A method for growing a diamond film on a surface of a GaN substrate without damage and a GaN-based high electron mobility transistor

Abstract

The application provides a method for growing a diamond film on a GaN substrate surface without damage, which comprises the following steps: S1, pretreatment; S2, protective growth of a first step: continuously inputting H2 with a flow rate of 300-500 sccm into the growth chamber, then setting a microwave power = 2500-3000 W, a chamber pressure = 80-90 Torr; then inputting CH4 gas to grow for a first diamond growth time, and the ratio of gas flow rates H2:CH4 = 100:6-10; the first growth time is 10-20 min; S3, protective growth of a second step: inputting N2 again to grow for a second diamond growth time, and the ratio of gas flow rates H2:N2 = 100:0.01-0.04; the second growth time is 5-15 min; then stopping inputting N2; S4, later stability growth: entering a third diamond growth time for growth; the third growth time is 50-400 min. The application solves the problem that GaN substrates are easily etched and damaged when directly growing a diamond on the GaN substrate in the prior art, not only realizes growing a diamond film on a GaN substrate surface without damage, but also has high diamond film quality, good interface combination and low interface thermal resistance.

Description

Technical Field

[0001] This invention relates to the field of power device technology, and in particular to a method for non-destructive growth of diamond films on GaN substrates and GaN-based high electron mobility transistors. Background Technology

[0002] The rapid development of the national economy has posed challenges to the demand for electricity. With the emphasis on energy conservation and emission reduction, the effective conversion and control technologies of electricity from generation to consumption have become crucial for energy saving. Electricity encompasses not only power systems such as photovoltaics and microgrids, but also fast charging for electric vehicles, commercial and urban residential cooling and heating systems, and even aerospace fields. Improving the management and control of power networks is of great significance for energy conservation and emission reduction. Improving the utilization rate of electricity belongs to power electronics, in which power electronic devices and power converters play a major role. Currently, to achieve miniaturization and lightweighting of power conversion modules, there is a demand for high-speed, high-temperature, and high-power power devices. Gallium nitride (GaN) material, with its excellent noise figure, high breakdown voltage, and high oscillation frequency, has become the superior material for high-frequency high-power electronic devices and high-power microwave and millimeter-wave fields. GaN-based high electron mobility transistors (HEMTs) have begun large-scale commercial use, with output power densities far exceeding those of traditional Si and GaAs devices (theoretically more than ten times higher), meeting the high-performance requirements of next-generation emerging technologies for semiconductor devices. GaN-HEMTs perform well in high-power applications across military, aerospace, automotive, industrial, and everyday use. Particularly in the field of high-power radio frequency devices, GaN-HEMTs are indispensable components in high-power electronic countermeasures weapons and phased-array radars, possessing significant application value and attracting widespread international attention. However, as the output power and frequency of GaN devices continue to increase, the heat generated in their active regions is also increasing, posing challenges to the output power, frequency, and reliability of GaN devices. Dissipating the heat generated by GaN devices would greatly improve their performance.

[0003] Diamond possesses extremely high thermal conductivity, and combining diamond with GaN devices can significantly aid in heat dissipation. GaN devices are fabricated from GaN substrates with multiple functional layers. The top layer is typically a GaN transition layer or an AlGaN (aluminum gallium nitride, obtained by replacing some Ga in GaN with Al) barrier layer, collectively referred to as the GaN layer. The heat-generating region is located within this GaN layer. Directly growing a diamond film on the GaN substrate surface (direct growth method) allows the diamond to contact the heat-generating region of the GaN device as closely as possible, maximizing its heat dissipation capabilities. Other bonding methods, such as welding and bonding, have numerous drawbacks. For example, grinding and polishing the diamond before bonding not only adds to the process but also presents significant technical challenges in large-area planarization due to diamond being the hardest material in the world. Furthermore, bonding methods suffer from uneven interface bonding and bonding voids. In comparison, the direct growth method has significant advantages, specifically: better interface (low interface thermal resistance, high bonding strength), fewer process steps, lower cost, and the ability to grow large-area diamond (greater than 3 inches). Furthermore, it can be directly integrated with existing semiconductor processes, making it the most promising method for large-area industrial applications.

[0004] However, the following problems exist in directly growing diamond on GaN substrates:

[0005] ① The most significant problem is that the hydrogen-rich, high-temperature environment during diamond growth easily etches and damages the GaN layer. Specifically, GaN is prone to self-decomposition at high temperatures, and the self-decomposition products react with hydrogen atoms to generate NH3 and GaH, thereby damaging the GaN device structure and significantly affecting its electrical performance, even causing it to fail. ② Severe thermal mismatch. The significant difference in thermal expansion coefficients between diamond and GaN layers leads to substantial stress accumulation during the cooling process after diamond growth. Under this stress, the diamond layer experiences crystal structure mismatch with the GaN layer, affecting the interfacial bonding strength between it and the GaN substrate, making the diamond layer prone to detachment from the GaN substrate. ③ Severe lattice mismatch between diamond and GaN layers increases the tensile stress between grains in the crystal, further inducing crystal defects such as mismatched dislocations, thus affecting the growth quality of the diamond crystal. The growth quality of the diamond crystal directly affects its thermal conductivity and the interfacial bonding strength.

[0006] To address the aforementioned issues, when fabricating diamond films on GaN substrates using direct growth methods, a small amount of N2 is typically introduced alongside H2 and carbon-containing gases to suppress GaN decomposition, thereby reducing the degree of etching damage to the GaN layer. Alternatively, an intermediate layer can be deposited on the GaN substrate surface first, followed by the deposition of a diamond film on the intermediate layer. This intermediate layer's protection helps to mitigate etching damage to some extent. For example:

[0007] Patent CN115377193A discloses a method for preparing GaN epitaxial diamond. The key points are: growing a 200nm thick silicon nitride layer on the surface of gallium nitride as an intermediate layer, and then growing diamond on the intermediate layer using MPCVD method. During the growth process, a mixed gas of H2, CH4 and N2 in a certain proportion is introduced simultaneously, and finally a dense diamond film is obtained.

