Manufacturing method for SiC single crystals

Abstract

SOLUTION: To provide a method for manufacturing an SiC single crystal by a solution method in which alloy of Si and a metal element M which increases the solubility of C is previously impregnated as melt into an SiC sintered compact having the relative density of 50 to 90%, and then, an SiC crucible made of the SiC sintered compact is allowed to house metal element M which increases the solubility of Si and C, and Si and the metal element M in the SiC crucible are fused to form Si-C solution.EFFECT: Because Si-C solution infiltrates into a sintered compact, SiC being a component of a SiC sintered compact is eluted into Si-C solution by heating even from inside the sintered compact, and Si and C are efficiently supplied to the Si-C solution. As a result, Si and C are supplied from the entire contact part of a SiC crucible with the Si-C solution evenly and appropriately, which makes it possible to stably manufacture a high-quality SiC single crystal at high growth rate and for a long period of time.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a silicon carbide (SiC) crystal growth technology, and more particularly to a method for manufacturing a SiC single crystal that enables stable production of a low-defect and high-quality SiC single crystal over a long period of time.

Background Art

[0002] SiC is a wide-bandgap semiconductor material, which has excellent thermal conductivity and chemical stability, and also has excellent basic physical properties as a power device from the viewpoints of breakdown characteristics and transistor characteristics such as saturation drift velocity. For these reasons, SiC is highly expected as a material for next-generation power devices, and the commercialization of SiC power devices has also been reported.

[0003] However, in addition to being expensive compared to Si substrates, SiC substrates have the problem that the reduction of defects and the improvement of quality in single crystal substrates are not sufficient. The main reason why it is difficult to manufacture a low-defect and high-quality SiC single crystal substrate is that SiC does not melt under normal pressure. In the case of Si widely used as a substrate for semiconductor devices, the melting point under normal pressure is 1,414 °C, and a low-defect and high-quality, large-diameter single crystal can be obtained from a Si melt by the CZ method or the FZ method.

[0004] On the other hand, in the case of SiC, when heated under normal pressure, it sublimates at a temperature of about 2,000 °C, so the crystal growth methods by the CZ method or the FZ method cannot be adopted. Therefore, currently, SiC single crystals are mainly manufactured by sublimation methods including the improved Lely method. The sublimation method is currently the only method for mass-producing SiC single crystals, and 4-inch diameter SiC single crystal substrates manufactured by this method are widely commercially available, and there are also reports of mass-producing 6-inch diameter SiC single crystal substrates.

[0005] However, even when power devices are fabricated using SiC single crystals obtained by sublimation, their properties are not always satisfactory. This is because reducing the defects in SiC single crystals is not easy. Crystal growth by sublimation is a precipitation phenomenon from the gas phase, resulting in slow growth rates and difficulty in controlling the temperature within the reaction space. In recent years, as a result of vigorous improvements and refinements, the dislocation density of micropipes has decreased, but lattice defects that affect the electrical properties of the device, such as through-helix dislocations, edge dislocations, and basal plane dislocations, still exist at a high density.

[0006] Therefore, recently, methods for growing SiC crystals using solution methods have attracted attention (for example, Japanese Patent Publication No. 2000-264790 (Patent Document 1), Japanese Patent Publication No. 2004-002173 (Patent Document 2), and Japanese Patent Publication No. 2006-143555 (Patent Document 3)). As mentioned above, SiC itself does not melt under normal pressure. Therefore, in the method for producing SiC single crystals using solution methods, carbon is dissolved in a Si molten liquid in a graphite crucible from the high-temperature part at the bottom of the crucible, and a SiC seed crystal is brought into contact with this Si-C molten liquid and epitaxially grown on the SiC seed crystal to obtain a SiC single crystal. In such solution methods, the crystal growth of SiC proceeds in a state very close to thermal equilibrium, so a SiC single crystal with fewer defects can be obtained compared to a SiC single crystal obtained by the sublimation method.

[0007] There are various solution methods for obtaining SiC single crystals, and in "Latest Technology of SiC Power Devices," Chapter 4, Section 1, 1.2 SiC Solution Growth Methods, pp. 41-43, S&T Publishing Co., Ltd., published May 14, 2010 (Non-Patent Literature 1), they are broadly classified into four types: Traveling Solvent Method (TSM), Slow Cooling Technique (SCT), Vapor Liquid Solid (VLS), and Top Seeded Solution Growth (TSSG). In this invention, unless otherwise specified, "solution method" refers to Top Seeded Solution Growth (TSSG).

