A method for optimizing growth of diamond single crystal blanks by MPCVD

Abstract

The application relates to the technical field of diamond synthesis, in particular to a method for optimizing growth of a diamond single crystal blank by MPCVD, which comprises the following steps: S1, seed pretreatment: impurity removal treatment is performed on diamond seeds to obtain pretreated seeds; S2, seed arrangement: the pretreated seeds are arranged on a growth base, and a predetermined interval is maintained between adjacent pretreated seeds through an interval control piece; S3, multi-atmosphere series epitaxial growth: the growth base is placed into a microwave plasma cavity for etching and repair treatment, epitaxial growth is performed on the pretreated seeds after the etching and repair treatment is completed, and a diamond blank is obtained; and S4, cyclic detection and regrowth: the diamond blank is taken out after a set growth time length is reached, quality detection and surface impurity removal treatment are performed, the diamond blank is returned to the microwave plasma cavity to repeatedly execute S3, and the cycle is performed until the cumulative thickness of the diamond blank reaches a target thickness. The application has the effect of improving the quality and yield of the blank.

Description

Technical Field

[0001] This application relates to the technical field of diamond synthesis, and in particular to a method for optimizing the growth of MPCVD diamond single crystal blanks. Background Technology

[0002] Currently, diamond, as a functional material with excellent physicochemical properties, has wide applications in gemstone decoration, precision machining, optical windows, and power electronic devices. Microwave plasma chemical vapor deposition (MPCVD) is the mainstream process for preparing high-quality gem-grade and electronic-grade single-crystal diamond. Its principle involves using 2450MHz microwaves to excite a H2 / CH4 mixed gas to form a high-temperature plasma within a vacuum chamber. The plasma contains active hydrogen atoms (H·) and carbon-containing free radicals (CH4·). x • Single-crystal diamond is grown epitaxially at the atomic level on a heated diamond seed substrate.

[0003] In related technologies, the MPCVD diamond single crystal blank growth process generally includes the following steps: placing a diamond seed crystal on a growth base inside a microwave resonant cavity, closing the cavity and drawing a vacuum, introducing process gas into the cavity and applying microwave power to excite plasma, performing epitaxial growth under the set process temperature, cavity pressure and microwave power conditions, and cooling and removing the blank after the growth reaches the set time.

[0004] Regarding the aforementioned technologies: Since MPCVD growth is a cumulative process lasting hundreds or even thousands of hours, there are complex coupling effects between the substrate state, the growth surface morphology, and the plasma environment. As the growth time increases, on the one hand, random nucleation of non-single-crystal phases (polycrystalline and graphite phases) inevitably occurs on the growth surface during continuous epitaxy. Once formed, these non-single-crystal phases act as new nucleation sites, accelerating the quality degradation of the surrounding area. On the other hand, the growth surface morphology gradually roughens with increasing thickness, and the accumulation of surface protrusions and depressions leads to increased differences in local growth rates, resulting in decreased crystal plane uniformity and deterioration of flatness. These defects accumulate and expand with the growth cycle, ultimately leading to a decline in blank quality and yield, failing to meet the requirements for preparing thick, high-quality single-crystal diamond blanks. Summary of the Invention

[0005] To improve the quality and yield of the blank, this application provides a method for optimizing the growth of MPCVD diamond single crystal blanks.

[0006] This application provides a method for optimizing the growth of MPCVD diamond single crystal blanks, which adopts the following technical solution:

[0007] A method for optimizing the growth of MPCVD diamond single crystal preforms includes the following steps:

[0008] S1. Seed pretreatment: The surface and edges of the diamond seed crystal are treated to remove the polycrystalline phase and graphite phase attached to the seed crystal surface, thus obtaining the pretreated seed crystal.

[0009] S2, Seed Arrangement: The pretreated seeds are arranged on the growth substrate, and a predetermined interval is maintained between adjacent pretreated seeds by a spacing control element;

[0010] S3. Multi-atmosphere tandem epitaxial growth: The growth substrate with the pretreated seed crystals arranged is placed into a microwave plasma cavity. H2, oxygen-containing process gas and nitrogen-containing process gas are introduced in sequence to etch and repair the growth surface of the pretreated seed crystals. After the etching and repair are completed, carbon source gas is introduced to excite microwave plasma to perform epitaxial growth on the pretreated seed crystals to obtain a diamond blank.

[0011] S4. Cyclic detection and regeneration: After the set growth time is reached, the diamond blank is taken out, and the growth surface of the diamond blank is subjected to quality inspection and surface impurity removal treatment. The treated diamond blank is returned to the microwave plasma cavity to repeat S3. The cycle continues until the cumulative thickness of the diamond blank reaches the target thickness.

[0012] By adopting the above technical solutions, the seed pretreatment in S1 removes the polycrystalline phase and graphite phase from the seed substrate at the source to eliminate non-single crystal nucleation sites; S2 precisely controls the seed spacing through the spacing control device to avoid squeezing interference caused by the horizontal expansion of adjacent crystals; S3 achieves substrate activation and purification, selective etching to remove non-single crystal phases and two-dimensional step flow growth-induced planarization before formal epitaxial growth through step-by-step etching repair of H2 → oxygen-containing process gas → nitrogen-containing process gas, effectively suppressing the accumulation of growth surface quality degradation defects; S4 cyclic detection and regeneration restores the high-quality and pure state of the blank growth surface before each growth cycle, realizing continuous, stable, and long-term cumulative growth of the blank.

[0013] Optionally, S3 includes the following steps performed sequentially in chronological order:

[0014] S31, H2 etching activation: H2 is introduced into the microwave plasma cavity to excite the microwave plasma to etch and activate the surface of the pretreated seed crystal to remove the residual non-diamond carbon phase on the surface and activate the diamond lattice surface activity.

