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

Abstract

The silicon carbide epitaxial substrate manufacturing apparatus has a chamber, a main piping section, a first ammonia gas supply section, a second ammonia gas supply section, a carrier gas supply section, and a raw material gas supply section. A silicon carbide substrate is disposed in the chamber. The main piping section is connected to the chamber. The first ammonia gas supply section is connected to the main piping section. The second ammonia gas supply section is connected to the main piping section. The carrier gas supply section is connected to the main piping section. The raw material gas supply section is connected to the main piping section. The concentration of ammonia gas in the first ammonia gas supply section is higher than the concentration of ammonia gas in the second ammonia gas supply section.

Description

[Technical field]

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

[0002] International Publication No. WO 2017 / 056691 (Patent Document 1) describes a method for forming a silicon carbide layer on a silicon carbide single crystal substrate using a mixed gas containing silane, ammonia, and hydrogen. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 056691 Summary of the Invention

[0004] A silicon carbide epitaxial substrate manufacturing apparatus according to the present disclosure includes a chamber, a main piping section, a first ammonia gas supply section, a second ammonia gas supply section, a carrier gas supply section, and a raw material gas supply section. A silicon carbide substrate is disposed in the chamber. The main piping section is connected to the chamber. The first ammonia gas supply section is connected to the main piping section. The second ammonia gas supply section is connected to the main piping section. The carrier gas supply section is connected to the main piping section. The raw material gas supply section is connected to the main piping section. The concentration of ammonia gas in the first ammonia gas supply section is higher than the concentration of ammonia gas in the second ammonia gas supply section. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a plan view illustrating a configuration of a silicon carbide epitaxial substrate according to this 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 an apparatus for manufacturing a silicon carbide epitaxial substrate in accordance with the first embodiment. [Figure 4] FIG. 4 is a partial cross-sectional schematic view showing the configuration of an apparatus for manufacturing a silicon carbide epitaxial substrate in accordance with the second embodiment. [Diagram 5] FIG. 5 is a partial cross-sectional schematic view showing the configuration of an apparatus for manufacturing a silicon carbide epitaxial substrate in accordance with the third embodiment. [Figure 6] FIG. 6 is a partial cross-sectional schematic view showing the configuration of an apparatus for manufacturing a silicon carbide epitaxial substrate in accordance with the fourth embodiment. [Figure 7] FIG. 7 is a flow diagram illustrating a schematic method for manufacturing a silicon carbide epitaxial substrate in accordance with the present embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view showing a step of forming a buffer layer. [Figure 9] FIG. 9 is a schematic cross-sectional view showing a step of forming the drift layer. [Figure 10] FIG. 10 is a schematic cross-sectional view showing a step of forming a body region. [Figure 11] FIG. 11 is a schematic cross-sectional view showing a step of forming a source region. [Figure 12] FIG. 12 is a schematic cross-sectional view showing a step of forming a trench in the first main surface. [Figure 13] FIG. 13 is a schematic cross-sectional view showing a step of forming a gate insulating film. [Figure 14] FIG. 14 is a schematic cross-sectional view showing a step of forming a gate electrode and an interlayer insulating film. [Figure 15] FIG. 15 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

[0006] [Overview of the embodiment of the present disclosure] First, an overview of the embodiments of the present disclosure will be described. In the crystallographic description in this specification, an individual orientation is represented by [], a collective orientation by <>, an individual plane by (), and a collective plane by {}. A negative index in crystallography is usually represented by placing a "-" (bar) above the number, but in this specification, a negative index in crystallography is represented by placing a negative sign before the number.

[0007] (1) A silicon carbide epitaxial substrate manufacturing apparatus according to the present disclosure includes a chamber, a main piping section, a first ammonia gas supply section, a second ammonia gas supply section, a carrier gas supply section, and a raw material gas supply section. A silicon carbide substrate is disposed in the chamber. The main piping section is connected to the chamber. The first ammonia gas supply section is connected to the main piping section. The second ammonia gas supply section is connected to the main piping section. The carrier gas supply section is connected to the main piping section. The raw material gas supply section is connected to the main piping section. The concentration of ammonia gas in the first ammonia gas supply section is higher than the concentration of ammonia gas in the second ammonia gas supply section.

[0008] (2) A silicon carbide epitaxial substrate manufacturing apparatus according to the present disclosure includes a chamber, a first ammonia gas supply unit, a second ammonia gas supply unit, a carrier gas supply unit, and a raw material gas supply unit. A silicon carbide substrate is disposed in the chamber. The first ammonia gas supply unit is connected to the chamber. The second ammonia gas supply unit is connected to the chamber. The carrier gas supply unit is connected to the chamber. The raw material gas supply unit is connected to the chamber. The concentration of ammonia gas in the first ammonia gas supply unit is higher than the concentration of ammonia gas in the second ammonia gas supply unit.

[0009] (3) In the apparatus for manufacturing a silicon carbide epitaxial substrate according to (1) or (2) above, the source gas supply unit may have a silicon-containing gas supply unit and a carbon-containing gas supply unit.

[0010] (4) In the apparatus for manufacturing a silicon carbide epitaxial substrate according to any one of (1) to (3) above, the concentration of ammonia gas in the first ammonia gas supply unit may be five or more times the concentration of ammonia gas in the second ammonia gas supply unit.

[0011] (5) In the apparatus for manufacturing a silicon carbide epitaxial substrate according to any one of (1) to (4) above, the second ammonia gas supply unit may contain ammonia gas diluted with hydrogen gas.

[0012] (6) In the apparatus for manufacturing a silicon carbide epitaxial substrate according to any one of (1) to (5) above, each of the first ammonia gas supply unit and the second ammonia gas supply unit may contain ammonia gas diluted with hydrogen gas.

[0013] (7) The silicon carbide epitaxial substrate manufacturing apparatus according to (1) above may include a first ammonia gas pipe connecting the first ammonia gas supply unit and the main piping unit, a second ammonia gas pipe connecting the second ammonia gas supply unit and the main piping unit, and a raw material gas pipe connecting the raw material gas supply unit and the main piping unit. Each of the connection unit between the first ammonia gas pipe and the main piping unit and the connection unit between the second ammonia gas pipe and the main piping unit may be located closer to the chamber than the connection unit between the raw material gas pipe and the main piping unit.

[0014] (8) The silicon carbide epitaxial substrate manufacturing apparatus according to (1) or (7) above may further include a third ammonia gas supply unit connected to the main piping unit.

[0015] (9) A silicon carbide epitaxial substrate manufacturing apparatus according to the present disclosure includes a chamber, a main piping section, an ammonia gas supply section, a first piping, a second piping, a third piping, a dilution gas supply section, a carrier gas supply section, and a raw material gas supply section. A silicon carbide substrate is disposed in the chamber. The main piping section is connected to the chamber. The first piping is connected to the ammonia gas supply section. The second piping connects the first piping to the main piping section. The third piping connects the first piping to the main piping section. The dilution gas supply section is connected to the third piping. The carrier gas supply section is connected to the main piping section. The raw material gas supply section is connected to the main piping section.

[0016] (10) A manufacturing apparatus for a silicon carbide epitaxial substrate according to the present disclosure includes a chamber, a main piping section, an ammonia gas supply section, a first piping, a second piping, a third piping, a first flow rate control section, a second flow rate control section, a carrier gas supply section, and a raw material gas supply section. A silicon carbide substrate is disposed in the chamber. The main piping section is connected to the chamber. The first piping is connected to the ammonia gas supply section. The second piping connects the first piping to the main piping section. The third piping connects the first piping to the main piping section. The first flow rate control section is disposed in the second piping. The second flow rate control section is disposed in the third piping. The carrier gas supply section is connected to the main piping section. The raw material gas supply section is connected to the main piping section. The second flow rate control section has a maximum flow rate that is 10 times or more the maximum flow rate of the first flow rate control section.

[0017] (11) The silicon carbide epitaxial substrate manufacturing apparatus according to the above (9) or (10) may include a source gas pipe connecting a source gas supply unit and a main pipe unit. Each of a connection unit between the second pipe and the main pipe unit and a connection unit between the third pipe and the main pipe unit may be located closer to the chamber than the connection unit between the source gas pipe and the main pipe unit.

[0018] (12) In the apparatus for manufacturing a silicon carbide epitaxial substrate according to any one of (9) to (11) above, the ammonia gas supply unit may contain ammonia gas diluted with hydrogen gas.

[0019] (13) In the apparatus for manufacturing a silicon carbide epitaxial substrate according to any one of (1) to (12) above, the carrier gas supply unit may contain hydrogen gas.

