Silicon carbide substrate, silicon carbide epitaxial substrate manufacturing method, and silicon carbide semiconductor device manufacturing method

Abstract

According to the present invention, a first main surface has a central measurement region, a first measurement region, a second measurement region, a third measurement region, and a fourth measurement region. When viewed along a straight line perpendicular to the first main surface, the shortest distance between a first outer rim of the first main surface and the center of each of the first measurement region, the second measurement region, the third measurement region, and the fourth measurement region is 10 mm. The concentration of titanium in the central measurement region is defined as a first concentration, and the average of the concentrations of titanium in the first measurement region, the second measurement region, the third measurement region, and the fourth measurement region is defined as a second concentration. The first concentration is lower than the second concentration. The second concentration is 5×1014 atoms / cm3 or lower.

Description

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

[0001] The present disclosure relates to a silicon carbide substrate, a method for manufacturing a silicon carbide epitaxial substrate, and a method for manufacturing a silicon carbide semiconductor device. This application claims priority to Japanese Patent Application No. 2022-167474, filed on October 19, 2022. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] Stephan G. Muller et al., "High Quality SiC Substrates for Semiconductor Devices: From Research to Industrial Production," Materials Science Forum Vols. 389-393, pp. 23-28, 2002 (Non-Patent Document 1), describes the results of measuring the concentration of metal impurities in silicon carbide crystals.

[0003] Stephan G. Muller and 14 others, "High Quality SiC Substrates for Semiconductor Devices: From Research to Industrial Production", Materials Science Forum Vols. 389-393, pp. 23-28, 2002.

[0004] A silicon carbide substrate according to the present disclosure has a first main surface. The first main surface includes a central measurement region, a first measurement region, a second measurement region, a third measurement region, and a fourth measurement region. When viewed along a line perpendicular to the first main surface, the central measurement region is at the center of the first main surface. When viewed along a line perpendicular to the first main surface, the first measurement region is in the <11-20> direction with respect to the central measurement region. When viewed along a line perpendicular to the first main surface, the second measurement region is in the <1-100> direction with respect to the central measurement region. When viewed along a line perpendicular to the first main surface, the third measurement region is opposite the first measurement region with respect to the central measurement region. When viewed along a line perpendicular to the first main surface, the fourth measurement region is opposite the second measurement region with respect to the central measurement region. When viewed along a line perpendicular to the first main surface, the shortest distance between the center of each of the first measurement region, the second measurement region, the third measurement region, and the fourth measurement region and the first outer circumferential edge of the first main surface is 10 mm. The titanium concentration in the central measurement region is defined as a first concentration. The average of the titanium concentrations in the first, second, third, and fourth measurement regions is defined as a second concentration. Each of the first and second concentrations is measured by secondary ion mass spectrometry. The first concentration is lower than the second concentration. The second concentration is 5×10 14 atoms / cm 3 The following is the result.

[0005] FIG. 1 is a schematic plan view showing the configuration of a silicon carbide substrate according to this embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1 . FIG. 3 is a schematic plan view showing the configuration of a silicon carbide epitaxial substrate according to this embodiment. FIG. 4 is a schematic cross-sectional view taken along line IV-IV in FIG. 3 . FIG. 5 is a schematic cross-sectional view showing an apparatus for manufacturing a silicon carbide single crystal according to this embodiment. FIG. 6 is a flow diagram generally showing a method for manufacturing a silicon carbide substrate according to this embodiment. FIG. 7 is a schematic cross-sectional view showing steps for growing a silicon carbide crystal. FIG. 8 is a flow diagram generally showing a method for manufacturing a silicon carbide semiconductor device according to this embodiment. FIG. 9 is a schematic cross-sectional view showing steps for preparing a silicon carbide substrate. FIG. 10 is a schematic cross-sectional view showing steps for forming a silicon carbide epitaxial layer. FIG. 11 is a schematic cross-sectional view showing steps for forming a body region. FIG. 12 is a schematic cross-sectional view showing steps for forming a source region. Fig. 13 is a cross-sectional view schematically showing a step of forming a trench in the third main surface of the silicon carbide epitaxial layer. Fig. 14 is a cross-sectional view schematically showing a step of forming a gate insulating film. Fig. 15 is a cross-sectional view schematically showing a step of forming a gate electrode and an interlayer insulating film. Fig. 16 is a cross-sectional view schematically showing the configuration of the silicon carbide semiconductor device according to this embodiment.

[0006] [Problem to be Solved by the Present Disclosure] An object of the present disclosure is to provide a silicon carbide substrate, a method for manufacturing a silicon carbide epitaxial substrate, and a method for manufacturing a silicon carbide semiconductor device, which are capable of improving the yield of silicon carbide semiconductor devices. [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a silicon carbide substrate, a method for manufacturing a silicon carbide epitaxial substrate, and a method for manufacturing a silicon carbide semiconductor device, which are capable of improving the yield of silicon carbide semiconductor devices.

[0007] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0008] (1) Silicon carbide substrate 100 according to the present disclosure has a first main surface 1. First main surface 1 has a central measurement region 65, a first measurement region 61, a second measurement region 62, a third measurement region 63, and a fourth measurement region 64. When viewed along a line perpendicular to first main surface 1, central measurement region 65 is at the center of first main surface 1. When viewed along a line perpendicular to first main surface 1, first measurement region 61 is in the <11-20> direction with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, second measurement region 62 is in the <1-100> direction with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, third measurement region 63 is on the opposite side of first measurement region 61 with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, fourth measurement region 64 is on the opposite side of second measurement region 62 with respect to central measurement region 65. When viewed along a line perpendicular to the first main surface 1, the shortest distance between the center of each of the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 and the first outer periphery 14 of the first main surface 1 is 10 mm. The titanium concentration in the central measurement region 65 is defined as a first concentration. The average value of the titanium concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is defined as a second concentration. Each of the first concentration and the second concentration is measured by secondary ion mass spectrometry. The first concentration is lower than the second concentration. The second concentration is 5×10 14 atoms / cm 3 The following is the result.

[0009] (2) According to silicon carbide substrate 100 according to (1) above, the first concentration is 1×10 13 atoms / cm 3 It may be the following:

[0010] (3) In silicon carbide substrate 100 according to (1) or (2) above, the value obtained by dividing the second concentration by the first concentration may be 50 or less.

[0011] (4) Silicon carbide substrate 100 according to the present disclosure has first main surface 1. First main surface 1 has central measurement region 65, first measurement region 61, second measurement region 62, third measurement region 63, and fourth measurement region 64. When viewed along a line perpendicular to first main surface 1, central measurement region 65 is at the center of first main surface 1. When viewed along a line perpendicular to first main surface 1, first measurement region 61 is in the <11-20> direction with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, second measurement region 62 is in the <1-100> direction with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, third measurement region 63 is on the opposite side of first measurement region 61 with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, fourth measurement region 64 is on the opposite side of second measurement region 62 with respect to central measurement region 65. When viewed along a line perpendicular to the first main surface 1, the shortest distance between the center of each of the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 and the first outer periphery 14 of the first main surface 1 is 10 mm. The chromium concentration in the central measurement region 65 is defined as a third concentration. The average value of the chromium concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is defined as a fourth concentration. Each of the third and fourth concentrations is measured by secondary ion mass spectrometry. The third concentration is lower than the fourth concentration. The fourth concentration is 3×10 14 atoms / cm 3 The following is the result.

[0012] (5) According to silicon carbide substrate 100 according to (4) above, the third concentration is 5×10 13 atoms / cm 3 It may be the following:

[0013] (6) In silicon carbide substrate 100 according to (4) or (5) above, the value obtained by dividing the fourth concentration by the third concentration may be 6 or less.

