A method and apparatus for producing a hexagonal boron nitride film

Abstract

The application discloses a method for preparing a hexagonal boron nitride film, which comprises the following steps: placing a carrier loaded with boron powder and a metal substrate in a reactor; heating the boron powder and the metal substrate; introducing a mixed gas of nitrogen and hydrogen into the reactor, ionizing and activating the gas by starting a radio frequency source; and combining the ionized plasma gas and the heated and evaporated boron powder on the surface of the metal substrate to deposit and form a hexagonal boron nitride film. The method for preparing the hexagonal boron nitride film uses boron powder and nitrogen as precursors, does not need to select boron-nitrogen compounds, is pollution-free in the whole preparation process, and can control the boron source and the nitrogen source separately, so that the hexagonal boron nitride film can be grown for a long time and stably.

Description

Technical Field

[0001] This invention relates to the field of hexagonal boron nitride thin film preparation technology, and specifically to a method and apparatus for preparing hexagonal boron nitride thin films. Background Technology

[0002] Existing methods for preparing hexagonal boron nitride mainly utilize chemical vapor deposition to grow hexagonal boron nitride films on copper foil surfaces, using single nitrogen-boron sources such as ammonia borane or borazine as precursors to grow single-layer or multi-layer hexagonal boron nitride on metal substrate surfaces.

[0003] In existing technologies, the preparation of hexagonal boron nitride thin films using chemical vapor deposition (CVD) typically employs either atmospheric pressure CVD or low-pressure CVD. However, both methods require precursors that readily form active fumed nitrogen and boron sources. Currently, most methods use ammonia borane as a precursor, which requires heating to undergo a decomposition reaction to provide an active nitrogen and boron source. This process is complex and non-uniform, and cannot provide a stable nitrogen and boron source for long-term and large-area hexagonal boron nitride thin film growth. Other precursors, such as borazine, boron chloride / ammonia, and boron fluoride / ammonia, are all toxic, requiring additional costs and raw material and exhaust gas treatment steps. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method and apparatus for preparing hexagonal boron nitride thin films, which can improve the controllability of hexagonal boron nitride preparation and ensure a pollution-free process.

[0005] To achieve the above objectives, the present invention provides a method for preparing hexagonal boron nitride thin films, comprising the following steps:

[0006] Both the carrier containing boron powder and the metal substrate are placed inside the reactor.

[0007] Heating of boron powder and metal substrate;

[0008] A mixture of nitrogen and hydrogen gas is introduced into the reactor, and a radio frequency source is turned on to ionize and activate the gas.

[0009] The gas ionized into plasma combines with the heated and evaporated boron powder on the surface of the metal substrate and deposits to form a hexagonal boron nitride thin film.

[0010] Furthermore, the metal substrate is a pure metal foil or an alloy foil, wherein the pure metal foil is one of copper, nickel, iron or chromium, and the alloy foil is a copper-nickel alloy or an iron-nickel alloy.

[0011] Furthermore, the metal substrate is first annealed and polished before being placed inside the reactor.

[0012] Furthermore, the annealing treatment of the metal substrate includes the following steps:

[0013] The pressure inside the reactor is evacuated to 10-15 Pa, and a mixture of Ar and H2 gas is introduced. The temperature of the metal substrate is raised to 1010-1070℃ within 0.5-1 h. After holding at this temperature for 6-12 h, it is annealed for 20-30 min. The flow rate of Ar is 50-200 sccm, and the flow rate of H2 is 5-60 sccm.

[0014] Furthermore, the metal substrate is polished by electrochemical polishing using a mixture of phosphoric acid solution and ethylene glycol solution in a 3:1 ratio. The polishing voltage is 1.5-2V, and the polishing time is 1.5-3h. After polishing, the substrate is rinsed with deionized water.

[0015] Furthermore, before introducing the mixed gas into the reactor, the gas pressure inside the reactor is reduced to below 100 Pa using a vacuum pump.

