A downward growing guided-mode method crystal growth method and applications

Abstract

The application relates to a downward growth mode crystal growth method and application. The method comprises the following steps: S1, placing a mold in a crucible containing raw materials, and making the use surface of the mold face downward, and then heating the crucible to melt the raw materials in the crucible into a melt; S2, lifting a seed crystal rod located vertically below the use surface of the mold until the seed crystal contacts the use surface of the mold, moving the seed crystal rod downward after fusion, and completing crystal pulling; S3, cooling the crucible until the growth area of the crystal covers the mold, and completing shoulder laying; S4, continuously cooling the crucible to make the crystal grow in diameter until the raw materials are consumed; S5, after the crystal is demolded, stopping moving the seed crystal rod, cooling and annealing the crystal, and ending the crystal growth. The downward growth crystal growth method is adopted, the problem of poor crystal quality in the prior art is effectively solved, and the quality of the grown crystal is higher.

Description

Technical Field

[0001] This application relates to the field of crystal preparation technology, and in particular to a downward growth method for crystal growth using a guided model and its application. Background Technology

[0002] The process by which a substance transforms from a gaseous phase to a liquid phase and then to a solid phase under certain conditions such as temperature, pressure, concentration, medium, and pH, to form crystals of specific dimensions, is called crystal growth. The main methods of crystal growth include flame crystal growth, Czochralski crystal growth, mold crystal growth, crucible descent crystal growth, bubble crystal growth, and directional solidification.

[0003] The edge-guided die method, also known as the edge-defined thin-film feeding (EFG) method, is mainly used to grow crystals of specific shapes. It is essentially a variation of the Czochralski method. Because the edge-guided die method can directly grow crystals such as sheets, wires, tubes, rods, and plates from the melt, and because it offers fast crystal growth and precise size control, it greatly simplifies the crystal processing procedure, saves materials, time, and energy, reduces production costs, and improves economic efficiency, thus gaining increasing attention.

[0004] The traditional mold-guided method involves placing the growth material in a crucible equipped with a mold, heating it to melt it, and then growing the crystal on top of the mold. This is followed by processes such as shoulder formation, diameter equalization, and tailing. However, during crystal growth using the traditional mold-guided method, volatiles are generated. Influenced by gas convection, these volatiles move upwards with the gas flow. Since the seed crystal is on top of the melt, volatiles easily adhere to the seed crystal, introducing impurities into the crystal and ultimately leading to growth failure or poor crystal quality. Furthermore, in the traditional mold-guided method, the heating zone is the crucible area, with only insulation material on top. The large temperature difference between the crucible and its top creates an excessive temperature gradient in the growth region, further reducing crystal quality.

[0005] Therefore, the traditional mold-guiding method needs to be improved to generate high-quality crystals. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this application provides a downward-growing guided-mold crystal growth method. This method effectively solves the problem that volatiles evaporate upwards and adhere to the seed crystal during crystal growth, leading to crystal growth failure or poor crystal quality, thus resulting in higher quality grown crystals.

[0007] Therefore, the first aspect of this application provides a downward-growing mode-guided crystal growth method, the method comprising the following steps:

[0008] S1, Place the mold in a crucible containing raw materials with the working side of the mold facing down, and then heat the crucible to melt the raw materials in the crucible into a melt;

[0009] S2, raise the seed crystal rod located vertically below the working surface of the mold until the seed crystal at the top of the seed crystal rod contacts the working surface of the mold, and after welding, move the seed crystal rod downward to complete the crystal pulling;

[0010] S3, the crucible is cooled down until the growth area of ​​the crystal covers the mold, thus completing the shoulder formation;

[0011] S4, continue to cool the crucible to allow the crystal to grow at a constant diameter until the raw material is exhausted;

[0012] S5, after the crystal is demolded, stop moving the seed crystal rod, and cool and anneal the crystal to end the crystal growth.

[0013] In the crystal growth method described in this application, the mold's surface faces downwards, allowing the crystal to grow downwards. This effectively prevents volatiles generated during growth from adhering to the seed crystal with the gas flow, thus avoiding the introduction of impurity phases into the crystal. Furthermore, as the crystal grows downwards, bubbles in the melt move upwards instead of downwards to the crystallization surface, preventing the formation of defects such as bubbles within the crystal and ultimately resulting in a high-quality crystal. Additionally, the crystal growth region in this method is located within the heating zone of the crucible, with no significant temperature abrupt changes and a small temperature gradient, leading to even higher quality crystals.

