A system and method for the production of large colorless diamonds by heteroepitaxy using synergistic effects of multi-frequency plasma resonance and thermal gradients

Abstract

The application discloses a kind of multi-frequency plasma resonance and thermal gradient coordination's heteroepitaxial large clara color diamond preparation system and method.The system is introduced into 2.45GHz and 5.8GHz double-frequency microwave in MPCVD reaction chamber simultaneously, realizes the superposition of low-energy high-density and high-energy low-density plasma, to optimize carbon cluster deposition energy distribution.Meanwhile, by temperature control heating, the substrate thermal gradient that decreases from center to edge is formed, and the seamless splicing growth of diamond crystal is promoted.The system integrates multi-path gas injection and in-situ Raman / photoluminescence feedback mechanism, dynamically controls color center doping and defect generation, realizes the stable preparation of high-purity color diamond with ≥6ct, defect density less than 10 6 cm ‑2 , and uniform color center distribution.

Description

Technical Field

[0001] This invention relates to the field of artificial gemstone material preparation technology, specifically to a heteroepitaxial large-carat colored diamond preparation system and method using multi-frequency plasma resonance and thermal gradient synergy. Background Technology

[0002] Single-crystal diamond, due to its excellent physicochemical properties, has broad application prospects in detectors, optoelectronic devices, and other fields. Currently, microwave plasma chemical vapor deposition (MPCVD) is commonly used in industry to epitaxially grow large-size single-crystal diamonds on high-temperature, high-pressure (HPHT) seed crystals. However, obtaining large-area, high-quality wafers remains a challenge. According to existing technologies, the maximum single-crystal area of ​​CVD diamond grown on single-crystal substrates using MPCVD is only about 2 inches in diameter, with a fastest growth rate of about 105 μm / h. For heteroepitaxial growth, due to lattice mismatch and thermal stress, it is even more difficult to obtain large-size, high-perfection single-crystal diamonds. It is known that heteroepitaxial growth of diamond on iridium (Ir) films / sapphire substrates can achieve relatively large grain sizes and high crystal quality. For example, some studies have used substrate surface patterning nucleation combined with epitaxial lateral overgrowth (ELO) to promote grain agglomeration, thereby preparing large-area heteroepitaxial single-crystal diamonds. However, such methods are complex, requiring patterning on the substrate or multi-step growth, and still face challenges such as grain boundary defects and stress, which limit further expansion of crystal size.

[0003] On the other hand, colored diamonds exhibit colors such as blue, yellow, and pink due to the doping of different elements (such as boron and nitrogen) or the presence of specific color center defects, making them valuable for jewelry and potential applications in quantum optics. However, introducing impurities during CVD growth often leads to a decrease in crystal quality and uneven color distribution. Firstly, conventional continuous doping easily results in uneven concentration distribution of dopant elements within the crystal. For example, when using nitrogen-containing gas for direct doping growth, the distribution of nitrogen in CVD diamond exhibits strong layered unevenness, forming gradient color bands. Studies have shown that this unevenness is mainly due to the layered step growth mechanism of CVD diamond. This results in inconsistent color and increased internal stress in the obtained nitrogen-doped diamond crystals, requiring post-treatment such as annealing to improve color and stress. Secondly, high-concentration doping (such as high nitrogen) can also promote the formation of non-diamond phases (such as graphite carbon clusters), further reducing crystal transparency and mechanical strength. Therefore, achieving uniform and controllable impurity incorporation while ensuring crystal integrity is a key technical challenge in the field of colored diamond preparation.

[0004] Furthermore, the current large-size single-crystal CVD diamond growth cycle is long (often lasting several days to weeks), and various parameters (plasma state, temperature field, gas phase composition, etc.) may drift during the growth process. The lack of real-time monitoring and control mechanisms may lead to fluctuations in crystal quality. However, traditional MPCVD equipment usually operates in open-loop mode with preset parameters and rarely has means to monitor the growth status in situ, let alone dynamically adjust process parameters based on monitoring data to optimize crystal quality. For example, although there are reports in experimental studies of using Raman spectroscopy to monitor diamond phase purity or using light reflection to measure growth rate, there is still no mature solution for introducing spectral-linked feedback control into industrial equipment to improve growth consistency.

[0005] Finally, current MPCVD growth of single-crystal diamond generally employs a single-frequency (2.45 GHz) microwave-excited plasma. While single-frequency microwave plasma generates a certain plasma density, its plasma electron energy distribution is singular, making it difficult to simultaneously achieve both deposition rate and quality. For example, high power results in high plasma electron temperatures, which can exacerbate the formation of non-diamond phases or etch the growth surface, while lower power reduces plasma density, leading to a decrease in growth rate. Experience in semiconductor plasma processing shows that introducing dual-frequency or multi-frequency excitation can decouple plasma density and energy distribution to some extent: high-frequency power is mainly used to maintain high plasma density, while low-frequency power can control ion bombardment energy. However, in the field of diamond CVD, there are no mature reports of using multi-frequency microwave plasma to improve the growth environment.

[0006] In summary, existing technologies for the preparation of large-size single-crystal diamonds (especially colored diamonds) via heteroepitaxial growth have the following shortcomings: 1) There is a lack of effective methods to address lattice mismatch and thermal stress, which limits the size of single crystals; 2) The distribution of doped color centers is uneven, requiring post-processing; 3) The growth process lacks closed-loop control, resulting in poor quality consistency; 4) Single-frequency plasma makes it difficult to simultaneously optimize the growth rate and crystal quality. Summary of the Invention

[0007] Technical Objective: To address the shortcomings of existing technologies, this invention discloses a heteroepitaxial large-carat colored diamond preparation system and method based on multi-frequency plasma resonance and thermal gradient synergy. This system achieves comprehensive optimization of key aspects of diamond epitaxial growth, such as nucleus merging, growth orientation, and doping introduction, by simultaneously exciting two microwave plasmas of different frequencies in the MPCVD reaction chamber and combining this with precise control of the substrate temperature field.

