A method for growing a large-size low-defect silicon carbide single crystal

Abstract

This invention provides a method for growing large-size, low-defect silicon carbide single crystals, belonging to the field of silicon carbide single crystal preparation technology. The method utilizes a large-size, low-defect silicon carbide single crystal growth apparatus, using silicon carbide powder as raw material, and performs a first-stage crystal growth based on the PVT method in the presence of an N-type dopant to obtain an ingot. Then, using a mixture of silicon powder, carbon powder, chromium powder, and a P-type dopant as raw material, and using the ingot as a seed crystal, a second-stage crystal growth is performed based on the LPE method to obtain a large-size, low-defect silicon carbide single crystal. The method provided by this invention can grow large-size, low-defect silicon carbide single crystals, and different types of doping can be achieved on the same silicon carbide single crystal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide single crystal preparation, and particularly relates to a growth method of large-size low-defect silicon carbide single crystal. BACKGROUND

[0002] The third generation semiconductor material represented by SiC has the characteristics of wide band gap, high critical breakdown electric field, high thermal conductivity, high carrier saturation drift speed, and has broad application prospects in high temperature, high frequency, high power, optoelectronics and radiation resistance. At present, the modified Lely method, that is, the physical vapor transport (PVT) method, is mostly used to grow large-size SiC crystals. Specifically, the SiC solid powder at the lower part of the reaction chamber under high temperature is sublimated to obtain non-stoichiometric SiC gas, the seed crystal is adhered to the upper part of the chamber, and the designed reaction chamber has a certain temperature gradient. The SiC gas that meets the conditions will be deposited on the surface of the seed crystal. Although the PVT method has the advantages of fast growth rate, relatively simple process conditions and equipment, the process stability and crystal quality are difficult to guarantee. For example, the SiC seed crystal is adhered to the graphite cover by glue, and due to the uneven distribution of the glue, a local temperature gradient is easily formed, thereby forming a hexagonal cavity in the local area, which deteriorates the crystal quality. Moreover, during the sublimation process of the SiC solid powder, carbon and silicon do not follow the stoichiometric ratio, and the atmosphere is easy to be rich in carbon in the later crystal growth period, thereby forming crystal defects such as carbon inclusions, microtubes and polytypes, which leads to the decrease of the crystal quality. In addition, the conventional PVT method cannot grow P-type and N-type semiconductors on the same crystal. m C n m C n Although the PVT method has the advantages of fast growth rate, relatively simple process conditions and equipment, the process stability and crystal quality are difficult to guarantee. For example, the SiC seed crystal is adhered to the graphite cover by glue, and due to the uneven distribution of the glue, a local temperature gradient is easily formed, thereby forming a hexagonal cavity in the local area, which deteriorates the crystal quality. Moreover, during the sublimation process of the SiC solid powder, carbon and silicon do not follow the stoichiometric ratio, and the atmosphere is easy to be rich in carbon in the later crystal growth period, thereby forming crystal defects such as carbon inclusions, microtubes and polytypes, which leads to the decrease of the crystal quality. In addition, the conventional PVT method cannot grow P-type and N-type semiconductors on the same crystal.

[0003] There are also reports in the prior art that the liquid phase epitaxy (LPE) method is used to prepare SiC crystals. This method can effectively heal the microtubes of the SiC crystal, but the growth rate is relatively slow, and due to the size limitation of the seed crystal, it is difficult to obtain large-diameter and thick SiC crystals, and therefore the cost is relatively high. In addition, the conventional LPE method also cannot grow P-type and N-type semiconductors on the same crystal. SUMMARY

[0004] The present application aims to provide a growth method of large-size low-defect silicon carbide single crystal. The method provided by the present application can grow large-size low-defect silicon carbide single crystal, and different types of doping can be realized on the same silicon carbide single crystal.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a growth method of large-size low-defect silicon carbide single crystal, which comprises the following steps:

[0007] ​The application provides a large-size low-defect silicon carbide single crystal growth device, which comprises an upper graphite crucible, a lower graphite crucible, a porous graphite cylinder, a porous graphite cylinder, a seed lifting rod, a graphite seed cover, a heat insulation felt and an induction coil; the upper graphite crucible is arranged at the top of the lower graphite crucible, and the bottom of the upper graphite crucible is communicated with the lower graphite crucible; a porous graphite cylinder is arranged in the upper graphite crucible and the lower graphite crucible respectively, and the porous graphite cylinder is arranged in the porous graphite cylinder; the periphery of the upper graphite crucible and the lower graphite crucible, the top of the upper graphite crucible and the bottom of the lower graphite crucible are all provided with the heat insulation felt; the outer side of the heat insulation felt is provided with the induction coil; wherein the upper graphite crucible is provided with an upper graphite cover at the top, and a through hole is arranged in the middle of the upper graphite cover; a diameter-expanding graphite ring is arranged between the porous graphite cylinder and the graphite seed cover in the through hole, the diameter-expanding graphite ring is used for supporting the seed crystal attached to the bottom surface of the graphite seed cover and realizing the diameter-expanding growth of the crystal ingot; the seed lifting rod is connected with the graphite seed cover through threads.

[0008] A mixture of silicon powder, carbon powder, chromium powder and P-type dopant is loaded between the porous graphite cylinder and the lower graphite crucible, silicon carbide powder is loaded between the porous graphite cylinder and the upper graphite crucible, and then a first-stage crystal growth is carried out based on the PVT method in the presence of an N-type dopant, so that a crystal ingot is obtained, wherein the initial temperature of the first-stage crystal growth is lower than 2150 DEG C; the crystal ingot is used as a seed crystal, and a second-stage crystal growth is carried out based on the LPE method, so that a large-size low-defect silicon carbide single crystal is obtained.

[0009] Preferably, the N-type dopant comprises a gaseous N-type dopant and / or a solid N-type dopant.

[0010] When the N-type dopant comprises a solid N-type dopant, a mixture of the silicon carbide powder and the solid N-type dopant is loaded between the porous graphite cylinder and the upper graphite crucible, and the loading height of the mixture of the silicon carbide powder and the solid N-type dopant is 150-245 mm.

[0011] Preferably, the solid N-type dopant comprises silicon nitride or carbonamide, and the mass ratio of the silicon carbide powder to the solid N-type dopant is (95-98):(2-5).

[0012] Preferably, the first-stage crystal growth is carried out under a pressure of 5-15 mbar; the time of the first-stage crystal growth is 80-120 h; the initial temperature of the first-stage crystal growth is 2050-2140 DEG C, and the temperature is raised to the end of the first-stage crystal growth at a temperature rising rate of 0.5-25 DEG C / h; during the first-stage crystal growth, the seed lifting rod moves downward at a speed of 0.1-0.2 mm / h.

[0013] Preferably, before the first stage of crystal growth, the process further includes: evacuating the pressure from atmospheric pressure to 10⁻⁵ mbar in 1–5 hours, then filling with protective gas to a pressure of 500–800 mbar while simultaneously raising the temperature to 1950–2050°C at a rate of 50–200°C / h, and holding the temperature and pressure for 2–5 hours; then reducing the pressure to 5–15 mbar in 15–30 hours while simultaneously raising the temperature to 2050–2140°C, and holding the temperature and pressure for 5–10 hours.

[0014] Preferably, when the N-type dopant includes a gaseous N-type dopant, the gaseous N-type dopant is introduced during the heat preservation and pressure holding process at a temperature of 1950–2050°C and a pressure of 500–800 mbar, and the flow rate of the gaseous N-type dopant is 10–30 slm; during the heat preservation and pressure holding process at a temperature of 2050–2140°C and a pressure of 5–15 mbar, the flow rate of the gaseous N-type dopant is adjusted to 5–15 slm.

[0015] Preferably, the seed crystal has a thickness of 450–1500 μm and a diameter of 149–150 mm.

[0016] Preferably, the P-type dopant includes one or more of elemental aluminum, elemental boron, elemental gallium, aluminum oxide, aluminum nitride, boron oxide, boron carbide, gallium oxide, and gallium carbide; the mass ratio of silicon powder, carbon powder, chromium powder, and P-type dopant is (35-45):(28-35):(15-35):(2-5);

[0017] The loading height of the mixture of silicon powder, carbon powder, chromium powder and P-type dopant is 100-350 mm.

[0018] Preferably, the second stage of crystal growth is carried out under a pressure of 300-800 mbar; the second stage of crystal growth takes 50-100 h; during the second stage of crystal growth, the temperature of the seed crystal lifting rod is 1980-2020℃, and the seed crystal lifting rod moves upward at a rate of 0.03-0.06 mm / h, with the seed crystal just coming into contact with the surface of the reaction liquid in the lower graphite crucible.