[0014] In some embodiments, the crucible includes a raw material zone that is not located vertically below the working surface of the mold.

[0015] Since the seed crystal is located vertically below the working surface of the mold, the above arrangement can further prevent volatiles in the melt generated by the melting of raw materials in the crucible from adhering to the seed crystal.

[0016] In some embodiments, the mold is provided with a mold bridge, which is placed in the raw material area of ​​the crucible; both the mold and the mold bridge are provided with capillary slits, and the capillary slits in the mold and the mold bridge are connected, so that the melted raw material flows to the working surface of the mold through the capillary action of the capillary slits.

[0017] Since the mold bridge is placed in the raw material area of ​​the crucible, the mold bridge can contact the melted raw material, thereby allowing the melt to flow to the working surface of the mold through the capillary action of the mold bridge and the capillary slits provided in the mold and the mold bridge.

[0018] In some specific embodiments, the crystal growth method employs components including a crucible (the height of the outer rim of the crucible can be higher than the overall height of the mold), a mold with mold bridges, a seed crystal, a seed crystal rod, and a heating device; wherein the crucible, the mold with mold bridges, and the seed crystal rod are all made of high-temperature resistant materials, and the heating device can use electromagnetic induction heating or resistance heating; the mold shape can be square, round, or various other shapes. When the above components are used for crystal growth, the mold with mold bridges is placed inside the crucible, with the mold's usable surface facing down, and the mold bridges on the mold placed in the raw material area of ​​the crucible; the heating device is used to heat the crucible.

[0019] In some embodiments, the angle α of the mold's usable surface is 30–90°. In some specific embodiments, the angle α of the mold's usable surface can be 30°, 45°, 60°, 75°, or 90°, etc. In some preferred embodiments, the angle α of the mold's usable surface is 45–75°. In some most preferred embodiments, the angle α of the mold's usable surface is 60°.

[0020] In this application, the angle α of the mold's usable surface is the angle between the capillary slit outlet inside the mold at the mold's usable surface and the horizontal plane, specifically as follows: Figure 1 As shown, during crystal growth, the crystal shape depends on the shape of the mold's surface, and the quality of the crystal also largely depends on the shape of this surface. The angle α of the mold's surface has a significant impact on heat and mass transfer within the crystal. Controlling the angle α of the mold's surface within the range of 45–75°, especially within 60°, effectively reduces the possibility of capillary gaps being filled by the melt, facilitates the removal of stress and impurities, and further improves the quality of the final crystal.

[0021] In some embodiments, the crucible is covered with an insulating material, which is a zirconia fiber brick with a thickness of 30-50 mm.

[0022] In this application, covering the outside of the crucible with insulating material helps maintain the temperature field environment for crystal growth and minimizes the radial temperature gradient of the melt, thereby improving crystal quality. Zirconia, with a melting point of 2700℃, is one of the best known refractory materials, and its use as insulating material does not react with the molten raw materials while providing excellent insulation. Furthermore, the thickness of the insulating material significantly affects crystal quality; too thin a material will not provide insulation, while too thick a material will not only increase the cost of crystal growth but also hinder heat dissipation within the crystal, negatively impacting its performance. This application utilizes zirconia fiber bricks with a thickness of 30–50 mm as insulating material to improve crystal quality.

[0023] In some embodiments, in step S2, the seed crystal rod moves downward at a rate of 5 to 25 mm / h.

[0024] In some specific embodiments, the downward movement rate of the seed crystal rod can be 5 mm / h, 10 mm / h, 15 mm / h, 20 mm / h, or 25 mm / h, etc. In some preferred embodiments, the downward movement rate of the seed crystal rod is 10–20 mm / h. In some most preferred embodiments, the downward movement rate of the seed crystal rod is 15 mm / h.

[0025] The downward movement rate of the seed crystal rod is one of the key technologies in crystal growth. An excessively high rate can cause lattice fracture, while an unstable rate can lead to numerous severe growth streaks in the crystal. This application utilizes real-time control of the seed crystal rod's movement speed based on the crystal's morphological characteristics during growth, and maintains the downward movement rate between 5 and 25 mm / h, thereby improving the intrinsic quality of the grown crystal.

