Flux for silicon carbide crystal growth, cubic silicon carbide crystal and growth method thereof

Abstract

The present invention provides a flux for silicon carbide crystal growth, a cubic silicon carbide crystal and a growth method thereof, belonging to the technical field of crystal growth, wherein the flux is an alloy comprising a rare earth metal, a transition metal and carbon: the molar ratio of the rare earth metal to the transition metal is 1:9 to 9:1. The flux provided by the present invention can reduce the growth temperature of silicon carbide crystals, realize the growth of silicon carbide crystals at a lower temperature, and at the same time can increase the solubility of carbon in silicon melt, increase the concentration of carbon in silicon melt in the early stage of crystal growth, and realize obtaining high-quality and large-sized silicon carbide crystals in a shorter time.

Description

Technical Field

[0001] The invention relates to the technical field of crystal growth, and in particular to a flux for silicon carbide crystal growth, a cubic silicon carbide crystal and a growth method thereof. Background Art

[0002] As the third generation wide bandgap semiconductor material, SiC has excellent physical properties such as large bandgap width, high critical breakdown field strength, high saturated electron velocity, high thermal conductivity, and stable chemical properties. It is an ideal material for preparing high-temperature, high-frequency, and high-power semiconductor devices. It is widely used in new energy vehicles, 5G communications, aerospace and other fields, filling the gaps in traditional semiconductor devices in practical applications. The existing SiC crystal growth methods mainly include physical vapor transport (PVT), high-temperature chemical vapor deposition (HTCVD) and solution growth (also called flux method). Among them, the PVT method is relatively mature and is the mainstream method for growing SiC crystals in industry. However, the growth temperature and energy consumption of this method are relatively high, and the grown crystals are usually accompanied by microscopic defects, and the crystal yield is low. The HTCVD method grows SiC crystals at a lower temperature and is relatively easier to control, but its growth rate is slow and the crystal size is small, which is not suitable for large-scale industrialization needs. In comparison, the solution method for growing SiC crystals is a crystal growth method that is close to the thermodynamic equilibrium state. The grown crystals have a lower defect density and can effectively avoid the microscopic defects existing in the PVT method for growing SiC crystals. However, the solubility of C in Si melt is extremely low, and the growth rate of SiC crystals simply relying on Si-C melt is slow. The prior art increases the solubility of C in Si melt by adding flux (Cr, Fe, Co, Ti, Sc, Al, Mn and rare earth elements (La, Ce, Pr, Tb, Dy). However, when the above flux is used, the solubility of C in Si melt is still very limited and cannot meet the needs of large-scale industrialization. Summary of the invention

[0003] In view of one or more technical problems existing in the prior art, the present invention provides a flux for growing a silicon carbide crystal, a cubic silicon carbide crystal and a growth method thereof. The flux provided by the present invention can reduce the growth temperature of the silicon carbide crystal, thereby realizing the growth of the silicon carbide crystal at a low temperature, and at the same time can increase the solubility of carbon in the silicon melt, thereby increasing the carbon concentration in the silicon melt in the early stage of crystal growth, thereby realizing high-quality and large-sized silicon carbide crystals in a shorter time.

[0004] In a first aspect, the present invention provides a flux for growing silicon carbide crystals, wherein the flux is an alloy comprising a rare earth metal, a transition metal and carbon;

[0005] The molar ratio of the rare earth metal to the transition metal is 1:9 to 9:1.

[0006] Preferably, the molar ratio of the rare earth metal to the transition metal is not less than 7:3;

[0007] The rare earth metal is a lanthanide metal, preferably one or more of La, Ce, and Pr; and / or

[0008] The transition metal is at least one of Ni and Co.

[0009] In a second aspect, the present invention provides a cubic silicon carbide crystal, which is grown by a liquid phase method from a raw material comprising the flux described in the first aspect and silicon.

[0010] Preferably, the growth temperature of the cubic silicon carbide crystal is 1300-1550°C.

