Method for producing sic single crystal and method for suppressing dislocations in sic single crystal

Abstract

SiC single crystals are manufactured by the following method: a molten alloy of silicon and a metallic element M that increases the solubility of carbon is impregnated into a SiC sintered body to form a SiC crucible; silicon and M are placed in the crucible and heated to melt the silicon and M and form a Si-C solution; silicon and carbon are dissolved from the crucible surface in contact with the solution into the solution; a SiC seed crystal is brought into contact with the upper layer of the solution using a solution method to grow a first SiC single crystal on the SiC seed crystal; and a second SiC single crystal is grown in bulk on the surface of the solution-grown first SiC single crystal using a sublimation or gas phase method. This method enables the manufacture of low-dislocation, high-quality SiC single crystals using a vapor phase method.

Description

Methods for manufacturing SiC single crystals and methods for suppressing dislocations in SiC single crystals This invention relates to silicon carbide (SiC) crystal growth technology. More specifically, this invention relates to a method for manufacturing SiC single crystals that enables the stable production of low-dislocation, high-quality SiC single crystals, and to a method for suppressing dislocations in SiC single crystals. SiC is a wide bandgap semiconductor material. Due to its excellent thermal conductivity and chemical stability, as well as its dielectric collapse and transistor properties (such as saturation drift velocity), SiC possesses fundamental physical properties that make it highly suitable for power devices. For these and other reasons, SiC holds great promise as a next-generation power device material. Commercialization of SiC power devices has already been reported. However, besides the lack of sufficiently low-dislocation and high-quality single-crystal substrates, SiC substrates are expensive compared to silicon substrates. The main reason why low-dislocation, high-quality SiC single-crystal substrates are difficult to manufacture is that SiC does not melt under atmospheric pressure. In the case of silicon, which is widely used as a semiconductor device substrate, the melting point at atmospheric pressure is 1,414°C, and low-dislocation, high-quality, large-diameter single crystals can be obtained from silicon melt using the Tchaikovsky (CZ) method or the floating zone (FZ) method. In contrast, because SiC sublimates at approximately 2,000°C when heated under atmospheric pressure, SiC single crystals cannot be manufactured using crystal growth methods based on the CZ or FZ methods. Therefore, SiC single crystals are currently primarily manufactured using sublimation methods, such as the modified Lely process. Sublimation is currently the only method for mass-producing SiC single crystals. 4-inch diameter SiC single crystal substrates manufactured in this way are widely available commercially, and 6-inch diameter SiC single crystal substrates are also now in mass production and commercially available. However, when SiC single crystals obtained through sublimation are used to manufacture power devices, the device characteristics are not always suitable. This is because achieving low dislocations in SiC single crystals is not easy. Crystal growth via sublimation involves a vapor deposition method. The growth rate is low, and temperature control within the reaction space is difficult. In recent years, due to significant technological improvements and refinements, the density of micropipe dislocations has been reduced. However, lattice dislocations affecting the electrical properties of devices, such as threaded helical dislocations (TSD), threaded edge dislocations (TED), and bottom plane dislocations (BPD), still exist at high densities within single crystals. Recently, the wafer size specification for semiconductor device substrates has shifted from 4-inch diameter to 6-inch diameter. As the diameter increases, the number of dislocations in the crystal rises, resulting in lower current device yields compared to 4-inch diameter wafers. The dislocation problem is likely to worsen as technology moves to larger diameter substrates (8 inches and above). In such cases, the quality of the seed crystal is crucial because seed crystals propagate dislocations via sublimation or gas phase growth. Clearly, as the single crystal diameter increases, high-quality, large-diameter seed crystals become necessary; however, the number of dislocations increases with increasing diameter, so high-quality seed crystals have not yet been achieved. On the other hand, in the case of crystal growth using solution methods, studies on solvent composition and crucible materials supplying carbon have shown that growth rates of approximately 200 µm / h can be achieved, and the resulting crystals have significantly fewer dislocations and much higher quality than those obtained through sublimation.Recently, solution-based SiC crystal growth methods have gained attention (see, for example, JP-A 2000-264790, JP-A 2004-002173, and JP-A 2006-143555). As mentioned above, SiC itself does not melt under atmospheric pressure. In solution-based SiC single crystal manufacturing methods, SiC single crystals are obtained by dissolving carbon from a high-temperature zone at the bottom of a graphite crucible into a silicon melt within the crucible, bringing a SiC seed crystal into contact with this Si-C melt, or immersing a SiC seed crystal in this Si-C melt, and inducing epitaxial growth on the SiC seed crystal. In this solution method, because SiC crystal growth is carried out very close to thermal equilibrium compared to SiC single crystals obtained by sublimation, low-dislocation products can be obtained. Various techniques are available for solution methods to obtain SiC single crystals. In State-of-the-Art SiC Power Device Technology, Chapter 4, Section 1, 1.2: “SiC solution growth method,” pp. 41-43 (published May 14, 2010 by S&T Publishing, Inc.), these techniques are broadly categorized into four types: Moving Solvent Method (TSM), Slow Cooling Method (SCT), Vapor-Liquid-Solid (VLS), and Top Seed Solution Growth (TSSG). In this specification, unless otherwise stated, “solution method” refers to Top Seed Solution Growth (TSSG). In solution-based SiC single-crystal manufacturing methods, a silicon melt is first formed in a graphite crucible, and carbon is dissolved in the melt to form a Si-C solution. Because carbon in Si-C solutions has an extremely low solubility of approximately 1 atom%, transition metals are often added to Si-C solutions to promote carbon dissolution (see JP-A 2000-264790, JP-A 2004-002173, and JP-A 2006-143555). Elements reportedly added for this purpose include transition metals (such as Ti, Cr, Ni, and Fe), low-melting-point metals (such as Al, Sn, and Ga), and various rare earth elements. The type and amount of these added elements are determined based on several considerations. These include promoting carbon dissolution, ensuring SiC precipitates from the Si-C solution as the main phase and achieves a good liquid-phase equilibrium in the remaining solution, preventing the added elements from inducing the precipitation of carbides and other phases, ensuring stable precipitation of the target polymorph from the SiC crystal polymorph, and achieving a solution composition that maximizes the single crystal growth rate. Prior art solution-based SiC single crystal growth is typically carried out using procedures such as the following. First, the silicon starting material is placed in a crucible made of carbon or graphite and heated and melted under an inert atmosphere. The carbon component is supplied from the crucible to the silicon melt, forming a Si-C solution. In some cases, a carbon compound is placed in the crucible and melted together with the silicon starting material.After sufficient carbon components have dissolved in the Si-C solution, SiC seed crystals are brought into contact with the Si-C solution, and single crystals are grown using the temperature gradient already formed in the overall solution. However, this prior art solution method has some problems. One problem is that as SiC single crystal growth proceeds, the silicon component gradually disappears from the Si-C solution, and the solution composition slowly changes. When the solution composition changes during SiC single crystal growth, the SiC precipitation environment naturally changes. Therefore, it becomes difficult to stably continue SiC single crystal growth for a long period. The second problem is the excessive melting and incorporation of carbon from the crucible. As SiC single crystal growth proceeds, the silicon component gradually disappears from the Si-C solution, while carbon continues to be supplied from the crucible. A relative excess of carbon thus enters the Si-C solution, altering the Si / C ratio of the Si-C solution. The third problem is the precipitation of SiC polycrystals on the surface (especially the inner wall) of the crucible in contact with the Si-C solution. When excess carbon dissolves from the crucible into the Si-C solution, fine SiC polycrystals easily form on the inner wall of the crucible. During crystal growth, such SiC polycrystals float in the SiC solution and reach the vicinity of the solid-liquid interface between the SiC single crystal and the Si-C solution, interfering with the single crystal growth. Citation List: Patent Document 1: JP-A 2000-264790; Patent Document 2: JP-A 2004-002173; Patent Document 3: JP-A 2006-143555; Patent Document 4: JP-A 2015-110495; Patent Document 5: JP-A 2015-110496; Patent Document 6: JP-A 2015-110498; Patent Document 7: JP-A 2015-110499; Patent Document 8: JP-A 2015-110500; Patent Document 9: JP-A 2015-110501; Patent Document 10: JP-A 2017-031034; Patent Document 11: JP-A 2017-031036; Non-Patent Document 1: State-of-the-Art SiC Power Device Technology, Chapter 4, Section 1, 1.2: “SiC solution growth method,” pp. 41-43 (Published by S&T Publishing, Inc. on May 14, 2010) Non-Patent Document 2: Proceedings of 5. thAdvanced Power Semiconductor Subcommittee (2018), Vol. 05: “Low-TSD bulk growth by application of TSD conversion layer on solution-grown 4° off-axis C-face to sublimation process,” (Application of TSD conversion layer by solution growth for reduction of TSDs in 4H-SiC bulk crystals) pp. 125-126 Therefore, one object of the present invention is to provide a method for manufacturing low-dislocation, high-quality SiC single crystals even by gas-phase methods (such as sublimation or gas chromatography). Another object of the present invention is to provide a method for suppressing dislocations in SiC single crystals. SiC single crystals with fewer dislocations can be obtained by solution methods than those obtained by sublimation. However, in the case of crystal growth using a graphite crucible in conventional solution methods, voids are easily formed due to the influence of gas components present in the solvent and crucible. Therefore, after removing the bulk crystal from the crystal growth apparatus, crystals from near the seed crystal are avoided. Furthermore, in the case of crystal growth by