoiding significant physical damage, thereby simultaneously improving the nucleation behavior and interfacial bonding conditions of boron nitride, has become one of the key technical problems restricting the high-quality epitaxy of diamond-based boron nitride films, and new substrate pretreatment technologies are urgently needed to solve this problem.

[0019] Please see Figure 1 , Figure 1This is a schematic flowchart illustrating a method for preparing a diamond-based boron nitride thin film according to the present invention. The embodiment of the present invention provides a method for preparing a diamond-based boron nitride thin film, the method comprising: Step 1: Select a single-crystal diamond substrate.

[0020] Specifically, a (111) oriented single-crystal diamond substrate was selected, which was prepared by microwave plasma chemical vapor deposition.

[0021] In this embodiment, in order to select a single-crystal diamond substrate with a stable surface structure, a single-crystal diamond substrate prepared by microwave plasma chemical vapor deposition is selected, and the crystal orientation is (111). This single-crystal diamond substrate has the advantages of fewer impurities and defects and less thermal stress, which can provide a crystallographic basis for the subsequent control of interface bonding and nucleation behavior.

[0022] Furthermore, the thickness of the single-crystal diamond substrate is 1~1000μm, and the size is, for example, 5×5mm.

[0023] Step 2: Polish and clean the single-crystal diamond substrate sequentially to obtain the pretreated single-crystal diamond substrate.

[0024] Specifically, in this embodiment, the single-crystal diamond substrate is first polished to reduce its surface roughness. After polishing, the single-crystal diamond substrate is then cleaned to remove organic contaminants and residual impurities from its surface, thus obtaining a clean single-crystal diamond substrate.

[0025] Step 2.1: Perform chemical mechanical polishing or mechanical polishing on the surface of the single-crystal diamond substrate to obtain the polished single-crystal diamond substrate.

[0026] Specifically, chemical mechanical polishing or mechanical polishing can be used to smooth the surface of single-crystal diamond substrates, which can reduce surface roughness and mitigate the adverse effects of surface morphology undulations on subsequent nucleation uniformity and the consistency of interfacial chemical reactions.

[0027] Furthermore, the root mean square roughness (Rq) of the polished single-crystal diamond substrate surface is 0.3~0.7 nm.

[0028] Step 2.2: Immerse and clean the polished single-crystal diamond substrate in a piranha solution (concentrated sulfuric acid: hydrogen peroxide = 7:3) at 80~120℃ to remove organic contaminants from the surface of the polished single-crystal diamond substrate, and obtain the immersed and cleaned single-crystal diamond substrate.

[0029] Optionally, the soaking and rinsing time in the piranha solution is 20 to 30 minutes.

[0030] Step 2.3: At room temperature, the soaked and cleaned single-crystal diamond substrate is ultrasonically cleaned sequentially with acetone, ethanol and deionized water to obtain the pretreated single-crystal diamond substrate.

[0031] Specifically, at room temperature, the soaked and cleaned single-crystal diamond substrate is first ultrasonically cleaned with acetone, then ultrasonically cleaned with ethanol, and finally ultrasonically cleaned with deionized water to further remove residual impurities and obtain a clean single-crystal diamond substrate. This clean single-crystal diamond substrate is the pretreated single-crystal diamond substrate, which can reduce the interference of intrigued chemical bonds on the subsequent interfacial bonding and early nucleation reaction processes.

[0032] Optionally, the ultrasonic cleaning time in acetone, ethanol, and deionized water is 5 to 10 minutes.

[0033] Step 3: At room temperature, the cavity containing the pretreated single-crystal diamond substrate is subjected to a smoldering cleaning process using argon and nitrogen in sequence. Then, the temperature inside the cavity is raised to the growth temperature in a nitrogen atmosphere. This growth temperature is the temperature required to grow a boron nitride thin film.

[0034] Specifically, the pretreated single-crystal diamond substrate is fixed on the sample plate and sent into the cavity of the physical vapor deposition system. The protective cover is opened, and then the cavity containing the pretreated single-crystal diamond substrate is subjected to a glow cleaning treatment at room temperature to remove residual impurities in the cavity and stabilize the cavity atmosphere.