[0015] S32, Oxygen-containing etching for impurity removal: On the basis of continuously introducing H2, the oxygen-containing process gas is introduced into the microwave plasma cavity, and the oxygen-containing plasma is used to selectively etch the growth surface to remove residual and newly formed polycrystalline phase and graphite phase on the growth surface.

[0016] S33, Nitrogen-containing repair and smoothing: Reduce the flow rate of the oxygen-containing process gas and introduce the nitrogen-containing process gas into the microwave plasma cavity while continuously introducing the H2, and use the nitrogen-containing plasma to induce two-dimensional step flow growth on the growth surface to smooth the growth surface morphology.

[0017] S34, Continuous growth with carbon source: The carbon source gas is introduced into the microwave plasma cavity, and single-crystal epitaxial growth is carried out under the condition of continuous introduction of H2, oxygen-containing process gas and nitrogen-containing process gas.

[0018] By employing the above technical solutions, S31 utilizes active hydrogen atoms in H2 plasma to etch away residual non-diamond carbon phases (graphite, amorphous carbon) on the surface and activates the diamond lattice surface activity by forming CH bonds with surface C through H·; S32 utilizes the difference in etching rate between polycrystalline and graphite phases and single-crystal diamond using oxygen-containing plasma to selectively and precisely remove polycrystalline and graphite impurities and preliminarily trim the micro-protrusions on the growth surface; S33 utilizes nitrogen-containing plasma to change <110> The crystal orientation growth surface can induce a transformation from a three-dimensional island growth mode to a two-dimensional step flow growth mode and repair the flatness of the growth surface; S34 introduces carbon source gas into the high-quality growth surface after sufficient etching and repair to start epitaxial growth, and achieves stable single-crystal epitaxial continuous growth under the continuous synergistic effect of H2, oxygen-containing and nitrogen-containing process gases.

[0019] Optionally, in S34, the volumetric flow rate ratio of the carbon source gas to the H2 is 3%-12%; in S32, the flow rate of the oxygen-containing process gas is 6%-15% of the target process flow rate of the introduced carbon source gas; and in S33, the flow rate of the nitrogen-containing process gas is 0.001%-0.1% of the target process flow rate of the introduced carbon source gas.

[0020] By adopting the above technical solutions, a volumetric flow rate ratio of carbon source gas to H2 of 3%-12% ensures a reasonable growth rate while guaranteeing the quality of single crystal growth; when the oxygen-containing process gas is 6%-15% of the target process flow rate of the carbon source gas, it can effectively etch and remove polycrystalline phases and graphite phases without causing excessive damage to the single crystal diamond substrate; when the nitrogen-containing process gas is 0.001%-0.1% of the target process flow rate of the carbon source gas, it can effectively induce two-dimensional step flow growth and repair local defects without affecting the optical quality of the crystal due to excessive embedding of nitrogen atoms into the diamond lattice.

[0021] Optionally, the continuous growth process of S34 adopts a gradient heating method, which is to gradually increase the temperature from the initial temperature to the process growth temperature at a set heating rate, and to maintain the temperature for a set time after each heating stage before entering the next heating stage.

[0022] The set heating rate is 5℃ / h-10℃ / h; the gradient heating is completed within 24-48h in the early stage of growth; and the process growth temperature is 800℃-1050℃.

[0023] By adopting the above technical solution, the gradient heating method avoids thermal stress cracking and lattice defects in the seed crystal caused by sudden temperature changes. A heating rate of 5℃ / h-10℃ / h ensures temperature uniformity on the seed crystal growth surface, mitigating localized uneven growth rates caused by temperature differences across the growth surface. The gradient heating to the process growth temperature of 800-1050℃ is completed within the first 24-48 hours of growth, allowing the growth surface to form a uniform, impurity-free initial single crystal layer under stable temperature conditions.

[0024] Optionally, after the seed arrangement is completed in step S2 and before step S3, an H2 plasma in-situ pre-etching step is performed in the microwave plasma cavity. The H2 plasma in-situ pre-etching step is used to activate the surface of the pretreated seed arranged on the growth substrate in situ and remove the non-diamond phase re-adsorbed on the surface of the pretreated seed during the handling and arrangement process.

[0025] By adopting the above technical solution, the H2 plasma in-situ pre-etching step provides in-situ cavity purification based on the laser micro-etching and acid washing treatment in S1. After the seed arrangement is completed in S2 and the cavity is evacuated, H2 is introduced to excite plasma. Active hydrogen atoms are used to remove trace carbon impurities and water vapor contamination re-adsorbed on the surface of the pretreated seed during the handling and arrangement process, while activating the seed surface to provide a pure growth starting surface for the subsequent multi-atmosphere tandem epitaxial growth in S3.

[0026] Optionally, the impurity removal process in S1 includes laser micro-engraving, acid washing, and cleaning performed sequentially. The laser micro-engraving is used to remove polycrystalline phases and graphite phases attached to the surface and edges of the seed crystal. The acid washing process uses oxidizing acid to immerse and clean the seed crystal after laser micro-engraving to remove residual impurities and metallic impurities.

[0027] By employing the above technical solution, laser micro-etching achieves targeted removal of the polycrystalline and graphite phases on the surface and edges of the seed crystal without damaging adjacent single-crystal regions by ablation of the polycrystalline and graphite impurity regions; acid washing utilizes the oxidizing properties of oxidizing acid to remove residual carbon generated by laser micro-etching, non-diamond carbon phases in the heat-affected zone, and residual metal contaminants on the surface, and chemically etches and activates the surface; cleaning removes organic residues and acid residues. These three steps are performed sequentially to purify the seed crystal surface.

[0028] Optionally, the spacing control element is a homogeneous diamond strip, which is sandwiched between adjacent pretreated seeds along the seed arrangement direction.

