Liquid metal-based boron-doped diamond film and preparation method thereof

Abstract

The invention relates to the field of semiconductors, in particular to a boron-doped diamond film based on liquid metal and a preparation method of the boron-doped diamond film. The invention discloses a preparation method of a boron-doped diamond film based on liquid metal. The preparation method comprises the following steps: pretreating a substrate; ga-B alloy is prepared; the Ga-B alloy is covered on a substrate which is subjected to pretreatment; and exhausting, ventilating and controlling the temperature to realize the growth of the boron-doped diamond film based on the liquid metal. The limitation that liquid metal only catalyzes sp2 carbon is broken through, low-temperature synthesis of sp3 bonded diamond is achieved through simple temperature control of the tubular furnace and the normal-pressure environment, high-temperature and high-pressure equipment and a complex high-vacuum system are not needed, the equipment cost and the process complexity are remarkably reduced, and a new path is provided for low-cost and high-performance preparation of the BDD film.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductors, and particularly relates to a boron-doped diamond film based on liquid metal and a preparation method thereof. BACKGROUND

[0002] Diamond has an irreplaceable application prospect in high-temperature and high-power electronic devices, quantum computing and sensing, etc. due to its extremely high hardness, excellent thermal conductivity, high carrier mobility and wide bandgap characteristics. Among them, boron-doped diamond (BDD) realizes p-type semiconductor characteristics by replacing lattice carbon with boron atoms, and 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, and there is an urgent demand for it in high-end scenarios such as new energy vehicle power modules and deep space exploration electronic equipment.

[0003] Existing BDD preparation technologies mainly include high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD) methods, but both have significant limitations. Specifically, in the HPHT technology, graphite carbon is dissolved and diamond crystals are precipitated under a high pressure of 5-7 GPa and a high temperature of 1300-1700°C, with alloys such as iron, nickel, germanium, and cobalt as catalysts. Although this technology can achieve high boron doping (boron content ≥ 3 × 10 20 cm -3 ), it has high equipment complexity, high energy consumption, and difficulty in preparing large-size silicon-based films, and cannot be compatible with semiconductor integrated processes. In the CVD technology, mainstream technologies such as hot wire CVD and microwave plasma CVD can prepare BDD films, but still face key problems: first, boron doping relies on gaseous boron sources such as B(OCH3)3 and B2H6, and the adsorption of boron species on the surface of the silicon substrate is easily affected by gas flow disturbance and low interface binding energy, resulting in a doping uniformity deviation of more than ± 15%; second, the growth temperature is maintained at 850-1100°C, which is higher than the compatible temperature of the silicon-based process, easily causing lattice damage of the substrate and internal stress of the film.

[0004] Liquid metals (such as gallium and gallium-based alloys) provide a new path for diamond growth due to their high electron density on the liquid surface / interface, excellent carbon solubility, and catalytic activity. Under normal or low pressure environments, liquid metals can significantly reduce the activation energy of carbon-hydrogen bond (C-H) breaking, efficiently generating carbon active species; at the same time, they can act as carbon solvents, allowing the dissolved carbon to directionally diffuse to the surface of the diamond seed crystal without dissolving the seed crystal or the growing diamond. However, in existing technologies, the application of liquid metals still has multiple defects and deficiencies: (1) Process conditions are harsh. Related technologies show that traditional BDD preparation generally relies on extreme environment. The HPHT method requires 5-7 GPa high pressure and 1600-1700 °C high temperature, and the cost of equipment is more than one million yuan. The hot wire CVD method requires 2100-2300 °C filament temperature, and the energy consumption is 1.5 times that of conventional MPCVD. The conventional MPCVD requires 10 -3 Pa high vacuum, the cost of vacuum maintenance is high and time-consuming, and it is difficult to adapt to mass production demand.

[0005] (2) The uniformity and stability of doping are insufficient. Related technologies show that the uniformity of BDD doping is poor, and high boron doping easily introduces impurity phases such as non-diamond carbon. Subsequent etching, acid washing and other treatments will damage the film structure, resulting in reduced thermal conductivity and affecting the long-term stability of the device.

[0006] (3) There are limitations in liquid metal catalysis: existing liquid metals can only prepare sp 2 bonded carbon materials, and cannot synthesize BDD at low temperature and low pressure. The gaseous boron source reacts with gallium to form Ga2O3 and GaB2, and the boron utilization rate is low, which cannot realize the collaborative doping of boron and carbon.