[0008] In the solution method for producing SiC single crystals, a Si melt is first formed in a graphite crucible, and C is dissolved in it to form a Si-C solution. However, the solubility of C in the Si-C solution is extremely low, about 1 atomic percent. Therefore, transition metals are generally added to the Si-C solution to facilitate the dissolution of C (Patent Documents 1-3). Reported additive elements include transition metal elements such as Ti, Cr, Ni, and Fe, as well as low-melting-point metal elements such as Al, Sn, and Ga, and various rare earth elements. The type and amount of such additive elements are determined by considering factors such as promoting the dissolution of C, ensuring that SiC precipitates from the Si-C solution as a primary crystal with the remainder in equilibrium as a liquid phase, preventing the additive elements from precipitating carbides or other phases, ensuring the stable precipitation of the desired polymorph among the SiC crystal polymorphs, and creating a solution composition that maximizes the single crystal growth rate.

[0009] Conventional solution-based growth of SiC single crystals is generally carried out according to the following procedure. First, Si raw materials are placed in a crucible made of carbon or graphite and heated and melted under an inert gas atmosphere. The carbon component is supplied from the crucible into the Si melt, forming a Si-C solution. In some cases, a carbon compound is placed in the crucible along with the Si raw materials and melted. After the carbon component is sufficiently dissolved in the Si-C solution, a SiC seed crystal is brought into contact with the Si-C solution, and the single crystal is grown using the temperature gradient formed throughout the solution.

[0010] However, conventional solution methods have the following problems. First, as the SiC single crystal grows, the Si component is gradually lost from the Si-C solution, and the solution composition gradually changes. If the solution composition changes during the growth of the SiC single crystal, the SiC precipitation environment will naturally change. As a result, it becomes difficult to stably continue SiC single crystal growth for a long period of time. Second, there is the problem of excessive dissolution of C from the crucible. As the SiC single crystal grows, the Si component is gradually lost from the Si-C solution, while C is continuously supplied from the crucible. Therefore, the Si-C solution ends up with a relative excess of C dissolved in it, and the Si / C composition ratio of the Si-C solution changes. Third, there is the problem of SiC polycrystal precipitation on the crucible surface (especially the inner wall) that is in contact with the Si-C solution. As described above, when an excess of carbon dissolves from the crucible into the Si-C solution, fine SiC polycrystals tend to form on the inner wall surface of the crucible. These SiC polycrystals (miscellaneous crystals) then float in the SiC solution and reach the vicinity of the solid-liquid interface between the growing SiC single crystal and the Si-C solution, thereby inhibiting single crystal growth. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2000-264790 [Patent Document 2] Japanese Patent Publication No. 2004-002173 [Patent Document 3] Japanese Patent Publication No. 2006-143555 [Patent Document 4] Japanese Patent Publication No. 2015-110495 [Patent Document 5] Japanese Patent Publication No. 2015-110496 [Patent Document 6] Japanese Patent Publication No. 2015-110498 [Patent Document 7] Japanese Patent Publication No. 2015-110499 [Patent Document 8] Japanese Patent Publication No. 2015-110500 [Patent Document 9] Japanese Patent Publication No. 2015-110501 [Patent Document 10] Japanese Patent Publication No. 2017-031034 [Patent Document 11] Japanese Patent Publication No. 2017-031036 [Non-patent literature]

[0012] [Non-Patent Document 1] "Latest Technologies in SiC Power Devices," Chapter 4, Section 1, 1.2 SiC Solution Growth Methods, pp. 41-43, S&T Publishing Co., Ltd., published May 14, 2010. [Overview of the project] [Problems that the invention aims to solve]

[0013] This invention has been made in view of the problems of such conventional methods, and aims to provide a method that reduces compositional variations in the Si-C solution and suppresses the formation of SiC polycrystals precipitated on the inner surface of the crucible, thereby enabling the production of high-quality SiC single crystals with a faster growth rate and fewer defects compared to conventional methods using graphite crucibles. [Means for solving the problem]

[0014] In conventional solution methods, a crucible made of heat-resistant carbon material, such as a graphite crucible, is used to contain the Si-C solution, while simultaneously replenishing the solution by dissolving carbon from the crucible. However, in this case, as SiC crystal growth progresses, a decrease in the composition ratio of Si component in the Si-C solution is unavoidable.

[0015] The inventors have proposed a method of supplying Si and C as a Si-C solution from SiC in a solution method (Japanese Patent Application Laid-Open No. 2015-110495 (Patent Document 4), Japanese Patent Application Laid-Open No. 2015-110496 (Patent Document 5), Japanese Patent Application Laid-Open No. 2015-110498 (Patent Document 6), Japanese Patent Application Laid-Open No. 2015-110499 (Patent Document 7), Japanese Patent Application Laid-Open No. 2015-110500 (Patent Document 8), Japanese Patent Application Laid-Open No. 2015-110501 (Patent Document 9), Japanese Patent Application Laid-Open No. 2017-031034 (Patent Document 10), Japanese Patent Application Laid-Open No. 2017-031036 (Patent Document 11)). However, in order to improve productivity, it is necessary to more efficiently elute SiC from the SiC crucible to improve the growth rate. However, while the contact area between the Si-C solution and the SiC crucible is rate-determining for the amount of SiC eluted from the SiC crucible, the contact area between the Si-C solution and the SiC crucible is limited. Furthermore, as the volume of the SiC solution is increased, the ratio of the contact area to the volume decreases, resulting in further insufficient elution of SiC.

