Method for expanding the diameter of a single crystal of silicon carbide

Abstract

The present invention provides a method for expanding the diameter of a silicon carbide single crystal, which sequentially includes the following steps: (1) placing raw materials in a graphite crucible, fixing a SiC seed crystal to a seed crystal rod, and selecting a seed crystal plane with a lower crystal growth rate as the crystal growth plane; (2) placing the graphite crucible in a growth furnace, and then evacuating the growth furnace; (3) introducing a functional gas and a protective gas into the growth furnace, and controlling the gas pressure in the growth furnace; (4) heating the graphite crucible so that the raw materials are completely melted to form a melt; (5) lowering the seed crystal rod so that the side surface of the seed crystal is immersed in the melt; (6) adjusting the position of the graphite crucible in the induction coil and the seed crystal facing away from the heat preservation structure so that the axial temperature gradient is 0.5-5 °C / cm, thereby increasing the growth rate of the {10-10} plane and the {11-20} plane on the side surface of the seed crystal to expand the diameter and prepare a silicon carbide single crystal. The method of the present invention can efficiently obtain a large-size silicon carbide seed crystal with a low defect density.

Description

Technical Field

[0001] The present invention belongs to the field of silicon carbide crystal preparation. Specifically, the present invention relates to a method for expanding the diameter of silicon carbide single crystals. Background Art

[0002] Silicon carbide (SiC) is one of the wide-bandgap semiconductor materials that have received extensive attention. It has the advantages of low density, large bandgap (at room temperature, the bandgap of 4H-SiC is 3.2 eV), high breakdown field strength (about 10 times that of Si), high saturated electron mobility (about 2 times that of Si), high thermal conductivity (3 times that of Si, 10 times that of GaAs), and good chemical stability. It is an ideal substrate material for making high-frequency, high-voltage, high-power devices and blue light-emitting diodes. Silicon carbide has important application potential in the fields of electric vehicles, rail transit, high-voltage power transmission and transformation, photovoltaic, 5G communication, etc.

[0003] The growth of SiC single crystals mainly includes physical vapor transport method, liquid phase method, and high-temperature chemical vapor deposition method. Among them, the currently most important and mature one is the physical vapor transport method. The liquid phase method has a low growth temperature, a relatively stable growth environment, a growth process close to thermodynamic equilibrium conditions, good crystal quality, and has good prospects in terms of diameter expansion and p-type doping. In recent years, it has received widespread attention from the academic and industrial circles.

[0004] So far, SiC power devices have mainly been fabricated on commercially available single crystal substrates with a diameter of 150 mm (6 inches). In order to further reduce the cost of SiC power devices, it is necessary to further increase the size of SiC single crystal substrates and increase the number of devices that can be fabricated on a single SiC substrate. Therefore, it is very necessary to obtain larger diameter SiC single crystal substrates.

[0005] Generally, researchers usually use two methods to expand the diameter of silicon carbide crystals:

[0006] (1) The method of gradually expanding the diameter with a small seed crystal. That is, a seed crystal with a certain diameter and good crystal quality is used for growth. By designing a suitable temperature field, a large radial temperature gradient is achieved, so that the convexity of the growth interface is large, and the purpose of expanding the crystal diameter is achieved. The diameter can be expanded by 2 - 6 mm each time; then the expanded silicon carbide single crystal is cut, ground, and polished, and the obtained wafer is used as the seed crystal for the next diameter expansion. The above process is continuously repeated. However, the crystals obtained by this method have a large convexity and large stress in the crystals, resulting in an increase in crystal defects or even cracking. Therefore, if the crystal quality is to be ensured, the diameter can only be expanded slowly. This iterative process of diameter expansion often takes years, and the time required to expand 2 inches is about 5 - 10 years. The cycle is long and the efficiency is low, which hinders the rapid development of the silicon carbide industrial chain.

