Device and method for growing silicon carbide crystals by top seed crystal method

Abstract

The invention belongs to the technical field of crystal growth, and relates to a device for growing silicon carbide crystals by a top seed crystal method and a growth method.The device comprises a graphite crucible, a first resistance heater, a second resistance heater, a third resistance heater and an induction coil, and the induction coil is used for heating and preserving heat of a whole heat preservation bin; the first resistance heater and the second resistance heater are arranged on the lower side of the circular outer bottom surface of the graphite crucible and share the same rotating shaft with the outer bottom surface of the graphite crucible; the third resistance heater is arranged on the upper side of the crucible cover and is parallel to the upper surface of the crucible cover; different resistance heaters and induction coils are arranged at different positions for common heating, the radial temperature gradient and the axial temperature gradient of the melt are adjusted, the situations of solution wrapping and spontaneous nucleation are reduced, the carbon dissolution rate, the carbon transportation rate and the growth rate of carbon and silicon on seed crystals are balanced, and the growth rate of carbon and silicon on the seed crystals is increased. The crystal growth rate is increased; and the crystal quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of crystal growth, and in particular relates to a device and a growth method for growing silicon carbide crystals using a top seed crystal method. Background Art

[0002] As a third-generation semiconductor, silicon carbide has the characteristics of wide bandgap, high breakdown electric field strength, good thermal stability and high conductivity. It has been widely used in important fields such as power electronics, 5G communications, and new energy. Due to its excellent physical and electrical properties, silicon carbide substrates have become an indispensable material for energy-saving applications at the electronic equipment and system levels. They are widely used in the manufacture of high-temperature, high-frequency, high-power, radiation-resistant, short-wavelength luminescent and optoelectronic integrated devices. Since the top seeding method for growing silicon carbide crystals is closer to thermodynamic equilibrium conditions, it can theoretically reduce the defect density and grow large-sized, high-quality silicon carbide crystals. The basic principle of the top seeding method for growing silicon carbide crystals is that solute carbon dissolves in a melt composed of silicon and co-solvents in a high-temperature environment. Driven by the temperature gradient, the solute carbon reaches the growth interface and forms supersaturation, and finally precipitates on the seed crystal to achieve the growth of silicon carbide crystals. In the process of growing silicon carbide crystals by the top seeding method, it is necessary to keep the dissolution rate of carbon at the interface between the graphite crucible wall and the auxiliary solution, the transport rate of the dissolved carbon at the interface between the graphite crucible wall and the auxiliary solution to the silicon carbide seed crystal growth interface, and the growth rate of silicon carbide at the silicon carbide seed crystal growth interface equal as much as possible. When this equilibrium state is maintained, increasing the temperature can increase the dissolution rate of carbon, thereby increasing the crystal growth rate, and lowering the temperature will lead to a decrease in the crystal growth rate.

[0003] However, it is difficult for the existing top seed method to maintain this equilibrium state in the existing silicon carbide crystal growth furnace. When this equilibrium state is destroyed, increasing the temperature will cause the carbon dissolution rate to be too fast, which may increase the spontaneous nucleation in the melt. Lowering the temperature will cause the carbon dissolution rate to be too slow, which may cause solution encapsulation. Most of the top seed method silicon carbide crystal growth furnaces use induction heating. When producing large-sized silicon carbide crystals, the increase in the diameter of the crucible will produce a large radial temperature difference inside the melt, which will lead to poor quality of the grown silicon carbide crystals. Therefore, the silicon carbide crystals grown by the top seed method used in the market are generally small in size.

[0004] Therefore, in order to better balance the relationship between the crystal growth rate and the quality of silicon carbide crystals, it is urgent to propose a silicon carbide crystal growth method or device to solve the above technical problems. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a device for growing silicon carbide crystals by a top seeding method, comprising: a graphite crucible, a first resistance heater, a second resistance heater, a third resistance heater, and an induction coil, wherein the graphite crucible is in the shape of a cylindrical trough with an opening upward, the graphite crucible is surrounded by a heat preservation chamber, the induction coil is surrounded by the heat preservation chamber, and the induction coil is used to heat and preserve the entire heat preservation chamber;

[0006] The top opening of the graphite crucible is covered with a crucible cover, and the crucible cover is provided with a cover hole which is connected to the inside and outside of the graphite crucible from top to bottom, and the cover hole is used to pull out the seed crystal rod;

[0007] The first resistance heater and the second resistance heater are arranged on the lower side of the circular outer bottom surface of the graphite crucible, the first resistance heater is in the shape of a disk, and the second resistance heater is in the shape of a ring. The disk heating surface of the first resistance heater and the ring heating surface of the second resistance heater are parallel to the outer bottom surface of the graphite crucible, and the first resistance heater, the second resistance heater and the outer bottom surface of the graphite crucible have the same rotation axis;

[0008] The third resistance heater is arranged on the upper side of the crucible cover, the third resistance heater is annular, the annular inner hole of the third resistance heater is not smaller than the cover hole, and the heating annular surface of the third resistance heater is parallel to the upper surface of the crucible cover.