[0016] As a result of intensive studies to solve the above problems, the inventors impregnated a SiC sintered body having a relative density of 50 to 90% with an alloy of Si and a metal element M that increases the solubility of C in advance as a melt to form a SiC crucible. Next, the SiC crucible is filled with Si and a metal element M that increases the solubility of C. The Si and the metal element M in the SiC crucible are melted to form a Si-C solution. By heating the SiC crucible, Si and C, which are the constituent components of the SiC sintered body, are eluted into the Si-C solution from the surface of the SiC sintered body that contacts the Si-C solution. At the same time, SiC seed crystals are brought into contact with the upper part of the Si-C solution, and a SiC single crystal is grown on the SiC seed crystals. As a result, the Si-C solution penetrates to the inside of the SiC sintered body, and SiC is efficiently eluted into the Si-C solution. This reduces the compositional variation of the Si-C solution and suppresses the generation of polycrystalline SiC deposited on the inner surface of the crucible. It has been found that a high-quality SiC single crystal with a fast growth rate and low defects can be produced compared to the conventional method using a graphite crucible, and thus the present invention has been completed.

[0017] Therefore, the present invention provides a method for manufacturing a SiC single crystal described below. 1. In a SiC crucible formed of a SiC sintered body having a relative density of 50 to 90%, a metal element M that increases the solubility of Si and C is contained, Si and the metal element M are melted to form a Si-M solution, and by heating the SiC crucible, Si and C sourced from SiC, which is a component of the SiC crucible, are eluted into the Si-M solution from the surface of the SiC crucible in contact with the Si-M solution. At the same time, an SiC seed crystal is brought into contact with the upper part of the Si-C solution, which is the Si-M solution from which Si and C have been eluted, and a SiC single crystal is grown on the SiC seed crystal to produce a SiC single crystal. The method comprises: The metal element M that enhances the solubility of C is one or both of the following metal elements: at least one first metal element M1 selected from the group La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Lu, and at least one second metal element M2 selected from the group Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. Si, and Applicable Before containing the metal element M in the SiC crucible, an alloy of Si and the metal element M is used as a melt and impregnated in the SiC sintered body in advance, which is a method for producing a SiC single crystal. 2 . The metal element M is both the first metal element M1 and the second metal element M2, and the total content of the metal element M in the Si-C solution is 1 to 80 atomic% with respect to the total amount of Si and M 1 The manufacturing method described. 3 . The content of the first metal element M1 in the Si-C solution is 10 atomic% or more with respect to the total amount of Si and M, and the content of the second metal element M2 in the Si-C solution is 1 atomic% or more with respect to the total amount of Si and M 2 The manufacturing method described. 4 . The oxygen content of the SiC sintered body is 100 ppm or less, and the manufacturing method according to any one of 1 to 3 The manufacturing method according to any one of the above. 5 . [[ID=�4]]The growth of the SiC single crystal is carried out at a temperature of 1,300 to 2,300 °C for the Si-C solution, and the manufacturing method according to any one of 1 to 4 The manufacturing method according to any one of the above. 6 . The SiC crucible is carried out in a state of being accommodated in a second crucible made of a heat-resistant carbon material, and the manufacturing method according to any one of 1 to5 A manufacturing method described in any of the following. [Effects of the Invention]

[0018] Conventional SiC crucibles were dense, causing Si and C to dissolve locally from high-temperature areas such as the corners of the crucible bottom, where the Si-C solution came into contact. However, according to the present invention, the relative density of the sintered body is 50-90%, allowing the Si-C solution to penetrate into the interior of the sintered body. Therefore, upon heating, SiC, a component of the SiC sintered body, dissolves into the Si-C solution from within the sintered body as a source of Si and C, efficiently supplying Si and C to the Si-C solution. As a result, Si and C are supplied uniformly and without excess or deficiency from the entire contact area of ​​the SiC crucible with the Si-C solution, making it possible to stably produce high-quality SiC single crystals at a fast growth rate over a long period of time. The SiC single crystals obtained in this way are suitable for SiC semiconductor devices such as power devices. [Brief explanation of the drawing]