[0007] Therefore, the existing technology still needs to be improved and developed. SUMMARY

[0008] In view of the deficiencies of the prior art described above, the purpose of the present application is to provide a boron-doped diamond film based on liquid metal and a preparation method thereof.

[0009] The present application uses a tube furnace as a growth device, first pretreats a single crystal silicon wafer; then mixes solid boron powder with liquid gallium to form a uniform Ga-B alloy, which completely covers the pretreated silicon substrate and is assembled into a quartz boat; the quartz boat is pushed into the constant temperature zone of the tube furnace, first vacuumized to remove residual air, then high-purity H2 is introduced for flushing, and then CH4 / H2 mixed gas is introduced, and the high-quality BDD film is grown on the surface of the silicon substrate at 0.8-1.2 atm, 750-850 °C for 150-200 min, using the catalytic and transport functions of liquid gallium.

[0010] This method breaks through the limitation of liquid metal only catalyzing sp 2 bonded carbon, and realizes the low-temperature synthesis of sp 3 bonded diamond through simple temperature control and normal pressure environment in a tube furnace, without the need for high-temperature and high-pressure equipment and complex high-vacuum systems, significantly reducing equipment cost and process complexity, and providing a new path for low-cost and high-performance preparation of BDD film.

[0011] The technical solution of the present application is as follows: A preparation method of a boron-doped diamond film based on liquid metal, comprising the following steps: Pretreat the substrate; preparing Ga-B alloy; covering the Ga-B alloy on the pretreated substrate; exhausting, ventilating and temperature controlling to realize the growth of boron-doped diamond film based on liquid metal.

[0012] Further, the B concentration in the Ga-B alloy is 0.5-2at%.

[0013] Further limiting the B concentration in the Ga-B alloy, the boron concentration in this range can ensure the uniform distribution of boron in the diamond film. If the boron concentration is too high, non-diamond carbon impurities and other impurities may be introduced during the growth process. These impurities will affect the electrical and thermal properties of the film, leading to a decrease in the thermal conductivity of the film, and thus affecting the long-term stability of the device. When the boron concentration is 0.5-2at%, the fluidity of liquid gallium can make boron uniformly distributed in the alloy, and then uniformly doped into the diamond lattice during the film growth process. This uniform doping can ensure the consistency of the electrical properties of each part of the film, improving the reliability and stability of the device.

[0014] Further, the preparation of the Ga-B alloy includes the following steps: mixing solid boron powder with liquid gallium, with the mass of solid boron powder accounting for 0.5%-2% of the total mass of solid boron powder and liquid gallium, heating and stirring at 30-40℃ for 10-30min to form the Ga-B alloy.

[0015] Heating and stirring at a lower temperature of 30-40℃ can fully mix the solid boron powder with the liquid gallium. The dissolution of solid boron powder in liquid gallium is a combination of physical and chemical processes, and appropriate temperature and stirring time can promote the dissolution and dispersion of boron powder. If the temperature is too high, unnecessary chemical reactions may occur between boron powder and gallium, generating other compounds and affecting the doping effect of boron; if the temperature is too low or the stirring time is insufficient, the boron powder may not be fully dissolved and dispersed, resulting in uneven distribution of boron in the alloy. Through this precisely controlled preparation method, a uniform Ga-B alloy can be obtained, providing a stable boron source for subsequent film growth, thereby ensuring the uniformity and stability of boron doping in the film and further improving the quality and performance of the film.

[0016] Further, the exhausting, ventilating and temperature controlling includes the following steps: Exhausting: vacuumizing and excluding air; Ventilating: introducing reducing gas or mixed gas containing reducing gas; Temperature controlling: introducing gaseous carbon source, adjusting the gas pressure to 0.8-1.2atm, heating to 750-850℃ at a heating rate of 10-20℃ / min, and holding for 150-200min.

[0017] Further, the flow rate of the ventilation gas is 100-150 sccm; The flow rate of the temperature control gas is 5-8 sccm. Further, the reducing gas is H2, and the mixed gas containing the reducing gas is a mixture of H2 and an inert gas. The carbon source includes one or more than two of CH4, C2H2, C2H4 and C3H8.

