WO2024048157A1 - Silicon carbide substrate, method for producing silicon carbide substrate, method for producing silicon carbide single crystal, epitaxial substrate, and method for producing semiconductor device - Google Patents

Abstract

A silicon carbide substrate according to the present invention has a main surface. The main surface is composed of an outer peripheral part which is a portion within 5 mm from the outer peripheral edge of the main surface, and a central part which is surrounded by the outer peripheral part. The central part is composed of a central region which has a diameter that is equal to a half of the maximum diameter of the main surface, and which is centered on the center of the main surface, and an outer peripheral region which surrounds the central region. The average nitrogen concentration in the central region is higher than the average nitrogen concentration in the outer peripheral region. The average nitrogen concentration in the central region is 1 × 10¹⁶ cm^-3 or less. The electrical resistance at any given position in the central part is 1 × 10⁶ Ωcm or more. The (0001) misorientation between any given two points, which are 1 cm away from each other, in the central part is 35 seconds or less.

Description

Silicon carbide substrate, method for manufacturing silicon carbide substrate, method for manufacturing silicon carbide single crystal, method for manufacturing epitaxial substrate and semiconductor device

The present disclosure relates to a silicon carbide substrate, a method for manufacturing a silicon carbide substrate, a method for manufacturing a silicon carbide single crystal, an epitaxial substrate, and a method for manufacturing a semiconductor device. This application claims priority based on Japanese Patent Application No. 2022-138114, which is a Japanese patent application filed on August 31, 2022. All contents described in the Japanese patent application are incorporated herein by reference.

JP 2015-13761 A (Patent Document 1) describes a silicon carbide single crystal substrate in which the {0001} plane orientation difference between two arbitrary points 1 cm apart in the main surface is 35 seconds or less. .

Japanese Patent Application Publication No. 2015-13761

A silicon carbide substrate according to the present disclosure includes a main surface. The main surface is composed of an outer peripheral part within 5 mm from the outer peripheral edge of the main surface, and a central part surrounded by the outer peripheral part. The central portion includes a central region having a diameter that is half the maximum diameter of the main surface and centered on the center of the main surface, and an outer peripheral region surrounding the central region. The average value of nitrogen concentration in the central region is higher than the average value of nitrogen concentration in the peripheral region. The average value of the nitrogen concentration in the central region is 1×10 ¹⁶ cm ⁻³ or less. In the central portion, the electrical resistivity at any position is 1×10 ⁶ Ωcm or more. In the center, the {0001} plane orientation difference between any two points 1 cm apart is 35 seconds or less.

FIG. 1 is a schematic plan view showing the configuration of a silicon carbide substrate according to the first embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. FIG. 3 is a schematic plan view showing measurement points of X-ray diffraction. FIG. 4 is an enlarged view of region IV in FIG. FIG. 5 is a schematic cross-sectional view for explaining the {0001} plane orientation difference. FIG. 6 is a flow diagram outlining the method for manufacturing a silicon carbide substrate according to this embodiment. FIG. 7 is a schematic plan view showing the configuration of the third main surface of the seed substrate. FIG. 8 is a schematic cross-sectional view taken along line VIII-VIII in FIG. 7. FIG. 9 is a partially cross-sectional schematic diagram showing the structure of the crucible. FIG. 10 is a schematic cross-sectional view showing a silicon carbide crystal growth process. FIG. 11 is a schematic plan view showing the configuration of a growth surface of silicon carbide crystal. FIG. 12 is a schematic cross-sectional view showing a step of heating silicon carbide crystal. FIG. 13 is a schematic cross-sectional view showing a step of cutting a silicon carbide crystal. FIG. 14 is a flowchart schematically showing a method for manufacturing a semiconductor device according to this embodiment. FIG. 15 is a schematic cross-sectional view showing a step of forming a buffer layer on a silicon carbide substrate. FIG. 16 is a schematic cross-sectional view showing a step of forming an electron transit layer and an electron supply layer. FIG. 17 is a schematic cross-sectional view showing the configuration of the semiconductor device according to this embodiment.

[Problems to be solved by this disclosure]

An object of the present disclosure is to reduce variations in characteristics of semiconductor devices.
[Effects of this disclosure]

According to the present disclosure, variations in characteristics of semiconductor devices can be reduced.
[Description of embodiments of the present disclosure]

First, embodiments of the present disclosure will be listed and described.

(1) Silicon carbide substrate 100 according to the present disclosure includes main surface 1. The main surface 1 includes an outer peripheral part 20 within 5 mm from the outer peripheral edge of the main surface 1, and a central part 10 surrounded by the outer peripheral part 20. The central portion 10 includes a central region 11 having a diameter half the maximum diameter of the main surface 1 and centered on the center of the main surface 1, and an outer peripheral region 12 surrounding the central region 11. The average value of the nitrogen concentration in the central region 11 is higher than the average value of the nitrogen concentration in the outer peripheral region 12. The average value of the nitrogen concentration in the central region 11 is 1×10 ¹⁶ cm ⁻³ or less. In the central portion 10, the electrical resistivity at any position is 1×10 ⁶ Ωcm or more. In the central portion 10, the {0001} plane orientation difference between any two points 1 cm apart is 35 seconds or less.

(2) According to the silicon carbide substrate 100 according to (1) above, the p-type impurity and the compensation impurity do not need to be doped.

(3) According to the silicon carbide substrate 100 according to (1) or (2) above, the value obtained by dividing the average value of the nitrogen concentration in the outer peripheral region 12 by the average value of the nitrogen concentration in the central region 11 is 0.7 or more. It may be 0.9 or less.

(4) According to the silicon carbide substrate 100 according to (1) or (2) above, the average value of the nitrogen concentration in the outer peripheral region 12 is 1×10 ¹⁵ cm ⁻³ or more and less than 1×10 ¹⁶ cm ⁻³ . It's okay.

(5) According to the silicon carbide substrate 100 according to any one of (1) to (4) above, the maximum diameter may be 100 mm or more.

(6) According to silicon carbide substrate 100 according to any one of (1) to (5) above, the angle between main surface 1 and {0001} plane may be 1° or less.

(7) According to silicon carbide substrate 100 according to any one of (1) to (6) above, the polytype of silicon carbide that constitutes silicon carbide substrate 100 may be 4H.

(8) Epitaxial substrate 200 according to the present disclosure includes silicon carbide substrate 100 according to any one of (1) to (7) above, nitride epitaxial layer 30 provided on silicon carbide substrate 100, It is equipped with

(9) A method for manufacturing a semiconductor device 400 according to the present disclosure includes the following steps. The epitaxial substrate 200 described in (8) above is prepared. Electrodes are formed on epitaxial substrate 200.

