Method for producing silicon carbide substrate, method for producing silicon carbide epitaxial substrate, method for producing silicon carbide semiconductor device, and silicon carbide substrate

Abstract

To provide a method for producing a silicon carbide substrate that is capable of determining temperature conditions while suppressing particle scattering from the inner wall surface of the furnace.SOLUTION: A method for producing a silicon carbide substrate according to the present disclosure includes: a first step of removing particles attached to an inner wall surface of a furnace by introducing hydrogen gas into the furnace while a substrate is placed on a first susceptor disposed in the furnace; a second step, following the first step, of forming a first silicon carbide layer on the inner wall surface by flowing hydrogen gas, source gas, and dopant gas into the furnace; a third step, following the second step, of placing a first silicon carbide single crystal substrate on a second susceptor disposed in the furnace; a fourth step of forming a second silicon carbide layer on the first silicon carbide single crystal substrate by flowing hydrogen gas, source gas, and dopant gas into the furnace while the first silicon carbide single crystal substrate is placed on the second susceptor disposed in the furnace; and a fifth step of determining temperature conditions using the second silicon carbide layer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a silicon carbide substrate, a method for manufacturing a silicon carbide epitaxial substrate, a method for manufacturing a silicon carbide semiconductor device, and a silicon carbide substrate. [Background technology]

[0002] International Publication No. 2020 / 115950 (Patent Document 1) describes a method for manufacturing a silicon carbide epitaxial substrate, including a step of forming a first silicon carbide layer by epitaxial growth on a first silicon carbide substrate using a first ammonia gas as a dopant gas, a step of measuring the thickness of the first silicon carbide layer and the carrier concentration of the first silicon carbide layer, and a step of calculating formation conditions for a second silicon carbide layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 115950 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a method for manufacturing a silicon carbide substrate that is capable of determining temperature conditions while suppressing scattering of particles from the inner wall surface of a furnace. [Means for solving the problem]

[0005] The method for manufacturing a silicon carbide substrate according to the present disclosure includes a first step of removing particles adhering to an inner wall surface of a furnace by flowing hydrogen gas into the furnace while the substrate is placed on a first susceptor placed in the furnace, a second step of forming a first silicon carbide layer on the inner wall surface by flowing hydrogen gas, a raw material gas, and a dopant gas into the furnace after the first step, a third step of placing the first silicon carbide single crystal substrate on the second susceptor placed in the furnace after the second step, a fourth step of forming a second silicon carbide layer on the first silicon carbide single crystal substrate by flowing hydrogen gas, a raw material gas, and a dopant gas into the furnace while the first silicon carbide single crystal substrate is placed on the second susceptor placed in the furnace, and a fifth step of determining a temperature condition using the second silicon carbide layer. The susceptor temperature in the fourth step is equal to or lower than the temperature inside the furnace in the second step. The flow rate of the dopant gas in the fourth step is equal to or lower than the flow rate of the dopant gas in the second step. Effect of the Invention

[0006] According to the present disclosure, it is possible to provide a method for manufacturing a silicon carbide substrate that is capable of suppressing adhesion of particles that can determine temperature conditions while suppressing scattering of particles from the inner wall surface of a furnace. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic plan view showing the configuration of a silicon carbide substrate in accordance with the first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a partial cross-sectional schematic view showing the configuration of a manufacturing apparatus for a silicon carbide substrate. [Figure 4] FIG. 4 is a flow diagram illustrating roughly the method for manufacturing a silicon carbide substrate according to the first embodiment. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing a state in which a substrate is placed on a first susceptor disposed in a furnace. [Figure 6]FIG. 6 is a schematic diagram showing the changes over time of the temperature and the flow rate of hydrogen gas inside the furnace in a process of removing particles adhering to the inner wall surface with a substrate placed on a first susceptor placed in the furnace. [Figure 7] FIG. 7 is a schematic cross-sectional view showing a step of removing particles adhering to an inner wall surface in a state in which a substrate is placed on a first susceptor that is placed in a furnace. [Figure 8] FIG. 8 is a schematic diagram showing the changes over time of the temperature inside the furnace, the flow rate of hydrogen gas, and the flow rate of ammonia gas in the first growth step. [Figure 9] FIG. 9 is a schematic cross-sectional view showing a step of forming a first silicon carbide layer on the inner wall surface. [Figure 10] FIG. 10 is a cross-sectional view illustrating a step of placing a first silicon carbide single crystal substrate inside a furnace. [Figure 11] FIG. 11 is a schematic diagram showing the changes over time of the susceptor temperature, the flow rate of hydrogen gas, and the flow rate of ammonia gas in the second growth step. [Figure 12] FIG. 12 is a cross-sectional view illustrating a step of forming a second silicon carbide layer on a first silicon carbide single crystal substrate. [Figure 13] FIG. 13 is a cross-sectional schematic view showing a configuration of a silicon carbide substrate according to the second embodiment. [Figure 14] FIG. 14 is a flow diagram illustrating roughly the method for manufacturing a silicon carbide substrate according to the second embodiment. [Figure 15] FIG. 15 is a schematic cross-sectional view showing a step of arranging a first silicon carbide single crystal substrate in the method for manufacturing a silicon carbide substrate in accordance with the second embodiment. [Figure 16] FIG. 16 is a schematic diagram showing changes over time in the susceptor temperature, the flow rate of hydrogen gas, and the flow rate of ammonia gas in the first growth step in the method for manufacturing a silicon carbide substrate according to the second embodiment. [Figure 17] FIG. 17 is a schematic cross-sectional view showing a step of forming a second silicon carbide layer on the third silicon carbide layer. [Figure 18]FIG. 18 is a flowchart roughly illustrating a method for manufacturing a silicon carbide semiconductor device according to this embodiment. [Figure 19] FIG. 19 is a cross-sectional schematic diagram showing the configuration of a silicon carbide epitaxial substrate in accordance with this embodiment. [Figure 20] FIG. 20 is a schematic cross-sectional view showing a step of forming a body region. [Figure 21] FIG. 21 is a schematic cross-sectional view showing a step of forming a source region. [Figure 22] FIG. 22 is a schematic cross-sectional view showing a step of forming a trench in the sixth main surface of the second silicon carbide epitaxial layer. [Diagram 23] FIG. 23 is a schematic cross-sectional view showing a step of forming a gate insulating film. [Figure 24] FIG. 24 is a schematic cross-sectional view showing a step of forming a gate electrode and an interlayer insulating film. [Diagram 25] FIG. 25 is a schematic cross-sectional view showing the configuration of a silicon carbide semiconductor device in accordance with this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described.

[0009] (1) A method for manufacturing a silicon carbide substrate 100 according to the present disclosure includes a first step of removing particles 90 adhering to an inner wall surface 205 of a furnace 220 by flowing hydrogen gas into the furnace 220 while a substrate 99 is placed on a first susceptor 211 arranged in the furnace 220; a second step of forming a first silicon carbide layer 10 on the inner wall surface 205 by flowing hydrogen gas, a source gas, and a dopant gas into the furnace 220 after the first step; The method includes a third step of arranging the first silicon carbide single crystal substrate 71 on the second susceptor 212 arranged in the furnace 220, a fourth step of forming a second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71 by flowing hydrogen gas, a source gas, and a dopant gas into the furnace 220 in a state where the first silicon carbide single crystal substrate 71 is arranged on the second susceptor 212 arranged in the furnace 220, and a fifth step of determining a temperature condition using the second silicon carbide layer 20. The susceptor temperature in the fourth step is equal to or lower than the susceptor temperature in the second step. The flow rate of the dopant gas in the fourth step is equal to or lower than the flow rate of the dopant gas in the second step.

[0010] (2) According to the method for manufacturing a silicon carbide substrate 100 relating to (1) above, the first silicon carbide layer 10 may have a first layer 11 and a second layer 12. The first layer 11 may be in contact with the inner wall surface 205. The second layer 12 may be provided on the first layer 11. The nitrogen concentration of the first layer 11 may be higher than the nitrogen concentration of the second layer 12. The temperature inside the furnace 220 when the second layer 12 is formed may be higher than the temperature inside the furnace 220 when the first layer 11 is formed.

[0011] (3) The method for manufacturing a silicon carbide substrate 100 according to the present disclosure includes the following steps: a first step of removing particles 90 adhering to an inner wall surface 205 of a furnace 220 by flowing hydrogen gas into the furnace 220 with a substrate 99 placed on a first susceptor 211 placed in the furnace 220; a second step of, after the first step, placing a first silicon carbide single crystal substrate 71 on a second susceptor 212 placed in the furnace 220; and a second step of flowing hydrogen gas and a raw material into the furnace 220 with the first silicon carbide single crystal substrate 71 placed inside the furnace 220. The method includes a third step of forming a third silicon carbide layer 30 on the first silicon carbide single crystal substrate 71 while forming a first silicon carbide layer 10 on the inner wall surface 205 by flowing a gas and a dopant gas, a fourth step of forming a second silicon carbide layer 20 on the third silicon carbide layer 30 by flowing hydrogen gas, a raw material gas, and a dopant gas into the furnace 220 after the third step, and a fifth step of determining a temperature condition using the second silicon carbide layer 20. The susceptor temperature in the fourth step is equal to or lower than the susceptor temperature in the third step. The flow rate of the dopant gas in the fourth step is equal to or lower than the flow rate of the dopant gas in the third step.

[0012] (4) According to the method for manufacturing a silicon carbide substrate 100 relating to (3) above, the first silicon carbide layer 10 may have a first layer 11 and a second layer 12. The first layer 11 may be in contact with the inner wall surface 205. The second layer 12 may be provided on the first layer 11. The nitrogen concentration of the first layer 11 may be higher than the nitrogen concentration of the second layer 12. The susceptor temperature when the second layer 12 is formed may be higher than the susceptor temperature when the first layer 11 is formed.

[0013] (5) According to any one of the methods for manufacturing silicon carbide substrate 100 described above in (1) to (4), first susceptor 211 and second susceptor 212 may be different from each other.

[0014] (6) According to any one of the methods for manufacturing silicon carbide substrate 100 described above in (1) to (4), first susceptor 211 and second susceptor 212 may be the same.

[0015] (7) According to any one of the above (1) to (6) methods for manufacturing silicon carbide substrate 100, the method may further include, after the first step, a step of calculating a susceptor temperature in the first step based on an etching amount of substrate 99.

[0016] (8) According to any one of the methods for manufacturing silicon carbide substrate 100 described above in (1) to (7), the first step may be performed after maintenance of furnace 220.

