Silicon carbide substrate, silicon-carbide epitaxial substrate, method for producing silicon carbide substrate, and method for producing silicon-carbide semiconductor device

Abstract

This silicon carbide substrate has a main surface. The silicon carbide substrate contains a plurality of carbon inclusions. The main surface has a plurality of pits formed therein. The plurality of carbon inclusions each have a maximum length of 2-50 μm along a direction perpendicular to the main surface, and the plurality of pits each have an area of 3,000 μm2 or larger. The ratio of the area density of the plurality of pits to the area density of the plurality of carbon inclusions is 0.008 or less.

Description

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

[0001] The present disclosure relates to a silicon carbide substrate, a silicon carbide epitaxial substrate, a method for manufacturing a silicon carbide substrate, and a method for manufacturing a silicon carbide semiconductor device. This application claims priority to Japanese Patent Application No. 2022-078328, filed May 11, 2022. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] WO 2016 / 063632 (Patent Document 1) describes a method for cleaning a silicon carbide substrate.

[0003] International Publication No. 2016 / 063632

[0004] A silicon carbide substrate according to the present disclosure has a main surface. The silicon carbide substrate includes a plurality of carbon inclusions. A plurality of pits are formed in the main surface. When viewed in a direction perpendicular to the main surface, the maximum length of each of the plurality of carbon inclusions is 2 μm or more and 50 μm or less, and the area of ​​each of the plurality of pits is 3000 μm. 2 The ratio of the areal density of the plurality of pits to the areal density of the plurality of carbon inclusions is 0.008 or less.

[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 cross-sectional view showing the configuration of carbon inclusions. FIG. 4 is a schematic plan view showing the configuration of a first pit. FIG. 5 is a schematic plan view showing the configuration of a second pit. FIG. 6 is a schematic plan view showing the configuration of a silicon carbide epitaxial substrate according to this embodiment. FIG. 7 is a schematic cross-sectional view taken along line VII-VII in FIG. 6. FIG. 8 is a schematic plan view showing the configuration of a third pit. FIG. 9 is a schematic plan view showing the configuration of a fourth pit. FIG. 10 is a schematic cross-sectional view showing an apparatus for producing a silicon carbide single crystal according to this embodiment. FIG. 11 is a schematic cross-sectional view showing an example of the arrangement of silicon carbide raw materials arranged in the apparatus for producing a silicon carbide single crystal according to this embodiment. FIG. 12 is a flow diagram showing an outline of a method for producing a silicon carbide substrate according to this embodiment. FIG. 13 is a schematic cross-sectional view showing the configuration of a silicon carbide substrate. FIG. 14 is a cross-sectional view schematically showing the structure of the silicon carbide substrate after a first chemical mechanical polishing step. FIG. 15 is a cross-sectional view schematically showing the structure of the silicon carbide substrate after a cleaning step. FIG. 16 is a flowchart generally showing a method for manufacturing a silicon carbide semiconductor device according to this embodiment. FIG. 17 is a cross-sectional view schematically showing the step of forming a body region. FIG. 18 is a cross-sectional view schematically showing the step of forming a source region. FIG. 19 is a cross-sectional view schematically showing the step of forming a trench in a third main surface of the silicon carbide epitaxial layer. FIG. 20 is a cross-sectional view schematically showing the step of forming a gate insulating film. FIG. 21 is a cross-sectional view schematically showing the step of forming a gate electrode and an interlayer insulating film. FIG. 22 is a cross-sectional view schematically showing the structure 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 improve the yield of silicon carbide semiconductor devices. [Effects of the Present Disclosure] According to the present disclosure, it is possible to improve the yield of silicon carbide semiconductor devices. [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0007] (1) Silicon carbide substrate 100 according to the present disclosure has a main surface 1. Silicon carbide substrate 100 includes a plurality of carbon inclusions 5. A plurality of pits 11 are formed in main surface 1. When viewed in a direction perpendicular to main surface 1, the maximum length of each of the plurality of carbon inclusions 5 is not less than 2 μm and not more than 50 μm, and the area of ​​each of the plurality of pits 11 is 3000 μm. 2 The ratio of the surface density of the plurality of pits 11 to the surface density of the plurality of carbon inclusions 5 is 0.008 or less.

[0008] (2) According to silicon carbide substrate 100 in accordance with (1) above, the ratio of the areal density of pits 11 to the areal density of carbon inclusions 5 may be equal to or less than 0.004.

[0009] (3) According to the silicon carbide substrate 100 according to (1) or (2) above, the surface density of the plurality of carbon inclusions 5 is 155 pieces / cm 2 It may be the following:

[0010] (4) According to the silicon carbide substrate 100 according to the above (3), the surface density of the plurality of carbon inclusions 5 is 100 pieces / cm 2 It may be the following:

[0011] (5) According to the silicon carbide substrate 100 according to the above (4), the surface density of the plurality of carbon inclusions 5 is 50 pieces / cm 2 It may be the following:

[0012] (6) According to silicon carbide substrate 100 according to any one of (1) to (5) above, the maximum diameter of the main surface may be 150 mm or more.

[0013] (7) A silicon carbide epitaxial substrate 200 according to the present disclosure includes a silicon carbide substrate 100 and a silicon carbide epitaxial layer 20. The silicon carbide substrate 100 includes a plurality of carbon inclusions 5. The silicon carbide epitaxial layer 20 is provided on the silicon carbide substrate 100. A plurality of pits 21 are formed on the main surface 3 of the silicon carbide epitaxial layer 20. When viewed in a direction perpendicular to the main surface 3, the maximum length of each of the plurality of carbon inclusions 5 is not less than 2 μm and not more than 50 μm, and the area of ​​each of the plurality of pits 21 is not less than 5000 μm. 2 The ratio of the surface density of the plurality of pits 21 to the surface density of the plurality of carbon inclusions 5 is 0.01 or less.

[0014] (8) According to silicon carbide epitaxial substrate 200 according to (7) above, the ratio of the areal density of pits 21 to the areal density of the plurality of carbon inclusions 5 may be 0.005 or less.

[0015] (9) According to silicon carbide epitaxial substrate 200 according to (7) or (8) above, main surface 3 may have a maximum diameter of 150 mm or more.

[0016] (10) A method for manufacturing a silicon carbide semiconductor device according to the present disclosure includes the following steps: preparing silicon carbide epitaxial substrate 200 according to any one of (7) to (9) above; and processing silicon carbide epitaxial substrate 200.

[0017] (11) A method for manufacturing a silicon carbide substrate 100 according to the present disclosure includes the following steps: Chemical mechanical polishing is performed on the silicon carbide substrate 110 using a first polishing liquid. After chemical mechanical polishing is performed on the silicon carbide substrate 110, the silicon carbide substrate 110 is cleaned using a cleaning liquid. After cleaning the silicon carbide substrate 110 using the cleaning liquid, chemical mechanical polishing is performed on the silicon carbide substrate 110 using a second polishing liquid. The silicon carbide substrate 110 includes a plurality of carbon inclusions 5. The first polishing liquid includes permanganate. The second polishing liquid does not include permanganate. The cleaning liquid is a mixture of sulfuric acid, hydrogen peroxide solution, and ultrapure water.

[0018] (12) According to the method for manufacturing silicon carbide substrate 100 according to (11) above, the abrasive grains used in the second polishing liquid may contain colloidal silica.

[0019] (13) According to the method for manufacturing silicon carbide substrate 100 according to (11) or (12) above, the abrasive grains used in the first polishing liquid do not need to contain colloidal silica.

[0020] (14) In the method for manufacturing silicon carbide substrate 100 according to any one of (11) to (13) above, the second polishing liquid may have a hydrogen ion exponent of less than 7.

