Hetero-epitaxial growth of high thermal conductivity protective diamond thin film and preparation method thereof

Abstract

The application relates to the photoelectric field and discloses a hetero-epitaxial growth high-thermal-conductivity protective diamond film and a preparation method thereof, which comprises the following steps: placing a substrate on a sample table of a pulse laser deposition system, placing a target material on a target holder, and performing pulse laser deposition of a protective layer on the surface of the substrate; placing the deposited substrate on a sample table of a microwave plasma chemical vapor deposition system, inputting hydrogen and argon, and performing plasma cleaning on the surface of the protective layer; stopping the input of the argon, inputting methane gas and oxygen gas, and growing diamond on the surface of the protective layer; stopping the input of the methane and the oxygen, reducing the hydrogen flow, the gas pressure and the microwave power, reducing the cooling rate to be lower than 1 DEG C per second, and taking out the substrate with the high-thermal-conductivity protective diamond film after breaking the vacuum. The damage of the protective layer prepared through pulse laser deposition to the protected substrate is very low, and the diamond layer is successfully grown on the protective layer through hetero-epitaxy, so that the direct interface thermal resistance between the diamond and the substrate can be greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronics, and particularly relates to a heteroepitaxial growth of high-thermal-conductivity protective diamond film and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the semiconductor industry, the traditional silicon-based power semiconductor devices have gradually failed to meet the development needs of higher frequency, higher temperature and higher power. The third generation semiconductor materials GaN (gallium nitride) and AlN (aluminum nitride) are widely used in high-frequency and high-power fields due to their advantages of wide band gap, small dielectric constant, strong radiation resistance and high breakdown field strength. However, the power of the semiconductor material GaN has reached its limit. In order to further improve the power of the chip, a new heat dissipation scheme is needed to reduce the thermal resistance generated by the chip during operation.

[0003] Diamond has the highest thermal conductivity, stiffness and hardness, and also has high optical transmission characteristics and low expansion coefficient in a relatively large wavelength range. These properties make diamond an application material that can significantly reduce thermal resistance. Existing research on the combination of diamond and GaN has attracted much attention. There are three main ways to combine GaN and diamond. The first way is to combine diamond with GaN wafers. The second way is to grow GaN on single-crystal or polycrystalline diamond substrates. The third way is to grow nanocrystalline or polycrystalline diamond on the front or back surface of GaN. Research on these three combination methods has been successful. The stability and heat dissipation capacity of existing diamond grown on GaN have been improved, but the interface thermal resistance between diamond and GaN cannot be effectively reduced, which limits the heat dissipation performance of GaN devices. In addition, when using chemical deposition method to grow diamond on the surface of GaN, the hydrogen plasma involved in the growth process will etch the surface of GaN, increasing the risk of subsequent lattice mismatch.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a heteroepitaxial growth of high-thermal-conductivity protective diamond film and a preparation method thereof, wherein a protective layer is prepared between the substrate and the high-thermal-conductivity protective diamond film, which can provide more nucleation sites and ensure that the substrate is not damaged when growing diamond, so as to improve the thermal conductivity of semiconductor materials.

[0006] The technical scheme of the present application is as follows:

[0007] The present application provides a preparation method of a heteroepitaxial growth of high-thermal-conductivity protective diamond film, which comprises the following steps:

[0008] (1) placing a substrate on a sample table of a pulsed laser deposition system, placing a target material on a target holder, and depositing a protective layer on a surface of the substrate by pulsed laser deposition;

[0009] (2) placing the deposited substrate on a sample table of a microwave plasma chemical vapor deposition system, and introducing hydrogen and argon to perform plasma cleaning on the surface of the protective layer;

[0010] (3) stopping the introduction of argon, introducing methane and oxygen, and growing diamond on the surface of the protective layer;

[0011] (4) stopping the introduction of methane and oxygen, reducing the flow rate, pressure and microwave power of hydrogen, and reducing the cooling rate to less than 1℃ per second, and taking out the substrate with the high-thermal-conductivity protective diamond film after breaking the vacuum.

[0012] The application can protect the substrate from plasma etching during the growth of diamond by depositing a protective layer on the surface of the substrate, the deposited protective layer has a good surface morphology, can provide more nucleation sites for diamond, is conducive to the formation of high-density diamond particles, forms an excellent coverage on the surface of the protective layer, and can fully exert the heat dissipation performance of diamond, effectively reduces the interfacial thermal resistance between the substrate and the diamond film, and improves the heat conduction capacity of the semiconductor.