[0018] Further, when the reducing gas or the mixed gas containing the 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.

[0019] Further, the pretreatment includes nano-diamond seed crystal adhesion treatment. The nano-diamond seed crystal adhesion treatment includes the following steps: immersing the substrate in a nano-diamond seed crystal acetone suspension solution with a concentration of 0.1-0.5 g / L, and performing ultrasonic treatment at a power of 20-60 W for 5-10 min.

[0020] Further, the pretreatment includes oxide layer removal treatment. The oxide layer removal treatment includes the following steps: placing the substrate in a hydrofluoric acid solution or an ammonium fluoride solution or a hydrofluoric acid-nitric acid mixed solution or a buffered oxide etching solution and performing ultrasonic cleaning for 5-8 min.

[0021] Further, when the Ga-B alloy is coated on the pretreated substrate, the coating thickness is 10-30 μm. After the Ga-B alloy is coated on the pretreated substrate, the substrate is assembled into a quartz boat, and then the exhaust, ventilation and temperature control are performed in a tube furnace.

[0022] Further, the pretreatment includes oxide layer removal treatment and nano-diamond seed crystal adhesion treatment in sequence.

[0023] The application also provides a liquid metal-based boron-doped diamond film.

[0024] The liquid metal-based boron-doped diamond film is a 6-8 μm continuous and dense film.

[0025] Compared with the prior art, the application has the following beneficial effects: (1) Mild process and low cost, easy mass production: no high pressure, high temperature or high vacuum equipment is needed, only a tube furnace is used as the core, growth is performed at 0.8-1.2 atm normal pressure and 750-850℃ low temperature, the process is simplified, the equipment and operation cost are reduced, the operation is easy to standardize, and it is suitable for large-scale mass production.

[0026] (2) Boron is uniformly doped, and the film is stable: by pre-preparing Ga-B alloy to supply boron source, and by using the fluidity of liquid gallium to achieve uniform distribution of boron; only dilute hydrochloric acid is used to remove residual alloy, avoiding damage to the film, the concentration of boron element fluctuates little, the thermal conductivity and long-term stability are excellent, and solid-state boron doping is non-toxic.

[0027] (3) Breakthrough the limitation of liquid metal, directional generation of sp 3 Bonded diamond: liquid gallium has the functions of catalysis (reducing the bond breaking energy of methane C-H) and transportation (mediating carbon-boron diffusion), solving the problem that the existing liquid metal can only prepare sp 2 bonded diamond, realizing the low-temperature synthesis of sp 3 bonded diamond.

[0028] (4) Performance and efficiency are considered, and the application is wide: 150-200min can prepare 6-8μm continuous and dense film, meeting the needs of high-power devices, detection electrodes and other scenes, low cost and high performance, suitable for new energy, deep space exploration, sewage treatment and other fields. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A schematic diagram of the growth of the boron-doped diamond film based on liquid metal obtained in Example 1 of the present application in a tube furnace.

[0030] Figure 2 A SEM morphology diagram of the boron-doped diamond film based on liquid metal obtained in Example 1 of the present application.

[0031] Figure 3 An EDX test diagram of the boron-doped diamond film based on liquid metal obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0032] The present application provides a boron-doped diamond film based on liquid metal and a preparation method thereof. In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0033] The present application provides a preparation method of a boron-doped diamond film based on liquid metal, comprising the following steps: Step 1: Silicon substrate pretreatment The semiconductor-grade single crystal silicon wafer is sequentially subjected to dilute hydrofluoric acid deoxidation layer and nanodiamond seed crystal ultrasonic adhesion treatment to adapt to the growth requirements of liquid metal medium.

[0034] Specifically, a single crystal silicon wafer with a thickness of 0.5-1mm is selected as a substrate, and the surface cleaning and activation treatment is carried out according to the following process: Step one (1): First, immerse the single crystal silicon wafer in a 2% to 5% by mass hydrofluoric acid solution and ultrasonically clean for 5 to 8 minutes to remove the natural oxide layer on the surface.

[0035] Then, ultrasonically clean with deionized water for 3 to 5 times, each time for 3 to 5 minutes, to remove residual hydrofluoric acid and oxide layer debris.