[0016] Furthermore, the boron powder is heated at a temperature of 500-1000℃ and has a mass of 200mg; the metal substrate is heated at a temperature of 1010-1070℃ and has an area of ​​1.5*1.5cm; the nitrogen flow rate is 50-200sccm; and the hydrogen flow rate is 5-60sccm.

[0017] An apparatus for preparing hexagonal boron nitride thin films, used in any of the methods described above, includes a tube furnace, a radio frequency source, a first heating unit, a second heating unit, and a vacuum pump. The tube furnace is provided with a radio frequency source at one end and a vacuum pump at the other end, and passes sequentially through the first heating unit and the second heating unit from the radio frequency source toward the vacuum pump.

[0018] Furthermore, the radio frequency source includes a copper coil and a power supply. The copper coil is wound around the outside of the tube furnace, and the power supply can provide alternating current to the copper coil to generate an electromagnetic field.

[0019] Furthermore, the center distance between the first heating unit and the second heating unit is 30-50cm, and the center distance between the copper coil and the first heating unit is 80-90cm.

[0020] The beneficial effects of the above-mentioned method and apparatus for preparing hexagonal boron nitride thin films are as follows: 1. Boron powder and nitrogen are used as precursors, and different isotopes of the boron powder can be selected to prepare different isotopic hexagonal boron nitride. Activation of nitrogen is achieved using a radio frequency source, eliminating the need to select the more reactive but toxic NH3 as the nitrogen source. Therefore, the entire preparation process does not use any toxic chemicals, is pollution-free, and requires no additional cost for raw material and exhaust gas treatment.

[0021] 2. During the growth process, the boron source is provided by evaporated boron powder, and the nitrogen source is provided by nitrogen gas. Since the sublimation rate of boron powder is stable at a stable temperature, and a stable nitrogen gas supply can be ensured by using a flow meter, a stable nitrogen and boron source supply can be provided for long-term growth, thereby achieving uniform growth of hexagonal boron nitride films over a long period of time and improving the quality of hexagonal boron nitride films.

[0022] 3. The supply rates of nitrogen and boron sources can be independently controlled. The supply rate of boron source can be controlled by adjusting the boron powder quality and heating temperature, while the supply rate of nitrogen source can be controlled by adjusting the nitrogen flow rate and radio frequency power. The control of the two sources is independent of each other. By controlling the nitrogen-boron ratio, hexagonal boron nitride with different crystal domain shapes can be obtained.

[0023] 4. The radio frequency source coil is located at a certain distance from the heating unit, which ensures that the high-energy plasma and the metal substrate do not overlap in space. This solves the problem that the plasma bombardment of the film surface during plasma-enhanced chemical vapor deposition causes a decrease in film quality due to the overlap between the film growth position and the plasma position. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly described below. In all the drawings, the elements or parts are not necessarily drawn to scale.

[0025] Figure 1 A flowchart of a method for preparing hexagonal boron nitride thin films provided by the present invention;

[0026] Figure 2 A schematic diagram of an apparatus for preparing hexagonal boron nitride thin films provided by the present invention;

[0027] Figure 3 This is a photograph of the growth of hexagonal boron nitride domains in Embodiment 1 of the present invention;

[0028] Figure 4 This is a growth photograph of hexagonal boron nitride domains in Embodiment 2 of the present invention;

[0029] Figure 5 This is a growth photograph of the hexagonal boron nitride thin film of Embodiment 3 of the present invention;

[0030] Figure 6 This is a growth photograph of the hexagonal boron nitride domains in Embodiment 4 of the present invention;

[0031] Figure label:

[0032] 1-Tube furnace, 2-Radio frequency source, 21-Copper coil, 3-First heating unit, 4-Second heating unit, 5-Vacuum pump, 6-Quartz boat, 7-Quartz plate. Detailed Implementation

[0033] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0034] Please see Figure 1 This invention provides a method and apparatus for preparing hexagonal boron nitride thin films, wherein the preparation method includes the following steps:

[0035] Both the carrier containing boron powder and the metal substrate are placed inside the reactor.