[0026] In some embodiments, the cooling rate in step S3 is 2–5 °C / h. In some specific embodiments, the cooling rate in step S3 can be 2 °C / h, 3 °C / h, 4 °C / h, or 5 °C / h, etc. In some preferred embodiments, the cooling rate in step S3 can be 3–4 °C / h.

[0027] In some embodiments, the cooling rate in step S4 is 0.5–2 °C / h. In some specific embodiments, in step S4, while keeping the crystal growth morphology unchanged, the cooling rate is controlled by a series PID controller along with the seed rod moving speed and the desired seed rod moving speed, and the cooling rate is controlled within the range of 0.5–2 °C / h. In some preferred embodiments of this application, the cooling rate is 1–1.5 °C / h.

[0028] In this application, by controlling the cooling rate during the shoulder formation process and the constant diameter growth process, the intrinsic quality of the grown crystal can be further improved.

[0029] In some embodiments, in step S5, the cooling rate of the cooling annealing is 150-250°C / h, and the temperature after cooling annealing is 20-25°C (room temperature).

[0030] In some specific embodiments, in step S5, the cooling rate of the cooling annealing can be 150℃ / h, 180℃ / h, 200℃ / h, 230℃ / h, or 250℃ / h, etc. In some preferred embodiments, the cooling rate of the cooling annealing is 180–230℃ / h. In some most preferred embodiments, the cooling rate of the cooling annealing is 200℃ / h.

[0031] In this application, cooling and annealing the grown crystal under the above-mentioned parameter conditions can effectively eliminate the complex internal stress inside the crystal, thereby improving the quality of the crystal.

[0032] In this application, crystal growth can be carried out under a protective atmosphere. Different protective atmospheres can be selected for different crystals being grown. For example, when the crystal being grown is β-gallium oxide, the protective atmosphere can be a mixture of oxygen and an inert gas, with a pressure ratio of oxygen to inert gas of, for example, 1:(19-99); when the crystal being grown is sapphire, the protective atmosphere is an inert gas. In this application, the inert gas can be, for example, any one or more of nitrogen, argon, helium, neon, and xenon.

[0033] The second aspect of this application provides the use of the method described in the first aspect of this application in the preparation of β-gallium oxide crystals and sapphire crystals.

[0034] The crystal growth method described in this application can effectively improve the quality of crystals, and therefore can be well applied in the preparation of β-gallium oxide crystals and sapphire crystals.

[0035] In summary, the beneficial technical effects of this application are as follows: The crystal growth method described in this application involves downward crystal growth, effectively preventing volatiles generated during the growth process from adhering to the seed crystal with the gas flow, thus avoiding the introduction of impurity phases into the crystal. Furthermore, with the crystal growing downwards, bubbles in the melt move upwards and do not move downwards to the crystallization surface, preventing defects such as bubbles from forming within the crystal, ultimately resulting in a high-quality crystal. Simultaneously, the crystal growth region in this method is located within the heating zone of the crucible, with no obvious temperature abrupt changes around it, resulting in a small temperature gradient and higher quality crystals. This method has excellent application prospects in the preparation of β-gallium oxide and sapphire crystals. Attached Figure Description

[0036] Figure 1 A schematic diagram of the angle α of the mold surface described in this application.

[0037] Figure 2 This is a schematic diagram of the assembly structure of the components used in the growth of β-gallium oxide crystal in Example 1.

[0038] Figure 3 This is a cross-sectional view of the assembly structure of the components used in the growth of β-gallium oxide crystal in Example 1. Detailed Implementation

[0039] To make this application easier to understand, the following detailed description will be provided with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of application of this application. Unless otherwise specified, the raw materials or components used in this application can be obtained commercially or by conventional methods.