[0035] Step 3.1: At room temperature, argon gas is introduced into the cavity containing the pretreated single-crystal diamond substrate to perform the first ignition cleaning of the cavity's internal environment. After the first ignition cleaning is completed, the argon gas is turned off, and nitrogen gas is introduced into the cavity to perform the second ignition cleaning of the cavity's internal environment, until the second ignition cleaning of the cavity is completed.

[0036] Specifically, the pretreated single-crystal diamond substrate is fixed on the sample disk and fed into the cavity of the physical vapor deposition system. Then, argon gas at a flow rate of 50-100 sccm is introduced into the cavity to perform a first glow cleaning of the internal environment of the cavity. The first glow cleaning takes 2-5 minutes. After the first glow cleaning is completed, the argon gas supply is turned off. Since there is still some argon gas in the cavity that was introduced for the first glow cleaning, nitrogen gas at a flow rate of 1-20 sccm is introduced into the cavity to cause the nitrogen to glow, thereby performing a second glow cleaning of the internal environment of the cavity. This removes residual impurities in the cavity and stabilizes the atmosphere in the cavity. The second glow cleaning takes 2-5 minutes.

[0037] Step 3.2: After completing the ignition cleaning of the cavity, the cavity is subjected to gradient heating in a nitrogen atmosphere until it reaches the growth temperature.

[0038] Specifically, after completing the ignition cleaning of the cavity in step 3.1, the protective cover is closed, and nitrogen gas with a flow rate of 20~40 sccm is introduced into the cavity. The internal environment of the cavity is then subjected to gradient heating treatment to bring the temperature inside the cavity to 700~800℃, which is the process temperature required for subsequent boron nitride thin film growth. The nitrogen gas is then turned off. This ensures that the single crystal diamond substrate has a stable thermal and atmospheric environment before entering the nucleation control stage. The growth temperature is 700~800℃, the heating rate is 30~40℃ / min below 500℃, the heating rate is 10~20℃ / min in the 500~700℃ range, and the heating rate is 5~10℃ / min in the 700~800℃ range.

[0039] Step 4: Under the growth temperature conditions, the surface of the pretreated single-crystal diamond substrate is subjected to ignition activation treatment using argon gas to obtain the ignition activated single-crystal diamond substrate.

[0040] Specifically, in the heated physical vapor deposition system, argon gas is introduced into the cavity under the growth temperature conditions. The surface of the pretreated single-crystal diamond substrate is activated under the argon atmosphere. The inert bombardment effect of argon plasma is used to desorb the contaminants adsorbed on the surface of the pretreated single-crystal diamond substrate and effectively remove the non-intrinsic chemical bonds such as CH and CO bonds on the surface of the pretreated single-crystal diamond substrate. At the same time, it induces local rearrangement of carbon atoms on the surface, thereby obtaining a chemically purer and more ordered interface surface, providing an activation basis for subsequent interface bonding reactions.

[0041] In one specific embodiment, step 4 may include: Under the growth temperature conditions, argon gas with a flow rate of 80~100 sccm is introduced, and a substrate bias voltage of 150~340V is applied to the pretreated single crystal diamond substrate to perform a stun activation treatment on the surface of the pretreated single crystal diamond substrate, so that the surface of the pretreated single crystal diamond substrate undergoes interfacial chemical activation and removal of intrinsic chemical bonds, resulting in a stun activated single crystal diamond substrate.

[0042] Specifically, after removing the protective cover, argon gas with a flow rate of 80-100 sccm is introduced into the vacuum chamber under the growth temperature conditions. After evacuating and introducing argon gas to form a low-pressure atmosphere, a substrate bias voltage of 150-340V is applied to the pretreated single-crystal diamond substrate (by applying radio frequency bias voltage to the sample disk or substrate electrode), causing the argon gas in the chamber to undergo Paschen breakdown and forming a local glow discharge near the single-crystal diamond substrate, thereby igniting the plasma and performing a glow treatment on the surface of the pretreated single-crystal diamond substrate. During the argon glow activation process, the argon plasma mainly plays the role of surface cleaning, removing intrinsic CH and CO bonds, and promoting atomic rearrangement of the surface, thereby improving the cleanliness, flatness, and interface structure order of the single-crystal diamond substrate surface without introducing significant lattice damage.

[0043] Optionally, the activation treatment time is 30~60s.