methods such as sublimation, growth is unstable in the early stages. Therefore, after bulk growth, the portion of the crystal near the seed crystal is of poor quality and is excluded from device applications. Moreover, according to Proceedings of 5 thAdvanced Power Semiconductor Subcommittee (2018), Vol. 05: “Low-TSD bulk growth by application of TSD conversion layer on solution-grown 4° off-axis C-face to sublimation process,” (Application of TSD conversion layer by solution growth for reduction of TSDs in 4H-SiC bulk crystals) pp. 125-126. By using a solution method to grow SiC single crystals on a 4° off-axis C-face of 4H-SiC, a growth surface with low helical dislocation (TSD) density can be obtained. However, when chemical mechanical polishing or other processes are performed to remove deposits and surface irregularities on the growth surface, dislocation reconversion occurs in the subsequent bulk growth using a vapor phase method, leading to an increase in dislocations. Furthermore, because the seed crystal used in the sublimation method, as reported above, is grown in a solution on a 4° off-axis C-face, solvent retention often becomes problematic as the growth thickness increases. That is, the quality of the crystals in the early stage of growth is important for achieving higher quality by gas phase method after solution growth. It is necessary to stabilize the carbon concentration in the solvent after removing the gas components that cause voids and defects from the early stage of growth. Therefore, in the first embodiment, the present invention provides a method for manufacturing SiC single crystals, the method comprising the following steps in sequence: forming a SiC crucible by alloying silicon with a metal element M that increases the solubility of carbon into a melt and immersing the melt into a SiC sintered body having a relative density of 50 to 90%; placing silicon and the metal element M in the SiC crucible and heating the crucible to melt the silicon and the metal element M in the crucible and form a Si-C solution; dissolving the silicon and carbon constituting the SiC crucible from the surface of the SiC crucible in contact with the Si-C solution into the Si-C solution; growing a first SiC single crystal on the SiC seed crystal by contacting the top portion of the Si-C solution with the SiC seed crystal by a solution method; and growing a second SiC single crystal on the surface of the solution-grown first SiC single crystal by a sublimation method or a gas method. In a preferred embodiment of the manufacturing method of the first state sample according to the present invention, the metal element M placed in the SiC crucible is an unbonded metal element or an alloy including multiple metal elements but excluding silicon.In another preferred embodiment of the above manufacturing method, the metal element M comprises: at least one first metal element M1 selected from the group consisting of: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, and Lu; and at least one second metal element M2 selected from the group consisting of: Ti, V, Cr, Mn, Fe, Co, Ni, and Cu; and / or at least one third metal element M3 selected from the group consisting of: Ga, Ge, Sn, Pb, and Zn. In the above embodiment, the metal element M may include the first metal element M1 and the second metal element M2. The total content of metal element M in the Si-C solution may be from 1 to 80 atomic percent of the combined amount of silicon and metal element M. The content of the first metal element M1 in the Si-C solution may be at least 1 atomic percent of the combined amount of silicon and metal element M, and the content of the second metal element M2 and the third metal element M3 in the Si-C solution may each be at least 1 atom of the combined amount of silicon and metal element M. In yet another preferred embodiment, the SiC sintered body has an oxygen content of 100 ppm or less. In yet another preferred embodiment, the first SiC single crystal is grown by solution method at a Si-C solution temperature between 1,300 and 2,300 °C. In yet another preferred embodiment, fabrication is performed in a SiC crucible held in a second crucible made of heat-resistant carbon material. In yet another preferred embodiment, the first SiC single crystal grown by solution method has a thickness from 10 to 1,000 µm. In yet another preferred embodiment, the SiC crucible and Si-C solution are reused repeatedly. In the second embodiment, the present invention provides a method for suppressing dislocations in SiC single crystals. This method includes the following steps, in sequence: forming a SiC crucible by immersing an alloy of silicon and a metal element M that increases the solubility of carbon into a melt and then immersing the melt into a SiC sintered body having a relative density of 50% to 90%; placing silicon and the metal element M in the SiC crucible and heating the SiC crucible to melt the silicon and the metal element M and form a Si-C solution; dissolving the silicon and carbon constituting the SiC crucible from the surface of the SiC crucible in contact with the Si-C solution into the Si-C solution; and contacting a SiC seed crystal with the top portion of the Si-C solution using a solution method to grow a first SiC single crystal on the SiC seed crystal. In a preferred embodiment of the dislocation suppression method of the second embodiment of the present invention, the method further includes the step of bulk growing a second SiC single crystal on the surface of the solution-grown first SiC single crystal using a sublimation method or a gas method. In another preferred embodiment, the misalignment suppression method further includes the following steps: providing a SiC single crystal wafer obtained from a second SiC single crystal grown by sublimation or gas method as a seed crystal, and growing a third SiC single crystal on the SiC seed crystal by solution method.In another preferred embodiment, the dislocation suppression method further includes the step of bulk growing a fourth SiC single crystal on the surface of a solution-grown third SiC single crystal by sublimation or a gas-phase method. [Advantages of the Invention] Even when using SiC wafers cut from SiC ingots manufactured by a gas-phase method (such as sublimation), the present invention can reduce the number of dislocations by growing SiC single crystals on SiC wafers using a specific solution method. Furthermore, low-dislocation, high-quality SiC single crystals can be obtained by bulk growing the growth surface of this SiC single crystal using a gas-phase method (such as sublimation or a gas-phase method). Specifically, by using a solution method to grow crystals from approximately 10 µm to approximately 1,000 µm on SiC wafers manufactured by sublimation, dislocations can be significantly reduced. Even if SiC wafers have more dislocations due to their large diameter, the quality of bulk crystals obtained by sublimation or a gas-phase method can be increased by reducing the number of dislocations in this way, and using the resulting wafer as a seed (substrate). The object, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. The method for manufacturing SiC single crystals of the present invention uses a solution method, wherein a seed crystal is brought into contact with a Si-C solution (Si-C melt) held in a crucible; this method is called top seed solution growth (TSSG). That is, the SiC single crystal manufacturing method of the present invention is characterized by including the following steps: forming a SiC crucible by immersing an alloy of silicon and a metal element M that increases the solubility of carbon into a melt and immersing the melt into a SiC sintered body having a relative density of 50 to 90%; placing silicon and the metal element M in the SiC crucible and heating the crucible to melt the silicon and the metal element M in the crucible and form a Si-C solution; dissolving the silicon and carbon constituting the SiC crucible from the surface of the SiC crucible in contact with the Si-C solution into the Si-C solution; contacting the top portion of the SiC seed crystal with the Si-C solution by a solution method to grow a first SiC single crystal on the SiC seed crystal; and bulk growing a second SiC single crystal on the surface of the solution-grown first SiC single crystal by a sublimation method or a gas method. Figure 1 is a cross-sectional view showing an example of a SiC single crystal manufacturing apparatus (furnace) that can be suitably used when growing SiC single crystals by solution method. This figure shows: a SiC crucible 1 for holding the Si-C solution, a second crucible 2 made of heat-resistant carbon material for holding the SiC crucible 1, a SiC single crystal 3 (seed crystal), a Si-C solution 4 held in the SiC crucible 1, a shaft 5 for rotating the SiC crucible 1 and the second crucible 2 during SiC single crystal growth, a shaft 6 for holding the SiC single crystal 3 and rotating the SiC single crystal 3 during crystal growth, a heatsink 7 made of graphite or the like, a heat shield 8 made of graphite or the like, a top cover 9 for preventing the evaporation of the Si-C solution, and a radio frequency (RF) coil 10 for the interior of the furnace and for setting the Si-C solution to a given temperature and temperature distribution. Although not shown in the illustrations, the heating furnace is also equipped with an exhaust port and exhaust valve for venting the furnace atmosphere, and an inlet port and inlet valve for introducing gas into the furnace. Typically, the crucible is filled with silicon before heating, although a carbon source may be added together with the silicon. When the inside of the crucible is heated, immediately after heating, the silicon and carbon constituting the crucible dissolve from the SiC crucible surface, which is in contact with the silicon melt or with the Si-C solution after the carbon has dissolved, into the silicon melt or the Si-C solution. Before heating, SiC and silicon may also be added together or together with silicon and carbon to the crucible. In an embodiment of the invention, the SiC crucible 1 is composed of a SiC sintered body. This SiC sintered body has a relative density of at least 50%, and preferably at least 70%, but not more than 90%, more preferably not more than 88%, and more preferably not more than 85%. As used in this article, "relative density" refers to the measured or calculated density of the SiC sintered body relative to the true density of SiC, which is 3.22 g / cm³. 3The ratio (%); that is, the value obtained by dividing the measured density or calculated density of the SiC sintered body by the true density of SiC, expressed as a percentage. The measured density is, for example, the value obtained by measuring the SiC sintered body using the Archimedes method. The calculated density is the value obtained by dividing the weight of the SiC sintered body by the volume of the SiC sintered body, which is calculated from the measured dimensions of the SiC sintered body (i.e., in the case of a cylindrical crucible, the outer diameter, height, inner diameter (cavity diameter), and cavity height). The SiC crucible formed from the SiC sintered body having a relative