[0008] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] A system for preparing large-carat colored diamonds via heteroepitaxial deposition using multi-frequency plasma resonance and thermal gradient synergy includes:

[0010] A microwave plasma excitation device includes a first microwave source and a second microwave source, wherein the first microwave source and the second microwave source have different frequencies and are both coupled to a reaction chamber to simultaneously generate a coexisting first plasma and a second plasma within the chamber.

[0011] A substrate stage is used to fix a heterogeneous substrate and, in conjunction with a temperature control device, to establish a temperature gradient field on the heterogeneous substrate that gradually decreases from the center to the edge.

[0012] A gas supply device includes at least one main gas channel and at least one doping gas channel. The main gas channel is used to supply carbon-containing gas and carrier gas into the reaction chamber to maintain the reaction atmosphere required for diamond growth. The doping gas channel is used to selectively introduce doping gas containing impurity elements into the reaction chamber.

[0013] In-situ monitoring devices, including Raman spectrometer and photoluminescence spectrometer, are used to detect the quality and color center characteristics of diamond crystals grown in the reaction chamber in real time.

[0014] The control system is electrically connected to the first microwave source, the second microwave source, the temperature control device, the gas supply device, and the in-situ monitoring device. It is configured to dynamically adjust the microwave source power output, temperature gradient field parameters, and the timing and flow rate of dopant gas based on the data obtained from the in-situ monitoring device, so as to form a closed-loop control during the diamond epitaxial growth process and optimize the crystal growth rate, defect density, and doping uniformity.

[0015] Preferably, the heterogeneous substrate comprises a sapphire single-crystal substrate and an Ir metal thin layer formed on the surface of the substrate, wherein a single-atom-thick layer of graphene is coated on the Ir metal thin layer as a lattice buffer isolation layer.

[0016] Preferably, the operating frequency of the first microwave source is 2.45 GHz, and the operating frequency of the second microwave source is 5.80 GHz; the power ratio of the two microwave sources when they operate synchronously is adjustable so that the first plasma exhibits high density and low electron temperature characteristics, and the second plasma exhibits low density and high electron temperature characteristics, and a plasma region with a bimodal electron energy distribution is formed by superimposing them in the reaction chamber.

[0017] Preferably, the temperature control device includes a zone heater or temperature control component for maintaining the temperature of the central region of the substrate stage at 1000-1100℃ and the temperature of the peripheral region of the substrate stage at 800-900℃, thereby forming a gradient temperature field with a temperature difference of 200-300℃ from the center to the edge on the substrate surface.

[0018] Preferably, the doping gas channel of the gas supply device includes multiple independently controlled gas inlets for introducing different doping gases, wherein the doping gases include one or more selected from nitrogen, borane, phosphine, and sodium-containing compound gases, to impart predetermined color or electrical properties to the grown diamond crystal.

[0019] Preferably, the Raman spectrometer of the in-situ monitoring device is used to monitor the intensity, full width at half maximum (FWHM), and shift of the characteristic Raman peaks of the diamond crystal to assess crystal quality and stress; the photoluminescence spectrometer is used to monitor the luminescence intensity and spectral lines of the color centers in the diamond to assess the concentration and distribution of the doped color centers; the control system is equipped with a feedback algorithm to calculate the adjustment amount based on the signal deviation output by the Raman spectrometer and the photoluminescence spectrometer, and adjust the corresponding process parameters to keep the monitoring signal within the predetermined target range.

[0020] This invention also provides a method for preparing large-carat heteroepitaxial colored diamonds using multi-frequency plasma resonance and thermal gradient synergy, characterized in that it is applied to the aforementioned heteroepitaxial large-carat colored diamond preparation system using multi-frequency plasma resonance and thermal gradient synergy, specifically including the following steps:

[0021] S1. Select a substrate with a small lattice mismatch with diamond as the substrate, and deposit a layer of sp on the surface of the substrate. 2 The hybrid carbon atom layer serves as a buffer layer;

[0022] S2. Place the substrate in the microwave plasma CVD reaction chamber, heat the central region of the substrate to a first temperature, and heat the edge region of the substrate to a second temperature, so that a temperature gradient decreasing from the center to the edge is established on the substrate surface.

[0023] S3. Introduce carbon-containing reactive gas and carrier gas into the reaction chamber, and simultaneously excite microwaves of the first frequency and the second frequency to generate a dual-frequency plasma with both high-density low-energy components and low-density high-energy components.

[0024] S4. Diamond heteroepitaxial growth is performed on a substrate under the action of dual-frequency plasma. The temperature gradient promotes the lateral expansion of diamond grains on the substrate surface and their fusion to grow into a continuous single crystal film.

[0025] S5. During the diamond growth process, doping gas is introduced in a way that is synchronized with the dual-frequency plasma timing, so that the doping elements are incorporated into the growing diamond lattice according to a predetermined rule, thereby forming the color center or impurity distribution of the target color. The introduction of the doping gas includes controlling the timing of the doping gas introduction, the pulse width or the flow rate, so that it is coordinated with the modulation period of the second frequency microwave power.

[0026] S6. Real-time monitoring of diamond growth status is carried out using in-situ Raman spectroscopy and photoluminescence spectroscopy. Based on the monitored crystal quality parameters and color center concentration parameters, the power of the first frequency microwave and the second frequency microwave, the temperature setting of the temperature gradient, or the flow rate of the doping gas are dynamically adjusted to correct growth deviations in real time.