[0044] Step 5: While maintaining the ignition treatment conditions, nitrogen gas is introduced to assist in the ignition activation treatment of the surface of the single crystal diamond substrate after ignition activation. After the nitrogen ignition is stable, the argon gas is turned off to complete the interface pre-nitriding and the construction of nitrogen-related active sites, and the surface-treated single crystal diamond substrate is obtained.

[0045] Specifically, after completing the argon-induced luminescence interface chemical activation and intrinsic chemical bond removal treatment, nitrogen gas is introduced into the cavity while maintaining the luminescence treatment conditions. Nitrogen gas is gradually introduced under continuous argon gas flow, forming a mixed atmosphere of argon and nitrogen, creating a luminescence plasma environment under this mixed atmosphere. During this process, the argon plasma provides stable luminescence and energy coupling conditions, promoting the effective excitation and dissociation of nitrogen in the plasma, thereby forming a reaction system dominated by low-energy reactive nitrogen species in the interface region. Subsequently, while maintaining the luminescence state, the argon gas is turned off (when the glow color in the cavity turns purplish-pink), leaving only the nitrogen atmosphere. This allows the plasma to gradually transition to a pure nitrogen luminescence state (glow color is reddish-purple), performing nitrogen-assisted activation treatment on the surface of the single-crystal diamond substrate. In this process, the carbon dangling bonds exposed on the diamond surface after the preceding argon ignition treatment undergo a controlled reaction with active nitrogen species, preferentially inducing the formation of CN-related chemical bonds at the interface. This achieves a slight pre-nitriding treatment on the surface of the single-crystal diamond substrate and constructs stable and controllable nitrogen-related active sites on the surface of the single-crystal diamond substrate, providing favorable conditions for subsequent boron nitride nucleation and interfacial bonding reactions.

[0046] In one specific embodiment, step 5 may include: While maintaining the ignition treatment conditions, nitrogen gas with a flow rate of 20~40 sccm is introduced into the argon ignition state, so that the nitrogen gas is excited to form active nitrogen species under the assistance of argon plasma, so as to perform auxiliary ignition activation treatment on the surface of the single crystal diamond substrate after ignition activation. After the nitrogen ignition stabilizes, the argon gas is turned off. After the auxiliary ignition activation treatment is completed, the surface-treated single crystal diamond substrate is obtained.

[0047] Specifically, under the conditions of maintaining a substrate bias voltage of 150-340V and a temperature at the growth temperature, nitrogen gas with a flow rate of 20-40 sccm is introduced into the argon-assisted glow state. This allows the nitrogen to be excited to form active nitrogen species under the assistance of the argon plasma, thus performing a glow treatment on the surface of the single-crystal diamond substrate. Once the glow color turns purplish-pink, it indicates that the nitrogen glow is stable. At this point, the argon gas is gradually shut off, leaving only nitrogen to participate in the interface activation process. The entire assisted glow activation process takes approximately 60-180 seconds. During the nitrogen-assisted glow treatment, the plasma effect is mainly focused on surface chemical activation and interface bonding regulation, rather than physical bombardment or etching by high-energy particles. This effectively improves the chemical reactivity and interface bonding ability of the single-crystal diamond substrate surface without introducing significant lattice damage. By completing the aforementioned interface pre-nitridation and construction of nitrogen-related active sites before boron nitride growth, B atoms can preferentially achieve stable adsorption near nitrogen-related active sites during subsequent boron nitride growth, and synergize with the pre-formed CN bonds at the interface to promote the orderly construction of BN covalent bonds; thus providing favorable interface conditions for uniform nucleation and high-quality epitaxial growth of boron nitride films.

[0048] like Figure 2 As shown, Figure 2 Figure a shows the schematic state of the diamond-boron nitride interface formed on a single-crystal diamond substrate treated with conventional polishing and cleaning methods. It can be seen that the interface lacks stable and controllable nitrogen-related active sites and has poor interfacial bonding order. Figure 2 Figure b shows the interface between diamond and boron nitride formed by the preparation method of this embodiment. It can be seen that after nitrogen-assisted ignition activation and slight pre-nitriding treatment, CN-related chemical bonds are preferentially formed on the diamond surface and stable nitrogen-related active sites are constructed. This completes the pre-construction of the interface chemical state before boron nitride growth, providing favorable interface conditions for the uniform nucleation and orderly growth of the subsequent boron nitride film.