[0007] (2) Method for expanding the diameter of a spliced seed crystal. That is, multiple smaller-sized seed crystals are cut into a specific shape and then spliced into a larger-sized seed crystal, and the spliced seed crystal is used for growth to obtain a crystal with a larger diameter. However, the crystals grown by this method cannot achieve perfect lattice-scale connection at the splicing points, and a large number of microtubes and dislocation defects are often generated at the splicing points, and even obvious grain boundaries are generated, so high-quality crystals cannot be obtained. A large number of researchers have tried to improve this diameter-expanding method, attempting to quickly obtain high-quality silicon carbide crystals with large size and low defect density through spliced seed crystals.

[0008] Chinese Patent CN105671638A discloses a method for preparing a large-diameter SiC seed crystal. The method includes: trimming and cutting a small-diameter SiC seed crystal; bonding and fixing it on a seed crystal holder in a close-packed splicing manner to form a first layer of seed crystals, and then bonding and fixing a second layer of seed crystals above the gaps between the small-diameter SiC seed crystals in the first layer of seed crystals so that the second layer of seed crystals covers the gaps formed by the first layer of seed crystals to form a double-layer spliced arrangement of seed crystals, and then polishing and annealing to promote lateral growth to obtain a complete large-diameter SiC seed crystal. However, the SiC seed crystal prepared by this method is polygonal, and there are blank areas at the edges of the seed crystal. A complete circular SiC seed crystal cannot be obtained by using this method; at the same time, two layers of SiC seed crystals need to be spliced and arranged in this method, and this method will cause problems such as large total thickness deviation and even dropping, which is not conducive to the growth of high-quality SiC single crystals.

[0009] Chinese Patent CN115592829A discloses a splicing structure, manufacturing method and silicon carbide crystal for expanding the diameter of a silicon carbide seed crystal. The splicing structure cuts the seed crystal from three selected cutting directions, so as to keep all parts of the spliced silicon carbide crystal in the same crystal orientation, and performs a specific chamfering treatment at the cutting points for large-size seed crystal splicing growth. Although the silicon carbide ingot after diameter-expanding growth by this splicing structure is in the same crystal orientation to reduce the generation of grain boundaries, and has been chamfered to reduce the influence of cracks at the splicing points, this way of splicing seed crystals cannot achieve perfect lattice-scale connection at the splicing points, and a large number of microtubes and dislocation defects are often generated at the splicing points, which is not conducive to obtaining high-quality SiC single crystals.

[0010] Chinese Patent CN106435732A discloses a method for quickly preparing a large-size SiC single crystal ingot. In this method, small-size SiC wafers are processed into the required shape and combined and arranged and fixed on a graphite seed crystal holder, and conditions suitable for lateral growth of the crystal are adopted to fill the gaps between the small-size wafers with laterally grown single crystals. This method realizes the elimination of cracks at the cracks of the seed crystal in a single crystal furnace, and has high requirements for growth process control. Although the gaps between the small-size wafers are filled with laterally grown single crystals, perfect lattice-scale connection still cannot be achieved, and defects such as microtubes and dislocations will be generated, which cannot be used to prepare high-quality SiC single crystals.

[0011] Chinese Patent CN105525351A discloses an efficient SiC crystal diameter expansion method. This method uses a large-sized seed crystal composed of spliced small-sized seed crystals for growth. By depositing a dense polycrystalline silicon carbide layer on the graphite substrate and the surface on the side of the graphite substrate facing the seed crystal, the back evaporation damage at the seed crystal joints is reduced, and the crystal quality is improved. When splicing the seed crystals using this method, although the probability of evaporation at the seed crystal splices is reduced, cracks at the seed crystal splices will generate serious crystal defects during the subsequent crystal growth process and will not disappear with the optimization of the growth process. Therefore, this method cannot prepare high-quality SiC crystals.

[0012] Chinese Patent CN111705363A discloses a rapid diameter expansion growth method for silicon carbide single crystals. This method uses a silicon carbide single crystal material with a certain thickness as the seed crystal, and polishes its circumferential surface through curved surface chemical mechanical polishing technology for lateral diameter expansion growth. A growth component flow guide plate is placed in the crystal growth chamber and the silicon carbide powder material to control the preferential diameter expansion growth of the silicon carbide single crystal, and then axial growth is carried out; the surface layer and internal structure materials of the growth chamber are coated with a metal or alloy compound material, which can inhibit the nucleation and growth of silicon carbide on its surface to inhibit the formation of polycrystals, effectively avoiding the termination of diameter expansion due to parasitic polycrystals generated during the diameter expansion of the silicon carbide single crystal. This method requires a silicon carbide single crystal material with a certain thickness (greater than 3 mm) as the seed crystal, and the side surface of the crystal needs to be polished using curved surface chemical mechanical polishing technology. The graphite parts during the growth process also need to be coated with a metal or alloy compound, resulting in high costs and low efficiency.