[0014] (7) Silicon carbide substrate 100 according to the present disclosure has a first main surface 1. First main surface 1 has a central measurement region 65, a first measurement region 61, a second measurement region 62, a third measurement region 63, and a fourth measurement region 64. When viewed along a line perpendicular to first main surface 1, central measurement region 65 is at the center of first main surface 1. When viewed along a line perpendicular to first main surface 1, first measurement region 61 is in the <11-20> direction with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, second measurement region 62 is in the <1-100> direction with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, third measurement region 63 is on the opposite side of first measurement region 61 with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, fourth measurement region 64 is on the opposite side of second measurement region 62 with respect to central measurement region 65. When viewed along a line perpendicular to the first main surface 1, the shortest distance between the center of each of the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 and the first outer periphery 14 of the first main surface 1 is 10 mm. The copper concentration in the central measurement region 65 is defined as a fifth concentration. The average value of the copper concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is defined as a sixth concentration. Each of the fifth and sixth concentrations is measured by secondary ion mass spectrometry. The fifth concentration is 2×10 14 atoms / cm 3 The sixth concentration is 5×10 14 atoms / cm 3 The following is the result.

[0015] (8) Silicon carbide substrate 100 according to the present disclosure has a first main surface 1. First main surface 1 has a central measurement region 65, a first measurement region 61, a second measurement region 62, a third measurement region 63, and a fourth measurement region 64. When viewed along a line perpendicular to first main surface 1, central measurement region 65 is at the center of first main surface 1. When viewed along a line perpendicular to first main surface 1, first measurement region 61 is in the <11-20> direction with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, second measurement region 62 is in the <1-100> direction with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, third measurement region 63 is on the opposite side of first measurement region 61 with respect to central measurement region 65. When viewed along a line perpendicular to first main surface 1, fourth measurement region 64 is on the opposite side of second measurement region 62 with respect to central measurement region 65. When viewed along a line perpendicular to the first main surface 1, the shortest distance between the center of each of the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 and the first outer periphery 14 of the first main surface 1 is 10 mm. The aluminum concentration in the central measurement region 65 is defined as a seventh concentration. The average value of the aluminum concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is defined as an eighth concentration. Each of the seventh and eighth concentrations is measured by secondary ion mass spectrometry. The seventh concentration is 2×10 13 atoms / cm 3 The eighth concentration is 6×10 13 atoms / cm 3 The following is the result.

[0016] (9) According to silicon carbide substrate 100 described in any one of (1) to (8) above, first main surface 1 may have a maximum diameter W1 of 150 mm or more.

[0017] (10) According to silicon carbide substrate 100 described in any one of (1) to (9) above, the nitrogen concentration in central measurement region 65 is 1×10 17 atoms / cm 3 It may be more than that.

[0018] (11) A method for manufacturing a silicon carbide epitaxial substrate 200 according to the present disclosure includes the following steps: Silicon carbide substrate 100 according to any one of (1) to (10) above is prepared. Silicon carbide epitaxial layer 20 is formed on silicon carbide substrate 100.

[0019] (12) A method for manufacturing silicon carbide semiconductor device 400 according to the present disclosure includes the following steps: Silicon carbide substrate 100 according to any one of (1) to (10) above is prepared. Silicon carbide epitaxial layer 20 is formed on silicon carbide substrate 100. Silicon carbide epitaxial layer 20 is processed.

[0020] [Details of the Embodiments of the Present Disclosure] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the same or corresponding parts in the following drawings are given the same reference numerals, and their description will not be repeated. In the crystallographic descriptions in this specification, individual orientations are indicated by [ ], collective orientations by < >, individual planes by ( ), and collective planes by {}. Furthermore, for negative indices, in crystallography, a "-" (bar) is placed before the number, but in this specification, a negative sign is placed before the number.

[0021] <Silicon Carbide Substrate> First, the configuration of silicon carbide substrate 100 according to this embodiment will be described. Fig. 1 is a plan view schematically showing the configuration of silicon carbide substrate 100 according to this embodiment. Fig. 2 is a cross-sectional view schematically showing the configuration of silicon carbide substrate 100 along line II-II in Fig. 1.

[0022] 1 and 2 , silicon carbide substrate 100 according to this embodiment mainly has a first main surface 1, a second main surface 2, and a peripheral side surface 9. The second main surface 2 is opposite to the first main surface 1. The peripheral side surface 9 is continuous with each of the first main surface 1 and the second main surface 2. The ridge line between first main surface 1 and peripheral side surface 9 forms a first peripheral edge 14. From another perspective, first peripheral edge 14 is the peripheral edge of first main surface 1. The peripheral side surface 9 has, for example, an orientation flat 7 and an arc-shaped portion 8.

[0023] As shown in FIG. 1 , when viewed along a straight line perpendicular to the first main surface 1 (hereinafter also referred to as a plan view), the orientation flat 7 is linear. The orientation flat 7 extends, for example, along a first direction 101. The arc-shaped portion 8 is continuous with the orientation flat 7. In the plan view, the arc-shaped portion 8 is arc-shaped. The first main surface 1 extends along each of the first direction 101 and the second direction 102. In the plan view, the second direction 102 is perpendicular to the first direction 101.

[0024] The first direction 101 is, for example, the <11-20> direction. The first direction 101 may be, for example, the [-1-120] direction. The first direction 101 may be a direction obtained by projecting the <11-20> direction onto the first main surface 1. From another perspective, the first direction 101 may be, for example, a direction including a <11-20> direction component.

[0025] The second direction 102 is, for example, the <1-100> direction. The second direction 102 may be, for example, the [1-100] direction. The second direction 102 may be, for example, a direction obtained by projecting the <1-100> direction onto the first main surface 1. From another perspective, the second direction 102 may be, for example, a direction including a <1-100> direction component.

[0026] The third direction 103 is perpendicular to each of the first direction 101 and the second direction 102, and is a direction from the first main surface 1 to the second main surface 2. The schematic plan view shown in FIG. 1 is a schematic plan view seen in the third direction 103.

[0027] First main surface 1 may be a {0001} plane, or may be a plane inclined with respect to the {0001} plane. When first main surface 1 is inclined with respect to the {0001} plane, the inclination angle (off angle θ) with respect to the {0001} plane is, for example, 1° or more and 8° or less. When first main surface 1 is inclined with respect to the {0001} plane, the inclination direction (off direction) of first main surface 1 is, for example, the <11-20> direction. The off angle θ may be 2° or more and 6° or less.

[0028] The maximum diameter of the first main surface 1 is defined as a first maximum diameter W1. The first maximum diameter W1 is, for example, 150 mm (6 inches) or more. The first maximum diameter W1 may be 200 mm (8 inches) or more. The upper limit of the first maximum diameter W1 is not particularly limited, but may be, for example, 400 mm (16 inches) or less. The first maximum diameter W1 is the longest linear distance between two different points on the first outer peripheral edge 14.

[0029] In this specification, 6 inches refers to 150 mm or 152.4 mm (6 inches x 25.4 mm / inch). 8 inches refers to 200 mm or 203.2 mm (8 inches x 25.4 mm / inch). 16 inches refers to 400 mm or 406.4 mm (16 inches x 25.4 mm / inch).

[0030] <Metallic Impurities> As shown in FIG. 1 , the first principal surface 1 has a central measurement region 65, a first measurement region 61, a second measurement region 62, a third measurement region 63, and a fourth measurement region 64. The central measurement region 65, the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 are each a region for measuring the concentration of metallic impurities on the first principal surface 1. In this specification, metallic impurities are specifically titanium (Ti), chromium (Cr), copper (Cu), aluminum (Al), iron (Fe), nickel (Ni), or the like. In plan view, the line connecting points on the first principal surface 1 that are 10 mm shortest from the first outer periphery 14 is defined as the imaginary line 12. In other words, in plan view, the shortest distance D between the first outer periphery 14 and the imaginary line 12 is 10 mm.

