Method for simultaneously producing multiple sheets of sic single crystal substrate

Abstract

Provided is a method capable of simultaneously producing multiple sheets of an SiC single crystal substrate having a small amount of warpage, a low basal plane dislocation density, and a large crystal growth thickness. This method involves: a step for preparing a plurality of containers; a step for arranging, in each of the containers, an SiC single crystal as a seed crystal and SiC powder mixture containing SiC powder and a liquid phase generation aid so as to form an SiC powder mixture layer in which the SiC powder mixture is in contact with at least one plane of the SiC single crystal, wherein the liquid phase generation aid contains an oxide; a step for arranging the containers so as to be aligned with each other in the horizontal direction and / or the vertical direction in a firing furnace; and a step for heating the inside of the firing furnace so as to form a temperature gradient in which the temperature is increased or decreased from an upper portion toward a lower portion to subject the containers containing the seed crystal and the SiC powder mixture to heat treatment at an average furnace temperature of 2240-2560°C, thereby growing the SiC single crystal on the seed crystal.

Description

Method for simultaneously manufacturing multiple SiC single crystal substrates

[0001] The present disclosure relates to a method for simultaneously producing multiple SiC single crystal substrates.

[0002] Silicon carbide (SiC) has attracted attention as a wide-bandgap material capable of controlling high voltages and high power with low loss. In particular, in recent years, power semiconductor devices using SiC materials (SiC power devices) are expected to be used in a variety of applications because they are more compact, consume less power, and are more efficient than those using Si semiconductors. For example, the use of SiC power devices can reduce the size and increase the efficiency of converters, inverters, on-board chargers, etc. for electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs).

[0003] When manufacturing SiC power devices, nitrogen-doped low-resistivity SiC wafers are used as base substrates. Low-resistivity SiC wafers can generally be produced by a method called sublimation recrystallization. However, due to the large thermal gradient generated in the manufacturing furnace, thermal distortion is likely to occur within the crystal, resulting in a high crystal defect density. Furthermore, if defects, particularly basal plane dislocations known as device killer defects, exist within the SiC wafer, electrical resistance increases during device operation, resulting in a problem of degraded device characteristics. Known methods for reducing defects within wafers include the repeated a-face (RAF) method and solution growth. However, the RAF method is difficult to achieve large diameters and is expensive, and the solution growth method has problems such as the tendency for inclusions to occur within the crystal.

[0004] As another example of a manufacturing method for reducing defects, Patent Document 1 (Japanese Patent No. 4069508) discloses a method for manufacturing a SiC single crystal with closed micropipes, characterized by embedding a SiC single crystal in SiC powder and heat-treating the SiC single crystal. Furthermore, Patent Document 2 (Japanese Patent No. 7339434) discloses a method for manufacturing a SiC single crystal substrate, including the steps of: placing a SiC single crystal as a seed crystal and a SiC powder layer in contact with each other in a container; and placing the container in an effective heating zone in a firing furnace, the temperature of which is controlled within a set temperature range of ±50°C, to perform heat treatment, thereby growing a SiC single crystal on the seed crystal. This manufacturing method is said to be capable of manufacturing a SiC single crystal substrate with a low basal plane dislocation density and a small amount of warpage, since the heat treatment is performed under a smaller temperature gradient.

[0005] Patent No. 4069508 Patent No. 7339434

[0006] As mentioned above, various methods for reducing defects (dislocations) in SiC single crystal substrates have been investigated, but further improvements are needed. For example, Patent Document 1 addresses the reduction of micropipes, but has the problem of not reducing dislocations other than micropipes because a new SiC single crystal is not grown on the SiC single crystal embedded in SiC powder. Furthermore, Patent Document 2 can reduce basal plane dislocation density, but it is unclear whether multiple substrates can be grown simultaneously, and there is no mention of the thickness of the resulting SiC single crystal substrate. In this regard, in order to improve productivity, it is desirable to be able to grow a large number of SiC single crystal substrates while maintaining quality.

[0007] The present inventors have now discovered that by heat treating a SiC single crystal as a seed crystal and a SiC mixed powder layer containing a liquid phase generation aid in a state of contact with each other in a firing furnace having a predetermined temperature gradient, it is possible to simultaneously produce a plurality of SiC single crystal substrates having a small amount of warpage, a low basal plane dislocation density, and a large crystal growth thickness.

[0008] Therefore, an object of the present invention is to provide a method capable of simultaneously manufacturing a plurality of SiC single crystal substrates having a small amount of warpage, a low basal plane dislocation density, and a large crystal growth thickness.

[0009] The present disclosure provides the following aspects. [Aspect 1] A method for simultaneously producing a plurality of SiC single crystal substrates, comprising the steps of: preparing a plurality of containers; arranging, in each of the plurality of containers, a SiC single crystal as a seed crystal and a SiC mixed powder containing SiC powder and a liquid phase generation assistant agent, such that the SiC mixed powder forms a SiC mixed powder layer in contact with at least one surface of the SiC single crystal, the liquid phase generation assistant agent including an oxide; arranging the plurality of containers so that they are lined up horizontally and / or vertically in a sintering furnace; and heating the interior of the sintering furnace to form a temperature gradient in which the temperature increases or decreases from top to bottom, and performing a heat treatment on the plurality of containers containing the seed crystals and the SiC mixed powder at an average furnace temperature of 2240 to 2560°C, thereby growing SiC single crystals on the seed crystals. [Aspect 2] The method according to Aspect 1, wherein the oxide includes a rare earth element. [Aspect 3] The method according to Aspect 1 or Aspect 2, wherein the content of the oxide is 0.5 to 33.0 wt % relative to the content of the SiC powder. [Aspect 4] The method according to any one of Aspects 1 to 3, wherein the average furnace temperature of the heat treatment is 2370 to 2515°C. [Aspect 5] The method according to any one of Aspects 1 to 4, wherein the temperature gradient is 0.01 to 0.40°C / mm. [Aspect 6] The method according to any one of Aspects 1 to 5, wherein the heat treatment is performed with a temperature gradient set so that the side of the container closer to the seed crystal is at a lower temperature than the side of the container closer to the SiC mixed powder layer. [Aspect 7] The method according to any one of Aspects 1 to 6, wherein the number of containers is 2 to 80. [Aspect 8] The method according to any one of Aspects 2 to 7, wherein the rare earth element includes at least one selected from the group consisting of Gd, Sm, La, Nd, Y, and Ce. [Aspect 9] The method according to any one of Aspects 1 to 8, wherein a dense body having a relative density of 90% or more is disposed on a bottom surface and / or an upper surface of the SiC mixed powder layer (excluding the surface in contact with the seed crystal). [Aspect 10] The method according to any one of Aspects 1 to 9, wherein a dense body having a relative density of 90% or more is disposed on an outer periphery of the SiC mixed powder layer.[Aspect 11] The method according to any one of Aspects 1 to 10, wherein a dense body having a relative density of 90% or more is disposed on a bottom surface and / or an top surface of the SiC mixed powder layer (excluding the surface in contact with the seed crystal), and a dense body having a relative density of 90% or more is disposed on an outer periphery of the SiC mixed powder layer. [Aspect 12] The method according to any one of Aspects 1 to 11, wherein the sintering furnace is equipped with an upper heater in an upper part of the sintering furnace and a lower heater in a lower part of the sintering furnace, and wherein the upper heater and the lower heater are set to different temperatures during the heat treatment so as to produce the temperature gradient and the average temperature in the furnace.