[0011] The present invention provides in a third aspect a method for growing the cubic silicon carbide crystal according to the second aspect, the method comprising the following steps:

[0012] In a protective atmosphere, a mixture of flux and silicon is heated to obtain a melt;

[0013] The melt is brought into contact with a silicon carbide seed crystal to perform crystal growth, thereby obtaining the cubic silicon carbide crystal.

[0014] Preferably, the method for preparing the flux comprises: mixing rare earth metals, transition metals and carbon blocks, and performing arc melting to obtain the flux.

[0015] Preferably, the temperature of the heating treatment is 1300-1550° C.; and / or

[0016] The silicon carbide seed crystal is a silicon carbide wafer.

[0017] Preferably, during the crystal growth process, the seed rod fixed with the silicon carbide seed crystal is pulled at a speed of 5 to 20 μm / h; and / or

[0018] During the crystal growth process, the seed crystal rod fixed with the silicon carbide seed crystal rotates at a speed of 5-100 r / min.

[0019] Preferably, after the crystal growth, the method further comprises the step of removing residues on the surface of the cubic silicon carbide crystal using a mixed acid and water; the mixed acid comprises HNO3 and HF.

[0020] Preferably, the volume ratio of HNO3 to HF in the mixed acid is 2:1.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] The flux for silicon carbide crystal growth provided by the present invention is an alloy including rare earth metals, transition metals and carbon. This type of flux can reduce the melting temperature of raw materials for preparing silicon carbide crystals, reduce the temperature of silicon carbide crystal growth, achieve the growth of silicon carbide crystals at low temperatures (1300-1550°C), and avoid the influence of excessive temperature on the stability and growth quality of silicon carbide crystals; at the same time, it can increase the solubility of carbon in silicon melt, increase the concentration of carbon in silicon melt in the early stage of crystal growth, and increase the growth rate of cubic silicon carbide crystals. On the premise of ensuring the growth quality of cubic silicon carbide crystals, the crystal growth time is shortened and the growth efficiency of cubic silicon carbide crystals is improved. Compared with the use of traditional fluxes, the temperature of growing high-quality and large-size silicon carbide crystals using the flux provided by the present invention is lower, the efficiency is higher (the growth time is shorter), and no other substances are generated between the flux and silicon and carbon, which is conducive to improving the quality of silicon carbide single crystals.

[0023] The method for growing cubic silicon carbide crystals provided by the present invention has a simple process, a low growth temperature, and a high growth efficiency, and can achieve a lower temperature and more efficient growth of high-quality, large-sized cubic silicon carbide crystals, overcoming the problems of poor crystal stability, a long preparation process, and low production efficiency in the existing large-sized cubic silicon carbide crystal growth process. In addition, during the growth of cubic silicon carbide crystals, rare earth metals and transition metals in the flux are not consumed and can be reused. Only silicon needs to be added to the raw material to continue the growth of cubic silicon carbide crystals, which is conducive to reducing the cost of growing cubic silicon carbide crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 is a physical picture of the cubic silicon carbide crystal grown in Example 1 of the present invention;

[0026] Figure 2 is the Raman spectrum of the cubic silicon carbide crystal grown in Example 1 of the present invention;

[0027] Figure 3 is the rocking curve of the cubic silicon carbide crystal grown in Example 1 of the present invention;

[0028] Figure 4 The present invention provides a flow chart of cubic silicon carbide crystal growth. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are 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.

[0030] In a first aspect, the present invention provides a flux for growing silicon carbide crystals. The flux is an alloy comprising a rare earth metal, a transition metal and carbon; the molar ratio of the rare earth metal to the transition metal is 1:9 to 9:1.