[0031] 1 , the center of the central measurement area 65 is set to be a fifth center 95. In a plan view, the central measurement area 65 is at the center of the first main surface 1. In other words, in a plan view, the fifth center 95 coincides with the center of the first main surface 1. In a plan view, the center of the first main surface 1 is at the center of a circle whose diameter is the first maximum diameter W1.

[0032] 1, in a plan view, the first measurement region 61 is in the <11-20> direction relative to the central measurement region 65. In other words, in a plan view, the first measurement region 61 is in a first direction 101 relative to the central measurement region 65. The center of the first measurement region 61 is defined as a first center 91. In a plan view, the shortest distance between the first center 91 and the first outer peripheral edge 14 is 10 mm. In other words, in a plan view, the first center 91 is on the imaginary line 12.

[0033] 1, in a plan view, the second measurement region 62 is in the <1-100> direction relative to the central measurement region 65. In other words, in a plan view, the second measurement region 62 is in the second direction 102 relative to the central measurement region 65. The center of the second measurement region 62 is defined as a second center 92. In a plan view, the shortest distance between the second center 92 and the first outer peripheral edge 14 is 10 mm. In other words, in a plan view, the second center 92 is on the imaginary line 12.

[0034] As shown in FIG. 1 , in a plan view, the third measurement area 63 is located opposite the first measurement area 61 with respect to the central measurement area 65. From another perspective, in a plan view, the central measurement area 65 is located between the first measurement area 61 and the third measurement area 63. The center of the third measurement area 63 is defined as a third center 93. In a plan view, the shortest distance between the third center 93 and the first outer peripheral edge 14 is 10 mm. In other words, in a plan view, the third center 93 is on the virtual line 12. In a plan view, the first center 91, the third center 93, and the fifth center 95 may be on the same straight line.

[0035] As shown in FIG. 1 , in a plan view, the fourth measurement area 64 is opposite the second measurement area 62 with respect to the central measurement area 65. From another perspective, in a plan view, the central measurement area 65 is between the second measurement area 62 and the fourth measurement area 64. The center of the fourth measurement area 64 is defined as a fourth center 94. In a plan view, the shortest distance between the fourth center 94 and the first outer peripheral edge 14 is 10 mm. In other words, in a plan view, the fourth center 94 is on the imaginary line 12. In a plan view, the second center 92, the fourth center 94, and the fifth center 95 may be on the same straight line.

[0036] In a plan view, the shape of each of central measurement region 65, first measurement region 61, second measurement region 62, third measurement region 63, and fourth measurement region 64 is, for example, a square. The length of one side of each of central measurement region 65, first measurement region 61, second measurement region 62, third measurement region 63, and fourth measurement region 64 is, for example, 50 μm or more and 100 μm or less. One side of each of central measurement region 65, first measurement region 61, second measurement region 62, third measurement region 63, and fourth measurement region 64 is, for example, parallel to first direction 101.

[0037] The concentration of metal impurities is measured by secondary ion mass spectrometry (SIMS). In SIMS, for example, oxygen (O ２ ＋ ) or cesium (Cs ＋ ) is used. A primary ion beam is scanned in each measurement region. Secondary ions are detected at the center of each measurement region. Specifically, for example, secondary ions are detected in a circular region centered on a first center 91. The diameter of the circular region is, for example, approximately 30 μm or more and 150 μm or less. By analyzing the detected secondary ions, the concentration of metal impurities in the first measurement region 61 is measured. In a similar manner, the concentration of metal impurities in each measurement region is measured.

[0038] <Titanium Concentration> The titanium concentration in the central measurement region 65 is defined as a first concentration. The average of the titanium concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is defined as a second concentration. The first concentration is lower than the second concentration.

[0039] The first concentration is, for example, 1×10 13 atoms / cm 3 The first concentration is, for example, 1×10 10 atoms / cm 3 It may be 5×10 or more. 10 atoms / cm 3 The first concentration may be, for example, 1×10 12 atoms / cm 3It may be less than or equal to 1×10 11 atoms / cm 3 It may be the following:

[0040] The second concentration is 5×10 14 atoms / cm 3 The second concentration is 1×10 12 atoms / cm 3 It may be 1×10 or more. 13 atoms / cm 3 The second concentration may be, for example, 1.5×10 14 atoms / cm 3 It may be 5×10 or less. 13 atoms / cm 3 It may be the following:

[0041] The value obtained by dividing the second concentration by the first concentration is, for example, 50 or less. The value obtained by dividing the second concentration by the first concentration may, for example, be greater than 1 or may be 3 or greater. The value obtained by dividing the second concentration by the first concentration may, for example, be 11 or less, or may be 5 or less. Herein, when dividing the second concentration by the first concentration, if the first concentration is equal to or less than the lower limit of detection of SIMS, a calculation is performed in which the value of the first concentration is used as the lower limit of detection of SIMS and the second concentration is divided by the first concentration. Similarly, when dividing the second concentration by the first concentration, if the second concentration is equal to or less than the lower limit of detection of SIMS, a calculation is performed in which the value of the second concentration is used as the lower limit of detection of SIMS and the second concentration is divided by the first concentration.

[0042] <Chromium Concentration> The chromium concentration in the central measurement region 65 is defined as a third concentration. The average of the chromium concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is defined as a fourth concentration. The third concentration is lower than the fourth concentration.

[0043] The third concentration is, for example, 5×10 13 atoms / cm 3 The third concentration is, for example, 1×10 10 atoms / cm 3 It may be 1×10 or more. 11 atoms / cm 3The third concentration may be, for example, 5×10 12 atoms / cm 3 It may be 5×10 or less. 11 atoms / cm 3 It may be the following:

[0044] The fourth concentration is 3×10 14 atoms / cm 3 The fourth concentration is, for example, 1×10 13 atoms / cm 3 It may be 5×10 or more. 13 atoms / cm 3 The fourth concentration may be, for example, 2×10 14 atoms / cm 3 It may be less than or equal to 1×10 14 atoms / cm 3 It may be the following:

[0045] The value obtained by dividing the fourth concentration by the third concentration is, for example, 6 or less. The value obtained by dividing the fourth concentration by the third concentration may, for example, be greater than 1 or may be 1.5 or greater. The value obtained by dividing the fourth concentration by the third concentration may, for example, be 4 or less or may be 2.5 or less. Herein, when dividing the fourth concentration by the third concentration, if the third concentration is equal to or less than the lower limit of detection of SIMS, a calculation is performed in which the value of the third concentration is used as the lower limit of detection of SIMS and the fourth concentration is divided by the third concentration. Similarly, when dividing the fourth concentration by the third concentration, if the fourth concentration is equal to or less than the lower limit of detection of SIMS, a calculation is performed in which the value of the fourth concentration is used as the lower limit of detection of SIMS and the fourth concentration is divided by the third concentration.

[0046] <Copper Concentration> The copper concentration in the central measurement region 65 is set to a fifth concentration. The average of the copper concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is set to a sixth concentration. The fifth concentration may be lower than the sixth concentration.

[0047] The fifth concentration is 2×10 14 atoms / cm 3 The fifth concentration is, for example, 1×10 11 atoms / cm 3It may be 5×10 or more. 11 atoms / cm 3 The fifth concentration may be, for example, 1×10 13 atoms / cm 3 It may be less than or equal to 1×10 12 atoms / cm 3 It may be the following:

[0048] The sixth concentration is 5×10 14 atoms / cm 3 The sixth concentration is, for example, 3.5×10 14 atoms / cm 3 or less, or 2.0 × 10 14 atoms / cm 3 The sixth concentration may be, for example, 1.0×10 12 atoms / cm 3 or more, or 1.0 × 10 13 atoms / cm 3 It may be more than that.