[0020] (14) A method for manufacturing a silicon carbide epitaxial substrate according to the present disclosure includes the following steps: A buffer layer is formed by epitaxial growth on a silicon carbide substrate using ammonia gas supplied from a first ammonia gas supply unit; A drift layer is formed by epitaxial growth on the buffer layer using ammonia gas supplied from a second ammonia gas supply unit; A concentration of ammonia gas in the first ammonia gas supply unit is higher than ammonia gas concentration in the second ammonia gas supply unit.

[0021] (15) According to the method for manufacturing a silicon carbide epitaxial substrate according to (14) above, the concentration of ammonia gas in the first ammonia gas supply section may be five or more times the concentration of ammonia gas in the second ammonia gas supply section.

[0022] (16) According to the method for producing a silicon carbide epitaxial substrate according to the above (14) or (15), the silicon carbide substrate may have a primary surface in contact with the buffer layer. The primary surface may be a plane inclined at an angle of 6° or less with respect to the (0001) plane or the (000-1) plane.

[0023] (17) In a method for manufacturing a silicon carbide semiconductor device according to the present disclosure, a silicon carbide epitaxial substrate is prepared using the method for manufacturing a silicon carbide epitaxial substrate according to any one of (14) to (16) above. An electrode is formed on the silicon carbide epitaxial substrate.

[0024] [Details of the embodiment of the present disclosure] Hereinafter, the details of the embodiments of the present disclosure will be described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.

[0025] Fig. 1 is a plan view schematic diagram showing a configuration of a silicon carbide epitaxial substrate 100 according to this embodiment. Fig. 2 is a cross-sectional schematic diagram taken along line II-II in Fig. 1. As shown in Figs. 1 and 2, the silicon carbide epitaxial substrate 100 according to this embodiment has a silicon carbide substrate 10 and a silicon carbide epitaxial layer 20. The silicon carbide epitaxial layer 20 is on the silicon carbide substrate 10. The silicon carbide epitaxial layer 20 is in contact with the silicon carbide substrate 10.

[0026] Silicon carbide epitaxial layer 20 forms a front surface (first main surface 1) of silicon carbide epitaxial substrate 100. Silicon carbide substrate 10 forms a back surface (second main surface 2) of silicon carbide epitaxial substrate 100.

[0027] 1, silicon carbide epitaxial substrate 100 has an outer peripheral edge 5. Outer peripheral edge 5 is continuous with each of first main surface 1 and second main surface 2. Outer peripheral edge 5 has, for example, an orientation flat 3 and an arc-shaped portion 4.

[0028] 1 , when viewed in a direction from the silicon carbide epitaxial layer 20 toward the silicon carbide substrate 10, a direction from the center A of the first main surface 1 toward the orientation flat 3 is defined as a first direction 101. When viewed in a direction from the silicon carbide epitaxial layer 20 toward the silicon carbide substrate 10, a direction perpendicular to the first direction 101 is defined as a second direction 102. The orientation flat 3 extends along the second direction 102. When viewed in a direction from the silicon carbide epitaxial layer 20 toward the silicon carbide substrate 10, the first main surface 1 extends along each of the first direction 101 and the second direction 102.

[0029] 1, when viewed in a direction from silicon carbide epitaxial layer 20 toward silicon carbide substrate 10, orientation flat 3 is linear. Arc-shaped portion 4 is continuous with orientation flat 3. Arc-shaped portion 4 is arc-shaped. A notch may be provided instead of orientation flat 3. In this case, first direction 101 is a direction from center A of first main surface 1 toward the notch.

[0030] The first direction 101 is, for example, the <1-100> direction. The first direction 101 may be, for example, the [1-100] direction. The first direction 101 may be, for example, a direction obtained by projecting the <1-100> direction onto the first main surface 1. From another perspective, the first direction 101 may be, for example, a direction including a <1-100> directional component.

[0031] The second direction 102 is, for example, the <11-20> direction. The second direction 102 may be, for example, the [11-20] direction. The second direction 102 may be a direction obtained by projecting the <11-20> direction onto the first main surface 1. From another perspective, the first direction 101 may be, for example, a direction including a <11-20> directional component.

[0032] The first main surface 1 may be a surface 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, 2° or more and 6° or less. 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. From another perspective, the second direction 102 may be the off direction of the first main surface 1.

[0033] As shown in FIG. 1, the maximum diameter W1 of the first main surface 1 is, for example, 100 mm (4 inches). The maximum diameter W1 may be 150 mm (6 inches) or more, or 200 mm (8 inches) or more. There is no particular upper limit to the maximum diameter W1. The maximum diameter W1 may be, for example, 250 mm (10 inches) or less. The maximum diameter W1 is the maximum distance between any two points on the outer circumferential edge 5.

[0034] 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). 10 inches means 250 mm or 254 mm (10 inches x 25.4 mm / inch).

[0035] The polytype of silicon carbide constituting silicon carbide substrate 10 is, for example, 4H. Similarly, the polytype of silicon carbide constituting silicon carbide epitaxial layer 20 is, for example, 4H. As shown in Fig. 2, third direction 103 is a direction from silicon carbide epitaxial layer 20 toward silicon carbide substrate 10. Third direction 103 is perpendicular to each of first direction 101 and second direction 102.

[0036] As shown in Fig. 2, silicon carbide epitaxial layer 20 has buffer layer 11 and drift layer 14. Buffer layer 11 is on silicon carbide substrate 10. Buffer layer 11 is continuous with silicon carbide substrate 10. Drift layer 14 is on buffer layer 11. Drift layer 14 is continuous with buffer layer 11. Drift layer 14 constitutes first main surface 1. In third direction 103, buffer layer 11 is located between silicon carbide substrate 10 and drift layer 14.

[0037] Silicon carbide substrate 10 has a third main surface 8. Third main surface 8 is opposite second main surface 2. Third main surface 8 is in contact with buffer layer 11. Third main surface 8 is, for example, a (0001) plane. Third main surface 8 may be, for example, a plane inclined at an angle of 6° or less with respect to the (0001) plane or the (000-1) plane. The inclination angle with respect to the (0001) plane or the (000-1) plane may be 4° or less, or may be 3° or less.

[0038] The thickness of the buffer layer 11 is defined as a first thickness T1. The first thickness T1 is, for example, 1 μm or more. The first thickness T1 may be, for example, 2 μm or more, 3 μm or more, or 5 μm or more. The first thickness T1 may be 20 μm or less, or 10 μm or less.

[0039] The thickness of the drift layer 14 is set to a second thickness T2. The second thickness T2 may be greater than the first thickness T1. The second thickness T2 is, for example, 5 μm or more. The second thickness T2 may be, for example, 10 μm or more, 30 μm or more, or 50 μm or more. The second thickness T2 may be 100 μm or less, or 80 μm or less.

[0040] The silicon carbide substrate 10 contains nitrogen (N) as an n-type impurity. The conductivity type of the silicon carbide substrate 10 is n-type. The silicon carbide epitaxial layer 20 contains nitrogen as an n-type impurity. The conductivity type of the silicon carbide epitaxial layer 20 is n-type. Specifically, each of the buffer layer 11 and the drift layer 14 contains nitrogen as an n-type impurity. The nitrogen concentration of the buffer layer 11 is higher than the nitrogen concentration of the drift layer 14. The conductivity type of each of the buffer layer 11 and the drift layer 14 is n-type.

[0041] The nitrogen concentration of the buffer layer 11 is, for example, 3×10 18 cm -3 The nitrogen concentration in the buffer layer 11 is, for example, 5×10 18 cm -3 It may be more than 7 x 10 18 cm -3 It may be more than 9 x 10 18 cm -3 The nitrogen concentration of the buffer layer 11 may be, for example, 5×10 19 cm -3 It may be less than or equal to 1 x 10 19 cm -3 It may be the following.

[0042] The nitrogen concentration in the drift layer 14 is, for example, 1×1015 cm -3 The nitrogen concentration in the drift layer 14 is, for example, 3×10 15 cm -3 It may be more than 7 x 10 15 cm -3 It may be more than 1 x 10 16 cm -3 The nitrogen concentration in the drift layer 14 may be, for example, 1×10 18 cm -3 It may be less than or equal to 1 x 10 17 cm -3 It may be the following.

[0043] The buffer layer 11 may be composed of a single layer, or may be composed of two or more layers having different nitrogen concentrations. The buffer layer 11 may have, for example, a first buffer region 7 and a second buffer region 6. The first buffer region 7 is provided on a silicon carbide substrate. The second buffer region 6 is provided on the first buffer region 7.

