A high-quality synthetic diamond production process

Abstract

The application discloses a high-quality synthetic diamond preparation process and relates to the technical field of diamond preparation. The process comprises the following steps: selecting a molybdenum sheet plated with a nano-diamond transition layer as a substrate, performing chemical mechanical polishing, ultrasonic cleaning and hydrogen plasma activation, adopting a microwave plasma chemical vapor deposition method, controlling the volume ratio of methane and hydrogen, the reaction temperature and the microwave power, and making the deposition thickness reach 20 micrometers; then, the film layer together with the substrate is placed into a high-pressure system without a catalyst for processing, so as to realize thermal recrystallization of the internal structure of the diamond and phase transformation of non-diamond phases; through the migration of light element impurities and the adsorption of carbon powder, the purity of the diamond crystal body is greater than 99.95%; finally, the high-quality single-crystal diamond with complete structure, low impurity content and stable crystal performance is obtained through temperature and pressure reduction processing and surface cleaning, and is suitable for high-precision fields such as high-end optoelectronics, quantum sensing and semiconductors, so that high-quality diamond preparation and application are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of diamond preparation, in particular to a preparation process of high-quality synthetic diamond. BACKGROUND

[0002] Diamond is widely used in high-tech fields such as precision cutting tools, optoelectronic devices, power semiconductors, quantum sensors, etc. due to its extremely high hardness, excellent thermal conductivity, excellent optical performance and stable chemical inertness. However, natural diamond resources are scarce and the acquisition process is costly, making it difficult to meet the growing demand for high-end applications. Therefore, how to efficiently and cost-effectively synthesize high-quality diamond has become the focus of current research and industry.

[0003] Currently, synthetic diamond mainly adopts high temperature and high pressure method (HTHP), chemical vapor deposition method (CVD) and detonation method.

[0004] Among them, high temperature and high pressure method uses metal catalysts (such as Fe, Ni, Co) to promote the conversion of graphite to diamond under high pressure and high temperature conditions, which is suitable for the growth of large-size single crystals. However, metal elements are easy to form inclusions or introduce impurities during the synthesis process, which seriously affects the optical transparency and structural integrity of diamond. In addition, the non-uniformity of reaction chamber temperature and pressure control easily leads to stress concentration in the crystal, resulting in cracks or dislocations, which further limits its application in high-end electronic and optical fields.

[0005] Chemical vapor deposition method forms diamond film by depositing active carbon atoms on the substrate surface through the cracking of carbon-containing gas (such as CH4 and H2 mixed gas) under low pressure, which has the advantages of high purity and strong controllability. However, the growth rate of chemical vapor deposition method is slow, which is difficult to meet the demand of large-scale production. At the same time, the substrate pretreatment process is complex, and any mistake may introduce amorphous carbon or graphite phase impurities. In addition, the plasma excitation process is extremely sensitive to gas pressure and power, and any fluctuation may easily lead to the doping of impurity elements (such as nitrogen and oxygen), affecting the dielectric and mechanical properties of diamond.

[0006] Detonation method generates nanodiamond under extreme conditions through high-energy explosion. Although the process is fast and cost-effective, the product particle size distribution is uneven, and there are a large number of functional groups on the surface, which requires complex chemical post-processing, and it is difficult to control the crystal form and impurity content, limiting its application in high-end materials.

[0007] Technical problems of the prior art: (1) Metal catalysts in high temperature and high pressure method introduce impurities or structural defects, and the stress control of the crystal is insufficient; (2) The growth rate of chemical vapor deposition method is slow, and non-diamond impurities are easy to be introduced, and the phase structure stability is poor; (3) The product quality of detonation method is uncontrollable, the post-processing burden is heavy, and it is difficult to meet the comprehensive requirements of high-end applications for diamond crystal purity, structural integrity and physical property stability.

[0008] In summary, it is found that the prior art at least has the following technical problems:

[0009] The prior art of diamond preparation has the technical problems of easy introduction of impurities, poor stability of structural defects and difficult control of quality, resulting in low purity, low structural integrity and low structural stability of the prepared diamond crystal. SUMMARY

[0010] The purpose of the present application is to provide a high-quality synthetic diamond preparation process to solve the technical problems of easy introduction of impurities, poor stability of structural defects and difficult control of quality in the prior art of diamond preparation.

[0011] The technical effects of the preferred technical solutions among the many technical solutions provided by the present application are described in detail below.

