Method for improving quality of joint between diamonds

Abstract

The present invention relates to the field of CVD diamond growth. Disclosed is a method for improving the quality of a joint between diamonds, which method is used for solving the problems of non-uniform quality, large dislocation density and poor bonding strength of a joint. In the present invention, a joint between diamonds is subjected to laser cutting, such that the a V-shaped groove is formed in the joint. Moreover, an oxygen-containing gas is introduced to preferentially make the V-shaped groove in the joint grow and restore, and after restoration is completed, comprehensive growth of a substrate is conducted, thereby improving the quality of the joint, thus obtaining a high-quality and large-area monocrystalline diamond.

Description

A method for improving the quality of diamond joints Technical Field

[0001] The present invention relates to a method for improving the quality of diamond joints, and prepares large-size, high-quality diamond wafers by microwave plasma chemical vapor deposition (MPCVD) technology. Background Art

[0002] Diamond has become one of the most promising semiconductor materials due to its high thermal conductivity, high breakdown electric field, and high carrier mobility. However, compared with other semiconductor materials (such as Si, SiC, and GaN), the biggest obstacle to diamond's application is the lack of high-quality, inch-scale single crystals.

[0003] The main methods for producing large-scale single-crystal diamond wafers include heteroepitaxial growth, three-dimensional growth, and splicing growth. Splicing growth is currently the most commonly used method among all preparation routes. The splicing method, also known as the mosaic method, is a method for producing large-scale single crystals by closely arranging multiple small-area conventional single-crystal diamond seeds and then depositing and growing them into a large-area single-crystal diamond on top. The splicing growth method has obvious advantages in producing large-area single-crystal diamonds and can produce inch-scale single-crystal diamond wafers. However, the splicing method also has disadvantages. The splicing joints are enriched with various defects such as dislocations, polycrystalline, interfaces, and microcracks, which affect mechanical strength, optical transmittance, and electrical properties. This makes it impossible to obtain high-quality large-scale diamonds, limiting the advanced applications of large-scale spliced ​​diamonds.

[0004] CN114150376A describes a method for growing large-scale single-crystal diamond by splicing together single-crystal diamond epitaxial wafers in parallel along a step-flow growth direction, which serve as the splicing substrate. This patent, which splices multiple epitaxial wafers vertically, fails to overcome the problems of high stress at the joints, small bonding area, high defect density, and low splicing quality.

[0005] CN108754600A describes a method for growing large-area single-crystal diamond by splicing. Two single-crystal diamonds are cut to form two parallel splicing bevels, which are then spliced ​​together. While this method increases the splicing area by splicing the bevels, it also creates a narrow gap at the joint, making it difficult for active methyl groups and atoms such as hydrogen and oxygen to enter the gap during growth. Only the upper surface of the exposed diamond joint is susceptible to healing, resulting in a small healing area and poor strength, leading to high stress within the crystal and low quality.

[0006] CN110184653A describes a method for improving the quality of large-scale single-crystal diamond seams. The seam between two single-crystal diamond sheets is grooved, then spliced ​​and grown, and the two sheets are joined together through lateral epitaxy. This method creates a rectangular opening at the joint, with a 90° vertex. This creates a localized electric field-enhancing tip effect, increasing the likelihood of high internal stress, cracks, and polycrystalline formation at the joint. The long distance between the bottoms makes healing difficult, reducing the quality of the joint.

[0007] Therefore, in order to solve the above problems, the present invention proposes a method for improving the quality of diamond joints. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for improving the quality of diamond splicing, which solves the problem of dislocation defects and poor splicing quality in the diamond splicing in the prior art.

[0009] In order to achieve the above object, the present invention provides a method for improving the quality of diamond joints, comprising the following steps:

[0010] S1. Select a high-quality diamond seed crystal as a substrate (1), and deposit and grow an epitaxial layer (2) on the diamond substrate by microwave plasma chemical vapor deposition;

[0011] S2, separating the diamond epitaxial layer (2) from the substrate layer (1) by laser cutting, and pre-treating the epitaxial layer (2) and the substrate layer (1) so that the treated epitaxial layer (2') has the same thickness as the diamond substrate layer (1');