[0044] The nitrogen concentration in the first buffer region 7 may be higher than the nitrogen concentration in the second buffer region 6. The nitrogen concentration in the first buffer region 7 is, for example, 8×10 18 cm -3 The nitrogen concentration in the second buffer region 6 is, for example, 1×10 18 cm -3 The nitrogen concentration in the drift layer 14 is, for example, 7×10 15 cm -3 It is.

[0045] The thickness of the first buffer region 7 may be greater than the thickness of the second buffer region 6. The thickness of the first buffer region 7 is, for example, 1 to 10 μm. The thickness of the second buffer region 6 is, for example, 1 to 10 μm. The thickness of the drift layer 14 is, for example, 10 μm. By sandwiching the second buffer region 6 between the first buffer region 7 and the drift layer 14, the occurrence of defects due to the difference in crystal lattice constants can be suppressed.

[0046] (Silicon carbide epitaxial substrate manufacturing equipment) First Embodiment Fig. 3 is a partial cross-sectional schematic diagram showing the configuration of an apparatus for manufacturing silicon carbide epitaxial substrate 100 according to the first embodiment. As shown in Fig. 3, the apparatus for manufacturing silicon carbide epitaxial substrate 100 is, for example, a hot-wall type horizontal CVD (Chemical Vapor Deposition) apparatus. Manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 mainly includes chamber 201, heating element 203, quartz tube 204, holder 210, a heat insulating material (not shown), and an induction heating coil (not shown).

[0047] The heating element 203 has, for example, a cylindrical shape, and defines a chamber 201 therein. The heating element 203 is made of, for example, graphite. The heating element 203 is provided inside a quartz tube 204. A heat insulating material surrounds the outer periphery of the heating element 203. The induction heating coil is wound, for example, along the outer periphery 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 holder 210 is heated by the heating element 203.

[0048] Holder 210 is formed to be surrounded by inner wall surface 205 of heating element 203. Silicon carbide substrate 10 is placed on holder 210. Holder 210 is made of, for example, silicon carbide. Silicon carbide substrate 10 is placed on holder 210. Holder 210 is placed on stage 206. Stage 206 is supported by rotation shaft 209 so as to be rotatable about its axis. Holder 210 rotates as stage 206 rotates.

[0049] Manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 further includes main piping section 207 and gas exhaust port 208. Main piping section 207 is a gas supply port. Main piping section 207 is connected to chamber 201. Gas exhaust port 208 is connected to an exhaust pump (not shown). Arrows in FIG. 3 indicate the flow of gas. Gas is introduced from main piping section 207 into chamber 201 and exhausted from gas exhaust port 208. The pressure inside chamber 201 is adjusted by the balance between the amount of gas supplied and the amount of gas exhausted.

[0050] 3, the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 includes a first ammonia gas supply unit 231, a second ammonia gas supply unit 232, a carrier gas supply unit 234, a raw material gas supply unit 233, a first ammonia gas pipe 251, a second ammonia gas pipe 252, a raw material gas pipe 253, and a carrier gas pipe 254. Each of the first ammonia gas supply unit 231, the second ammonia gas supply unit 232, the carrier gas supply unit 234, and the raw material gas supply unit 233 is connected to the chamber 201.

[0051] The first ammonia gas supply unit 231 is connected to the main piping unit 207. The first ammonia gas piping 251 connects the first ammonia gas supply unit 231 and the main piping unit 207. The second ammonia gas supply unit 232 is connected to the main piping unit 207. The second ammonia gas piping 252 connects the second ammonia gas supply unit 232 and the main piping unit 207.

[0052] The carrier gas supply unit 234 is connected to the main piping unit 207. The carrier gas piping 254 connects the carrier gas supply unit 234 and the main piping unit 207. The source gas supply unit 233 is connected to the main piping unit 207. The source gas piping 253 connects the source gas supply unit 233 and the main piping unit 207.

[0053] The first ammonia gas supply unit 231 is configured to be able to supply ammonia gas. The first ammonia gas supply unit 231 may be filled with diluted ammonia gas. Specifically, the first ammonia gas supply unit 231 may contain ammonia gas diluted with hydrogen gas. The concentration of ammonia gas in the first ammonia gas supply unit 231 is, for example, 1%. The concentration of ammonia gas in the first ammonia gas supply unit 231 may be, for example, not less than 0.5% and not more than 50%. The concentration of ammonia gas is expressed in volume percent.

[0054] The second ammonia gas supply unit 232 is configured to be able to supply ammonia gas. The second ammonia gas supply unit 232 may be filled with diluted ammonia gas. Specifically, the second ammonia gas supply unit 232 may contain ammonia gas diluted with hydrogen gas. The concentration of ammonia gas in the second ammonia gas supply unit 232 is, for example, 0.1%. The concentration of ammonia gas in the first ammonia gas supply unit 231 may be, for example, 0.01% or more, 0.05% or more, 1% or less, or 0.2% or less.

[0055] The concentration of ammonia gas in the first ammonia gas supply unit 231 is higher than the concentration of ammonia gas in the second ammonia gas supply unit 232. Specifically, the concentration of ammonia gas in the first ammonia gas supply unit 231 may be two or more times, five or more times, or ten or more times the concentration of ammonia gas in the second ammonia gas supply unit 232. The concentration of ammonia gas in the first ammonia gas supply unit 231 may be 100 or less times, 50 or less times, or 20 or less times the concentration of ammonia gas in the second ammonia gas supply unit 232.

[0056] The carrier gas supply unit 234 is configured to be able to supply a carrier gas. The carrier gas is, for example, hydrogen gas. The carrier gas may be, for example, argon gas. The carrier gas may be, for example, a mixed gas of hydrogen gas and argon gas. The carrier gas supply unit 234 is, for example, a gas cylinder filled with hydrogen.

[0057] The raw material gas supply unit 233 is configured to be able to supply a raw material gas. The raw material gas is a gas that is a raw material for silicon carbide. The raw material gas is, for example, propane (C 3 H 8 ) gas and silane (SiH 4 ) gas. The raw material gas may be diluted with hydrogen. The raw material gas supply unit 233 may have a carbon-containing gas supply unit and a silicon-containing gas supply unit. Specifically, the raw material gas supply unit 233 has a gas cylinder capable of supplying a gas containing a compound containing carbon and hydrogen (e.g., propane gas), and a gas cylinder capable of supplying a gas containing a compound containing silicon and hydrogen (e.g., silane gas).

[0058] A connection portion between the first ammonia gas pipe 251 and the main pipe section 207 is a first connection portion 261. A connection portion between the second ammonia gas pipe 252 and the main pipe section 207 is a second connection portion 262. A connection portion between the raw material gas pipe 253 and the main pipe section 207 is a third connection portion 263. A connection portion between the carrier gas pipe 254 and the main pipe section 207 is a fourth connection portion 264.

[0059] Each of the first connection part 261 and the second connection part 262 is located closer to the chamber 201 than the third connection part 263. From another perspective, each of the first connection part 261 and the second connection part 262 may be located downstream of the third connection part 263 in the direction in which the gas flows in the main piping part 207. The third connection part 263 may be located closer to the chamber 201 than the fourth connection part 264. The first connection part 261 may be located closer to the chamber 201 than the second connection part 262.

[0060] The manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 has a first flow rate control unit 241, a second flow rate control unit 242, a third flow rate control unit 243, and a fourth flow rate control unit 244. The first flow rate control unit 241 controls the flow rate of gas flowing through the first ammonia gas pipe 251. The second flow rate control unit 242 controls the flow rate of gas flowing through the second ammonia gas pipe 252. The third flow rate control unit 243 controls the flow rate of gas flowing through the raw material gas pipe 253. The fourth flow rate control unit 244 controls the flow rate of gas flowing through the carrier gas pipe 254. Each control unit is, for example, an MFC (Mass Flow Controller).

[0061] In the process of forming the buffer layer 11, a high-concentration ammonia gas is supplied to the main piping section 207 using the first ammonia gas piping 251 and the first ammonia gas supply section 231. In the process of forming the drift layer 14, a low-concentration ammonia gas is supplied to the main piping section 207 using the second ammonia gas piping 252 and the second ammonia gas supply section 232.

[0062] <Second embodiment> Next, the configuration of the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the second embodiment will be described. The manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the second embodiment differs from the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment mainly in that it does not have a second ammonia gas supply unit 232, and is otherwise similar to the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment. Below, the configuration different from the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment will be mainly described.

