JP2015214489A - Methods for manufacturing silicon carbide substrate and silicon carbide ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide silicon carbide substrates and silicon carbide ingots excellent in the uniformity of properties and also to provide manufacturing methods therefor.SOLUTION: The silicon carbide ingot manufacturing method comprising: a preparation step (S10) for preparing a base substrate of which an off angle in an off direction in one of the <11-20> and <1-100> directions relative to the (0001) face is 0.1° or more and 10° or less, and which is formed of a single crystal silicon carbide; and a deposition step (S20) for growing a silicon carbide layer on a surface of the base substrate. The deposition step (S20) forms a region having a (0001) facet surface 5 on a surface of a grown silicon carbide layer at an end of the upstream side where an acute intersection angle is formed provided that the <0001> direction angle of the base substrate in the off angle intersects a surface of the base substrate.

Description

  The present invention relates to a silicon carbide substrate, a silicon carbide ingot, and a method for manufacturing the same, and more particularly to a silicon carbide substrate, a silicon carbide ingot, and a method for manufacturing the same, in which variations in characteristics such as impurity concentration are small.

  Conventionally, silicon carbide (SiC) has been studied as a next-generation semiconductor material that replaces silicon (Si). In order to manufacture the substrate made of silicon carbide, a method of manufacturing a substrate by growing a silicon carbide single crystal on a seed substrate to form a silicon carbide ingot and slicing the silicon carbide ingot is known. In this case, a seed crystal is prepared using a (0001) plane (so-called c plane) or a crystal plane with an off angle of 10 ° or less from the c plane as a growth plane, and a silicon carbide single crystal is formed on the growth plane of the seed crystal. A growth method is used (for example, see Japanese Patent Application Laid-Open No. 2004-323348 (hereinafter referred to as Patent Document 1)). When a silicon carbide single crystal is grown on such a seed crystal growth surface, a (0001) facet plane is formed near the center of the surface of the grown silicon carbide single crystal.

  In Patent Document 1, in order to prevent the formation of heterogeneous polymorphic crystals and different orientation crystals and to prevent the occurrence of screw dislocations, a dislocation control seed crystal having a region capable of generating screw dislocations is prepared, and the dislocation control seed crystal is formed on the dislocation control seed crystal. A silicon carbide single crystal is grown. Further, in Patent Document 1, a c-plane facet is formed on the surface of the silicon carbide single crystal in the growth process of the silicon carbide single crystal, and the (0001) facet surface and the region capable of generating the screw dislocation partially overlap. In addition, a silicon carbide single crystal is grown. In Patent Document 1, it is said that the growth of a silicon carbide single crystal as described above can suppress the formation of different polymorphic crystals and different orientation crystals in the silicon carbide single crystal and the occurrence of screw dislocations. Further, in Patent Document 1, a (0001) facet is formed so as to overlap with a region capable of generating a screw dislocation by a method of controlling a concentration distribution of a reaction gas in a growth process of a silicon carbide single crystal or a temperature distribution of a seed crystal. It has been suggested to adjust the position of the surface.

JP 2004-323348 A

  Here, the (0001) facet plane on the surface of the above-described silicon carbide single crystal is relatively easy to incorporate nitrogen (N) from other portions of the surface during crystal growth. Therefore, during the growth of the above-described silicon carbide single crystal, a high concentration nitrogen region in which the nitrogen concentration is higher than other regions is formed in a portion below the surface where the (0001) facet surface is formed. Since the nitrogen concentration in silicon carbide affects the properties of the silicon carbide single crystal such as conductivity and light transmission, it is desirable that the nitrogen concentration be as uniform as possible in the ingot and the substrate formed from the ingot. However, in a silicon carbide ingot formed by a conventional method, the arrangement and size of the (0001) facet surface have not been particularly adjusted in order to obtain an ingot and a substrate having a uniform nitrogen concentration. Therefore, in the obtained silicon carbide ingot, although the (0001) facet surface may be disposed at a position near the end of the ingot, a high-concentration nitrogen region having a certain size is formed inside the ingot. . For this reason, a high concentration nitrogen region is arranged inside a region having a uniform nitrogen concentration (that is, a region other than the high concentration nitrogen region) in the substrate cut out from the ingot. That is, conventionally, it has been difficult to form a region having a uniform nitrogen concentration as a region including a central portion of the silicon carbide substrate.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a silicon carbide substrate, a silicon carbide ingot, and a method for manufacturing the same, which are excellent in uniformity of characteristics. is there.

  The inventor completed the present invention as a result of diligent research on crystal growth of silicon carbide. That is, the inventor, as the base substrate (seed substrate), has an off angle in a predetermined direction (off angle direction) with respect to the (0001) plane of 0.1 ° to 10 °, more preferably 1 ° to 10 °. When using a silicon carbide substrate that is less than or equal to ° C. and growing a silicon carbide single crystal on the surface of the base substrate, by adjusting the off-angle direction and off-angle of the base substrate, and further the process conditions of the crystal growth step, The (0001) facet surface formed on the growth surface of the growing silicon carbide single crystal is formed at the end of the growth surface, and the (0001) facet surface can be formed sufficiently smaller than the planar size of the base substrate. I found it. In this way, in the formed silicon carbide single crystal, the proportion of the portion (high concentration nitrogen region) located below the (0001) facet plane can be reduced, and as a result, the region having a relatively low nitrogen concentration can be increased. They can be formed together. Based on such knowledge, the method for manufacturing a silicon carbide ingot according to the present invention provides an off-angle direction off-direction that is either <11-20> direction or <1-100> direction with respect to the (0001) plane. A step of preparing a base substrate made of single-crystal silicon carbide having an angle of 0.1 ° to 10 °, more preferably 1 ° to 10 °, and a step of growing a silicon carbide layer on the surface of the base substrate With. In the step of growing the silicon carbide layer, in the off-angle direction, when considering the crossing angle at which the <0001> direction axis of the base substrate crosses the surface of the base substrate, the upstream side on which the crossing angle becomes an acute angle A region having a (0001) facet surface is formed on the surface of the grown silicon carbide layer.

  In this way, by forming the (0001) facet surface in which nitrogen is easily taken in at the end of the ingot, a region having a relatively high nitrogen concentration (a high concentration nitrogen region located below the (0001) facet surface). Can be disposed at the end of the silicon carbide ingot. Therefore, a region having a relatively low nitrogen concentration (a region other than the high concentration nitrogen region) can be formed as a collective region including the central portion of the silicon carbide ingot. For this reason, when a silicon carbide substrate is cut out from the ingot, a silicon carbide substrate in which a region having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate can be easily obtained. As described above, since a region having a relatively low nitrogen concentration (a region in which nitrogen is not taken up so much and where the nitrogen concentration is stable) can be formed in a wide region including the central portion of the substrate, a semiconductor element is formed on the substrate surface. A semiconductor element can be formed efficiently.

  Here, when a silicon carbide substrate is cut out from a silicon carbide ingot in which a high-concentration nitrogen region having a certain size is formed, for example, at the center portion, the nitrogen concentration around the high-concentration nitrogen region on the surface of the silicon carbide substrate The low region (low concentration nitrogen region) is surrounded. Therefore, when a device is formed on the surface of a silicon carbide substrate, if the device is formed in a region where the nitrogen concentration is relatively low, the device is formed avoiding the high concentration nitrogen region (that is, high concentration). Since the device is formed avoiding the nitrogen region and the boundary region between the high-concentration nitrogen region and the low-nitrogen concentration region, there is a problem that the utilization efficiency of the substrate is lowered. However, according to the present invention, since the high concentration nitrogen region is arranged at the end of the silicon carbide substrate, the low concentration nitrogen region is formed at the center of the surface of the silicon carbide substrate. And since a device can be concentrated and formed in the said low concentration nitrogen area | region, the utilization of a board | substrate can be aimed at.

  A silicon carbide ingot according to the present invention is manufactured using the above-described method for manufacturing a silicon carbide ingot. In this case, a region having a relatively low nitrogen concentration (a region other than the high concentration nitrogen region) can be formed as a collective region including the central portion of the silicon carbide ingot. Therefore, by cutting a silicon carbide substrate from the silicon carbide ingot, it is possible to easily obtain a silicon carbide substrate in which a region having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate.

  A method for manufacturing a silicon carbide substrate according to the present invention includes a step of preparing a silicon carbide ingot using the method for manufacturing a silicon carbide ingot and a step of slicing the silicon carbide ingot.

  In this case, in the silicon carbide ingot, a region having a relatively low nitrogen concentration (a region other than the high concentration nitrogen region) can be formed as a collective region including the central portion of the silicon carbide ingot. Therefore, in the slicing step, by cutting out the silicon carbide substrate from the silicon carbide ingot, it is possible to easily obtain a silicon carbide substrate in which a region having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate. it can.

  A silicon carbide substrate according to the present invention is manufactured using the method for manufacturing a silicon carbide substrate. In this way, it is possible to easily realize a silicon carbide substrate in which a region having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate.

  In the method for manufacturing a silicon carbide ingot according to the present invention, the off angle in the off angle direction which is either the <11-20> direction or the <1-100> direction with respect to the (0001) plane is 0.1 ° or more. A step of preparing a base substrate made of single-crystal silicon carbide, and a step of growing a silicon carbide layer on the surface of the base substrate. In the off-angle direction, when considering the crossing angle in which the <0001> direction axis of the base substrate intersects the surface of the base substrate in the off-angle direction, the upstream end that is the side on which the crossing angle becomes an acute angle In FIG. 2, a region having a (0001) facet surface is formed on the surface of the grown silicon carbide layer. In the silicon carbide layer after the step of growing the silicon carbide layer, the portion located under the region having the (0001) facet surface is a portion other than the portion located under the region having the (0001) facet surface in the silicon carbide layer. The transmittance per unit thickness of light having a wavelength of 450 nm to 500 nm is lower.

  In this way, by forming the (0001) facet surface that is easy to capture nitrogen at the end of the ingot, the light transmittance is increased due to the nitrogen captured from the facet surface during the growth of the silicon carbide layer. Since the lowered region is disposed at the end portion of the ingot (the portion below the (0001) facet surface), the other portions including the center portion of the silicon carbide ingot are regions having a relatively high light transmittance. be able to. For this reason, when a silicon carbide substrate is cut out from the ingot, a silicon carbide substrate in which a region having a relatively high light transmittance is formed in a wide region including the central portion of the substrate can be easily obtained. As described above, since a region having a relatively high light transmittance (a region in which nitrogen is not taken in so much and the nitrogen concentration and transmittance are stable) can be formed in a wide region including the central portion of the substrate, a semiconductor element is formed on the substrate surface. When forming the semiconductor element, the semiconductor element can be formed efficiently.