[0013] Chinese Patent CN116479527B discloses a silicon carbide crystal diameter expansion growth device, method, and silicon carbide crystal. The silicon carbide crystal diameter expansion growth device includes a graphite crucible, a silicon carbide seed crystal, and a diameter expansion part. The silicon carbide seed crystal is fixed to the inner top wall of the graphite crucible; the diameter expansion part is connected to the inner side wall of the graphite crucible, and the diameter expansion part is formed with a diameter expansion channel and a plurality of drainage annular grooves. The diameter expansion channel extends along the axial direction of the silicon carbide seed crystal, and the plurality of drainage annular grooves are sequentially spaced and coaxially arranged in the axial direction of the diameter expansion channel. The diameter expansion channel is communicated with the inner side wall of the graphite crucible through the plurality of drainage annular grooves. During growth, the silicon carbide raw material atmosphere is transported along the diameter expansion channel to the crystal surface to achieve diameter expansion growth. This device has a complex structure and high requirements for growth process control, and is not suitable for large-scale industrialization.

[0014] Some researchers have also tried to solve the problem of high defect density at the joints of spliced seeds by epitaxial growth. For example, Chinese patents CN110541199A and CN110541199B disclose a method for preparing high-quality SiC seeds with a diameter of 8 inches or more, which includes: cutting, splicing, grinding, and polishing small-sized SiC wafers or SiC crystals, and then performing homoepitaxial growth; first performing lateral epitaxial growth, and performing lateral epitaxial growth at the splicing gap to fill the gap; then, after the splicing gap is filled, changing the growth conditions to promote the growth rate of the (0001) plane of the seed crystal, greatly reducing the defect density of the seed crystal growth surface, and obtaining high-quality SiC seeds with a diameter of 8 inches or more without cracks and with low defect density. However, this method requires the use of a silicon carbide epitaxial growth furnace, with a complex process, difficult process control, and high cost.

[0015] Some researchers have also tried to solve the problem of high defect density at the joints of spliced seeds by the liquid-phase method. For example, Chinese invention CN116815291A discloses a method for growing large-sized silicon carbide single crystals using spliced seeds by the liquid-phase method. In the liquid-phase method during the growth of single crystals, the continuous growth of single crystals is achieved through step flow, and when the step height and width during the growth process are sufficient to cover the joints, the joints can be closed. However, in the liquid-phase method, high step height and width mean a small step flow density on the crystal surface, and such large steps are likely to cause inclusions and high-quality silicon carbide crystals cannot be obtained.

[0016] Therefore, there is an urgent need for a method for expanding the diameter of silicon carbide single crystals, which has a fast diameter expansion speed and low cost and can efficiently obtain high-quality large-sized silicon carbide crystals. Summary of the Invention

[0017] The object of the present invention is to provide a method for expanding the diameter of silicon carbide single crystals. The method of the present invention has a fast diameter expansion speed and can efficiently obtain large-sized silicon carbide seeds with a low defect density. The method of the present invention can increase the diameter of silicon carbide single crystals by 4-10 mm only through a single short-time (20-80 h) diameter expansion growth.

[0018] The above object of the present invention is achieved by the following technical solutions.

