A method for growing a low-warp polycrystalline diamond film layer using multi-stage size seed crystals

Abstract

The application discloses a method for growing a low-warp polycrystalline diamond film layer by using multi-stage size seed crystals, which comprises seed crystal pretreatment, heterogeneous substrate pretreatment, seed crystal coating, hydrogen plasma annealing for fixing seed crystals, gradient temperature rising nucleation stage, transition growth stage, film growth stage, gradient temperature reduction in-situ annealing, and obtaining a low-warp polycrystalline diamond film layer. The micron-level large seed crystals are matched with the nano-level small seed crystals in a multi-stage complex system, the large seed crystals serve as core nucleation sites to guide coarse grain growth, the number of coarse grain boundaries is small, and the intrinsic stress caused by grain refinement is greatly reduced from the source; the small seed crystals fill the blank gaps between the large seed crystals, ensure global uniform nucleation of the substrate, eliminate the defects of local exposure and stress concentration of a single micron seed crystal, solve the problems of uneven nucleation, many film layer defects, large internal stress and serious warp deformation in the prior art single seed crystal process, and realize stable preparation of a large-area, high-flatness, low-warp, high-crystallization-quality polycrystalline diamond film layer.

Description

Technical Field

[0001] This invention relates to the field of diamond preparation technology, and in particular to a method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals and the polycrystalline diamond films thereof. Background Technology

[0002] Polycrystalline diamond (PCD) films, due to their extremely high thermal conductivity (up to 2000 W / (m•K)), excellent chemical stability, wide spectral transmittance, and ultra-high hardness, have broad application prospects in fields such as thermal management heat sinks, optical windows, microwave devices, semiconductor substrates, and precision machining. Microwave plasma chemical vapor deposition (MPCVD) has the advantages of large deposition area, uniform plasma, and high diamond crystal quality, making it the mainstream process for the industrial production of large-size thick-film polycrystalline diamond films.

[0003] In the MPCVD growth of polycrystalline diamond, excessive film stress is a core bottleneck restricting the mass production of large-size, thick-film diamonds. Film stress is divided into two categories: intrinsic stress, caused by grain boundaries, lattice defects, and doping impurities; and thermal stress, caused by the difference in thermal expansion coefficients between diamond and substrate materials such as silicon, molybdenum, and tungsten, resulting in mismatched deformation during heating and cooling. As film thickness increases and substrate size enlarges, stress accumulates continuously, easily causing film warping, surface microcracks, overall film peeling, and even substrate fragmentation, significantly reducing yield.

[0004] In the MPCVD growth of polycrystalline diamond, diamond seed crystals are typically pre-placed on the substrate surface to induce nucleation and growth. Traditional methods usually use seed crystals of a single size, either entirely nanoscale (e.g., 50 nm, 100 nm) or entirely microscale (e.g., 2–4 μm). Studies have shown that using single-size nanoscale seed crystals results in extremely high nucleation density (up to 10⁻⁶). 8 ~10¹ 0 The number of grains per cm² leads to severe grain refinement, a surge in the number of grain boundaries, a significant increase in intrinsic stress, and severe film warping and deformation. In contrast, single micron-sized seed crystals have a low nucleation density, poor seed crystal distribution uniformity, and no seed crystals exposed in some areas of the substrate. This results in voids, localized stress concentrations, and poor film continuity after growth. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for growing low-warpage polycrystalline diamond films using multi-size seed crystals and the resulting polycrystalline diamond film. Through a stress control mechanism involving multi-size seed crystal synergistic nucleation, gradient temperature field growth, and in-situ annealing at reduced temperature, the grain structure and stress distribution of the film are optimized from the nucleation source, effectively reducing the growth stress and warpage deformation of the diamond film.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] On one hand, the present invention provides a method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals, comprising the following steps: S1, Seed Crystal Pretreatment Select at least two different sizes of single-crystal diamond seed crystals, including a first seed crystal and a second seed crystal; the first seed crystal has a particle size of 1 to 500 μm, and the second seed crystal has a particle size of 10 to 1000 nm; After acid washing, water washing, and drying, the first and second seed crystals were subjected to surface smoothing treatment. After the treatment, the two types of seed crystals were dispersed in a mixed solution of DMSO, isopropanol, and acetone (volume ratio 5:3:2) and ultrasonically dispersed to prepare first and second seed crystal suspensions with concentrations of 0.1–5 mg / mL.

[0008] The seed crystal pickling and surface leveling processes are as follows: The acid solution is a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1, and the water bath temperature is controlled at 60-80 ℃. Micron-sized seed crystals are immersed in aqua regia at a constant temperature for 30–60 minutes with intermittent slight stirring to dissolve surface metal abrasives, nickel-iron catalyst residues, surface graphite, and amorphous carbon. The nano-seed crystals were immersed in aqua regia at 60 ℃ for 10-15 minutes to shorten the acid washing time and avoid excessive etching of the nano-seed crystals, which would lead to size decay. After pickling, first soak in 5% dilute ammonia water for 5 minutes to neutralize the residual strong acid, then use deionized water for ultrasonic rinsing 3 times, 10 minutes each time, until the pH value of the rinsing water is neutral. Then, dry at 60 ℃ for 60 min; The specific process for surface planarization of the first seed crystal (1-500 μm) is as follows: The cleaned first seed crystal is placed in an MPCVD chamber, a vacuum is drawn, hydrogen gas is introduced, and microwaves are activated to form hydrogen plasma. The seed crystal surface is etched for 0.5-3 hours under conditions of 90-400 Torr pressure and 800-900℃ temperature. This effectively eliminates surface defects introduced during the seed crystal preparation process. The specific process for surface planarization of the second seed crystal (10-1000 nm) is as follows: The cleaned second seed crystal is placed in the MPCVD chamber, a vacuum is drawn, hydrogen gas is introduced, and microwaves are turned on to form hydrogen plasma. The surface of the seed crystal is etched for 0.1-0.5 hours under the conditions of pressure 90-400 Torr and temperature 650-700℃.

[0009] S2, Substrate Pretreatment Silicon, silicon carbide, gallium nitride, molybdenum, or tungsten are selected as heterogeneous substrates. They are then subjected to mechanical polishing, ultrasonic degreasing with organic solvents, and acid etching to remove the surface oxide layer. The cleaned substrates are then sent into the MPCVD chamber and subjected to in-situ plasma cleaning at 700–850°C for 10–30 min in a hydrogen plasma atmosphere to remove residual impurities on the substrate surface, ensuring the cleanliness and flatness of the substrate surface and providing a good substrate for seed crystal adhesion and film growth.

[0010] S3, multi-level seed crystal layered coating The first seed crystal suspension was spin-coated onto the surface of the heterogeneous substrate using a spin coater at a speed of 500–3000 r / min for 100–500 s. After coating, the substrate was dried at a constant temperature of 80–120℃ for 20–40 min, controlling the areal density of the first seed crystal on the heterogeneous substrate surface to be 10³–10⁻⁶. 5 pcs / cm²; The second seed crystal suspension is then spin-coated onto the surface of the heterogeneous substrate at a speed of 300–2000 r / min for 100–500 s. After coating, the substrate is dried at a constant temperature of 90–130℃ for 20–40 min, controlling the areal density of the first seed crystal on the heterogeneous substrate surface to be 10. 6 ~10 9 pcs / cm²

[0011] By arranging large and small seed crystals in a layered composite manner, the large seed crystals serve as a framework support, while the small seed crystals fill the gaps, achieving full coverage and gapless arrangement of seed crystals on the substrate surface, thus balancing nucleation uniformity and film structure stability.

[0012] S4, hydrogen plasma annealing to fix the seed crystal The heterogeneous substrate coated with multi-level seed crystals is placed in the MPCVD reaction chamber, and hydrogen gas of 300-3000 sccm is introduced. The chamber pressure is 80-120 Torr, the temperature is 700-850℃, and plasma annealing is performed for 20-40 min.

[0013] The plasma activation process enhances the adsorption and bonding force between the seed crystal and the substrate, enabling multi-level seed crystals to firmly adhere to the surface of the heterogeneous substrate. This effectively prevents the seed crystals from falling off or shifting during subsequent high-temperature growth, ensuring nucleation stability.

[0014] S5, Gradient heating nucleation stage The temperature is increased to 300–500℃ at a rate of 3–10℃ / min and held for 10–30 min. Then, the temperature is increased to 600–750℃ at a rate of 1–5℃ / min and held for 10–20 min. Finally, the temperature is slowly increased to 800–900℃ at a rate of 1–5℃ / min. A mixed reaction gas CH4 / H2 is introduced, with a hydrogen flow rate of 300–3000 sccm and a methane volume percentage of 4%–6%. The chamber pressure is adjusted to 8–200 Torr and the microwave power to 3–50 kW. Nucleation is continued for 0.5–2 h to grow a diamond nucleation layer on the surface of the heterogeneous substrate.

[0015] The gradient heating mode can avoid seed crystal thermal damage and initial stress concentration caused by rapid heating, ensuring a dense and uniform nucleation layer.

[0016] S6, Transitional Growth Stage Keeping the hydrogen flow rate constant, the volume percentage of methane in the mixed reaction gas is adjusted to 1%–3%, the temperature of the heterostructure substrate is raised to 880–920℃, and growth continues for 0.5–2 h to achieve a smooth transition from fine crystal nuclei to continuous diamond films.

[0017] By reducing the carbon source concentration and slightly increasing the growth temperature, the optimal growth of fine crystal nuclei and grain fusion are achieved, eliminating micro-voids and defects in the nucleation layer, realizing a smooth transition from fine crystal nuclei to continuous and dense diamond films, and alleviating the initial stress accumulation of the film layer.

[0018] S7, Film-forming growth stage Adjust the microwave power to 5–100 kW, the chamber pressure to 10–375 Torr, and the heterostructure substrate temperature to 850–950 °C. Continuously introduce a mixed reactive gas and introduce a trace amount of nitrogen or oxygen as an auxiliary gas into the hydrogen carrier gas. The auxiliary gas flow rate is 30–80 ppm to help refine the grains, optimize the film crystal orientation, and improve film uniformity. After continuous growth for 20–50 hours, microwave treatment is paused, carbon source and auxiliary gas are turned off, and the film is cooled to room temperature and held for 10–30 minutes to perform a staged intermediate stress release, releasing the thermal and lattice stress accumulated during film growth. After stress release, film growth parameters are restored and deposition continues, repeating the above growth-stress release steps until the polycrystalline diamond film reaches the target thickness, completing film preparation. The segmented growth and segmented stress release mode can effectively avoid stress superposition caused by long-term continuous growth and significantly reduce the warping tendency of the film. S8, Gradient cooling in-situ annealing for stress relief After the film growth is completed, turn off the microwave and stop the flow of reaction gas. Keep the hydrogen flow rate constant and slowly cool down to 600-700℃ at a rate of 1-5℃ / min. Hold at this temperature for 30-120 min for in-situ hydrogen annealing. Then, the temperature is reduced to 300-400℃ at a rate of 3-10℃ / min, and then allowed to cool naturally to room temperature. After depressurization, a low-warpage polycrystalline diamond film is obtained.

[0019] Gradient cooling combined with high-temperature in-situ annealing can completely relieve residual stress in the film layer and prevent stress mutations and film warping and cracking caused by excessively rapid cooling.

[0020] Furthermore, the particle size ratio of the first seed crystal to the second seed crystal is 10:1 to 10000:1.

[0021] Furthermore, the areal density ratio of the first seed crystal to the second seed crystal is 1:10 to 1:10000.

[0022] On the other hand, the present invention provides a polycrystalline diamond film layer, which is prepared by the above-described method of growing a low-warpage polycrystalline diamond film layer using multi-level size seed crystals.

[0023] The beneficial effects of this invention are: This invention employs a multi-level composite system combining micron-sized large seed crystals with nano-sized small seed crystals. The first seed crystal acts as the core nucleation site, guiding the growth of coarse grains. The reduced number of coarse grain boundaries significantly reduces the intrinsic stress caused by grain refinement from the source. The nano-sized seed crystals fill the gaps between the large seed crystals, ensuring uniform nucleation across the entire substrate and eliminating defects such as localized exposure and stress concentration caused by a single micron-sized seed crystal. The synergistic effect of the coarse-fine composite grain structure results in reduced warpage and the absence of microcracks and film peeling compared to traditional single nano-seed crystal processes.

[0024] This invention controls the distribution of coarse-grained and fine-grained regions within the film by adjusting the surface density and size ratio of two-stage seed crystals. The coarse-grained region reduces the difference in crystal growth scale, while the fine-grained region buffers and disperses local stress, preventing stress accumulation in local areas and achieving uniform stress distribution throughout the entire region. This simultaneously solves the defects of stress concentration and uniform grain size in traditional single-seed crystal processes.

[0025] This invention utilizes a first seed crystal uniform array to form a stable nucleation framework, with high-density nano-seed crystals filling the gaps. Macroscopically, the entire substrate has no blank areas, and microscopically, the gaps between grains are completely filled. The film density and thickness uniformity are significantly superior to single-seed crystal processes, making it suitable for the mass production needs of large-size wafers. During the film formation stage, this invention employs periodic intermediate shutdowns to release stress, gradient cooling combined with long-term in-situ annealing at medium temperature. This process releases accumulated thermal and growth stresses step-by-step, resolving the warping problem caused by the mismatch in thermal expansion between diamond and the substrate. Attached Figure Description

[0026] Figure 1 is a schematic diagram of the fracture morphology of diamond film grown by a single nano-seed crystal in Comparative Example 1. Figure 2 is a schematic diagram of the fracture morphology of the diamond film layer grown by multi-stage seed crystal in Embodiment 1 of the present invention; Detailed Implementation To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0027] This embodiment describes a method for growing low-warpage polycrystalline diamond films using seed crystals of various sizes, comprising the following steps: S1, Seed crystal pretreatment: Single-crystal diamond seed crystals with a particle size of 40μm and 200μm (mass ratio 2:1) (first seed crystal), and single-crystal diamond seed crystals with a particle size of 100nm (second seed crystal) were selected. Aqua regia with a volume ratio of 3:1 was used in a 70°C water bath. The first seed crystal was soaked for 45 minutes, and the second seed crystal was soaked for 12 minutes at 60°C. After acid washing, the crystal was neutralized by soaking in 5% dilute ammonia water for 5 minutes, ultrasonically rinsed with deionized water 3 times for 10 minutes each time, and dried at 60°C for 60 minutes.

[0028] The specific process for the first seed crystal surface planarization treatment is as follows: The cleaned seed crystal is placed in the MPCVD chamber, a vacuum is drawn, hydrogen gas is introduced, and microwaves are turned on to form hydrogen plasma. The seed crystal surface is etched for 0.5 hours under conditions of 120 Torr pressure and 800℃ temperature. This effectively eliminates surface defects introduced during the seed crystal preparation process.

[0029] The specific process for the second seed crystal surface planarization treatment is as follows: The cleaned seed crystal is placed in the MPCVD chamber, a vacuum is drawn, hydrogen gas is introduced, and microwaves are turned on to form hydrogen plasma. The seed crystal surface is etched for 0.5 hours under the conditions of 100 Torr pressure and 650℃ temperature.

[0030] Two types of seed crystals were dispersed in a mixed solution of DMSO, isopropanol, and acetone in a volume ratio of 5:3:2, respectively, and ultrasonically dispersed to prepare a first seed crystal suspension with a concentration of 1 mg / mL and a second seed crystal suspension with a concentration of 1 mg / mL.

[0031] S2, Substrate pretreatment: A 4-inch single-crystal silicon substrate was selected, and after mechanical polishing, ultrasonic degreasing with ethanol, and acid etching with dilute hydrochloric acid to remove the oxide layer, it was sent into the MPCVD chamber and cleaned in situ with hydrogen plasma at 800℃ for 20 minutes.

[0032] S3, multi-level seed crystal layered coating: First, a seed crystal suspension is spin-coated onto the silicon substrate at a speed of 1500 r / min for 3 s, followed by drying at 100℃ for 30 min, with the areal density controlled at 10. 4 Seed crystals / cm²; then spin-coat the second seed crystal suspension at 1000 r / min for 5 s, dry at 110℃ for 30 min, controlling the areal density to 10. 7 pcs / cm²

[0033] S4, hydrogen plasma annealing to fix the seed crystal: The heterostructure with multi-level seed crystals coated is placed in the MPCVD reaction chamber, and hydrogen gas of 2000 sccm is introduced. The chamber pressure is 100 Torr, the temperature is 800℃, and plasma annealing is performed for 30 min to fix the seed crystals.

[0034] S5, Gradient heating nucleation: After hydrogen plasma annealing, the temperature was increased to 400℃ at 5℃ / min and held for 20 min, then increased to 750℃ at 3℃ / min and held for 15 min, and finally increased to 850℃ at 3℃ / min. A mixed reaction gas CH4 / H2 was introduced, containing 2000 sccm of hydrogen and 5% methane by volume, with a cavity pressure of 112.5 Torr and a microwave power of 10 kW, and nucleation was continued for 2 h.

[0035] S6, Transitional Growth: Keeping the hydrogen flow rate constant, the methane volume percentage was adjusted to 2%, the substrate temperature was raised to 900℃, and growth was carried out for 1 hour.

[0036] S7, Film formation and growth: Adjust the microwave power to 30kW, the cavity pressure to 225Torr, and the substrate temperature to 920℃. Keep the hydrogen and methane flow rates constant and introduce 50ppm nitrogen to assist growth. After continuous growth for 30h, stop the microwave, turn off the carbon source and auxiliary gas, cool down to room temperature and hold for 20min to release stress, then reheat and continue growth for 30h. Repeat this step twice to complete the deposition of polycrystalline diamond film.

[0037] S8, Gradient cooling annealing: After the film growth is completed, the microwave is turned off and the reaction gas is stopped. The hydrogen flow rate is kept constant, and the temperature is lowered to 650°C at 2°C / min. The temperature is held for 60 min for in-situ annealing, and then the temperature is lowered to 350°C at 5°C / min. After that, the temperature is allowed to cool naturally to room temperature, and the material is discharged after depressurization to obtain a low-warpage polycrystalline diamond film.

[0038] Example 2 This embodiment describes a method for growing low-warpage polycrystalline diamond films using seed crystals of various sizes, which differs from Embodiment 1 in that: A first seed crystal with a particle size of 50 μm and a second seed crystal with a particle size of 100 nm were selected. The density of the first seed crystal was 10. 4 The surface density of the second seed crystal is 10 per cm². 7 The number of pieces per cm² is the same as in Example 1.

[0039] Comparative Example 1 This embodiment describes a method for growing low-warpage polycrystalline diamond films using seed crystals of various sizes, which differs from Embodiment 1 in that: Single-crystal diamond seed crystals with particle sizes of 20nm and 50nm were selected, with a mass ratio of 2:1. The remaining process steps were the same as in Example 1.

[0040] The warpage, surface roughness, and defect rate of the diamond films prepared in Examples 1, 2, and the comparative examples were tested, and the results are as follows: 1. Comparative film: warpage 180~220μm / 100mm, surface roughness Ra≥300nm, film void and microcrack defect rate 8.2%; 2. Film layer of Example 1: warpage 21-35 μm / 100 mm, surface roughness Ra ≤ 100 nm, defect rate 0.3%; 3. Film layer of Example 2: warpage 18~32μm / 100mm, surface roughness Ra≤80nm, defect rate 0.25%.

[0041] Test results show that the multi-stage seed crystal growth process of this invention can significantly reduce the warpage of diamond films, significantly optimize the flatness of the films, reduce the defect rate, and produce films of far superior quality to those produced by the traditional single seed crystal process.

[0042] Based on the disclosure in the foregoing specification, those skilled in the art can make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals, characterized in that: Includes the following steps: S1, Seed Crystal Pretreatment Select single-crystal diamond seed crystals of different sizes, wherein the single-crystal diamond seed crystals include at least a first seed crystal and a second seed crystal, wherein the particle size of the first seed crystal is 1 to 500 μm and the particle size of the second seed crystal is 10 to 1000 nm; The first and second seed crystals were respectively subjected to acid washing, water washing and surface leveling treatment; The processed first and second seed crystals were dispersed in organic solvents to obtain first seed crystal suspension and second seed crystal suspension, respectively. S2, Heterogeneous substrate pretreatment The heterogeneous substrate was sequentially polished, degreased, acid-etched, and cleaned with hydrogen plasma for 10–30 min. S3, Coated Seed Crystal The first seed crystal suspension and the second seed crystal suspension were sequentially coated onto the surface of the heterogeneous substrate, and the areal density of the first seed crystal on the surface of the heterogeneous substrate was controlled to be 10³~10. 5 The number of crystal faces per cm² is 10, and the crystal density of the second seed crystal is 10. 6 ~10 9 pcs / cm²; S4, hydrogen plasma annealing to fix the seed crystal The heterostructure with multi-level seed crystals coated is placed in the MPCVD reaction chamber, and 300-3000 sccm of hydrogen gas is introduced. The chamber pressure is 80-120 Torr, the temperature is 700-850℃, and plasma annealing is performed for 20-40 min. S5, Gradient heating nucleation stage The temperature is increased to 300–500℃ at a rate of 3–10℃ / min and held for 10–30 min. Then, the temperature is increased to 600–750℃ at a rate of 1–5℃ / min and held for 10–20 min. Finally, the temperature is slowly increased to 800–900℃ at a rate of 1–5℃ / min. A mixed reaction gas CH4 / H2 is introduced, with a hydrogen flow rate of 300–3000 sccm and a methane volume percentage of 4%–6%. The chamber pressure is adjusted to 8–200 Torr and the microwave power to 3–50 kW. Nucleation is continued for 0.5–2 h to grow a diamond nucleation layer on the surface of the heterogeneous substrate. S6, Transitional Growth Stage Keeping the hydrogen flow rate constant, the volume percentage of methane in the mixed reaction gas was adjusted to 1%–3%, the temperature of the heterostructure substrate was raised to 880–920℃, and growth continued for 0.5–2 h. S7, Film-forming growth stage Adjust the chamber pressure to 10–375 Torr, microwave power to 5–100 kW, and heterostructure substrate temperature to 850–950 °C. Continuously introduce mixed reaction gas and introduce auxiliary gas into the hydrogen carrier gas at a flow rate of 30–80 ppm. After continuous growth for 20–50 h, microwave treatment is paused, carbon source and auxiliary gas are turned off, and the temperature is lowered to room temperature and held for 10–30 min to release intermediate stress. After stress release is completed, film growth parameters are restored and deposition continues. Repeat step S7 until the polycrystalline diamond film growth is complete; S8, Gradient cooling in-situ annealing After film growth is complete, turn off the microwave and stop the flow of reaction gas. Keep the hydrogen flow rate constant and slowly cool down to 600-700℃ at a rate of 1-5℃ / min. Hold at this temperature for 30-120 min for in-situ hydrogen annealing. Then, the temperature is reduced to 300-400℃ at a rate of 3-10℃ / min, and then allowed to cool naturally to room temperature. After depressurization, a low-warpage polycrystalline diamond film is obtained.

2. The method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals according to claim 1, characterized in that: The particle size ratio of the first seed crystal to the second seed crystal is 10:1 to 10000:

1.

3. The method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals according to claim 1, characterized in that: The areal density ratio of the first seed crystal to the second seed crystal is 1:10 to 1:10000.

4. The method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals according to claim 1, characterized in that: The heterogeneous substrate is one of silicon substrate, silicon carbide substrate, gallium nitride substrate, molybdenum substrate, and tungsten substrate.

5. The method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals according to claim 1, characterized in that: In step S1, the organic solvent is a mixed solution of DMSO, isopropanol, and acetone in a volume ratio of 5:3:

2.

6. The method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals according to claim 1, characterized in that: In step S1, the concentration of seed crystals in both the first seed crystal suspension and the second seed crystal suspension is 0.1–5 mg / mL.

7. The method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals according to claim 1, characterized in that: The heterogeneous substrate pretreatment in step S2 specifically includes: The heterogeneous substrate was sequentially subjected to mechanical polishing, ultrasonic degreasing with organic solvents, and acid etching to remove the surface oxide layer. The heterogeneous substrate is then placed into the MPCVD chamber and subjected to in-situ plasma cleaning at 700–850°C for 10–30 min in a hydrogen plasma atmosphere.

8. The method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals according to claim 1, characterized in that: The seed crystal coating in step S3 specifically involves: The first seed crystal suspension was spin-coated onto the surface of the heterogeneous substrate using a spin coater at a speed of 500–3000 r / min for 100–500 s. After coating, the substrate was dried at a constant temperature of 80–120℃ for 20–40 min, controlling the areal density of the first seed crystal on the heterogeneous substrate surface to be 10³–10⁻⁶. 5 pcs / cm²; The second seed crystal suspension is then spin-coated onto the surface of the heterogeneous substrate at a speed of 300–2000 r / min for 100–500 s. After coating, the substrate is dried at a constant temperature of 90–130℃ for 20–40 min, controlling the areal density of the first seed crystal on the heterogeneous substrate surface to be 10. 6 ~10 9 pcs / cm² 9. The method for growing low-warpage polycrystalline diamond films using multi-level size seed crystals according to claim 1, characterized in that: In step S7, the auxiliary gas is nitrogen or oxygen.

10. A polycrystalline diamond film, characterized in that: It is prepared by the method described in any one of claims 1 to 9, which uses multi-level size seed crystals to grow low-warpage polycrystalline diamond films.

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