Method for depositing low-roughness diamond passivation layer on GaN wafer

Abstract

The invention provides a method for depositing a low-roughness diamond passivation layer on a GaN wafer. The method comprises the following steps: carrying out silicon nitride deposition on a silicon-based GaN wafer to obtain the silicon-based GaN wafer loaded with a silicon nitride dielectric layer; the preparation method comprises the following steps: immersing a silicon nitride dielectric layer into a modified diamond nucleation liquid A to adsorb a diamond seed crystal, carrying out primary microwave plasma chemical vapor deposition after spin coating, and forming a diamond passivation layer on the surface of the silicon nitride dielectric layer adsorbed with a diamond seed layer to obtain a silicon-based GaN wafer sequentially loaded with the diamond passivation layer and the silicon nitride layer; and immersing the wafer into the modified diamond nucleation liquid B, and carrying out diamond deposition after the wafer adsorbs a diamond seed crystal through spin coating to obtain the silicon-based GaN wafer loaded with a diamond passivation layer-silicon nitride layer with a certain thickness. According to the method, the diamond seed crystal is introduced to the surface of the wafer for multiple times, grain coarsening in the diamond deposition process is inhibited, and the polycrystalline diamond passivation layer with low surface roughness is prepared on the GaN wafer.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology and heat dissipation of electronic devices, and specifically to a method for depositing a low-roughness diamond passivation layer on a GaN wafer. Background Technology

[0002] Third-generation semiconductor power devices, represented by gallium nitride (GaN), offer significant advantages in high-power applications. However, their actual power density is far lower than the theoretical value, primarily due to severe heat accumulation during high-power operation, which limits device performance and reliability. Therefore, developing efficient thermal management technologies, especially integrating high thermal conductivity materials with the near-junction region of GaN devices, has become a key research direction.

[0003] Diamond is considered an ideal heat dissipation material due to its extremely high thermal conductivity and other excellent properties. Microwave plasma chemical vapor deposition (MPCVD) is commonly used to grow diamond passivation layers on GaN to improve heat dissipation efficiency. However, during the deposition process, polycrystalline diamond exhibits grain coarsening, leading to increased surface roughness of the film. This not only increases the difficulty of subsequent wafer fabrication processes such as photolithography but also affects device reliability and process compatibility.

[0004] Existing technologies for reducing roughness primarily focus on increasing the initial nucleation density, such as through bias-assisted nucleation or mechanical scraping. However, these methods may damage the substrate, and excessively high nucleation densities can introduce too many grain boundaries and impurities, thereby increasing the thermal resistance of the diamond / GaN interface and hindering heat dissipation. Furthermore, post-processing planarization methods using plasma etching suffer from slow etching rates and high costs due to the strong chemical inertness of diamond, and may also lead to new surface morphology problems due to differences in etching rates across different crystal planes. Summary of the Invention

[0005] Diamond is the material with the highest thermal conductivity in nature, exhibiting excellent heat dissipation in small, high-power devices and serving as a key material for addressing the self-heating effect in electronic devices. Current diamond passivation processes employ a single-stage nucleation growth method, resulting in a continuous increase in the surface roughness of the diamond film as its thickness increases. When this surface roughness reaches a certain level, it significantly complicates subsequent device fabrication processes.