[0049] The value obtained by dividing the sixth concentration by the fifth concentration is, for example, equal to or greater than 1 and equal to or less than 2.5. In this specification, when dividing the sixth concentration by the fifth concentration, if the fifth concentration is equal to or less than the lower limit of detection of SIMS, a calculation is performed in which the value of the fifth concentration is used as the lower limit of detection of SIMS and the sixth concentration is divided by the fifth concentration. Similarly, when dividing the sixth concentration by the fifth concentration, if the sixth concentration is equal to or less than the lower limit of detection of SIMS, a calculation is performed in which the value of the sixth concentration is used as the lower limit of detection of SIMS and the sixth concentration is divided by the fifth concentration.

[0050] <Aluminum Concentration> The aluminum concentration in the central measurement region 65 is set to a seventh concentration. The average of the aluminum concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is set to an eighth concentration. The seventh concentration may be lower than the eighth concentration.

[0051] The seventh concentration is 2×10 13 atoms / cm 3 The seventh concentration is, for example, 1×10 10 atoms / cm 3 It may be 1×10 or more.11 atoms / cm 3 The seventh concentration may be, for example, 1×10 13 atoms / cm 3 It may be less than or equal to 1×10 12 atoms / cm 3 It may be the following:

[0052] The eighth density is 6×10 13 atoms / cm 3 The eighth concentration is, for example, 1×10 11 atoms / cm 3 It may be 1×10 or more. 12 atoms / cm 3 The eighth concentration may be, for example, 4.5×10 13 atoms / cm 3 or less, or 2×10 13 atoms / cm 3 It may be the following:

[0053] The value obtained by dividing the eighth concentration by the seventh concentration is, for example, equal to or greater than 1 and equal to or less than 3. In this specification, when dividing the eighth concentration by the seventh concentration, if the seventh concentration is equal to or less than the lower limit of detection of SIMS, a calculation is performed in which the value of the seventh concentration is used as the lower limit of detection of SIMS and the eighth concentration is divided by the seventh concentration. Similarly, when dividing the eighth concentration by the seventh concentration, if the eighth concentration is equal to or less than the lower limit of detection of SIMS, a calculation is performed in which the value of the eighth concentration is used as the lower limit of detection of SIMS and the eighth concentration is divided by the seventh concentration.

[0054] <Iron Concentration> The iron concentration in the central measurement region 65 is set to a ninth concentration. The average value of the iron concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is set to a tenth concentration. The ninth concentration is, for example, 2×10 14 atoms / cm 3 The tenth concentration is, for example, 2×10 14 atoms / cm 3 The following is the result.

[0055] <Nickel Concentration> The nickel concentration in the central measurement region 65 is set to an eleventh concentration. The average value of the nickel concentrations in the first measurement region 61, the second measurement region 62, the third measurement region 63, and the fourth measurement region 64 is set to a twelfth concentration. The eleventh concentration is, for example, 5×10 14 atoms / cm 3 The twelfth concentration is, for example, 5×10 14 atoms / cm 3 The following is the result.

[0056] <Nitrogen Concentration> The nitrogen concentration in first main surface 1 is, for example, 1×10 17 atoms / cm 3 The concentration of nitrogen in first main surface 1 is, for example, 1×10 18 atoms / cm 3 It may be 1×10 or more. 19 atoms / cm 3 The concentration of nitrogen in the first main surface 1 may be 1×10 21 atoms / cm 3 It may be less than or equal to 1×10 20 atoms / cm 3 It may be the following:

[0057] Similar to the concentration of metal impurities, the nitrogen concentration on the first main surface 1 is measured using SIMS. The nitrogen concentration in the central measurement region 65 measured using SIMS is taken as the nitrogen concentration on the first main surface 1.

[0058] <Silicon carbide epitaxial substrate> Next, the configuration of silicon carbide epitaxial substrate 200 according to this embodiment will be described. Fig. 3 is a plan view schematically showing the configuration of silicon carbide epitaxial substrate 200 according to this embodiment. Fig. 4 is a cross-sectional view schematically showing the configuration of silicon carbide epitaxial substrate 200 according to this embodiment. The cross-sectional view shown in Fig. 4 corresponds to the cross-sectional view shown in Fig. 2.

[0059] 3 and 4 , silicon carbide epitaxial substrate 200 according to this embodiment mainly has a third main surface 3, a second main surface 2, and an outer peripheral side surface 9. The second main surface 2 is opposite to the third main surface 3. The outer peripheral side surface 9 is continuous with each of the second main surface 2 and the third main surface 3. The ridge line between the third main surface 3 and the outer peripheral side surface 9 forms a second outer peripheral edge 24. From another perspective, the second outer peripheral edge 24 is the outer peripheral edge of the third main surface 3.

[0060] The third main surface 3 may be a {0001} plane or a plane inclined relative to the {0001} plane. When the third main surface 3 is inclined relative to the {0001} plane, the inclination angle relative to the {0001} plane is an off angle θ.

[0061] The maximum diameter of the third main surface 3 is defined as a second maximum diameter W2. The second maximum diameter W2 is, for example, 150 mm (6 inches) or more. The second maximum diameter W2 may be 200 mm (8 inches) or more. The upper limit of the second maximum diameter W2 is not particularly limited, but may be, for example, 400 mm (16 inches) or less. The second maximum diameter W2 is the longest linear distance between two different points on the second outer peripheral edge 24.

[0062] 4 , silicon carbide epitaxial substrate 200 according to the present embodiment mainly includes silicon carbide substrate 100 according to the present embodiment (see FIGS. 1 and 2 ), and silicon carbide epitaxial layer 20. Silicon carbide epitaxial layer 20 is provided on silicon carbide substrate 100. At first main surface 1, silicon carbide substrate 100 is in contact with silicon carbide epitaxial layer 20.

[0063] <Silicon Carbide Single Crystal Manufacturing Apparatus> Fig. 5 is a cross-sectional schematic diagram showing a silicon carbide single crystal manufacturing apparatus according to this embodiment. As shown in Fig. 5, the silicon carbide single crystal manufacturing apparatus mainly includes a crucible 50, a base member 57, a guide member 70, and a heating unit (not shown). The crucible 50 is made of graphite. The crucible 50 includes a raw material storage unit 52 and a lid unit 51. The lid unit 51 is disposed on the raw material storage unit 52. A heating unit is disposed around the outer periphery of the crucible 50.

[0064] As shown in Fig. 5, silicon carbide source material 45 is placed in source material storage unit 52. Silicon carbide source material 45 is, for example, polycrystalline silicon carbide powder. Silicon carbide seed substrate 44 is fixed to lid 51 using, for example, an adhesive (not shown). Silicon carbide seed substrate 44 is, for example, a hexagonal silicon carbide substrate of polytype 4H. Silicon carbide seed substrate 44 has a diameter of, for example, 150 mm.

[0065] Silicon carbide seed substrate 44 has fourth main surface 4 and fifth main surface 5. Fourth main surface 4 faces lid portion 51. Fifth main surface 5 is opposite fourth main surface 4.

[0066] Base member 57 is disposed inside crucible 50. Base member 57 is disposed facing silicon carbide raw material 45. As shown in Fig. 5 , a through hole 55 is provided in the center of base member 57. Fifth main surface 5 faces silicon carbide raw material 45 via through hole 55.