[0019] The present invention provides a method for expanding the diameter of silicon carbide single crystals, which successively includes the following steps:

[0020] (1) Place the raw materials in a graphite crucible, and fix the SiC seed on the seed rod, and select the seed crystal plane with a lower crystal growth rate as the crystal growth surface;

[0021] (2) Place the graphite crucible in a growth furnace, and then evacuate the growth furnace;

[0022] (3) Introduce functional gas and protective gas into the growth furnace and control the air pressure inside the growth furnace;

[0023] (4) Heat the graphite crucible to completely melt the raw material to form a melt;

[0024] (5) Lower the seed rod so that the side surface of the seed crystal is immersed in the melt;

[0025] (6) Adjust the position of the graphite crucible in the induction coil and the seed crystal facing away from the heat preservation structure so that the axial temperature gradient is 0.5 - 5 °C / cm, thereby making the growth rates of the {10 - 10} plane and the {11 - 20} plane on the side surface of the seed crystal faster to expand the diameter and prepare a silicon carbide single crystal;

[0026] (7) Optionally, subject the silicon carbide single crystal obtained in step (6) to grinding and polishing processing, and use the processed silicon carbide single crystal as a new SiC seed crystal, and repeat steps (1) to (6) to further expand the diameter and prepare a silicon carbide single crystal.

[0027] The inventors of the present application unexpectedly found that by selecting a seed crystal plane with a lower crystal growth rate as the crystal growth plane and cooperating with a specific growth process, especially an axial temperature gradient of 0.5 - 5 °C / cm, the growth rates of the {10 - 10} plane and the {11 - 20} plane on the side surface of the seed crystal can be made faster, and thus a silicon carbide single crystal can be prepared by expanding the diameter.

[0028] The inventors of the present application also unexpectedly found that if a specific raw material, growth atmosphere, and specific growth plane combination are further used for liquid-phase silicon carbide crystal growth, cooperating with a specific growth process, the growth rate of the growth plane (Si plane or C plane) can be made slower, while the growth rates of the side surfaces ({10 - 10} plane and {11 - 20} plane) are faster, thereby realizing rapid diameter expansion of the silicon carbide crystal. Specifically, under certain specific combinations of metal raw materials, growth atmospheres, and specific growth planes for liquid-phase silicon carbide crystal growth, the growth rate of the growth plane is extremely low. At this time, the growth rate of the side surface is highlighted, and the crystal tends to grow laterally with diameter expansion. At this time, matching with a temperature field structure and growth process with a smaller axial temperature gradient can make the diameter expansion effect more prominent.

[0029] In the present invention, selecting a seed crystal plane (Si plane or C plane) with a lower crystal growth rate as the crystal growth plane can be achieved by a trial method. Specifically, growth can be first carried out on the Si plane and then on the C plane to determine which plane has a lower growth rate.

[0030] In the specific implementation of the present invention, the selection of a specific crystal plane (Si plane or C plane) should be matched with the selected metal raw material system and growth atmosphere, and a crystal plane with a lower growth rate under this metal raw material system and growth atmosphere should be selected.

[0031] Preferably, in the method of the present invention, the SiC seed crystal is a SiC wafer with a 0° tilt angle.

[0032] Preferably, in the method of the present invention, the SiC wafer is a semi-insulating, n-type or p-type wafer with a size of 4 to 8 inches.

[0033] Preferably, in the method of the present invention, the raw material consists of Si, optional Al, optional transition metals, and optional rare earth metals.

[0034] Preferably, in the method of the present invention, the atomic molar ratio of Si, Al, transition metals, and rare earth metals is Si:Al:transition metals:rare earth metals = (30 - 70):(0 - 15):(0 - 60):(0 - 40).

[0035] Preferably, in the method of the present invention, the transition metals are selected from one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn.

[0036] Preferably, in the method of the present invention, the rare earth metals are selected from one or more of La, Ce, Pr, and Nd.

[0037] Preferably, in the method of the present invention, the functional gas includes nitrogen. Nitrogen can play a role in stabilizing the SiC crystal form and can also enter the crystal as a dopant to obtain an n-type conductive SiC single crystal.

[0038] Preferably, in the method of the present invention, the protective gas includes argon and / or helium.

[0039] Preferably, in the method of the present invention, the partial pressure of the functional gas is 0% - 100% of the total pressure, more preferably 5% - 40%, and the total pressure of the gas is 0.1 - 2 atm, more preferably 0.2 - 0.6 atm.

[0040] Preferably, in the method of the present invention, the graphite crucible is made of high-purity graphite with a purity of greater than or equal to 99.95%.