[0012] In order to solve the above technical problems, the present application provides the following technical solutions:

[0013] The present application provides a high-quality synthetic diamond preparation process, comprising the following steps:

[0014] S1, substrate pretreatment;

[0015] S1.1, material selection: molybdenum sheet substrate with nano-diamond transition layer plated on the surface;

[0016] S1.2, surface treatment: after chemical mechanical polishing, ultrasonic cleaning is performed, and the substrate is activated by hydrogen plasma;

[0017] S2, CVD diamond film growth;

[0018] S2.1, place the molybdenum sheet substrate into a microwave plasma CVD system, use reaction gas with a volume ratio of CH4 / H2 of 1:100, a total gas pressure of 10 kPa, and a gas flow rate of 500 sccm, control the substrate temperature at 980-1000℃, the microwave power at 3KW, and the growth rate at 15-20μm / h, and continue to grow until the diamond film thickness reaches 20μm;

[0019] S2.2, in-situ doping during diamond film growth is inhibited to avoid the generation of amorphous carbon;

[0020] S3, HTHP catalyst-free thermal recrystallization;

[0021] S3.1, packaging: place the diamond film and the molybdenum sheet substrate as a whole into a high-purity graphite crucible, and fill it with metal-free carbon powder;

[0022] S3.2, high pressure treatment: at a pressure of 6.3GPa and a temperature of 1500℃, keep the temperature and pressure for 1.5 hours;

[0023] S4, cooling and decompression and sample extraction;

[0024] S4.1, gradually cooling and releasing pressure to normal pressure according to a preset cooling curve and decompression curve, to avoid cracks in the generated diamond crystals caused by residual stress;

[0025] S4.2, after the sample is taken out, the generated diamond crystals are soaked in hot acid liquid to remove surface graphite residues;

[0026] S5, structure inspection; S5.1, verification of single crystal integrity; S5.2, crystal defect evaluation;

[0027] S6, post-processing and functionalization; S6.1, surface roughening; S6.2, terminal application adaptation processing.

[0028] In one of the embodiments, in the step S1.1, the thermal expansion coefficient of the molybdenum sheet substrate plated with a nano-diamond transition layer matches that of diamond, Δα≤1×10 -6 / K, for reducing interface stress.

[0029] In one of the embodiments, in the step S1.2, first, the substrate is polished by CMP chemical mechanical polishing, so that the surface roughness of the substrate is <1 nm; the polished substrate is sequentially cleaned by ultrasonic cleaning with acetone, ethanol and deionized water for at least 10 minutes; the cleaned substrate is treated by hydrogen plasma with a power of 300 W and a hydrogen flow of 200 sccm for at least 30 minutes, for forming dangling bonds on the substrate surface to enhance the nucleation density in CVD.

[0030] In one of the embodiments, in the step S2.2, argon assisted plasma is introduced in the microwave plasma CVD system to stabilize the plasma and inhibit nitrogen / oxygen impurity adsorption; and a double-layer gas distributor is used to make the gas diffuse uniformly and avoid local carbon concentration being too high.

[0031] In one of the embodiments, in the step S3.1, the purity of the high-purity graphite crucible is >99.999%; the non-metallic carbon powder with a particle size <10 μm is filled as a pressure transmission medium to isolate metal contamination; the outer layer of the high-purity graphite crucible is wrapped with a ZrO2 heat insulation layer to reduce the temperature gradient.

[0032] In one of the embodiments, in the step S3.2, the pressure rise rate is controlled at 50 MPa / s and the temperature rise rate is controlled at 100 ℃ / min, to avoid thermal shock leading to film peeling; the pressure fluctuation in the high-purity graphite crucible is controlled to be <±3%, and the temperature distribution change gradient is <10 ℃ / mm.

[0033] In one of the embodiments, in the step S3, dislocation and twin defects are eliminated by high pressure induced dynamic recombination of subgrain boundaries inside the diamond film; non-diamond carbon phase is transformed into single crystal diamond structure by phase transition of sp 2 To sp 3 ; and light element impurities in the generated single crystal diamond crystal migrate to the grain boundary and are discharged by carbon powder adsorption, achieving a bulk phase purity of > 99.95%.