[0021] (15) In the method for manufacturing silicon carbide substrate 100 according to any one of (11) to (14) above, the first polishing liquid may have a hydrogen ion exponent of less than 9.

[0022] (16) According to the method for manufacturing silicon carbide substrate 100 according to any one of (11) to (15) above, the volume of the sulfuric acid may be 10 times the volume of the hydrogen peroxide solution, and the volume of the ultrapure water may be 1 to 10 times the volume of the hydrogen peroxide solution.

[0023] (17) According to the method for manufacturing silicon carbide substrate 100 according to any one of (11) to (16) above, the maximum length of each of the plurality of carbon inclusions 5 may be 2 μm or more and 50 μm or less when viewed in a direction perpendicular to the main surface of silicon carbide base material 110.

[0024] (18) According to the method for manufacturing silicon carbide substrate 100 according to any one of (11) to (17) above, the surface density of the plurality of carbon inclusions 5 is 600 pieces / cm 2 The following may be used. [Details of 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 designated by the same reference numerals, and descriptions thereof 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 above the number, but in this specification, a negative sign is placed before the number.

[0025] <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.

[0026] 1 and 2 , silicon carbide substrate 100 according to the present embodiment mainly has a first main surface 1, a second main surface 2, and a first outer peripheral edge 19. Second main surface 2 is located on the opposite side to first main surface 1. First outer peripheral edge 19 is continuous with each of first main surface 1 and second main surface 2. First outer peripheral edge 19 has, for example, an orientation flat 7 and an arc-shaped portion 8.

[0027] As shown in Figure 1, the orientation flat 7 is linear when viewed in a direction perpendicular to the first main surface 1. The orientation flat 7 extends along a first direction 101. The arc-shaped portion 8 is continuous with the orientation flat 7. The arc-shaped portion 8 is arc-shaped when viewed in a direction perpendicular to the first main surface 1. The first main surface 1 extends along each of the first direction 101 and the second direction 102. When viewed in a direction perpendicular to the first main surface 1, the second direction 102 is perpendicular to the first direction 101.

[0028] The first direction 101 is, for example, the <11-20> direction. The first direction 101 may be, for example, the [11-20] 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.

[0029] 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.

[0030] 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) 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 may be 2° or more and 6° or less.

[0031] The maximum diameter W1 of the first main surface 1 is, for example, 100 mm (4 inches) or more. The maximum diameter W1 of the first main surface 1 may be 150 mm (6 inches) or more, or 200 mm (8 inches) or more. The maximum diameter W1 of the first main surface 1 is not particularly limited, but may be, for example, 400 mm (16 inches) or less. The maximum diameter W1 of the first main surface 1 is the longest linear distance between two different points on the first outer peripheral edge 19.

[0032] In this specification, 4 inches refers to 100 mm or 101.6 mm (4 inches x 25.4 mm / inch). 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).

[0033] As shown in Figure 2, silicon carbide substrate 100 according to this embodiment includes carbon inclusions 5 and silicon carbide regions 10. Carbon inclusions 5 are clumps of carbon. As shown in Figure 2, in a cross-sectional view, carbon inclusions 5 are not particularly limited, and may be, for example, substantially circular or substantially elliptical. Silicon carbide regions 10 are located around carbon inclusions 5. Carbon inclusions 5 are embedded in silicon carbide regions 10.

[0034] 3 is a schematic cross-sectional view showing the configuration of carbon inclusions 5. The cross section shown in FIG. 3 is parallel to first main surface 1. As shown in FIG. 3, the maximum length X of carbon inclusions 5 is 2 μm or more and 50 μm or less when viewed in a direction perpendicular to first main surface 1. The maximum length X of carbon inclusions 5 is not particularly limited, but may be, for example, 5 μm or more, or 10 μm or more. The maximum length X of carbon inclusions 5 is not particularly limited, but may be, for example, 40 μm or less, or 30 μm or less.

[0035] The surface density of the carbon inclusions 5 is, for example, 155 pieces / cm 2 The surface density of the carbon inclusions 5 is not particularly limited, but may be, for example, 100 pieces / cm 2 It may be 50 pieces / cm or less. 2 or less, or 25 particles / cm 2 It may be 10 pieces / cm or less. 2 The surface density of the carbon inclusions 5 is not particularly limited, but may be, for example, 0.1 pieces / cm 2 or more, or 1 piece / cm 2 It may be more than that.

[0036] Next, a method for measuring the areal density of the carbon inclusions 5 will be described. The areal density of the carbon inclusions 5 can be measured using a Nomarski-type optical microscope. As a Nomarski-type optical microscope, for example, a microscope (MX-51) manufactured by Olympus Corporation can be used. The magnification of the microscope is, for example, about 50 times or more and 200 times or less.

[0037] As shown in FIG. 1 , the measurement regions for carbon inclusions 5 are, for example, a first measurement region 61, a second measurement region 62, a third measurement region 63, a fourth measurement region 64, and a fifth measurement region 65. The center of the first measurement region 61 is located 60 mm away from the center of the first main surface 1 in the first direction 101. The center of the second measurement region 62 is located 60 mm away from the center of the first main surface 1 in the second direction 102. The center of the third measurement region 63 is located 60 mm away from the center of the first main surface 1 in the opposite direction to the first direction 101. The center of the fourth measurement region 64 is located 60 mm away from the center of the first main surface 1 in the opposite direction to the second direction 102. The center of the fifth measurement region 65 coincides with the center of the first main surface 1. Each measurement region is rectangular in shape. The length of each measurement region in the first direction 101 is 0.4 mm. The length of each measurement region in the second direction 102 is 0.3 mm.

[0038] In each measurement region, the focus of the microscope is shifted from second main surface 2 to first main surface 1 of silicon carbide substrate 100, and the number of carbon inclusions 5 is visually counted at a plurality of cross-sectional positions E parallel to second main surface 2. For example, the microscope is focused at a plurality of cross-sectional positions E divided equally into 10 sections in the thickness direction of silicon carbide substrate 100, and the number of carbon inclusions 5 is counted at each of the plurality of cross-sectional positions E.

[0039] The value obtained by dividing the number of carbon inclusions 5 by the measurement area is taken as the areal density of carbon inclusions 5 at the cross-sectional position E. The average value of the areal densities of carbon inclusions 5 at the multiple cross-sectional positions E is taken as the areal density of silicon carbide substrate 100 in each measurement region. However, carbon inclusions 5 exposed on each of first main surface 1 and second main surface 2 are not counted. The average value of the areal density of carbon inclusions 5 in each measurement region is taken as the areal density of carbon inclusions 5 in silicon carbide substrate 100 according to this embodiment.

[0040] As shown in Fig. 2, a first pit 11 is formed in the first main surface 1. The first pit 11 is a bottomed hole that opens to the first main surface 1. The depth of the first pit 11 (first depth D1) is, for example, 2 µm or more. The first depth D1 is not particularly limited, but may be, for example, 5 µm or more, or 10 µm or more. The first depth D1 is not particularly limited, but may be, for example, 50 µm or less, or 100 µm or less.

[0041] 4 is a schematic plan view showing the configuration of the first pit 11. As shown in FIG. 4, the shape of the first pit 11 is not particularly limited, but may be, for example, substantially circular. When viewed in a direction perpendicular to the first main surface 1, the area of ​​the first pit 11 is 3000 μm 2 The area of ​​the first pit 11 is not particularly limited, but may be, for example, 3500 μm 2 It may be 4000 μm or more. 2 The area of ​​the first pit 11 is not particularly limited, but may be, for example, 9000 μm 2 It may be 6000 μm or less. 2 It may be the following:

[0042] The ratio of the areal density of the first pits 11 to the areal density of the carbon inclusions 5 is 0.008 or less. The ratio of the areal density of the first pits 11 to the areal density of the carbon inclusions 5 is not particularly limited, but may be, for example, 0.006 or less, or 0.004 or less. The ratio of the areal density of the first pits 11 to the areal density of the carbon inclusions 5 is not particularly limited, but may be, for example, 0.001 or more, or 0.002 or more.