[0009] Preferably, a disc-shaped crucible tray is provided at the bottom of the graphite crucible, a crucible support rod is provided at the bottom of the crucible tray, the crucible support rod, the crucible tray and the graphite crucible have the same rotating axis, the crucible support rod is torque-connected with a rotating mechanism, and the rotating mechanism drives the graphite crucible to rotate around the central axis of the graphite crucible through the crucible support rod and the crucible tray.

[0010] Preferably, temperature monitoring devices are arranged inside the melt at intervals of 1-10 mm along a direction parallel to the bottom of the graphite crucible and 1-30 mm away from the bottom of the graphite crucible, temperature monitoring devices are arranged at intervals of 1-10 mm along a direction parallel to the top liquid level of the melt and 1-30 mm away from the top liquid level, temperature monitoring devices are arranged at intervals of 1-10 mm along a direction parallel to the side wall of the graphite crucible and 1-30 mm away from the side wall of the graphite crucible, and temperature monitoring devices are arranged in the melt at intervals of 1-10 mm along the central axis from the seed crystal to the bottom of the graphite crucible.

[0011] Preferably, the insulation bin is cylindrical, and the wall thickness of the insulation bin surrounding the graphite crucible is uniform; a bin opening is provided on the top of the insulation bin for the seed crystal rod to enter and exit, and the bin opening is opposite to the cover hole.

[0012] The present invention also discloses a method for growing silicon carbide crystals using a top seeding method. The method is used in the device for growing silicon carbide crystals using the top seeding method, and comprises the following steps:

[0013] S1, adding silicon and solvent raw materials into a graphite crucible;

[0014] S2, the top seed crystal method silicon carbide crystal growth furnace is evacuated to a vacuum state, so that the pressure inside the top seed crystal method silicon carbide crystal growth furnace is less than 1×10 —4 Pa;

[0015] S3, turning on the induction coil to heat the graphite crucible, so that the temperature of the silicon and the solvent raw materials is heated to 800° C.-1000° C.;

[0016] S4, introducing inert gas to make the internal pressure of the graphite crucible at 0.5atm-1.0atm;

[0017] S5, turning on the first resistance heater, the second resistance heater and the third resistance heater, adjusting the power of the induction coil, so that the silicon and the solvent raw materials are melted to form a melt, and heating the temperature of the melt to 1800° C.-2000° C.;

[0018] S6, the seed crystal rod controls the seed crystal to descend at a speed of 20-60 mm / h until the seed crystal is 40 mm-45 mm away from the melt surface;

[0019] S7, the seed crystal rod controls the seed crystal to descend at a speed of 15-25mm / h, and finally the seed crystal is 1mm-5mm away from the melt surface, so that the seed crystal rod drives the seed crystal to rotate, the seed crystal speed is 0-30rpm, the crucible support rod and the crucible tray drive the crucible to rotate, the crucible speed is 0-10rpm, and the seed crystal rotates in the opposite direction to the crucible, stops lifting, and stays for 0.5h-1.5h;

[0020] S8, the seed crystal rod controls the seed crystal to descend at a speed of 10-15 mm / h, so that the seed crystal is immersed in the graphite crucible at 0.1 mm-1 mm from the melt surface, and stays for 1 h-2 h;

[0021] S9, the seed crystal rod controls the seed crystal to rise at a speed of 10-15mm / h, and stops rising after reaching 0.1mm-1mm above the melt surface, and the crystal growth time is 30-80h;

[0022] S10, after the growth is completed, the seed crystal rod is controlled to pull the crystal out of the melt at a speed of 15-25 mm / h, and the rotation of the seed crystal and the crucible is stopped;

[0023] S11, pulling the crystal at a speed of 20-60 mm / h to a height of 40 mm-45 mm above the melt level;

[0024] S12. Slowly cool the temperature of the monitoring point to room temperature at a cooling rate of 1-4°C / min to complete the growth of silicon carbide crystals.

[0025] Preferably, in step S1, silicon and solvent include: Si, Cr, Al, wherein the molar fractions of Si, Cr, and Al are 65%, 35%, and 5%, respectively.

[0026] Preferably, in step S9, the height of the induction coil is moved downward during the crystal growth process so that the moving distance of the induction coil is equal to the descending distance of the melt level.

[0027] Preferably, in step S4, the inert gas includes: argon and helium.

[0028] Preferably, in step S7, the residence time after stopping the lifting is 1 hour.

