A low-stress high-uniformity MPCVD heat sink sheet and a preparation method thereof

Abstract

This invention discloses a low-stress, high-uniformity MPCVD heat sink and its preparation method. First, a 4-6 inch single-crystal silicon substrate undergoes precision polishing and ultrasonic-assisted nanodiamond powder seeding pretreatment to obtain high-density, uniform nucleation sites. Then, a high-low temperature segmented variable-temperature nucleation process is used to obtain a dense, continuous diamond nucleus layer. Subsequently, a three-stage growth process with gradients in temperature, pressure, and methane concentration, combined with a concentration gradient transition section and pulsed argon gas modification, optimizes grain growth and reduces microscopic defects. After growth, high-temperature atmosphere homogenization combined with a slow gradient cooling process achieves uniform stress release in the film layer. Finally, chemical substrate removal and double-sided precision polishing yield the low-stress, high-uniformity MPCVD heat sink. This invention can stably prepare large-size MPCVD heat sinks with a stable residual stress controlled at 63-68 MPa, thickness uniformity ≤±3.6%, and thermal conductivity exceeding 1770 W / m·K. It also possesses low residual stress, high structural uniformity, and excellent thermal conductivity.

Description

Technical Field

[0001] This invention relates to the field of MPCVD heat sink preparation technology, and more specifically to a low-stress, high-uniformity MPCVD heat sink and its preparation method. Background Technology

[0002] Diamond possesses ultra-high thermal conductivity, excellent mechanical strength, extremely low coefficient of thermal expansion, and good electrochemical stability, making it a core strategic heat dissipation material in high-end electronic heat dissipation, semiconductor packaging, MEMS microdevices, and electrochemical functional devices. With the rapid iteration of next-generation AI computing chips, high-frequency microwave devices, and third-generation semiconductor power devices towards higher integration, higher heat flux density, and miniaturization, the operating heat density of these devices has increased significantly. Traditional heat dissipation materials such as copper, aluminum, and silicon carbide can no longer meet the stringent requirements of ultra-high heat dissipation, low deformation, and high stability. Diamond heat sinks, with their superior comprehensive thermal performance, have become the optimal solution for thermal management of high-end chips.

[0003] Among various diamond preparation processes, MPCVD (microwave plasma chemical vapor deposition) technology has become the mainstream core technology for the industrial preparation of diamond heat sinks because it can prepare high-purity, large-size, and highly dense polycrystalline diamond films, with strong process controllability and stable finished product performance.

[0004] However, existing traditional MPCVD fabrication processes still have many problems: 1) Traditional constant parameter growth mode is prone to causing disordered growth and uneven size distribution of diamond film grains, resulting in poor consistency of film microstructure. This directly leads to insufficient uniformity of thermal conductivity across the entire product and local differences in heat dissipation performance, making it unsuitable for high-precision semiconductor packaging requirements; 2) There is a significant lattice mismatch and difference in thermal expansion coefficient between diamond film and single-crystal silicon substrate. Combined with problems such as abrupt changes in traditional process parameters and excessively fast cooling rates, this results in concentrated residual stress and uneven stress distribution inside the film. After removing the substrate, defects such as heat sink warping, deformation, and cracking are very likely to occur, resulting in low product yield and difficulty in stably fabricating flat heat sinks of 4 inches and above.

[0005] In summary, existing MPCVD diamond heat sink fabrication processes are inadequate. Therefore, this invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to address the problems mentioned in the background section by providing a low-stress, high-uniformity MPCVD heat sink and its preparation method.

[0007] To achieve the above objectives, the present invention specifically adopts the following technical solution: A method for preparing a low-stress, high-uniformity MPCVD heat sink sheet includes steps S1 to S4.

[0008] S1. Place the pretreated single-crystal silicon substrate in the reaction chamber of the MPCVD equipment, introduce methane and hydrogen, and first nucleate at 600-700℃ for 10-20 minutes to form a large number of small and uniform initial crystal nuclei; then raise the temperature to 800-900℃ to continue nucleation for 20-30 minutes, so that the crystal nuclei grow and connect with each other to form a continuous and dense film; a diamond crystal nucleus layer substrate is obtained on the surface of the single-crystal silicon substrate.