[0063] 4 is a partial cross-sectional schematic diagram showing the configuration of a manufacturing apparatus 250 for a silicon carbide epitaxial substrate 100 according to the second embodiment. As shown in FIG. 4, the manufacturing apparatus 250 for a silicon carbide epitaxial substrate 100 according to the second embodiment includes a chamber 201, a first ammonia gas supply unit 231, a carrier gas supply unit 234, a raw material gas supply unit 233, a dilution gas supply unit 235, a main piping unit 207, a carrier gas piping 254, a raw material gas piping 253, a first piping 271, a second piping 272, a third piping 273, a fourth piping 274, and a fifth piping 275.

[0064] The first pipe 271 is connected to the first ammonia gas supply unit 231. The second pipe 272 connects the first pipe 271 and the main pipe unit 207. The third pipe 273 connects the first pipe 271 and the main pipe unit 207. The dilution gas supply unit 235 is connected to the third pipe 273. The fourth pipe 274 connects the third pipe 273 and the dilution gas supply unit 235. The connection portion between the fourth pipe 274 and the third pipe 273 is located between the connection portion between the first pipe 271 and the third pipe 273 and the connection portion between the third pipe 273 and the main pipe unit 207.

[0065] The fifth pipe 275 is connected to the third pipe 273. The connection between the fifth pipe 275 and the third pipe 273 is located between the connection between the fourth pipe 274 and the third pipe 273 and the connection between the third pipe 273 and the main pipe section 207. The fifth pipe 275 is provided with an exhaust valve 278. The exhaust valve 278 allows gas to flow in the exhaust direction when the internal pressure of the fifth pipe 275 reaches a designated pressure. The carrier gas supply section 234 is connected to the main pipe section 207. The raw material gas supply section 233 is connected to the main pipe section 207.

[0066] The dilution gas supply unit 235 is configured to be able to supply a dilution gas. The dilution gas is, for example, hydrogen gas. The dilution gas may be, for example, argon gas. The dilution gas supply unit 235 is, for example, a gas cylinder filled with hydrogen.

[0067] The connection between the third pipe 273 and the main pipe section 207 is a fifth connection section 265. The connection between the second pipe 272 and the main pipe section 207 is a sixth connection section 266. Each of the fifth connection section 265 and the sixth connection section 266 is located closer to the chamber 201 than the third connection section 263. From another perspective, each of the fifth connection section 265 and the sixth connection section 266 may be located downstream of the third connection section 263 in the direction in which the gas flows in the main pipe section 207. The fifth connection section 265 may be located closer to the chamber 201 than the sixth connection section 266.

[0068] The manufacturing apparatus 250 of the silicon carbide epitaxial substrate 100 has a fifth flow rate control unit 245, a sixth flow rate control unit 246, a seventh flow rate control unit 247, and an eighth flow rate control unit 248. The fifth flow rate control unit 245 controls the flow rate of the gas flowing through the second pipe 272. The sixth flow rate control unit 246 controls the flow rate of the gas flowing through the upstream part of the third pipe 273. The sixth flow rate control unit 246 is provided upstream of the connection part between the third pipe 273 and the fourth pipe 274. The seventh flow rate control unit 247 controls the flow rate of the gas flowing through the fourth pipe 274. The eighth flow rate control unit 248 controls the flow rate of the gas flowing through the downstream part of the third flow path. The eighth flow rate control unit 248 is provided downstream of the connection part between the third pipe 273 and the fourth pipe 274. Each control unit is, for example, an MFC.

[0069] In the process of forming the buffer layer 11, ammonia gas having the same concentration as the ammonia concentration in the first ammonia gas supply unit 231 is supplied to the main piping unit 207 using the first piping 271, the second piping 272, and the first ammonia gas supply unit 231. In the process of forming the drift layer 14, diluted low-concentration ammonia gas is supplied to the main piping unit 207 using the first piping 271, the third piping 273, the fourth piping 274, the first ammonia gas supply unit 231, and the dilution gas supply unit 235.

[0070] <Third embodiment> Next, the configuration of the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the third embodiment will be described. The manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the third embodiment differs from the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment mainly in that it does not have a first ammonia gas supply unit 231, and is otherwise similar to the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment. Below, the configuration different from the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment will be mainly described.

[0071] 5 is a partial cross-sectional schematic diagram showing the configuration of a manufacturing apparatus 250 for a silicon carbide epitaxial substrate 100 according to the third embodiment. As shown in FIG. 5, the manufacturing apparatus 250 for a silicon carbide epitaxial substrate 100 according to the third embodiment includes a chamber 201, a second ammonia gas supply unit 232, a main piping unit 207, a carrier gas piping 254, a source gas piping 253, a first piping 271, a second piping 272, a third piping 273, a first flow rate control unit 241, a second flow rate control unit 242, a carrier gas supply unit 234, and a source gas supply unit 233.

[0072] The first pipe 271 is connected to the second ammonia gas supply unit 232. The second pipe 272 connects the first pipe 271 and the main pipe unit 207. The third pipe 273 connects the first pipe 271 and the main pipe unit 207. The carrier gas pipe 254 connects the carrier gas supply unit 234 and the main pipe unit 207. The raw material gas pipe 253 connects the raw material gas supply unit 233 and the main pipe unit 207.

[0073] The first flow control unit 241 is disposed on the second pipe 272. The second flow control unit 242 is disposed on the third pipe 273. The maximum flow rate of the second flow control unit 242 is 10 times or more the maximum flow rate of the first flow control unit 241. The maximum flow rate of the second flow control unit 242 may be 20 times or more, or 50 times or more the maximum flow rate of the first flow control unit 241. The maximum flow rate of the second flow control unit 242 may be 500 times or less, or 200 times or less the maximum flow rate of the first flow control unit 241.

[0074] The connection portion between the third pipe 273 and the main pipe section 207 is a seventh connection portion 267. The connection portion between the second pipe 272 and the main pipe section 207 is an eighth connection portion 268. Each of the seventh connection portion 267 and the eighth connection portion 268 is located closer to the chamber 201 than the third connection portion 263. From another perspective, each of the seventh connection portion 267 and the eighth connection portion 268 may be located downstream of the third connection portion 263 in the gas flow direction in the main pipe section 207. The seventh connection portion 267 may be located closer to the chamber 201 than the eighth connection portion 268.

[0075] In the process of forming the buffer layer 11, a large flow rate of ammonia gas is supplied to the main piping section 207 using the first piping 271, the third piping 273, the second ammonia gas supply section 232, and the second flow rate control section 242. In the process of forming the drift layer 14, a small flow rate of ammonia gas is supplied to the main piping section 207 using the first piping 271, the second piping 272, the second ammonia gas supply section 232, and the first flow rate control section 241.

[0076] <Fourth embodiment> Next, the configuration of the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the fourth embodiment will be described. The manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the fourth embodiment differs from the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment mainly in that it has a third ammonia gas supply unit 236, and is otherwise similar to the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment. Below, the configuration different from the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the first embodiment will be mainly described.

[0077] 6 is a partial cross-sectional schematic diagram showing the configuration of a manufacturing apparatus 250 for a silicon carbide epitaxial substrate 100 according to the fourth embodiment. As shown in FIG. 6, the manufacturing apparatus 250 for a silicon carbide epitaxial substrate 100 includes a first ammonia gas supply unit 231, a second ammonia gas supply unit 232, a third ammonia gas supply unit 236, a carrier gas supply unit 234, a raw material gas supply unit 233, a first ammonia gas pipe 251, a second ammonia gas pipe 252, a third ammonia gas pipe 276, a raw material gas pipe 253, and a carrier gas pipe 254.

[0078] The third ammonia gas supply unit 236 is connected to the main piping unit 207. The third ammonia gas piping 276 connects the third ammonia gas supply unit 236 and the main piping unit 207. The third ammonia gas supply unit 236 is configured to be able to supply ammonia gas. The third ammonia gas supply unit 236 is filled with ammonia gas diluted with a carrier gas.

[0079] Specifically, the third ammonia gas supply unit 236 may contain ammonia gas diluted with hydrogen gas. The concentration of ammonia gas in the third ammonia gas supply unit 236 is different from each of the concentration of ammonia gas in the first ammonia gas supply unit 231 and the concentration of ammonia gas in the second ammonia gas supply unit 232. The concentration of ammonia gas in the third ammonia gas supply unit 236 may be lower than the concentration of ammonia gas in the first ammonia gas supply unit 231. The concentration of ammonia gas in the third ammonia gas supply unit 236 may be higher than the concentration of ammonia gas in the second ammonia gas supply unit 232.

[0080] The connection between the third ammonia gas supply unit 236 and the main piping unit 207 is a ninth connection unit 269. The ninth connection unit 269 is located closer to the chamber 201 than the third connection unit 263. From another perspective, the ninth connection unit 269 may be located downstream of the third connection unit 263 in the gas flow direction in the main piping unit 207.