[0010] FIG. 1 is a schematic cross-sectional view showing one embodiment of an arrangement of a SiC mixed powder layer and a seed crystal in a container. FIG. 2 is a schematic cross-sectional view showing another embodiment of an arrangement of a SiC mixed powder layer and a seed crystal in a container. FIG. 3 is a schematic cross-sectional view showing another embodiment of an arrangement of a SiC mixed powder layer and a seed crystal in a container. FIG. 4 is a schematic cross-sectional view showing another embodiment of an arrangement of a SiC mixed powder layer and a seed crystal in a container. FIG. 5 is a schematic cross-sectional view showing one embodiment of an arrangement of a SiC mixed powder layer, a seed crystal, and a dense body in a container. FIG. 6 is a schematic cross-sectional view showing another embodiment of an arrangement of a SiC mixed powder layer, a seed crystal, and a dense body in a container. FIG. 7 is a schematic cross-sectional view showing another embodiment of an arrangement of a SiC mixed powder layer, a seed crystal, and a dense body in a container. FIG. 8 is a schematic cross-sectional view showing another embodiment of an arrangement of a SiC mixed powder layer, a seed crystal, and a dense body in a container. FIG. 9 is a schematic cross-sectional view showing another embodiment of an arrangement of a SiC mixed powder layer, a seed crystal, and a dense body in a container. Fig. 1 is a top view of a SiC single crystal substrate 20 for explaining a method for measuring the amount of warpage of the SiC single crystal substrate 20. Fig. 2 is a schematic cross-sectional view of a SiC single crystal substrate 20 for explaining a method for measuring the amount of warpage of the SiC single crystal substrate 20. Fig. 3 is a schematic cross-sectional view of a SiC single crystal substrate 20 for explaining a method for measuring the amount of warpage of the SiC single crystal substrate 20.

[0011] The present invention relates to a method for simultaneously producing multiple SiC single crystal substrates. In this production method, first, multiple containers are prepared. Then, in each of the multiple containers, a SiC single crystal serving as a seed crystal and a SiC mixed powder containing SiC powder and a liquid phase generation additive are placed so that the SiC mixed powder forms a SiC mixed powder layer in contact with at least one surface of the SiC single crystal. The liquid phase generation additive contains an oxide. Next, the multiple containers are arranged horizontally and / or vertically in a sintering furnace. Finally, the interior of the sintering furnace is heated to form a temperature gradient in which the temperature increases or decreases from top to bottom, and the multiple containers containing the seed crystals and SiC mixed powder are heat-treated at an average furnace temperature of 2240 to 2560°C. This allows SiC single crystals to grow on the seed crystals. In this way, by heat treating the SiC single crystal as a seed crystal and the SiC mixed powder layer containing the liquid phase generation aid in a state of contact with each other in a firing furnace having a predetermined temperature gradient, it is possible to simultaneously manufacture a plurality of SiC single crystal substrates having a small amount of warpage, a low basal plane dislocation density, and a large crystal growth thickness.

[0012] As mentioned above, various methods for reducing defects (dislocations) in SiC single crystal substrates have been investigated, but further improvements are needed. For example, Patent Document 1 addresses the reduction of micropipes, but has the problem of not being able to reduce dislocations other than micropipes because a new SiC single crystal is not grown on the SiC single crystal embedded in SiC powder. Furthermore, Patent Document 2 can reduce the basal plane dislocation density, but it is unclear whether multiple substrates can be grown simultaneously, and there is no mention of the thickness of the resulting SiC single crystal substrate. In this regard, to improve productivity, it is desirable to be able to achieve crystal growth of a large number of SiC single crystal substrates while maintaining quality. According to the present invention, such problems are advantageously solved. Specifically, the crystal growth thickness is 50 μm or more, the amount of warpage is 40 μm or less, and the basal plane dislocation density is 100 cm －２ A plurality of the following SiC single crystal substrates can be manufactured simultaneously.

[0013] (1) Preparation of Containers Since the present invention is a method for simultaneously producing multiple SiC single crystal substrates, first, multiple containers for containing seed crystals and SiC mixed powder are prepared. The material of the containers is not particularly limited as long as it does not sublimate or melt at the furnace temperature during heat treatment, but graphite or SiC is preferable. The inner and outer walls of the containers may be coated. Examples of coating materials include SiC, TiC, TaC, NbC, and WC. The shape of the container is not particularly limited, but it is preferable that the container has an internal space capable of accommodating the seed crystals 4 and the SiC mixed powder layer 6, an open-top container body 2a, and a container lid 2b that fits into the open-top portion of the container body 2a, as shown in FIG. 1 .