[0036] Heating of boron powder and metal substrate;

[0037] A mixture of nitrogen and hydrogen gas is introduced into the reactor, and the radio frequency source is turned on to ionize and activate the nitrogen gas.

[0038] The gas ionized into plasma combines with the heated and evaporated boron powder on the surface of the metal substrate and deposits to form a hexagonal boron nitride thin film.

[0039] Specifically, elemental boron powder refers to commercially available boron powder, including ordinary boron powder and isotopes. 10 B. 11 B. Both nitrogen and argon are commercially available high-purity gases with a purity of 5N or higher. Nitrogen is used to provide the nitrogen source required for the growth of hexagonal boron nitride, while argon serves as the carrier gas to provide a protective atmosphere. The support system includes a quartz boat and a quartz plate. The quartz boat serves as the carrier for loading the boron powder, and the quartz plate serves as the carrier for supporting the metal substrate.

[0040] Specifically, the metal substrate is a commercially available high-purity metal foil, which can be a pure metal foil, such as high-melting-point transition metals like copper, nickel, iron, and chromium, or an alloy foil, such as a copper-nickel alloy or an iron-nickel alloy. The alloy foil is prepared by electroplating followed by annealing.

[0041] Specifically, the metal substrate needs to undergo pretreatment, including annealing and polishing. The annealing steps are as follows:

[0042] The pressure inside the reactor is evacuated to 10-15 Pa, and a mixture of Ar and H2 gas is introduced. The temperature of the metal substrate is raised to 1010-1070℃ within 0.5-1 h. After holding at this temperature for 6-12 h, it is annealed for 20-30 min. The flow rate of Ar is 50-200 sccm, and the flow rate of H2 is 5-60 sccm. Annealing can make the surface of the metal substrate smooth, promote grain growth, and remove oxides and organic contaminants from the substrate surface.

[0043] The metal substrate is then electrochemically polished to minimize its surface roughness, thereby reducing the nucleation density of hexagonal boron nitride and increasing the grain size. The electrochemical polishing solution is a mixture of phosphoric acid and ethylene glycol in a 3:1 ratio. During constant-voltage polishing, the polishing voltage is 1.5-2V, preferably 1.8V, and the polishing time is 1.5-3 hours, preferably 2.5 hours. After polishing, the metal substrate is rinsed thoroughly with deionized water to complete the polishing process.

[0044] Specifically, before introducing the mixed gas into the reactor, the gas pressure inside the reactor is reduced to below 100 Pa using a vacuum pump.

[0045] Specifically, the heating temperature of the boron powder is 500-1000℃, the mass is 200mg, the heating temperature of the metal substrate is 1010-1070℃, the area is 1.5*1.5cm, the flow rate of nitrogen is 50-200sccm, and the flow rate of hydrogen is 5-60sccm. Adjusting the mass of the boron powder and the heating temperature can control the supply rate of the boron source, and adjusting the flow rate of nitrogen and the radio frequency power can control the supply rate of the nitrogen source. By controlling the nitrogen-boron ratio, hexagonal boron nitride with different crystal domain shapes can be obtained.

[0046] Apparatus used in the above preparation method, such as Figure 2 As shown, it includes a tube furnace, a radio frequency source, a first heating unit, a second heating unit, and a vacuum pump. One end of the tube furnace is equipped with a radio frequency source, and the other end is equipped with a vacuum pump. The tube furnace passes through the first heating unit and the second heating unit in sequence from the radio frequency source toward the vacuum pump.

[0047] Specifically, the radio frequency (RF) source includes a copper coil and a power supply. The copper coil is wound around the outside of the tube furnace, and the power supply provides alternating current to the copper coil, causing it to generate an electromagnetic field. The RF source provides the copper coil with an electromagnetic field frequency of 13.56MHz and a power of 20-500W. The center-to-center distance between the first and second heating units is 30-50cm, and the center-to-center distance between the copper coil and the first heating unit is 80-90cm.