[0017] (9) The method for manufacturing silicon carbide epitaxial substrate 200 according to the present disclosure has the following steps. Temperature conditions for epitaxial growth are determined using the method for manufacturing silicon carbide substrate 100 according to any one of (1) to (8) above. Silicon carbide epitaxial layer 60 is formed on second silicon carbide single crystal substrate 72 using the determined temperature conditions.

[0018] (10) A method for manufacturing silicon carbide semiconductor device 400 according to the present disclosure has the following steps. Temperature conditions for epitaxial growth are determined using a method for manufacturing silicon carbide substrate 100 according to any one of (1) to (9) above. Silicon carbide epitaxial layer 60 is formed on second silicon carbide single crystal substrate 72 using the determined temperature conditions. Electrode 127 is formed on silicon carbide epitaxial layer 60.

[0019] (11) The silicon carbide substrate 100 according to the present disclosure has a silicon carbide single crystal substrate 71, a third silicon carbide layer 30, and a second silicon carbide layer 20. The third silicon carbide layer 30 is provided on the silicon carbide single crystal substrate 71. The second silicon carbide layer 20 is provided on the third silicon carbide layer 30. The third silicon carbide layer 30 has a third layer 33 and a fourth layer 34. The third layer 33 is provided on the silicon carbide single crystal substrate 71. The fourth layer 34 is provided on the third layer 33. The second silicon carbide layer 20 constitutes the surface. The nitrogen concentration of each of the third layer 33 and the second silicon carbide layer 20 is higher than the nitrogen concentration of the fourth layer 34. The nitrogen concentration of each of the third layer 33 and the second silicon carbide layer 20 is greater than 1×10 17 cm -3 More than 3×10 18 cm-3 The nitrogen concentration in the fourth layer 34 is 3×10 15 cm -3 More than 2×10 16 cm -3 The following is the result.

[0020] (12) According to silicon carbide substrate 100 according to (11) above, third layer 33 and second silicon carbide layer 20 may each have a thickness smaller than the thickness of fourth layer .

[0021] (13) According to silicon carbide substrate 100 according to (11) or (12) above, third layer 33 and second silicon carbide layer 20 may each have a thickness of 0.5 μm or more and 3 μm or less. Fourth layer 34 may have a thickness of 4 μm or more and 7 μm or less.

[0022] [Details of the embodiment of the present disclosure] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals, and the description thereof will not be repeated. In the crystallographic description in this specification, an individual orientation is indicated by [], a collective orientation by <>, an individual plane by (), and a collective plane by {}. In addition, for negative indices, a "-" (bar) is placed before the number in crystallography, but in this specification, a negative sign is placed before the number.

[0023] (First embodiment) <Silicon carbide substrate> First, the configuration of the silicon carbide substrate 100 according to the first embodiment will be described. FIG. 1 is a plan view schematic diagram showing the configuration of the silicon carbide substrate 100 according to the first embodiment. FIG. 2 is a cross-sectional view schematic diagram taken along line II-II in FIG. 1. As shown in FIG. 1 and FIG. 2, the silicon carbide substrate 100 according to the first embodiment mainly includes a first silicon carbide single crystal substrate 71 and a second silicon carbide layer 20. The second silicon carbide layer 20 is provided, for example, on the first silicon carbide single crystal substrate 71. The second silicon carbide layer 20 is in contact with the first silicon carbide single crystal substrate 71. The second silicon carbide layer 20 is, for example, a silicon carbide epitaxial layer. From another viewpoint, the second silicon carbide layer 20 is, for example, a layer formed by epitaxial growth.

[0024] The second silicon carbide layer 20 constitutes a front surface (first main surface 1) of the silicon carbide substrate 100. The first silicon carbide single crystal substrate 71 constitutes a back surface (second main surface 2) of the silicon carbide substrate 100. As shown in Fig. 1, the silicon carbide substrate 100 has an outer circumferential edge 6. The outer circumferential edge 6 has, for example, an orientation flat 7 and an arc-shaped portion 8.

[0025] 1 , the orientation flat 7 is linear when viewed along a straight line 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 along a straight line perpendicular to the first main surface 1.

[0026] 1, when viewed along a straight line perpendicular to the first main surface 1, the first main surface 1 extends along each of a first direction 101 and a second direction 102. When viewed along a straight line perpendicular to the first main surface 1, the second direction 102 is a direction perpendicular to the first direction 101.

[0027] 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, for example, 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> directional component.

[0028] 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 principal surface 1. From another perspective, the second direction 102 may be, for example, a direction including a <1-100> directional component.

[0029] The first main surface 1 may be a {0001} plane, or may be a plane inclined with respect to the {0001} plane. When the 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, greater than 0° and equal to or less than 8°. When the first main surface 1 is inclined with respect to the {0001} plane, the inclination direction (off direction) of the first main surface 1 is, for example, the <11-20> direction.

[0030] As shown in FIG. 1, the maximum diameter W of the first main surface 1 is not particularly limited, but is, for example, 100 mm (4 inches) or more. The maximum diameter W may be 125 mm (5 inches) or more, 150 mm (6 inches) or more, or 200 mm (8 inches) or more. The maximum diameter W is not particularly limited, but may be, for example, 400 mm (16 inches) or less. When viewed along a straight line perpendicular to the first main surface 1, the maximum diameter W is the longest straight line distance between two different points on the outer circumferential edge 6.

[0031] In this specification, 4 inches means 100 mm or 101.6 mm (4 inches x 25.4 mm / inch). 6 inches means 150 mm or 152.4 mm (6 inches x 25.4 mm / inch). 8 inches means 200 mm or 203.2 mm (8 inches x 25.4 mm / inch). 16 inches means 400 mm or 406.4 mm (16 inches x 25.4 mm / inch).

[0032] 2, first silicon carbide single crystal substrate 71 has a second main surface 2 and a third main surface 3. The third main surface 3 is opposite to the second main surface 2. At the third main surface 3, first silicon carbide single crystal substrate 71 is in contact with second silicon carbide layer 20. The polytype of silicon carbide constituting first silicon carbide single crystal substrate 71 is, for example, 4H. Similarly, the polytype of silicon carbide constituting second silicon carbide layer 20 is, for example, 4H.

[0033] The direction from second main surface 2 toward first main surface 1 is defined as third direction 103. The thickness of first silicon carbide single crystal substrate 71 in third direction 103 is defined as first thickness H1. First thickness H1 is, for example, not less than 300 μm and not more than 700 μm.

[0034] The first silicon carbide single crystal substrate 71 contains nitrogen (N) as an n-type impurity. The conductivity type of the first silicon carbide single crystal substrate 71 is n-type. The nitrogen concentration of the first silicon carbide single crystal substrate 71 is, for example, 1×10 18 / cm 3 More than 1×10 19 / cm 3 The following is the result.

[0035] The thickness of second silicon carbide layer 20 in third direction 103 is set to second thickness H2. Second thickness H2 is, for example, not less than 5 μm and not more than 8 μm. Second thickness H2 may be, for example, not less than 5.5 μm, or not less than 6 μm. Second thickness H2 may be, for example, not more than 7.5 μm, or not more than 7 μm.

[0036] The second silicon carbide layer 20 contains nitrogen as an n-type impurity. The conductivity type of the second silicon carbide layer 20 is n-type. The nitrogen concentration of the second silicon carbide layer 20 is equal to or lower than the nitrogen concentration of the first silicon carbide single crystal substrate 71. The nitrogen concentration of the second silicon carbide layer 20 is 1×10 17 cm -3 More than 3×10 18 cm -3 The nitrogen concentration of the second silicon carbide layer 20 is, for example, 3×10 17 cm -3 It may be more than 5 x 10 17 cm -3 The nitrogen concentration of the second silicon carbide layer 20 may be, for example, 1×10 18 cm -3 It may be less than or equal to 8 x 10 17 cm -3 It may be the following.

[0037] The nitrogen concentration is measured, for example, by secondary ion mass spectrometry (SIMS). In SIMS, for example, a secondary ion mass spectrometer IMS7f manufactured by Cameca can be used. The measurement conditions in SIMS are, for example, O2 + A measurement condition in which the primary ion energy is 8 keV can be used.

[0038] Silicon carbide substrate 100 is a dummy substrate prepared when determining temperature conditions for epitaxial growth. Silicon carbide substrate 100 is not usually used as a part of a silicon carbide semiconductor device, but may constitute a part of the silicon carbide semiconductor device.

[0039] <Silicon carbide substrate manufacturing equipment> Next, the configuration of an apparatus for manufacturing silicon carbide substrate 100 will be described. Fig. 3 is a partial cross-sectional schematic diagram showing the configuration of the apparatus for manufacturing silicon carbide substrate 100. The apparatus 300 for manufacturing silicon carbide substrate 100 is, for example, a hot-wall type horizontal CVD (Chemical Vapor Deposition) apparatus. As shown in Fig. 3, the apparatus 300 for manufacturing silicon carbide substrate 100 mainly includes a gas supply unit 235, a control unit 245, a furnace 220, and an induction heating coil (not shown).

[0040] The furnace 220 includes a reaction chamber 201, a heating element 203, a quartz tube 204, and a heat insulating material (not shown). The heating element 203 has, for example, a cylindrical shape, and forms the reaction chamber 201 inside. The heating element 203 is made of, for example, graphite. The heating element 203 is provided inside the quartz tube 204. The heating element 203 constitutes an inner wall surface 205 of the furnace 220. The heat insulating material surrounds the outer periphery of the heating element 203. The induction heating coil is wound, for example, along the outer periphery surface of the quartz tube 204. The induction heating coil is configured so that an alternating current can be supplied to it by an external power source (not shown). This causes the heating element 203 to be induction heated. As a result, the reaction chamber 201 is heated by the heating element 203.

[0041] The reaction chamber 201 is a space surrounded by an inner wall surface 205. Hereinafter, the reaction chamber 201 is also referred to as the inside of the furnace 220. A susceptor for holding a silicon carbide single crystal substrate is provided in the reaction chamber 201. Specifically, for example, a first susceptor 211 is provided. The first susceptor 211 is made of silicon carbide. A first pocket 219 is provided in the first susceptor 211. The first susceptor 211 has a first bottom surface 215. The first bottom surface 215 constitutes the bottom surface of the first pocket 219. The silicon carbide single crystal substrate is placed on the first susceptor 211. Specifically, the silicon carbide single crystal substrate is placed in the first pocket 219. The first susceptor 211 is placed on a stage 202. Specifically, a first susceptor 211 is placed on a mounting surface 206 of a stage 202. The stage 202 is supported rotatably by a rotation shaft 209. When the stage 202 rotates, the first susceptor 211 rotates.