[0019] Preferably, a graphite hard felt support is provided at the bottom of the insulation felt located at the bottom of the lower graphite crucible, and the bottom of the graphite hard felt support is connected to the rotating rod; during the second stage of crystal growth, the rotation speed of the rotating rod is 4 to 6 rpm.

[0020] This invention provides a method for growing large-size, low-defect silicon carbide single crystals. Specifically, it utilizes a large-size, low-defect silicon carbide single crystal growth apparatus, using silicon carbide powder as raw material, and performs a first-stage crystal growth based on the PVT method in the presence of N-type dopant to obtain a crystal ingot. Then, using a mixture of silicon powder, carbon powder, chromium powder, and P-type dopant as raw material, and the crystal ingot as a seed crystal, a second-stage crystal growth is performed based on the LPE method to obtain a large-size, low-defect silicon carbide single crystal. This invention improves upon the PVT and LPE methods for preparing silicon carbide crystals by employing two heating systems, enabling effective control of P-type and N-type doping, and fabricating P-type and N-type semiconductors on the same silicon carbide single crystal. This invention also improves the seed crystal fixing method by using a mechanical seed crystal placement method to avoid crystal defects caused by unstable seed crystal bonding processes. Furthermore, this invention mitigates carbon enrichment in the powder by utilizing the lower LPE device to provide a more sufficient Si atmosphere source to the upper PVT device, thereby reducing carbon enrichment during the PVT crystal growth process and minimizing crystal defects caused by carbon enrichment in the powder source. This invention employs a two-stage material system and a crystal growth system. First, a large-diameter ingot is obtained through the PVT method, which serves as a seed crystal. Then, the LPE method is used for defect healing to prepare large-size, low-defect silicon carbide single crystals. This improves crystal quality while reducing production costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the large-size, low-defect silicon carbide single crystal growth device in this invention;

[0022] Figure 2 This is a partially enlarged structural diagram of point A in the large-size, low-defect silicon carbide single crystal growth apparatus of the present invention;

[0023] Explanation of reference numerals in the attached diagram: 1. Seed crystal lifting rod; 2. Insulating felt; 3. Graphite seed crystal cover; 4. Expanded diameter graphite ring; 5. Graphite pressure ring; 6. Upper graphite cover; 7. Upper graphite crucible; 8. Seed crystal; 9. Graphite paper; 10. Porous graphite cylinder; 11. Silicon carbide powder (or a mixture of silicon carbide powder and solid N-type dopant); 12. Mixture of silicon powder, carbon powder, chromium powder and P-type dopant; 13. Upper induction coil; 14. Lower induction coil; 15. Porous graphite cylinder; 16. Graphite hard felt base; 17. Rotating rod; 18. Lower graphite crucible;

[0024] Figure 3 The image shows the finished product of the mechanically assembled, diameter-expanded graphite ring-grown ingot prepared in Example 1 after processing (the edges of the ingot are ground and polished).

[0025] Figure 4 A physical image of the ingot obtained from mechanically assembled, diameter-expanded graphite ring-grown crystals prepared for Comparative Example 1;

[0026] Figure 5A photograph of the ingot obtained from mechanically assembled, diameter-expanded graphite ring-growth crystals prepared in Example 1;

[0027] Figure 6 Comparison of etched dislocations between silicon carbide single crystals prepared in Example 2 and silicon carbide single crystals prepared by PVT bonding seed crystals;

[0028] Figure 7 The diagram shows the P-type and N-type doping concentrations of the silicon carbide single crystal prepared in Example 2. Detailed Implementation

[0029] This invention provides a method for growing large-size, low-defect silicon carbide single crystals, comprising the following steps:

[0030] A large-size, low-defect silicon carbide single crystal growth apparatus is provided, comprising an upper graphite crucible, a lower graphite crucible, a porous graphite cylinder, a porous graphite tube, a seed crystal lifting rod, a graphite seed crystal cover, an insulating felt, and an induction coil. The upper graphite crucible is positioned on top of the lower graphite crucible, and its bottom is connected to the lower graphite crucible. A porous graphite cylinder is respectively disposed within both the upper and lower graphite crucibles, and a porous graphite tube is disposed within each porous graphite cylinder. The heat-insulating felt is provided around the crucible, above the upper graphite crucible, and at the bottom of the lower graphite crucible; the induction coil is provided on the outside of the heat-insulating felt; wherein, the top of the upper graphite crucible is provided with an upper graphite cover, and a through hole is provided in the middle of the upper graphite cover; an expanded diameter graphite ring is provided in the through hole between the porous graphite cylinder and the graphite seed crystal cover, the expanded diameter graphite ring is used to support the seed crystal attached to the bottom surface of the graphite seed crystal cover and realize the expansion diameter growth of the ingot; the seed crystal lifting rod is connected to the graphite seed crystal cover by threads;