[0019] [Figure 1] This is a cross-sectional view showing an example of the main part of a SiC single crystal manufacturing apparatus, which is preferably used when growing SiC single crystals. [Figure 2] This is a conceptual diagram illustrating the process of Si and C dissolving from within a SiC crucible into a Si-C solution when growing a SiC single crystal using a SiC crucible formed from a SiC sintered body with a relative density of 50-90%. [Figure 3] This is a conceptual diagram illustrating the process of Si and C dissolving from within a SiC crucible into a Si-C solution when growing a SiC single crystal using a conventional dense SiC crucible. [Figure 4] This is an observation photograph of the growth surface of the SiC single crystal obtained in Example 1. [Figure 5] This is an observation photograph of the growth surface of the SiC crystal obtained in Comparative Example 1. [Modes for carrying out the invention]

[0020] The present invention will be described in more detail below. The present invention provides a method for producing a SiC single crystal by a solution method (i.e., seeding solution growth (TSSG)) in which a seed crystal is brought into contact with a Si-C solution (Si-C melt) contained in a crucible to grow a SiC single crystal. The method involves placing a metal element M that enhances the solubility of Si and C in a SiC crucible formed of a SiC sintered body with a relative density of 50-90%, melting Si and the metal element M to form a Si-C solution, heating the SiC crucible to dissolve Si and C, which are components of the SiC crucible, into the Si-C solution from the surface of the SiC crucible that is in contact with the SiC solution, and bringing a SiC seed crystal into contact with the upper part of the SiC solution to grow a SiC single crystal on the SiC seed crystal. The method is characterized by pre-impregnating the SiC sintered body with a molten alloy of Si and the metal element M before adding the metal element M, which enhances the solubility of Si and C, to the SiC crucible.

[0021] Figure 1 is a cross-sectional view showing an example of a SiC single crystal manufacturing apparatus (heating furnace) suitably used when growing SiC single crystals in the present invention. In the figure, 1 is a SiC crucible which is a container for the Si-C solution, 2 is a second crucible made of heat-resistant carbon material that houses the SiC crucible 1, 3 is a SiC single crystal (seed crystal), 4 is the Si-C solution contained in the SiC crucible 1, 5 is a rotating shaft for rotating the SiC crucible 1 and the second crucible 2 during the crystal growth of the SiC single crystal, 6 is a rotating shaft that holds the SiC single crystal 3 and rotates it during the crystal growth of the SiC single crystal, 7 is a susceptor made of graphite material or the like, 8 is an insulating material made of graphite material or the like, 9 is a top lid to suppress the volatilization of the SiC solution, and 10 is a high-frequency coil for heating the inside of the furnace to bring the Si-C solution to a predetermined temperature and temperature distribution. Although not shown in the diagram, the furnace is equipped with an exhaust port and exhaust valve for creating a vacuum, and a gas inlet and gas inlet valve for introducing gas.

[0022] Before heating, the crucible is usually filled with Si, but a C source may also be filled in. When the inside of the crucible is heated, immediately after heating, Si and C, which are components of the SiC crucible, leach into the Si molten liquid or the Si-C solution from the surface of the SiC crucible that comes into contact with the Si-C solution after the C has dissolved. It is also possible to fill the crucible with SiC along with Si or Si and C before heating.

[0023] In the present invention, the relative density of the SiC sintered body is 50% or more, preferably 70% or more, 90% or less, preferably 88% or less, and more preferably 85% or less. Here, relative density refers to the true density of SiC, which is 3.22 g / cm³. 3 The ratio (%) of the measured or calculated density of the SiC sintered body to the true density of SiC, i.e., the percentage of the value obtained by dividing the measured or calculated density of the SiC sintered body by the true density of SiC. The measured density is, for example, the value (density) of the SiC sintered body measured by the Archimedes method. The calculated density is the value (density) obtained by dividing the mass of the SiC sintered body by the volume of the SiC sintered body 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 (diameter of the housing), and height of the housing).

[0024] SiC crucibles formed from SiC sintered bodies with a relative density within the aforementioned range can be obtained by methods such as dry pressing or slip casting, but are not limited to these manufacturing methods.

[0025] The Si-C solution 4 contained in the SiC crucible 1 has a metal element M added to increase the solubility of carbon (C) in the Si-C solution. When using a Si-C solution with a metal element M added to increase the solubility of carbon, using a SiC crucible is advantageous because it suppresses the formation of metal carbides formed by the bonding of the added metal element M with carbon (C). When using a 13C crucible (graphite crucible), if the Si composition ratio in the Si-C solution decreases or if carbon dissolves in excess, resulting in a low Si / C composition ratio, the metal element M added to facilitate the dissolution of carbon tends to bond with carbon, leading to the formation of metal carbides. Such metal carbides have a high melting point, and if they float in the Si-C solution and adhere to the vicinity of the seed crystal surface, SiC single crystals cannot be formed. In contrast, when using a SiC crucible, excess carbon (C) does not dissolve in the Si-C solution, and as a result, the formation of metal carbides is suppressed, thus making it less likely for the growth of SiC single crystals to be inhibited.