[0031] The flux for silicon carbide crystal growth provided by the present invention is an alloy including rare earth metals, transition metals and carbon. This type of flux can reduce the melting temperature of raw materials for preparing silicon carbide crystals, reduce the temperature of silicon carbide crystal growth, achieve the growth of silicon carbide crystals at low temperatures (1300-1550°C), and avoid the influence of excessive temperature on the stability and growth quality of silicon carbide crystals; at the same time, it can increase the solubility of carbon in silicon melt, increase the concentration of carbon in silicon melt in the early stage of crystal growth, and increase the growth rate of cubic silicon carbide crystals. On the premise of ensuring the growth quality of cubic silicon carbide crystals, the crystal growth time is shortened and the growth efficiency of cubic silicon carbide crystals is improved. Compared with the use of traditional fluxes, the temperature of growing high-quality and large-size silicon carbide crystals using the flux provided by the present invention is lower, the efficiency is higher (the growth time is shorter), and no other substances are generated between the flux and silicon and carbon, which is conducive to improving the quality of silicon carbide single crystals.

[0032] It should be noted that the inventors have found that within the above-mentioned molar ratio range of rare earth metal to transition metal, the greater the molar ratio of rare earth metal to transition metal, the lower the melting temperature of silicon carbide crystal raw material and the relatively lower the growth temperature of silicon carbide crystal.

[0033] According to some preferred embodiments, the molar ratio of the rare earth metal to the transition metal is not less than 7:3; the inventors of the present invention found that when the molar ratio of the rare earth metal to the transition metal is ≥7:3, high-quality silicon carbide crystals can be grown at 1300°C.

[0034] In some preferred embodiments of the present invention, the ratio of the total molar number of the rare earth metal and the transition metal to the molar number of the carbon is 2:3.

[0035] According to some preferred embodiments, the rare earth metal is a lanthanide metal, preferably one or more of La, Ce, and Pr. The types of rare earth metals of the present invention include but are not limited to the above types.

[0036] According to some preferred embodiments, the transition metal is at least one of Ni and Co.

[0037] In a second aspect, the present invention provides a cubic silicon carbide crystal, which is grown by a liquid phase method from a raw material comprising the flux described in the first aspect and silicon.

[0038] According to some preferred embodiments, the growth temperature of the cubic silicon carbide crystal is 1300-1550°C (for example, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C or 1550°C). The present invention adopts the above-mentioned flux to achieve the growth of high-quality cubic silicon carbide crystals at low temperature (1300°C), and the crystal growth temperature is significantly lower than the growth temperature of cubic silicon carbide crystals using existing fluxes, and the obtained cubic silicon carbide crystals have higher quality and better stability.

[0039] It should be noted that the purity of the rare earth metal and transition metal in the present invention is not less than 99.95 wt%, and the purity of carbon and silicon is not less than 99.9999 wt%.

[0040] The present invention provides in a third aspect a method for growing the cubic silicon carbide crystal according to the second aspect, the method comprising the following steps:

[0041] In a protective atmosphere, a mixture of flux and silicon is heated to obtain a melt;

[0042] The melt is brought into contact with a silicon carbide seed crystal to perform crystal growth, thereby obtaining the cubic silicon carbide crystal.

[0043] The present invention uses an alloy including rare earth metals, transition metals and carbon as a flux to reduce the melting temperature of raw materials for preparing silicon carbide crystals, and can achieve the growth of cubic silicon carbide crystals at low temperatures, avoiding the influence of excessive temperature on the stability and growth quality of cubic silicon carbide crystals; at the same time, it can increase the solubility of carbon in the melt, increase the carbon concentration in the melt in the early stage of cubic silicon carbide crystal growth, and improve the growth rate of cubic silicon carbide crystals. On the premise of ensuring the growth quality of cubic silicon carbide crystals, the crystal growth time is shortened and the growth efficiency of cubic silicon carbide crystals is improved. The growth method of cubic silicon carbide crystals provided by the present invention has simple process, low growth temperature and high growth efficiency, and can achieve the growth of high-quality and large-sized cubic silicon carbide crystals at lower temperatures and more efficiently, overcoming the problems of the existing large-sized cubic silicon carbide crystal growth process, poor crystal stability, long preparation process and low production efficiency. In addition, during the growth of cubic silicon carbide crystals, the rare earth metals and transition metals in the flux are not consumed and can be reused. Only silicon needs to be added to the raw materials to continue the growth of cubic silicon carbide crystals, which is beneficial to reducing the cost of growing cubic silicon carbide crystals.