[0031] A mixture of silicon powder, carbon powder, chromium powder, and P-type dopant is loaded between the porous graphite cylinder and the lower graphite crucible. Silicon carbide powder is loaded between the porous graphite cylinder and the upper graphite crucible. Then, in the presence of N-type dopant, a first-stage crystal growth is performed based on the PVT method to obtain a crystal ingot. The initial temperature of the first-stage crystal growth is below 2150°C. Using the crystal ingot as a seed crystal, a second-stage crystal growth is performed based on the LPE method to obtain a large-size, low-defect silicon carbide single crystal.

[0032] This invention first describes a large-size, low-defect silicon carbide single crystal growth apparatus. For example... Figure 1 and 2As shown, the large-size, low-defect silicon carbide single crystal growth apparatus of the present invention includes an upper graphite crucible 7, a lower graphite crucible 18, a porous graphite cylinder 10, a porous graphite tube 15, a seed crystal lifting rod 1, a graphite seed crystal cover 3, a heat insulation felt 2, and an induction coil. The upper graphite crucible 7 is disposed on top of the lower graphite crucible 18, and the bottom of the upper graphite crucible 7 is connected to the lower graphite crucible 18. A porous graphite cylinder 10 is disposed in both the upper graphite crucible 7 and the lower graphite crucible 18, and a porous graphite tube 15 is disposed in the porous graphite cylinder 10. A porous graphite tube 15 is disposed in the porous graphite cylinder 10. A silicon carbide powder (or a mixture of silicon carbide powder and solid N-type dopant) 11 is placed between the porous graphite cylinder 10 and the upper graphite crucible 7 to provide a large amount of silicon carbide raw material. The porous graphite cylinder 10 and the lower graphite crucible 7 are connected in series. A mixture 12 of silicon powder, carbon powder, chromium powder, and P-type dopant is placed between the graphite crucibles 18 to provide raw materials and element doping for the LPE method of silicon carbide preparation. Insulation felt 2 is provided around the upper graphite crucible 7 and the lower graphite crucible 18, as well as above the upper graphite crucible 7 and at the bottom of the lower graphite crucible 18. An induction coil is provided on the outside of the insulation felt 2. An upper graphite cover 6 is provided on the top of the upper graphite crucible 7, with a through hole in the middle of the upper graphite cover 6. An expanded-diameter graphite ring 4 is provided in the through hole between the porous graphite cylinder 15 and the graphite seed crystal cover 3. The expanded-diameter graphite ring 4 supports the seed crystal 8 attached to the bottom surface of the graphite seed crystal cover 3 and enables the expansion growth of the ingot. The seed crystal lifting rod 1 is connected to the graphite seed crystal cover 3 by a thread.

[0033] As an embodiment of the present invention, the seed crystal lifting rod 1 is made of high-density graphite round bar, which can be connected to the graphite seed crystal cover 3 by threads, and the temperature of the seed crystal lifting rod 1 can be measured by an infrared thermometer.

[0034] As an embodiment of the present invention, the heat insulation felt 2 can be made of soft felt or graphite hard felt, or the inner ring can be made of graphite hard felt and the outer ring can be made of soft felt.

[0035] In one embodiment of the present invention, the induction coil includes an upper induction coil 13 and a lower induction coil 14; the upper induction coil 13 corresponds to the upper graphite crucible 7, and the lower induction coil 14 corresponds to the lower graphite crucible 18; and the upper induction coil 13 and the lower induction coil 14 are independently controlled to heat the upper graphite crucible 7 and the lower graphite crucible 18 respectively, so as to control the temperature of the upper graphite crucible 7 and the lower graphite crucible 18, so as to provide a heat source for the reaction and a suitable axial-radial temperature gradient. By adjusting the power, time and pressure of the upper induction coil 13 and the lower induction coil 14, and coordinating with the lifting height control of the seed crystal lifting rod 1, the different doping types, concentrations and doped layer thicknesses of the silicon carbide single crystal can be adjusted.