[0034] In one of the embodiments, in the step S4.1, the preset cooling curve is linear cooling, and the cooling rate is controlled to be ≤ 50 ℃ / min; the preset pressure reduction curve is linear pressure reduction, and the pressure reduction rate is controlled to be ≤ 0.2 GPa / min; in the step S4.2, the volume ratio of the hot acid liquid is H2SO4:HNO3=3:1.

[0035] In one of the embodiments, in the step S5.1, the generated diamond crystal is detected by XRD to confirm that the half-height width of the crystal face diffraction peak of the diamond crystal is < 0.1°; the intensity ratio of the diamond characteristic peak in the Raman spectrum is > 99%, and there is no graphite D / G peak signal; in the step S5.2, TEM observation shows that the dislocation density is < 10 6 cm -2 , and electron paramagnetic resonance detection shows that the nitrogen vacancy center concentration is < 1 ppb.

[0036] In one of the embodiments, in the step S6.1, the diamond crystal is subjected to reactive ion etching to form a micron-level conical structure, thereby improving the light extraction efficiency of the diamond crystal; in the step S6.2, as an optical grade diamond, the diamond crystal is subjected to ultra-precision polishing to a surface roughness of < 0.5 nm; as a tool grade diamond, the diamond crystal is cut into a preset geometric shape by laser, and the interface bonding force is enhanced by chemical Ni plating.

[0037] The high-quality synthetic diamond preparation process provided by the application is a set of processes for preparing high-quality diamond by combining "nano transition layer guidance + high-purity CVD deposition + non-catalytic thermal recrystallization purification" in one, which is proposed for the key problems in the existing diamond synthesis process, such as easy introduction of impurities, poor stability of structural defects, and difficulty in product quality control, and significantly improves the crystallization quality and purity of the diamond material, and has the following beneficial effects:

[0038] 1. Low-defect nucleation and strong directional growth of crystal

[0039] By selecting a molybdenum sheet substrate coated with a nano diamond transition layer, and combining with fine pretreatment methods such as chemical mechanical polishing and hydrogen plasma activation, the orientation consistency and surface matching of the diamond crystal nucleus are significantly improved, the risk of amorphous carbon formation in the initial growth process is effectively reduced, and the crystallization integrity of the film layer is improved.

[0040] 2、Stable high purity CVD film deposition

[0041] By using a CH4 / H2 atmosphere with a volume fraction of 1:100, precise control of the temperature at 980-1000℃, a gas pressure of 10 kPa, a gas flow rate of 500 sccm, and a power of 3 kW, the diamond film is kept pure and dense at a high growth rate of 15-20 μm / h, and light element doping and non-diamond phase deposition caused by plasma fluctuation are avoided.

[0042] 3、Using non-catalytic HTHP thermal recrystallization technology to improve the integrity of the crystal structure

[0043] The diamond film formed by the CVD method is subjected to high-pressure high-temperature thermal recrystallization treatment in a metal carbon powder-free filling environment, by giving a pressure of 6.3 GPa, a high temperature of 1500℃, and a conversion time of 1.5 h, effectively promoting the reconstruction of the subgrain boundary of the synthesized diamond crystal, eliminating dislocations and twin defects, and converting the residual sp 2 carbon phase to sp 3 phase, thereby obtaining higher crystal integrity and purity.

[0044] 4、Light element impurity migration and purity improvement

[0045] By high temperature and high pressure induced impurity migration to the grain boundary, and cooperating with the carbon powder adsorption and discharge mechanism, the bulk phase purity is improved to more than 99.95%, effectively avoiding the problem of performance degradation caused by impurities in the crystal when the diamond crystal is applied in high-end optical or semiconductor applications with high quality requirements.

[0046] 5、Crystal preparation whole process stress control crystal integrity is high

[0047] By programming control of the cooling and pressure reduction curve, the thermal stress concentration of the crystal in the phase transition and thermal shrinkage process is avoided, the microcracks are avoided from the source, and the structural stability of the crystal is ensured.

[0048] 6、Suitable for terminal multi-scene functional treatment

[0049] The last stage of the process provides surface roughening and application scene function adaptation process steps, which can realize diversified post-processing such as optical coating, electrode contact, and electrochemical modification according to different application requirements, and improve the universality and industrial adaptability of the diamond crystal.

[0050] In summary, the process scheme provided by the present application has made breakthroughs in structural integrity, crystalline purity, process stability, and impurity control. In addition, the functional adaptation treatment of step S6.2 is particularly suitable for the demand for high-quality single crystal diamond in the fields of high-end electronics, quantum devices, and optical windows. Attached Figure Description

[0051] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments 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.