density within the above range can be obtained by, for example, dry pressing or slip casting, although the manufacturing method is not limited to these methods. A metal element M that increases the solubility of carbon in the Si-C solution is added to the Si-C solution 4 held in the SiC crucible 1. It is advantageous to add the metal element M that increases the solubility of carbon to the Si-C solution because when using the SiC crucible, the formation of metal carbides due to the bonding between the added metal element M and carbon is prevented. When using a carbon crucible (graphite crucible), the silicon ratio in the Si-C solution decreases, or excess carbon enters the solution, reducing the Si / C ratio. This makes it easier for the added metal element M, which promotes carbon dissolution, to combine with carbon, resulting in the formation of metal carbides. Such metal carbides have high melting points and float in the Si-C solution; if these floating metal carbides reach the vicinity of the seed crystal surface and deposit there, SiC single crystal formation becomes impossible. In contrast, when using a SiC crucible, excess carbon C does not enter the Si-C solution. Therefore, metal carbide formation is suppressed, and SiC single crystal growth is not hindered. When silicon and a metal element M that increases the solubility of carbon are placed in a SiC crucible 1 formed from a SiC sintered body with a relative density of 50% to 90%, the pores of which are empty and not filled by Si-C solution or other melts (solid at room temperature), such as the state of the SiC crucible before use, and when silicon and metal element M are melted to form a Si-C solution, if the metal element M placed in the crucible is unbonded or is an alloy that does not contain silicon, the low-melting-point metal or alloy preferentially penetrates into the SiC sintered body, and the metal element M reacts with the SiC crucible, causing the composition of the Si-C solution in the SiC crucible to ultimately deviate from the desired composition. Therefore, in this invention, before placing silicon and the metal element M that increases carbon solubility in the SiC crucible, an alloy of silicon and metal element M, preferably an alloy having a substantially similar compositional ratio to the Si-C solution during SiC single crystal growth, is melted and pre-impregnated into the SiC sintered body, i.e., pre-impregnated into the pores of the SiC sintered body, to provide the SiC crucible 1. Specifically, the method may involve placing the alloy in the SiC crucible and heat-treating it within a temperature range, for example, at least 1,300°C, and preferably at least 1,500°C, but not exceeding 2,300°C, and preferably not exceeding 2,000°C. The heat treatment time is typically from 1 to 10 hours.Impregnation can be carried out under an inert atmosphere (such as argon or nitrogen), a vacuum (reduced pressure) atmosphere, or a combination thereof (e.g., an inert atmosphere followed by a reduced pressure atmosphere). Examples of metallic element M include: at least one first metallic element M1, selected from the group consisting of: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, and Lu; at least one second metallic element M2, selected from the group consisting of: Ti, V, Cr, Mn, Fe, Co, Ni, and Cu; and at least one third metallic element M3, selected from the group consisting of: Ga, Ge, Sn, Pb, and Zn. The total content of metallic element M in the Si-C solution is preferably at least 1 atomic% of the combined amount of silicon and M, and particularly at least 20 atomic% but preferably not more than 80 atomic% and particularly not more than 50 atomic%. In this invention, the metal element M placed in an unheated crucible along with silicon and arbitrarily added carbon and / or SiC is preferably an unbonded metal element M or an alloy comprising multiple metal elements M but excluding silicon, particularly an alloy comprising multiple metal elements M. The metal element M may be composed individually of any one of the first to third metal elements M1, M2, and M3, or may be composed of suitable combinations of these metal elements, although it is preferably composed of the first metal element M1 combined with the second metal element M2 and / or the third metal element M3. A combination of metal elements M1 and M2 is particularly preferred. In this case, the content of the first metal element M1 in the Si-C solution is preferably at least 1 atomic% of the combined amount of silicon and M, more preferably at least 5 atomic%, but more preferably not more than 50 atomic%, and more preferably not more than 40 atomic%. Furthermore, the respective contents of the second metal element M2 and the third metal element M3 in the Si-C solution are preferably at least 1 atomic% of the combined amount of silicon and M, more preferably at least 2 atomic%, but not exceeding 30 atomic%, and more preferably not exceeding 20 atomic%. In the implementation of the present invention, using an apparatus such as described above, the SiC crucible 1 is inductively heated by an RF coil 10 to form a temperature distribution suitable for crystal growth in the Si-C solution 4. Consequently, silicon and carbon in the SiC constituting the SiC crucible 1, which is in contact with the Si-C solution 4, dissolve from the SiC crucible 1 into the Si-C solution 4. Next, a SiC seed crystal 3 is brought into contact with the Si-C solution 4 at the top of the SiC crucible 1 to grow a SiC single crystal on the SiC seed crystal 3. Therefore, the temperature on the inner surface of the SiC crucible in contact with the Si-C solution is sufficiently high to dissolve silicon and carbon in the SiC constituting the crucible into the Si-C solution 4. Furthermore, the temperature near the solid-liquid interface between the SiC seed crystal 3 and the Si-C solution 4 is made high enough for SiC to grow single crystals on the SiC seed crystal 3.In the SiC single crystal growth step, by appropriately controlling the induction heating conditions from the RF coil, appropriately setting the relative position of the crucible and the RF coil (especially in the vertical direction), and appropriately rotating the crucible and the SiC single crystal (seed), a desired temperature distribution can be formed in the Si-C solution. In this way, the growth rate of the SiC single crystal and the rate at which the SiC crucible components dissolve into the Si-C solution can be appropriately controlled. During crystal growth, the temperature of the Si-C solution is preferably controlled within a range of at least 1,300°C, more preferably at least 1,500°C, but more preferably not exceeding 2,300°C, and more preferably not exceeding 2,000°C. The seed crystal is brought into contact with the top of the Si-C solution in the SiC crucible to grow the SiC single crystal on the seed crystal. Therefore, in at least a portion of the contact area between the SiC crucible and the Si-C solution, a high-temperature region is formed in the Si-C solution that allows components from the SiC crucible to dissolve into the Si-C solution. Simultaneously, in the contact region between the Si-C solution and the seed crystal or the growth surface of the SiC single crystal grown on the seed crystal, a low-temperature region is formed in the Si-C solution where SiC can grow into a single crystal on the seed crystal or the SiC single crystal grown on the seed crystal. The Si-C solution has a temperature distribution, preferably such that the temperature gradually increases from the vicinity of the seed crystal towards the inner surface of the SiC crucible (i.e., the surface in contact with the Si-C solution) (especially the entire Si-C solution), and preferably such that the temperature gradually increases from the top to the bottom of the Si-C solution (especially the entire Si-C solution). In this case, an effective method is to set the temperature difference between the high-temperature region and the low-temperature region to, for example, at least 5°C, especially at least 10°C, and not exceeding 200°C, especially not exceeding 100°C. The temperature gradient in the Si-C solution is preferably at least 1°C / cm, especially at least 5°C / cm, and preferably not exceeding 50°C / cm, especially not exceeding 30°C / cm. SiC single crystal growth is usually carried out under helium, argon, or other inert atmospheres. Figure 1 shows the method of heating the crucible under radio frequency (RF) waves. However, the heating method is not limited to RF wave heating. Depending on factors such as the controlled temperature of the Si-C solution, other methods such as resistance heating can be used. Figure 2 is a diagram illustrating how silicon and carbon dissolve from the SiC crucible into the Si-C solution when growing SiC crystals using a SiC crucible formed from a SiC sintered body with a relative density of 50% to 90%. By creating a temperature distribution suitable for crystal growth in the Si-C solution 4, silicon and carbon from the SiC constituting the SiC crucible 1 dissolve from the surface of the SiC crucible 1 (especially the high-temperature region) in contact with the Si-C solution 4 into the Si-C solution 4. The dissolved silicon and carbon become the fresh silicon and carbon components in the Si-C solution 4 and serve as the component source for the single crystal grown on the SiC seed crystal 3. This diagram also shows the second crucible 2, the rotating shaft 6, and the top cover 9, all corresponding to similar features in Figure 1.In an environment where silicon and carbon dissolve from SiC crucible 1 into Si-C solution 4, no SiC polycrystals precipitate on the crucible surface in contact with the Si-C solution. This is because the conditions under which the SiC constituting SiC crucible 1 dissolves into the Si-C solution to become silicon and carbon do not allow silicon and carbon to precipitate out of SiC. In other words, by using a crucible made of SiC as a container for the Si-C solution, SiC polycrystal precipitation on the crucible surface in contact with the Si-C solution is suppressed. Furthermore, by using a SiC crucible formed from a SiC sintered body with a relative density of 50% to 90%, the Si-C solution not only contacts the surface of the SiC crucible but also penetrates into the interior (pores) of the sintered body. The arrows in Figure 2 indicate that SiC dissolves efficiently and is supplied from inside the SiC crucible, increasing the crystal growth rate and suppressing SiC polycrystals. Therefore, a state similar to that shown in Figure 2 in the solution appears to be achieved. When the relative density of the SiC sintered body constituting the SiC crucible is less than 50%, SiC decomposes into SiC particles when the SiC crucible dissolves, resulting in a noticeable state where SiC particles float in the Si-C solution. At a relative density greater than 90%, the SiC solution virtually does not penetrate into the interior (pores) of the sintered body, thus failing to achieve efficient dissolution of SiC in the SiC solution. In contrast, Figure 3 illustrates the process by which silicon and carbon dissolve from the SiC crucible into the Si-C solution when growing SiC crystals using a conventional dense SiC