[0008] Patent CN104328390A discloses a method for preparing a GaN / diamond film composite. The key points are: in a plasma environment, CH4 and a high-concentration nitrogen source are first introduced to passivate the GaN substrate; then the nitrogen source is turned off, while H2 and CH4 are continuously introduced, and the CH4 gas flow rate is rapidly increased to achieve rapid diamond nucleation on the GaN substrate surface; subsequently, the CH4 gas flow rate is reduced to allow for stable diamond film growth; after growth, CH4 is turned off, and the nitrogen source is introduced again to heat the GaN / diamond film composite, thereby releasing the growth stress inside the diamond film. The final prepared diamond film is dense, with a thickness of 15μm-45μm.

[0009] Although the aforementioned patents all produced dense diamond films, they have the following drawbacks:

[0010] a. Introducing N2 at the early stage of growth or even continuing to introduce it until the end of growth can accelerate the growth of the diamond film and inhibit GaN decomposition to some extent, but it also seriously reduces the quality of the diamond film. Specifically, although N2 can significantly increase the diamond growth rate, the disadvantage of this excessively rapid growth is poor crystal quality at the interface, decreased interfacial bonding, and increased stress. Although some growth stress can be released through heat treatment, it can still easily lead to problems such as film peeling or increased thermal resistance in the later stages.

[0011] b. While a thicker intermediate layer protects the GaN layer from etching damage to some extent, it also increases the interfacial thermal resistance. This prevents the heat generated by the GaN layer from being effectively conducted to the diamond layer, thus hindering the utilization of diamond's high thermal conductivity and severely impacting the heat dissipation performance of the fabricated GaN device. Passivation to avoid introducing an intermediate layer can reduce interfacial thermal resistance to some extent, but the GaN layer is more susceptible to H2 etching damage due to the lack of protection. However, if a thinner intermediate layer is introduced, it is also prone to varying degrees of etching or even penetration in a hydrogen-rich, high-temperature environment, posing a significant risk to the quality of the GaN device.

[0012] The above analysis shows that when growing diamond directly on a GaN substrate, the key to solving the thermal bottleneck of GaN power devices using the direct growth method is to avoid etching damage to the GaN layer while ensuring high diamond quality, low interfacial thermal resistance, and good interfacial adhesion, so as to guarantee good electrical performance of the final GaN device. Summary of the Invention

[0013] To address the shortcomings of existing technologies, this invention provides a method for non-destructive growth of diamond films on GaN substrates. This method solves the problems in existing technologies where direct diamond growth on GaN substrates easily causes etching damage to the GaN substrate, and results in low diamond quality, high interfacial thermal resistance, or poor interfacial bonding, thus affecting the performance of GaN power devices.

[0014] According to an embodiment of the present invention, a method for growing a diamond film on a GaN substrate without damage is characterized by comprising the following steps:

[0015] S1, Pretreatment: Provide a GaN substrate, with one bottom surface covered by SiN. x Dielectric layer; Post-adjustment SiN x The thickness of the dielectric layer is 10-20 nm; then on SiN x After diamond powder is used to implant crystals on the surface of the dielectric layer, the GaN substrate is placed in the growth chamber of the MPCVD equipment.

[0016] S2, Protective Growth Step 1: Continuously introduce H2 at a flow rate of 300-500 sccm into the growth chamber, then set the microwave power to 2500-3000W and the chamber pressure to 80-90 Torr; then introduce CH4 gas to perform the first diamond growth time, with the gas flow rate ratio H2:CH4 = 100:6-10; the first growth time is 10-20 min.

[0017] S3, the second step of protective growth: N2 is introduced again to carry out the second growth time of diamond, and the gas flow ratio H2:N2 = 100:0.01-0.04; the second growth time is 5-15 min; then the N2 is stopped.

[0018] S4, Later Stable Growth: Growth during the third growth period of diamond; the third growth period is 50-400 min.

[0019] On the other hand, according to embodiments of the present invention, a GaN-based high electron mobility transistor is also provided, which has a diamond film prepared by the aforementioned method for non-destructive growth of a diamond film on a GaN substrate surface.

[0020] The technical principle of this invention is as follows:

[0021] Generally speaking, diamond nuclei (also called grains) grow epitaxially in a suitable atmosphere, following their original structure and morphology, and the nuclei increase in volume in all directions along the X, Y, and Z axes. This invention relates to SiN… x After diamond nuclei are implanted on the surface of the silicon nitride dielectric layer away from the GaN substrate, diamond films are grown using MPCVD (microwave plasma chemical vapor deposition). First, growth gases H2 and CH4 are introduced, and the process parameters are controlled to suppress diamond growth in the Z-axis direction (longitudinal direction) (i.e., to suppress its thickness increase), while simultaneously promoting diamond growth primarily on the SiN substrate. x A protective film is grown on the implanted surface of the dielectric layer (in the X and Y axis directions, or on the horizontal plane) until it covers the entire implanted surface, and then stabilized to complete the entire growth process; simultaneously, an appropriate amount of N2 is introduced during the growth process and the timing of N2 input is controlled, combined with a relatively thin SiN layer. x The bonding effect of the dielectric layer makes the protective film more compact, thus blocking the high-temperature hydrogen-rich environment from damaging SiN. x The etching and decomposition of the dielectric layer and GaN substrate simultaneously results in fewer growth defects, stronger interfacial adhesion, and lower thermal resistance in the diamond film. The specific growth process is as follows:

[0022] (1) The first step of protective growth:

[0023] ① Rapid "spreading" lays the foundation for a dense protective film and the formation of high-quality diamond: First, by controlling the power and cavity pressure to a relatively low value, the shape of the high-temperature plasma sphere above the GaN substrate is controlled to be a flattened ellipsoid. This minimizes the ellipsoid's dimension in the diamond thickness direction (i.e., its length in the Z-axis direction) while maximizing its horizontal extent. This allows the plasma sphere's energy to be distributed as evenly as possible in the X and Y axes. At this point, the energy on the GaN substrate's implanted surface is increased, and the energy uniformity is also improved. However, the energy in the Z-axis direction is significantly reduced, thereby reducing the vertical movement of hydrocarbon active groups and primarily increasing their horizontal movement, i.e., increasing their interaction with SiN. x The probability of frictional collisions on the surface of the dielectric layer, thereby increasing the interaction between hydrocarbon active groups and SiN. x The increased collision probability of isolated diamond grains on the dielectric layer surface leads to preferential reactions in the X and Y axes, promoting lateral grain extension. Grains with similar lattice orientations that are close to each other bond and aggregate to form larger diamond grains, reducing surface energy and eventually eliminating grain boundaries. This results in improved grain quality and thermal conductivity, laying the foundation for high-quality and high-thermal-conductivity diamonds. These large diamond grains expand to a larger scale within the horizontal plane along the X and Y axes and then converge into a surface. Secondly, the introduction of a high flow rate of CH4 in this step increases the number of hydrocarbon active groups in the growth environment, promoting the growth rate of diamond grains and further accelerating the convergence into a surface. Therefore, diamond grains can rapidly "cover" the SiN layer. x The surface of the dielectric layer lays a good foundation for the formation of a dense protective film and high-quality diamond.

[0024] ②SiN x The protective function of the dielectric layer and its enhancement of interfacial bonding and reduction of interfacial thermal resistance: because the diamond film is made of SiN... x Growth occurs at the interface of the dielectric layer surface, and the high-temperature atmosphere inside the MPCVD equipment makes it easy for C atoms to combine with SiN. x This forms stronger Si-CN bonds, allowing newly formed C atoms to cover the interface through Si-CN bonds, forming a dense protective film; on the one hand, it protects SiN x The dielectric layer provides protection, reducing the degree of etching and decomposition, preventing it from being etched through, and thus avoiding etching damage to the underlying GaN substrate; on the other hand, it enhances the bonding between the diamond film and SiN. x The interfacial bonding strength of the dielectric layer; on the other hand, due to SiN x The dielectric layer is etched and decomposed to a lesser extent, so a thinner dielectric layer is sufficient to meet the requirements, and a thinner dielectric layer also reduces the interfacial thermal resistance.

[0025] ③ To prevent the passage of N2, the protective film formed is made denser, and the quality of the diamond and the interfacial bonding strength are improved: During the diamond growth process, N2 can simultaneously and significantly promote growth in all directions along the X, Y, and Z axes, resulting in the formation of a thicker film layer before the "coverage" process is fully completed, thus enhancing the SiN... x In some areas of the surface, Si-CN bonds cannot form in time, which on the one hand causes the Si-CN bonds to be unable to bond with SiN. x Insufficient surface coverage reduces the protective effect and interfacial bonding strength. Furthermore, rapid increases in diamond film thickness can easily lead to defects at the interface or within the diamond, lowering diamond quality. This invention innovatively avoids introducing N2 during this rapid "coverage" process, thereby ensuring that diamond grows primarily along the X and Y axes while suppressing growth along the Z axis. This allows for the full formation of Si-CN bonds to protect the dielectric layer surface and enhance interfacial bonding strength, laying the foundation for the formation of a high-quality diamond film.

[0026] (2) The second step of protective growth involves introducing N2 to further protect and enhance the interfacial bonding strength: After completing the previous step, keep all process conditions unchanged and immediately introduce N2, controlling the N2 flow rate to be low (to suppress growth in the Z-axis direction as much as possible); under these process conditions, N2 and C atoms will quickly form CN bonds, and since the process conditions at this time still mainly promote the growth of diamond in the X and Y axes, and the thickness of the diamond film is still very small, N2 can quickly form CN bonds with a small number of C atoms on the surface of the dielectric layer that have not yet formed Si-CN bonds. The CN bonds and Si atoms then form new Si-CN bonds (which can be called the "mending" effect of N2), so that the SiN that has not yet formed bonds in the previous step can be bonded. x The surface is also covered and protected by bonded C atoms (i.e., C atoms in the Si-CN bonds), making the Si-CN bonds at the interface more compact and beneficial to SiN. x The surface provides more comprehensive protection and further enhances the interfacial bonding strength. This step is controlled to be completed within a short time to control the thickness of the diamond film, thereby better utilizing the aforementioned "repairing" effect of N2. The protective growth is now complete.