[0043] As shown in FIG. 2 , second pits 12 may be formed in the first main surface 1. The second pits 12 are bottomed holes that open to the first main surface 1. The depth of the second pits 12 (second depth D2) is smaller than the depth of the first pits 11 (first depth D1). The second depth D2 is, for example, 1 μm or more. The second depth D2 is not particularly limited, but may be, for example, 2.5 μm or more, or 5 μm or more. The second depth D2 is not particularly limited, but may be, for example, 25 μm or less, or 50 μm or less.

[0044] 5 is a schematic plan view showing the configuration of the second pit 12. As shown in FIG. 5, the shape of the second pit 12 is not particularly limited, but may be, for example, substantially circular. The area of ​​the second pit 12 is smaller than the area of ​​the first pit 11. When viewed in a direction perpendicular to the first main surface 1, the area of ​​the second pit 12 is 3000 μm 2 The area of ​​the second pit 12 is not particularly limited, but is, for example, 1 μm 2 It may be 10 μm or more. 2 The area of ​​the second pit 12 is not particularly limited, but may be, for example, 2000 μm 2 It may be less than 1000 μm 2 It may be the following:

[0045] Next, a method for measuring the first pits 11 and the second pits 12 will be described. The first pits 11 and the second pits 12 can be identified by observing the first main surface 1 of the silicon carbide substrate 100 using, for example, a defect inspection device having a confocal differential interference microscope. As a defect inspection device having a confocal differential interference microscope, for example, a WASAVI series "SICA 6X" manufactured by Lasertec Corporation can be used. The magnification of the objective lens is 10x. Light having a wavelength of 546 nm is irradiated onto the first main surface 1 of the silicon carbide substrate 100 from a light source such as a mercury xenon lamp, and the reflected light of the light is observed by a light receiving element. A threshold value, which is an index of the measurement sensitivity of the SICA, is, for example, ThreshS40.

[0046] <Silicon carbide epitaxial substrate> Next, the configuration of silicon carbide epitaxial substrate 200 according to this embodiment will be described. Fig. 6 is a plan view schematically showing the configuration of silicon carbide epitaxial substrate 200 according to this embodiment. Fig. 7 is a cross-sectional view schematically showing a silicon carbide epitaxial substrate 200 taken along line VII-VII in Fig. 6. The cross-sectional view shown in Fig. 7 corresponds to the cross-sectional view shown in Fig. 2.

[0047] 6 , silicon carbide epitaxial substrate 200 according to the present embodiment has third main surface 3 and second outer peripheral edge 29. Second outer peripheral edge 29 has, for example, orientation flat 7 and arc-shaped portion 8. Second outer peripheral edge 29 is continuous with third main surface 3.

[0048] The third main surface 3 may be a {0001} plane, or may be a plane inclined with respect to the {0001} plane. When the third main surface 3 is inclined with respect to the {0001} plane, the inclination angle (off angle) with respect to the {0001} plane is, for example, 1° or more and 8° or less. When the third main surface 3 is inclined with respect to the {0001} plane, the inclination direction (off direction) of the third main surface 3 is, for example, the <11-20> direction. The off angle may be, for example, 2° or more and 6° or less.

[0049] 7 , silicon carbide epitaxial substrate 200 according to this embodiment includes silicon carbide substrate 100 according to this embodiment and silicon carbide epitaxial layer 20. Silicon carbide epitaxial layer 20 is provided on silicon carbide substrate 100. Silicon carbide epitaxial layer 20 fills each of first pit 11 and second pit 12. From another perspective, a portion of silicon carbide epitaxial layer 20 is provided inside each of first pit 11 and second pit 12.

[0050] Silicon carbide epitaxial layer 20 has a third main surface 3 and a fourth main surface 4. Fourth main surface 4 is located on the opposite side to third main surface 3. Fourth main surface 4 is in contact with first main surface 1. From another perspective, silicon carbide epitaxial layer 20 is in contact with silicon carbide substrate 100 at fourth main surface 4. Silicon carbide substrate 100 includes carbon inclusions 5. Silicon carbide epitaxial substrate 200 may or may not include carbon inclusions 5.

[0051] As shown in Fig. 7, a third pit 21 is formed in the third main surface 3. The third pit 21 is a bottomed hole that opens to the third main surface 3. The depth of the third pit 21 (third depth D3) is, for example, 2 µm or more. The third depth D3 is not particularly limited, but may be, for example, 5 µm or more, or 10 µm or more. The third depth D3 is not particularly limited, but may be, for example, 50 µm or less, or 100 µm or less.

[0052] 8 is a schematic plan view showing the configuration of the third pit 21. As shown in FIG. 8, the shape of the third pit 21 is not particularly limited, but may be, for example, substantially circular. When viewed in a direction perpendicular to the third main surface 3, the area of ​​the third pit 21 is 5000 μm 2 The area of ​​the third pit 21 is not particularly limited, but may be, for example, 5500 μm 2 It may be 6000 μm or more. 2 The area of ​​the third pit 21 is not particularly limited, but may be, for example, 11000 μm 2 It may be less than 8000 μm 2 The area of ​​the third pit 21 may be larger than the area of ​​the first pit 11. When viewed in a direction perpendicular to the third main surface 3, the third pit 21 is disposed at a position overlapping the first pit 11.

[0053] The ratio of the areal density of the third pits 21 to the areal density of the carbon inclusions 5 is 0.01 or less. The ratio of the areal density of the third pits 21 to the areal density of the carbon inclusions 5 is not particularly limited, but may be, for example, 0.005 or less, or 0.003 or less. The ratio of the areal density of the third pits 21 to the areal density of the carbon inclusions 5 is not particularly limited, but may be, for example, 0.001 or more, or 0.002 or more.

[0054] As shown in FIG. 7 , a fourth pit 22 may be formed in the third main surface 3. The fourth pit 22 is a bottomed hole that opens to the third main surface 3. The depth of the fourth pit 22 (fourth depth D4) is smaller than the depth of the third pit 21 (third depth D3). The fourth depth D4 is, for example, 1 μm or more. The fourth depth D4 is not particularly limited, but may be, for example, 2.5 μm or more, or 5 μm or more. The fourth depth D4 is not particularly limited, but may be, for example, 25 μm or less, or 50 μm or less.

[0055] 9 is a schematic plan view showing the configuration of the fourth pit 22. As shown in FIG. 9, the shape of the fourth pit 22 is not particularly limited, but may be, for example, substantially circular. The area of ​​the fourth pit 22 is smaller than the area of ​​the third pit 21. When viewed in a direction perpendicular to the third main surface 3, the area of ​​the fourth pit 22 is 5000 μm 2 The area of ​​the fourth pit 22 is not particularly limited, but is, for example, 1 μm 2 It may be 10 μm or more. 2 The area of ​​the fourth pit 22 is not particularly limited, but may be, for example, 4000 μm 2 It may be 3000 μm or less. 2 The area of ​​the fourth pit 22 may be larger than the area of ​​the second pit 12. When viewed in a direction perpendicular to the third main surface 3, the fourth pit 22 is disposed at a position overlapping the second pit 12.