[0029] The beneficial effects of the present invention are:

[0030] The present invention adopts a method of arranging different resistance heaters and induction coils at different positions for joint heating. The third resistance heater is used to heat the upper surface of the melt, and the radial temperature of the upper surface of the melt and the axial temperature gradient in the melt are adjusted, so as to reduce the occurrence of solution wrapping and spontaneous nucleation. The arrangement of the first resistance heater and the second resistance heater can increase the axial temperature gradient of the melt, increase the transport rate of the carbon solute, and thus increase the crystal growth rate. At the same time, the arrangement of the first resistance heater and the second resistance heater can adjust the radial temperature gradient of the melt, thereby improving the crystal quality, and at the same time can meet the growth of large-size crystals by the top seed method. The temperature of the first resistance heater is always higher than that of the second resistance heater. Through the arrangement of the first resistance heater, the second resistance heater, the third resistance heater and the induction coil, an upward driving force is induced in the melt and in the central area at the bottom of the graphite crucible. After adding the resistance heater, the height of the induction coil is adjusted to prevent the carbon below the melt from dissolving too quickly, thereby causing an imbalance in the carbon dissolution, carbon transport, and the growth rate of carbon and silicon on the seed crystal.

[0031] Therefore, the present invention can better dynamically balance the relationship between the crystal growth rate and the quality of the silicon carbide crystal, and improve the growth quality of the silicon carbide crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a general structural diagram of a device and a growth method for growing silicon carbide crystals using a top seed crystal method.

[0033] In the figure, 1, graphite crucible; 2, first resistance heater; 3, second resistance heater; 4, third resistance heater; 5, induction coil; 6, insulation chamber; 7, crucible cover; 8, cover hole; 9, seed crystal rod; 10, melt; 11, seed crystal; 12, crucible tray; 13, crucible support rod; 14, chamber opening. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] like Figure 1 As shown, the device for growing silicon carbide crystals by the top seeding method of this embodiment includes: a graphite crucible 1, a first resistance heater 2, a second resistance heater 3, a third resistance heater 4, and an induction coil 5. The graphite crucible 1 is in the shape of a cylindrical trough with an opening upward, and the graphite crucible 1 is surrounded by a heat preservation chamber 6. The induction coil 5 surrounds the heat preservation chamber 6, and the induction coil 5 is used to heat and keep the entire heat preservation chamber 6 warm; the side of the melt 10 is heated by the induction coil 5;

[0036] The top opening of the graphite crucible 1 is covered with a crucible cover 7, and the crucible cover 7 is provided with a cover hole 8 which is connected to the inside and outside of the graphite crucible 1 from top to bottom, and the cover hole 8 is used to pull the seed crystal rod 9;

[0037] The first resistance heater 2 and the second resistance heater 3 are arranged on the lower side of the circular outer bottom surface of the graphite crucible 1. The first resistance heater 2 is in the shape of a disk, and the second resistance heater 3 is in the shape of a ring. The disk heating surface of the first resistance heater 2 and the ring heating surface of the second resistance heater 3 are parallel to the outer bottom surface of the graphite crucible 1, and the first resistance heater 2 and the second resistance heater 3 have the same rotation axis as the outer bottom surface of the graphite crucible 1; the first resistance heater 2 and the second resistance heater 3 heat the lower surface of the melt 10. Since the first resistance heater 2, the second resistance heater 3 and the center of the graphite crucible 1 are located on the same central axis, and the first resistance heater 2 is flush with the second resistance heater 3, the axial temperature gradient of the melt 10 can be increased, the transport rate of the carbon solute can be increased, and the crystal growth rate can be increased; the temperature of the first resistance heater 2 is always 20-50K higher than that of the second resistance heater 3. Through the arrangement of the first resistance heater 2, the second resistance heater 3, the third resistance heater 4 and the induction coil 5, an upward driving force is induced in the melt 10 and in the central area at the bottom of the graphite crucible 1;

[0038] The third resistance heater 4 is arranged on the upper side of the crucible cover 7. The third resistance heater 4 is in a circular ring shape. The annular inner hole of the third resistance heater 4 is not smaller than the cover hole 8. The heating annular surface of the third resistance heater 4 is parallel to the upper surface of the crucible cover 7. The third resistance heater 4 is used to heat the upper surface of the melt 10, adjust the radial temperature of the upper surface of the melt 10 and the axial temperature gradient in the melt 10, so as to reduce the occurrence of solution wrapping and spontaneous nucleation.

[0039] When silicon carbide crystals grow, the graphite crucible 1 is filled with melt 10, the seed crystal rod 9 extends into the graphite crucible 1 from top to bottom, the lower end of the seed crystal rod 9 is at the upper surface of the melt 10, the seed crystal 11 is adhered to the lower end of the seed crystal rod 9, and then the seed crystal rod 9 is extended into the crucible, the seed crystal 11 contacts the melt 10, and the silicon carbide crystal grows on the seed crystal 11.

