Method for improving crystal quality of diamond single crystal

Abstract

The invention discloses a method for improving the crystal quality of a diamond single crystal, and relates to the technical field of diamond preparation, and the method comprises the following steps: setting MPCVD basic growth parameters, establishing an initial temperature field, introducing a dynamic temperature modulation mechanism, breaking through the limitation of a static temperature field through a temperature fluctuation program, and improving the crystal quality of the diamond single crystal. The method has the advantages that periodic temperature fluctuation is introduced through a dynamic temperature modulation mechanism, uniform distribution of plasmas is realized in combination with an alternating magnetic field applied outside the deposition chamber, and a pulse type auxiliary gas injection mode is matched, so that the problem of crystal internal stress concentration caused by non-uniform temperature field distribution in the existing MPCVD process is effectively solved; dynamic temperature fluctuation promotes periodic release of crystal stress, an alternating magnetic field optimizes the uniformity of a temperature field, pulse gas injection reduces impurity segregation and promotes atom rearrangement, the generation probability of crystal microcracks is reduced through the synergistic effect of multiple means, and finally remarkable attenuation of the thermal stress of the diamond single crystal is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of diamond preparation, in particular to a method for improving the quality of diamond single crystals. Background Art

[0002] Diamond is a superhard material with excellent physical and chemical properties. Its Mohs hardness reaches 10, making it the hardest substance known in nature. It also possesses extremely high thermal conductivity, good optical transparency, excellent electrical insulation, and chemical stability. These unique properties make diamond valuable for applications in multiple fields. In industry, it is widely used to make high-precision cutting tools and abrasives. In optics, diamond can be used as a highly transparent optical window material from the ultraviolet to the infrared band, suitable for optical devices in extreme environments. In the semiconductor field, diamond, due to its wide bandgap and high electron mobility, is an ideal substrate material for the preparation of high-frequency, high-temperature, and high-power electronic devices. It also has broad application prospects in cutting-edge fields such as quantum computing and heat dissipation modules.

[0003] The existing technology has certain defects. In the existing technology, the continuous introduction of oxygen will etch the surface of the diamond single crystal, increase the defect density, change the growth pattern, and reduce the crystal quality. Secondly, the temperature field distribution in the existing MPCVD process is uneven, which leads to stress concentration inside the crystal and produces microcracks, affecting the mechanical strength and optical properties. Therefore, we propose a method to improve the quality of diamond single crystals. Summary of the Invention

[0004] The object of the present invention is to provide a method for improving the quality of diamond single crystals.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for improving the quality of diamond single crystal, comprising a quality improvement method, characterized in that the quality improvement method comprises the following steps:

[0006] Step 1: Clean the diamond single crystal seed crystal with anhydrous ethanol and acetone in sequence, dry it with ultrasonic wave, place it on the molybdenum base in the MPCVD deposition chamber, and check the operation of the equipment;

[0007] Step 2: Set the basic MPCVD growth parameters, establish the initial temperature field, introduce a dynamic temperature modulation mechanism, and break the limitations of the static temperature field through the temperature fluctuation program;

[0008] Step 3: Introduce hydrogen and methane as the main reaction gases into the deposition chamber to form a stable plasma environment, maintain a reducing atmosphere, and supply the carbon atoms required for diamond growth;

[0009] Step 4: Apply an alternating magnetic field outside the deposition chamber to enhance the uniformity of the plasma distribution, control the uniformity of the temperature field, and optimize the internal stress of the crystal in combination with dynamic temperature modulation;

[0010] Step 5: A pulsed injection mode is used for auxiliary gases containing nitrogen and argon to avoid impurity segregation. The micro-perturbation generated by the gas pulse promotes atomic rearrangement near the growth interface, reducing stress concentration and impurity incorporation.

