Apparatus and method for growing large size diamonds

Abstract

The application provides a device and a method for growing large-size diamond, and relates to the field of diamond growth. The device for growing large-size diamond comprises a sample holder, at least two sample holder grooves are arranged in the sample holder, a limiting strip is arranged between adjacent sample holder grooves and is not communicated with each other, a chamfer is arranged on one edge or opposite two edges of a top of a seed crystal, the chamfers of the seed crystals arranged in adjacent sample holder grooves are oppositely arranged, the height of the seed crystal is greater than the height of the limiting strip, and the depth of the chamfer is greater than the difference between the height of the seed crystal and the height of the limiting strip. The application solves the problem that the joint is suspended during the growth of the seed crystal, stabilizes the temperature of the splicing joint area, reduces the generation of defects in the splicing joint area, and improves the splicing success rate between the seed crystals.

Description

Technical Field

[0001] This invention relates to the field of diamond growth, and in particular to an apparatus and method for growing large-sized diamonds. Background Technology

[0002] Mosaic splicing growth technology for large-size single-crystal diamond has received widespread attention in recent years as an important solution to overcome crystal size limitations. This technology achieves epitaxial fusion of adjacent seed crystals in a high-temperature, high-pressure (HTHP) or chemical vapor deposition (CVD) environment by precisely controlling the geometric arrangement and crystal orientation of the seed crystals. Current technical approaches mainly attempt to achieve atomic-level matching of the seed crystal splicing interface by optimizing the step height difference of the seed crystals (typically controlled within ±0.5 µm) and the interface tilt angle (accurate to the order of 0.1˚), combined with submicron-level gap control (<1 µm). However, experimental data show that even when the splicing seam 4 between the seed crystals is reduced to 0.3 µm, significant temperature field distortion still exists in the splicing seam 4 region. (See splicing seam 4 for reference.) Figure 8 .

[0003] The core mechanism of the temperature field distortion phenomenon at the splice seam stems from the fundamental difference in the interfacial heat transfer mode at splice seam 4. In typical CVD / HTHP processes, the seed crystal body achieves efficient heat dissipation through solid-state heat conduction, while the gap between the seed crystals contains only a gaseous medium (such as a H2 / Ar mixture), whose thermal conductivity drops sharply, forming a significant thermal resistance barrier, which is the problem of seed crystal suspension during growth. According to finite element simulations, at a substrate temperature of 900℃, a vertical temperature gradient of 150~200℃ can be formed on both sides of the gap between the approximately 0.3 µm seed crystals, and its heat flux density is 2~3 orders of magnitude lower than that of the seed crystal body.

[0004] This asymmetric thermal transport ultimately leads to multiple interfacial mismatch effects: First, the difference in thermal expansion between the high-temperature region (center of seam 4) and the low-temperature region (seed crystal body) generates shear stress. X-ray diffraction (XRD) strain analysis confirms that this stress, within the range of 2–4 MPa, is sufficient to induce dislocation slip (critical shear stress approximately 1 MPa). Second, the diffusion coefficient of hydrocarbon groups in the gaseous medium increases exponentially with increasing temperature (D = D0exp(-Ea / kT), Ea ≈ 2.1). The carbon source supersaturation (ΔC / C0) at the splice seam 4 is 3-5 times higher than that at the surface of seed crystal 12, inducing abnormal lateral epitaxial growth and forming a micron-scale protrusion structure. More importantly, the hysteresis of gas thermal conduction (response time τ≈d² / α_gas, where α_gas is the gas thermal diffusivity) causes the temperature oscillation amplitude to reach ±25℃ during the dynamic growth process. Through in-situ observation by synchrotron radiation, it was found that this fluctuation causes the step flow velocity at the interface to produce a periodic variation of 12%~18%, which eventually forms a periodic defect array with a spacing of about 300 nm at the interface.

[0005] In summary, there is an urgent need for a device that can solve the temperature field distortion phenomenon during the growth of diamond seed crystals. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides an apparatus for growing large-sized diamonds, which can solve the problem of seed crystals being suspended at the seams during the growth process.