(10) The method for manufacturing silicon carbide single crystal 59 according to the present disclosure includes the following steps. Seed substrate 150 having main surface 1 and silicon carbide raw material 156 are prepared. By sublimating silicon carbide raw material 156, silicon carbide crystal 57 grows on main surface 151. After the process of growing silicon carbide crystals 57 on main surface 151 by sublimating silicon carbide raw material 156, the electrical resistivity of silicon carbide crystals 57 is increased by heating silicon carbide crystals 57 at a temperature of 2000° C. or higher. do. The main surface 151 includes an outer peripheral part 120 within 5 mm from the outer peripheral edge of the main surface 151 and a central part 110 surrounded by the outer peripheral part 120. In the central portion 110, the {0001} plane orientation difference between any two points 1 cm apart is 35 seconds or less. Growth surface 50 of silicon carbide crystal 57 includes a first region 51 having a diameter half the maximum diameter of silicon carbide crystal 57 and centered at the center of the growth surface, and a second region 52 surrounding first region 51. It is made up of. In the step of growing silicon carbide crystal 57 on main surface 151 by sublimating silicon carbide raw material 156, the {0001} facet is exposed to first region 51 and not exposed to second region 52.

(11) According to the method for manufacturing silicon carbide single crystal 59 described in (10) above, the angle between main surface 151 and the {0001} plane may be 1° or less.

(12) In the method for manufacturing silicon carbide substrate 100 according to the present disclosure, silicon carbide single crystal 59 is prepared using the method for manufacturing silicon carbide single crystal 59 described in (10) or (11) above. Silicon carbide single crystal 59 is cut. The angle between cut surface 58 of silicon carbide single crystal 59 and the {0001} plane is 1° or less.
[Details of embodiments of the present disclosure]

Hereinafter, details of embodiments of the present disclosure will be described based on the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals, and the description thereof will not be repeated. In the crystallographic descriptions in this specification, individual orientations are indicated by [], collective orientations are indicated by <>, individual planes are indicated by (), and collective planes are indicated by {}, respectively. Regarding negative indexes, a "-" (bar) is supposed to be placed above the number in terms of crystallography, but in this specification, a negative sign is placed in front of the number.

First, the configuration of silicon carbide substrate 100 according to the first embodiment will be described. FIG. 1 is a schematic plan view showing the configuration of silicon carbide substrate 100 according to the first embodiment.

As shown in FIG. 1, silicon carbide substrate 100 according to the first embodiment has main surface 1 (first main surface 1). The first main surface 1 extends along each of a first direction 101 and a second direction 102. The first direction 101 is, for example, the <11-20> direction, although it is not particularly limited. The second direction 102 is, for example, the <1-100> direction, although it is not particularly limited. The polytype of silicon carbide constituting silicon carbide substrate 100 may be 4H.

FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. The cross section shown in FIG. 2 is perpendicular to the first main surface 1 and parallel to the first direction 101. As shown in FIG. 2, silicon carbide substrate 100 according to this embodiment has second main surface 2 and first outer circumferential side surface 3. As shown in FIG. The first main surface 1 is on the opposite side of the second main surface 2. The first outer peripheral side surface 3 is continuous with each of the first main surface 1 and the second main surface 2. The thickness of silicon carbide substrate 100 is, for example, 300 μm or more and 700 μm or less. The third direction 103 is a direction perpendicular to each of the first direction 101 and the second direction 102. The thickness direction of silicon carbide substrate 100 is third direction 103 .

The first principal surface 1 is a {0001} plane or a plane inclined in the off direction with respect to the {0001} plane. The first principal surface 1 is, for example, a (0001) plane or a plane inclined in the off direction with respect to the (0001) plane. In this case, the second principal surface 2 (see FIG. 2) is, for example, a (000-1) plane or a plane inclined in the off direction with respect to the (000-1) plane.

The first main surface 1 may be, for example, a (000-1) plane or a plane inclined in the off direction with respect to the (000-1) plane. In this case, the second principal surface 2 (see FIG. 2) is, for example, a (0001) plane or a plane inclined in the off direction with respect to the (0001) plane. The off direction is, for example, the first direction 101, although it is not particularly limited.

As shown in FIG. 2, the angle between the first principal surface 1 and the {0001} plane is a third angle θ3. The third angle θ3 is, for example, 1° or less. The third angle θ3 is not particularly limited, but may be, for example, 0.8° or less, 0.6° or less, or 0.4° or less. The third angle θ3 is not particularly limited, but may be, for example, 0.1° or more.

Referring to FIG. 1, the maximum diameter of the first main surface 1 is the first diameter W1. The first diameter W1 is, for example, 100 mm or more. The first diameter W1 may be, for example, 150 mm or more, or 200 mm or more. The first diameter W1 is not particularly limited, but may be, for example, 300 mm or less. The first main surface 1 has a first outer peripheral edge 4 . When viewed in a direction perpendicular to the first main surface 1, the first diameter W1 is the longest straight distance between two different points on the first outer peripheral edge 4.

The first main surface 1 is composed of a first outer peripheral portion 20 and a first central portion 10. The first outer circumferential portion 20 is a portion within 5 mm from the first outer circumferential edge 4 of the first main surface 1 . From another perspective, when viewed in a direction perpendicular to the first main surface 1, the first outer peripheral edge 4, the first outer peripheral part 20, and the first central part 10 in the radial direction of the first main surface 1 The distance from the boundary (third distance W3) is 5 mm. The first central portion 10 is surrounded by a first outer peripheral portion 20. The first central portion 10 is continuous with the first outer peripheral portion 20.

The first central portion 10 is composed of a first central region 11 and a first outer peripheral region 12. The first outer peripheral region 12 surrounds the first central region 11 . The first outer peripheral region 12 is continuous with the first central region 11 . The first outer peripheral region 12 is annular. When viewed in a direction perpendicular to the first main surface 1, the first central region 11 is circular. The first central region 11 has a diameter that is half the maximum diameter (first diameter W1) of the first main surface 1. The diameter of the first central region 11 is the second diameter W2. The second diameter W2 is half the first diameter W1. The first central region 11 is a circle centered on the center 13 of the first main surface 1 . From another perspective, the center 13 of the first central region 11 coincides with the center 13 of the first main surface 1.

Silicon carbide substrate 100 contains nitrogen as an n-type impurity. The average value of the nitrogen concentration in the first central region 11 is higher than the average value of the nitrogen concentration in the first peripheral region 12. The average value of the nitrogen concentration in the first central region 11 is 1×10 ¹⁶ cm ⁻³ or less. The average value of the nitrogen concentration in the first central region 11 is not particularly limited, but may be, for example, 1×10 ¹⁵ cm ⁻³ or more, or 2×10 ¹⁵ cm ⁻³ or more. In any region of the first central region 11, the nitrogen concentration may be 1×10 ¹⁶ cm ⁻³ or less. In any region of the first central region 11, the nitrogen concentration may be 1×10 ¹⁵ cm ⁻³ or more.