[0006] This invention provides a method for depositing a low-roughness diamond passivation layer on a GaN wafer. By modifying the surface of ultra-nanocrystalline diamond, it enables the diamond to attract the substrate, forming a seed layer uniformly dispersed on the substrate. Two diamond deposition processes are performed. First, hydrogen-terminated diamond seed crystals are adsorbed onto a silicon nitride layer, completing the first seeding. Then, diamond deposition is performed. This layer of diamond has a high average grain size, meaning it has less grain boundary content, which improves the overall heat dissipation capacity of the wafer. The second seeding is completed by the adsorption of oxygen-terminated diamond seed crystals onto the hydrogen-terminated surface of the first diamond layer. Subsequently, a second layer of small-grained diamond is grown to cover the coarse grains on the surface of the first diamond film. This achieves ultra-low surface roughness while maintaining high thermal conductivity of the underlying layer. This addresses the problem of high diamond surface roughness and poor compatibility with GaN device fabrication processes in existing technologies.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for depositing a low-roughness diamond passivation layer on a GaN wafer includes the following steps: S1. Silicon nitride is deposited on the surface of GaN wafer by atomic layer deposition to obtain silicon-based GaN wafer with silicon nitride dielectric layer; S2. Immerse the silicon-based GaN wafer carrying the silicon nitride dielectric layer into the modified diamond nucleation solution A to perform diamond seed adsorption. Since the silicon nitride surface is negatively charged and the hydrogen-terminated nanodiamond seeds in the modified diamond nucleation liquid A are positively charged, the diamond seeds will spontaneously combine to the silicon nitride surface through electrostatic attraction, forming a uniform diamond seed layer. S3. Take out the silicon-based GaN wafer with silicon nitride dielectric layer that has completed adsorption, place it on a spin coater for spin coating, so that the diamond nucleation liquid dispersant remaining on the wafer surface can evaporate evenly until it disappears, avoiding the problem of diamond seed agglomeration and uneven seeding caused by the natural evaporation of nucleation liquid, leaving a uniformly distributed diamond seed layer on the surface of the silicon nitride layer. S4. Using microwave plasma chemical vapor deposition, diamond is deposited on the surface of the silicon nitride layer with diamond seed layer after the homogenization treatment to form the first coarse-grained diamond film. In the early stages of diamond growth, before a dense diamond film is formed, the silicon nitride layer is exposed to the hydrogen plasma environment of the MPCVD system and is etched thinner by the hydrogen plasma. Based on the etching rate of silicon nitride, the thickness of the silicon nitride layer prepared using the ALD system can be adjusted in advance so that only 2 nm of the silicon nitride dielectric layer remains after diamond growth as a phonon bridge and stress buffer layer, thereby reducing the contribution of the low thermal conductivity silicon nitride to the interfacial thermal resistance. S5. The silicon-based GaN wafer with coarse-grained diamond passivation layer-silicon nitride layer is immersed in modified diamond nucleation solution B for diamond seed adsorption. S6. Take out the silicon-based GaN wafer with coarse-grained diamond passivation layer-silicon nitride layer that has completed adsorption, place it on a spin coater for spin coating, and leave ultra-nanocrystalline diamond on the surface of the diamond layer as seed crystals for the second growth. S7. Microwave plasma chemical vapor deposition is performed again to form a second nanodiamond passivation layer, resulting in a silicon-based GaN wafer sequentially loaded with a low surface roughness diamond passivation layer and a silicon nitride layer. Because the surface of the first diamond film has hydrogen terminals, it can adsorb ultra-nano diamond particles with oxygen terminals in the modified diamond nucleation liquid B, so that ultra-nanocrystalline diamond seeds cover the coarse diamond grains on the film surface, forming a diamond seed layer again. Then, through microwave plasma chemical vapor deposition, a nano-diamond film with smaller grain size is gradually formed, covering the surface of the first large-size diamond film.

[0008] Preferably, the thickness of the silicon nitride dielectric layer in S1 is 8-9 nm, the cavity temperature during silicon nitride deposition is 260-280 ℃, the radio frequency source power is 100-110 W, the reaction gas flow rate is 100 mL / min, and the reaction chamber pressure is 200 Pa.

[0009] Preferably, the silicon nitride deposition in S1 uses triethylsilane as the silicon source and nitrogen as the nitrogen source.

[0010] Using triethylsilicon as the silicon source and nitrogen as the nitrogen source, these two precursor gases are alternately injected into the reaction chamber. When triethylsilicon and ammonia are adsorbed on the substrate surface, they react chemically to form silicon nitride. After the reaction, a cleaning gas (such as nitrogen) is introduced to remove unreacted triethylsilicon and ammonia residues from the wafer surface, preparing for the next deposition round. Only one atomic layer of material is deposited on the surface at a time until the desired thickness of the silicon nitride dielectric layer is achieved. Silicon nitride is resistant to etching by hydrogen plasma, providing excellent protection before the diamond film closes. Furthermore, the silicon nitride surface exhibits a negative Zeta potential in water-based nucleation liquid A, enabling it to form an electrostatic self-assembly process with nanodiamond seeds in hydrogen-terminated nucleation liquid A, significantly increasing the diamond nucleation density and resulting in a smooth, dense, high-quality nanodiamond film more quickly.