[0042] Manufacturing apparatus 300 for silicon carbide substrate 100 further includes gas inlet 207 and gas exhaust outlet 208. Gas exhaust outlet 208 is connected to an exhaust pump (not shown). Arrows in FIG. 3 indicate the flow of gas. Gas is introduced into reaction chamber 201 from gas inlet 207 and exhausted from gas exhaust outlet 208. The pressure inside reaction chamber 201 is adjusted by balancing the amount of gas supplied and the amount of gas exhausted.

[0043] The gas supply unit 235 is configured to be able to supply a mixed gas containing a raw material gas, a dopant gas, and a carrier gas to the reaction chamber 201. Specifically, the gas supply unit 235 includes, for example, a first gas supply unit 231, a second gas supply unit 232, a third gas supply unit 233, and a fourth gas supply unit 234.

[0044] The first gas supply unit 231 is configured to be able to supply a first gas containing, for example, carbon atoms. The first gas supply unit 231 is, for example, a gas cylinder filled with the first gas. The first gas is, for example, propane (C3H8) gas. The first gas may be, for example, methane (CH4) gas, ethane (C2H6) gas, acetylene (C2H2) gas, or the like.

[0045] The second gas supply unit 232 is configured to be able to supply a second gas containing, for example, silicon atoms. The second gas supply unit 232 is, for example, a gas cylinder filled with the second gas. The second gas is, for example, silane (SiH4) gas. The second gas may be a mixed gas of silane gas and a gas other than silane.

[0046] The third gas supply unit 233 is configured to be able to supply a third gas containing, for example, nitrogen atoms. The third gas supply unit 233 is, for example, a gas cylinder filled with the third gas. The third gas is a doping gas. The third gas is, for example, ammonia gas. Ammonia gas is more easily thermally decomposed than nitrogen gas having a triple bond.

[0047] The fourth gas supply unit 234 is configured to be able to supply a fourth gas (carrier gas) such as hydrogen, for example. The fourth gas supply unit 234 is, for example, a gas cylinder filled with hydrogen.

[0048] The control unit 245 is configured to be able to control the flow rate of the mixed gas supplied from the gas supply unit 235 to the reaction chamber 201. Specifically, the control unit 245 may include a first gas flow rate control unit 241, a second gas flow rate control unit 242, a third gas flow rate control unit 243, and a fourth gas flow rate control unit 244. Each control unit may be, for example, an MFC (Mass Flow Controller). The control unit 245 is disposed between the gas supply unit 235 and the gas inlet 207.

[0049] <Method for manufacturing silicon carbide substrate> Next, a method for manufacturing the silicon carbide substrate 100 according to the first embodiment will be described. Fig. 4 is a flow diagram that illustrates a schematic diagram of the method for manufacturing the silicon carbide substrate 100 according to the first embodiment. As illustrated in Fig. 4, the method for manufacturing the silicon carbide substrate 100 according to the first embodiment mainly includes a step (S10) of removing particles 90 adhering to the inner wall surface 205 in a state in which the substrate 99 is placed on the first susceptor 211 placed in the furnace 220, a step (S20) of calculating the susceptor temperature based on the etching amount of the substrate 99, a first growth step (S30), a step (S40) of placing the first silicon carbide single crystal substrate 71 on the second susceptor 212 placed in the furnace 220, a second growth step (S50), and a step (S60) of determining temperature conditions using the second silicon carbide layer 20.

[0050] First, a step (S10) of removing particles adhering to the inner wall surface 205 is performed with the substrate 99 placed on the first susceptor 211 arranged in the furnace 220. The step (S10) of removing particles adhering to the inner wall surface 205 with the substrate 99 placed on the first susceptor 211 arranged in the furnace 220 is performed, for example, after maintenance of the furnace 220. Specifically, after at least one of replacement of members constituting the furnace 220 and cleaning of the members is performed, the step (S10) of removing particles adhering to the inner wall surface 205 with the substrate 99 placed on the first susceptor 211 arranged in the furnace 220 is performed.

[0051] Fig. 5 is a schematic cross-sectional view showing a state in which a substrate 99 is placed on a first susceptor 211 disposed in a furnace 220. As shown in Fig. 5, a plurality of particles 90 are attached to an inner wall surface 205 of the furnace 220. The plurality of particles 90 are particles that are attached to the inner wall surface 205 when maintenance of the furnace 220 is performed.

[0052] As shown in FIG. 5, first, substrate 99 is placed on first susceptor 211. First susceptor 211 is placed on stage 202. Substrate 99 has third silicon carbide single crystal substrate 73, first buffer layer 41, and first drift layer 42. First buffer layer 41 is provided on third silicon carbide single crystal substrate 73. First drift layer 42 is provided on first buffer layer 41. First drift layer 42 constitutes the surface of substrate 99.

[0053] First buffer layer 41 and first drift layer 42 are, for example, silicon carbide epitaxial layers formed by epitaxial growth. From another perspective, substrate 99 is, for example, a silicon carbide epitaxial substrate. Third silicon carbide single crystal substrate 73, first buffer layer 41, and first drift layer 42 each contain nitrogen as an n-type impurity. Each of third silicon carbide single crystal substrate 73, first buffer layer 41, and first drift layer 42 has an n-type conductivity type.

[0054] Next, the temperature inside the furnace 220 starts to rise. During the temperature rise, hydrogen (H2) gas as a carrier gas is introduced from the fourth gas supply unit 234 into the reaction chamber 201. From another point of view, hydrogen gas is caused to flow inside the furnace 220 with the substrate 99 placed on the first susceptor 211 arranged in the furnace 220.

[0055] 6 is a schematic diagram showing the time changes of the susceptor temperature and the flow rate of hydrogen gas in a step (S10) of removing particles adhering to an inner wall surface 205 with a substrate 99 placed on the first susceptor 211 arranged in a furnace 220. In FIG. 6, the upper vertical axis indicates the susceptor temperature, and the lower vertical axis indicates the flow rate of hydrogen gas. In FIG. 6, the horizontal axis indicates time. Note that in this specification, the susceptor temperature is the temperature at the center of a first bottom surface 215 of the first susceptor 211, or the temperature at the center of a second bottom surface 216 of a second susceptor 212 described later.

[0056] As shown in FIG. 6, in a step (S10) of removing particles adhering to an inner wall surface 205 with a substrate 99 placed on a first susceptor 211 placed in a furnace 220, the susceptor temperature is increased to a first temperature B1. The first temperature B1 is, for example, 1640° C. The first temperature B1 may be, for example, 1610° C. or more and 1670° C. or less. The flow rate of hydrogen gas is increased to a first flow rate C1. The first flow rate C1 is, for example, 148 SLM. The first flow rate C1 may be, for example, 140 SLM or more and 155 SLM or less. From the first time point T1 to the second time point T2, the susceptor temperature is maintained at the first temperature B1, and the flow rate of hydrogen gas is maintained at the first flow rate C1.

[0057] 7 is a schematic cross-sectional view showing a step (S10) of removing particles adhering to inner wall surface 205 in a state in which substrate 99 is placed on first susceptor 211 arranged in furnace 220. As shown in FIG. 7, the hydrogen gas causes a plurality of particles 90 adhering to inner wall surface 205 to flow. This removes the plurality of particles 90 adhering to inner wall surface 205. Some of the plurality of particles 90 may remain attached to inner wall surface 205. First drift layer 42 of substrate 99 is hydrogen etched. The time from first point T1 to second point T2 is, for example, 30 minutes or more and 40 minutes or more.

[0058] After the second time point T2, the temperature inside the furnace 220 starts to decrease. Specifically, the susceptor temperature decreases from the first temperature B1 to room temperature (27° C.). After the second time point T2, the supply of hydrogen gas is stopped. The substrate 99 is removed from the inside of the furnace 220.

[0059] Next, a step (S20) of calculating the susceptor temperature based on the etching amount of the substrate 99 is performed. Specifically, a value (etching amount) is calculated by subtracting the thickness of the substrate 99 after the step (S10) of removing particles adhering to the inner wall surface 205 in a state where the substrate 99 is placed on the first susceptor 211 placed in the furnace 220 from the thickness of the substrate 99 before the step (S10) of removing particles adhering to the inner wall surface 205 in a state where the substrate 99 is placed on the first susceptor 211 placed in the furnace 220. The susceptor temperature is calculated based on the calculated etching amount. Specifically, a calibration curve (first calibration curve) showing the relationship between the etching amount and the susceptor temperature is prepared in advance. Using the first calibration curve, the susceptor temperature is calculated based on the above-mentioned etching amount.

[0060] Next, a first growth step (S30) is performed. As shown in Fig. 4, the first growth step (S30) includes a first etching step (S31) and a step (S32) of forming a first silicon carbide layer 10 on inner wall surface 205.

[0061] First, the pressure in the reaction chamber 201 is reduced, for example, with no silicon carbide single crystal substrate or susceptor placed on the stage 202. Specifically, the pressure in the reaction chamber 201 is reduced from atmospheric pressure to, for example, 1×10 -2 The pressure is reduced to about Pa. Next, the temperature inside the furnace 220 starts to increase. During the temperature increase, hydrogen gas is introduced into the reaction chamber 201 from the fourth gas supply unit 234.

[0062] Fig. 8 is a schematic diagram showing the time variations of the temperature, the flow rate of hydrogen gas, and the flow rate of ammonia gas in the furnace 220 in the first growth step (S30). As shown in Fig. 8, in the first growth step (S30), a first etching step (S31) is performed from a third time point T3 to a fourth time point T4. Note that in this specification, the temperature in the furnace 220 refers to the temperature at the center of the mounting surface 206 of the stage 202 (see Fig. 3).

[0063] In the first etching step (S31), the temperature inside the furnace 220 is maintained at a second temperature B2, and the flow rate of the hydrogen gas is maintained at a second flow rate C2. The second temperature B2 is, for example, 1680° C. The second temperature B2 may be, for example, not less than 1660° C. and not more than 1700° C. The second flow rate C2 is, for example, 148 SLM. The second flow rate C2 may be, for example, not less than 140 SLM and not more than 155 SLM.

[0064] From the third point in time T3 to the fourth point in time T4, the inner wall surface 205 is hydrogen etched. The time from the third point in time T3 to the fourth point in time T4 is, for example, 20 minutes. In the first etching step (S31), ammonia gas is not supplied to the reaction chamber 201. In other words, in the first etching step (S31), the flow rate of the ammonia gas is 0 sccm.