[0014] (2) Arrangement of SiC Mixed Powder and Seed Crystal Next, a SiC single crystal serving as a seed crystal 4 and a SiC mixed powder containing SiC powder and a liquid phase generation aid are arranged in each of the multiple containers 2 so that the SiC mixed powder forms a SiC mixed powder layer 6 in contact with at least one surface of the SiC single crystal. The seed crystal 4 is typically composed of a SiC single crystal and has a crystal growth surface. The polytype, off-axis angle, and polarity of the SiC single crystal, as well as the type and concentration of dopants that may be contained in the SiC single crystal, are not particularly limited, but 4H, 6H, or 3C polytype is preferred. Alternatively, a SiC single crystal formed on a Si substrate may be used as the seed crystal 4. The crystal growth surface on the SiC single crystal serving as the seed crystal 4 may be the Si-face or the C-face, or both the Si-face and the C-face. The diameter of the seed crystal 4 is not particularly limited, but may be 100 mm (4 inches), 150 mm (6 inches), or 200 mm (8 inches).

[0015] The SiC mixed powder layer 6 typically refers to the SiC mixed powder spread in a layer inside the container 2. The SiC mixed powder is preferably prepared by uniformly mixing the SiC powder and the liquid phase generating aid. This mixing method is not particularly limited as long as the SiC powder and the liquid phase generating aid can be uniformly mixed, and may be, for example, ball mill mixing, mixer mixing, or the like. Furthermore, when mixing the SiC powder and the liquid phase generating aid, a dispersant or the like may be added in order to suppress aggregation, etc.

[0016] The SiC powder may be either α-SiC or β-SiC, as long as it serves as a SiC source during crystal growth. There are no particular limitations on the particle size or purity of the SiC powder, and any commercially available powder can be used. However, in order to produce a high-purity SiC single crystal substrate, it is desirable that the SiC powder also be high-purity.

[0017] The liquid phase generating aid is an aid that generates a liquid phase in the heat treatment described below (particularly near the crystal growth temperature (e.g., the average furnace temperature)), and exhibits the function of dissolving SiC particles (SiC powder) by melting itself to generate a liquid phase. The liquid phase generating aid contains an oxide. The oxide contained in the liquid phase generating aid preferably contains a metal element (i.e., in the form of a metal oxide), and more preferably contains a rare earth element. Preferred examples of rare earth elements include Gd, Sm, La, Nd, Y, Ce, and combinations thereof, and more preferably Gd, Sm, La, and combinations thereof. Preferred examples of metal elements other than rare earth elements include Al and Nb. The oxide contained in the liquid phase generating aid may contain an element other than a metal element, and a preferred example of such an element is Si.

[0018] The content of the oxide contained in the liquid phase generating aid is preferably 0.5 to 37.0 wt %, more preferably 0.5 to 33.0 wt %, even more preferably 1.0 to 25.0 wt %, particularly preferably 2.0 to 17.0 wt %, and most preferably 4.0 to 10.0 wt %, relative to the content of the SiC powder (based on 100 wt %).

[0019] As shown in FIGS. 1 to 4 , the SiC mixed powder is arranged to form a SiC mixed powder layer 6 that contacts at least one surface of the SiC single crystal serving as the seed crystal 4. That is, as long as the seed crystal 4 and the SiC mixed powder layer 6 are in contact with each other, there is no particular limitation on their arrangement positions. For example, as shown in FIG. 1 , the seed crystal 4 may be arranged on the inner bottom surface of the container 2, and the SiC mixed powder layer 6 may be arranged thereon. Alternatively, as shown in FIG. 2 , the seed crystal 4 may be embedded in the SiC mixed powder layer 6 in the container 2. Alternatively, as shown in FIG. 3 , the seed crystal 4 may be placed on the upper surface of the SiC mixed powder layer 6 arranged on the inner bottom surface of the container 2. Furthermore, as long as the seed crystal 4 and the SiC mixed powder layer 6 are in contact with each other, a lateral space may be provided so that the side surfaces (outer peripheral edges) of the seed crystal 4 and the SiC mixed powder layer 6 do not contact the inner wall of the container 2. There are no particular limitations on the method for filling the SiC mixed powder into the container 2, and it may be carried out by a known method such as press filling or vibration filling.

[0020] As shown in FIGS. 5 to 7 , a dense body 8 may be disposed on the bottom surface and / or top surface of the SiC mixed powder layer 6 (excluding the surface in contact with the seed crystal 4). By disposing the dense body 8 in this manner, it is possible to prevent impurities from entering from the inner bottom surface of the container 2 and / or the container lid 2 b, thereby enabling the growth of a higher-purity SiC single crystal. For example, when the seed crystal 4 is not disposed on the top surface of the SiC mixed powder layer 6, the dense body 8 may be disposed on the top surface of the SiC mixed powder layer 6 as shown in FIG. 5 . When the seed crystal 4 is not disposed on the inner bottom surface of the container 2, the dense body 8 may be disposed between the SiC mixed powder layer 6 and the inner bottom surface of the container 2 as shown in FIG. 6 . When the seed crystal 4 is embedded in the SiC mixed powder layer 6, the dense body 8 may be disposed on the top surface of the SiC mixed powder layer 6 and / or between the SiC mixed powder layer 6 and the inner bottom surface of the container 2 as shown in FIG. 7 .

[0021] As shown in Figures 8 and 9, a dense body 8 may be disposed on the outer periphery of the SiC mixed powder layer 6. By disposing the dense body 8 in this manner, it is possible to prevent impurities from entering from the side surface of the container 2, and to grow a SiC single crystal with higher purity. For example, as shown in Figure 8, the dense body 8 may be disposed between the outer periphery of the SiC mixed powder layer 6 and the inner wall of the container 2. In this case, it is preferable that the dense body 8 contacts at least the outer periphery of the SiC mixed powder layer 6. In particular, as shown in Figure 9, it is preferable that the dense body 8 is disposed on the bottom surface and / or the top surface of the SiC mixed powder layer 6 (excluding the surface in contact with the seed crystal 4), and that the dense body 8 is disposed on the outer periphery of the SiC mixed powder layer 6.

[0022] The dense body 8 is preferably a solid having a relative density of 90% or more, more preferably 95% or more, and even more preferably 99% or more. The higher the relative density, the more effectively impurities can be prevented from entering. The relative density can be determined, for example, by dividing the bulk density of the dense body measured by Archimedes' method by the theoretical density of the dense body and multiplying the result by 100. The dense body 8 is not particularly limited as long as it does not sublimate or melt at the furnace temperature during heat treatment and does not react with SiC. Examples of materials for such dense body 8 include carbides such as TiC, TaC, NbC, and WC, and Si ３ N ４ The dense body 8 may have any shape, but is preferably layered.