[0036] In one embodiment of the present invention, a graphite hard felt support 16 is provided at the bottom of the insulating felt 2 located at the bottom of the lower graphite crucible 18, and the bottom of the graphite hard felt support 16 is connected to the rotating rod 17. In the present invention, the rotating rod 17 is preferably made of high-purity quartz. In the second-stage crystal growth process of silicon carbide single crystal in the present invention, it can rotate at a certain rate to increase the uniformity of the liquid phase reactants and obtain high-quality crystals.

[0037] As an embodiment of the present invention, the bottom surface of the graphite seed crystal cover 3 is provided with an annular groove, and the top of the expanded diameter graphite ring 4 extends into the annular groove; specifically, the expanded diameter graphite ring 4 and the graphite seed crystal cover 3 can be connected by threads.

[0038] In one embodiment of the present invention, the annular groove of the graphite seed crystal cover 3 is detachably connected to a graphite pressure ring 5, for example, by a threaded connection. The graphite pressure ring 5 includes a vertical structure and a horizontal structure. The inner side of the vertical structure is connected to the annular groove of the graphite seed crystal cover 3, the bottom of the vertical structure is connected to one end of the horizontal structure, and the other end of the horizontal structure extends into the vertical structure. The top surface of the horizontal structure is used to support the seed crystal 8. In this invention, the graphite pressure ring 5 can prevent the seed crystal 8 from falling off and effectively avoid crystal defects caused by uneven adhesion of the seed crystal 8.

[0039] As an embodiment of the present invention, a transverse support portion is provided on the upper inner wall of the expanded graphite ring 4. The support portion is used to support the graphite pressure ring 5 and realize the expansion growth of the ingot.

[0040] In one embodiment of the present invention, graphite paper 9 is disposed between the supporting part and the graphite pressure ring 5; the thickness of the graphite paper is preferably 0.5-1.5 mm. In the present invention, the coefficients of thermal expansion of graphite and SiC differ greatly at high temperatures, and the graphite paper 9 can play a flexible buffering role.

[0041] In addition, the upper graphite cover 6 in this invention is mainly used to support the upper insulation felt 2 and improve the insulation performance of the system.

[0042] In this invention, the porous graphite cylinder 10 has a hollow structure, and the material of the porous graphite cylinder 10 is porous graphite, with a preferred porosity of 40-60%. The preferred use of the above-mentioned structure and material of the porous graphite cylinder 10 in this invention helps to increase the contact area between the reaction liquid and the graphite, providing a more stable carbon source. Simultaneously, the higher porosity also filters large metal inclusions; furthermore, it can sieve the atmosphere, blocking large particulate impurities (mainly large Si molecules at high temperatures). m C n(and carbon particles), thereby obtaining a pure and stable silicon carbide gas flow and reducing crystal defects.

[0043] In this invention, the porous graphite cylinder 15 has a hollow structure, and the material of the porous graphite cylinder 15 is porous graphite, with a preferred porosity of 40-60%. The porous graphite cylinder 15 with the above-mentioned structure and material can block carbon particle inclusions, filter particulate carbon, increase the contact area between the mixed molten metal and the carbon source, and provide a stable carbon source; moreover, it can screen Si. m C n The atmosphere serves to purify and stabilize the atmosphere during the first stage of crystal growth.

[0044] This invention involves loading a mixture of silicon powder, carbon powder, chromium powder, and a P-type dopant between a porous graphite cylinder and a lower graphite crucible, and loading silicon carbide powder between the porous graphite cylinder and an upper graphite crucible. Then, in the presence of an N-type dopant, a first-stage crystal growth process is performed using the PVT method to obtain an ingot. Using the ingot as a seed crystal, a second-stage crystal growth process is performed using the LPE method to obtain a large-size, low-defect silicon carbide single crystal. The raw materials and methods for growing large-size, low-defect silicon carbide single crystals in this invention are described in detail below.

[0045] In this invention, the P-type dopant preferably includes one or more of elemental aluminum, elemental boron, elemental gallium, aluminum oxide, aluminum nitride, boron oxide, boron carbide, gallium oxide, and gallium carbide; the mass ratio of silicon powder, carbon powder, chromium powder, and P-type dopant is preferably (35-45):(28-35):(15-35):(2-5), more preferably (35-42):(32-35):(20-30):(3-5). In this invention, the loading height of the mixture of silicon powder, carbon powder, chromium powder, and P-type dopant is preferably 100-350 mm, more preferably 150 mm.

