Mould for growing gallium oxide single crystal by edge-defined film-fed growth method and gallium oxide single crystal growth method

Abstract

The invention relates to the technical field of crystal growth, in particular to a mold for growing a gallium oxide single crystal by an edge-defined film-fed growth method and a gallium oxide single crystal growth method. The mold is formed by connecting two partition plates through a fixing part, and a slit is reserved between the partition plates. Steps are arranged on the two radial sides of the top end of the mold, the bottom end of the mold is of an inverted trapezoidal structure, the two waists of a trapezoid are arc-shaped, and the bottom end of the mold is of an inverted trapezoidal structure, so that the temperature difference and temperature gradient of the surface of the mold are reduced, temperature distribution on the two sides of the mold is more symmetrical, and a more reasonable thermal field can be provided for size expansion of gallium oxide crystals.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal growth, and in particular to a mold for growing a gallium oxide single crystal using a guided mold method and a gallium oxide single crystal growth method. Background Art

[0002] As a new type of ultra-wide bandgap semiconductor, β-Ga2O3 has the advantages of large bandgap width (4.85eV), high breakdown field strength (8MV / cm) and can be prepared by melt method. It has significant advantages over traditional semiconductors in terms of preparation cost and theoretical performance limit. With the increasing requirements of industries such as electric vehicles for high-power semiconductor devices, as well as the potential demand in high-voltage fields such as high-voltage power transmission and rail transportation, β-Ga2O3 is expected to be widely used in high-power and high-voltage fields.

[0003] As one of the melt growth technologies, the guided mold method has become the mainstream method for growing β-Ga2O3 crystals at home and abroad due to its fast crystal growth speed, stable and controllable solid-liquid interface, and good crystal uniformity. This method introduces a mold into the crucible and uses the capillary effect of the melt to make the melt rise along the mold to the mold surface and then contact the preheated seed crystal, thereby starting the crystal growth process.

[0004] However, in the practice of growing β-Ga2O3 crystals by the guided mold method, the combination of the circular iridium crucible and the plate-shaped iridium mold in the center has brought about a temperature distribution problem that cannot be ignored. Specifically, when the coil is inductively heated, the junction area between the crucible wall and the bottom surface becomes the main heating element in the insulation structure, resulting in the highest temperature in this area. Since the bottom corners on both sides of the plate-shaped mold are close to this high-temperature area, they are subjected to strong heat conduction and heat radiation, causing the temperature on both sides and the surface of the mold to present an uneven distribution state with high on both sides and low in the middle. This uneven temperature distribution is particularly prominent in the crystal shouldering stage. The drastic change in the temperature gradient along the length of the mold can easily lead to a series of problems such as flat shouldering, impure crystals, small shouldering angles and long shouldering time, which in turn increases the difficulty of crystal growth and reduces the yield rate. This not only affects the quality of β-Ga2O3 crystals, but also restricts its application potential in high-voltage and high-power fields.

[0005] Therefore, in order to give full play to the advantages of β-Ga2O3 materials and improve the quality and efficiency of β-Ga2O3 crystals grown by the guided mode method, it is urgent to optimize the design of crucibles and molds, improve the heating and insulation structure, and effectively solve the problem of uneven temperature distribution. This will lay a solid foundation for the widespread application of β-Ga2O3 crystals in electric vehicles, high-voltage power transmission, rail transportation and other fields. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a mold and a growth method for growing gallium oxide single crystals by the guided mold method, aiming to solve the problem that the existing mold has a large temperature difference in the length direction, a drastic temperature gradient change, and is easy to cause difficulty in crystal shouldering, thereby affecting the yield.

[0007] The technical solution of the present invention is as follows:

[0008] A mold for growing gallium oxide single crystal by guided mode method, characterized in that it includes:

[0009] At least two baffles, the baffles are connected to each other through a fixing portion, a slit is formed between two adjacent baffles, and the slit is used for allowing the gallium oxide melt to rise to the top of the mold under the action of capillary effect;

[0010] The top of the mold is a step top structure for placing seed crystals; the bottom of the mold is an inverted trapezoidal structure, and the two sides of the trapezoid are arc-shaped, which is used to reduce the temperature difference and temperature gradient on the mold surface.

[0011] The partitions are two long strip partitions that are arranged in mirror symmetry.

[0012] There are multiple slits, which increase the supply of gallium oxide melt in a parallel feeding form, thereby ensuring the continuity and stability of the growth process of thick gallium oxide single crystals.

[0013] The slit width between two adjacent partitions is in the range of 0.1 to 0.5 mm, and the width of each slit is the same, so as to ensure the stability of the overall feeding capacity and feeding speed, thereby ensuring uniform growth of the single crystal.