[0027] (3) Later stability growth: Stop the introduction of N2 to stabilize the growth of diamond and improve the quality of diamond growth until the diamond film thickness reaches the target value.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. A non-destructive growth of diamond films on GaN substrates has been achieved. This invention utilizes controlled plasma sphere shape and size, combined with a high methane flow rate and the elimination of N2 introduction, to allow the diamond film to primarily grow on SiN substrates. xExtending along the X and Y axes of the dielectric layer surface, a dense Si-CN bonded film rapidly forms, covering the SiN. x The surface of the dielectric layer thus affects SiN x After the dielectric layer has formed sufficient protection, a small amount of N2 is introduced to "weave" the layers, making the Si-CN bonds more compact and further strengthening the protective effect. Then, the nitrogen source is turned off to reduce the growth rate for subsequent stable growth. It can be seen that the rapidly formed dense Si-CN bonds are crucial for SiN... x The dielectric layer provides better protection, while SiN x The dielectric layer itself also prevents the plasma from etching the GaN substrate. Under this dual protection, diamond films can be grown on the GaN substrate surface without damage. Characterization and analysis of the prepared GaN material show that the overall interface of the material is intact, the functional layers are clearly separated, there is no etching phenomenon, the diamond surface is intact, there are no pores, and no carbon elements enter the GaN layer.

[0030] 2. Good interfacial bonding. The full formation and coverage of Si-CN bonds significantly improve the bonding between the diamond film and SiN. x The bonding strength between the dielectric layers is increased, thereby indirectly improving the bonding strength between the diamond film and the GaN substrate.

[0031] 3. High-quality diamond film. During the initial growth phase, the X and Y axes grow rapidly, while the Z axis grows more slowly, allowing C atoms to quickly bond and spread across the interface, minimizing defect formation. The absence of N2 in the early stages also avoids the problem of numerous lattice defects caused by rapid growth. N2 is introduced after the "spreading" process is complete, utilizing its "mending" effect to further prevent interface defects. Later growth stages avoid the adverse effects of N2, resulting in high stability and ensuring diamond quality.

[0032] 4. Low interfacial thermal resistance. SiN x The thinner dielectric layer reduces the SiN x The interfacial thermal resistance is inherent in the dielectric layer itself; however, the high quality and good thermal conductivity of the formed diamond film further reduce this interfacial thermal resistance. The thermal conductivity of the prepared diamond sample was tested, and through fitting, the thermal conductivity of diamond was found to be approximately 800 W / (m·K), which is significantly higher than the thermal conductivity values ​​of commonly used heat dissipation materials (SiN). x The thermal conductivity of the medium is around 100, while that of copper, a commonly used heat dissipation material for semiconductors, is around 400.

[0033] 5. The present invention selects SiN x As a dielectric layer material, since the surface material of GaN-based electronic devices fabricated by existing processes is itself SiN... xTherefore, this invention can be directly integrated into existing device production lines for mass production. The process is simple, the cost is low, and it is easy to promote.

[0034] 6. The GaN-based high electron mobility transistor has a high thermal conductivity diamond film prepared by the above method, which has good heat dissipation and stable quality, thus ensuring its good electrical performance and quality reliability, and has good market prospects.

[0035] Preferably, in step S4, before entering the third growth time, the CH4 gas flow rate is reduced to a gas flow rate ratio of H2:CH4 = 100:1-5.

[0036] Beneficial effects: Reducing the CH4 gas flow rate can further decrease the growth rate and increase the stability of growth; in addition, reducing the CH4 flow rate is equivalent to increasing the H2 ratio, since diamond is mainly composed of sp(II,III) gas. 3 Phase composition, mixed with sp 2 The phase (mainly graphite, and a certain amount of graphite will also be produced under these process conditions), while H2 affects sp 2 The etching rate relative to sp 3 Faster, in this step we increase the H2 ratio, the result is sp 2 Relatively reduced, sp 3 The relative increase results in more sp in the grown diamond. 3 Its quality is higher.

[0037] Preferably, in step S4, during the third growth time, the microwave power is set to 3500-4500W and the chamber pressure to 100-120 Torr.

[0038] Beneficial effects: The higher microwave power and chamber pressure (relative to the previous steps) result in a plasma sphere with a lower flatness ellipsoid shape, that is, an increased ellipsoidal dimension in the Z-axis direction compared to the previous steps. This increases the energy distribution in the Z-axis direction, thereby releasing the previously suppressed Z-axis growth in this step, promoting Z-axis growth and resulting in a rapid increase in diamond thickness. Furthermore, since there is no N2 promoting effect, the Z-axis growth is not too fast, ensuring the stability of diamond growth and thus resulting in high-quality diamond growth.

[0039] Preferably, the method further includes the following step: S5, cooling: after the third growth time, the gas supply is stopped, and then the microwave power and chamber pressure are uniformly reduced to 0 within 1-2 hours, and then left to stand for a certain period of time.

[0040] Beneficial effects: Slow cooling can alleviate stress buildup and prevent the diamond coating from peeling off or cracking.

[0041] Preferably, the crystal implantation method is one or a combination of spin coating crystal implantation, self-adsorption crystal implantation, and self-assembly crystal implantation.

[0042] Preferably, the spin coating method for crystal implantation includes the following steps: adding diamond powder to a solvent to prepare a diamond powder suspension; then adsorbing the GaN substrate onto a spin coater, and then dripping the diamond powder suspension into it, and rotating for a certain period of time.

[0043] Beneficial effects: This method can obtain a uniformly implanted crystal surface through physical means, and the operation steps are simple and effective.

[0044] Preferably, the diamond powder has a particle size of 0.1-5 μm.

[0045] Beneficial effect: Smaller particle size is beneficial for obtaining a denser nucleation layer.

[0046] Preferably, the mass ratio of diamond powder to solvent is 1-5:100, and the volume of the diamond powder suspension added is 5-30 mL.

[0047] Preferably, the adjustment of SiN x The method used to determine the thickness of the dielectric layer includes either LPCVD or PECVD. Attached Figure Description

[0048] Figure 1 This is a diagram of the diamond growth process in Embodiment 1 of the present invention.

[0049] Figure 2 This is a FIB-SEM image (dual-beam electron microscope image) of the GaN composite diamond film substrate obtained in Example 1 of the present invention.

