A thermal field structure and device and method for preparing gallium oxide single crystal based on guided mode method

Abstract

The present invention relates to the technical field of gallium oxide crystal growth, and in particular to a thermal field structure and a device and method for preparing gallium oxide single crystals based on a guided mold method. The present invention changes the inner cavity at the bottom of the thermal field structure from a circular cavity to an elliptical cavity, so that the thermal field structure in the width direction of the mold extends toward the mold side, thereby improving the thermal insulation of the thermal field structure on both sides of the mold, and then prompting the mold core to move closer to the edges on both sides of the mold, ensuring the constant temperature gradient on the mold surface during the shouldering process of the crystal, avoiding temperature differences, and improving production efficiency. In addition, since the extended thermal field structure will make the air inlet airflow closer to the mold surface, resulting in the problem of cold airflow directly blowing the crystallization area on the mold surface, a drainage port is added below the air inlet to guide the cold airflow to the crucible position, thereby ensuring the effect of the mold core moving closer to the edges on both sides of the mold.

Description

Technical Field

[0001] The present invention relates to the technical field of gallium oxide crystal growth, and in particular to a thermal field structure and a device and method for preparing a gallium oxide single crystal based on a guided mode method. Background Art

[0002] Gallium oxide (Ga2O3) is a transparent semiconductor oxide. Among its five isomers (α, β, ε, δ, γ), the β phase is the most stable configuration and can be transformed from other metastable phases of gallium oxide by high temperature treatment in air for a long enough time. β-Ga2O3 material has a large bandgap (4.9eV) and a high critical electric field strength (theoretical value is about 8MV cm -1 ), excellent thermal stability and chemical stability make it a new generation of power semiconductor materials, and it is widely used in metal oxide semiconductor field effect transistors (MOSFET), Schottky barrier diodes (SBD) and photodetectors.

[0003] The parameter commonly used in comparing the performance of power semiconductor materials is the Baliga figure of merit (BFOM), and the Baliga figure of merit of β-Ga2O3 (3214) is 4 to 10 times that of the third-generation semiconductor materials GaN (846) and SiC (317). Compared with third-generation semiconductor materials such as SiC and GaN, β-Ga2O3 can be prepared as a single crystal by the melt method, and the growth cost is relatively low. However, the problem faced by the growth of β-Ga2O3 crystals is that gallium oxide will decompose when it approaches its melting temperature, thus affecting the stability and crystal quality of crystal growth. The methods for growing large-sized β-Ga2O3 crystals are mainly the descent method, the pulling method, and the guided mold method. The crucible descent method, also known as the vertical Bridgman method, uses a vertically placed crucible to solidify the melt from bottom to top or from top to bottom. It has been publicly reported that 6-inch β-Ga2O3 crystals have been grown, but the traditional single crystal growth furnace uses a single crucible to descend and grow a single crystal, which has a low growth efficiency. The Czochralski method tends to grow cylindrical ingots. The team of the Leibniz Institute for Crystal Growth in Germany pioneered the use of the Czochralski method to grow large-sized gallium oxide crystals, and as early as 2016, it had grown a 2-inch β-Ga2O3 single crystal. The guided-mode method uses the capillary effect to pull the material into the desired shape. Japan's Novel Crystal Technologies (NCT) has commercialized 2-inch and 4-inch β-Ga2O3 substrates using the guided-mode method.

[0004] The guided mode method is an improved and innovative crystal growth method based on the Czochralski method. The schematic diagram of the guided mode method for growing β-Ga2O3 single crystal is shown in the figure. Figure 1As shown. The biggest difference between the guided mold method and the Czochralski method is the mold placed in the middle. The mold has a small slit. Under the action of surface tension, the melt will follow the slit to reach the mold surface. At this time, the seed crystal is lowered to contact the melt to continue the crystal growth process. Compared with the Czochralski method, since the melt flows upward from the bottom of the crucible and the crystal growth front is located on the mold surface, the gallium-iridium floating objects will not have a significant effect on the seed crystal induction. In addition, since the crystals grown by the guided mold method are mostly plate-shaped, the heat dissipation is better than that of the Czochralski method, and there is no need to adjust the growth interface by crystal rotation, the guided mold method has a more obvious advantage in growing low-resistance β-Ga2O3 crystals than the Czochralski method.