[0056] The maximum diameter W1 of the third main surface 3 is, for example, 100 mm (4 inches) or more. The maximum diameter W1 of the third main surface 3 may be 150 mm (6 inches) or more, or 200 mm (8 inches) or more. The maximum diameter W1 of the third main surface 3 is not particularly limited, but may be, for example, 400 mm (16 inches) or less. The maximum diameter W1 of the third main surface 3 is the longest linear distance between two different points on the second outer peripheral edge 29.

[0057] <Silicon carbide single crystal manufacturing apparatus> Figure 10 is a cross-sectional schematic diagram showing a silicon carbide single crystal manufacturing apparatus according to this embodiment. As shown in Figure 10, the silicon carbide single crystal manufacturing apparatus mainly includes a crucible 50, a cover member 57, a guide member 58, and a resistance heater (not shown). Crucible 50 includes a raw material container 52 and a lid 51. Lid 51 is disposed on raw material container 52.

[0058] As shown in Fig. 10, 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 unit 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.

[0059] The cover member 57 is disposed inside the crucible 50. The cover member 57 is disposed facing the surface of the silicon carbide raw material 45. The distance (fifth distance D5) between the surface of the silicon carbide raw material 45 and the cover member 57 is, for example, 50 mm or less. The guide member 58 is disposed between the cover member 57 and the silicon carbide seed substrate 44. The guide member 58 contacts each of the surface of the cover member 57 and the end of the silicon carbide seed substrate 44. The distance (sixth distance D6) between the surface of the silicon carbide raw material 45 and the back surface of the silicon carbide seed substrate 44 is, for example, 125 mm or more.

[0060] As shown in FIG. 10 , a through-hole 55 is provided in the center of the cover member 57. The surface of the silicon carbide source material 45 faces the back surface of the silicon carbide seed substrate 44 through the through-hole 55. The area of ​​the through-hole 55 is set to 40% or less of the area of ​​the back surface of the silicon carbide seed substrate 44. This makes it possible to prevent carbon flying from near the silicon carbide source material 45 from being incorporated into the silicon carbide single crystal 300 growing on the silicon carbide seed substrate 44. The silicon carbide source material 45 may be provided with a hole 43. The bottom surface of the crucible 50 is exposed to the hole 43. As described above, the silicon carbide seed substrate 44 and the silicon carbide source material 45 are placed in the crucible 50.

[0061] 11 is a cross-sectional schematic diagram showing an example of the arrangement of silicon carbide raw material 45 arranged in the silicon carbide single crystal manufacturing apparatus according to this embodiment. As shown in FIG. 11 , silicon carbide raw material 45 does not need to be provided with hole 43. In this case, silicon carbide raw material 45 completely covers the bottom surface of crucible 50. This makes it possible to prevent carbon from flying in from the bottom surface of crucible 50.

[0062] <Method for manufacturing silicon carbide substrate> Next, a method for manufacturing silicon carbide substrate 100 according to this embodiment will be described. Fig. 12 is a flow diagram schematically showing the method for manufacturing silicon carbide substrate 100 according to this embodiment. As shown in Fig. 12, the method for manufacturing silicon carbide substrate 100 according to this embodiment mainly includes a crystal growth step (S10), a double-side mechanical polishing step (S20), a first chemical mechanical polishing step (S30), a cleaning step (S40), and a second chemical mechanical polishing step (S50).

[0063] First, the crystal growth step (S10) is carried out. The crucible 50 is heated to a temperature of, for example, 2100° C. or higher and 2300° C. or lower. While the temperature of the crucible 50 is rising, the pressure of the atmospheric gas in the 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.

[0064] Next, the pressure of the ambient 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 recrystallizes on the back surface of silicon carbide seed substrate 44. Silicon carbide single crystal 300 begins to grow on the back surface of silicon carbide seed substrate 44. While silicon carbide single crystal 300 is growing, the pressure in crucible 50 is maintained at, for example, about 0.1 kPa or more and 3 kPa or less. As described above, silicon carbide single crystal 300 is formed using the sublimation method. Next, silicon carbide single crystal 300 is cut into a plurality of silicon carbide substrates 110 using a saw wire.

[0065] Fig. 13 is a cross-sectional schematic diagram showing the configuration of a silicon carbide substrate 110. The silicon carbide substrate 110 is the silicon carbide substrate 100 before polishing. As shown in Fig. 13, the silicon carbide substrate 110 has a first main surface 1 and a second main surface 2. The second main surface 2 is located on the opposite side to the first main surface 1. The silicon carbide substrate 110 includes carbon inclusions 5 and a silicon carbide region 10.

[0066] When viewed in a direction perpendicular to first main surface 1 of silicon carbide substrate 110, carbon inclusion 5 has a maximum length X of 2 μm or more and 50 μm or less (see FIG. 3 ). The maximum length X of carbon inclusion 5 is not particularly limited, but may be, for example, 5 μm or more, or 10 μm or more. The maximum length X of carbon inclusion 5 is not particularly limited, but may be, for example, 40 μm or less, or 30 μm or less.

[0067] The surface density of the carbon inclusions 5 is, for example, 600 pieces / cm 2 The surface density of the carbon inclusions 5 is not particularly limited, but may be, for example, 155 pieces / cm 2 It may be 100 pieces / cm or less. 2 It may be 50 pieces / cm or less. 2 or less, or 25 particles / cm 2 It may be 10 pieces / cm or less. 2 The surface density of the carbon inclusions 5 is not particularly limited, but may be, for example, 0.1 pieces / cm 2or more, or 1 piece / cm 2 The method for measuring the surface density of the carbon inclusions 5 is as described above.

[0068] Next, a double-side mechanical polishing step (S20) is carried out. Specifically, the silicon carbide substrate 110 is placed between a first platen and a second platen so that the first main surface 1 faces the first platen (not shown) and the second main surface 2 corresponds to the second platen (not shown). Next, a slurry is introduced between the first main surface 1 and the first platen and between the second main surface 2 and the second platen. The slurry contains, for example, diamond abrasive grains and water. The diameter of the diamond abrasive grains is, for example, 1 μm or more and 3 μm or less. A load is applied to the first main surface 1 by the first platen and a load is applied to the second main surface 2 by the second platen, thereby mechanically polishing both sides of the silicon carbide substrate 110.

[0069] Next, a first chemical mechanical polishing step (S30) is performed. Chemical mechanical polishing is performed on the silicon carbide substrate 110 using a first polishing liquid. The first polishing liquid contains a permanganate. The permanganate is, for example, potassium permanganate or sodium permanganate. The abrasive grains used in the first chemical mechanical polishing step (S30) do not need to contain colloidal silica. The abrasive grains used in the first chemical mechanical polishing step (S30) are, for example, alumina. Alumina is harder than colloidal silica and can therefore effectively polish the silicon carbide substrate 110.

[0070] The hydrogen ion exponent (pH) of the first polishing liquid may be less than 9. The hydrogen ion exponent (pH) of the first polishing liquid is not particularly limited, but may be, for example, less than 8 or less than 7. The hydrogen ion exponent (pH) of the first polishing liquid is not particularly limited, but may be, for example, greater than 1 or greater than 3.

[0071] The first polishing liquid may be, for example, "DSC-0201" manufactured by Fujimi Incorporated Co., Ltd. The first polishing liquid may be, for example, "NANOBIX" manufactured by Mitsui Mining & Smelting Co., Ltd. or "SC-2000" manufactured by SINMAT.