[0050] Figure 3 This is an OM image (optical microscope image) of the diamond surface after protective growth in Embodiment 1 of the present invention.

[0051] Figure 4 This is a TEM cross-sectional view of the GaN composite diamond film substrate obtained in Example 1 of the present invention.

[0052] Figure 5 This is a partially enlarged TEM cross-sectional view of the GaN composite diamond film substrate obtained in Example 1 of the present invention.

[0053] Figure 6 This is a microscopic EDX-mapping analysis diagram of the cross-section of the GaN composite diamond film substrate obtained in Example 1 of the present invention.

[0054] Figure 7 This is a graph showing the normalized transient reflectivity variation of the thermal conductivity test in Embodiment 1 of the present invention.

[0055] Figure 8 This is a TTR model fitting diagram for thermal conductivity testing in Embodiment 1 of the present invention.

[0056] Figure 9 This is a FIB-SEM image of the GaN composite diamond film substrate obtained in Comparative Example 1 of this invention.

[0057] Figure 10 This is a partially enlarged FIB-SEM image of the GaN composite diamond film substrate obtained in Comparative Example 1 of this invention.

[0058] Figure 11 This is an OM image of the diamond surface obtained in Comparative Example 1 of the present invention.

[0059] Figure 12 This is a SEM cross-sectional view of the GaN composite diamond film substrate obtained in Comparative Example 2 of the present invention.

[0060] Figure 13 This is a SEM cross-sectional view of the GaN composite diamond film substrate obtained in Comparative Example 3 of the present invention. Detailed Implementation

[0061] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0062] In the embodiments and comparative examples of this invention:

[0063] 1. The sample preparation and characterization testing equipment information is as follows:

[0064] Microwave plasma chemical vapor deposition apparatus: Seki 6500 6kW MPCVD system;

[0065] FIB device: G5 UX;

[0066] TEM equipment: Talos F200X;

[0067] EDS device: Talos F200X self-configured Super-X EDS system;

[0068] SEM equipment: HITACHI UHR FE-SEM SU8000;

[0069] Optical microscope: OLYMPUSBX51TRF.

[0070] 2. Generally, GaN substrates have a base layer, and according to the different base layers, they can be divided into SiC-based GaN substrates, Si-based GaN substrates, sapphire-based GaN substrates, and GaN-based GaN substrates. The first three are non-self-supporting GaN substrates, and the last one is a self-supporting GaN substrate.

[0071] On a GaN substrate with multiple functional layers, the substrate layer is the bottom layer. The bottom surface of the GaN substrate furthest from the substrate layer is generally referred to as the front surface. The SiN... x The dielectric layer covers the front side of the GaN substrate.

[0072] In other words, the raw material used in this invention, namely the GaN substrate, has a SiN layer on it. x The dielectric, which contains SiN x The bonding between the dielectric and the front side of the GaN substrate is relatively strong, which also ensures that the diamond film layer prepared in this invention can be indirectly and firmly bonded to the GaN substrate.

[0073] However, in existing technologies, the SiN layer inherent on the GaN substrate... x The dielectric thickness is too small and needs to be increased according to the process conditions of this invention to provide protection without significantly affecting the interfacial thermal resistance. The increased thickness is achieved by adjusting the thickness of the inherent SiN... x On the basis of the dielectric, a SiN layer of a certain thickness is then prepared. x The medium is prepared to achieve the required total thickness; the preparation method includes LPCVD (low-pressure chemical vapor deposition) or PECVD (plasma-enhanced chemical vapor deposition), both of which are existing technologies.

[0074] 3. In the later stable growth step, O2 can also be introduced, and the flow rate of O2 is 0.5-3 sccm; O2 has a positive effect on sp. 2 The etching rate of the phase is very fast, but it also etches sp. 3 Therefore, introducing a small amount of O2 can significantly reduce the sp content in diamond. 2 This improves the quality of diamonds without causing them to stop growing due to excessive injection.

[0075] Example 1

[0076] A method for growing a diamond film on a GaN substrate without damage includes the following steps:

[0077] S1 provides a 3-inch SiC-based GaN substrate, and its front side has a built-in SiN layer. x The medium is then pretreated:

[0078] SS1, in the self-contained SiN x A SiN layer is deposited on the surface of the dielectric material away from the GaN substrate. x The dielectric material constitutes the total SiN x Dielectric layer, and SiN x The total thickness of the dielectric layer is 15 nm; the deposition method chosen is LPCVD.

[0079] SS2 will be covered with SiNx GaN substrate with dielectric layer (hereinafter referred to as SiN) x The GaN substrate was sequentially placed in acetone, anhydrous ethanol, and water, and ultrasonically cleaned for 10 minutes each, with an ultrasonic power of approximately 200 W, to remove SiN. x Organic impurities on the GaN substrate surface were removed, and the substrate was dried with N2 to obtain clean SiN. x -GaN substrate;

[0080] SS3, on SiN x Diamond powder was used to implant crystals onto the surface of the dielectric layer away from the GaN substrate using a spin-coating method. The specific steps were as follows: diamond powder with a particle size of 0.1 μm was selected, and a diamond powder-alcohol suspension was prepared at a mass ratio of diamond powder to alcohol of 5:100; then the SiN... x - The GaN substrate is adsorbed onto the spin coater through the SiC substrate layer, and then 30 mL of the diamond powder alcohol suspension is dropped in. The spin coater is rotated at 500 r / min for 60 s, and then at 5000 r / min for 60 s to complete the crystal implantation operation.

[0081] At this point, the preprocessing is complete, and SiN is obtained. x SiN with diamond grains on the surface of the dielectric layer x -GaN substrate.