[0007] The apparatus for growing large-size diamonds provided by the present invention includes a sample holder, wherein the sample holder has at least two sample holder slots, and a limiting strip is provided between adjacent sample holder slots and they are not connected to each other. The sample holder slots are used to place external seed crystals, and one or two opposite sides of the top of the seed crystal are provided with a chamfer. The chamfers of the seed crystals located in adjacent sample holder slots are arranged opposite each other, and the height of the limiting strip is between the top of the seed crystal and the lowest point of the chamfer.

[0008] In one feasible embodiment, the width of the limiting strip is 0.2~1.0 mm.

[0009] In one possible implementation, the limiting strip is prism in shape and the top surface is an arc surface.

[0010] In one possible embodiment, the limiting strip is in the shape of a triangular prism and the top edge is provided with rounded corners, the size of which is 0.1-0.5 mm.

[0011] In one feasible embodiment, the two inner corners of the limiting strip at the bottom are the same, and both are 30~45˚.

[0012] In one feasible embodiment, the difference between the height of the seed crystal and the height of the limiting strip is 0.2~1.0 mm.

[0013] In one feasible embodiment, the chamfer angle is 15~75˚ and the chamfer depth is 0.01~0.6mm.

[0014] In one feasible embodiment, several sidewalls of the seed crystal are respectively attached to the inner wall of the sample holder slot and the sidewall of the limiting strip.

[0015] The present invention also provides a method for growing large-size diamonds, using the apparatus for growing large-size diamonds as provided in the first aspect of the present invention, comprising the following steps:

[0016] Step 1) Place several independent seed crystals into different sample slots, and then grow the seed crystals once. During the growth process, the growth surface of the seed crystal will gradually cross the limiting strip, thereby splicing adjacent seed crystals together, eliminating the gap between adjacent seed crystals, and thus establishing a temperature transfer channel between adjacent seed crystals.

[0017] Step 2) Perform a second growth on the seed crystal after the first growth in Step 1). During the second growth, the growth surface of the seed crystal in the first growth is used as the bottom surface to directly contact the sample holder.

[0018] In one feasible implementation, the following technical features are also included:

[0019] Step 2) also includes trimming the seed crystal that has completed the first growth in step 1) by laser processing. After trimming, the seed crystal is then grown a second time. During the second growth process, the growth surface of the seed crystal in the first growth is used as the bottom surface to directly contact the sample holder.

[0020] The apparatus and method for growing large-size diamonds provided by this invention have the following beneficial effects:

[0021] 1) In this invention, a limiting strip is set between adjacent seed crystals, and the depth of the chamfer of the seed crystal is greater than the difference between the height of the seed crystal and the height of the limiting strip. Therefore, when the seed crystal grows upward and outward, it will first stick to the limiting strip and grow past it. When the seed crystals on both sides of the limiting strip have both grown past the limiting strip during the growth process, they will grow together and then continue to grow upward. At this time, for the seed crystal above the limiting strip, its heat transfer is carried out through itself and the limiting strip, which solves the problem of the seed crystal being suspended at the joint during the growth process, stabilizes the temperature of the splicing joint area, reduces the generation of defects in the splicing joint area, and improves the splicing success rate between seed crystals.

[0022] 2) Furthermore, the grooved sample holder can effectively limit the seed crystal, prevent the seed crystal from shifting during growth, and improve the success rate of seed crystal splicing. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of one possible structure of the present invention.

[0024] Figure 2 This is a schematic diagram of one possible structure of the present invention.

[0025] Figure 3 This is a schematic diagram of the seed crystal epitaxial layer in this invention.

[0026] Figure 4 This is a schematic diagram of the structure of Embodiment 1 of the present invention.

[0027] Figure 5 This is a schematic diagram of the structure of Embodiment 2 of the present invention.

[0028] Figure 6 This is a cross-sectional view of the sample holder and the grooved sample holder in this invention.

[0029] Figure 7 This is a top view of the sample holder and the slotted sample holder in this invention.