  In the silicon carbide ingot according to the present invention, the off angle in the off angle direction which is either the <11-20> direction or the <1-100> direction with respect to the (0001) plane is 0.1 ° or more and 10 ° or less. A base substrate made of single crystal silicon carbide and a silicon carbide layer formed on the surface of the base substrate. A silicon carbide layer grown at the upstream end, which is the side where the crossing angle becomes an acute angle when the crossing angle at which the <0001> direction axis of the base substrate crosses the surface of the base substrate is considered in the off-angle direction A region having a (0001) facet surface is formed on the surface.

  In the silicon carbide ingot, the portion of the silicon carbide layer located under the region having the (0001) facet plane has a nitrogen concentration higher than the portion other than the portion located under the region having the (0001) facet plane in the silicon carbide layer. It may be a high-concentration nitrogen region where is high.

  In this way, by forming the (0001) facet surface in which nitrogen is easily taken in at the end of the ingot, a region having a relatively high nitrogen concentration (a high concentration nitrogen region located below the (0001) facet surface). Can be disposed at the end of the silicon carbide ingot. Therefore, a region having a relatively low nitrogen concentration (a region other than the high concentration nitrogen region) can be formed as a collective region including the central portion of the silicon carbide ingot. For this reason, when a silicon carbide substrate is cut out from the ingot, a silicon carbide substrate in which a region having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate can be easily obtained. As described above, since a region having a relatively low nitrogen concentration (a region in which nitrogen is not taken up so much and where the nitrogen concentration is stable) can be formed in a wide region including the central portion of the substrate, a semiconductor element is formed on the substrate surface. A semiconductor element can be formed efficiently.

  A silicon carbide substrate according to the present invention is obtained by slicing the silicon carbide ingot. In this way, it is possible to easily obtain a silicon carbide substrate in which a region having a relatively low nitrogen concentration (or a region having a high light transmittance) is formed in a wide region including the central portion of the substrate.

  The silicon carbide substrate according to the present invention is obtained by slicing the silicon carbide ingot after removing the high concentration nitrogen region from the silicon carbide ingot. In this case, the high concentration nitrogen region (region with low light transmittance) is removed in advance, so that the region with lower nitrogen concentration than the high concentration nitrogen region (region with higher light transmittance than the high concentration nitrogen region). A silicon carbide substrate is formed using the silicon carbide ingot that has become only. For this reason, a silicon carbide substrate in which fluctuations in nitrogen concentration and light transmittance are reduced can be obtained.

  The silicon carbide substrate according to the present invention has a high nitrogen concentration at one end in either the <11-20> direction or the <1-100> direction, which is relatively higher than the other portions. A concentration nitrogen region is formed. The high concentration nitrogen region has a <0001> direction axis of the silicon carbide substrate with respect to the surface of the silicon carbide substrate in either the <11-20> direction or the <1-100> direction (off-angle direction). When the crossing angle is considered, the crossing angle may be formed at the upstream end, which is the side where the crossing angle becomes an acute angle. In this way, when growing a silicon carbide ingot for forming a silicon carbide substrate, the high-concentration nitrogen region is easily arranged at the end of the silicon carbide substrate by controlling the arrangement of the (0001) facet plane. Can be made.

  According to the present invention, it is possible to obtain a silicon carbide ingot and a silicon carbide substrate having excellent uniformity in characteristics such as nitrogen concentration.

It is a flowchart for demonstrating the manufacturing method of the silicon carbide ingot according to this invention. It is a flowchart for demonstrating the manufacturing method of the silicon carbide substrate according to this invention. It is a schematic diagram for demonstrating an example of the film-forming process shown in FIG. It is a plane schematic diagram of the silicon carbide ingot according to the present invention. It is a cross-sectional schematic diagram in the line segment VV shown in FIG. FIG. 6 is a schematic plan view showing a silicon carbide substrate cut out from the silicon carbide ingot shown in FIGS. 4 and 5. It is a cross-sectional schematic diagram of the crystal growth apparatus for implementing the film-forming process shown in FIG. It is a schematic plan view showing another example of a silicon carbide substrate according to the present invention. FIG. 6 is a schematic plan view showing a first modification of the silicon carbide ingot according to the present invention. FIG. 10 is a schematic plan view showing a silicon carbide substrate cut out from the silicon carbide ingot shown in FIG. 9. FIG. 11 is a schematic plan view showing a modification of the silicon carbide substrate shown in FIG. 10. It is a plane schematic diagram which shows the 2nd modification of the silicon carbide ingot according to this invention. FIG. 13 is a schematic plan view showing a silicon carbide substrate cut out from the silicon carbide ingot shown in FIG. 12. FIG. 14 is a schematic plan view showing a modification of the silicon carbide substrate shown in FIG. 13. FIG. 12 is a schematic plan view showing a third modification of the silicon carbide ingot according to the present invention. FIG. 16 is a schematic plan view showing a silicon carbide substrate cut out from the silicon carbide ingot shown in FIG. 15. FIG. 17 is a schematic plan view showing a modification of the silicon carbide substrate shown in FIG. 16.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  A method for manufacturing a silicon carbide ingot and a silicon carbide substrate according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, in the method for manufacturing a silicon carbide ingot (hereinafter also referred to as an ingot) according to the present invention, a preparation step (S10) is first performed. Specifically, a support member 2 as shown in FIG. 3 is arranged in a processing vessel of a crystal growth apparatus for forming an ingot, and a base which is a seed substrate for forming the ingot on the support member 2 The substrate 1 is mounted. The planar shape of the base substrate 1 is circular. Here, the main surface of base substrate 1 is a silicon carbide (SiC) substrate having an off angle with respect to the (0001) plane of 0.1 ° to 10 °, more preferably 0.5 ° to 8 °. is there. In the present specification, individual plane orientations are represented by (hkil), and generic plane orientations including (hkil) and plane orientations equivalent to crystal geometry are represented by {hkil}. Further, an individual direction is represented by [hkil], and a direction including [hkil] and a crystal geometrically equivalent direction is represented by <hkil>. As for the negative index, in crystal geometry, it is common to express “−” (bar) on the number representing the index, but in this specification, before the number representing the index. Represented with a negative sign (-).

  Next, a film forming step (S20) is performed. Specifically, after setting the pressure and atmosphere inside the processing vessel of the crystal growth apparatus to predetermined conditions, silicon carbide is used on the surface 4 of the base substrate 1 by using a sublimation reprecipitation method or the like while the base substrate 1 is heated. A single crystal is grown. Thus, silicon carbide ingot 10 as shown in FIGS. 3 to 5 is formed. In the film forming step (S20), a (0001) facet surface 5 (hereinafter also referred to as a facet surface 5) is formed on the surface of the ingot 10. The process conditions of the film forming step (S20) are set so that the facet surface 5 is arranged at one outer peripheral end when viewed from the upper surface of the ingot 10 as shown in FIG. The process conditions will be described later.

  Further, the region connected under the facet surface 5 has a nitrogen concentration relative to that of the other regions because the nitrogen intake amount from the facet surface 5 is larger than the nitrogen intake amount in the other regions. The high-concentration nitrogen region 6 becomes higher. That is, when silicon carbide constituting ingot 10 is grown, relatively more nitrogen is taken into silicon carbide from facet surface 5 on the surface of the grown silicon carbide than in other regions, and therefore in high concentration nitrogen region 6. The nitrogen concentration is relatively higher than the nitrogen concentration in the low concentration nitrogen region 7 which is another region.

  The facet surface 5 is located at the end in the off-angle direction indicated by the arrow 26. As described above, an arbitrary method can be used as a method (process condition) for arranging the facet surface 5 at the end of the ingot 10. For example, as shown in FIG. 7, in a crystal growth apparatus including a crucible 11 and a heating coil 12, the growth top surface of an ingot 10 that grows on the surface of the base substrate 1 (the base substrate 1 in the ingot 10 in FIG. The surface on the opposite side to the position on the side or the surface of the ingot 10 facing the supply direction of the source gas indicated by the arrow 13 in FIG. 7 is always flat (the surface of the base substrate 1 and the growth top surface of the ingot 10 are The ingot 10 is grown so that it becomes parallel. In addition, for the base substrate 1 that is a seed substrate, the main surface (the surface on which the crystal that becomes the ingot 10 grows) is in the <11-20> direction or the <1-100> direction with respect to the (0001) plane. It is preferable that the angle is 1 ° or more and 10 ° or less. The inclination angle of the main surface may be not less than 0.1 ° and not more than 10 °. By using such a base substrate 1, a (0001) facet surface 5 is generated only slightly at the end of the ingot 10 as shown in FIG. In the crystal growth apparatus shown in FIG. 7, the support member 2 shown in FIG. 3 is not described, and the base substrate 1 is arranged directly on the inner wall of the crucible 11, but as shown in FIG. Alternatively, the support member 2 may be disposed on the base substrate 1, and the base substrate 1 may be fixed on the inner wall of the crucible 11 via the support member 2.

  Here, the (0001) facet plane 5 is to make the growth top surface of the ingot 10 as flat as possible (for example, formed so that the growth top surface extends in a direction perpendicular to the crystal growth direction). Is at the end of the ingot 10 and is minimized. Thus, in order to make the growth outermost surface flat, the temperatures of the central portion 14, the end portion 15 and the outermost peripheral portion 16 on the growth outermost surface of the ingot 10 shown in FIG. 7 are important. Here, the end portion 15 is in the end portion region of the ingot 10 and is at a position that is a distance within 10% of the diameter of the ingot 10 from the inner wall of the crucible 11. Assuming that the temperature of the central portion 14 is Ta, the temperature of the end portion 15 is Tb, and the temperature of the outermost peripheral portion 16 is Tc, the relationship satisfies the relational expression Tc> Tb ≧ Ta, and the temperature Tb and the temperature Ta The temperature gradient ((absolute value of difference between temperature Ta and temperature Tb) / (distance between center portion 14 and end portion 15)) preferably satisfies the relationship of 10 ° C./cm or less.

