Single crystal diamond splicing seam epitaxial healing method based on in-situ high-temperature annealing strengthening

Abstract

The invention relates to a single crystal diamond splicing seam epitaxial healing method based on in-situ high-temperature annealing strengthening, and belongs to the field of artificial diamonds. The method comprises the following steps: selecting a single crystal diamond as a seed crystal, pretreating the seed crystal, then carrying out multi-stage surface replication growth in a microwave plasma chemical vapor deposition (MPCVD) reaction cavity, fragmenting the crystal subjected to surface replication growth to obtain a single crystal diamond sheet, and pretreating the single crystal diamond sheet, a plurality of single crystal diamond sheets are spliced and subjected to multi-stage epitaxial growth healing in an MPCVD reaction cavity, under the condition that vacuum is not damaged in the same reaction cavity, the reaction cavity is filled with hydrogen or inert gas to replace a carbon-containing reaction atmosphere, in-situ high-temperature annealing is carried out, critical driving force is provided for point defect healing and dislocation recombination at an interface, and therefore the single crystal diamond sheets are subjected to multi-stage epitaxial growth healing in the MPCVD reaction cavity. Therefore, the defect density of the interface can be obviously reduced, the interface stress is completely released, and the electrical, thermal and mechanical properties of the healing interface are infinitely close to those of a bulk single crystal material.

Description

Technical Field

[0001] This invention belongs to the field of diamond manufacturing, and specifically relates to a method for healing seams in single-crystal diamond splices. Background Technology

[0002] Single-crystal diamond splice refers to the seam where diamond single crystal wafers are tightly joined to form a large-size substrate. Epitaxial growth is an effective method for fabricating large-size wafers by healing single-crystal diamond splices. However, during epitaxial growth, due to factors such as non-equilibrium growth kinetics, lattice mismatch, and thermal stress, the newly grown healed interface region typically traps a large number of point defects (such as vacancies and interstitial atoms) and line defects (dislocations). These defects are "frozen" in the lattice, severely degrading the thermal conductivity, carrier mobility, and mechanical strength of the healed interface.

[0003] Conventional processes typically involve furnace cooling after growth or simple cryogenic holding. This method fails to provide sufficient energy for defect migration and healing, resulting in permanent defect retention. While existing technologies recognize the importance of annealing, there is a general lack of in-situ, high-strength, short-time annealing solutions specifically for the unique structure of diamond seams. Improper annealing, such as insufficient temperature or excessive time, can either have minimal effect or lead to diamond graphitization or grain growth, introducing secondary damage. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for effectively eliminating interface defects in the healing of single-crystal diamond splice seams and releasing interface stress through precisely controlled in-situ high-temperature annealing, thereby significantly improving the overall performance.

[0005] The technical solution adopted by this invention to solve the above problems is as follows: a method for epitaxial healing of single-crystal diamond splice seams based on in-situ high-temperature annealing, characterized in that: single-crystal diamond is selected as seed crystal, the seed crystal is pretreated, and then multi-stage surface replication growth is performed in the microwave plasma chemical vapor deposition (MPCVD) reaction chamber. The surface-replicated crystal is sliced ​​to obtain single-crystal diamond sheets, the single-crystal diamond sheets are pretreated, several single-crystal diamond sheets are spliced ​​together and multi-stage epitaxial growth healing is performed in the MPCVD reaction chamber. Under the condition of not breaking the vacuum in the same reaction chamber, the reaction chamber is filled with hydrogen or an inert gas to replace the carbon-containing reaction atmosphere. The reaction chamber parameters are adjusted, and in-situ high-temperature annealing is performed. The cathodoluminescence spectral signal intensity of the healing interface is not less than 90% of the signal intensity of the adjacent single-crystal body region and / or 1332 cm⁻¹ in the micro-area Raman spectroscopy measurement. -1 The peak position shift of the characteristic peak does not exceed 0.1 cm. -1 .

[0006] Preferably, methane is used as the carbon source and hydrogen is used as the carrier gas and etching gas in each stage of the multi-stage epitaxial growth and healing process.