[0011] Preferably, the preparation process of the modified diamond nucleation liquid A in S2 is as follows: ultra-nano diamond powder is spread on a quartz boat, then transferred to a tube furnace, hydrogen gas is introduced, and annealing is performed under a hydrogen atmosphere; the annealed ultra-nano diamond powder is dispersed in deionized water, and the modified diamond nucleation liquid is obtained by ultrasonic vibration and centrifugation. During this process, the diamond surface will chemically react with hydrogen gas to produce CH and other groups. These groups will cause the diamond surface to exhibit a positive Zeta potential in aqueous solution, which is opposite to the surface potential of the silicon nitride dielectric layer. The diamond seeds and the surface of the silicon nitride dielectric layer attract each other, achieving uniform nucleation without damaging the sample.

[0012] Preferably, the rotation speed of the spin coater in S3 is 1400 rpm.

[0013] Preferably, the process parameters for plasma chemical vapor deposition in S4 are: microwave power 2-2.5 kW, deposition temperature 680-700℃, deposition atmosphere is a mixture of methane and hydrogen gas, and deposition time 40-50 minutes.

[0014] More preferably, the methane volume concentration in the mixed gas is 5% at the beginning of plasma chemical vapor deposition for nucleation, the nucleation time is 5 minutes, and after nucleation, the methane concentration is reduced to 3% by volume for diamond layer growth.

[0015] Preferably, the preparation process of the modified diamond nucleation liquid B in S5 is as follows: ultra-nano diamond powder is spread on a quartz boat, then transferred to a tube furnace, air is introduced, and annealing is carried out in an air atmosphere to cause partial oxidation on its surface and generate oxygen-containing groups; the annealed ultra-nano diamond powder is dispersed in anhydrous ethanol, and the modified diamond nucleation liquid B is obtained by ultrasonic vibration and centrifugation.

[0016] Preferably, the rotation speed of the spin coater in S6 is 1000 rpm.

[0017] Preferably, the process parameters for plasma chemical vapor deposition in S7 are: microwave power 2-2.2 kW, deposition temperature 650-660 ℃, deposition atmosphere is a mixture of methane and hydrogen gas, and deposition time 14-20 minutes.

[0018] Compared with existing technologies, the ALD silicon nitride introduced in this invention can adsorb diamond seed crystals in the nucleation liquid, achieving uniform and rapid nucleation. In the early stages of diamond deposition, this silicon nitride layer protects the underlying GaN from damage by H plasma and is etched thinner to an extremely thin 2 nm before the diamond forms a dense film, minimizing the contribution of its low thermal conductivity to the thermal resistance of the diamond / GaN interface. The phonon frequency and coefficient of thermal expansion of silicon nitride are between those of diamond and GaN, enabling it to act as a phonon bridge and stress buffer layer, improving phonon throughput at the diamond / GaN interface. Specifically, it offers the following advantages: This invention employs a two-stage diamond nucleation growth process. The first seeding and growth produces a coarse-grained diamond layer with high crystal quality and high thermal conductivity, enhancing the overall heat dissipation capacity of the wafer. The second seeding and growth process inhibits further growth of the underlying grains, resulting in a fine-grained diamond layer. This allows for the smoothing of the wafer surface without damaging the original material, filling the gaps and depressions between the large diamond grains in the first layer, reducing the difficulty of subsequent processing, and improving the precision of the photolithography patterning process.

[0019] A thin layer of ALD silicon nitride was used as the dielectric layer during fabrication. The silicon nitride was partially etched during the process, achieving an extremely thin layer of 2 nm, which significantly reduced the adverse effects of the layer's low thermal conductivity on interfacial heat transfer. The silicon nitride layer possesses a thermal expansion coefficient and phonon frequency between diamond and GaN, reducing lattice distortion at the interface, minimizing its impact on the electrical properties of GaN, and simultaneously enhancing interfacial thermal transport capacity and improving interfacial heat transfer efficiency.