crucible (e.g., a SiC crucible formed from a SiC sintered body with a relative density greater than 90%). In this situation, because the Si-C solution 4 only contacts the surface of the SiC crucible 1 and insufficient silicon and carbon dissolve into the Si-C solution 4, the supply of SiC (dissolving into the Si-C solution) from the SiC crucible is not uniform in the contact area between the SiC crucible and the Si-C solution. Instead, SiC dissolution preferentially occurs in the high-temperature region of the SiC crucible (especially in the lower corner indicated by the arrow in Figure 3), making it difficult for SiC single crystals to grow for a long time. This diagram also shows that the second crucible 2, SiC seed crystal 3, rotating shaft 6, and top cover 9 all correspond to similar features in Figure 1. Furthermore, in the SiC crucible 1 of this invention, because the SiC sintered body (more precisely, the pores in the SiC sintered body) is pre-impregnated with a molten alloy of silicon and metal element M (preferably a molten alloy having substantially the same compositional proportions as the Si-C solution used when growing SiC single crystals), when silicon and metal element M are melted to form a Si-C solution, metal element M does not preferentially react with the SiC crucible, so the Si-C solution in the SiC crucible remains at the desired composition. Silicon and carbon continuously dissolve from the SiC crucible. Typically, by rotating the crucible and seed crystal simultaneously for single crystal growth, the composition in the Si-C solution can be made uniform due to the stirring effect. In Figure 1, the SiC crucible 1 is placed in a second crucible 2 made of heat-resistant carbon material.In this invention, which uses a SiC crucible formed from a SiC sintered body having a relative density of 50% to 90%, the Si-C solution sometimes leaks through pores in the SiC sintered body to the outer surface of the SiC crucible. Therefore, it is preferable to place the SiC crucible in a second crucible. In this case, the second crucible 2 is preferably formed of a material having a density that prevents the Si-C solution from leaking. Using a second crucible also has the advantage of promoting control of the temperature distribution in the Si-C solution. Oxygen is usually present as an impurity in the SiC sintered body constituting the SiC crucible. The oxygen contained in the SiC sintered body forms oxide (SiO). Because the boiling point of SiO is about 1,880°C, when the temperature of the Si-C solution is equal to or higher than this boiling point, there is a risk that SiO will be incorporated into the crystal growth surface and create voids in the SiC single crystal when SiO vaporizes in the Si-C solution containing dissolved SiC and this gaseous SiO reaches the interface (solid-liquid interface) between the grown SiC single crystal and the Si-C solution. When oxygen present in the SiC sintered body dissolves into the Si-C solution containing dissolved SiC, and the temperature of the Si-C solution is below the boiling point of SiO, there is a risk that oxygen will be incorporated into and voids will be generated in the SiC single crystal when oxygen reacts with silicon in the Si-C solution to form SiO and this SiO reaches the interface (solid-liquid interface) between the grown SiC single crystal and the Si-C solution. Therefore, the SiC sintered body preferably has an oxygen content of no more than 100 ppm. In the solution method, a SiC single crystal is provided as a seed crystal. The seed crystal used for this purpose can be, for example, a SiC single crystal obtained by sublimation or a SiC single crystal obtained by the solution method (here, "solution method" is broadly understood to include the above-mentioned moving solvent method, slow cooling technology, vapor-liquid-solid method, and top seed crystal solution growth method). In the SiC single crystal manufacturing method of the present invention, a SiC crucible is obtained by impregnating a SiC sintered body with a relative density of 50% to 90% with an alloy of silicon and a metal element M that increases the solubility of carbon. Under heating of the crucible, the SiC constituting the SiC sintered body and serving as the source of silicon and carbon dissolves from the interior of the sintered body into a Si-C solution, thereby efficiently supplying silicon and carbon to the Si-C solution. Therefore, silicon and carbon are supplied uniformly and in appropriate amounts from the entire contact area between the SiC crucible and the Si-C solution, enabling the stable manufacture of high-quality SiC single crystals over a long period at a fast growth rate. The SiC single crystal grown by the above solution method preferably has a thickness of at least 10 µm, and more preferably at least 50 µm. There is no specific upper limit to the thickness of the SiC single crystal grown by the solution method. When a single crystal with higher crystallinity must be used as a seed crystal (substrate) in the following vapor phase growth method, the thickness can be set to more than 1,000 µm. However, the thickness is typically preferred to be 1,000 µm or less, and from a productivity standpoint, 150 µm or less. The growth surface of the SiC single crystal obtained by the above solution method is a high-quality surface with several defects (such as dislocations).In this case, the obtained SiC single crystal can be directly provided to the next step, namely, after simply removing the adhering solvent by surface treatment (such as hydrofluoric acid treatment) without any further specific processing (such as grinding), a step of bulk SiC single crystal growth by sublimation or gas phase method. Furthermore, to eliminate strain, defects, etc., that occur in SiC single crystals obtained by solution method due to processing, such surface damage can be improved by, for example, environmental heat treatment. Moreover, in the implementation of this invention, the SiC crucible and Si-C solution can be repeatedly used to manufacture SiC single crystals by the above-mentioned solution method. In this invention, a second SiC single crystal is then bulk grown on the surface of the first SiC single crystal grown by solution method by sublimation or gas phase method. In this way, SiC can be bulk grown by direct gas phase growth while maintaining the low dislocation states of the first SiC single crystal grown by solution method. Here, the bulk growth of a second SiC single crystal by sublimation involves: placing a solid SiC starting material (usually powder) at the bottom of a graphite crucible arranged in a manufacturing apparatus; heating the bottom of the crucible to a high temperature (at least 2,000°C, for example, between 2,200°C and 2,600°C) to perform SiC sublimation; conveying the material in an inert atmosphere within the apparatus; and then recrystallizing the SiC seed crystal placed in a low-temperature region to grow a bulk single crystal. Bulk growth of SiC single crystals by gas method involves crystal growth by introducing externally sourced silane (SiH₂) in a thin-film CVD process. 4) With hydrocarbon gases (e.g., C) 2H 4) The gas is heated to between approximately 2,100°C and 2,300°C onto SiC seed crystals. The introduced gas reacts in the gas phase, temporarily forming clusters. These clusters are introduced into the growth region, where they decompose again, ultimately becoming the reaction precursors Si and SiC. 2 and Si 2C (a reaction precursor similar to sublimation recrystallization) and induction of crystal growth on SiC seed crystals. Method for suppressing dislocations in SiC single crystals: The method for suppressing dislocations in SiC single crystals according to the present invention is characterized by the following steps: forming a SiC crucible by immersing an alloy of silicon and a metal element M that increases the solubility of carbon into a melt and then immersing the melt into a SiC sintered body having a relative density of 50% to 90%; placing silicon and metal element M in the SiC crucible and heating the SiC crucible to melt the silicon and metal element M in the crucible and form a Si-C solution; dissolving the silicon and carbon constituting the SiC crucible from the surface of the SiC crucible in contact with the Si-C solution into the Si-C solution; and contacting the top portion of the SiC seed crystal with the Si-C solution using a solution method to grow a first SiC single crystal on the SiC seed crystal. Here, "solution method" is the same as the solution method described above. In this way, defects such as dislocations on the growth surface of the SiC single crystal can be suppressed (dislocations are reduced). Here, "misalignment" refers to thread misalignment (thread helix misalignment (TSD), thread edge misalignment (TED)) and bottom surface misalignment (BPD). These misalignments are observed using the following alkaline etching method or X-ray reflection topology, and the results are used to determine the number of misalignments (misalignment density) to assess the degree of misalignment suppression (misalignment reduction). <Alkaline Etching Method> A SiC crystal with a mirror-polished Si surface having an arithmetic mean roughness Ra (JIS B0601 (2001)) of no more than 10 nm is immersed in molten KOH at 500°C for approximately 10 minutes, and the thread misalignments (thread helix misalignment (TSD), thread edge misalignment (TED)) and bottom surface misalignment (BPD) appearing on the Si surface are observed as etched holes of different shapes. The number of misalignments per square centimeter (misalignment density) is determined by counting the misalignments observed in the complex domain under a 100× magnification optical microscope on the examined surface after molten KOH treatment. <X-ray Reflection Topology> Using an X-ray topology system, dislocations within the crystal are non-destructively examined by measuring the X-ray refraction intensity when the sample surface is irradiated with S-rays at an acute angle. Black dots in the resulting X-ray topology are identified as spiral dislocations (TSDs), and filamentary features are identified as bottom-plane dislocations (BPDs). The number of dislocations per square centimeter (dislocation density) is determined by counting the dislocations observed in a field of view with a given surface area. Preferably, the method for suppressing dislocations in SiC single crystals of this invention also includes the step of bulk growing a second SiC single crystal on the surface of a solution-grown SiC single crystal using a sublimation or gas method. Here, the sublimation and gas methods are the same as described above. This maintains the bulk-grown SiC single crystal in a low-dislocation state. The method for suppressing dislocations in SiC single crystals according to the present invention preferably further includes the following steps: providing a SiC single crystal wafer obtained from a second SiC single crystal grown by sublimation or gas method as a seed crystal, and growing a third SiC single crystal on the SiC seed crystal by solution method.In this way, defects (such as dislocations) on the growth surface of SiC single crystals can be suppressed. The method of suppressing