[0081] Manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 includes first flow rate control unit 241, second flow rate control unit 242, third flow rate control unit 243, fourth flow rate control unit 244, and ninth flow rate control unit 249. Ninth flow rate control unit 249 controls the flow rate of gas flowing through third ammonia gas pipe 276.

[0082] In the process of forming the first buffer region 7, a high concentration ammonia gas is supplied to the main piping section 207 using the first ammonia gas pipe 251 and the first ammonia gas supply unit 231. In the process of forming the second buffer region 6, a medium concentration ammonia gas is supplied to the main piping section 207 using the third ammonia gas pipe 276 and the third ammonia gas supply unit 236. In the process of forming the drift layer 14, a low concentration ammonia gas is supplied to the main piping section 207 using the second ammonia gas pipe 252 and the second ammonia gas supply unit 232.

[0083] In addition, in the methods for manufacturing silicon carbide epitaxial substrates according to the first to fourth embodiments, at least any of the first ammonia gas pipe 251, the second ammonia gas pipe 252, the raw material gas pipe 253, the carrier gas pipe 254, the first pipe 271, the second pipe 272, the third pipe 273, the fourth pipe 274, the fifth pipe 275, the third ammonia gas pipe 276, and the main pipe section 207 may or may not be heated.

[0084] The main pipe section 207 may be one main pipe or multiple main pipes. The main pipe section 207 may have, for example, a first main pipe (not shown), a second main pipe (not shown), and a third main pipe (not shown). The carrier gas supply section and the silane gas supply section may be connected to, for example, the first main pipe. The carrier gas supply section and the propane gas supply section may be connected to, for example, the second main pipe. The carrier gas supply section and the ammonia gas supply section may be connected to, for example, the third main pipe.

[0085] The first ammonia gas supply unit 231 is connected to the first ammonia gas pipe 251, but can also be connected to the chamber 201 without going through the main pipe unit 207. In this case, the first ammonia gas pipe 251 (a portion between the first flow rate control unit 241 and the chamber 201) may be connected to the carrier gas supply unit 234 via the flow rate control unit.

[0086] The second ammonia gas supply unit 232 is connected to the second ammonia gas pipe 252, but can also be connected to the chamber 201 without passing through the main pipe unit 207. In this case, the second ammonia gas pipe 252 (a portion between the second flow rate control unit 242 and the chamber 201) may be connected to the carrier gas supply unit 234 via the flow rate control unit.

[0087] The raw material gas supply unit 233 is connected to the raw material gas pipe 253, but can also be connected to the chamber 201 without passing through the main pipe unit 207. In this case, the raw material gas supply unit 233 (a portion between the third flow rate control unit 243 and the chamber 201) can be connected to the carrier gas supply unit 234 via a flow rate control unit.

[0088] (Method for manufacturing silicon carbide epitaxial substrate) Next, a method for manufacturing silicon carbide epitaxial substrate 100 in accordance with this embodiment will be described.

[0089] Fig. 7 is a flow diagram illustrating a schematic diagram of a method for manufacturing a silicon carbide epitaxial substrate 100 according to this embodiment. As shown in Fig. 7, the method for manufacturing a silicon carbide epitaxial substrate 100 according to this embodiment includes a step (S10) of forming a buffer layer 11 and a step (S20) of forming a drift layer 14.

[0090] First, a silicon carbide substrate 10 is prepared. A silicon carbide single crystal of polytype 4H is manufactured, for example, by sublimation. Next, the silicon carbide single crystal is sliced, for example, by a wire saw, to prepare the silicon carbide substrate 10. The silicon carbide substrate 10 contains an n-type impurity, for example, nitrogen. The conductivity type of the silicon carbide substrate 10 is, for example, an n-type. Next, mechanical polishing is performed on the silicon carbide substrate 10. Next, chemical mechanical polishing is performed on the silicon carbide substrate 10.

[0091] Next, silicon carbide substrate 10 is placed in chamber 201 of manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the first embodiment. Specifically, silicon carbide substrate 10 is placed inside chamber 201 in a state where it is placed on holder 210.

[0092] Next, a step (S10) of forming buffer layer 11 is performed. FIG. 8 is a schematic cross-sectional view showing the step of forming buffer layer 11. As shown in FIG. 8, buffer layer 11 is formed by epitaxial growth on silicon carbide substrate 10. In the epitaxial growth, for example, silane (SiH 4 ) and propane (C 3 H 8 ) is used as the carrier gas, and hydrogen (H 2 ) is used. After the temperature of holder 210 reaches, for example, about 1600° C., a source gas, a dopant gas, and a carrier gas are supplied to chamber 201. Specifically, a mixed gas containing silane, propane, ammonia, and hydrogen is introduced into chamber 201 through main piping section 207. In chamber 201, each gas is thermally decomposed, and buffer layer 11 is formed on silicon carbide substrate 10.

[0093] The flow rate of the silane gas supplied to the chamber 201 is adjusted to, for example, 46 sccm. The flow rate of the silane gas may be, for example, 30 sccm or more and 60 sccm or less. The flow rate of the propane gas supplied to the chamber 201 is adjusted to, for example, 14 sccm. The flow rate of the propane gas may be, for example, 10 sccm or more and 20 sccm or less. The flow rate of the hydrogen gas supplied to the chamber 201 is adjusted to, for example, 120 slm. The flow rate of the hydrogen gas may be, for example, 100 slm or more and 150 slm or less.

[0094] In forming the buffer layer 11, the ammonia gas supplied from the first ammonia gas supply unit 231 is used as a dopant gas. As described above, the first ammonia gas supply unit 231 contains ammonia gas diluted with hydrogen gas. The concentration of the ammonia gas in the first ammonia gas supply unit 231 is, for example, 1%. The flow rate of the ammonia gas supplied to the chamber 201 is controlled using the first flow rate control unit 241. For example, the flow rate of the ammonia gas diluted to a concentration of 1% by dilution with hydrogen gas is, for example, 10 sccm or more and 200 sccm or less. Note that this flow rate, when converted to the flow rate of ammonia gas with a concentration of 100%, is, for example, 0.1 sccm or more and 2.0 sccm or less.

[0095] As described above, the buffer layer 11 is formed on the silicon carbide substrate 10 using the ammonia gas supplied from the first ammonia gas supply unit 231. The buffer layer 11 has a thickness of, for example, 1 μm or more. The buffer layer 11 has a nitrogen concentration of, for example, 3×10 18 cm -3 That's all.

[0096] Next, a step (S20) is performed of forming drift layer 14. Fig. 9 is a schematic cross-sectional view showing the step of forming drift layer 14. As shown in Fig. 9, drift layer 14 is formed on buffer layer 11 by epitaxial growth.

[0097] The flow rate of the silane gas supplied to the chamber 201 is adjusted to, for example, 115 sccm. The flow rate of the silane gas may be, for example, 80 sccm or more and 150 sccm or less. The flow rate of the propane gas supplied to the chamber 201 is adjusted to, for example, 37.5 sccm. The flow rate of the propane gas may be, for example, 25 sccm or more and 50 sccm or less. The flow rate of the hydrogen gas supplied to the chamber 201 is adjusted to, for example, 120 slm. The flow rate of the hydrogen gas may be, for example, 100 slm or more and 150 slm or less.

[0098] In forming the drift layer 14, the ammonia gas supplied from the second ammonia gas supply unit 232 is used as a dopant gas. As described above, the second ammonia gas supply unit 232 contains ammonia gas diluted with hydrogen gas. The concentration of the ammonia gas in the second ammonia gas supply unit 232 is, for example, 0.1%. The flow rate of the ammonia gas supplied to the chamber 201 is controlled using the second flow rate control unit 242. For example, the flow rate of the ammonia gas diluted to a concentration of 0.1% by dilution with hydrogen gas is, for example, 10 sccm or more and 200 sccm or less. Note that this flow rate, when converted to the flow rate of ammonia gas with a concentration of 100%, is, for example, 0.01 sccm or more and 0.2 sccm or less.

[0099] The concentration of ammonia gas in the first ammonia gas supply unit 231 is higher than the concentration of ammonia gas in the second ammonia gas supply unit 232. Specifically, the concentration of ammonia gas in the first ammonia gas supply unit 231 may be two or more times, five or more times, or ten or more times the concentration of ammonia gas in the second ammonia gas supply unit 232. The concentration of ammonia gas in the first ammonia gas supply unit 231 may be 100 or less times, 50 or less times, or 20 or less times the concentration of ammonia gas in the second ammonia gas supply unit 232.