[0007] Preferably, a single crystal diamond with a six-sided orientation of (100) and a size of 5mm-20mm is selected as the seed crystal, with a nitrogen impurity content of less than 50ppb and an XRD half-width of less than 80 arcseconds.

[0008] Preferably, the pretreatment refers to polishing and cleaning the seed crystal or the sliced ​​single-crystal diamond sheet with nanodiamond polishing slurry until the surface roughness Ra < 0.3 nm; using reactive ion etching with oxygen / argon plasma for final slight etching to remove the polishing damage layer and make the surface atomically smooth; ultrasonically cleaning the seed crystal with acetone, ethanol and deionized water for more than 15 minutes in sequence, boiling it in a concentrated nitric acid / concentrated sulfuric acid mixture with a volume ratio of 1:3 for more than 30 minutes, and then rinsing it with ultrapure water until neutral.

[0009] Preferably, the seed crystal undergoes multi-stage surface replication growth in a methane and hydrogen atmosphere: the first stage uses low-concentration methane (0.1%-4% by volume) as the carbon source, with a growth power of 2.0kW-4.0kW, a growth pressure of 80Torr-150Torr, a growth temperature of 800℃-950℃, and a growth time of 0.5h-48h to obtain a single-layer high-quality crystal; the second stage uses high-concentration methane (4%-15% by volume) as the carbon source, with a growth power of 4.0kW-10.0kW, a growth pressure of 100Torr-200Torr, a growth temperature of 900℃-1000℃, and a growth time of 2-3 weeks to obtain a high-quality diamond crystal.

[0010] Preferably, the slicing involves dividing the surface-replicated crystal into single-crystal diamond sheets of the same thickness, ensuring that the crystal orientation of all six faces is (100) during the slicing process.

[0011] Preferably, 2-8 sliced ​​single-crystal diamond sheets are selected and spliced ​​together. The thickness of the selected single-crystal diamond sheets is 0.2mm-1mm, and the thickness difference is 0.1um-20um. Multi-stage epitaxial growth and healing are then performed: First stage growth, controlling the spacing between the single-crystal diamond sheets to be 1-20um, the CH4 / H2 volume ratio to be 3.5%-9.5%, the oxygen concentration to be 0.1%-10%, the growth temperature to be 950℃-1200℃, the reaction pressure to be 100Torr-200 Torr, the microwave power to be 3.5 kW-10kW, and the growth time to be 20h-200h; Second stage growth, the CH4 / H2 volume ratio to be 1.2%-3.5%, the oxygen concentration to be 0.1%-5%, the growth temperature to be 850℃-1000℃, the reaction pressure to be 100Torr-150 Torr, the microwave power to be 3.5 kW-6kW, and the growth time to be 20h-200h.

[0012] Preferably, the in-situ high-temperature annealing involves adjusting the microwave power of the reaction chamber to 4.0-6.0 kW, and rapidly raising the temperature of the diamond crystal to the critical high-temperature range of 1100°C to 1800°C within 3 minutes in a hydrogen plasma atmosphere. The temperature is then monitored in real time using an infrared thermometer or a bicolor pyrometer. The crystal is held at this critical high-temperature range for 2 to 120 minutes. After the holding period, the temperature is rapidly cooled to below 800°C at a rate of less than or equal to 50°C / minute, followed by natural cooling or continued cooling according to a program.

[0013] Preferably, the critical high temperature range is 1150°C to 1250°C, and the holding time in the critical high temperature range is 2-15 minutes.

[0014] Preferably, annealing is performed in a pure hydrogen atmosphere, and the hydrogen pressure in the reaction chamber is maintained at 50-200 Torr during annealing, utilizing the etching effect of hydrogen atoms on non-sp³ bonded carbon to synergistically purify the interface.

[0015] Compared with the prior art, the advantages of the present invention are as follows: 1. Achieved "atomic-level repair" of interface defects: At critical temperatures above 1100°C, atoms in the diamond lattice acquire extremely high kinetic energy. This enables point defect recombination: vacancies and interstitial atoms can overcome energy barriers to migrate, thus meeting and annihilating each other; and dislocation slip and recombination are also achieved: dislocation lines can slip, climb, and even cancel each other out with dislocations of opposite sign, effectively reducing dislocation density. Consequently, after annealing, the cathodoluminescence (CL) signal intensity of the healed interface can be increased to over 90% of that in the bulk region, indicating a significant reduction in the density of its non-radiative recombination centers.