[0030] Figure 8 This is a schematic diagram of the splicing seam between seed crystals in the prior art.

[0031] Figure 9 This is a schematic diagram illustrating the growth of seed crystals at the splice seam when the seam is suspended.

[0032] Figure 10 This is a schematic diagram showing the growth of seed crystals at the splicing seam when using the present invention.

[0033] Figure Labels

[0034] Sample tray 1

[0035] Sample holder slot 11

[0036] Seed Crystal 12

[0037] Limit bar 2

[0038] Epitaxial layer 3

[0039] seam 4 Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In the description of the present invention, it should be noted that the terms "left side", "right side", "upper side", "lower side", "above", "below", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0041] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0043] This invention provides an apparatus for growing large-sized diamonds, in conjunction with the following references. Figure 6 and Figure 7 For reference Figures 1-5 The sample holder 1 includes at least two sample holder slots 11. A limiting strip 2 is provided between adjacent sample holder slots 11, and they are not connected to each other. Each sample holder slot 11 is used to place an external seed crystal 12. One edge or two opposite edges of the top of each seed crystal 12 are chamfered. Each sample holder slot 11 holds only one seed crystal 12. The seed crystal 12 is an ungrown diamond; a large size is defined as a diamond with one side > 40mm. The limiting strip 2 can isolate the seed crystals 12 in adjacent sample holder slots 11. (Continue reading...) Figure 1 or Figure 2The chamfers of the seed crystals 12 located in the adjacent sample holder slots 11 are arranged opposite each other. The height of the limiting strip 2 is between the top of the seed crystal 12 and the lowest point of the chamfer. This can be interpreted as: the height of the seed crystal 12 is greater than the height of the limiting strip 2, and the depth of the chamfer is greater than the difference between the height of the seed crystal 12 and the height of the limiting strip 2. For further information on the height relationship between the limiting strip 2 and the seed crystal 12, please refer to [reference needed]. Figure 1 or Figure 2 ,in, The height of seed crystal 12, The depth of the 12 chamfer on the seed crystal. Given the height of limit bar 2, the above three conditions must be met: As an explanation, because the chamfer depth of the seed crystal 12 in this invention is greater than the difference between the height of the seed crystal 12 and the height of the limiting strip 2, when the seed crystal 12 grows upward and outward, it will first adhere to the limiting strip 2 and then grow past it. When the seed crystals 12 on both sides of the limiting strip 2 have both grown past the limiting strip 2 during the growth process, they will grow together and then continue to grow upward. At this time, for the seed crystal 12 located above the limiting strip 2, its heat transfer is carried downward through itself and the limiting strip 2. The area of ​​the original splice seam 4 is filled by the limiting strip 2, thereby changing the heat conduction medium from gas to solid. This solves the problem of temperature field distortion at the splice seam 4 during the growth of the seed crystal 12, that is, the problem of suspension. The grown seed crystal 12 will form the epitaxial layer 3. Epitaxial layer 3, as Figure 3 As shown In addition, the sample holder slot 11 can effectively limit the seed crystal 12, prevent the seed crystal 12 from shifting during the growth process, and improve the success rate of splicing the seed crystal 12.

[0044] In the apparatus for growing large-size diamonds provided in this embodiment of the invention, the width of the limiting strip 2 is 0.2~1.0 mm, preferably 0.2 mm.

[0045] In the apparatus for growing large-size diamonds provided in this embodiment of the invention, the limiting strip 2 is prism in shape and the top surface is arc-shaped.

[0046] In the apparatus for growing large-size diamonds provided in this embodiment of the invention, the limiting strip 2 is shaped like a triangular prism with rounded corners at the top edge, the rounded corners being 0.1~0.5 mm in size. Further, the two inner angles at the bottom of the limiting strip 2 are identical, both being 30~45˚.

[0047] Optionally, the difference between the height of the seed crystal 12 and the height of the limiting strip 2 is 0.2~1.0 mm, preferably 0.2 mm.

