Preparation method of high-quality self-supporting polycrystalline diamond substrate

Abstract

The invention discloses a preparation method of a high-quality self-supporting polycrystalline diamond substrate. The preparation method comprises the following steps: obtaining a larger first substrate and a smaller second substrate; the molybdenum substrate is a polished molybdenum metal substrate; sowing diamond seed crystals on the first substrate by using an ultrasonic sowing method, and growing a nanocrystalline diamond epitaxial layer by using a CVD (Chemical Vapor Deposition) process; cutting the first substrate by using precise laser to obtain an annular polycrystalline diamond solid seed crystal of which the inner diameter is greater than that of the second substrate; placing a second substrate in the inner diameter of the second substrate, guiding generated tiny diamond grains to the second substrate through a boundary induction mechanism and applying direct current bias voltage, and uniformly wrapping the tiny diamond grains to form a self-supporting polycrystalline diamond substrate; according to the preparation method of the self-supporting polycrystalline diamond substrate, the orientation consistency and the crystallization quality of a diamond film are remarkably improved, and the prepared self-supporting polycrystalline diamond substrate has the advantages of being low in surface roughness, compact in structure, simplified in follow-up process and the like.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a method for preparing a high-quality self-supporting polycrystalline diamond substrate. Background Technology

[0002] As electronic devices continue to evolve towards higher power, higher frequency, and higher integration, thermal management has become an increasingly important factor restricting their performance and reliability. Polycrystalline diamond, due to its extremely high thermal conductivity (1000–2200 W / m·K), excellent mechanical strength, good electrical insulation, and outstanding chemical stability, is considered a highly promising heat sink material for next-generation high-power electronic and optoelectronic devices. Its coefficient of thermal expansion (approximately 1.5) Polycrystalline diamond (PCD) is similar to wide-bandgap semiconductor materials such as GaN and SiC, effectively reducing interface cracking or device failure caused by thermal stress. Due to its robust sp³ hybrid lattice structure, PCD allows phonons to propagate quickly and has a long mean free path, significantly improving thermal conductivity. Its thermal conductivity is more than 5 times that of copper and 20 times that of silicon, far exceeding that of commonly used heat sink materials. Furthermore, its high resistivity and breakdown field strength (>10 MV / cm) give it both thermal conductivity and electrical insulation properties, making it particularly suitable as an insulating heat sink in power modules.

[0003] In practical applications, polycrystalline diamond wafers have been widely used in high-power GaN HEMTs, SiC MOSFETs, and other wide-bandgap devices as substrates or heat diffusion layers, effectively improving device operating frequency and power density. In high-frequency RF amplifiers for 5G communication base stations and radar, the use of diamond heat sinks can increase device output power by 30% and reduce junction temperature by more than 15°C. In the fields of high-brightness LEDs and lasers, diamond serves as both a heat sink and an optical window material. Its high transmittance from ultraviolet to infrared allows it to maintain light extraction efficiency while conducting heat, making it suitable for heat dissipation and packaging of high-power laser chips. In summary, due to its excellent thermal properties and structural stability, polycrystalline diamond is gradually becoming a core material for thermal management of next-generation high-power electronic devices. With continuous breakthroughs in key technologies such as cost control, large-size fabrication, and interface engineering, its application prospects in RF devices, power electronics, and laser systems are very broad.

[0004] Despite the significant performance advantages of polycrystalline diamond, its extremely high hardness and excellent mechanical rigidity make it prone to brittle fracture during micro- and nano-fabrication processes. It is susceptible to crack initiation and propagation under mechanical or thermal stress. Therefore, polycrystalline diamond is extremely prone to breakage during polishing and integration with other materials, which not only affects the yield of the target product but also significantly increases the application cost. Experiments have shown that when polycrystalline diamond is grown on a molybdenum metal substrate, it can detach completely from the substrate during the cooling phase of the growth process, with the detached surface roughness remaining essentially consistent with that of the substrate. Traditional polycrystalline diamond growth typically uses seed crystals with diameters ranging from 7-50 nm. This results in a high initial roughness for polycrystalline diamond grown using conventional seeding methods, necessitating subsequent grinding and polishing processes, which significantly increases the application cost. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a method for preparing high-quality self-supporting polycrystalline diamond substrates. The technical problem to be solved by this invention is achieved through the following technical solution: A method for preparing a high-quality self-supporting polycrystalline diamond substrate, comprising: Obtain a first substrate and a second substrate; wherein the size of the first substrate is larger than the size of the second substrate, and the second substrate is a polished molybdenum metal substrate; Diamond seeds were seeded on the first substrate using an ultrasonic seeding method, and then a nanocrystalline diamond epitaxial layer was grown using a CVD process. A ring-shaped polycrystalline diamond solid seed crystal with an inner diameter larger than that of the second substrate was obtained by using precision laser cutting to grow a first substrate with a nanocrystalline diamond epitaxial layer. The second substrate is placed in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal. Through the boundary induction mechanism and the application of DC bias, the tiny diamond grains generated by the previous plasma etching of the ring-shaped polycrystalline diamond solid seed crystal are guided to the second substrate and uniformly wrapped on the second substrate, thereby growing a self-supporting polycrystalline diamond substrate on the second substrate. The surface of the self-supporting polycrystalline diamond substrate is subjected to hydrogen plasma etching to remove amorphous carbon and graphite phases, thereby obtaining the final polycrystalline diamond substrate.

[0006] In one embodiment of the present invention, the material of the first substrate includes, but is not limited to, silicon, graphite, molybdenum, and gallium nitride.

[0007] In one embodiment of the present invention, the first substrate is a silicon substrate with (111) crystal orientation.

[0008] In one embodiment of the present invention, the first substrate has a size of 3-6 inches, a roughness Ra1≤1μm, and a thickness of 1-7mm.

[0009] In one embodiment of the present invention, the second substrate has a size of 1-5 inches, a roughness Ra2≤1nm, and a thickness of 1-7mm.

[0010] In one embodiment of the present invention, the step of seeding diamond crystals on the first substrate using an ultrasonic seeding method, and then growing a nanocrystalline diamond epitaxial layer using a CVD process, includes: The first substrate is ultrasonically seeded using a diamond powder solution with diamond particles of 3-50 nm in size as the seed solution. The ultrasonic time is 10-30 min. Then the first substrate is placed on a heating table and heated to dry at a temperature of 50-70 °C. The first substrate with seed crystals spin-coated is placed into the MPCVD equipment, and the chamber pressure is evacuated to 0.001 mbar or below. Injecting into the MPCVD equipment , The flow rate is 100-800 sccm; When the cavity pressure reaches 15-20 Torr, turn on the microwave source to raise the cavity pressure to 120-200 Torr, with a power of 3000-5000W and a first substrate surface temperature of 800-1000℃. Injecting into the MPCVD equipment , and The growth process of nanocrystalline diamond was then initiated. The flow rate is 8-80 sccm. The flow rate is 0.1-0.8 sccm. The flow rate was 0-2 sccm, the growth rate was maintained at 10-20 μm / h, and the growth time was 15-20h; Stop feeding after growth is complete. , and Slowly reduce the cavity pressure and power to prevent the solid crystal seed nanocrystalline diamond from cracking due to thermal stress. Pump the cavity pressure to 20 Torr and reduce the power to 600W. Once the cavity temperature stabilizes, turn off the microwave source and stop the flow of electricity. The chamber pressure was reduced to 0.001 mbar, and the pump was turned off. Air was introduced into the chamber to break the vacuum, and the first substrate with the nanocrystalline diamond epitaxial layer was removed from the chamber.

[0011] In one embodiment of the present invention, the second substrate is placed within the inner diameter of the annular polycrystalline diamond seed crystal. Through a boundary induction mechanism and by applying a DC bias, the extremely small diamond grains generated by the previous plasma etching of the annular polycrystalline diamond seed crystal are guided to the second substrate and uniformly encapsulated thereon, thereby growing a self-supporting polycrystalline diamond substrate on the second substrate. This includes: The second substrate is placed in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal, and together they are placed into the MPCVD equipment, and the chamber pressure is evacuated to 0.001 mbar or below. Injecting into the MPCVD equipment , The flow rate is 100-800 sccm; When the cavity pressure reaches 15-20 Torr, the microwave source is turned on to raise the cavity pressure to 120-200 Torr, with a power of 3000-5000W. The surface temperature of the second substrate is 800-1000℃. A DC bias of 0.5-2 kW is applied under the second substrate to guide the extremely small diamond grains generated by plasma etching of the ring-shaped polycrystalline diamond solid seed crystals to the second substrate and uniformly coat the second substrate. Injecting into the MPCVD equipment , and They began the growth process of self-supporting polycrystalline diamond. The flow rate is 8-80 sccm. The flow rate is 0.01-0.5 sccm. The flow rate is 0-2 sccm; the growth rate is maintained at 4-8 μm / h, the growth time is 75-100h, and the thickness of the polycrystalline diamond layer is guaranteed to be ≥150μm to achieve self-support of the polycrystalline diamond layer. Stop feeding after growth is complete. , and Slowly reduce the cavity pressure and power to prevent the polycrystalline diamond from cracking due to thermal stress; evacuate the cavity pressure to 20 Torr and reduce the power to 600W. Once the cavity temperature stabilizes, turn off the microwave source; stop the flow of microwaves. The chamber pressure was reduced to 0.001 mbar, and the pump was turned off. Air was introduced into the chamber to break the vacuum, and the second substrate, the obtained self-supporting polycrystalline diamond substrate, and the ring-shaped polycrystalline diamond solid seed crystal were removed from the chamber.

[0012] In one embodiment of the present invention, the surface of the self-supporting polycrystalline diamond substrate is subjected to hydrogen plasma etching to remove amorphous carbon and graphite phases, thereby obtaining the final polycrystalline diamond substrate, including: The self-supporting polycrystalline diamond substrate is placed face up in an MPCVD device and etched for 10-20 minutes at 200-400°C in a hydrogen plasma atmosphere to remove amorphous carbon and graphite phases from the grown self-supporting polycrystalline diamond substrate, resulting in a polycrystalline diamond substrate with a surface roughness ≤3 nm on one side.

[0013] The method for preparing a high-quality self-supporting polycrystalline diamond substrate provided in this invention is the first to propose a method for growing polycrystalline diamond using solid seed crystals, combined with a molybdenum metal self-exfoliation polycrystalline diamond growth process, to achieve a self-supporting high-quality polycrystalline diamond substrate with low surface roughness on one side. Specifically, it has the following beneficial effects: 1. Solid-state seed crystals—micro-sized diamond particles induced growth. For the first time, nanocrystalline diamond fragments prepared by hydrogen plasma etching are proposed as solid-state seed crystals, with particle sizes much smaller than those of traditional artificial seeding powders. Combined with a high-precision polished molybdenum substrate, extremely low roughness (Rq≤3 nm) is achieved at the interface between the seed crystal and the molybdenum metal substrate, effectively improving the uniformity and nucleation density of the crystal nuclei, ultimately obtaining high-crystal quality, easily machinable self-supporting polycrystalline diamond.

[0014] 2. Direct supply of finished products with ultra-low single-sided roughness. Through optimization of hydrogen plasma deep etching, the self-supporting polycrystalline diamond prepared can achieve a single-sided roughness at the nanometer level. It can be used directly for device manufacturing or scientific research testing without the need for traditional grinding and polishing processes, which greatly improves R&D efficiency and lowers the threshold for material application.

[0015] 3. It possesses both high yield and low cost, making it a promising industrialization prospect. The overall preparation method eliminates the need for complex substrate separation and mechanical polishing, omitting multiple intermediate steps. It boasts advantages such as strong process controllability, good repeatability, and easy capacity scaling, which significantly promotes the large-scale application of polycrystalline diamond in electronic device substrates and functional materials. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a method for preparing a high-quality self-supporting polycrystalline diamond substrate provided in an embodiment of the present invention; Figures 2 to 4 This is a schematic diagram of the process flow for growing a nanocrystalline diamond epitaxial layer on a first substrate according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the preparation of ring-shaped polycrystalline diamond solid seed crystals using a first substrate with a nanocrystalline diamond epitaxial layer in an embodiment of the present invention; Figures 6 to 7 This is a schematic diagram of the process flow for preparing high-quality self-supporting polycrystalline diamond substrates according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the final polycrystalline diamond substrate obtained in an embodiment of the present invention; Figure 9This is a physical image of a high-quality self-supporting polycrystalline diamond substrate with low single-sided roughness prepared according to an embodiment of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0018] Addressing the problems existing in the prior art, this invention proposes a method for preparing high-quality, self-supporting polycrystalline diamond substrates based on solid seed engineering, focusing on optimizing polycrystalline diamond growth seed crystals. This method achieves extremely low surface roughness (≤3nm) on the polycrystalline diamond substrate, allowing for the skipping of some grinding and polishing processes and direct use in subsequent polycrystalline diamond experiments. This reduces the defect rate of polycrystalline diamond due to subsequent processing steps, significantly lowering the application cost of polycrystalline diamond materials. Specific embodiments are given below.

[0019] Example 1 This invention provides a method for preparing a high-quality self-supporting polycrystalline diamond substrate, such as... Figure 1 As shown, the method may include the following steps: S1, Obtain the first substrate and the second substrate; The first substrate and the second substrate are used to grow polycrystalline diamond. The first substrate is larger than the second substrate, and the second substrate is a polished molybdenum metal substrate. In this embodiment of the invention, the first substrate is used to prepare polycrystalline diamond solid seed crystals, and the material of the first substrate includes, but is not limited to, silicon, graphite, molybdenum, and gallium nitride.

[0020] For example, one possible implementation method is: The first substrate is a silicon substrate with (111) crystal orientation.

[0021] The first substrate and the second substrate may be circular, with the diameter representing the size of the circle.

[0022] Regarding the dimensions and other related parameters, one possible implementation method is... The first substrate has a size of 3-6 inches, a roughness Ra1 ≤ 1 μm, and a thickness of 1-7 mm. The second substrate has a size of 1-5 inches, a roughness Ra2 ≤ 1 nm, and a thickness of 1-7 mm.

[0023] S2, diamond seeds are seeded on the first substrate using ultrasonic seeding, and then a nanocrystalline diamond epitaxial layer is grown using CVD (Chemical Vapor Deposition) process. In one optional implementation, S2 may include the following steps: S21, ultrasonic seeding is performed on the first substrate, using a diamond powder solution with diamond particle size of 3-50nm as the seed seeding solution, the ultrasonic time is 10-30min, and then the first substrate is placed on a heating table to be heated and dried at a heating temperature of 50-70℃. Please see Figure 2 and Figure 3 , where 1 represents the first substrate and 2 represents a diamond powder solution with diamond particle size of 3-50nm.

[0024] S22, the first substrate with seed crystals spin-coated is placed into the MPCVD (Microwave Plasma Chemical Vapor Deposition) equipment, and the chamber pressure is evacuated to 0.001 mbar or below; S23, Injecting air into the MPCVD equipment , The flow rate is 100-800 sccm; S24, when the cavity pressure reaches 15-20 Torr, turn on the microwave source to raise the cavity pressure to 120-200 Torr, with a power of 3000-5000W and a first substrate surface temperature of 800-1000℃. S25, Injecting air into the MPCVD equipment , and The growth process of nanocrystalline diamond was then initiated. The flow rate is 8-80 sccm. The flow rate is 0.1-0.8 sccm. The flow rate was 0-2 sccm, the growth rate was maintained at 10-20 μm / h, and the growth time was 15-20h; Furthermore, during the growth process, it is necessary to ensure that the diamond maintains a high secondary nucleation rate and that the grain size of the solid seed polycrystalline diamond is small.

[0025] S26, after growth is complete, stop the flow. , and Slowly reduce the cavity pressure and power to prevent the solid crystal seed nanocrystalline diamond from cracking due to thermal stress. Pump the cavity pressure to 20 Torr and reduce the power to 600W. Once the cavity temperature stabilizes, turn off the microwave source and stop the flow of electricity. The chamber pressure was reduced to 0.001 mbar, and the pump was turned off. Air was introduced into the chamber to break the vacuum, and the first substrate with the nanocrystalline diamond epitaxial layer was removed from the chamber.

[0026] See also Figure 4 Understand S2, where 3 represents the nanocrystalline diamond epitaxial layer.

[0027] S3, using precision laser cutting to grow a first substrate with a nanocrystalline diamond epitaxial layer, to obtain a ring-shaped polycrystalline diamond solid seed crystal with an inner diameter larger than that of the second substrate; Please see Figure 5 It is understood that the nanocrystalline diamond epitaxial layer has been transformed into a ring-shaped polycrystalline diamond solid seed crystal.

[0028] In this embodiment of the invention, the inner diameter of the annular polycrystalline diamond solid seed crystal can be slightly larger than the radius of the second substrate. For example, the inner diameter of the annular polycrystalline diamond solid seed crystal is 1 to 2 inches larger than the radius of the second substrate.

[0029] S4, the second substrate is placed in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal. Through the boundary induction mechanism and the application of DC bias, the tiny diamond grains generated by the previous plasma etching of the ring-shaped polycrystalline diamond solid seed crystal are guided to the second substrate and uniformly wrapped on the second substrate, thereby growing a self-supporting polycrystalline diamond substrate on the second substrate. In one optional implementation, S4 may include the following steps: S41, the second substrate is placed in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal, and together they are placed into the MPCVD equipment, and the chamber pressure is evacuated to 0.001 mbar or below; The second substrate does not have any artificially spin-coated polycrystalline diamond seed crystals. Please refer to [link / reference]. Figure 6 Understand, where 4 represents the second substrate.

[0030] S42, Injecting power into the MPCVD equipment , The flow rate is 100-800 sccm; S43, when the cavity pressure reaches 15-20 Torr, turn on the microwave source to raise the cavity pressure to 120-200 Torr, with a power of 3000-5000W, and the surface temperature of the second substrate is 800-1000℃. Apply a DC bias of 0.5-2 kW under the second substrate to guide the extremely small diamond grains generated by plasma etching of the ring-shaped polycrystalline diamond solid seed crystal to the second substrate and uniformly coat the second substrate; S44, Injecting power into the MPCVD equipment , and They began the growth process of self-supporting polycrystalline diamond. The flow rate is 8-80 sccm. The flow rate is 0.01-0.5 sccm. The flow rate is 0-2 sccm; the growth rate is maintained at 4-8 μm / h, the growth time is 75-100h, and the thickness of the polycrystalline diamond layer is guaranteed to be ≥150μm to achieve self-support of the polycrystalline diamond layer. Please see Figure 7 Understand, where 5 represents a polycrystalline diamond substrate.

[0031] S45, after growth is complete, stop the flow. , and Slowly reduce the cavity pressure and power to prevent the polycrystalline diamond from cracking due to thermal stress; evacuate the cavity pressure to 20 Torr and reduce the power to 600W. Once the cavity temperature stabilizes, turn off the microwave source; stop the flow of microwaves. The chamber pressure was reduced to 0.001 mbar, and the pump was turned off. Air was introduced into the chamber to break the vacuum, and the second substrate, the obtained self-supporting polycrystalline diamond substrate, and the ring-shaped polycrystalline diamond solid seed crystal were removed from the chamber.

[0032] Among them, the ring-shaped polycrystalline diamond solid seed crystal can be reused.

[0033] S4 can be used to form self-supporting polycrystalline diamond substrates with high uniformity and low surface roughness.

[0034] S5, perform hydrogen plasma etching on the surface of the self-supporting polycrystalline diamond substrate to remove amorphous carbon and graphite phases, and obtain the final polycrystalline diamond substrate.

[0035] In one optional implementation, S5 may include: The self-supporting polycrystalline diamond substrate, with its surface facing upwards, is placed in an MPCVD (Multi-Level Chemical Deposition) device and etched for 10-20 minutes at 200-400°C in a hydrogen plasma atmosphere. This process removes amorphous carbon and graphite phases from the grown self-supporting polycrystalline diamond substrate, yielding a polycrystalline diamond substrate with a surface roughness ≤3 nm on one side. Please refer to [link to relevant documentation]. Figure 8 and Figure 9 understand.

[0036] The method for preparing a high-quality self-supporting polycrystalline diamond substrate provided in this invention is the first to propose a method for growing polycrystalline diamond using solid seed crystals, combined with a molybdenum metal self-exfoliation polycrystalline diamond growth process, to achieve a self-supporting high-quality polycrystalline diamond substrate with low surface roughness on one side. Specifically, it has the following beneficial effects: 1. Solid-state seed crystals—micro-sized diamond particles induced growth. For the first time, nanocrystalline diamond fragments prepared by hydrogen plasma etching are proposed as solid-state seed crystals, with particle sizes much smaller than those of traditional artificial seeding powders. Combined with a high-precision polished molybdenum substrate, extremely low roughness (Rq≤3 nm) is achieved at the interface between the seed crystal and the molybdenum metal substrate, effectively improving the uniformity and nucleation density of the crystal nuclei, ultimately obtaining high-crystal quality, easily machinable self-supporting polycrystalline diamond.

[0037] 2. Direct supply of finished products with ultra-low single-sided roughness. Through optimization of hydrogen plasma deep etching, the self-supporting polycrystalline diamond prepared can achieve a single-sided roughness at the nanometer level. It can be used directly for device manufacturing or scientific research testing without the need for traditional grinding and polishing processes, which greatly improves R&D efficiency and lowers the threshold for material application.

[0038] 3. It possesses both high yield and low cost, making it a promising industrialization prospect. The overall preparation method eliminates the need for complex substrate separation and mechanical polishing, omitting multiple intermediate steps. It boasts advantages such as strong process controllability, good repeatability, and easy capacity scaling, which significantly promotes the large-scale application of polycrystalline diamond in electronic device substrates and functional materials.

[0039] Example 2 This invention provides another method for preparing high-quality self-supporting polycrystalline diamond substrates, wherein, For S1, obtain the first substrate and the second substrate; Wherein, the size of the first substrate is larger than the size of the second substrate, and the second substrate is a polished molybdenum metal substrate; Specifically, the first substrate is a silicon substrate with a (111) crystal orientation. The first substrate has a size of 4 inches, a roughness Ra1 = 10 nm, and a thickness of 3 mm. The second substrate has a size of 3 inches, a roughness Ra2 = 1 nm, and a thickness of 3.2 mm.

[0040] For S2, diamond seeds are seeded on the first substrate using ultrasonic seeding, and then a nanocrystalline diamond epitaxial layer is grown using CVD process. Specifically, the following steps are included: S21, ultrasonic seeding is performed on the first substrate, using a diamond powder solution with a diamond particle size of 15nm as the seed seeding solution, the ultrasonic time is 20min, and then the first substrate is placed on a heating table to be heated and dried at a heating temperature of 55℃. S22, the first substrate with the seed crystals spin-coated is placed into the MPCVD equipment, and the chamber pressure is evacuated to 0.001mbar or below; S23, Injecting air into the MPCVD equipment , The flow rate is 200 sccm; S24, when the cavity pressure reaches 15 Torr, turn on the microwave source to raise the cavity pressure to 140 Torr, with a power of 3000W and a first substrate surface temperature of 800℃. S25, Injecting air into the MPCVD equipment , and The growth process of nanocrystalline diamond was then initiated. The flow rate is 10 sccm. The flow rate is 0.2 sccm. The flow rate was 1 sccm, the growth rate was maintained at 10-20 μm / h, and the growth time was 15-20h; Furthermore, during the growth process, it is necessary to ensure that the diamond maintains a high secondary nucleation rate and that the grain size of the solid seed polycrystalline diamond is small.

[0041] S26, after growth is complete, stop the flow. , and Slowly reduce the cavity pressure and power to prevent the solid crystal seed nanocrystalline diamond from cracking due to thermal stress. Pump the cavity pressure to 20 Torr and reduce the power to 600W. Once the cavity temperature stabilizes, turn off the microwave source and stop the flow of electricity. The chamber pressure was reduced to 0.001 mbar, and the pump was turned off. Air was introduced into the chamber to break the vacuum, and the first substrate with the nanocrystalline diamond epitaxial layer was removed from the chamber.

[0042] For S3, a first substrate with a nanocrystalline diamond epitaxial layer grown on it is cut using a precision laser to obtain a ring-shaped polycrystalline diamond solid seed crystal with an inner diameter larger than that of the second substrate. This results in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal being 3.2 inches.

[0043] For S4, the second substrate is placed in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal. Through the boundary induction mechanism and the application of DC bias, the tiny diamond grains generated by the previous plasma etching of the ring-shaped polycrystalline diamond solid seed crystal are guided to the second substrate and uniformly wrapped on the second substrate, thereby growing a self-supporting polycrystalline diamond substrate on the second substrate. Specifically, the following steps are included: S41, the second substrate is placed in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal, and together they are placed into the MPCVD equipment, and the chamber pressure is evacuated to 0.001 mbar or below; The second substrate does not have any artificially spin-coated polycrystalline diamond seed crystals.

[0044] S42, Injecting power into the MPCVD equipment , The flow rate is 200 sccm; S43, when the cavity pressure reaches 15 Torr, turn on the microwave source to raise the cavity pressure to 140 Torr, with a power of 3000W. The surface temperature of the second substrate is 800℃. Apply a DC bias voltage of 1kW under the second substrate to guide the extremely small diamond grains generated by plasma etching of the ring-shaped polycrystalline diamond solid seed crystal to the second substrate and uniformly coat the second substrate. S44, Injecting power into the MPCVD equipment , and They began the growth process of self-supporting polycrystalline diamond. The flow rate is 10 sccm. The flow rate is 0.01 sccm. The flow rate is 0.5 sccm; the growth rate is maintained at 6 μm / h, the growth time is 100h, and the thickness of the polycrystalline diamond layer is guaranteed to be ≥150 μm to achieve self-support of the polycrystalline diamond layer. S45, after growth is complete, stop the flow. , and Slowly reduce the cavity pressure and power to prevent the polycrystalline diamond from cracking due to thermal stress; evacuate the cavity pressure to 20 Torr and reduce the power to 600W. Once the cavity temperature stabilizes, turn off the microwave source; stop the flow of microwaves. The chamber pressure was reduced to 0.001 mbar, and the pump was turned off. Air was introduced into the chamber to break the vacuum, and the second substrate, the obtained self-supporting polycrystalline diamond substrate, and the ring-shaped polycrystalline diamond solid seed crystal were removed from the chamber.

[0045] For S5, hydrogen plasma etching is performed on the surface of the self-supporting polycrystalline diamond substrate to remove amorphous carbon and graphite phases, and the final polycrystalline diamond substrate is obtained. Specifically, it includes: The self-supporting polycrystalline diamond substrate is placed face up in an MPCVD device and etched at 200°C in a hydrogen plasma atmosphere for 20 minutes to remove amorphous carbon and graphite phases from the grown self-supporting polycrystalline diamond substrate, resulting in a polycrystalline diamond substrate with a surface roughness of 2.76 nm.

[0046] This invention introduces a ring-shaped solid seed structure for the first time, which significantly improves the orientation consistency and crystal quality of diamond films. The self-supporting polycrystalline diamond substrate prepared has advantages such as low surface roughness, dense structure, and simplified subsequent processes. It is suitable for high-end electronic device substrates and material research platforms and has good prospects for promotion and application.

[0047] It should be noted that, in the description of this invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0049] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-quality self-supporting polycrystalline diamond substrate, characterized in that, include: Obtain a first substrate and a second substrate; wherein the size of the first substrate is larger than the size of the second substrate, and the second substrate is a polished molybdenum metal substrate; Diamond seeds were seeded on the first substrate using an ultrasonic seeding method, and then a nanocrystalline diamond epitaxial layer was grown using a CVD process. A ring-shaped polycrystalline diamond solid seed crystal with an inner diameter larger than that of the second substrate was obtained by using precision laser cutting to grow a first substrate with a nanocrystalline diamond epitaxial layer. The second substrate is placed in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal. Through the boundary induction mechanism and the application of DC bias, the tiny diamond grains generated by the previous plasma etching of the ring-shaped polycrystalline diamond solid seed crystal are guided to the second substrate and uniformly wrapped on the second substrate, thereby growing a self-supporting polycrystalline diamond substrate on the second substrate. The surface of the self-supporting polycrystalline diamond substrate is subjected to hydrogen plasma etching to remove amorphous carbon and graphite phases, thereby obtaining the final polycrystalline diamond substrate.

2. The method according to claim 1, characterized in that, The materials of the first substrate include, but are not limited to, silicon, graphite, molybdenum, and gallium nitride.

3. The method according to claim 1, characterized in that, The first substrate is a silicon substrate with (111) crystal orientation.

4. The method according to claim 1, characterized in that, The first substrate has a size of 3-6 inches, a roughness Ra1≤1μm, and a thickness of 1-7mm.

5. The method according to claim 1, characterized in that, The second substrate has a size of 1-5 inches, a roughness Ra2≤1nm, and a thickness of 1-7mm.

6. The method according to claim 1, characterized in that, The process of seeding diamond crystals on the first substrate using ultrasonic seeding and then growing a nanocrystalline diamond epitaxial layer using CVD technology includes: The first substrate is ultrasonically seeded using a diamond powder solution with diamond particles of 3-50 nm in size as the seed solution. The ultrasonic time is 10-30 min. Then the first substrate is placed on a heating table and heated to dry at a temperature of 50-70 °C. The first substrate with the seed crystals spin-coated is placed into the MPCVD equipment, and the chamber pressure is evacuated to 0.001 mbar or below. Injecting into the MPCVD equipment , The flow rate is 100-800 sccm; When the cavity pressure reaches 15-20 Torr, turn on the microwave source to raise the cavity pressure to 120-200 Torr, with a power of 3000-5000W and a first substrate surface temperature of 800-1000℃. Injecting into the MPCVD equipment , and The growth process of nanocrystalline diamond was then initiated. The flow rate is 8-80 sccm. The flow rate is 0.1-0.8 sccm. The flow rate was 0-2 sccm, the growth rate was maintained at 10-20 μm / h, and the growth time was 15-20h; Stop feeding after growth is complete. , and Slowly reduce the cavity pressure and power to prevent the solid crystal seed nanocrystalline diamond from cracking due to thermal stress. Pump the cavity pressure to 20 Torr and reduce the power to 600W. Once the cavity temperature stabilizes, turn off the microwave source and stop the flow of electricity. The chamber pressure was reduced to 0.001 mbar, and the pump was turned off. Air was introduced into the chamber to break the vacuum, and the first substrate with the nanocrystalline diamond epitaxial layer was removed from the chamber.

7. The method according to claim 1, characterized in that, The second substrate is placed within the inner diameter of the annular polycrystalline diamond seed crystal. Through a boundary induction mechanism and by applying a DC bias, the extremely small diamond grains generated by the previous plasma etching of the annular polycrystalline diamond seed crystal are guided onto the second substrate and uniformly encapsulated thereon, thereby growing a self-supporting polycrystalline diamond substrate on the second substrate. This includes: The second substrate is placed in the inner diameter of the ring-shaped polycrystalline diamond solid seed crystal, and together they are placed into the MPCVD equipment, and the chamber pressure is evacuated to 0.001 mbar or below. Injecting into the MPCVD equipment , The flow rate is 100-800 sccm; When the cavity pressure reaches 15-20 Torr, the microwave source is turned on to raise the cavity pressure to 120-200 Torr, with a power of 3000-5000W. The surface temperature of the second substrate is 800-1000℃. A DC bias of 0.5-2 kW is applied under the second substrate to guide the extremely small diamond grains generated by plasma etching of the ring-shaped polycrystalline diamond solid seed crystals to the second substrate and uniformly coat the second substrate. Injecting into the MPCVD equipment , and They began the growth process of self-supporting polycrystalline diamond. The flow rate is 8-80 sccm. The flow rate is 0.01-0.5 sccm. The flow rate is 0-2 sccm; the growth rate is maintained at 4-8 μm / h, the growth time is 75-100h, and the thickness of the polycrystalline diamond layer is guaranteed to be ≥150μm to achieve self-support of the polycrystalline diamond layer. Stop feeding after growth is complete. , and Slowly reduce the cavity pressure and power to prevent the polycrystalline diamond from cracking due to thermal stress; evacuate the cavity pressure to 20 Torr and reduce the power to 600W. Once the cavity temperature stabilizes, turn off the microwave source; stop the flow of microwaves. The chamber pressure was reduced to 0.001 mbar, and the pump was turned off. Air was introduced into the chamber to break the vacuum, and the second substrate, the obtained self-supporting polycrystalline diamond substrate, and the ring-shaped polycrystalline diamond solid seed crystal were removed from the chamber.

8. The method according to claim 1, characterized in that, The surface of the self-supporting polycrystalline diamond substrate is subjected to hydrogen plasma etching to remove amorphous carbon and graphite phases, obtaining the final polycrystalline diamond substrate, including: The self-supporting polycrystalline diamond substrate is placed face up in an MPCVD device and etched for 10-20 minutes at 200-400°C in a hydrogen plasma atmosphere to remove amorphous carbon and graphite phases from the grown self-supporting polycrystalline diamond substrate, resulting in a polycrystalline diamond substrate with a surface roughness ≤3 nm on one side.

Images