[0049] Step 6: Under the growth temperature conditions, grow a boron nitride film on the surface of the surface-treated single-crystal diamond substrate to obtain a diamond-based boron nitride film.

[0050] Specifically, in a physical vapor deposition system, under growth temperature conditions, a boron nitride film is deposited on the surface of a surface-treated single-crystal diamond substrate to obtain a diamond-based boron nitride film. Under the interfacial conditions of the single-crystal diamond substrate prepared in step 5, the B atoms introduced during the boron nitride growth process can preferentially achieve stable adsorption near the nitrogen-related active sites already constructed on the surface of the single-crystal diamond substrate, and synergize with the CN-related chemical bonds pre-formed at the interface to promote the orderly construction of BN covalent bonds. This allows the boron nitride film to achieve a high and uniform nucleation density in the early stages of growth and promotes the continuous growth of the boron nitride film.

[0051] In one specific embodiment, step 6 may include: Under the specified growth temperature conditions, boron nitride thin films were grown on the surface of surface-treated single-crystal diamond substrates using physical vapor deposition (PVD) to obtain diamond-based boron nitride thin films. The growth power was 80-100W, the growth time was 5-10 hours, and a mixture of nitrogen and argon was introduced as the working atmosphere during the growth process. The flow rate of nitrogen was 20-40 sccm, the flow rate of argon was 40-80 sccm, the pressure was 30-60 mbar, and the substrate bias voltage was 150-340 V.

[0052] Under the above process conditions, combined with the nitrogen-related active sites and CN interface bonding structure constructed by the aforementioned interface pretreatment, the nucleation process of boron nitride thin films gradually changes from random and discrete island-like nucleation to a more uniform and continuous nucleation mode, providing a stable foundation for subsequent increases in film thickness and further improvement in structural order.

[0053] Step 7: In a nitrogen atmosphere, the growth temperature is lowered to room temperature to obtain a cooled diamond-based boron nitride film.

[0054] Specifically, the growth temperature is cooled to room temperature at a cooling rate of 5~15℃ / min in a nitrogen atmosphere to obtain a cooled diamond-based boron nitride film.

[0055] In this embodiment, after the boron nitride thin film deposition is completed, the diamond-based boron nitride thin film prepared in step 6 is first subjected to controlled cooling in a pure nitrogen atmosphere. The film is slowly cooled to room temperature at a cooling rate of 5-15°C / min, and then the cooled diamond-based boron nitride thin film is removed. The cooling rate sampled in this embodiment helps to effectively alleviate the thermal stress introduced by the difference in thermal expansion coefficients between the boron nitride thin film and the single-crystal diamond substrate, promotes the stability of the interface transition layer, and reduces the risk of cracking or local peeling of the boron nitride thin film during cooling, thereby improving the adhesion and structural stability of the boron nitride thin film.

[0056] Step 8: Heat the diamond-based boron nitride film to the annealing temperature in a nitrogen atmosphere, and anneal the cooled diamond-based boron nitride film to obtain the final diamond-based boron nitride film.

[0057] Specifically, after step 7, the cooled diamond-based boron nitride film is placed in a rapid thermal annealing furnace for annealing. Under a pure nitrogen atmosphere, the nitrogen flow rate is maintained at 800-1000 sccm, and the sample is heated to an annealing temperature of 900-1000℃ at a heating rate of 15-20℃ / min. This temperature is then maintained for 20-30 minutes to effectively repair internal defects in the diamond-based boron nitride film and release residual stress, thereby improving the crystallinity and density of the film. After annealing, the film is slowly cooled to room temperature at a cooling rate of 5-15℃ / min to further reduce thermal stress caused by differences in thermal expansion coefficients and prevent film cracking and detachment. The entire annealing process is carried out under atmospheric pressure or slightly positive pressure to ensure the stability and purity of the nitrogen environment and to avoid adverse effects of external impurities on the diamond-based boron nitride film and its interface.

[0058] After completing the deposition and annealing of the boron nitride thin film, this embodiment also performed a series of characterization analyses on the surface morphology of the finally prepared diamond-based boron nitride thin film.