[0044] According to some preferred embodiments, the method for preparing the flux comprises: mixing rare earth metals, transition metals and carbon blocks, and performing arc melting to obtain the flux.

[0045] It should be noted that arc melting uses a water-cooled copper crucible as the first electrode and a tungsten needle as the second electrode. During the arc melting process, a mixture of rare earth metals, transition metals and carbon blocks is placed in a water-cooled copper crucible, and the arc melting process is carried out under an inert gas protective atmosphere.

[0046] In some specific embodiments of the present invention, the method for preparing the flux comprises: RE )、Transition metals( M ) and carbon are placed in a water-cooled copper crucible, the water-cooled copper crucible is used as the first electrode, and a tungsten needle is used as the second electrode, and alloying and melting are performed by an arc melting method under an inert gas atmosphere to obtain the flux, wherein the ratio of the total molar number of rare earth metals and transition metals to the molar number of carbon blocks is 2:3; the molar ratio of rare earth metals to transition metals is 1:9~9:1; the purity of rare earth metals and transition metals is ≥99.95wt%, and the purity of carbon is ≥99.9999 wt%; in the process of preparing the flux by the arc melting method, the melting needs to be repeated several times to ensure uniform mixing.

[0047] According to some preferred embodiments, the temperature of the heat treatment is 1300-1550°C (for example, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C or 1550°C). During the growth process of cubic silicon carbide crystals, the crystal stability is low, and if the temperature is too high, the crystal transformation is likely to occur, affecting the quality and performance of the crystal. The above-mentioned flux used in the present invention can reduce the melting temperature of the raw materials for preparing cubic silicon carbide crystals (as low as 1300°C), thereby reducing the growth temperature of cubic silicon carbide crystals, achieving the growth of cubic silicon carbide crystals at lower temperatures, avoiding the influence of excessive temperature on the stability and growth quality of cubic silicon carbide crystals, and obtaining high-quality cubic silicon carbide crystals.

[0048] According to some preferred embodiments, the silicon carbide seed crystal is a silicon carbide wafer. The silicon carbide seed crystal of the present invention is one of 3C-SiC wafer, 4H-SiC wafer and 6H-SiC wafer.

[0049] According to some preferred embodiments, during the crystal growth process, the seed rod fixed with the silicon carbide seed crystal is pulled at a speed of 5 to 20 μm / h (for example, 5 μm / h, 6 μm / h, 7 μm / h, 8 μm / h, 9 μm / h, 10 μm / h, 11 μm / h, 12 μm / h, 13 μm / h, 14 μm / h, 15 μm / h, 16 μm / h, 17 μm / h, 18 μm / h, 19 μm / h or 20 μm / h); the inventors found that too low a pulling speed will lead to slow crystal growth, decreased crystal quality, increased crystal surface roughness, increased crystal internal defects and other problems; while too high a crystal pulling speed will lead to uneven crystal growth, increased grain boundary area, larger grain size and other problems; and / or

[0050] During the crystal growth process, the seed rod fixed with the silicon carbide seed crystal rotates at a speed of 1 to 40 r / min (for example, it can be 1 r / min, 5 r / min, 10 r / min, 15 r / min, 20 r / min, 25 r / min, 30 r / min, 35 r / min or 40 r / min); the inventors found that too low a speed makes the solution not stirred sufficiently and the carbon dissolving capacity is insufficient, while too high a speed easily causes large fluctuations on the growth surface, which is not conducive to crystal growth.

[0051] According to some preferred embodiments, after the crystal growth, the step of removing the residue on the surface of the cubic silicon carbide crystal by using mixed acid and water is also included; the mixed acid contains HNO3 and HF. After the crystal growth, the crystal still maintains a high rotation speed, which can effectively shake off the small droplets (residues) adhering to the growth surface, first treat with a mixed acid solution containing HNO3 and HF (the volume ratio of HNO3 and HF is 2:1) to remove the small droplets (residues) on the surface of the crystal, and then rinse with clean water to clean the acid on the surface to obtain a high-purity cubic silicon carbide crystal.

