Thermal field structure for growing silicon carbide single crystals
By using a multi-segment induction heating unit and a resistance heater combined with inert gas to regulate the temperature gradient during the silicon carbide single crystal growth process, the problems of difficult temperature gradient control and unstable liquid convection were solved, thus achieving high-quality and low-cost silicon carbide single crystal growth.
Patent Information
- Application Number
- CN202322179297.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-14
- Publication Date
- 2026-02-03
- Estimated Expiration
- 2033-08-14
AI Technical Summary
Existing technologies for growing silicon carbide single crystals suffer from challenges such as difficulty in controlling the temperature gradient, low bottom heating efficiency, and unstable liquid convection, resulting in poor crystal growth quality and high costs.
The system employs several induction heating units with different electrical conductivity on the sidewalls and a bottom heating mechanism with resistance heating to regulate the axial temperature gradient, reduce the radial temperature gradient, and use inert gas to regulate the bottom temperature, thus providing a stable carbon source.
This resulted in a more stable carbon source supply, reduced crystal stress, improved the growth quality and efficiency of silicon carbide single crystals, and lowered costs.
Smart Images
Figure CN223866832U_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of silicon carbide crystal growth, specifically relating to a thermal field structure for growing silicon carbide single crystals. Background Technology
[0002] Physical vapor transport (PVT) is the mainstream method for SiC crystal growth internationally. Currently, micropipes in SiC crystals grown using this method have been largely eliminated (density less than 0.2 cm³). -2 However, this method still suffers from high dislocation density, low yield, difficulty in diameter expansion, and high cost. The top-seeded solution growth method utilizes a high-temperature liquid composed of silicon and a flux to dissolve a graphite crucible and obtain carbon. The longitudinal temperature gradient of the liquid generates convection, allowing carbon to be transported to the top silicon carbide growth surface. In the low-temperature region surrounding the silicon carbide seed crystal, carbon supersaturation leads to silicon carbide precipitation, achieving silicon carbide crystal growth. Crystals grown using this method offer advantages such as microtube-free growth, easy diameter expansion, and easy P-type doping. In the top-seeded solution growth method for silicon carbide crystals, the axial convection generated by the liquid temperature gradient is crucial for providing a carbon source for crystal growth; however, an excessively large radial temperature gradient can cause stress and cracking in the silicon carbide crystal.
[0003] Existing technology relies on an integral graphite induction heater for induction heating; however, this technology has the following problems:
[0004] 1) Temperature gradient is difficult to control: The resistivity of the sidewall heaters is the same in the axial direction, and the induction heating efficiency is the same. The axial temperature gradient of the liquid is mainly provided by heat dissipation from the liquid surface. The temperature field distribution can only be fine-tuned by adjusting the relative position of the heater and the induction coil, but this method has a small temperature gradient control range.
[0005] 2) Low bottom heating efficiency: Due to the magnetic field distribution generated by the induction coil and the influence of the skin effect, the bottom heating efficiency of the heater is low and it cannot effectively provide an axial temperature gradient for the liquid. Since the heating of the heater is mainly concentrated on the side wall, the radial temperature gradient of the liquid is large, which causes large stress on the grown crystal.
[0006] 3) Unstable liquid convection: The longitudinal temperature gradient of the liquid is not easy to adjust, which leads to unstable liquid convection and unstable carbon source supply to the crystal growth surface. Utility Model Content
[0007] The purpose of this invention is to provide a thermal field structure for growing silicon carbide single crystals. By using several induction heating units with different conductivity on the sidewalls and a resistance-type bottom heating mechanism, the axial temperature gradient control range of the liquid inside the crucible is expanded. Furthermore, the resistance-type bottom heating mechanism avoids the problem of insufficient bottom heating caused by the skin effect, ensuring sufficient and uniform heating at the bottom of the crucible. This reduces the radial temperature gradient of the liquid inside the crucible, thereby reducing crystal stress. This provides a more stable carbon source for crystal growth, resulting in high-quality crystal growth and demonstrating good practicality.