[0100] As described above, the drift layer 14 is formed on the buffer layer 11 using the ammonia gas supplied from the second ammonia gas supply unit 232. The drift layer 14 has a thickness of, for example, 5 μm or more. The nitrogen concentration of the drift layer 14 is, for example, 1×10 15 cm -3 More than 1×10 17 cm -3 In this manner, silicon carbide epitaxial substrate 100 is manufactured as follows.

[0101] 3, in a part or all of the step of forming the buffer layer 11, the ammonia gas supplied from the first ammonia gas supply unit 231 and the ammonia gas supplied from the second ammonia gas supply unit 232 may be used simultaneously, and in a step of forming the drift layer 14, the ammonia gas supplied from the second ammonia gas supply unit 232 may be used. That is, in a part or all of the step of forming the buffer layer 11 and the step of forming the drift layer 14, the ammonia gas supplied from the second ammonia gas supply unit 232 may be used.

[0102] This makes it possible to eliminate the moment when the ammonia gas supplied from the two paths is switched, and makes it possible to suppress the formation of a layer between the buffer layer 11 and the drift layer 14 in which the nitrogen concentration drops sharply.

[0103] 4, in a part or all of the process of forming the buffer layer 11, the ammonia gas supplied from the first pipe 271, the second pipe 272, and the first ammonia gas supply unit 231, and the diluted low-concentration ammonia gas supplied from the first pipe 271, the third pipe 273, the fourth pipe 274, the first ammonia gas supply unit 231, and the dilution gas supply unit 235 may be used simultaneously, and in a process of forming the drift layer 14, the diluted low-concentration ammonia gas supplied from the first pipe 271, the third pipe 273, the fourth pipe 274, the first ammonia gas supply unit 231, and the dilution gas supply unit 235 may be used. That is, in a part or all of the process of forming the buffer layer 11 and the process of forming the drift layer 14, the diluted low-concentration ammonia gas supplied from the first pipe 271, the third pipe 273, the fourth pipe 274, the first ammonia gas supply unit 231, and the dilution gas supply unit 235 may be used.

[0104] This makes it possible to eliminate the moment when the ammonia gas supplied from the two paths is switched, and makes it possible to suppress the formation of a layer between the buffer layer 11 and the drift layer 14 in which the nitrogen concentration drops sharply.

[0105] 5, in a part or all of the process of forming the buffer layer 11, a large flow rate of ammonia gas may be used by using the first pipe 271, the third pipe 273, the second ammonia gas supply unit 232, and the second flow control unit 242, and a small flow rate of ammonia gas may be used by using the first pipe 271, the second pipe 272, the second ammonia gas supply unit 232, and the first flow control unit 241 at the same time, and in a process of forming the drift layer 14, a small flow rate of ammonia gas may be used by using the first pipe 271, the second pipe 272, the second ammonia gas supply unit 232, and the first flow control unit 241. That is, in a part or all of the process of forming the buffer layer 11 and the process of forming the drift layer 14, a small flow rate of ammonia gas may be used by using the first pipe 271, the second pipe 272, the second ammonia gas supply unit 232, and the first flow control unit 241.

[0106] This makes it possible to eliminate the moment when the ammonia gas supplied from the two paths is switched, and makes it possible to suppress the formation of a layer between the buffer layer 11 and the drift layer 14 in which the nitrogen concentration drops sharply.

[0107] Next, a method for manufacturing a silicon carbide epitaxial substrate in which nitrogen is doped during silicon carbide epitaxial growth is disclosed, in which ammonia gas is passed through a pre-heating region 211 for thermal decomposition before it reaches the silicon carbide substrate 10 on which a silicon carbide epitaxial layer is formed.

[0108] Since the ammonia gas as the nitrogen source is thermally decomposed in the pre-heating region 211 before reaching the silicon carbide substrate 10, the in-plane distribution of nitrogen becomes uniform within the wide surface of the silicon carbide substrate 10 where epitaxial growth is taking place. As a result, the in-plane concentration distribution of nitrogen doped into the growing silicon carbide epitaxial layer also becomes uniform.

[0109] In the preheating region 211, the gas passes through a region where the wall surfaces of the members in the chamber 201 are at 1300° C. or higher, so that the ammonia gas can be sufficiently thermally decomposed in advance without causing any significant disturbance in the gas flow.

[0110] Here, the preheating region 211 means a space for heating the flowing gas, and includes a long, thin tube heated from the outside, a space with a heat transfer coil installed inside, a large space with fins or the like formed on the inner wall surface, etc.

[0111] The upper limit of the temperature of the wall surface of the region is preferably 1350° C. or higher in order to ensure reliable pyrolysis even if the length of the chamber is somewhat short, and is preferably 1800° C. or lower in terms of thermal efficiency. For example, pre-heating region 211 may be a region from the end of chamber 201 to silicon carbide substrate 10 closest to the end of chamber 201. Pre-heating region 211 is preferably 50 mm or more and 1000 mm or less.

[0112] Next, a silicon carbide semiconductor manufacturing apparatus will be disclosed, which is an apparatus for manufacturing a silicon carbide epitaxial substrate that dopes nitrogen during silicon carbide epitaxial growth, and has a pre-heating region 211 for thermally decomposing ammonia gas before the ammonia gas reaches the silicon carbide substrate 10 on which a silicon carbide epitaxial layer is formed.

[0113] Since the ammonia gas as the nitrogen source is thermally decomposed in the pre-heating region 211 before reaching the silicon carbide substrate 10, the in-plane distribution of nitrogen becomes uniform within the wide surface of the silicon carbide substrate 10 where epitaxial growth is taking place. As a result, the in-plane concentration distribution of nitrogen doped into the growing silicon carbide epitaxial layer also becomes uniform.

[0114] In the preheating region 211, the gas passes through a region where the wall surfaces of the members in the chamber 201 are at 1300° C. or higher, so that the ammonia gas can be sufficiently thermally decomposed in advance without causing any significant disturbance in the gas flow.

[0115] Here, the preheating region 211 means a space for heating the flowing gas, and includes a long, thin tube heated from the outside, a space with a heat transfer coil installed inside, a large space with fins or the like formed on the inner wall surface, etc.

[0116] The upper limit of the temperature of the wall surface of the region is preferably 1350° C. or higher in order to ensure reliable pyrolysis even if the length of the chamber is somewhat short, and is preferably 1800° C. or lower in terms of thermal efficiency. For example, pre-heating region 211 may be a region from the end of chamber 201 to silicon carbide substrate 10 closest to the end of chamber 201. Pre-heating region 211 is preferably 50 mm or more and 1000 mm or less.

[0117] (Method for manufacturing silicon carbide semiconductor device) Next, a method for manufacturing the silicon carbide semiconductor device 300 according to this embodiment will be described.

[0118] First, a silicon carbide epitaxial substrate 100 according to this embodiment is prepared (see FIG. 9). Next, a step of forming a body region is performed. FIG. 10 is a schematic cross-sectional view showing the step of forming a body region. Specifically, p-type impurities such as aluminum are ion-implanted into drift layer 14 of silicon carbide epitaxial layer 20. This forms body region 113 having p-type conductivity. Body region 113 has a thickness of, for example, 0.9 μm.

[0119] Next, a step of forming a source region is performed. Fig. 11 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 may be higher than the concentration of the p-type impurity contained in the body region 113.

[0120] 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 drift layer 14. The concentration of the p-type impurity contained in the contact region 118 may be higher than the concentration of the n-type impurity contained in the source region 114.

[0121] Next, activation annealing is performed to activate the implanted impurities. The temperature of the activation annealing is, for example, about 1700° C. The time of the activation annealing is, for example, about 30 minutes. The atmosphere of the activation annealing is, for example, an Ar atmosphere.

[0122] Next, a step of forming a trench in the first main surface 1 is performed. FIG. 12 is a cross-sectional view showing the step of forming a trench in the first main surface 1. As shown in FIG. 12, a mask 117 having an opening is formed on the first main surface 1 including the source region 114 and the contact region 118. The source region 114, the body region 113, and a part of the drift layer 14 are removed by etching using the mask 117. As an etching method, for example, reactive ion etching, particularly inductively coupled plasma reactive ion etching, can be used. Specifically, for example, SF is used as a reactive gas. 6 or Sci-Fi 6 and O 2 By etching, a recess is formed in the first main surface 1.

[0123] Next, thermal etching is performed on the recessed portion. 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 first main surface 1. The at least one or more types of halogen atoms include at least one of chlorine (Cl) atoms and fluorine (F) atoms. The atmosphere can be, for example, Cl 2 , BCl 3 ,SCIENCE FICTION 6 or CF 4 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. The reactive gas may contain a carrier gas in addition to the above-mentioned chlorine gas and oxygen gas. As the carrier gas, for example, nitrogen gas, argon gas, or helium gas can be used.