[0065] After the first etching step (S31), the temperature inside the furnace 220 decreases from the second temperature B2 to the third temperature B3 from the fourth time point T4 to the fifth time point T5. The third temperature B3 is, for example, 1590°C. The third temperature B3 may be, for example, not less than 1570°C and not more than 1610°C. From the fourth time point T4 to the fifth time point T5, the flow rate of the hydrogen gas decreases from the second flow rate C2 to the third flow rate C3. The third flow rate C3 is, for example, 147 SLM. The third flow rate C3 may be, for example, not less than 140 SLM and not more than 155 SLM.

[0066] From the fourth time point T4 to the fifth time point T5, the source gas and the dopant gas are introduced into the reaction chamber 201. From another point of view, for example, a mixed gas containing silane, propane, ammonia, and hydrogen is introduced into the reaction chamber 201. In the reaction chamber 201, each gas is thermally decomposed. From the fourth time point T4 to the fifth time point T5, the flow rate of the ammonia gas increases from 0 sccm to a tenth flow rate D1. The tenth flow rate D1 is, for example, 0.02 sccm. The tenth flow rate D1 may be, for example, 0.01 sccm or more and 0.05 sccm or less.

[0067] Next, a step (S32) of forming a first silicon carbide layer 10 on the inner wall surface 205 is performed. As shown in FIG. 8, in the step (S32) of forming a first silicon carbide layer 10 on the inner wall surface 205, a step (S33) of forming a first layer 11 is first performed. Specifically, from the fifth time point T5 to the sixth time point T6, the temperature inside the furnace 220 is maintained at the third temperature B3, the flow rate of the hydrogen gas is maintained at the third flow rate C3, and the flow rate of the ammonia gas is maintained at the tenth flow rate D1. From the fifth time point T5 to the sixth time point T6, the flow rate of the silane gas is maintained at, for example, 40 sccm, and the flow rate of the propane gas is maintained at, for example, 40 sccm. The time from the fifth time point T5 to the sixth time point T6 is, for example, 30 minutes.

[0068] Fig. 9 is a schematic cross-sectional view showing the step (S32) of forming first silicon carbide layer 10 on inner wall surface 205. As shown in Fig. 9, in the step (S33) of forming first layer 11, first layer 11 is formed on inner wall surface 205. When first layer 11 is formed, nitrogen is introduced into first layer 11 as an n-type impurity.

[0069] 8, after the step (S33) of forming first layer 11, the temperature inside furnace 220 increases from third temperature B3 to fourth temperature B4 from sixth point in time T6 to seventh point in time T7. Fourth temperature B4 is, for example, 1640° C. Fourth temperature B4 may be, for example, not less than 1610° C. and not more than 1670° C.

[0070] From the sixth time point T6 to the seventh time point T7, the flow rate of the hydrogen gas decreases from the third flow rate C3 to the fourth flow rate C4. The fourth flow rate C4 is, for example, 132 SLM. The fourth flow rate C4 may be, for example, 125 SLM or more and 140 SLM or less.

[0071] From the sixth point in time T6 to the seventh point in time T7, the flow rate of the ammonia gas increases from a tenth flow rate D1 to an eleventh flow rate D2. The eleventh flow rate D2 is, for example, 0.2 sccm. The eleventh flow rate D2 may be, for example, 0.1 sccm or more and 0.5 sccm or less.

[0072] From the seventh time T7 to the eighth time T8, the step (S34) of forming the second layer 12 is performed. In the step (S34) of forming the second layer 12, the temperature inside the furnace 220 is maintained at the fourth temperature B4, the flow rate of the hydrogen gas is maintained at the fourth flow rate C4, and the flow rate of the ammonia gas is maintained at the eleventh flow rate D2. In the step (S34) of forming the second layer 12, the flow rate of the silane gas is maintained at, for example, 140 sccm, and the flow rate of the propane gas is set to, for example, 210 sccm. The time from the seventh time T7 to the eighth time T8 is, for example, 50 minutes. The fourth temperature B4 is higher than the third temperature B3. From another perspective, the temperature inside the furnace 220 when the second layer 12 is formed is higher than the temperature inside the furnace 220 when the first layer 11 is formed.

[0073] As shown in Fig. 9, the second layer 12 is formed on the first layer 11. When the second layer 12 is formed, nitrogen is introduced into the second layer 12 as an n-type impurity. As described above, the first silicon carbide layer 10 is formed on the inner wall surface 205 by flowing hydrogen, a raw material gas, and a dopant gas into the furnace 220. The first silicon carbide layer 10 covers the inner wall surface 205. The first silicon carbide layer 10 covers at least a portion of the multiple particles 90 adhering to the inner wall surface 205.

[0074] After the step (S32) of forming first silicon carbide layer 10 on inner wall surface 205, the temperature inside furnace 220 starts to decrease. Specifically, the temperature inside furnace 220 is decreased from fourth temperature B4 to room temperature (27°C). After the step (S32) of forming first silicon carbide layer 10 on inner wall surface 205, the supply of source gas, dopant gas, and hydrogen gas is stopped. As described above, the first growth step (S30) is performed.

[0075] The first silicon carbide layer 10 will be described. As shown in FIG. 9, the first silicon carbide layer 10 has a first layer 11 and a second layer 12. The first layer 11 is in contact with an inner wall surface 205. The first layer 11 is in contact with each of the plurality of particles 90. The second layer 12 is provided on the first layer 11. The second layer 12 is in contact with each of the plurality of particles 90.

[0076] At least a portion of each of the plurality of particles 90 is covered by the first silicon carbide layer 10. A portion of each of the plurality of particles 90 may be exposed from the first silicon carbide layer 10. The first silicon carbide layer 10 contains nitrogen. Specifically, the first layer 11 and the second layer 12 each contain nitrogen. The nitrogen concentration of the first layer 11 is higher than the nitrogen concentration of the second layer 12.

[0077] Next, a step (S40) of placing the first silicon carbide single crystal substrate 71 on the second susceptor 212 placed in the furnace 220 is performed. FIG. 10 is a schematic cross-sectional view showing the step (S40) of placing the first silicon carbide single crystal substrate 71 on the second susceptor 212 placed in the furnace 220. As shown in FIG. 10, the first silicon carbide single crystal substrate 71 is placed inside the furnace 220. Specifically, first, a silicon carbide single crystal having a polytype of 4H is manufactured, for example, by sublimation. Next, the first silicon carbide single crystal substrate 71 is prepared by slicing the silicon carbide single crystal, for example, by a wire saw. The first silicon carbide single crystal substrate 71 contains an n-type impurity, for example, nitrogen. The conductivity type of the first silicon carbide single crystal substrate 71 is, for example, n-type. Next, the first silicon carbide single crystal substrate 71 is mechanically polished. Next, first silicon carbide single crystal substrate 71 is subjected to chemical mechanical polishing.

[0078] The first silicon carbide single crystal substrate 71 is placed on the second susceptor 212. The second susceptor 212 is placed on the mounting surface 206 of the stage 202. The configuration of the second susceptor 212 is substantially the same as the configuration of the first susceptor 211. The second susceptor 212 is provided with a second pocket 218. The second susceptor 212 has a second bottom surface 216. The second bottom surface 216 forms the bottom surface of the second pocket 218. The second susceptor 212 may be the same as the first susceptor 211, or may be different from the first susceptor 211.

[0079] The first silicon carbide single crystal substrate 71 has a second main surface 2 and a third main surface 3. At the second main surface 2, the first silicon carbide single crystal substrate 71 is in contact with the second susceptor 212. The third main surface 3 is opposite the second main surface 2.

[0080] Next, a second growth step (S50) is performed. As shown in Fig. 4, the second growth step (S50) includes a second etching step (S51) and a step (S52) of forming a second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71.

[0081] First, the pressure in the reaction chamber 201 is reduced with the first silicon carbide single crystal substrate 71 placed on the second susceptor 212. Specifically, the pressure in the reaction chamber 201 is reduced from atmospheric pressure to, for example, 1×10 -2 The pressure is reduced to about Pa. Next, the temperature inside the furnace 220 starts to increase. During the temperature increase, hydrogen gas is introduced into the reaction chamber 201 from the fourth gas supply unit 234.

[0082] 11 is a schematic diagram showing the time variations of the susceptor temperature, the hydrogen gas flow rate, and the ammonia gas flow rate in the second growth step (S50). As shown in FIG 11, in the second growth step (S50), a second etching step (S51) is performed from a ninth time T9 to a tenth time T10.

[0083] In the second etching step (S51), the susceptor temperature is maintained at a fifth temperature B5, and the flow rate of the hydrogen gas is maintained at a fifth flow rate C5. The fifth temperature B5 is, for example, 1680°C. The fifth temperature B5 may be, for example, not less than 1660°C and not more than 1700°C. The fifth flow rate C5 is, for example, 148 SLM. The fifth flow rate C5 may be, for example, not less than 140 SLM and not more than 155 SLM.

[0084] From a ninth point T9 to a tenth point T10, third main surface 3 of first silicon carbide single crystal substrate 71 is hydrogen etched. The time from the ninth point T9 to the tenth point T10 is, for example, 20 minutes. In the second etching step (S51), ammonia gas is not supplied to reaction chamber 201. In other words, in the second etching step (S51), the flow rate of ammonia gas is 0 sccm.

[0085] After the second etching step (S51), the susceptor temperature is decreased from the fifth temperature B5 to the sixth temperature B6 from the tenth time T10 to the eleventh time T11. The sixth temperature B6 is equal to or lower than the third temperature B3 (see FIG. 8). The sixth temperature B6 may be substantially the same as the third temperature B3. The sixth temperature B6 is, for example, 1590° C. The sixth temperature B6 may be, for example, not lower than 1570° C. and not higher than 1610° C. From the tenth time T10 to the eleventh time T11, the flow rate of the hydrogen gas is decreased from the fifth flow rate C5 to the sixth flow rate C6. The sixth flow rate C6 may be substantially the same as the third flow rate C3 (see FIG. 8). The sixth flow rate C6 is, for example, 147 SLM. The sixth flow rate C6 may be, for example, not lower than 140 SLM and not higher than 155 SLM.

[0086] Between a tenth time point T10 and an eleventh time point T11, ammonia gas as a dopant gas is introduced into the reaction chamber 201. Specifically, between the tenth time point T10 and the eleventh time point T11, the flow rate of the ammonia gas increases from 0 sccm to a twelfth flow rate D3. The twelfth flow rate D3 is equal to or lower than the tenth flow rate D1 (see FIG. 8). The twelfth flow rate D3 may be substantially the same as the tenth flow rate D1. The twelfth flow rate D3 is, for example, 0.02 sccm. The twelfth flow rate D3 may be, for example, equal to or higher than 0.01 sccm and equal to or lower than 0.05 sccm.