[0029] By adopting the above technical solution, homogeneous diamond strips of the same material as the seed crystals are used as spacer control components, avoiding contamination from impurities introduced due to differences in the material of the spacer control components or thermal stress caused by mismatched coefficients of thermal expansion. The homogeneous diamond strips are sandwiched between adjacent pretreated seed crystals to precisely control the predetermined spacing between the seed crystals, leaving space for polycrystalline growth to prevent direct contact between adjacent crystals or squeezing due to horizontal expansion. At the same time, it reduces the temperature difference between crystals and improves the temperature uniformity at the bottom of the growth process in the early stage of growth.

[0030] Optionally, when the diamond blanks processed in S4 are returned to the microwave plasma cavity, they are re-fixed on the growth base in the same arrangement as in S2. The predetermined interval between adjacent diamond blanks is maintained by the homogeneous diamond strips. The homogeneous diamond strips are replaced or laser micro-engraved before each cycle. The process growth temperature of subsequent cycles is reduced by 5°C-20°C compared to the previous cycle, and it is no longer reduced when the process growth temperature drops to 800°C.

[0031] By adopting the above technical solution, the homogeneous diamond strips are replaced or laser micro-engraved before each cycle to ensure that the spacer control components are in a clean state, avoiding the influence of polycrystalline phases deposited on their surface in the previous growth round on subsequent growth. The consistency of the arrangement ensures the repeatability and stability of the plasma environment. The gradual reduction of the process growth temperature in subsequent cycles adapts to the actual situation of increased heat conduction distance between the growth surface and the bottom of the substrate due to increased blank thickness, and changes in heat dissipation conditions of the growth surface, maintaining the stability of the actual temperature of the growth surface. The process growth temperature is no longer reduced beyond 800℃, as 800℃ is the minimum process temperature required to maintain single-crystal diamond epitaxial growth; below this temperature, insufficient carbon source decomposition efficiency and excessively low growth rate will result.

[0032] Optionally, the quality inspection in S4 includes at least one of optical microscopy observation, Raman spectroscopy detection, and X-ray diffraction detection, and the surface impurity removal treatment includes laser cutting and trimming the edge polycrystalline material of the diamond blank and acid washing of the laser-cut diamond blank with oxidizing acid.

[0033] By employing the above technical solutions, optical microscopy can be used to assess the polycrystalline phase distribution and surface smoothness of the growth surface; Raman spectroscopy can be used to assess the purity of the single-crystal diamond phase through the intensity and full width at half maximum (FWHM) of the diamond characteristic peaks; and X-ray diffraction can be used to assess crystal orientation consistency and lattice quality. Laser cutting trimming targets the polycrystalline phases accumulated at the edges of the blank during cyclic growth. It removes these phases from the blank edges through targeted ablation, ensuring the cutting action is controllable and limited to the polycrystalline region at the blank edges, without affecting the already grown single-crystal layer on the blank growth surface. This eliminates the interference of edge polycrystalline phases on subsequent epitaxial growth while preserving the effective single-crystal growth thickness. Oxidizing acid washing further removes residual carbon, non-diamond carbon phases, and residual metal contaminants generated during laser cutting, restoring the blank to a pure state and providing a suitable growth substrate for subsequent cyclic growth.

[0034] Optionally, the oxidizing acid solution is any one of concentrated sulfuric acid, a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid, aqua regia, a mixed acid solution of chromic acid and concentrated sulfuric acid, or a mixed acid solution of hydrogen peroxide and concentrated sulfuric acid.

[0035] By adopting the above technical solutions, various types of oxidizing acids can be selected according to the specific type and degree of impurities on the surface of the blank. Concentrated sulfuric acid is suitable for removing residual carbon and surface activation; a mixture of concentrated sulfuric acid and concentrated nitric acid has a high efficiency in oxidizing and removing graphite phases; aqua regia is suitable for removing metal contaminants, especially precious metal residues; a mixture of chromic acid and concentrated sulfuric acid has strong oxidizing properties and is suitable for removing stubborn impurities; a mixture of hydrogen peroxide and concentrated sulfuric acid is suitable for removing organic residues and carbon impurities.

[0036] In summary, this application includes at least one of the following beneficial technical effects:

[0037] 1. By combining laser micro-carving and acid cleaning in the S1 seed pretreatment, the polycrystalline phase and graphite phase nucleation sites of the seed substrate are eliminated from the source, ensuring the purity of the single crystal growth substrate of the seed itself. In conjunction with the homogeneous diamond strip in S2, the spacing between adjacent seed crystals is precisely controlled to avoid mutual interference between adjacent crystals during the growth process from a physical dimension.

[0038] 2. Through the multi-atmosphere series treatment of the four sub-steps S31-S34 in S3, the substrate activation and purification, selective etching to remove non-single crystal phases and two-dimensional step flow growth-induced planarization are completed in sequence before the formal epitaxial growth. The atmospheres of each sub-step are gradually superimposed to form a progressive growth surface pretreatment, so that the growth surface reaches a high-quality, pure and flat state before the carbon source is introduced.

[0039] 3. By using the S4 cycle detection and closed-loop control mechanism to restore the purity of the blank growth surface before each growth cycle, and in conjunction with the strategy of gradient heating and gradual reduction of process temperature, the single continuous growth cycle is extended, alleviating the growth time limitation caused by the deterioration of growth surface quality in traditional processes. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating a method for optimizing the growth of MPCVD diamond single crystal blanks in an embodiment of this application.

[0041] Figure 2 This is a schematic diagram of the arrangement of the 7 seed crystals 1 in the embodiments of this application.

[0042] Figure 3 This is a schematic diagram of the arrangement of 14 seed crystals 1 in an embodiment of this application.

[0043] Figure 4 This is a schematic diagram comparing the surface morphology before and after seed growth in the embodiments of this application.