[0082] S2, the first step of protective growth: pre-treated SiN x The GaN substrate was placed in the growth chamber of a microwave plasma chemical vapor deposition (PCCVD) apparatus. H2 was introduced at 500 sccm to excite the plasma. The microwave power (output power) and chamber pressure were then slowly increased until the microwave power reached 3000 W and the chamber pressure reached 90 Torr. Simultaneously, the chamber was cooled by circulating cooling water to ensure the outer wall temperature did not exceed 50°C. The CH4 flow meter was then turned on, and high-purity CH4 was introduced at a flow rate of 50 sccm. Under this high-concentration CH4 atmosphere, the SiN substrate was then... x Diamond is grown on the implanted surface of the GaN substrate for 10 minutes, which completes the first step of protective growth.

[0083] S3, second step of protective growth: introduce high-purity N2 at a flow rate of 0.05 sccm, and keep the flow rates of H2 and CH4 constant. Grow for 10 minutes, then turn off the N2.

[0084] S4, Post-Stage Stability Growth: After turning off N2, the flow rate of high-purity CH4 was first reduced to 25 sccm, then the microwave power was increased to 3500W, and the chamber pressure was increased to 110 Torr. Simultaneously, the chamber was cooled by circulating cooling water to ensure that the outer wall temperature of the chamber did not exceed 50℃. Then, in this low-concentration CH4 atmosphere, SiN... x Diamond growth continued on the seeded surface of the GaN substrate for 50 minutes, and then the introduction of H2 and CH4 was stopped, thus completing the later stage of stable growth.

[0085] S5, Cooling: Within 2 hours, the power and chamber pressure are slowly reduced to 0. During this process, the temperature inside the chamber also slowly decreases. Then, the chamber is allowed to cool for another 0.5 hours. Finally, the product is taken out of the growth chamber, resulting in a GaN composite diamond film substrate with a thickness of 3.8 μm.

[0086] Example 2

[0087] A method for growing a diamond film on a GaN substrate without damage includes the following steps:

[0088] S1 provides a 2-inch Si-based GaN substrate, and its front side has a built-in SiN layer. x The medium is then pretreated:

[0089] SS1, in the self-contained SiN x A SiN layer is deposited on the surface of the dielectric material away from the GaN substrate. x The dielectric material constitutes the total SiN x Dielectric layer, and SiN x The total thickness of the dielectric layer is 10 nm; the deposition method chosen is LPCVD.

[0090] SS2 will be covered with SiN x GaN substrate with dielectric layer (hereinafter referred to as SiN) x The GaN substrate was sequentially placed in acetone, anhydrous ethanol, and water, and ultrasonically cleaned for 10 minutes each, with an ultrasonic power of approximately 200 W, to remove SiN. x Organic impurities on the GaN substrate surface were removed, and the substrate was dried with N2 to obtain clean SiN. x -GaN substrate;

[0091] SS3, on SiN x Diamond powder was used to implant crystals onto the surface of the dielectric layer away from the GaN substrate using a spin-coating method. The specific steps were as follows: diamond powder with a particle size of 2.5 μm was selected, and a diamond powder suspension was prepared at a mass ratio of diamond powder to water of 2.5:100; then the SiN... x- The GaN substrate is adsorbed onto the spin coater through the SiC substrate layer, and then 18 mL of the diamond powder suspension is dropped in. The spin coater is rotated at 500 r / min for 60 s, and then at 5000 r / min for 60 s to complete the crystal implantation operation.

[0092] At this point, the preprocessing is complete, and SiN is obtained. x SiN with diamond grains on the surface of the dielectric layer x -GaN substrate.

[0093] S2, the first step of protective growth: pre-treated SiN x The GaN substrate was placed in the growth chamber of a microwave plasma chemical vapor deposition (PCCVD) apparatus. H2 was introduced at 400 sccm to excite the plasma. The microwave power and chamber pressure were then slowly increased until the microwave power reached 2500 W and the chamber pressure reached 80 Torr. Simultaneously, the chamber was cooled by circulating cooling water to ensure the outer wall temperature did not exceed 50°C. The CH4 flow meter was then turned on, and high-purity CH4 was introduced at a flow rate of 32 sccm. Subsequently, under this high-concentration CH4 atmosphere, the SiN substrate was deposited... x Diamond is grown on the implanted surface of the GaN substrate for 15 minutes, which completes the first step of protective growth.

[0094] S3, second step of protective growth: introduce high-purity N2 at a flow rate of 0.1 sccm, and keep the flow rates of H2 and CH4 constant. Grow for 15 minutes, then turn off the N2.

[0095] S4, Post-Stage Stability Growth: After turning off N2, the flow rate of high-purity CH4 was first reduced to 10 sccm, then the microwave power was increased to 4000W, and the chamber pressure was increased to 100 Torr. Simultaneously, the chamber was cooled by circulating cooling water to ensure that the outer wall temperature of the chamber did not exceed 50℃. Then, under this low-concentration CH4 atmosphere, SiN... x Diamond growth continued on the seeded surface of the GaN substrate for 200 minutes, and then the introduction of H2 and CH4 was stopped, thus completing the later stage of stable growth.

[0096] S5, Cooling: Within 1.5 hours, the power and chamber pressure are slowly reduced to 0. During this process, the temperature inside the chamber is also slowly reduced. Then, the chamber is allowed to cool for another 0.5 hours. Finally, the product is taken out of the growth chamber, and a GaN composite diamond film substrate with a thickness of 2μm is obtained.