[0067] The guide member 70 is disposed between the base member 57 and the lid portion 51. The guide member 70 contacts the surface of the base member 57 and each of the ends of the silicon carbide seed substrate 44. The guide member 70 is made of graphite. The guide member 70 has a hollow annular shape. The diameter of the guide member 70 increases as it approaches the base member 57 from the silicon carbide seed substrate 44. The guide member 70 has an outer peripheral surface 71 and an inner peripheral surface 72. The outer peripheral surface 71 faces the crucible 50. The inner peripheral surface 72 is opposite the outer peripheral surface 71. The inner peripheral surface 72 surrounds the fifth main surface 5.

[0068] The maximum thickness H between the inner circumferential surface 72 and the outer circumferential surface 71 is, for example, 10 mm or less. The maximum thickness H is not particularly limited. The maximum thickness H may be, for example, 9 mm or less, or 7 mm or less. The maximum thickness H may be, for example, 5 mm or more, or 6 mm or more. The guide member 70 has a thin portion and a thick portion. The maximum thickness H is the maximum value of the distance between the inner circumferential surface 72 and the outer circumferential surface 71 along a straight line perpendicular to the inner circumferential surface 72.

[0069] <Method for manufacturing silicon carbide substrate> Next, a method for manufacturing silicon carbide substrate 100 will be described. Fig. 6 is a flow chart schematically showing a method for manufacturing silicon carbide substrate 100 according to the present embodiment. As shown in Fig. 6, the method for manufacturing silicon carbide substrate 100 according to the present embodiment mainly includes a step (S10) of preparing a guide member, a step (S20) of purifying the guide member in a halogen atmosphere, and a step (S30) of growing a silicon carbide crystal.

[0070] First, a guide member preparing step (S10) is performed. A graphite member is prepared. The graphite member has a shape of, for example, a rectangular parallelepiped. The graphite member is processed to prepare guide member 70 (see FIG. 5).

[0071] Next, a step (S20) of purifying the guide member in a halogen atmosphere is performed. Specifically, the guide member 70 is placed in a purification treatment device (not shown). Halogen gas is supplied into the purification treatment device. The halogen gas is, for example, chlorine gas. The purification treatment device is heated until the temperature inside the purification treatment device reaches the maximum temperature. Specifically, the temperature inside the purification treatment device is increased for, for example, 5 to 7 days. The maximum temperature inside the purification treatment device is, for example, 2150°C to 2300°C. Once the temperature inside the purification treatment device has reached the maximum temperature, the temperature inside the purification treatment device is maintained for, for example, 5 to 40 hours. As a result, metal impurities contained in the guide member 70 react with the halogen gas, and the metal impurities are removed from the guide member 70. The halogen gas that has reacted with the metal impurities is exhausted from the purification treatment device. The purification treatment device is then cooled. Specifically, the purification treatment device is cooled for, for example, 3 to 5 days. As described above, the guide member 70 is purified in a halogen atmosphere.

[0072] Next, the step (S30) of growing a silicon carbide crystal is carried out. Fig. 7 is a cross-sectional schematic diagram showing the step of growing a silicon carbide crystal. Crucible 50 is heated until the temperature of crucible 50 reaches a temperature of, for example, 2100°C or higher and 2300°C or lower. While the temperature of crucible 50 is increasing, the pressure of the atmospheric gas within crucible 50 is maintained at, for example, about 80 kPa. The atmospheric gas contains an inert gas such as argon gas, helium gas, or nitrogen gas.

[0073] Next, the pressure of the atmospheric gas in crucible 50 is reduced to, for example, 1.0 kPa. As a result, silicon carbide source material 45 begins to sublimate, and the sublimated silicon carbide gas is recrystallized on fifth main surface 5 of silicon carbide seed substrate 44. Silicon carbide single crystal 300 begins to grow on fifth main surface 5 of silicon carbide seed substrate 44. From another perspective, silicon carbide single crystal 300 begins to grow in the space surrounded by inner circumferential surface 72. While silicon carbide single crystal 300 is growing, the pressure in crucible 50 is maintained at, for example, approximately 0.1 kPa or more and 3 kPa or less. As described above, silicon carbide single crystal 300 is formed using the sublimation method.

[0074] After the growth of silicon carbide single crystal 300 is completed, silicon carbide single crystal 300 is sliced. Silicon carbide single crystal 300 is sliced ​​along a plane intersecting the growth direction of silicon carbide single crystal 300. In this manner, silicon carbide substrate 100 according to this embodiment is obtained (see FIG. 1 ).

[0075] <Method of Manufacturing Silicon Carbide Semiconductor Device> Next, a method of manufacturing the silicon carbide semiconductor device 400 according to this embodiment will be described. Fig. 8 is a flow diagram that schematically shows the method of manufacturing the silicon carbide semiconductor device 400 according to this embodiment. As shown in Fig. 8, the method of manufacturing the silicon carbide semiconductor device 400 according to this embodiment mainly includes a step (S1) of preparing a silicon carbide substrate, a step (S2) of forming a silicon carbide epitaxial layer, and a step (S3) of processing the silicon carbide epitaxial layer.

[0076] The step (S1) of preparing a silicon carbide substrate and the step (S2) of forming a silicon carbide epitaxial layer constitute a step (S40) of manufacturing a silicon carbide epitaxial substrate. In other words, the method of manufacturing silicon carbide epitaxial substrate 200 according to this embodiment mainly includes the step (S1) of preparing a silicon carbide substrate and the step (S2) of forming a silicon carbide epitaxial layer.

[0077] First, the step (S1) of preparing a silicon carbide substrate is performed. Fig. 9 is a schematic cross-sectional view showing the step (S1) of preparing a silicon carbide substrate. As shown in Fig. 9, a silicon carbide substrate 100 according to this embodiment is prepared.

[0078] Next, the step (S2) of forming a silicon carbide epitaxial layer is performed. FIG. 10 is a cross-sectional schematic diagram showing the step (S2) of forming a silicon carbide epitaxial layer. As shown in FIG. 10 , silicon carbide epitaxial layer 20 is formed by epitaxial growth on first main surface 1 of silicon carbide substrate 100. In the epitaxial growth, silane (SiH 4 ) and propane (C 3 H 8 ), for example, are used as source gases, and hydrogen (H 2 ) is used as a carrier gas. The temperature of the epitaxial growth is, for example, approximately 1400° C. or higher and 1700° C. or lower. In the epitaxial growth, an n-type impurity such as nitrogen is introduced into silicon carbide epitaxial layer 20. In this way, silicon carbide epitaxial substrate 200 according to this embodiment is prepared. In other words, silicon carbide epitaxial substrate 200 is manufactured in the step (S40) of manufacturing a silicon carbide epitaxial substrate.

[0079] 10 , silicon carbide epitaxial layer 20 may have a buffer layer 41 and a drift layer 42. Buffer layer 41 is in contact with silicon carbide substrate 100. Drift layer 42 is provided on buffer layer 41. The nitrogen concentration contained in drift layer 42 may be lower than the nitrogen concentration contained in buffer layer 41. Drift layer 42 constitutes third main surface 3.

[0080] Next, the step (S3) of processing the silicon carbide epitaxial layer is performed. Specifically, the following processing is performed on silicon carbide epitaxial layer 20. First, ions are implanted into silicon carbide epitaxial layer 20.

[0081] 11 is a schematic cross-sectional view showing a step of forming a body region. In the step of forming the body region, p-type impurities such as aluminum are ion-implanted into third main surface 3 of silicon carbide epitaxial layer 20. This forms body region 113 having p-type conductivity. Portions where body region 113 is not formed become drift layer 42 and buffer layer 41. The thickness of body region 113 is, for example, 0.9 μm. Silicon carbide epitaxial layer 20 includes buffer layer 41, drift layer 42, and body region 113.