  In order to realize such a temperature condition, it is necessary to reduce the temperature distribution on the back surface side of the base substrate 1 (that is, the upper surface side of the crucible 11 in FIG. 7) (to reduce the temperature variation). Specifically, it is preferable to adopt a configuration in which, for example, the diameter of the heat radiating hole formed on the upper surface side of the crucible 11 is made larger than the diameter of the ingot 10. Thereby, the curvature radius between the center part 14 and the edge part 15 in the surface of the ingot 10 can be made into 3 times or more of the radius of the ingot 11. FIG. Here, the radius of curvature is calculated as follows, for example. First, the height of the ingot 10 (the distance from the surface of the base substrate 1 to the surface of the ingot 10) is measured at a pitch of 5 mm between the central portion 14 and the end portion 15. Then, the radius of the arc corresponding to the surface of the ingot 10 between the pitches is calculated from the difference in height between the pitches. And let the minimum radius among the radius of the circular arc calculated about each pitch between the center part 14 and the edge part 15 be the said curvature radius.

  Further, the flatness of the surface of the ingot 10 may be measured by the following measuring method. That is, the height of the surface of the ingot 10 from the reference plane is measured at a plurality of positions (measurement points) arranged in a cross direction (preferably in a matrix of 5 mm pitch) at a pitch of 5 mm from the center of the surface of the ingot 10. To do. And the difference of the said height is measured between adjacent measurement points. Furthermore, an angle corresponding to the inclination of the surface of the ingot 10 between adjacent measurement points is obtained from a tangent (tan) that can be determined from the difference in height and the distance between the measurement points. For the plurality of angles thus obtained, the average of the angles is preferably 10 ° or less. Furthermore, it is preferable that all measured angles are 10 ° or less. However, as a measurement point, an area that is a distance within 10% of the diameter of the ingot 10 from the outermost peripheral portion of the ingot 10 is excluded.

  As for the relationship between the temperature Tc and the temperature Tb, the absolute value of the difference between the temperature Tb and the temperature Tc is 1 ° C. or more and 50 ° C. or less (more specifically, the temperature Tc is higher than the temperature Tb. It is high temperature and the difference between the temperature Tb and the temperature Tc is 1 ° C. or more and 50 ° C. or less). Here, when the absolute value of the difference is less than 1 ° C., it becomes easy for polycrystals of silicon carbide to adhere and grow on the inner peripheral surface of the crucible 11 made of graphite, resulting in hindering the growth of the single crystal ingot. become. Moreover, when the said difference exceeds 50 degreeC, the temperature of the end surface part of the ingot 10 also rises by the influence of the radiant heat etc. from the crucible 11 side. As a result, the temperature difference between the central portion 14 and the end portion 15 increases, and the flatness on the surface of the ingot 10 cannot be maintained.

  By growing under the above conditions, the surface of the ingot 10 becomes flat, and the (0001) facet surface 5 is generated only at the end of the ingot 10. The width of the (0001) facet surface 5 (the width of the base substrate 1 in the off direction) is preferably 10% or less of the diameter of the ingot 10.

  In order to arrange the (0001) facet surface 5 at the end of the ingot 10 as described above, there is always no temperature distribution in the radial direction of the ingot 10 from the start to the end of the ingot 10 growth. It is preferable to make the environment (a state where the temperature difference in the radial direction is small). For this reason, attention should be paid to the temperature management as follows in each of the temperature raising process and the late stage of growth separately from the initial stage of growth.

  For example, when a general high-frequency heating furnace is used to heat the crucible 11, the side surface of the crucible 11 is heated, and thus a temperature distribution is likely to occur in the radial direction of the ingot 10 in the temperature raising step. Therefore, when the time from the normal temperature to the bottom surface temperature of the crucible 11 is 2000 ° C. or more is 1 hour or less, the atmospheric pressure of 40 kPa or more and 100 kPa or less is maintained at the expected growth temperature for 5 minutes or more, and the temperature distribution is maintained. After homogenization, the atmospheric pressure is preferably reduced to the expected growth pressure.

  Further, at the later stage of growth, the ingot 10 grows to a height of 1 cm or more, so that the temperature of the growth outermost surface rises from the initial growth stage. As a result, the temperature gradient between the growth outermost surface of the ingot 10 and the raw material is reduced. For this reason, the temperature environment at the end 15 and the outermost peripheral portion 16 may change from the initial growth state, and in some cases, the magnitude relationship between the temperature Tb at the end 15 and the temperature Tc at the outermost peripheral portion 16 may be reversed. It is done. In such a state, the shape of the ingot 10 becomes concave, and the (0001) facet surface 5 moves from the end of the ingot 10 toward the center.

  Therefore, in the latter stage of growth, the environment in which the condition of temperature Tc> temperature Tb is always satisfied is maintained by raising the side surface temperature of the crucible 11 from the initial stage of growth or increasing the heat radiation amount from the upper side of the crucible 11. There is a need. In addition, since the possibility of cracking increases when the surface shape of the ingot 10 is concave, the surface shape of the ingot 10 is preferably flat and slightly convex. Furthermore, it is preferable that the outermost surface of the raw material for forming the ingot 10 is flattened in advance so that there is no variation in the raw material loading depth.

  In the ingot 10 according to the present invention formed by the method as described above, the size of the (0001) facet surface 5 is small and the flatness of the surface of the ingot 10 is high. For this reason, the dislocation occurrence probability is almost uniform over the entire surface of the ingot 10 and decreases uniformly as the ingot 10 grows. That is, the ingot 10 according to the present invention can reduce dislocations in substantially the entire region.

  In addition, as a method for generating facets only at the end portions in the ingot 10, a method in which the temperature of the portion where the facets are generated is made higher than the temperature of the other portions can be used. That is, the relationship between the temperature Td of the facet side end 17 and the temperature Te of the facet side outermost peripheral part 18 in FIG. 7 is Te> Td, and the temperature difference between the facet side end 17 and the facet side outermost peripheral part 18 ( That is, it is preferable to set Te−Td) to 20 ° C. or more and 100 ° C. or less. Further, when the temperature difference between the central portion 14 and the end portion 15 is large, the facet region is widened. Therefore, the temperature gradient between the central portion 14 and the end portion 15 may be 20 ° C./cm or less. preferable.

  Further, a relatively large temperature difference is formed only between the facet side end portion 17 and the facet side outermost peripheral portion 18, and in other portions of the outer peripheral portion of the ingot 10, the end portion 15 and the outermost peripheral portion 16 The temperature difference between them is preferably 20 ° C. or less. In order to do this, for example, only the portion where the facet surface 5 is formed can be heated. As the heating method, for example, when the method of heating the crucible 11 is an induction heating method, the center line of the crucible 11 is set at a predetermined distance from the center line of the coil 12 used for heating to the side on which the (0001) facet surface 5 is formed. There is a method of shifting by a distance (for example, about 1 mm or more and 5 mm or less). Regardless of the heating method, the thickness of the heat insulating material around the crucible 11 is thicker than others only in the vicinity of the region where the facet surface 5 is formed (for example, about 2 mm or more and 10 cm or less than the thickness of the heat insulating material in other portions). (Thick). Alternatively, it is possible to use a method of closing a hole (heat radiating hole) formed for heat dissipation in a region facing the portion where the facet surface 5 is formed in the upper part of the crucible 11.

  Further, for example, as shown in FIG. 3, the temperature adjusting member 3 is disposed inside the support member 2, and the heating temperature of the region where the facet surface 5 is to be formed (the end portion of the base substrate 1) is set to the temperature of other portions. The position of the facet surface 5 may be arranged at the end of the ingot 10 by a method of changing the temperature (for example, making it higher than the temperature of other portions). As such a temperature adjusting member 3, for example, a heating member such as an electric heater can be used. Further, as a method of arranging facet surface 5 at the end of ingot 10, for example, a source gas for growing silicon carbide on base substrate 1 is intensively supplied to a region where facet surface 5 is to be formed. Or adjusting the arrangement of the discharge part when the raw material gas used for the growth of silicon carbide is discharged from the inside of the processing vessel, and the growth rate of silicon carbide in the region where the facet surface 5 is to be formed is changed to another region. You may use the method of raising more.

  Next, a post-processing step (S30) is performed. Specifically, the formed ingot 10 is taken out from the inside of the processing container, the surface layer is ground, a mark indicating the crystal orientation of the ingot 10 is formed on the ingot 10, and the base substrate 1 is separated from the ingot 10. Necessary post-processing such as.

  Here, regarding the outermost surface 9 (see FIG. 5) of the portion where silicon carbide has grown in the obtained ingot 10, the maximum radius of curvature in the cross section shown in FIG. 5 is the planar shape of the ingot 10 shown in FIG. It is preferable that the radius is 3 times or more of the radius of a circumscribed circle (in the case where the planar shape is a circular ingot 10 as shown in FIG. 4).

  The high-concentration nitrogen region 6 is disposed on the upstream side in the off-angle direction indicated by the arrow 26. Here, the off-angle direction is a direction in which the off-angle in the base substrate 1 is set, and is, for example, either the <11-20> direction or the <1-100> direction. Further, in a state where the <0001> direction axis of the base substrate 1 and the surface 4 of the base substrate 1 intersect, the direction in which the <0001> direction axis is inclined with respect to the normal of the surface 4 is the upstream side. The direction opposite to the upstream side is defined as the downstream side. The nitrogen concentration in the high concentration nitrogen region 6 is 1.1 times or more that of the nitrogen region in the low concentration nitrogen region 7. The nitrogen concentration can be evaluated by SIMS, for example.

  Further, the transmittance of light having a wavelength of 450 nm or more and 500 nm or less per unit thickness in the high concentration nitrogen region 6 is the unit thickness in the low concentration nitrogen region 7 that is a portion other than the high concentration nitrogen region 6 of the ingot 10. The light transmittance is lower than the above. The transmittance of the light can be measured using, for example, FTIR (Fourier transform infrared spectrometer).

  For example, the thickness of the substrate 20 is 400 μm, the light transmittance of the wavelength in the thickness direction of the substrate 20 in the high concentration nitrogen region 6 of the substrate 20, and the thickness of the substrate 20 in the low concentration nitrogen region 7 of the substrate 20. A method of measuring the transmittance of light having the above wavelength in the vertical direction using a visible light spectrometer can be used.

