Liquid metal-based boron-doped diamond thin film and method for preparing the same

Abstract

This application relates to the semiconductor field, specifically to a boron-doped diamond thin film based on liquid metal and its preparation method. The method for preparing a boron-doped diamond thin film based on liquid metal includes the following steps: pretreating a substrate; preparing a Ga-B alloy; covering the pretreated substrate with the Ga-B alloy; and achieving the growth of the boron-doped diamond thin film based on liquid metal through degassing, gas circulation, and temperature control. This application overcomes the limitation of liquid metal only catalyzing sp2+. 2 The limitations of carbon can be overcome by using a tubular furnace for simple temperature control and atmospheric pressure to achieve sp... 3 The low-temperature synthesis of bonded diamond eliminates the need for high-temperature, high-pressure equipment and complex high-vacuum systems, significantly reducing equipment costs and process complexity, and providing a new pathway for the low-cost, high-performance preparation of BDD thin films.

Description

Technical Field

[0001] This application relates to the semiconductor field, and mainly to a boron-doped diamond thin film based on liquid metal and its preparation method. Background Technology

[0002] Diamond, with its extremely high hardness, excellent thermal conductivity, high carrier mobility, and wide bandgap properties, has irreplaceable application prospects in high-temperature, high-power electronic devices, quantum computing, and sensing. Among them, boron-doped diamond (BDD) achieves p-type semiconductor characteristics by replacing lattice carbon with boron atoms. Its electrical properties can be precisely controlled by boron concentration, making it a core candidate material for devices in high-temperature, high-frequency, and strong electric field environments. There is an urgent need for it in high-end applications such as power modules for new energy vehicles and electronic equipment for deep space exploration.

[0003] Existing BDD (Bright Vapor Deposition) preparation technologies are mainly divided into two categories: high-temperature high-pressure (HPHT) and chemical vapor deposition (CVD), but both have significant limitations. Specifically, HPHT technology requires a high pressure of 5-7 GPa and a high temperature of 1300-1700℃, using alloys such as iron, nickel, germanium, and cobalt as catalysts to dissolve graphite carbon and precipitate diamond crystals. While this technology can achieve high boron doping (boron content ≥ 3 × 10⁻⁶), it is not universally applicable. 20 cm -3 However, while the equipment is complex and energy-intensive, it is difficult to prepare large-size silicon-based thin films and cannot be compatible with semiconductor integration processes. In terms of CVD technology, although mainstream technologies (such as hot-filament CVD and microwave plasma CVD) can prepare BDD thin films, they still face key problems: First, boron doping depends on gaseous boron sources, such as B(OCH3)3 and B2H6. The adsorption of boron species on the silicon substrate surface is easily affected by airflow disturbance and low interfacial binding energy, resulting in doping uniformity deviations exceeding ±15%. Second, the growth temperature is mostly maintained at 850-1100℃, which is higher than the silicon-based process compatibility temperature, which can easily cause substrate lattice damage and film internal stress.

[0004] Liquid metals (such as gallium and gallium-based alloys) offer a novel pathway for diamond growth due to their high electron density at the liquid surface / interface, excellent carbon solubility, and catalytic activity. Under normal or low pressure, liquid metals can significantly reduce the activation energy of hydrocarbon CH bond breaking, efficiently generating carbon-active species; simultaneously, they can act as carbon solvents, allowing dissolved carbon to diffuse directionally to the surface of the diamond seed crystal without dissolving the seed crystal or the growing diamond. However, the application of liquid metals in current technologies still suffers from several defects and shortcomings:

[0005] (1) Harsh process conditions. Related technologies indicate that traditional BDD preparation generally relies on extreme environments. The HPHT method requires a high pressure of 5-7 GPa and a high temperature of 1600-1700℃, with equipment costs exceeding ten million yuan; the hot-filament CVD method requires a filament temperature of 2100-2300℃, consuming 1.5 times the energy of conventional MPCVD; traditional MPCVD requires 10... -3 High vacuum (Pa) requires high maintenance costs and is time-consuming, making it difficult to adapt to mass production needs.

[0006] (2) Insufficient doping uniformity and stability. Related technologies indicate that BDD doping has poor uniformity, and high boron doping easily introduces impurity phases such as non-diamond carbon. Subsequent etching, acid washing and other treatments will damage the thin film structure, leading to a decrease in thermal conductivity and affecting the long-term stability of the device.