[0059] To address the issue that the surface condition of diamond substrates affects the nucleation density and grain size distribution of boron nitride (BN) films, and further influences the internal point defect structure of BN films, atomic force microscopy (AFM) was used for characterization. The results are as follows: Figure 3 As shown.

[0060] Figure 3 Figure a shows the surface morphology of a single-crystal diamond substrate after conventional mechanical polishing. It can be seen that the surface of the single-crystal diamond substrate exhibits densely distributed polishing textures along a single direction, with noticeable surface undulations and a surface roughness R. q The value is 0.643 nm, indicating that while the polishing process reduces the overall roughness, it introduces strong anisotropic morphological features, which can easily lead to uneven nucleation conditions during subsequent film growth.

[0061] Figure 3 Figure b shows the surface morphology of a boron nitride film grown on a single-crystal diamond substrate treated with only conventional polishing and cleaning methods. The surface exhibits obvious discrete island-like nucleation characteristics, significantly increased surface undulations, and a high surface roughness R0. q The result of reaching 4.742 nm indicates that the boron nitride film grown after conventional treatment grows in a non-uniform island-like manner in the early stage of nucleation, with discrete grain size distribution and defect-rich regions easily forming near the interface and grain boundaries.

[0062] Figure 3 Figure c shows the surface morphology of a boron nitride thin film grown on a single-crystal diamond substrate treated by the method provided in this invention. It can be seen that the surface of the boron nitride thin film is more continuous and smoother, with significantly reduced overall undulation, and its surface roughness R... q The surface roughness was reduced to 1.014 nm. Compared with the sample without interface pretreatment, the surface roughness was significantly reduced, indicating that the nucleation process of the boron nitride film grown after the pretreatment of this invention was more uniform, and the grains could grow stably and gradually merge under relatively consistent nucleation conditions. This is beneficial to suppressing the generation and enrichment of point defects in the nucleation region and near the grain boundaries, and provides favorable conditions for obtaining boron nitride films with a denser structure and lower defect density.

[0063] Furthermore, to address the macroscopic instability issues such as interfacial stress concentration and film wrinkling during the fabrication of large-size diamond-based boron nitride films, the surface morphology of boron nitride films prepared by different methods was observed using scanning electron microscopy (SEM), such as... Figure 4 As shown in Figure a, the surface of the boron nitride film not grown using the method provided in this invention exhibits a distinct wrinkled structure. These wrinkles are polygonal in distribution, indicating that the residual stress generated during the growth and cooling process of the boron nitride film is primarily released through surface undulations. In contrast, as... Figure 4 As shown in Figure b, no obvious wrinkles were observed on the surface of the boron nitride film grown by the method of the present invention, and the surface morphology was more uniform and continuous. This indicates that the enhanced interfacial bonding continuity is conducive to the more uniform dispersion and release of the internal stress of the boron nitride film during growth and cooling, providing favorable conditions for the preparation of large-size diamond-based boron nitride films with good continuity.

[0064] Finally, to address the problem that existing diamond interface cleaning processes easily introduce surface damage, leading to the formation of amorphous layers or disordered regions at the interface, thus affecting the continuity of boron nitride crystal orientation, the prepared samples were characterized using high-resolution transmission electron microscopy (HRTEM). Figure 5 Figure a shows the interface morphology of diamond and boron nitride formed without the method of this invention. It can be seen that the lattice fringes near the interface have poor continuity, the interface transition region is relatively wide and the contrast is chaotic, exhibiting certain disordered structural characteristics; Figure 5 Figure b shows the interface morphology of diamond and boron nitride formed by the method of the present invention. It can be seen that the interface transition layer is more uniform and the continuity of the lattice fringes is significantly improved. This indicates that the present invention effectively avoids the interface damage introduced by the traditional strong cleaning process while improving the surface chemical activity. It is beneficial to maintain the orderly growth of boron nitride at the interface and reduce the enrichment of amorphous structures.