[0023] (3) Arrangement of Multiple Containers in Sintering Furnace As described above, multiple containers 2 containing the SiC mixed powder layer 6, the seed crystal 4, and optionally the dense body 8 are arranged in the sintering furnace 10 so as to be aligned horizontally and / or vertically. From the viewpoint of improving productivity, it is desirable to arrange a large number of containers 2 in the sintering furnace 10. Therefore, the number of containers 2 is preferably two or more, more preferably 2 to 80, even more preferably 15 to 80, and particularly preferably 50 to 80, and may be, for example, 2 to 15 or 15 to 50. More specifically, when multiple containers 2 are arranged vertically (e.g., stacked), the number of containers 2 arranged vertically is preferably 2 to 30, more preferably 5 to 30, even more preferably 10 to 30, and particularly preferably 20 to 30, and may be, for example, 2 to 5, 5 to 10, or 10 to 20. When multiple containers 2 are arranged horizontally, either individually or as sets of vertically arranged containers 2, the number of containers 2 and / or sets arranged horizontally is preferably 2 to 10, more preferably 4 to 10, even more preferably 6 to 10, and particularly preferably 8 to 10, for example, 2 to 4, 4 to 6, or 6 to 8. As shown in FIG. 10 , the firing furnace 10 preferably includes an upper heater 12 arranged at the top of the firing furnace 10, a lower heater 14 arranged at the bottom of the firing furnace 10, a base 16 for placing the multiple containers 2, and a gas pipe 18 for supplying gas G into the firing furnace 10. This configuration effectively creates a temperature gradient in the firing furnace 10 in the subsequent heat treatment process, where the temperature increases or decreases from top to bottom.

[0024] (4) Heat Treatment After placing the plurality of containers 2 in the sintering furnace 10, the interior of the sintering furnace 10 is heated to form a temperature gradient in which the temperature increases or decreases from the top to the bottom, and the plurality of containers 2 containing the seed crystals 4 and the SiC mixed powder layer 6 are heat-treated at an average furnace temperature of 2240 to 2560°C, thereby growing SiC single crystals on the seed crystals 4. In this case, as shown in FIG. 10 , the sintering furnace 10 preferably includes an upper heater 12 at the top of the sintering furnace 10 and a lower heater 14 at the bottom of the sintering furnace 10, and the upper heater 12 and the lower heater 14 are preferably set to different temperatures during the heat treatment so as to achieve the above-mentioned temperature gradient and the above-mentioned average furnace temperature. Note that when heating is performed to form a temperature gradient in which the temperature increases from the top to the bottom of the sintering furnace 10, the set temperature of the lower heater 14 may be set higher than the set temperature of the upper heater 12. Conversely, when heating is performed so as to form a temperature gradient in which the temperature decreases from the top to the bottom of the firing furnace 10, the set temperature of the lower heater 14 should be lower than the set temperature of the upper heater 12.

[0025] The container 2 is preferably placed in the effective heating zone within the firing furnace 10. Here, the "effective heating zone" refers to "a charging zone in a heat treatment device that can maintain the metal product within an allowable temperature range depending on the purpose of the heat treatment," as defined by JIS B 6905:1995. The temperature of the effective heating zone of the firing furnace 10 can be controlled by adjusting the heater output of the upper heater 12 and the lower heater 14 provided in the firing furnace 10. This allows the upper and lower temperatures of the heating zone within the firing furnace 10 to be varied, thereby forming a unidirectional temperature gradient within the firing furnace 10.

[0026] The temperature gradient is preferably 0.01 to 0.40°C / mm, more preferably 0.05 to 0.30°C / mm, and even more preferably 0.08 to 0.14°C / mm. Furthermore, it is preferable to perform the heat treatment by providing a temperature gradient such that the side of the container 2 closer to the seed crystal 4 is at a lower temperature than the side of the container 2 closer to the SiC mixed powder layer 6. For example, when heating is performed to form a temperature gradient in which the temperature increases from the top to the bottom of the sintering furnace 10, the seed crystal 4 may be placed on the SiC mixed powder layer 6 within the container 2. Conversely, when heating is performed to form a temperature gradient in which the temperature decreases from the top to the bottom of the sintering furnace 10, the SiC mixed powder layer 6 may be placed on the seed crystal 4 within the container 2.

[0027] The average furnace temperature for the heat treatment is 2240 to 2560°C, preferably 2370 to 2515°C, more preferably 2390 to 2480°C, and even more preferably 2410 to 2450°C. The average furnace temperature may be determined as the average of the maximum and minimum temperatures in the effective heating zone within the firing furnace 10. Typically, the space temperatures near the bottom and top of the effective heating zone within the firing furnace 10 are measured, and the average of these space temperatures can be used as the average furnace temperature. The holding time at the average furnace temperature is not particularly limited; the longer the holding time, the thicker the SiC single crystal can be grown, and therefore the holding time can be set according to the desired thickness. The heat treatment may be performed under atmospheric pressure or under pressure, such as by hot pressing.

[0028] The firing furnace 10 used for the heat treatment is not particularly limited as long as it allows crystal growth of SiC on the seed crystal 4, and may be a known firing furnace such as a resistance furnace, an arc furnace, or an induction furnace. The atmosphere inside the firing furnace 10 during firing is preferably a vacuum, nitrogen, an inert gas, or a mixed atmosphere of nitrogen and an inert gas. The material and resistivity of the heaters 12 and 14 are not particularly limited, but they are preferably made of graphite.

[0029] (5) Polishing After growing a SiC single crystal on the seed crystal 4 in this manner, it is preferable to polish the surface of the SiC single crystal. For example, the desired SiC single crystal substrate can be obtained by polishing using diamond abrasive grains and then finishing by chemical mechanical polishing (CMP).

[0030] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0031] Example 1 (1) Preparation of SiC mixed powder Commercially available β-SiC powder (volume-based D50 particle size: 65.0 μm) and an oxide (Gd ２ O ３ ) (volume-based D50 particle size: 5.0 μm) was weighed so that the oxide content relative to the SiC powder content was 8.1 wt %, and then placed in a polypropylene container together with pebbles and water. The polypropylene container was placed on a pot stand, and the polypropylene container was rotated at a speed of 50 rpm to mix the raw materials. The slurry obtained by mixing the raw materials was dried in a dryer and collected to obtain a SiC mixed powder.