[0007] (3) Limitations of liquid metal catalysis: Existing liquid metals can only prepare sp 2 Bonded carbon materials cannot be synthesized with BDD at low temperatures and pressures. Currently, gaseous boron sources readily react with gallium to form Ga2O3 and GaB2, resulting in low boron utilization and hindering the achievement of synergistic doping of boron and carbon.

[0008] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the purpose of this application is to provide a boron-doped diamond thin film based on liquid metal and a method for preparing the same.

[0010] This application uses a tube furnace as the growth equipment. First, the single-crystal silicon wafer is pretreated. Then, solid boron powder and liquid gallium are mixed to form a uniform Ga-B alloy, which is then used to completely cover the pretreated silicon substrate and assembled into a quartz boat. The quartz boat is pushed into the constant temperature zone of the tube furnace. First, a vacuum is drawn to remove residual air, then high-purity H2 is introduced for rinsing, followed by the introduction of a CH4 / H2 mixed gas. The temperature is maintained at 0.8-1.2 atm and 750-850℃ for 150-200 min. High-quality BDD thin films are grown on the surface of the silicon substrate by utilizing the catalytic and transport functions of liquid gallium.

[0011] This method breaks through the limitation of liquid metals only catalyzing sp 2 The limitations of carbon can be overcome by using a tubular furnace for simple temperature control and atmospheric pressure to achieve sp... 3 The low-temperature synthesis of bonded diamond eliminates the need for high-temperature, high-pressure equipment and complex high-vacuum systems, significantly reducing equipment costs and process complexity, and providing a new pathway for the low-cost, high-performance preparation of BDD thin films.

[0012] The technical solution of this application is as follows:

[0013] A method for preparing boron-doped diamond thin films based on liquid metal includes the following steps:

[0014] Pre-treat the substrate;

[0015] Preparation of Ga-B alloys;

[0016] The Ga-B alloy is coated onto a pretreated substrate;

[0017] Through exhaust, ventilation, and temperature control, boron-doped diamond films based on liquid metal are grown.

[0018] Furthermore, in the Ga-B alloy, the B concentration is 0.5-2 at%.

[0019] Further limiting the boron concentration in the Ga-B alloy within this range ensures uniform boron distribution in the diamond film. Excessive boron concentration can introduce impurities such as non-diamond carbon during growth. These impurities affect the electrical and thermal properties of the film, leading to decreased thermal conductivity and consequently impacting long-term device stability. However, when the boron concentration is between 0.5-2 at%, the fluidity of liquid gallium allows for uniform boron distribution within the alloy, enabling uniform doping into the diamond lattice during film growth. This uniform doping ensures consistent electrical properties across the film, improving device reliability and stability.

[0020] Furthermore, the preparation of the Ga-B alloy includes the following steps: the solid boron powder and liquid gallium are mixed at a mass ratio of 0.5% to 2% of the total mass of the solid boron powder and liquid gallium, and heated and stirred at 30 to 40°C for 10 to 30 minutes to form the Ga-B alloy.

[0021] Heating and stirring at a relatively low temperature of 30-40℃ allows for thorough mixing of solid boron powder and liquid gallium. The dissolution of solid boron powder in liquid gallium is a combination of physical and chemical processes; appropriate temperature and stirring time promote the dissolution and dispersion of the boron powder. If the temperature is too high, unnecessary chemical reactions may occur between the boron powder and gallium, forming other compounds that affect the boron doping effect. If the temperature is too low or the stirring time is insufficient, the boron powder may not dissolve and disperse sufficiently, resulting in uneven boron distribution in the alloy. This precisely controlled preparation method yields a uniform Ga-B alloy, providing a stable boron source for subsequent thin film growth, thus ensuring the uniformity and stability of boron doping in the film and further improving the quality and performance of the film.

[0022] Furthermore, the exhaust, ventilation, and temperature control include the following steps:

[0023] Exhaust: drawing a vacuum and removing air;

[0024] Ventilation: Introducing a reducing gas or a mixture containing a reducing gas;

[0025] Temperature control: Introduce a gaseous carbon source, adjust the gas pressure to 0.8~1.2 atm, heat to 750-850℃ at a heating rate of 10~20℃ / min, and hold for 150-200min.