[0012] S3, arranging the diamond epitaxial layer (2') and the substrate layer (1') in the same direction as the growth lines, laser cutting the joint between the diamond substrate layer (1') and the epitaxial layer (2'), with the cutting angle being a 30°-60° bevel, so that a V-shaped groove (3) is formed at the joint between the diamond substrate layer (1') and the epitaxial layer (2'), thereby forming a V-shaped spliced ​​diamond substrate (4);

[0013] S4. Plasma etching is performed on the V-shaped spliced ​​diamond substrate (4), and the processed substrate (4') is introduced into a microwave plasma growth system. At the same time, oxygen-containing gas is introduced to preferentially grow V-shaped grooves. After the V-shaped grooves are filled, the supply of oxygen-containing gas is stopped.

[0014] Furthermore, the method further includes S5, continuing the growth in the microwave plasma growth system until high-quality large-area single crystal diamond is obtained after the growth is completed.

[0015] Furthermore, the diamond seed crystal in step S1 is a chemical vapor deposition high-quality diamond seed crystal with all six sides being (100).

[0016] Furthermore, in step S1, the nitrogen content of the diamond substrate (1) is 20-100 ppb, and the surface roughness is 1.0-10 nm.

[0017] Furthermore, the thickness of the diamond epitaxial layer (2') and the diamond substrate layer (1') after being processed in step S2 is 0.3-0.5 mm.

[0018] Furthermore, the preprocessing steps in step S2 are:

[0019] Step 1: grinding the cut diamond substrate layer (1) and the epitaxial layer (2) to a surface roughness of 1.0-10 nm;

[0020] Step 2: pickling for 30 min-60 min;

[0021] Step 3: Ultrasonic cleaning for 20-60 min to remove the laser-burned carbonized parts;

[0022] Step 4: Drying.

[0023] Furthermore, the ultrasonic cleaning in step 2 is performed by using acetone and anhydrous ethanol for 10-30 min respectively.

[0024] Furthermore, in step S3, before laser cutting the joint between the diamond substrate layer (1') and the epitaxial layer (2'), the upper surfaces (5, 6) are cut to form deviation angles (12, 13).

[0025] Furthermore, the deviation angle (12, 13) is 2°-15°, preferably 3°-10°.

[0026] Furthermore, the cutting angle in step S3 is preferably 30°-45°, more preferably 45°.

[0027] Furthermore, in step S3, the depth of the V-groove is 1 / 3-1 / 2 of the thickness of the diamond substrate (4), preferably 1 / 4-1 / 3.

[0028] Furthermore, step S4 further includes performing ultrasonic cleaning after the plasma etching is completed to remove the carbonized parts caused by laser burning. The ultrasonic cleaning is preferably performed using acetone and anhydrous ethanol for 10-30 minutes respectively.

[0029] Furthermore, in step 1, the plasma etching is performed in H2 or H2 / O2 mixed gas for 20 min-40 min, wherein the volume ratio of O2 to H2 is 0-0.02.

[0030] Furthermore, in step S4, the microwave plasma growth system is a H2 / CH4 mixed gas, wherein the volume ratio of CH4 to H2 is 0.02-0.05.

[0031] Furthermore, in step S4, the initial volume ratio of oxygen-containing gas to methane is 0.001-0.005. As the growth time increases, the volume ratio of oxygen-containing gas to methane is gradually reduced until the cut V-grooves are filled, and the supply of oxygen-containing gas is stopped.

[0032] Furthermore, in step S4, the oxygen-containing gas is selected from one or more of the group consisting of O2 and CO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without inventiveness.

[0034] FIG1 is a flow chart of a method for improving the quality of diamond joints proposed by the present invention.

[0035] Figure 2 is a schematic diagram of the present invention's method for cutting the upper surface at an offset angle and then cutting the joint. 2(a) shows laser cutting the upper surface to form an offset angle, and 2(b) shows cutting the joint of the substrate with the offset angle to form a V-groove at the joint.

[0036] Figure 3 shows optical microscope images (100×) of the spliced ​​growth obtained in the Examples and Comparative Examples. Figure 3(a) shows Example 1, Figure 3(b) shows Example 2, Figure 3(c) shows Example 3, Figure 3(d) shows Comparative Example 2, Figure 3(e) shows Comparative Example 3, Figure 3(f) shows Comparative Example 4, and Figure 3(g) shows Comparative Example 5.