[0026] When a SiC crucible 1, formed from a SiC sintered body with a relative density of 50-90%, is filled with metal elements M that increase the solubility of Si and C in an empty state where its voids are not filled with a molten liquid (solid at room temperature) such as a Si-C solution, for example, in the state of a SiC crucible before use, and Si and the metal elements M are melted to form a Si-C solution, if the metal elements M are filled in as a single element or as an alloy that does not contain Si, the metal or alloy with the lower melting point will preferentially penetrate the SiC sintered body, causing a reaction between the metal elements M and the SiC crucible, and resulting in problems such as the composition of the Si-C solution in the SiC crucible deviating from the desired composition. Therefore, in this invention, before placing the metal element M that increases the solubility of Si and C into the SiC crucible, an alloy of Si and the metal element M, preferably an alloy with a composition ratio approximately the same as that of the Si-C solution used to grow SiC single crystals, is pre-impregnated into the voids of the SiC sintered body, i.e., this is called the SiC crucible 1. Specifically, the alloy is placed in the SiC crucible and heat-treated in a range of, for example, 1,300°C or higher, particularly 1,500°C or higher, and 2,300°C or lower, particularly 2,000°C or lower. The heat treatment time is usually 1 to 10 hours. The impregnation atmosphere may be an inert gas atmosphere such as argon gas, a gas atmosphere such as nitrogen gas, or a vacuum atmosphere.

[0027] Examples of metal element M include at least one first metal element M1 selected from the group La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Lu; at least one second metal element M2 selected from the group Ti, V, Cr, Mn, Fe, Co, Ni, and Cu; and at least one third metal element M3 selected from the group Ga, Ge, Sn, Pb, and Zn. The total content of metal element M in the Si-C solution is preferably 1 atomic% or more, particularly 20 atomic% or more, and 80 atomic% or less, particularly 50 atomic% or less, relative to the total amount of Si and M. When including metal element M in the Si-C solution, the metal element M can be packed into the crucible before heating, along with Si and optionally added C and / or SiC, either individually or as an alloy.

[0028] The first to third metal elements M1, M2, and M3 may be used individually or in combination, but a combination of metal element M1 and metal element M2 is preferred. In this case, it is preferable that the content of the first metal element M1 in the Si-C solution be 10 atomic percent or more, particularly 12 atomic percent or more, relative to the total amount of Si and M, and that the content of the second metal element M2 in the Si-C solution be 1 atomic percent or more, particularly 10 atomic percent or more, relative to the total amount of Si and M.

[0029] In this invention, using the apparatus described above, induction heating from the high-frequency coil 10 to the SiC crucible 1 creates a temperature distribution in the Si-C solution 4 suitable for crystal growth, and Si and C, originating from SiC, which are components of the Si-C solution 4, are dissolved into the Si-C solution 4 from the SiC crucible 1 that is in contact with the Si-C solution 4. Then, at the top of the SiC crucible 1, the SiC seed crystal 3 is brought into contact with the Si-C solution 4, and a SiC single crystal is grown on the SiC seed crystal 3. Therefore, the temperature of the inner surface of the SiC crucible in contact with the Si-C solution is set to a temperature high enough to dissolve Si and C, which are constituent elements of SiC, into the Si-C solution 4. In addition, the temperature near the solid-liquid interface between the SiC seed crystal 3 and the Si-C solution 4 is set to a temperature sufficient for SiC to grow as a single crystal on the SiC seed crystal 3.

[0030] In the SiC single crystal growth process, by appropriately controlling the induction heating conditions from the high-frequency coil, appropriately setting the positional relationship (especially the vertical positional relationship) between the crucible and the high-frequency coil, and appropriately rotating the crucible and the SiC single crystal (seed crystal), a desired temperature distribution can be formed in the Si-C solution. This allows for appropriate control of the SiC single crystal growth rate and the dissolution rate of the SiC crucible components into the Si-C solution.

[0031] The temperature of the Si-C solution during crystal growth is preferably controlled to be above 1,300°C, particularly above 1,500°C, and below 2,300°C, particularly below 2,000°C. A seed crystal is brought into contact with the Si-C solution in the upper part of the SiC crucible, and a SiC single crystal is grown on the seed crystal. Therefore, the contact area between the SiC crucible and the SiC solution is a high-temperature range in which at least a portion of the SiC solution can dissolve its components from the SiC crucible into the SiC solution, while the contact area between the growth surface of the seed crystal or the SiC single crystal grown on the seed crystal and the SiC solution is a low-temperature range in which SiC can grow as a single crystal on the seed crystal or on the SiC single crystal grown on the seed crystal. Furthermore, the temperature distribution of the Si-C solution preferably has a gradual increase in temperature from the vicinity of the seed crystal towards the inner surface of the SiC crucible (i.e., the contact surface with the Si-C solution), and more preferably, the temperature distribution also preferably has a gradual increase in temperature from the upper to the lower part of the Si-C solution. In this case, the temperature difference between the high-temperature and low-temperature regions is preferably, for example, 5°C or more, particularly 10°C or more, and 200°C or less, particularly 100°C or less. The gradient of the temperature distribution of the Si-C solution is preferably 1°C / cm or more, particularly 5°C / cm or more, and 50°C / cm or less, particularly 30°C / cm or less. SiC single crystal growth is usually carried out in an inert gas atmosphere such as helium gas or argon gas.