[0005] The guided mold method for growing gallium oxide single crystals usually uses fine seed crystals for radial growth (hereinafter referred to as shouldering) and then is used for equal-diameter pulling. The temperature distribution on the mold surface is particularly critical during the shouldering process. The temperature distribution with a cold center and hot sides helps to slowly reduce the power while steadily shouldering. However, due to the heat dissipation of the mold itself, the hot center of the mold surface cannot be close to the edge (such as Figure 2 As shown in the figure, the power control during the shouldering process of the crystal is affected. Once the shouldering position passes through the mold core and enters the overcooling area during the crystal growth process, the sudden cooling will cause the shouldering to be too fast and cause the phenomenon of stray crystals.

[0006] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a thermal field structure and a device and method for preparing gallium oxide single crystals based on the guided mold method, aiming to solve the problem that the thermal center of the existing mold is far away from the edge, resulting in excessive temperature drop once the shoulder position passes the thermal center of the mold, which will lead to excessive shoulder release and the occurrence of stray crystal phenomenon.

[0008] The technical solution of the present invention is as follows:

[0009] According to a first aspect of the present invention, a thermal field structure for preparing gallium oxide single crystals based on a guided mold method is provided. The overall appearance of the thermal field structure is cylindrical. An inner cavity penetrating the upper and lower end surfaces and used for inserting a seed rod is arranged in the center of the thermal field structure along the axial direction. The inner cavity at the lower part of the thermal field structure has an elliptical cross-sectional shape.

[0010] Optionally, the height of the lower portion of the thermal field structure is 10-50 mm.

[0011] Optionally, the ellipse is composed of two semicircles and a rectangle, one long side of the rectangle is the diameter of one semicircle, and the other long side of the rectangle is the diameter of another semicircle.

[0012] Optionally, the radius of the semicircle is 30-80 mm, and the centers of the two semicircles are 5-30 mm apart.

[0013] Optionally, air inlets communicating with the inside and outside for internal ventilation are provided on both sides of the thermal field structure, and a drainage port is provided below the air inlet. The drainage port penetrates from the outside to the inside to the lower end surface of the thermal field structure, and the drainage port is used to guide the cold air flow to the crucible position.

[0014] Optionally, the cross-sectional shape of the drainage port on the lower end surface of the thermal field structure is a rectangle, the length of the rectangle is 20-40 mm, and the width is 3-20 mm. ， The direction of the long side of the rectangle is the same as the thickness direction of the mold.

[0015] A second aspect of the present invention provides a device for preparing gallium oxide single crystals based on the guided mode method, wherein the device comprises the thermal field structure for preparing gallium oxide single crystals based on the guided mode method described in the present invention.

[0016] Optionally, the device further comprises a heat preservation structure, the thermal field structure is located above the heat preservation structure, and the heat preservation structure comprises an induction coil, a crucible and a mold embedded in the crucible, which are coaxially installed from outside to inside.

[0017] Optionally, the material of the crucible is iridium material, and the material of the thermal field structure is alumina ceramic material or zirconia ceramic material.

[0018] A third aspect of the present invention provides a method for preparing a gallium oxide single crystal based on a guided mode method, wherein a gallium oxide single crystal is prepared by using the device for preparing a gallium oxide single crystal based on a guided mode method described in the present invention to obtain a gallium oxide single crystal.