[0048] Optionally, the chamfer angle is 15~75˚, the chamfer depth is 0.01~0.6 mm, preferably 15˚, 30˚ and 45˚, and the chamfer depth is 0.01~0.6 mm, preferably 0.05 mm. Figure 1 and Figure 2 China and Israel This indicates the depth of the 12-bevel chamfer on the seed crystal.

[0049] Optionally, see Figures 1-5 The several sidewalls of the seed crystal 12 are respectively attached to the inner wall of the sample holder slot 11 and the sidewall of the limiting strip 2, that is, the size of the sample holder slot 11 should match the size of the seed crystal 12.

[0050] In the apparatus for growing large-size diamonds provided in this embodiment of the invention, the chamfer angle is 15~75˚.

[0051] The present invention also provides a method for growing large-size diamonds, using the apparatus for growing large-size diamonds as provided in the embodiments of the present invention, comprising the following steps:

[0052] Step 1) Place several independent seed crystals into different sample slots, and then grow the seed crystals once. During the growth process, the growth surface of the seed crystal will gradually cross the limiting strip, thereby splicing adjacent seed crystals together, eliminating the gap between adjacent seed crystals, and thus establishing a temperature transfer channel between adjacent seed crystals.

[0053] Step 2) Perform a second growth on the seed crystal after the first growth in Step 1). During the second growth, the growth surface of the seed crystal in the first growth is used as the bottom surface to directly contact the sample holder.

[0054] Furthermore, the single-growth process performed in step 1) may also include the following technical features:

[0055] 1) The oxygen volume content is 0.01%~4% based on the total volume of hydrogen and oxygen;

[0056] 2) During etching, the hydrogen flow rate is 100~1000 sccm;

[0057] 3) When etching, if oxygen is introduced, the oxygen flow rate should be ≤10 sccm;

[0058] 4) The etching temperature is 600~1100℃ during etching;

[0059] 5) The etching time is 0.1~2 hours.

[0060] 6) When performing chemical deposition, the chemical vapor deposition power is 3000~6000W;

[0061] 7) During chemical deposition, the chemical vapor deposition pressure is 10~35 kPa;

[0062] 8) The volume content of the introduced hydrogen gas is 88-98%, and the hydrogen flow rate is 100-1000 sccm;

[0063] 9) The volumetric content of the introduced methane is 2-12%, and the methane flow rate is 5-100 sccm;

[0064] 10) If nitrogen is introduced, the volume content of nitrogen shall be ≤1%, and the nitrogen flow rate shall be 1~3 sccm;

[0065] 11) If nitric oxide is introduced, the volume content of nitric oxide shall be ≤1%, and the flow rate of nitric oxide shall be 2~6 sccm;

[0066] 12) If carbon monoxide is introduced, the volume content of carbon monoxide shall be ≤2% and the flow rate of carbon monoxide shall be ≤10 sccm.

[0067] 13) If carbon dioxide is introduced, the volume content of carbon dioxide shall be ≤2% and the flow rate of carbon dioxide shall be ≤10 sccm.

[0068] 14) If argon gas is introduced, the volume content of argon gas shall be ≤5% and the argon gas flow rate shall be ≤10 sccm;

[0069] 15) If helium is introduced, the volume content of helium shall be ≤5% and the flow rate of helium shall be ≤10 sccm;

[0070] 16) If oxygen is introduced, the volume content of oxygen shall be ≤2% and the oxygen flow rate shall be ≤10 sccm;

[0071] 17) The chemical vapor deposition temperature of each seed crystal 12 is 860~1200℃; the growth time is 50~200h; the growth rate is 15~25um / h; and the growth thickness is 0.7~1.5mm.

[0072] Step 2) Perform a second growth on the seed crystal 12 after the first growth in Step 1).

[0073] Furthermore, step 2) also includes trimming the seed crystal that underwent the first growth in step 1) using laser processing. After trimming, the seed crystal is then subjected to a second growth. During the second growth, the growth surface of the seed crystal from the first growth is used as the bottom surface to directly contact the sample holder. Preferably, the height of the non-beveled portion of the seed crystal 12 is trimmed to 0.05~0.2mm, that is, 0.05mm ≤ ≤0.2mm, sample flatness less than 0.05mm.