[0040] Furthermore, a disc-shaped crucible tray 12 is provided at the bottom of the graphite crucible 1, and a crucible support rod 13 is provided at the bottom of the crucible tray 12. The crucible support rod 13, the crucible tray 12, and the graphite crucible 1 have the same rotation axis. The crucible support rod 13 is torque-connected with a rotating mechanism, and the rotating mechanism drives the graphite crucible 1 to rotate around the central axis of the graphite crucible 1 through the crucible support rod 13 and the crucible tray 12; the seed crystal rod 9 can also be set to be rotatable, and the rotation direction of the seed crystal rod 9 and the crucible is still opposite.

[0041] Further, temperature monitoring points are arranged at intervals of 1-10 mm inside the melt 10 in a direction parallel to the bottom of the graphite crucible 1 and 1-30 mm away from the bottom of the graphite crucible 1; temperature monitoring points are arranged at intervals of 1-10 mm in a direction parallel to the top liquid surface of the melt 10 and 1-30 mm away from the top liquid surface; temperature monitoring points are arranged at intervals of 1-10 mm in a direction parallel to the side wall of the graphite crucible 1 and 1-30 mm away from the side wall of the graphite crucible 1; and temperature monitoring points are arranged at intervals of 1-10 mm along the central axis from the seed crystal 11 to the bottom of the graphite crucible 1 in the melt 10;

[0042] Exemplarily, temperature monitoring points are set at intervals of 5 mm along the central axis from the seed crystal 11 to the bottom of the graphite crucible 1 in the melt 10, temperature monitoring points are set at intervals of 5 mm inside the melt 10 in a direction parallel to the bottom of the graphite crucible 1 and 10 mm away from the bottom of the graphite crucible 1, temperature monitoring points are set at intervals of 5 mm in a direction parallel to the top liquid level of the melt 10 and 10 mm away from the top liquid level, and temperature monitoring points are set at intervals of 5 mm in a direction parallel to the side wall of the graphite crucible 1 and 10 mm away from the side wall of the graphite crucible 1.

[0043] Furthermore, the insulation chamber 6 is cylindrical, and the wall thickness of the insulation chamber 6 surrounding the graphite crucible 1 is uniform; a chamber opening 14 is provided on the top of the insulation chamber 6 for the seed crystal rod 9 to enter and exit, and the chamber opening 14 is opposite to the cover hole 8.

[0044] The present invention also discloses a method for growing silicon carbide crystals using a top seeding method. The method is used in the device for growing silicon carbide crystals using the top seeding method, and comprises the following steps:

[0045] S1, adding silicon and solvent raw materials into a graphite crucible;

[0046] S2, the top seed crystal method silicon carbide crystal growth furnace is evacuated to a vacuum state, so that the pressure inside the top seed crystal method silicon carbide crystal growth furnace is less than 1×10 —4 Pa;

[0047] S3, turning on the induction coil to heat the graphite crucible, so that the temperature of the silicon and the solvent raw materials is heated to 800° C.-1000° C.;

[0048] S4, introducing inert gas to make the internal pressure of the graphite crucible at 0.5atm-1.0atm;

[0049] S5, turning on the first resistance heater, the second resistance heater and the third resistance heater, adjusting the power of the induction coil, so that the silicon and the solvent raw materials are melted to form a melt, and heating the temperature of the melt to 1800° C.-2000° C.;

[0050] S6, the seed crystal rod controls the seed crystal to descend at a speed of 20-60 mm / h until the seed crystal is 40 mm-45 mm away from the melt surface;

[0051] S7, the seed crystal rod controls the seed crystal to descend at a speed of 15-25mm / h, and finally the seed crystal is 1mm-5mm away from the melt surface, so that the seed crystal rod drives the seed crystal to rotate, the seed crystal speed is 0-30rpm, the crucible support rod and the crucible tray drive the crucible to rotate, the crucible speed is 0-10rpm, and the seed crystal rotates in the opposite direction to the crucible, stops lifting, and stays for 0.5h-1.5h;

[0052] S8, the seed crystal rod controls the seed crystal to descend at a speed of 10-15 mm / h, so that the seed crystal is immersed in the graphite crucible at 0.1 mm-1 mm from the melt surface, and stays for 1 h-2 h;

[0053] S9, the seed crystal rod controls the seed crystal to rise at a speed of 10-15mm / h, and stops rising after reaching 0.1mm-1mm above the melt surface, and the crystal growth time is 30-80h;

[0054] S10, after the growth is completed, the seed crystal rod is controlled to pull the crystal out of the melt at a speed of 15-25 mm / h, and the rotation of the seed crystal and the crucible is stopped;

[0055] S11, pulling the crystal at a speed of 20-60 mm / h to a height of 40 mm-45 mm above the melt level;

[0056] S12. Slowly cool the temperature of the monitoring point to room temperature at a cooling rate of 1-4°C / min to complete the growth of silicon carbide crystals.