[0036] The deoxidation step of the silicon substrate in this application preferably uses hydrofluoric acid. The core reason is that hydrofluoric acid can efficiently and selectively dissolve the natural oxide layer (SiO2) on the surface of the silicon substrate, the reaction is mild and will not damage the silicon substrate body, and the residual after cleaning can be easily removed by deionized water, which can avoid the introduction of additional impurities affecting the subsequent Ga-B alloy and substrate bonding and boron doping uniformity. In addition, the hydrofluoric acid cleaning process is mature, easy to operate, and has good compatibility with the subsequent nanodiamond seed crystal attachment process, which can create a clean and activated substrate surface for uniform seed crystal adsorption and ensure the growth quality of the BDD film.

[0037] This step can also use the following suitable reagents: 10% to 20% by mass ammonium fluoride solution (mildly removes the oxide layer with lower corrosion than hydrofluoric acid), diluted hydrofluoric acid-nitric acid mixture (higher etching efficiency, requires precise control of concentration and processing time), and buffered oxide etching liquid (BOE, mixed from hydrofluoric acid and ammonium fluoride in a certain proportion, stable etching rate, can reduce substrate surface roughness changes).

[0038] Step one (2): Then immerse the single crystal silicon wafer in a nanodiamond seed crystal acetone suspension with a concentration of 0.1 to 0.5 g / L, and use ultrasonic treatment with a power of 20 to 60 W for 5 to 10 minutes to make the nanodiamond seed crystals uniformly adsorb on the surface of the single crystal silicon wafer.

[0039] Then, ultrasonically clean with acetone and deionized water for 3 to 5 minutes respectively to remove the seed crystals that are not firmly adsorbed and residual acetone.

[0040] During this process, the ultrasonic attachment of the seed crystals can shorten the diffusion distance of carbon active species on the surface of the silicon substrate, reduce the diamond nucleation activation energy, guide the directional growth of the crystal, reduce the grain boundary defects, and thus improve the density and crystalline quality of the subsequently grown film, and finally complete the substrate pretreatment.

[0041] The preparation of the nano-diamond seed crystal acetone suspension includes the following steps: first, select high-purity nano-diamond seed crystals with uniform particle size, weigh the corresponding mass of the nano-diamond seed crystals according to the target concentration (0.1-0.5 g / L), and add them to a sufficient amount of analytical pure acetone solvent; then, place the mixed system in an ultrasonic cleaning instrument with a power of 20-60 W, and ultrasonically treat for 10-15 min to make the nano-diamond seed crystals fully dispersed in the acetone, avoiding seed crystal agglomeration; after ultrasonic treatment, observe whether there is obvious precipitation in the system by standing for 5-10 min, if there is a small amount of precipitation, ultrasonic dispersion for a short time (3-5 min) again, and finally obtain a nano-diamond seed crystal acetone suspension which is uniform, stable and has no obvious agglomeration. The suspension needs to be prepared for use to ensure the uniformity of the seed crystal dispersion and the subsequent adsorption on the surface of the silicon substrate.

[0042] Step two: Ga-B alloy medium preparation and quartz boat assembly Prepare a uniform Ga-B alloy, which completely covers the pretreated silicon substrate and is assembled into a quartz boat.

[0043] Specifically: Step two (1): alloy preparation According to the mass of solid boron powder accounting for 0.5%-2% of the total mass of solid boron powder and liquid gallium, mix high-purity solid boron powder with liquid gallium, place them in a quartz boat, heat and stir at 30-40℃ for 10-30 min, so that the boron powder is completely dissolved to form a uniform Ga-B alloy (boron concentration 0.5-2 at%).

[0044] Step two (2): quartz boat assembly Lay the pretreated silicon substrate on the bottom of the quartz boat, slowly pour the Ga-B alloy, and make sure that the alloy completely covers the surface of the pretreated silicon substrate, with a covering thickness of 10-30 μm, and complete the quartz boat assembly.

[0045] Step three: tube furnace growth system debugging and BDD film growth In the tube furnace, through exhaust, ventilation and temperature control, the liquid gallium function is used to realize the growth of BDD film.

[0046] Specifically: Step three (1): push the quartz boat assembled in step two into the constant temperature zone of the tube furnace, and after closing the furnace door, vacuumize to 1×10 -2 Pa or below to exclude residual air in the chamber.