[0037] Figure 4 shows optical microscope images (400x) of a diamond grown after forming a V-groove at the joint and a rectangular groove at the joint. Figure 4(a) shows a diamond obtained using the method for improving the quality of diamond joints proposed in this invention. Figure 4(b) shows a diamond obtained by vertically cutting the joint to form a rectangular groove.

[0038] Including: 1. Diamond substrate layer; 1', processed diamond substrate layer; 2. Epitaxial layer formed after MPCVD epitaxial growth; 2', processed diamond epitaxial layer; 3. V-groove formed at the joint; 4. V-jointed diamond substrate; 4', processed V-jointed diamond substrate; 5. Upper surface of substrate layer 1'; 6. Upper surface of epitaxial layer 2'; 7. Cutting bevel formed by laser cutting the joint of substrate layer 1; 8. Cutting bevel formed by laser cutting the joint of epitaxial layer 2; 9. Joint formed by preferential growth of V-grooves; 10. Grown diamond substrate; 11. Large-sized diamond growth layer; 12 , the deviation angle formed by laser cutting the diamond upper surface 5; 13. The deviation angle formed by laser cutting the diamond upper surface 6; 14. The upper surface with the deviation angle 12 after cutting; 15. The upper surface with the deviation angle 13 after cutting; 16. The substrate with the deviation angle 12; 17. The substrate with the deviation angle 13; 18. The V-groove formed at the joint of the substrates with the deviation angle; 19. The cutting intersection formed by the upper surface 14 and the V-groove 18; 20. The cutting intersection formed by the upper surface 15 and the V-groove 18. DETAILED DESCRIPTION

[0039] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a method for improving the quality of diamond joints. Referring to Figures 1 and 2, the method includes the following steps:

[0040] S1. Select a high-quality diamond seed crystal as a substrate layer (1), and perform homoepitaxial growth on the substrate diamond by MPCVD to obtain an epitaxial layer (2);

[0041] S2, separating the diamond epitaxial layer (2) from the substrate layer (1) by laser cutting, and pre-treating the epitaxial layer (2) and the substrate layer (1) so that the thickness of the diamond epitaxial layer (2) and the diamond substrate layer (1) are consistent;

[0042] S3, arranging the diamond epitaxial layer (2) and the substrate layer (1) in the same direction as the growth lines, and laser cutting the joint between the diamond substrate layer (1) and the epitaxial layer (2), with the cutting angle being a 30°-60° bevel, so that a V-shaped groove (3) is formed at the joint between the diamond substrate layer (1) and the epitaxial layer (2);

[0043] S4. Plasma etching is performed on the V-shaped spliced ​​diamond substrate (4), and the processed substrate (4') is introduced into a microwave plasma growth system. At the same time, oxygen-containing gas is introduced to preferentially grow V-shaped grooves. After the V-shaped grooves are filled, the supply of oxygen-containing gas is stopped.

[0044] In step S1, the diamond seed crystal is preferably a high-quality chemical vapor deposition diamond seed crystal with all six faces (100); the nitrogen content is preferably 20-100 ppb, and the surface roughness is preferably 1.0-10 nm. Different diamond crystal faces have different growth conditions. The (100) crystal face grows stably and is most suitable for producing high-quality epitaxial thin films. The (110) crystal face has the fastest growth rate, but the growth quality of this crystal face is not as high as that of the (100) face. The (111) crystal face has problems such as twins, impurities, or defects, making growth very difficult. Therefore, a diamond seed crystal with all six faces (100) is preferably used as the substrate.

[0045] There is no particular limitation on the growth conditions of the MPCVD method in step S1, as long as homoepitaxial growth of diamond can be achieved, for example, growth is performed at a temperature of 700-1200° C. and a pressure of 150-180 torr for a sufficient time until the desired diamond epitaxial layer thickness is obtained.