[0048] Several embodiments of the method and apparatus for preparing hexagonal boron nitride thin films described above are as follows:

[0049] Implementation Method 1:

[0050] A quartz boat 6 carrying boron powder is placed inside a tube furnace 1 at the position corresponding to the first heating unit 3. The metal substrate is copper foil. The annealed and polished copper foil is placed on a quartz plate 7. The quartz plate 7 is placed inside the tube furnace 1 at the position corresponding to the second heating unit 4. The pressure inside the tube is evacuated to about 10 Pa by a vacuum pump 5, and 100 sccm of Ar and 40 sccm of H2 are introduced into the tube. The temperature of the copper foil is raised to 1050℃ within 1 hour.

[0051] After the copper foil is heated to 1050℃, the Ar flow rate in the tube is kept at 100 sccm and the H2 flow rate at 40 sccm. The boron powder temperature is raised to 700℃ within 30 minutes to evaporate the boron powder.

[0052] After the boron powder temperature reaches 700℃, the Ar supply is stopped, and 100 sccm of N2 and 40 sccm of H2 are introduced into the tube furnace. The exhaust valve is closed and the vacuum pump is turned on to reduce the furnace pressure to below 100 Pa. The RF power is set to 100W, and the RF power supply is turned on to ionize N2 into plasma, promoting the decomposition of N2 to form active nitrogen atoms. The active nitrogen atoms mix with the evaporated boron powder and combine on the surface of the copper foil to deposit hexagonal boron nitride. After 5 minutes of growth, the RF power supply is turned off and heating is stopped. The temperature of the copper foil and boron powder is then reduced to room temperature within 20 minutes. Figure 3 This is a photograph of the growth of hexagonal boron nitride domains on a copper foil substrate obtained in this embodiment.

[0053] Implementation Method Two:

[0054] A quartz boat carrying boron powder is placed in the tube furnace at the position corresponding to the first heating unit. The metal substrate is copper foil. The annealed and polished copper foil is placed on a quartz plate, and the quartz plate is placed in the tube furnace at the position corresponding to the second heating unit. The pressure inside the tube is evacuated to about 10 Pa by a vacuum pump, and 100 sccm of Ar and 40 sccm of H2 are introduced into the tube. The temperature of the copper foil is raised to 1050℃ within 1 hour.

[0055] After the copper foil is heated to 1050℃, the Ar flow rate in the tube is kept at 100 sccm and the H2 flow rate at 40 sccm. The boron powder temperature is raised to 500℃ within 30 minutes to evaporate the boron powder.

[0056] After the boron powder temperature reaches 500℃, the Ar supply is stopped, and 100 sccm of N2 and 40 sccm of H2 are introduced into the tube furnace. The exhaust valve is closed and the vacuum pump is turned on to reduce the furnace pressure to below 100 Pa. The RF power is set to 100W, and the RF power supply is turned on to ionize N2 into plasma, promoting the decomposition of N2 to form active nitrogen atoms. The active nitrogen atoms mix with the evaporated boron powder and combine on the surface of the copper foil to deposit hexagonal boron nitride. After 10 minutes of growth, the RF power supply is turned off and heating is stopped. The temperature of the copper foil and boron powder is then reduced to room temperature within 20 minutes. Figure 4 This is a photograph of the growth of hexagonal boron nitride domains on a copper foil substrate obtained in this embodiment.

[0057] Compared with the first embodiment, the second embodiment lowers the temperature of the boron powder and prolongs the growth time. As can be seen from the growth photographs, the growth rate of hexagonal boron nitride domains is slower and takes longer after the temperature of the boron powder is lowered.

[0058] Implementation Method 3:

[0059] A quartz boat carrying boron powder is placed in the tube furnace at the position corresponding to the first heating unit. The metal substrate is copper foil. The annealed and polished copper foil is placed on a quartz plate, and the quartz plate is placed in the tube furnace at the position corresponding to the second heating unit. The pressure inside the tube is evacuated to about 10 Pa by a vacuum pump, and 100 sccm of Ar and 40 sccm of H2 are introduced into the tube. The temperature of the copper foil is raised to 1050℃ within 1 hour.