[0019] Beneficial effect: The present invention changes the inner cavity at the bottom of the thermal field structure from a circular cavity to an elliptical cavity, so that the thermal field structure in the width direction of the mold extends toward the mold side, thereby improving the thermal insulation of the thermal field structure on both sides of the mold, and then prompting the mold heat center to move closer to the edges on both sides of the mold, ensuring the constant temperature gradient of the mold surface during the shouldering process of the crystal, avoiding temperature drop, and improving production efficiency. In addition, since the extended thermal field structure will make the air inlet airflow closer to the mold surface, resulting in the problem of cold airflow directly blowing the crystallization area on the mold surface, a drainage port is added below the air inlet to guide the cold airflow to the crucible position, thereby ensuring the effect of the mold heat center moving closer to the edges on both sides of the mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the guided mode method for growing β-Ga2O3 crystals.

[0021] Figure 2 Schematic diagram of mold surface temperature distribution.

[0022] Figure 3 Schematic diagrams of a thermal field structure with a circular inner cavity (left) and a thermal field structure with an elliptical inner cavity and a drainage port (right).

[0023] Figure 4 Schematic cross-sectional views of a thermal field structure with a circular inner cavity (left) and a thermal field structure with an elliptical inner cavity and a drainage port (right).

[0024] Figure 5 The X-direction cross-sectional temperature cloud diagram (50K isotherm, X-direction refers to the mold width direction) of the thermal field structure with a circular inner cavity (left) and the thermal field structure with an elliptical inner cavity and a drainage port (right).

[0025] Figure 6 The mold surface temperature cloud diagrams are for the thermal field structure with a circular inner cavity (left) and the thermal field structure with an elliptical inner cavity and a drainage port (right).

[0026] Figure 7 The X-axis velocity cloud diagram of the mold surface for the thermal field structure with a circular inner cavity (left) and the thermal field structure with an elliptical inner cavity and a drainage port (right).

[0027] Figure 8 The X-axis velocity vector diagram of the mold surface for the thermal field structure with a circular inner cavity (left) and the thermal field structure with an elliptical inner cavity and a drainage port (right).

[0028] Fig. 9 The air flow statistics diagram of the thermal field structure with a circular inner cavity (left) and the thermal field structure with an elliptical inner cavity and a drainage port (right).

[0029] Fig.10 Schematic diagram of the operating process of preparing gallium oxide single crystals using a device for preparing gallium oxide single crystals based on the guided mode method. DETAILED DESCRIPTION

[0030] The present invention provides a thermal field structure and a device and method for preparing gallium oxide single crystals based on a guided mode method. 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.

[0031] For the growth of gallium oxide crystals by the guided mold method, one of the problems is that during the crystal growth process, the temperature of the mold surface is difficult to control during the seed crystal shouldering process. The heat center of the mold surface using the traditional thermal field structure is often far away from the edge of the mold. Once the shouldering process begins, the mold surface covered by the crystal rises in temperature due to the obstruction of radiation heat dissipation, while the mold surface not covered by the crystal, that is, the crystal edge, has a lower temperature than the crystal itself and accelerates the shouldering. Once the shouldering position passes through the mold hot center area and enters the cold center area, the high temperature difference between the cold center and the hot center will increase the crystal shouldering speed by several times, resulting in the high frequency generation of the impure crystal area in the final stage of shouldering, thereby affecting the growth efficiency of the crystal. Therefore, the present invention designs a new thermal field structure to position the mold hot center as close to the mold edge as possible to reduce the uncontrollable interval in the crystal shouldering process, while adjusting the mold hot center position by modifying the mold structure has a long cycle and is expensive.

[0032] Based on this, an embodiment of the present invention provides a thermal field structure for preparing gallium oxide single crystals based on a guided mold method. The overall appearance of the thermal field structure is cylindrical. The center of the thermal field structure is provided with an inner cavity that penetrates the upper and lower end surfaces and is used to insert a seed crystal rod along the axial direction. The cross-sectional shape of the inner cavity at the lower part of the thermal field structure is an ellipse. Figure 3-4 shown.

[0033] In one embodiment, air inlets communicating with the inside and outside for internal ventilation are provided on both sides of the thermal field structure, and a drainage port is provided below the air inlet. The drainage port penetrates from the outside to the inside to the lower end surface of the thermal field structure, and the drainage port is used to guide the cold air flow to the crucible position.