[0013] In the method, the thickness of the protective layer is 50-300 nm in step (1). The deposition mode of pulsed laser deposition first forms micro-islands and then forms a film, and the thickness of the protective layer is controlled in the range of 50-300 nm to ensure that the protective layer covers the substrate as thin as possible, avoids the etching of the substrate by hydrogen plasma during the growth of diamond, and forms a good surface morphology to provide abundant nucleation sites for diamond.

[0014] In the method, the substrate is one of silicon, germanium, gallium arsenide, indium phosphide, silicon carbide, gallium nitride and diamond in step (1).

[0015] In the method, the morphology of the target material is one of block, sheet, wire and powder in step (1); the target material is one of metal, ceramic, glass and crystal; and the crystal is one of silicon carbide, silicon oxide and silicon single crystal.

[0016] In the method, the distance between the target material and the substrate is 100-180 mm in step (1).

[0017] The preparation method of the hetero-epitaxial growth of high-thermal-conductivity protective diamond film, wherein in step (1), the system parameters during the pulse laser deposition of the protective layer on the surface of the substrate are as follows: the power of the laser in the pulse laser deposition system is 10-1000 W, the pulse width is 1-500 ns, and the repetition frequency is 20-100 kHz.

[0018] The preparation method of the hetero-epitaxial growth of high-thermal-conductivity protective diamond film, wherein in step (1), the pulse laser deposition of the protective layer comprises the following steps:

[0019] First, the mechanical pump is used to pump the vacuum to a vacuum degree of 1-10 Pa, and then the molecular pump is used to pump the vacuum to a vacuum degree of 1×10 -4 ~55×10 -4 Pa;

[0020] Nitrogen is introduced at a flow rate of 20-100 sccm, the cavity pressure is controlled to be 0.5-20 Pa, the laser energy is increased to 50 mJ in the nitrogen atmosphere, the deposition is performed for 2-4 minutes, the laser energy is reduced to 5 mJ, argon is introduced at a flow rate of 20-100 sccm, a bias voltage of 50 V is added, and the deposition is continued for 4-6 minutes.

[0021] The preparation method of the hetero-epitaxial growth of high-thermal-conductivity protective diamond film, wherein in step (2), the plasma cleaning of the surface of the protective layer by introducing hydrogen and argon comprises the following steps:

[0022] The vacuum is pumped to a vacuum degree of 0.1 Pa;

[0023] Hydrogen is introduced at a flow rate of 5-120 sccm and a pressure of 3-5 torr, the microwave power is turned on to ignite, and the ignition microwave power is 1-2 kW;

[0024] The hydrogen flow rate is increased to 120-600 sccm, the pressure is 10-120 Torr, the microwave power is 1-1.5 kW, and the temperature is increased to 150-250℃;

[0025] Argon is introduced at a flow rate of 1-15 sccm, the cavity pressure is controlled to be 1-3 kPa, and the surface of the protective layer is plasma cleaned for 10-30 minutes;

[0026] In step (2), the purity of the hydrogen and the argon is not less than 7N.

[0027] The preparation method of the heterogeneous epitaxial growth high-thermal-conductivity protective diamond film, wherein in step (3), the proportion of the methane gas is 3-5% of the hydrogen flow, the proportion of the oxygen gas is 1-3% of the hydrogen flow, the cavity gas pressure is 50-120 torr, the microwave power is 1-10 kW, the surface temperature of the protective layer is 700-1000 DEG C, and the growth time is 4-12 h; and the purity of the methane gas is not less than 6N.

[0028] The application further provides a heterogeneous epitaxial growth high-thermal-conductivity protective diamond film, which is prepared by the preparation method of the heterogeneous epitaxial growth high-thermal-conductivity protective diamond film.

[0029] The preparation method of the heterogeneous epitaxial growth high-thermal-conductivity protective diamond film can effectively reduce the interface thermal resistance between the substrate and the diamond, and the protective layer provides more nucleation points for the growth of the diamond, so that the density of the diamond grown on the substrate is improved, the high-density diamond particles are grown on the protective layer, and an excellent coverage is formed on the surface of the protective layer, so that the heat dissipation performance of the diamond can be fully exerted, and the problem of thermal resistance of high-frequency and high-power chips and other devices is effectively solved.