[0026] Furthermore, during ventilation, the flow rate is 100~150 sccm;

[0027] During temperature control, the flow rate is 5~8 sccm;

[0028] Furthermore, the reducing gas is H2, and the mixed gas containing the reducing gas is a mixture of H2 and an inert gas;

[0029] The carbon source includes one or a mixture of two or more of CH4, C2H2, C2H4, and C3H8.

[0030] Furthermore, when the reducing gas or the mixture containing the reducing gas contains H2 and the carbon source is CH4, the flow ratio of CH4 to H2 is 1:20 to 1:30.

[0031] Furthermore, the pretreatment includes a nanodiamond seed crystal attachment treatment;

[0032] The nanodiamond seed crystal attachment treatment includes the following steps: immersing the substrate in an acetone suspension of nanodiamond seed crystals with a concentration of 0.1~0.5g / L, and ultrasonically treating it with a power of 20~60W for 5~10min.

[0033] Furthermore, the pretreatment includes an oxide layer removal process;

[0034] The deoxidation process includes the following steps: ultrasonically cleaning the substrate in a hydrofluoric acid solution, ammonium fluoride solution, hydrofluoric acid-nitric acid mixture, or buffer oxide etching solution for 5-8 minutes.

[0035] Furthermore, when the Ga-B alloy is applied to the pretreated substrate, the thickness of the coating is 10~30μm;

[0036] The Ga-B alloy is coated onto a pretreated substrate and then assembled into a quartz boat; subsequently, the venting, ventilation, and temperature control are performed in a tube furnace.

[0037] Furthermore, the pretreatment sequentially includes oxide layer removal treatment and nanodiamond seed crystal attachment treatment.

[0038] This application also provides a boron-doped diamond thin film based on liquid metal.

[0039] The boron-doped diamond film based on liquid metal is a continuous dense film of 6-8 μm.

[0040] Compared with the prior art, this application has the following beneficial effects:

[0041] (1) The process is mild and low-cost, and easy to mass-produce: No high pressure, high temperature or high vacuum equipment is required. It only uses a tube furnace as the core and grows at a normal pressure of 0.8-1.2 atm and a low temperature of 750-850℃. This simplifies the process and reduces equipment and operating costs. The operation is easy to standardize and is suitable for large-scale mass production.

[0042] (2) Uniform boron doping and stable film: The boron source is supplied by pre-prepared Ga-B alloy, and the uniform distribution of boron is achieved by taking advantage of the fluidity of liquid gallium; only dilute hydrochloric acid is used to remove residual alloy to avoid damaging the film. The boron concentration fluctuates little, and the thermal conductivity and long-term stability are excellent. Furthermore, solid boron doping is non-toxic.

[0043] (3) Overcoming the limitations of liquid metals, directionally generating sp 3 Bonded diamond: Liquid gallium possesses both catalytic (reducing the CH bond breaking energy of methane) and transport (mediating carbon-boron diffusion) functions, overcoming the limitation of existing liquid metals that can only produce sp. 2 The carbon problem, achieving SP 3 Low-temperature synthesis of bonded diamond.

[0044] (4) It combines performance and efficiency and has a wide range of applications: 6-8μm continuous dense film can be prepared in 150-200min, which meets the needs of high power devices, detection electrodes and other scenarios. It combines low cost and high performance and is suitable for new energy, deep space exploration, sewage treatment and other fields. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the growth of boron-doped diamond thin film based on liquid metal obtained in Example 1 of this application in a tube furnace.

[0046] Figure 2 This is a SEM image of the boron-doped diamond film based on liquid metal obtained in Example 1 of this application.

[0047] Figure 3 This is an EDX image of the boron-doped diamond thin film based on liquid metal obtained in Example 1 of this application. Detailed Implementation

[0048] This application provides a boron-doped diamond thin film based on liquid metal and a method for preparing the same. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0049] This application provides a method for preparing boron-doped diamond thin films based on liquid metal, comprising the following steps:

[0050] Step 1: Silicon substrate pretreatment

[0051] Semiconductor-grade single-crystal silicon wafers were sequentially subjected to dilute hydrofluoric acid deoxidation and ultrasonic attachment of nanodiamond seed crystals to adapt to the growth requirements of liquid metal media.