[0087] Next, a step (S52) of forming a second silicon carbide layer 20 on a first silicon carbide single crystal substrate 71 is performed. Specifically, as shown in Fig. 11, from an eleventh point in time T11 to a twelfth point in time T12, the susceptor temperature is held at a sixth temperature B6, the flow rate of hydrogen gas is held at a sixth flow rate C6, and the flow rate of ammonia gas is held at a twelfth flow rate D3. From the eleventh point in time T11 to the twelfth point in time T12, the flow rate of silane gas is held at, for example, 40 sccm, and the flow rate of propane gas is held at, for example, 40 sccm. The time from the eleventh point in time T11 to the twelfth point in time T12 is, for example, 1 hour and 45 minutes.

[0088] The susceptor temperature (sixth temperature B6) in the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71 is equal to or lower than the temperature inside the furnace 220 (see FIG. 8) in the step (S32) of forming the first silicon carbide layer 10 on the inner wall surface 205. Specifically, the sixth temperature B6 is, for example, substantially the same as the temperature inside the furnace 220 (third temperature B3) in the step (S33) of forming the first layer 11. The sixth temperature B6 is lower than the temperature inside the furnace 220 (fourth temperature B4) in the step (S34) of forming the second layer 12. From another perspective, the susceptor temperature in the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71 is lower than the temperature inside the furnace 220 in at least a part of the step (S32) of forming the first silicon carbide layer 10 on the inner wall surface 205. For the same ammonia gas flow rate, the amount of nitrogen incorporation in the silicon carbide layer formed increases as the temperature inside the furnace 220 decreases. Similarly, for the same ammonia gas flow rate, the amount of nitrogen incorporation in the silicon carbide layer formed increases as the susceptor temperature decreases.

[0089] The flow rate of the dopant gas (sixth flow rate C6) in the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71 is equal to or lower than the flow rate of the dopant gas in the step (S32) of forming the first silicon carbide layer 10 on the inner wall surface 205. Specifically, the sixth flow rate C6 is, for example, substantially the same as the flow rate of the dopant gas (third flow rate C3) in the step (S33) of forming the first layer 11. The sixth flow rate C6 is lower than the flow rate of the dopant gas (fourth flow rate C4) in the step (S34) of forming the second layer 12. From another viewpoint, the flow rate of the dopant gas in the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71 is lower than the flow rate of the dopant gas in at least a part of the step (S32) of forming the first silicon carbide layer 10 on the inner wall surface 205.

[0090] 12 is a cross-sectional schematic diagram showing the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71. As shown in FIG. 12, in the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71, the first silicon carbide single crystal substrate 71 is placed on the second susceptor 212 arranged in the furnace 220, and hydrogen, a source gas, and a dopant gas are flowed into the furnace 220 to form the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71. The second silicon carbide layer 20 is formed by epitaxial growth, for example. The second silicon carbide layer 20 contains nitrogen as an n-type impurity. The conductivity type of the second silicon carbide layer 20 is n-type.

[0091] In the step (S52) of forming second silicon carbide layer 20 on first silicon carbide single crystal substrate 71, fourth silicon carbide layer 19 is formed on first silicon carbide layer 10. Fourth silicon carbide layer 19 covers first silicon carbide layer 10. Fourth silicon carbide layer 19 is in contact with a plurality of particles 90, for example. Fourth silicon carbide layer 19 may cover a plurality of particles 90. The nitrogen concentration of fourth silicon carbide layer 19 is higher than the nitrogen concentration of second layer 12. The nitrogen concentration of fourth silicon carbide layer 19 may be substantially the same as the nitrogen concentration of first layer 11.

[0092] After the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71, the temperature inside the furnace 220 starts to decrease. Specifically, the susceptor temperature is decreased from the sixth temperature B6 to room temperature (27° C.). After the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71, the supply of the source gas, dopant gas, and hydrogen gas is stopped. As described above, the second growth step (S50) is performed. After the second growth step (S50), the silicon carbide substrate 100 is removed from the furnace 220. As described above, the silicon carbide substrate 100 according to the first embodiment is manufactured.

[0093] Next, a step (S60) of determining temperature conditions is performed using second silicon carbide layer 20. Specifically, first, the nitrogen concentration is measured at the center of second silicon carbide layer 20. In measuring the nitrogen concentration at the center of second silicon carbide layer 20, for example, the above-mentioned method for measuring the nitrogen concentration is used.

[0094] The susceptor temperature is calculated based on the measured nitrogen concentration. Specifically, a calibration curve (second calibration curve) showing the relationship between the nitrogen concentration and the susceptor temperature is prepared in advance. Using the second calibration curve, the susceptor temperature is calculated based on the above-mentioned nitrogen concentration. Compared with the step (S20) of calculating the susceptor temperature based on the etching amount of the substrate 99, in the step (S60) of determining the temperature conditions using the second silicon carbide layer 20, the susceptor temperature can be calculated with higher accuracy. Based on the calculated susceptor temperature, the temperature conditions when manufacturing a silicon carbide epitaxial substrate using the furnace 220 are determined.

[0095] In the above, the first silicon carbide layer 10 has been described as having two layers, the first layer 11 and the second layer 12, but the configuration of the first silicon carbide layer 10 is not limited to the above configuration. The first silicon carbide layer 10 may be composed of one layer. Specifically, the first silicon carbide layer 10 may be composed of only one of the first layer 11 and the second layer 12.

[0096] Second embodiment <Silicon carbide substrate> Next, the configuration of silicon carbide substrate 100 according to the second embodiment will be described. Silicon carbide substrate 100 according to the second embodiment differs from silicon carbide substrate 100 according to the first embodiment mainly in having third silicon carbide layer 30, and is substantially the same as the silicon carbide substrate 100 according to the first embodiment in other respects. The following description will focus on the differences from the configuration of silicon carbide substrate 100 according to the first embodiment.

[0097] Fig. 13 is a cross-sectional schematic diagram showing a configuration of a silicon carbide substrate 100 according to the second embodiment. The cross section shown in Fig. 13 corresponds to the cross section shown in Fig. 2. As shown in Fig. 13, the silicon carbide substrate 100 according to the second embodiment has a third silicon carbide layer 30.

[0098] The third silicon carbide layer 30 is provided on the first silicon carbide single crystal substrate 71. The third silicon carbide layer 30 is provided between the first silicon carbide single crystal substrate 71 and the second silicon carbide layer 20. From another perspective, the second silicon carbide layer 20 is provided on the third silicon carbide layer 30. The third silicon carbide layer 30 is, for example, a silicon carbide epitaxial layer. In other words, the third silicon carbide layer 30 is, for example, a layer formed by epitaxial growth.

[0099] The third silicon carbide layer 30 has a third layer 33 and a fourth layer 34. The third layer 33 is provided on a silicon carbide single crystal substrate. The thickness of the third layer 33 in the third direction 103 is defined as a third thickness H3. The third thickness H3 is, for example, not less than 0.5 μm and not more than 3 μm. The third thickness H3 may be, for example, not less than 0.8 μm, or not less than 1 μm. The third thickness H3 may be, for example, not more than 2.5 μm, or not more than 2 μm.

[0100] The fourth layer 34 is provided on the third layer 33. The fourth layer 34 is provided between the third layer 33 and the second silicon carbide layer 20. The thickness of the fourth layer 34 in the third direction 103 is designated as a fourth thickness H4.

[0101] The fourth thickness H4 is, for example, 4 μm or more and 7 μm or less. The fourth thickness H4 may be, for example, 4.5 μm or more, or 5 μm or more. The fourth thickness H4 may be, for example, 6.5 μm or less, or 6 μm or less. The third thickness H3 is smaller than the fourth thickness H4.

[0102] In silicon carbide substrate 100 according to the second embodiment, second thickness H2 is not less than 0.5 μm and not more than 3 μm. Second thickness H2 may be, for example, not less than 0.8 μm, or not less than 1 μm. Second thickness H2 may be, for example, not more than 2.5 μm, or not more than 2 μm. Second thickness H2 is smaller than fourth thickness H4.

[0103] The third silicon carbide layer 30 contains nitrogen as an n-type impurity. The third silicon carbide layer 30 has an n-type conductivity. Specifically, each of the third layer 33 and the fourth layer 34 contains nitrogen as an n-type impurity. The third layer 33 and the fourth layer 34 have an n-type conductivity.

[0104] The nitrogen concentration of the third layer 33 may be substantially the same as the nitrogen concentration of the second silicon carbide layer 20. The nitrogen concentration of the third layer 33 may be 1×10 17 cm -3 More than 3×10 18 cm -3 The nitrogen concentration of the third layer 33 is, for example, 3×10 17 cm -3 May be more than 5 x 10 17 cm -3 The nitrogen concentration of the third layer 33 may be, for example, 1×10 18 cm -3 It may be less than or equal to 8 x 10 17 cm -3 It may be the following.

[0105] The nitrogen concentration of the fourth layer 34 is lower than the nitrogen concentration of each of the third layer 33 and the second silicon carbide layer 20. The nitrogen concentration of the fourth layer 34 is 3×10 15 cm -3 More than 2×10 16 cm -3The nitrogen concentration of the fourth layer 34 is, for example, 6×10 15 cm -3 It may be more than 9 x 10 15 cm -3 The nitrogen concentration of the fourth layer 34 may be, for example, 1.5×10 16 cm -3 It may be less than or equal to 1 x 10 16 cm -3 It may be the following.

[0106] <Method for manufacturing silicon carbide substrate> Next, the configuration of the method for manufacturing the silicon carbide substrate 100 according to the second embodiment will be described. The method for manufacturing the silicon carbide substrate 100 according to the second embodiment differs from the method for manufacturing the silicon carbide substrate 100 according to the first embodiment mainly in that the second silicon carbide layer 20 is formed in the first growth step (S30), and is substantially the same as the method for manufacturing the silicon carbide substrate 100 according to the first embodiment in other respects. Below, the differences from the method for manufacturing the silicon carbide substrate 100 according to the first embodiment will be mainly described.

[0107] Fig. 14 is a flow diagram that illustrates a manufacturing method of the silicon carbide substrate 100 according to the second embodiment. As illustrated in Fig. 14, in the manufacturing method of the silicon carbide substrate 100 according to the second embodiment, after the step (S10) of removing the particles 90 adhering to the inner wall surface 205 in a state in which the substrate 99 is placed on the first susceptor 211 placed in the furnace 220 and before the first growth step (S30), a step (S40) of placing the first silicon carbide single crystal substrate 71 on the second susceptor 212 placed in the furnace 220 is performed. Specifically, after the step (S20) of calculating the temperature inside the furnace 220 based on the etching amount of the substrate 99, a step (S40) of placing the first silicon carbide single crystal substrate 71 on the second susceptor 212 placed in the furnace 220 is performed.