[0052] Figure 1 This is a schematic flowchart of the high-quality synthetic diamond preparation process of the present invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0054] The specific implementation provides a high-quality synthetic diamond preparation process. The process includes using a molybdenum sheet with a nanodiamond transition layer as a substrate. After chemical mechanical polishing, ultrasonic cleaning, and hydrogen plasma activation, microwave plasma chemical vapor deposition is employed. The volume ratio of methane to hydrogen, reaction temperature, and microwave power are controlled to achieve a deposition thickness of 20 μm. Subsequently, the film layer, along with the substrate, is placed in a catalyst-free high-pressure system for treatment, achieving thermal recrystallization of the diamond's internal structure and phase transformation of the non-diamond phase. Through the migration of light element impurities and the adsorption of carbon powder, the purity of the diamond crystal bulk phase is achieved to be greater than 99.95%. Finally, after cooling and depressurization treatment and surface cleaning, high-quality single-crystal diamond with a complete structure, low impurity content, and stable crystal performance is obtained. This process is suitable for high-precision fields such as high-end optoelectronics, quantum sensing, and semiconductors, enabling the preparation and application of high-quality diamond. It effectively solves the technical problems of existing diamond preparation technologies, such as easy introduction of impurities, poor structural defect stability, and difficulty in quality control.

[0055] The first implementation of a high-quality synthetic diamond preparation process, for example Figure 1 As shown, it includes multiple steps S1 to S6, wherein the steps are performed in the following order: Figure 1 The steps shown are performed sequentially from S1 to S6; specifically: S1, substrate pretreatment;

[0056] S1.1 Material selection: Molybdenum substrate with a nano-diamond transition layer deposited on its surface;

[0057] S1.2 Surface treatment: After chemical mechanical polishing, ultrasonic cleaning is performed, and the substrate is activated by hydrogen plasma;

[0058] S2, CVD diamond film growth;

[0059] S2.1, Put the molybdenum sheet substrate into the microwave plasma CVD system, the reaction gas is CH4 / H2 with a volume ratio of 1:100, the total gas pressure is 10 kPa, the gas flow rate is 500 sccm, the substrate temperature is controlled at 980-1000 DEG C, the microwave power is 3 KW, and the growth rate is 15-20 mu m / h, and the growth is continued until the diamond film thickness reaches 20 mu m; wherein the microwave plasma CVD system is a microwave plasma CVD (Microwave PCVD, MPCVD);

[0060] S2.2, In-situ doping is inhibited during diamond film growth to avoid the generation of amorphous carbon;

[0061] S3, HTHP catalyst-free thermal recrystallization;

[0062] S3.1, Packaging: the diamond film and the molybdenum sheet substrate are put into a high-purity graphite crucible as a whole, and filled with metal-free carbon powder;

[0063] S3.2, High pressure treatment: the pressure is 6.3 GPa, the temperature is 1500 DEG C, and the pressure holding time is 1.5 hours;

[0064] S4, Cooling, pressure reduction and sample extraction;

[0065] S4.1, According to the preset cooling curve and pressure reduction curve, gradually cool and release the pressure to atmospheric pressure to avoid cracks in the generated diamond crystal caused by residual stress;

[0066] S4.2, After taking out the sample, the generated diamond crystal is soaked in hot acid liquid to remove the surface graphite residue;

[0067] S5, Structure inspection; S5.1, verification of single crystal integrity; S5.2, crystal defect evaluation;

[0068] S6, Post-processing and functionalization; S6.1, surface roughening; S6.2, terminal application adaptation processing.

[0069] The high-quality synthetic diamond preparation process of the application proposes a set of composite preparation process of high-quality diamond integrating "nano transition layer guidance + high-purity CVD deposition + catalyst-free thermal recrystallization purification", which solves and significantly improves the crystallization quality and purity of diamond material, and has the following advantages: low defect nucleation and strong directional growth of crystal: by selecting a molybdenum sheet substrate coated with a nano diamond transition layer, and combining with fine pretreatment methods such as chemical mechanical polishing and hydrogen plasma activation, the orientation consistency and surface matching of the diamond crystal nucleus are significantly improved, the risk of amorphous carbon formation in the initial growth process is effectively reduced, and the crystalline integrity of the film layer is improved.