[0072] 14 is a cross-sectional schematic diagram showing the configuration of the silicon carbide substrate 110 after the first chemical mechanical polishing step. As shown in FIG. 14 , the first polishing liquid 30 remains on the first main surface 1 of the silicon carbide substrate 110. The first polishing liquid 30 contains manganese. The polishing liquid containing manganese reacts with the silicon carbide region 10 near the carbon inclusion 5, softening (activating) the silicon carbide region 10 near the carbon inclusion 5. When additional chemical mechanical polishing is performed in this state, the silicon carbide region 10 near the carbon inclusion 5 is removed along with the carbon inclusion 5. As a result, a large pit (first pit 11) may be formed in the first main surface 1.

[0073] In the method for manufacturing silicon carbide substrate 100 according to this embodiment, a cleaning step (S40) is performed to suppress formation of first pits 11. First, silicon carbide base material 110 is cleaned while running pure water. The flow rate of the pure water is, for example, 1 liter per minute. The time for cleaning with running pure water is, for example, 1 minute.

[0074] Next, the silicon carbide substrate 110 is cleaned using a cleaning liquid. The step of cleaning the silicon carbide substrate 110 using a cleaning liquid is performed after the first chemical mechanical polishing step (S30). In the step of cleaning the silicon carbide substrate 110 using the cleaning liquid, metal impurities such as manganese are mainly removed from the silicon carbide substrate 110.

[0075] The cleaning solution is a mixture of sulfuric acid, hydrogen peroxide, and ultrapure water. In other words, the cleaning solution is a mixture of sulfuric acid and hydrogen peroxide. For example, concentrated sulfuric acid with a mass percentage concentration of 98% can be used as the sulfuric acid. For example, hydrogen peroxide with a mass percentage concentration of 30% can be used as the hydrogen peroxide.

[0076] The volume ratio of sulfuric acid, hydrogen peroxide, and ultrapure water contained in the cleaning solution is, for example, 10 (sulfuric acid):1 (hydrogen peroxide):1 (ultrapure water). The volume ratio of sulfuric acid, hydrogen peroxide, and ultrapure water may be, for example, 10 (sulfuric acid):1 (hydrogen peroxide):1 (ultrapure water) to 10 (sulfuric acid):1 (hydrogen peroxide):10 (ultrapure water). In other words, the volume of sulfuric acid may be 10 times the volume of hydrogen peroxide, and the volume of ultrapure water may be 1 to 10 times the volume of hydrogen peroxide. The cleaning time is, for example, 20 minutes or more.

[0077] Fig. 15 is a cross-sectional schematic diagram showing the configuration of the silicon carbide substrate 110 after the cleaning step. As shown in Fig. 15, the first polishing liquid 30 has been removed from the first main surface 1 of the silicon carbide substrate 110. This makes it possible to suppress softening of the silicon carbide region 10 near the carbon inclusion 5. The carbon inclusion 5 may remain in the silicon carbide substrate 110 in a state exposed to the first main surface 1.

[0078] Next, a second chemical mechanical polishing step (S50) is performed. After the cleaning step (S40), the silicon carbide substrate 110 is subjected to chemical mechanical polishing using a second polishing liquid. The second polishing liquid does not contain permanganate. The abrasive grains used in the step of chemical mechanical polishing the silicon carbide substrate 110 using the second polishing liquid may contain colloidal silica.

[0079] The hydrogen ion exponent (pH) of the second polishing liquid may be smaller than 7. The hydrogen ion exponent (pH) of the second polishing liquid is not particularly limited, but may be, for example, smaller than 6 or smaller than 5. The hydrogen ion exponent (pH) of the second polishing liquid is not particularly limited, but may be, for example, larger than 1 or larger than 3. The hydrogen ion exponent of the second polishing liquid may be smaller or larger than the hydrogen ion exponent of the first polishing liquid.

[0080] As the second polishing liquid, for example, "DSC-0902" manufactured by Fujimi Incorporated can be used. As the second polishing liquid, for example, "CL-4005" manufactured by Yamaguchi Seiken Co., Ltd. can also be used. The second polishing liquid does not contain manganese. Therefore, it is possible to suppress softening of silicon carbide region 10 near carbon inclusion 5. As a result, it is possible to suppress the formation of large pits (first pits 11) in first main surface 1. Note that by removing only carbon inclusions 5 exposed to first main surface 1, small pitches (second pits 12) may be formed in first main surface 1. In this manner, silicon carbide substrate 100 according to this embodiment is obtained.

[0081] <Method of Manufacturing Silicon Carbide Semiconductor Device> Next, a method of manufacturing silicon carbide semiconductor device 400 according to this embodiment will be described. Fig. 16 is a flowchart that schematically shows the method of manufacturing silicon carbide semiconductor device 400 according to this embodiment. As shown in Fig. 16, the method of manufacturing silicon carbide semiconductor device 400 according to this embodiment mainly includes a step (S1) of preparing silicon carbide epitaxial substrate 200 and a step (S2) of processing silicon carbide epitaxial substrate 200.

[0082] First, there is performed the step (S1) of preparing silicon carbide epitaxial substrate 200. In the step (S1) of preparing silicon carbide epitaxial substrate 200, first, silicon carbide substrate 100 according to the present embodiment is prepared (see FIG. 1 ).

[0083] Next, silicon carbide epitaxial layer 20 is formed on silicon carbide substrate 100. Specifically, silicon carbide epitaxial layer 20 is formed by epitaxial growth on first main surface 1 of silicon carbide substrate 100. In the epitaxial growth, for example, silane (SiH4) and propane (C3H8) are used as source gases, and hydrogen (H2) is used as a carrier gas. The temperature of the epitaxial growth is, for example, about 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 (see FIG. 6 ).

[0084] Next, a step (S2) is performed of processing silicon carbide epitaxial substrate 200. Specifically, silicon carbide epitaxial substrate 200 is processed as follows: First, ions are implanted into silicon carbide epitaxial substrate 200.

[0085] 17 is a cross-sectional view showing a process of forming the body region. For ease of explanation, carbon inclusions 5, first pits 11, second pits 12, third pits 21, and fourth pits 22 are omitted from the figures following FIG.

[0086] 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. Body region 113 has a thickness of, for example, 0.9 μm. Silicon carbide epitaxial layer 20 includes buffer layer 41, drift layer 42, and body region 113.

[0087] Next, a step of forming a source region is performed. FIG. 18 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 impurity contained in the source region 114 is higher than the concentration of the p-type impurity contained in the body region 113.

[0088] 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.

[0089] 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.

[0090] Next, a step of forming trenches in the third main surface 3 of the silicon carbide epitaxial layer 20 is performed. FIG. 19 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.

[0091] 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.

[0092] 19 , 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.

[0093] Next, a step of forming a gate insulating film is performed. Figure 20 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.

[0094] Next, a step of forming a gate electrode is performed. FIG. 21 is a cross-sectional view showing a 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 by, for example, a low pressure chemical vapor deposition (LPCVD) method.

[0095] 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.

[0096] 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).

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 22 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.

[0101] Next, the effects of the silicon carbide substrate, silicon carbide epitaxial substrate, method for manufacturing a silicon carbide substrate, and method for manufacturing a silicon carbide semiconductor device according to the present embodiment will be described.

[0102] Typically, silicon carbide substrate 100 contains a certain number of carbon inclusions 5. Carbon inclusions 5 exposed on first main surface 1 of silicon carbide substrate 100 are removed in a chemical mechanical polishing step. As a result, large pits (first pits 11) are formed on first main surface 1 of silicon carbide substrate 100.

[0103] Silicon carbide region 10 around carbon inclusion 5 has poorer crystallinity than silicon carbide region 10 without carbon inclusion 5. Therefore, silicon carbide region 10 around carbon inclusion 5 is more likely to be chemically eroded by the polishing liquid used in the chemical mechanical polishing step than silicon carbide region 10 without carbon inclusion 5. When chemical mechanical polishing is performed on silicon carbide substrate 100 using the polishing liquid, the polishing liquid remains on first main surface 1 of silicon carbide substrate 100.