[0046] The pretreatment steps in step S2 are as follows: step 1, grinding the cut diamond substrate layer (1) and epitaxial layer (2) to a surface roughness of 1.0-10 nm; step 2, pickling for 30 min-60 min, preferably using a mixed acid of sulfuric acid and nitric acid with a volume ratio of 3:1 to pickle the ground sample for 0.5-1h; step 3, ultrasonic cleaning for 20-60 min, preferably using acetone and anhydrous ethanol for ultrasonic cleaning for 10-30 min respectively to remove the laser-burned carbonized part; step 4, drying. The thickness of the treated diamond epitaxial layer (2') and the diamond substrate layer (1') is 0.3-0.5 mm, and the height difference is within 10 μm. By grinding the diamond substrate layer (1) and the epitaxial layer (2) together, the height of the substrate layer and the epitaxial layer is kept consistent, the growth temperature difference and growth rate difference at the splicing point are avoided, which helps to improve the splicing quality. Controlling the direction of the growth lines to be consistent during splicing helps to bridge the splicing point.

[0047] In step S3, before laser cutting the joint of the diamond substrate layer (1') and the epitaxial layer (2'), the upper surface (5, 6) is preferably cut at an inclined angle so that the upper surface (14, 15) after cutting forms an offset angle (12, 13) with the lower surface of the diamond. The offset angle treatment of the seed crystal blocks to be spliced ​​helps to optimize the growth of the upper surface of the diamond. The preparation of the offset angle can promote the flow of surface steps, blunt the vertical edges, weaken the edge effect, and effectively stabilize the growth surface, accelerate the growth rate, and help increase the uniformity of diamond growth. On the other hand, it helps to reduce the sharpness of the intersection. The cutting intersection (19, 20) formed by the first offset angle cutting and the second V-groove cutting at the joint is relatively gentle, which can further avoid the local discharge effect and further improve the quality of the joint. Experiments show that as the offset angle increases, the edge effect first decreases and then increases. This may be related to the changes in the local electric field strength and plasma density. The offset angle is preferably 2°-15°, and more preferably 3°-10°.

[0048] The cutting angle in step S3 is 30°-60°, preferably 30°-45°, and more preferably 45°. The cutting angle is the acute angle formed by the cutting bevel (7, 8) and the lower surface. If the cutting angle is too large, the required growth area will be large, increasing the difficulty of healing the joint. If the cutting angle is too small, the plasma energy will have difficulty entering the joint, resulting in slow growth of the diamond joint. When the cutting angle is between 30° and 60°, it helps to limit the propagation of dislocations, further reducing the dislocation density in the single crystal CVD diamond, and improving the quality of diamond growth.

[0049] The depth of the V-groove in step S3 is 1 / 3-1 / 2 of the thickness of the diamond substrate (4), preferably 1 / 4-1 / 3, which is beneficial to improving the healing speed of the joint while maintaining the bonding strength, and is industrially feasible.

[0050] The etching conditions of the plasma etching in step S4 are not particularly limited, as long as the upper surface of the diamond can be etched. The etching gas is preferably H2 or a H2 / O2 mixed gas, with a volume ratio of O2 to H2 of 0-0.02; the etching time is preferably 20-40 minutes, and more preferably 0.5 hours. After the plasma etching is completed, an ultrasonic cleaning step is performed, wherein the ultrasonic cleaning is performed using acetone and anhydrous ethanol for 10-30 minutes respectively to remove the laser-burned carbonized parts. After ultrasonic cleaning, a processed substrate (4') is obtained.