[0108] Fig. 15 is a schematic cross-sectional view showing the step (S40) of arranging first silicon carbide single crystal substrate 71 in the method for manufacturing silicon carbide substrate 100 in accordance with the second embodiment. As shown in Fig. 15, after the step (S20) of calculating the susceptor temperature based on the etching amount of substrate 99 and before the first growth step (S30), first silicon carbide single crystal substrate 71 is arranged on second susceptor 212.

[0109] Next, a first growth step (S30) is performed. As shown in Fig. 14, the first growth step (S30) includes a step (S70) of forming a third silicon carbide layer 30 on the first silicon carbide single crystal substrate 71 while forming a first silicon carbide layer 10 on the inner wall surface 205, and a step (S80) of forming a second silicon carbide layer 20 on the third silicon carbide layer 30. In a first etching step (S31), the third main surface 3 of the first silicon carbide single crystal substrate 71 is hydrogen etched.

[0110] 16 is a schematic diagram showing the changes over time of the temperature inside furnace 220, the flow rate of hydrogen gas, and the flow rate of ammonia gas in the first growth step (S30) in the manufacturing method of silicon carbide substrate 100 according to the second embodiment. As shown in FIG. 16, after the first etching step (S31), the susceptor temperature decreases from the third temperature B3 to the seventh temperature B7 from the fourth time point T4 to the thirteenth time point T13. The seventh temperature B7 is, for example, 1590° C. The seventh temperature B7 may be, for example, not less than 1570° C. and not more than 1610° C.

[0111] From the fourth time point T4 to the thirteenth time point T13, the flow rate of the hydrogen gas decreases from the second flow rate C2 to a seventh flow rate C7. The seventh flow rate C7 is, for example, 147 SLM. The seventh flow rate C7 may be, for example, 140 SLM or more and 155 SLM or less.

[0112] From the fourth time point T4 to the thirteenth time point T13, the source gas and the dopant gas are introduced into the reaction chamber 201. The flow rate of the ammonia gas increases from 0 sccm to a thirteenth flow rate D4. The thirteenth flow rate D4 is, for example, 0.02 sccm. The thirteenth flow rate D4 may be, for example, 0.01 sccm or more and 0.05 sccm or less.

[0113] Next, a step (S70) of forming a third silicon carbide layer 30 on the first silicon carbide single crystal substrate 71 while forming the first silicon carbide layer 10 on the inner wall surface 205 is performed. As shown in FIG. 16, in the step (S70) of forming a third silicon carbide layer 30 on the first silicon carbide single crystal substrate 71 while forming the first silicon carbide layer 10 on the inner wall surface 205, a step (S71) of forming the first layer 11 and the third layer 33 is first performed. Specifically, from the thirteenth time point T13 to the fourteenth time point T14, the susceptor temperature is held at the seventh temperature B7, the flow rate of the hydrogen gas is held at the seventh flow rate C7, and the flow rate of the ammonia gas is held at the thirteenth flow rate D4. From the thirteenth time point T13 to the fourteenth time point T14, the flow rate of the silane gas is held at, for example, 40 sccm, and the flow rate of the propane gas is held at, for example, 40 sccm. The time from the thirteenth point in time T13 to the fourteenth point in time T14 is, for example, 15 minutes.

[0114] Fig. 17 is a schematic cross-sectional view showing the step (S80) of forming second silicon carbide layer 20 on third silicon carbide layer 30. As shown in Fig. 17, in the step (S71) of forming first layer 11 and third layer 33, first layer 11 is formed on inner wall surface 205, and third layer 33 is formed on first silicon carbide single crystal substrate 71. When third layer 33 is formed, nitrogen is introduced into third layer 33 as an n-type impurity.

[0115] 16, after the step (S71) of forming the first layer 11 and the third layer 33, the susceptor temperature increases from a seventh temperature B7 to an eighth temperature B8 from a fourteenth point in time T14 to a fifteenth point in time T15. The eighth temperature B8 is, for example, 1640° C. The eighth temperature B8 may be, for example, not less than 1610° C. and not more than 1670° C.

[0116] From the fourteenth time point T14 to the fifteenth time point T15, the flow rate of the hydrogen gas decreases from the seventh flow rate C7 to the eighth flow rate C8. The eighth flow rate C8 is, for example, 132 SLM. The eighth flow rate C8 may be, for example, 125 SLM or more and 140 SLM or less.

[0117] From the fourteenth time point T14 to the fifteenth time point T15, the flow rate of the ammonia gas increases from the thirteenth flow rate D4 to the fourteenth flow rate D5. The fourteenth flow rate D5 is, for example, 0.2 sccm. The fourteenth flow rate D5 may be, for example, 0.1 sccm or more and 0.5 sccm or less.

[0118] From a fifteenth time point T15 to a sixteenth time point T16, a process (S72) of forming a second layer and a fourth layer is performed. In the process (S72) of forming the second layer and the fourth layer, the susceptor temperature is maintained at an eighth temperature B8, the flow rate of the hydrogen gas is maintained at an eighth flow rate C8, and the flow rate of the ammonia gas is maintained at a fourteenth flow rate D5. In the process (S72) of forming the second layer and the fourth layer, the flow rate of the silane gas is maintained at, for example, 140 sccm, and the flow rate of the propane gas is maintained at, for example, 210 sccm.

[0119] The eighth temperature B8 is higher than the seventh temperature B7. From another perspective, the susceptor temperature when the fourth layer 34 is formed is higher than the susceptor temperature when the third layer 33 is formed. The time from the fifteenth point in time T15 to the sixteenth point in time T16 is, for example, 30 minutes.

[0120] The growth rate of fourth layer 34 is faster than the growth rates of third layer 33 and second silicon carbide layer 20. For this reason, when the thickness of the silicon carbide layer formed on first silicon carbide single crystal substrate 71 is the same, the time required to form the silicon carbide layer on first silicon carbide single crystal substrate 71 can be shortened compared to the case where only second silicon carbide layer 20 is formed on first silicon carbide single crystal substrate 71. For this reason, in the step (S60) of determining the temperature conditions using second silicon carbide layer 20, the time required to obtain a silicon carbide layer thickness (for example, 5 μm) required for measuring the nitrogen concentration can be shortened.

[0121] 17, the second layer 12 is formed on the first layer 11, and the fourth layer 34 is formed on the third layer 33. When the fourth layer 34 is formed, nitrogen is introduced into the fourth layer 34 as an n-type impurity. As described above, by flowing hydrogen, a raw material gas, and a dopant gas into the furnace 220, the first silicon carbide layer 10 is formed on the inner wall surface 205, and the third silicon carbide layer 30 is formed on the first silicon carbide single crystal substrate 71.

[0122] As shown in FIG. 16, after the step (S70) of forming a third silicon carbide layer 30 on a first silicon carbide single crystal substrate 71 while forming a first silicon carbide layer 10 on an inner wall surface 205, the susceptor temperature decreases from an eighth temperature B8 to a ninth temperature B9 from a sixteenth time point T16 to a seventeenth time point T17. The ninth temperature B9 is, for example, 1590° C. The ninth temperature B9 may be, for example, not less than 1570° C. and not more than 1610° C. The ninth temperature B9 is not more than the seventh temperature B7. The ninth temperature B9 may be substantially the same as the seventh temperature B7.

[0123] From the 16th time point T16 to the 17th time point T17, the flow rate of the hydrogen gas increases from the eighth flow rate C8 to a ninth flow rate C9. The ninth flow rate C9 is, for example, 147 SLM. The ninth flow rate C9 may be, for example, not less than 140 SLM and not more than 155 SLM. The ninth flow rate C9 is not more than the seventh flow rate C7. The ninth flow rate C9 may be substantially the same as the seventh flow rate C7.

[0124] From the 16th time point T16 to the 17th time point T17, the flow rate of the ammonia gas decreases from the 14th flow rate D5 to the 15th flow rate D6. The 15th flow rate D6 is, for example, 0.02 sccm. The 15th flow rate D6 may be, for example, 0.01 sccm or more and 0.05 sccm or less. The 15th flow rate D6 is equal to or less than the 13th flow rate D4. The 15th flow rate D6 may be substantially the same as the 13th flow rate D4.

[0125] Next, a step (S80) of forming a second silicon carbide layer 20 on the third silicon carbide layer 30 is performed. As shown in FIG. 16, from the 17th time T17 to the 18th time T18, the susceptor temperature is held at the ninth temperature B9, the flow rate of hydrogen gas is held at the ninth flow rate C9, and the flow rate of ammonia gas is held at the fifteenth flow rate D6. From the 17th time T17 to the 18th time T18, the flow rate of silane gas is held at, for example, 40 sccm, and the flow rate of propane gas is held at, for example, 40 sccm. The time from the 17th time T17 to the 18th time T18 is, for example, 15 minutes. As a result, as shown in FIG. 17, the second silicon carbide layer 20 is formed on the third silicon carbide layer 30, and the fourth silicon carbide layer 19 is formed on the first silicon carbide layer 10.

[0126] After the step (S80) of forming the second silicon carbide layer 20 on the third silicon carbide layer 30, the temperature inside the furnace 220 starts to decrease. Specifically, the susceptor temperature is decreased from the ninth temperature B9 to room temperature (27°C). After the step (S80) of forming the second silicon carbide layer 20 on the third silicon carbide layer 30, the supply of the source gas, dopant gas, and hydrogen gas is stopped. In this manner, the silicon carbide substrate 100 according to the second embodiment is manufactured.

[0127] (Method for manufacturing silicon carbide semiconductor device) Next, a method for manufacturing the silicon carbide semiconductor device 400 according to this embodiment will be described. Fig. 18 is a flow chart that outlines the method for manufacturing the silicon carbide semiconductor device 400 according to this embodiment. As shown in Fig. 18, the method for manufacturing the silicon carbide semiconductor device 400 according to this embodiment mainly includes a step (S1) of manufacturing a silicon carbide epitaxial substrate and a step (S2) of forming an electrode on the silicon carbide epitaxial layer.

[0128] First, a step (S1) of manufacturing a silicon carbide epitaxial substrate is performed. The step (S1) of manufacturing a silicon carbide epitaxial substrate includes a step (S100) of determining temperature conditions and a step (S110) of forming a silicon carbide epitaxial layer on a second silicon carbide single crystal substrate 72. First, a step (S100) of determining temperature conditions is performed. In the step (S100) of determining temperature conditions, the temperature conditions in epitaxial growth described below are determined using the method for manufacturing the silicon carbide substrate 100 according to the first embodiment or the method for manufacturing the silicon carbide substrate 100 according to the second embodiment described above.