[0082] Next, a step of forming a source region is performed. FIG. 12 is a schematic cross-sectional view showing the step of forming the source region. Specifically, n-type impurities such as phosphorus are ion-implanted into the body region 113. This forms a source region 114 having n-type conductivity. The thickness of the source region 114 is, for example, 0.4 μm. The concentration of the n-type impurities contained in the source region 114 is higher than the concentration of the p-type impurities contained in the body region 113.

[0083] Next, a p-type impurity such as aluminum is ion-implanted into the source region 114 to form a contact region 118. The contact region 118 is formed to penetrate the source region 114 and the body region 113 and to be in contact with the drift layer 42. The concentration of the p-type impurity contained in the contact region 118 is higher than the concentration of the n-type impurity contained in the source region 114.

[0084] Next, activation annealing is performed to activate the implanted impurities. The temperature of the activation annealing is, for example, 1500° C. or higher and 1900° C. or lower. The activation annealing time is, for example, about 30 minutes. The atmosphere of the activation annealing is, for example, an argon atmosphere.

[0085] Next, a step of forming trenches in the third main surface 3 of the silicon carbide epitaxial layer 20 is performed. FIG. 13 is a cross-sectional schematic diagram showing the step of forming trenches in the third main surface 3 of the silicon carbide epitaxial layer 20. A mask 117 having openings is formed on the third main surface 3 including the source region 114 and the contact region 118. The source region 114, the body region 113, and a portion of the drift layer 42 are removed by etching using the mask 117. For example, inductively coupled plasma reactive ion etching can be used as the etching method. Specifically, for example, inductively coupled plasma reactive ion etching using SF or a mixed gas of SF and O as the reactive gas is used. Recesses are formed in the third main surface 3 by etching.

[0086] Next, thermal etching is performed on the recesses. Thermal etching can be performed, for example, by heating the mask 117 formed on the third main surface 3 in an atmosphere containing a reactive gas having at least one type of halogen atom. The at least one type of halogen atom includes at least one of chlorine (Cl) atoms and fluorine (F) atoms. The atmosphere can include, for example, Cl2, BCl3, SF6, or CF4. For example, thermal etching is performed using a mixed gas of chlorine gas and oxygen gas as the reactive gas, and setting the heat treatment temperature to, for example, 700°C or higher and 1000°C or lower. The reactive gas may contain a carrier gas in addition to the above-mentioned chlorine gas and oxygen gas. Examples of the carrier gas that can be used include nitrogen gas, argon gas, and helium gas.

[0087] 13 , a trench 56 is formed in the third main surface 3 by thermal etching. The trench 56 is defined by a sidewall surface 53 and a bottom wall surface 54. The sidewall surface 53 is formed by the source region 114, the body region 113, and the drift layer 42. The bottom wall surface 54 is formed by the drift layer 42. Next, the mask 117 is removed from the third main surface 3.

[0088] Next, a step of forming a gate insulating film is performed. FIG. 14 is a schematic cross-sectional view showing the step of forming a gate insulating film. Specifically, silicon carbide epitaxial substrate 200 having trench 56 formed in third main surface 3 is heated in an oxygen-containing atmosphere at a temperature of, for example, 1300° C. or higher and 1400° C. or lower. This forms gate insulating film 115 that is in contact with drift layer 42 at bottom wall surface 54, in contact with drift layer 42, body region 113, and source region 114 at sidewall surface 53, and in contact with source region 114 and contact region 118 at third main surface 3.

[0089] Next, a step of forming a gate electrode is performed. FIG. 15 is a schematic cross-sectional view showing the step of forming a gate electrode and an interlayer insulating film. The gate electrode 127 is formed inside the trench 56 so as to be in contact with the gate insulating film 115. The gate electrode 127 is disposed inside the trench 56 and is formed on the gate insulating film 115 so as to face each of the sidewall surface 53 and the bottom wall surface 54 of the trench 56. The gate electrode 127 is formed, for example, by a low pressure chemical vapor deposition (LPCVD) method.

[0090] Next, an interlayer insulating film 126 is formed. The interlayer insulating film 126 is formed so as to cover the gate electrode 127 and to be in contact with the gate insulating film 115. The interlayer insulating film 126 is formed by, for example, chemical vapor deposition. The interlayer insulating film 126 is made of, for example, a material containing silicon dioxide. Next, the interlayer insulating film 126 and part of the gate insulating film 115 are etched so as to form openings over the source region 114 and the contact region 118. As a result, the contact region 118 and the source region 114 are exposed from the gate insulating film 115.

[0091] Next, a step of forming a source electrode is performed. The source electrode 116 is formed so as to be in contact with each of the source region 114 and the contact region 118. The source electrode 116 is formed by, for example, a sputtering method. The source electrode 116 is made of, for example, a material containing Ti (titanium), Al (aluminum), and Si (silicon).

[0092] Next, alloying annealing is performed. Specifically, the source electrode 116 in contact with each of the source region 114 and the contact region 118 is maintained at a temperature of, for example, 900° C. or higher and 1100° C. or lower for about 5 minutes. As a result, at least a portion of the source electrode 116 is silicided. This forms the source electrode 116 in ohmic contact with the source region 114. The source electrode 116 may also form an ohmic contact with the contact region 118.

[0093] Next, the source wiring 119 is formed. The source wiring 119 is electrically connected to the source electrode 116. The source wiring 119 is formed so as to cover the source electrode 116 and the interlayer insulating film 126.

[0094] Next, a step of forming a drain electrode is carried out. First, silicon carbide substrate 100 is polished at second main surface 2. This reduces the thickness of silicon carbide substrate 100. Next, drain electrode 123 is formed. Drain electrode 123 is formed so as to be in contact with second main surface 2. In this manner, silicon carbide semiconductor device 400 according to this embodiment is manufactured.

[0095] 16 is a cross-sectional schematic diagram showing the configuration of a silicon carbide semiconductor device according to this embodiment. The silicon carbide semiconductor device 400 is, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The silicon carbide semiconductor device 400 mainly includes a silicon carbide epitaxial substrate 200, a gate electrode 127, a gate insulating film 115, a source electrode 116, a drain electrode 123, a source wiring 119, and an interlayer insulating film 126. The silicon carbide epitaxial substrate 200 includes a buffer layer 41, a drift layer 42, a body region 113, a source region 114, and a contact region 118. The silicon carbide semiconductor device 400 may be, for example, an IGBT (Insulated Gate Bipolar Transistor) or the like.

[0096] Next, the effects of the method for manufacturing silicon carbide substrate 100, silicon carbide epitaxial substrate 200, and silicon carbide semiconductor device 400 according to this embodiment will be described.

[0097] When the concentration of metal impurities is high in first main surface 1 of silicon carbide substrate 100, defects (particularly threading screw dislocations) tend to increase in silicon carbide epitaxial layer 20 formed on silicon carbide substrate 100. In this case, the yield of silicon carbide semiconductor device 400 decreases. In other words, by reducing the concentration of metal impurities in first main surface 1, the yield of silicon carbide semiconductor device 400 can be improved. However, even when the concentration of metal impurities in the central portion of first main surface 1 is low, the yield of silicon carbide semiconductor device 400 may be lower than expected.

[0098] In a detailed investigation into the cause of the above phenomenon, the inventors focused on the distribution of the concentration of metal impurities on first main surface 1. Specifically, even when the concentration of metal impurities is low in the central portion of first main surface 1, the concentration of metal impurities is sometimes high in the outer periphery of first main surface 1.