[0044] Explanation of reference numerals in the attached figures:

[0045] 1. Seed crystal; 2. Growth substrate; 3. Homogeneous diamond strip. Detailed Implementation

[0046] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0047] This application discloses a method for optimizing the growth of MPCVD diamond single crystal blanks.

[0048] Reference Figure 1-4 A method for optimizing the growth of MPCVD diamond single crystal blanks includes the following steps:

[0049] S1. Seed 1 pretreatment: The surface and edges of the diamond seed (hereinafter referred to as seed 1) are treated to remove the polycrystalline phase and graphite phase attached to the surface of seed 1, and a pretreated seed is obtained.

[0050] In this embodiment, seed crystal 1 is selected with all four sides being [missing information]. <110> (001) crystal plane diamond seed crystals. The geometric specifications of seed crystal 1 are: side length 7-30mm, thickness 0.5-1.5mm. Seed crystals 1 arranged in the same batch should be seed crystals 1 of the same specifications (same side length and thickness) to ensure that the growth surfaces of each seed crystal 1 are on the same horizontal plane and to ensure uniform plasma coverage.

[0051] Select <110> The technical basis for crystal orientation seeding is as follows: during continuous long-term growth (more than 50 hours), <100> The horizontal expansion of the crystal plane causes compression and loss of effective size between crystals in the seed crystals. After the top surface expands in the early stage, the edge expands over time. <100> The high ridges shrink the area, which is not conducive to long-term continuous growth and the preparation of large-sized blanks. <110> Crystalline seed crystals do not suffer from the compression problems caused by horizontal expansion, resulting in better crystal plane uniformity. <110> The serrated morphology of the growth surface is highly compatible with the subsequent nitrogen-containing process gas repair process.

[0052] The impurity removal process includes laser micro-engraving, acid pickling, and cleaning performed sequentially. The specific steps are as follows:

[0053] First, using a microscope with a magnification of at least 50x and a polarizing microscope, the surface and edges of seed crystal 1 were comprehensively inspected, and the distribution location and area of ​​the polycrystalline phase and graphite impurity phase were marked. Then, laser micro-etching was performed: the marked polycrystalline phase and graphite impurity phase areas were ablated and removed using laser micro-etching, ensuring that the polycrystalline phase and graphite phase were completely removed without damaging adjacent single crystal areas.

[0054] Next, acid pickling is performed: the laser-micro-engraved seed crystal 1 is immersed in an oxidizing acid solution for cleaning to remove residual impurities and metallic impurities. The oxidizing acid solution can be selected from any one of concentrated sulfuric acid, a mixture of concentrated sulfuric acid and concentrated nitric acid, aqua regia, a mixture of chromic acid and concentrated sulfuric acid, or a mixture of hydrogen peroxide and concentrated sulfuric acid. In this embodiment, concentrated sulfuric acid with a concentration ≥68% is preferably used, the pickling temperature is 270-350℃, and the pickling time is 20-45 minutes.

[0055] The main purposes of acid pickling include: removing residual carbon and non-diamond carbon phase in the heat-affected zone generated by laser micro-etching, removing residual metal contaminants on the surface of seed crystal 1, and chemically etching and activating the surface of seed crystal 1.

[0056] Finally, cleaning is performed: after pickling, isopropanol (IPA) organic solvent ultrasonic cleaning is performed to remove organic contaminants and pickling residues. The mixture is then rinsed multiple times with deionized water to thoroughly remove isopropanol residues, water-soluble impurities, and surface oxide layers, followed by drying.

[0057] After step S1, pretreated seed crystals with clean surfaces, intact crystal orientations, and complete removal of polycrystalline and graphite impurity phases are obtained.

[0058] S2. Seed Crystal Arrangement: Pretreated seed crystals are arranged on the growth substrate 2, and adjacent pretreated seed crystals are kept at a predetermined interval by a spacing control element. In this embodiment, the spacing control element is a homogeneous diamond strip 3. The homogeneous diamond strip 3 is sandwiched between adjacent pretreated seed crystals along the arrangement direction of seed crystal 1.

[0059] Specifically, the pretreated seed crystals 1 are placed on the growth pedestal 2, with a uniform spacing of 0.3-1.5 mm between each seed crystal. The growth pedestal 2 is the base inside the MPCVD cavity used to support the seed crystals 1. In this embodiment, the growth pedestal 2 adopts a temperature-uniform bottom wedge-shaped step-by-step trenching structure. This structure includes a pedestal body and multiple trenches set on the upper surface of the pedestal body. The depth of each trench is adapted to the thickness of the seed crystal 1. The seed crystal 1 is embedded in the trench so that the growth surface of the seed crystal 1 is basically flush with or slightly higher than the upper surface of the pedestal body. The bottom of the pedestal body is provided with a wedge-shaped structure, which is used to adjust the height position of the pedestal body in the cavity so that the growth surface of the seed crystal 1 is in the optimal working area of ​​the plasma ball.

[0060] Homogeneous diamond strips 3 are embedded at the gaps between the seed crystals 1 and the seed crystals 1, ensuring that the growth surfaces are horizontal and facing upwards, and that the seed crystals 1 are not in direct contact. The design range of the gaps between the seed crystals 1 and the seed crystals 1 is based on the following: if the gap is too small (less than 0.3 mm), the seed crystals 1 may experience contact stress due to slight lateral growth during subsequent growth; if the gap is too large (greater than 1.5 mm), the temperature uniformity at the bottom of the gap is poor, and the gap area is more likely to become a preferred site for polycrystalline nucleation.

[0061] The specifications for the homogeneous diamond strip 3 are as follows: the material is the same as that of the seed crystal 1; the width is 0.3-2mm; the length is equivalent to that of the selected seed crystal 1; and the thickness is 70%-80% of the thickness of the seed crystal 1.