[0011] Step 6: Use the online Raman spectroscopy monitoring system to collect data in real time, pay attention to the characteristic peaks, adjust the dynamic temperature modulation amplitude, magnetic field intensity and pulse gas period, and control the crystal quality;

[0012] Step 7: After the diamond single crystal growth is completed, turn off the relevant gases, keep hydrogen flowing and cool down, take out the crystal and perform surface morphology and internal defect inspection.

[0013] As a further solution of the present invention: in step 1, the diamond single crystal seed crystal is placed in anhydrous ethanol, acetone, and anhydrous ethanol in sequence for ultrasonic cleaning, with each cleaning time being 10 minutes to 30 minutes to remove oil and impurities on the surface of the seed crystal. After cleaning, it is blown dry with high-purity nitrogen. At the same time, the sealing of the deposition chamber is checked to ensure that the microwave power supply, temperature control system, gas flow controller, pressure sensor and cooling system are operating normally.

[0014] As a further solution of the present invention: in the step 2, the microwave power is set to 8kW-12kW, the working pressure is maintained at 18kPa-26kPa, the initial growth temperature is 1050℃-1250℃, and the equipment is started to form a stable initial temperature field in the deposition chamber. On this basis, a dynamic temperature modulation mechanism is introduced: every 1h-1.5h of growth, the temperature fluctuation program is started to make the temperature linearly rise and fall at a rate of 5℃ / min-6℃ / min in the range of 1080℃-1150℃, forming a periodic temperature fluctuation, heating for 15min → keeping warm for 10min → cooling for 15min, so as to break the limitations of the static temperature field.

[0015] As a further solution of the present invention: In step three, hydrogen and methane are introduced into the deposition chamber as main reaction gases, wherein the hydrogen flow rate is 500sccm-800sccm, and the methane flow rate is 75sccm-100sccm, and they are continuously introduced to form a stable plasma environment in the deposition chamber. Hydrogen is used to maintain the reducing atmosphere of the plasma, and methane is used as a carbon source to supply the carbon atoms required for diamond growth, thereby ensuring the stability of the basic growth conditions.

[0016] As a further embodiment of the present invention, in step 4, an alternating magnetic field with a magnetic field strength of 0.1T-0.3T and a frequency of 50Hz-100Hz is applied outside the deposition chamber, causing the charged particles in the plasma to perform spiral motion along the magnetic field lines, thereby enhancing the uniform distribution of the plasma in the deposition area and thereby regulating the uniformity of the temperature field. At the same time, combined with the dynamic temperature modulation in step 2, the regulation relationship between temperature fluctuation and internal stress of the crystal is determined by the following formula:

[0017]

[0018] Where: σ(t) is the thermal stress inside the crystal at time t, σ0 is the initial thermal stress, e is the base of the natural logarithm, which is determined by the static temperature field, and α is the temperature fluctuation stress attenuation coefficient, which ranges from 0.01 to 0.03. is the temperature change rate, β is the magnetic field stress control coefficient, ranging from 0.5 to 1.2, B(t) is the magnetic field intensity at time t, and τ is the magnetic field action time;

[0019] This formula shows that based on the synergistic effect of dynamic temperature fluctuations and alternating magnetic fields, the thermal stress inside the crystal can be effectively attenuated and stress optimization can be achieved.

[0020] As a further solution of the present invention: in the step five, a pulse injection mode is adopted for the auxiliary gas: with a cycle of 15s-25s, nitrogen is introduced at a flow rate of 0.5sccm-15sccm and argon at a flow rate of 30sccm-120sccm in the first 8s-12s, and the gas is turned off in the last 8s-12s. Pulse injection can avoid impurity segregation caused by long-term introduction of auxiliary gas, and at the same time, the micro-disturbance generated by the gas pulse is used to promote atomic rearrangement near the growth interface, thereby reducing stress concentration and impurity incorporation.

[0021] As a further solution of the present invention: in step 6, the Raman spectrum data of the diamond single crystal is collected in real time by an online Raman spectrum monitoring system, focusing on the 1332 cm -1 The half-height width of the characteristic peak and 1571cm -1 If the half-width increases by more than 10%-12% and the defect peak intensity increases, the amplitude of dynamic temperature modulation, magnetic field strength and pulse gas cycle are immediately adjusted to achieve closed-loop dynamic control of growth parameters and ensure the stability of crystal quality.