[0060] After the copper foil is heated to 1050℃, the Ar flow rate in the tube is kept at 100 sccm and the H2 flow rate at 40 sccm. The boron powder temperature is raised to 700℃ within 30 minutes to evaporate the boron powder.

[0061] After the boron powder temperature reaches 700℃, the Ar supply is stopped, and 100 sccm of N2 and 40 sccm of H2 are introduced into the tube furnace. The exhaust valve is closed and the vacuum pump is turned on to reduce the furnace pressure to below 100 Pa. The RF power is set to 100W, and the RF power supply is turned on to ionize N2 into plasma, promoting the decomposition of N2 to form active nitrogen atoms. The active nitrogen atoms mix with the evaporated boron powder and combine on the surface of the copper foil to deposit hexagonal boron nitride. After 15 minutes of growth, the RF power supply is turned off and heating is stopped. The temperature of the copper foil and boron powder is then reduced to room temperature within 20 minutes. Figure 5 This is a photograph of the growth of hexagonal boron nitride domains on a copper foil substrate obtained in this embodiment.

[0062] Compared with Embodiment 1, Embodiment 3 extends the growth time and successfully prepares a continuous hexagonal boron nitride film on the copper foil surface.

[0063] Implementation Method Four:

[0064] A quartz boat carrying boron powder is placed in the tube furnace at the position corresponding to the first heating unit. The metal substrate is copper foil. The annealed and polished copper foil is placed on a quartz plate, and the quartz plate is placed in the tube furnace at the position corresponding to the second heating unit. The pressure inside the tube is evacuated to about 10 Pa by a vacuum pump, and 100 sccm of Ar and 40 sccm of H2 are introduced into the tube. The temperature of the copper foil is raised to 1050℃ within 1 hour.

[0065] After the copper foil is heated to 1050℃, the Ar flow rate in the tube is kept at 100 sccm and the H2 flow rate at 40 sccm. The boron powder temperature is raised to 700℃ within 30 minutes to evaporate the boron powder.

[0066] After the boron powder temperature reaches 700℃, the Ar supply is stopped, and 100 sccm of N2 and 40 sccm of H2 are introduced into the tube furnace. The exhaust valve is closed and the vacuum pump is turned on to reduce the furnace pressure to below 100 Pa. The RF power is set to 50W, and the RF power supply is turned on to ionize N2 into plasma, promoting the decomposition of N2 to form active nitrogen atoms. The active nitrogen atoms mix with the evaporated boron powder and combine on the surface of the copper foil to deposit hexagonal boron nitride. After 5 minutes of growth, the RF power supply is turned off and heating is stopped. The temperature of the copper foil and boron powder is then reduced to room temperature within 20 minutes. Figure 6 This is a photograph of the growth of hexagonal boron nitride domains on a copper foil substrate obtained in this embodiment.

[0067] Compared with Implementation Method 1, Implementation Method 4 reduces the radio frequency power, and it can be seen that the growth rate of hexagonal boron nitride domains is slower.

[0068] As can be seen from the above four embodiments, the preparation rate of hexagonal boron nitride thin films is affected by factors such as the evaporation temperature of boron powder, the power of the radio frequency source for cracking nitrogen molecules, and the growth time.

[0069] The beneficial effects of the above-mentioned method and apparatus for preparing hexagonal boron nitride thin films are as follows: 1. Boron powder and nitrogen are used as precursors, and different isotopes of the boron powder can be selected to prepare different isotopic hexagonal boron nitride. Activation of nitrogen is achieved using a radio frequency source, eliminating the need to select the more reactive but toxic NH3 as the nitrogen source. Therefore, the entire preparation process does not use any toxic chemicals, is pollution-free, and requires no additional cost for raw material and exhaust gas treatment.