[0062] Homogeneous diamond strips 3 are embedded in the gaps between adjacent seed crystals 1, with the top surface of the homogeneous diamond strip 3 being lower than the growth surface of the seed crystal 1. The thickness parameters of the homogeneous diamond strip 3 are determined based on the following: when the thickness is less than 70% of the thickness of the seed crystal 1, the diamond strip is prone to cracking and jumping under high temperature conditions, affecting the growth stability of the seed crystal 1; when the thickness is greater than 80% of the thickness of the seed crystal 1, the diamond strip is prone to polycrystalline formation due to excessively fast growth rate, which also affects the overall uniformity.

[0063] The core functions of the homogeneous diamond strip 3 are: first, to reserve a polycrystalline growth interval between the seed crystals 1 to prevent direct contact between adjacent crystals; and second, to reduce the temperature difference between crystals in the early stage of growth and improve the temperature uniformity at the bottom of the growth.

[0064] Place the growth substrate 2, with the pretreated seed crystal and homogeneous diamond strip 3 arranged on it, into the MPCVD chamber and close the chamber. Start the vacuum pump to evacuate the chamber until the vacuum level inside the chamber is ≤10. -3Pa removes residual air, moisture, and impurities from the cavity. After vacuuming, a pressure test is performed on the cavity. The pressure test method is as follows: after turning off the vacuum pump, observe the change in the vacuum level inside the cavity within a set time. If the change in vacuum level is less than the set threshold, the pressure test is considered successful. Subsequent steps can only be performed after confirming that the pressure test is successful. If the pressure test fails, the leak test must be repeated.

[0065] In this embodiment, after S2 completes the seed arrangement and the cavity is evacuated and pressure maintained, and before S3, an in-situ H2 plasma pre-etching step is performed within the microwave plasma cavity. The H2 plasma in-situ pre-etching step is used to in-situ activate the surface of the pretreated seed crystals arranged on the growth substrate 2 and remove the non-diamond phase re-adsorbed on the surface of the pretreated seed crystals during handling and arrangement. The process parameters for this step are: H2 flow rate 500 sccm-10 slm, cavity pressure 110-180 Torr, microwave power 6 kW-15 kW, etching temperature 800-1000℃, and etching time 10-30 min.

[0066] Figure 2 The arrangement of the 7 seed crystals 1 in this embodiment is shown: including one seed crystal 1 located in the center and 6 seed crystals 1 arranged around it, with homogeneous diamond strips 3 sandwiched between adjacent seed crystals 1 as spacing control elements.

[0067] Figure 3 This embodiment illustrates the arrangement of the 14-bit seed crystal 1 combination: in Figure 2 Based on the 7-position combination, an additional ring of seed crystals 1 is added around the perimeter and spaced by homogeneous diamond strips 3. This embodiment does not limit the specific number and arrangement of the seed crystals 1 combination; it can be flexibly selected according to the MPCVD cavity size and the number of target blanks.

[0068] S3, Multi-atmosphere tandem epitaxial growth: The growth substrate 2 with pretreated seed crystals is placed into the microwave plasma cavity, and the four sub-steps S31-S34 are performed sequentially in time.

[0069] It should be noted that the atmosphere introduction method for the four sub-steps S31-S34 is a progressive superposition method. That is, S31 introduces only H2; S32 introduces oxygen-containing process gas while continuously introducing H2; S33 introduces nitrogen-containing process gas while continuously introducing H2 and reducing the oxygen-containing process gas flow rate; and S34 introduces carbon source gas while continuously introducing H2, oxygen-containing process gas, and nitrogen-containing process gas. The flow rate baseline relationship for each atmosphere is as follows: the target process flow rate of the carbon source gas is set based on the H2 flow rate; the flow rate of the oxygen-containing process gas is based on a percentage of the target process flow rate of the introduced carbon source gas; and the flow rate of the nitrogen-containing process gas is based on a percentage of the target process flow rate of the introduced carbon source gas.

[0070] Carbon source gas refers to a gas that can decompose in a plasma environment to provide carbon atoms for diamond epitaxial growth, including but not limited to any one of CH4, C2H2, and C2H4; oxygen-containing process gas refers to a gas that can decompose in a plasma environment to generate active oxygen atoms, including but not limited to any one of CO2 and O2; nitrogen-containing process gas refers to a gas that can decompose in a plasma environment to generate active nitrogen atoms, including but not limited to any one of N2 and NH3. In this embodiment, CH4 is preferred as the carbon source gas, CO2 is preferred as the oxygen-containing process gas, and N2 is preferred as the nitrogen-containing process gas.

[0071] S31, H2 etching activation. H2 is introduced into the microwave plasma cavity to excite the microwave plasma to etch and activate the surface of the pretreated seed crystals, thereby removing residual non-diamond carbon phases and activating the diamond lattice surface activity.

[0072] In this step, only H2 is introduced; no carbon source gas or oxygen- or nitrogen-containing process gases are introduced. The H2 flow rate ranges from 500 sccm to 10 slm. The chamber pressure is 110–180 Torr; the microwave frequency is 2450 MHz; and the microwave power is 6 kW–15 kW (using a power ramp-up method, gradually increasing from the initial power to the target power of 6 kW–15 kW at a rate of 0.5 kW / min–2 kW / min). The H2 etching activation time is 10–30 min.

[0073] The effects of H2 etching activation include: active H· in the plasma undergoes an etching reaction with the residual non-diamond carbon phase on the surface of the pretreated seed crystal to remove carbon impurities; H· forms CH bonds with carbon atoms on the surface of the pretreated seed crystal to saturate dangling bonds, inhibit the formation of surface defects, and activate the surface activity of the diamond lattice.