[0057] Furthermore, in step S1, silicon and solvent include: Si, Cr, Al, wherein the molar fractions of Si, Cr, and Al are 65%, 35%, and 5%, respectively.

[0058] Furthermore, in step S9, the height of the induction coil is moved downward during the crystal growth process so that the moving distance of the induction coil is equal to the distance the melt level drops.

[0059] Furthermore, in step S4, the inert gas includes argon and helium.

[0060] Furthermore, in step S7, the dwell time after stopping the lifting is 1 hour.

[0061] Example

[0062] This embodiment uses the first resistance heater 2, the second resistance heater 3, the third resistance heater 4 and the induction coil 5 for joint heating.

[0063] The third resistance heater 4 is used to heat the upper surface of the melt 10 to adjust the radial temperature of the upper surface of the melt 10 and the axial temperature gradient in the melt 10, thereby reducing the occurrence of solution wrapping and spontaneous nucleation.

[0064] A first resistance heater 2 and a second resistance heater 3 are arranged below the graphite crucible 1. The first resistance heater 2 and the second resistance heater 3 heat the lower surface of the melt 10. The second resistance heater 3 is in the shape of a ring, the first resistance heater 2 is in the shape of a circle, the center of the first resistance heater 2 and the center of the crucible are located on the same central axis, and the first resistance heater 2 is flush with the second resistance heater 3. The arrangement of the first resistance heater 2 and the second resistance heater 3 can increase the axial temperature gradient of the melt 10, increase the transport rate of the carbon solute, and thus improve the crystal growth rate.

[0065] An annular induction coil 5 is arranged on the side of the graphite crucible 1 , and the side of the melt 10 is heated by the induction coil 5 .

[0066] The temperature of the first resistance heater 2 is always 20-50K higher than the temperature of the second resistance heater 3. Exemplarily, the temperature of the first resistance heater 2 is always 30K higher than the temperature of the second resistance heater 3. Through the arrangement of the first resistance heater 2, the second resistance heater 3, the third resistance heater 4 and the induction coil 5, an upward driving force is induced in the melt and in the central area of ​​the bottom of the graphite crucible.

[0067] Further, temperature monitoring points are arranged at intervals of 1-10 mm inside the melt 10 in a direction parallel to the bottom of the graphite crucible 1 and 1-30 mm away from the bottom of the graphite crucible 1; temperature monitoring points are arranged at intervals of 1-10 mm in a direction parallel to the top liquid surface of the melt 10 and 1-30 mm away from the top liquid surface; temperature monitoring points are arranged at intervals of 1-10 mm in a direction parallel to the side wall of the graphite crucible 1 and 1-30 mm away from the side wall of the graphite crucible 1; and temperature monitoring points are arranged at intervals of 1-10 mm along the central axis from the seed crystal 11 to the bottom of the graphite crucible 1 in the melt 10;

[0068] Exemplarily, temperature monitoring points are set at intervals of 5 mm along the central axis from the seed crystal 11 to the bottom of the graphite crucible 1 in the melt 10, temperature monitoring points are set at intervals of 5 mm inside the melt 10 in a direction parallel to the bottom of the graphite crucible 1 and 10 mm away from the bottom of the graphite crucible 1, temperature monitoring points are set at intervals of 5 mm in a direction parallel to the top liquid level of the melt 10 and 10 mm away from the top liquid level, and temperature monitoring points are set at intervals of 5 mm in a direction parallel to the side wall of the graphite crucible 1 and 10 mm away from the side wall of the graphite crucible 1.

[0069] The main heating devices are the first resistance heater 2 , the second resistance heater 3 and the induction coil 5 , so the heating power ratio of the first resistance heater 2 , the second resistance heater 3 and the induction coil 5 is adjusted first.

[0070] The first step: start the induction coil 5 and adjust the power of the induction coil 5 so that the temperature of the temperature monitoring point 5 mm from the seed crystal 11 to the bottom of the graphite crucible 1 along the central axis in the melt 10 is maintained at 1950-2000 degrees Celsius.

[0071] Step 2: Reduce the power of the induction coil by 5-10% in sequence, start the first resistance heater 2 and the second resistance heater 3 and increase the power of the first resistance heater 2 and the second resistance heater 3 in sequence, observe the temperature of the monitoring points, so that the temperature of the melt 10 in the graphite crucible 1 is maintained at 1800-2000 degrees Celsius at the temperature monitoring points set at 5mm intervals at 10mm from the top liquid surface in the direction parallel to the top liquid surface of the melt 10, and the temperature of the melt 10 in the graphite crucible 1 is maintained at 1800-2000 degrees Celsius at the temperature monitoring points set at 5mm intervals at 10mm from the side wall of the graphite crucible 1 in the direction parallel to the side wall of the graphite crucible 1 The control process is stopped when the temperature of the melt 10 in the graphite crucible 1 is 2050 degrees Celsius and is greater than the temperature of the temperature monitoring points arranged at 5 mm intervals at 10 mm away from the top liquid surface in a direction parallel to the top liquid surface of the melt 10. When the temperatures of the temperature monitoring points arranged at 5 mm intervals at 10 mm away from the bottom of the graphite crucible 1 and parallel to the bottom of the graphite crucible 1 are all greater than the temperatures of the temperature monitoring points arranged at 5 mm intervals at 10 mm away from the side wall of the graphite crucible 1 in the graphite crucible 1. It is preliminarily determined to be the power of the first resistance heater 2, the second resistance heater 3 and the induction coil 5.