[0041] Preferably, in the method of the present invention, the inner diameter of the graphite crucible is 20 - 150 mm larger than the diameter of the SiC seed crystal. A larger crucible can make the distance between the side of the seed crystal and the inner wall of the crucible farther, resulting in better heat dissipation on the side of the seed crystal and being beneficial to diameter expansion growth.

[0042] Preferably, in the method of the present invention, the wall thickness of the graphite crucible is greater than or equal to 10 mm.

[0043] Preferably, in the method of the present invention, the density of the graphite crucible is 1.7-2.0 g / cm 3 .

[0044] Preferably, in the method of the present invention, the evacuation of the growth furnace in step (2) is to evacuate the growth furnace to less than or equal to 1×10 -4 Pa.

[0045] Preferably, in the method of the present invention, the axial temperature gradient is 0.5-2 °C / cm.

[0046] Preferably, in the method of the present invention, the growth rate of the crystal growth surface in step (1) is less than 50 μm / h, preferably less than 20 μm / h.

[0047] Preferably, in the method of the present invention, the diameter expansion for preparing the silicon carbide single crystal in step (6) is carried out by a method including the following steps: periodically accelerating and decelerating the rotation of the SiC seed crystal and the graphite crucible, and simultaneously slowly pulling up the SiC seed crystal.

[0048] Preferably, in the method of the present invention, the periodic acceleration and deceleration rotation helps to obtain a more uniform temperature field and helps to obtain higher quality crystals. The periodic acceleration and deceleration rotation is carried out under the following conditions: the SiC seed crystal and the graphite crucible rotate in opposite directions with periodic acceleration and deceleration, the rotation speed is ±0-300 r / min, and the rotational acceleration is ±0-40 r / min 2 .

[0049] Preferably, in the method of the present invention, the rotation speed is ±60-180 r / min.

[0050] Preferably, in the method of the present invention, the pulling is carried out at a rate of 1-1000 μm / h. More preferably, the pulling is carried out at a rate approximately equal to the crystal growth rate.

[0051] In a specific embodiment of the present invention, since the growth rate of the growth surface of the present invention is relatively slow, if the growth rate is about 20 μm / h, the thickness of the wafer is 600 μm after 30 hours of growth. After the growth is completed, the seed crystal for further diameter expansion can be directly obtained by grinding and polishing, omitting the cutting process in the diameter expansion growth by other methods, which can improve the efficiency.

[0052] The present invention has at least the following beneficial effects compared with the prior art:

[0053] (1) The method of the present invention can achieve rapid diameter expansion without using a spliced seed crystal. The diameter of the silicon carbide single crystal can be increased by 4-10 mm only through a single short-time diameter expansion growth (20-80 h). Compared with the spliced seed crystal diameter expansion method, the method of the present invention has no splicing area, and the obtained crystal has better quality and smaller defect density. Compared with the small seed crystal step-by-step diameter expansion method, the method of the present invention requires less time and higher efficiency. In addition, the method of the present invention is more suitable for successive single-piece diameter expansion. After the end of one diameter expansion growth, the relatively thin wafer obtained by growth can be directly ground and polished to obtain a seed crystal for further diameter expansion growth, eliminating the cutting process in the diameter expansion growth of other methods and further improving the diameter expansion efficiency.

[0054] (2) The method of the present invention uses the liquid phase method as the diameter expansion growth method. The liquid phase method has the advantages of low temperature, relatively stable growth environment, growth process close to thermodynamic equilibrium conditions, and good crystal quality, and can obtain high-quality and low-stress diameter expansion crystals. Brief Description of the Drawings

[0055] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings, wherein:

[0056] Figure 1 Shows the external shape of the silicon carbide crystal obtained in Example 1 of the present invention;

[0057] Figure 2 Shows the external shape of the silicon carbide crystal obtained in Example 2 of the present invention;

[0058] Figure 3 Shows the external shape of the silicon carbide wafer obtained in Example 3 of the present invention;

[0059] Figure 4 Shows the X-ray rocking curve diagram of the silicon carbide wafer obtained in Example 3 of the present invention;

[0060] Figure 5 Shows the external shape of the silicon carbide crystal obtained in Comparative Example 1 of the present invention;

[0061] Figure 6 Shows the external shape of the silicon carbide crystal obtained in Comparative Example 2 of the present invention. Detailed Embodiments

[0062] The present invention will be further described in detail below in conjunction with the specific embodiments. The embodiments given are only for clarifying the present invention, rather than for limiting the scope of the present invention.