  According to such an ingot 10, since the high concentration nitrogen region 6 having a relatively high nitrogen concentration is arranged at the end of the ingot 10, the low concentration nitrogen region 7 that is a region having a relatively low nitrogen concentration is provided. It can be formed as a collective region including the central portion of the ingot 10. Therefore, when cutting silicon carbide substrate 20 from ingot 10, silicon carbide substrate 20 in which relatively low concentration nitrogen region 7 is formed in a wide region including the central portion of the substrate can be easily obtained.

  Next, using ingot 10 obtained as described above, silicon carbide substrate 20 shown in FIG. 6 is manufactured using the process shown in FIG. A method for manufacturing silicon carbide substrate 20 will be specifically described with reference to FIG.

  In the method for manufacturing a silicon carbide substrate according to the present invention, first, as shown in FIG. 2, an ingot preparation step (S40) is performed. In the step (S40), an ingot 10 made of silicon carbide obtained by performing the step shown in FIG. 1 is prepared.

  Next, a slicing step (S50) is performed. Specifically, in the step (S50), the ingot 10 is sliced by an arbitrary method. As a method for slicing, for example, a method using a wire saw or a method using a cutting member (for example, an inner peripheral blade) having hard abrasive grains such as diamond arranged on the surface can be used. An arbitrary direction can be adopted as a direction for slicing the ingot 10. For example, the ingot 10 may be sliced in a direction along the surface 4 of the base substrate 1 (a direction along the straight line 8 shown in FIG. 5). . In this case, high-concentration nitrogen region 6 can be arranged at the end of silicon carbide substrate 20 in the cut silicon carbide substrate 20. Alternatively, along a plane defined by the off-angle direction of base substrate 1 and a perpendicular to surface 4 of base substrate 1 (that is, the cross section of ingot 10 shown in FIG. 5 is the main surface of silicon carbide substrate 20). The ingot 10 may be sliced.

  Next, a post-processing step (S60) is performed. Specifically, the mirror surface state is finished to an arbitrary surface state by grinding and polishing the surface and / or the back surface of the sliced substrate. In this way, silicon carbide substrate 20 as shown in FIG. 6 is obtained. In silicon carbide substrate 20, most of the main surface including the central portion is low-concentration nitrogen region 7, and high-concentration nitrogen region 6 is disposed at the end. In addition, as shown in FIG. 8, recesses 21 may be formed on the outer periphery of silicon carbide substrate 20 by removing high concentration nitrogen region 6 by grinding or the like. In this case, almost the entire surface of silicon carbide substrate 20 becomes low-concentration nitrogen region 7, and silicon carbide substrate 20 with uniform characteristics can be obtained.

  Further, according to such silicon carbide substrate 20, a silicon carbide epitaxial layer having excellent uniformity of characteristics can be easily formed on the surface of silicon carbide substrate 20.

  In the post-processing step (S30) shown in FIG. 1, after removing the high-concentration nitrogen region 6 from the ingot 10 by a method such as grinding, the silicon carbide substrate manufacturing method shown in FIG. As shown in FIG. 8, there can be obtained silicon carbide substrate 20 having no high concentration nitrogen region, that is, the entire surface being a low concentration nitrogen region. Silicon carbide substrate 20 shown in FIG. 8 basically has the same configuration as silicon carbide substrate 20 shown in FIG. 6, except that high-concentration nitrogen region 6 shown in FIG. 6 is removed. Therefore, in silicon carbide substrate 20 shown in FIG. 8, recess 21 is formed in a part of the outer peripheral end that is the region where high concentration nitrogen region 6 was located. When silicon carbide substrate 20 is obtained by slicing ingot 10 in a direction along line 8 in FIG. 5, recess 21 is located at the end of silicon carbide substrate 20 in the off-angle direction.

  Moreover, in the manufacturing method of the ingot 10 and the silicon carbide substrate 20 described above, a circular substrate is used as the base substrate 1, but a substrate having any other shape can be used as the base substrate 1. For example, when a substrate having a quadrangular planar shape is used as the base substrate 1, an ingot 10 having a substantially quadrangular planar shape can be obtained as shown in FIG. Also in this case, by controlling the process conditions in the film forming step (S20) shown in FIG. 1, the facet surface 5 can be arranged at the end when the ingot 10 is viewed in plan. The cross section taken along line VV in FIG. 9 is the same as the cross section shown in FIG. And the maximum curvature radius in the outermost surface of the obtained ingot 10 (maximum curvature radius of the outermost surface 9 of FIG. 5) becomes 3 times or more of the radius of the circumscribed circle 25 of the planar shape of the ingot 10 shown in FIG. It is preferable.

  In this case as well, the ingot 10 is sliced along a direction parallel to the surface 4 of the base substrate 1 (that is, the direction shown by the straight line 8 in FIG. 5), whereby a planar silicon carbide substrate 20 as shown in FIG. Can be obtained. Also in silicon carbide substrate 20 shown in FIG. 10, high concentration nitrogen region 6 is arranged at the end, and the other region is low concentration nitrogen region 7. Such a silicon carbide substrate 20 can also provide the same effect as silicon carbide substrate 20 shown in FIG.

  Further, by removing high concentration nitrogen region 6 from the silicon carbide substrate 20 shown in FIG. 10 by grinding or the like, silicon carbide substrate 20 whose entire surface becomes low concentration nitrogen region 7 as shown in FIG. 11 is obtained. You can also. The high-concentration nitrogen region 6 may be removed from the ingot 10 in advance in the step of forming the ingot 10 (specifically, the post-treatment step (S30) shown in FIG. 1). Such silicon carbide substrate 20 can also provide the same effect as silicon carbide substrate 20 shown in FIG.

  As base substrate 1 for forming ingot 10, a substrate having a rectangular planar shape as shown in FIG. 12 and made of silicon carbide single crystal can also be used. Also in this case, the ingot 10 having a planar shape as shown in FIG. 12 can be formed by using the ingot manufacturing method shown in FIG. Note that the cross-sectional shape of the ingot 10 along the line segment V-V shown in FIG. 12 is basically the same as the cross-sectional shape of the ingot 10 shown in FIG. In the ingot 10 shown in FIG. 12, the maximum curvature radius of the outermost surface 9 (see FIG. 5) is preferably at least three times the radius of the circumscribed circle 25 of the planar shape of the ingot 10 shown in FIG. .

  Then, by slicing and post-processing the ingot 10 shown in FIG. 12 by the method shown in FIG. 2, a silicon carbide substrate 20 having a rectangular planar shape as shown in FIG. 13 can be obtained. Note that the slice direction is a direction parallel to the paper surface of FIG. 12 (a direction along the surface of the base substrate). Also in silicon carbide substrate 20, high-concentration nitrogen region 6 is formed at the end, while most other regions are low-concentration nitrogen regions 7. Such a silicon carbide substrate 20 can provide the same effect as the substrate shown in FIG.

  Further, by removing high concentration nitrogen region 6 from silicon carbide substrate 20 shown in FIG. 13, silicon carbide substrate 20 whose entire surface becomes low concentration nitrogen region 7 as shown in FIG. 14 may be obtained. it can. In this case, silicon carbide substrate 20 shown in FIG. 14 may be obtained by removing high concentration nitrogen region 6 from ingot 10 at the stage of forming ingot 10 shown in FIG. 12 and then slicing ingot 10. .

  Further, as the base substrate 1, a substrate having a hexagonal planar shape can be used. When such a substrate is used as the base substrate 1, an ingot 10 having a hexagonal planar shape can be obtained as shown in FIG. Also in the ingot 10, the (0001) facet plane 5 can be disposed at the end of the outermost surface 9 (see FIG. 5) of the crystal growth portion of the ingot 10. In addition, about the ingot 10 shown in FIG. 15, sectional drawing in line segment VV is the same as that of the sectional view shown in FIG. The maximum curvature radius on the outermost surface 9 of the obtained ingot 10 (the maximum curvature radius of the outermost surface 9 in FIG. 5) is three times or more than the radius of the circumscribed circle 25 of the planar shape of the ingot 10 shown in FIG. It is preferable that

  Then, by slicing and processing the ingot 10 shown in FIG. 15 by the method shown in FIG. 2, a silicon carbide substrate 20 having a hexagonal planar shape as shown in FIG. 16 can be obtained. Note that the slice direction is a direction parallel to the paper surface of FIG. 15 (a direction along the surface of the base substrate 1). Also in silicon carbide substrate 20, high-concentration nitrogen region 6 is arranged at the end, while the remaining region is low-concentration nitrogen region 7. In this case, the same effect as that of the substrate shown in FIG. 6 can be obtained.

  Further, by removing high concentration nitrogen region 6 from the silicon carbide substrate 20 shown in FIG. 16 using grinding or the like, the silicon carbide substrate whose entire surface becomes low concentration nitrogen region 7 as shown in FIG. 20 can also be obtained. In this case, silicon carbide substrate 20 shown in FIG. 17 may be obtained by removing high concentration nitrogen region 6 from ingot 10 at the stage where ingot 10 shown in FIG. 15 is formed, and then slicing ingot 10. .

  Here, although there is a part which overlaps with embodiment mentioned above, the characteristic structure of this invention is enumerated.

  As shown in FIG. 1, the method for manufacturing silicon carbide ingot 10 according to the present invention is in the off-angle direction which is either the <11-20> direction or the <1-100> direction with respect to the (0001) plane. A step of preparing a base substrate 1 having an off angle of 0.1 ° to 10 °, more preferably 1 ° to 10 ° and made of single crystal silicon carbide (preparation step (S10)); And a step of growing a silicon carbide layer on the surface (film formation step (S20)). In the film forming step (S20), when the crossing angle at which the <0001> direction axis of the base substrate 1 crosses the surface 4 of the base substrate 1 in the off-angle direction is considered, the crossing angle is an acute angle side. At the upstream end, a region having a (0001) facet surface 5 is formed on the surface of the grown silicon carbide layer.

  In this way, by forming the (0001) facet surface 5 in which nitrogen is easily taken in at the end of the ingot 10, a relatively high nitrogen concentration region (high concentration nitrogen located below the (0001) facet surface) Region 6) can be located at the end of silicon carbide ingot 10. Therefore, a region having a relatively low nitrogen concentration (low concentration nitrogen region 7 other than the high concentration nitrogen region) can be formed as a collective region including the central portion of silicon carbide ingot 10. Therefore, when cutting silicon carbide substrate 20 from ingot 10, silicon carbide substrate 20 in which low-concentration nitrogen region 7 is formed in a wide region including the central portion of the substrate can be easily obtained. Thus, since the low concentration nitrogen region 7 (that is, a region where nitrogen concentration is not so much and stable nitrogen concentration) can be formed in a wide region including the central portion of the substrate, a semiconductor element is formed on the surface of the silicon carbide substrate 20. In this case, the semiconductor device can be efficiently formed by increasing the utilization efficiency of the substrate.