[0034] Based on the known thermal field structure (see CN112877770A), the embodiment of the present invention changes the inner cavity at the bottom of the thermal field structure from a circular cavity to an elliptical cavity, and sets a drainage port below the air inlet. The thermal field structure designed in this way can meet the mold insulation, so that the hot center position of the mold surface is close to the edge, and at the same time avoids the cold air flow blowing directly on the mold surface due to the extension of the thermal field structure causing the air inlet to be too close to the mold, thereby solving the problem that the hot center position of the mold is far away from the edge. The thermal field structure has a wide applicability and has no effect on the applicability of other accessories. It can be applied to growth furnaces of various structures. The purpose of adjusting the hot center position of the mold and the direction of the airflow is achieved through the newly designed thermal field structure. The mold required for the growth of large-sized crystals is large, and the area outside the hot center of the mold is larger. The temperature distribution of the mold can be indirectly adjusted through the thermal field structure designed, which greatly reduces the formation of impurities caused by excessive temperature drop after crossing the hot center of the mold during the shouldering process, and finally achieves the purpose of growing high-quality gallium oxide crystals with higher efficiency.

[0035] In short, the key to the embodiment of the present invention is to use the thermal insulation performance of the thermal field structure to move the mold core toward the edge of the mold, thereby ensuring the constant temperature gradient on the mold surface during the shouldering process of the crystal, avoiding temperature drops, and improving production efficiency; another key to the embodiment of the present invention is to solve the problem of cold air flow from the air inlet directly blowing the mold, further ensuring the stability of the temperature field and flow field in the crystallization area, thereby growing high-quality gallium oxide crystals more efficiently and stably.

[0036] from Figure 6 It can be seen that the thermal field structure of the drainage elliptical cavity (i.e., the thermal field structure with an elliptical inner cavity and a drainage port) has a thermal center on the mold surface significantly closer to the edge of the mold compared to the thermal field structure of the circular cavity (i.e., the thermal field structure with a circular inner cavity), which greatly reduces the supercooling area after the crystal passes the thermal center during the crystal growth process. Figure 5 , Figures 7 to 9 It can be seen that the drainage rate of the drainage port of the drainage elliptical cavity thermal field structure reaches 45%, which can effectively guide the cold air flow from the air inlet to the crucible position, thereby avoiding the cold air flow directly blowing the mold, and further reducing the impact of the cold air flow on the mold surface temperature.

[0037] In one embodiment, the height of the lower portion of the thermal field structure is 10-50 mm, such as 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, etc.

[0038] In one embodiment, the ellipse is composed of two semicircles and a rectangle, one long side of the rectangle is the diameter of one semicircle, and the other long side of the rectangle is the diameter of another semicircle. Figure 3 shown.

[0039] In one embodiment, the radius of the semicircle is 30-80 mm (such as 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, etc.), and the distance between the centers of the two semicircles is 5-30 mm (such as 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, etc.). Designing an ellipse of this size is more conducive to ensuring that the mold core is close to the edges on both sides of the mold.

[0040] In one embodiment, the cross-sectional shape of the drainage port at the lower end surface of the thermal field structure is a rectangle, the length of the rectangle is 20-40 mm (such as 20 mm, 30 mm, 40 mm, etc.), and the width is 3-20 mm (such as 3 mm, 4 mm, 8 mm, 10 mm, 15 mm, 20 mm, etc.) ， The direction of the long side of the rectangle is the same as the thickness direction of the mold.

[0041] An embodiment of the present invention provides a device for preparing gallium oxide single crystal based on the guided mode method, wherein the device includes the thermal field structure for preparing gallium oxide single crystal based on the guided mode method described in the embodiment of the present invention.