[0014] The ratio of the slit width to the mold thickness is 1:8 to 1:160.

[0015] The material of the partition is a noble metal that is resistant to oxidation at high temperatures.

[0016] The noble metal is iridium or an alloy containing iridium.

[0017] The bottom side length of the inverted trapezoidal structure is approximately 1 / 4 of the length of the mold, and the thickness is 20%-40% of the thickness of the mold.

[0018] A method for growing a gallium oxide single crystal using the above mold is characterized in that it comprises the following steps:

[0019] Placing a gallium oxide raw material in a crucible and heating it until it melts, and using the slit to guide the melt to rise to the surface of the mold;

[0020] Place a seed crystal on the mold surface, adjust the heating power so that the mold surface temperature is slightly higher than the crystal melting temperature, and then "seed";

[0021] By lifting the seed crystal and adjusting the heating power, "necking" is achieved to reduce dislocations in the seed crystal;

[0022] Reduce the RF coil power to allow the seed crystal to grow in width and thickness and cover the mold, entering the "shoulder release" stage;

[0023] Continue to adjust the RF coil power to maintain a stable growth rate and temperature gradient, and enter the "equal diameter" growth stage;

[0024] After the crystal grows to the target size, the crystal is pulled off the mold surface, which is called "lifting".

[0025] Slowly reduce the RF power to room temperature to prevent the crystal from cracking.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] A new solution is provided for directly adjusting the temperature difference on the mold surface and reducing the difficulty of the crystal shouldering process. By digging out an arc-shaped block from each bottom corner on both sides of the mold, the heat transfer from the crucible to the two sides of the mold is reduced, thereby reducing the maximum temperature on both sides of the mold, reducing the temperature difference and temperature gradient on the mold surface, and facilitating the stable and controllable shouldering process; the reduction of the maximum temperature on both sides of the mold makes the temperature difference on the mold surface more uniform, which is conducive to the smooth progress of the equal diameter stage, and the thickness of the grown crystals is consistent and uniform; the mold structure of the present invention is reasonable and reduces the use of precious metal Ir, saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the mold structure for removing arc-shaped blocks from the bottom corners on both sides of an embodiment of the present invention.

[0029] Figure 2 (a) is a temperature diagram of the upper surface of the traditional mold in Example 1; (b) is a temperature diagram of the upper surface of the example mold in Example 1.

[0030] Figure 3 (a) is a temperature diagram of the conventional mold in Example 1 in the front view direction; (b) is a temperature diagram of the embodiment mold in Example 1 in the front view direction.

[0031] Figure 4 It is a temperature gradient comparison diagram along the length direction of the mold between the traditional mold in Example 1 and the example mold.

[0032] Figure 5 FIG. 1 is a diagram of gallium oxide crystals grown on a mold according to an embodiment of the present invention.

[0033] Figure 6 (a) is a temperature diagram of the upper surface of the traditional mold in Example 2; (b) is a temperature diagram of the upper surface of the example mold in Example 2.

[0034] Figure 7 (a) is a temperature diagram of the conventional mold in Example 2 in the front view direction; (b) is a temperature diagram of the example mold in Example 2 in the front view direction.

[0035] Figure 8 It is a temperature gradient comparison diagram along the length direction of the mold between the traditional mold in Example 2 and the example mold. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] See also Figure 1 , Figure 1 This is a schematic diagram of the structure of the mold for growing β-Ga2O3 crystals by the guided mold method of the present invention. As shown in the figure, a mold for growing β-Ga2O3 crystals by the guided mold method includes two partitions arranged in mirror symmetry. The width of the slit between the two partitions is between 0.1-0.5 mm, and the ratio to the mold thickness (4-16 mm) is between 1:8 and 1:160, ensuring that the melt can rise to the top of the mold 1 evenly and stably along the slit. The top of the partition is in a step shape 2, with a step height of between 16-70 mm and a thickness of 1-2 mm, to provide stable support and positioning during the crystal growth process. An arc block is dug out at each bottom corner of the bottom 3 of the mold, forming an inverted trapezoidal structure. The bottom corners on both sides of the lower end of the partition are arc-shaped 4.

