10 is processed into a cylindrical shape and then is subjected to the laser processing, there is a high possibility that defects will occur.

In contrast, in the SiC ingot 10 of the present embodiment, in the XZ cut surface (a cut surface that passes through the center and is in the <11-20> direction), an angle θ1 between the inner boundary 6 between the facet 4 and the step-flow growth region 5 and the crystal growth direction 8 is 56° or less. For this reason, the positional deviation between the plane coordinates of the facet 4 at the first end 1 and the plane coordinates of the facet 4 at the second end 2 is sufficiently small. Therefore, in a case in which the SiC ingot 10 is processed into a cylindrical shape and is subjected to the laser processing, processing stability is improved. The angle θ1 between the inner boundary 6 and the crystal growth direction 8 is preferably 50° or less, more preferably 45° or less, even more preferably 40° or less, still even more preferably 35° or less, and further more preferably 30° or less. The smaller the angle θ1 between the inner boundary 6 and the crystal growth direction 8, the better the processing stability becomes in a case in which the SiC ingot processed into a cylindrical shape is subjected to the laser processing, which is preferable. In addition, the SiC ingot 10 in which the angle θ1 between the inner boundary 6 and the crystal growth direction 8 is 10° or more can be easily manufactured, and is therefore preferable.

In the inner boundary 6 extending from the first end 1 toward the second end 2, an angle inclined in the [−1-120] direction with respect to a thickness direction from the first end 1 toward the second end 2 is preferably more than 0° and 56° or less. In other words, it is preferable that the inner boundary 6 be inclined in the −X direction with respect to the Z direction (the crystal growth direction indicated by reference sign 8 in FIG. 1). This is because it can be estimated from the plane coordinates of the facet 4 at the second end 2 that the facet 4 is not present at a region in the SiC ingot 10 on an inner side from the plane coordinates of the facet 4 at the second end 2. Therefore, in a case in which the SiC ingot 10 is processed into a cylindrical shape and is subjected to the laser processing, processing stability is further improved. The angle of inclination of the inner boundary 6 in the [−1-120] direction with respect to the thickness direction from the first end 1 toward the second end 2 is preferably 50° or less, more preferably 45° or less, even more preferably 40° or less, still even more preferably 35° or less, and further more preferably 30° or less.

In the SiC ingot 10 of the present embodiment, the angle θ1 between the inner boundary 6 and the crystal growth direction 8 is constant (in other words, the inner boundary 6 in the XZ cut surface is a straight line). The angle θ1 between the inner boundary 6 and the crystal growth direction 8 in the SiC ingot 10 may vary depending on the position in the Z direction. In this case, the average value of the angles θ1 between the inner boundary 6 and the crystal growth direction 8 is treated as the angle θ1 between the inner boundary 6 and the crystal growth direction 8. The angle θ1 between the inner boundary 6 and the crystal growth direction 8 is the average value of the angles θ1 between the inner boundary 6 and the crystal growth direction 8 measured at five different positions in the Z direction.

In the SiC ingot 10 of the present embodiment, as shown in FIG. 1, a distance between the inner boundary 6 and the outer boundary 7 in the XZ cut surface preferably increases as the inner boundary 6 and the outer boundary 7 are close to the second end 2 from the first end 1. In other words, it is preferable that the area of the facet 4 at the second end 2 be larger than the area of the facet 4 at the first end 1. This is because the occurrence of crystals of heterogeneous polymorphs can be suppressed, and the SiC single crystal can be grown more stably. In addition, this is because it can be estimated from the plane coordinates of the facet 4 at the second end 2 that the facet 4 is not present at a region in the SiC ingot 10 which is wider than the plane coordinates of the facet 4 at the second end 2.

Method for Manufacturing SiC Ingot

Next, a method for manufacturing the SiC ingot 10 according to the present embodiment will be described with reference to an example. FIG. 3 is a cross-sectional view showing an example of a manufacturing apparatus used when manufacturing the SiC ingot 10 according to the present embodiment. The apparatus for manufacturing the SiC ingot 10 shown in FIG. 3 includes a crucible 20, a heat insulating material 30, a liner quartz tube 40, a quartz tube 50, and a reflectance measuring instrument 60.