[0022] As a further solution of the present invention: in step seven, after the diamond single crystal grows to the target thickness, the methane, nitrogen, argon and oxygen are first turned off, and hydrogen is continuously introduced. The temperature of the deposition chamber is lowered to room temperature at a rate of 5°C / min-10°C / min. After cooling is completed, the crystal is taken out and a scanning electron microscope and a Raman spectrometer are used to comprehensively detect the surface morphology and internal defects of the crystal to ensure that the crystal defect density and impurity content meet the application requirements of high-quality diamond single crystals.

[0023] By adopting the above technical solution, compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. This invention introduces periodic temperature fluctuations through a dynamic temperature modulation mechanism, combines it with an alternating magnetic field applied outside the deposition chamber to achieve uniform plasma distribution, and uses a pulsed auxiliary gas injection mode to effectively solve the problem of uneven temperature field distribution in existing MPCVD processes that leads to stress concentration within the crystal. Dynamic temperature fluctuations promote the periodic release of crystal stress, the alternating magnetic field optimizes temperature field uniformity, and pulsed gas injection reduces impurity segregation and promotes atomic rearrangement. The synergistic effect of these multiple measures reduces the probability of crystal microcracks, ultimately achieving significant attenuation of thermal stress in diamond single crystals and improving the mechanical strength and optical transparency of the crystal.

[0025] 2. By periodically introducing and shutting off oxygen during the growth of diamond single crystals, the present invention not only uses oxygen to effectively remove vacancy defects formed by nitrogen incorporation and reduce hydrogen and non-diamond impurity levels, but also avoids the etching effect of continuous oxygen flow on the crystal surface, preventing an increase in defect density and a change in the growth pattern. This method solves the problem of crystal quality degradation caused by continuous oxygen flow in the prior art. It significantly reduces the internal defect density and impurity content of diamond single crystals without reducing the growth rate, allowing the grown crystals to maintain the transparent or translucent state of the original seed crystal, effectively enhancing the application value of diamond single crystals in scientific research and industrial fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the dynamic temperature-magnetic field coordinated control process in an embodiment of the present invention;

[0027] Figure 2 Schematic diagram of the method steps in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0029] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Please see the attached Figure 1 -Attached Figure 2 The present invention provides a method for improving the quality of diamond single crystal, including a quality improvement method, characterized in that the quality improvement method includes the following steps:

[0031] Step 1: Clean the diamond single crystal seed crystal with anhydrous ethanol and acetone in sequence, dry it with ultrasonic wave, place it on the molybdenum base in the MPCVD deposition chamber, and check the operation of the equipment;

[0032] Step 2: Set the basic MPCVD growth parameters, establish the initial temperature field, introduce a dynamic temperature modulation mechanism, and break the limitations of the static temperature field through the temperature fluctuation program;

[0033] Step 3: Introduce hydrogen and methane as the main reaction gases into the deposition chamber to form a stable plasma environment, maintain a reducing atmosphere, and supply the carbon atoms required for diamond growth;

[0034] Step 4: Apply an alternating magnetic field outside the deposition chamber to enhance the uniformity of the plasma distribution, control the uniformity of the temperature field, and optimize the internal stress of the crystal in combination with dynamic temperature modulation;

[0035] Step 5: A pulsed injection mode is used for auxiliary gases containing nitrogen and argon to avoid impurity segregation. The micro-perturbation generated by the gas pulse promotes atomic rearrangement near the growth interface, reducing stress concentration and impurity incorporation.

[0036] Step 6: Use the online Raman spectroscopy monitoring system to collect data in real time, pay attention to the characteristic peaks, adjust the dynamic temperature modulation amplitude, magnetic field intensity and pulse gas period, and control the crystal quality;

[0037] Step 7: After the diamond single crystal growth is completed, turn off the relevant gases, keep hydrogen flowing and cool down, take out the crystal and perform surface morphology and internal defect inspection.