The average value of the nitrogen concentration in the first outer peripheral region 12 may be 1×10 ¹⁵ cm ⁻³ or more and less than 1×10 ¹⁶ cm ⁻³ . The average value of the nitrogen concentration in the first outer peripheral region 12 is not particularly limited, but may be, for example, 1.5×10 ¹⁵ cm ⁻³ or more, or 2×10 ¹⁵ cm ⁻³ or more. The average value of the nitrogen concentration in the first outer peripheral region 12 is not particularly limited, but may be, for example, 9×10 ¹⁵ cm ⁻³ or less, or 8×10 ¹⁵ cm ⁻³ or less.

The value obtained by dividing the average value of the nitrogen concentration in the first outer peripheral region 12 by the average value of the nitrogen concentration in the first central region 11 may be, for example, 0.7 or more and 0.9 or less. The value obtained by dividing the average value of the nitrogen concentration in the first peripheral region 12 by the average value of the nitrogen concentration in the first central region 11 is not particularly limited, but may be, for example, 0.72 or more, or 0.74 or more. It may be. The value obtained by dividing the average value of the nitrogen concentration in the first peripheral region 12 by the average value of the nitrogen concentration in the first central region 11 is not particularly limited, but may be, for example, 0.88 or less, or 0.86 or less. It may be.

Silicon carbide substrate 100 does not need to be doped with p-type impurities and compensation impurities. Specifically, silicon carbide substrate 100 is not actively doped with p-type impurities and compensation impurities during the manufacturing process. P-type impurities and compensation impurities may be incorporated into silicon carbide substrate 100 as unintended impurities during the manufacturing process. If the concentration of each of the p-type impurity and the compensation impurity is 1×10 ¹⁶ cm ⁻³ or less, it is determined that the p-type impurity and the compensation impurity are not doped.

The p-type impurity is, for example, aluminum (Al) or boron (B). A compensation impurity is an impurity having a deep level. Specifically, the compensation impurity is vanadium (V) or titanium (Ti).

The concentration of impurities is measured, for example, by secondary ion mass spectrometry (SIMS). In SIMS, for example, IMS7f, which is a secondary ion mass spectrometer manufactured by Cameca, can be used. As the measurement conditions in SIMS, for example, the primary ion is O ₂ ⁺ and the primary ion energy is 8 keV.

In the first central portion 10, the electrical resistivity at any position is 1×10 ⁶ Ωcm or more. The electrical resistivity in the first central portion 10 is not particularly limited, but may be, for example, 1×10 ⁸ Ωcm or more, 1×10 ¹⁰ Ωcm or more, or 1×10 ¹² Ωcm or more. There may be. The electrical resistivity in the first central portion 10 is not particularly limited, but may be, for example, 1×10 ¹⁴ Ωcm or less, or 1×10 ¹³ Ωcm or less.

The electrical resistivity of the first central portion 10 is measured using, for example, COREMA-WT, which is an electrical resistivity measuring device manufactured by Semimap. The voltage applied to the object to be measured is, for example, 5.0V.

Next, a method for measuring the {0001} plane orientation difference will be explained. The surface orientation difference at any position within the first principal surface 1 can be measured by, for example, X-ray diffraction. For example, Cu-Kα1 is used as an X-ray source, and the (0004) peak is measured. The wavelength is 1.5405 angstroms (monochromatic).

FIG. 3 is a schematic plan view showing measurement points for X-ray diffraction. As shown in FIG. 3, the {0001} plane orientation difference is measured at 49 (7 points x 7 points) measurement points 5 on the first principal surface 1. Along the first direction 101, seven X-ray diffraction measurement points 5 are arranged at 1 cm intervals. Similarly, along the second direction 102, seven X-ray diffraction measurement points 5 are arranged at 1 cm intervals. One of the measurement points 5 may be located at the center of the first main surface 1.

FIG. 4 is an enlarged view of region IV in FIG. 3. The measurement point 5 has a first measurement position 61 and a second measurement position 62. For example, at the first measurement position 61 within the first principal surface 1, the {0001} plane orientation is measured using X-rays. The X-ray spot diameter D is, for example, 3 mm. When measuring the {0001} plane orientation at the first measurement position 61, the center of the X-ray spot is adjusted to be located at the first measurement position 61. Similarly, when measuring the {0001} plane orientation at a second measurement position 62 1 cm away from the first measurement position 61, the X-ray spot is adjusted so that the center of the X-ray spot coincides with the second measurement position 62. The position of is adjusted. In other words, the center of the first X-ray spot S1 and the center of the second X-ray spot S2 are 1 cm apart.

Next, the {0001} plane orientation difference will be explained. FIG. 5 is a schematic cross-sectional view for explaining the {0001} plane orientation difference. The diagram shown in FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. When observing the vicinity of first main surface 1 of silicon carbide substrate 100 in detail, silicon carbide substrate 100 is composed of a large number of domains with slightly different plane orientations. In other words, even when first principal surface 1 of silicon carbide substrate 100 is a {0001} plane on average, the {0001} plane orientation at each position within the plane of first principal surface 1 is It is slightly shifted from the normal direction n of surface 1.

As shown in FIG. 5, the {0001} plane orientation c1 at the first measurement position 61 of the first principal surface 1 is shifted in a certain direction by a first angle θ1 from the normal direction n of the first principal surface 1. There is. Similarly, the {0001} plane orientation c2 at the second measurement position 62, which is 1 cm away from the first measurement position 61, is shifted in a certain direction by a second angle θ2 from the normal direction n of the first principal surface 1. .

In this embodiment, the {0001} plane orientation difference is the absolute value of the difference between the first angle θ1 and the second angle θ2. That is, the {0001} plane orientation is measured at two arbitrary points separated by 1 cm, and the {0001} plane orientation difference between the two points is calculated.

According to the silicon carbide substrate 100 according to the present embodiment, the {0001} plane orientation difference between any two points 1 cm apart in the first central portion 10 is 35 seconds or less. The {0001} plane orientation difference between any two points separated by 1 cm is not particularly limited, but may be, for example, 33 seconds or less, or 31 seconds or less. The {0001} plane orientation difference between any two points 1 cm apart is not particularly limited, but may be, for example, 10 seconds or more, 15 seconds or more, or 20 seconds or more. It may be 25 seconds or more.

<Method for manufacturing silicon carbide substrate>

Next, a method for manufacturing silicon carbide substrate 100 according to this embodiment will be described. FIG. 6 is a flow diagram showing an overview of the method for manufacturing silicon carbide substrate 100 according to this embodiment. As shown in FIG. 6, the method for manufacturing silicon carbide substrate 100 according to the present embodiment includes a step of preparing a seed substrate and a silicon carbide raw material (S10), a step of growing a silicon carbide crystal (S20), The method mainly includes a step of heating the silicon carbide crystal (S30) and a step of cutting the silicon carbide crystal (S40).