[0032] (2) Arrangement of SiC mixed powder and SiC single crystal The SiC mixed powder obtained in (1) above was filled into a graphite container and tapped to smooth the SiC mixed powder so that the outermost layer of the SiC mixed powder was visually flat. A commercially available SiC single crystal substrate (4H-SiC, diameter 150 mm (6 inches), off-angle 4°, thickness 0.35 mm) serving as a seed crystal was placed on the SiC mixed powder so that only the Si surface of the seed crystal was in contact with the powder. The graphite container was closed with a graphite lid to form a single graphite sheath. Multiple such graphite sheaths (a total of four in this example) were prepared.

[0033] (3) Arrangement of Multiple Graphite Saggers in a Resistance Furnace Two of the graphite saggers prepared in (2) above were arranged vertically and two of these were arranged horizontally in the effective heating zone of a sintering furnace (resistance furnace) via graphite spacers each 5 mm thick, resulting in a total of four graphite saggers being arranged in the furnace.

[0034] (4) Heat treatment was performed on all graphite saggers by adjusting the heater output to form a temperature gradient of 0.11°C / mm inside the firing furnace such that the temperature increased from the top to the bottom, and heating was performed in an argon atmosphere at an average furnace temperature of 2430°C for 20 hours. As a result, SiC single crystals were grown on the seed crystals in all graphite saggers, thereby obtaining SiC single crystal substrates.

[0035] (5) Measurement of Crystal Growth Thickness of SiC Single Crystal Substrates The thickness of 25 randomly selected locations on the SiC single crystal substrates obtained in (4) above was measured with a micrometer, and the arithmetic mean value was calculated. Using a similar method, the thickness of the seed crystal was also calculated at the time of (2) above. The crystal growth thickness (μm) was then calculated by subtracting the arithmetic mean value of the seed crystal thickness from the arithmetic mean value of the SiC single crystal substrate thickness. It was confirmed that the crystal growth thickness of all four SiC single crystal substrates was 100 μm or more.

[0036] Of all the SiC single crystal substrates whose crystal growth thickness was determined by the above method, the SiC single crystal substrate with the smallest crystal growth thickness was ranked and evaluated according to the following evaluation criteria. The results are shown in Table 3. <Evaluation criteria> - Evaluation A: The crystal growth thickness of the SiC single crystal substrate with the smallest crystal growth thickness is 100 μm or more - Evaluation B: The crystal growth thickness of the SiC single crystal substrate with the smallest crystal growth thickness is 50 μm or more and less than 100 μm - Evaluation C: The crystal growth thickness of the SiC single crystal substrate with the smallest crystal growth thickness is less than 50 μm

[0037] (6) Polishing The surfaces (Si-face and C-face) of the obtained SiC single crystal were polished using diamond abrasive grains, and then finished by chemical mechanical polishing (CMP).

[0038] (7) Measurement of Warpage Amount of SiC Single Crystal Substrate The amount of warpage was measured for the polished surfaces of all of the SiC single crystal substrates obtained in (6) above using a high-precision laser measuring device (LT-9010M manufactured by Keyence Corporation). As shown in Figure 11, in the plan view figure when the surface (SiC single crystal 30) of SiC single crystal substrate 20 was viewed from above, two lines X and Y that intersected each other at right angles were drawn passing through point G, which was the center of gravity of the plan view figure, and two points A and B were determined on line X, each 70 mm away from point G, and two points C and D were determined on line Y, each 70 mm away from point G. 12, among the line segments extending perpendicular to the line segment AB from any point on the curve AB between points A and B on the surface (SiC single crystal 30) of the SiC single crystal substrate 20, point P on the curve AB was determined as the longest line segment (for example, in FIG. 12, there are points P and O as arbitrary points on the curve AB, and among the line segments extending perpendicular to the line segment AB from these points, the longest line segment is the line segment extended from point P). The distance between the line segment AB and point P was then defined as the amount of warpage α. 13, among the line segments extending perpendicular to the line segment CD from any point on the curve CD between points C and D on the surface of the SiC single crystal substrate 20 (SiC single crystal 30), point R on the curve CD was determined as the longest line segment (for example, in FIG. 13, points R, O, etc. are arbitrary points on the curve CD, and among the line segments extending perpendicular to the line segment CD from these points, the longest line segment is the line segment extended from point R). The distance between the line segment CD and point R was then defined as the amount of warpage β. The average value of these amounts of warpage α and β was defined as the amount of warpage of the SiC single crystal substrate.

[0039] Of all the SiC single crystal substrates whose warpage was determined by the above method, the SiC single crystal substrate with the largest amount of warpage was ranked and evaluated according to the following evaluation criteria. The results are shown in Table 3. <Evaluation criteria> - Evaluation A: The SiC single crystal substrate with the largest amount of warpage had a warpage of 30 μm or less - Evaluation B: The SiC single crystal substrate with the largest amount of warpage had a warpage of more than 30 μm and 40 μm or less - Evaluation C: The SiC single crystal substrate with the largest amount of warpage exceeded 40 μm

[0040] (8) Measurement of basal plane dislocation density of SiC single crystal substrates All of the SiC single crystal substrates obtained in (6) above were placed in a nickel crucible together with KOH crystals. This crucible was etched in an electric furnace at 500°C for 10 minutes. The samples (SiC single crystal substrates) after etching were cleaned, and their surfaces were observed under an optical microscope to determine the types of defects from the shapes of the pits. The number of basal plane dislocations was measured, and the number of basal plane dislocations (number) was calculated based on the area (cm) of the observed region. ２ ) to obtain the basal plane dislocation density (cm －２ Specifically, 100 visual fields of 2.8 mm length × 3.6 mm width were photographed at a magnification of 20x for any location on the sample surface to measure the total number of basal plane dislocations, and this total was calculated based on the total area of ​​100 visual fields, which is 10.1 cm². ２ The basal plane dislocation density was calculated by dividing