dislocations in SiC single crystals according to the present invention even more preferably includes a step of bulk growing a fourth SiC single crystal on the surface of a solution-grown SiC single crystal by sublimation or gas method. This keeps the bulk-grown SiC single crystal in a lower dislocation state. [Examples] Examples and comparative examples are given below to illustrate the invention more specifically, although the invention is not limited to these examples. In these examples, sample processing and sample inspection and evaluation (including dislocation inspection) were performed under the following conditions. [Alkali Etching Method] A SiC crystal with a Si surface having an arithmetic mean roughness Ra (JIS B0601 (2001)) polished to no more than 10 nm was immersed in molten KOH at 500°C for about 10 minutes, and thread dislocations (thread helix dislocation (TSD), thread edge dislocation (TED)) and bottom surface dislocation (BPD) appearing on the Si surface were observed as etched holes of different shapes. Specifically, grinding is performed from the seed side (Si face) to the growth side (C face), and misalignment inspection is conducted in the thickness direction. The etched pits are classified as follows: relatively large hexagons are identified as threaded helical dislocations (TSD), small hexagons as threaded edge dislocations (TED), and elliptical (teardrop-shaped) pits as bottom surface dislocations (BPD). Furthermore, the number of dislocations observed on the inspected surface after molten KOH treatment in the complex domain under a 100× magnification optical microscope is counted, and the dislocation density is determined. It should be noted that the etched pits only develop on the Si face and not on the C face. The Si face requires mirror polishing (Ra: 10 nm or less) because etching magnifies the scratches left behind, making the etched pits difficult to observe. [X-ray Reflection Topology] Using X-ray reflection topology, dislocations inside the crystal are inspected by the X-ray refraction intensity when the sample is irradiated with X-rays at an acute angle. This technique is characterized by reflecting dislocations up to 10 µm deep from the surface, enabling comparison of films and samples of different thicknesses. Because X-ray reflection topology is a non-destructive method, it can examine growth surfaces where C-plane growth occurs, regardless of whether the surface being examined is a Si or C-plane. Dislocations on the X-ray topology are distinguished by identifying black spots as threaded helical dislocations (TSDs) and filamentous features as bottom-plane dislocations (BPDs). The following examples use Rigaku Corporation's XRT-micron, an X-ray topology system. [Raman Spectroscopy] When light illuminates a substance, the interaction between light and the substance results not only in reflection, refraction, and absorption, but also in a phenomenon called scattering. One such scattering effect caused by molecular vibrations is Raman scattering (inelastic scattering), where light is scattered at wavelengths different from the incident wavelength.Raman spectroscopy is a spectroscopic method that measures the wavelength and scattering intensity of Raman lines to identify and quantify the energy levels of substances. In this embodiment, SiC polymorphs are determined by analyzing the Raman shifts in Raman spectra obtained by laser irradiation. [Hydrofluorine and Nitric Acid Treatment] Hydrofluorine and nitric acid treatment involves immersing the sample at above 250°C in hydrofluoric acid and nitric acid prepared by mixing hydrofluoric acid, nitric acid, and water in a 1:1:2 ratio for 6 hours to remove the solvent and foreign matter adhering to the SiC crystals. After treatment, the sample is ultrasonically cleaned with pure water and then dried. [Direct Observation of Appearance] The appearance of the sample is examined by eye and by taking images using a single-lens reflex camera (EOS-X7, from Canon Inc.) equipped with a close-up lens (EFS 60 mm) under LED light irradiation from above the crystal sample. [Penetrating Observation] Penetrating observation of the sample was performed by capturing penetrating images using a single-lens reflex camera (EOS-X7, from Canon Inc.) equipped with a close-up lens (EFS 60 mm) under LED light illuminating the crystal sample from below (as in direct observation of the appearance). Example 1: SiC single crystal fabrication (crystal growth) was carried out in a fabrication apparatus similar to that shown in Figure 1, using a crucible-shaped SiC sintered body with an outer diameter of 60 mm, a height of 70 mm, an inner diameter (cavity diameter) of 50 mm, a cavity height of 60 mm, a relative density of 80%, and an oxygen content of 80 ppm. A Pr-Fe-Si alloy (composition: Pr 20 atom%; Fe 20 atom%; Si 60 atom%) corresponding to the total pore volume of the SiC sintered body (equivalent to 20% of the SiC sintered body volume) was added to a crucible-shaped SiC sintered body and heat-treated at 1,500°C in an argon atmosphere for 10 hours to impregnate the alloy into the pores of the SiC sintered body to form SiC crucible 1. Next, unbonded metallic forms of Pr, Fe, and Si were added to give a composition of Pr 20 atom%; Fe 20 atom%; Si 60 atom%; based on density calculations, the amounts were adjusted to give a Si-C solution depth of 27 mm. A 21 mm diameter × 0.3 mm thick single crystal (polymorph: 4H; coaxial, high-grade) was used as seed crystal 3. This single crystal was manufactured by sublimation and attached to a 19 mm diameter graphite seed axis (rotation axis 6) so that growth occurred on the C-plane. Crystal growth was performed at 2,000°C under an argon atmosphere by rotating the SiC crucible 1 and the seed axis (rotation axis 6) in opposite directions (one direction clockwise and the other counterclockwise) at individual speeds of 20 rpm and pulling the ingot at a rate of 0.1 mm / hr for 5 hours. Figure 4 shows the appearance of the growth surface (C-plane) of the obtained SiC single crystal sample, which is a plane perpendicular (orthogonal) to the seed axis direction. The actual dimensions of the photograph in Figure 4 are 27 mm high and 23 mm wide.In evaluating the appearance of the obtained SiC single crystal, Figure 4 shows that the growth surface of the SiC single crystal was found to be a crystal without any polycrystalline deposition. The growth rate of the SiC single crystal was 180 µm / hr. Grinding and polishing to provide a tilt in the thickness direction proceeded from the seed crystal portion (Si face) of the obtained SiC single crystal sample to the growth portion, forming a bevel (Si face) with a mirror-polished 2.6° tilt angle. Next, etch holes were developed on this bevel (Si face) using alkaline etching, and the type and number of dislocations were examined (Figures 5 and 6). Dislocations can be distinguished by their shape and size into threaded helical dislocations (TSD), threaded edge dislocations (TED), and bottom dislocations (BPD). In Figures 5 and 6, these dislocations are represented as TSD, TED, and BPD, respectively. These three types of dislocations were counted in each region of the bevel of the SiC single crystal sample (where observable). The number of dislocations in the seed crystal portion (Figure 5) was 5,152 / cm². 2 The number of dislocations in the solution-grown portion (Figure 6) is 952 / cm. 2 This confirms the reduction in dislocations due to the solution method. Furthermore, in the solution-grown portion (Figure 6), the number of bottom dislocations (BPD) is 0 / cm. 2Bottom misalignment is a killer misalignment that causes reduced yield during component manufacturing. Example 2: SiC single crystal manufacturing (crystal growth) was performed in a manufacturing apparatus similar to that shown in Figure 1, using a crucible-shaped SiC sintered body with an outer diameter of 90 mm, a height of 70 mm, an inner diameter (cavity diameter) of 80 mm, a cavity height of 60 mm, a relative density of 80%, and an oxygen content of 50 ppm. An amount of Nd-Fe-Si alloy (composition: Nd 20 atoms; Fe 20 atoms; Si 60 atoms) corresponding to the total pore volume of the SiC sintered body (equivalent to 20% of the SiC sintered body volume) was added to the crucible-shaped sintered body and heat-treated at 1,500°C in an argon atmosphere for 10 hours to impregnate the alloy into the pores of the SiC sintered body to form SiC crucible 1. Next, unbonded metallic forms of Nd, Fe, and Si were added to give a composition of 20 atomic% Nd, 20 atomic% Fe, and 60 atomic% Si; the amounts were adjusted based on density calculations to give a Si-C solution depth of 27 mm. A 50 mm diameter × 0.3 mm thick single crystal (polymorph: 4H; coaxial, baffle grade) was used as seed crystal 3. This single crystal was manufactured by sublimation and attached to a 49 mm diameter graphite seed axis (rotation axis 6) so that growth occurred on the C-plane. Crystal growth was carried out at 2,000 °C under an argon atmosphere by rotating the SiC crucible 1 and the seed axis (rotation axis 6) in opposite directions (one direction clockwise and the other counterclockwise) at separate speeds of 5 rpm and pulling the ingot at a rate of 0.1 mm / hr for 2 hours. Figure 7 shows the appearance of the growth surface (C-plane) of the obtained SiC single crystal sample. The actual dimensions of the photograph in Figure 4 are 51 mm high and 51 mm wide. Regarding the appearance of the obtained SiC single crystals, Figure 7 shows that the growth surface of the SiC single crystal is flat and free of attached polycrystals. In Figure 7, the circular black area represents a region where some Si-C solution adhered to the growth surface and formed protruding droplets when the seed crystal was separated from the Si-C solution after crystal growth was completed; this area was not the target of evaluation (this also applies to the black areas in Figures 10 and 15 below). The SiC single crystal grew to 300 µm in 2 hours, so the growth rate was 150 µm / hr. The crystal faces (Si faces) of the seed portion and the crystal faces (i.e., the growth faces, (C faces)) of the obtained SiC single crystal samples were ground to remove 100 µm of material, followed by polishing to a mirror finish. Dislocations on the polished surfaces were then examined using X-ray reflection topology (Figures 8 and 9). Therefore, the solution-grown portion (Figure 9) had fewer dislocations than the seed portion (Figure 8), confirming the reduction in the number of dislocations due to the solution method. Among the observed misalignments, the black dots in Figures 8 and 9 represent thread misalignment (TSD, TED), and the filamentous features represent bottom misalignment (BPD).Here, the SiC wafer used as a seed crystal has many dislocations and is of the baffle level, which cannot be used for device fabrication. However, the number of dislocations in the SiC single crystal is reduced by solution growth. Threaded helical dislocations (TSD), threaded edge dislocations (TED), and bottom surface dislocations (BPD) are counted in each field of view (2.1 mm × 1.6 mm area) on the polished surface of the SiC single crystal sample. Therefore, in the solution growth section (Fig. 9), the number of bottom surface