[0047] Step three (2): then introduce a reducing gas or a mixed gas containing a reducing gas with a flow rate of 100-150 sccm, and flush the chamber for 5-10 min.

[0048] 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.

[0049] High-purity H2 is preferably used, because H2 can effectively remove residual air (especially oxygen) in the tube furnace chamber, assist the generation of carbon active species by methane cracking during heating, and does not introduce impurities, while being able to stably maintain a growth gas pressure of 1 atm, and being well adapted to the catalytic transport function of liquid gallium; in addition to H2, a mixed gas of an inert gas (such as argon or nitrogen) and H2 (which needs to ensure that H2 accounts for a certain proportion to ensure the efficiency of methane cracking) can also be used. Such gases can meet the needs of chamber atmosphere control, assist carbon source cracking, and do not interfere with the growth of BDD films.

[0050] Step three (3): Then, CH4 is introduced as a carbon source, the CH4 flow is controlled to be 5-8 sccm (CH4 / H2 flow ratio 1:20-1:30), the tube furnace pressure is adjusted to 0.8-1.2 atm, and heating is performed at a temperature increasing rate of 10-20 ℃ / min to 750-850 ℃, and the BDD film is grown by maintaining the temperature for 150-200 min.

[0051] During the growth process, liquid gallium has both catalytic and transport functions: on the one hand, it reduces the activation energy of the C-H bond of methane, and promotes the generation of carbon active species; on the other hand, it acts as a solvent to make carbon and boron atoms directionally diffuse to the surface of the silicon substrate and participate in diamond lattice substitution.

[0052] In the present application, CH4 is preferably used as a carbon source, because CH4 has an appropriate carbon content, is easy to break the C-H bond to generate carbon active species under the catalysis of liquid gallium, and the decomposition products only contain carbon and hydrogen (hydrogen can react with residual impurities or be discharged with the gas flow, without introducing additional impurities), which can adapt to the 1 atm normal pressure and 800 ℃ low-temperature growth conditions, and ensure the purity and crystalline quality of the BDD film; in addition to CH4, other hydrocarbons containing carbon (such as C2H2, C2H4, and C3H8) can also be used as a carbon source, which can also generate carbon active species under the catalysis of liquid gallium, and meet the carbon source demand for the growth of BDD films.

[0053] Step four: sample post-processing and performance characterization After the growth is completed, the sample is allowed to cool for a period of time, washed with dilute hydrochloric acid, and cleaned with deionized water; the film quality is detected by SEM and EDX in multiple dimensions, and data support is provided for BDD performance characterization.

[0054] Specifically: Step four (1): After the growth is completed, first close the CH4 inlet valve, continue to pass H2 for 8 min, then close the tube furnace heating module, and after the temperature in the furnace is naturally cooled to room temperature (25-30℃), the quartz boat is taken out. The sample is immersed in a dilute hydrochloric acid solution with a mass concentration of 5-10%, ultrasonic cleaned at 20-60 W for 5-10 min to remove the residual Ga-B alloy and unreacted boron powder on the surface, and then ultrasonic cleaned with deionized water for 3-5 times (3-5 min each time).

[0055] Step four (2): The surface morphology and cross-sectional thickness of the BDD film are observed by a scanning electron microscope (SEM) to ensure that the film is continuous and has a thickness of 6-8 μm. The element composition of the film is analyzed by an X-ray energy spectrometer (EDX) to verify that the boron element is uniformly distributed, and the performance of the sample is characterized.

[0056] First, from the perspective of process conditions, the present application breaks through the limitations of traditional preparation techniques as described in the background. The preparation method provided by the present application does not require high pressure, high temperature or high vacuum equipment, and grows at a low temperature of 750-850℃ under normal pressure with a tube furnace as the core. This mild process condition greatly simplifies the preparation process and reduces equipment cost and operating cost. The reduction of equipment cost and operating cost helps to improve the economic benefits of production, and the operation is easy to standardize, which provides the possibility for large-scale production.