[0065] In summary, the multi-scale characterization results from atomic force microscopy, scanning electron microscopy, and high-resolution transmission electron microscopy demonstrate that the nitrogen-assisted ignition activation and slight nitriding pretreatment method provided in this invention can effectively control the interfacial chemical state of the single-crystal diamond substrate surface without introducing significant lattice damage. By introducing stable nitrogen-related active sites at the interface and promoting the formation of CN phase bonds, this invention effectively improves the initial nucleation conditions of boron nitride films on single-crystal diamond substrates, enhances nucleation uniformity, and reduces the enrichment tendency of defects such as nitrogen vacancies at the interface and in the nucleation region.

[0066] Meanwhile, due to the enhanced interfacial continuity, the internal stress generated during the growth and cooling of the boron nitride film can be more uniformly dispersed and released at the interface, thereby suppressing the generation of macroscopic stress instability phenomena such as wrinkles, and obtaining a boron nitride film with good surface continuity and uniformity.

[0067] The method for preparing diamond-based boron nitride thin films provided by this invention can simultaneously meet key requirements such as low interface damage, high nucleation activity, and controllable stress release, effectively solving problems such as uneven nucleation, enrichment of interface defects, and macroscopic morphology instability in the existing epitaxial growth process of diamond-based boron nitride thin films.

[0068] Example 2 Based on Example 1, this invention also provides a diamond-based boron nitride thin film, which is the final diamond-based boron nitride thin film prepared using the preparation method described in Example 1.

[0069] The principle and beneficial effects of the diamond-based boron nitride thin film provided in this embodiment of the invention are similar to those in Embodiment 1, and will not be repeated here.

[0070] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a diamond-based boron nitride thin film, characterized in that, include: Single-crystal diamond substrates were selected; The single-crystal diamond substrate is pretreated by polishing and cleaning in sequence to obtain a pretreated single-crystal diamond substrate; At room temperature, the cavity containing the pretreated single-crystal diamond substrate is subjected to a smoldering cleaning process using argon and nitrogen in sequence. Then, the temperature inside the cavity is raised to the growth temperature in a nitrogen atmosphere. The growth temperature is the temperature required to grow a boron nitride thin film. Under the growth temperature conditions, the surface of the pretreated single-crystal diamond substrate is subjected to smoldering activation treatment using argon gas to obtain a smoldering activated single-crystal diamond substrate. Nitrogen gas is introduced while maintaining the ignition treatment conditions. Nitrogen gas is used to assist the ignition activation treatment on the surface of the ignition activated single crystal diamond substrate. After the nitrogen ignition is stabilized, the argon gas is turned off to complete the interface pre-nitriding and the construction of nitrogen-related active sites, and a surface-treated single crystal diamond substrate is obtained. Under the growth temperature conditions, a boron nitride film is grown on the surface of the surface-treated single-crystal diamond substrate to obtain a diamond-based boron nitride film. In a nitrogen atmosphere, the growth temperature is cooled to room temperature to obtain a cooled diamond-based boron nitride film. The diamond-based boron nitride film after cooling is annealed by heating to the annealing temperature in a nitrogen atmosphere to obtain the final diamond-based boron nitride film.

2. The preparation method according to claim 1, characterized in that, Selecting single-crystal diamond substrates, including: A single-crystal diamond substrate with (111) crystal orientation was selected and prepared by microwave plasma chemical vapor deposition.

3. The preparation method according to claim 1, characterized in that, The single-crystal diamond substrate is pretreated by polishing and cleaning in sequence to obtain a pretreated single-crystal diamond substrate, comprising: The surface of the single-crystal diamond substrate is subjected to chemical mechanical polishing or mechanical polishing to obtain a polished single-crystal diamond substrate; The polished single-crystal diamond substrate was immersed and cleaned with a piranha solution at 80~120℃ to remove surface organic contaminants, resulting in an immersed and cleaned single-crystal diamond substrate. The pretreated single-crystal diamond substrate was ultrasonically cleaned sequentially with acetone, ethanol and deionized water at room temperature to obtain the pretreated single-crystal diamond substrate.