[0074] S32, Oxygen-containing etching for impurity removal. CO2 is introduced into the microwave plasma cavity while H2 is continuously supplied. Oxygen-containing plasma is used to selectively etch the growth surface to remove residual and newly formed polycrystalline and graphite phases.

[0075] In this step, H2 and oxygen-containing process gas CO2 are introduced, but carbon source gas and nitrogen-containing process gas are not introduced. The CO2 flow rate is 6%-15% of the target process flow rate of the carbon source gas. The oxygen etching and impurity removal time is 10-30 minutes. The cavity pressure and microwave power are consistent with S31.

[0076] CO2 decomposes in a plasma environment to produce reactive oxygen atoms (CO2→CO+O·). These reactive oxygen atoms have a higher etching rate on polycrystalline diamond and graphite phases than on single-crystal diamond, thus achieving selective removal of polycrystalline and graphite impurities on the growth surface without damaging the single-crystal diamond substrate. Simultaneously, CO2 has an etching and smoothing effect on the minute protrusions on the growth surface, providing initial flatness adjustment.

[0077] The oxygen-containing etching in S32 needs to be performed before the nitrogen-containing repair in S33 because if nitrogen-containing repair is performed first, N atoms will form CN bonds on the surface of the polycrystalline and graphite phases. These CN bonds hinder the etching of active oxygen atoms, thus reducing the removal efficiency of the polycrystalline and graphite phases by subsequent oxygen-containing etching. Therefore, removing the polycrystalline and graphite phases first through oxygen-containing etching in S32, and then smoothing the growth surface through nitrogen-containing repair in S33, is the key sequence of steps in the multi-atmosphere tandem processing of this application.

[0078] S33, nitrogen-containing repair and smoothing. The flow rate of oxygen-containing process gas CO2 is reduced, and nitrogen-containing process gas N2 is introduced into the microwave plasma cavity while continuously introducing H2. Two-dimensional step flow growth is induced by nitrogen-containing plasma to smooth the growth surface morphology.

[0079] In this step, H2, CO2 (oxygen-containing process gas at reduced flow rates), and N2 (nitrogen-containing process gas) are introduced, but no carbon source gas is introduced. The CO2 flow rate is reduced to 1%-5% of the target process flow rate of the carbon source gas. The N2 flow rate is 0.001%-0.1% of the target process flow rate of the carbon source gas. The nitrogen-containing repair and smoothing time is 10-30 minutes.

[0080] N2 compatibility <110> The core mechanism of crystal orientation growth surfaces includes the following four aspects:

[0081] First, changes in surface energy and shifts in growth patterns: <110> The crystal orientation growth surface has a serrated morphology with high-density steps. Nitrogen atoms change the surface energy by adsorbing onto the edges of the steps, transforming the rough three-dimensional island growth mode into a smooth two-dimensional step flow growth mode, thus giving the growth surface a smooth surface.

[0082] Second, suppressing non-diamond phases: The etching and surface diffusion regulation of N2 promotes the re-vaporization or reconstruction of the formed non-diamond phases (polycrystalline, graphite phases), removes surface defects, and ensures the integrity of the diamond lattice arrangement.

[0083] Third, defect repair and enhanced migration: N atoms can firmly bind with surface carbon vacancies to form CN bonds (CN bond pinning effect), which hinders the expansion of dislocation sources and the development of etch pits; at the same time, N atoms enhance the surface diffusion and migration ability of adjacent carbon atoms, enabling surface atoms to move and repair local incomplete lattice structures.

[0084] Fourth, growth rate regulation: N2 has the ability to accelerate diamond growth, so its content range must be strictly controlled to avoid runaway growth rate and nitrogen atoms becoming embedded in the diamond lattice as impurities, forming nitrogen color centers that affect the optical quality and electrical properties of the crystal.

[0085] S34, continuous growth with carbon source. Carbon source gas CH4 is introduced into the microwave plasma cavity, and single-crystal epitaxial growth is carried out under the conditions of continuous introduction of H2, oxygen-containing process gas CO2, and nitrogen-containing process gas N2.

[0086] The volumetric flow rate ratio of the carbon source gas CH4 to H2 is 3%-12%. The CO2 flow rate is maintained at 1%-5% of the target process flow rate of the carbon source gas (consistent with the reduced flow rate in S33), and the N2 flow rate is maintained at 0.001%-0.1% of the target process flow rate of the carbon source gas. The chamber pressure is 110-180 Torr; the microwave power is 6kW-15kW; and the process growth temperature is 800-1050℃. The typical growth rate is 6-10 μm / h. A single continuous growth cycle is 180-240 h.

[0087] The set growth time is determined based on the quality status of the growth surface. When observable signs of quality degradation appear on the growth surface (such as the polycrystalline phase area exceeding 5% of the total growth surface area, or surface flatness deterioration leading to protrusion height exceeding 50 μm), the set growth time has been reached, and the blank must be removed for cyclic inspection and re-growth. A typical set growth time is 180-240 hours. The target thickness is determined based on the final product requirements, typically ranging from 1 mm to 10 mm.

[0088] The continuous growth process of S34 employs a gradient heating method. This method involves gradually increasing the temperature from the initial temperature to the process growth temperature at a set heating rate, maintaining a set duration after each heating stage before moving to the next. The heating rate is a slow increase of 5℃ / h to 10℃ / h. The process growth temperature is 800-1050℃. The gradient heating window is 24-48 hours (starting from the beginning of growth), with the gradient reaching the process growth temperature completed within the initial 24-48 hours of growth.

[0089] The initial temperature is the base temperature inside the cavity after S31-S33, typically ranging from 750℃ to 850℃. The gradient heating method can avoid thermal stress cracking of seed crystal 1 caused by sudden temperature changes. At the same time, the isothermal holding stage after each heating stage ensures that the temperature of the growth surface of seed crystal 1 is fully homogenized, alleviating the uneven local growth rate caused by temperature differences in different areas of the growth surface.