First, a seed substrate 150 is prepared. Seed substrate 150 has a third main surface 151. FIG. 7 is a schematic plan view showing the configuration of the third main surface 151 of the seed substrate 150. As shown in FIG. 7, the third main surface 151 extends along each of the first direction 101 and the second direction 102. The first direction 101 is, for example, the <11-20> direction, although it is not particularly limited. The second direction 102 is, for example, the <1-100> direction, although it is not particularly limited. The polytype of silicon carbide constituting seed substrate 150 may be 4H.

FIG. 8 is a schematic cross-sectional view taken along line VIII-VIII in FIG. 7. The cross section shown in FIG. 8 is perpendicular to the third main surface 151 and parallel to the first direction 101. As shown in FIG. 8, the seed substrate 150 has a fourth main surface 152 and a second outer peripheral side surface 153. The fourth main surface 152 is on the opposite side of the third main surface 151. The second outer peripheral side surface 153 is continuous with each of the third main surface 151 and the fourth main surface 152. The third direction 103 is a direction perpendicular to each of the first direction 101 and the second direction 102.

The third principal surface 151 is a {0001} plane or a plane inclined in the off direction with respect to the {0001} plane. The first principal surface 1 is, for example, a (0001) plane or a plane inclined in the off direction with respect to the (0001) plane. In this case, the fourth principal surface 152 (see FIG. 8) is, for example, a (000-1) plane or a plane inclined in the off direction with respect to the (000-1) plane.

The third principal surface 151 may be, for example, a (000-1) plane or a plane inclined in the off direction with respect to the (000-1) plane. In this case, the fourth principal surface 152 (see FIG. 8) is, for example, a (0001) plane or a plane inclined in the off direction with respect to the (0001) plane. The off direction is, for example, the first direction 101, although it is not particularly limited.

The angle between the third principal surface 151 and the {0001} plane is a fourth angle θ4. The fourth angle θ4 is, for example, 1° or less. The fourth angle θ4 is not particularly limited, but may be, for example, 0.8° or less, 0.6° or less, or 0.4° or less. The fourth angle θ4 is not particularly limited, but may be, for example, 0.1° or more.

Referring to FIG. 7, the maximum diameter of the third main surface 151 is a fourth diameter W4. The fourth diameter W4 is, for example, 100 mm or more. The fourth diameter W4 may be, for example, 150 mm or more, or 200 mm or more. The fourth diameter W4 is not particularly limited, but may be, for example, 300 mm or less. The third main surface 151 has a second outer peripheral edge 154. When viewed in a direction perpendicular to the third main surface 151, the fourth diameter W4 is the longest straight distance between two different points on the second outer peripheral edge 154.

As shown in FIG. 7, the third main surface 151 is composed of a second outer peripheral portion 120 and a second central portion 110. The second outer peripheral portion 120 is a portion within 5 mm from the second outer peripheral edge 154 of the third main surface 151. From another perspective, when viewed in a direction perpendicular to the third main surface 151, the second outer peripheral edge 154, the second outer peripheral portion 120, and the second central portion 110 in the radial direction of the third main surface 151 The distance from the boundary (sixth distance W6) is 5 mm. The second central portion 110 is surrounded by a second outer peripheral portion 120. The second central portion 110 is continuous with the second outer peripheral portion 120.

The second central portion 110 is composed of a second central region 111 and a second outer peripheral region 112. The second outer peripheral region 112 surrounds the second central region 111 . The second outer peripheral region 112 is continuous with the second central region 111. The second outer peripheral region 112 is annular. When viewed in a direction perpendicular to the third main surface 151, the second central region 111 is circular. The second central region 111 has a diameter that is half the maximum diameter of the third main surface 151. The diameter of the second central region 111 is a fifth diameter W5. The fifth diameter W5 is half the fourth diameter W4. The second central region 111 is a circle centered on the center 113 of the third main surface 151. From another perspective, the center 113 of the second central region 111 coincides with the center 113 of the third main surface 151.

In the second central portion 110, the {0001} plane orientation difference between any two points 1 cm apart is 35 seconds or less. The {0001} plane orientation difference between any two points separated by 1 cm is not particularly limited, but may be, for example, 33 seconds or less, or 31 seconds or less. The {0001} plane orientation difference between any two points 1 cm apart is not particularly limited, but may be, for example, 8 seconds or more, 12 seconds or more, or 20 seconds or more. It may be 25 seconds or more.

Next, a step (S20) of growing silicon carbide crystals is performed. FIG. 9 is a schematic partial cross-sectional view showing the structure of the crucible. The crucible 130 is made of graphite. The crucible 130 has a housing section 132 and a lid section 131. The lid part 131 is arranged on the accommodating part 132. An induction heating coil (not shown) is arranged helically around the outer periphery of crucible 130. By applying electric power to the induction heating coil, the crucible 130 is heated by electromagnetic induction.

As shown in FIG. 9, silicon carbide raw material 156 is placed in storage portion 132. Silicon carbide raw material 156 is, for example, polycrystalline silicon carbide powder. Seed substrate 150 is fixed to lid 131 using, for example, an adhesive (not shown). Seed substrate 150 has a third main surface 151 and a fourth main surface 152. Third main surface 151 faces silicon carbide raw material 156. The fourth main surface 152 faces the lid portion 131. Third main surface 151 of seed substrate 150 is arranged to face the surface of silicon carbide raw material 156. As described above, seed substrate 150 and silicon carbide raw material 156 are placed in crucible 130.

FIG. 10 is a schematic cross-sectional view showing the growth process of silicon carbide crystal 57. First, the pressure in crucible 130 is reduced while the temperature of third main surface 151 of seed substrate 150 is lower than the temperature of silicon carbide raw material 156. The pressure of the atmospheric gas in the crucible 130 is reduced to, for example, 1.0 kPa. As a result, silicon carbide raw material 156 starts to sublimate, and the sublimated silicon carbide gas recrystallizes on third main surface 151 of seed substrate 150 . On third principal surface 151, silicon carbide crystal 57 grows as a single crystal. While silicon carbide crystal 57 is growing, the pressure within crucible 130 is maintained at, for example, approximately 0.1 kPa or more and 3 kPa or less.

As described above, by sublimating silicon carbide raw material 156, silicon carbide crystal 57 grows on third main surface 151. In the step of growing silicon carbide crystal 57, the temperature of silicon carbide crystal 57 is, for example, 2100° C. or more and 2300° C. or less. The temperature of silicon carbide crystal 57 is not particularly limited, and may be, for example, 2125° C. or higher, or 2150° C. or higher. The temperature of silicon carbide crystal 57 is not particularly limited, and may be, for example, 2250° C. or lower, or 2275° C. or lower.