[0070] 2. During the growth process, the boron source is provided by evaporated boron powder, and the nitrogen source is provided by nitrogen gas. Since the sublimation rate of boron powder is stable at a stable temperature, and a stable nitrogen gas supply can be ensured by using a flow meter, a stable nitrogen and boron source supply can be provided for long-term growth, thereby achieving uniform growth of hexagonal boron nitride films over a long period of time and improving the quality of hexagonal boron nitride films.

[0071] 3. The supply rates of nitrogen and boron sources can be independently controlled. The supply rate of boron source can be controlled by adjusting the boron powder quality and heating temperature, while the supply rate of nitrogen source can be controlled by adjusting the nitrogen flow rate and radio frequency power. The control of the two sources is independent of each other. By controlling the nitrogen-boron ratio, hexagonal boron nitride with different crystal domain shapes can be obtained.

[0072] 4. The radio frequency source coil is located at a certain distance from the heating unit, which ensures that the high-energy plasma and the metal substrate do not overlap in space. This solves the problem that the plasma bombardment of the film surface during plasma-enhanced chemical vapor deposition causes a decrease in film quality due to the overlap between the film growth position and the plasma position.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method of producing a hexagonal boron nitride film, characterized by, The method comprises the following steps: The metal substrate is first annealed and polished, and the annealing of the metal substrate comprises the following steps: The pressure in the reactor is reduced to 10-15 Pa, and a mixed gas of Ar and H2 is introduced, and the temperature of the metal substrate is raised to 1010-1070 DEG C within 0.5-1 h, and after holding for 6-12 h, annealing for 20-30 min, wherein the flow rate of Ar is 50-200 sccm, and the flow rate of H2 is 5-60 sccm; The carrier loaded with elemental boron powder and the metal substrate are placed in the reactor; The boron powder and the metal substrate are heated; A mixed gas of nitrogen and hydrogen is introduced into the reactor, and a radio frequency source is turned on to ionize and activate the gas; The heating temperature of the boron powder is 500-1000 DEG C, the heating temperature of the metal substrate is 1010-1070 DEG C, the flow rate of nitrogen is 50-200 sccm, and the flow rate of hydrogen is 5-60 sccm, and by controlling the nitrogen-boron ratio, hexagonal boron nitride with different domain shapes is obtained; The gas ionized into plasma and the boron powder evaporated by heating are combined on the surface of the metal substrate to form a hexagonal boron nitride thin film.

2. The method of claim 1, wherein the method is characterized by: The metal substrate is a pure metal foil or an alloy foil, the pure metal foil is one of copper, nickel, iron or chromium, and the alloy foil is a copper-nickel alloy or an iron-nickel alloy.

3. The method of claim 1, wherein the method is characterized by: The polishing of the metal substrate is electrochemical polishing, a mixed solution of a phosphoric acid solution and a glycol solution is mixed at a ratio of 3:1, the polishing voltage is 1.5-2 V, the polishing time is 1.5-3 h, and after polishing, the metal substrate is rinsed with deionized water.

4. The method of claim 1, wherein the method is characterized by: Before the mixed gas is introduced into the reactor, the gas pressure in the reactor is reduced to below 100 Pa by a vacuum pump.

5. The method of claim 1, wherein the method is characterized by: The mass of the boron powder is 200 mg, and the area of the metal substrate is 1.5*1.5 cm.

6. An apparatus for producing a hexagonal boron nitride film, for use in the method according to any one of claims 1 to 5, characterized in that The device comprises a tube furnace, a radio frequency source, a first heating unit, a second heating unit and a vacuum pump, one end of the tube furnace is provided with the radio frequency source, the other end is provided with the vacuum pump, and the first heating unit and the second heating unit are sequentially passed through from the direction of the radio frequency source to the vacuum pump; The center distance of the first heating unit and the second heating unit is 30-50 cm, and the center distance of the copper coil and the first heating unit is 80-90 cm.

7. The apparatus of claim 6, wherein the substrate is heated to a temperature of about 600 °C to about 800 °C. The radio frequency source comprises a copper coil and a power supply, the copper coil is wound outside the tube furnace, and the power supply can provide alternating current to the copper coil to generate an electromagnetic field.

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