[0129] Next, a step (S110) of forming a silicon carbide epitaxial layer on second silicon carbide single crystal substrate 72 is performed. First, second silicon carbide single crystal substrate 72 is prepared. Specifically, a silicon carbide single crystal of polytype 4H is manufactured, for example, by sublimation. Next, second silicon carbide single crystal substrate 72 is prepared by slicing the silicon carbide single crystal, for example, by a wire saw. Next, second silicon carbide single crystal substrate 72 is mechanically polished. Next, second silicon carbide single crystal substrate 72 is chemically mechanically polished.

[0130] Second silicon carbide single crystal substrate 72 has fourth main surface 14 and fifth main surface 15. Fifth main surface 15 is opposite fourth main surface 14. Second silicon carbide single crystal substrate 72 contains an n-type impurity such as nitrogen. The conductivity type of second silicon carbide single crystal substrate 72 is, for example, n-type.

[0131] Next, second silicon carbide epitaxial layer 60 is formed on second silicon carbide single crystal substrate 72. Specifically, second silicon carbide epitaxial layer 60 is formed by epitaxial growth on fourth main surface 14 using manufacturing apparatus 300 (see FIG. 3 ) used in the temperature condition determining step (S100). Specifically, a second buffer layer 61 is formed on fourth main surface 14. A second drift layer 62 is formed on second buffer layer 61.

[0132] 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 inside the furnace 220 when the second buffer layer 61 is formed is, for example, not less than 1570°C and not more than 1610°C. The temperature inside the furnace 220 when the second drift layer 62 is formed is, for example, not less than 1610°C and not more than 1670°C. In the epitaxial growth, an n-type impurity such as nitrogen is introduced into the second silicon carbide epitaxial layer 60.

[0133] 19 is a cross-sectional schematic diagram showing a configuration of a silicon carbide epitaxial substrate 200 according to this embodiment. Silicon carbide epitaxial substrate 200 has a sixth main surface 16. Sixth main surface 16 is the surface of silicon carbide epitaxial substrate 200. A second drift layer 62 constitutes sixth main surface 16.

[0134] Next, a step (S2) of forming an electrode on the silicon carbide epitaxial layer is performed. Specifically, the following processing is performed on silicon carbide epitaxial substrate 200. First, ions are implanted into silicon carbide epitaxial substrate 200.

[0135] 20 is a cross-sectional view showing a step of forming a body region. In the step of forming a body region, p-type impurities such as aluminum are ion-implanted into sixth main surface 16 of second silicon carbide epitaxial layer 60. This forms body region 113 having p-type conductivity. A portion where body region 113 is not formed becomes second drift layer 62 and second buffer layer 61. Body region 113 has a thickness of, for example, 0.9 μm. Second silicon carbide epitaxial layer 60 includes second buffer layer 61, second drift layer 62, and body region 113.

[0136] Next, a step of forming a source region is performed. Fig. 21 is a schematic cross-sectional view showing the step of forming a source region. Specifically, n-type impurities such as phosphorus are ion-implanted into the body region 113. This forms a source region 114 having an 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.

[0137] 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 so as to penetrate the source region 114 and the body region 113 and to be in contact with the second drift layer 62. 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.

[0138] Next, activation annealing is performed to activate the implanted impurities. The temperature of the activation annealing is, for example, 1500° C. to 1900° C. The activation annealing time is, for example, about 30 minutes. The atmosphere of the activation annealing is, for example, an argon atmosphere.

[0139] Next, a step of forming a trench in the sixth main surface 16 of the second silicon carbide epitaxial layer 60 is performed. FIG. 22 is a cross-sectional schematic diagram showing a step of forming a trench in the sixth main surface 16 of the second silicon carbide epitaxial layer 60. A mask 117 having an opening is formed on the sixth main surface 16 including the source region 114 and the contact region 118. The source region 114, the body region 113, and a part of the second drift layer 62 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 SF6 or a mixed gas of SF6 and O2 as a reactive gas is used. A recess is formed in the sixth main surface 16 by etching.

[0140] Next, thermal etching is performed in the recess. The thermal etching can be performed, for example, by heating in an atmosphere containing a reactive gas having at least one or more types of halogen atoms, with the mask 117 formed on the sixth main surface 16. The at least one or more types of halogen atoms include at least one of chlorine (Cl) atoms and fluorine (F) atoms. The atmosphere includes, for example, Cl2, BCl3, SF6, or CF4. For example, a mixed gas of chlorine gas and oxygen gas is used as the reactive gas, and the thermal etching is performed at a heat treatment temperature of, for example, 700°C or more and 1000°C or less. Note that the reactive gas may contain a carrier gas in addition to the above-mentioned chlorine gas and oxygen gas. For example, nitrogen gas, argon gas, or helium gas can be used as the carrier gas.

[0141] 22, a trench 56 is formed in the sixth main surface 16 by thermal etching. The trench 56 is defined by a sidewall surface 53 and a bottom wall surface 54. The sidewall surface 53 is composed of the source region 114, the body region 113, and the second drift layer 62. The bottom wall surface 54 is composed of the second drift layer 62. Next, the mask 117 is removed from the sixth main surface 16.

[0142] Next, a step of forming a gate insulating film is performed. Fig. 23 is a cross-sectional schematic diagram showing the step of forming a gate insulating film. Specifically, silicon carbide epitaxial substrate 200 having trench 56 formed in sixth main surface 16 is heated in an atmosphere containing oxygen at a temperature of, for example, 1300°C or more and 1400°C or less. As a result, gate insulating film 115 is formed which is in contact with second drift layer 62 at bottom wall surface 54, in contact with second drift layer 62, body region 113, and source region 114 at side wall surface 53, and in contact with source region 114 and contact region 118 at sixth main surface 16.

[0143] Next, a step of forming a gate electrode is performed. Fig. 24 is a schematic cross-sectional view showing a step of forming a gate electrode and an interlayer insulating film. Gate electrode 127 is formed inside trench 56 so as to contact gate insulating film 115. Gate electrode 127 is disposed inside trench 56, and is formed on gate insulating film 115 so as to face each of sidewall surface 53 and bottom wall surface 54 of trench 56. Gate electrode 127 is formed, for example, by LPCVD (Low Pressure Chemical Vapor Deposition).

[0144] Next, the 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, for example, by chemical vapor deposition. The interlayer insulating film 126 is made of a material containing, for example, silicon dioxide. Next, the interlayer insulating film 126 and the gate insulating film 115 are partly etched so as to form openings on 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.

[0145] Next, a step of forming a source electrode is performed. The source electrode 116 is formed so as to contact 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 including Ti (titanium), Al (aluminum) and Si (silicon).

[0146] 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 held at a temperature of, for example, 900° C. or more and 1100° C. or less for about 5 minutes. As a result, at least a portion of the source electrode 116 is silicided. As a result, the source electrode 116 in ohmic junction with the source region 114 is formed. The source electrode 116 may be in ohmic junction with the contact region 118.

[0147] 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.

[0148] Next, a step of forming a drain electrode is performed. First, the sixth main surface 16 of the second silicon carbide single crystal substrate 72 is polished. This reduces the thickness of the second silicon carbide single crystal substrate 72. Next, the drain electrode 123 is formed. The drain electrode 123 is formed so as to be in contact with the sixth main surface 16. In this manner, the silicon carbide semiconductor device 400 according to this embodiment is manufactured.

[0149] 25 is a cross-sectional schematic diagram showing the configuration of the 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 second buffer layer 61, a second drift layer 62, 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.

[0150] Next, the effects of the method for manufacturing silicon carbide substrate 100 in accordance with this embodiment will be described.

[0151] When epitaxial growth is performed using a furnace, by-products composed of silicon carbide are deposited on the members constituting the furnace. Therefore, after epitaxial growth is performed for a certain period of time, furnace maintenance is usually performed. In the furnace maintenance, at least one of replacement of the members constituting the furnace and cleaning of the members constituting the furnace is performed.

[0152] The state of the furnace after the furnace maintenance is changed compared to the state of the furnace before the furnace maintenance, and as a result, the temperature inside the furnace during epitaxial growth is changed after the furnace maintenance compared to the state of the furnace before the furnace maintenance. Therefore, a process of determining the temperature conditions is required after the furnace maintenance.

[0153] Furthermore, after furnace maintenance, fine particles adhere to the components constituting the furnace. If the particles scatter onto the substrate during epitaxial growth, the yield of silicon carbide epitaxial substrates decreases.

[0154] The method for manufacturing the silicon carbide substrate 100 according to the first embodiment includes a step (S10) of removing particles 90 adhering to the inner wall surface 205 with the substrate 99 disposed inside the furnace 220, a step (S32) of forming a first silicon carbide layer 10 on the inner wall surface 205, a step (S52) of forming a second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71, and a step (S60) of determining temperature conditions using the second silicon carbide layer 20. Therefore, after removing the particles 90 adhering to the inner wall surface 205, the particles 90 that could not be removed can be covered with the first silicon carbide layer 10. This makes it possible to determine the temperature conditions while suppressing the particles 90 from scattering from the inner wall surface of the furnace 220.

[0155] According to the method for manufacturing the silicon carbide substrate 100 according to the first embodiment, the susceptor temperature in the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71 is equal to or lower than the temperature inside the furnace 220 in the step (S32) of forming the first silicon carbide layer 10 on the inner wall surface 205. The flow rate of the dopant gas in the step (S52) of forming the second silicon carbide layer 20 on the first silicon carbide single crystal substrate 71 is equal to or lower than the flow rate of the dopant gas in the step (S32) of forming the first silicon carbide layer 10 on the inner wall surface 205. Therefore, the configuration of the first silicon carbide layer 10 can be made closer to the configuration of the silicon carbide epitaxial layer of the silicon carbide epitaxial substrate manufactured using the furnace 220. This can reduce the influence of gas released from the silicon carbide layer formed on the inner wall surface of furnace 220 on the formation of the silicon carbide epitaxial layer of the silicon carbide epitaxial substrate.