[0097] Example 3

[0098] A method for growing a diamond film on a GaN substrate without damage includes the following steps:

[0099] S1 provides a 4-inch sapphire-based GaN substrate, and its front side has a built-in SiN layer. x The medium is then pretreated:

[0100] SS1, in the self-contained SiN x A SiN layer is deposited on the surface of the dielectric material away from the GaN substrate. x The dielectric material constitutes the total SiN x Dielectric layer, and SiN x The total thickness of the dielectric layer is 20 nm; the deposition method chosen is LPCVD.

[0101] SS2 will be covered with SiN x GaN substrate with dielectric layer (hereinafter referred to as SiN) x The GaN substrate was sequentially placed in acetone, anhydrous ethanol, and water, and ultrasonically cleaned for 10 minutes each, with an ultrasonic power of approximately 200 W, to remove SiN. x Organic impurities on the GaN substrate surface were removed, and the substrate was dried with N2 to obtain clean SiN. x -GaN substrate;

[0102] SS3, on SiN x Diamond powder was used to implant crystals onto the surface of the dielectric layer away from the GaN substrate using a spin-coating method. The specific steps were as follows: diamond powder with a particle size of 5 μm was selected, and a diamond powder-to-alcohol suspension was prepared at a mass ratio of diamond powder to alcohol of 1:100; then the SiN... x - The GaN substrate is adsorbed onto the spin coater through the SiC substrate layer, and then 5 mL of the diamond powder alcohol suspension is dropped in. The spin coater is rotated at 500 r / min for 60 s, and then at 5000 r / min for 60 s to complete the crystal implantation operation.

[0103] At this point, the preprocessing is complete, and SiN is obtained. x SiN with diamond grains on the surface of the dielectric layer x -GaN substrate.

[0104] S2, the first step of protective growth: pre-treated SiN x The GaN substrate was placed in the growth chamber of a microwave plasma chemical vapor deposition (PCCVD) apparatus. H2 was introduced at 300 sccm to excite the plasma. The microwave power and chamber pressure were then slowly increased until the microwave power reached 2750 W and the chamber pressure reached 85 Torr. Simultaneously, the chamber was cooled by circulating cooling water to ensure the outer wall temperature did not exceed 50°C. The CH4 flow meter was then turned on, and high-purity CH4 was introduced at a flow rate of 18 sccm. Subsequently, under this high-concentration CH4 atmosphere, the SiN substrate was deposited... xDiamond is grown on the implanted surface of the GaN substrate for 20 minutes, which completes the first step of protective growth.

[0105] S3, second step of protective growth: introduce high-purity N2 at a flow rate of 0.12 sccm, and keep the flow rates of H2 and CH4 constant. Grow for 5 minutes, then turn off the N2.

[0106] S4, Post-Stage Stability Growth: After turning off N2, the flow rate of high-purity CH4 was first reduced to 3 sccm, then the microwave power was increased to 4500W, and the chamber pressure was increased to 120 Torr. Simultaneously, the chamber was cooled by circulating cooling water to ensure that the outer wall temperature of the chamber did not exceed 50℃. Then, in this low-concentration CH4 atmosphere, SiN... x Diamond growth continued on the seeded surface of the GaN substrate for 400 minutes, and then the introduction of H2 and CH4 was stopped, thus completing the later stage of stable growth.

[0107] S5, Cooling: Within 1 hour, the power and chamber pressure are slowly reduced to 0. During this process, the temperature inside the chamber is also slowly reduced. Then, the chamber is allowed to cool for another 0.5 hours. Finally, the product is taken out of the growth chamber, and a GaN composite diamond film substrate with a thickness of 2μm is obtained.

[0108] Comparative Example 1

[0109] The difference from Example 1 is as follows:

[0110] Diamond films were prepared by a direct one-step growth method. The specific process parameters were as follows: H2 flow rate of 500 sccm, microwave power of 3500 W, chamber pressure of 110 Torr, high-purity CH4 flow rate of 50 sccm, and growth time of 70 min.

[0111] Comparative Example 2

[0112] The difference from Example 1 is as follows:

[0113] Diamond films were prepared using a two-step growth method. After the first protective growth step, the growth time of the first protective growth step was extended to 20 minutes, and the second protective growth step was omitted, and the subsequent stability growth was carried out directly.

[0114] Comparative Example 3

[0115] The difference from Example 1 is as follows:

[0116] Diamond films were prepared using a two-step growth method. In the first step of protective growth, N2 was introduced and the growth time of the first step of protective growth was extended to 20 minutes. The second step of protective growth was omitted, and the subsequent stability growth was carried out directly.

[0117] Characterization test

[0118] 1. The GaN composite diamond film substrate obtained in Example 1 was characterized and tested. The results are as follows:

[0119] (1) FIB-SEM image as shown Figure 2 As shown, the material interface is intact, the functional layers are clearly separated, and there is no etching.

[0120] (2) The OM image of the diamond surface after protective growth is shown below. Figure 3 As shown, the surface is intact and there are no pores, so it provides good protection for the GaN substrate.

[0121] (3) To verify the feasibility of the present invention from a more microscopic perspective, TEM cross-sectional analysis was performed on the material, such as... Figure 4 As shown, the overall interface of the GaN composite diamond film substrate is intact and the layers are clearly defined; after magnification of a local area, as shown... Figure 5 As shown, the functional layers are clearly defined, and no etching occurs.

[0122] (4) To further confirm that the present invention achieves damage-free growth of diamond films on GaN substrates, microscopic EDX-mapping analysis was performed on the material cross-section, such as... Figure 6 As shown, the C elements are clearly distributed, and no C elements enter the GaN layer.