  In the silicon carbide ingot manufacturing method, the silicon carbide layer after the step of growing the silicon carbide layer (film formation step (S20)), the portion located under the region having the (0001) facet plane is in the silicon carbide layer. The high-concentration nitrogen region 6 in which the nitrogen concentration is higher than the portion (low-concentration nitrogen region 7) other than the portion located under the region having the (0001) facet surface may be used.

  In this case, a high-concentration nitrogen region 6 is formed under the region having the (0001) facet surface 5, and a portion including the other central portion of the ingot becomes a low-concentration nitrogen region 7 having a lower nitrogen concentration than the high-concentration nitrogen region 6. Therefore, by slicing silicon carbide ingot 10, silicon carbide substrate 20 in which a wide region including the central portion of the surface is low concentration nitrogen region 7 can be easily obtained.

  In the silicon carbide ingot manufacturing method, the width of the high-concentration nitrogen region 6 in the off-angle direction (the direction along the arrow 26 shown in FIG. 6) is 1/10 or less of the width of the base substrate 1 in the off-angle direction. There may be. In this case, since the size of the high concentration nitrogen region 6 is sufficiently small with respect to the entire silicon carbide ingot 10, the high concentration nitrogen region 6 is formed on the surface (main surface) of the silicon carbide substrate 20 obtained from the silicon carbide ingot 10. Occupied area can be reduced. As a result, the width of the low concentration nitrogen region 7 (the nitrogen concentration is stable) on the surface of the silicon carbide substrate 20 can be made sufficiently wide. Moreover, since the high concentration nitrogen area | region 6 can be easily removed in the outer periphery grinding molding process of the silicon carbide ingot 10, it can suppress that the time required for the process of the said silicon carbide ingot 10 becomes long.

  The method for manufacturing the silicon carbide ingot may further include a step of removing the high-concentration nitrogen region (post-treatment step (S30) in FIG. 1). In this case, most of the silicon carbide ingot 10 can be constituted by the low concentration nitrogen region 7. For this reason, since the surface of silicon carbide substrate 20 cut out from silicon carbide ingot 10 can be constituted only by low-concentration nitrogen region 7, silicon carbide substrate 20 having a stable nitrogen concentration and excellent uniformity can be obtained.

  In the method for manufacturing a silicon carbide ingot, the transmittance of light having a wavelength of 450 nm or more and 500 nm or less per unit thickness in the high-concentration nitrogen region 6 is a silicon carbide layer (a silicon carbide layer grown on the base substrate 1). May be lower than the light transmittance per unit thickness in a portion other than the high concentration nitrogen region (low concentration nitrogen region 7).

  Here, the light transmittance of the silicon carbide ingot 10 tends to decrease as the nitrogen concentration increases. Therefore, the light transmittance characteristic is also different between the high concentration nitrogen region 6 and the region other than the high concentration nitrogen region (low concentration nitrogen region 7). Therefore, according to the present invention, the region where the light transmittance is relatively low (the high-concentration nitrogen region 6) is disposed at the end of the silicon carbide ingot 10, so that the light transmittance is high. With respect to the characteristics as described above, the region having a relatively high light transmittance (low-concentration nitrogen region 7) can be formed as a grouped region including the central portion of the silicon carbide ingot 10. For this reason, when silicon carbide substrate 20 is cut out from silicon carbide ingot 10, silicon carbide substrate 20 in which the region having a relatively high light transmittance is formed in a wide region including the central portion of the substrate can be easily obtained. Can do.

  In the method for manufacturing silicon carbide ingot 10 described above, the micropipe density of the portion (high concentration nitrogen region 6) located under the region having the (0001) facet surface is below the region having the (0001) facet surface in the silicon carbide layer. It may be higher than the micropipe density in the portion other than the above-described portion (low concentration nitrogen region 7). In this case, since the high-concentration nitrogen region 6 in which the micropipe density is relatively high is disposed at the end of the silicon carbide ingot 10, the micropipe density is also relatively low in terms of the characteristics of the micropipe density. The region (low-concentration nitrogen region 7) can be formed as a collective region including the central portion of silicon carbide ingot 10. For this reason, when silicon carbide substrate 20 is cut out from silicon carbide ingot 10, the silicon carbide substrate in which the region having a relatively low micropipe density (low-concentration nitrogen region 7) is formed in a wide region including the central portion of the substrate. 20 can be easily obtained.

  In the method for manufacturing silicon carbide ingot 10, the maximum radius of curvature on the surface of silicon carbide layer (outermost surface 9 shown in FIG. 5) after the step of growing the silicon carbide layer (film formation step (S20)) is the base It may be three times or more the radius of the circumscribed circle 25 relating to the planar shape of the substrate 1. Further, the maximum radius of curvature on the surface of the silicon carbide layer (outermost surface 9 in FIG. 5) is the maximum radius of curvature in a region (outermost surface) including a portion farthest from the surface of base substrate 1 in the silicon carbide layer. It is preferable.

  In this case, since the volume of the silicon carbide layer formed on base substrate 1 can be made sufficiently large, the volume of silicon carbide ingot 10 can be made sufficiently large as a result. Therefore, when silicon carbide substrate 20 is cut out from silicon carbide ingot 10, silicon carbide substrate 20 having a large area can be obtained efficiently. The planar shape of the silicon carbide layer (silicon carbide epitaxial growth layer composed of high-concentration nitrogen region 6 and low-concentration nitrogen region 7) is larger than the planar shape of base substrate 1 (for example, away from base substrate 1). The silicon carbide layer may be formed so that the planar shape increases in accordance with (or has a sidewall inclined toward the outside as the distance from the base substrate 1 increases).

  Silicon carbide ingot 10 according to the present invention is manufactured using the method for manufacturing silicon carbide ingot 10. In this case, a region having a relatively low nitrogen concentration (low concentration nitrogen region 7) can be formed as a grouped region including the central portion of silicon carbide ingot 10. Therefore, by cutting silicon carbide substrate 20 from silicon carbide ingot 10, silicon carbide substrate 20 in which low concentration nitrogen region 7 having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate can be easily obtained. Can do.

  As shown in FIG. 2, the method for manufacturing silicon carbide substrate 20 according to the present invention includes a step of preparing a silicon carbide ingot using the method of manufacturing silicon carbide ingot 10 (ingot preparation step (S40)), A step of slicing the silicon carbide ingot 10 (slicing step (S50)).

  In this case, in silicon carbide ingot 10, a region having a relatively low nitrogen concentration (low concentration nitrogen region 7 that is a region other than the high concentration nitrogen region) is formed as a grouped region including the central portion of silicon carbide ingot 10. Is done. Therefore, in the slicing step (S50), the silicon carbide substrate 20 is cut out from the silicon carbide ingot 10 so that the low concentration nitrogen region 7 having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate. The silicon substrate 20 can be obtained easily.

  In the method for manufacturing a silicon carbide substrate, in the step of preparing a silicon carbide ingot (ingot preparation step (S40)), in the silicon carbide layer after the step of growing a silicon carbide layer (film formation step (S20)), (0001 ) The portion located under the region having the facet plane has a higher nitrogen concentration than the portion other than the portion (low concentration nitrogen region 7) located under the region having the (0001) facet plane in the silicon carbide layer. The concentration nitrogen region 6 may be provided. The silicon carbide substrate manufacturing method includes a step of removing the high-concentration nitrogen region 6 from the silicon carbide ingot 10 before the slicing step (S50) for slicing the silicon carbide ingot 10 (for example, a post-processing step (S30 in FIG. 1). And a step of removing the high-concentration nitrogen region 6 included in (1) by grinding).

  From a different point of view, the method for manufacturing silicon carbide substrate 20 according to the present invention includes a step of preparing a silicon carbide ingot using the method for manufacturing silicon carbide ingot 10 as shown in FIG. In the step of preparing the silicon carbide ingot (ingot preparation step (S40)), the silicon carbide layer after the step of growing the silicon carbide layer (film formation step (S20)) is provided (preparation step (S40)). ) The portion located under the region having the facet plane has a higher nitrogen concentration than the portion other than the portion (low concentration nitrogen region 7) located under the region having the (0001) facet plane in the silicon carbide layer. Further, a step of removing the high concentration nitrogen region 6 from the silicon carbide ingot 10 (for example, a post-processing step (S 0), a step of removing the high-concentration nitrogen region 6 by grinding), and a step of removing the high-concentration nitrogen region 6 and then slicing the silicon carbide ingot 10 (slicing step (S50)). With.

  In this case, by removing the high-concentration nitrogen region 6 from the silicon carbide ingot 10 from which the silicon carbide substrate 20 is cut, the uniformity of the nitrogen concentration and transmittance in the silicon carbide ingot 10 can be improved.

  Silicon carbide substrate 20 according to the present invention is manufactured using the above-described method for manufacturing a silicon carbide substrate. In this way, silicon carbide substrate 20 in which low-concentration nitrogen region 7 having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate can be easily realized.

  The method for manufacturing a silicon carbide ingot according to the present invention is performed in an off-angle direction (direction indicated by an arrow 26 in FIG. 3) which is either the <11-20> direction or the <1-100> direction with respect to the (0001) plane. ) Having an off angle of 0.1 ° to 10 °, more preferably 1 ° to 10 °, and preparing a base substrate 1 made of single crystal silicon carbide (preparation step (S10)), And a step (film formation step (S20)) for growing a silicon carbide layer on the surface of the base substrate 1. In the film formation step (S20), the <0001> direction axis of the base substrate 1 in the off-angle direction is A region having a (0001) facet surface 5 is formed on the surface of the grown silicon carbide layer at the upstream end where the crossing angle is an acute angle when the crossing angle intersecting the surface 4 is considered. DoIn the silicon carbide layer after the film forming step (S20), a portion (high concentration nitrogen region 6) located under the region having the (0001) facet surface 5 is below the region having the (0001) facet surface 5 in the silicon carbide layer. The transmittance per unit thickness of light having a wavelength of 450 nm or more and 500 nm or less is lower than the portion other than the portion located at (low concentration nitrogen region 7).