[0040] Example 1: Growth of β-gallium oxide crystals

[0041] The components used in crystal growth include: a crucible (the height of the outer rim of the crucible is higher than the overall height of the mold), a mold with mold bridges, a seed crystal, a seed crystal rod, a heating device, and insulation material. The mold is square, measuring 20mm × 12mm, with an angle α of 90° on the mold's usable surface. Connecting capillary slits are provided within the mold and mold bridges. A schematic diagram of the assembly structure of each component during crystal growth is shown below. Figure 2 As shown, the cross-sectional view of the assembly structure of each component is as follows. Figure 3 As shown; the mold with mold bridge is placed inside the crucible, with the mold's working surface facing down, and the mold bridge on the mold is placed in the raw material area of ​​the crucible; the heating device is a medium-frequency induction coil used to heat the crucible (not shown in the figure), and the heat insulation material is 40mm thick zirconia fiber brick, which is wrapped around the outside of the crucible (not shown in the figure); the seed crystal is set at the top of the seed crystal rod, and the seed crystal and the seed crystal rod are set vertically below the working surface of the mold.

[0042] The growth process is as follows:

[0043] 1. Place 300 grams of high-purity gallium oxide raw material (6N purity) in the raw material area of ​​the crucible;

[0044] 2. Under a protective atmosphere of 99% argon and 1% oxygen at 0.5 MPa, the crucible is heated with a medium-frequency induction coil to the melting point of gallium oxide (1840℃) until the gallium oxide raw material melts into a melt. At this time, the volatiles can be seen moving upward, but the volatiles will not come into contact with the seed crystal, and there are no impurities on the surface of the seed crystal.

[0045] 3. The gallium oxide seed crystal is raised using a seed crystal rod until it contacts the working surface of the mold;

[0046] 4. After the front end of the gallium oxide seed crystal is melted back and then fused together, the seed crystal rod is slowly moved downward at a speed of 15 mm / h, and the seed crystal rod drives the seed crystal to grow downward;

[0047] 5. The crucible is slowly cooled at a rate of 3°C, and the crystal gradually enlarges until the crystal growth area covers the entire mold, completing the shoulder formation.

[0048] 6. Observe the crystal morphology characteristics. Under the premise of keeping the morphology characteristics unchanged, slowly cool the crucible at a cooling rate of 1-1.5℃. The crystal grows with constant diameter until the gallium oxide material in the crucible is exhausted. During the growth process, because the bubbles move upward, there are almost no bubbles in the constant diameter part.

[0049] 7. After the crystal is separated from the mold, stop moving the seed crystal rod, and then slowly cool down and anneal at a cooling rate of 200℃ / h until it returns to room temperature (25℃). The growth of β-gallium oxide crystal is then complete.

[0050] Example 2: Growth of β-gallium oxide crystals

[0051] The growth process is basically the same as in Example 1, except that the angle α of the mold surface used in the crystal growth component is 60°.

[0052] Example 3: Growth of β-gallium oxide crystals

[0053] The growth process is basically the same as in Example 1, except that the angle α of the mold surface used in the crystal growth component is 45°.

[0054] Example 4: Growth of β-gallium oxide crystals

[0055] The growth process is basically the same as in Example 1, except that the angle α of the mold surface used in the crystal growth component is 30°.

[0056] Example 5: Growth of β-gallium oxide crystals

[0057] The growth process is basically the same as in Example 1, except that the insulation material used in the crystal growth components is a 30mm thick zirconia fiber brick.

[0058] Example 6: Growth of β-gallium oxide crystals

[0059] The growth process is basically the same as in Example 1, except that the insulation material used in the crystal growth components is a 50mm thick zirconia fiber brick.

[0060] Example 7: Growth of β-gallium oxide crystals

[0061] The growth process is basically the same as in Example 1, except that in step 4 of the crystal growth process, after the front end of the gallium oxide seed crystal is melted back and then fused, the seed crystal rod is slowly moved downward at a speed of 5 mm / h, and the seed crystal rod drives the seed crystal to grow downward.

[0062] Example 8: Growth of β-gallium oxide crystals

[0063] The growth process is basically the same as in Example 1, except that in step 4 of the crystal growth process, after the front end of the gallium oxide seed crystal is melted back and then fused, the seed crystal rod is slowly moved downward at a speed of 25 mm / h, and the seed crystal rod drives the seed crystal to grow downward.

[0064] Example 9: Growth of β-gallium oxide crystals

[0065] The growth process is basically the same as in Example 1, except that in step 5 of the crystal growth process, the crucible is slowly cooled at a cooling rate of 5°C, and the crystal gradually enlarges until the crystal growth area covers the entire mold, thus completing the shoulder formation.