[0020] During the preparation process, based on the characteristics of the substrate surface material, hydrogen-terminated diamond nucleating liquid and oxygen-terminated diamond nucleating liquid were used successively to achieve uniform adsorption and high-quality deposition of diamond, reduce the porosity of the diamond layer, and improve the overall quality and thermal conductivity of the diamond layer. Attached Figure Description

[0021] Figure 1 This is a structural diagram of a silicon-based GaN wafer provided in Embodiment 1 of the present invention; Figure 2 This is a structural diagram of a silicon-based GaN wafer with a silicon nitride layer provided in Embodiment 1 of the present invention; Figure 3 This is a structural diagram of a silicon-based GaN wafer with a rough surface diamond passivation layer-silicon nitride layer provided in Embodiment 1 of the present invention; Figure 4 This is a structural diagram of a silicon-based GaN wafer with a low surface roughness diamond passivation layer-silicon nitride layer provided in Embodiment 1 of the present invention; Figure 5This is a SEM image of the surface morphology of a silicon-based GaN wafer with a low surface roughness diamond passivation layer-silicon nitride layer provided in Embodiment 1 of the present invention. Figure 6 SEM images of the sample surface morphology provided for comparative purposes in this invention; Wherein: 1-Si layer; 2-GaN layer; 3-Silicon nitride layer; 4-Rough surface diamond passivation layer; 5-Smooth surface diamond layer. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example 1

[0023] A method for depositing a low-roughness diamond passivation layer on a GaN wafer includes the following steps: S1. A silicon-based GaN wafer with a diameter of 2 inches and a thickness of 1 mm (its structure is as follows) Figure 1 The sample was cleaned by ultrasonic cleaning with acetone for 10 minutes, followed by ultrasonic cleaning in alcohol for 10 minutes, and then dried with nitrogen for later use. S2. Using atomic layer deposition (ALD) with triethylsilane as the silicon source and nitrogen as the nitrogen source, silicon nitride is deposited on the gallium nitride to obtain a silicon-based GaN wafer with a silicon nitride dielectric layer. Its structure is shown in the figure below. Figure 2 As shown, during the silicon nitride deposition process, the chamber temperature is 280 ℃, the radio frequency source power is 110 W, the reaction gas flow rate is 100 mL / min, the reaction chamber pressure is about 200 Pa, and the thickness of the silicon nitride dielectric layer is 9 nm. S3. Spread the ultra-nano diamond powder on a quartz boat, then transfer it to a tube furnace, introduce hydrogen gas, and anneal at 650°C in a hydrogen atmosphere for 8 hours; disperse the annealed ultra-nano diamond powder in deionized water, and obtain modified diamond nucleation liquid A by ultrasonic vibration and centrifugation. S4. Immerse the silicon-based GaN wafer with the silicon nitride dielectric layer in modified diamond nucleation solution A and soak it at room temperature and pressure for 15 minutes to perform diamond seed adsorption. S5. Take out the silicon-based GaN wafer with silicon nitride dielectric layer that has been adsorbed and place it on a spin coater with a speed of 1400 rpm for 2 min to leave a uniformly distributed diamond seed layer on the surface of the silicon nitride layer. S6. Using microwave plasma chemical vapor deposition, diamond is deposited on the silicon nitride surface with the adsorbed diamond seed layer to form the first diamond passivation layer. Simultaneously, the silicon nitride layer is etched and thinned to 2 nm, resulting in a silicon-based GaN wafer sequentially containing a diamond passivation layer and a silicon nitride layer, as shown in the diagram. Figure 3 As shown; The process parameters are as follows: cavity pressure 11000 Pa, microwave power 2.5 kW, deposition temperature 700 ℃, deposition atmosphere is a mixture of methane and hydrogen gas, the volume concentration of methane in the mixture is 5% at the beginning of plasma chemical vapor deposition, nucleation is performed for 5 min, after nucleation is completed, the methane concentration is reduced to 3% by volume, diamond layer is grown for 50 min.

[0024] S7. Spread the ultra-nano diamond powder on a quartz boat, then transfer it to a tube furnace, introduce air, and anneal at 400°C in an air atmosphere for 5 hours; disperse the annealed ultra-nano diamond powder in anhydrous ethanol, and obtain modified diamond nucleation liquid B by ultrasonic vibration and centrifugation. S8. Immerse the silicon-based GaN wafer with diamond passivation layer-silicon nitride layer into modified diamond nucleation solution B and soak it for 15 minutes at room temperature and pressure to perform diamond seed adsorption. S9. Take out the silicon-based GaN wafer with diamond passivation layer-silicon nitride layer that has been adsorbed and place it on a spin coater with a speed of 1000 rpm for 2 min to leave a uniformly distributed diamond seed layer on the surface of the diamond layer. S10. Using microwave plasma chemical vapor deposition, a second fine-grained diamond passivation layer is formed on a silicon-based GaN wafer with a coarse-grained diamond passivation layer-silicon nitride layer adsorbed with a diamond seed layer, resulting in a silicon-based GaN wafer sequentially loaded with a low-surface-roughness diamond passivation layer-silicon nitride layer.