[0099] The inventors have studied ways to reduce the concentration of metal impurities in the outer periphery of first main surface 1. The inventors have focused on guide member 70. When producing silicon carbide substrate 100, guide member 70 is arranged between base member 57 and lid portion 51 in order to control the temperature distribution in silicon carbide single crystal 300 (see FIG. 5 ). When silicon carbide single crystal 300 grows, silicon carbide raw material 45 sublimes, generating silicon carbide gas. Guide member 70 is etched by the silicon carbide gas. As a result, metal impurities contained in guide member 70 are released into crucible 50. An inner circumferential surface 72 of guide member 70 surrounds silicon carbide single crystal 300. Therefore, metal impurities released from guide member 70 are likely to be mixed into the outer periphery of silicon carbide single crystal 300. This is thought to result in a higher concentration of metal impurities in the outer periphery of silicon carbide substrate 100 compared to the concentration of metal impurities in the center of silicon carbide substrate 100 .

[0100] The inventors focused on a purification treatment for guide member 70. If the purification treatment is performed on the graphite member before processing the graphite member, but not on guide member 70, metal impurities inside the graphite member cannot be sufficiently removed. In this case, the concentration of metal impurities near inner circumferential surface 72 of guide member 70 cannot be sufficiently reduced. The inventors prepared guide member 70 by processing a graphite member, and then performed a purification treatment on guide member 70. This makes it possible to sufficiently remove metal impurities near inner circumferential surface 72 of guide member 70. By fabricating silicon carbide substrate 100 using guide member 70 with a low concentration of metal impurities near inner circumferential surface 72, the concentration of metal impurities in the outer periphery of silicon carbide substrate 100 can be reduced. As a result, the yield of silicon carbide semiconductor device 400 can be improved.

[0101] In silicon carbide substrate 100 according to this embodiment, the first concentration is lower than the second concentration. The second concentration is 5×10 14 atoms / cm 3 This makes it possible to suppress an increase in defects in silicon carbide epitaxial layer 20 due to metal impurities contained in silicon carbide substrate 100. This makes it possible to suppress a decrease in the yield of silicon carbide semiconductor devices 400.

[0102] In silicon carbide substrate 100 according to this embodiment, the third concentration is lower than the fourth concentration. 14 atoms / cm 3 This makes it possible to suppress an increase in defects in silicon carbide epitaxial layer 20 due to metal impurities contained in silicon carbide substrate 100. This makes it possible to suppress a decrease in the yield of silicon carbide semiconductor devices 400.

[0103] According to the silicon carbide substrate 100 according to this embodiment, the fifth concentration is 2×10 14 atoms / cm 3 The sixth concentration is 5×10 14 atoms / cm 3This makes it possible to suppress an increase in defects in silicon carbide epitaxial layer 20 due to metal impurities contained in silicon carbide substrate 100. This makes it possible to suppress a decrease in the yield of silicon carbide semiconductor devices 400.

[0104] According to silicon carbide substrate 100 according to this embodiment, the seventh concentration is 2×10 13 atoms / cm 3 The eighth concentration is 6×10 13 atoms / cm 3 This makes it possible to suppress an increase in defects in silicon carbide epitaxial layer 20 due to metal impurities contained in silicon carbide substrate 100. This makes it possible to suppress a decrease in the yield of silicon carbide semiconductor devices 400.

[0105] (Sample Preparation) First, silicon carbide substrates 100 according to Samples 1 to 4 were prepared. Silicon carbide substrate 100 according to Sample 1 is a comparative example. Silicon carbide substrates 100 according to Samples 2 to 4 are examples. Silicon carbide substrates 100 according to Samples 1 to 4 were fabricated by carrying out the silicon carbide crystal growth step (S30) described above using the silicon carbide single crystal manufacturing apparatus shown in FIG.

[0106] In producing silicon carbide substrate 100 in accordance with Sample 1, guide member 70 was produced by purifying a graphite member and then processing it into a hollow ring shape. In the method for manufacturing silicon carbide substrate 100 in accordance with Sample 1, the purification process was not carried out after guide member 70 was produced. In producing silicon carbide substrate 100 in accordance with Sample 1, maximum thickness H of guide member 70 was set to 20 mm or less.

[0107] Silicon carbide substrates 100 according to Samples 2 to 4 were fabricated using the above-described method for manufacturing silicon carbide substrate 100 (see FIGS. 6 and 7 ). In fabricating silicon carbide substrate 100 according to Sample 2, maximum thickness H of guide member 70 was set to 20 mm or less. In fabricating silicon carbide substrate 100 according to Sample 3, maximum thickness H of guide member 70 was set to 10 mm or less. In fabricating silicon carbide substrate 100 according to Sample 4, maximum thickness H of guide member 70 was set to 7 mm or less.

[0108] (Experimental Method) SIMS was used to measure the concentrations of metal impurities in each of central measurement region 65, first measurement region 61, second measurement region 62, third measurement region 63, and fourth measurement region 64 of silicon carbide substrate 100 according to Sample 1 to Sample 4. Specifically, the concentrations of titanium, chromium, copper, and aluminum were measured.

[0109] (Experimental results)

[0110]

[0111] Table 1 shows the titanium concentration on the first main surface 1. In Table 1, "ND" means that the titanium concentration is below the lower detection limit of SIMS (1×10 13 atoms / cm 3 In Table 1, "ND" indicates that the value was not detected because it was lower than the detection limit (1 × 10 13 atoms / cm 3 ) and the second concentration was divided by the first concentration to calculate the value.

[0112] As shown in Table 1, the second concentration in the silicon carbide substrates 100 according to Samples 2 to 4 was lower than the second concentration in the silicon carbide substrate 100 according to Sample 1. The second concentration in the silicon carbide substrates 100 according to Samples 2 to 4 was 5×10 14 atoms / cm 3 In silicon carbide substrates 100 according to Samples 2 to 4, the value obtained by dividing the second concentration by the first concentration was 50 or less.

[0113] From the above results, it was confirmed that the second concentration was reduced in silicon carbide substrate 100 according to the example, compared to silicon carbide substrate 100 according to the comparative example.

[0114]

[0115] Table 2 shows the concentration of chromium on the first main surface 1. In Table 2, "ND" means that the concentration of chromium is below the lower detection limit of SIMS (5×10 13 atoms / cm 3 In Table 2, "ND" indicates that the value was not detected because it was lower than the detection limit (5 × 10 13 atoms / cm 3 ) and the value was calculated by dividing the fourth concentration by the third concentration.

[0116] As shown in Table 2, the fourth concentration in silicon carbide substrates 100 according to Samples 2 to 4 was lower than the fourth concentration in silicon carbide substrate 100 according to Sample 1. The fourth concentration in silicon carbide substrates 100 according to Samples 2 to 4 was 3×10 14 atoms / cm 3 In silicon carbide substrates 100 according to samples 2 to 4, the value obtained by dividing the fourth concentration by the third concentration was 6 or less.

[0117] From the above results, it was confirmed that the fourth concentration was reduced in silicon carbide substrate 100 according to the example, compared to silicon carbide substrate 100 according to the comparative example.

[0118]

[0119] Table 3 shows the copper concentration on the first main surface 1. In Table 3, "ND" means that the copper concentration is below the lower detection limit of SIMS (2×10 14 atoms / cm 3 In Table 3, "ND" indicates that the value was not detected because it was lower than the detection limit (2 × 10 14 atoms / cm 3 ) and the value was calculated by dividing the sixth concentration by the fifth concentration.

[0120] As shown in Table 3, the sixth concentration in silicon carbide substrates 100 according to Samples 2 to 4 was lower than the sixth concentration in silicon carbide substrate 100 according to Sample 1. The sixth concentration in silicon carbide substrates 100 according to Samples 2 to 4 was 5×10 14 atoms / cm 3 It was as follows.

[0121] From the above results, it was confirmed that the sixth concentration was reduced in silicon carbide substrate 100 according to the example, compared to silicon carbide substrate 100 according to the comparative example.