[0009] Furthermore, the preprocessing method in S1 includes: After chemical mechanical polishing of the monocrystalline silicon substrate, an ultrasonic-assisted nanodiamond powder seeding process is used to pretreat the polished monocrystalline silicon substrate to ensure that the diamond nucleation density on the surface of the monocrystalline silicon substrate is not less than 10. 9 cm -2 ; The ultrasonic-assisted nanodiamond powder seeding process specifically involves dispersing nanodiamond powder with a particle size of 5–10 nm in anhydrous ethanol at a concentration of 0.1–0.5 g / L to prepare a uniform nanodiamond suspension; then completely immersing a chemically and mechanically polished single-crystal silicon substrate in the nanodiamond suspension and ultrasonically treating it for 10–20 min.

[0010] The monocrystalline silicon substrate has a diameter of 4 to 6 inches. The monocrystalline silicon substrate is chemically and mechanically polished to achieve a surface roughness Ra ≤ 0.5 nm and a surface flatness ≤ 5 μm.

[0011] Furthermore, the heating rate in S1 is 5–10 °C / min.

[0012] S2. Diamond thin film is grown on a single-crystal silicon substrate with a diamond nucleus layer using a gradient methane flow process. Argon gas is intermittently introduced during the film growth process to obtain a diamond thick film composite substrate.

[0013] Furthermore, in S2, a gradient methane flow process is used to grow diamond thin films on a single-crystal silicon substrate with a diamond nucleus layer. The thin film growth process includes three growth stages, and a concentration gradient transition section is set between each adjacent growth stage. In the first growth stage, the methane concentration is 3-4%, the film growth time is 1-50 h, and the pressure is 10.66-13.33 kPa, which promotes the lateral growth of grains and forms a dense underlayer with a grain size controlled at 1-3 μm. In the second growth stage, the methane concentration is 4-5%, the film growth time is 50-150 h, and the pressure is 13.33-16.00 kPa, which maintains a stable growth rate and gradually grows the grain size to 5-15 μm. In the third growth stage, the methane concentration is 5-6%, the film growth time is 150-300 h, and the pressure is 16.00-19.99 kPa, which accelerates the longitudinal growth and grows the grain size to 20-50 μm.

[0014] Furthermore, the duration of the concentration gradual transition period is 5–10 hours, and the methane concentration change rate is 0.1–0.2% per hour to avoid stress concentration caused by sudden concentration changes.

[0015] Furthermore, the temperature of the first growth stage is 800–850℃, the temperature of the second growth stage is 850–900℃, and the temperature of the third growth stage is 900–950℃.

[0016] Furthermore, in step S2, argon gas is intermittently introduced using a pulsed introduction method, with a pulse period of 10–30 min, an argon gas introduction time of 5–15 min, and a flow rate of 50–200 cm³. 3 / min.

[0017] During the instantaneous period of each argon pulse, the methane concentration is briefly increased to 6-8%, and after the pulse ends, the methane concentration drops back to the baseline gradient concentration of the current growth stage.

[0018] S3. After growth is completed, the temperature is lowered to 700-800℃ in a hydrogen plasma atmosphere, nitrogen and argon are introduced, and the temperature is maintained for 1-2 hours to homogenize the internal stress of the film. Then, the temperature is lowered to room temperature at a rate of 0.1-0.3℃ / min to obtain the diamond / silicon composite substrate.

[0019] Furthermore, the flow rate of nitrogen gas introduced into S3 is 5-20 cm³. 3 / min, argon gas flow rate 100-200 cm³ / min 3 / min.

[0020] Furthermore, in step S3, when the hydrogen plasma atmosphere is cooled to 700–800°C, the cooling rate is 0.1–0.3°C / min, and the hydrogen flow rate is maintained at 100–200 cm³ during the cooling process. 3 / min.