[0025] The process parameters are: cavity pressure 11000 Pa, microwave power 2.2 kW, deposition temperature 660 ℃, deposition atmosphere is a mixture of methane and hydrogen, wherein the methane volume concentration is 3%, and diamond layer is grown for 20 minutes.

[0026] The structure of the silicon-based GaN wafer with a low surface roughness diamond passivation layer-silicon nitride layer is as follows: Figure 4 SEM images of the surface morphology of its diamond passivation layer are as follows: Figure 5 As shown, the prepared diamond passivation layer has fine grains and excellent uniformity on its surface. Example 2

[0027] A method for depositing a low-roughness diamond passivation layer on a GaN wafer includes the following steps: S1. Clean the silicon-based GaN wafer with a diameter of 2 inches and a thickness of 1 mm by ultrasonic cleaning with acetone for 10 minutes, then transfer it to alcohol for ultrasonic cleaning for 10 minutes, and then dry it with nitrogen for later use. S2. Using atomic layer deposition (ALD) with triethylsilane as the silicon source and nitrogen as the nitrogen source, silicon nitride is deposited on gallium nitride to obtain a silicon-based GaN wafer with a silicon nitride dielectric layer. During the silicon nitride deposition process, the chamber temperature is 260 °C, the radio frequency source power is 100 W, the reaction gas flow rate is 100 mL / min, the reaction chamber pressure is about 200 Pa, and the thickness of the silicon nitride dielectric layer is 8 nm. S3. Spread the ultra-nano diamond powder on a quartz boat, then transfer it to a tube furnace, introduce hydrogen gas, and anneal at 650°C in a hydrogen atmosphere for 8 hours; disperse the annealed ultra-nano diamond powder in deionized water, and obtain modified diamond nucleation liquid A by ultrasonic vibration and centrifugation. S4. Immerse the silicon-based GaN wafer with the silicon nitride dielectric layer in modified diamond nucleation solution A and soak it at room temperature and pressure for 15 minutes to perform diamond seed adsorption. S5. Take out the silicon-based GaN wafer with silicon nitride dielectric layer that has been adsorbed and place it on a spin coater with a speed of 1400 rpm for 2 min to leave a uniformly distributed diamond seed layer on the surface of the silicon nitride layer. S6. Microwave plasma chemical vapor deposition is used to deposit diamond on the silicon nitride surface with diamond seed layer to form the first diamond passivation layer. At the same time, the silicon nitride layer is etched and thinned to 2 nm to obtain a silicon-based GaN wafer with diamond passivation layer and silicon nitride layer sequentially. The process parameters are as follows: cavity pressure 10000 Pa, microwave power 2 kW, deposition temperature 680 ℃, deposition atmosphere is a mixture of methane and hydrogen gas, the volume concentration of methane in the mixture is 5% at the beginning of plasma chemical vapor deposition, nucleation is performed for 5 min, after nucleation is completed, the methane concentration is reduced to 3% by volume, diamond layer is grown for 40 min.

[0028] S7. Spread the ultra-nano diamond powder on a quartz boat, then transfer it to a tube furnace, introduce air, and anneal at 400°C in an air atmosphere for 5 hours; disperse the annealed ultra-nano diamond powder in anhydrous ethanol, and obtain modified diamond nucleation liquid B by ultrasonic vibration and centrifugation. S8. Immerse the silicon-based GaN wafer with diamond passivation layer-silicon nitride layer into modified diamond nucleation solution B and soak it for 15 minutes at room temperature and pressure to perform diamond seed adsorption. S9. Take out the silicon-based GaN wafer with diamond passivation layer-silicon nitride layer that has been adsorbed and place it on a spin coater with a speed of 1000 rpm for 2 min to leave a uniformly distributed diamond seed layer on the surface of the diamond layer. S10. Using microwave plasma chemical vapor deposition, a second fine-grained diamond passivation layer is formed on a silicon-based GaN wafer with a coarse-grained diamond passivation layer-silicon nitride layer adsorbed with a diamond seed layer, resulting in a silicon-based GaN wafer sequentially loaded with a low-surface-roughness diamond passivation layer-silicon nitride layer.