[0051] In step S4, the microwave plasma growth system is a H2 / CH4 mixed gas, wherein the volume ratio of CH4 to H2 is 0.02-0.05. In step S4, the oxygen-containing gas is selected from one or more of the group consisting of O2 and CO2; initially, the volume ratio of the oxygen-containing gas to CH4 is 0.01-0.03. As the growth time increases, the volume ratio of the oxygen-containing gas to methane is gradually reduced until the cut V-groove is filled, and the supply of oxygen-containing gas is stopped. Due to the height difference between the V-groove and the upper surface, the upper surface (5, 6) is close to the plasma and has a higher temperature, while the cutting bevel (7, 8) is far from the plasma and has a lower temperature. The temperature difference will lead to uneven diamond growth at the joint. To solve this problem, the inventors discovered that by controlling the concentration of the oxygen-containing gas in the inlet raw material, preferential growth of the V-shaped cutting surface can be achieved. By introducing oxygen-containing gases such as O2 and CO2 into the growth system, oxygen atoms with higher etching efficiency preferentially contact the upper surface, thereby inhibiting the growth of the upper surface. The bottom of the V-groove is far away, making it difficult for oxygen atoms to reach it. The concentration of oxygen atoms at the V-groove is lower than that at the upper surface of the non-cut diamond, allowing the V-groove to grow preferentially. As the deposition time increases, the V-groove gradually grows, and the height from the upper surface of the diamond decreases, gradually reducing the concentration of oxygen-containing gas to avoid the inhibition of oxygen atoms on the growth of the joint. After the V-groove is filled, the supply of oxygen-containing gas is stopped. Diamonds are continuously deposited on the entire upper surface of the healed diamond substrate (10), thereby obtaining large-sized diamonds with high quality and uniform quality at the joint.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] (1) The present invention forms a V-shaped groove by beveling the diamond joint, which increases the growth area of ​​the joint, improves the bonding strength, and is conducive to the healing of the joint. The apex of the opening is less than 90°, which can effectively alleviate the problems caused by the tip effect, reduce the probability of high internal stress, cracks, polycrystalline and other problems at the joint, and improve the quality of the joint. Cutting the upper surface of the seed crystal at an offset angle before splicing helps to improve the uniformity of the growth of the upper surface of the diamond, helps to further alleviate the tip effect, and improve the quality of the joint.

[0054] (2) The present invention controls the oxygen concentration to preferentially grow the joint, which is easy to operate, solves the problem of growth rate differences, and improves the uniformity of diamond quality at the joint.

[0055] (3) The present invention uses the MPCVD method to prepare diamonds, and other impurities grow into the diamond lattice, which is conducive to the growth of high-purity, high-quality diamonds.

[0056] (4) The present invention obtains large-scale, high-quality single-crystal diamonds with excellent purity, mechanical strength, optical transmittance, electrical properties and other comprehensive properties, breaking through the limitations of advanced applications of large-scale spliced ​​diamonds.

[0057] The technical solution of the present invention is further described below based on specific embodiments. The protection scope of the present invention is not limited to the following embodiments, which are listed for illustrative purposes only and do not limit the present invention in any way.

[0058] In all embodiments and comparative examples of the present invention, the laser used is a domestically produced 532 nm laser.

[0059] The evaluation items and analysis methods of the samples in all embodiments and comparative examples of the present invention are as follows:

[0060] 1) Growth rate

[0061] The average growth rate (μm / h) is calculated by dividing the thickness (μm) of the diamond growth layer deposited on the substrate by the growth time (h). Since the thickness of the diamond growth layer is somewhat uneven, the growth rates at the highest and lowest points are measured to obtain the growth rate range.

[0062] 2) Raman spectroscopy

[0063] The quality and stress of diamonds can be judged by measuring the position and half-maximum width of the diamond Raman spectrum. The half-maximum width (FWHM) of the diamond Raman spectrum refers to the peak width when the spectral intensity drops to half of the peak value on both sides of the half-maximum height of the Raman peak. It reflects the crystal quality of the diamond. The higher the quality, the smaller the half-maximum width of the Raman spectrum. The standard Raman scattering peak of diamond is located at 1332 cm -1 The difference between the sample FWHM and the standard Raman spectroscopy reflects the diamond crystal stress.

[0064] 3) Transmittance

[0065] The transmittance of diamond is measured by Fourier transform infrared spectroscopy. The transmittance of diamond is related to the diamond defect density. The higher the diamond defect density, the lower the transmittance. Conversely, the higher the transmittance, the lower the diamond defect density and the better the quality. Example 1

[0066] Step 1: Select a single crystal diamond seed with a crystal orientation of (100). The seed crystal requires a nitrogen concentration of about 100 ppb, a surface roughness of about 5 nm, and a size of 15×15×1 mm. 3 High-quality single-crystal diamond seed crystals were prepared; after acid pretreatment, homoepitaxial growth was carried out. The treated single-crystal diamond substrate was placed in the chamber of a microwave plasma device, and 500 sccm of hydrogen and 25 sccm of methane were introduced. The growth power was selected to be 6000 W, the pressure was 18 KPa, and the growth temperature was controlled at about 850°C. Under this process, a 5.0 mm diamond growth layer was grown.