As shown in FIG. 10, silicon carbide crystal 57 has a growth surface 50 facing silicon carbide raw material 156. As silicon carbide crystal 57 grows, growth surface 50 approaches silicon carbide raw material 156. From another perspective, from the start of crystal growth to the end of crystal growth, growth surface 50 of silicon carbide crystal 57 moves toward silicon carbide raw material 156. As silicon carbide crystal 57 grows, the diameter of silicon carbide crystal 57 increases. Silicon carbide crystal 57 has a third central region 55 and a third outer peripheral region 56. The third central region 55 is a region formed by stacking {0001} facet surfaces. The third outer peripheral region 56 surrounds the third central region 55. The third outer peripheral region 56 is a region formed by stacking non-facet surfaces.

FIG. 11 is a schematic plan view showing the configuration of a growth surface 50 of silicon carbide crystal 57. As shown in FIG. 11, growth surface 50 of silicon carbide crystal 57 is composed of a first region 51 and a second region 52. First region 51 has a diameter that is half the maximum diameter of silicon carbide crystal 57 . The maximum diameter of silicon carbide crystal 57 is seventh diameter W7. The diameter of the first region 51 is the eighth diameter W8. The eighth diameter W8 is half the seventh diameter W7. The center of the first region 51 coincides with the center of the growth surface 50. The second region 52 surrounds the first region 51. The second region 52 is continuous with the first region 51.

In the step of growing silicon carbide crystal 57 on third principal surface 151 by sublimating silicon carbide raw material 156, {0001} facet surface 60 is exposed to first region 51 and exposed to second region 52. do not. As shown in FIG. 11, the {0001} facet surface 60 is exposed in at least a portion of the first region 51. The {0001} facet surface 60 may include the center 53 of the growth surface 50. The {0001} facet surface 60 may be a (0001) facet surface or a (000-1) facet surface.

On the facet surface 60, steps (not shown) may be formed in a spiral shape around the dislocation line of the screw dislocation. Silicon carbide crystal 57 may be grown in a spiral step flow manner using screw dislocation as a step source. In the growth surface 50, the region other than the facet surface is a non-facet surface. The non-faceted surface is exposed in the second region 52. A portion of the non-facet surface may be exposed to the first region 51.

Compared to non-facet surfaces, nitrogen is more likely to be taken in on facet surfaces. Therefore, the nitrogen concentration on the facet surface is higher than the nitrogen concentration on the non-facet surface. The nitrogen concentration in the first region 51 may be higher than the nitrogen concentration in the second region 52.

As shown in FIG. 11, the maximum diameter of the {0001} facet surface 60 when viewed in the direction perpendicular to the third principal surface 151 is the ninth diameter W9. The ninth diameter W9 is smaller than the eighth diameter W8. The ninth diameter W9 is not particularly limited, but may be, for example, 0.1 times or more, or 0.2 times or more the seventh diameter W7.

Next, a step (S30) of heating the silicon carbide crystal is performed. FIG. 12 is a schematic cross-sectional view showing a step of heating silicon carbide crystal 57.

After silicon carbide crystal 57 is removed from crucible 130 , it is placed inside heating device 301 . As shown in FIG. 12, silicon carbide crystal 57 is annealed with silicon carbide crystal 57 disposed inside heating device 301. As shown in FIG. Silicon carbide crystal 57 is heated, for example, at a temperature of 2000° C. or higher. Silicon carbide crystal 57 is heated, for example, in an argon atmosphere at a temperature of 2500° C. or higher for about one hour.

Next, silicon carbide crystal 57 is rapidly cooled. As a result, point defects are formed in silicon carbide crystal 57. As a result, the electrical resistivity of silicon carbide crystal 57 increases. The electrical resistivity of silicon carbide crystal 57 is, for example, 1×10 ¹² Ωcm or more. Through the above steps, silicon carbide single crystal 59 according to this embodiment is manufactured (see FIG. 13).

Next, a step (S40) of cutting the silicon carbide single crystal is performed. FIG. 13 is a schematic cross-sectional view showing a step of cutting a silicon carbide single crystal. For example, silicon carbide single crystal 59 is sliced along a plane perpendicular to the central axis of silicon carbide single crystal 59 using a saw wire. In the step of cutting the silicon carbide single crystal (S40), the angle between the cut surface 58 of the silicon carbide single crystal 59 and the {0001} plane (fifth angle θ5) is 1° or less. In other words, silicon carbide single crystal 59 is cut such that the angle between first principal surface 1 of silicon carbide substrate 100 and the {0001} plane is 1° or less. Thereby, a plurality of silicon carbide substrates 100 according to this embodiment are obtained (see FIG. 1).

<Method for manufacturing semiconductor devices>

Next, a method for manufacturing the semiconductor device 400 according to this embodiment will be described. FIG. 14 is a flowchart schematically showing a method for manufacturing the semiconductor device 400 according to this embodiment. As shown in FIG. 14, the method for manufacturing a semiconductor device 400 according to this embodiment mainly includes a step of preparing an epitaxial substrate 200 (S1) and a step of forming an electrode on the epitaxial substrate 200 (S2). have.

First, a step (S1) of preparing the epitaxial substrate 200 is performed. In the step (S1) of preparing epitaxial substrate 200, first, silicon carbide substrate 100 according to this embodiment is prepared (see FIG. 1).

Next, buffer layer 31 is formed on silicon carbide substrate 100. FIG. 15 is a schematic cross-sectional view showing a step of forming buffer layer 31 on silicon carbide substrate 100. Buffer layer 31 is formed on first main surface 1 of silicon carbide substrate 100 by epitaxial growth. The buffer layer 31 is formed by, for example, MOCVD (Metal Organic Chemical Vapor Deposition).

The buffer layer 31 is made of aluminum gallium nitride (AlGaN), for example. The thickness of the buffer layer 31 is, for example, 150 nm. For example, TMA (trimethylaluminum) is used as a raw material gas for aluminum (Al). For example, TMG (trimethyl gallium) is used as a raw material for gallium (Ga). For example, ammonia is used as a raw material for nitrogen (N).

Next, an electron transit layer 32 and an electron supply layer 33 are formed. FIG. 16 is a schematic cross-sectional view showing the process of forming the electron transit layer 32 and the electron supply layer 33. First, the electron transit layer 32 is formed on the buffer layer 31 by MOCVD. The electron transit layer 32 is made of, for example, gallium nitride (GaN). The thickness of the electron transit layer 32 is, for example, 1 μm.

Next, an electron supply layer 33 is formed on the electron transit layer 32. The electron supply layer 33 is formed, for example, by MOCVD. The electron supply layer 33 is made of, for example, AlGaN. The thickness of the electron supply layer 33 is, for example, 20 μm. A two-dimensional electron gas is generated in a portion of the electron transit layer 32 near the interface between the electron transit layer 32 and the electron supply layer 33.