[0027] S7. Continue the above growth process until a diamond single crystal of a set thickness or weight is obtained. Stop the microwave plasma and cool the chamber. Remove the epitaxially grown colored diamond wafer.

[0028] Preferably, the doping gas is a nitrogen-containing gas, and the power output of the second frequency microwave is periodically and alternately modulated so that a high-energy plasma pulse corresponds to each nitrogen doping, so as to promote the combination of nitrogen atoms with lattice vacancies to form nitrogen-vacancy color centers.

[0029] Preferably, in step S5, by changing the type or concentration of doping gas at different growth stages, the diamond crystal can achieve different colors in different regions. The doping gases introduced successively include nitrogen and borane, so that the color of the diamond crystal gradually changes from blue to yellow from one end to the other.

[0030] Preferably, in step S6, feedback control is used to maintain the intensity of the diamond peak in the Raman spectrum during the diamond crystal growth process above a preset lower limit and the intensity of the D band below a preset upper limit, and to maintain the intensity of the emission peak of the target color center in the photoluminescence spectrum within a preset range.

[0031] Beneficial Effects: The heteroepitaxial large-carat colored diamond preparation system and method based on multi-frequency plasma resonance and thermal gradient synergy provided by this invention has the following beneficial effects:

[0032] 1. This invention utilizes the substrate temperature gradient to induce lateral epitaxial growth of diamond, and with the help of a buffer layer to reduce the stress at the heterostructure interface, it achieves seamless grain splicing, breaking through the bottleneck of limited grain size in traditional heteroepitaxial growth, and can obtain large-area single-crystal diamond substrates; the dual-frequency microwave plasma simultaneously provides high-density low-temperature plasma and high-energy components, so that the deposition rate and crystal quality are optimized in a balanced way. Compared with single-frequency plasma growth, it can improve the growth rate while maintaining low defects and shorten the time required to prepare large-carat crystals.

[0033] 2. By using multi-channel gas doping synchronized with plasma timing, this invention can precisely control the introduction and distribution of color centers during the growth process, avoiding the concentration gradient and stress concentration caused by conventional doping. The resulting colored diamond has a uniform and pure color, and can achieve multiple colors such as blue, pink, and yellow or gradient transitions as needed, without the need for cumbersome post-processing. This invention is equipped with in-situ Raman and photoluminescence spectroscopy monitoring combined with a data-driven feedback control system, which can correct anomalies in a timely manner during the growth process, ensuring the consistency and repeatability of crystal quality. This intelligent control makes the long-cycle growth process stable and reliable, reduces the scrap rate, and improves the yield of industrial production. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0035] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0036] Figure 2 This is a schematic diagram of the temperature gradient distribution on the substrate surface in the system of the present invention;

[0037] Figure 3 This is a schematic diagram comparing the electron energy distribution of dual-frequency microwave plasma and traditional single-frequency plasma. Detailed Implementation

[0038] The present invention will now be described more clearly and completely by way of a preferred embodiment in conjunction with the accompanying drawings, but this does not limit the invention to the scope of the described embodiment.

[0039] like Figure 1 As shown, this invention discloses a heteroepitaxial large-carat colored diamond preparation system based on multi-frequency plasma resonance and thermal gradient synergy, comprising:

[0040] A vacuum reaction chamber 3, which contains a substrate stage 4 and a gas feeding device;

[0041] The microwave plasma excitation device includes a first microwave source 1 and a second microwave source 2. The first microwave source 1 and the second microwave source 2 have different frequencies and are both coupled to a reaction chamber to simultaneously generate a coexisting first plasma and a second plasma within the chamber. In a specific embodiment, the operating frequency of the first microwave source is 2.45 GHz, and the operating frequency of the second microwave source is 5.80 GHz. The power ratio of the two microwave sources when they operate synchronously is adjustable so that the first plasma exhibits high density and low electron temperature characteristics, and the second plasma exhibits low density and high electron temperature characteristics, and they are superimposed in the reaction chamber to form a plasma region with a bimodal electron energy distribution.

[0042] The substrate stage 4 is used to fix the heterogeneous substrate 5 and, in conjunction with the temperature control device, to establish a temperature gradient field on the heterogeneous substrate 5 that gradually decreases from the center to the edge.

[0043] A gas supply device includes at least one main gas channel 6 and at least one doping gas channel 7. The main gas channel is used to supply carbon-containing gas and carrier gas into the reaction chamber to maintain the reaction atmosphere required for diamond growth. The doping gas channel is used to selectively introduce doping gas containing impurity elements into the reaction chamber.

[0044] The in-situ monitoring device, including a Raman spectrometer 8 and a photoluminescence spectrometer 9, is used to detect the quality and color center characteristics of the diamond crystals grown in the reaction chamber in real time.

[0045] The control system 10 is electrically connected to the first microwave source, the second microwave source, the temperature control device, the gas supply device, and the in-situ monitoring device. It is configured to dynamically adjust the microwave source power output, temperature gradient field parameters, and the timing and flow rate of the doping gas based on the data obtained from the in-situ monitoring device, so as to form a closed-loop control during the diamond epitaxial growth process and optimize the crystal growth rate, defect density, and doping uniformity.

[0046] This invention also provides a method for preparing large-carat heteroepitaxial colored diamonds using multi-frequency plasma resonance and thermal gradient synergy, characterized in that it is applied to the aforementioned heteroepitaxial large-carat colored diamond preparation system using multi-frequency plasma resonance and thermal gradient synergy, specifically including the following steps:

[0047] S1. Select a substrate with a small lattice mismatch with diamond as the substrate, and deposit a layer of sp² hybrid carbon atoms on the surface of the substrate as a buffer layer.