[0124] 12, trench 106 is formed in first main surface 1 by thermal etching. Trench 106 is defined by side surface 123 and a bottom surface 124. Side surface 123 is composed of source region 114, body region 113, and drift layer 14. Bottom surface 124 is composed of drift layer 14. Next, mask 117 is removed from first main surface 1.

[0125] Next, a step of forming a gate insulating film is performed. Fig. 13 is a cross-sectional schematic diagram showing the step of forming a gate insulating film. Specifically, silicon carbide epitaxial substrate 100 having trench 106 formed in first main surface 1 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 drift layer 14 at bottom surface 124, in contact with drift layer 14, body region 113, and source region 114 at side surface 123, and in contact with source region 114 and contact region 118 at first main surface 1.

[0126] Next, a step of forming a gate electrode is performed. Fig. 14 is a schematic cross-sectional view showing a step of forming a gate electrode and an interlayer insulating film. The gate electrode 127 is formed in the trench 106 so as to contact the gate insulating film 115. The gate electrode 127 is disposed in the trench 106, and is formed on the gate insulating film 115 so as to face each of the side surface 123 and the bottom surface 124 of the trench 106. The gate electrode 127 is formed, for example, by a low pressure chemical vapor deposition (LPCVD) method.

[0127] 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.

[0128] Next, a step of forming a source electrode is performed. The source electrode 116 is formed so as to be in contact with each of the source region 114 and the contact region 118. The source electrode 116 is formed by, for example, a sputtering method. The source electrode 116 is made of, for example, a material including Ti, Al, and Si.

[0129] 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 higher and 1100° C. or lower 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.

[0130] 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.

[0131] Next, a step of forming the drain electrode 120 is performed. First, the silicon carbide substrate 10 is polished at the second main surface 2. Next, the drain electrode 120 is formed. The drain electrode 120 is formed so as to be in contact with the silicon carbide substrate 10 at the second main surface 2. In this manner, the silicon carbide semiconductor device 300 according to this embodiment is manufactured.

[0132] (Silicon carbide semiconductor device) Next, the configuration of the silicon carbide semiconductor device 300 according to this embodiment will be described. FIG. 15 is a schematic cross-sectional view showing the configuration of the silicon carbide semiconductor device 300 according to this embodiment. As shown in FIG. 15, the silicon carbide semiconductor device 300 according to this embodiment mainly includes a silicon carbide epitaxial substrate 100, a gate insulating film 115, a gate electrode 127, a source electrode 116, a drain electrode 120, a source wiring 119, and an interlayer insulating film 126. The silicon carbide epitaxial substrate 100 includes a silicon carbide substrate 10, a silicon carbide epitaxial layer 20, a first main surface 1, and a second main surface 2. The silicon carbide epitaxial layer 20 includes a buffer layer 11, a drift layer 14, a body region 113, a source region 114, and a contact region 118.

[0133] The body region 113 is formed on the drift layer 14. The body region 113 is in contact with the drift layer 14. The body region 113 contains p-type impurities such as aluminum. The body region 113 has a p-type conductivity. The source region 114 is formed on the body region 113. The source region 114 contains n-type impurities such as phosphorus. The source region 114 has an n-type conductivity. The concentration of the n-type impurities contained in the source region 114 may be higher than the concentration of the p-type impurities contained in the body region 113. The body region 113 is a p-type region. The drift layer 14 is an n-type region. A body diode is formed between the p-type region and the n-type region.

[0134] The contact region 118 penetrates the source region 114 and the body region 113. The contact region 118 is in contact with each of the source region 114, the body region 113, and the drift layer 14. The contact region 118 contains a p-type impurity such as aluminum. The concentration of the p-type impurity contained in the contact region 118 may be higher than the concentration of the n-type impurity contained in the source region 114.

[0135] A trench 106 is provided in the first main surface 1. The trench 106 is defined by a side surface 123 and a bottom surface 124. The side surface 123 is formed by the source region 114, the body region 113, and the drift layer 14. The bottom surface 124 is formed by the drift layer 14.

[0136] The gate insulating film 115 is in contact with the drift layer 14 at a bottom surface 124, and is in contact with each of the drift layer 14, the body region 113, and the source region 114 at a side surface 123. The gate electrode 127 is disposed on the gate insulating film 115. The gate electrode 127 is in contact with the gate insulating film 115 inside the trench 106. The gate electrode 127 faces each of the side surface 123 and the bottom surface 124 of the trench 106.

[0137] The interlayer insulating film 126 covers the gate electrode 127. The interlayer insulating film 126 is in contact with the gate insulating film 115. The interlayer insulating film 126 is made of a material containing, for example, silicon dioxide. The source electrode 116 is in contact with each of the source region 114 and the contact region 118. The source electrode 116 is made of a material containing, for example, Ti, Al, and Si. The source wiring 119 is in contact with the source electrode 116. The source wiring 119 is electrically connected to the source electrode 116. The source wiring 119 covers the source electrode 116 and the interlayer insulating film 126. The drain electrode 120 is in contact with the silicon carbide substrate 10 on the second main surface 2.

[0138] Next, the effects of the manufacturing apparatus 250 for manufacturing silicon carbide epitaxial substrate 100, the manufacturing method for silicon carbide epitaxial substrate 100, and the manufacturing method for silicon carbide semiconductor device 300 according to this embodiment will be described.

[0139] Nitrogen gas or ammonia gas is used to dope nitrogen into each of the buffer layer 11 and the drift layer 14. Ammonia gas is more easily thermally decomposed than nitrogen gas having triple bonds. Therefore, the flow rate of ammonia gas required to achieve the same nitrogen concentration is significantly smaller than that of nitrogen gas.

[0140] In addition, in silicon carbide epitaxial substrate 100, the nitrogen concentration in buffer layer 11 is higher than the nitrogen concentration in drift layer 14. The nitrogen concentration in buffer layer 11 may be 10 or 100 times higher than the nitrogen concentration in drift layer 14. Therefore, the flow rate of ammonia gas required to form buffer layer 11 is significantly higher than the flow rate of ammonia gas required to form drift layer 14. In a flow rate control unit (MFC), there is a limit to the range of flow rates of gas that can be flowed. Therefore, it has been difficult to precisely control the flow rate of ammonia gas required to form buffer layer 11 and the flow rate of ammonia gas required to form drift layer 14 using one flow rate control unit (MFC).

[0141] According to the manufacturing apparatus 250 and the manufacturing method of the silicon carbide epitaxial substrate 100 of the present disclosure, the buffer layer 11 is formed by epitaxial growth on the silicon carbide substrate 10 using the ammonia gas supplied from the first ammonia gas supply unit 231. The drift layer 14 is formed by epitaxial growth on the buffer layer 11 using the ammonia gas supplied from the second ammonia gas supply unit 232. The concentration of the ammonia gas in the first ammonia gas supply unit 231 is higher than the concentration of the ammonia gas in the second ammonia gas supply unit 232. This allows the buffer layer 11 to be formed with an optimal ammonia gas concentration for forming the buffer layer 11, and the drift layer 14 to be formed with an optimal ammonia gas concentration for forming the drift layer 14. As a result, the controllability of the nitrogen concentration in each of the buffer layer 11 and the drift layer 14 can be improved.

[0142] According to the manufacturing apparatus 250 and the manufacturing method for silicon carbide epitaxial substrate 100 according to the present disclosure, the concentration of ammonia gas in the first ammonia gas supply unit 231 may be five times or more the concentration of ammonia gas in the second ammonia gas supply unit 232. This can further improve the controllability of the nitrogen concentration in each of the buffer layer 11 and the drift layer 14.

[0143] According to the manufacturing apparatus 250 and the manufacturing method of the silicon carbide epitaxial substrate 100 of the present disclosure, each of the connection portion between the first ammonia gas pipe 251 and the main pipe portion 207 and the connection portion between the second ammonia gas pipe 252 and the main pipe portion 207 may be located closer to the chamber 201 than the connection portion between the source gas pipe 253 and the main pipe portion 207. This makes it easier for the ammonia gas to mix with the source gas. As a result, the controllability of the nitrogen concentration in each of the buffer layer 11 and the drift layer 14 can be further improved.

[0144] According to the manufacturing apparatus 250 and the manufacturing method for silicon carbide epitaxial substrate 100 according to the present disclosure, a third ammonia gas supply unit 236 connected to the main piping unit 207 may be provided. This allows for improved controllability of the nitrogen concentration in each buffer region when buffer regions having different nitrogen concentrations are formed.