[0057] Secondly, in terms of film quality, the present method helps to improve the compactness and crystalline quality of the film. In the pretreatment step, the substrate is treated to provide a good foundation for the growth of the subsequent film. During the growth process, liquid gallium plays a key catalytic and transport function. Liquid gallium can reduce the activation energy of C-H bond breaking of methane, promoting the generation of carbon active species. Carbon active species are the basic units of diamond film formation, and their generation efficiency and stability directly affect the quality of the film. At the same time, as a solvent, liquid gallium enables carbon and boron atoms to directionally diffuse to the surface of the silicon substrate and participate in diamond lattice substitution. This directional diffusion ensures the ordered 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, and reducing grain boundary defects can improve the compactness of the film, making the film structure more compact, reducing the presence of internal pores and impurities, and thus improving the crystalline quality, laying a foundation for the preparation of high-performance BDD films.

[0058] The present application is further described below through specific examples.

[0059] Example 1 In view of the need for high-quality BDD films for new energy vehicle power modules, the method provided by the present application is used to grow boron-doped diamond films on a silicon substrate to verify the process feasibility and film performance. The specific steps are as follows: Step one: Pretreatment of the silicon substrate A semiconductor-grade single crystal silicon wafer with a thickness of 0.8 mm and a size of 2 cm x 2 cm was selected for surface cleaning and activation treatment: (1) Oxide layer removal: the single crystal silicon wafer was placed in a 3% hydrofluoric acid solution, and an ultrasonic cleaner was started with a power of 40 W for 6 min to remove the surface natural oxide layer; then the wafer was ultrasonically cleaned with deionized water for 3 times, 3 min each time, to remove residual hydrofluoric acid and oxide layer debris; (2) Seed crystal adhesion: a 0.3 g / L nano-diamond seed crystal acetone suspension was prepared, the single crystal silicon wafer was immersed in the suspension, and ultrasonic treatment was performed at a power of 30 W for 8 min to make the seed crystals uniformly adsorbed on the surface of the silicon wafer; then the wafer was ultrasonically cleaned with acetone and deionized water for 4 min respectively to remove the unfirmly adsorbed seed crystals and residual acetone, and the pretreatment of the silicon substrate was completed.

[0060] Preparation of nano-diamond seed crystal acetone suspension: high-purity nano-diamond seed crystals with uniform particle size were selected, and the corresponding mass of nano-diamond seed crystals was weighed according to the target concentration (0.3 g / L), and then added to a sufficient amount of analytical pure acetone solvent; then the mixed system was placed in an ultrasonic cleaner with a power of 20-60 W, and ultrasonic treatment was performed for 10-15 min to make the nano-diamond seed crystals fully dispersed in the acetone, avoiding seed crystal agglomeration, and obtaining the nano-diamond seed crystal acetone suspension.

[0061] Step two: Ga-B alloy medium preparation and quartz boat assembly (1) Alloy preparation: high-purity solid boron powder and liquid gallium were weighed according to the mass of solid boron powder accounting for 1% of the total mass of solid boron powder and liquid gallium, and were placed together in a 50 mL quartz boat; the quartz boat was placed on a heating table in a glove box, heated at 35°C and stirred at 600 r / min for 10 min to make the boron powder completely dissolved to form a uniform Ga-B alloy with a boron concentration of 1 at%.

[0062] (2) Quartz boat assembly: the pretreated silicon substrate was laid flat on the bottom of the quartz boat, and the prepared Ga-B alloy was slowly poured to ensure that the alloy completely covered the surface of the silicon substrate, and the covering thickness was controlled to be 20 μm by vernier caliper measurement, and the quartz boat assembly was completed.

[0063] Step three: tube furnace growth system debugging and BDD film growth (1) Chamber preparation: the quartz boat assembled in step two was pushed into the constant temperature zone of the tube furnace, and the furnace door was closed; the vacuum pump was started, and the chamber vacuum degree was pumped to below 5 x 10 -3 Pa to exclude residual air.

[0064] (2) Atmosphere flushing: high-purity H2 was introduced with a flow rate of 120 sccm, and the chamber was flushed for 8 min to further remove impurities in the chamber.

[0065] (3) Growth parameter control: keep H2 flow constant, introduce high purity CH4, control CH4 flow at 6 seem (CH4 / H2 flow ratio 1:20); adjust the tube furnace gas pressure to 1 atm, heat to 800℃ at a heating rate of 20℃ / min, and keep the temperature for 180 min for BDD film growth.

[0066] 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 diamond lattice substitution.