[0048] Specifically, a heterogeneous substrate is provided, the structure of which is a sapphire (Al2O3) substrate surface coated with an iridium (Ir) metal thin layer oriented (100). Preferably, a single-atom-thickness graphene (i.e., sp) layer is deposited on the Ir thin layer by chemical vapor deposition. 2 The monolayer graphene, with its atomically flat surface, acts as a lattice buffer and stress isolation layer during the early stages of diamond growth, preventing direct chemical reactions between carbon and metal or the formation of carbides, and providing a weakly bound van der Waals epitaxial surface for the diamond grains.

[0049] S2. Place the substrate in the microwave plasma CVD reaction chamber, heat the central region of the substrate to a first temperature, and heat the edge region of the substrate to a second temperature, so that a temperature gradient decreasing from the center to the edge is established on the substrate surface.

[0050] Specifically, the substrate is fixed on a substrate stage within the MPCVD reaction chamber. A zoned temperature control device is activated, raising the temperature of the central region of the substrate to 1000-1100°C, while maintaining the temperature of the substrate edge region at a lower level of approximately 800-900°C, thereby creating a temperature gradient field on the substrate surface that gradually decreases from the center outwards. Computational fluid dynamics (CFD) simulations are used to optimize the chamber structure and airflow distribution to ensure that this temperature gradient is stable and controllable. For example, in one embodiment of the invention, by introducing an annular cooling airflow around the substrate and concentrating microwave power deposition at the center, a radial temperature gradient approximately 200°C higher at the center than at the edge is achieved. Figure 2 As shown, the horizontal axis represents the position of the substrate along its radius, and the vertical axis represents the temperature. It can be seen that the temperature at the center of the substrate is approximately 1100℃, and the temperature at the edge is approximately 900℃, exhibiting an approximately linear decreasing gradient from the center to the edge. This gradient temperature field helps guide the lateral epitaxial growth of the grains; that is, the higher temperature in the central region promotes rapid growth in the vertical direction, while the lower temperature at the edge inhibits the local vertical growth rate and encourages the lattice to expand horizontally, thereby promoting seamless fusion of adjacent grains in the lateral direction.

[0051] S3. Carbon-containing reactive gas and carrier gas are introduced into the reaction chamber, and microwaves of the first frequency and the second frequency are excited simultaneously to generate a dual-frequency plasma with both high-density low-energy components and low-density high-energy components.

[0052] Specifically, a mixture of methane and hydrogen gas (e.g., CH4 concentration 1–5%) is introduced into the reaction chamber, with the total pressure adjusted to, for example, the typical growth range of 20–40 kPa. A first microwave source (e.g., 2.45 GHz) and a second microwave source (e.g., 5.8 GHz) are activated, simultaneously coupling microwave power to the reaction zone according to a preset power ratio, exciting the generation of a high-density and stable plasma sphere. Thanks to the combined effect of the dual-frequency microwaves, the generated plasma contains a superposition of two energy components: firstly, a high-density, low-electron-temperature plasma excited by the lower-frequency microwave (2.45 GHz), characterized by the generation of abundant CH3 radicals and other growth materials but with mild bombardment of the growth surface; secondly, a relatively low-density but high-electron-energy plasma excited by the higher-frequency microwave (5.8 GHz), capable of providing high-energy ion / electron bombardment to enhance surface atomic migration and etching of the non-diamond phase. By adjusting the ratio of the two microwave powers, the present invention can form a bimodal electron energy distribution: the low-energy portion ensures sufficient nucleation and growth rates, while the high-energy tail helps to selectively etch the graphite phase and generate point defects (such as lattice vacancies) when needed. Figure 3The diagram schematically illustrates the electron energy distribution generated by the dual-frequency plasma described in this invention. The horizontal axis represents electron energy (normalized units), and the vertical axis represents relative particle number density. Curve A represents the near-Maxwell distribution of a single-frequency 2.45 GHz plasma, and curve B represents the bimodal energy distribution of the dual-frequency plasma of this invention (low-energy high-density peak B1 and high-energy low-density tail B2). A comparison with conventional single-frequency plasma shows that the electron spectrum of the dual-frequency plasma simultaneously encompasses both low-energy high-density and high-energy components. This energy distribution optimizes the carbon cluster formation mechanism: on the one hand, it ensures the required sp(s) density for diamond formation... 3 On the one hand, the bonded carbon radicals are continuously supplied, and on the other hand, high-energy electrons effectively remove sp from the growth surface. 2 Carbon atoms can be inserted into lattice vacancies under certain conditions, thereby supporting subsequent seamless epitaxial splicing and color center introduction.

[0053] S4. Diamond heteroepitaxial growth is performed on the substrate under the action of dual-frequency plasma. The temperature gradient promotes the lateral expansion of diamond grains on the substrate surface and their fusion to grow into a continuous single crystal film.

[0054] Specifically, under the action of dual-frequency plasma, carbon atoms on the substrate begin to deposit and nucleate to grow diamond. Due to the presence of a single layer of graphene buffering on the substrate surface, carbon atoms can freely migrate on the weakly bound surface, finding suitable orientations to bind into the diamond lattice. This process is similar to van der Waals epitaxy, allowing the nascent diamond crystals to grow on the Ir substrate with a near-eutectic orientation and lower stress. Simultaneously, in the high-temperature region at the center of the substrate, diamond grains grow vertically at a high rate; in the cooler edge regions, vertical growth is suppressed, and grains expand more laterally. As growth progresses, grains from different regions gradually meet laterally and seamlessly merge into a continuous crystalline film. Notably, by controlling the amplitude and distribution of the temperature gradient, the timing of grain merging and stress release can be adjusted. For example, a larger temperature difference (>200℃) is beneficial for rapidly promoting central grain coverage of the edges, but an excessively high gradient may introduce thermal stress; while a too small temperature difference may result in insignificant differences in anisotropic growth rates, which is not conducive to grain boundary elimination. This invention preferably employs a center-to-edge temperature difference of approximately 200°C to achieve a good trade-off between grain size expansion and stress balance. Under fully optimized conditions, this invention can achieve large-area single-crystal diamond films in a single epitaxial process on a heterogeneous substrate without requiring additional patterned substrates or multi-stage processes.