As described above, the epitaxial substrate 200 is prepared. As shown in FIG. 16, epitaxial substrate 200 includes silicon carbide substrate 100 and nitride epitaxial layer 30. The nitride epitaxial layer 30 includes a buffer layer 31, an electron transit layer 32, and an electron supply layer 33. Buffer layer 31 is provided on silicon carbide substrate 100. The electron transit layer 32 is provided on the buffer layer 31. The electron supply layer 33 is provided on the electron transit layer 32.

Next, a step of forming electrodes is performed. First, source electrode 41 and drain electrode 42 are formed. Specifically, a first resist pattern (not shown) is formed on the electron supply layer 33. In the first resist pattern, openings are formed in regions where the source electrode 41 and the drain electrode 42 are each formed.

Next, a first metal laminated film is formed on the first resist pattern using, for example, a vacuum evaporation method. The first metal laminated film includes, for example, a titanium (Ti) film and an aluminum (Al) film. Next, the first metal laminated film formed on the first resist pattern is removed by lift-off. As a result, a source electrode 41 and a drain electrode 42 made of the first metal laminated film are formed on the electron supply layer 33.

Next, alloying annealing may be performed. Specifically, source electrode 41 and drain electrode 42 are annealed. The annealing temperature is, for example, 600°C. Thereby, each of the source electrode 41 and the drain electrode 42 may be in ohmic contact with the electron supply layer 33.

Next, a gate electrode 43 is formed. Specifically, a second resist pattern (not shown) is formed on the electron supply layer 33. In the second resist pattern, an opening is formed in the region where the gate electrode 43 is to be formed.

Next, a second metal laminated film is formed on the second resist pattern using, for example, a vacuum evaporation method. The second metal laminated film includes, for example, a nickel (Ni) film and a gold (Au) film. Next, the second metal laminated film formed on the second resist pattern is removed by lift-off. As a result, a gate electrode 43 made of the second metal laminated film is formed on the electron supply layer 33.

FIG. 17 is a schematic cross-sectional view showing the configuration of a semiconductor device 400 according to this embodiment. The semiconductor device 400 is, for example, a field effect transistor, more specifically a high electron mobility transistor (HEMT). The semiconductor device 400 mainly includes an epitaxial substrate 200, a gate electrode 43, a source electrode 41, and a drain electrode 42.

As shown in FIG. 17, each of the gate electrode 43, source electrode 41, and drain electrode 42 is provided on the epitaxial substrate 200. Specifically, each of the gate electrode 43, the source electrode 41, and the drain electrode 42 is in contact with the electron supply layer 33. Gate electrode 43 may be located between source electrode 41 and drain electrode 42.

Next, the effects of the silicon carbide substrate, the method of manufacturing a silicon carbide substrate, the method of manufacturing a silicon carbide single crystal, the epitaxial substrate, and the method of manufacturing a semiconductor device according to the present embodiment will be described.

When producing silicon carbide crystal 57 having semi-insulating properties, heat treatment may be performed at a temperature of 2000° C. or higher while nitrogen taken into silicon carbide crystal 57 is reduced as much as possible. In this case, it was difficult to reduce the {0001} plane orientation difference in the main surface of silicon carbide substrate 100 obtained from silicon carbide crystal 57.

The inventor conducted extensive research into the cause of the large {0001} plane orientation difference on the principal surface of semi-insulating silicon carbide substrate 100, and as a result, obtained the following knowledge. Normally, when silicon carbide crystal 57 is grown using a sublimation method, temperature is controlled so that a {0001} facet is formed over a wide range of growth surface 50 of silicon carbide crystal 57.

However, the nitrogen concentration on the facet surface is higher than that on the non-facet surface. Nitrogen taken into silicon carbide crystal 57 on the facet plane causes a difference in lattice constant, which causes distortion and curves the crystal plane. As a result, the {0001} plane orientation difference becomes large on the main surface of silicon carbide substrate 100. Therefore, in order to reduce the {0001} plane orientation difference on the main surface of silicon carbide substrate 100, it is desirable to reduce the area of the facet plane.

Furthermore, if the {0001} plane orientation difference in the main surface of seed substrate 150 is large, the large {0001} plane orientation difference will also be inherited in silicon carbide crystal 57 formed on seed substrate 150. Therefore, in order to reduce the {0001} plane orientation difference on the main surface of silicon carbide substrate 100, it is desirable to reduce the {0001} plane orientation difference on the main surface of seed substrate 150.

In the method for manufacturing silicon carbide single crystal 59 according to the present disclosure, the {0001} plane orientation difference between any two points 1 cm apart in central portion 110 of main surface 151 of seed substrate 150 is 35 seconds or less. . Growth surface 50 of silicon carbide crystal 57 includes a first region 51 having a diameter half the maximum diameter of silicon carbide crystal 57 and centered on the center of growth surface 50, and a second region 52 surrounding first region 51. It is composed of. In the step of growing silicon carbide crystal 57 on main surface 151 by sublimating silicon carbide raw material 156, {0001} facet surface 60 is exposed to first region 51 and not exposed to second region 52.

According to the method for manufacturing silicon carbide single crystal 59 according to the present disclosure, the area of {0001} facet surface 60 can be reduced. Therefore, the area of the growth surface 50 into which nitrogen is taken can be reduced. As a result, the occurrence of curvature in the growth surface 50 can be suppressed. Therefore, a semi-insulating silicon carbide substrate 100 with reduced {0001} plane orientation difference can be obtained.

The first main surface 1 of the silicon carbide substrate 100 according to the present disclosure includes a first outer peripheral part 20 within 5 mm from the outer peripheral edge of the first main surface 1, and a first central part 10 surrounded by the first outer peripheral part 20. It is made up of. The first central portion 10 includes a first central region 11 having a diameter half the maximum diameter of the first main surface 1 and centered on the center of the first main surface 1, and a first central region 11 surrounding the first central region 11. The outer circumferential region 12 is composed of an outer circumferential region 12. The average value of the nitrogen concentration in the first central region 11 is higher than the average value of the nitrogen concentration in the first peripheral region 12. The average value of the nitrogen concentration in the first central region 11 is 1×10 ¹⁶ cm ⁻³ or less. In the first central portion 10, the electrical resistivity at any position is 1×10 ⁶ Ωcm or more. In the first central portion 10, the {0001} plane orientation difference between any two points 1 cm apart is 35 seconds or less. Thereby, silicon carbide substrate 100 in which the {0001} plane orientation difference in first principal surface 1 is reduced is obtained. Generally, due to variations in the off-angle of silicon carbide substrate 100, the morphology of the surface of the epitaxial layer may become rough, and the nitrogen concentration of the epitaxial layer may vary within the plane of silicon carbide substrate 100. In this case, there is a possibility that variations in the characteristics of the semiconductor device 400 will increase. According to silicon carbide substrate 100 according to the present disclosure, variations in characteristics of semiconductor device 400 can be reduced.