[0070] Stable high-purity CVD film layer deposition: using a CH4 / H2 atmosphere with a volume fraction of 1:100, temperature control at 980-1000℃, gas pressure of 10kPa, gas flow rate of 500sccm, and power of 3kW, a high growth rate of 15-20μm / h is achieved while maintaining the purity and density of the diamond film, avoiding light element doping and non-diamond phase deposition caused by plasma fluctuations.

[0071] By using the non-catalytic HTHP thermal recrystallization technology, the integrity of the crystal structure is improved: the diamond film formed by the CVD method is subjected to high-pressure and high-temperature thermal recrystallization treatment in a non-metal carbon powder filling environment, by giving a pressure of 6.3GPa, a high temperature of 1500℃ and a conversion time of 1.5h, effectively promoting the reconstruction of the subgrain boundary of the synthesized diamond crystal, eliminating dislocations and twin defects, and making the residual sp 2 carbon phase to sp 3 phase conversion, thereby obtaining higher crystal integrity and purity.

[0072] Light element impurity migration and purity improvement: by high temperature and high pressure induced impurity migration to the grain boundary, and cooperating with the carbon powder adsorption and discharge mechanism, the bulk phase purity is improved to more than 99.95%, effectively avoiding the performance degradation problem of diamond crystals in high-end optical or semiconductor applications due to impurities in the crystal.

[0073] Crystal preparation whole process stress control crystal integrity: by programming control of cooling and pressure reduction curve, the thermal stress concentration of the crystal in the phase transition and thermal shrinkage process is avoided, the microcracks are avoided from the source, and the structure stability of the crystal is ensured.

[0074] Suitable for terminal multi-scene functional treatment: the surface roughening and application scene function adaptation process provided in the last stage of the process can realize various post-treatments such as optical coating, electrode contact, and electrochemical modification according to different application requirements, and improve the versatility and industrial adaptability of the diamond crystal.

[0075] In summary, the process scheme provided by the present application has made breakthroughs in structure integrity, crystalline purity, process stability, and impurity control. In addition, the functional adaptation process of step S6.2 is particularly suitable for the demand of high-quality single crystal diamond in the fields of high-end electronics, quantum devices, and optical windows.

[0076] As one of the optional embodiments:

[0077] As to the specific indexes of the above S1.1 and S1.2 steps, in the S1.1 step, in order to solve the problem of film layer peeling or stress concentration caused by thermal expansion mismatch of the traditional metal substrate, a molybdenum sheet substrate plated with a nano-diamond transition layer is selected, so that the thermal expansion coefficient of the substrate matches that of the diamond, and Δα≤1×10-6 / K, for reducing the interface stress.

[0078] In the S1.1 step, the molybdenum sheet substrate with the thermal expansion coefficient matching that of the diamond can significantly reduce the interface stress concentration caused by thermal expansion mismatch in the high-temperature deposition and high-pressure recrystallization process, and effectively prevent the generation of film layer peeling or crystal cracks.

[0079] In the subsequent process, the film-substrate interface stability can be improved, and the deposition layer integrity can be ensured.

[0080] In the S1.2 step, first, the substrate is subjected to CMP (Chemical Mechanical Polishing) to make the substrate surface roughness <1 nm; the polished substrate is subjected to ultrasonic cleaning with acetone, ethanol and deionized water for at least 10 minutes; and the cleaned substrate is subjected to hydrogen plasma activation treatment at a power of 300 W and a hydrogen flow of 200 sccm for at least 30 minutes, for forming dangling bonds on the substrate surface to enhance the nucleation density in CVD.

[0081] In application, after CMP (Chemical Mechanical Polishing) polishing, the substrate surface roughness is <1 nm, which ensures the atomic-level flatness of the deposition interface; and then, ultrasonic cleaning with acetone, ethanol and deionized water for at least 10 minutes in each step can completely remove the surface organic contamination and particle residues.

[0082] In the subsequent process, the nucleation uniformity and film layer density can be significantly improved, and the problems of abnormal nucleation and structural defects caused by surface contamination or roughness can be overcome.

[0083] As to the specific indexes of the above S2.2 step, in the S2.2 step, argon auxiliary plasma is introduced into the microwave plasma CVD system to stabilize the plasma and inhibit nitrogen / oxygen impurity adsorption; and a double-layer gas distributor is used to make the gas uniformly diffuse and avoid excessive local carbon concentration.