[0008] This utility model is mainly achieved through the following technical solutions:
[0009] A thermal field structure for growing silicon carbide single crystals includes a heat-insulating base, a sidewall heating mechanism, and a bottom heating mechanism. A crucible is disposed inside the heat-insulating base. A sidewall heating mechanism is disposed between the heat-insulating base and the sidewall of the crucible, and a bottom heating mechanism for resistance heating is disposed between the heat-insulating base and the bottom of the crucible. The sidewall heating mechanism includes several induction heating units with different electrical conductivities arranged sequentially from top to bottom, and an induction coil is correspondingly disposed on the outer side of the heat-insulating base.
[0010] To better realize this utility model, the resistivity of the several induction heating units arranged from top to bottom increases sequentially.
[0011] To better realize this utility model, the adjacent induction heating units are further fitted and snapped together, and the connection points of the adjacent induction heating units are respectively provided with mutually fitting stepped snap-fit surfaces.
[0012] To better realize this utility model, furthermore, 3-10 induction heating units are arranged sequentially from top to bottom between the heat preservation base and the side wall of the crucible.
[0013] To better realize this utility model, further, three induction heating units are arranged sequentially from top to bottom between the heat preservation base and the side wall of the crucible. The resistivity of the middle induction heating unit is 1.2 times that of the top induction heating unit, and the resistivity of the bottom induction heating unit is 1.4 times that of the top induction heating unit.
[0014] To better realize this utility model, the bottom heating mechanism further includes, from top to bottom, an insulating heat-conducting layer, a bottom heating unit, and an insulating layer. The two sides of the bottom heating unit are connected to the crucible and the heat-insulating base respectively through the insulating heat-conducting layer and the insulating layer. Preferably, the induction heating unit is an induction graphite heater, and the bottom heating unit is a resistance graphite heater.
[0015] To better realize this utility model, the insulating layer is further provided with a number of air holes, and the bottom heating unit is provided with a number of inert gas channels.
[0016] To better realize this utility model, the bottom heating unit is further arranged in an arc shape or a spiral shape.
[0017] To better realize this utility model, further, the insulating layer is provided with a number of air holes on the periphery of the bottom heating unit arranged in an arc shape, and the insulating layer is provided with a number of air holes at the spiral start and spiral middle part of the bottom heating unit arranged in a spiral shape.
[0018] To better realize this utility model, the insulating and thermally conductive layer is further prepared from any one of boron nitride, beryllium oxide, and aluminum nitride materials.
[0019] The beneficial effects of this utility model are as follows:
[0020] (1) This invention uses induction heating units with different conductivity in multiple segments on the sidewall for induction heating and resistance heating through a bottom heating mechanism to control the increase of the axial temperature gradient of the liquid. At the same time, bottom heating helps to reduce the radial temperature gradient of the liquid. This invention effectively solves the problems of difficult adjustment of liquid temperature gradient, excessive radial temperature gradient during crystal growth leading to stress in silicon carbide crystals, unstable liquid convection, and unstable carbon source supply to the crystal growth surface. This invention is more conducive to controlling the liquid temperature gradient, providing a more stable carbon source, and promoting stable crystal growth.
[0021] (2) The temperature gradient of this invention is jointly regulated by the sidewall heating mechanism, the bottom heating mechanism, and the inert gas. When it is necessary to increase the axial temperature gradient, it can be achieved by increasing the resistivity difference between the upper and lower induction heating units at the sidewall and increasing the power of the bottom heating unit; when it is necessary to decrease the axial temperature gradient, it can be achieved by decreasing the resistivity difference between the upper and lower induction heating units at the sidewall, decreasing the power of the bottom heating unit, and introducing inert gas into the bottom heating unit. This invention is more conducive to controlling the liquid temperature gradient, providing a more stable carbon source for crystal growth, enabling high-quality crystal growth, and has good practicality.
[0022] (3) During the growth of silicon carbide single crystals, the driving force for liquid convection transporting the carbon source originates from the axial temperature gradient. Therefore, the resistivity of the sidewall heating mechanism increases sequentially from top to bottom, resulting in sequentially increasing heating efficiency, with higher temperatures along the axial direction, thus providing an axial temperature gradient for the liquid. In addition, resistance heating can be performed using a bottom heating mechanism to solve the problem of low bottom heating efficiency caused by magnetic field distribution and skin effect. An insulating thermally conductive layer is provided between the bottom heating unit and the crucible, which is beneficial for uniform heating of the bottom of the crucible.