dislocations (BPD), which has a significant impact on the yield of device fabrication, is 0 / cm. 2 The number of dislocations and other faults is also greatly reduced. That is, the number of dislocations in the seed crystal portion (Figure 8) is 50,115 / cm. 2 In the solution-grown portion (Figure 9), the number of dislocations was 1,144 / cm. 2This represents a reduction of approximately 98%. Furthermore, these results clearly demonstrate that even SiC wafers containing numerous dislocations and unsuitable for device fabrication under these conditions can be transformed into high-quality SiC single-crystal wafers when grown using a solution method as a seed crystal. These wafers can be directly used for device fabrication or as seed crystals (substrate) for vapor phase growth methods (such as sublimation or gas methods). Example 3 Next, solution growth was performed with the SiC single-crystal seed crystal being off-axis (the (0001) Si plane is slightly tilted to the surface normal in a specific direction ([11-20] direction)). That is, a SiC single crystal with a diameter of 50 mm and a thickness of 0.3 mm (polymorph: 4H; 4° off-axis, baffle level) attached to a 49 mm diameter graphite seed axis, such that growth occurs on the C-plane, was used as seed crystal 3. In addition, the SiC crucible and the metal composition (composition) placed in SiC crucible 1 are the same as in Example 2, and the SiC single crystal fabrication (crystal growth) is performed in a fabrication apparatus similar to that shown in Figure 1. Crystal growth is carried out at 2,000°C under an argon atmosphere by rotating SiC crucible 1 and the seed axis (rotation axis 6) in opposite directions (one direction clockwise and the other counterclockwise) at individual speeds of 5 rpm and pulling the ingot at a rate of 0.1 mm / hr for 2 hours. Figure 10 shows the appearance of the growth surface (C-plane) of the obtained SiC single crystal sample. The actual dimensions of the photograph in Figure 10 are 51 mm high and 51 mm wide. In evaluating the appearance of the obtained SiC single crystal, the growth surface of the SiC single crystal is flat and free of attached polycrystals. The growth surface of the SiC single crystal was examined using a laser microscope (magnification: 5×), thus confirming the formation of a giant step along the off-axis direction [11-20] on the C-plane (000-1). Next, to examine the crystal cross-section of the SiC single crystal sample, the sample was cut parallel to the off-axis direction [11-20] and perpendicular to the C-plane (000-1), and the cross-section was examined. Therefore, within the total thickness of 300 µm of the solution-grown portion, it was confirmed that the Si-C solution component (hereinafter also referred to as "solvent") was retained in the solution-grown portion (here, "retention" means that the solution-grown portion unintentionally includes the Si-C solution component) to a thickness of at least 150 µm on the surface layer side (Fig. 12). This is likely because the formation of a giant step due to the growth of an off-axis SiC single crystal (off-axis substrate) promotes solvent retention. Figure 12 shows a cross-section of the crystal, captured by a single-lens reflex camera (EOS-X7, from Canon Inc.) equipped with a close-up lens (EFS 60 mm) under LED white light illuminating the crystal sample from below. However, despite the presence of solvent in the resulting SiC single crystal sample, the growth thickness of the SiC single crystal was 300 µm within 2 hours, resulting in a growth rate of 150 µm / hr.Because a normal crystal with a thickness of up to 150 µm is obtained on the seed side of the solution-grown portion, grinding is performed to remove a 200 µm thick material portion from the crystal plane of the solution-grown portion and to remove a 100 µm thick material portion from the crystal plane of the seed portion. Then, polishing is performed to give the surface a mirror finish (arithmetic mean roughness Ra: 10 µm or less). The dislocations on these polished surfaces are then examined using X-ray reflection topology (Figures 13 and 14). The solution-grown portion (Figure 14) was found to have fewer dislocations than the seed portion (Figure 13), confirming the reduction in dislocations due to the solution method. Here, the SiC wafer used as the seed has many dislocations and is at the baffle level, unusable for device applications, but the dislocations are reduced through solution growth using the solution method. Threaded helical misalignment (TSD), threaded edge misalignment (TED), and bottom misalignment (BPD) are counted in each field of view (2.1 mm × 1.6 mm area) on the polished surface of the SiC single crystal sample. Therefore, in the solution growth section (Fig. 14), the number of bottom misalignment (BPD), which is a killer misalignment that has a great impact on the yield of device manufacturing, is 0 / cm. 2 The number of dislocations and other faults is also greatly reduced. That is, the number of dislocations in the seed crystal portion (Fig. 13) is 29,762 / cm. 2 In the solution-grown portion (Fig. 14), the number of dislocations was 4,062 / cm. 2This represents a reduction of approximately 86%. Comparative Example 1: SiC single crystal fabrication (crystal growth) was performed in a fabrication apparatus similar to that shown in Figure 1, using a graphite crucible with an outer diameter of 90 mm, an inner diameter of 80 mm, an outer height of 90 mm, and an inner height of 90 mm. Unbonded metallic forms of Nd, Fe, and Si were each added to the graphite crucible, resulting in a composition of Nd 16 atomic%, Fe 20 atomic%, and Si 64 atomic%, with the amount adjusted to a Si-C solution depth of 27 mm based on density calculations. A 50 mm diameter × 0.3 mm thick single crystal (polymorph: 4H; coaxial, baffle-grade) was used as a seed crystal, attached to a 49 mm diameter graphite seed axis in a manner where growth occurs on the C-plane. Crystal growth was performed at 2,000°C under an argon atmosphere by rotating the crucible and seed axis in opposite directions (one direction clockwise and the other counterclockwise) at individual speeds of 5 rpm and pulling the ingot at a rate of 0.1 mm / hr for 2 hours. The SiC single crystal sample obtained in 5 hours had a growth thickness of 300 µm, representing a growth rate of 60 µm / hr. This is lower than the growth rate of 150 µm / hr in Example 2. Figure 15 shows the appearance of the growth surface (C-plane) on the obtained SiC single crystal sample. The actual dimensions of the photograph in Figure 15 are 51 mm high and 51 mm wide. When the appearance of the SiC single crystal obtained here is compared with the appearance of the SiC single crystal sample in Example 2 (Figure 7), no abnormalities in the growth surface are observed in either sample. Next, in order to examine the crystal cross-section of the SiC single crystal sample, the sample was cut perpendicular to the growth surface (C-plane), and then the cross-section was examined. The SiC single crystal sample obtained in Example 2 was prepared and the cross-section was examined in a similar manner. Therefore, in Comparative Example 1 (Fig. 16), numerous voids were observed in the solution growth portion near the seed crystal, while in Example 2 (Fig. 17), no voids were observed in the solution growth portion. This is likely because, in the early stages of growth, gaseous components (oxygen, nitrogen, etc.) present in the graphite crucible escape, hindering normal solution growth. In contrast, in this invention, because a crucible-shaped SiC sintered body with a low oxygen content (50 ppm) is used, crystal growth appears to proceed stably from the early stages without gas escaping from the crucible. Based on these results, when using a graphite crucible, it is necessary to grow a relatively thick layer of 200 to 300 µm to obtain a normal crystal growth surface, which is disadvantageous from a mass production point of view. Furthermore, additional difficulties are anticipated in the growth of off-axis SiC single crystals (off-axis substrates) used as seed crystals, where the solvent tends to become trapped in the solution growth portion. Since most SiC seed crystals used in the vapor phase method are 4° off-axis substrates, the generation of voids in the early stages of growth is naturally a critical issue.EXAMPLE 4 The SiC crucibles used in the present invention (i.e., SiC crucibles obtained by impregnating SiC sintered bodies having relative densities ranging from 50 to 90% with a fusion gold of silicon and a metal element M that increase the solubility of carbon) are suitable for long-term growth because the composition of the Si-C solution (solvent) does not fluctuate. Moreover, the time required for the growth of low misaligned SiC crystals using the SiC crucible of the present invention is about 1 to 2 hours. Therefore, the possibility of reusing the SiC crucible used in the present invention with the Si-C solution (solvent) was studied under consideration of mass manufacturing. The study method involves repeating the crystal growth of the SiC single crystal without displacing the SiC crucible and Si-C solution (solvent) under the same conditions as in Example 2, i.e., using the same Si-C crucible and Si-C solution continuously without displacement, and determining the effect on the crystal quality of the resulting SiC single crystal sample. Namely, the crystal growth of SiC single crystals and evaluation of the crystal quality of each obtained SiC single crystal sample were performed in duplicate (five times). The evaluations performed were to examine the crystal appearance (determination of the presence or absence of polycrystal deposition and abnormal growth (e.g., two-dimensional nucleus growth)) and the determination of the growth rate, both in the same manner as in Example 2. The solvent stagnation (section test) performed in the compared embodiment was examined, and the crucible appearance was examined. Table 1 presents these results. Table 1. From these results, it was confirmed that the growth rate decreased with increasing number of crystal growth repeats, but because the appearance and cross-sectional appearance of the SiC single crystal sample did not cause problems and the crucible was also normal, it was confirmed that approximately five crystal growth rounds were feasible. The reason for the decrease in growth rate is thought to be that the SiC polycrystals formed in the crucible after crystal growth consume carbon that is supplied to the crystal seed (SiC single crystal). Thinking from an efficiency viewpoint, further increase in the number of repeated crystal growth rounds and stable crystal growth should be feasible if one is to establish a continuous growth system that can carry out the next crystal growth with Si-C solution in the crucible without cooling after crystal growth. Compared embodiment 2 performed SiC single crystal growth under the same conditions as compared embodiment 1, except that the crystal growth was performed repeatedly without displacement using the same graphite crucible and Si-C solution (solvent) continuously. Evaluation was performed in the same manner as in Example 4 . Table 2 presents these results. Table 2 These