[0046] In this invention, the N-type dopant preferably includes a gaseous N-type dopant or a solid N-type dopant. The gaseous N-type dopant is preferably nitrogen, and the solid N-type dopant preferably includes silicon nitride (Si3N4) or carbamide (CH4N2O). In this invention, when the N-type dopant is a solid N-type dopant, it is preferable to load the mixture of silicon carbide powder and solid N-type dopant between the porous graphite cylinder and the upper graphite crucible. The loading height of the mixture of silicon carbide powder and solid N-type dopant is preferably 150-245 mm, more preferably 200 mm. The mass ratio of silicon carbide powder to solid N-type dopant is preferably (95-98):(2-5), more preferably (96-97):(3-4).

[0047] After the raw material for growing large-size, low-defect silicon carbide single crystals is loaded, the present invention performs a first-stage crystal growth based on the PVT method to obtain an ingot. In this invention, the first-stage crystal growth is preferably carried out under a pressure of 5–15 mbar, specifically 5 mbar, 10 mbar, or 15 mbar; the first-stage crystal growth time is preferably 80–120 h, more preferably 100 h; the initial temperature of the first-stage crystal growth is preferably 2050–2140 °C, more preferably 2050–2070 °C, and preferably heated at a rate of 0.5–25 °C / h until the end of the first-stage crystal growth, more preferably at a rate of 2–3 °C / h. In this invention, during the first-stage crystal growth process, the seed crystal lifting rod preferably moves downward at a rate of 0.1–0.2 mm / h, specifically 0.1 mm / h, 0.15 mm / h, or 0.2 mm / h; the initial position of the seed crystal lifting rod is as follows: Figure 1 As shown. In this invention, the first stage of crystal growth is preferably carried out in a protective atmosphere, and the protective gas providing the protective atmosphere is preferably argon or helium.

[0048] In this invention, the first stage before crystal growth preferably further includes: evacuating the pressure from atmospheric pressure to 10 kWh over 1 to 5 hours. -5 The process involves applying a protective gas to a pressure of 500–800 mbar, simultaneously raising the temperature to 1950–2050 °C at a rate of 50–200 °C / h, and holding this temperature and pressure for 2–5 hours. After 15–30 hours, the pressure is reduced to 5–15 mbar while the temperature is raised to 2050–2140 °C, and held for 5–10 hours. A further preferred step before the first stage of crystal growth includes: evacuating the pressure from atmospheric pressure to 10 mbar within 3 hours. - 5 Then, pressurize with protective gas to a pressure of 800 mbar while simultaneously raising the temperature to 1980–2000 °C at a rate of 100–150 °C / h, and hold at that temperature and pressure for 5 hours. After 30 hours, reduce the pressure to 10–15 mbar while simultaneously raising the temperature to 2050–2070 °C, and hold at that temperature and pressure for 5 hours.

[0049] In this invention, when the N-type dopant includes a gaseous N-type dopant, it is preferable to charge the gaseous N-type dopant during a heat-holding and pressure-holding process at a temperature of 1950–2050°C and a pressure of 500–800 mbar. The flow rate of the gaseous N-type dopant is preferably 10–30 slm, more preferably 20 slm. During a heat-holding and pressure-holding process at a temperature of 2050–2140°C and a pressure of 5–15 mbar, it is preferable to adjust the flow rate of the gaseous N-type dopant to 5–15 slm, more preferably 10 slm.

[0050] In this invention, after the first stage of crystal growth, it is preferable to further include: increasing the pressure from the pressure of the first stage of crystal growth to 500-800 mbar in 5-10 hours; when the N-type dopant includes gaseous N-type dopant, it is preferable to stop charging the gaseous N-type dopant after increasing the pressure from the pressure of the first stage of crystal growth to 500-800 mbar.

[0051] After obtaining the ingot, this invention uses the ingot as a seed crystal to perform a second-stage crystal growth based on the LPE method, resulting in a large-size, low-defect silicon carbide single crystal. In this invention, the thickness of the seed crystal is preferably 450–1500 μm, and the diameter is preferably 149–150 mm. In this invention, the second-stage crystal growth is preferably carried out under a pressure of 300–800 mbar, more preferably 750 mbar; the duration of the second-stage crystal growth is preferably 50–100 h, more preferably 80–100 h; during the second-stage crystal growth process, the temperature of the seed crystal lifting rod is preferably 1980–2020 °C, and the seed crystal lifting rod preferably moves upward at a rate of 0.03–0.06 mm / h, with the seed crystal just coming into contact with the reaction liquid surface in the lower graphite crucible. In this invention, during the second-stage crystal growth process, the rotational speed of the rotating rod is preferably 4–6 rpm.