[0041] Of all the SiC single crystal substrates whose basal plane dislocation densities were determined by the above method, the SiC single crystal substrate with the highest basal plane dislocation density was ranked according to the following evaluation criteria. The results are shown in Table 3. <Evaluation criteria> - Rating A: The SiC single crystal substrate with the highest basal plane dislocation density had a basal plane dislocation density of 80 cm －２ Below - Evaluation B: The basal plane dislocation density of the SiC single crystal substrate with the highest basal plane dislocation density is 80 cm －２ Over 100cm －２ Below - Evaluation C: The basal plane dislocation density of the SiC single crystal substrate with the highest basal plane dislocation density is 100 cm －２ exceed

[0042] Example 2: (i) in (1) above, the oxide content relative to the SiC powder content is 16.2 wt%; (ii) in (2) above, TaC polycrystalline dense body (relative density 90% or more) is placed on the bottom and outer periphery of the graphite container; (iii) in (3) above, three graphite sheaths are placed horizontally and five are placed vertically in the sintering furnace; (iv) in (4) above, the temperature gradient of 0.17 ° C / mm is formed so that the temperature increases from the top to the bottom in the sintering furnace, and the average temperature in the furnace is heated to 2445 ° C. The SiC single crystal substrate was produced and evaluated in the same manner as in Example 1. The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of the obtained substrate are as shown in Table 3.

[0043] Example 3: (i) in (1) above, the oxide content relative to the SiC powder content is 32.4 wt%; (ii) in (2) above, TaC polycrystalline dense body (relative density 90% or more) is arranged on the outer periphery of the graphite container; (iii) in (3) above, three graphite sheaths are arranged horizontally and 25 are arranged vertically in the sintering furnace; (iv) in (4) above, the temperature gradient of 0.06 ° C / mm is formed so that the temperature increases from the top to the bottom in the sintering furnace, and the average temperature in the furnace is heated to 2490 ° C. The SiC single crystal substrate was produced and evaluated in the same manner as in Example 1. The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of the obtained substrate are as shown in Table 3.

[0044] Example 4 SiC single crystal substrates were produced and evaluated in the same manner as in Example 1, except that (i) in (1) above, the oxide content relative to the SiC powder content was set to 4.1 wt %, (ii) in (3) above, 10 graphite scabbards were arranged horizontally and 5 graphite scabbards were arranged vertically in the firing furnace, and (iii) in (4) above, a temperature gradient of 0.28°C / mm was formed inside the firing furnace so that the temperature increased from top to bottom, and heating was performed at an average furnace temperature of 2450°C. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrates are shown in Table 3.

[0045] Example 5: (i) in (1), the oxide content relative to the SiC powder content is 2.0 wt%; (ii) in (2), TaC polycrystalline dense body (relative density 90% or more) is placed on the bottom of the graphite container; (iii) in (3), two graphite sheaths are arranged horizontally and 30 are arranged vertically in the sintering furnace; (iv) in (4), the temperature gradient of 0.01 ° C / mm is formed so that the temperature increases from the top to the bottom in the sintering furnace, and the average temperature in the furnace is heated to 2508 ° C., except that, in the same manner as in Example 1, SiC single crystal substrate is produced and evaluated.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of the obtained substrate are as shown in Table 3.

[0046] Example 6: (i) in (1), the oxide content relative to the SiC powder content is 1.0 wt%; (ii) in (2), TaC polycrystalline dense body (relative density 90% or more) is placed on the bottom of the graphite container; (iii) in (3), 7 graphite sheaths are arranged horizontally and 10 vertically in the sintering furnace; (iv) in (4), the temperature gradient of 0.12 ° C / mm is formed so that the temperature increases from the top to the bottom in the sintering furnace, and the average temperature in the furnace is heated to 2445 ° C. The SiC single crystal substrate was prepared and evaluated in the same manner as in Example 1. The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of the obtained substrate are as shown in Table 3.

[0047] Example 7: (i) in (1) above, the oxide content relative to the SiC powder content is 0.8 wt%; (ii) in (2) above, TaC polycrystalline dense body (relative density 90% or more) is placed on the bottom of a graphite container; (iii) in (3) above, one graphite sheath is arranged horizontally and two vertically in the sintering furnace; (iv) in (4) above, the temperature gradient of 0.14 ° C / mm is formed so that the temperature increases from the top to the bottom in the sintering furnace, and the average temperature in the furnace is heated to 2375 ° C. The SiC single crystal substrate was produced and evaluated in the same manner as in Example 1. The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of the obtained substrate are as shown in Table 3.

[0048] Example 8: (i) in (1) above, the oxide content relative to the SiC powder content is 24.3 wt%; (ii) in (2) above, TaC polycrystalline dense body (relative density 90% or more) is placed on the bottom and outer periphery of the graphite container; (iii) in (3) above, two graphite sheaths are placed horizontally and one vertically in the sintering furnace; (iv) in (4) above, the temperature gradient of 0.21 ° C / mm is formed so that the temperature increases from the top to the bottom in the sintering furnace, and the average temperature in the furnace is heated to 2463 ° C. The SiC single crystal substrate was produced and evaluated in the same manner as in Example 1. The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of the obtained substrate are as shown in Table 3.

[0049] Example 9 SiC single crystal substrates were produced and evaluated in the same manner as in Example 1, except that (i) in the above (2), a commercially available SiC single crystal substrate serving as a seed crystal was placed at the bottom of a graphite container with the Si surface of the substrate facing upward, and the SiC mixed powder was filled from above, and (ii) in the above (4), the interior of the firing furnace was heated to form a temperature gradient in which the temperature decreased from the top to the bottom. The evaluation results for the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrates are shown in Table 3.