[0023] (4) This utility model uses inert gas to cool the bottom heating unit of the resistance heating, thereby reducing the axial temperature gradient of the liquid. During operation, the inert gas can enter and exit through the vent, carrying away excess heat and preventing the bottom temperature from becoming too high. This, combined with the power control of the bottom heating unit, enables the overall adjustment of the crucible bottom temperature.
[0024] (5) The sidewall of this utility model is provided with multiple induction heating units, which generate a longitudinal temperature gradient by using induction heating units with different resistivities. A resistance graphite heater is provided at the bottom for resistance heating, and inert gas can be introduced through the gap between the heating elements to adjust the temperature. The multiple induction graphite heaters on the sidewall, the resistance graphite heater at the bottom, and the inert gas make the temperature gradient of the thermal field of this utility model easier to adjust and the temperature gradient adjustment range is larger, so that the liquid can provide a carbon source for silicon carbide crystal growth efficiently and stably, which is conducive to the efficient and stable growth of crystals. Attached Figure Description
[0025] Figure 1 This is a schematic diagram of the structure of this utility model;
[0026] Figure 2 This is a schematic diagram of the bow-shaped graphite heating element structure described in this utility model;
[0027] Figure 3 This is a schematic diagram of the spiral graphite heating element structure described in this utility model;
[0028] Figure 4 A simulation diagram of the surface temperature of an existing heater;
[0029] Figure 5 A simulation diagram of the surface temperature of the thermal field for a heating mechanism with only sidewall heating elements;
[0030] Figure 6 This is a simulation diagram of the surface temperature of the thermal field structure of this utility model.
[0031] The components are: 1. Graphite shaft, 2. Graphite support, 3. Seed crystal, 4. Crucible, 5. Insulating and heat-conducting layer, 6. Resistance graphite heater, 7. Insulating layer, 8. Pores, 9. Induction graphite heater, 10. Induction coil, 11. Quartz cover, 12. Insulation layer, 13. Crucible lid. Detailed Implementation
[0032] Example 1:
[0033] A thermal field structure for growing silicon carbide single crystals includes a heat-insulating base, inside which a crucible 4 is disposed. Several induction heating units are arranged sequentially from top to bottom between the crucible 4 and the sidewall of the heat-insulating base. An induction coil 10 is correspondingly disposed on the outer side of the heat-insulating base. Each induction heating unit on the sidewall has a different electrical conductivity. A bottom heating unit is disposed between the crucible 4 and the bottom of the heat-insulating base. The bottom heating unit is connected to the crucible 4 above via an insulating thermally conductive layer 5, and to the heat-insulating base below via an insulating layer 7.
[0034] Preferably, the induction heating unit is an induction graphite heater 9, and the bottom heating unit is a resistance graphite heater 6. The sidewalls of this invention are induction heated by multiple induction graphite heaters 9 with different conductivity, while the bottom is resistively heated by the resistance graphite heater 6. This ultimately increases the axial temperature gradient of the liquid inside the crucible 4, while bottom heating helps reduce the radial temperature gradient of the liquid. During operation, the bottom graphite heater uses resistance heating, which avoids the skin effect problem of induction heating, allowing for more thorough bottom heating, resulting in a smaller radial temperature gradient of the liquid and less stress on the grown silicon carbide.
[0035] Preferably, the resistivity of the several induction graphite heaters 9 arranged from top to bottom gradually increases. During operation, because the resistivity of the induction graphite heaters 9 at the bottom of the side wall is higher, the heating efficiency is greater, so the temperature of the crucible 4 gradually increases from top to bottom, thereby providing an axial temperature gradient for the liquid, which is conducive to the liquid convection and provides a carbon source for silicon carbide growth.