[0038] The mold is consistent with the four-inch traditional plate-shaped iridium mold in height, length and thickness, and can be 20-80mm in height, 50-200mm in length, and 4-16mm in thickness. The thickness of the slit in the middle of the mold can be 0.1-0.5mm. If the slit is too wide, it is easy to weaken the siphon effect of the mold seam, resulting in insufficient feeding. Compared with the traditional mold, the improvement made in the embodiment of the present invention is to dig out an arc block at each of the four bottom corners on both sides of the traditional mold. The length of the bottom edge of the arc block is 1 / 4 of the length of the mold, the length in the height direction is consistent with the length of the bottom edge, and the thickness should account for 20%-40% of the thickness of the mold. Such a design reduces the volume near the bottom corners on both sides of the mold, thereby reducing the heat transfer of the crucible to the two sides of the mold, and the temperature difference on the mold surface is effectively controlled. Through simulation analysis, the surface temperature difference of the mold in the embodiment is reduced by more than 25% compared with the traditional mold, and the temperature gradient is also effectively controlled, which is conducive to achieving large-angle shoulder release and improving the yield rate. At the same time, the amount of iridium is saved and the cost is reduced.

[0039] The above mold is used to grow gallium oxide crystals. The specific steps are as follows:

[0040] First, the raw materials are placed in a crucible and heated to melt. The molten raw materials rise to the mold surface along the mold seam under the capillary effect. At this time, the seed crystal rod is lowered and the heating power is adjusted to make the mold surface temperature slightly higher than the crystal melting temperature. This stage is called "seeding". When the seed crystal is fully in contact with the melt on the mold surface and properly melted, the seed crystal is lifted up at a relatively fast speed, and the power is adjusted to complete the "necking". The necking process can reduce defects such as dislocations in the seed crystal and improve the crystal quality. The "shoulder release" stage is to reduce the RF coil power so that the seed crystal grows in the width and thickness directions and covers the mold. After the shoulder release stage, the RF coil power is continued to be adjusted to enter the "equal diameter" growth stage. After the crystal grows to the target size, the process of pulling the crystal off the mold surface is called "lifting". Finally, the RF power is slowly reduced to reduce the temperature to room temperature to prevent the crystal from cracking.

[0041] Example 1

[0042] The molds of this embodiment are respectively a traditional mold and an invention embodiment mold, the size of the mold bottom surface is 120mm×15.2mm, the size of the mold surface is 120mm×13mm, the mold height is 45mm, the step thickness is 1.5mm, and the step height is 40mm. Among them, the mold of the invention embodiment has a curved block of 30mm×30mm×4.45mm cut out at the bottom corners on both sides. This embodiment uses the same heating power to perform fluent simulation on the traditional mold and the invention embodiment mold, and obtains Figure 2-4 Results shown.

[0043] Figure 2 (a) and (b) are the mold surface temperature distribution of the conventional mold and the mold of the invention embodiment, respectively. It can be seen intuitively from the figure that the temperature distribution on both sides of the mold surface of the invention embodiment is more symmetrical; the surface temperature difference of the conventional mold is 15.729K, and the surface temperature difference of the mold of the invention embodiment is 10.309K. The surface temperature difference of the mold of the invention embodiment is about 34% lower than that of the conventional mold, indicating that under the same thermal field conditions, the surface temperature distribution of the mold of the invention embodiment is more uniform, and it is not easy to have problems such as crystal cracking and dislocation caused by overcooling of the mold center. Figure 3 The temperature diagram of the mold in the front view direction shown shows that the temperature curve of the mold of the embodiment of the invention has smaller fluctuations, indicating that the overall temperature distribution of the mold of the embodiment of the invention is more uniform. Figure 4 The temperature gradient diagram in the length direction of the mold shown shows that the temperature gradient of the mold of the embodiment of the invention is small and increases slowly, indicating that the design of digging out the arc block makes it easier for the crystal to spread over the entire mold, which is beneficial to the shouldering and equal diameter process of the crystal. Figure 5 This is a gallium oxide crystal grown using the mold of the embodiment of the present invention. It can be seen from the figure that the crystal is smoothly shouldered to 110 mm, the crystal is symmetrical without cracks, and the quality is high.

[0044] Example 2

[0045] The molds of this embodiment are respectively a traditional mold and an invention embodiment mold, the size of the mold bottom surface is 170mm×15.2mm, the size of the mold surface is 170mm×13mm, the mold height is 50mm, the step thickness is 1.5mm, and the step height is 45mm. Among them, the mold of the invention embodiment has a 42.5mm×42.5mm×4.45mm arc block dug out at the bottom corners on both sides. This embodiment uses the same heating power to perform fluent simulation on the traditional mold and the invention embodiment mold, and obtains Figure 6-8 Results shown.