results indicate that no polycrystalline deposition was observed on the SiC single-crystal sample during the first crystal growth round, but polycrystalline deposition occurred during the second round. Furthermore, the crystal growth cycle was halted due to the graphite crucible cracking during the second crystal growth round. The reuse of the Si-C solution (solvent) in the graphite crucible appears to have caused problems. Moreover, in Comparative Example 2, the growth rate of the second crystal growth round decreased by 57% compared to the growth rate of the first round. This is likely because after the first crystal growth round, the Si-C solution (solvent) cooled and SiC precipitated as a coating on the graphite crucible wall, hindering carbon dissolution from the crucible during the second crystal growth round. In contrast, in Example 4, the reduction in growth rate was small because the composition of the Si-C solution (solvent) was adjusted knowing that SiC would dissolve from the crucible. As indicated above, high-quality SiC single crystals can be stably and efficiently manufactured by repeatedly using the SiC crucible (i.e., a SiC crucible obtained by impregnating a SiC sintered body with a relative density of 50 to 90% with a molten alloy of silicon and a metal element M that increases the solubility of carbon) and a Si-C solution (solvent). Example 5 (i) SiC single crystal manufacturing by solution method (crystal growth) was carried out in a manufacturing apparatus similar to that shown in Figure 1, using a crucible shape and a SiC sintered body with an outer diameter of 180 mm, a height of 60 mm, an inner diameter (cavity diameter) of 150 mm, a cavity height of 40 mm, a relative density of 80%, and an oxygen content of 40 ppm. An amount of Nd-Fe-Si alloy (composition: Nd 20 atom%; Fe 20 atom%; Si 60 atom%) corresponding to the total pore volume of the SiC sintered body (equivalent to 20% of the SiC sintered body volume) was added to a crucible-shaped sintered body and heat-treated at 1,500°C in an argon atmosphere for 10 hours to impregnate the alloy into the pores of the SiC sintered body to form SiC crucible 1. Next, unbonded metallic forms of Nd, Fe, and Si were added to give the composition Nd 20 atom%; Fe 20 atom%; Si 60 atom%; based on density calculations, the amount was adjusted to give a Si-C solution depth of 27 mm. A 100 mm diameter × 1 mm thick single crystal (polymorph: 4H; 4° off-axis, baffle grade) was used as seed crystal 3, which was attached to a 99 mm diameter graphite seed axis (rotation axis 6) in a manner that growth occurred on the C-plane. Crystal growth was performed at 2,000°C under an argon atmosphere by rotating the SiC crucible 1 and the seed axis (rotation axis 6) in opposite directions (one direction clockwise and the other counterclockwise) at individual speeds of 5 rpm and pulling the ingot at a rate of 0.1 mm / hr for 1 hour. Dislocation observation of the C-face of the seed crystal to be used was performed beforehand using X-ray reflection topology.The obtained SiC single crystal sample (1) was evaluated, and the crystal plane (growth plane (C plane)) of the solution-grown portion of the SiC single crystal sample shown in Figure 18 has a mirror-like appearance as in Example 3, with giant steps uniformly formed on the C plane (000-1) in the direction of [11-20]. The polymorph of the obtained SiC single crystal sample was identified by Raman spectroscopy, and it was confirmed that the whole sample was 4H-SiC. The growth thickness of the solution-grown portion of the SiC single crystal sample was 100 µm in one hour, so the growth rate was 100 µm / hr. Next, the obtained SiC single crystal sample (1) was subjected to hydrofluoric acid treatment, followed by ultrasonic cleaning and drying to remove the solvent components attached to the growth plane. Then, the dislocations on the solution-grown plane (C plane) were examined by X-ray reflection topology. Thread helix misalignment (TSD), thread edge misalignment (TED), and bottom misalignment (BPD) are counted in each field of view (2.1 mm × 1.6 mm area). Therefore, in the solution growth section, the bottom misalignment (BPD), which is the killer misalignment that has a great impact on the yield of component manufacturing, is 0 / cm. 2 Furthermore, other dislocations are also greatly reduced. That is, the number of dislocations in the seed crystal portion is 32,506 / cm. 2 In the solution-grown section, the number of dislocations decreased to 4,020 / cm. 2 These results demonstrate that the present invention enables uniform crystal growth even in large-diameter solution growth. (ii) Bulk growth via sublimation: Next, the number of dislocations is reduced to 4,020 / cm. 2The SiC single crystal sample (1) was used as a seed crystal, and bulk growth was performed by sublimation as follows. The SiC single crystal sample (seed crystal) 11 was placed on the inner wall of the top (top cover 12a) of the reaction vessel 12 shown in FIG. 19, with the solution growth portion 11b facing down, and the SiC powder 13, which is the starting material, was placed directly below it. The reaction vessel 12 was installed in the sublimation reactor 20 shown in FIG. 20. Normal conditions were used for SiC growth in the sublimation reactor 20 in FIG. 20. Specifically, the starting material temperature was set between 2,200°C and 2,500°C, the seed crystal temperature was set between 2,100°C and 2,400°C, the temperature gradient was set from 1°C / cm to 50°C / cm, the pressure was set from 100 to 5,000 Pa (argon atmosphere), and the growth rate was set from 0.05 to 0.2 µm / hr. The resulting SiC single crystal (SiC ingot) sample (2) had a growth thickness of 5 mm. This sample was cut, then ground and polished to yield four 1 mm thick wafers. Dislocation observation of the wafers was performed using X-ray reflection topology in the same manner as described above, resulting in a dislocation count ranging from 4,210 to 4,400 / cm². 2 Furthermore, this wafer (misalignment count 4,210 / cm) 2 Under the conditions described in (i) above, solution growth was performed again to obtain a SiC single crystal sample (3). X-ray reflection topology was applied to the crystal planes of the obtained SiC single crystal sample (3) in the same manner as described above, and the threaded helical dislocation (TSD), threaded edge dislocation (TED), and bottom surface dislocation (BPD) were counted. In the solution growth section, the bottom surface dislocation (BPD), a killer dislocation that has a significant impact on the yield of device manufacturing, was 0 / cm. 2 Other misalignments were also greatly reduced, with the number of misalignments decreasing to 590 / cm. 2 Next, this SiC single crystal sample (4) was used as a seed crystal, and bulk growth was performed again by sublimation under the conditions described in (ii) above, resulting in a SiC single crystal sample (5). The obtained SiC single crystal sample (5) was subjected to dislocation observation by X-ray reflection topology in the same manner as described above, and the number of dislocations was found to be 625 to 643 / cm. 2Compared to the SiC single crystal sample (4) mentioned above, the increase in the number of dislocations may be due to the re-transformation or new formation of dislocations during bulk growth via sublimation. From the above results, it is evident that solution growth of a seed crystal (SiC wafer) manufactured via sublimation to a thickness of approximately 100 µm using the solution method of this invention reduces dislocations. Furthermore, even when this material is used as a seed crystal (substrate) for bulk growth via sublimation, a low dislocation state is maintained. These results also indicate that when a SiC single crystal with a low dislocation state is solution grown again using the solution method of this invention, dislocations are further reduced, demonstrating that it is feasible to maintain a further reduced dislocation state during bulk growth by using this material as a seed crystal. 1: SiC crucible 2: Second crucible 3: SiC single crystal (seed crystal) 4: Si-C solution 5, 6: Rotating shaft 7: Heater 8: Heat shield 9: Top cover 10: RF coil 11: Seed crystal 11a: Seed crystal part 11b: Solution growth part 11c: Grown SiC single crystal 12: Reaction vessel 12a: Top cover 12b: Carbon container 13: SiC powder 20: Sublimation reactor 21: RF coil 1 22: RF coil 2 23: Heat shield 24: Heat insulation body 25: Lifting platform [Figure 1] is a cross-sectional view showing an example of the main components of a SiC single crystal manufacturing apparatus that can be suitably used when growing SiC single crystals. [Figure 2] is a schematic diagram showing how silicon and carbon dissolve from the inside of the SiC crucible into the Si-C solution when growing SiC single crystals using a SiC crucible formed from a SiC sintered body having a relative density of 50 to 90%. [Figure 3] is a schematic diagram showing how silicon and carbon dissolve from the inside of the SiC crucible into the Si-C solution when growing SiC single crystals using a conventional dense SiC crucible. [Figure 4] is an image showing the appearance of the growth surface (C-plane) of the SiC single crystal obtained in Example 1. [Figure 5] is an image showing the results of misalignment observation of the seed portion of the SiC single crystal sample in Example 1. [Figure 6] is an image showing the results of misalignment observation of the solution growth portion (growth surface) of the SiC single crystal sample in Example 1. [Figure 7] An image showing the appearance of the growth surface (C-plane) of the SiC single crystal in Example 2. [Figure 8] An X-ray reflection topology of the seed portion of the SiC single crystal sample in Example 2. [Figure 9] An X-ray reflection topology of the solution-grown portion (growth surface) of the SiC single crystal sample in Example 2. [Figure 10] An image showing the appearance of the growth surface (C-plane) of the SiC single crystal in Example 3. [Figure 11] A laser micrograph of the growth surface (C-plane) of the SiC single crystal sample in Example 3. [Figure 12] An image of a cross-section of the SiC single crystal sample in Example 3. [Figure 13] An X-ray reflection topology of the seed portion of the SiC single crystal sample in Example 3. [Figure 14] An X-ray reflection topology of the solution-grown portion (growth surface) of the SiC single crystal sample in Example 3. [Figure 15] An image showing the appearance of the growth surface (C-plane) of the SiC single crystal in Comparative Example 1. [Figure 16] is an image of a cross-section of the SiC single crystal sample in Comparative Example 1. [Figure 17] is an image of a cross-section of the SiC single crystal sample in Example 2. [Figure 18] is an image of the appearance of the growth surface (C-plane) of the SiC single crystal in Example 5. [Figure 19] is a schematic cross-sectional view of the reaction vessel during bulk growth by sublimation. [Figure 20] is a schematic cross-sectional view of the reaction apparatus during bulk growth by sublimation. 1: SiC crucible 2: Second crucible 3: SiC single crystal (seed crystal) 4: Si-C solution 5: Shaft 6: Shaft 7: Heater 8: Hot Screen 9: Top Cover 10: RF coil