[0067] Step 2: Laser slicing was performed with a slicing thickness of 0.4 mm. Two or more diamond slices were selected as seed crystals for splicing. The sliced ​​diamond slices were mounted on a grinding workpiece with pyrophyllite. The surfaces and the sides of the slicing were ground for 3.0 hours using 230-mesh, 800-mesh, and 2000-mesh diamond powders, respectively, to achieve a smooth surface at the joint between the two single-crystal diamonds. The ground surfaces and sides were mechanically polished, first using a speed of 50 r / min for 5 hours for coarse grinding, then a speed of 80 r / min for 1 hour for fine grinding, and finally a speed of 120 r / min for 20 minutes. After polishing, the height difference at the joint was 1 μm, and the surface roughness was 0.5 nm. The polished samples were pickled with sulfuric acid and nitric acid in a volume ratio of 3:1 for 30 minutes. The samples were then ultrasonically cleaned with acetone and anhydrous ethanol for 30 minutes, respectively, and dried at room temperature.

[0068] Step 3: Arrange the diamond sheets in the same direction as the growth lines, determine the joint surface, and use a laser to bevel the joint. The bevel angle is 45° and the cutting depth is 1 / 4 of the thickness of the diamond sheet. Set the laser power to 11 W and the laser step length to 2 mm / s. Perform the laser bevel according to the set bevel size.

[0069] Step 4: Etch the sample after laser treatment. Plasma etching is performed on the substrate surface under hydrogen / oxygen plasma conditions. The volume ratio of oxygen to hydrogen is 1%, the etching temperature is 800°C, and the time is 20 minutes. After etching, ultrasonic cleaning is performed with acetone and ethanol for 30 minutes respectively to remove the carbonized part caused by laser ablation. The treated single crystal diamond substrate is placed in the chamber of a microwave plasma equipment. 500 sccm of hydrogen, 25 sccm of methane, and 0.125 sccm of oxygen are introduced. The growth power is selected to be 6000 W, the pressure is 18 KPa, and the growth temperature is controlled at about 800°C. As the growth time progresses, the oxygen content is gradually reduced (see Table 1). After the V-groove is filled, the oxygen supply is stopped. The concentrations of other gases remain unchanged. The total growth time is 150 hours.

[0070] Step 5: After the growth is completed, the spliced ​​single crystal diamond is taken out to obtain 30×15×1.5mm 3 Single crystal diamond with high quality seams.

[0071] Table 1 Oxygen gradient decrease over time

[0072]

[0073] Example

[0074] In step 3, the bevel cutting angle is 45°, the cutting depth is 1 / 3 of the thickness of the diamond sheet, and the remaining operations are the same as in Example 1. Example 2

[0075] In step 3, the bevel cutting angle is 30°, the cutting depth is 1 / 4 of the thickness of the diamond sheet, and the remaining operations are the same as in Example 1. Example 3

[0076] In step 3, the bevel cutting angle is 40°, the cutting depth is 1 / 4 of the thickness of the diamond sheet, and the remaining operations are the same as in Example 1. Example 4

[0077] In step three, there are two steps of cutting:

[0078] The first step of cutting: using an 11 W laser to bevel the upper surface of the sliced ​​single crystal diamond sheet, the deviation angle is 7°±1°;

[0079] The second step is cutting: the 11 W laser power is also used to cut the diamond joints, with a bevel angle of 45° and a cutting depth of 1 / 4 of the thickness of the diamond sheet;

[0080] The remaining operations are the same as those in Example 1.

[0081] Comparative Example 1:

[0082] In step 3, the joint is not beveled but cut vertically, so that a rectangular groove is formed at the joint. The cutting depth is 1 / 4 of the thickness of the diamond sheet, and the groove width / depth is about 10. The rest of the operations are the same as in Example 1.

[0083] Comparative Example 2:

[0084] In step 3, the bevel cutting angle is 45°, the cutting depth is the same as the thickness of the diamond sheet, and the remaining operations are the same as in Example 1.

[0085] Comparative Example 3:

[0086] In step 3, the bevel cutting angle is 20°, the cutting depth is 1 / 4 of the thickness of the diamond sheet, and the remaining operations are the same as in Example 1.

[0087] Comparative Example 4:

[0088] In step 3, the bevel cutting angle is 70°, the cutting depth is 1 / 4 of the thickness of the diamond sheet, and the remaining operations are the same as in Example 1.