[0052] In this invention, the thickness of the large-size, low-defect silicon carbide single crystal is preferably 25-40 mm, more preferably 35 mm; the diameter is preferably 150-190 mm, more preferably 180 mm.

[0053] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] Examples 1-2 and Comparative Example 1

[0055] according to Figure 1 as well as Figure 2 Provides large-size, low-defect silicon carbide single crystal growth equipment;

[0056] A mixture of silicon powder, carbon powder, chromium powder, and P-type dopant (metallic Al) was loaded between a porous graphite cylinder and a lower graphite crucible, while silicon carbide powder was loaded between the porous graphite cylinder and an upper graphite crucible. Then, a vacuum was applied from atmospheric pressure for 3 hours to 10... -5 The process involves pressurizing the protective gas under MAB (Magnetic Protective Gas) and performing the first stage of crystal growth using the PVT (Polyvinyl Transformation) method to obtain an ingot. Using this ingot as a seed crystal, the second stage of crystal growth is performed using the LPE (Liquid Polymerization) method to obtain a large-size, low-defect silicon carbide single crystal. Specific process conditions are shown in Table 1.

[0057] Table 1 Process conditions for growing crystal ingots

[0058]

[0059]

[0060] Table 2. Process conditions for growing large-size, low-defect silicon carbide single crystals

[0061]

[0062]

[0063] The performance of the ingots and silicon carbide single crystals prepared in the examples was tested, as follows:

[0064] Figure 3 The image shows the finished product of the mechanically assembled expanded graphite ring crystal growth ingot prepared in Example 1 after processing (the edges of the ingot are polished). The results show that the diameter of the mechanically expanded ring crystal ingot can reach 170-175 mm after rolling the outer diameter, and the thickness can be greater than 20 mm.

[0065] Figure 4 The image shows a physical picture of the ingot obtained by mechanically assembled expanded graphite ring growth prepared in Comparative Example 1. The results show that due to unreasonable process parameters (the initial temperature of the first stage of crystal growth is relatively high, at 2150℃), the growth rate is too fast (greater than 25g / h), resulting in edge single crystals, large internal stress, and crystal cracking.

[0066] Figure 5 The image shows a physical picture of the ingot obtained by mechanically assembling and expanding graphite ring growth in Example 1. The results show that due to the fast growth rate (17g / h), the single crystal diameter can reach 170-174mm and the single crystal thickness can reach about 25mm.

[0067] Figure 6 The images show a comparison of etched dislocations in the silicon carbide single crystal prepared in Example 2 and the silicon carbide single crystal prepared by PVT bonding seed crystal. (a) shows the etched dislocations in the silicon carbide single crystal prepared by PVT bonding seed crystal, while (b) and (c) show the etched dislocations in the silicon carbide single crystal prepared in Example 2. The results show that the BPD and TED of the silicon carbide single crystal prepared by the method of this invention are significantly reduced, with the BPD decreasing from the original 10... 4 Reduced to 10 2 Order of magnitude, TED consists of 10 4 Reduced to 10 3 This greatly improved the quality of the crystal.

[0068] Figure 7The diagram shows the P-type and N-type doping concentrations of the silicon carbide single crystal prepared in Example 2. The results show that the N-type doping concentration is around 10... 19～20 The order of magnitude, with P-type doping concentration in the range of 10 20 Order of magnitude.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for growing large-size, low-defect silicon carbide single crystals, comprising the following steps: A large-size, low-defect silicon carbide single crystal growth apparatus is provided, comprising an upper graphite crucible, a lower graphite crucible, a porous graphite cylinder, a porous graphite tube, a seed crystal lifting rod, a graphite seed crystal cover, an insulating felt, and an induction coil. The upper graphite crucible is positioned on top of the lower graphite crucible, and its bottom is connected to the lower graphite crucible. A porous graphite cylinder is respectively disposed within both the upper and lower graphite crucibles, and a porous graphite tube is disposed within each porous graphite cylinder. The heat-insulating felt is provided around the crucible, above the upper graphite crucible, and at the bottom of the lower graphite crucible; the induction coil is provided on the outside of the heat-insulating felt; wherein, the top of the upper graphite crucible is provided with an upper graphite cover, and a through hole is provided in the middle of the upper graphite cover; an expanded diameter graphite ring is provided in the through hole between the porous graphite cylinder and the graphite seed crystal cover, the expanded diameter graphite ring is used to support the seed crystal attached to the bottom surface of the graphite seed crystal cover and realize the expansion diameter growth of the ingot; the seed crystal lifting rod is connected to the graphite seed crystal cover by threads; A mixture of silicon powder, carbon powder, chromium powder, and P-type dopant is loaded between the porous graphite cylinder and the lower graphite crucible. Silicon carbide powder is loaded between the porous graphite cylinder and the upper graphite crucible. Then, in the presence of N-type dopant, a first-stage crystal growth is performed based on the PVT method to obtain a crystal ingot. The initial temperature of the first-stage crystal growth is below 2150°C. Using the crystal ingot as a seed crystal, a second-stage crystal growth is performed based on the LPE method to obtain a large-size, low-defect silicon carbide single crystal.