[0050] Example 10 (i) in above (2), the commercially available SiC single crystal substrate of seed crystal is placed at the bottom of graphite container, so that the Si surface of substrate is facing up, and the TaC polycrystalline dense body (relative density 90% or more) is placed on the outer periphery of the graphite container, then fill in SiC mixed powder from above, and then place the TaC polycrystalline dense body (relative density 90% or more) on the upper surface of the powder layer; (ii) in above (4), heat the inside of sintering furnace so as to form the temperature gradient that the temperature decreases from top to bottom, except that, carry out the preparation and evaluation of SiC single crystal substrate in the same manner as in example 2.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0051] Example 11 (i) in above (2), the commercially available SiC single crystal substrate of seed crystal is placed at the bottom of graphite container, so that the Si surface of substrate is facing up, and the TaC polycrystalline dense body (relative density 90% or more) is placed on the outer periphery of the graphite container, and then fill SiC mixed powder from above; (ii) in above (4), the inside of sintering furnace is heated so as to form the temperature gradient that the temperature decreases from the top to the bottom, except that, in the same manner as in example 3, prepare and evaluate SiC single crystal substrate.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0052] Example 12 SiC single crystal substrates were produced and evaluated in the same manner as in Example 4, except that (i) in the above (2), a commercially available SiC single crystal substrate serving as a seed crystal was placed at the bottom of a graphite container with the Si surface of the substrate facing upward, and the SiC mixed powder was filled from above, and (ii) in the above (4), the interior of the firing furnace was heated to form a temperature gradient in which the temperature decreased from the top to the bottom. The evaluation results for the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrates are shown in Table 3.

[0053] Example 13: (i) in above (2), the commercially available SiC single crystal substrate of seed crystal is placed at the bottom of graphite container, so that the Si surface of substrate is facing up, and then fill SiC mixed powder from above, and then place TaC polycrystalline dense body (relative density 90% or more) on the upper surface of powder layer; (ii) in above (4), heat the inside of sintering furnace so as to form the temperature gradient that temperature decreases from top to bottom, except for that, carry out the preparation and evaluation of SiC single crystal substrate in the same manner as in example 5.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0054] Example 14 (i) in above (2), the commercially available SiC single crystal substrate of seed crystal is placed at the bottom of graphite container, so that the Si surface of substrate is facing up, and then fill SiC mixed powder from above, and then place TaC polycrystalline dense body (relative density 90% or more) on the upper surface of powder layer; (ii) in above (4), heat the inside of sintering furnace so as to form the temperature gradient that temperature decreases from top to bottom, except for that, carry out the preparation and evaluation of SiC single crystal substrate in the same manner as in example 6.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0055] Example 15 (i) in above (2), the commercially available SiC single crystal substrate of seed crystal is placed at the bottom of graphite container, so that the Si surface of substrate is facing up, and then fill SiC mixed powder from above, and then place TaC polycrystalline dense body (relative density 90% or more) on the upper surface of the powder layer; (ii) in above (4), heat the inside of sintering furnace so as to form the temperature gradient that the temperature decreases from top to bottom, except for that, carry out the preparation and evaluation of SiC single crystal substrate in the same manner as in example 7.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0056] Example 16 (i) in above (2), the commercially available SiC single crystal substrate of seed crystal is placed at the bottom of graphite container, so that the Si surface of substrate is facing up, and the TaC polycrystalline dense body (relative density 90% or more) is placed on the outer periphery of the graphite container, then fill in SiC mixed powder from above, and then place the TaC polycrystalline dense body (relative density 90% or more) on the upper surface of the powder layer; (ii) in above (4), heat the inside of sintering furnace so as to form the temperature gradient that the temperature decreases from top to bottom, except that, carry out the preparation and evaluation of SiC single crystal substrate in the same manner as in example 8.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0057] Example 17 In the above (1), Sm was used as the oxide serving as the liquid phase generation aid. ２ O ３Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 1. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0058] Example 18 In the above (1), La was used as the oxide serving as the liquid phase generation aid. ２ O ３ Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 1. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0059] Example 19 In the above (1), Nd was used as the oxide serving as the liquid phase generation aid. ２ O ３ Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 1. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0060] Example 20 (i) In the above (1), Y was used as the oxide serving as the liquid phase generation aid. ２ O ３ (ii) in above (2), TaC polycrystalline dense body (relative density 90% or more) is placed on the bottom of graphite container, except for that, in the same manner as in example 1, make and evaluate SiC single crystal substrate.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0061] Example 21 (i) In the above (1), CeO was used as the oxide serving as the liquid phase generation aid. ２ (ii) in above (2), TaC polycrystalline dense body (relative density 90% or more) is placed on the bottom of graphite container, except for that, in the same manner as in example 1, make and evaluate SiC single crystal substrate.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0062] Example 22 SiC single crystal substrates were produced and evaluated in the same manner as in Example 1, except that in (2) above, the graphite container was filled approximately halfway with SiC mixed powder, the powder was leveled, a commercially available SiC single crystal substrate to serve as a seed crystal was placed on the powder, and the SiC mixed powder was poured onto the substrate to embed the seed crystal. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrates are shown in Table 3.

[0063] Example 23 (i) In the above (1), Sm was used as the oxide serving as the liquid phase generation aid. ２ O ３ (ii) in above (2), TaC polycrystalline dense body (relative density 90% or more) is placed on the bottom of graphite container and on the top surface of powder layer, except for that, in the same manner as in example 22, make and evaluate SiC single crystal substrate.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0064] Example 24 In the above (1), Al was used as the oxide serving as the liquid phase generation aid. ２ O ３ Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 4. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0065] Example 25 (i) In the above (1), Al was used as the oxide serving as the liquid phase generation aid. ２ O ３ (ii) in above (2), further arrange TaC polycrystalline dense body (relative density 90% or more) on the outer periphery of the inside of graphite container, except for that, in the same manner as in example 7, make and evaluate SiC single crystal substrate.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0066] Example 26 In the above (1), Al was used as the oxide serving as the liquid phase generation aid. ２ O ３Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 5. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0067] Example 27 In the above (1), Nb was used as the oxide serving as the liquid phase generation aid. ２ O ５ Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 4. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0068] Example 28 (i) In the above (1), Nb was used as the oxide serving as the liquid phase generation aid. ２ O ５ (ii) in above (2), further arrange TaC polycrystalline dense body (relative density 90% or more) on the outer periphery of the inside of graphite container, except for that, in the same manner as in example 7, make and evaluate SiC single crystal substrate.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0069] Example 29 In the above (1), Nb was used as the oxide serving as the liquid phase generation aid. ２ O ５ Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 5. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0070] Example 30 In the above (1), SiO was used as the oxide serving as the liquid phase generation aid. ２ Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 4. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0071] Example 31 (i) In the above (1), SiO was used as the oxide serving as the liquid phase generation aid. ２(ii) in above (2), further arrange TaC polycrystalline dense body (relative density 90% or more) on the outer periphery of the inside of graphite container, except for that, in the same manner as in example 7, make and evaluate SiC single crystal substrate.The evaluation results of the crystal growth thickness, warpage and basal plane dislocation density of obtained substrate are as shown in table 3.