[0032] Although Figure 1 shows a configuration in which the crucible is heated by high frequency, the heating method is not limited to high frequency and may be carried out by other methods such as resistance heating, depending on the control temperature of the Si-C solution.

[0033] Figure 2 is a diagram conceptually illustrating how Si and C dissolve from a SiC crucible, formed from a SiC sintered body with a relative density of 50-90%, into a Si-C solution when growing SiC crystals using the crucible. When a temperature distribution suitable for crystal growth is formed in the Si-C solution 4, Si and C originating from the SiC component of the SiC crucible 1 dissolve into the Si-C solution 4 from the surface of the SiC crucible 1 (especially in the high-temperature region) that is in contact with the Si-C solution 4. The dissolved Si and C become new Si and C components in the Si-C solution 4, and serve as the source of single crystals that grow on the SiC seed crystal 3. In the figure, 2 is the second crucible, 6 is the rotation axis, and 9 is the top lid, each corresponding to Figure 1.

[0034] In an environment where Si and C elute from SiC crucible 1 into Si-C solution 4, the problem of SiC polycrystalline deposition on the crucible surface in contact with the Si-C solution does not occur. This is because, under conditions where SiC, a component of SiC crucible 1, elutes into Si-C solution 4 as Si and C, there is no room for Si and C to precipitate as SiC. In other words, by using a crucible made of SiC as the container for the Si-C solution, the deposition of SiC polycrystalline on the crucible surface in contact with the Si-C solution is suppressed.

[0035] Furthermore, by using a SiC crucible formed from a SiC sintered body with a relative density of 50-90%, the Si-C solution not only comes into contact with the surface of the SiC crucible but also penetrates into the interior (pores) of the sintered body. As shown by the arrows in Figure 2, SiC is efficiently dissolved and supplied from inside the SiC crucible, improving the crystal growth rate and suppressing SiC polycrystalline formation. As a result, the state in the solution shown in Figure 2 is expected to be achieved. If the relative density of the SiC sintered body constituting the SiC crucible is less than 50%, when the SiC crucible dissolves, the SiC breaks down into SiC particles, and a significant amount of SiC particles float in the Si-C solution. If it exceeds 90%, penetration of the SiC solution into the interior (pores) of the sintered body hardly occurs, and efficient dissolution of SiC into the SiC solution cannot be achieved.

[0036] In contrast, Figure 3 is a diagram conceptually illustrating how Si and C dissolve from a SiC crucible into a Si-C solution when growing SiC crystals using a conventional dense SiC crucible (for example, a SiC crucible formed from a SiC sintered body with a relative density exceeding 90%). In this case, the Si-C solution 4 only comes into contact with the surface of the SiC crucible 1, and the dissolution of Si and C into the Si-C solution 4 is insufficient. As a result, the supply of SiC from the SiC crucible 1 (dissolution into the Si-C solution) is not uniform at the contact point between the SiC crucible and the Si-C solution. Consequently, the dissolution of SiC proceeds predominantly in the high-temperature parts of the SiC crucible, particularly in the bottom corners as indicated by the arrows in Figure 3, making it difficult to grow SiC single crystals over long periods. In the diagram, 2 is the second crucible, 3 is the SiC seed crystal, 6 is the rotation axis, and 9 is the top lid, each corresponding to Figure 1.

[0037] Furthermore, in the present invention, in the SiC crucible 1, an alloy of Si and a metal element M, preferably an alloy with a composition ratio approximately the same as that of the Si-C solution used to grow SiC single crystals, is pre-impregnated into the SiC sintered body (inside the voids of the SiC sintered body) as a melt. As a result, when Si and the metal element M are melted to form a Si-C solution, the metal element M does not preferentially react with the SiC crucible, and the composition of the Si-C solution inside the SiC crucible is maintained at the desired composition.

[0038] Si and C continuously leach from the SiC crucible, but normally, if the crucible and seed crystal are rotated while growing a single crystal, the Si-C solution can be homogenized in composition due to the stirring effect.