[0052] Specifically, a single-crystal silicon wafer with a thickness of 0.5~1mm is selected as the substrate, and surface cleaning and activation treatments are carried out sequentially according to the following process:

[0053] Step 1 (1): First, place the monocrystalline silicon wafer in a hydrofluoric acid solution with a mass concentration of 2%~5% and ultrasonically clean it for 5~8 minutes to remove the natural oxide layer on the surface.

[0054] Then, ultrasonically clean with deionized water 3-5 times, each time for 3-5 minutes, to remove residual hydrofluoric acid and oxide layer debris.

[0055] In this application, hydrofluoric acid is preferentially used for the silicon substrate oxide removal step. The core reason is that hydrofluoric acid can efficiently and selectively dissolve the natural oxide layer (SiO2) on the silicon substrate surface. The reaction is mild and will not damage the silicon substrate itself. At the same time, any residue after cleaning can be easily removed with deionized water, avoiding the introduction of additional impurities that may affect the subsequent bonding of Ga-B alloys to the substrate and the uniformity of boron doping. In addition, the hydrofluoric acid cleaning process is mature, simple to operate, and has good compatibility with the subsequent nanodiamond seed crystal attachment treatment. It can create a clean and activated substrate surface for uniform seed crystal adsorption, ensuring the growth quality of the BDD film.

[0056] The following suitable reagents can also be used in this step: 10%~20% ammonium fluoride solution (gently removes the oxide layer, less corrosive than hydrofluoric acid), diluted hydrofluoric acid-nitric acid mixture (higher etching efficiency, requires precise control of concentration and processing time), buffered oxide etching solution (BOE, a mixture of hydrofluoric acid and ammonium fluoride in proportion, with stable etching rate and can reduce changes in substrate surface roughness).

[0057] Step 1 (2): Next, immerse the monocrystalline silicon wafer in an acetone suspension of nanodiamond seed crystals with a concentration of 0.1~0.5g / L, and use 20~60W power to ultrasonically treat it for 5~10min so that the nanodiamond seed crystals are uniformly adsorbed on the surface of the monocrystalline silicon wafer.

[0058] Then, ultrasonically clean with acetone and deionized water for 3-5 minutes each to remove unadsorbed seed crystals and residual acetone.

[0059] In this process, the seed crystal attached by ultrasound can shorten the diffusion distance of carbon active species on the silicon substrate surface, reduce the diamond nucleation activation energy, guide the directional growth of crystals, reduce grain boundary defects, and thus improve the compactness and crystal quality of the subsequently grown film, and finally complete the substrate pretreatment.

[0060] The preparation of the acetone suspension of nanodiamond seed crystals includes the following steps: First, select high-purity nanodiamond seed crystals with uniform particle size, weigh the corresponding mass of nanodiamond seed crystals according to the target concentration (0.1~0.5 g / L), and add them to sufficient analytical grade acetone solvent; then, place the mixture in an ultrasonic cleaner with a power of 20~60W and sonicate for 10~15 min to fully disperse the nanodiamond seed crystals in the acetone and avoid seed crystal agglomeration; after sonication, observe whether there is obvious precipitation in the system by standing for 5~10 min. If a small amount of precipitation exists, sonicate again for a short time (3~5 min) to disperse it, finally obtaining a uniform and stable acetone suspension of nanodiamond seed crystals without obvious agglomeration. This suspension should be prepared and used immediately to ensure the seed crystal dispersion and the uniformity of subsequent adsorption on the silicon substrate surface.

[0061] Step 2: Preparation of Ga-B alloy dielectric and assembly of quartz boat

[0062] A uniform Ga-B alloy was prepared, which was then used to completely cover a pretreated silicon substrate and assembled into a quartz boat.

[0063] Specifically:

[0064] Step 2 (1): Alloy preparation

[0065] The high-purity solid boron powder and liquid gallium are mixed at a mass of 0.5% to 2% of the total mass of solid boron powder and liquid gallium. The mixture is placed in a quartz boat, heated at 30 to 40°C and stirred for 10 to 30 minutes to completely dissolve the boron powder and form a uniform Ga-B alloy (boron concentration 0.5-2 at%).