[0021] S4. The single-crystal silicon substrate in the diamond / silicon composite substrate is removed by chemical etching to obtain a diamond thin film substrate. The diamond thin film substrate is then subjected to double-sided precision polishing and shaping to obtain the MPCVD heat sink product.

[0022] As an inventive concept with the same technical solution described above, this invention also claims protection for a low-stress, high-uniformity MPCVD heat sink sheet, which is prepared by any of the preparation methods described above.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention involves chemically and mechanically polishing a monocrystalline silicon substrate to control its surface roughness Ra ≤ 0.5 nm and flatness ≤ 5 μm, resulting in an atomically smooth substrate and eliminating the negative impact of microscopic unevenness, scratches, and step defects on subsequent thin film growth. Simultaneously, an ultrasonic-assisted nanodiamond powder seeding process is employed, using 5–10 nm ultrafine diamond powder at a dispersion concentration of 0.1–0.5 g / L, to achieve a diamond nucleation density ≥ 102 on the substrate. 9 cm -2 This allows for the formation of uniform, dense, and sufficiently numerous initial nucleation sites on the surface of a single-crystal silicon substrate; 2. In the first growth stage of this invention, a low-concentration methane and low-pressure, low-temperature environment promotes the lateral spread of grains, forming a dense and uniform underlying film and solidifying a low-defect substrate. In the second growth stage, the methane concentration, temperature, and pressure are steadily increased to maintain a stable growth rate and achieve smooth grain transition growth. In the third growth stage, the parameters are further increased to accelerate the longitudinal growth of grains and improve the film thickness and density. At the same time, a 5-10 hour concentration gradient transition section is set between each growth stage, with a low-speed concentration gradient of 0.1-0.2% per hour to avoid lattice distortion and stress concentration problems caused by sudden changes in process parameters, effectively weakening the lattice mismatch stress between the diamond film and the silicon substrate and reducing the residual stress inside the film. 3. After the thin film growth is completed, the present invention employs a high-temperature heat preservation modification process in a hydrogen plasma atmosphere, combined with a specific ratio of nitrogen and argon gas for synergistic atmosphere treatment. This process can repair microscopic defects generated during the thin film growth process, promote the rearrangement of carbon atom lattice within the film layer, and achieve a uniform distribution of residual stress. At the same time, by using a gradient cooling of 0.1 to 0.3 °C / min, the secondary thermal stress generated by rapid cooling is avoided, further releasing the internal stress of the film layer. This significantly improves the structural stability of the diamond / silicon composite substrate, reduces the problems of film warping, cracking, and deformation that occur in subsequent substrate removal and polishing processes, and improves the yield of finished products. 4. This invention completely removes the single-crystal silicon substrate by chemical etching to obtain a self-supporting diamond thin film substrate without substrate constraints, eliminating the interfacial stress and performance limitations caused by the substrate. Then, through double-sided precision polishing and shaping, the overall thickness uniformity and surface flatness of the film are optimized, and finally a low-stress, high-uniformity MPCVD heat sink is obtained. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The materials and instruments used in the following embodiments are all commercially available.

[0025] In a first aspect, embodiments of the present invention provide a method for preparing a low-stress, high-uniformity MPCVD heat sink sheet, comprising steps S1 to S4.

[0026] S1. The pretreated single-crystal silicon substrate is placed in the reaction chamber of the MPCVD equipment, and methane and hydrogen are introduced. Nucleation is first carried out at 600-700℃ for 10-20 min, and then the temperature is increased to 800-900℃ for another 20-30 min to obtain a diamond nucleus layer substrate on the surface of the single-crystal silicon substrate. The pressure during nucleation is 10.5-16.0 kPa.

[0027] Furthermore, the preprocessing method in S1 includes: After chemical mechanical polishing of the monocrystalline silicon substrate, an ultrasonic-assisted nanodiamond powder seeding process is used to pretreat the polished monocrystalline silicon substrate to ensure that the diamond nucleation density on the surface of the monocrystalline silicon substrate is not less than 10. 9 cm -2 ; The ultrasonic-assisted nanodiamond powder seeding process specifically involves dispersing nanodiamond powder with a particle size of 5–10 nm in anhydrous ethanol at a concentration of 0.1–0.5 g / L to prepare a uniform nanodiamond suspension; then completely immersing a chemically and mechanically polished single-crystal silicon substrate in the nanodiamond suspension and ultrasonically treating it for 10–20 min.