[0072] Example 32 In the above (1), SiO was used as the oxide serving as the liquid phase generation aid. ２ Except for using the above-mentioned SiC single crystal substrate, the SiC single crystal substrate was produced and evaluated in the same manner as in Example 5. The evaluation results of the crystal growth thickness, warpage, and basal plane dislocation density of the obtained substrate are shown in Table 3.

[0073] Example 33 (Comparative) SiC single crystal substrates were produced and evaluated in the same manner as in Example 1, except that in (4) above, a temperature gradient was not formed (i.e., the temperature at the top and bottom of the effective heating zone were made approximately the same) and heating was performed at an average furnace temperature of 2450° C. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrates are shown in Table 3.

[0074] Example 34 SiC single crystal substrates were produced and evaluated in the same manner as in Example 1, except that in (4) above, a temperature gradient of 0.36°C / mm was formed inside the firing furnace so that the temperature increased from the top to the bottom, and heating was performed at an average furnace temperature of 2450°C. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrates were as shown in Table 3.

[0075] Example 35: Except for changing the oxide content relative to the SiC powder content in (1) above to 36.5 wt %, a SiC single crystal substrate was produced and evaluated in the same manner as in Example 1. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrate were as shown in Table 3.

[0076] Example 36 SiC single crystal substrates were produced and evaluated in the same manner as in Example 1, except that in (4) above, a temperature gradient of 0.06° C. / mm was formed inside the firing furnace so that the temperature increased from the top to the bottom, and heating was performed at an average furnace temperature of 2550° C. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrates were as shown in Table 3.

[0077] Example 37 (Comparative) A SiC single crystal substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, no liquid phase generation aid was added, i.e., commercially available β-SiC powder (volume-based D50 particle size: 65.0 μm) was used instead of the SiC mixed powder. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrate are as shown in Table 3.

[0078] Example 38 SiC single crystal substrates were produced and evaluated in the same manner as in Example 1, except that in (4) above, a temperature gradient of 0.28°C / mm was formed inside the firing furnace so that the temperature increased from the top to the bottom, and heating was performed at an average furnace temperature of 2250°C. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrates are shown in Table 3.

[0079] Example 39 (Comparative) SiC single crystal substrates were produced and evaluated in the same manner as in Example 1, except that in (4) above, a temperature gradient of 0.14°C / mm was formed inside the firing furnace so that the temperature increased from the top to the bottom, and heating was performed at an average furnace temperature of 2225°C. The evaluation results for the crystal growth thickness, amount of warpage, and basal plane dislocation density of the obtained substrates are shown in Table 3.

[0080]

[0081]

[0082]

[0083] The results of Examples 1 to 32, 34 to 36, and 38 revealed that by heat treating a SiC single crystal as a seed crystal and a SiC mixed powder layer containing a liquid phase generation aid in a state of contact with each other in a firing furnace having a predetermined temperature gradient (preferably in an effective heating zone), it is possible to simultaneously produce multiple SiC single crystal substrates with a small amount of warpage, a low basal plane dislocation density, and a large crystal growth thickness, although the cause is unknown. On the other hand, the results of Examples 33, 37, and 39 (comparison) revealed that high-quality SiC single crystal substrates cannot be obtained unless a temperature gradient is formed, a liquid phase generation aid is not added, or the average temperature in the furnace is not controlled.

[0084] 2 container 2a container body 2b container lid 4 seed crystal 6 SiC mixed powder layer 8 dense body 10 firing furnace 12 upper heater 14 lower heater 16 base 18 gas pipe 20 SiC single crystal substrate 30 SiC single crystal G gas

Claims

1. A method for simultaneously producing a plurality of SiC single crystal substrates, comprising the steps of: preparing a plurality of containers; arranging, in each of the plurality of containers, a SiC single crystal as a seed crystal and a SiC mixed powder containing SiC powder and a liquid phase generation aid so that the SiC mixed powder forms a SiC mixed powder layer in contact with at least one surface of the SiC single crystal, wherein the liquid phase generation aid contains an oxide; arranging the plurality of containers so that they are lined up horizontally and / or vertically in a firing furnace; heating the interior of the firing furnace to form a temperature gradient in which the temperature increases or decreases from top to bottom, and heat treating the plurality of containers containing the seed crystals and the SiC mixed powder at an average furnace temperature of 2240 to 2560°C, thereby growing SiC single crystals on the seed crystals.

2. The method of claim 1, wherein the oxide comprises a rare earth element.

3. The method according to claim 1 or 2, wherein the content of said oxide is 0.5 to 33.0% by weight relative to the content of said SiC powder.

4. The method according to claim 1 or 2, wherein the average temperature in the furnace during the heat treatment is 2370 to 2515°C.

5. The method according to claim 1 or 2, wherein the temperature gradient is 0.01 to 0.40°C / mm.

6. The method according to claim 1 or 2, wherein the heat treatment is performed by providing a temperature gradient such that the side of the container closer to the seed crystal is at a lower temperature than the side of the container closer to the SiC mixed powder layer.

7. The method of claim 1 or 2, wherein the number of containers is 2 to 80.

8. The method of claim 2, wherein said rare earth element comprises at least one selected from the group consisting of Gd, Sm, La, Nd, Y, and Ce.

9. The method according to claim 1 or 2, wherein a dense body having a relative density of 90% or more is disposed on the bottom surface and / or top surface of the SiC mixed powder layer (excluding the surface in contact with the seed crystal).

10. The method according to claim 1 or 2, wherein a dense body having a relative density of 90% or more is disposed on the outer periphery of the SiC mixed powder layer.

11. The method according to claim 1 or 2, wherein a dense body having a relative density of 90% or more is disposed on the bottom surface and / or the top surface of the SiC mixed powder layer (excluding the surface in contact with the seed crystal), and a dense body having a relative density of 90% or more is disposed on the outer periphery of the SiC mixed powder layer.

12. The method according to claim 1 or 2, wherein the firing furnace is provided with an upper heater in an upper part of the firing furnace and a lower heater in a lower part of the firing furnace, and during the heat treatment, the upper heater and the lower heater are set to different temperatures so as to produce the temperature gradient and the average temperature in the furnace.