[0036] Preferably, 3-10 induction graphite heaters 9 are arranged sequentially from top to bottom between the crucible 4 and the side wall of the insulation base, and the resistivity of the induction graphite heaters 9 increases sequentially from top to bottom. Preferably, the inner diameter of the induction graphite heater 9 matches the outer diameter of the crucible 4, and the upper inner ring of each induction graphite heater 9 protrudes, while the lower outer ring protrudes. During installation, the lower ends and upper ends of two adjacent induction graphite heaters 9 fit together, ensuring that each heater segment is coaxial.
[0037] Preferably, an inert gas channel is provided in the gap of the resistive graphite heater 6, and the inert gas enters and exits through the pores 8 of the lower insulating layer 7. This invention reduces the axial temperature gradient of the liquid by cooling the resistive graphite heater 6 with inert gas.
[0038] Preferably, the pores 8 in the insulating layer 7 are connected to the gap between the graphite heating element and the pores. During operation, inert gas can enter and exit through the pores 8, carrying away excess heat and preventing the bottom temperature from becoming too high. This helps to adjust the bottom temperature of the crucible 4 in conjunction with the power of the graphite heating element. Helium, neon, or argon is used as the inert gas.
[0039] Preferably, such as Figure 2 , Figure 3 As shown, the bottom resistive graphite heater 6 is arranged in an arc shape or a spiral shape.
[0040] Preferably, the insulating and thermally conductive layer 5 is made of boron nitride, beryllium oxide, or aluminum nitride. During operation, the bottom resistance graphite heater 6 is energized, and the insulating and thermally conductive layer 5 comes into contact with the heating element, ensuring uniform heating of the bottom of the crucible 4 while providing insulation.
[0041] Preferably, the crucible 4 is a graphite crucible 4, and the crucible lid 13 on the top of the crucible 4 is connected to the crucible 4 by threads or snaps; during operation, the raw material is placed into the crucible 4, and the crucible lid 13 is covered to prevent volatiles from entering the insulation layer 12. At the same time, the raw material melts and dissolves the graphite crucible 4, providing a carbon source for silicon carbide growth.
[0042] During operation, the sidewalls are induction heated using multi-segment induction graphite heaters 9, while the bottom is resistance heated using resistance graphite heaters 6. A high-purity graphite crucible 4 with an open top is placed inside the heaters, containing high-purity silicon and fluxing agents. The sidewall heaters and the bottom insulation layer 7 are separated from the quartz cover 11 by insulating material. Heating is performed in an inert gas atmosphere such as helium, neon, or argon, melting the material inside the crucible 4 and dissolving it to obtain the carbon required for growth. A seed crystal 3 is attached to a graphite support 2, and growth occurs through a graphite shaft 1 that brings the seed crystal 3 into contact with the liquid surface.
[0043] The driving force for liquid convection transporting the carbon source originates from the axial temperature gradient. During growth, the resistivity of the sidewall heaters increases sequentially from top to bottom, resulting in successively higher heating efficiency and temperatures, thus providing an axial temperature gradient for the liquid. Furthermore, resistance heating can be achieved using a bottom graphite heater, addressing the low heating efficiency at the bottom caused by magnetic field distribution and the skin effect. An insulating thermally conductive layer 5 exists between the bottom resistance graphite heater 6 and the crucible 4, promoting uniform heating of the bottom of the crucible 4. The gap in the bottom resistance graphite heater 6 is connected to the lower vent 8, allowing inert gas to be introduced for cooling when needed.
[0044] This invention solves problems such as difficulty in adjusting the liquid temperature gradient, excessive radial temperature gradient leading to stress in silicon carbide crystals, unstable liquid convection, and unstable carbon source supply to the crystal growth surface. The temperature gradient in this invention is jointly regulated by multiple induction graphite heaters 9 on the sidewalls, a resistance graphite heater 6 at the bottom, and an inert gas. When an increase in the axial temperature gradient is needed, it can be achieved by increasing the resistivity difference between the upper and lower induction graphite heaters 9 and by increasing the power of the bottom resistance graphite heater 6; when a decrease in the axial temperature gradient is needed, it can be achieved by decreasing the resistivity difference between the upper and lower induction graphite heaters 9, decreasing the power of the bottom resistance graphite heater 6, and introducing inert gas inside the resistance graphite heater 6. This invention is more conducive to controlling the liquid temperature gradient, providing a more stable carbon source, and promoting stable crystal growth.