[0052] According to some preferred embodiments, the volume ratio of HNO3 to HF in the mixed acid is 2:1.

[0053] In some specific embodiments of the present invention, the method for growing cubic silicon carbide crystals comprises the following steps: (1) placing a mixture of flux and silicon in a high-purity graphite crucible in a protective atmosphere and heating the mixture to a molten state to obtain a melt; wherein the heating temperature is 1300-1550°C. (2) Keeping the heating temperature constant, slowly lower the graphite holder assembly of the seed crystal rod fixed with the SiC seed crystal to 0.5~5 mm below the melt surface, and rotate the seed crystal rod to grow cubic silicon carbide crystals. The growth temperature of cubic silicon carbide crystals is 1300~1550℃. During the growth of cubic silicon carbide crystals, the rotation speed of the seed crystal rod is 1~40 r / min, and the seed crystal rod rises (pulled upward) at a speed of 5~20μm / h; (3) After the growth of the cubic silicon carbide crystal is completed, the cubic silicon carbide crystal is quickly removed from the solution (at this time, the crystal still maintains a high rotation speed, which can effectively shake off the large droplets adhering to the growth surface); (4) First treat with a mixed acid solution containing HNO3 and HF (the volume ratio of HNO3 and HF is 2:1), and then rinse with clean water to obtain cubic silicon carbide crystals.

[0054] In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention is further described below in conjunction with the examples. The present invention does not specifically limit the sources of the reagents used in the examples and comparative examples, and the reagents can be directly purchased or synthesized by themselves.

[0055] The testing method for the performance data of the cubic silicon carbide crystals grown in the embodiments of the present invention and the comparative examples is as follows:

[0056] Crystal growth rate: First, use a standard vernier caliper to measure the thickness of the crystal at different positions (usually 5 points) and calculate the average value; then, subtract the thickness of the seed crystal from the average value to obtain the actual thickness of the crystal growth; finally, divide the actual crystal thickness by the total crystal growth time to obtain the actual growth rate of the crystal.

[0057] Crystal size and quality measurement: Place the processed crystal on standard coordinate paper or standard caliper to confirm the size; Use laser confocal Raman scattering to measure the crystal form; Use XRD diffractometer to measure the rocking curve of the crystal to determine its crystalline quality.

[0058] Example 1

[0059] (1) First, rare earth metals ( RE )、Transition metals( M ) is mixed with carbon, and then placed in a water-cooled copper base crucible as the first electrode, and tungsten needle is used as the second electrode for arc melting in an arc furnace. The protective atmosphere is Ar gas. In order to ensure the uniformity of the sample, the sample is repeatedly stir-fried and melted several times to obtain a uniform composition. RE -M -C alloy. The molar ratio of rare earth metal RE, transition metal M and carbon is 7:3:15; RE For La, M For you.

[0060] (2) The RE-MC alloy obtained in step (1) is placed together with excess silicon in a high-purity graphite crucible (purity ≥ 99.9999 wt%), and the mixture is heated to a molten state at 1300° C. using argon as a protective gas, and then kept at this temperature for 2 h to obtain a melt.

[0061] (3) Slowly lower the graphite support assembly with the SiC seed crystal (4H crystal type, Si side facing downward) to 0.5~5 mm below the melt surface obtained in step (2); and rotate the seed crystal rod at a rotation speed of 1~40 r / min to grow cubic silicon carbide crystals. The crystal growth temperature is 1300°C. After the crystal growth is completed, the crystal is quickly removed from the solution to obtain large-sized cubic silicon carbide crystals.