[0028] Furthermore, the heating rate in S1 is 5–10 °C / min.

[0029] S2. Diamond thin film is grown on a single-crystal silicon substrate with a diamond nucleus layer using a gradient methane flow process. Argon gas is intermittently introduced during the film growth process to obtain a diamond thick film composite substrate.

[0030] Furthermore, in S2, a gradient methane flow process is used to grow diamond thin films on a single-crystal silicon substrate with a diamond nucleus layer. The thin film growth process includes three growth stages, and a concentration gradient transition section is set between each adjacent growth stage. The methane concentration in the first growth stage is 3-4%, and the film growth time is 1-50 h; the methane concentration in the second growth stage is 4-5%, and the film growth time is 50-150 h; the methane concentration in the third growth stage is 5-6%, and the film growth time is 150-300 h.

[0031] Furthermore, the duration of the concentration gradual transition period is 5–10 hours, and the methane concentration change rate is 0.1–0.2% per hour.

[0032] Furthermore, the temperature of the first growth stage is 800–850℃, the temperature of the second growth stage is 850–900℃, and the temperature of the third growth stage is 900–950℃.

[0033] Furthermore, in step S2, argon gas is intermittently introduced using a pulsed introduction method, with a pulse period of 10–30 min, an argon gas introduction time of 5–15 min, and a flow rate of 50–200 cm³. 3 / min.

[0034] S3. After growth is completed, the temperature is lowered to 700-800℃ in a hydrogen plasma atmosphere, nitrogen and argon are introduced, and the temperature is maintained for 1-2 hours. Then, the temperature is lowered to room temperature at a rate of 0.1-0.3℃ / min to obtain the diamond / silicon composite substrate.

[0035] Furthermore, the flow rate of nitrogen gas introduced into S3 is 5-20 cm³. 3 / min, argon gas flow rate 100-200 cm³ / min 3 / min.

[0036] Furthermore, in step S3, when the hydrogen plasma atmosphere is cooled to 700–800°C, the cooling rate is 0.1–0.3°C / min, and the hydrogen flow rate is maintained at 100–200 cm³ during the cooling process. 3 / min.

[0037] S4. The single-crystal silicon substrate in the diamond / silicon composite substrate is removed by chemical etching to obtain a diamond thin film substrate. The diamond thin film substrate is then subjected to double-sided precision polishing and shaping to obtain the MPCVD heat sink product.

[0038] Specifically, a diamond / silicon composite substrate is immersed in a mixed solution of hydrofluoric acid and nitric acid (volume ratio 3:1) and etched at room temperature for 30–60 min to obtain a diamond thin film substrate. The diamond thin film substrate undergoes double-sided precision polishing and shaping, sequentially using a diamond grinding wheel for coarse polishing (particle size 10–20 μm), diamond micron powder for medium polishing (particle size 1–3 μm), and nano-diamond for fine polishing (particle size 0.1–0.5 μm), to achieve a surface roughness Ra ≤ 10 nm and a film thickness controlled between 200–1000 μm, resulting in an MPCVD heat sink product.

[0039] Secondly, embodiments of the present invention provide a low-stress, high-uniformity MPCVD heat sink sheet, which is prepared using the aforementioned preparation method.