[0090] During the gradient heating process, it is necessary to continuously observe whether the morphology of the growth surface is good: visually observe through the cavity observation window whether there are obvious polycrystalline nucleation points or surface roughening on the growth surface. If the growth surface maintains a mirror-like luster and there are no visible polycrystalline points, it is judged as good nucleation; if the morphology is not good, adjust the temperature and return to continuous growth; if the morphology is good, continue to gradient heat to the target process temperature and enter the stable growth stage of the blank. The temperature control endpoint standard is that the growth surface forms an initial single crystal layer of uniform thickness without impurities, and the seed crystal 1 is tightly connected to the homogeneous diamond strip 3, maintaining the flatness of the growth surface and the advantage of single crystal directional growth throughout the process.

[0091] The main process parameters for the stable growth stage of the preform are: cavity pressure 110-180 Torr; microwave power 6kW-15kW (dynamically adjusted according to cavity temperature feedback); growth temperature 800-1050℃ (maintained within the target temperature range); typical growth rate 6-10μm / h. A single continuous growth cycle is 180-240h.

[0092] S4. Cyclic Detection and Regeneration: After the set growth time is reached, the diamond blank is taken out, and the growth surface of the diamond blank is subjected to quality inspection and surface impurity removal treatment. The treated diamond blank is returned to the microwave plasma cavity to repeat S3. The cycle continues until the cumulative thickness of the diamond blank reaches the target thickness.

[0093] Quality inspection includes at least one of optical microscopy, Raman spectroscopy, and X-ray diffraction to evaluate the following indicators: the distribution and proportion of polycrystalline and graphite phases; the smoothness of the growth surface (the degree of protrusions and depressions); and whether the current thickness of the blank has reached the target value. The purpose of quality inspection is to record and monitor the quality status of the blank growth surface, providing a basis for adjusting the process parameters of subsequent cyclic growth.

[0094] Surface impurity removal includes laser cutting to trim the polycrystalline edges of the diamond blank and acid washing with oxidizing acid after laser cutting. Specifically, after each cycle, the distribution and thickness of the polycrystalline phase at the blank edge are determined by microscopic observation to assess whether laser cutting is necessary. If so, a pulsed laser is used to perform targeted ablation along the polycrystalline region at the blank edge, stripping the accumulated polycrystalline phase from the diamond blank edge. Laser cutting parameters are selected based on the polycrystalline layer thickness, and the cutting range is limited to the polycrystalline region at the edge of the diamond blank, avoiding damage to the single-crystal layer on the growth surface of the blank, thus preventing damage to the already grown high-quality single crystals.

[0095] After laser cutting and finishing, the diamond blank is immersed in an oxidizing acid solution for pickling to remove residual carbon generated during laser cutting, non-diamond carbon phases in the heat-affected zone, and residual metallic contaminants on the blank surface. The oxidizing acid solution can be any of the following: concentrated sulfuric acid, a mixture of concentrated sulfuric acid and concentrated nitric acid, aqua regia, a mixture of chromic acid and concentrated sulfuric acid, or a mixture of hydrogen peroxide and concentrated sulfuric acid. In this embodiment, concentrated sulfuric acid with a concentration ≥68% is preferred. The pickling temperature is 270-350℃, and the pickling time is 20-45 minutes. After pickling, the blank is sequentially ultrasonically cleaned with isopropanol (IPA) and rinsed with deionized water, and finally dried to restore the blank to a pure state.

[0096] When the processed diamond blanks are returned to the microwave plasma cavity, they are re-fixed onto the growth substrate 2 in the same arrangement as in S2. Adjacent diamond blanks are maintained at a predetermined interval by homogeneous diamond strips 3, and these homogeneous diamond strips 3 are replaced or laser-micro-engraved before each cycle. In subsequent cycles (S34), the process growth temperature is reduced by 5℃-20℃ compared to the previous cycle to accommodate the increased heat conduction distance between the growth surface and the bottom of the substrate due to the increased blank thickness, and to maintain the stability of the growth surface temperature. The process growth temperature is reduced to 800℃ and then no further reduction is made; 800℃ is the minimum process temperature required to maintain single-crystal diamond epitaxial growth.

[0097] This closed-loop control mechanism ensures that the blank growth surface is in a pure state before each growth cycle begins, thereby achieving continuous, stable, and long-term growth.

[0098] Once the cumulative thickness of the diamond single-crystal blank reaches the target value, stop the gas flow in the following order: stop the flow of carbon source gas CH4, stop the flow of oxygen-containing process gas CO2, stop the flow of nitrogen-containing process gas N2, stop the flow of H2, and turn off the microwave power. Remove the blank after the MPCVD chamber has naturally cooled to room temperature.

[0099] The final finishing process after the blank thickness meets the standard only requires trimming the edges of the blank: removing a small amount of trace impurities generated during the growth process; there is no need to cut or polish the growth surface to avoid introducing impurities and reduce cutting losses.

[0100] After growth, the connection between the homogeneous diamond strip 3 and the seed crystal 1 or blank is divided into two categories: weak connection (polycrystalline thin film or graphite bonding layer) can be directly peeled off by light touch; dense connection (dense connection of deposited thin film, which is less common) is separated by laser cutting. During the growth process, the homogeneous diamond strip 3 also deposits a diamond film, but because its height is lower than that of the seed crystal 1 (relatively lower temperature), its growth rate is slower than that of the main seed crystal 1. As the blank thickness continues to increase, the effective growth of the homogeneous diamond strip 3 gradually weakens and even stops.