2. The growth method according to claim 1, characterized in that, The N-type dopant includes gaseous N-type dopant and / or solid N-type dopant; When the N-type dopant includes a solid N-type dopant, the mixture of silicon carbide powder and solid N-type dopant is loaded between the porous graphite cylinder and the upper graphite crucible, and the loading height of the mixture of silicon carbide powder and solid N-type dopant is 150-245 mm.

3. The growth method according to claim 2, characterized in that, The solid N-type dopant includes silicon nitride or carbamide, and the mass ratio of silicon carbide powder to solid N-type dopant is (95-98):(2-5).

4. The growth method according to any one of claims 1 to 3, characterized in that, The first stage of crystal growth is carried out under a pressure of 5 to 15 mbar; the first stage of crystal growth takes 80 to 120 hours; the initial temperature of the first stage of crystal growth is 2050 to 2140°C, and the temperature is increased at a rate of 0.5 to 25°C / h until the end of the first stage of crystal growth; during the first stage of crystal growth, the seed crystal lifting rod moves downward at a rate of 0.1 to 0.2 mm / h.

5. The growth method according to claim 4, characterized in that, The first stage, preceding crystal growth, also includes: evacuating the pressure from atmospheric pressure to 10 kWh over 1–5 hours. -5 Then, pressurize with protective gas to a pressure of 500–800 mbar while simultaneously raising the temperature to 1950–2050 °C at a rate of 50–200 °C / h, and hold at the temperature and pressure for 2–5 h; after 15–30 h, reduce the pressure to 5–15 mbar while simultaneously raising the temperature to 2050–2140 °C, and hold at the temperature and pressure for 5–10 h.

6. The growth method according to claim 5, characterized in that, When the N-type dopant includes a gaseous N-type dopant, the gaseous N-type dopant is introduced during the heat and pressure holding process at a temperature of 1950–2050°C and a pressure of 500–800 mbar, and the flow rate of the gaseous N-type dopant is 10–30 slm; during the heat and pressure holding process at a temperature of 2050–2140°C and a pressure of 5–15 mbar, the flow rate of the gaseous N-type dopant is adjusted to 5–15 slm.

7. The growth method according to claim 4, characterized in that, The seed crystal has a thickness of 450–1500 μm and a diameter of 149–150 mm.

8. The growth method according to claim 1, characterized in that, The P-type dopant includes one or more of elemental aluminum, elemental boron, elemental gallium, aluminum oxide, aluminum nitride, boron oxide, boron carbide, gallium oxide, and gallium carbide; the mass ratio of silicon powder, carbon powder, chromium powder, and P-type dopant is (35-45):(28-35):(15-35):(2-5); The loading height of the mixture of silicon powder, carbon powder, chromium powder and P-type dopant is 100-350 mm.

9. The growth method according to claim 1 or 8, characterized in that, The second stage of crystal growth is carried out under a pressure of 300-800 mbar; the second stage of crystal growth takes 50-100 h; during the second stage of crystal growth, the temperature of the seed crystal lifting rod is 1980-2020℃, and the seed crystal lifting rod moves upward at a rate of 0.03-0.06 mm / h, with the seed crystal just coming into contact with the surface of the reaction liquid in the lower graphite crucible.

10. The growth method according to claim 9, characterized in that, A graphite hard felt support is provided at the bottom of the insulation felt located at the bottom of the lower graphite crucible, and the bottom of the graphite hard felt support is connected to the rotating rod; during the second stage of crystal growth, the rotation speed of the rotating rod is 4 to 6 rpm.

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