[0030] The preparation method of the heterogeneous epitaxial growth high-thermal-conductivity protective diamond film provided by the application can transfer the target material from the target to the substrate to form a protective layer according to the stoichiometry by using a pulsed laser deposition system, the damage to the substrate is low, the protective layer can effectively avoid the direct interface thermal resistance between the substrate and the diamond, the protective layer grows columnar on the surface of the substrate, can form a good surface morphology to provide abundant nucleation sites for the diamond grown by the subsequent microwave plasma chemical vapor deposition system, the diamond can accelerate the growth on the protective layer and form high-density diamond particles, the diamond will not damage the substrate during the growth of the diamond, and the diamond can form a good coverage on the protective layer and fully exert the heat dissipation performance of the diamond. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a scanning electron microscope photo of the surface morphology of the silicon carbide protective layer in Example 1 of the application.

[0032] Figure 2 It is a scanning electron microscope photo of the surface morphology of the silicon carbide protective layer in Example 1 of the application.

[0033] Figure 3 It is a scanning electron microscope photo of the cross-sectional morphology of the sapphire substrate / gallium nitride substrate / silicon carbide protective layer in Example 1 of the application.

[0034] Figure 4 Figure 8 is a point analysis energy spectrum component distribution data graph of the silicon carbide protective layer in Example 1 of the present application.

[0035] Figure 5 Figure 9 is a point analysis energy spectrum component percentage data graph of the silicon carbide protective layer in Example 1 of the present application.

[0036] Figure 6 Figure 10 is a scanning electron microscope photograph of the surface morphology of the high thermal conductivity protective diamond film in Example 1 of the present application.

[0037] Figure 7 Figure 11 is a scanning electron microscope photograph of the cross-sectional morphology of the sapphire substrate / gallium nitride substrate / silicon carbide protective layer / high thermal conductivity protective diamond film in Example 1 of the present application.

[0038] Figure 8 Figure 12 is a scanning electron microscope photograph of the cross-sectional morphology of the high thermal conductivity protective diamond film in Example 1 of the present application.

[0039] Figure 9 Figure 13 is a scanning electron microscope photograph of the surface morphology of the comparative example of the present application.

[0040] Figure 10 Figure 14 is a surface temperature graph of the diamond film grown after the protective layer of different thicknesses in Examples 1-3 and the comparative example of the present application. DETAILED DESCRIPTION

[0041] The present application provides a heteroepitaxial growth of a high thermal conductivity protective diamond film and a preparation method thereof. In order to make the purpose, technical solutions and effects 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 are not used to limit the present application.

[0042] Diamond has very high thermal conductivity, which is more than 5 times that of copper, and can quickly conduct heat in a high temperature environment, having good heat dissipation performance. Diamond can effectively reduce the heat generated by high-power and high-frequency semiconductors. Although the stability of growing diamond on the surface of a high-power semiconductor has been solved, the interfacial thermal resistance between the semiconductor and the diamond cannot be effectively reduced, resulting in that the heat dissipation performance of the diamond cannot be effectively played. Therefore, how to optimize the interfacial thermal resistance between the diamond and the substrate becomes a key point.

[0043] The hydrogen plasma involved in the existing chemical deposition method will generally etch the substrate, and the present application deposits a protective layer between the substrate and the diamond by pulse laser deposition (PLD) in physical vapor deposition. The plasma involved is generally the plasma of the target material, and will not react with the substrate and cause damage. It can also provide high energy to excite high chemical bond atoms, which is better than general low temperature deposition and more conducive to subsequent nucleation and deposition of diamond, thereby improving the thermal conductivity of the substrate.

[0044] In summary, the protective layer is prepared between the substrate and the diamond thin film using the pulse laser deposition system, which is simple and reliable, can be adapted to processing of various materials including metals, ceramics, plastics, etc. The processing parameters of different materials can be adjusted as needed, which has high flexibility and can be customized as needed. By adjusting the laser parameters and processing path, the processing speed is fast, which can save energy and material consumption. The most important advantage is that the material is transferred from the target to the substrate according to the stoichiometry, which improves the deposition effect and has very good application prospects.

[0045] Specifically, the present application provides a preparation method for heteroepitaxial growth of high-thermal-conductivity protective diamond thin film, which is suitable for the field of optoelectronics, and comprises the following steps:

[0046] (1) placing the substrate on the sample table of the pulse laser deposition system, placing the target material on the target holder, and depositing a protective layer on the surface of the substrate by pulse laser deposition.

[0047] In this step (1), the substrate can be one of silicon, germanium, gallium arsenide, indium phosphide, silicon carbide, gallium nitride and diamond, and the target material can be one of metal, ceramic, glass and crystal.