[0062] The cubic silicon carbide crystal grown in this embodiment is a large cubic silicon carbide crystal (3C-SiC single crystal) with a size of 4 inches. Figure 1 As shown in the figure, it can be observed that the crystal surface is flat and there are no macro defects such as bubbles. It should be noted that SiC crystal growth is a step flow growth, and the lines on the crystal surface are the growth steps of the SiC crystal. The small amount of white spots on the crystal surface are residual flux. The obtained SiC crystal is first treated with a mixed acid solution of HNO3 and HF to remove the flux on the crystal surface, and then rinsed with clean water several times to clean the surface acid, and finally rinsed with alcohol several times to obtain a large-sized, high-purity cubic silicon carbide crystal.

[0063] The Raman spectrum of the crystal (such as Figure 2 ) It can be seen that the Raman peak shift is 796 cm -1 It shows that the crystal form is 3C crystal form. It should be noted that the Raman spectrum ( Figure 2 ) represents the Raman shift, and the ordinate represents the Raman peak intensity.

[0064] The rocking curve of the crystal (such as Figure 3 ) shows that the half-height width is 39.6 arcsec, indicating that the crystal is of high quality. It should be noted that the rocking curve ( Figure 3 ) represents the angle on the horizontal axis and the intensity on the vertical axis.

[0065] Examples 2-6 are substantially the same as Example 1, except for the type of flux, as shown in Table 1 below.

[0066] Example 7

[0067] The same as Example 1, except that: in the flux, the rare earth metal RE , transition metals M The molar ratio of carbon is 9:1:15.

[0068] Examples 8-12 are substantially the same as Example 7, except that the types of flux are different, as shown in Table 1 below.

[0069] Embodiment 13

[0070] The same as Example 1, except that the rare earth metal in the flux of step (1) RE , transition metals M The molar ratio of carbon to hydrogen is 1:1:3; the heating temperature in step (2) and the crystal growth temperature in step (3) are both 1550°C.

[0071] Examples 14-18 are substantially the same as Example 13, except that the types of flux are different, as shown in Table 1 below.

[0072] Embodiment 19

[0073] The same as Example 1, except that the rare earth metal in the flux of step (1) RE , transition metals M The molar ratio of carbon to carbon is 3:7:15; the heating temperature in step (2) and the crystal growth temperature in step (3) are both 1550°C.

[0074] Examples 20-24 are substantially the same as Example 19, the only difference being the type of flux, as shown in Table 1 below.

[0075] Embodiment 25

[0076] The same as Example 1, except that the rare earth metal in the flux of step (1) RE , transition metals M The molar ratio of carbon to carbon is 1:9:15; the heating temperature in step (2) is 1550°C.

[0077] Table 1. Comparison of growth parameters of cubic silicon carbide crystals of Examples 1-30 of the present invention

[0078]

[0079]

[0080] It should be noted that the above embodiments can be used with Figure 1 High-quality, large-sized cubic silicon carbide crystals with similar size and quality are not listed here one by one.

[0081] Comparative Example 1

[0082] They are basically the same as Example 1, with the only difference being that the flux does not contain carbon, that is, the flux is La-Ni alloy.

[0083] Comparative Example 2

[0084] It is basically the same as Example 2, except that the flux does not contain carbon, that is, the flux is La-Co alloy.

[0085] Comparative Example 3

[0086] It is basically the same as Example 3, except that the flux does not contain carbon, that is, the flux is a Ce-Ni alloy.

[0087] Comparative Example 4

[0088] It is basically the same as Example 4, except that the flux does not contain carbon, that is, the flux is a Ce-Co alloy.

[0089] Comparative Example 5

[0090] It is basically the same as Example 5, except that the flux does not contain carbon, that is, the flux is a Pr-Ni alloy.

[0091] Comparative Example 6

[0092] It is basically the same as Example 6, except that the flux does not contain carbon, that is, the flux is a Pr-Co alloy.

[0093] In Comparative Examples 1-6, since the flux is an alloy consisting only of rare earth metals and transition metals and does not contain carbon, it takes a long time to dissolve a large amount of carbon in the melt, and the carbon concentration is insufficient in the early stage of crystal growth, resulting in lower crystal quality.