[0055] S5. During the diamond growth process, doping gas is introduced in a way that is synchronized with the timing of dual-frequency plasma, so that doping elements are incorporated into the growing diamond lattice according to a predetermined rule, thereby forming the color center or impurity distribution of the target color. The introduction of doping gas includes controlling the timing, pulse width or flow rate of doping gas to coordinate with the modulation period of the second frequency microwave power.

[0056] Specifically, during the epitaxial growth of diamond, a dopant gas is introduced through a multi-channel gas supply system to obtain colored diamond products. A key feature of this invention is the synchronization and coordination of the timing and dosage of the dopant gas introduction with the multi-frequency plasma state. For example, for pink diamonds requiring the formation of nitrogen-vacancy (NV) color centers, nitrogen gas (N2) can be introduced after the crystal has grown to a certain thickness. 2 A small amount of nitrogen gas is periodically introduced as a dopant source in a pulsed manner. When the high-energy electron component in the plasma periodically increases (e.g., by modulating a 5.8 GHz microwave to form a power pulse), a nitrogen gas pulse injection is synchronously triggered, allowing nitrogen atoms to enter the growth surface during the high-energy phase of the plasma. At this time, the high-energy electron bombardment generates a small number of vacancy defects in the crystal lattice, which combine with the adjacent nitrogen atoms to form stable NV centers. By controlling the pulse period and duty cycle, the nitrogen doping concentration in the crystal lattice and the NV center formation efficiency can be precisely controlled. Similarly, for the preparation of blue diamond, boron-doped gas (such as B2H6) can be used for continuous micro-doping; while for the preparation of yellow (golden yellow) diamond, an appropriate amount of nitrogen gas can be doped, but excessive vacancies should be avoided so that it exists mainly in the form of elemental nitrogen. In the system of this invention, the doping gas path has a fast-response mass flow control valve, which can realize gas on / off in milliseconds, thereby achieving synchronization with microwave power modulation. Under optimized timing control, the distribution of dopants in the crystal lattice will no longer exhibit the striped unevenness caused by conventional continuous doping, but will instead be nearly uniform or distributed according to a preset gradient. For example, by continuously adding trace amounts of doping throughout the growth process and supplementing it with high-energy cleaning plasma, a monochromatic diamond with uniform color can be obtained; by changing the type and concentration of dopants in stages, a color gradient region that gradually transitions from the inside to the outside can also be formed in the same crystal (for example, a blue core and a colorless outer layer forming a blue-white gradient effect).

[0057] S6. Real-time monitoring of diamond growth status is performed using in-situ Raman spectroscopy and photoluminescence spectroscopy. Based on the monitored crystal quality parameters and color center concentration parameters, the power of the first frequency microwave and the second frequency microwave, the temperature setting of the temperature gradient, or the flow rate of the doping gas are dynamically adjusted to correct growth deviations in real time.

[0058] Throughout the growth process, the in-situ optical monitoring module of this invention performs real-time measurements of key growth indicators. Among these, Raman spectroscopy can be used to detect the mass of the diamond crystal layer (e.g., 1332 cm⁻¹) online. -1 Diamond peak strength, half-width at half-maximum, and 1350 cm⁻¹ -1 The presence or absence of the non-diamond D peak (left and right) is used to assess crystal purity and defect status; photoluminescence (PL) spectroscopy is used to detect color center concentration and uniformity (e.g., NV). - The luminescence intensity of the color center at 637 nm, the 500 nm band caused by boron doping, etc. The monitoring data is transmitted to the electronic control system for analysis through a high-speed data interface. When signs of deviation from the target are detected in the growth process (e.g., the Raman D peak intensity exceeds the threshold indicating an increase in non-diamond phase, or the PL signal of a specific color center is lower than the expected value), the control system will automatically adjust the relevant process parameters to correct it. For example: (1) Power adjustment: If an increase in non-diamond phase is detected, the control system will temporarily increase the high-frequency microwave (5.8 GHz) power or reduce the total pressure to enhance the etching effect and remove sp. 2 Conversely, to increase the growth rate, the high-frequency power ratio can be appropriately reduced. (2) Gas flow rate adjustment: If insufficient color center concentration is detected, the frequency or duty cycle of the doping gas pulse is temporarily increased; if excessive doping is found to cause an increase in lattice stress (which can be inferred from Raman peak shift and birefringence), the doping flow rate is reduced and the pure growth time is extended to release stress. (3) Temperature field adjustment: In the later stage of growth, in order to eliminate stress concentration at the edge of the wafer, the substrate edge temperature can be finely adjusted to slightly change the gradient to promote stress relaxation. These adjustments are all calculated and executed in real time by the control system according to the pre-established data model or algorithm to achieve closed-loop control. For example, the control algorithm can be set to make the Raman peak intensity I related to a certain defect more than the value of the Raman peak. def Maintain below the target value: when I def When the threshold is exceeded, the high-frequency microwave power is automatically reduced. (where k is the feedback gain, I) set To reduce plasma energy density and suppress further defect formation (by setting a threshold), the intensity of the color center PL is controlled by adjusting the doping flux. Similarly, the concentration of the color center can be controlled using the following feedback mechanism: when the intensity of the color center emission peak in the in-situ PL spectrum... Below the target value At that time, the system increases the flow rate of the doped gas according to the following pattern. ,in To adjust the gain for doping flow rate, To adjust the flow rate of the doping gas, The luminous intensity of the target color center, This represents the currently measured luminescence intensity. Through the aforementioned closed-loop feedback mechanism, this invention can maintain the optimal balance of process parameters during long-term growth, significantly improving the quality uniformity and repeatability of large-size diamond crystals.