[0084] In application, by introducing argon to stabilize the plasma, the nitrogen and oxygen active particle concentration in the reaction zone can be effectively diluted, and impurity doping can be reduced; by using a double-layer gas distributor, the gas flow field distribution is optimized, and excessive local carbon source concentration is avoided to cause non-diamond phase deposition; amorphous carbon generation is controlled, the film layer purity and phase structure uniformity are improved, and the problems of impurity doping and film layer amorphization caused by unstable plasma and uneven carbon source distribution are overcome.

[0085] Regarding the specific indicators for steps S3.1 and S3.2 above, in step S3.1, the purity of the high-purity graphite crucible is >99.999%; the particle size of the filled metal-free carbon powder is <10μm, which serves as a pressure transmission medium to isolate metal contamination; and the outer layer of the high-purity graphite crucible is wrapped with a ZrO2 heat insulation layer to reduce the temperature gradient.

[0086] In applications, high-purity graphite crucibles can prevent the introduction of impurities under high-temperature conditions; the use of carbon powder pressure transmission medium with a particle size of <10μm can tightly fill the gaps and shield the diffusion of metal impurities; the ZrO2 heat insulation layer wrapped around the graphite crucible can reduce the temperature gradient and improve the temperature control uniformity of the reaction zone; thus, the risk of impurity introduction is reduced, the uniformity of the crystal structure is improved, and the problems of metal contamination and thermal stress affecting crystal quality in high-pressure systems are solved.

[0087] In step S3.2, the pressure increase rate is required to be controlled at 50 MPa / s and the heating rate is required to be controlled at 100 °C / min to avoid thermal shock causing film peeling; the pressure fluctuation inside the high-purity graphite crucible is controlled to be <±3% and the temperature distribution gradient is controlled to be <10 °C / mm.

[0088] When applying the technology, by controlling the pressure increase rate to 50 MPa / s and the heating rate to 100 ℃ / min, the warping or cracking of the diamond film caused by thermal shock can be effectively avoided; and the pressure fluctuation inside the graphite crucible is <±3% and the temperature gradient is <10 ℃ / mm, which can ensure the stability of the heat treatment environment.

[0089] In step S3, dislocations and twin defects are eliminated by dynamically reorganizing the positions of subgrain boundaries (i.e., lattice distortion regions) within the diamond film under high pressure; the non-diamond carbon phase undergoes sp2444-fold thermal oxidation under high temperature and pressure. 2 to sp 3 The phase transition transforms the crystal into a single-crystal diamond structure; and the light element impurities in the generated single-crystal diamond crystal migrate to the grain boundaries and are removed by adsorption of carbon powder, achieving a bulk purity of >99.95%.

[0090] In application, by completing the transformation of sp2 carbon into sp3 diamond structure and the migration of impurities to grain boundaries and adsorption by carbon powder, the bulk purity reaches >99.95%.

[0091] This step can improve crystal integrity, eliminate dislocations and impurities, obtain high-purity crystals, and solve the problem of removing non-diamond phases, dislocation defects, and light element impurities.

[0092] Regarding the specific indicators of steps S4.1 and S4.2 above, in step S4.1, the preset cooling curve is linear cooling, and the cooling rate is controlled to be ≤50℃ / min; the preset pressure reduction curve is linear pressure reduction, and the pressure reduction rate is controlled to be ≤0.2GPa / min.

[0093] By adopting continuous linear cooling and linear pressure reduction, residual thermal stress can be avoided from gathering in the crystal, thereby reducing thermal cracks or dislocation recombination; the integrity and physical stability of the finished crystal are improved, and the problem of thermal stress damage in the rapid cooling / pressure reduction process is overcome.

[0094] In step S4.2, the volume ratio of the hot acid liquid is H2SO4:HNO3=3:1.

[0095] In application, the hot acid liquid with the ratio can remove residual graphite or carbon impurities on the surface of the crystal, avoid the influence of the contaminated layer on the optical / electronic performance, improve the cleanliness of the crystal surface, ensure the subsequent processing performance, remove the residual graphite in processing, and improve the consistency of the material.

[0096] Regarding the specific indexes of the above S5.1 and S5.2 steps, in step S5.1, the generated diamond crystal is detected by XRD to confirm that the half-height width of the crystal face diffraction peak of the diamond crystal is less than 0.1°; the intensity ratio of the diamond characteristic peak in the Raman spectrum is greater than 99%, and there is no graphite D / G peak signal.