[0072] Step 3: Using the above-preliminarily determined powers of the first resistance heater 2, the second resistance heater 3 and the induction coil 5, the powers of the induction coil are reduced or increased by 1-2% in sequence, and the powers of the first resistance heater 2 and the second resistance heater 3 are increased or decreased in sequence, so that the temperature of the melt 10 in the graphite crucible 1 is maintained at 1800-2000 degrees Celsius at the temperature monitoring points arranged at intervals of 5 mm at a distance of 10 mm from the top liquid surface in a direction parallel to the top liquid surface of the melt 10, and the temperature of the melt 10 in the graphite crucible 1 is maintained at 1800-2000 degrees Celsius at the temperature monitoring points arranged at intervals of 5 mm at a distance of 10 mm from the side wall of the graphite crucible 1 in a direction parallel to the side wall of the graphite crucible 1 When the temperature of the temperature monitoring points arranged every 5 mm at a distance of 10 mm from the top liquid surface of the melt 10 in the graphite crucible 1 is 0-2050 degrees Celsius and is greater than the temperature of the temperature monitoring points arranged every 5 mm at a distance of 10 mm from the top liquid surface in a direction parallel to the top liquid surface of the melt 10 in the graphite crucible 1; when the temperature of the temperature monitoring points arranged every 5 mm at a distance of 10 mm from the bottom of the graphite crucible 1 and parallel to the bottom of the graphite crucible 1 in the melt 10 are all greater than the temperature of the temperature monitoring points arranged every 5 mm at a distance of 10 mm from the side wall of the graphite crucible 1 in the graphite crucible 1 along the direction parallel to the side wall of the graphite crucible 1 by 20-40 degrees Celsius, the final power of the first resistance heater 2, the second resistance heater 3 and the induction coil 5 is determined.

[0073] The final power of the first resistance heater 2, the second resistance heater 3 and the induction coil 5 is adopted. The heat generated by the induction coil 5 on the crucible is high in the middle and low on both sides, so the height of the induction coil 5 can be adjusted to adjust the melt temperature field, flow field, and thus regulate the crystal growth rate and quality.

[0074] The center of the induction coil 5 is aligned with the center of the melt 10, and the induction coil 5 is moved axially by 1-2 mm in sequence, so that the center of the induction coil 5 does not exceed the liquid level of the melt 10. The above scheme is adopted to carry out a silicon carbide crystal growth experiment. After the crystal growth is completed, the melt is cooled. When there is no obvious floating crystal on the surface morphology of the cooled melt, this height is determined to be the induction coil height.

[0075] The third resistance heater 4 has a relatively small power, and is mainly used to adjust the radial temperature of the melt 10 near the liquid surface and the solubility of the melt 10 near the liquid surface to prevent the generation of polycrystals. After the heating power ratio of the first resistance heater 2, the second resistance heater 3 and the induction coil 5 is adjusted, the radial temperature of the melt 10 near the liquid surface and the solubility of the melt 10 near the liquid surface are adjusted by changing the power of the third resistance heater 4 to prevent the generation of polycrystals.

[0076] When adjusting the power of the third resistance heater 4, keep the power of the first resistance heater 2, the second resistance heater 3 and the induction coil 5 unchanged, turn on the third resistance heater 4, and increase the power of the third resistance heater in sequence, first give a first gradient (for example, 500-1000w), keep the melt surface temperature at 1800-2000 degrees Celsius, when the first gradient is changed and the temperature radial temperature gradient change rate is less than 8-15%, then give a second gradient (for example, 50-100w) (the first gradient is greater than the second gradient), keep the melt surface temperature at 1800-2000 degrees Celsius, when the second gradient is changed and the temperature radial temperature gradient change rate is less than 1-3%, it is determined as the target power, and ensure that the axial temperature gradient change rate of the melt center is less than 10%.