[0045] Example 2:
[0046] A thermal field structure for growing silicon carbide single crystals, such as Figure 1 As shown, a crucible 4 is disposed inside the insulation layer 12, with an opening at the top. A crucible lid 13 is disposed between the top of the insulation layer 12 and the crucible 4, and a resistance graphite heater 6 is disposed between their bottoms. Several induction graphite heaters 9 with different electrical conductivities are disposed between the insulation layer 12 and the side wall of the crucible 4. An induction coil 10 is wound around the outside of the insulation layer 12.
[0047] Preferably, this invention includes three induction graphite heaters 9, with the inner diameter of each heater matching the outer diameter of the crucible 4 to facilitate heat conduction. The resistivity of the three induction graphite heaters 9, arranged sequentially from top to bottom, gradually increases to 10 μΩ·m, 12 μΩ·m, and 14 μΩ·m, respectively. During induction heating, the lower heater on the sidewall has a higher resistivity, resulting in greater heating efficiency and a higher temperature. This provides a longitudinal temperature gradient for the liquid, promoting convection and facilitating the provision of a carbon source for silicon carbide growth.
[0048] Preferably, an insulating and heat-conducting layer 5 is provided above the bottom resistive graphite heater 6 and between it and the crucible 4, and an insulating layer 7 is provided below the resistive graphite heater 6 and between it and the insulation layer 12. Preferably, the insulating layer 7 is in close contact with the resistive graphite heater 6, and the insulating and heat-conducting layer 5 is located between the crucible 4 and the resistive graphite heater 6, and is in close contact with both. Preferably, the gap between the resistive graphite heater 6 has several interconnected inert gas channels, and the inert gas enters and exits through the pores 8 in the lower insulating layer 7. The pores 8 in the insulating layer 7 are connected to the gap between the resistive graphite heater 6. Preferably, the insulating and heat-conducting layer 5 is made of hexagonal boron nitride, which has good insulation and thermal conductivity, and can make the bottom of the crucible 4 heat up evenly while providing insulation. The cooling gas is helium.
[0049] Preferably, such as Figure 2 As shown, the resistance graphite heater 6 adopts an arc-shaped arrangement for resistance heating, avoiding the skin effect of induction heating and the problem of insufficient heating at the bottom of the crucible 4 due to the magnetic field distribution. It reduces the radial temperature gradient of the liquid, thereby reducing the stress on the grown silicon carbide crystal. At the same time, it can increase the axial temperature gradient of the liquid, generating stronger convection and making the carbon source for silicon carbide growth more abundant.
[0050] Preferably, the crucible 4 and the crucible lid 13 are connected by threads. During loading, the crucible lid 13 is opened to facilitate the filling of raw materials; after loading, the crucible lid 13 is closed to prevent the raw materials from evaporating and entering the insulation layer 12 during the growth process. The top center of the crucible lid 13 has a circular opening, and the insulation layer 12 above the crucible lid 13 has a central opening to facilitate monitoring by an infrared thermometer during the growth process.
[0051] Preferably, a quartz cover 11 is provided on the outer wall of the insulation layer 12, and the inner diameter of the quartz cover 11 matches the outer diameter of the insulation layer 12. Preferably, the insulation layer 12 is made of carbon fiber felt, and the inner diameter of the insulation layer 12 matches the outer diameter of the induction graphite heater 9.
[0052] like Figures 4-6 As shown, the heating effect of the thermal field is verified through simulation. Figure 4 As shown, using an integral heater as a control, the temperature of the liquid surface heated by it was 23.8℃ lower than that at the bottom of crucible 4, resulting in a smaller axial temperature gradient. Radially, the temperature difference between the center and the edge was 12.8℃. Figure 5 As shown, if only a segmented induction heater is used, the temperature of the liquid surface is 32.8℃ lower than that of the bottom of crucible 4; radially, the temperature difference between the center and the edge is 20.8℃. Figure 6As shown, when heated using the thermal field of this invention, the liquid inside the crucible 4 has a surface temperature 66.6°C lower than its bottom temperature axially; radially, the temperature difference between the center and the edge is 12°C, effectively increasing the axial temperature gradient while decreasing the radial temperature gradient. Therefore, this invention significantly improves the axial temperature gradient range through the synergistic heating of the sidewall and bottom heating mechanisms; the bottom heating mechanism, using resistance heating, effectively reduces the radial temperature gradient, solving the problem of low bottom heating efficiency caused by magnetic field distribution and the skin effect. This provides a more stable carbon source for crystal growth, enabling high-quality crystal growth and demonstrating good practicality.