[0016] 2. Efficiently releases interfacial stress: A slight difference in lattice constant and coefficient of thermal expansion exists between the epitaxially grown healed layer and the original unit cell, resulting in internal stress at the interface. High-temperature annealing provides the thermal driving force for stress relaxation, allowing the lattice constant to tend towards matching through dislocation movement and fine-tuning of atomic positions. After annealing, micro-area Raman spectroscopy characterization shows that the characteristic peak shift (Δω) across the healed interface can be reduced to 0.1 cm⁻¹. -1 The following indicates that the interfacial stress has been almost completely released.

[0017] 3. Avoidance of secondary damage to material properties: The strategy of "rapid heating and cooling" and "short holding time" is scientifically based on the following: Thermodynamically, the driving force for the phase transformation from diamond to graphite is insufficient to overcome the kinetic barrier in a short time, thus effectively suppressing graphitization. Kinetically, the short holding time is sufficient to drive the movement of point defects and dislocations, but not enough to induce significant grain boundary migration or recrystallization, maintaining the single-crystal integrity of the epitaxial layer. Raman spectroscopy shows no obvious D peaks and G peaks (characteristic peaks of graphite) after annealing, and XRD analysis shows that the crystal quality is improved without degradation.

[0018] 4. Improved process integration and reliability: "In-situ" annealing means that the sample is never contaminated in the ultra-high vacuum environment, avoiding interface contamination and oxidation problems introduced by secondary processing after removal. This integrated "growth-annealing" process greatly improves the product yield and performance consistency. Detailed Implementation

[0019] The present invention will be described in further detail below. The embodiments described are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] The single-crystal diamond epitaxial growth healing method of this application involves the selection of single-crystal diamond seed crystals (seed crystals), polishing and cleaning of seed crystals, surface replication growth of seed crystals, slab division, polishing and cleaning of single-crystal diamond slabs, step-by-step splicing growth of slab single-crystal diamond seed crystals, and in-situ high-temperature annealing (so that the spliced ​​diamond is functionally infinitely close to a complete and flawless single crystal).

[0021] Methane (CH4) with a purity higher than 99.99999% was used as the carbon source in all stages, and hydrogen (H2) with a purity higher than 99.99999% was used as the carrier gas and etching gas.

[0022] Single-crystal diamond with a six-sided orientation of (100) and a size of 5mm-20mm was selected as the seed crystal. The seed crystal had a nitrogen impurity content of less than 50ppb, an XRD half-width of less than 80 arcseconds (low dislocation, no cracks, no inclusions), and uniform stress.

[0023] The seed crystal is polished using a nanodiamond polishing slurry through mechanical and chemical polishing until the surface roughness Ra < 0.3 nm. Reactive ion etching is then performed with oxygen / argon plasma for final slight etching to remove the polishing damage layer, achieving an "atomic-level smooth" surface.

[0024] Cleaning of the seed crystals: ultrasonically clean with acetone, ethanol, and deionized water for 15 minutes each. Boil in a 1:3 volume ratio of concentrated nitric acid / concentrated sulfuric acid mixture for 30 minutes, then rinse with ultrapure water until neutral.

[0025] Surface replication growth of seed crystals: The first stage uses low methane concentration (volume concentration: 0.1%-4%), power 2.0kW-4.0kW, pressure 80Torr-150Torr, and temperature 800℃-950℃ for "surface repair" growth, with a growth time of 0.5h-48h, to obtain a high-quality crystal layer. The second stage uses high methane concentration (volume concentration: 4%-15%), power 4.0kW-10.0kW, pressure 100Torr-200Torr, and temperature 900℃-1000℃ for growth, with a growth time of 2-3 weeks, to obtain a high-quality crystal.