[0040] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0041] Example 1 S1. Select a 4.5-inch (100) crystal plane single crystal silicon substrate and perform chemical mechanical polishing on the single crystal silicon substrate to achieve a surface roughness Ra of 0.3 nm and a surface flatness of 3 μm. S2. Ultrasonic-assisted nanodiamond powder seeding process: Nanodiamond powder with a particle size of 7.5 nm is dispersed in anhydrous ethanol at a concentration of 0.3 g / L and ultrasonically dispersed for 45 min. The single-crystal silicon substrate treated in S1 is then immersed in the suspension and ultrasonically treated for 15 min, so that the nanodiamond powder is uniformly adsorbed on the surface of the single-crystal silicon substrate and the nucleation density reaches 1.2 × 10⁻⁶. 9 cm -2 ; S3. Place the pretreated single-crystal silicon substrate from S2 into the reaction chamber of the MPCVD equipment, introduce methane and hydrogen, and use a variable-temperature nucleation process, i.e. nucleation at 650℃ for 15 minutes, then increase the temperature to 850℃ at a rate of 7.5℃ / min, and nucleate again for 25 minutes. After nucleation in step S4, the sample obtained in step S3 was grown using a gradient methane process: 0–50 h, methane concentration 3.5%, pressure 12 kPa, temperature 825 °C, with the bottom layer grain size controlled at 1–3 μm; 50–150 h, methane concentration 4.5%, pressure 110 Torr, temperature 875 °C, with the grain size controlled at 5–15 μm; 150–300 h, methane concentration 5.5%, pressure 18 kPa, temperature 925 °C, with the grain size controlled at 20–50 μm. A gradual concentration transition section was set between each stage, with a transition time of 7.5 h and a methane concentration change rate of 0.15% / h. During this process, argon gas was pulsed in, with an argon flow rate of 125 cm³ / h. 3 / min, pulse cycle 20min, argon gas introduction time 10min; methane concentration increases to 7% when argon gas is introduced; methane concentration returns to the original concentration when argon gas is stopped; S5. After growth, in-situ stress control is performed, the temperature is lowered to 750℃, and a hydrogen flow rate of 250 cm³ is maintained. 3 / min, pressure 12kPa; nitrogen gas introduced 12.5cm 3 / min and argon 150cm 3 The temperature was maintained at 0.2℃ / min for 1.5 hours to homogenize the internal stress of the membrane; then the temperature was slowly lowered to room temperature at a rate of 0.2℃ / min, while maintaining a hydrogen flow rate of 150 cm³ / min during the cooling process. 3 / min; S6. The sample obtained in S5 was immersed in a mixed solution of hydrofluoric acid and nitric acid (volume ratio 3:1) and etched at room temperature for 45 min to obtain a diamond film substrate. The diamond film substrate was then subjected to double-sided precision polishing, sequentially using a diamond grinding wheel for coarse polishing (15 μm particle size), diamond micro powder for medium polishing (2 μm particle size), and nano-diamond for fine polishing (0.3 μm particle size). After polishing, the surface roughness Ra reached 8 nm, and the film thickness reached 490 μm. Example 2 S1. Select a 6-inch (100) crystal plane single crystal silicon substrate and perform chemical mechanical polishing on the single crystal silicon substrate to make the surface roughness Ra reach 0.5nm and the surface flatness reach 5μm.

[0042] S2. Ultrasonic-assisted nanodiamond powder seeding process: 10nm nanodiamond powder is dispersed in anhydrous ethanol at a concentration of 0.5g / L and ultrasonically dispersed for 60min; the S1-treated monocrystalline silicon substrate is immersed in the suspension and ultrasonically treated for 20min, allowing the nanodiamond powder to be uniformly adsorbed on the surface of the monocrystalline silicon substrate, achieving a substrate nucleation density of 1.0×10⁻⁶. 9 cm -2 .

[0043] S3. Place the pretreated single-crystal silicon substrate from S2 into the reaction chamber of the MPCVD equipment, introduce methane and hydrogen, and use a variable-temperature nucleation process: first nucleate at 700℃ for 20 minutes, then raise the temperature to 900℃ at a rate of 10℃ / min and continue nucleation for 30 minutes to form a continuous and dense diamond nucleus layer on the surface of the single-crystal silicon substrate.