[0077] Growth method / steps:

[0078] Add silicon and solvent (Si, Cr, Al with molar fractions of 65%, 35%, 5% respectively) into a graphite crucible;

[0079] The top seed method silicon carbide crystal growth furnace is evacuated to a vacuum state, so that the pressure inside the top seed method silicon carbide crystal growth furnace is less than 1×10 —4 Pa;

[0080] Turn on the induction coil to heat the graphite crucible so that the temperature of silicon and solvent raw materials is heated to 800°C-1000°C;

[0081] Introduce an inert gas (such as argon) to make the internal pressure of the graphite crucible be 0.5atm-1.0atm;

[0082] Turning on the first resistance heater, the second resistance heater and the third resistance heater at a predetermined power, and adjusting the induction coil to a predetermined power, so that the silicon and the solvent raw materials are melted to form a melt, and the temperature of the melt is heated to 1800° C.-2000° C.;

[0083] The seed crystal rod controls the seed crystal to descend at a speed of 20-60 mm / h until the seed crystal is 40 mm-45 mm away from the melt surface;

[0084] The seed crystal rod controls the seed crystal to descend at a speed of 15-25mm / h, and finally the seed crystal is 1mm-5mm away from the melt surface. The seed crystal rod is set to drive the seed crystal to rotate, and the seed crystal speed is 0-30rpm. The crucible support structure drives the crucible to rotate, and the crucible speed is 0-10rpm. The seed crystal rotates in the opposite direction to the crucible, and the lifting and lowering are stopped and stayed for 1h.

[0085] The seed crystal rod controls the seed crystal to descend at a speed of 10-15 mm / h, so that the seed crystal is immersed in the melt liquid surface in the graphite crucible at 0.1 mm-1 mm and stays for 1h-2h.

[0086] The seed crystal rod controls the seed crystal to rise at a speed of 10-15mm / h, and stops rising when it is 0.1mm-1mm above the melt surface. The crystal growth time is 30-80h. During this process, the height of the induction coil is moved downward so that the moving distance of the induction coil is equal to the distance the melt surface drops.

[0087] After the growth is completed, the seed crystal rod is controlled to pull the crystal out of the melt at a speed of 15-25 mm / h, and the rotation of the seed crystal and the crucible is stopped;

[0088] The crystal is pulled up at a speed of 20-60 mm / h to a height of 40 mm-45 mm above the melt level;

[0089] The temperature of the monitoring point is slowly cooled to room temperature at a cooling rate of 1-4°C / min to complete the growth of silicon carbide crystals.

[0090] In summary, the present invention adopts a method of co-heating by arranging different resistance heaters and induction coils at different positions. The third resistance heater is used to heat the upper surface of the melt, and the radial temperature of the upper surface of the melt and the axial temperature gradient in the melt are adjusted, thereby reducing the occurrence of solution wrapping and spontaneous nucleation. The setting of the first resistance heater and the second resistance heater can increase the axial temperature gradient of the melt, increase the transport rate of carbon solute, and thus increase the crystal growth rate. The setting of the first resistance heater and the second resistance heater can both adjust the radial temperature gradient of the melt, improve the crystal quality, and at the same time meet the growth of large-size crystals by the top seeding method, so the present invention has broad application prospects.

[0091] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A device for growing silicon carbide crystals by a top seeding method, characterized in that: include: A graphite crucible (1), a first resistance heater (2), a second resistance heater (3), a third resistance heater (4), and an induction coil (5); the graphite crucible (1) is in the shape of a cylindrical trough with an opening facing upward; a heat preservation chamber (6) surrounds the periphery of the graphite crucible (1); the induction coil (5) surrounds the periphery of the heat preservation chamber (6); and the induction coil (5) is used to heat and preserve the entire heat preservation chamber (6); The top opening of the graphite crucible (1) is covered with a crucible cover (7), and the crucible cover (7) is provided with a cover hole (8) which is connected to the inside and outside of the graphite crucible (1) from top to bottom, and the cover hole (8) is used to pull out the seed crystal rod (9); The first resistance heater (2) and the second resistance heater (3) are arranged on the lower side of the circular outer bottom surface of the graphite crucible (1); the first resistance heater (2) is in the shape of a disk, and the second resistance heater (3) is in the shape of a ring; the disk heating surface of the first resistance heater (2) and the ring heating surface of the second resistance heater (3) are both parallel to the outer bottom surface of the graphite crucible (1); the first resistance heater (2) and the second resistance heater (3) rotate on the same axis as the outer bottom surface of the graphite crucible (1); The third resistance heater (4) is arranged on the upper surface of the crucible cover (7), the third resistance heater (4) is in the shape of a ring, the annular inner hole of the third resistance heater (4) is not smaller than the cover hole (8), and the heating annular surface of the third resistance heater (4) is parallel to the upper surface of the crucible cover (7).