[0089] Comparative Example 5:

[0090] In step 4, the oxygen concentration is maintained at the initial value and does not decrease. The remaining operations are the same as those in Example 1.

[0091] The experimental results are as follows:

[0092] Table 2 Experimental results

[0093]

[0094] As shown in Figure 3, the joints of Examples 1-3 (Figures 3(a)-3(c)) all healed without polycrystals. Comparative Examples 3 (Figure 3(e)) and 4 (Figure 3(f)) also healed, but there were height differences at the joints, resulting in uneven diamond growth. Comparative Examples 2 (Figure 3(d)) and 5 (Figure 3(g)) failed to heal. As shown in Figure 4, the joints of Example 1 (Figure 4(a)) healed naturally and smoothly, with uniform diamond growth and high quality. Comparative Example 1 (Figure 4(b)) exhibited a large amount of polycrystals at the joints, and some areas did not heal smoothly.

[0095] Examples 1-5 can heal smoothly at the joints without polycrystals, and the joints are of high quality. The large-sized single crystal diamonds generated have high crystal quality, low dislocation density, uniform growth, low internal stress, and high transmittance, which can meet various industrial needs.

[0096] Example 5 performed two cuts, the first time cutting the upper surface at an offset angle, and the second time cutting the joint at a V-groove, which can further avoid local discharge effects and edge effects, improve the uniformity of crystal growth, and achieve the best quality at the joint, the highest crystal quality of diamond, the lowest internal stress, and the best transmittance.

[0097] By comparing Example 1 and Comparative Example 1, it can be seen that V-groove cutting at the splicing has better splicing quality. Comparative Example 1 cuts the splicing at a rectangular groove, and there is a 90° vertex at the opening, which leads to an enhanced tip effect of the local electric field, and a large amount of polycrystals appear at the joint, which does not heal smoothly.

[0098] By comparing Example 1, Example 2, and Comparative Example 2, it can be seen that as the cutting depth increases, the healing difficulty increases and the growth rate decreases. In Comparative Example 2, since the cutting depth is too deep, healing is difficult and the growth is poor, resulting in the joint being unable to heal within the same growth time.

[0099] By comparing Example 1, Examples 3-4, and Comparative Examples 3-4, it can be seen that selecting a suitable cutting angle can improve the quality of the splicing, resulting in a faster growth rate, better transmittance, higher diamond crystal quality, lower internal stress, lower defect density, and better overall performance in all aspects of high-quality diamond. In Comparative Example 3, the cutting angle is too large. Although the growth rate is fast, the diamond loss during the cutting process is greater, the economic efficiency is poor, and the transmittance of the resulting diamond is poor. In Comparative Example 4, the cutting angle is too small. The growth area of ​​the splicing is small, the bonding strength is low, the defect density is high, and the quality of the splicing is poor.

[0100] Comparing Example 1 and Comparative Example 5, it can be seen that controlling the slow reduction of oxygen concentration can achieve preferential growth of V-grooves, avoid polycrystalline formation at the joint, and improve the uniformity of diamond growth. Comparative Example 5, in which the slow reduction of oxygen concentration was not controlled, resulted in inconsistent diamond growth rates between the upper surface and the joint, an increased height difference, the formation of a large amount of polycrystalline, and low-quality joints.

[0101] The method for improving the quality of diamond joints proposed in the present invention improves the quality of the joints and obtains high-quality, large-area single-crystal diamond with excellent comprehensive properties such as purity, mechanical strength, and optical transmittance.

[0102] Those skilled in the art should note that the embodiments described in the present invention are merely exemplary and that various other substitutions, changes, and improvements may be made within the scope of the present invention. Therefore, the present invention is not limited to the above embodiments, but is only limited by the claims.