(Sample preparation)

First, silicon carbide crystal 57 having a polytype of 4H was produced using the manufacturing conditions related to Samples 1 to 7. In the manufacturing conditions for Samples 1 to 7, first, a seed substrate 150 and a silicon carbide raw material 156 were placed in a crucible 130 . The diameter of the third main surface 151 of the seed substrate 150 was 120 mm. The third principal surface 151 was a (000-1) plane. The thickness of the seed substrate 150 was 1 mm. Next, silicon carbide crystal 57 was formed on third main surface 151 of seed substrate 150 using a sublimation method. After silicon carbide crystal 57 was removed from crucible 130 , it was placed inside heating device 301 . Silicon carbide crystal 57 was heated at a temperature of 2500° C. in heating device 301.

Next, silicon carbide crystal 57 was rapidly cooled. As a result, point defects were formed in silicon carbide crystal 57. As a result, the electrical resistivity of silicon carbide crystal 57 increased. The electrical resistivity of silicon carbide crystal 57 was, for example, 1×10 ¹² Ωcm or more. Next, the silicon carbide single crystal was sliced using a saw wire, thereby obtaining silicon carbide substrates 100 according to samples 1 to 7.

Under the manufacturing conditions for Sample 1, the {0001} plane orientation difference on the third main surface 151 of the seed substrate 150 was 58 seconds. In the crystal growth using the sublimation method, the diameter of the {0001} facet surface 60 on the growth surface 50 was 38 mm.

Under the manufacturing conditions for Sample 2, the {0001} plane orientation difference on the third main surface 151 of the seed substrate 150 was 57 seconds. In crystal growth using the sublimation method, the diameter of the {0001} facet surface 60 on the growth surface 50 was 66 mm.

Under the manufacturing conditions for Sample 3, the {0001} plane orientation difference on the third main surface 151 of the seed substrate 150 was 27 seconds. In the crystal growth using the sublimation method, the diameter of the {0001} facet surface 60 on the growth surface 50 was 36 mm.

Under the manufacturing conditions for Sample 4, the {0001} plane orientation difference on the third main surface 151 of the seed substrate 150 was 20 seconds. In the crystal growth using the sublimation method, the diameter of the {0001} facet surface 60 on the growth surface 50 was 34 mm.

Under the manufacturing conditions for Sample 5, the {0001} plane orientation difference on the third main surface 151 of the seed substrate 150 was 8 seconds. In the crystal growth using the sublimation method, the diameter of the {0001} facet surface 60 on the growth surface 50 was 30 mm.

Under the manufacturing conditions for Sample 6, the {0001} plane orientation difference on the third main surface 151 of the seed substrate 150 was 12 seconds. In crystal growth using the sublimation method, the diameter of the {0001} facet surface 60 on the growth surface 50 was 32 mm.

Under the manufacturing conditions for Sample 7, the {0001} plane orientation difference on the third main surface 151 of the seed substrate 150 was 24 seconds. In the crystal growth using the sublimation method, the diameter of the {0001} facet surface 60 on the growth surface 50 was 64 mm.

(Measuring method)

{0001} plane orientation difference was measured in first central portion 10 of each silicon carbide substrate 100 of Samples 1 to 7. The plane orientation difference was measured by X-ray diffraction. Cu-Kα1 was used as an X-ray source, and the (0004) peak was measured. The wavelength was 1.5405 angstroms. As shown in FIG. 3, the {0001} plane orientation was measured at 49 (7 points x 7 points) measurement points 5 in the first central portion 10. Among the 49 measurement points 5 that were measured, the maximum value of the {0001} plane orientation difference between two points 1 cm apart was determined.

(Measurement result)

Table 1 shows the maximum value of the {0001} plane orientation difference in the first central portion 10 of each of the silicon carbide substrates 100 of Samples 1 to 7. As shown in Table 1, the maximum values of the {0001} plane orientation differences at the first central portion 10 of the first main surface 1 of the silicon carbide substrates 100 of Samples 1 to 7 are 60 seconds, 74 seconds, and 35 seconds, respectively. seconds, 22 seconds, 10 seconds, 15 seconds and 45 seconds. According to the above results, by reducing the maximum value of the {0001} plane orientation difference in third principal surface 151 of seed substrate 150 and reducing the diameter of facet surface 60 in growth surface 50 of silicon carbide crystal 57, It was confirmed that silicon carbide substrate 100 in which the maximum value of the {0001} plane orientation difference on first principal surface 1 was reduced could be obtained.

The present disclosure includes the embodiments described below.
(Additional note 1)
having a main surface;
The main surface is composed of an outer peripheral part within 5 mm from the outer peripheral edge of the main surface, and a central part surrounded by the outer peripheral part,
The central portion has a diameter that is half the maximum diameter of the main surface and is composed of a central region centered on the center of the main surface, and an outer peripheral region surrounding the central region,
The average value of nitrogen concentration in the central region is higher than the average value of nitrogen concentration in the peripheral region,
The average value of the nitrogen concentration in the central region is 1×10 ¹⁶ cm ⁻³ or less,
In the central portion, the electrical resistivity at any position is 1×10 ⁶ Ωcm or more,
A silicon carbide substrate, wherein the {0001} plane orientation difference between any two points 1 cm apart in the central portion is 35 seconds or less.
(Additional note 2)
The silicon carbide substrate according to Supplementary Note 1, wherein the p-type impurity and the compensation impurity are not doped.
(Additional note 3)
The silicon carbide substrate according to Supplementary Note 1 or 2, wherein a value obtained by dividing the average value of the nitrogen concentration in the outer peripheral region by the average value of the nitrogen concentration in the central region is 0.7 or more and 0.9 or less.
(Additional note 4)
The silicon carbide substrate according to appendix 1 or 2, wherein the average value of nitrogen concentration in the outer peripheral region is 1×10 ¹⁵ cm ⁻³ or more and less than 1×10 ¹⁶ cm ⁻³ .
(Appendix 5)
The silicon carbide substrate according to Appendix 1 or 2, wherein the maximum diameter is 100 mm or more.
(Appendix 6)
The silicon carbide substrate according to Supplementary Note 1 or 2, wherein the angle between the main surface and the {0001} plane is 1° or less.
(Appendix 7)
The silicon carbide substrate according to appendix 1 or 2, wherein the polytype of silicon carbide constituting the silicon carbide substrate is 4H.
(Appendix 8)
A silicon carbide substrate according to any one of Supplementary Note 1 or 2,
An epitaxial substrate comprising: a nitride epitaxial layer provided on the silicon carbide substrate.
(Appendix 9)
A step of preparing the epitaxial substrate described in Appendix 8;
A method for manufacturing a semiconductor device, comprising the step of forming an electrode on the epitaxial substrate.
(Appendix 10)
A step of preparing a seed substrate having a main surface and a silicon carbide raw material;
growing silicon carbide crystals on the main surface by subliming the silicon carbide raw material;
After the step of growing silicon carbide crystals on the main surface by sublimating the silicon carbide raw material, increasing the electrical resistivity of the silicon carbide crystals by heating the silicon carbide crystals at a temperature of 2000° C. or higher. comprising a process and,
The main surface is composed of an outer peripheral part within 5 mm from the outer peripheral edge of the main surface, and a central part surrounded by the outer peripheral part,
In the central part, the {0001} plane orientation difference between any two points separated by 1 cm is 35 seconds or less,
The growth surface of the silicon carbide crystal includes a first region having a diameter that is half the maximum diameter of the silicon carbide crystal and centered on the center of the growth surface, and a second region surrounding the first region. has been
In the step of growing a silicon carbide crystal on the main surface by sublimating the silicon carbide raw material, the {0001} facet surface is exposed to the first region and not exposed to the second region. Method for producing single crystals.
(Appendix 11)
The method for producing a silicon carbide single crystal according to appendix 10, wherein the angle between the main surface and the {0001} plane is 1° or less.
(Appendix 12)
a step of preparing a silicon carbide single crystal using the method for producing a silicon carbide single crystal according to Appendix 10 or Appendix 11;
cutting the silicon carbide single crystal,
The method for manufacturing a silicon carbide substrate, wherein the angle between the cut surface of the silicon carbide single crystal and the {0001} plane is 1° or less.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the claims rather than the above description, and it is intended that equivalent meanings to the claims and all changes within the range be included.