[0063] Example 1

[0064] The method provided in this example includes the following steps:

[0065] (1) Place the raw materials in a graphite crucible, and fix a 4-inch semi-insulating 4H-SiC seed crystal with a 0° angle on a graphite seed crystal rod; wherein, the inner diameter of the graphite crucible is 150 mm and the wall thickness is 15 mm; the raw materials are composed of Si, Al, Cr, and Ce elements, and the atomic molar ratio is Si:Al:Cr:Ce = 40:5:50:5; since the growth on the Si face and the C face was carried out under the same conditions in advance using this raw material formula, it was found that the growth rate of the Si face is much lower than that of the C face. Therefore, the Si face is selected as the growth face in this embodiment;

[0066] (2) Place the graphite crucible in a growth furnace, and then evacuate the growth furnace to 3×10 -5 Pa;

[0067] (3) Introduce argon and control the air pressure in the growth furnace to 0.4 atm;

[0068] (4) Heat the graphite crucible to completely melt the metal raw materials to form a melt;

[0069] (5) Lower the seed crystal so that the seed crystal contacts the melt, and continue to lower it so that the side of the seed crystal is immersed in the melt;

[0070] (6) Adjust the position of the graphite crucible in the induction coil and the seed crystal facing away from the heat preservation structure so that the axial temperature gradient is about 1 °C / cm. This results in a low growth rate on the growth face, while the growth rates on the side faces ({10-10} face and {11-20} face) are relatively fast;

[0071] (7) Periodically accelerate and decelerate the rotation of the SiC seed crystal and the graphite crucible, with a rotation speed of 160 r / min and a rotational acceleration of ±20 r / min 2 ; at the same time, slowly lift the SiC seed crystal at a speed of 20 μm / h;

[0072] (8) After 20 hours of growth, separate the seed crystal from the liquid surface, cool it to room temperature and take it out to obtain a larger-diameter single crystal of silicon carbide.

[0073] The external shape diagram of the silicon carbide crystal grown in this embodiment is as Figure 1 shown. It can be seen that there are no macroscopic defects on the crystal surface except for the adhered metal residues, and the growth rate of the crystal growth face is 12 μm / h. Figure 1 It shows that the crystal has an obvious diameter expansion trend. After 20 hours of growth, the crystal diameter increases from 100 mm to 104.3 mm, and the diameter expansion speed reaches 0.22 mm / h.

[0074] It should be noted that the crystal appears hexagonal because 4H-SiC is a polar crystal with a hexagonal structure, and its interfacial energy anisotropy is very obvious. Moreover, since the liquid phase method is a growth method that is nearly in equilibrium thermodynamically, the crystal appears hexagonal.

[0075] Example 2

[0076] The method provided in this example includes the following steps:

[0077] (1) Place the raw materials in a graphite crucible, and fix a 4-inch n-type 4H-SiC seed crystal with a 0° angle on the graphite seed crystal rod; among them, the inner diameter of the graphite crucible is 150 mm and the wall thickness is 15 mm; the raw materials are composed of Si, Ti, and Pr elements, and the atomic molar ratio is Si:Ti:Pr = 50:42:8; since the growth on the Si surface and the C surface was carried out under the same conditions in advance using this raw material formula, it was found that the growth rate of the C surface is much lower than that of the Si surface. Therefore, the C surface is selected as the growth surface in this example;

[0078] (2) Place the graphite crucible in the growth furnace, and then evacuate the growth furnace to 3×10 -5 Pa;

[0079] (3) Introduce nitrogen and argon and control the pressure in the growth furnace to be 0.5 atm, where the partial pressure of nitrogen is 5% of the total pressure;