  In this way, by forming the (0001) facet surface 5 in which nitrogen is easily taken in at the end of the silicon carbide ingot 10, the nitrogen taken in from the (0001) facet surface 5 during the growth of the silicon carbide layer is formed. Since the region where the light transmittance is reduced due to this (high concentration nitrogen region 6) is arranged at the end of silicon carbide ingot 10 (the portion under (0001) facet 5), the center of silicon carbide ingot 10 Other portions including the portion (low-concentration nitrogen region 7) can be a region having a relatively high light transmittance. For this reason, when the silicon carbide substrate 20 is cut out from the silicon carbide ingot 10, the region where the light transmittance is relatively high (the low concentration nitrogen region 7) is formed in a wide region including the central portion of the substrate. The silicon substrate 20 can be obtained easily. As described above, since a region having a relatively high light transmittance (a region in which nitrogen is not taken in so much and the nitrogen concentration and transmittance are stable) can be formed in a wide region including the central portion of the substrate, a semiconductor element is formed on the substrate surface. When forming the semiconductor element, the semiconductor element can be formed efficiently.

  Silicon carbide ingot 10 according to the present invention has an off angle in the off angle direction that is either the <11-20> direction or the <1-100> direction with respect to the (0001) plane of 0.1 ° or more and 10 °. Hereinafter, it is more preferably 1 ° to 10 °, and includes a base substrate 1 made of single crystal silicon carbide and a silicon carbide layer formed on the surface of the base substrate 1. In the off-angle direction, when the crossing angle at which the <0001> direction axis of the base substrate intersects the surface 4 of the base substrate 1 is considered, the carbonization grown on the upstream end, which is the side where the crossing angle becomes an acute angle, A region having a (0001) facet surface 5 is formed on the surface of the silicon layer.

  In silicon carbide ingot 10, a portion of the silicon carbide layer located under the region having (0001) facet surface 5 is a portion other than the portion located under the region having (0001) facet surface in the silicon carbide layer ( It may be a high concentration nitrogen region 6 having a higher nitrogen concentration than the low concentration nitrogen region 7).

  In this way, by forming the (0001) facet surface 5 in which nitrogen is easily taken in at the end of the ingot 10, a relatively high nitrogen concentration region (the high concentration located below the (0001) facet surface 5). A nitrogen region 6) can be arranged at the end of the silicon carbide ingot 10. Therefore, a region having a relatively low nitrogen concentration (low concentration nitrogen region 7) can be formed as a collective region including the central portion of silicon carbide ingot 10. Therefore, when cutting silicon carbide substrate 20 from ingot 10, silicon carbide substrate 20 in which low-concentration nitrogen region 7 is formed in a wide region including the central portion of the substrate can be easily obtained.

  In silicon carbide ingot 10, the nitrogen concentration in high concentration nitrogen region 6 is 1.1 times or more the nitrogen concentration in a portion (low concentration nitrogen region 7) other than the portion located under the region having (0001) facet surface 5. It may be.

  In this case, the high-concentration nitrogen region 6 and the low-concentration nitrogen region 7 can be easily discriminated based on the nitrogen concentration, light transmittance, and the like. Therefore, the high-concentration nitrogen region 6 is removed from the silicon carbide ingot 10 by grinding, or the silicon carbide substrate 20 is cut out from the silicon carbide ingot 10 to form the device on the surface of the silicon carbide substrate 20. It is possible to easily perform an operation such as forming a device so as to avoid the region 6 (or so as not to cross the boundary between the high concentration nitrogen region 6 and the low concentration nitrogen region 7).

  In silicon carbide ingot 10, the width of high concentration nitrogen region 6 in the off angle direction may be 1/10 or less of the width of base substrate 1 in the off angle direction. In this case, since the size of the high-concentration nitrogen region 6 is reduced, the size of the region other than the high-concentration nitrogen region 6 (low-concentration nitrogen region 7) can be secured sufficiently large.

  In the silicon carbide ingot 10, the transmittance of light having a wavelength of 450 nm or more and 500 nm or less per unit thickness in the high concentration nitrogen region 6 is a portion other than the high concentration nitrogen region (low concentration nitrogen region 7 in the silicon carbide layer). ) May be lower than the light transmittance per unit thickness.

  In this case, the high-concentration nitrogen region 6 and the low-concentration nitrogen region 7 can be easily discriminated by the light transmittance. For this reason, operations such as removing the high-concentration nitrogen region 6 from the silicon carbide ingot 10 by grinding can be easily performed.

  In silicon carbide ingot 10, the transmittance in high concentration nitrogen region 6 may be 5% or more lower than the transmittance in low concentration nitrogen region 7, which is a portion other than the high concentration nitrogen region in the silicon carbide layer. . In this case, the high-concentration nitrogen region 6 and the low-concentration nitrogen region 7 can be easily distinguished from the difference in transmittance.

  In silicon carbide ingot 10, the micropipe density of the portion (high concentration nitrogen region 6) located under the region having the (0001) facet surface is located under the region having (0001) facet surface 5 in the silicon carbide layer. It may be higher than the micropipe density in a portion other than the portion (low concentration nitrogen region 7). In this case, the portion other than the portion located under the region having the (0001) facet surface 5 (the low concentration nitrogen region 7 where the micropipe density is relatively low) includes the central portion of the silicon carbide ingot 10. Formed as a region. For this reason, when silicon carbide substrate 20 is cut out from ingot 10, silicon carbide substrate 20 in which the region having a relatively low micropipe density is formed in a wide region including the central portion of the substrate can be easily obtained.

  In silicon carbide ingot 10, the micropipe density of the portion (high concentration nitrogen region 6) located below the region having (0001) facet surface 5 is located below the region having (0001) facet surface 5 in the silicon carbide layer. It may be 1.2 times or more the micropipe density in the part other than the part to be performed (low concentration nitrogen region 7).

  In this case, since the micropipe density is relatively low in the low-concentration nitrogen region 7, which is a portion other than the portion located under the region having the (0001) facet surface 5, the central portion is included. Silicon carbide ingot 10 having a reduced micropipe density in the region can be obtained.

  In silicon carbide ingot 10, the maximum radius of curvature at the surface of the silicon carbide layer (outermost surface 9 shown in FIG. 5) may be three times or more the radius of circumscribed circle 25 relating to the planar shape of base substrate 1. In this case, since the volume of the silicon carbide layer formed on base substrate 1 can be made sufficiently large, the volume of silicon carbide ingot 10 can be made sufficiently large as a result.

  Silicon carbide substrate 20 according to the present invention is obtained by slicing silicon carbide ingot 10 described above. In this way, it is possible to easily obtain silicon carbide substrate 20 in which low-concentration nitrogen region 7 (or a region with high light transmittance) having a relatively low nitrogen concentration is formed in a wide region including the central portion of the substrate. it can.

  Silicon carbide substrate 20 according to the present invention may be obtained by slicing silicon carbide ingot 10 after removing high-concentration nitrogen region 6 from silicon carbide ingot 10. In this way, the high-concentration nitrogen region 6 (region having a low light transmittance) is removed in advance, so that the low-concentration nitrogen region 7 having a lower nitrogen concentration than the high-concentration nitrogen region 6 (having a high light transmittance). Silicon carbide substrate 20 is formed using silicon carbide ingot 10 in which most of the region (higher than the concentration nitrogen region) (or only the low concentration nitrogen region 7) is formed. Therefore, silicon carbide substrate 20 in which fluctuations in nitrogen concentration and light transmittance are reduced can be obtained.

  In silicon carbide substrate 20, variation with respect to the average value of nitrogen concentration may be 10% or less. In this case, the variation in nitrogen concentration is sufficiently small so that the characteristics of silicon carbide substrate 20 are not adversely affected, so that silicon carbide substrate 20 with uniform characteristics can be obtained reliably.

  In silicon carbide substrate 20, the variation of the average dislocation density may be 80% or less. Further, the variation with respect to the average value of the dislocation density in the low concentration nitrogen region 7 may be 80% or less. In this case, the variation in dislocation density as described above can suppress the change in characteristics within the main surface of silicon carbide substrate 20 to a practically satisfactory level.

  In silicon carbide substrate 20 according to the present invention, the nitrogen concentration is relatively higher at one end in either the <11-20> direction or the <1-100> direction than the other portions. A high concentration nitrogen region 6 is formed. Further, the high concentration nitrogen region 6 has a <0001> direction axis of the silicon carbide substrate 20 of the silicon carbide substrate 20 in either the <11-20> direction or the <1-100> direction (off-angle direction). When considering a crossing angle intersecting the surface, the crossing angle may be formed at an upstream end which is a side where the crossing angle becomes an acute angle. In this way, when the silicon carbide ingot 10 used for forming the silicon carbide substrate 20 is grown, the high concentration nitrogen region 6 can be easily formed by controlling the arrangement of the (0001) facet surface 5. 20 ends.

  The silicon carbide substrate 20 may have a size (for example, a maximum width in plan view) of 4 inches or more. When the present invention is applied to a silicon carbide substrate 20 having a size of 4 inches or more, a remarkable effect can be obtained particularly in terms of device manufacturing efficiency.

  In silicon carbide substrate 20, the nitrogen concentration in high concentration nitrogen region 6 may be 1.1 times or more the nitrogen concentration in other portions. In this case, the high-concentration nitrogen region 6 and other portions (low-concentration nitrogen region 7) other than the high-concentration nitrogen region can be easily discriminated based on the light transmittance or the like.

  In silicon carbide substrate 20, the width of high-concentration nitrogen region 6 in either the <11-20> direction or the <1-100> direction is 1/10 of the width of silicon carbide substrate 20 in the above direction. It may be the following. In this case, since the size of the high-concentration nitrogen region 6 is reduced, the size of the region other than the high-concentration nitrogen region 6 (low-concentration nitrogen region 7) can be secured sufficiently large.

  Further, in the silicon carbide substrate 20, the transmittance of light having a wavelength of 450 nm or more and 500 nm or less per unit thickness in the high concentration nitrogen region 6 is in a portion other than the high concentration nitrogen region (low concentration nitrogen region 7). The wavelength per unit thickness may be lower than the light transmittance of 450 nm or more and 500 nm or less. Further, the transmittance in the high concentration nitrogen region 6 may be 5% or more lower than the transmittance in a portion other than the high concentration nitrogen region (low concentration nitrogen region 7).

  In this case, the high-concentration nitrogen region 6 and the low-concentration nitrogen region 7 can be easily discriminated by the light transmittance. For this reason, when forming a device on the surface of silicon carbide substrate 20, the device avoids high-concentration nitrogen region 6 (or does not straddle the boundary between high-concentration nitrogen region 6 and other regions). Can be easily performed.