[0039] In Figure 1, a second crucible 2 made of a heat-resistant carbon material is used to house the SiC crucible 1, and the SiC crucible 1 is housed inside the second crucible 2 made of a heat-resistant carbon material. However, in the present invention, which uses a SiC crucible formed from a SiC sintered body with a relative density of 50-90%, the Si-C solution may leak out from the outer surface of the SiC crucible through the voids in the SiC sintered body. Therefore, it is preferable to house the SiC crucible inside the second crucible. In this case, it is preferable that the second crucible 2 is made of a material that is dense enough to prevent the Si-C solution from leaking out. Furthermore, using a second crucible has the advantage of making it easier to control the temperature distribution in the Si-C solution.

[0040] Furthermore, the SiC sintered body that makes up a SiC crucible typically contains oxygen as an impurity. The oxygen contained in the SiC sintered body forms an oxide (SiO), and since the boiling point of SiO is approximately 1,880°C, if the temperature of the Si-C solution is above this boiling point, SiO will gasify in the Si-C solution as SiC dissolves. If this gas reaches the interface (solid-liquid interface) between the Si-C solution and the growing SiC single crystal, it may be incorporated on the crystal growth surface, potentially causing voids in the SiC single crystal. Also, if the oxygen contained in the SiC sintered body dissolves into the Si-C solution as SiC dissolves, and the temperature of the Si-C solution is below the boiling point of SiO, it will react with Si in the Si-C solution to form SiO. If this gas reaches the interface (solid-liquid interface) between the Si-C solution and the growing SiC single crystal, it may be incorporated on the crystal growth surface, potentially causing voids in the SiC single crystal. For this reason, a SiC sintered body with an oxygen content of 100 ppm or less is preferable.

[0041] In the solution method, a SiC single crystal is prepared as a seed crystal. This seed crystal can be either a SiC single crystal obtained by the sublimation method or a SiC single crystal obtained by the solution method (here, this refers to a broad definition of the solution method, including the solvent transfer crystal growth method, slow cooling method, vapor-liquid-solid-vapor method, and seed solution growth method mentioned above).

[0042] According to the present invention's method for manufacturing SiC single crystals, a SiC crucible is used which is made of a SiC sintered body with a relative density of 50-90% and is impregnated with an alloy of Si and a metal element M that enhances the solubility of C. Therefore, when the SiC crucible is heated, SiC, which is a component of the SiC sintered body, dissolves from within the sintered body into the Si-C solution as a source of Si and C, and Si and C are efficiently supplied to the Si-C solution. As a result, Si and C are supplied uniformly and without excess or deficiency from the entire contact area with the Si-C solution in the SiC crucible, making it possible to stably produce high-quality SiC single crystals at a fast growth rate (e.g., 10 μm / hr or more, particularly 100 μm / hr or more, with no particular upper limit, but for example 400 μm / hr) without the adhesion of SiC polycrystals, over a long period of time (e.g., 1 hour or more, particularly 5 hours or more, with no particular upper limit, but for example 15 hours). [Examples]

[0043] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0044] [Example 1] A SiC sintered crucible (outer diameter φ60 mm, height 70 mm, inner diameter (diameter of the containment section) φ50 mm, height of the containment section 60 mm, relative density 80%, oxygen content 15 ppm) was used as SiC crucible 1, and SiC single crystals were manufactured (crystal growth) using the manufacturing apparatus shown in Figure 1. A Pr-Fe-Si alloy with a composition of Pr: 16 atomic%, Fe: 20 atomic%, and Si: 64 atomic%, equivalent to the total volume of the voids in the SiC sintered body (20 volume percent of the SiC sintered body), was placed in SiC crucible 1, and heat treatment was performed at 1,500°C for 10 hours in an argon atmosphere to impregnate the voids in the SiC sintered body with the alloy. Subsequently, Pr, Fe, and Si were added as elemental metals, with compositions of Pr: 16 atomic%, Fe: 20 atomic%, and Si: 64 atomic%, and the quantities were adjusted based on density calculations so that the Si-C solution reached a depth of 27 mm. Seed crystal 3 consisted of a single crystal (polytype: 4H) measuring φ21 mm × 10.4 mm, bonded to a φ19 mm graphite seed shaft with the growth surface being a chamfer. SiC crucible 1 and the seed shaft (rotating shaft 6) were rotated in opposite directions (i.e., one clockwise and the other counterclockwise) at 20 rpm each, and crystal growth was carried out in an argon atmosphere at 2,000°C for 10 hours with a pulling speed of 0.1 mm / hr.

[0045] When the obtained crystals were evaluated, as shown in the observation photograph of the growth surface of the SiC single crystal in Figure 4, a flat single crystal without defects and no SiC polycrystalline adhesion was obtained. The growth thickness was 2,550 μm after 10 hours, and the growth rate was 255 μm / hr.