Claims

1. A method for improving the quality of the joint of diamond, characterized in that The method includes the following steps: S1. Select a high-quality diamond seed crystal as the substrate layer (1), and deposit and grow an epitaxial layer (2) on the substrate diamond by microwave plasma chemical vapor deposition; S2. Separate the diamond epitaxial layer (2) from the substrate layer (1) by laser cutting, and pre-treat the epitaxial layer (2) and the substrate layer (1) so that the thickness of the treated epitaxial layer (2') is the same as that of the substrate layer (1'); S3. Arrange the diamond epitaxial layer (2') and the substrate layer (1') in the same direction of the growth texture, and perform laser cutting on the joint of the diamond substrate layer (1') and the epitaxial layer (2') at an inclined plane with an angle of 30°-60°, so that a V-shaped groove (3) is formed at the joint of the diamond substrate layer (1') and the epitaxial layer (2'), thereby forming a diamond substrate (4) with a V-shaped joint; S4. Perform plasma etching on the diamond substrate (4) with a V-shaped joint, introduce the treated substrate (4') into the microwave plasma growth system, and simultaneously introduce an oxygen-containing gas to preferentially grow the V-shaped groove, and stop providing the oxygen-containing gas after the V-shaped groove is filled; 2. A method for improving the quality of the joint of diamond according to claim 1, characterized in that, It also includes S5. Continue to grow in the microwave plasma growth system until a high-quality large-area single-crystal diamond is obtained after the growth is completed; 3. The method for improving the quality of the diamond joint according to claim 1, characterized in that, In the step S1, the diamond seed crystal is a high-quality chemical vapor deposition diamond seed crystal with (100) on all six sides; 4. The method for improving the quality of the joint of diamond according to claim 1, wherein, In the step S1, the nitrogen content of the diamond substrate layer (1) is 20-100 ppb, and the surface roughness is 1.0-10 nm; 5. The method for improving the quality of the joint of diamond according to claim 1, wherein In the step S2, the thickness of the treated epitaxial layer (2') and the substrate layer (1') is 0.3-0.5 mm; 6. The method for improving the quality of the diamond splicing according to claim 1, wherein, The pre-treatment steps in the step S2 are as follows: Step 1. Grind the cut diamond substrate layer (1) and the epitaxial layer (2), and the surface roughness is 1.0-10 nm; Step 2. Acid pickling for 30 min-60 min; Step 3. Ultrasonic cleaning for 20-60 min; Step 4. Drying; 7. The method for improving the quality of the joint of diamond according to claim 6, wherein In the step 3, the ultrasonic cleaning is to ultrasonically clean with acetone and absolute ethanol for 10-30 min respectively to remove the laser-burned carbonized part; 8. The method for improving the quality of the diamond splicing according to claim 1, wherein, In the step S3, before performing laser cutting on the joint of the diamond substrate layer (1') and the epitaxial layer (2'), cut the upper surface (5, 6) to form a deviation angle (12, 13); 9. The method for improving the quality of the joint of diamond according to claim 8, wherein, The deviation angle (12, 13) is 2°-15°, preferably 3°-10°; 10. The method for improving the quality of the joint of diamond according to claim 1, wherein In the step S3, the cutting angle is preferably 30°-45°, more preferably 45°; 11. The method for improving the quality of the joint of diamonds according to claim 1, characterized in that, In the step S3, the depth of the V-shaped groove is 1 / 3-1 / 2 of the diamond substrate (4), preferably 1 / 4-1 / 3; 12. The method for improving the quality of the diamond splicing according to claim 1, characterized in that In the step S4, ultrasonic cleaning is also included after the plasma etching is completed to remove the laser-burned carbonized part. The ultrasonic cleaning is preferably to ultrasonically clean with acetone and absolute ethanol for 10-30 min respectively; 13. The method for improving the quality of the diamond splicing according to claim 12, wherein, In the step 1, the plasma etching is to etch for 20 min-40 min under H2 or a H2 / O2 mixed gas, and the volume ratio of O2 to H2 is 0-0.02; 14. The method for improving the quality of the diamond joint according to claim 1, characterized in that, In the step S4, the microwave plasma growth system uses a H2 / CH4 mixed gas, where the volume ratio of CH4 to H2 is 0.02 - 0.

05.

15. A method for improving the quality of the joint of diamond according to claim 14, characterized in that, In the step S4, the volume ratio of the initial oxygen-containing gas to methane is 0.001 - 0.

005. As the growth time extends, the volume ratio of the oxygen-containing gas to methane gradually decreases until the cut V-groove is filled, and then the supply of the oxygen-containing gas is stopped.

16. The method for improving the quality of the joint of diamond according to claim 1, wherein, In the step S4, the oxygen-containing gas is selected from one or more of the group consisting of O2 and CO2.

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