[0097] In application, the XRD measurement shows that the half-height width of the crystal face diffraction peak is less than 0.1° and the Raman peak intensity ratio is greater than 99%, indicating that the diamond crystal has ordered arrangement inside and no graphite D / G peak signal is detected; it can accurately confirm whether there are obvious impurities or structural defects in the diamond crystal, and provide accurate quality evaluation basis for the quality inspection link and verify the reliability of the crystal structure.

[0098] In step S5.2, the TEM observation shows that the dislocation density is less than 10 6 cm -2 , and the electron paramagnetic resonance (EPR) detects that the nitrogen vacancy center concentration is less than 1 ppb.

[0099] By detecting the dislocation density by transmission electron microscopy (TEM) and the nitrogen vacancy concentration by EPR (electron paramagnetic resonance), it can be shown that the crystal defects are extremely low and the impurity control is appropriate; it reflects the high-purity, low-defect crystal quality and verifies the effectiveness of the technical scheme in defect control and doping suppression.

[0100] Regarding the specific indexes of the above S6.1 step, in step S6.1, the diamond crystal is etched by reactive ion etching to form a micron-level conical structure, which improves the light extraction efficiency of the diamond crystal.

[0101] In application, the reactive ion etching forms a micron-level conical structure to improve the light extraction efficiency of the diamond, which is helpful in laser, semiconductor and other optical applications to enhance the light extraction rate and meet the requirements of photonic device use, and overcome the light loss problem caused by high refractive index of diamond.

[0102] The second embodiment of the high-quality synthetic diamond preparation process differs from the first embodiment in that, in step S6.2, when the generated diamond needs to be an optical-grade diamond, the diamond crystal is super-polished to a surface roughness <0.5 nm.

[0103] In application, if the diamond crystal is for optical use, the diamond crystal needs to be super-polished to a surface roughness <0.5 nm to improve light transmission and interface finish.

[0104] When the generated diamond is a tool-grade diamond, the diamond crystal is cut into a preset geometric shape by laser and is plated with Ni by electroless plating to enhance the interface bonding force.

[0105] In application, if it is for tool use, the interface is strengthened by laser cutting + electroless plating Ni to adapt to the cutting or grinding tool process.

[0106] By processing the adaptation process, it helps to realize seamless conversion from material preparation end to terminal application, meets the specific requirements of high-end optical and industrial tool different fields for crystal post-processing, and makes the high-quality diamond crystal diversified in use.

[0107] The third embodiment of the high-quality synthetic diamond preparation process differs from the first embodiment in that, in step S1.1 material selection, the substrate can be an ultrapure SiC single crystal substrate.

[0108] In application, the ultrapure SiC single crystal substrate refers to an ultrapure SiC single crystal substrate with a purity of 99.9999%, which has a similar lattice constant to diamond and excellent thermal conductivity, can further improve the interface bonding quality and thermal stability, is suitable for high-end electronic-grade diamond preparation, and can also reduce the stress and impurity diffusion of the diamond crystal during preparation, improve the interface quality, and overcome the risk of thermal stress and impurity conduction that may exist in metal substrates through high-purity non-metal substrates.

[0109] The technical features of the above embodiments can be combined in any manner. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described.