[0059] S7. Continue the above growth process until a diamond single crystal of a set thickness or weight is obtained. Stop the microwave plasma and cool the chamber. Remove the epitaxially grown colored diamond wafer.

[0060] Example 1

[0061] This embodiment uses the system and method provided by the present invention to prepare a blue boron-doped single-crystal diamond on a sapphire / Ir substrate. The specific steps are as follows:

[0062] (1) Substrate preparation: A c-plane sapphire single wafer with a diameter of Ø15mm and a thickness of 500μm was selected, and a 200nm thick Ir(100) oriented metal thin film was deposited on it by magnetron sputtering. The substrate was placed in a vacuum CVD furnace and a methane-hydrogen (CH4:H2=1:4) mixture was introduced. The substrate was pretreated at 800℃ for 30 minutes to form a single-atom-thick graphene layer on the Ir surface. The substrate was then removed for use. The root mean square roughness of the graphene layer surface was <0.5nm by atomic force microscopy, which provided a high-quality flat interface for diamond epitaxy.

[0063] (2) Growth Condition Setting: The above-mentioned substrate is mounted at the center of the substrate stage in the MPCVD reaction chamber. The reaction chamber is evacuated to 10 °C. -3 After Pa, high-purity H2 gas is introduced to increase the pressure to 20 kPa, and the substrate stage heater is turned on to raise the temperature of the substrate center to 1050°C and stabilize the edge at 850°C. Then, methane gas is introduced to achieve a methane concentration of 4% (the rest is hydrogen), and the total pressure is adjusted to 30 kPa.

[0064] (3) Plasma excitation: A 2.45 GHz magnetron microwave source (power set to 3 kW) and a 5.8 GHz solid-state microwave source (power set to 1 kW) were activated, and the two microwave sources were coupled into the reaction chamber through a common coupler. A stable spherical plasma with a diameter of approximately 30 mm was successfully ignited above the substrate, covering the entire substrate surface. At this time, in-situ Raman monitoring showed a plasma density of 1332 cm⁻¹. -1 The gradual appearance of diamond peaks indicates the beginning of diamond nucleation.

[0065] (4) Growth and Doping: During the first 2 hours of growth, no doping was introduced, and a colorless diamond buffer layer of approximately 50 μm thickness was deposited in a pure methane-hydrogen environment. Subsequently, the borane (B2H6) doping gas path was turned on, and an equivalent boron concentration of 100 ppm was continuously added to the main gas flow to begin the boron doping growth stage. Since boron doping may reduce the growth rate, the microwave power was appropriately increased from 2.45 GHz to 3.5 kW in this stage to compensate. Growth continued for approximately 48 hours while keeping other parameters constant, and the total deposition thickness reached approximately 1.2 mm. Throughout the growth process, the substrate temperature gradient and microwave power ratio remained stable, and no plasma drift or extinction occurred.

[0066] (5) Real-time monitoring and adjustment: Crystal quality was continuously monitored by in-situ Raman spectroscopy. The results showed that the diamond peak intensity increased rapidly in the undoped stage and there was no obvious non-diamond D band, indicating excellent crystal quality. After doping began, the Raman spectrum showed a slight linewidth broadening, which the control system determined to be an increase in stress caused by boron doping, but within a safe range and no intervention was required. In-situ PL monitoring detected a gradually increasing emission peak (corresponding to the boron-related color center) near 500 nm, and the difference in PL intensity measured at different locations on the wafer was less than 5%, indicating uniform doping. In order to ensure that the crystal was free of cracks, the control system increased the substrate edge temperature by 50°C (reducing the gradient) in the last 6 hours of growth to slowly anneal the stress. No other adjustments were made.

[0067] (6) Cooling and Removal: After growth, gradually reduce the microwave power to 0 and shut off the gas, allowing the reaction chamber to cool naturally to room temperature before removing the sample. The obtained sample is a polyhedral single-crystal diamond with a diameter of approximately 15 mm and a weight of approximately 6.3 carats. The crystal is uniformly light blue and optically transparent with no visible inclusions.

[0068] (7) Quality Inspection: Observation using a high-magnification optical microscope revealed no grain boundaries or polycrystalline splicing traces, proving that the crystal is a continuous single crystal. Raman spectroscopy showed a depth of 1332 cm⁻¹. -1 The sharp and symmetrical peaks indicate low crystal stress. The dislocation density, estimated using X-ray topological methods, is approximately 5 × 10⁻⁶. 5 cm -2 The concentration is on the order of magnitude lower than the target value. Secondary ion mass spectrometry (SIMS) showed that boron was uniformly distributed along both the radial and thickness directions, with a concentration of approximately 5 × 10⁻⁶. 17 cm -3 This corresponds to the typical concentration range of light blue natural type IIb diamonds. The above results confirm that the method of this invention successfully prepared high-quality, large-size boron-doped single-crystal diamonds, whose performance indicators meet the requirements of high-end blue gemstones.

[0069] Example 2

[0070] This embodiment demonstrates the process of preparing heteroepitaxial growth of pink (NV center) single-crystal diamond ≥6 carats by using nitrogen-vacancy color center doping according to the present invention.