  In silicon carbide substrate 20, the micropipe density in high concentration nitrogen region 6 may be higher than the micropipe density in a portion other than high concentration nitrogen region (low concentration nitrogen region 7). Furthermore, in the silicon carbide substrate 20, the micropipe density in the high concentration nitrogen region 6 may be 1.2 times or more the micropipe density in a portion other than the high concentration nitrogen region (low concentration nitrogen region 7).

  In this case, since the micropipe density is reduced for the low-concentration nitrogen region 7, which is a region occupying most of the silicon carbide substrate, when the silicon carbide epitaxial layer is formed on the surface of the silicon carbide substrate 20, In the silicon carbide epitaxial layer, generation of defects due to the micropipe on the silicon carbide substrate 20 side can be suppressed.

  In the silicon carbide substrate, variation with respect to the average value of nitrogen concentration may be 10% or less. In this case, since the variation in nitrogen concentration is sufficiently small so as not to adversely affect the characteristics of the silicon carbide substrate, a silicon carbide substrate having uniform characteristics can be obtained with certainty.

  In the silicon carbide substrate, the dispersion with respect to the average value of the dislocation density may be 80% or less. Further, the variation with respect to the average value of the dislocation density in the low concentration nitrogen region may be 80% or less. In this case, if the dislocation density varies as described above, the change in characteristics within the main surface of the silicon carbide substrate can be suppressed to a practically satisfactory level.

  As described above, according to the method for manufacturing a silicon carbide ingot according to the present invention, the facet can be brought close to the end of the silicon carbide ingot 10. In this case, by grinding only the end portion of the ingot 10 and slicing the ingot 10, it is possible to obtain the substrate 20 without the entire facet. Here, the amount of nitrogen doping and main dislocations differ between facets and regions other than facets. When the size of the substrate 20 is less than 4 inches, the influence is not large. However, when the size of the substrate is 4 inches or more, the influence becomes strong, so the effect of the present invention is particularly remarkable.

  Further, when the polishing process is performed on the substrate 20, for example, the nitrogen doping amount of the silicon carbide substrate affects the CMP polishing rate. For this reason, the nitrogen doping amount of the substrate 20 is preferably uniform. Further, when the substrate size is 4 inches or more, the warpage of the substrate 20 and the TTV also increase as the substrate size increases. Further, the influence of the nitrogen doping amount becomes significant. That is, warpage and TTV are also improved by reducing the variation in the internal stress distribution due to impurities such as nitrogen as the variation in nitrogen doping amount on the substrate surface is reduced.

  In addition, the above-described nitrogen doping amount and the like are also affected by a device forming step (for example, a heat treatment step). That is, when the nitrogen doping amount is different, the light absorptance of the substrate is changed, so that a local temperature difference occurs when the substrate is heated. When the size of the substrate 20 is small, the influence of the temperature difference was not large due to the effect of heat conduction. However, when the substrate size becomes a large diameter of 4 inches or more, the effect of heat conduction decreases as the temperature increases. A temperature distribution in the substrate 20 is likely to occur. As a result, since the temperature condition varies in the plane of the substrate, there is a problem that a uniform film cannot be formed on the substrate surface. However, in the substrate obtained from the ingot 10 according to the present invention, the nitrogen doping amount is uniform. Therefore, the occurrence of the above problems can be suppressed.

  The nitrogen doping amount (nitrogen concentration) described above can be measured by SIMS. For example, in the ingot 10 made of silicon carbide according to the present invention, the nitrogen concentration in the portion where the nitrogen doping amount is high is 1.5 times or more the nitrogen concentration in other regions.

  For the substrate 20 cut out from the ingot 10 according to the present invention, the transmittance of light having a wavelength of 400 nm or more and 500 nm or less preferably satisfies the following conditions when the thickness of the substrate 20 is 400 μm. That is, when the light transmittance is measured at a plurality of locations (for example, 10 locations including the central portion) of the substrate 20 using a visible light spectrometer, the average transmittance is preferably 20% or more and 65% or less. . In addition, for most of the main surface of the substrate (region having an area ratio of 70% or more), the local transmittance is within ± 20% of the average transmittance with respect to the average transmittance. preferable. Moreover, it is preferable that the refractive index of the board | substrate 20 is 2.5 or more and 2.8 or less.

  Further, the dislocation density of the substrate was measured by visualizing dislocations by treating the substrate surface by etching using molten salt KOH as an etching solution. Specifically, the molten salt KOH is heated to 500 ° C., and the substrate 20 is immersed in the molten molten salt KOH solution for about 1 to 10 minutes. As a result, pits are formed on the surface of the substrate 20 corresponding to the presence of dislocations. Then, the number of pits was counted with a Nomarski differential interference microscope, and the number of pits per unit area (that is, the number of dislocations per unit area) was calculated by dividing by the area of the measurement range.

Here, dislocation density micropipe density of the base substrate 1 (MPD): 10~100 / cm -2, the etch pit density (EPD): When 1～5E4cm ^-2, the base substrate in the ingot 10 in accordance with the present invention When the number of dislocations is measured for the substrate 20 obtained by slicing at a position at a distance of 1 to 20 mm, the micropipe density and the etch pit density are reduced to about 1/2 to 1/20 with respect to the base substrate 1.

(Example)
In order to confirm the effect of the present invention, ingots and substrates were manufactured and characteristics were measured by the following methods.

(sample)
The silicon carbide ingot and the silicon carbide ingot were sliced as follows to prepare samples of examples and comparative examples of the present invention for silicon carbide substrates.

<Base Substrate for Samples of Examples and Comparative Examples of the Present Invention>
In order to manufacture a silicon carbide ingot, a silicon carbide single crystal substrate having the following conditions was prepared as a base substrate. Specifically, in order to manufacture the ingot according to the present invention, six 4H type SiC single crystal substrates (three for the example and three for the comparative example) were prepared as the base substrate 1. The base substrate 1 can have a diameter of 50 to 180 mm and a thickness of 100 to 2000 μm. Here, the thickness of the base substrate 1 was set to 800 μm. The main surface of the base substrate 1 has an off angle of 4 ° in the <11-20> direction with respect to the (0001) plane. With respect to the surface of the base substrate 1, at least the surface side on which crystals are grown is mirror-polished. The dislocation density of the base substrate 1, micropipe density (MPD) is 10 to 100 cm ^-2, the etch pit density (EPD) was 1~5E4cm ^-2. These dislocation densities were measured as follows. That is, after the base substrate 1 was immersed in KOH heated to 500 ° C. for 1 to 10 minutes, the surface of the base substrate was observed with a Nomarski differential interference microscope, and the number of pits was counted. Then, the number of pits per unit area was calculated from the area of the observed region and the count number.

(experimental method)
Ingot manufacturing:
<Ingot of Example>
A silicon carbide ingot of the example was manufactured by forming a silicon carbide epitaxial layer on the surface of the base substrate for the example described above. Specifically, base substrate 1 and powdered SiC as a raw material were introduced into a graphite crucible. The distance between the raw material and the base substrate was in the range of 10 mm to 100 mm. The growth method is manufactured by a method generally called a sublimation method or an improved Rayleigh method. Specifically, this crucible was placed inside a heating furnace and heated. At the time of temperature increase, the atmospheric pressure was set in the range of 50 kPa to atmospheric pressure. The temperature during crystal growth was such that the crucible lower part temperature was 2200 ° C. or higher and 2500 ° C. or lower, and the crucible upper part temperature was 2000 ° C. or higher and 2350 ° C. or lower. Moreover, the temperature of the crucible lower part was made higher than the crucible upper part temperature. The atmospheric pressure is controlled within the range of 0.1 to 20 kPa after the temperature is raised to the temperature during crystal growth. Further, as the atmospheric gas, any one of He, Ar, N ₂ or a mixed gas was used. Here, Ar + N ₂ gas was used as the atmospheric gas. Moreover, at the time of cooling, first, the atmospheric pressure was raised to the range of 50 kPa to atmospheric pressure, and then the temperature of the heating furnace was lowered.

  Further, at the time of the above-described crystal growth, the growth outermost surface of the ingot 10 growing on the surface of the base substrate 1 (indicated by the surface opposite to the side on which the base substrate 1 is located in the ingot 10 in FIG. 7 or the arrow 13 in FIG. 7) The ingot 10 was grown so that the surface of the ingot 10 facing the supply direction of the raw material gas to be always flat as shown in FIG. Specifically, as described in FIG. 7, when the temperature of the central portion 14 of the ingot 10 of FIG. 7 is Ta, the temperature of the end portion 15 is Tb, and the temperature of the outermost peripheral portion 16 is Tc, the relationship is Tc > Tb ≧ Ta satisfies the relational expression, and the temperature Tb and the temperature Ta have a temperature gradient ((absolute value of the difference between the temperature Ta and the temperature Tb) / (between the central portion 14 and the end portion 15). Crystal growth was performed so that the distance)) satisfied the relationship of 10 ° C./cm or less. Specifically, the diameter of the heat radiation hole of the felt located on the upper surface side of the crucible was made larger than the diameter of the ingot 10. By this method, an ingot having silicon carbide grown on the base substrate was taken out.

<Ingot of comparative example>
Moreover, the silicon carbide ingot of the comparative example was manufactured by forming a silicon carbide epitaxial layer on the surface of the base substrate for the comparative example. Here, basically, the ingot of the comparative example was manufactured by the same method as the manufacturing method of the ingot of the above-described embodiment. A heat dissipation hole was formed. By doing in this way, since the thermal radiation effect became large only in the vicinity of the said thermal radiation hole, the temperature gradient of the center part 14 and the edge part 15 of the ingot formed became 10 degrees C / cm or more. Thus, the ingot of the comparative example in which the silicon carbide was grown was taken out.

Measuring the flatness of the outermost surface in an ingot:
The surface flatness of the ingots of Examples and Comparative Examples described above was measured. The flatness of the ingot is the area (at the center) excluding the range of 10% of the diameter of the ingot on the outer peripheral side with respect to the diameter of the ingot, and the height of the ingot (from the surface of the base substrate to the surface of the ingot) The distance was measured. Although it is preferable to take a height distribution over the entire surface of the ingot, the height of the ingot may be simply measured at a pitch of 1 to 5 mm in the cross direction from the center of the ingot.