[0053] In use, this invention involves winding an induction coil 10 within a single-crystal furnace to provide a high-frequency induced magnetic field to the induction graphite heater 9. The number of segments and resistivity of the induction graphite heater 9 can be replaced according to temperature gradient requirements, while the power of the resistance graphite heater 6 is adjusted based on the silicon carbide crystal growth status. The pores 8 in the insulating layer 7 are connected to a gas flow meter to control the input of inert gas, which, in conjunction with the power of the resistance graphite heater 6, regulates the bottom temperature of the crucible 4.
[0054] In summary, by adjusting the resistivity gradient of the multi-segment induction heating unit, regulating the power of the bottom heating unit, and adjusting the inert gas flow rate, this invention can more easily adjust the liquid temperature gradient, and the temperature gradient adjustment range is larger, making the silicon carbide growth process more efficient and stable.
[0055] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present utility model shall fall within the protection scope of the present utility model.
Claims
1. A thermal field structure for growing silicon carbide single crystals, characterized in that, It includes a heat-insulating base, a side wall heating mechanism, and a bottom heating mechanism. A crucible (4) is arranged inside the heat-insulating base. A side wall heating mechanism is arranged between the side wall of the heat-insulating base and the crucible (4), and a bottom heating mechanism with resistance heating is arranged between the bottom of the heat-insulating base and the bottom of the crucible (4). The side wall heating mechanism includes several induction heating units with different electrical conductivity arranged sequentially from top to bottom, and an induction coil (10) is arranged on the outer side of the heat-insulating base. The bottom heating mechanism includes an insulating heat-conducting layer (5), a bottom heating unit, and an insulating layer (7) arranged sequentially from top to bottom. The two sides of the bottom heating unit are connected to the crucible (4) and the heat-insulating seat through the insulating heat-conducting layer (5) and the insulating layer (7), respectively.
2. The thermal field structure for growing silicon carbide single crystals according to claim 1, characterized in that, The resistivity of the several induction heating units arranged from top to bottom increases sequentially.
3. The thermal field structure for growing silicon carbide single crystals according to claim 1, characterized in that, Adjacent induction heating units are fitted together, and the connection points of adjacent induction heating units are respectively provided with mutually fitting stepped fitting surfaces.
4. The thermal field structure for growing silicon carbide single crystals according to any one of claims 1-3, characterized in that, The heat-insulating base and the side wall of the crucible (4) are provided with 3-10 induction heating units from top to bottom.
5. The thermal field structure for growing silicon carbide single crystals according to claim 4, characterized in that, Three induction heating units are arranged sequentially from top to bottom between the heat-insulating base and the side wall of the crucible (4). The resistivity of the middle induction heating unit is 1.2 times that of the top induction heating unit, and the resistivity of the bottom induction heating unit is 1.4 times that of the top induction heating unit.
6. The thermal field structure for growing silicon carbide single crystals according to claim 1, characterized in that, The insulating layer (7) is provided with a number of air holes (8), and the bottom heating unit is provided with a number of inert gas channels.
7. The thermal field structure for growing silicon carbide single crystals according to claim 1 or 6, characterized in that, The bottom heating units are arranged in an arc shape or a spiral shape.
8. The thermal field structure for growing silicon carbide single crystals according to claim 7, characterized in that, The insulating layer (7) has several air holes (8) on the periphery of the bottom heating unit arranged in an arc shape, and the insulating layer (7) has several air holes (8) at the beginning and middle of the spiral arrangement of the bottom heating unit.
9. The thermal field structure for growing silicon carbide single crystals according to claim 1, characterized in that, The insulating and thermally conductive layer (5) is prepared from any one of boron nitride, beryllium oxide, and aluminum nitride.