The crucible 20 is made of, for example, graphite. The crucible 20 includes an accommodation portion 21 and a lid 22. A gas discharge path 23 is formed between the accommodation portion 21 and the lid 22. The gas discharge path 23 is provided at least at one location on the outer side surface of the crucible 20 and may be provided at a plurality of locations. The gas discharge path 23 may be provided in a ring shape around the outer side surface of the crucible 20 between the accommodation portion 21 and the lid 22. The accommodation portion 21 is supported by and fixed to a support 24. The lid 22 is suspended by a suspension member 25 and can be moved up and down. A distance between the accommodation portion 21 and the lid 22 can be changed by moving the suspension member 25 up and down. That is, the width of the gas discharge path 23 in the Z direction can be freely designed.

A seed crystal S and a SiC raw material M are disposed in the film deposition space A in the crucible 20. Gas sublimated from the SiC raw material M is recrystallized on the surface of the seed crystal S, and thus the SiC single crystal that will become the crystal growth portion of the SiC ingot 10 is grown. A residual gas in the film deposition space A is discharged to the outside of the crucible 20 through the gas discharge path 23.

The atmospheric pressure in the film deposition space A during the crystal growth is set to be more than 0.3 Torr and less than 10 Torr. If the pressure in the film deposition space A is too low, a dopant element such as nitrogen cannot be sufficiently supplied into the crystal, and the resistivity of the SiC ingot 10 becomes high. The resistivity of the SiC ingot 10 is a parameter that affects the laser processing. In addition, if the pressure in the film deposition space A is too high, a sufficient amount of a sublimation gas is not generated from the SiC source material M; and as a result, productivity decreases.

The bulk density of the graphite forming the side surface of the crucible 20 is set to be more than 1.75 g/cm³and less than 2.00 g/cm³. A part of the residual gas in the film deposition space A permeates through the crucible 20 and escapes to the outside. If the bulk density of the graphite forming the crucible 20 is low, a large amount of the residual gas will be discharged from portions other than the gas discharge path 23. The residual gas discharged from portions other than the gas discharge path 23 deteriorates the heat insulating material 30. On the other hand, if the bulk density of the graphite forming the crucible 20 is too high, the amount of thermal conductivity of the graphite becomes too large, and thus it is not possible to achieve an appropriate temperature distribution inside the crucible 20.

The volume G of the graphite forming the crucible 20 is set to be 1.5 to 4.0 times the volume F based on the diameter of the seed crystal S. The volume F corresponds to the inner volume of the crucible 20 and can be calculated by π×d³/2, where d is the diameter of the seed crystal S. If the volume G of the graphite forming the crucible 20 is small, the amount of the residual gas that permeates the crucible 20 increases, and this causes the heat insulating material 30 to deteriorate. If the volume G of the graphite is too large, the wall thickness of the crucible 20 becomes too large, and thus it is not possible to achieve an appropriate temperature distribution inside the crucible 20.

The heat insulating material 30 has an approximately cylindrical shape and is disposed to cover the periphery of the crucible 20. The volume of the heat insulating material 30 is more than one time and less than three times the volume of the crucible 20. The volume of the heat insulating material 30 is the volume of the heat insulating material 30 itself and is the volume of the area surrounded by the outer surface and the inner surface of the heat insulating material 30. The volume of the crucible 20 is the volume of the inside surrounded by the outer surface of the crucible 20. By setting the volume of the heat insulating material 30 within the above range, it is possible to achieve an appropriate temperature distribution inside the crucible 20. The temperature distribution inside the crucible 20 affects the formation of the facet 4.

The outer diameter of the heat insulating material 30 is set to be 1.2 times or more and 1.5 times or less the outer diameter of the crucible 20. The heat insulating material 30 located on the side surface of the crucible 20 is in direct contact with the crucible 20 which generates heat due to induction heating, and thus heat insulating performance is easily deteriorated. By setting the outer shape of the heat insulating material 30 within the above range, it is possible to achieve an appropriate temperature distribution inside the crucible 20 while preventing deterioration of the heat insulating material 30.

The liner quartz tube 40 is disposed around the heat insulating material 30. At least a part of the liner quartz tube 40 faces the end portion of the gas discharge path 23. The residual gas discharged from the gas discharge path 23 is blown onto the liner quartz tube 40, is adhered to the inner wall of the liner quartz tube 40, and is solidified. The reflectance of the liner quartz tube 40 increases due to the adhesion of the solidified residual gas. The liner quartz tube 40 is supported by a support 41. As the support 41 moves up and down, the liner quartz tube 40 also moves up and down. During the crystal growth, the liner quartz tube 40 is moved downward at a constant speed.