[0044] S4. After nucleation, a gradient methane flow rate process was used for diamond thick film growth: 0–50 h, methane concentration 4%, chamber pressure 13.33 kPa, growth temperature 850 °C, bottom grain size controlled at 1–3 μm; 50–150 h, methane concentration 5%, chamber pressure 16.00 kPa, growth temperature 900 °C, grain size controlled at 5–15 μm; 150–300 h, methane concentration 6%, chamber pressure 19.99 kPa, growth temperature 950 °C, grain size controlled at 20–50 μm. A gradual concentration transition section was set between each adjacent growth stage, with a transition time of 10 h and a methane concentration change rate of 0.2% / h. Argon gas was pulsed throughout the growth process at a flow rate of 200 cm³ / h. 3 / min, pulse period 30min, single argon gas introduction time 15min; the argon gas introduction momentarily increases the methane concentration to 8%, and after the pulse ends, the methane concentration drops back to the current stage baseline concentration.

[0045] S5. After the thin film growth is completed, in-situ stress control is performed by cooling to 800℃ in a hydrogen plasma atmosphere while maintaining a hydrogen flow rate of 300 cm³. 3 / min, chamber pressure 13.33kPa; nitrogen gas introduced 20cm 3 / min, argon gas 200cm 3 The temperature was maintained at 0.1℃ / min for 2 hours to achieve stress homogenization within the membrane layer; subsequently, the temperature was slowly lowered to room temperature at a rate of 0.1℃ / min, while maintaining a hydrogen flow rate of 200 cm³ / min throughout the cooling process. 3 / min.

[0046] S6. The composite substrate obtained in S5 is immersed in a mixed solution of hydrofluoric acid / nitric acid with a volume ratio of 3:1 and etched at room temperature for 60 min to remove the single crystal silicon substrate, thereby obtaining a self-supporting diamond film substrate. The diamond film substrate is then subjected to double-sided precision polishing, which is performed sequentially using a 20μm particle size diamond grinding wheel for rough polishing, a 3μm particle size diamond micro powder for medium polishing, and a 0.5μm particle size nano diamond for fine polishing. After polishing, the surface roughness Ra is 7nm and the film thickness is 500μm.

[0047] Example 3 S1. Select a 4-inch (100) crystal plane single crystal silicon substrate and perform chemical mechanical polishing on the single crystal silicon substrate to make the surface roughness Ra reach 0.5nm and the surface flatness reach 5μm.

[0048] S2. Ultrasonic-assisted nanodiamond powder seeding process: 5nm nanodiamond powder is dispersed in anhydrous ethanol at a concentration of 0.1g / L and ultrasonically dispersed for 30min; the S1-treated monocrystalline silicon substrate is immersed in the suspension and ultrasonically treated for 10min, allowing the nanodiamond powder to be uniformly adsorbed on the surface of the monocrystalline silicon substrate, achieving a substrate nucleation density of 1.0×10⁻⁶.9 cm -2 .

[0049] S3. Place the pretreated single-crystal silicon substrate from S2 into the reaction chamber of the MPCVD equipment, introduce methane and hydrogen, and use a variable-temperature nucleation process: first nucleate at 600℃ for 15 minutes, then raise the temperature to 800℃ at a rate of 5℃ / min and continue nucleation for 20 minutes to form a continuous and dense diamond nucleus layer on the surface of the single-crystal silicon substrate.

[0050] S4. After nucleation, a gradient methane flow rate process was used for diamond thick film growth: 0–50 h, methane concentration 3%, chamber pressure 10.66 kPa, growth temperature 800 °C, bottom grain size controlled at 1–3 μm; 50–150 h, methane concentration 4%, chamber pressure 13.33 kPa, growth temperature 850 °C, grain size controlled at 5–15 μm; 150–300 h, methane concentration 5%, chamber pressure 16.00 kPa, growth temperature 900 °C, grain size controlled at 20–50 μm. A gradual concentration transition section was set between each adjacent growth stage, with a transition time of 5 h and a methane concentration change rate of 0.1% / h. Argon gas was pulsed throughout the growth process at a flow rate of 50 cm³ / h. 3 / min, pulse period 10min, single argon gas introduction time 5min; the argon gas introduction momentarily increases the methane concentration to 6%, and after the pulse ends, the methane concentration drops back to the current stage baseline concentration.