[0048] In the embodiment of the present application, the substrate is gallium nitride. When the protective object is a material such as metal, ceramic, glass or crystal, the target material can also be metal, ceramic, glass or crystal. The morphology of the target material can be block, sheet, wire or powder. Pulse laser deposition can be used for a variety of materials and can be adapted to samples of different shapes and sizes. There is no special limitation on the morphology of the target material, which has the advantages of simplicity and convenience.

[0049] The crystal can be one of silicon carbide, silicon oxide and silicon single crystal, and preferably the target material is silicon carbide. Silicon carbide has approximately the same lattice parameters as diamond, with a lattice mismatch of about 3.5% between silicon carbide and diamond. The crystal quality of the diamond grown on the silicon carbide protective layer is high, which can effectively reduce the direct interfacial thermal resistance between the substrate and the diamond, thereby improving the thermal conductivity of the substrate.

[0050] In this step (1), before placing the target material and the substrate, the target material and the substrate need to be cleaned and inspected to ensure that the surfaces are smooth and flat, and appropriate clamps or fixing devices are used to ensure that the target material and the substrate are firmly fixed on the processing platform.

[0051] In this step (1), when placing the target material and the substrate, the position alignment between the target material and the substrate needs to be ensured, and the distance between the target material and the substrate needs to be adjusted according to the specific processing requirements and material properties.

[0052] Further, the distance between the target material and the substrate is 100mm~180mm. If the target-substrate distance is too close, it will cause the deposition area to be non-uniform and the edge deposition rate to be low, and if the target-substrate distance is too far, it will cause the overall deposition rate to be too low. Controlling the target-substrate distance to be 100mm~180mm is beneficial to obtaining a smooth silicon carbide protective layer in a short time.

[0053] In this step (1), after the substrate and the target material are fixed, vacuum is drawn, first using a mechanical pump to draw vacuum to a vacuum degree of 1~10Pa, and then using a molecular pump to draw vacuum to a vacuum degree of 1×10 -4 ~55×10 -4 Pa, and after the vacuum is drawn, the laser power is turned on to deposit. The vacuum drawing process can be 15 minutes. Drawing vacuum to a high degree of vacuum through a molecular pump can ensure that a high-uniformity plume is generated in the chamber and the purpose of depositing a protective layer is achieved.

[0054] In this step (1), the system parameters when depositing the protective layer on the surface of the substrate by pulsed laser are as follows: the power of the laser in the pulsed laser deposition system is 10~1000W, the pulse width is 1~500ns, and the repetition frequency is 20~100kHz.

[0055] In this step (1), there is a detailed deposition step. Specifically, the pulsed laser deposition of the protective layer includes the following steps:

[0056] Nitrogen is introduced at a flow rate of 20~100sccm, and the chamber pressure is controlled at 0.5-20Pa. The laser energy is increased to 50mJ in a nitrogen atmosphere, and deposition is performed for 2~4 minutes. The laser energy is reduced to 5mJ, argon is introduced at a flow rate of 20~100sccm, a bias voltage of 50V is added, and deposition is continued for 4~6 minutes.

[0057] In the process of the pulse laser deposition of the protective layer, the nitrogen and argon can promote the deposition of the protective layer to form a good surface morphology. The flow rate of the nitrogen and argon should not be too high to avoid the failure of the vacuum pumping. The flow rate of the nitrogen is controlled to balance the vacuum pumping. The pulse laser deposition pressure is generally around 0.1-50 Pa, and a uniform plume can be generated. In the process of the pulse laser deposition of the protective layer, the cavity pressure is controlled to be 0.5-20 Pa, preferably 1 Pa. The cavity pressure is related to the surface roughness of the film. The pulse laser deposition cavity pressure is controlled to be 1 Pa. The deposited film can form a complete crystal structure, which is beneficial to reduce the lattice mismatch degree. The kinetic energy of the evaporated particles can be appropriately reduced. The particles can be effectively prevented from colliding with the substrate due to high energy and causing local damage to the previously deposited protective layer and re-sputtering. The deposition of the high-quality protective layer is facilitated. The surface morphology of the deposited protective layer is the best under the deposition pressure of 1 Pa.