[0042] Specifically, the device also includes a heat preservation structure, and the thermal field structure is located above the heat preservation structure. The heat preservation structure includes an induction coil, a crucible and a mold embedded in the crucible, which are coaxially installed from the outside to the inside. The device also includes a seed crystal rod. The materials used for the crucible, the mold and the seed crystal rod are all high-melting-point precious metal iridium, with a melting point of up to 2450°C. The crucible serves as a carrier for the melt and the mold. At the same time, heat is generated under the action of the induction coil as a heat source during the growth process. The surface of the mold is polished, and there is a gap in the middle, which serves as a channel for the melt to rise under capillary action. The induction coil is a copper hollow coil with flowing cooling water inside. The water temperature is constant at 27°C to avoid changes in the cooling water temperature affecting the heating efficiency. The material of the heat preservation structure is a split zirconia brick, which can withstand a high temperature of about 2700°C. The material of the thermal field structure is alumina ceramic or zirconia ceramic material.

[0043] The key to the device for preparing gallium oxide single crystal based on the guided mode method provided by the embodiment of the present invention is that the thermal field structure of the embodiment of the present invention is used to replace the known thermal field structure, and the other components remain unchanged, so the more detailed details of the device are not repeated here.

[0044] The device for preparing gallium oxide single crystal based on the guided mode method provided by the embodiment of the present invention has the following technical effects:

[0045] 1) Based on the original thermal field structure, the embodiment of the present invention adjusts the circular cavity structure at the bottom of the thermal field structure to an elliptical cavity structure, and opens a drainage port on this basis, which has no effect on the applicability of other components, so that it can be applied to different models of gallium oxide single crystal production furnaces.

[0046] 2) The device of the embodiment of the present invention has a better growth effect on large-sized crystals. This is because the mold size required for the growth of large-sized crystals is larger and the size of the supercooling area outside the heat center is longer. The device effectively moves the heat center of the mold outward while keeping the structural dimensions of important components such as iridium unchanged.

[0047] 3) The device of the embodiment of the present invention not only moves the core of the mold outward, but also reduces the cold airflow directly blowing the mold, effectively ensuring the stability of the temperature field and flow field in the crystallization area, thereby growing high-quality gallium oxide crystals more efficiently and stably.

[0048] An embodiment of the present invention provides a method for preparing a gallium oxide single crystal based on a guided mode method, wherein a gallium oxide single crystal is prepared by using an apparatus for preparing a gallium oxide single crystal based on a guided mode method described in an embodiment of the present invention to obtain a gallium oxide single crystal.

[0049] By adopting the method for preparing gallium oxide single crystal based on the guided mode method provided in the embodiment of the present invention, high-quality gallium oxide single crystal can be prepared, thereby improving the growth efficiency.

[0050] Combination Fig.10 As shown, the operation steps of preparing gallium oxide single crystals by using the device for preparing gallium oxide single crystals based on the guided mode method described in the embodiment of the present invention specifically include:

[0051] Cleaning of iridium: polish, ultrasonically clean, blow dry, rinse with alcohol, blow dry again, seal and store in a bag for loading.

[0052] Filling the raw materials: Place the cleaned iridium on the scale and clear it to zero. After pouring in the raw materials, wipe off the raw material powder that has fallen on the mold surface, mold steps, and pot edge with dust-free paper dipped in alcohol.

[0053] Clean and place the pad: clean the volatiles, measure the size of the gap between the insulation, and ensure that the gap is consistent in distance from front to back and left to right and remains level.

[0054] Clean the thermal field structure: polish the inner wall of the thermal field structure and blow it with an air gun until there are no volatiles.

[0055] Place the iridium crucible, mold, and seed crystal installation: Place the loaded crucible in the center of the horizontal calibration and cover it with the lid. Place the mold in the center of the crucible and start installing the seed crystal.

[0056] Material discharge: lay a layer of powder material on the surface of the mold as a judgment of the material discharging point.

[0057] Thermal field assembly: Place the thermal field structure and adjust its position so that it is in the center of the thermal field.

[0058] Furnace loading and vacuum filling: After the furnace is loaded, close the furnace door tightly, start vacuuming, stop pumping until vacuum is reached, and start filling with protective gas.

[0059] Start the heating program: After the gas is filled, the temperature starts to rise. Manually input the starting power and click Update. After the temperature starts to rise, the crystal is obtained through melting, pulling and growth, and cooling. Take out the crystal for processing and testing. At the same time, compare and observe and record the temperature.