1 First main surface (principal surface), 2 Second main surface, 3 First outer peripheral side, 4 First outer peripheral edge, 5 Measurement point, 10 First central part (central part), 11 First central region (central region ), 12 first outer peripheral region (outer peripheral region), 13, 53, 113 center, 20 first outer peripheral part (outer peripheral part), 30 nitride epitaxial layer, 31 buffer layer, 32 electron transit layer, 33 electron supply layer, 41 Source electrode, 42 Drain electrode, 43 Gate electrode, 50 Growth surface, 51 First region, 52 Second region, 55 Third central region, 56 Third outer region, 57 Silicon carbide crystal, 58 Cut surface, 59 Single silicon carbide Crystal, 60 facet surface, 61 first measurement position, 62 second measurement position, 100 silicon carbide substrate, 101 first direction, 102 second direction, 103 third direction, 110 second central part (center part), 111 second 2 central area (central area), 112 second outer peripheral area (outer peripheral area), 120 second outer peripheral part (outer peripheral part), 130 crucible, 131 lid part, 132 accommodating part, 150 seed substrate, 151 third main surface (main surface), 152 fourth principal surface, 153 second outer peripheral side surface, 154 second outer peripheral edge, 156 silicon carbide raw material, 200 epitaxial substrate, 301 heating device, 400 semiconductor device, D spot diameter, S1 first spot, S2 second Spot, W1 first diameter, W2 second diameter, W3 third distance, W4 fourth diameter, W5 fifth diameter, W6 sixth distance, W7 seventh diameter, W8 eighth diameter, W9 ninth diameter, c1, c2 {0001} plane orientation, n normal direction.

Claims (12)

1. having a main surface;
   The main surface is composed of an outer peripheral part within 5 mm from the outer peripheral edge of the main surface, and a central part surrounded by the outer peripheral part,
   The central portion has a diameter that is half the maximum diameter of the main surface and is composed of a central region centered on the center of the main surface, and an outer peripheral region surrounding the central region,
   The average value of nitrogen concentration in the central region is higher than the average value of nitrogen concentration in the peripheral region,
   The average value of the nitrogen concentration in the central region is 1×10 ¹⁶ cm ⁻³ or less,
   In the central portion, the electrical resistivity at any position is 1×10 ⁶ Ωcm or more,
   A silicon carbide substrate, wherein the {0001} plane orientation difference between any two points 1 cm apart in the central portion is 35 seconds or less.
2. The silicon carbide substrate according to claim 1, wherein the p-type impurity and the compensation impurity are not doped.
3. The silicon carbide substrate according to claim 1 or 2, wherein a value obtained by dividing the average value of the nitrogen concentration in the outer peripheral region by the average value of the nitrogen concentration in the central region is 0.7 or more and 0.9 or less.
4. The silicon carbide substrate according to claim 1 or 2, wherein the average value of nitrogen concentration in the outer peripheral region is 1×10 ¹⁵ cm ^-3 or more and less than 1×10 ¹⁶ cm ^-3 .
5. The silicon carbide substrate according to any one of claims 1 to 4, wherein the maximum diameter is 100 mm or more.
6. The silicon carbide substrate according to any one of claims 1 to 5, wherein the angle between the main surface and the {0001} plane is 1° or less.
7. The silicon carbide substrate according to any one of claims 1 to 6, wherein the polytype of silicon carbide constituting the silicon carbide substrate is 4H.
8. The silicon carbide substrate according to any one of claims 1 to 7,
   An epitaxial substrate comprising: a nitride epitaxial layer provided on the silicon carbide substrate.
9. preparing an epitaxial substrate according to claim 8;
   A method for manufacturing a semiconductor device, comprising the step of forming an electrode on the epitaxial substrate.
10. A step of preparing a seed substrate having a main surface and a silicon carbide raw material;
    growing silicon carbide crystals on the main surface by subliming the silicon carbide raw material;
    After the step of growing silicon carbide crystals on the main surface by sublimating the silicon carbide raw material, increasing the electrical resistivity of the silicon carbide crystals by heating the silicon carbide crystals at a temperature of 2000° C. or higher. comprising a process and,
    The main surface is composed of an outer peripheral part within 5 mm from the outer peripheral edge of the main surface, and a central part surrounded by the outer peripheral part,
    In the central part, the {0001} plane orientation difference between any two points separated by 1 cm is 35 seconds or less,
    The growth surface of the silicon carbide crystal includes a first region having a diameter that is half the maximum diameter of the silicon carbide crystal and centered on the center of the growth surface, and a second region surrounding the first region. has been
    In the step of growing a silicon carbide crystal on the main surface by sublimating the silicon carbide raw material, the {0001} facet surface is exposed to the first region and not exposed to the second region. Method for producing single crystals.
11. The method for manufacturing a silicon carbide single crystal according to claim 10, wherein the angle between the main surface and the {0001} plane is 1° or less.
12. preparing a silicon carbide single crystal using the method for producing a silicon carbide single crystal according to claim 10 or 11;
    a step of cutting the silicon carbide single crystal,
    The method for manufacturing a silicon carbide substrate, wherein the angle between the cut plane of the silicon carbide single crystal and the {0001} plane is 1° or less.

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