  Thus, when measuring in a cross direction, flatness is measured as follows. That is, the height of the surface of the ingot 10 is measured at a plurality of positions (measurement points) arranged in a cross direction (preferably in a matrix of 5 mm pitch) at a pitch of 5 mm from the center of the surface of the ingot. Then, the difference in height between adjacent measurement points is calculated. Further, an angle (inclination angle) corresponding to the inclination of the surface of the ingot between adjacent measurement points is obtained from a tangent (tan) that can be determined from the difference in height and the distance between the measurement points.

Board manufacturing:
The ingots of the above-described examples and comparative examples were molded into a cylindrical shape after measuring the surface shape as described above. And the silicon carbide substrate was manufactured by slicing the said ingot in the direction along the surface of the base substrate using the wire saw. The thickness of the substrate was 400 μm to 500 μm. Furthermore, after slicing, the silicon carbide substrate was subjected to a double-sided mirror polishing process. As a result, the thickness of the silicon carbide substrate was in the range of 350 μm to 420 μm.

Measurement of nitrogen concentration:
With respect to the prepared substrate, the nitrogen concentration was measured for a region located under the (0001) facet surface of the ingot and having a relatively high nitrogen concentration (high concentration nitrogen region) and other regions. As a measuring method, SIMS (secondary ion mass spectrometry) was used. In addition, in order to suppress measurement variation, the measurement thickness was set to 10 μm.

Transmittance measurement:
About the produced board | substrate, the light transmittance was measured about the said high concentration nitrogen area | region and another area | region. As a measuring method, the transmittance of light having a wavelength in the range of 400 nm to 500 nm was measured using a visible light spectrometer.

Measurement of dislocation density:
About the produced board | substrate, the dislocation density in the surface was measured. Specifically, the following method was used. First, the silicon carbide substrate was immersed in a molten salt KOH solution heated to 500 ° C. for 1 to 10 minutes. Thereafter, the surface of the silicon carbide substrate was observed with a Nomarski differential interference microscope, and the number of formed pits was counted. For counting the number, it is preferable to calculate the average density per unit area by counting the total number of pits after taking the entire mapping photograph. However, for example, in the case of a silicon carbide substrate having a diameter of 2 inches, the number of pits per unit area is counted for a total of five points at a position about 18 mm away from the center of the substrate and in the cross direction, and the average is taken. As described above, the average density of pits at five or more measurement locations may be used as the pit density. Further, as the evaluated silicon carbide substrate, a substrate at a position 20 mm away from the outermost surface of the base substrate of the manufactured ingot was selected and compared with the data of the base substrate.

(result)
About Ingot:
In the ingot of the example, the (0001) facet surface was disposed on the outermost surface at the end portion (upstream end portion) in the off-angle direction of the base substrate. The width in the off-angle direction of the (0001) facet surface in plan view was 12.5 mm when the ingot diameter was 163 mm, 11 mm when the ingot diameter was 115 mm, and 5.5 mm when the ingot diameter was 63 mm. The average ingot height was 13 mm when the ingot diameter was 163 mm, 8 mm when the ingot diameter was 115 mm, and 4 mm when the ingot diameter was 63 mm. And the inclination angle which shows the flatness of the surface was 10 degrees or less on average, and there was sufficient flatness.

  On the other hand, in the ingot of the comparative example, a (0001) facet surface was generated at the center of the outermost surface of the ingot. The width in the off-angle direction of the (0001) facet surface was in the range of 12% to 45% of the ingot diameter. In addition, the inclination angle indicating the flatness of the surface exceeded 10 ° on average.

About the board:
In the substrate cut out from the ingot of the example, a high concentration nitrogen region having a relatively high nitrogen concentration was formed in a region located under the (0001) facet surface (region located at the end of the substrate). The arrangement of the high concentration nitrogen region almost coincided with the position of the facet. Further, although there is a distribution in the height direction of the ingot, the width of the high concentration nitrogen region is generally in the range of 3 to 9.5% with respect to the ingot diameter.

  On the other hand, also for the substrate cut out from the ingot of the comparative example, a high-concentration nitrogen region was formed in the region located under the (0001) facet surface (region located in the center of the substrate). The high-concentration nitrogen region in the comparative example also almost coincided with the facet position. Further, in the height direction of the ingot, there was a distribution of the size of the high concentration nitrogen region, and the width of the high concentration nitrogen region was in the range of 5 to 45% with respect to the ingot diameter. Even in the comparative example, there was a portion where the width (size) of the high concentration region was 10% or less with respect to the ingot diameter, but this was a region of 5 mm or less from the surface position of the base substrate. This is because, in this range, the flatness on the surface of the grown silicon carbide is relatively maintained because the total growth amount of silicon carbide is still small, and the flatness is always maintained during crystal growth. The result is different from the example.

About nitrogen concentration:
Regarding the substrate of the example, the nitrogen concentration in the high concentration nitrogen region was 1.2E19 cm ⁻³ , and the nitrogen concentration in other regions was 8E18 to 1E19 cm ⁻³ . Further, the nitrogen concentration at any five points in the region other than the high concentration nitrogen region was in a range of 20% with respect to the average concentration at the five points.

Regarding the substrate of the comparative example, the nitrogen concentration in the high concentration nitrogen region was 1.2E19 cm ⁻³ , and the nitrogen concentration in other regions was 8E18 to 1E19 cm ⁻³ .

About transmittance:
About the board | substrate of an Example and a comparative example, the transmittance | permeability of the light whose wavelength is 400-500 nm was 10-20% in the high concentration nitrogen area | region. Moreover, the transmittance | permeability was 25 to 35% in the other area | region in the said board | substrate. Further, regarding a silicon carbide substrate cut out from a low nitrogen-doped ingot different from this experiment, the transmittance in the high concentration nitrogen region is 35 to 45%, and in the other regions, the transmittance is 45 to 65%. It was. Moreover, all the refractive indexes of the silicon carbide substrate obtained by calculating from the wavelength characteristics of the transmittance were 2.5 to 2.8.

About dislocation density:
The measurement was performed on the substrate obtained by slicing at a position 20 mm from the base substrate in the ingot. Here, the dislocation density of the base substrate, the micropipe density ^{(MPD): 10~100 / cm -2} , the etch pit density (EPD): When 1~5E4cm ^-2, the substrate examples, a high concentration of nitrogen Outside the region, both MPD and EPD could be reduced from 1/2 to 1/20 with respect to the base substrate.

  On the other hand, in the case of the substrate of the comparative example, the MPD and EPD were reduced to 1/2 to 2.5 with respect to the base substrate, but there were cases where it increased on the contrary.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is particularly advantageously applied to a method for manufacturing a silicon carbide ingot and a silicon carbide substrate.

  1 base substrate, 2 support member, 3 temperature adjusting member, 4 surface, 5 facet surface, 6 high concentration nitrogen region, 7 low concentration nitrogen region, 8 straight line, 9 outermost surface, 10 ingot, 11 crucible, 12 coil, 13 arrow , 14 Center part, 15 End part, 16 Outermost peripheral part, 17 Facet side upper end part, 18 Facet side outermost peripheral part, 20 Silicon carbide substrate, 21 Recessed part, 25 circumscribed circle, 26 arrows.

Claims (8)

The off angle in the off angle direction which is either the <11-20> direction or the <1-100> direction with respect to the (0001) plane is 0.1 ° or more and 10 ° or less, and the diameter is 50 mm to 180 mm. Preparing a base substrate made of single crystal silicon carbide;
And a step of growing a silicon carbide layer on the surface of the base substrate,
In the step of growing the silicon carbide layer, when the crossing angle in which the <0001> direction axis of the base substrate crosses the surface of the base substrate is considered in the off-angle direction, the crossing angle becomes an acute angle. Forming an area having a (0001) facet surface on the surface of the grown silicon carbide layer at the upstream end which is the side;
In the step of growing the silicon carbide layer, the temperature of the center portion of the surface of the grown silicon carbide layer is Ta, the temperature of the outermost peripheral portion is Tc, and the distance from the outermost peripheral portion is the diameter of the silicon carbide layer. When the temperature of the end region, which is a position within 10%, is Tb,
Tc> Tb ≧ Ta
And satisfy the condition
A silicon carbide ingot satisfying a condition that a temperature gradient defined as (absolute value of difference between temperature Ta and temperature Tb) / (distance between the central portion and the end region) is 10 ° C./cm or less. Manufacturing method.   In the silicon carbide layer after the step of growing the silicon carbide layer, a portion located below the region having the (0001) facet surface is located below the region having the (0001) facet surface in the silicon carbide layer. The method for manufacturing a silicon carbide ingot according to claim 1, wherein the silicon carbide ingot is a high-concentration nitrogen region in which a nitrogen concentration is higher than a portion other than the portion.   The method for manufacturing a silicon carbide ingot according to claim 2, wherein a width of the high-concentration nitrogen region in the off-angle direction is 1/10 or less of a width of the base substrate in the off-angle direction.   The method for manufacturing a silicon carbide ingot according to claim 2, further comprising a step of removing the high concentration nitrogen region.   The transmittance of light having a wavelength of 450 nm or more and 500 nm or less per unit thickness in the high concentration nitrogen region is the transmission of the light per unit thickness in a portion other than the high concentration nitrogen region in the silicon carbide layer. The manufacturing method of the silicon carbide ingot of any one of Claims 2-4 lower than a rate.   The micropipe density of the portion located under the region having the (0001) facet surface is higher than the micropipe density in the portion other than the portion located under the region having the (0001) facet surface in the silicon carbide layer. The manufacturing method of the silicon carbide ingot of any one of Claims 1-5.   The maximum curvature radius on the surface of the silicon carbide layer after the step of growing the silicon carbide layer is at least three times the radius of a circumscribed circle related to the planar shape of the base substrate. 2. A method for producing a silicon carbide ingot according to item 1. Using the method for producing a silicon carbide ingot according to claim 1, comprising preparing a silicon carbide ingot;
In the step of preparing the silicon carbide ingot, a portion of the silicon carbide layer after the step of growing the silicon carbide layer that is located below the region having the (0001) facet plane is the (0001) in the silicon carbide layer. ) It is a high concentration nitrogen region where the nitrogen concentration is higher than the portion other than the portion located under the region having the facet surface,
Removing the high concentration nitrogen region from the silicon carbide ingot;
And a step of slicing the silicon carbide ingot after performing the step of removing the high-concentration nitrogen region.

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