[0071] (1) Substrate preparation: Same as in Example 1, a sapphire / Ir substrate was used and a graphene buffer layer was pre-formed.

[0072] (2) Growth conditions: The substrate was placed in the MPCVD chamber, and a temperature gradient field with a center temperature of 1020℃ and an edge temperature of 820℃ was set. A CH4 / H2 (concentration 3%) atmosphere was introduced, and the total pressure was 25kPa.

[0073] (3) Plasma excitation: 2.45 GHz microwave (power 2.5 kW) and 5.8 GHz microwave (power 0.8 kW) are turned on for plasma ignition. After a stable plasma sphere is formed, pure diamond is grown to a thickness of about 20 μm as an undoped template layer.

[0074] (4) Doping Stage: Initiating the nitrogen doping gas path. To form NV centers, a pulsed nitrogen doping strategy was adopted: a nitrogen pulse was introduced every 5 minutes for 10 seconds, with an N2 concentration of approximately 1000 ppm during the pulse. No nitrogen was introduced at other times, resulting in an average nitrogen concentration of approximately 33 ppm. Simultaneously, the output power of the 5.8 GHz microwave source was synchronously modulated with a square wave at a 5-minute cycle: 5 seconds before each nitrogen pulse, the 5.8 GHz power was instantaneously increased to 1.5 kW and maintained for 15 seconds before decreasing back to 0.8 kW. This ensured that a high-energy phase existed in the plasma at each nitrogen introduction moment, activating a small number of vacancies in the lattice for nitrogen atoms to occupy and form NV centers. Through the above periodic operation, growth continued for 72 hours, resulting in a crystal with a thickness of approximately 0.8 mm.

[0075] (5) Monitoring and Feedback: Raman monitoring showed that after each high-energy pulse, trace amounts of non-diamond carbon might be momentarily generated in the crystal (the Raman D band appears briefly), but this was subsequently eliminated, and the overall Raman spectrum still maintained diamond characteristics. PL monitoring detected a gradual increase in the luminescence of the NV-center at 637 nm. In the later stages of growth, the NV luminescence intensity tended to saturate, indicating that the center concentration had reached a certain level. Based on this, the control system reduced the frequency of subsequent nitrogen pulses (changing it to once every 10 minutes) to avoid quenching effects caused by excessively high center concentrations. Overall, the monitoring feedback ensured that the NV center concentration remained within the ideal range.

[0076] (6) Results: After cooling and removing the sample, the obtained diamond crystal weighed approximately 6.5 carats and exhibited a uniform pale pink hue throughout. Photoluminescence spectroscopy was used to test different locations, and the intensity distribution of the 637 nm NV-zero phonon line (ZPL) was uniform, indicating that the color center concentration varied by less than ±5% from the center to the edge. Electron spin resonance (ESR) measurements estimated the NV center concentration to be approximately 1 × 10⁻⁶.17 cm -3 The samples exhibit a high level of color density, with the vast majority being isolated NV centers rather than clusters. Compared to pink diamonds obtained through conventional CVD nitrogen doping followed by annealing, the samples in this embodiment exhibit a stable pink color without post-treatment and have low internal stress (<0.1 GPa as determined by the Raman peak position). This demonstrates that the present invention can directly form high-quality NV centers during the growth process, providing excellent materials for quantum device fabrication.

[0077] The effectiveness and superiority of the present invention have been fully verified through the above embodiments. These embodiments are only for applications with specific doping elements and colors. Those skilled in the art can adjust the doping type, microwave frequency combination, temperature gradient magnitude, etc., as needed to prepare single-crystal diamonds of other colors or for other applications. For example, a similar method can be used to introduce silane (SiH4) gas to obtain red / orange diamonds containing Si-V color centers, or stress-controlled optical element-grade diamonds can be obtained by changing the temperature gradient mode. All these variations are based on the overall concept of the present invention and fall within the protection scope of the present invention.

Claims

1. A heteroepitaxial large-carat colored diamond preparation system based on multi-frequency plasma resonance and thermal gradient synergy, characterized in that, include: A microwave plasma excitation device includes a first microwave source and a second microwave source, wherein the first microwave source and the second microwave source have different frequencies and are both coupled to a reaction chamber to simultaneously generate a coexisting first plasma and a second plasma within the chamber. A substrate stage is used to fix a heterogeneous substrate and, in conjunction with a temperature control device, to establish a temperature gradient field on the heterogeneous substrate that gradually decreases from the center to the edge. A gas supply device includes at least one main gas channel and at least one doping gas channel. The main gas channel is used to supply carbon-containing gas and carrier gas into the reaction chamber to maintain the reaction atmosphere required for diamond growth. The doping gas channel is used to selectively introduce doping gas containing impurity elements into the reaction chamber. In-situ monitoring devices, including Raman spectrometer and photoluminescence spectrometer, are used to detect the quality and color center characteristics of diamond crystals grown in the reaction chamber in real time. The control system is electrically connected to the first microwave source, the second microwave source, the temperature control device, the gas supply device, and the in-situ monitoring device. It is configured to dynamically adjust the microwave source power output, temperature gradient field parameters, and the timing and flow rate of dopant gas based on the data obtained from the in-situ monitoring device, so as to form a closed-loop control during the diamond epitaxial growth process and optimize the crystal growth rate, defect density, and doping uniformity.

2. The heteroepitaxial large-carat colored diamond preparation system based on multi-frequency plasma resonance and thermal gradient synergy as described in claim 1, characterized in that, The heterogeneous substrate includes a sapphire single-crystal substrate and an Ir metal thin layer formed on the surface of the substrate, wherein a single-atom-thick layer of graphene is coated on the Ir metal thin layer as a lattice buffer isolation layer.