4. The preparation method according to claim 1, characterized in that, At room temperature, the cavity containing the pretreated single-crystal diamond substrate is sequentially cleaned with argon and nitrogen gases to induce a glow, followed by raising the temperature within the cavity to the growth temperature in a nitrogen atmosphere, including: Argon gas is introduced into the cavity containing the pretreated single-crystal diamond substrate at room temperature to perform the first ignition cleaning of the internal environment of the cavity. After the first ignition cleaning is completed, the argon gas is turned off and nitrogen gas is introduced into the cavity to perform the second ignition cleaning of the internal environment of the cavity, until the second ignition cleaning of the cavity is completed. After the chamber is cleaned to ignite, it is subjected to a gradient heating process in a nitrogen atmosphere until it reaches the growth temperature, wherein the growth temperature is 700~800℃, the heating rate is 30~40℃ / min below 500℃, the heating rate is 10~20℃ / min in the 500~700℃ range, and the heating rate is 5~10℃ / min in the 700~800℃ range.

5. The preparation method according to claim 1, characterized in that, Under the growth temperature conditions, the surface of the pretreated single-crystal diamond substrate is subjected to a scintillation activation treatment using argon gas to obtain a scintillation activated single-crystal diamond substrate, comprising: Under the growth temperature conditions, argon gas with a flow rate of 80~100 sccm is introduced, and a substrate bias voltage of 150~340V is applied to the pretreated single-crystal diamond substrate to perform a spark activation treatment on the surface of the pretreated single-crystal diamond substrate, so that the surface of the pretreated single-crystal diamond substrate undergoes interfacial chemical activation and removal of intrinsic chemical bonds, thereby obtaining the spark activated single-crystal diamond substrate, wherein the spark activation treatment time is 30~60s.

6. The preparation method according to claim 1, characterized in that, While maintaining the ignition treatment conditions, nitrogen gas is introduced to assist in the ignition activation treatment of the surface of the ignited single-crystal diamond substrate. After the nitrogen ignition stabilizes, the argon gas is turned off to complete the interface pre-nitriding and the construction of nitrogen-related active sites, resulting in a surface-treated single-crystal diamond substrate, including: While maintaining the ignition treatment conditions, nitrogen gas with a flow rate of 20-40 sccm is introduced into the argon ignition state, so that the nitrogen gas is excited to form active nitrogen species under the assistance of argon plasma, so as to perform auxiliary ignition activation treatment on the surface of the single crystal diamond substrate after ignition activation. After the nitrogen ignition stabilizes, the argon gas is turned off. After the auxiliary ignition activation treatment is completed, the single crystal diamond substrate with the completed surface treatment is obtained. The auxiliary ignition activation treatment time is about 60-180 s.

7. The preparation method according to claim 1, characterized in that, Under the stated growth temperature conditions, a boron nitride thin film is grown on the surface of the surface-treated single-crystal diamond substrate to obtain a diamond-based boron nitride thin film, comprising: Under the specified growth temperature conditions, a boron nitride thin film is grown on the surface of the surface-treated single-crystal diamond substrate using physical vapor deposition to obtain the diamond-based boron nitride thin film. The second growth temperature is 600~800℃, the growth power is 80~100W, the growth time is 5~10 hours, and a mixture of nitrogen and argon is introduced as the working atmosphere during the growth process. The nitrogen flow rate is 20~40 sccm, the argon flow rate is 40~80 sccm, the pressure is 30~60 mbar, and the substrate bias voltage is 150~340V.

8. The preparation method according to claim 1, characterized in that, In a nitrogen atmosphere, the growth temperature is lowered to room temperature to obtain a cooled diamond-based boron nitride film, comprising: In a nitrogen atmosphere, the growth temperature is cooled to room temperature at a cooling rate of 5~15℃ / min to obtain a cooled diamond-based boron nitride film.

9. The preparation method according to claim 1, characterized in that, The diamond-based boron nitride film after cooling is annealed at the annealing temperature under a nitrogen atmosphere to obtain the final diamond-based boron nitride film, comprising: Under a nitrogen atmosphere, the nitrogen flow rate is maintained at 800~1000 sccm, and the temperature is increased to the annealing temperature of 900~1000℃ at a heating rate of 15~20℃ / min. The annealing temperature is then maintained for 20~30 min to anneal the cooled diamond-based boron nitride film. After annealing, the temperature is reduced to room temperature at a cooling rate of 5~15℃ / min to obtain the final diamond-based boron nitride film.

10. A diamond-based boron nitride thin film, characterized in that, The diamond-based boron nitride film is the final diamond-based boron nitride film prepared by the preparation method according to any one of claims 1 to 9.

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