[0051] S5. After the thin film growth is completed, in-situ stress control is performed by cooling to 700℃ in a hydrogen plasma atmosphere while maintaining a hydrogen flow rate of 200 cm³. 3 / min, chamber pressure 10.66kPa; nitrogen gas introduced 5cm 3 / min, argon gas 100cm 3 The temperature was maintained at 0.3℃ / min for 1 hour to achieve stress homogenization within the membrane layer; subsequently, the temperature was slowly lowered to room temperature at a rate of 0.3℃ / min, while maintaining a hydrogen flow rate of 100 cm³ / min throughout the cooling process. 3 / min.

[0052] S6. The composite substrate obtained in S5 is immersed in a mixed solution of hydrofluoric acid / nitric acid with a volume ratio of 3:1 and etched at room temperature for 30 min to remove the single crystal silicon substrate, thereby obtaining a self-supporting diamond film substrate. The diamond film substrate is then subjected to double-sided precision polishing, which is performed sequentially using a 15μm diamond grinding wheel for rough polishing, a 2μm diamond micro powder for medium polishing, and a 0.3μm nano diamond for fine polishing. After polishing, the surface roughness Ra is 8nm and the film thickness is 480μm.

[0053] The MPCVD heat sinks prepared in Examples 1-3 were tested below. The test results are shown in Table 1. The test methods are as follows: 1) The residual stress of the sample was non-destructively tested using X-ray diffraction (XRD); 2) The room temperature thermal conductivity of the sample was obtained by laser flare method (LFA): the average growth rate of the film was calculated from the total deposition thickness and the total growth time. The sample thickness uniformity and surface roughness were tested by full-area scanning with a white light interferometer.

[0054] Table 1 Test data for Examples 1-3 As shown in Table 1, the residual stress of the MPCVD heat sink sheet prepared by this invention is stably controlled within 63–68 MPa, significantly reducing the internal stress of the film layer. Simultaneously, the thickness uniformity of the finished product is controlled within ±3.6%, and the surface roughness and thermal conductivity of the samples from each embodiment show minimal differences and excellent overall consistency. This indicates that the MPCVD heat sink sheet prepared by this invention possesses both the advantages of low residual stress and high structural uniformity.

[0055] Comparative Example 1 The difference between this comparative example and Example 1 is that the three-stage temperature, pressure, and methane concentration gradient settings are cancelled, and there is no pulsed argon gas introduction throughout the process; the total growth time is 300 hours, the methane concentration is fixed at 5%, the growth temperature is 875℃, and the chamber pressure is 14.66 kPa throughout the process, and there is no concentration gradient transition section. All other process parameters and steps are completely consistent with Example 1.

[0056] Comparative Example 2 The difference between this comparative example and Example 1 is that the low-temperature insulation stress homogenization treatment and slow gradient cooling are omitted; after the film growth is completed, it is directly cooled naturally in the furnace at a cooling rate of 1.2℃ / min. All other process parameters and steps are completely consistent with Example 1.

[0057] The MPCVD heat sinks prepared in Comparative Examples 1-2 were tested below. The test results of Example 1 and Comparative Examples 1-2 are shown in Table 2: Table 2 Test data for Example 1 and Comparative Examples 1-2 As can be seen from Example 1, Comparative Examples 1-2 and Table 2, Comparative Example 1 cancels the three-stage temperature, pressure and methane concentration gradient settings and has no pulsed argon gas introduced throughout the process; the grain growth is disordered and there are many micro-defects, which ultimately manifests as increased residual stress, poor film thickness uniformity, large surface roughness, and low thermal conductivity and growth rate. Comparative Example 2 eliminated the high-temperature atmosphere heat preservation and homogenization process and the ultra-slow gradient cooling process, and formed the sample by natural rapid cooling. The residual stress, thickness uniformity and surface quality of the sample were significantly deteriorated.