[0066] Example 10: Growth of β-gallium oxide crystals

[0067] The growth process is basically the same as in Example 1, except that in step 5 of the crystal growth process, the crucible is slowly cooled at a rate of 2°C, and the crystal gradually enlarges until the crystal growth area covers the entire mold, thus completing the shoulder formation.

[0068] Example 11: Growth of β-gallium oxide crystals

[0069] The growth process is basically the same as in Example 1. The difference is that in step 6 of the crystal growth process, the crystal morphology is observed. Under the premise of keeping the morphology unchanged, the crucible is slowly cooled at a cooling rate of 0.5-2℃. The crystal grows with constant diameter until the gallium oxide material in the crucible is exhausted.

[0070] Example 12: Growth of β-gallium oxide crystals

[0071] The growth process is basically the same as in Example 1, except that in step 6 of the crystal growth process, the crucible is slowly cooled at a rate of 2°C, and the crystal grows with constant diameter until the gallium oxide material in the crucible is exhausted.

[0072] Example 13: Growth of β-gallium oxide crystals

[0073] The growth process is basically the same as in Example 1. The difference is that in step 7 of the crystal growth process, after the crystal is separated from the mold, the seed crystal rod is stopped from moving, and then the crystal is slowly cooled and annealed at a cooling rate of 150°C / h until it returns to room temperature (25°C), and the growth of β-gallium oxide crystal ends.

[0074] Example 14: Growth of β-gallium oxide crystals

[0075] The growth process is basically the same as in Example 1. The difference is that in step 7 of the crystal growth process, after the crystal is separated from the mold, the seed crystal rod is stopped from moving, and then the crystal is slowly cooled and annealed at a cooling rate of 230°C / h until it returns to room temperature (25°C), and the growth of β-gallium oxide crystal ends.

[0076] Example 15: Growth of β-gallium oxide crystals

[0077] The growth process is basically the same as in Example 1. The difference is that in step 7 of the crystal growth process, after the crystal is separated from the mold, the seed crystal rod is stopped from moving. Then, the crystal is slowly cooled and annealed at a cooling rate of 250°C / h until it returns to room temperature (25°C), and the growth of β-gallium oxide crystal ends.

[0078] Example 16: Growth of Sapphire Crystals

[0079] The components used for crystal growth are basically the same as in Example 2, except that the heating device is a tungsten-molybdenum resistance heater used to heat the crucible.

[0080] The growth process is as follows:

[0081] 1. Place 300 grams of high-purity alumina raw material (purity 6N) in the raw material area of ​​the crucible after isostatic pressing and high-temperature sintering;

[0082] 2. Under a protective atmosphere of pure argon at 0.5 MPa, the crucible is heated with a tungsten-molybdenum resistance heater to the melting point of alumina (2050℃) until the alumina raw material melts into a molten body. At this point, the volatiles can be seen moving upward, but the volatiles do not come into contact with the seed crystal, and there are no impurities on the surface of the seed crystal.

[0083] 3. The sapphire seed crystal is raised using the seed crystal rod until it contacts the usable surface of the mold;

[0084] 4. After the front end of the sapphire seed crystal is melted back and then fused, the seed crystal rod is slowly moved downward at a speed of 20mm / h, and the seed crystal rod drives the seed crystal to grow downward;

[0085] 5. The crucible is slowly cooled at a rate of 4°C, and the crystal gradually enlarges until the crystal growth area covers the entire mold, completing the shoulder formation.

[0086] 6. Observe the crystal morphology characteristics. Under the premise of keeping the morphology characteristics unchanged, slowly cool the crucible at a cooling rate of 1-1.5℃. The crystal grows with constant diameter until the alumina material in the crucible is exhausted. During the growth process, because the bubbles move upward, there are almost no bubbles in the constant diameter part.

[0087] 7. The crystal automatically separates from the mold, the seed crystal rod stops moving, and then the crystal is slowly cooled and annealed at a cooling rate of 180℃ / h until it returns to room temperature (25℃). The sapphire crystal growth is then complete.