[0038] In one embodiment of the present invention: in step 1, the diamond single crystal seed crystal is placed in anhydrous ethanol, acetone, and anhydrous ethanol in turn for ultrasonic cleaning, with each cleaning time being 10 minutes to 30 minutes to remove oil and impurities on the surface of the seed crystal. After cleaning, it is blown dry with high-purity nitrogen. At the same time, the sealing of the deposition chamber is checked to ensure that the microwave power supply, temperature control system, gas flow controller, pressure sensor and cooling system are operating normally.

[0039] In one embodiment of the present invention: in step 2, the microwave power is set to 8kW-12kW, the working pressure is maintained at 18kPa-26kPa, the initial growth temperature is 1050℃-1250℃, and the equipment is started to form a stable initial temperature field in the deposition chamber. On this basis, a dynamic temperature modulation mechanism is introduced: every 1h-1.5h of growth, the temperature fluctuation program is started to make the temperature linearly rise and fall at a rate of 5℃ / min-6℃ / min in the range of 1080℃-1150℃, forming a periodic temperature fluctuation, heating for 15min → keeping warm for 10min → cooling for 15min, so as to break the limitations of the static temperature field.

[0040] In one embodiment of the present invention: In step three, hydrogen and methane are introduced into the deposition chamber as main reaction gases, wherein the hydrogen flow rate is 500sccm-800sccm, and the methane flow rate is 75sccm-100sccm, and they are continuously introduced to form a stable plasma environment in the deposition chamber. Hydrogen is used to maintain the reducing atmosphere of the plasma, and methane is used as a carbon source to supply the carbon atoms required for diamond growth, thereby ensuring the stability of the basic growth conditions.

[0041] In one embodiment of the present invention, in step 4, an alternating magnetic field with a magnetic field strength of 0.1T-0.3T and a frequency of 50Hz-100Hz is applied outside the deposition chamber, causing the charged particles in the plasma to perform spiral motion along the magnetic field lines, thereby enhancing the uniform distribution of the plasma in the deposition area and thereby regulating the uniformity of the temperature field. Simultaneously, in combination with the dynamic temperature modulation in step 2, the regulation relationship between temperature fluctuation and internal stress of the crystal is determined by the following formula:

[0042]

[0043] Where: σ(t) is the thermal stress inside the crystal at time t, σ0 is the initial thermal stress, e is the base of the natural logarithm, which is determined by the static temperature field, and α is the temperature fluctuation stress attenuation coefficient, which ranges from 0.01 to 0.03. is the temperature change rate, β is the magnetic field stress control coefficient, ranging from 0.5 to 1.2, B(t) is the magnetic field intensity at time t, and τ is the magnetic field action time;

[0044] This formula shows that based on the synergistic effect of dynamic temperature fluctuations and alternating magnetic fields, the thermal stress inside the crystal can be effectively attenuated and stress optimization can be achieved.

[0045] In one embodiment of the present invention: in step five, a pulse injection mode is adopted for the auxiliary gas: with a cycle of 15s-25s, nitrogen is introduced at a flow rate of 0.5sccm-15sccm and argon at a flow rate of 30sccm-120sccm in the first 8s-12s, and the gas is turned off in the last 8s-12s. Pulse injection can avoid impurity segregation caused by long-term introduction of auxiliary gas, and at the same time, the micro-disturbance generated by the gas pulse is used to promote atomic rearrangement near the growth interface, thereby reducing stress concentration and impurity incorporation.

[0046] In one embodiment of the present invention, in step 6, the Raman spectrum data of the diamond single crystal is collected in real time by an online Raman spectrum monitoring system, focusing on the 1332 cm -1 The half-height width of the characteristic peak and 1571cm -1 If the half-width increases by more than 10%-12% and the defect peak intensity increases, the amplitude of dynamic temperature modulation, magnetic field strength and pulse gas cycle are immediately adjusted to achieve closed-loop dynamic control of growth parameters and ensure the stability of crystal quality.