The quartz tube 50 surrounds the crucible 20, the heat insulating material 30, and the liner quartz tube 40. The quartz tube 50 is covered with an upper lid 51 and a lower lid 52. The quartz tube 50 makes it easier to control the atmosphere in the film deposition space A.

The reflectance measuring instrument 60 measures the reflectance of the portion of the liner quartz tube 40 to which the residual gas discharged from the gas discharge path 23 is applied. The reflectance of this portion increases as the amount of the gas discharged from the gas discharge path 23 increases. In the apparatus for manufacturing the SiC ingot 10 shown in FIG. 3, the amount of the gas discharged from the gas discharge path 23 is evaluated on the basis of the change in the reflectance of the liner quartz tube 40.

The liner quartz tube 40 is moved downward at a constant speed by the support 41 during the crystal growth. For this reason, the position in the liner quartz tube 40 to which the residual gas is applied is constantly changing. If the amount of the gas discharged from the gas discharge path 23 is constant, the reflectance of the portion of the liner quartz tube 40 of which the reflectance is measured by the reflectance measuring instrument 60 is constant.

In order to manufacture the SiC ingot 10 of which the angle θ1 between the inner boundary 6 between the facet 4 and the step-flow growth region 5 and the crystal growth direction 8 is 56° or less, it is necessary to keep the flow of the sublimation gas in the film deposition space A approximately constant. When the amount of the gas discharged from the gas discharge path 23 changes, the flow of the sublimation gas in the film deposition space A changes.

In the apparatus for manufacturing the SiC ingot 10 shown in FIG. 3, in a case in which the reflectance of the liner quartz tube 40 which is measured by the reflectance measuring instrument 60 changes during the crystal growth, the width of the gas discharge path 23 can be changed by moving the suspension member 25 up and down. As a result, the amount of the gas discharged from the gas discharge path 23 is kept approximately constant.

For example, in a case in which the reflectance of the liner quartz tube 40 which is measured by the reflectance measuring instrument 60 decreases during the crystal growth, the amount of the gas discharged from the gas discharge path 23 is reduced, and thus the width of the gas discharge path 23 is to be increased. For example, in a case in which the reflectance of the liner quartz tube 40 which is measured by the reflectance measuring instrument 60 changes to be higher value during the crystal growth, the amount of the gas discharged from the gas discharge path 23 is increased, and thus the width of the gas discharge path 23 is to be reduced.

In the method for manufacturing the SiC ingot 10 of the present embodiment, as described above, the amount of the gas discharged from the gas discharge path 23 can be controlled by changing the width of the gas discharge path 23 in the manufacturing apparatus shown in FIG. 3. As a result, it is possible to control the temperature distribution and the flow of the sublimation gas within the film deposition space A, and it is possible to manufacture the SiC ingot 10 according to the present embodiment of which the angle θ1 between the inner boundary 6 between the facet 4 and the step-flow growth region 5 and the crystal growth direction 8 is 56° or less.

Another Example

The SiC ingot 10 according to the present embodiment may be manufactured using a manufacturing method, which will be described below. FIG. 4 is a cross-sectional view showing another example of the manufacturing apparatus used when manufacturing the SiC ingot according to the present embodiment. The apparatus for manufacturing the SiC ingot 10 shown in FIG. 4 includes a crucible 20, a heat insulating material 30, a quartz tube 50, a weight measuring instrument 70, and an evaluation substrate 71.

The apparatus for manufacturing the SiC ingot 10 shown in FIG. 4 is provided with the evaluation substrate 71 instead of the liner quartz tube 40 in the apparatus for manufacturing the SiC ingot 10 shown in FIG. 3, and the weight measuring instrument 70 instead of the reflectance measuring instrument 60 in the apparatus for manufacturing the SiC ingot 10 shown in FIG. 3. The configurations of the crucible 20, the heat insulating material 30, and the quartz tube 50 in the apparatus for manufacturing the SiC ingot 10 shown in FIG. 4 are the same as those in the apparatus for manufacturing the SiC ingot 10 shown in FIG. 3.

In the apparatus for manufacturing the SiC ingot 10 shown in FIG. 4, the residual gas discharged from the gas discharge path 23 is blown onto the evaluation substrate 71. The residual gas blown onto the evaluation substrate 71 is adhered to the surface of the evaluation substrate 71 and is solidified. The weight of the evaluation substrate 71 increases due to the solidified residual gas.