Claims

1. A method for preparing a low-stress, high-uniformity MPCVD heat sink, characterized in that, Includes the following steps: S1. Place the pretreated single-crystal silicon substrate in the reaction chamber of the MPCVD equipment, introduce methane and hydrogen, first nucleate at 600-700℃ for 10-20 min, then raise the temperature to 800-900℃ to continue nucleation for 20-30 min, and obtain a diamond nucleus layer substrate on the surface of the single-crystal silicon substrate. S2. Diamond thin film is grown on a single crystal silicon substrate with a diamond nucleus layer using a gradient methane flow process. Argon gas is intermittently introduced during the film growth process to obtain a diamond thick film composite substrate. S3. After growth is completed, the temperature is lowered to 700-800℃ in a hydrogen plasma atmosphere, nitrogen and argon are introduced, and the temperature is maintained for 1-2 hours. Then, the temperature is lowered to room temperature at a rate of 0.1-0.3℃ / min to obtain diamond / silicon composite substrate. S4. The single-crystal silicon substrate in the diamond / silicon composite substrate is removed by chemical etching to obtain a diamond thin film substrate. The diamond thin film substrate is then subjected to double-sided precision polishing and shaping to obtain the MPCVD heat sink product.

2. The method for preparing a low-stress, high-uniformity MPCVD heat sink as described in claim 1, characterized in that, The preprocessing method in S1 includes: After chemical mechanical polishing of the monocrystalline silicon substrate, an ultrasonic-assisted nanodiamond powder seeding process is used to pretreat the polished monocrystalline silicon substrate to ensure that the diamond nucleation density on the surface of the monocrystalline silicon substrate is not less than 10. 9 cm -2 ; The ultrasonic-assisted nanodiamond powder seeding process specifically involves dispersing nanodiamond powder with a particle size of 5–10 nm in anhydrous ethanol at a concentration of 0.1–0.5 g / L to prepare a uniform nanodiamond suspension; then completely immersing a chemically and mechanically polished single-crystal silicon substrate in the nanodiamond suspension and ultrasonically treating it for 10–20 min.

3. The method for preparing a low-stress, high-uniformity MPCVD heat sink as described in claim 1, characterized in that, The heating rate in S1 is 5–10 °C / min.

4. The method for preparing a low-stress, high-uniformity MPCVD heat sink as described in claim 1, characterized in that, In S2, a gradient methane flow process is used to grow diamond thin films on a single-crystal silicon substrate with a diamond nucleus layer. The thin film growth process includes three growth stages, and a concentration gradient transition section is set between each adjacent growth stage. The methane concentration in the first growth stage is 3-4%, and the film growth time is 1-50 h; the methane concentration in the second growth stage is 4-5%, and the film growth time is 50-150 h; the methane concentration in the third growth stage is 5-6%, and the film growth time is 150-300 h.

5. The method for preparing a low-stress, high-uniformity MPCVD heat sink as described in claim 4, characterized in that, The duration of the concentration gradual transition period is 5–10 hours, and the methane concentration change rate is 0.1–0.2% per hour.

6. The method for preparing a low-stress, high-uniformity MPCVD heat sink as described in claim 4, characterized in that, The temperature for the first growth stage is 800–850℃, the temperature for the second growth stage is 850–900℃, and the temperature for the third growth stage is 900–950℃.

7. The method for preparing a low-stress, high-uniformity MPCVD heat sink as described in claim 1, characterized in that, In step S2, argon gas is intermittently introduced using a pulsed injection method, with a pulse period of 10–30 min, an argon gas injection time of 5–15 min, and a flow rate of 50–200 cm³. 3 / min.

8. The method for preparing a low-stress, high-uniformity MPCVD heat sink as described in claim 1, characterized in that, Nitrogen gas is introduced into S3 at a flow rate of 5-20 cm / s. 3 / min, argon gas flow rate 100-200 cm³ / min 3 / min.

9. The method for preparing a low-stress, high-uniformity MPCVD heat sink as described in claim 1, characterized in that, In step S3, when the temperature in the hydrogen plasma atmosphere is lowered to 700–800°C, the cooling rate is 0.1–0.3°C / min, and the hydrogen flow rate is maintained at 100–200 cm³ / min during the cooling process. 3 / min.

10. A low-stress, high-uniformity MPCVD heat sink, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 9.

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