[0074] Furthermore, the secondary growth process performed in step 2) may also include the following technical features:

[0075] 1) The oxygen volume content is 0.01%~4% based on the total volume of hydrogen and oxygen;

[0076] 2) During etching, the hydrogen flow rate is 100~1000 sccm;

[0077] 3) During etching, the oxygen flow rate is 0~10 sccm;

[0078] 4) The etching temperature is 600~1100℃ during etching;

[0079] 5) The etching time is 1-3 hours.

[0080] 6) When performing chemical deposition, the chemical vapor deposition power is 3000~6000W;

[0081] 7) During chemical deposition, the chemical vapor deposition pressure is 10~35 kPa;

[0082] 8) The volume content of the introduced hydrogen gas is 88-98%, and the hydrogen flow rate is 100-1000 sccm;

[0083] 9) The volumetric content of the introduced methane is 2-12%, and the methane flow rate is 5-100 sccm;

[0084] 10) If nitrogen is introduced, the volume content of nitrogen shall be ≤1%, and the nitrogen flow rate shall be 1~3 sccm;

[0085] 11) If nitric oxide is introduced, the volume content of nitric oxide shall be ≤1%, and the flow rate of nitric oxide shall be 2~6 sccm;

[0086] 12) If carbon monoxide is introduced, the volume content of carbon monoxide shall be ≤2% and the flow rate of carbon monoxide shall be ≤10 sccm.

[0087] 13) If carbon dioxide is introduced, the volume content of carbon dioxide shall be ≤2% and the flow rate of carbon dioxide shall be ≤10 sccm.

[0088] 14) If argon gas is introduced, the volume content of argon gas shall be ≤5% and the argon gas flow rate shall be ≤10 sccm;

[0089] 15) If helium is introduced, the volume content of helium shall be ≤5% and the flow rate of helium shall be ≤10 sccm;

[0090] 16) If oxygen is introduced, the volume content of oxygen shall be ≤2% and the oxygen flow rate shall be ≤10 sccm;

[0091] 17) The chemical vapor deposition temperature of each seed crystal 12 is 860~1200℃; the growth time is 50~200h; the growth rate is 5~10um / h; and the growth thickness is 0.7~1.5mm.

[0092] Example 1

[0093] In this embodiment, the sample holder 1 includes two sample holder slots 11, each containing two seed crystals 12, hereinafter referred to as seed crystal A and seed crystal B. The limiting strip 2 is prism-shaped with an arc-shaped top surface. The chamfer angle β of the seed crystal 12 is 30˚, the chamfer depth of the seed crystal 12 is 0.05mm, and the difference between the height a of the seed crystal 12 and the height h of the limiting strip 2 is 0.2mm.

[0094] Table 1 shows the temperatures of seed crystal A, seed crystal B, and the gap measured during one growth process:

[0095] Table 1

[0096] reaction time Seed crystal A temperature gap Seed crystal B temperature 1h 750℃ 900℃ 760℃ 6h 830℃ 910℃ 840℃ 8h 870℃ 930℃ 880℃ 10h 925℃ 940℃ 928℃

[0097] As can be clearly seen from Table 1, the sample holder 1 designed in this invention and the two-step growth method can reduce the temperature difference between the gap and the center of the wafer during the second fine growth, reducing the temperature difference to within 20°C, thereby achieving seamless splicing between adjacent seed crystals. Please refer to the renderings. Figure 9 and Figure 10 .

[0098] Example 2

[0099] In this embodiment, the sample holder 1 includes two sample holder slots 11, each containing two seed crystals 12, hereinafter referred to as seed crystal A and seed crystal B. The limiting strip 2 is a triangular prism with rounded corners at the top edge, the rounded corners being 0.2 mm in size. The angles θ at the two interior angles θ at the bottom of the limiting strip 2 are 45˚. The chamfer β of the seed crystal 12 has an angle of 30˚, and the chamfer depth of the seed crystal 12 is 0.05 mm. Continue reading Figure 1 The difference between the height a of seed crystal 12 and the height h of limiting strip 2 is 0.2 mm.