Claims

1. A high quality synthetic diamond production process characterized by, The process comprises the following steps: S1, substrate pretreatment; S1.1, material selection: molybdenum sheet substrate plated with nanodiamond transition layer on the surface; S1.2, surface treatment: after chemical mechanical polishing, ultrasonic cleaning is performed, and the substrate is activated by hydrogen plasma; S2, CVD diamond film growth; S2.1, place the molybdenum sheet substrate into a microwave plasma CVD system, use reaction gas with a volume ratio of CH4 / H2 of 1:100, a total gas pressure of 10 kPa, and a gas flow rate of 500 sccm, control the substrate temperature at 980-1000℃, the microwave power at 3KW, and the growth rate at 15-20μm / h, and continuously grow until the diamond film thickness reaches 20μm; S2.2, in-situ doping during diamond film growth is inhibited to avoid the generation of amorphous carbon; In step S2.2, argon auxiliary plasma is introduced into the microwave plasma CVD system to stabilize the plasma and inhibit nitrogen / oxygen impurity adsorption; a double-layer gas distributor is used to uniformly diffuse the gas and avoid local carbon concentration being too high; S3, HTHP catalyst-free thermal recrystallization; S3.1, packaging: place the diamond film and the molybdenum sheet substrate as a whole into a high-purity graphite crucible and fill it with metal-free carbon powder; S3.2, high-pressure treatment: at a pressure of 6.3GPa and a temperature of 1500℃, maintain the temperature and pressure for 1.5 hours; S4, temperature and pressure reduction and sample extraction; S4.1, gradually reduce the temperature and release the pressure to atmospheric pressure according to the preset temperature and pressure reduction curves to avoid cracks in the generated diamond crystals caused by residual stress; In step S4.1, the preset temperature reduction curve is linear temperature reduction, and the temperature reduction rate is controlled to be ≤50℃ / min; the preset pressure reduction curve is linear pressure reduction, and the pressure reduction rate is controlled to be ≤0.2GPa / min; S4.2, after taking out the sample, use hot acid liquid to soak the generated diamond crystals to remove the surface graphite residue; In step S4.2, the volume ratio of H2SO4:HNO3 in the hot acid liquid is 3:1; S5, structure inspection; S5.1, verify the integrity of the single crystal; S5.2, evaluate the crystal defects; S6, post-processing and functionalization; S6.1, surface roughening; S6.2, terminal application adaptation processing.

2. The high-quality synthetic diamond preparation process according to claim 1, characterized in that, In the S1.1 step, the thermal expansion coefficient of the molybdenum sheet substrate plated with the nanodiamond transition layer matches that of the diamond, Δα≤1×10 -6 / K, for reducing the interface stress.

3. The high-quality synthetic diamond preparation process according to claim 1, characterized in that, In step S1.2, first polish the substrate by CMP chemical mechanical polishing to make the substrate surface roughness <1nm; Ultrasonically clean the polished substrate with acetone, ethanol, and deionized water for at least 10 minutes each; After cleaning the substrate, activate the substrate with hydrogen plasma at a power of 300W and a hydrogen flow rate of 200sccm for at least 30 minutes to form dangling bonds on the substrate surface to enhance the nucleation density in CVD.

4. The high-quality synthetic diamond preparation process according to claim 1, characterized in that, In step S3.1, the purity of the high-purity graphite crucible is >99.999%; the metal-free carbon powder with a particle size <10μm is used as a pressure transmission medium to isolate metal contamination; The high-purity graphite crucible is wrapped with a ZrO2 heat insulation layer outside to reduce the temperature gradient.

5. The high-quality synthetic diamond preparation process of claim 1, wherein, In the step S3.2, the pressure increase rate is controlled at 50 MPa / s and the temperature increase rate is controlled at 100 ℃ / min to avoid film layer peeling caused by thermal shock; The pressure fluctuation in the high-purity graphite crucible is controlled to be less than ±3%, and the temperature distribution change gradient is less than 10 ℃ / mm.

6. The high-quality synthetic diamond preparation process of claim 1, wherein, In step S3, dislocations and twin defects are eliminated by high-pressure-induced dynamic reorganization of subgrain boundaries within the diamond film; the non-diamond carbon phase undergoes sp244-fold reaction under high temperature and high pressure. 2 to sp 3 The phase transition transforms the crystal into a single-crystal diamond structure; and the light element impurities in the generated single-crystal diamond crystal migrate to the grain boundaries and are removed by adsorption of carbon powder, achieving a bulk purity of >99.95%.

7. The high-quality synthetic diamond preparation process of claim 1, wherein, In the step S5.1, the generated diamond crystal is subjected to XRD detection, and it is confirmed that the half-height width of the crystal face diffraction peak of the diamond crystal is less than 0.1°, the intensity ratio of the diamond characteristic peak in the Raman spectrum is greater than 99%, and there is no graphite D / G peak signal; In step S5.2, the TEM observed dislocation density < 10 6 cm -2 , electron paramagnetic resonance detected nitrogen-vacancy center concentration < 1 ppb.

8. The high-quality synthetic diamond preparation process of claim 1, wherein, In the step S6.1, the diamond crystal is subjected to reactive ion etching to form a micron-level conical structure, thereby improving the light output efficiency of the diamond crystal; In the step S6.2, as an optical-grade diamond, the diamond crystal is subjected to ultra-precision polishing to a surface roughness of less than 0.5 nm; as a tool-grade diamond, the diamond crystal is cut into a preset geometric shape by laser and is subjected to chemical Ni plating to enhance the interface bonding force.

Images