[0047] In one embodiment of the present invention: in step seven, after the diamond single crystal grows to the target thickness, the methane, nitrogen, argon and oxygen are first turned off, and hydrogen is continuously introduced, and the temperature of the deposition chamber is lowered to room temperature at a rate of 5°C / min-10°C / min. After cooling is completed, the crystal is taken out, and a scanning electron microscope and a Raman spectrometer are used to comprehensively detect the surface morphology and internal defects of the crystal to ensure that the crystal defect density and impurity content meet the application requirements of high-quality diamond single crystals.

[0048] In one embodiment of the present invention, the purity of hydrogen is above 99.999%, and the purity of methane is above 99.99%, so as to reduce the influence of gas impurities on the growth of diamond single crystal.

[0049] In one embodiment of the present invention, the alternating magnetic field is generated by an electromagnetic coil, the number of turns of the electromagnetic coil is 100-200 turns, and the coil current is 5A-10A, so as to ensure the generation of a stable alternating magnetic field.

[0050] In one embodiment of the present invention, the pulse injection mode is implemented by a PLC control system with a control accuracy of ±0.1s to precisely control the injection time and the shut-off time of the auxiliary gas.

[0051] In one embodiment of the present invention, the sampling frequency of the online Raman spectroscopy monitoring system is 1 time / minute, 1332 cm -1 The half-height width of the characteristic peak is monitored with an accuracy of ±0.1cm -1 , to monitor the crystal quality of diamond single crystals in real time and accurately.

[0052] In one embodiment of the present invention, the micro-perturbation generated by the gas pulse changes the fluid dynamic conditions near the growth interface, so that the atoms obtain additional migration energy, thereby promoting atomic rearrangement. The correlation between the perturbation intensity and the atomic rearrangement efficiency satisfies the following relationship: when the pressure fluctuation amplitude of the pulse gas is in the range of 0.5-2kPa, the atomic rearrangement efficiency increases linearly with the increase of the pressure fluctuation amplitude

[0053] In one embodiment of the present invention, the online Raman spectroscopy monitoring system has a detection wavelength range of 400-800 nm, a sampling frequency of 1-5 times / minute, and is equipped with a real-time data processing module, which is based on a machine learning algorithm to analyze the 1332 cm -1 Characteristic peaks and 1571cm -1 The intensity and half-height width of the defect peak are analyzed, and adjustment instructions for the dynamic temperature modulation amplitude, magnetic field strength and pulse gas period are automatically generated based on the analysis results.

[0054] In one embodiment of the present invention: the auxiliary gas also includes oxygen, which is introduced in coordination with nitrogen and argon in a pulsed injection mode, specifically with a cycle of 20 seconds, with an oxygen flow rate of 0.1-5sccm, a nitrogen flow rate of 1-10sccm, and an argon flow rate of 50-100sccm in the first 5 seconds, and all auxiliary gases are turned off in the last 15 seconds. This pulse strategy uses oxygen at a low flow rate in a short time to remove vacancy defects formed by nitrogen doping, while avoiding crystal surface etching caused by continuous introduction. Through the sequential coordination of oxygen and nitrogen and argon gases, a balance between defect removal and growth interface protection is achieved.

[0055] In one embodiment of the present invention, the matching of the frequency (50 Hz-100 Hz) of the alternating magnetic field and the magnetic field strength (0.1-0.3 T) satisfies the electron cyclotron resonance condition, wherein the electron cyclotron frequency w ce =qB / m, q is the electron charge, m is the electron mass, when B=0.1T, w ce ≈2.8GHz, forming a resonance effect with the microwave frequency of 2.45GHz, enhancing the confinement effect of electrons in the plasma, and at the same time filling w ce >>w coll , w coll The electron collision frequency is set to ensure that the charged particles are not dominated by collisions when they make spiral motion along the magnetic field lines, thereby improving the spatial distribution uniformity of the plasma in the deposition area by more than 30%.