[0046] exist Figure 6 In the figure, the surface temperature difference of the conventional mold is 22.914K, and the surface temperature difference of the mold of the embodiment of the invention is 16.636K. The surface temperature difference of the mold of the embodiment of the invention is reduced by about 27% compared with the conventional mold, indicating that the design of digging out the arc block effectively reduces the surface temperature difference of the mold and reduces the probability of defects such as crystal cracking and dislocation. And under the same thermal field conditions, the temperature distribution on the surface of the mold of the embodiment of the invention is more symmetrical than that of the conventional mold, which is conducive to better achieving symmetrical shoulder release. Figure 7 It shows that the temperature distribution of the entire mold of the embodiment of the invention is more uniform. Figure 8 It shows that the temperature gradient of the mold in the embodiment of the invention increases slowly along the length direction and the overall temperature gradient is smaller, so the crystals are easier to cover the mold surface, which can effectively expand the crystal size.

[0047] The embodiment of the present invention provides a method for growing a gallium oxide single crystal by a guided mode method, which comprises the following steps:

[0048] The mold described in the embodiment of the present invention is placed in the center of the crucible, and the gallium oxide crystal is obtained by sequentially performing processes such as seeding, necking, shouldering, equalizing the diameter, and lifting.

[0049] Compared with conventional molds, the mold surface temperature difference is smaller and the temperature is more symmetrical under the same thermal field conditions, and the temperature gradient increases slowly along the length of the mold, which can provide a more reasonable temperature field for the size expansion of gallium oxide crystals. The demand for iridium is reduced, and the cost is reduced.

[0050] In summary, the embodiment of the present invention effectively reduces the heat conduction and heat radiation from the crucible to the two sides of the mold by digging out the arc-shaped blocks at the bottom corners of the two sides of the mold. This is mainly reflected in that the temperature distribution on both sides of the mold is more symmetrical, which is conducive to achieving symmetrical shoulder release; the temperature difference on the mold surface is reduced, which is conducive to reducing defects such as cracking and dislocation caused by overcooling of the crystal center and overheating on both sides; the temperature gradient along the length of the mold is reduced and grows slowly, which is conducive to the size enlargement and stable growth of gallium oxide crystals.

[0051] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A mold for growing gallium oxide single crystals by a guided mode method, characterized in that: include: At least two baffles, the baffles are connected to each other through a fixing portion, a slit is formed between two adjacent baffles, and the slit is used for allowing the gallium oxide melt to rise to the top of the mold under the action of capillary effect; The top of the mold is a step top structure for placing seed crystals; the bottom of the mold is an inverted trapezoidal structure, and the two sides of the trapezoid are arc-shaped, which is used to reduce the temperature difference and temperature gradient on the mold surface.

2. The mold for growing gallium oxide single crystal by guided mode method according to claim 1, characterized in that: The partitions are two long strip partitions that are arranged in mirror symmetry.

3. The mold for growing gallium oxide single crystal by guided mode method according to claim 1, characterized in that: There are multiple slits, which increase the supply of gallium oxide melt in a parallel feeding form, thereby ensuring the continuity and stability of the growth process of thick gallium oxide single crystals.

4. The mold for growing gallium oxide single crystal by guided mode method according to claim 2 or 3, characterized in that: The slit width between two adjacent partitions is in the range of 0.1 to 0.5 mm, and the width of each slit is the same, so as to ensure the stability of the overall feeding capacity and feeding speed, thereby ensuring uniform growth of the single crystal.

5. The mold for growing gallium oxide single crystal by guided mode method according to claim 4, characterized in that: The ratio of the slit width to the mold thickness is 1:8 to 1:

160.

6. The mold for growing gallium oxide single crystal by guided mode method according to any one of claims 1 to 5, characterized in that: The material of the partition is a noble metal that is resistant to oxidation at high temperatures.

7. The mold for growing gallium oxide single crystal by guided mode method according to claim 6, characterized in that: The noble metal is iridium or an alloy containing iridium.

8. The mold for growing gallium oxide single crystal by guided mode method according to claim 1, characterized in that: The bottom side length of the inverted trapezoidal structure is approximately 1 / 4 of the length of the mold, and the thickness is 20%-40% of the thickness of the mold.

9. A method for growing a gallium oxide single crystal using the mold according to any one of claims 1 to 8, characterized in that: The following steps are involved: Placing a gallium oxide raw material in a crucible and heating it until it melts, and using the slit to guide the melt to rise to the surface of the mold; Place a seed crystal on the mold surface, adjust the heating power so that the mold surface temperature is slightly higher than the crystal melting temperature, and then "seed"; By lifting the seed crystal and adjusting the heating power, "necking" is achieved to reduce dislocations in the seed crystal; Reduce the RF coil power to allow the seed crystal to grow in width and thickness and cover the mold, entering the "shoulder release" stage; Continue to adjust the RF coil power to maintain a stable growth rate and temperature gradient, and enter the "equal diameter" growth stage; After the crystal grows to the target size, the crystal is pulled off the mold surface, i.e. "lifted off"; Slowly reduce the RF power to room temperature to prevent the crystal from cracking.

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