[0080] (4) Heat the graphite crucible to completely melt the metal raw materials to form a melt;

[0081] (5) Lower the seed crystal so that the seed crystal contacts the melt, and continue to lower it so that the side surface of the seed crystal is immersed in the melt;

[0082] (6) Adjust the position of the graphite crucible in the induction coil and the seed crystal facing away from the heat preservation structure to make the axial temperature gradient about 0.8 °C / cm, which results in a low growth rate on the growth surface and a relatively high growth rate on the side surfaces ({10-10} plane and {11-20} plane);

[0083] (7) Periodically accelerate and decelerate the rotation of the SiC seed crystal and the graphite crucible, with a rotation speed of 180 r / min and a rotational acceleration of ±10 r / min 2 ; at the same time, slowly lift the SiC seed crystal at a speed of 15 μm / h;

[0084] (8) After growing for 20 hours, separate the seed crystal from the liquid surface, cool it to room temperature and take it out to obtain a larger diameter single crystal of silicon carbide.

[0085] The external shape diagram of the silicon carbide crystal grown in this example is as shown in Figure 2As shown, it can be seen that there are no macroscopic defects on the crystal surface except for a spontaneous nucleation particle, and the growth rate of the crystal growth surface is 19.4 μm / h. Figure 2 It is shown that the crystal has an obvious tendency of diameter expansion. After 20 hours of growth, the crystal diameter increases from 100 mm to 103.4 mm, and the diameter expansion rate reaches 0.17 mm / h.

[0086] Example 3

[0087] The method used in this example is basically the same as that in Example 1. The only difference is that the growth time is changed to 60 h, and the crystal is polished after growth to prepare a larger-diameter silicon carbide seed crystal. Repeat the steps of Example 1 four times to further obtain a larger-diameter silicon carbide seed crystal, and process the finally obtained silicon carbide crystal into a wafer. As Figure 3 shown, the crystal diameter becomes 150 mm, completing the diameter expansion from 4 inches to 6 inches. Its X-ray rocking curve diagram is as Figure 4 shown. The full width at half maximum of the rocking curve is 30.74 arcseconds, indicating high crystal quality.

[0088] Comparative Example 1

[0089] The method used in this comparative example is basically the same as that in Example 1. The difference is that the C plane is selected as the growth surface. The external shape diagram of the silicon carbide crystal grown in this comparative example is as Figure 5 shown. The growth rate of the crystal growth surface is 143.9 μm / h. It can be seen that the crystal has no obvious tendency of diameter expansion, and even shows a diameter reduction. The crystal diameter decreases from 100 mm to 98.2 mm. This is because in this metal raw material system, the growth rate of the C plane is much greater than that of the Si plane and the side surface, resulting in most of the solute being consumed by the growth of the C plane, and the side surface growth is not dominant, so the diameter expansion cannot be achieved.

[0090] Comparative Example 2

[0091] The method used in this comparative example is basically the same as that in Example 1. The difference is that the axial temperature gradient is about 7 °C / cm and the growth time is 60 h. The external shape diagram of the silicon carbide crystal grown in this comparative example is as Figure 6 shown. The growth rate of the crystal growth surface is 50.7 μm / h. It can be seen that after the axial temperature gradient increases, the growth rate of the growth surface increases, and due to the too large axial temperature gradient, spontaneous nucleation occurs on the raw material surface and adheres to the growth surface to form huge polycrystalline particles. The crystal diameter increases from 100 mm to 108.3 mm, and the diameter expansion rate is 0.14 mm / h, which is less than that in Example 1, and the crystal quality is poor.

[0092] Embodiments and comparative examples of the present invention illustrate that by using a specific growth surface for liquid-phase growth of silicon carbide crystals and simultaneously matching a temperature field structure with a relatively small axial temperature gradient, rapid diameter expansion of silicon carbide single crystals can be achieved, and high-quality large-size silicon carbide crystals can be obtained.