[0060] In summary, the present invention provides a thermal field structure and a device and method for preparing gallium oxide single crystals based on the guided mold method. The present invention is based on the known thermal field structure and designs a structure that can meet the needs of mold insulation, so that the hot center position of the mold surface is close to the edge, while avoiding the cold airflow blowing directly on the mold surface due to the extension of the thermal field structure causing the air inlet to be too close to the mold, thereby solving the problem that the hot center position of the mold is far away from the edge. The thermal field structure has a wide range of applicability and does not affect the applicability of other accessories. It can be applied to growth furnaces of various structures. The device for preparing gallium oxide single crystals based on the guided mold method of the present invention achieves the purpose of adjusting the hot center position of the mold and the direction of the airflow through a newly designed thermal field structure. The mold required for the growth of large-sized crystals is large, and the area outside the hot center of the mold is larger. The temperature distribution of the mold can be indirectly adjusted through the designed thermal field structure, which greatly reduces the formation of impurities caused by excessive temperature drop after passing the hot center of the mold during the shouldering process, and finally achieves the purpose of growing high-quality gallium oxide crystals with higher efficiency.

[0061] 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 thermal field structure for preparing gallium oxide single crystals based on a guided mold method, wherein the overall appearance of the thermal field structure is cylindrical, and the center of the thermal field structure is provided with an inner cavity penetrating the upper and lower end surfaces and used to insert a seed crystal rod along the axial direction, characterized in that: The cross-sectional shape of the inner cavity at the lower part of the thermal field structure is elliptical.

2. The thermal field structure for preparing gallium oxide single crystal based on the guided mode method according to claim 1, characterized in that: The height of the lower part of the thermal field structure is 10-50 mm.

3. The thermal field structure for preparing gallium oxide single crystal based on the guided mode method according to claim 1, characterized in that: The oval is composed of two semicircles and a rectangle, one long side of the rectangle is the diameter of one semicircle, and the other long side of the rectangle is the diameter of another semicircle.

4. The thermal field structure for preparing gallium oxide single crystal based on the guided mode method according to claim 3, characterized in that: The radius of the semicircle is 30-80 mm, and the distance between the centers of the two semicircles is 5-30 mm.

5. The thermal field structure for preparing gallium oxide single crystal based on the guided mode method according to claim 1, characterized in that: Air inlets communicating with each other for internal ventilation are arranged on both sides of the thermal field structure, and a drainage port is arranged below the air inlet. The drainage port penetrates from the outside to the inside to the lower end surface of the thermal field structure, and the drainage port is used to guide the cold air flow to the crucible position.

6. The thermal field structure for preparing gallium oxide single crystal based on the guided mode method according to claim 5, characterized in that: The cross-sectional shape of the drainage port on the lower end surface of the thermal field structure is a rectangle, the length of the rectangle is 20-40 mm, and the width is 3-20 mm. ， The direction of the long side of the rectangle is the same as the thickness direction of the mold.

7. A device for preparing gallium oxide single crystal based on guided mode method, characterized in that: The device comprises the thermal field structure for preparing gallium oxide single crystal based on the guided mode method as described in any one of claims 1 to 6.

8. The device for preparing gallium oxide single crystal based on guided mode method according to claim 7, characterized in that: The device also includes a heat preservation structure. The thermal field structure is located above the heat preservation structure. The heat preservation structure includes an induction coil, a crucible and a mold embedded in the crucible, which are coaxially installed from outside to inside.

9. The device for preparing gallium oxide single crystal based on guided mode method according to claim 8, characterized in that: The material of the crucible is iridium material, and the material of the thermal field structure is alumina ceramic material or zirconia ceramic material.

10. A method for preparing gallium oxide single crystal based on guided mode method, characterized in that: The device for preparing gallium oxide single crystal based on the guided mode method as described in any one of claims 7 to 9 is used to prepare gallium oxide single crystal to obtain gallium oxide single crystal.

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