[0122]

[0123] Table 4 shows the aluminum concentration on the first main surface 1. In Table 4, "ND" means that the aluminum concentration is below the lower detection limit of SIMS (2×10 13 atoms / cm 3 In Table 4, "ND" indicates that the value was not detected because it was lower than the detection limit (2 × 10 13 atoms / cm 3 ) and the value was calculated by dividing the eighth concentration by the seventh concentration.

[0124] As shown in Table 4, the eighth concentration in silicon carbide substrates 100 according to Samples 2 to 4 was lower than the eighth concentration in silicon carbide substrate 100 according to Sample 1. The eighth concentration in silicon carbide substrates 100 according to Samples 2 to 4 was 6×10 13 atoms / cm 3 It was as follows.

[0125] From the above results, it was confirmed that the eighth concentration was reduced in silicon carbide substrate 100 according to the example, compared to silicon carbide substrate 100 according to the comparative example.

[0126] With respect to numerical values ​​and numerical ranges set forth herein, unless otherwise specified, any numerical value therebetween and within that numerical range should be considered to be specifically set forth.

[0127] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0128] 1 First main surface, 2 Second main surface, 3 Third main surface, 4 Fourth main surface, 5 Fifth main surface, 7 Orientation flat, 8 Arc-shaped portion, 9 Outer peripheral side surface, 12 Virtual line, 14 First outer peripheral edge, 20 Silicon carbide epitaxial layer, 24 Second outer peripheral edge, 41 Buffer layer, 42 Drift layer, 44 Silicon carbide seed substrate, 45 Silicon carbide raw material, 50 Crucible, 51 Lid portion, 52 Raw material storage portion, 53 Side wall surface, 54 Bottom wall surface, 55 Through hole, 56 Trench, 57 Base member, 61 First measurement region, 62 Second measurement region, 63 Third measurement region, 64 Fourth measurement region, 65 Central measurement region, 70 Guide member, 71 Outer peripheral surface, 72 Inner peripheral surface, 91 First center, 92 Second center, 93 Third center, 94 Fourth center, 95 Fifth center, 100 Silicon carbide substrate, 101 First direction, 102 Second direction, 103 Third direction, 113 Body region, 114 Source region, 115 Gate insulating film, 116 Source electrode, 117 Mask, 118 Contact region, 119 Source wiring, 123 Drain electrode, 126 Interlayer insulating film, 127 Gate electrode, 200 Silicon carbide epitaxial substrate, 300 Silicon carbide single crystal, 400 Silicon carbide semiconductor device, D Shortest distance, H Maximum thickness, W1 First maximum diameter (maximum diameter), W2 Second maximum diameter, θ Off angle.

Claims

1. A main surface is provided. The main surface includes, when viewed along a straight line perpendicular to the main surface, a central measurement region at the center of the main surface, a first measurement region in a <11-20> direction relative to the central measurement region, a second measurement region in a <1-100> direction relative to the central measurement region, a third measurement region opposite the first measurement region relative to the central measurement region, and a fourth measurement region opposite the second measurement region relative to the central measurement region; When viewed along a straight line perpendicular to the main surface, the shortest distance between the center of each of the first measurement area, the second measurement area, the third measurement area, and the fourth measurement area and the outer periphery of the main surface is 10 mm; a concentration of titanium in the central measurement region is a first concentration; When the average value of the titanium concentrations in the first measurement region, the second measurement region, the third measurement region, and the fourth measurement region is defined as a second concentration, each of the first concentration and the second concentration is measured by secondary ion mass spectrometry; the first concentration is lower than the second concentration; The second concentration is 5×10 14 atoms / cm 3 The silicon carbide substrate is as follows:

2. The first concentration is 1×10 13 atoms / cm 3 The silicon carbide substrate according to claim 1 , wherein:

3. The silicon carbide substrate according to claim 1 , wherein a value obtained by dividing said second concentration by said first concentration is 50 or less.

4. A main surface is provided. The main surface includes, when viewed along a straight line perpendicular to the main surface, a central measurement region at the center of the main surface, a first measurement region in a <11-20> direction relative to the central measurement region, a second measurement region in a <1-100> direction relative to the central measurement region, a third measurement region opposite the first measurement region relative to the central measurement region, and a fourth measurement region opposite the second measurement region relative to the central measurement region; When viewed along a straight line perpendicular to the main surface, the shortest distance between the center of each of the first measurement area, the second measurement area, the third measurement area, and the fourth measurement area and the outer periphery of the main surface is 10 mm; the concentration of chromium in the central measurement area is a third concentration; When the average value of the chromium concentrations in the first measurement area, the second measurement area, the third measurement area, and the fourth measurement area is defined as a fourth concentration, each of the third concentration and the fourth concentration is measured by secondary ion mass spectrometry; the third concentration is lower than the fourth concentration; The fourth concentration is 3×10 14 atoms / cm 3 The silicon carbide substrate is as follows:

5. The third concentration is 5×10 13 atoms / cm 3 The silicon carbide substrate according to claim 4 , wherein:

6. The silicon carbide substrate according to claim 4 , wherein a value obtained by dividing said fourth concentration by said third concentration is 6 or less.

7. A main surface is provided. The main surface includes, when viewed along a straight line perpendicular to the main surface, a central measurement region at the center of the main surface, a first measurement region in a <11-20> direction relative to the central measurement region, a second measurement region in a <1-100> direction relative to the central measurement region, a third measurement region opposite the first measurement region relative to the central measurement region, and a fourth measurement region opposite the second measurement region relative to the central measurement region; When viewed along a straight line perpendicular to the main surface, the shortest distance between the center of each of the first measurement area, the second measurement area, the third measurement area, and the fourth measurement area and the outer periphery of the main surface is 10 mm; the concentration of copper in the central measurement area is a fifth concentration; When the average value of the copper concentrations in the first measurement area, the second measurement area, the third measurement area, and the fourth measurement area is defined as a sixth concentration, each of the fifth concentration and the sixth concentration is measured by secondary ion mass spectrometry; The fifth concentration is 2×10 14 atoms / cm 3 is as follows: The sixth concentration is 5×10 14 atoms / cm 3 The silicon carbide substrate is as follows:

8. A main surface is provided. The main surface includes, when viewed along a straight line perpendicular to the main surface, a central measurement region at the center of the main surface, a first measurement region in a <11-20> direction relative to the central measurement region, a second measurement region in a <1-100> direction relative to the central measurement region, a third measurement region opposite the first measurement region relative to the central measurement region, and a fourth measurement region opposite the second measurement region relative to the central measurement region; When viewed along a straight line perpendicular to the main surface, the shortest distance between the center of each of the first measurement area, the second measurement area, the third measurement area, and the fourth measurement area and the outer periphery of the main surface is 10 mm; the concentration of aluminum in the central measurement region is a seventh concentration; When the average value of the aluminum concentrations in the first measurement region, the second measurement region, the third measurement region, and the fourth measurement region is defined as an eighth concentration, each of the seventh concentration and the eighth concentration is measured by secondary ion mass spectrometry; The seventh concentration is 2×10 13 atoms / cm 3 is as follows: The eighth concentration is 6×10 13 atoms / cm 3 The silicon carbide substrate is as follows:

9. The silicon carbide substrate according to claim 1 , wherein said main surface has a maximum diameter of 150 mm or greater.

10. The concentration of nitrogen in the central measurement area is 1×10 17 atoms / cm 3 The silicon carbide substrate according to claim 1 .

11. A step of preparing a silicon carbide substrate according to any one of claims 1 to 8; and forming a silicon carbide epitaxial layer on the silicon carbide substrate.

12. A step of preparing a silicon carbide substrate according to any one of claims 1 to 8; forming a silicon carbide epitaxial layer on the silicon carbide substrate; and processing the silicon carbide epitaxial layer.