[0093] The above embodiments are used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for the diameter expansion of silicon carbide single crystals, which successively includes the following steps: (1) Place the raw materials in a graphite crucible, and fix the SiC seed crystal on the seed crystal rod. Select the seed crystal plane with a lower crystal growth rate as the crystal growth plane; (2) Place the graphite crucible in a growth furnace, and then evacuate the growth furnace; (3) Introduce a functional gas and a protective gas into the growth furnace, and control the gas pressure in the growth furnace; (4) Heat the graphite crucible so that the raw materials are completely melted to form a melt; (5) Lower the seed crystal rod so that the side of the seed crystal is immersed in the melt; (6) Adjust the position of the graphite crucible in the induction coil and the seed crystal facing away from the insulation structure so that the axial temperature gradient is 0.5 - 5 °C / cm, thereby making the growth rates of the {10 - 10} plane and the {11 - 20} plane on the side of the seed crystal faster to expand the diameter and prepare a silicon carbide single crystal; Among them, The functional gas includes nitrogen, and, Control the total pressure of the gas in the growth furnace to be 0.1 - 2 atm.

2. The method according to claim 1, the method further includes: Subject the silicon carbide single crystal obtained in step (6) to grinding and polishing, and use the processed silicon carbide single crystal as a new SiC seed crystal, and repeat steps (1) to (6) to further expand the diameter and prepare a silicon carbide single crystal.

3. The method according to claim 1, wherein, The SiC seed crystal is a SiC wafer with a 0° deviation angle.

4. The method according to claim 3, wherein, The SiC wafer is a semi-insulating, n-type or p-type 4 - 8 inch wafer.

5. The method according to claim 1, wherein The raw materials are composed of Si, optionally Al, optionally transition metals, and optionally rare earth metals.

6. The method according to claim 5, wherein, The atomic molar ratio of Si, Al, transition metals, and rare earth metals is Si:Al:transition metals:rare earth metals = (30 - 70):(0 - 15):(0 - 60):(0 - 40).

7. The method according to claim 5, wherein The transition metals are selected from one or more of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn.

8. The method according to claim 5, wherein The rare earth metals are selected from one or more of La, Ce, Pr, and Nd.

9. The method according to claim 1, wherein The protective gas includes argon and / or helium.

10. The method according to claim 1, wherein, The partial pressure of the functional gas is 0% - 100% of the total pressure.

11. The method according to claim 10, wherein, The partial pressure of the functional gas is 5% - 40% of the total pressure.

12. The method according to claim 1, wherein, The total pressure of the gas is 0.2 - 0.6 atm.

13. The method according to claim 1, wherein, The graphite crucible is made of high-purity graphite with a purity greater than or equal to 99.95%.

14. The method according to claim 1, wherein, The inner diameter of the graphite crucible is 20 - 150 mm larger than the diameter of the SiC seed crystal.

15. The method according to claim 1, wherein The wall thickness of the graphite crucible is greater than or equal to 10 mm.

16. The method according to claim 1, wherein, The density of the graphite crucible is 1.7~2.0 g / cm 3 .

17. The method according to claim 1, wherein, The evacuation of the growth furnace in step (2) evacuates the growth furnace to be less than or equal to 1×10 -4 Pa.

18. The method according to claim 1, wherein The axial temperature gradient is 0.5 - 2 °C / cm.

19. The method according to claim 1, wherein, The crystal plane growth rate of the crystal growth plane in step (1) is less than 50 μm / h.

20. The method according to claim 1, wherein The crystal plane growth rate of the crystal growth plane in step (1) is less than 20 μm / h.

21. The method according to claim 1, wherein, The diameter expansion and preparation of the silicon carbide single crystal in step (6) are carried out by a method including the following steps: Periodically accelerate and decelerate the rotation of the SiC seed crystal and the graphite crucible, and at the same time slowly lift the SiC seed crystal.

22. The method according to claim 21, wherein The periodic acceleration and deceleration rotation are carried out under the following conditions: the SiC seed crystal and the graphite crucible rotate periodically with opposite directions, the rotation speed is ±0 to 300 r / min, and the rotational acceleration is ±0 to 40 r / min 2 .

23. The method according to claim 22, wherein, The rotation speed is ±60 - 180 r / min.

24. The method according to claim 21, wherein The lifting is carried out at a rate of 1 - 1000 μm / h.

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