[0104] In particular, a polishing liquid containing manganese is likely to erode silicon carbide regions 10 around carbon inclusions 5. In this case, silicon carbide regions 10 around carbon inclusions 5 are largely removed in the chemical mechanical polishing step, resulting in the formation of large pits (first pits 11) in first main surface 1 of silicon carbide substrate 100. As a result, the yield of silicon carbide semiconductor devices 400 decreases. When the areal density of carbon inclusions 5 is high, the areal density of first pits 11 also increases.

[0105] In silicon carbide substrate 100 according to the present embodiment, the ratio of the areal density of first pits 11 to the areal density of carbon inclusions 5 is equal to or less than 0.008. This makes it possible to reduce the number of first pits 11 even when the areal density of carbon inclusions 5 is relatively high. This makes it possible to improve the yield of silicon carbide semiconductor devices.

[0106] In silicon carbide epitaxial substrate 200 according to this embodiment, the ratio of the areal density of third pits 21 to the areal density of carbon inclusions 5 is equal to or less than 0.01. This makes it possible to reduce the number of third pits 21 even when the areal density of carbon inclusions 5 is relatively high. This makes it possible to improve the yield of silicon carbide semiconductor devices.

[0107] According to the method for manufacturing the silicon carbide substrate 100 of this embodiment, first, a first chemical mechanical polishing is performed on the silicon carbide substrate 110 using a first polishing liquid containing permanganate. By using the first polishing liquid containing permanganate, which is a strong oxidizing agent, the polishing efficiency for the silicon carbide substrate 110 can be improved. Next, the silicon carbide substrate 110 is cleaned using a mixed liquid of sulfuric acid, hydrogen peroxide solution, and ultrapure water. This makes it possible to effectively remove manganese ions attached to the silicon carbide substrate 110 by utilizing a strong reducing action. Therefore, it is possible to suppress the manganese ions from corroding the silicon carbide region 10 around the carbon inclusion 5.

[0108] Next, a second chemical mechanical polishing is performed on the silicon carbide substrate 110 using a second polishing liquid that does not contain permanganate. This reduces damage to the first main surface 1 of the silicon carbide substrate 110 compared to when the first polishing liquid containing permanganate is used. As a result, it is possible to suppress the formation of large pits (first pits 11) in the first main surface 1 of the silicon carbide substrate 110. This makes it possible to improve the yield of silicon carbide semiconductor devices.

[0109] According to the method for manufacturing silicon carbide substrate 100 according to this embodiment, the abrasive grains used in the step of performing chemical mechanical polishing on silicon carbide substrate 110 using the second polishing liquid may contain colloidal silica. By using relatively soft abrasive grains such as colloidal silica, it is possible to prevent first main surface 1 of silicon carbide substrate 110 from being significantly polished. As a result, it is possible to further prevent large pits (first pits 11) from being formed in first main surface 1 of silicon carbide substrate 110.

[0110] According to the method for manufacturing the silicon carbide substrate 100 according to this embodiment, the hydrogen ion exponent of the second polishing liquid may be smaller than 7. The smaller the hydrogen ion exponent of the second polishing liquid (in other words, the higher the acidity), the higher the reactivity of manganese, and the more likely it is that large pits (first pits 11) will be formed in the first main surface 1 of the silicon carbide substrate 110. By increasing the hydrogen ion exponent of the second polishing liquid, it is possible to further suppress the formation of large pits (first pits 11) in the first main surface 1 of the silicon carbide substrate 110.

[0111] According to the method for manufacturing the silicon carbide substrate 100 according to this embodiment, the hydrogen ion exponent of the first polishing liquid may be smaller than 9. The smaller the hydrogen ion exponent of the first polishing liquid (in other words, the higher the acidity), the higher the reactivity of manganese, and the more likely it is that large pits (first pits 11) will be formed in the first main surface 1 of the silicon carbide substrate 110. By increasing the hydrogen ion exponent of the first polishing liquid, it is possible to further suppress the formation of large pits (first pits 11) in the first main surface 1 of the silicon carbide substrate 110.

[0112] According to the method for manufacturing silicon carbide substrate 100 according to this embodiment, the volume of sulfuric acid may be 10 times the volume of hydrogen peroxide solution, and the volume of ultrapure water may be 1 to 10 times the volume of hydrogen peroxide solution. Sulfuric acid generates heat when dissolved in ultrapure water, thereby increasing the reactivity of the cleaning solution. By increasing the volume ratio of ultrapure water to sulfuric acid, manganese can be effectively removed.

[0113] According to the method for manufacturing silicon carbide substrate 100 according to this embodiment, the surface density of carbon inclusions 5 is 600 pieces / cm 2 This makes it possible to reduce the number of first pits 11 even when the areal density of carbon inclusions 5 is relatively high, thereby improving the yield of silicon carbide semiconductor devices.

[0114] Next, experimental results using examples will be described. First, the crystal growth step (S10) was performed. The silicon carbide substrate 110 according to Samples 2 to 4 was manufactured using the crystal growth method shown in FIG. 10. The silicon carbide substrate 110 according to Sample 5 was manufactured using the crystal growth method shown in FIG. 11. The silicon carbide substrate 110 according to Sample 1 was manufactured using a conventional crystal growth method. In the conventional crystal growth method, the cover member 57 and the guide member 58 were removed from the manufacturing apparatus shown in FIG. 11.

[0115] The surface density of the carbon inclusions 5 contained in the silicon carbide substrate 110 according to Samples 1 to 5 was measured using a Nomarski-type optical microscope. The surface density (first surface density A) of the carbon inclusions 5 contained in the silicon carbide substrate 110 according to Samples 1 to 5 was 580 pieces / cm 2 , 154 pieces / cm 2 , 96 pieces / cm 2 , 22 pieces / cm 2 and 4.0 pieces / cm 2 Next, the silicon carbide substrates 110 according to Samples 1 to 5 were subjected to a double-side mechanical polishing step (S20).

[0116] Next, a first chemical mechanical polishing step (S30) was carried out. The silicon carbide substrate 110 was subjected to chemical mechanical polishing using a first polishing liquid. The first polishing liquid contained permanganate. "DSC-0201" manufactured by Fujimi Incorporated was used as the first polishing liquid.

[0117] Next, a cleaning step (S40) was performed. The silicon carbide substrate 110 of Samples 1 and 2 was only cleaned with pure water. The silicon carbide substrate 110 of Sample 3 was cleaned with pure water and citric acid. The cleaning solution for the citric acid cleaning was a mixture of citric acid and ultrapure water. Citric acid with a mass percentage concentration of 90% was used. Because citrate ions form a complex with manganese ions, manganese can be effectively removed using citric acid. The volume ratio of citric acid to ultrapure water was 1 (citric acid):10 (ultrapure water). The silicon carbide substrate 110 was immersed in the cleaning solution for the citric acid cleaning for 20 minutes. Next, the silicon carbide substrate 110 was cleaned with pure water.

[0118] The silicon carbide substrates 110 of Samples 4 and 5 were subjected to pure water cleaning and sulfuric acid / hydrogen peroxide cleaning. The cleaning solution for the sulfuric acid / hydrogen peroxide cleaning was a mixture of sulfuric acid, hydrogen peroxide solution, and ultrapure water. Concentrated sulfuric acid with a mass percentage concentration of 98% was used as the sulfuric acid. Hydrogen peroxide solution with a mass percentage concentration of 30% was used as the hydrogen peroxide solution. The volume ratio of sulfuric acid, hydrogen peroxide solution, and ultrapure water contained in the cleaning solution was 10 (sulfuric acid):1 (hydrogen peroxide solution):1 (ultrapure water). The silicon carbide substrates 110 were immersed in the acid cleaning solution for the sulfuric acid / hydrogen peroxide cleaning for 20 minutes. Next, the silicon carbide substrates 110 were cleaned with pure water.