[0056] Example 1, please refer to the attached Figure 1 -Attached Figure 2 , a method for improving the quality of diamond single crystals:

[0057] Seed crystal pretreatment and equipment inspection: 3 diamond single crystal seed crystals with a size of 5mm×5mm were placed in anhydrous ethanol (analytical grade), acetone (analytical grade) and anhydrous ethanol in turn, and ultrasonically cleaned using a KQ-500DE CNC ultrasonic cleaner. Each cleaning time was 20 minutes. After cleaning, they were blown dry with high-purity nitrogen (purity 99.999%) and placed on the molybdenum base in the center of the MPCVD deposition chamber. The sealing of the deposition chamber was checked to ensure the normal operation of the 2.45GHz microwave power supply (power 10kW), temperature control system (accuracy ±1℃), gas flow controller (accuracy ±1sccm), pressure sensor (range 0-100kPa) and water circulation cooling system.

[0058] Basic parameter setting and dynamic temperature modulation: set the microwave power to 10 kW, the working pressure to 22 kPa, the initial growth temperature to 1150 °C, start the equipment to form a stable temperature field, and start the temperature fluctuation program every 1 h of growth: increase the temperature from 1150 °C to 1180 °C at a rate of 5 °C / min (15 min), keep it warm for 10 min, and then decrease it to 1150 °C at a rate of 5 °C / min (15 min), forming a temperature fluctuation cycle of 30 min.

[0059] Main gas introduction: 600 sccm of hydrogen and 80 sccm of methane were introduced for 30 minutes to form a stable plasma environment, maintain a reducing atmosphere and supply carbon atoms.

[0060] Dynamic temperature-magnetic field coordinated control: an alternating magnetic field with a magnetic field strength of 0.2T and a frequency of 75Hz is applied outside the deposition chamber to make the plasma uniformly distributed. Combined with temperature fluctuations, the formula The stress was regulated, where α = 0.02, β = 0.8, and the temperature change rate and magnetic field action time were monitored in real time.

[0061] Pulsed auxiliary gas injection: with a cycle of 20 s, 5 sccm nitrogen and 80 sccm argon were introduced in the first 10 s and then turned off in the last 10 s to avoid impurity segregation and promote atomic rearrangement.

[0062] Online monitoring and parameter adjustment: Real-time monitoring is performed by inViaReflex confocal Raman spectrometer. -1 The peak half-height width increases by more than 10% or 1571 cm -1 When the peak intensity increases, adjust the temperature fluctuation range to ±15°C and the magnetic field strength to 0.25T.

[0063] Post-treatment: After 48 hours of growth, methane, nitrogen, and argon were turned off, hydrogen was maintained at 600 sccm, and the temperature was lowered to room temperature at 8°C / min. The surface morphology was observed using a SU8010 scanning electron microscope, and Raman spectroscopy showed that the surface morphology was 1332 cm -1 Peak half-height width from 5.2cm-1 Down to 3.1cm -1 , the defect peak intensity is reduced by 60%.

[0064] Example 2, please refer to the attached Figure 1 -Attached Figure 2 , a method for improving the quality of diamond single crystals:

[0065] Seed crystal pretreatment and equipment inspection: Place a diamond single crystal seed crystal with a size of 8mm×8mm in anhydrous ethanol, acetone and anhydrous ethanol in turn, and ultrasonically clean it for 15min, 25min and 15min respectively. After drying with high-purity nitrogen, place it on a molybdenum base. Check the equipment to ensure that the microwave power supply (power 8kW), temperature control system, gas flow controller, etc. are operating normally.

[0066] Basic parameter settings and dynamic temperature modulation: Microwave power was set at 8 kW, operating pressure at 18 kPa, and initial temperature at 1050°C. Every 1.5 hours of growth, a temperature fluctuation program was initiated: increasing the temperature from 1050°C to 1200°C at a rate of 6°C / min (25 minutes), holding for 12 minutes, and then decreasing the temperature to 1050°C at a rate of 6°C / min (25 minutes), resulting in a 62-minute temperature fluctuation cycle.