3. The heteroepitaxial large-carat colored diamond preparation system based on multi-frequency plasma resonance and thermal gradient synergy as described in claim 1, characterized in that, The first microwave source operates at a frequency of 2.45 GHz, and the second microwave source operates at a frequency of 5.80 GHz. The power ratio of the two microwave sources when they operate synchronously is adjustable so that the first plasma exhibits high density and low electron temperature characteristics, and the second plasma exhibits low density and high electron temperature characteristics, and they are superimposed in the reaction chamber to form a plasma region with a bimodal electron energy distribution.

4. The heteroepitaxial large-carat colored diamond preparation system based on multi-frequency plasma resonance and thermal gradient synergy according to claim 1, characterized in that, The temperature control device includes a zone heater or temperature control component, used to maintain the temperature of the central region of the substrate stage at 1000-1100℃ and the temperature of the peripheral region of the substrate stage at 800-900℃, thereby forming a gradient temperature field with a temperature difference of 200-300℃ from the center to the edge on the substrate surface.

5. The heteroepitaxial large-carat colored diamond preparation system based on multi-frequency plasma resonance and thermal gradient synergy according to claim 1, characterized in that, The gas supply device includes a plurality of independently controlled gas inlets for introducing different doping gases, wherein the doping gases include one or more selected from nitrogen, borane, phosphine, and sodium-containing compound gases, to impart predetermined color or electrical properties to the grown diamond crystal.

6. The heteroepitaxial large-carat colored diamond preparation system based on multi-frequency plasma resonance and thermal gradient synergy according to claim 1, characterized in that, The Raman spectrometer of the in-situ monitoring device is used to monitor the intensity, full width at half maximum (FWHM), and shift of characteristic Raman peaks in diamond crystals to assess crystal quality and stress. The photoluminescence spectrometer is used to monitor the luminescence intensity and spectral lines of color centers in diamond to assess the concentration and distribution of doped color centers. The control system is equipped with a feedback algorithm that calculates the adjustment amount based on the signal deviation output by the Raman spectrometer and the photoluminescence spectrometer, and adjusts the corresponding process parameters to keep the monitoring signal within the predetermined target range.

7. A method for preparing large-carat heteroepitaxial colored diamonds using multi-frequency plasma resonance and thermal gradient synergy, characterized in that, The heteroepitaxial large-carat colored diamond preparation system based on the multi-frequency plasma resonance and thermal gradient synergy described in any one of claims 1-6 specifically includes the following steps: S1. Select a substrate with a small lattice mismatch with diamond as the substrate, and deposit a layer of sp on the surface of the substrate. 2 The hybrid carbon atom layer serves as a buffer layer; S2. Place the substrate in the microwave plasma CVD reaction chamber, heat the central region of the substrate to a first temperature, and heat the edge region of the substrate to a second temperature, so that a temperature gradient decreasing from the center to the edge is established on the substrate surface. S3. Introduce carbon-containing reactive gas and carrier gas into the reaction chamber, and simultaneously excite microwaves of the first frequency and the second frequency to generate a dual-frequency plasma with both high-density low-energy components and low-density high-energy components. S4. Diamond heteroepitaxial growth is performed on a substrate under the action of dual-frequency plasma. The temperature gradient promotes the lateral expansion of diamond grains on the substrate surface and their fusion to grow into a continuous single crystal film. S5. During the diamond growth process, doping gas is introduced in a way that is synchronized with the dual-frequency plasma timing, so that the doping elements are incorporated into the growing diamond lattice according to a predetermined rule, thereby forming the color center or impurity distribution of the target color. The introduction of the doping gas includes controlling the timing of the doping gas introduction, the pulse width or the flow rate, so that it is coordinated with the modulation period of the second frequency microwave power. S6. Real-time monitoring of diamond growth status is carried out using in-situ Raman spectroscopy and photoluminescence spectroscopy. Based on the monitored crystal quality parameters and color center concentration parameters, the power of the first frequency microwave and the second frequency microwave, the temperature setting of the temperature gradient, or the flow rate of the doping gas are dynamically adjusted to correct growth deviations in real time. S7. Continue the above growth process until a diamond single crystal of a set thickness or weight is obtained. Stop the microwave plasma and cool the chamber. Remove the epitaxially grown colored diamond wafer.

8. The method for preparing large-carat colored diamonds by multi-frequency plasma resonance and thermal gradient synergy according to claim 7, characterized in that, The doping gas is a nitrogen-containing gas, and the power output of the second frequency microwave is periodically and alternately modulated, so that a high-energy plasma pulse corresponds to each nitrogen doping, so as to promote the combination of nitrogen atoms with lattice vacancies to form nitrogen-vacancy color centers.

9. The method for preparing large-carat heteroepitaxial colored diamonds by synergistic multi-frequency plasma resonance and thermal gradient as described in claim 7, characterized in that, In step S5, by changing the type or concentration of doping gas at different growth stages, the diamond crystal can be made to have different colors in different regions. The doping gases introduced successively include nitrogen and borane, so that the color of the diamond crystal gradually changes from blue to yellow from one end to the other.

10. The method for preparing large-carat heteroepitaxial colored diamonds by synergistic multi-frequency plasma resonance and thermal gradient as described in claim 7, characterized in that, In step S6, feedback control is used to maintain the intensity of the diamond peak in the Raman spectrum during the diamond crystal growth process above the preset lower limit and the intensity of the D band below the preset upper limit, and to maintain the intensity of the emission peak of the target color center in the photoluminescence spectrum within the preset range.

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