[0156] The method for manufacturing the silicon carbide substrate 100 according to the second embodiment includes a step (S70) of forming a third silicon carbide layer 30 on the first silicon carbide single crystal substrate 71 while forming the first silicon carbide layer 10 on the inner wall surface 205, and a step (S80) of forming a second silicon carbide layer 20 on the third silicon carbide layer 30. The step (S70) of forming the third silicon carbide layer 30 on the first silicon carbide single crystal substrate 71 while forming the first silicon carbide layer 10 on the inner wall surface 205 is performed after the step (S40) of placing the first silicon carbide single crystal substrate 71 inside the furnace 220. Therefore, the formation of the first silicon carbide layer 10 and the formation of the second silicon carbide layer 20 can be performed in a single growth step. This makes it possible to reduce the time required for reducing the pressure inside the furnace, increasing the temperature before the growth step, and decreasing the temperature after the growth step, compared to the case where the first silicon carbide layer 10 and the second silicon carbide layer 20 are formed in two growth steps. As a result, the time required to determine the temperature conditions can be reduced.

[0157] According to the method for manufacturing the silicon carbide substrate 100 according to the second embodiment, the susceptor temperature in the step (S80) of forming the second silicon carbide layer 20 on the third silicon carbide layer 30 is equal to or lower than the susceptor temperature in the step (S70) of forming the third silicon carbide layer 30 on the first silicon carbide single crystal substrate 71 while forming the first silicon carbide layer 10 on the inner wall surface 205. The flow rate of the dopant gas in the step (S80) of forming the second silicon carbide layer 20 on the third silicon carbide layer 30 is equal to or lower than the flow rate of the dopant gas in the step (S70) of forming the third silicon carbide layer 30 on the first silicon carbide single crystal substrate 71 while forming the first silicon carbide layer 10 on the inner wall surface 205. Therefore, the configuration of the first silicon carbide layer 10 can be made closer to the configuration of the silicon carbide epitaxial layer of the silicon carbide epitaxial substrate manufactured using the furnace 220. This can reduce the influence of gas released from the silicon carbide layer formed on the inner wall surface of furnace 220 on the formation of the silicon carbide epitaxial layer of the silicon carbide epitaxial substrate.

[0158] According to the method for manufacturing silicon carbide substrate 100 in accordance with the present embodiment, the susceptor temperature is calculated based on the amount of etching of substrate 99. Therefore, in the step (S60) of determining the temperature conditions using second silicon carbide layer 20, the susceptor temperature calculated based on the amount of etching of substrate 99 can be used. This allows the susceptor temperature to be calculated with higher accuracy. As a result, the temperature conditions can be determined more accurately.

[0159] According to the method for manufacturing the silicon carbide substrate 100 according to this embodiment, the first silicon carbide layer 10 has a first layer 11 and a second layer 12. The nitrogen concentration of the first layer 11 is higher than the nitrogen concentration of the second layer 12. This makes it possible to make the configuration of the first silicon carbide layer 10 closer to the configuration of the silicon carbide epitaxial layer of the silicon carbide epitaxial substrate manufactured using the furnace 220. This makes it possible to reduce the influence of gas released from the silicon carbide layer formed on the inner wall surface of the furnace 220 on the formation of the silicon carbide epitaxial layer of the silicon carbide epitaxial substrate.

[0160] The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is defined by the claims rather than the above-described embodiments, and it is intended to include the equivalent meaning of the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0161] 1 First main surface 2 Second main surface 3 Third main surface 6 Outer rim 7 Orientation Flat 8 Arc-shaped section 10 First silicon carbide layer 11 1st layer 12 2nd layer 14 Fourth main surface 15 5th main surface 16 6th main surface 19 Fourth silicon carbide layer 20 Second silicon carbide layer 30 Third silicon carbide layer 33 3rd layer 34 4th layer 41 First buffer layer 42 First drift layer 53 Side wall 54 Bottom wall 56 Trench 60 Second silicon carbide epitaxial layer (silicon carbide epitaxial layer) 61 Second buffer layer 62 Second drift layer 71 First silicon carbide single crystal substrate (silicon carbide single crystal substrate) 72 Second silicon carbide single crystal substrate 73 Third Silicon Carbide Single Crystal Substrate 90 Particles 99 Substrate 100 Silicon carbide substrate 101 1st direction 102 Second direction 103 Third direction 113 Body Region 114 Source Region 115 Gate insulating film 116 Source Electrode 117 Mask 118 Contact Area 119 Source wiring 123 Drain electrode 126 Interlayer insulating film 127 Gate electrode (electrode) 200 Silicon carbide epitaxial substrate 201 Reaction chamber 202 Stage 203 Heating element 204 Quartz tube 205 Inner wall surface 206 Placement surface 207 Gas inlet 208 Gas exhaust port 209 Rotational Axis 211 No. 1 susceptor 212 Second susceptor 215 1st bottom 216 2nd bottom surface 218 Second Pocket 219 First Pocket 220 Furnace 231 First Gas Supply Unit 232 Second Gas Supply Unit 233 Third Gas Supply Section 234 4th Gas Supply Section 235 Gas Supply Section 241 First gas flow control section 242 Second gas flow rate control section 243 Third gas flow control section 244 Fourth gas flow control section 245 Control Unit 300 Manufacturing equipment 400 Silicon carbide semiconductor device B1 1st temperature B2 2nd temperature B3 3rd temperature B4 4th temperature B5 5th temperature B6 6th temperature B7 7th temperature B8 8th temperature B9 9th temperature C1 1st flow rate C2 2nd flow rate C3 3rd flow rate C4 4th flow rate C5 5th flow rate C6 6th flow rate C7 7th flow rate C8 8th flow rate C9 9th flow rate D1 10th flow rate D2 11th flow rate D3 12th flow rate D4 13th flow rate D5 14th flow rate D6 15th flow rate H1 First thickness H2 Second thickness H3 3rd thickness H4 4th thickness T1 Time 1 T2 Time 2 T3 Time 3 T4 Time 4 T5 5th time point T6 6th point T7 7th time point T8 8th time point T9 9th time point T10 10th time point T11 11th time point T12 12th time point T13 13th time point T14 14th time point T15 15th time point T16 16th time point T17 17th time point T18 18th time point W Maximum diameter

Claims

1. a first step of removing particles adhering to an inner wall surface of a furnace by flowing hydrogen gas into the furnace while a substrate is placed on a first susceptor placed in the furnace; a second step of forming a first silicon carbide layer on the inner wall surface by flowing the hydrogen gas, the source gas, and the dopant gas into the furnace after the first step; a third step of disposing a first silicon carbide single crystal substrate on a second susceptor disposed in the furnace after the second step; a fourth step of forming a second silicon carbide layer on the first silicon carbide single crystal substrate by flowing the hydrogen gas, the source gas, and the dopant gas into the furnace while the first silicon carbide single crystal substrate is placed on the second susceptor that is placed in the furnace; and a fifth step of determining a temperature condition using the second silicon carbide layer; a susceptor temperature in the fourth step is equal to or lower than a temperature inside the furnace in the second step; a flow rate of the dopant gas in the fourth step is equal to or lower than a flow rate of the dopant gas in the second step.

2. the first silicon carbide layer includes a first layer in contact with the inner wall surface and a second layer provided on the first layer, The nitrogen concentration of the first layer is higher than the nitrogen concentration of the second layer, 2 . The method for manufacturing a silicon carbide substrate according to claim 1 , wherein a temperature inside said furnace when said second layer is formed is higher than a temperature inside said furnace when said first layer is formed.

3. a first step of removing particles adhering to an inner wall surface of a furnace by flowing hydrogen gas into the furnace while a substrate is placed on a first susceptor placed in the furnace; a second step of disposing a first silicon carbide single crystal substrate on a second susceptor disposed in the furnace after the first step; a third step of forming a third silicon carbide layer on the first silicon carbide single crystal substrate while forming a first silicon carbide layer on the inner wall surface by flowing the hydrogen gas, a source gas, and a dopant gas into the furnace in a state in which the first silicon carbide single crystal substrate is placed on the second susceptor that is placed in the furnace; a fourth step of forming a second silicon carbide layer on the third silicon carbide layer by flowing the hydrogen gas, the source gas, and the dopant gas into the furnace after the third step; and a fifth step of determining a temperature condition using the second silicon carbide layer; the susceptor temperature in the fourth step is equal to or lower than the susceptor temperature in the third step; a flow rate of the dopant gas in the fourth step is equal to or lower than a flow rate of the dopant gas in the third step.

4. the first silicon carbide layer includes a first layer in contact with the inner wall surface and a second layer provided on the first layer, The nitrogen concentration of the first layer is higher than the nitrogen concentration of the second layer, 4. The method for manufacturing a silicon carbide substrate according to claim 3, wherein a susceptor temperature when said second layer is formed is higher than a susceptor temperature when said first layer is formed.

5. The method for manufacturing a silicon carbide substrate according to claim 1 , wherein the first susceptor and the second susceptor are different from each other.

6. The method for manufacturing a silicon carbide substrate according to claim 1 , wherein the first susceptor and the second susceptor are the same.

7. 5 . The method for manufacturing a silicon carbide substrate according to claim 1 , further comprising, after said first step, a step of calculating a susceptor temperature in said first step based on an etching amount of said substrate. 6 .

8. The method for manufacturing a silicon carbide substrate according to claim 1 , wherein the first step is performed after maintenance of the furnace.

9. determining temperature conditions for epitaxial growth by using the method for manufacturing a silicon carbide substrate according to any one of claims 1 to 4; and forming a silicon carbide epitaxial layer on the second silicon carbide single crystal substrate using the determined temperature conditions.

10. determining temperature conditions for epitaxial growth by using the method for manufacturing a silicon carbide substrate according to any one of claims 1 to 4; forming a silicon carbide epitaxial layer on the second silicon carbide single crystal substrate using the determined temperature conditions; and forming an electrode on the silicon carbide epitaxial layer.

11. a silicon carbide single crystal substrate; a third silicon carbide layer provided on the silicon carbide single crystal substrate; a second silicon carbide layer provided on the third silicon carbide layer; The third silicon carbide layer comprises: a third layer provided on the silicon carbide single crystal substrate; a fourth layer disposed on the third layer; the second silicon carbide layer constitutes a surface, a nitrogen concentration of each of the third layer and the second silicon carbide layer is higher than a nitrogen concentration of the fourth layer; The nitrogen concentration of each of the third layer and the second silicon carbide layer is 1×10 １７ cm －３ Above 3 x 10 １８ cm －３ is as follows: The nitrogen concentration of the fourth layer is 3×10 １５ cm －３ Above 2 x 10 １６ cm －３ The silicon carbide substrate is as follows:

12. The silicon carbide substrate according to claim 11 , wherein a thickness of each of said third layer and said second silicon carbide layer is smaller than a thickness of said fourth layer.

13. The third layer and the second silicon carbide layer each have a thickness of 0.5 μm or more and 3 μm or less, 13. The silicon carbide substrate according to claim 11, wherein the fourth layer has a thickness of not less than 4 μm and not more than 7 μm.

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