[0029] The process parameters are: cavity pressure 11000 Pa, microwave power 2 kW, deposition temperature 650 ℃, deposition atmosphere is a mixture of methane and hydrogen, wherein the methane volume concentration is 3%, and diamond layer is grown for 14 minutes. Example 3

[0030] A method for depositing a low-roughness diamond passivation layer on a GaN wafer includes the following steps: S1. Clean the silicon-based GaN wafer with a diameter of 2 inches and a thickness of 1 mm by ultrasonic cleaning with acetone for 10 minutes, then transfer it to alcohol for ultrasonic cleaning for 10 minutes, and then dry it with nitrogen for later use. S2. Using atomic layer deposition (ALD) with triethylsilane as the silicon source and nitrogen as the nitrogen source, silicon nitride is deposited on gallium nitride to obtain a silicon-based GaN wafer with a silicon nitride dielectric layer. During the silicon nitride deposition process, the chamber temperature is 270 °C, the radio frequency source power is 105 W, the reaction gas flow rate is 100 mL / min, the reaction chamber pressure is about 200 Pa, and the thickness of the silicon nitride dielectric layer is 8.5 nm. S3. Spread the ultra-nano diamond powder on a quartz boat, then transfer it to a tube furnace, introduce hydrogen gas, and anneal at 650°C in a hydrogen atmosphere for 8 hours; disperse the annealed ultra-nano diamond powder in deionized water, and obtain modified diamond nucleation liquid A by ultrasonic vibration and centrifugation. S4. Immerse the silicon-based GaN wafer with the silicon nitride dielectric layer in modified diamond nucleation solution A and soak it at room temperature and pressure for 15 minutes to perform diamond seed adsorption. S5. Take out the silicon-based GaN wafer with silicon nitride dielectric layer that has been adsorbed and place it on a spin coater with a speed of 1400 rpm for 2 min to leave a uniformly distributed diamond seed layer on the surface of the silicon nitride layer. S6. Microwave plasma chemical vapor deposition is used to deposit diamond on the silicon nitride surface with diamond seed layer to form the first diamond passivation layer. At the same time, the silicon nitride layer is etched and thinned to 2 nm to obtain a silicon-based GaN wafer with diamond passivation layer and silicon nitride layer sequentially. The process parameters are as follows: cavity pressure 10500 Pa, microwave power 2.25 kW, deposition temperature 690 ℃, deposition atmosphere is a mixture of methane and hydrogen gas, the volume concentration of methane in the mixture is 5% at the beginning of plasma chemical vapor deposition, nucleation is performed for 5 min, after nucleation is completed, the methane concentration is reduced to 3% by volume, diamond layer is grown for 50 min.

[0031] S7. Spread the ultra-nano diamond powder on a quartz boat, then transfer it to a tube furnace, introduce air, and anneal at 400°C in an air atmosphere for 5 hours; disperse the annealed ultra-nano diamond powder in anhydrous ethanol, and obtain modified diamond nucleation liquid B by ultrasonic vibration and centrifugation. S8. Immerse the silicon-based GaN wafer with diamond passivation layer-silicon nitride layer into modified diamond nucleation solution B and soak it for 15 minutes at room temperature and pressure to perform diamond seed adsorption. S9. Take out the silicon-based GaN wafer with diamond passivation layer-silicon nitride layer that has been adsorbed and place it on a spin coater with a speed of 1000 rpm for 2 min to leave a uniformly distributed diamond seed layer on the surface of the diamond layer. S10. Using microwave plasma chemical vapor deposition, a second fine-grained diamond passivation layer is formed on a silicon-based GaN wafer with a coarse-grained diamond passivation layer-silicon nitride layer adsorbed with a diamond seed layer, resulting in a silicon-based GaN wafer sequentially loaded with a low-surface-roughness diamond passivation layer-silicon nitride layer.

[0032] The process parameters are: cavity pressure 11000 Pa, microwave power 2.1 kW, deposition temperature 655 ℃, deposition atmosphere is a mixture of methane and hydrogen, wherein the methane volume concentration is 3%, and diamond layer is grown for 17 minutes.

[0033] The performance of the silicon-based GaN wafers with nanodiamond passivation layer-silicon nitride layer prepared in Examples 2-3 is similar to that in Example 1.