2. The device for growing silicon carbide crystals by top seeding method according to claim 1, characterized in that: A disc-shaped crucible tray (12) is provided at the bottom of the graphite crucible (1), and a crucible support rod (13) is provided at the bottom of the crucible tray (12). The crucible support rod (13), the crucible tray (12), and the graphite crucible (1) have the same rotation axis, and the crucible support rod (13) is torque-connected to a rotating mechanism, and the rotating mechanism drives the graphite crucible (1) to rotate around the central axis of the graphite crucible (1) through the crucible support rod (13) and the crucible tray (12).

3. The device for growing silicon carbide crystals by top seeding method according to claim 1, characterized in that: Temperature monitoring devices are arranged inside the melt (10) at intervals of 1-10 mm along a direction parallel to the bottom of the graphite crucible (1) and 1-30 mm away from the bottom of the graphite crucible (1); temperature monitoring devices are arranged in the melt (10) in the graphite crucible (1) at intervals of 1-10 mm along a direction parallel to the top liquid surface of the melt (10) and 1-30 mm away from the top liquid surface; temperature monitoring devices are arranged in the melt (10) in the graphite crucible (1) at intervals of 1-10 mm along a direction parallel to the side wall of the graphite crucible (1) and 1-30 mm away from the side wall of the graphite crucible (1); and temperature monitoring devices are arranged in the melt (10) at intervals of 1-10 mm along the central axis from the seed crystal (11) to the bottom of the graphite crucible (1).

4. The device for growing silicon carbide crystals by top seeding method according to claim 1, characterized in that: The heat preservation chamber (6) is cylindrical, and the wall thickness of the heat preservation chamber (6) surrounding the graphite crucible (1) is uniform; a chamber opening (14) is provided on the top of the heat preservation chamber (6) for the seed crystal rod (9) to enter and exit, and the chamber opening (14) is directly opposite to the cover hole (8).

5. A method for growing silicon carbide crystals by top seeding, characterized in that: The growth method is used in the device for growing silicon carbide crystals by the top seed method according to any one of claims 1 to 4, and the method comprises the following steps: S1, adding silicon and solvent raw materials into a graphite crucible; S2, the top seed crystal method silicon carbide crystal growth furnace is evacuated to a vacuum state, so that the pressure inside the top seed crystal method silicon carbide crystal growth furnace is less than 1×10 —4 Pa; S3, turning on the induction coil to heat the graphite crucible, so that the temperature of the silicon and the solvent raw materials is heated to 800° C.-1000° C.; S4, introducing inert gas to make the internal pressure of the graphite crucible at 0.5atm-1.0atm; S5, turning on the first resistance heater, the second resistance heater and the third resistance heater, adjusting the power of the induction coil, so that the silicon and the solvent raw materials are melted to form a melt, and heating the temperature of the melt to 1800° C.-2000° C.; S6, the seed crystal rod controls the seed crystal to descend at a speed of 20-60 mm / h until the seed crystal is 40 mm-45 mm away from the melt surface; S7, the seed crystal rod controls the seed crystal to descend at a speed of 15-25mm / h, and finally the seed crystal is 1mm-5mm away from the melt surface, so that the seed crystal rod drives the seed crystal to rotate, the seed crystal speed is 0-30rpm, the crucible support rod and the crucible tray drive the crucible to rotate, the crucible speed is 0-10rpm, and the seed crystal rotates in the opposite direction to the crucible, stops lifting, and stays for 0.5h-1.5h; S8, the seed crystal rod controls the seed crystal to descend at a speed of 10-15 mm / h, so that the seed crystal is immersed in the graphite crucible at 0.1 mm-1 mm from the melt surface, and stays for 1 h-2 h; S9, the seed crystal rod controls the seed crystal to rise at a speed of 10-15 mm / h, and stops rising after reaching 0.1 mm-1 mm above the melt surface, and the crystal growth time is 30-80 hours; S10, after the growth is completed, the seed crystal rod is controlled to pull the crystal out of the melt at a speed of 15-25 mm / h, and the rotation of the seed crystal and the crucible is stopped; S11, pulling the crystal at a speed of 20-60 mm / h to a height of 40 mm-45 mm above the melt level; S12. Slowly cool the temperature of the monitoring point to room temperature at a cooling rate of 1-4°C / min to complete the growth of silicon carbide crystals.

6. The method for growing silicon carbide crystals by top seeding method according to claim 5, characterized in that: In the step S1, the silicon and the solvent include: Si, Cr, and Al, wherein the molar fractions of Si, Cr, and Al are 65%, 35%, and 5%, respectively.

7. The method for growing silicon carbide crystals by top seeding method according to claim 5, characterized in that: In the step S9, the height of the induction coil is moved downward during the crystal growth process so that the moving distance of the induction coil is equal to the falling distance of the melt level.

8. The method for growing silicon carbide crystals by top seeding method according to claim 5, characterized in that: In step S4, the inert gas includes argon and helium.

9. The method for growing silicon carbide crystals by top seeding method according to claim 5, characterized in that: In step S7, the dwell time after stopping the lifting is 1 hour.

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