[0066] Step 2 (2): Quartz Boat Assembly

[0067] The pretreated silicon substrate is laid flat on the bottom of the quartz boat, and the Ga-B alloy is slowly poured in to ensure that the alloy completely covers the surface of the pretreated silicon substrate. The coverage thickness is controlled to be 10~30μm, and the quartz boat assembly is completed.

[0068] Step 3: Tube furnace growth system commissioning and BDD thin film growth

[0069] BDD thin film growth is achieved in a tube furnace by exhausting, venting, and controlling the temperature, utilizing liquid gallium.

[0070] Specifically:

[0071] Step 3 (1): Push the quartz boat assembled in Step 2 into the constant temperature zone of the tube furnace, close the furnace door, and evacuate to 1×10⁻⁶. -2 Below Pa, remove residual air from the chamber.

[0072] Step 3 (2): Then introduce reducing gas or a mixture of reducing gas at a flow rate of 100~150 sccm to flush the chamber for 5~10 minutes.

[0073] The reducing gas is preferably high-purity H2; the mixed gas containing the reducing gas is preferably a mixture of high-purity H2 and an inert gas.

[0074] High-purity H2 is preferred because it effectively removes residual air (especially oxygen) from the tubular furnace chamber, preventing oxidation, and assists in the cracking of methane to generate active carbon species during heating without introducing impurities. It also maintains a stable growth pressure of 1 atm and is well-suited to the catalytic transport function of liquid gallium. Besides H2, a mixture of inert gases (such as argon or nitrogen) and H2 can also be used (the H2 content must be ensured to guarantee methane cracking efficiency). These gases can meet the requirements for chamber atmosphere control, assisting carbon source cracking, and not interfering with BDD thin film growth.

[0075] Step 3 (3): Next, CH4 is introduced as a carbon source, and the CH4 flow rate is controlled at 5~8 sccm (CH4 / H2 flow rate ratio 1:20~1:30). The gas pressure of the tubular furnace is adjusted to 0.8-1.2 atm, and the temperature is heated to 750-850℃ at a heating rate of 10~20℃ / min. The temperature is held for 150-200min to grow the BDD film.

[0076] During the growth process, liquid gallium has both catalytic and transport functions: on the one hand, it reduces the activation energy of methane CH bond breaking and promotes the generation of carbon active species; on the other hand, it acts as a solvent to allow carbon and boron atoms to diffuse directionally to the silicon substrate surface and participate in diamond lattice substitution.

[0077] In this application, CH4 is preferred as the carbon source because it has a suitable carbon content, easily breaks CH bonds to generate carbon active species under liquid gallium catalysis, and the decomposition products contain only carbon and hydrogen (hydrogen can react with residual impurities or be discharged with gas flow without introducing additional impurities). It can be adapted to the low-temperature growth conditions of 1 atm atmospheric pressure and 800℃, ensuring the purity and crystal quality of the BDD film. In addition to CH4, other hydrocarbon compounds (such as C2H2, C2H4, and C3H8) can also be used as carbon sources. These carbon sources can also be decomposed under liquid gallium catalysis to generate carbon active species, meeting the carbon source requirements for BDD film growth.

[0078] Step 4: Sample post-processing and performance characterization

[0079] After growth, the film is allowed to cool for a period of time, then cleaned with dilute hydrochloric acid and deionized water. The film quality is then assessed using SEM and EDX to provide data support for BDD performance characterization.

[0080] Specifically:

[0081] Step 4 (1): After growth, first close the CH4 inlet valve, continue to purge with H2 for 5~8 minutes, then close the tube furnace heating module. After the furnace temperature naturally cools to room temperature (25~30℃), remove the quartz boat. Immerse the sample in a 5%~10% dilute hydrochloric acid solution and ultrasonically clean it at 20~60W for 5~10 minutes to remove residual Ga-B alloy and unreacted boron powder from the surface. Then ultrasonically clean it with deionized water 3~5 times (3~5 minutes each time).

[0082] Step 4 (2): Observe the surface morphology and cross-sectional thickness of the BDD film using a scanning electron microscope (SEM) to ensure that the film is continuous and has a thickness of 6-8 μm. Analyze the elemental composition of the film using energy dispersive X-ray spectroscopy (EDX) to verify the uniform distribution of boron and complete the characterization of the sample performance.