[0123] (5) Thermal conductivity testing: The thermal conductivity of the prepared diamond samples was characterized using the transient thermal reflectance method. Measurements were taken at six randomly selected sites. A 355nm frequency-doubled Nd:YAG laser (3.49eV, above the GaN bandgap) with a pulse duration of 10ns and a spot size of 90μm was used as the heating pulse to induce a rapid temperature rise on the AlGaN / GaN surface. A 532nm frequency-doubled Nd:YAG laser with a continuous wave spot size of 2μm was used to monitor changes in surface reflectivity, thereby monitoring the temperature rise. Figure 7 The figure shows the normalized transient reflectivity changes at different selected test points. The reflectivity change reaches its peak after laser pulse heating and then decays as heat diffuses into the GaN and diamond layers. It can be seen that the prepared diamond has excellent thermal conductivity uniformity. (As shown in the figure...) Figure 8 As shown, the thermal conductivity of diamond is approximately 800 W / (m·K).

[0124] 2. The GaN composite diamond film substrate obtained in Example 1 was characterized and tested. The results are as follows:

[0125] FIB-SEM image as follows Figure 9As shown, the overall material interface has been damaged, and FIB analysis reveals severe film damage, rendering it ineffective as a device material. A magnified view of the local area is shown below. Figure 10 As shown, the etching phenomenon is severe.

[0126] Figure 11 The OM diagram of the diamond surface shows that the diamond grown by the direct one-step growth method has many pores on the surface, and the pores are easily corroded by plasma, causing functional damage to the device.

[0127] 3. The GaN composite diamond film substrate obtained in Comparative Example 2 was characterized and tested. The results are as follows:

[0128] SEM cross-sectional image as follows Figure 12 As shown in the figure, the areas marked (red circles) indicate that some interfaces have developed voids or been damaged. This indicates that the growth process did not involve the addition of N2, resulting in the failure to form a sufficiently dense protective film layer, which led to the aforementioned problems.

[0129] 4. The GaN composite diamond film substrate obtained in Comparative Example 3 was characterized and tested. The results are as follows:

[0130] SEM cross-sectional image as follows Figure 13 As shown, if N2 is directly introduced, the diamond grows too fast in the early stage, and before the dielectric layer on the GaN substrate surface has fully formed a strengthening bond (i.e., Si-CN bond) it covers the entire surface and increases its thickness. Therefore, the film has poor thermal shock resistance, is prone to cracking, and has low nucleation quality, resulting in uneven growth in the later stage.

[0131] It should be noted that: a) High / low concentration CH4 atmosphere or similar descriptions refer to a higher concentration of CH4 in the growth atmosphere, i.e., a higher proportion of CH4 flow rate in the H2 flow rate. b) Figure 1 The plasma sphere shown is the bright part of the plasma region that is visible to the naked eye.

[0132] Finally, it should be noted that 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for non-destructive growth of diamond films on GaN substrates, characterized in that, Includes the following steps: S1, Pretreatment: Provide a GaN substrate, with one bottom surface covered by SiN. x Dielectric layer; Post-adjustment SiN x The thickness of the dielectric layer is 10-20 nm; then on SiN x After diamond powder is used to implant crystals on the surface of the dielectric layer, the GaN substrate is placed in the growth chamber of the MPCVD equipment. S2, Protective Growth Step 1: Continuously introduce H2 at a flow rate of 300-500 sccm into the growth chamber, then set the microwave power to 2500-3000W and the chamber pressure to 80-90 Torr; then introduce CH4 gas to perform the first diamond growth time, with the gas flow rate ratio H2:CH4 = 100:6-10; the first growth time is 10-20 min; S3, the second step of protective growth: N2 is introduced again to carry out the second growth time of diamond, and the gas flow ratio H2:N2=100:0.01-0.04; the second growth time is 5-15 minutes; then the N2 is stopped. S4, Later Stable Growth: Growth during the third growth period of diamond; the third growth period is 50-400 min; In step S4, before entering the third growth time, the CH4 gas flow rate is reduced to a gas flow rate ratio of H2:CH4 = 100:1-5.

2. The method for non-destructive growth of diamond film on GaN substrate surface as described in claim 1, characterized in that, In step S4, during the third growth time, the microwave power is set to 3500-4500W and the chamber pressure to 100-120 Torr.

3. The method for non-destructive growth of diamond film on GaN substrate surface as described in claim 1, characterized in that, It also includes the following steps: S5, Cooling: After the third growth time, stop the gas supply, then reduce the microwave power and chamber pressure to 0 uniformly within 1-2 hours, and then let it stand for a certain period of time.

4. The method for non-destructive growth of diamond film on GaN substrate surface as described in claim 1, characterized in that, The crystal implantation method is one or a combination of spin coating crystal implantation, self-adsorption crystal implantation, and self-assembly crystal implantation.

5. The method for non-destructive growth of diamond film on GaN substrate surface as described in claim 4, characterized in that, The spin coating method for crystal implantation includes the following steps: adding diamond powder to a solvent to prepare a diamond powder suspension; then adsorbing the GaN substrate onto a spin coater, and then dripping the diamond powder suspension into it, and rotating for a certain period of time.

6. The method for non-destructive growth of diamond film on GaN substrate surface as described in claim 5, characterized in that, The diamond powder has a particle size of 0.1-5 μm.

7. The method for non-destructive growth of diamond film on GaN substrate surface as described in claim 5, characterized in that, The mass ratio of diamond powder to solvent is 1-5:100, and the volume of the diamond powder suspension added is 5-30 mL.

8. The method for non-destructive growth of diamond film on GaN substrate surface as described in claim 1, characterized in that, The adjustment of SiN x The method used to determine the thickness of the dielectric layer includes either LPCVD or PECVD.

9. A GaN-based high electron mobility transistor, characterized in that, The GaN-based high electron mobility transistor has a diamond film prepared by a method for non-destructive growth of diamond film on a GaN substrate surface as described in any one of claims 1-8.

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