[0119] Next, the manganese (Mn) concentration was measured using a TXRF-3760 manufactured by Rigaku Corporation. The X-ray power was 35 kV-255 mA. The incident direction was 39°. The incident angle of W-Ma was 0.500°. The measurement time for W-Ma was 10 seconds / point. The incident angle of W-Lb was 0.100°. The measurement time for W-Lb was 10 seconds / point.

[0120]

[0121] Table 1 shows the Mn concentration in the first main surface 1 of the silicon carbide substrate 110 according to Samples 1 to 5. As shown in Table 1, the Mn concentration in the first main surface 1 of the silicon carbide substrate 110 according to Samples 1 to 5 was 6.5×10 14 atoms / cm 2 , 6.5 × 10 14 atoms / cm 2 , 5.2 × 10 13 atoms / cm 2 , 3.6 × 10 9 atoms / cm 2 and 3.6 × 10 9 atoms / cm 2 From the above results, it was confirmed that the Mn concentration in first main surface 1 of silicon carbide substrate 110 was significantly reduced by performing cleaning with sulfuric acid and hydrogen peroxide.

[0122] Next, a second chemical mechanical polishing step (S50) was carried out. The second polishing liquid did not contain permanganate. "DSC-0902" manufactured by Fujimi Incorporated was used as the second polishing liquid. As described above, silicon carbide substrates 100 according to Samples 1 to 5 were prepared. A plurality of pits were formed on first main surface 1 of silicon carbide substrates 100 according to Samples 1 to 5.

[0123] Next, the areal density of pits on first main surface 1 of silicon carbide substrate 100 according to samples 1 to 5 was measured. The area of ​​the pits to be counted was 3000 μm 2 More specifically, the number of pits (first pits 11) was counted in the measurement area of ​​the first main surface 1 using a WASAVI series "SICA 6X" manufactured by Lasertec Corporation. The magnification of the objective lens was 10 times. The measurement area of ​​the first main surface 1 was an area excluding the area within 2 mm from the outer periphery of the first main surface 1. The surface density of the pits observed using SICA was defined as the second surface density B1 (number / cm 2 )

[0124] Next, a Nomarski-type optical microscope was used to observe the pits on the first main surface 1. The diameter of the pits to be counted was 50 μm or more. The shape of the pits to be counted was hexagonal. The surface density of the pits observed using the Nomarski-type optical microscope was defined as a third surface density B2 (number / cm 2 )

[0125] Next, silicon carbide epitaxial layer 20 was formed on first main surface 1 of silicon carbide substrate 100 according to Samples 1 to 5. The surface density of pits on third main surface 3 of silicon carbide epitaxial layer 20 was measured. The area of ​​the pits to be counted was 5000 μm 2 More specifically, the number of pits (third pits 21) was counted in the measurement area of ​​the third main surface 3 using a WASAVI series "SICA 6X" manufactured by Lasertec Corporation. The magnification of the objective lens was 10 times. The measurement area of ​​the third main surface 3 was an area excluding the area within 2 mm from the outer periphery of the third main surface 3. The surface density of the pits observed using SICA was defined as the fourth surface density C (number / cm 2 )

[0126]

[0127] Table 2 shows the first areal density A, the second areal density B1, the third areal density B2, the fourth areal density C, the value (B1 / A) obtained by dividing the second areal density B1 by the first areal density A, the value (B2 / A) obtained by dividing the third areal density B2 by the first areal density A, and the value (C / A) obtained by dividing the fourth areal density C by the first areal density A. The value (B1 / A) obtained by dividing the second areal density B1 by the first areal density A corresponds to the ratio of the areal density of the first pits 11 to the areal density of the carbon inclusions 5. The value (C / A) obtained by dividing the fourth areal density C by the first areal density A corresponds to the ratio of the areal density of the third pits 21 to the areal density of the carbon inclusions 5.

[0128] As shown in Table 2, in silicon carbide substrates 100 according to samples 1 and 2, the ratio of the areal density of first pits 11 to the areal density of carbon inclusions 5 was greater than 0.008. In silicon carbide substrates 100 according to samples 3, 4, and 5, the ratio of the areal density of first pits 11 to the areal density of carbon inclusions 5 was 0.008 or less. From the above results, it was confirmed that in silicon carbide substrates 100 according to samples 3, 4, and 5, the proportion of carbon inclusions 5 that become first pits 11 can be significantly reduced.

[0129] As shown in Table 2, in silicon carbide epitaxial substrates 200 according to Samples 1 and 2, the ratio of the areal density of third pits 21 to the areal density of carbon inclusions 5 was greater than 0.01. In silicon carbide epitaxial substrates 200 according to Samples 3, 4, and 5, the ratio of the areal density of third pits 21 to the areal density of carbon inclusions 5 was 0.01 or less. From the above results, it was confirmed that in silicon carbide epitaxial substrates 200 according to Samples 3, 4, and 5, the proportion of carbon inclusions 5 that become third pits 21 can be significantly reduced.

[0130] The present disclosure includes the following embodiments: (Supplementary Note 1) A silicon carbide substrate having a main surface, the silicon carbide substrate including a plurality of carbon inclusions, a plurality of pits formed in the main surface, the maximum length of each of the plurality of carbon inclusions being 2 μm or more and 50 μm or less when viewed in a direction perpendicular to the main surface, and the area of ​​each of the plurality of pits being 3000 μm or less. 2 The silicon carbide substrate according to claim 1, wherein a ratio of an areal density of the pits to an areal density of the carbon inclusions is 0.008 or less. (Supplementary Note 2) The silicon carbide substrate according to Supplementary Note 1, wherein a ratio of an areal density of the pits to an areal density of the carbon inclusions is 0.004 or less. (Supplementary Note 3) The areal density of the carbon inclusions is 155 pcs / cm 2The silicon carbide substrate according to claim 1, wherein the surface density of the plurality of carbon inclusions is 100 pieces / cm 2 The silicon carbide substrate according to claim 3, wherein the surface density of the plurality of carbon inclusions is 50 pieces / cm 2 (Supplementary Note 6) The silicon carbide substrate according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the maximum diameter of the main surface is 150 mm or more. (Supplementary Note 7) A silicon carbide substrate comprising: a silicon carbide substrate; and a silicon carbide epitaxial layer provided on the silicon carbide substrate, wherein the silicon carbide substrate includes a plurality of carbon inclusions, and a plurality of pits are formed in the main surface of the silicon carbide epitaxial layer, and when viewed in a direction perpendicular to the main surface, the maximum length of each of the plurality of carbon inclusions is 2 μm or more and 50 μm or less, and the area of ​​each of the plurality of pits is 5000 μm. 2a silicon carbide epitaxial substrate according to claim 7, wherein the ratio of the areal density of the plurality of pits to the areal density of the plurality of carbon inclusions is 0.01 or less; (Supplementary Note 8) The silicon carbide epitaxial substrate according to claim 7, wherein the ratio of the areal density of the plurality of pits to the areal density of the plurality of carbon inclusions is 0.005 or less; (Supplementary Note 9) The silicon carbide epitaxial substrate according to claim 7 or 8, wherein the maximum diameter of the main surface is 150 mm or more; (Supplementary Note 10) A method for manufacturing a silicon carbide semiconductor device, comprising: preparing the silicon carbide epitaxial substrate according to claim 7 or 8; and processing the silicon carbide epitaxial substrate. (Appendix 11) A method for manufacturing a silicon carbide substrate, comprising: performing chemical mechanical polishing on a silicon carbide substrate using a first polishing liquid; after performing chemical mechanical polishing on the silicon carbide substrate, cleaning the silicon carbide substrate with a cleaning liquid; and after cleaning the silicon carbide substrate with the cleaning liquid, performing chemical mechanical polishing on the silicon carbide substrate using a second polishing liquid, wherein the silicon carbide substrate contains a plurality of carbon inclusions, the first polishing liquid contains permanganate, the second polishing liquid does not contain permanganate, and the cleaning liquid is a mixture of sulfuric acid, hydrogen peroxide solution, and ultrapure water. (Appendix 12) A method for manufacturing a silicon carbide substrate according to Appendix 11, wherein abrasive grains used in the second polishing liquid contain colloidal silica. (Appendix 13) A method for manufacturing a silicon carbide substrate according to Appendix 11 or Appendix 12, wherein the abrasive grains used in the first polishing liquid do not contain colloidal silica. (Appendix 14) The method for manufacturing a silicon carbide substrate according to appendix 11 or appendix 12, wherein the second polishing liquid has a hydrogen ion exponent smaller than 7. (Appendix 15) The method for manufacturing a silicon carbide substrate according to appendix 11 or appendix 12, wherein the first polishing liquid has a hydrogen ion exponent smaller than 9. (Appendix 16) The method for manufacturing a silicon carbide substrate according to appendix 11 or appendix 12, wherein a volume of the sulfuric acid is 10 times a volume of the hydrogen peroxide solution, and a volume of the ultrapure water is 1 to 10 times a volume of the hydrogen peroxide solution.(Supplementary Note 17) The method for manufacturing a silicon carbide substrate according to Supplementary Note 11 or Supplementary Note 12, wherein a maximum length of each of the plurality of carbon inclusions is 2 μm or more and 50 μm or less when viewed in a direction perpendicular to the main surface of the silicon carbide base material. (Supplementary Note 18) An areal density of the plurality of carbon inclusions is 600 pieces / cm. 2 13. A method for manufacturing a silicon carbide substrate according to claim 11 or 12, wherein:

[0131] 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 the above description, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0132] 1 First main surface (main surface), 2 Second main surface, 3 Third main surface (main surface), 4 Fourth main surface, 5 Carbon inclusion, 7 Orientation flat, 8 Arc-shaped portion, 10 Silicon carbide region, 11 First pit (pit), 12 Second pit (pit), 19 First outer peripheral edge, 20 Silicon carbide epitaxial layer, 21 Third pit, 22 Fourth pit, 29 Second outer peripheral edge, 30 First polishing liquid, 41 Buffer layer, 42 Drift layer, 43 Hole, 44 Silicon carbide seed substrate, 45 Silicon carbide raw material, 50 Crucible, 51 Lid, 52 Raw material storage portion, 53 Side wall surface, 54 Bottom wall surface, 55 Through hole, 56 Trench, 57 Cover member, 58 Guide member, 61 First measurement area, 62 Second measurement area, 63 Third measurement area, 64 4th measurement region, 65 fifth measurement region, 100 silicon carbide substrate, 101 first direction, 102 second direction, 110 silicon carbide base material, 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, A first areal density, B1 second areal density, B2 third areal density, C fourth areal density, D1 first depth, D2 second depth, D3 third depth, D4 fourth depth, D5 fifth distance, D6 sixth distance, E cross-sectional position, W1 maximum diameter, X length.

Claims

1. A silicon carbide substrate having a main surface, the silicon carbide substrate includes a plurality of carbon inclusions; A plurality of pits are formed on the main surface, When viewed in a direction perpendicular to the main surface, the maximum length of each of the plurality of carbon inclusions is 2 μm or more and 50 μm or less, and the area of ​​each of the plurality of pits is 3000 μm or less. 2 That's all. A silicon carbide substrate, wherein a ratio of an areal density of the plurality of pits to an areal density of the plurality of carbon inclusions is 0.008 or less.

2. 2 . The silicon carbide substrate according to claim 1 , wherein a ratio of an areal density of said plurality of pits to an areal density of said plurality of carbon inclusions is not more than 0.

004.

3. The surface density of the carbon inclusions is 155 pieces / cm 2 3. The silicon carbide substrate according to claim 1, wherein:

4. The surface density of the plurality of carbon inclusions is 100 pieces / cm 2 The silicon carbide substrate according to claim 3 , wherein:

5. The surface density of the plurality of carbon inclusions is 50 pieces / cm 2 The silicon carbide substrate according to claim 4 , wherein:

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

7. a silicon carbide substrate; a silicon carbide epitaxial layer provided on the silicon carbide substrate; the silicon carbide substrate includes a plurality of carbon inclusions; a plurality of pits are formed on a main surface of the silicon carbide epitaxial layer; When viewed in a direction perpendicular to the main surface, the maximum length of each of the plurality of carbon inclusions is 2 μm or more and 50 μm or less, and the area of ​​each of the plurality of pits is 5,000 μm or less. 2 That's all. A silicon carbide epitaxial substrate, wherein a ratio of an areal density of the plurality of pits to an areal density of the plurality of carbon inclusions is 0.01 or less.

8. 8. The silicon carbide epitaxial substrate according to claim 7, wherein a ratio of an areal density of said plurality of pits to an areal density of said plurality of carbon inclusions is not more than 0.

005.

9. 9. The silicon carbide epitaxial substrate according to claim 7, wherein the main surface has a maximum diameter of 150 mm or more.

10. A step of preparing a silicon carbide epitaxial substrate according to claim 7 or 8; and processing the silicon carbide epitaxial substrate.

11. performing chemical mechanical polishing on a silicon carbide substrate using a first polishing liquid; After performing chemical mechanical polishing on the silicon carbide substrate, cleaning the silicon carbide substrate with a cleaning liquid; After the step of cleaning the silicon carbide substrate with the cleaning liquid, a step of performing chemical mechanical polishing on the silicon carbide substrate with a second polishing liquid, the silicon carbide substrate includes a plurality of carbon inclusions; the first polishing liquid contains a permanganate; The second polishing liquid does not contain permanganate, The method for manufacturing a silicon carbide substrate, wherein the cleaning liquid is a mixture of sulfuric acid, hydrogen peroxide, and ultrapure water.

12. The method for manufacturing a silicon carbide substrate according to claim 11 , wherein the abrasive grains used in the second polishing liquid contain colloidal silica.

13. 13. The method for manufacturing a silicon carbide substrate according to claim 11 or 12, wherein the abrasive grains used in the first polishing liquid do not contain colloidal silica.

14. 13. The method for manufacturing a silicon carbide substrate according to claim 11, wherein the second polishing liquid has a hydrogen ion exponent of less than 7.

15. 13. The method for manufacturing a silicon carbide substrate according to claim 11, wherein the first polishing liquid has a hydrogen ion exponent of less than 9.

16. 13. The method for manufacturing a silicon carbide substrate according to claim 11 or 12, wherein a volume of the sulfuric acid is 10 times a volume of the hydrogen peroxide solution, and a volume of the ultrapure water is 1 to 10 times a volume of the hydrogen peroxide solution.

17. 13. The method for manufacturing a silicon carbide substrate according to claim 11 or 12, wherein a maximum length of each of the plurality of carbon inclusions is not less than 2 μm and not more than 50 μm when viewed in a direction perpendicular to a main surface of the silicon carbide base.

18. The surface density of the carbon inclusions is 600 pieces / cm 2 The method for manufacturing a silicon carbide substrate according to claim 11 or 12, wherein: