A self-assembled large-size single crystal diamond substrate and a method of manufacturing the same

Abstract

This invention provides a self-splicing large-size single-crystal diamond substrate and its manufacturing method, belonging to the field of single-crystal diamond technology. The method includes the following steps: in-situ printing a light-treated resin barrier layer on the non-splicing surface of the single-crystal diamond; mechanically grinding the splicing surface of the single-crystal diamond; immersing the splicing surface of the single-crystal diamond in a magnetic nanoparticle precursor dispersion; aligning the splicing surfaces of the single-crystal diamonds to be spliced ​​with each other, applying an external magnetic field in a specific direction to align and tightly adhere the splicing surfaces; subjecting the spliced ​​diamond to high-temperature annealing in a reducing atmosphere or vacuum environment; and placing the spliced ​​diamond in a strong acid cleaning solution to dissolve and remove residual metals and impurities from the diamond surface. This invention utilizes small-size single-crystal diamonds with excellent surface quality for splicing to obtain large-size single-crystal diamonds, preserving the thermal and mechanical properties of single-crystal diamonds while achieving wafer-level large-size expansion.

Description

Technical Field

[0001] This invention belongs to the field of single-crystal diamond technology, and more specifically, relates to a self-splicing large-size single-crystal diamond substrate and its manufacturing method. Background Technology

[0002] In recent years, with the explosive growth of 5G / 6G wireless communication, artificial intelligence, and computing chips, the market demand for high-frequency, high-output-power devices has become increasingly urgent, making gallium nitride (GaN) power devices the mainstream technology. However, when GaN high electron mobility transistors operate close to their electronic limits, the heat flux density of internal "hot spots" is extremely high. This severe self-heating effect limits the maximum output power of the device and leads to increased channel temperature. Studies have shown that for every 10°C increase in device temperature, the lifetime is halved. Therefore, effective heat dissipation management has become a key bottleneck restricting the reliability and lifespan of high-performance GaN devices.

[0003] Single-crystal diamond substrates, as a promising new functional material, are considered ideal for heat dissipation in high-performance electronic devices due to their excellent physical properties—including ultra-smooth surfaces with sub-nanometer roughness achievable through chemical mechanical polishing, excellent thermal conductivity up to 2200 W / (m·K), and outstanding mechanical strength. Heterogeneous integration of GaN wafers with single-crystal diamond substrates can significantly improve the thermal management capabilities of high-power GaN devices. However, the fabrication of high-quality, large-size single-crystal diamonds is extremely difficult due to limitations in existing CVD growth processes. Currently, the size of commercially available single-crystal diamonds is typically limited to 10 mm × 10 mm, or even smaller, greatly restricting their application in wafer-level semiconductor manufacturing.

[0004] In contrast, while polycrystalline diamond wafers have been successfully fabricated at large sizes (e.g., 2 to 4 inches) on substrates such as silicon using heterogeneous deposition technology, offering a size advantage for industrial mass production, their thermal and processing properties are limited. First, the dense grain boundaries in the polycrystalline structure produce severe phonon scattering, resulting in a thermal conductivity typically only 1000–1800 W / (m·K), and even below 800 W / (m·K) near the nucleation layer, far inferior to single-crystal diamond, making it difficult to fully meet the rapid heat expansion requirements under extremely high power densities. Second, polycrystalline diamond wafers typically grow in a columnar shape from nanoscale seed nucleation following the van der Waals drift model. This growth pattern results in films composed of grains with varying orientations. Due to the significant anisotropy of polycrystalline diamond, the hardness and polishing resistance of different crystal planes (e.g., the {111} plane versus the {100} plane) differ greatly, leading to uneven polishing rates. In addition, the grain boundaries are often rich in non-diamond carbon phases with lower hardness (such as amorphous carbon and graphite), which further exacerbates the irregularity of the polishing behavior.

[0005] To achieve heterogeneous integration of GaN and diamond, the surface roughness of the diamond must typically be reduced to below 0.3 nm. For polycrystalline diamonds, overcoming inherent grain boundary variations and crystal orientation differences to achieve this smoothness is not only extremely difficult but also very expensive to polish. Therefore, there is an urgent need for a low-cost method to manufacture large-size single-crystal diamond substrates that can retain the excellent surface quality and thermal properties of single-crystal diamonds while overcoming their size limitations. Summary of the Invention

[0006] The purpose of this invention is to provide a self-splicing large-size single-crystal diamond substrate and its manufacturing method, so as to overcome the defects of existing polycrystalline diamonds and small-size single-crystal diamonds. The self-splicing large-size single-crystal diamond substrate of this invention can not only retain the excellent surface quality and thermal properties of single-crystal diamonds, but also break through the small size limitation of single-crystal diamonds.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for manufacturing a self-splicing large-size single-crystal diamond substrate, comprising the following steps:

[0008] S1. Print a light-treated resin barrier layer in situ on the non-jointed surface of a single-crystal diamond.

[0009] S2. Mechanically grind the splicing surfaces of the single-crystal diamonds to expose the splicing surfaces;

[0010] S3. The splicing surface of the single crystal diamond is immersed in a magnetic nanoparticle precursor dispersion to allow the magnetic nanoparticles to grow on the splicing surface of the single crystal diamond.

[0011] S4. Make the splicing surfaces of the single crystal diamonds to be spliced ​​face each other, apply an external magnetic field in a specific direction to make the splicing surfaces of the single crystal diamonds to be spliced ​​aligned and tightly fitted.

[0012] S5. The assembled diamonds are subjected to high-temperature annealing in a reducing atmosphere.

[0013] S6. Place the assembled diamonds in a strong acid cleaning solution to dissolve and remove residual metal and impurities from the diamond surface.

[0014] Further, step S4 includes the following steps:

[0015] Place the single-crystal diamond to be spliced ​​in a non-magnetic flat-bottomed container, and inject a carrier liquid into the container, with the liquid level submerging 1 / 2 to 2 / 3 of the thickness of the single-crystal diamond; the carrier liquid is anhydrous ethanol or a mixture of deionized water and surfactant.

[0016] Furthermore, step S4 includes the following steps: while applying an external magnetic field, ultrasonic micro-perturbation is applied to the bottom of the container.

[0017] Furthermore, step S4 includes the following steps: after multiple single-crystal diamonds are spliced ​​together, the external magnetic field is kept on, and the carrier liquid is removed by vacuum suction or heating to evaporate.

[0018] Further, step S4 includes the following steps:

[0019] The single-crystal diamond to be spliced ​​is placed in the central region of a Helmholtz coil. By adjusting the coil current, the magnetic field strength is linearly increased within 10-30 seconds, and finally a uniform DC magnetic field parallel to the splicing plane of the single-crystal diamond is applied, with the magnetic induction intensity controlled between 20 mT and 50 mT.

[0020] Furthermore, the high-temperature annealing treatment is carried out under the following conditions: the spliced ​​diamonds are placed in a hydrogen pressure atmosphere of 6.6 kPa - 26.7 kPa, and first held at 450 °C for 60 min; then the temperature is raised to 700-800 °C and held at 70-90 min; finally the temperature is raised to 1000 °C and held at 1000 °C for 10-5 h.

[0021] Further, step S1 includes the following steps:

[0022] Using digital light processing equipment and a step-by-step multi-faceted projection light processing process, the light-processing resin barrier layer is printed step-by-step on the non-jointed surface of a single-crystal diamond. The light-processing resin barrier layer contains the following components: 50~60wt% hydroxyethyl methacrylate, 6~16wt% polyethylene glycol diacrylate, 21.5~23.5wt% diphenoxyethanol, 10~12wt% 2,4,6-trimethylbenzoyl, and 0.4~0.6wt% Sudan Red G.

[0023] Further, step S2 includes the following steps:

[0024] The single-crystal diamond is fixed in the grinding area using a lateral vacuum adsorption fixture, so that its splicing surface is parallel to the surface of the grinding disc. The grinding disc is then activated to grind the diamond to remove the light-treatment resin blocking layer that has overflowed and covered the sidewall surface of the single-crystal diamond.

[0025] Furthermore, the magnetic nanoparticle dispersion is prepared by the following method:

[0026] Preparation of an extract from dried pecan leaves;

[0027] Prepare a ferrous sulfate heptahydrate solution;

[0028] The extract was mixed with the ferrous sulfate heptahydrate solution to obtain a magnetic nanoparticle precursor dispersion.

[0029] In a second aspect, the present invention provides a self-splicing large-size single-crystal diamond substrate, obtained by any of the manufacturing methods described above.

[0030] Compared with the prior art, the present invention has the following technical effects:

[0031] This invention provides a method for manufacturing a large-size self-splicing single-crystal diamond substrate, which avoids the processing bottleneck of obtaining an ultra-smooth surface from large-size polycrystalline diamonds. It directly utilizes small-size single-crystal diamonds with excellent surface quality for splicing, thus preserving the thermal and mechanical properties of single-crystal diamonds while achieving wafer-level size expansion. The method utilizes the magnetic dipole interaction of magnetic nanoparticles to achieve non-contact automatic alignment and tight bonding, avoiding stress concentration and edge chipping problems that are prone to occur in traditional mechanical splicing. The method adopts a "positioning first, catalysis later" strategy. Magnetic nanoparticles act as "positioning anchors" during the assembly stage and are transformed in situ into "metal catalysts" during the high-temperature annealing stage, promoting the diffusion and recrystallization of carbon atoms at the diamond grain boundaries, achieving high-quality lattice healing, and ultimately preparing a large-size single-crystal diamond substrate. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the structure of a single-crystal diamond substrate provided in Embodiment 1 of the present invention;

[0034] Figure 2 This is a schematic diagram of the structure after in-situ printing of a light-treated resin barrier layer on the top, bottom, front, and rear sides of a single-crystal diamond substrate (with the left and right sides exposed), as provided in Embodiment 1 of the present invention.

[0035] Figure 3 This is a schematic diagram of the structure provided in Embodiment 1 of the present invention after loading magnetic nanoparticles on the exposed left and right sides of a single-crystal diamond substrate.

[0036] Figure 4 This is a schematic diagram of the structure of a 3×3 arrayed self-splicing large-size single-crystal diamond substrate with nine single-crystal diamonds provided in Embodiment 1 of the present invention.

[0037] in, Figure 1 , Figure 2 The labels for the attached figures are as follows:

[0038] 1. Light-treated resin barrier layer; 2. Magnetic nanoparticles. Detailed Implementation

[0039] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0040] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0041] This invention provides a self-splicing large-size single-crystal diamond substrate and its manufacturing method, including the following steps:

[0042] S1. Print a light-treated resin barrier layer in situ on the non-jointed surface of a single-crystal diamond.

[0043] S2. Mechanically grind the splicing surfaces of the single-crystal diamonds to expose the splicing surfaces;

[0044] S3. The splicing surface of the single crystal diamond is immersed in a magnetic nanoparticle precursor dispersion to allow the magnetic nanoparticles to grow on the splicing surface of the single crystal diamond.

[0045] S4. Make the splicing surfaces of the single crystal diamonds to be spliced ​​face each other, apply an external magnetic field in a specific direction to make the splicing surfaces of the single crystal diamonds to be spliced ​​aligned and tightly fitted.

[0046] S5. The assembled diamonds are subjected to high-temperature annealing in a reducing atmosphere.

[0047] S6. Place the spliced ​​diamonds in a strong acid cleaning solution to dissolve and remove residual metals and impurities from the diamond surface, ultimately obtaining a large-size single-crystal diamond substrate with a clean surface and lattice-level healing of the splice seams.

[0048] In step S1 above, specifically, a light-processing resin barrier layer is printed in stages on the non-jointed surfaces of a single-crystal diamond using a digital light processing device and a step-by-step multi-faceted projection light processing process. The light-processing resin barrier layer contains the following components: 50-60 wt% hydroxyethyl methacrylate, 6-16 wt% polyethylene glycol diacrylate, 21.5-23.5 wt% diphenoxyethanol, 10-12 wt% 2,4,6-trimethylbenzoyl (TPO), and 0.4-0.6 wt% Sudan Red G.

[0049] In one embodiment, the digital light processing equipment is a lifting platform (e.g., SLA, stereolithography) equipped with a high-precision angle indexing fixture. The setup includes a single-layer printing thickness of 1 μm, printing 30 layers, a laser wavelength of 365 nm, a 20 μm micro-spot at 90% power output, a high-speed scan of 2000 mm / s, a feed delay of 500 ms, and a squeegee speed of 30 mm / s. After printing one non-jointed surface, the fixture performs a precise 90° or 180° flip-positioning, repeating the photopolymerization printing process to complete the printing of the light-processing resin barrier layer on other non-jointed surfaces. Finally, a high-purity argon gas flow removes the non-crosslinked residual resin from the surface, yielding a resin / diamond composite structure.

[0050] In step S2 above, specifically, the single crystal diamond after photoprinting is fixed in the grinding area by a lateral vacuum adsorption fixture, the posture is adjusted so that the splicing surface is strictly parallel to the surface of the grinding disk, and the grinding disk is started to grind to remove the light-treated resin blocking layer that overflows and covers the side wall surface of the single crystal diamond.

[0051] In one embodiment, the grinding disc pressure is set to 10 kPa and the rotation speed to 30 rpm. Low-speed, flexible grinding is initiated, accompanied by a 260 mL / min flow rate of grinding fluid to remove the overflowing and coating of the light-treatment resin barrier layer on the sidewalls of the single-crystal diamond. This prevents the resin barrier layer from peeling off or breaking due to excessive shear force. When the resin barrier layer is observed to be completely removed and the single-crystal diamond substrate is about to be exposed, the pressure is gradually increased to 30 kPa, and the rotation speed is increased to 115 rpm. The extremely high hardness of the single-crystal diamond achieves a self-stopping grinding effect, thus accurately exposing the clean single-crystal diamond splicing surface while ensuring sharp edges without collapse.

[0052] In step S3 above, the magnetic nanoparticle precursor dispersion is prepared as follows: an extract of dried pecan leaves is prepared; a ferrous sulfate heptahydrate (FeSO4·7H2O) solution is prepared; the extract and the ferrous sulfate heptahydrate solution are mixed to obtain the magnetic nanoparticle precursor dispersion. Specifically, dried pecan leaves are used as a reducing agent source. After washing and drying, 60 g of the leaves are immersed in 1 L of deionized water and heated and stirred at 80 °C for 1 h. After cooling to 25 °C, the mixture is filtered, and the filtrate is collected as the plant reducing extract. A 1.5 wt% ferrous sulfate heptahydrate aqueous solution is prepared as the iron source precursor. The above plant reducing extract and ferrous sulfate solution are mixed at a volume ratio of 2:1 to obtain the magnetic nanoparticle precursor dispersion. The single-crystal diamond, after being processed in step S2 and exposing only the splicing surface, was immersed in the aforementioned magnetic nanoparticle precursor dispersion. The reaction system was placed in a constant-temperature shaker and continuously shaken at 160 rpm for 24 h at 25 ℃. After the reaction, the single-crystal diamond was removed and gently rinsed with deionized water to remove unbonded impurities from the surface. It was then placed in a drying oven and dried at 50 ℃ for 24 h to allow the magnetic nanoparticle layer to grow stably on the splicing surface of the single-crystal diamond.

[0053] In this step, iron ions (Fe²⁺) are directly reduced to nuclei and grow on the diamond splicing surface. The in-situ grown magnetic nanoparticles form a tighter chemical adsorption or physical interlocking with the microstructure of the diamond splicing surface, resulting in stronger adhesion. On the other hand, the mechanically ground diamond splicing surface is microscopically rough, with numerous nanoscale pits and steps. During growth, the magnetic nanoparticles embed themselves in these microscopic pits, forming a "mechanical interlocking effect," which greatly increases the shear resistance of the magnetic nanoparticles and prevents them from detaching from the diamond splicing surface under subsequent magnetic drag. Furthermore, the plant extract in this embodiment is rich in organic macromolecules such as polyphenols, proteins, and polysaccharides. While reducing iron oxide, these organic molecules act like natural glue, coating the surface of the magnetic nanoparticles and forming hydrogen bonds or van der Waals forces with the diamond splicing surface. This organic film not only prevents the magnetic nanoparticles from agglomerating but also further enhances their adhesion to the single-crystal diamond substrate. After the magnetic nanoparticles are generated, the moisture is removed by long-term constant-temperature drying, which causes the organic bonding layer between the magnetic nanoparticles and the diamond splicing surface to undergo dehydration condensation or hardening, thus "locking" the magnetic nanoparticles more tightly to the diamond splicing surface and achieving a good anti-detachment effect.

[0054] In step S4 above, specifically, the single-crystal diamonds to be spliced, processed in step S3, are placed in a non-magnetic (e.g., Teflon) flat-bottomed container. An appropriate amount of low-viscosity carrier liquid is injected into the container, with the liquid level submerging 1 / 2 to 2 / 3 of the thickness of the single-crystal diamonds. Then, the container containing the single-crystal diamonds is placed in the central region of a Helmholtz coil, and a magnetic field generator is activated to apply a uniform DC magnetic field parallel to the splicing plane of the single-crystal diamonds. The initial position of the single-crystal diamonds is adjusted so that their splicing surfaces are approximately opposite. Under the influence of the magnetic field, the two opposite splicing surfaces induce "N" and "S" characteristics, respectively. To eliminate minor misalignments or residual air bubbles at the splicing interface, high-frequency, low-amplitude ultrasonic micro-perturbations (e.g., high-frequency, low-amplitude ultrasonic micro-perturbations with a frequency of 40 kHz and a power density of 0.5 W / cm²) are applied to the bottom of the container simultaneously with the magnetic field. After multiple single-crystal diamonds are spliced ​​to form an array, the external magnetic field is kept on, and the carrier liquid is slowly removed by vacuum suction or heating to evaporate. After the liquid has completely evaporated, the magnetic nanoparticle layer forms a preliminary physical interlock in the dry state, completing the self-assembly process.

[0055] In one embodiment, the single-crystal diamonds to be joined are placed in the central region of a Helmholtz coil. By adjusting the coil current, the magnetic field strength is linearly increased within 10-30 seconds, ultimately applying a uniform DC magnetic field parallel to the joining plane of the single-crystal diamonds. The magnetic induction intensity is controlled between 20 mT and 50 mT. This intensity range is sufficient to overcome the resistance of the carrier fluid that induces diamond movement, while also preventing damage to the diamond edges due to violent collisions caused by excessive magnetic attraction.

[0056] Preferably, the carrier liquid is a mixture of anhydrous ethanol or deionized water and a surfactant. The surfactant can be SDS (sodium dodecyl sulfate), CTAB (hexadecyltrimethylammonium bromide), tert-octylphenol polyoxyethylene ether, or Triton X-100, etc., with a mass concentration of 0.05%-0.5% in the carrier liquid. Because deionized water or anhydrous ethanol has a high surface tension, without a surfactant, tiny diamond flakes may float on the surface and fail to sink, or be encapsulated by the liquid and unable to move. Adding a surfactant reduces the surface tension of the carrier liquid, improves the wettability of the carrier liquid on the surface of the single-crystal diamond, ensures that the carrier liquid uniformly coats the diamond sidewalls, prevents air bubbles from remaining in tiny seams, and reduces frictional resistance during the movement of the single-crystal diamond.

[0057] The carrier liquid in this invention has the following functions: providing a low-friction environment (lubrication): When a single-crystal diamond is placed at the bottom of a dry container, the friction is relatively large, and the weak magnetic force is insufficient to drive its movement. The low-viscosity carrier liquid can generate buoyancy or a lubricating layer, significantly reducing the frictional resistance between the single-crystal diamond and the bottom of the container, allowing the diamond to rotate and move freely in accordance with the direction of the magnetic field; serving as a transmission medium: allowing ultrasound to propagate in the liquid, eliminating bubbles and minor misalignments through high-frequency, low-amplitude ultrasonic micro-perturbations; buffering and damping: preventing the diamond from chipping due to a violent collision caused by excessive speed at the moment of magnetic attraction.

[0058] Furthermore, the embodiments of this invention also require strict control of the liquid level to submerge 1 / 2 to 2 / 3 of the thickness of the single-crystal diamond. This is done to prevent stacking (climbing): if the liquid level is too high (completely submerged), one diamond can easily climb onto another during magnetic adsorption or ultrasonic disturbance, leading to overlap. Controlling the liquid level below the top surface of the diamond utilizes the surface tension of the liquid (meniscus effect) to confine the diamonds to the same plane, forcing a two-dimensional side-to-side splicing rather than three-dimensional stacking. Secondly, it maintains a stable center of gravity: in the semi-submerged state, the diamonds are mainly held to the bottom of the container by gravity, ensuring the flatness (coplanarity) of the splicing. Thirdly, it utilizes capillary force: this specific liquid level height creates specific capillary forces at the diamond gaps, helping to further tighten the splicing seams during the liquid evaporation stage, forming a physical interlock.

[0059] In this step, the magnetic field is applied uniformly (uniform DC magnetic field). Because the magnetic nanoparticle layer is very thin and uniformly grown on the diamond splicing surface, the magnetic force acts on the entire magnetic layer, thus dragging the entire single-crystal diamond. Furthermore, the assembly is carried out in a low-viscosity carrier liquid. The liquid environment provides damping, making the movement of the diamond relatively smooth and avoiding drastic acceleration changes, thereby reducing the inertial impact force that could cause the magnetic nanoparticles to detach.

[0060] This invention employs an in-situ growth and drying / curing process to create a bonding force between the magnetic nanoparticles and the diamond interface that is significantly greater than the microscopic peeling force exerted by the magnetic field on the magnetic nanoparticles. As long as the magnetic field strength is controlled within a reasonable range (such as the aforementioned 20-50 mT), the magnetic force is sufficient to overcome the friction between the single-crystal diamond and the bottom of the container, but insufficient to destroy the bonding interface between the magnetic nanoparticles and the diamond.

[0061] In step S5 above, the magnetic iron oxide nanoparticles grown on the diamond surface are reduced to pure metallic iron clusters through high-temperature annealing. These iron clusters then act as catalysts at the subsequent single-crystal diamond splicing surfaces, promoting lattice healing. Because it is extremely difficult for carbon atoms to move directly in the solid state and form strong diamond covalent bonds (CC bonds), requiring very high energy, the presence of iron significantly lowers the energy threshold required for this process. The iron clusters provide a "channel" that allows carbon atoms to rapidly shuttle through, thereby connecting the two lattices. Ultimately, the iron clusters are "displaced" from the lattice, serving only as a catalytic medium.

[0062] It should be noted that although the high-temperature annealing temperature of 1000 ℃ is lower than the melting point of bulk iron (1538 ℃), the melting point of nanoscale iron particles is significantly reduced due to surface effects (even reaching a semi-molten state). Furthermore, the contact between iron and carbon forms a eutectic, further lowering the melting point. This means that under the high-temperature annealing conditions of this embodiment, the surface of the single-crystal diamond (especially amorphous carbon or high-energy carbon atoms on the cut facets) rapidly dissolves into the iron clusters. Driven by the concentration gradient, the carbon atoms dissolved in the iron clusters move freely within them. The iron clusters act as a "liquid bridge" connecting two independent single-crystal diamonds. When the carbon concentration in the iron clusters reaches supersaturation, or when they encounter an existing single-crystal diamond lattice on the other side (as a seed crystal), carbon atoms precipitate. These precipitated carbon atoms align neatly with the lattice orientation of the single-crystal diamonds on both sides, forming new carbon-carbon bonds (CC bonds). In this way, the two originally independent crystal faces are connected into one through these newly "grown" diamond layers. Because diamond lattices are very dense and cannot accommodate large iron atoms, as the diamonds at the seams continue to grow and heal, the iron clusters that originally occupied those spaces are "squeezed" to the surface or grain boundary by the newly formed diamond lattice and removed by subsequent strong acid cleaning solutions.

[0063] In one implementation, the diamond array (transferred to a dedicated graphite tray) that has undergone magnetic self-assembly in step S4 is placed into the reaction chamber of a tubular atmosphere furnace. The reaction chamber is then sealed, and a vacuum is first evacuated to 10... -3Below Pa, high-purity hydrogen gas is then introduced to maintain the pressure inside the chamber at 6.6 kPa - 26.7 kPa. The temperature is first increased to 450 °C at a rate of 5 °C / min and held at this temperature for 60 min; then, the temperature is increased to 700-800 °C and held at this temperature for 30-90 min; finally, the temperature is increased to 1000 °C and held at this temperature for 2-5 h. The furnace is then slowly cooled to room temperature before removal. This embodiment of the invention employs a graded high-temperature annealing process. The first stage of the graded annealing is set at 450 °C and held at this temperature for 60 min. This specific low-temperature range is designed for the pyrolytic removal of the light-treated resin barrier layer. At this temperature, organic resins, surfactants in the carrier liquid, and other organic matter decompose and vaporize and are carried away by the gas flow, without carbonizing to form hard residues that are difficult to remove. However, if the temperature is directly increased to 1000 °C, the light-treated resin barrier layer may rapidly carbonize or react adversely with the diamond surface, damaging the surface quality. This invention employs a staged heating process to achieve sequential control of removing the protective layer before metal catalysis. Before entering the 1000°C metal iron catalytic healing stage, the protective resin (phototreated resin barrier layer) has completely disappeared, and due to the previous physical isolation, there are no residual iron particles on the non-joined surfaces.

[0064] Hydrochloric acid solution is preferred as the strong acid cleaning solution. Specifically, the assembled diamond, after being cooled in the furnace, is transferred to an acid-resistant cleaning container. A hydrochloric acid solution with a mass concentration of 30%~38% is poured in, ensuring the liquid level completely submerges the assembled diamond. To ensure cleaning efficiency and deep impurity removal, ultrasonic vibration is applied at room temperature for 1-2 hours. During this process, the acid dissolves and removes metallic iron clusters from the surface and seams of the assembled diamond. After cleaning, the assembled diamond is removed and repeatedly rinsed with deionized water until neutral. Finally, it is blown dry or oven-dried to obtain a large-size single-crystal diamond substrate with a clean surface.

[0065] The method for manufacturing a self-splicing large-size single-crystal diamond substrate according to embodiments of the present invention has the following advantages:

[0066] (1) Breaking through size limitations and reducing processing costs: The embodiments of the present invention avoid the processing bottleneck of large-size polycrystalline diamonds having difficulty obtaining ultra-smooth surfaces. They directly use small-size single-crystal diamonds with excellent surface quality for splicing, which not only preserves the thermal and mechanical properties of single-crystal diamonds, but also realizes the expansion of wafer-level dimensions.

[0067] (2) High-precision self-assembly: By utilizing the magnetic dipole interaction of magnetic nanoparticles in conjunction with the carrier fluid environment and ultrasonic disturbance, non-contact alignment and tight bonding are achieved, avoiding stress concentration and edge breakage problems that are easy to occur in traditional mechanical splicing.

[0068] (3) High-quality lattice catalytic healing mechanism: The strategy of first positioning and then catalysis is adopted. Magnetic nanoparticles play the role of "positioning anchor" in the assembly stage and are transformed into "metal catalyst" in situ in the high-temperature annealing stage, which promotes the diffusion and recrystallization of carbon atoms at the diamond grain boundary and achieves high-quality lattice healing.

[0069] (4) Green and environmentally friendly with controllable process: The synthesis of magnetic nanoparticles is carried out by using dried walnut leaf extract, which avoids the use of strong chemical reducing agents and is environmentally friendly; combined with the selective protection and graded annealing process of light-treated resin blocking layer, the cleanliness and optical quality of the non-spliced ​​surface of single crystal diamond are ensured.

[0070] The following two specific embodiments further illustrate a self-splicing large-size single-crystal diamond substrate and its manufacturing method according to an embodiment of the present invention.

[0071] Example 1: 3×3 array splicing of nine single-crystal diamonds (30 mm × 30 mm)

[0072] This embodiment aims to utilize magnetic self-assembly technology to assemble nine 10 mm × 10 mm × 0.5 mm single-crystal diamond substrates into a single 30 mm × 30 mm medium-sized single-crystal diamond substrate. The structure of a single single-crystal diamond substrate is as follows: Figure 1 As shown.

[0073] S1, Step-by-step printing of resin barrier layer

[0074] The nine single-crystal diamonds were divided into three groups for differentiated light treatment:

[0075] Group A (center piece, 1 piece): Print the light-treated resin barrier layer 1 only on the top and bottom surfaces. All four sides (front, back, left, and right) must be used as splicing surfaces and no resin should be printed on them.

[0076] Group B (edge ​​parts, 4 pieces): Print a light-treated resin barrier layer 1 on the top, bottom and one designated outer side, leaving three sides as splicing surfaces.

[0077] Group C (corner pieces, 4 pieces): Print a light-treated resin barrier layer 1 (e.g., on the top, bottom, and two adjacent outer surfaces) on the top, bottom, and two adjacent outer surfaces. Figure 2 As shown in the figure, two inner sides are reserved as splicing surfaces.

[0078] The composition of the light-treated resin barrier layer is: 60 wt% hydroxyethyl methacrylate (HEMA), 6 wt% polyethylene glycol diacrylate (TEGDA), 21.5 wt% diphenoxyethanol (POE), 12 wt% 2,4,6-trimethylbenzoyl (TPO), and 0.5 wt% Sudan Red G. The above materials were prepared in the specified proportions, stirred in a water bath at 10 °C, and then placed in a vacuum mixer to remove air bubbles.

[0079] The specific printing parameters were uniformly set as follows: layer thickness 1 μm, 30 layers, laser wavelength 365 nm, power output 90%, and scanning speed 2000 mm / s. High-purity argon gas flow was used to remove non-crosslinked residual resin from the surface.

[0080] S2, All-around splicing surface grinding

[0081] Three sets of single-crystal diamonds were fixed using lateral vacuum adsorption fixtures. Due to the different pre-reserved surfaces of each set, the fixture angles needed to be adjusted to ensure that all sides not covered by resin were directly facing the grinding disc. A step-by-step grinding process was employed: first, a grinding fluid flow rate of 260 mL / min at 10 kPa and 30 rpm was used to remove any overflowing resin from the sidewalls; then, the pressure was increased to 30 kPa and 115 rpm, utilizing the hardness of the diamond to achieve self-stopping grinding. Finally, it was ensured that all inward-facing interface sidewalls (joining surfaces) had clean single-crystal surfaces exposed.

[0082] S3. Preparation of magnetic nanoparticle precursor dispersion

[0083] A plant-based reducing extract (60 g dried pecan leaves / 1 L water, extracted at 80 ℃ for 1 h) was mixed with a 1.5 wt% FeSO4·7H2O solution at a volume ratio of 2:1. All nine prepared single-crystal diamond slices were immersed in the magnetic nanoparticle precursor dispersion and reacted with shaking at 25 ℃ and 160 rpm for 24 h. At this point, only the exposed splicing surfaces would grow magnetic nanoparticles 2 (e.g., ...). Figure 3 (As shown), while the resin protective surface located on the periphery of the array will not grow. Clean and dry at 50 °C.

[0084] S4, Magnetic field-assisted 3×3 self-assembly

[0085] Nine single-crystal diamond wafers were placed in a Teflon container and filled with a mixed carrier solution of deionized water and sodium dodecyl sulfate (SDS) (the liquid level was 2 / 3 the thickness of the diamonds). The mass concentration of sodium dodecyl sulfate in the carrier solution was 0.1%.

[0086] The container was placed in the center of the uniform magnetic field of the Helmholtz coil. The magnetic field generator was activated, and the current was linearly increased over 20 seconds until a uniform DC magnetic field with a magnetic induction intensity of 35 mT was applied. Under the interaction of magnetic dipoles, the central component (Group A) first attracted the peripheral edge components (Group B), and finally the corner components (Group C) filled in. Simultaneously, the bottom ultrasonic generator was activated, applying a micro-perturbation at a frequency of 40 kHz and a power density of 0.5 W / cm² to eliminate minor misalignments between the wafers. After the 3×3 array was tightly bonded, the magnetic field was kept on, and the carrier liquid was slowly removed by vacuum suction. After drying, a physical interlock was formed.

[0087] S5, Catalytic Healing and Large-Size Substrate Molding

[0088] The splicing array was placed in a tube furnace and evacuated to 10°C. -3 Hydrogen gas was introduced after Pa, maintaining a pressure of 6.6 kPa - 26.7 kPa. The temperature was increased to 450 °C at 5 °C / min and held for 60 min to remove the resin; then the temperature was further increased to 750 °C and held for 45 min to ensure complete reduction of the magnetic nanoparticles to the metallic active state; then the temperature was increased to 1000 °C and held for 4 h. At high temperature, iron clusters catalyzed the simultaneous healing of 12 crisscrossing seams. After cooling, acid washing was performed to obtain a 30 mm × 30 mm single-crystal diamond substrate with a smooth surface and uniform thermal conductivity, as shown in the figure. Figure 4 As shown.

[0089] Example 2: Fabrication of a 4×4 large-size single-crystal diamond substrate of sixteen single-crystal diamonds (40 mm × 40 mm)

[0090] This embodiment aims to use magnetic self-assembly technology to splice 16 single-crystal diamond substrates of 10 mm × 10 mm × 0.5 mm into a large single-crystal diamond substrate of 40 mm × 40 mm.

[0091] S1, Step-by-step printing of resin barrier layer

[0092] The 16 single-crystal diamonds were divided into three groups for differentiated light treatment:

[0093] Group A (internal components, 4 pieces): Located in the center 2×2 area of ​​the 4×4 array. Only the top and bottom surfaces are printed with a light-treated resin barrier layer; the four sides (front, back, left, and right) are to be used as splicing surfaces and are not printed with resin.

[0094] Group B (edge ​​pieces, 8 pieces): Located in the non-corner areas around the array. A light-treated resin barrier layer is printed on the top, bottom, and one designated outer side, leaving three sides as splicing surfaces.

[0095] Group C (corner pieces, 4 pieces): Located at the four vertices of the array. A light-treated resin blocking layer is printed on the top, bottom, and two adjacent outer surfaces, with two inner surfaces reserved as splicing surfaces.

[0096] The composition of the light-treated resin barrier layer is the same as in Example 1.

[0097] The specific printing parameters were uniformly set as follows: layer thickness 1 μm, 30 layers, laser wavelength 365 nm, power output 90%, and scanning speed 2000 mm / s. High-purity argon gas flow was used to remove non-crosslinked residual resin from the surface.

[0098] S2, Batch sidewall treatment

[0099] Three sets of single-crystal diamonds were fixed in place using lateral vacuum adsorption fixtures. The fixture angles were adjusted according to the different reserved surfaces of each set to ensure that all sides not covered by resin were directly facing the grinding disc. A step-by-step grinding process was employed: first, the grinding disc pressure was set to 10 kPa and the rotation speed to 30 rpm, along with a grinding fluid flow rate of 260 mL / min to remove any overflowing resin from the sidewalls; then, the pressure was increased to 30 kPa and the rotation speed to 115 rpm, utilizing the hardness of the diamond to achieve self-stopping grinding. Ultimately, this ensured that all inward-facing interfaces had clean single-crystal surfaces exposed on their sidewalls.

[0100] S3. Preparation of magnetic nanoparticle precursor dispersion

[0101] A plant-based reducing extract (60 g dried pecan leaves / 1 L water, extracted at 80 ℃ for 1 h) was mixed with a 1.5 wt% FeSO4·7H2O solution at a volume ratio of 2:1. Sixteen pre-treated single-crystal diamond wafers were immersed in the magnetic nanoparticle precursor dispersion and reacted with shaking at 25 ℃ and 160 rpm for 24 h. At this point, magnetic nanoparticles grew only on the exposed splicing surfaces, while those on the resin-protected surfaces surrounding the array did not grow. The wafers were then washed and dried at 50 ℃.

[0102] S4, Magnetic field-assisted 4×4 self-assembly

[0103] Sixteen single-crystal diamond wafers were placed in a non-magnetic Teflon flat-bottomed container and filled with a mixed carrier solution of deionized water and tert-octylphenol polyoxyethylene ether (the liquid level was 2 / 3 the thickness of the diamonds). The mass concentration of tert-octylphenol polyoxyethylene ether in the carrier solution was 0.2%.

[0104] The container was placed at the center of a Helmholtz coil, and the magnetic field strength was linearly increased from 0 to 45 mT within 30 seconds and maintained constant. Under the influence of the strong magnetic field, the four inner components of group A first attracted the surrounding eight edge components of group B, and finally the four corner components of group C filled in, forming a tight 4×4 array. During this process, high-frequency, low-amplitude ultrasonic micro-perturbation at 40 kHz and 0.5 W / cm² was applied to ensure that there were no air bubbles left at all seams and that the alignment accuracy met the standards. Finally, while maintaining a 45 mT magnetic field environment, the carrier liquid was slowly removed by heating and evaporation to complete the pre-fixation.

[0105] S5, Catalytic Healing and Large-Size Substrate Molding

[0106] The spliced ​​array was placed in a tube atmosphere furnace and evacuated to 10°C. -3 After the pressure drops below Pa, high-purity hydrogen is introduced to maintain the pressure between 6.6 kPa and 26.7 kPa. The temperature is increased to 450 °C at a rate of 5 °C / min and held at that temperature for 60 min to pyrolyze and remove the photo-treated resin blocking layer. The temperature is then increased to 750 °C and held at that temperature for 60 min to ensure the magnetic nanoparticles are fully converted to the metallic active state. The temperature is then increased to 1000 °C, and considering the large number of seams in the 4×4 array, the holding time is set to 5 h. After cooling to room temperature in the furnace, residual iron particles are removed by strong acid cleaning, resulting in a clean, healed 40 mm × 40 mm large-size single-crystal diamond substrate.

[0107] In the preparation method of this invention, magnetic nanoparticles are grown in situ on the splicing surfaces of single-crystal diamonds via an "immersion-growth" method. Since all splicing surfaces of the single-crystal diamonds undergo the same grinding process, possessing uniform surface energy, and are all situated in a homogeneous magnetic nanoparticle precursor dispersion, thermodynamic equilibrium ensures that the amount of magnetic nanoparticles grown per unit area is highly consistent across all splicing surfaces. This results in a uniform amount of "iron source precursor" embedded in each splice seam, eliminating the problem of localized catalyst deficiency or excess.

[0108] Furthermore, unlike traditional mechanical splicing which typically employs a sequential "align one by one, press one by one" approach (which easily leads to accumulated errors and uneven internal stress distribution), the magnetic field-assisted assembly used in this invention is a "globally parallel mode." The uniform DC magnetic field exerts isotropic magnetic dipole forces on the magnetic diamonds at any position in the array. In step S4 above, all magnetic diamonds are simultaneously attracted to their neighboring magnetic diamonds under the magnetic field, causing all seams to be "locked" at the same instant. This globally synchronized locking force ensures that the initial gaps of all interfaces are compressed to the nanometer scale and remain consistent before entering the high-temperature stage.

[0109] In the high-temperature annealing of step S5 above, the spliced ​​single-crystal diamond array is placed in the isothermal zone of a tube furnace, where the temperature difference between points is extremely small (<±1℃). The healing of the diamond is based on the VLS (gas-liquid-solid) or SLS (solid-liquid-solid) mechanism, and its core rate-limiting step is the diffusion rate of carbon atoms in the molten iron catalyst. Since this diffusion coefficient is strictly dependent on temperature, the reaction kinetics at all seams are completely consistent under a uniform temperature field. Under the action of capillary force, the molten metallic iron will automatically fill any possible microscopic gap differences, acting as an "adaptive filler," thereby ensuring that the lattice growth and healing processes of all seams are synchronized, ultimately obtaining a large-size single-crystal diamond substrate with uniform stress distribution.

[0110] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for manufacturing a self-splicing large-size single-crystal diamond substrate, characterized in that, Includes the following steps: S1. Print a light-treated resin barrier layer in situ on the non-jointed surface of a single-crystal diamond. S2. Mechanically grind the splicing surfaces of the single-crystal diamonds to expose the splicing surfaces; S3. The splicing surface of the single crystal diamond is immersed in a magnetic nanoparticle precursor dispersion to allow the magnetic nanoparticles to grow on the splicing surface of the single crystal diamond. S4. Make the splicing surfaces of the single crystal diamonds to be spliced ​​face each other, apply an external magnetic field in a specific direction to make the splicing surfaces of the single crystal diamonds to be spliced ​​aligned and tightly fitted. S5. The assembled diamonds are subjected to high-temperature annealing in a reducing atmosphere. S6. Place the assembled diamonds in a strong acid cleaning solution to dissolve and remove residual metal and impurities from the diamond surface.

2. The method for manufacturing a self-splicing large-size single-crystal diamond substrate as described in claim 1, characterized in that, Step S4 includes the following steps: Place the single-crystal diamond to be spliced ​​in a non-magnetic flat-bottomed container, and inject a carrier liquid into the container, with the liquid level submerging 1 / 2 to 2 / 3 of the thickness of the single-crystal diamond; the carrier liquid is anhydrous ethanol or a mixture of deionized water and surfactant.

3. The method for manufacturing a self-splicing large-size single-crystal diamond substrate as described in claim 2, characterized in that, Step S4 includes the following steps: while applying an external magnetic field, ultrasonic micro-perturbation is applied to the bottom of the container.

4. The method for manufacturing a self-splicing large-size single-crystal diamond substrate as described in claim 2, characterized in that, Step S4 includes the following steps: after multiple single-crystal diamonds are spliced ​​together, the external magnetic field is kept on, and the carrier liquid is removed by vacuum suction or heating and evaporation.

5. The method for manufacturing a self-splicing large-size single-crystal diamond substrate as described in claim 1, characterized in that, Step S4 includes the following steps: The single-crystal diamond to be spliced ​​is placed in the central region of a Helmholtz coil. By adjusting the coil current, the magnetic field strength is linearly increased within 10-30 seconds, and finally a uniform DC magnetic field parallel to the splicing plane of the single-crystal diamond is applied, with the magnetic induction intensity controlled between 20 mT and 50 mT.

6. The method for manufacturing a self-splicing large-size single-crystal diamond substrate as described in claim 1, characterized in that, The high-temperature annealing process is carried out under the following conditions: the assembled diamonds are placed in a hydrogen pressure atmosphere of 6.6 kPa - 26.7 kPa, and first held at 450 °C for 60 min; then the temperature is raised to 700-800 °C and held at 70-90 min; finally the temperature is raised to 1000 °C and held at 1000 °C for 2-5 h.

7. The method for manufacturing a self-splicing large-size single-crystal diamond substrate as described in claim 1, characterized in that, Step S1 includes the following steps: Using digital light processing equipment and a step-by-step multi-faceted projection light processing process, the light-processing resin barrier layer is printed step-by-step on the non-jointed surface of a single-crystal diamond. The light-processing resin barrier layer contains the following components: 50~60wt% hydroxyethyl methacrylate, 6~16wt% polyethylene glycol diacrylate, 21.5~23.5wt% diphenoxyethanol, 10~12wt% 2,4,6-trimethylbenzoyl, and 0.4~0.6wt% Sudan Red G.

8. The method for manufacturing a self-splicing large-size single-crystal diamond substrate as described in claim 1, characterized in that, Step S2 includes the following steps: The single-crystal diamond is fixed in the grinding area using a lateral vacuum adsorption fixture, so that its splicing surface is parallel to the surface of the grinding disc. The grinding disc is then activated to grind the diamond to remove the light-treated resin blocking layer that has overflowed and covered the sidewall surface of the single-crystal diamond.

9. A method for manufacturing a self-splicing large-size single-crystal diamond substrate as described in any one of claims 1-8, characterized in that, The magnetic nanoparticle precursor dispersion was prepared by the following method: Preparation of an extract from dried pecan leaves; Prepare a ferrous sulfate heptahydrate solution; The extract was mixed with the ferrous sulfate heptahydrate solution to obtain a magnetic nanoparticle precursor dispersion.

10. A self-splicing large-size single-crystal diamond substrate, characterized in that, It is obtained by the manufacturing method according to any one of claims 1-9.

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