[0067] The main gases were introduced at a flow rate of 500 sccm of hydrogen and 75 sccm of methane for 40 minutes to establish a plasma environment.

[0068] Dynamic temperature-magnetic field coordinated control: Apply an alternating magnetic field with a strength of 0.1 T and a frequency of 50 Hz, combined with temperature fluctuations, with α = 0.015 and β = 0.5 in the formula, to control stress in real time.

[0069] Pulsed auxiliary gas injection: with a cycle of 15 seconds, 0.5 sccm nitrogen and 30 sccm argon were introduced in the first 8 seconds and then turned off in the last 7 seconds to reduce impurity segregation.

[0070] Online monitoring and parameter adjustment: Raman monitoring shows 1332cm -1 When the peak half-height width increases by 12%, the temperature fluctuation range is adjusted to ±10°C and the magnetic field intensity is adjusted to 0.15T.

[0071] Post-treatment: After 60 hours of growth, the non-hydrogen gas was turned off and the temperature was cooled to room temperature at 5°C / min. The test showed that there were no obvious microcracks on the crystal surface. -1 The peak half-height width dropped to 2.8 cm -1 , optical transmittance increased by 15%.

[0072] According to the above embodiments, it can be concluded that by introducing a dynamic temperature modulation mechanism to form periodic temperature fluctuations, applying an alternating magnetic field to achieve uniform plasma distribution, adopting a pulsed auxiliary gas injection mode, and regularly introducing and shutting off oxygen during the growth process, the problems of stress concentration caused by uneven temperature field distribution and crystal quality degradation caused by continuous oxygen supply in the existing MPCVD process are effectively solved. Dynamic temperature fluctuations promote the periodic release of crystal stress, the alternating magnetic field optimizes the temperature field uniformity, pulsed gas injection reduces impurity segregation and promotes atomic rearrangement, and regular oxygen supply both removes vacancy defects and avoids surface etching. Under the synergistic effect of multiple technical means, the probability of crystal microcracks and internal defect density are significantly reduced, the thermal stress of the diamond single crystal is attenuated, the mechanical strength and optical transparency of the crystal are improved, and the growth rate is maintained without reduction, so that the crystal maintains its original transparent state, effectively enhancing the application value of diamond single crystals in high-end fields.

[0073] Although the present invention is disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent variations, and modifications made to the above embodiments in accordance with the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for improving the quality of diamond single crystal, comprising: The quality improvement method comprises the following steps: Step 1: Clean the diamond single crystal seed crystal with anhydrous ethanol and acetone in sequence, dry it with ultrasonic wave, place it on the molybdenum base in the MPCVD deposition chamber, and check the operation of the equipment; Step 2: Set the basic MPCVD growth parameters, establish the initial temperature field, introduce a dynamic temperature modulation mechanism, and break the limitations of the static temperature field through the temperature fluctuation program; Step 3: Introduce hydrogen and methane as the main reaction gases into the deposition chamber to form a stable plasma environment, maintain a reducing atmosphere, and supply the carbon atoms required for diamond growth; Step 4: Apply an alternating magnetic field outside the deposition chamber to enhance the uniformity of the plasma distribution, control the uniformity of the temperature field, and optimize the internal stress of the crystal in combination with dynamic temperature modulation; Step 5: A pulsed injection mode is used for auxiliary gases containing nitrogen and argon to avoid impurity segregation. The micro-perturbation generated by the gas pulse promotes atomic rearrangement near the growth interface, reducing stress concentration and impurity incorporation. Step 6: Use the online Raman spectroscopy monitoring system to collect data in real time, pay attention to the characteristic peaks, adjust the dynamic temperature modulation amplitude, magnetic field intensity and pulse gas period, and control the crystal quality; Step 7: After the diamond single crystal growth is completed, turn off the relevant gases, keep hydrogen flowing and cool down, take out the crystal and perform surface morphology and internal defect inspection.