[0058] In the specific embodiment, the silicon carbide protective layer is deposited on the surface of the gallium nitride substrate by pulse laser deposition. After the pulse laser deposition system is pumped, the nitrogen is introduced. The flow rate of the nitrogen is controlled to ensure that the pulse laser deposition is performed in the nitrogen atmosphere with a cavity pressure of 1 Pa. The silicon carbide is deposited for about 3 minutes under high laser energy. After excitation, the silicon carbide is rapidly deposited on the surface of the gallium nitride substrate to form micro-islands and then a film. The presence of nitrogen can promote the formation of better lattice parameter transition growth of the silicon carbide and the gallium nitride material. The cavity pressure is maintained, and then the laser energy is reduced to 5 mJ. A certain amount of argon is introduced, and a bias voltage (50 V) is added to promote the columnar growth of the silicon carbide protective layer. The activation energy of the argon is low, which can promote the plasma activation to make the silicon carbide protective layer easier to deposit. The bias voltage can promote the adhesion and density of the silicon carbide deposition. The low-energy deposition time is about 5 minutes. Finally, the silicon carbide protective layer structure with micro-island and columnar growth is formed. The obtained surface morphology can provide more nucleation sites for the epitaxial growth of diamond, which is beneficial to improve the nucleation density and crystallization performance of diamond.

[0059] In this step (1), a protective layer with a thickness of 50-300 nm is obtained on the surface of the substrate by pulse laser deposition. The pulse laser deposition is performed in the form of micro-islands and then a film. By controlling the thickness of the protective layer to be 50-300 nm, the protective layer can cover the substrate as thin as possible to avoid the etching of the substrate by hydrogen plasma during the growth of diamond. At the same time, the good surface morphology formed can provide abundant nucleation sites for diamond.

[0060] (2) The deposited substrate is placed on the sample table of the microwave plasma chemical vapor deposition system, and hydrogen and argon are introduced to clean the surface of the protective layer by plasma.

[0061] In this step (2), the sample table surface needs to be clean and flat, and the sample table is wiped with alcohol in advance to prevent impurities from affecting. After fixing the substrate, vacuum is extracted to 0.1 Pa, and the purity of the introduced hydrogen and argon is not less than 7N.

[0062] In this step (2), after vacuum extraction, hydrogen is introduced for ignition and heating, and argon is introduced for plasma cleaning. Specifically, the following steps are included:

[0063] Vacuum extraction to a vacuum degree of 0.1 Pa,

[0064] Introduce hydrogen, the hydrogen flow rate is 5-120sccm, the gas pressure is 3-5torr, turn on the microwave power to ignite, the ignition microwave power is 1-2kW;

[0065] Increase the hydrogen flow rate to 120-600sccm, the gas pressure is 10-120Torr, the microwave power is 1-1.5kW, and the temperature is raised to 150-250℃;

[0066] Introduce argon, the argon flow rate is 1-15sccm, the cavity gas pressure is controlled to be 1-3kPa, and the surface of the protective layer is plasma cleaned for 10-30 minutes;

[0067] In this step (2), the plasma cleaning conditions are relatively mild, mainly for etching and cleaning of contaminated particles and grease graphite on the protective layer, and will not damage the good surface morphology of the protective layer. Moreover, due to the columnar growth characteristics of pulsed laser deposition, plasma cleaning after deposition can reduce the protruding column points on the surface of the protective layer, which is beneficial to further improve the surface performance of the protective layer.

[0068] (3) Stop introducing argon, introduce methane gas and oxygen gas, and grow diamond on the surface of the protective layer;

[0069] In this step (3), the hydrogen flow rate is kept constant, methane and oxygen are introduced for growth, diamond nucleation and growth starts, and the stagnation point covers the surface of the protective layer to achieve full surface coverage. Among them, the proportion of methane gas introduced accounts for 3-5% of the hydrogen flow rate, the proportion of oxygen gas introduced accounts for 1-3% of the hydrogen flow rate, the cavity gas pressure is 50-120torr, the microwave power is 1-10kW, the surface temperature of the protective layer is 700-1000℃, the growth time is 4-12h, and the purity of methane is not less than 6N. A small amount of added oxygen can improve the growth rate and quality of the diamond film.

[0070] (4) Stop the input of methane and oxygen, slowly reduce the hydrogen flow, gas pressure, microwave power, and the cooling rate is lower than 1℃ per second, and the substrate with high thermal conductivity protective diamond film is taken out after breaking the vacuum.

[0071] In this step (4), the substrate with high thermal conductivity protective diamond film is taken out after slowly reducing the hydrogen flow, gas pressure, microwave power, and the cooling rate is lower than 1℃ per second. During the cooling process, the gas pressure needs to be reduced when the microwave power is reduced, otherwise it is difficult to uniformly reduce the temperature and the plasma fireball becomes smaller, the heating range becomes smaller and uneven, and the hydrogen flow is too large to balance with the vacuum to obtain low pressure. Therefore, the adjustment of the microwave power, hydrogen flow and gas pressure needs to be balanced to better control the cooling rate, wherein the hydrogen flow is reduced to 50sccm, the gas pressure is reduced to 10Torr, and the microwave power is reduced to 800W. The cooling process generally takes about 15 minutes. By controlling the cooling rate below 1℃ / s, the stress between the high thermal conductivity protective diamond film and the substrate surface caused by thermal mismatch can be prevented.