[0083] First, from the perspective of process conditions, this application overcomes the limitations of traditional preparation techniques as described in the background section. The preparation method provided in this application does not require high-pressure, high-temperature, or high-vacuum equipment; instead, it uses a tube furnace as the core, growing at atmospheric pressure and a low temperature of 750-850℃. These mild process conditions greatly simplify the preparation process and reduce equipment and operating costs. The reduction in equipment and operating costs helps improve the economic efficiency of production, and the ease of standardization makes large-scale mass production possible.

[0084] Secondly, regarding film quality, this method helps improve the compactness and crystallinity of the film. In the pretreatment step, the substrate is treated to provide a good foundation for subsequent film growth. During growth, liquid gallium plays a crucial catalytic and transport role. Liquid gallium can lower the activation energy of methane CH bond breaking, promoting the formation of carbon active species. Carbon active species are the basic building blocks for diamond films, and their formation efficiency and stability directly affect the film quality. Simultaneously, liquid gallium acts as a solvent, allowing carbon and boron atoms to diffuse directionally to the silicon substrate surface, participating in diamond lattice substitution. This directional diffusion ensures the orderly arrangement of carbon and boron atoms on the substrate surface, reducing the generation of grain boundary defects. Grain boundary defects affect the electrical and mechanical properties of the film; reducing grain boundary defects improves film compactness, making the film structure more compact, reducing internal porosity and impurities, and thus improving crystallinity, laying the foundation for preparing high-performance BDD films.

[0085] The present application will be further described below through specific embodiments.

[0086] Example 1

[0087] To address the need for high-quality BDD thin films in power modules for new energy vehicles, boron-doped diamond thin films were grown on silicon substrates using the method provided in this application. The feasibility of the process and the performance of the thin films were verified. The specific steps are as follows:

[0088] Step 1: Pretreatment of silicon substrate

[0089] Select a semiconductor-grade single-crystal silicon wafer with a thickness of 0.8 mm and a size of 2 cm × 2 cm, and carry out surface cleaning and activation treatment in sequence: (1) Oxide layer removal: Place the single-crystal silicon wafer in a 3% hydrofluoric acid solution and turn on the ultrasonic cleaner at 40 W for 6 min to remove the natural oxide layer on the surface; then use deionized water to ultrasonically clean 3 times for 3 min each time to remove residual hydrofluoric acid and oxide layer debris; (2) Seed crystal adhesion: Prepare a nano-diamond seed crystal acetone suspension with a concentration of 0.3 g / L, immerse the single-crystal silicon wafer in the suspension, and ultrasonically treat it at 30 W for 8 min to make the seed crystal uniformly adsorbed on the surface of the silicon wafer; then use acetone and deionized water to ultrasonically clean for 4 min each to remove the seed crystal that is not firmly adsorbed and the residual acetone, and complete the pretreatment of the silicon substrate.

[0090] Preparation of acetone suspension of nanodiamond seed crystals: Select high-purity nanodiamond seed crystals with uniform particle size, weigh the corresponding mass of nanodiamond seed crystals according to the target concentration (0.3g / L), and add them to sufficient analytical grade acetone solvent; then place the mixed system in an ultrasonic cleaner with a power of 20~60W and ultrasonically treat for 10~15min to fully disperse the nanodiamond seed crystals in acetone and avoid seed crystal agglomeration, thus obtaining the acetone suspension of nanodiamond seed crystals.

[0091] Step 2: Preparation of Ga-B alloy dielectric and assembly of quartz boat

[0092] (1) Alloy preparation: Weigh high-purity solid boron powder and liquid gallium according to the mass of solid boron powder accounting for 1% of the total mass of solid boron powder and liquid gallium, and place them together in a 50mL quartz boat; place the quartz boat in the heating table in the glove box, heat at 35℃ and stir at 600r / min for 10min to completely dissolve the boron powder and form a uniform Ga-B alloy with a boron concentration of 1at.

[0093] (2) Quartz boat assembly: The pretreated silicon substrate is laid flat on the bottom of the quartz boat, and the prepared Ga-B alloy is slowly poured to ensure that the alloy completely covers the surface of the silicon substrate. The coverage thickness is controlled to be 20μm by measuring with vernier calipers to complete the quartz boat assembly.