[0101] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for optimizing the growth of MPCVD diamond single crystal blanks, characterized in that, Includes the following steps: S1, Seed (1) Pretreatment: The surface and edges of the diamond seed are treated to remove the polycrystalline phase and graphite phase attached to the surface of the seed (1) to obtain the pretreated seed; S2, Seed (1) Arrangement: Arrange the pretreated seed crystals on the growth base (2), and maintain a predetermined interval between adjacent pretreated seed crystals by an interval control element; S3. Multi-atmosphere tandem epitaxial growth: The growth substrate (2) with the pretreated seed crystals arranged is placed into the microwave plasma cavity. H2, oxygen-containing process gas and nitrogen-containing process gas are introduced in sequence to etch and repair the growth surface of the pretreated seed crystals. After the etching and repair are completed, carbon source gas is introduced to excite microwave plasma to perform epitaxial growth on the pretreated seed crystals to obtain diamond blanks. S4. Cyclic detection and regeneration: After the set growth time is reached, the diamond blank is taken out, and the growth surface of the diamond blank is subjected to quality inspection and surface impurity removal treatment. The treated diamond blank is returned to the microwave plasma cavity to repeat S3. The cycle continues until the cumulative thickness of the diamond blank reaches the target thickness.

2. The method for optimizing MPCVD diamond single crystal blank growth according to claim 1, characterized in that: S3 includes the following steps performed sequentially in chronological order: S31, H2 etching activation: H2 is introduced into the microwave plasma cavity to excite the microwave plasma to etch and activate the surface of the pretreated seed crystal to remove the residual non-diamond carbon phase on the surface and activate the diamond lattice surface activity. S32, Oxygen-containing etching for impurity removal: On the basis of continuously introducing H2, the oxygen-containing process gas is introduced into the microwave plasma cavity, and the oxygen-containing plasma is used to selectively etch the growth surface to remove residual and newly formed polycrystalline phase and graphite phase on the growth surface. S33, Nitrogen-containing repair and smoothing: Reduce the flow rate of the oxygen-containing process gas and introduce the nitrogen-containing process gas into the microwave plasma cavity while continuously introducing the H2, and use the nitrogen-containing plasma to induce two-dimensional step flow growth on the growth surface to smooth the growth surface morphology. S34, Continuous growth with carbon source: The carbon source gas is introduced into the microwave plasma cavity, and single-crystal epitaxial growth is carried out under the condition of continuous introduction of H2, oxygen-containing process gas and nitrogen-containing process gas.

3. The method for optimizing MPCVD diamond single crystal blank growth according to claim 2, characterized in that: In S34, the volumetric flow rate ratio of the carbon source gas to the H2 is 3%-12%; in S32, the flow rate of the oxygen-containing process gas is 6%-15% of the target process flow rate of the carbon source gas; and in S33, the flow rate of the nitrogen-containing process gas is 0.001%-0.1% of the target process flow rate of the carbon source gas.

4. The method for optimizing MPCVD diamond single crystal blank growth according to claim 2, characterized in that: The continuous growth process of S34 adopts a gradient heating method, which is to raise the temperature from the initial temperature to the process growth temperature in stages according to a set heating rate, and to maintain the temperature for a set time after each heating stage before entering the next heating stage. The set heating rate is 5℃ / h-10℃ / h; the gradient heating is completed within 24-48h in the early stage of growth; and the process growth temperature is 800℃-1050℃.

5. The method for optimizing MPCVD diamond single crystal blank growth according to claim 1, characterized in that: After the seed arrangement is completed in S2 and before S3, the process also includes an in-situ H2 plasma pre-etching step performed in the microwave plasma cavity. The in-situ H2 plasma pre-etching step is used to activate the surface of the pretreated seed arranged on the growth substrate (2) in situ and remove the non-diamond phase re-adsorbed on the surface of the pretreated seed during the handling and arrangement process.

6. The method for optimizing MPCVD diamond single crystal blank growth according to claim 1, characterized in that: The impurity removal process in S1 includes laser micro-engraving, acid washing and cleaning performed in sequence. The laser micro-engraving is used to remove the polycrystalline phase and graphite phase attached to the surface and edge of the seed crystal (1). The acid washing process uses oxidizing acid to soak and clean the seed crystal (1) after laser micro-engraving to remove residual impurities and metal impurities.

7. The method for optimizing MPCVD diamond single crystal blank growth according to claim 1, characterized in that: The spacing control element is a homogeneous diamond strip (3), which is sandwiched between adjacent pretreated seeds along the arrangement direction of the seed crystals (1).

8. The method for optimizing MPCVD diamond single crystal blank growth according to claim 7, characterized in that: When the diamond blanks processed in S4 are returned to the microwave plasma cavity, they are re-fixed on the growth base (2) in the same arrangement as in S2. The predetermined interval between adjacent diamond blanks is maintained by the homogeneous diamond strips (3). The homogeneous diamond strips (3) are replaced or laser micro-engraved before each cycle. The process growth temperature of subsequent cycles is reduced by 5°C-20°C compared to the previous cycle, and it is no longer reduced when the process growth temperature drops to 800°C.

9. The method for optimizing MPCVD diamond single crystal blank growth according to claim 1, characterized in that: The quality inspection in S4 includes at least one of optical microscopy observation, Raman spectroscopy detection and X-ray diffraction detection. The surface impurity removal treatment includes laser cutting and trimming the edge polycrystalline material of the diamond blank and acid washing of the laser-cut diamond blank with oxidizing acid.

10. The method for optimizing MPCVD diamond single crystal blank growth according to claim 6 or 9, characterized in that: The oxidizing acid solution is any one of concentrated sulfuric acid, a mixture of concentrated sulfuric acid and concentrated nitric acid, aqua regia, a mixture of chromic acid and concentrated sulfuric acid, or a mixture of hydrogen peroxide and concentrated sulfuric acid.

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