[0072] After the substrate is taken out, a high thermal conductivity protective diamond film with a thickness of 8-50μm is obtained on the surface of the protective layer, and the diamond particles in the film have high density, which can play a role in heat conduction and high thermal conductivity on the surface of the substrate, and can effectively improve the working performance of the semiconductor device in further application.

[0073] The application also provides a heteroepitaxial growth high thermal conductivity protective diamond film, which is prepared by the above-mentioned preparation method.

[0074] The heteroepitaxial growth high thermal conductivity protective diamond film and the preparation method thereof provided by the application have the following characteristics:

[0075] (1) The preparation method of the heteroepitaxial growth high thermal conductivity protective diamond film provided by the application is suitable for protecting high-power and high-frequency devices, and can effectively solve the heat dissipation problem. By using a pulsed laser deposition system (PLD), silicon carbide can be effectively transferred from the target to the substrate according to the stoichiometric ratio, and high-quality film growth can be achieved. The film can grow various materials, including metals, oxides, semiconductors, etc., and can also be suitable for processing samples of different shapes and sizes. It has the advantages of non-toxicity, harmlessness, simple operation, convenience, etc. The application deposits a protective layer between the substrate and the diamond film by pulsed laser deposition, without etching the substrate, and can effectively avoid the direct interface thermal resistance between the substrate and the diamond.

[0076] (2) The diamond density of the hetero-epitaxial growth high-thermal-conductivity protective diamond film of the present application is high, which can increase the thermal conductivity of the surface of the protected material. Preferably, the silicon carbide has a very high melting point, thermal stability and thermal conductivity, and the lattice mismatch between the silicon carbide and the diamond is small, about 3.5%, which makes the crystal quality of the diamond epitaxially grown on the silicon carbide protective layer high.

[0077] (3) The hetero-epitaxial growth high-thermal-conductivity protective diamond film of the present application is suitable for the deposition of diamond protection for other materials, such as metals, ceramics, glass, crystals and the like, in addition to being suitable for the deposition of diamond protection for gallium nitride materials.

[0078] (4) In the technical solution of the present application, methane, hydrogen and argon are used as gas raw materials to prepare diamond. The gas raw materials and tail gas are non-toxic and harmless, easy to handle, environmentally friendly, and raw materials are easy to obtain.

[0079] The present application is further illustrated by specific examples

[0080] The gallium nitride substrate used in the examples and comparative examples of the present application is a gallium nitride substrate deposited on a sapphire substrate.

[0081] Example 1

[0082] First, the gallium nitride is placed on the sample table of the pulsed laser deposition system, and the silicon carbide is placed on the target holder. The position of the target material and the substrate is accurately positioned, the distance between the target material and the substrate is 120 mm, the mechanical pump is used to pump to 10 Pa, and then the molecular pump is used to pump to a vacuum degree of 5x10 -4 Pa. After the vacuum pumping is completed, the laser power is turned on, the pulse laser power is 30 W, the pulse width is 132 ns, the repetition frequency is 50 kHz, the nitrogen flow is 50 sccm, the cavity gas pressure is controlled to be 1 Pa, the laser energy is increased to 50 mJ in the nitrogen atmosphere, the deposition is carried out for 3 minutes, the cavity gas pressure is maintained, the laser energy is reduced to 5 mJ, the argon flow is 50 sccm, and the deposition is continued for 5 minutes. A 200 nm silicon carbide protective layer is deposited on the gallium nitride substrate.

[0083] The deposited substrate is placed on the sample table of the microwave plasma chemical vapor deposition system, and pumped to a vacuum degree of 0.1 Pa. Hydrogen (purity 7N) is introduced for ignition and temperature rise. The hydrogen flow is slowly increased to 40 sccm and the gas pressure is increased to 5 Torr for ignition. The ignition microwave power is 1 kW. When the temperature rises, the hydrogen flow is increased to 300 sccm, the gas pressure is increased to 90 Torr, and the microwave power is adjusted to 1.5 kW. The temperature reaches 200°C. Then, argon (purity 7N) with a flow rate of 5 sccm is introduced, and the cavity gas pressure is controlled to be 2 kPa. The surface of the silicon carbide protective layer is plasma cleaned for 10 minutes.