The weight measuring instrument 70 measures the weight of the evaluation substrate 71. If the amount of the gas discharged from the gas discharge path 23 is constant, the acceleration of the weight increase of the evaluation substrate 71 is constant. In contrast, when the amount of the gas discharged from the gas discharge path 23 increases, the rate of the weight increase of the evaluation substrate 71 increases. In addition, when the amount of the gas discharged from the gas discharge path 23 decreases, the rate of the weight increase of the evaluation substrate 71 decreases.

In the apparatus for manufacturing the SiC ingot 10 shown in FIG. 4, the amount of the gas discharged from the gas discharge path 23 is evaluated on the basis of the change in the rate of the weight increase of the evaluation substrate 71.

In the method of manufacturing the SiC ingot 10 using the manufacturing apparatus shown in FIG. 4, as in the case of using the manufacturing apparatus shown in FIG. 3, the amount of the gas discharged from the gas discharge path 23 can be controlled by changing the width of the gas discharge path 23. As a result, it is possible to control the temperature distribution and the flow of the sublimation gas within the film deposition space A, and it is possible to manufacture the SiC ingot 10 according to the present embodiment of which the angle θ1 between the inner boundary 6 between the facet 4 and the step-flow growth region 5 and the crystal growth direction 8 is 56° or less.

In the above-described manufacturing method, as an example of a method for evaluating the amount of the gas discharged from the gas discharge path 23, the case in which a change in the reflectance of the liner quartz tube 40 or a change in the weight of the evaluation substrate 71 is used is described, but the physical quantity for evaluating the amount of the gas discharged from the gas discharge path 23 is not limited to the reflectance or the weight.

In the SiC ingot 10 of the present embodiment shown in FIG. 1, the shape of the facet 4 is controlled such that the positional deviation between the plane coordinates of the facet 4 at the first end 1 and the plane coordinates of the facet 4 at the second end 2 is sufficiently small. The SiC ingot 10 of the present embodiment can be processed by a known method to be a SiC ingot that is a cylindrical SiC single crystal.

In the SiC ingot processed into a cylindrical shape, as in the SiC ingot 10 of the present embodiment, in the XZ cut surface (a cut surface that passes through the center and is in the <11-20> direction), the angle θ1 between the inner boundary 6 between the facet 4 and the step-flow growth region 5 and the crystal growth direction 8 is 56° or less. For this reason, in the SiC ingot obtained by processing the SiC ingot 10 of the present embodiment into a cylindrical shape, the positional deviation between the plane coordinates of the facet 4 at the first end 1 and the plane coordinates of the facet 4 at the second end 2 is sufficiently small, and thus it is possible to reduce the number of times that the laser output is changed when cutting out the SiC substrate, and it is possible to easily and efficiently cut out the SiC substrate. The SiC ingot may have an orientation flat or a notch for identifying the direction of a crystal axis.

Method for Manufacturing SiC Substrate

A method for manufacturing a SiC substrate of a first embodiment includes a step of manufacturing the SiC ingot 10 of the embodiment described above by any of the methods described above, a step of processing the SiC ingot 10 into a cylindrical shape, and a step of slicing the SiC ingot that has been processed into a cylindrical shape.

A known method can be used as the step for processing the SiC ingot 10 into a cylindrical shape. In addition, as the step of slicing the SiC ingot, for example, a method in which the SiC ingot is processed with a laser to create cracks and cut out the SiC substrates can be used.

In the present embodiment, in each of a plurality of SiC substrates cut out from the SiC ingot, as in the SiC ingot 10 of the present embodiment, in the XZ cut surface (a cut surface that passes through the center and is in the <11-20> direction), the angle θ1 between the inner boundary 6 between the facet 4 and the step-flow growth region 5 and the crystal growth direction 8 is 56° or less. In addition, in a case in which the angle θ1 between the inner boundary 6 and the Z direction (the crystal growth direction) of all of the plurality of SiC substrates cut out from the same SiC ingot is 56° or less, the SiC ingot before cutting out can be said to correspond to the SiC ingot of the present embodiment.

A method for manufacturing a SiC substrate of a second embodiment includes a step of preparing the SiC ingot 10 of the embodiment described above, and a step of slicing the SiC ingot 10.

The step of preparing the SiC ingot