[0094] Comparative Example 7

[0095] It is basically the same as Example 1, except that the flux is a Ce-Cr-Si alloy, wherein the molar ratio of Ce, Cr and Si is 7:3:15.

[0096] Comparative Example 8

[0097] It is basically the same as Example 1, except that the flux is a Cr-Si alloy, wherein the molar ratio of Cr to Si is 2:3.

[0098] Comparative Example 9

[0099] It is basically the same as Example 1, except that the flux is a Ti-Si alloy, wherein the molar ratio of Ti to Si is 2:3.

[0100] The growth temperature of cubic silicon carbide crystal (3C-SiC crystal) using the flux system of Comparative Examples 7-9 is above 1600°C, and cubic silicon carbide crystal (3C-SiC crystal) cannot be grown at 1300°C.

[0101] Comparative Example 10

[0102] It is basically the same as Example 1, except that the flux is La-Fe-C alloy, wherein the molar ratio of La, Fe and C is 7:3:15.

[0103] Comparative Example 11

[0104] It is basically the same as Example 1, except that the flux is La-Cr-C alloy, wherein the molar ratio of La, Cr and C is 7:3:15.

[0105] The growth temperature of the cubic silicon carbide crystal (3C-SiC crystal) using the flux system of Comparative Examples 10-11 is above 1600°C, and the cubic silicon carbide crystal (3C-SiC crystal) cannot be grown at 1300°C.

[0106] Comparative Example 12

[0107] It is basically the same as Example 1, except that:

[0108] In step (1), the flux does not contain carbon, that is, the flux is La-Ni alloy;

[0109] In step (2), the La-Ni alloy, carbon powder and excess silicon obtained in step (1) are placed in a high-purity graphite crucible (purity ≥ 99.9999 wt%), and argon is used as a protective gas. The mixture is heated to a molten state at 1300° C. and then kept warm for 2 h to obtain a melt.

[0110] The inventors found that when carbon powder was added during the preparation of the melt, the carbon powder was not easily dissolved in the melt, and the concentration of carbon in the silicon melt in the early stage of crystal growth was not significantly increased (not much different from Comparative Example 1), and the quality of the obtained crystals was low.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flux for silicon carbide crystal growth, characterized in that: The flux is an alloy containing a rare earth metal, a transition metal and carbon; the rare earth metal is one or more of La, Ce and Pr; the transition metal is at least one of Ni and Co; The molar ratio of the rare earth metal to the transition metal is 1:9 to 9:

1.

2. The flux according to claim 1, characterized in that The molar ratio of the rare earth metal to the transition metal is not less than 7:

3.

3. A method for growing cubic silicon carbide crystals, characterized in that: The growth method comprises the following steps: In a protective atmosphere, heating the mixture of the flux according to claim 1 or 2 and silicon to obtain a melt; The melt is brought into contact with a silicon carbide seed crystal to perform crystal growth, thereby obtaining the cubic silicon carbide crystal.

4. The growth method according to claim 3, characterized in that: The preparation method of the flux comprises: mixing rare earth metal, transition metal and carbon block, and performing arc melting to obtain the flux.

5. The growth method according to claim 3, characterized in that: The temperature of the heating treatment is 1300-1550°C; and / or The silicon carbide seed crystal is a silicon carbide wafer.

6. The growth method according to claim 3, characterized in that: During the crystal growth process, the seed crystal rod fixed with the silicon carbide seed crystal is pulled at a speed of 5 to 20 μm / h; and / or During the crystal growth process, the seed crystal rod fixed with the silicon carbide seed crystal rotates at a speed of 5-100 r / min.

7. The growth method according to claim 3, characterized in that: After the crystal growth, the method further includes a step of removing residues on the surface of the cubic silicon carbide crystal by using a mixed acid and water; the mixed acid contains HNO3 and HF.

8. The growth method according to claim 7, characterized in that: The volume ratio of HNO3 to HF in the mixed acid is 2:1.

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