[0084] Keeping the hydrogen flow rate constant, after stopping the argon flow, introduce methane gas (6N purity) at 3% of the hydrogen flow rate and oxygen gas at 2% of the hydrogen flow rate. The chamber pressure is 95 torr, the microwave power is 3kW, and the substrate surface temperature is approximately 750℃. Diamond is grown on the surface of the silicon carbide protective layer with a thickness of 10μm for 6 hours.

[0085] Stop the flow of methane and oxygen, slowly reduce the hydrogen flow rate, gas pressure, and microwave power, and keep the cooling rate below 1°C per second until it reaches room temperature. After breaking the vacuum, remove the gallium nitride substrate with a highly thermally conductive protective diamond film and a silicon carbide protective layer.

[0086] After depositing a silicon carbide protective layer on the surface of a gallium nitride substrate, it was observed using a scanning electron microscope, such as... Figure 1 As shown, in Example 1, the silicon carbide protective layer formed a good surface morphology on the gallium nitride substrate, providing multiple nucleation sites for diamond nucleation. Point analysis energy dispersive spectroscopy (EDS) was performed on the surface of this silicon carbide protective layer, as shown... Figures 2-5 As shown, the surface gallium element was not reduced and volatilized under the protective layer, and the presence of aluminum element was due to the gallium nitride substrate being grown on the sapphire substrate.

[0087] After depositing a highly thermally conductive protective diamond film on the surface of the silicon carbide protective layer, it was observed using a scanning electron microscope, such as... Figure 6 As shown, high-density diamond particles are grown on the surface of the silicon carbide protective layer, forming a good cover for the silicon carbide protective layer and fully utilizing the heat dissipation performance of diamond, such as... Figures 7-8 As shown, the substrate was processed to form four layers: sapphire substrate / gallium nitride substrate / silicon carbide protective layer / high thermal conductivity protective diamond film, with a very significant deposition effect.

[0088] Example 2

[0089] Example 2 uses the same steps and parameters as Example 1, the only difference being that the thickness of the silicon carbide protective layer deposited by pulsed laser in Example 2 is 100 nm.

[0090] Example 3

[0091] Example 3 uses the same steps and parameters as Example 1, the only difference being that the thickness of the silicon carbide protective layer deposited by pulsed laser in Example 3 is 50 nm.

[0092] Comparative Example

[0093] As a comparative sample 1, the untreated gallium nitride substrate was used as a comparative sample 1, and the same steps and parameters as in Example 1 were used, except that no silicon carbide protective layer was deposited on the comparative sample 1 by the pulsed laser deposition system, and the gallium nitride substrate was directly placed in the microwave plasma chemical vapor deposition system for diamond growth as in Example 1.

[0094] After diamond growth, the surface temperature of the diamond film was measured by scanning electron microscopy, as shown in Figure 9 Without a silicon carbide protective layer, the gallium nitride substrate was directly grown into diamond, and the diamond could not achieve high density, and the surface of the gallium nitride was severely etched, which was in sharp contrast with Figure 6 which would seriously affect the performance of the gallium nitride device.

[0095] After the diamond was grown on the protective layer of different thicknesses in Examples 1-3 and the comparative example, the surface temperature of the diamond film of Examples 1-3 and the comparative example was measured after the respective sapphire substrate lower surface temperature was set to 70°C and the sample was placed in a room temperature environment for 20 minutes, as shown in Figure 10 wherein a) corresponds to the surface temperature of Example 1, the color temperature corresponds to about 53°C red; b) corresponds to the surface temperature of Example 2, the color temperature corresponds to about 50°C yellow; c) corresponds to the surface temperature of Example 3, the color temperature corresponds to about 50°C yellow; d) corresponds to the surface temperature of the comparative example, the color temperature corresponds to about 57°C purple. The deposition of silicon carbide protective layers of 200 nm, 100 nm and 50 nm thickness in Examples 1-3 improves the thermal conductivity, which shows that the gallium nitride is well protected and the diamond is successfully deposited on the silicon carbide protective layer and the interface thermal resistance is reduced. Among them, the diamond grown on the 200 nm thick silicon carbide protective layer in a) is the most uniform and has the best overall flatness, and the diamond grown on the 100 nm or 50 nm thick silicon carbide protective layer in b) or c) has poor flatness and also has a local area with a temperature that is too high, such as the partial purple color temperature in b).