[0034] Comparative Example 1 The difference from Example 1 is that steps S7, S8, S9, and S10 are not included in this comparative example, and the diamond deposition time in S6 is changed to 70 minutes, which is consistent with the total diamond growth time in Example 1.

[0035] The SEM images of the diamond passivation layer morphology on the silicon-based GaN wafer surface obtained in this comparative example are as follows: Figure 6 As shown, it can be seen that the diamond grains on the surface of the product obtained in the comparative example (silicon-based GaN wafer with diamond passivation surface) are coarse, with sharp edges and corners, and the surface has large undulations and differences, resulting in high roughness.

[0036] The surface roughness of the product prepared in Example 1 was significantly lower than that of the product prepared in the comparative example.

[0037] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for depositing a low-roughness diamond passivation layer on a GaN wafer, characterized in that, Includes the following steps: S1. Silicon nitride is deposited on the surface of GaN wafer by atomic layer deposition to obtain silicon-based GaN wafer with silicon nitride dielectric layer; S2. Immerse the silicon-based GaN wafer carrying the silicon nitride dielectric layer into the modified diamond nucleation solution A to perform diamond seed adsorption. S3. Take out the silicon-based GaN wafer with silicon nitride dielectric layer that has been adsorbed, place it on a spin coater for spin coating, and leave a diamond seed layer on the surface of the silicon nitride layer. S4. Perform microwave plasma chemical vapor deposition to deposit diamond on the surface of the silicon nitride layer with diamond seed layer adsorbed, forming the first coarse-grained diamond passivation layer, and obtain a silicon-based GaN wafer with coarse-grained diamond passivation layer and silicon nitride layer sequentially. S5. The silicon-based GaN wafer with coarse-grained diamond passivation layer-silicon nitride layer is immersed in modified diamond nucleation solution B for diamond seed adsorption. S6. Take out the silicon-based GaN wafer containing the coarse-grained diamond passivation layer-silicon nitride layer after adsorption, place it on a spin coater for spin coating, and leave an ultra-nanocrystalline diamond seed layer on the surface of the diamond layer. S7. Microwave plasma chemical vapor deposition is performed again to form a second fine-grained diamond passivation layer, resulting in a silicon-based GaN wafer sequentially loaded with a low-surface-roughness nanodiamond passivation layer and a silicon nitride layer.

2. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, The thickness of the silicon nitride layer in S1 is 8-9 nm.

3. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, In the silicon nitride deposition process described in S1, the chamber temperature is 260-280 ℃, the radio frequency source power is 100-110 W, the reaction gas flow rate is 100 mL / min, and the reaction chamber pressure is 200 Pa.

4. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, The silicon nitride deposition described in S1 uses triethylsilane as the silicon source and nitrogen as the nitrogen source.

5. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, The preparation process of the modified diamond nucleation liquid A described in S2 is as follows: ultra-nano diamond powder is spread on a quartz boat and then transferred to a tube furnace and annealed at 650°C under a hydrogen atmosphere for 8 hours; the annealed ultra-nano diamond powder is dispersed in deionized water to obtain the modified diamond nucleation liquid A.

6. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, The spin coater described in S3 has a rotation speed of 1400 rpm.

7. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, The process parameters for plasma chemical vapor deposition described in S4 are: microwave power 2-2.5kW, deposition temperature 680-700℃, deposition atmosphere is a mixture of methane and hydrogen gas, and deposition time 40-50 minutes.

8. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, The preparation process of the modified diamond nucleation liquid B described in S5 is as follows: ultra-nano diamond powder is spread on a quartz boat, then transferred to a tube furnace and annealed at 400°C in air atmosphere for 5 hours to cause partial oxidation on its surface and generate oxygen-containing groups; the annealed ultra-nano diamond powder is dispersed in anhydrous ethanol water to obtain the modified diamond nucleation liquid B.

9. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, The spin coater described in S6 has a rotation speed of 1000 rpm.

10. The method for depositing a low-roughness diamond passivation layer on a GaN wafer according to claim 1, characterized in that, The process parameters for plasma chemical vapor deposition described in S7 are: microwave power 2-2.2 kW, deposition temperature 650-660℃, deposition atmosphere is a mixture of methane and hydrogen gas, and deposition time 14-20 minutes.

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