[0100] As an explanation, compared with the prism limiting strip 2, the shape of the triangular prism limiting strip 2 can be adjusted more flexibly, especially the chamfer angle of the seed crystal 12, which is conducive to matching different growth requirements; if it is desired to shorten the splicing time of the seed crystal 12, the chamfer angle of the seed crystal 12 can be increased; if it is desired to extend the splicing time of the seed crystal 12, the chamfer angle of the seed crystal 12 can be decreased.

[0101] Table 2 shows the temperatures of seed crystal A, seed crystal B, and the gap measured during one growth process:

[0102] Table 2

[0103] reaction time Seed crystal A temperature gap Seed crystal A temperature 1h 755℃ 900℃ 765℃ 6h 860℃ 910℃ 865℃ 10h 910℃ 930℃ 913℃

[0104] As can be clearly seen from Table 2, by using the sample holder 1 designed in this invention and the two-step growth method, the temperature difference between the gap and the center of the wafer can be reduced to within 20°C during the second fine growth, thereby achieving seamless splicing between adjacent seed crystals. Please refer to the renderings. Figure 9 and Figure 10 .

[0105] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. An apparatus for growing large-sized diamonds, characterized in that: Includes a sample holder (1), wherein the sample holder (1) is provided with at least two sample holder slots (11), and a limiting strip (2) is provided between adjacent sample holder slots (11) and they are not connected to each other. A seed crystal is provided in the sample holder slot (11), and a chamfer is provided on one side or two opposite sides of the top of the seed crystal. The chamfers of the seed crystals located in the adjacent sample holder slots (11) are set opposite each other, and the height of the limiting strip (2) is between the top of the seed crystal and the lowest point of the chamfer.

2. The apparatus for growing large-size diamonds according to claim 1, characterized in that: The width of the limiting strip (2) is 0.2~1.0 mm; the shape of the limiting strip (2) is a prism and the top surface is an arc surface.

3. The apparatus for growing large-size diamonds according to claim 1, characterized in that: The limiting strip (2) is in the shape of a triangular prism and the top edge is rounded, the size of which is 0.1-0.5 mm.

4. The apparatus for growing large-size diamonds according to claim 3, characterized in that: The limiting strip (2) has the same two inner corners at the bottom, both of which are 30~45˚.

5. The apparatus for growing large-size diamonds according to claim 1, characterized in that: The difference between the height of the seed crystal (12) and the height of the limiting strip (2) is 0.2~1.0 mm.

6. The apparatus for growing large-size diamonds according to claim 1, characterized in that: The chamfer angle is 15~75˚, and the chamfer depth is 0.01~0.6 mm.

7. The apparatus for growing large-size diamonds according to claim 1, characterized in that: The sidewalls of the seed crystal (12) are respectively attached to the inner wall of the sample holder slot (11) and the sidewall of the limiting strip (2).

8. A method for growing large-size diamonds, using the apparatus for growing large-size diamonds as described in any one of claims 1 to 7, comprising the following steps: Step 1) Place several independent seed crystals (12) into different sample slots (11), and then grow the seed crystals (12) once. During the growth process, the growth surface of the seed crystals (12) will gradually cross the limiting strip (2), thereby making adjacent seed crystals (12) splice together, eliminating the gap between adjacent seed crystals (12), and thus establishing a heat transfer channel between adjacent seed crystals (12). Step 2) Perform a second growth on the seed crystal (12) after the first growth in step 1). During the second growth, the growth surface of the seed crystal (12) in the first growth is used as the bottom surface to directly contact the sample holder (1).

9. The method for growing large-size diamonds according to claim 8, comprising the following technical features: Step 2) also includes trimming the seed crystal (12) that has completed one growth in step 1) by laser processing. After trimming, the seed crystal (12) is grown a second time. During the second growth process, the growth surface of the seed crystal (12) in the first growth is used as the bottom surface to directly contact the sample holder (1).

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