[0096] It should be understood that the application is not limited to the above examples, and those of ordinary skill in the art can make improvements or modifications based on the above description, and all such improvements and modifications shall fall within the scope of the application.

Claims

1. A method for preparing a high thermal conductivity protective diamond thin film by heteroepitaxial growth, characterized in that, Includes the following steps: (1) Place the substrate on the sample stage of the pulsed laser deposition system, place the target on the target holder, and deposit a protective layer on the surface of the substrate using pulsed laser. In step (1), the pulsed laser deposition of the protective layer includes the following steps: First, use a mechanical pump to evacuate to a vacuum level of 1~10 Pa, then use a molecular pump to evacuate to a vacuum level of 1×10 Pa. -4 ~55×10 - 4 Pa; The system parameters for the pulsed laser deposition of the protective layer on the substrate surface are as follows: the laser power in the pulsed laser deposition system is 10~1000W, the pulse width is 1~500ns, and the repetition frequency is 20~100kHz. Nitrogen gas is introduced at a flow rate of 20-100 sccm, and the cavity pressure is controlled at 0.5-20 Pa. In the nitrogen atmosphere, the laser energy is increased to 50 mJ and deposited for 2-4 minutes. The laser energy is then reduced to 5 mJ, and argon gas is introduced at a flow rate of 20-100 sccm. A bias voltage of 50 V is added, and deposition continues for 4-6 minutes. (2) Place the deposited substrate on the sample stage of the microwave plasma chemical vapor deposition system, and introduce hydrogen and argon gas to perform plasma cleaning on the surface of the protective layer. (3) Stop the argon gas supply and introduce methane and oxygen gas to grow diamond on the surface of the protective layer; (4) Stop the introduction of methane and oxygen, reduce the hydrogen flow rate, gas pressure, microwave power, and cooling rate to less than 1°C per second. After breaking the vacuum, take out the substrate with the highly thermally conductive protective diamond film.

2. The method for preparing a high thermal conductivity protective diamond thin film by heteroepitaxial growth according to claim 1, characterized in that, In step (1), the thickness of the protective layer is 50~300nm.

3. The method for preparing a high thermal conductivity protective diamond thin film by heteroepitaxial growth according to claim 1, characterized in that, In step (1), the substrate is one of silicon, germanium, gallium arsenide, indium phosphide, silicon carbide, gallium nitride and diamond.

4. The method for preparing a high thermal conductivity protective diamond thin film by heteroepitaxial growth according to claim 1, characterized in that, In step (1), the target material has the following morphology: block, sheet, filament and powder; the target material is one of metal, ceramic, glass and crystal; the crystal is one of silicon carbide, silicon oxide and silicon single crystal.

5. The method for preparing a high thermal conductivity protective diamond thin film by heteroepitaxial growth according to claim 1, characterized in that, In step (1), the distance between the target and the substrate is 100mm~180mm.

6. The method for preparing a high thermal conductivity protective diamond thin film by heteroepitaxial growth according to claim 1, characterized in that, In step (2), the plasma cleaning of the protective layer surface by introducing hydrogen and argon includes the following steps: Evacuate to a vacuum level of 0.1 Pa; Hydrogen gas is introduced at a flow rate of 5-120 sccm and a pressure of 3-5 torr. The microwave power supply is turned on to ignite the ignition, and the microwave power of the ignition is 1-2 kW. Increase the hydrogen flow rate to 120~600 sccm, the gas pressure to 10~120 Torr, the microwave power to 1~1.5 kW, and the temperature to 150~250℃; Argon gas is introduced at a flow rate of 1-15 sccm and the cavity pressure is controlled at 1-3 kPa. The surface of the protective layer is then plasma-cleaned for 10-30 minutes. In step (2), the purity of the hydrogen and the argon is not less than 7N.

7. The method for preparing a high thermal conductivity protective diamond thin film by heteroepitaxial growth according to claim 1, characterized in that, In step (3), the proportion of methane gas introduced is 3-5% of the hydrogen gas flow rate, the proportion of oxygen gas introduced is 1-3% of the hydrogen gas flow rate, the cavity pressure is 50-120 torr, the microwave power is 1-10 kW, the surface temperature of the protective layer is 700-1000℃, and the growth time is 4-12 h; the purity of the methane gas is not less than 6N.

8. A heteroepitaxially grown high thermal conductivity protective diamond film, characterized in that, The diamond film with high thermal conductivity was prepared by the method for heteroepitaxial growth as described in any one of claims 1-7.

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