[0046] [Comparative Example 1] A SiC sintered crucible (outer diameter φ60 mm, height 70 mm, inner diameter (diameter of containment section) φ50 mm, height of containment section 60 mm, relative density 45%, oxygen content 15 ppm) was used, and SiC single crystals were manufactured (crystal growth) using the manufacturing apparatus shown in Figure 1. In the SiC crucible, Pr, Fe, and Si were placed as elemental metals without impregnating the pores of the SiC sintered body with alloy, so that the composition was Pr: 16 atomic%, Fe: 20 atomic%, and Si: 64 atomic%, and the amount was adjusted so that the depth of the Si-C solution was 27 mm based on density calculations. Seed crystal 3 was a φ21 mm × 10.4 mm single crystal (polytype: 4H) bonded to a φ19 mm graphite seed shaft so that the growth surface was a C-plane. The SiC crucible and seed shaft (rotating shaft 6) were rotated at 20 rpm each in opposite directions (i.e., one clockwise and the other counterclockwise), and crystal growth was performed in an argon atmosphere at 2,000°C for 10 hours with a pulling speed of 0.1 mm / hr.

[0047] When the obtained crystals were evaluated, it was found that polycrystalline SiC was attached to the entire surface, as shown in the observation photograph of the growth surface of the SiC single crystal in Figure 5. The growth thickness was 1,500 μm after 10 hours, and the growth rate was 150 μm / hr.

[0048] The melting points of each element in the raw materials for Example 1 and Comparative Example 1 were 935°C for Pr, 1,538°C for Fe, and 1,414°C for Si, with Pr having an extremely low melting point compared to the other elements. Furthermore, when the alloy, which was solidified from the Si-C solution remaining at the bottom of the SiC crucible after growing the SiC single crystal, was extracted and its composition was analyzed, it was found that in Example 1, Pr: 15.8 atomic%, Fe: 20.2 atomic%, and Si: 64.0 atomic%, which was almost the same as the predetermined composition, whereas in Comparative Example 1, Pr: 8.5 atomic%, Fe: 23.0 atomic%, and Si: 68.5 atomic%, the proportion of Pr was low, confirming a deviation from the predetermined composition.

[0049] In Comparative Example 1, despite using Si and metal element M (Pr, Fe, Si) with the same composition as in Example 1, SiC polycrystals adhered and the growth rate decreased. This is thought to be because, since the metals (Pr, Fe, Si) were charged individually, Pr, which has a lower melting point, melted first and penetrated the SiC crucible. As a result, Pr, which has high solubility for SiC, dissolved a large amount of SiC. With a Pr deficiency and a SiC solution whose composition deviated from the desired composition, a large amount of dissolved SiC was supplied, leading to a saturated state of SiC and the formation of SiC polycrystals. These SiC polycrystals then floated and adhered to the liquid surface. [Explanation of Symbols]

[0050] 1 SiC crucible 2. The Second Crucible 3 SiC single crystal (seed crystal) 4 Si-C solution 5, 6 Rotation axis 7 Susceptors 8. Insulation 9 Top lid 10 High-frequency coils

Claims

1. A method for producing a SiC single crystal, comprising: placing a metal element M that enhances the solubility of Si and C in a SiC crucible formed of a SiC sintered body with a relative density of 50 to 90%; melting Si and the metal element M to form a Si-M solution; heating the SiC crucible to dissolve Si and C, originating from SiC which is a component of the SiC crucible, into the Si-M solution from the surface of the SiC crucible that is in contact with the Si-M solution; and contacting a SiC seed crystal with the upper part of the Si-C solution, which is the Si-M solution in which the Si and C have been dissolved, to grow a SiC single crystal on the SiC seed crystal, wherein A method for producing a SiC single crystal, characterized in that the metal element M that enhances the solubility of C is one or both of the following metal elements: at least one first metal element M1 selected from the group La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Lu, and at least one second metal element M2 selected from the group Ti, V, Cr, Mn, Fe, Co, Ni, and Cu, and before placing Si and the metal element M in the SiC crucible, an alloy of Si and the metal element M is pre-impregnated into the SiC sintered body as a molten material.

2. The manufacturing method according to claim 1, wherein the metal element M is both the first metal element M1 and the second metal element M2, and the total content of the metal element M in the Si-C solution is 1 to 80 atomic percent relative to the total amount of Si and M.

3. The manufacturing method according to claim 2, wherein the content of the first metal element M1 in the Si-C solution is 10 atomic percent or more relative to the total amount of Si and M, and the content of the second metal element M2 in the Si-C solution is 1 atomic percent or more relative to the total amount of Si and M.

4. The manufacturing method according to claim 1, wherein the oxygen content of the SiC sintered body is 100 ppm or less.

5. The manufacturing method according to any one of claims 1 to 4, wherein the growth of a SiC single crystal is carried out in the Si-C solution at a temperature of 1,300 to 2,300°C.

6. The manufacturing method according to any one of claims 1 to 4, wherein the SiC crucible is housed in a second crucible made of a heat-resistant carbon material.

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