Claims

1. A method for manufacturing a SiC single crystal, comprising the following steps in sequence: forming a SiC crucible by alloying silicon with a metal element M that increases the solubility of carbon into a melt and immersing the melt into a SiC sintered body having a relative density of 50 to 90%; placing silicon and the metal element M in the SiC crucible and heating the crucible to melt the silicon and the metal element M in the crucible and form a Si-C solution; dissolving silicon and carbon constituting the SiC crucible from the surface of the SiC crucible in contact with the Si-C solution into the Si-C solution; contacting a SiC seed crystal with the upper part of the Si-C solution by a solution method to grow a first SiC single crystal on the SiC seed crystal; and bulk growing a second SiC single crystal on the surface of the solution-grown first SiC single crystal by a sublimation method or a gas method.

2. The manufacturing method of claim 1, wherein the metal element M placed in the SiC crucible is an unbonded metal element or an alloy comprising multiple metal elements but excluding silicon.

3. The manufacturing method of claim 1, wherein the metal element M comprises: at least one first metal element M1 selected from the group consisting of: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y and Lu; and at least one second metal element M2 selected from the group consisting of: Ti, V, Cr, Mn, Fe, Co, Ni and Cu; at least one third metal element M3 selected from the group consisting of: Ga, Ge, Sn, Pb and Zn; or at least one second metal element M2 and at least one third metal element M3.

4. The manufacturing method of claim 3, wherein the metal element M includes the first metal element M1 and the second metal element M2.

5. The manufacturing method of claim 3, wherein the total content of the metal element M in the Si-C solution is from 1 to 80 atoms of the combined amount of silicon and the metal element M.

6. The manufacturing method of claim 3, wherein the content of the first metal element M1 in the Si-C solution is at least 1 atom% of the combined amount of silicon and the metal element M, and the content of the second metal element M2 and the third metal element M3 in the Si-C solution is each at least 1 atom% of the combined amount of silicon and the metal element M.

7. The manufacturing method of any one of claims 1 to 6, wherein the SiC sintered body has an oxygen content of 100 ppm or less.

8. The manufacturing method of any one of claims 1 to 6, wherein the first SiC single crystal system is grown by solution method at a Si-C solution temperature between 1,300 and 2,300 °C.

9. The manufacturing method of any one of claims 1 to 6, wherein the manufacturing is carried out in the SiC crucible held in a second crucible made of heat-resistant carbon material.

10. The manufacturing method of any one of claims 1 to 6, wherein the first SiC single crystal grown by solution method has a thickness of 10 to 1,000 µm.

11. The manufacturing method of any one of claims 1 to 6, wherein the SiC crucible and the Si-C solution are used repeatedly.

12. A method for suppressing dislocations in a SiC single crystal, comprising the following steps in sequence: forming a SiC crucible by immersing an alloy of silicon and a metal element M that increases the solubility of carbon into a melt and immersing the melt into a SiC sintered body having a relative density of 50 to 90%; placing silicon and the metal element M in the SiC crucible and heating the SiC crucible to melt the silicon and the metal element M in the crucible and form a Si-C solution; dissolving the silicon and carbon constituting the SiC crucible from the surface of the SiC crucible in contact with the Si-C solution into the Si-C solution; and contacting a SiC seed crystal with the upper portion of the Si-C solution by a solution method to grow a first SiC single crystal on the SiC seed crystal.

13. The method of claim 12, further comprising the step of bulk growing a second SiC single crystal on the surface of a solution-grown first SiC single crystal by sublimation or gas method.

14. The method of claim 13, further comprising the steps of: providing a SiC single crystal wafer obtained from a second SiC single crystal grown by sublimation or gas method as a SiC seed crystal, and growing a third SiC single crystal on the SiC seed crystal by solution method.

15. The method of claim 14, further comprising the step of bulk growing a fourth SiC single crystal on the surface of a solution-grown third SiC single crystal by sublimation or gas method.

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