2. The method for improving the quality of diamond single crystal according to claim 1, characterized in that: In the step 1, the diamond single crystal seed crystal is placed in anhydrous ethanol, acetone, and anhydrous ethanol in sequence for ultrasonic cleaning, with each cleaning time being 10 minutes to 30 minutes. After cleaning, it is blown dry with high-purity nitrogen. At the same time, the sealing of the deposition chamber is checked to ensure that the microwave power supply, temperature control system, gas flow controller, pressure sensor, and cooling system are operating normally.

3. The method for improving the quality of diamond single crystal according to claim 1, characterized in that: In the step 2, the microwave power is set to 8kW-12kW, the working pressure is maintained at 18kPa-26kPa, the initial growth temperature is 1050℃-1250℃, and the equipment is started to form a stable initial temperature field in the deposition chamber. On this basis, a dynamic temperature modulation mechanism is introduced: every 1h-1.5h of growth, the temperature fluctuation program is started to make the temperature linearly rise and fall at a rate of 5℃ / min-6℃ / min in the range of 1080℃-1150℃, forming a periodic temperature fluctuation, heating for 15min → keeping warm for 10min → cooling for 15min.

4. The method for improving the quality of diamond single crystal according to claim 1, characterized in that: In the step three, hydrogen and methane are introduced into the deposition chamber as main reaction gases, wherein the hydrogen flow rate is 500 sccm-800 sccm and the methane flow rate is 75 sccm-100 sccm, and they are continuously introduced to form a stable plasma environment in the deposition chamber.

5. The method for improving the quality of diamond single crystal according to claim 1, characterized in that: In step 4, the alternating magnetic field applied outside the deposition chamber has a magnetic field strength of 0.1T-0.3T and a frequency of 50Hz-100Hz. At the same time, combined with the dynamic temperature modulation in step 2, the regulation relationship between temperature fluctuation and crystal internal stress is determined by the following formula: Where: σ(t) is the thermal stress inside the crystal at time t, σ0 is the initial thermal stress, e is the base of the natural logarithm, and α is the temperature fluctuation stress attenuation coefficient, which ranges from 0.01 to 0.

03. is the temperature change rate, β is the magnetic field stress control coefficient, ranging from 0.5 to 1.2, B(t) is the magnetic field intensity at time t, and τ is the magnetic field action time.

6. The method for improving the quality of diamond single crystal according to claim 1, characterized in that: In step 5, a pulsed injection mode is adopted for the auxiliary gas: with a cycle of 15s-25s, nitrogen gas is injected at a flow rate of 0.5sccm-15sccm and argon gas at a flow rate of 30sccm-120sccm for the first 8s-12s, and the gas is turned off for the last 8s-12s.

7. The method for improving the quality of diamond single crystal according to claim 1, characterized in that: In step 6, the Raman spectrum data of the diamond single crystal is collected in real time by an online Raman spectrum monitoring system, focusing on the 1332 cm -1 The half-height width of the characteristic peak and 1571cm -1 If the half-height width increases by more than 10%-12% and the defect peak intensity increases, the amplitude of dynamic temperature modulation, magnetic field strength and pulse gas cycle are immediately adjusted to achieve closed-loop dynamic control of growth parameters.

8. The method for improving the quality of diamond single crystal according to claim 1, characterized in that: In step seven, after the diamond single crystal grows to the target thickness, the methane, nitrogen, argon and oxygen gases are first turned off, and hydrogen is continuously introduced. The temperature of the deposition chamber is lowered to room temperature at a rate of 5°C / min-10°C / min. After cooling is completed, the crystal is taken out and a scanning electron microscope and a Raman spectrometer are used to comprehensively detect the surface morphology and internal defects of the crystal to ensure that the crystal defect density and impurity content meet the application requirements of high-quality diamond single crystals.

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