[0094] Step 3: Tube furnace growth system commissioning and BDD thin film growth

[0095] (1) Chamber preparation: Push the quartz boat assembled in step two into the constant temperature zone of the tube furnace and close the furnace door; start the vacuum pump and evacuate the chamber to a vacuum level of 5×10⁻⁶. -3 Below Pa, residual air is eliminated.

[0096] (2) Atmosphere flushing: High-purity H2 is introduced, and the flow rate is controlled at 120 sccm. The chamber is flushed for 8 minutes to further remove impurities from the chamber.

[0097] (3) Growth parameter control: Keep the H2 flow rate constant, introduce high-purity CH4, control the CH4 flow rate to 6 sccm (CH4 / H2 flow rate ratio 1:20); adjust the gas pressure of the tube furnace to 1 atm, heat to 800℃ at a heating rate of 20℃ / min, and hold for 180min to grow BDD film.

[0098] During the growth process, liquid gallium catalyzes the cracking of methane to generate carbon active species, and mediates the directional diffusion of carbon and boron atoms to the surface of the silicon substrate, participating in the substitution of the diamond lattice.

[0099] Step 4: Sample post-processing and performance testing and verification

[0100] (1) Sample post-treatment: After growth, first close the CH4 inlet valve, continue to circulate H2 for 8 min, and then close the tube furnace heating module; after the furnace temperature naturally cools to 26℃, take out the quartz boat. Immerse the sample in an 8% dilute hydrochloric acid solution and ultrasonically clean it with 40W power for 8 min to remove the residual Ga-B alloy and unreacted boron powder on the surface; then ultrasonically clean it three times with deionized water for 3 min each time.

[0101] (2) Performance testing:

[0102] SEM characterization: The film morphology was observed using a scanning electron microscope with the following parameters: accelerating voltage 2.00 kV, beam current 25 pA, and working distance 5.1-5.6 mm. Surface morphology images showed that the BDD film surface consisted of uniform grains without obvious pores or impurity phases, with grain sizes ranging from 50-100 nm. Cross-sectional morphology images showed that the film continuously covered the silicon substrate, with a cross-sectional thickness of up to 7 μm, exhibiting tight adhesion to the silicon substrate interface without peeling.

[0103] EDX characterization: Elemental analysis of the thin film was performed using the EDAX APEX system, and the results are shown in Table 1. The data shows that carbon accounts for 85.3% by mass and 92.6% by atoms in the film, boron is uniformly distributed, and only trace amounts of O and Si (partially from the substrate signal) are present. No Ga residue is observed, demonstrating uniform boron doping and the absence of inert impurity phases.

[0104] Table 1. Atomic percentage of BDD thin films tested with EDX

[0105]

[0106] Reference Figure 1The diagram illustrates the assembly structure within a tube furnace. The quartz tube provides a sealed environment for growth, while a quartz boat supports the silicon wafer (a pretreated silicon substrate) and the Ga-B alloy. The silicon wafer serves as the growth substrate for the BDD thin film, and the Ga-B alloy acts as both a boron source and a catalytic transport medium. A ceramic block supports the quartz boat. During growth within the tube furnace, this assembly utilizes the catalytic and transport properties of liquid gallium to achieve the growth of the BDD thin film on the silicon substrate surface.

[0107] Figure 2 This is a SEM image of the boron-doped diamond film based on liquid metal obtained in Example 1. From... Figure 2 (ab) As can be seen from the surface morphology, the BDD film surface is composed of uniform grains without obvious pores or impurity phases. The grain size is between 50-100 nm, which indicates that the film is densely grown and has good crystallinity. This shows that the method of this application can prepare a high-quality BDD film surface structure.

[0108] Figure 2 The (cd) cross-sectional morphology shows that the BDD film continuously covers the silicon substrate, with a cross-sectional thickness of about 7 μm, and the film is tightly bonded to the silicon substrate interface.