[0088] Test case

[0089] Sample preparation: The β-gallium oxide crystals prepared in Examples 1-15 and the sapphire crystals prepared in Example 16 were processed into single wafers with dimensions of 10mm × 10mm × 1mm. The following performance tests were performed on the single wafers using the following detection methods, and the presence of bubbles in the crystals was observed. The test results are detailed in Table 1:

[0090] Half-width at half-peak of rocking curvature: The half-width at half-peak of rocking curves of different single crystals was detected using an X-ray diffractometer.

[0091] Dislocation density: The dislocation density of different single crystal wafers was characterized by phosphoric acid etching.

[0092] Table 1

[0093]

[0094] As can be seen from the test results in Table 1, no bubbles were generated on the crystal surface of the β-gallium oxide crystals prepared in Examples 1-15 and the sapphire crystals prepared in Example 16 of this application. The half-width of the rocking curves of the crystals were all within 50 arcseconds, and the dislocation density was all within 500 dislocations / cm. 2 The crystal quality is excellent. This indicates that the downward growth method effectively avoids volatiles adhering to the seed crystal with the gas flow during growth, which would introduce impurities into the crystal, leading to growth failure or poor crystal quality. Furthermore, downward growth keeps the growth region within the heating zone, with no significant temperature abrupt changes and a small temperature gradient, resulting in higher crystal quality. Additionally, as the crystal grows downward, bubbles in the melt move upwards, preventing them from moving downwards to the crystallization surface and avoiding defects such as bubbles within the crystal.

[0095] The test results of the β-gallium oxide crystals prepared in Examples 1-15 show that adjusting the angle α of the mold's working surface, the thickness of the insulation material, the downward movement rate of the seed crystal rod, the cooling rate during the shoulder formation process, the cooling rate during the constant diameter growth process, and the cooling rate during the cooling annealing all affect the quality of the final crystal. Furthermore, using the relevant crystal growth conditions in Example 2 can result in a better quality final crystal.

[0096] It should be noted that the embodiments described above are only for explaining this application and do not constitute any limitation on this application. This application has been described with reference to typical embodiments, but it should be understood that the terms used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to this application within the scope of the claims, and revisions can be made to the invention without departing from the scope and spirit of this application. Although the application described herein relates to specific methods, materials, and embodiments, it does not mean that this application is limited to the specific examples disclosed herein; on the contrary, this application can be extended to all other methods and applications with the same function.

Claims

1. A method for growing crystals using a downward-growing, guided-mode method, characterized in that, The crystal growth method employs a growth apparatus including a crucible and a mold. The crucible includes an annular raw material region, and the mold has a mold bridge positioned within the annular raw material region of the crucible, with the working surface of the mold facing downwards through a cavity within the annular raw material region. Both the mold and the mold bridge have capillary slits, and these slits are interconnected. The molten raw material flows to the working surface of the mold through the capillary action of the capillary slits. The method includes the following steps: S1, Place the mold in a crucible containing raw materials with the working side of the mold facing down, and then heat the crucible to melt the raw materials in the crucible into a melt; S2, raise the seed crystal rod located vertically below the working surface of the mold until the seed crystal at the top of the seed crystal rod contacts the working surface of the mold, and after welding, move the seed crystal rod downward to complete the crystal pulling; S3, the crucible is cooled down until the growth area of ​​the crystal covers the mold, thus completing the shoulder formation; S4, continue to cool the crucible to allow the crystal to grow at a constant diameter until the raw material is exhausted; S5, After the crystal is demolded, stop moving the seed crystal rod, cool and anneal the crystal, and the crystal growth ends; The angle α of the usable surface of the mold is 45~60°; In step S2, the seed crystal rod moves downward at a rate of 10~20 mm / h.

2. The crystal growth method according to claim 1, characterized in that, The crucible is covered with a heat-insulating material, which is a zirconia fiber brick with a thickness of 30-50 mm.

3. The crystal growth method according to claim 1, characterized in that, In step S3, the cooling rate is 2~5℃ / h.

4. The crystal growth method according to claim 1, characterized in that, In step S4, the cooling rate is 0.5~2℃ / h.

5. The crystal growth method according to claim 1, characterized in that, In step S5, the cooling rate of the cooling annealing is 150~250℃ / h, and the temperature after cooling annealing is 20~25℃.

6. The application of the method as described in any one of claims 1-5 in the preparation of β-gallium oxide crystals and sapphire crystals.

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