[0026] Single-crystal diamond splicing growth: 2-8 single-crystal diamond wafers, with a thickness of 0.2mm-1mm, are placed on a deposition stage with a spacing of 1-20µm between each wafer. First-step growth control process: CH4 / H2 volume ratio: 3.5%-9.5%, appropriate oxygen content: 0.1%-10%, growth temperature: 950℃-1200℃, reaction pressure: 100 Torr-200 Torr, microwave power: 3.5 kW-10 kW, growth time: 20h-200h. Second-step growth control process: CH4 / H2 volume ratio: 1.2%-3.5%, appropriate oxygen content: 0.1%-5%, growth temperature: 850℃-1000℃, reaction pressure: 100 Torr-150 Torr, microwave power: 3.5 kW-6 kW, growth time: 20h-200h.

[0027] To eliminate defects at the splice seam interface and achieve dislocation healing, an in-situ high-temperature annealing process was employed to significantly reduce the interface defect density and completely release interface stress, making the electrical, thermal, and mechanical properties of the healed interface infinitely close to those of bulk single-crystal materials. The following high-temperature annealing process was further tested. Example 1

[0028] After the epitaxial growth of two 5mm×5mm-20mm×20mm single-crystal diamond wafers at the splice seam is completed, the process is performed directly within the MPCVD reaction chamber: S1: Immediately stop the CH4 intake and quickly replace the gas in the reaction chamber with pure H2.

[0029] S2: Within 2 minutes, microwave power is used to rapidly raise the crystal temperature from the growth temperature of 920°C to 1200°C, and the temperature is maintained for 30 minutes in a hydrogen plasma atmosphere.

[0030] S3: Then, it is cooled to 800°C at a rate of 20°C / minute, and then cooled with the furnace. Example 2

[0031] After the epitaxial growth of two 5mm×5mm-20mm×20mm single-crystal diamond wafers at the splice seam is completed, the process is performed directly within the MPCVD reaction chamber: S1: Immediately stop the CH4 intake and quickly replace the gas in the reaction chamber with pure H2.

[0032] S2: Increase the microwave power within 2 minutes to rapidly raise the sample temperature from the growth temperature of 920℃ to 1400℃, adjust the reaction chamber, and keep it at this temperature for 20 minutes in a hydrogen plasma atmosphere.

[0033] S3: Then, it is cooled to 600°C at a rate of 10°C / minute, and then cooled with the furnace. Example 3

[0034] After the epitaxial growth of two 5mm×5mm-20mm×20mm single-crystal diamond wafers at the splice seam is completed, the process is performed directly within the MPCVD reaction chamber: S1: Immediately stop the CH4 intake and quickly replace the gas in the reaction chamber with pure H2.

[0035] S2: Increase the microwave power within 2 minutes to rapidly raise the sample temperature from the growth temperature of 920℃ to 1600℃, and keep it at that temperature for 10 minutes under hydrogen plasma.

[0036] S3: Then, it is cooled to 700°C at a rate of 5°C / min, and then cooled with the furnace.

[0037] Comparative Example Under the same growth conditions as in Example 1, after growth, the high-temperature annealing described in this invention was not performed, but instead the furnace was cooled directly at a slow rate of 10°C / min.

[0038]

[0039] The in-situ high-temperature annealing process in this embodiment has a decisive effect on improving the crystal quality, stress state, and final performance of the healed interface.

[0040] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A method for epitaxial healing of single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening, characterized in that: Single-crystal diamond was selected as the seed crystal and pretreated. Then, multi-stage surface replication growth was performed in the microwave plasma chemical vapor deposition (MPCVD) reaction chamber. The surface-replicated crystal was sliced ​​to obtain single-crystal diamond wafers. These wafers were pretreated, and several wafers were spliced ​​together and subjected to multi-stage epitaxial growth and healing within the MPCVD reaction chamber. Without disrupting the vacuum within the same reaction chamber, the chamber was filled with hydrogen or replaced with an inert gas to replace the carbon-containing reaction atmosphere. The reaction chamber parameters were adjusted, and in-situ high-temperature annealing was performed. The cathodoluminescence spectral signal intensity at the healing interface was not less than 90% of the signal intensity of the adjacent single-crystal bulk region and / or the 1332 cm⁻¹ value in micro-area Raman spectroscopy measurements. -1 The peak position shift of the characteristic peak does not exceed 0.1 cm. -1 .

2. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 1, characterized in that: Methane was used as the carbon source and hydrogen as the carrier gas and etching gas in each stage of the multi-stage epitaxial growth and healing process.

3. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 1, characterized in that: Single-crystal diamond with a six-sided orientation of (100) and a size of 5mm-20mm was selected as the seed crystal. The nitrogen impurity content of the seed crystal was less than 50ppb and the XRD half-width was less than 80 arcseconds.

4. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 3, characterized in that: The pretreatment refers to polishing and cleaning the seed crystal or the sliced ​​single-crystal diamond sheet with nanodiamond polishing slurry until the surface roughness Ra < 0.3 nm; using reactive ion etching with oxygen / argon plasma for final slight etching to remove the polishing damage layer and make the surface atomically smooth; ultrasonically cleaning the seed crystal with acetone, ethanol and deionized water for more than 15 minutes in sequence, boiling it in a 1:3 volume ratio of concentrated nitric acid / concentrated sulfuric acid mixture for more than 30 minutes and rinsing it with ultrapure water until neutral.

5. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 1, characterized in that: The seed crystals undergo multi-stage surface replication growth in a methane and hydrogen atmosphere: The first stage uses low-concentration methane (0.1%-4% by volume) as the carbon source, with a growth power of 2.0 kW-4.0 kW, a growth pressure of 80 Torr-150 Torr, a growth temperature of 800℃-950℃, and a growth time of 0.5 h-48 h, yielding a single-layer high-quality crystal; the second stage uses high-concentration methane (4%-15% by volume) as the carbon source, with a growth power of 4.0 kW-10.0 kW, a growth pressure of 100 Torr-200 Torr, a growth temperature of 900℃-1000℃, and a growth time of 2-3 weeks, yielding a high-quality diamond crystal.

6. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 1, characterized in that: The slicing process involves dividing the surface-grown crystal into single-crystal diamond sheets of the same thickness, ensuring that the crystal orientation of all six faces is (100) during the slicing process.

7. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 1, characterized in that: Select 2-8 sliced ​​single-crystal diamond wafers, with a thickness of 0.2mm-1mm and a thickness difference of 0.1um-20um, and perform multi-stage epitaxial growth and healing: First stage growth: control the spacing between the single-crystal diamond wafers to 1-20um, the CH4 / H2 volume ratio to be 3.5%-9.5%, the oxygen concentration to be 0.1%-10%, the growth temperature to be 950℃-1200℃, the reaction pressure to be 100Torr-200 Torr, the microwave power to be 3.5 kW-10kW, and the growth time to be 20h-200h; Second stage growth: CH4 / H2 volume ratio to be 1.2%-3.5%, the oxygen concentration to be 0.1%-5%, the growth temperature to be 850℃-1000℃, the reaction pressure to be 100Torr-150 Torr, the microwave power to be 3.5 kW-6kW, and the growth time to be 20h-200h.

8. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 1, characterized in that: The in-situ high-temperature annealing involves adjusting the microwave power of the reaction chamber to 4.0-6.0kW, and rapidly raising the temperature of the diamond crystal to the critical high-temperature range of 1100℃ to 1800℃ within 3 minutes in a hydrogen plasma atmosphere. The crystal is then held at this critical high-temperature range for 2 to 120 minutes. After the holding period, the temperature is cooled to below 800℃ at a rate not exceeding 50℃ / minute, followed by natural cooling or continued cooling according to a program.

9. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 8, characterized in that: The critical high temperature range is 1150℃ to 1250℃, and the holding time in the critical high temperature range is 2-15 minutes.

10. The epitaxial healing method for single-crystal diamond splice seams based on in-situ high-temperature annealing strengthening according to claim 8, characterized in that: During annealing, the hydrogen pressure in the reaction chamber is maintained at 50-200 Torr, and the interface is purified by the etching effect of hydrogen plasma on non-sp³ bonded carbon.

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