[0067] Step four: sample post-processing and performance detection and verification (1) Sample post-processing: after the growth is completed, first close the CH4 inlet valve, continue to introduce H2 for 8 min, and then close the tube furnace heating module; after the temperature in the furnace naturally cools to 26℃, take out the quartz boat. Immersing the sample in a dilute hydrochloric acid solution with a mass concentration of 8%, ultrasonic cleaning for 8 min at a power of 40W to remove the residual Ga-B alloy and unreacted boron powder on the surface; then ultrasonic cleaning with deionized water for 3 times, each time for 3 min.

[0068] (2) Performance detection: SEM characterization: the film morphology was observed using a scanning electron microscope with the following parameters: acceleration voltage 2.00 kV, beam current 25 pA, working distance 5.1-5.6 mm. The surface morphology image shows that the BDD film surface is composed of uniform grains without obvious pores or impurity phases, and the grain size is 50-100 nm. The cross-sectional morphology image shows that the film continuously covers the silicon substrate with a cross-sectional thickness of 7 μm, and the interface with the silicon substrate is tightly bonded without peeling.

[0069] EDX characterization: EDAX APEX system was used for elemental analysis of the film, and the test results are shown in Table 1. The data shows that the mass fraction of carbon in the film is 85.3%, the atomic fraction is 92.6%, boron is uniformly distributed, only contains trace amounts of O and Si (partly from the substrate signal), and no Ga residue, proving that boron doping is uniform and no inert impurity phase is generated.

[0070] Table 1 EDX atomic percentage of BDD film

[0071] Referring to Figure 1 , a schematic diagram of the assembly structure in the tube furnace is shown. The quartz tube provides a closed environment for growth, the quartz boat is used to carry the silicon wafer (pre-treated silicon substrate) and Ga-B alloy, the silicon wafer is the growth substrate of the BDD film, and the Ga-B alloy serves as the boron source and catalytic transport medium, and the ceramic block serves as a support for the quartz boat. During the growth process in the tube furnace, with the help of this assembly, the catalytic and transport functions of liquid gallium are utilized to achieve the growth of BDD film on the surface of the silicon substrate.

[0072] Figure 2 Figure 2 is a SEM morphology diagram of the liquid metal-based boron-doped diamond film obtained in Example 1. From the diagram, it can be seen that the surface of the BDD film is composed of uniform grains without obvious pores or impurity phases, and the grain size is between 50-100 nm, which indicates that the film is dense and has good crystallinity, and the method of the present application can prepare a high-quality BDD film surface structure. Figure 2 (a-b) As can be seen from the surface morphology, the surface of the BDD film is composed of uniform grains without obvious pores or impurity phases, and the grain size is between 50-100 nm, which indicates that the film is dense and has good crystallinity, and the method of the present application can prepare a high-quality BDD film surface structure.

[0073] Figure 2 (c-d) The cross-sectional morphology shows that the BDD film is continuously covered on the silicon substrate, the cross-sectional thickness is about 7 μm, and the film is tightly combined with the silicon substrate interface.

[0074] Figure 3 Figure 3 is an EDX test diagram of the liquid metal-based boron-doped diamond film obtained in Example 1. According to the EDX test results, Figure 3 The EDX test results show that the signal peak of carbon element (C) in the film is very significant, and there is a signal peak of boron element (B), which proves that the boron element is successfully doped into the diamond film. In addition, the film only contains trace amounts of oxygen (O), silicon (Si), and no gallium (Ga) remains, which indicates that boron and carbon achieve good collaborative doping, and there is no Ga2O3, GaB2 and other inert impurity phases, further verifying the advantages of the method of the present application in boron doping uniformity and film purity.

[0075] It should be understood that the application of the present application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the present 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 controlling temperature to obtain liquid metal based boron-doped diamond film.

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: The solid boron powder and liquid gallium are mixed with the solid boron powder accounting for 0.5-2 % of the total mass of the solid boron powder and liquid gallium, heated and stirred 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, tin, lead, bismuth, thallium, and mixtures thereof. The exhausting, ventilating and temperature controlling The method comprises the following steps: exhausting: vacuumizing and excluding air; ventilating: introducing reducing gas or mixed gas containing reducing gas; temperature controlling: introducing gaseous carbon source, adjusting the air 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.

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 mixed gas containing reducing gas is 100-150 sccm. The flow rate of the gaseous carbon source is 5-8 sccm.

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 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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