[0109] Figure 3 This is an EDX image of the boron-doped diamond thin film based on liquid metal obtained in Example 1. According to... Figure 3 The EDX test results showed that the carbon (C) signal peak in the film was very significant, and the boron (B) signal peak was also present, proving that boron was successfully doped into the diamond film. Furthermore, the film contained only trace amounts of oxygen (O) and silicon (Si), with no gallium (Ga) residue, indicating that boron and carbon achieved good synergistic doping, and that there were no inert impurity phases such as Ga2O3 and GaB2, further verifying the advantages of the proposed method in terms of boron doping uniformity and film purity.

[0110] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for producing a boron-doped diamond thin film based on liquid metal, characterized by, The method comprises the following steps: preprocessing the substrate; preparing Ga-B alloy; covering the Ga-B alloy on the pretreated substrate; exhausting, ventilating and temperature controlling to obtain liquid metal based boron-doped diamond film; the ventilating and temperature controlling comprises the following steps: ventilating: introducing reducing gas or mixed gas containing reducing gas; temperature controlling: introducing gaseous carbon source, adjusting the gas pressure to 0.8-1.2 atm, heating to 750-850 ℃ at a heating rate of 10-20 ℃ / min, and keeping the temperature for 150-200 min.

2. The method of claim 1, wherein the liquid metal is selected from the group consisting of mercury, gallium, indium, tin, lead, bismuth, thallium, and mixtures thereof. the B concentration in the Ga-B alloy is 0.5-2 at%; the preparation of the Ga-B alloy comprises the following steps: mixing solid boron powder and liquid gallium at a ratio of 0.5%-2% of the mass of the solid boron powder to the total mass of the solid boron powder and the liquid gallium, heating and stirring at 30-40 ℃ for 10-30 min to form the Ga-B alloy.

3. The method of claim 1, wherein the liquid metal is selected from the group consisting of mercury, gallium, indium, and mixtures thereof. the exhausting comprises the following steps: exhausting: vacuumizing and removing air.

4. The method of claim 3, wherein the liquid metal is selected from the group consisting of mercury, gallium, indium, and mixtures thereof. the flow rate of the reducing gas or the mixed gas containing reducing gas is 100-150 sccm during the ventilating; the flow rate of the gaseous carbon source is 5-8 sccm during the temperature controlling.

5. The method of claim 3, wherein the liquid metal is selected from the group consisting of mercury, gallium, indium, and mixtures thereof. the reducing gas is H2, and the mixed gas containing reducing gas is a mixture of H2 and inert gas; the carbon source comprises one or more than two kinds of CH4, C2H2, C2H4 and C3H8.

6. The method of claim 5, wherein the liquid metal is selected from the group consisting of mercury, gallium, indium, and mixtures thereof. when the reducing gas or the mixed gas containing reducing gas contains H2 and the carbon source is CH4, the flow rate ratio of the CH4 to the H2 is 1:20-1:

30.

7. The method of claim 1, wherein the liquid metal is selected from the group consisting of mercury, gallium, indium, and mixtures thereof. the preprocessing comprises nano-diamond seed crystal adhesion treatment; the nano-diamond seed crystal adhesion treatment comprises the following steps: immersing the substrate in nano-diamond seed crystal acetone suspension liquid with a concentration of 0.1-0.5 g / L, and ultrasonic treating at a power of 20-60 W for 5-10 min; the preprocessing comprises oxide layer removal treatment; the oxide layer removal treatment comprises the following steps: placing the substrate in a hydrofluoric acid solution or an ammonium fluoride solution or a mixture of hydrofluoric acid and nitric acid or a buffer oxide etching solution and ultrasonic cleaning for 5-8 min; when the preprocessing comprises the nano-diamond seed crystal adhesion treatment and the oxide layer removal treatment, the oxide layer removal treatment is performed first, and then the nano-diamond seed crystal adhesion treatment is performed.

8. The method of claim 1, wherein the liquid metal is selected from the group consisting of mercury, gallium, indium, and mixtures thereof. when the Ga-B alloy is covered on the pretreated substrate, the covering thickness is 10-30 μm; after the Ga-B alloy is covered on the pretreated substrate, the substrate is assembled into a quartz boat, and then the exhausting, ventilating and temperature controlling are performed in a tube furnace.

9. A liquid metal based boron-doped diamond film prepared by the method according to any one of claims 1-8.

10. The liquid metal based boron-doped diamond film according to claim 9, wherein the liquid metal based boron-doped diamond film is a 6-8 μm continuous and dense film.

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