[0145] According to the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 according to the present disclosure, the first pipe 271 is connected to the ammonia gas supply unit. The second pipe 272 connects the first pipe 271 to the main pipe unit 207. The third pipe 273 connects the first pipe 271 to the main pipe unit 207. The dilution gas supply unit 235 is connected to the third pipe 273. The carrier gas supply unit 234 is connected to the main pipe unit 207. The raw material gas supply unit 233 is connected to the main pipe unit 207.

[0146] According to the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 of the present disclosure, a high concentration ammonia gas can be supplied to the main piping section 207 through the first piping 271 and the second piping 272. Furthermore, a diluted low concentration ammonia gas can be supplied to the main piping section 207 through the first piping 271 and the third piping 273. This allows the buffer layer 11 to be formed with an optimum ammonia gas concentration for forming the buffer layer 11, and the drift layer 14 to be formed with an optimum ammonia gas concentration for forming the drift layer 14. As a result, the controllability of the nitrogen concentration in each of the buffer layer 11 and the drift layer 14 can be improved.

[0147] According to the manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the present disclosure, the first pipe 271 is connected to an ammonia gas supply unit. The second pipe 272 connects the first pipe 271 to the main pipe unit 207. The third pipe 273 connects the first pipe 271 to the main pipe unit 207. The first flow rate control unit 241 is disposed in the second pipe 272. The second flow rate control unit 242 is disposed in the third pipe 273. The maximum flow rate of the second flow rate control unit 242 is 10 times or more the maximum flow rate of the first flow rate control unit 241.

[0148] According to the manufacturing apparatus 250 for the silicon carbide epitaxial substrate 100 of the present disclosure, a small flow rate of ammonia gas can be supplied to the main piping section 207 through the first piping 271 and the second piping 272. Also, a large flow rate of ammonia gas can be supplied to the main piping section 207 through the first piping 271 and the third piping 273. This allows the buffer layer 11 to be formed at an optimum ammonia gas flow rate for forming the buffer layer 11, and the drift layer 14 to be formed at an optimum ammonia gas flow rate for forming the drift layer 14. As a result, the controllability of the nitrogen concentration in each of the buffer layer 11 and the drift layer 14 can be improved.

[0149] The manufacturing apparatus 250 of the silicon carbide epitaxial substrate 100 according to the present disclosure may include a source gas pipe 253 connecting the source gas supply unit 233 and the main pipe unit 207. Each of the connection portion between the second pipe 272 and the main pipe unit 207 and the connection portion between the third pipe 273 and the main pipe unit 207 may be located closer to the chamber 201 than the connection portion between the source gas pipe 253 and the main pipe unit 207. This makes it easier for the ammonia gas to mix with the source gas. As a result, the controllability of the nitrogen concentration in each of the buffer layer 11 and the drift layer 14 can be further improved.

[0150] 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, not by the embodiments described above, and is intended to include the equivalent meanings and all modifications within the scope of the claims. [Explanation of symbols]

[0151] 1 First main surface 2 Second main surface 3. Orientation Flat 4 Arc-shaped section 5 Outer rim 6 Second buffer area 7 First buffer area 8 Third main surface 10 Silicon carbide substrate 11 Buffer layer 14 Drift Layer 20 Silicon carbide epitaxial layer 100 Silicon carbide epitaxial substrate 101 1st direction 102 Second direction 103 Third direction 106 Trench 113 Body Region 114 Source Region 115 Gate insulating film 116 Source Electrode 117 Mask 118 Contact Area 119 Source wiring 120 Drain electrode 123 Side 124 Bottom 126 Interlayer insulating film 127 Gate electrode 201 Chamber 203 Heating element 204 Quartz tube 205 Inner wall surface 206 Stages 207 Main piping section 208 Gas exhaust port 209 Rotational Axis 210 Holder 211 Preheating Area 231 First ammonia gas supply unit 232 Second ammonia gas supply unit 233 Raw gas supply section 234 Carrier gas supply unit 235 Dilution gas supply section 236 Third ammonia gas supply section 241 First flow control section 242 Second flow control section 243 Third flow control section 244 Fourth flow control section 245 5th flow control section 246 6th flow control section 247 7th flow control section 248 8th flow control section 249 9th flow control section 250 Manufacturing equipment 251 First ammonia gas pipe 252 Second ammonia gas piping 253 Raw gas piping 254 Carrier gas piping 261 First Connection 262 Second Connection 263 Third Connection 264 4th Connection 265 5th Junction 266 6th Junction 267 7th Junction 268 8th Junction 269 ​​9th Junction 271 First Pipe 272 Second Pipe 273 Third Pipe 274 4th Pipe 275 5th Pipe 276 3rd Ammonia Gas Pipe 278 Exhaust valve 300 Silicon carbide semiconductor device A center T1 First thickness T2 Second thickness W1 Maximum diameter

Claims

1. a chamber in which a silicon carbide substrate is disposed; A main piping section connected to the chamber; a first ammonia gas supply unit connected to the main piping unit and used when forming a buffer layer on the silicon carbide substrate; a second ammonia gas supply unit connected to the main piping unit and used when forming a drift layer on the buffer layer; A carrier gas supply section connected to the main piping section; a raw material gas supply unit connected to the main piping unit, a concentration of ammonia gas in the first ammonia gas supply unit is higher than a concentration of ammonia gas in the second ammonia gas supply unit, The apparatus for manufacturing a silicon carbide epitaxial substrate, wherein each of the first ammonia gas supply unit and the second ammonia gas supply unit is a dopant gas supply unit.

2. a chamber in which a silicon carbide substrate is disposed; a first ammonia gas supply unit connected to the chamber and used when forming a buffer layer on the silicon carbide substrate; a second ammonia gas supply unit connected to the chamber and used when forming a drift layer on the buffer layer; a carrier gas supply unit connected to the chamber; a source gas supply unit connected to the chamber, a concentration of ammonia gas in the first ammonia gas supply unit is higher than a concentration of ammonia gas in the second ammonia gas supply unit, The apparatus for manufacturing a silicon carbide epitaxial substrate, wherein each of the first ammonia gas supply unit and the second ammonia gas supply unit is a dopant gas supply unit.

3. 3 . The apparatus for manufacturing a silicon carbide epitaxial substrate according to claim 1 , wherein the source gas supply unit comprises a silicon-containing gas supply unit and a carbon-containing gas supply unit. 4 .

4. 3. The apparatus for manufacturing a silicon carbide epitaxial substrate according to claim 1, wherein a concentration of the ammonia gas in the first ammonia gas supply section is five times or more higher than a concentration of the ammonia gas in the second ammonia gas supply section.

5. 3 . The apparatus for manufacturing a silicon carbide epitaxial substrate according to claim 1 , wherein the second ammonia gas supply unit contains ammonia gas diluted with hydrogen gas. 4 .

6. 3 . The apparatus for manufacturing a silicon carbide epitaxial substrate according to claim 1 , wherein each of the first ammonia gas supply unit and the second ammonia gas supply unit contains ammonia gas diluted with hydrogen gas. 4 .

7. a first ammonia gas pipe connecting the first ammonia gas supply unit and the main pipe unit; a second ammonia gas pipe connecting the second ammonia gas supply unit and the main pipe unit; a raw material gas pipe connecting the raw material gas supply unit and the main pipe unit, 2. The silicon carbide epitaxial substrate manufacturing apparatus according to claim 1, wherein a connection portion between the first ammonia gas pipe and the main piping portion and a connection portion between the second ammonia gas pipe and the main piping portion are each located closer to the chamber than a connection portion between the source gas pipe and the main piping portion.

8. The apparatus for manufacturing a silicon carbide epitaxial substrate according to claim 1 , further comprising a third ammonia gas supply unit.

9. The silicon carbide epitaxial substrate manufacturing apparatus according to claim 1 , wherein the carrier gas supply unit contains hydrogen gas.

10. providing a silicon carbide substrate; A method for manufacturing a silicon carbide epitaxial substrate, comprising: forming an epitaxial layer on the silicon carbide substrate by using the silicon carbide epitaxial substrate manufacturing apparatus according to claim 1 or 2.

11. A process for preparing a chamber, a first ammonia gas supply unit connected to the chamber, and a second ammonia gas supply unit connected to the chamber; forming a buffer layer on a silicon carbide substrate by epitaxial growth using the ammonia gas supplied from the first ammonia gas supply unit; forming a drift layer on the buffer layer by epitaxial growth using the ammonia gas supplied from the second ammonia gas supply unit; a concentration of ammonia gas in the first ammonia gas supply unit is higher than a concentration of ammonia gas in the second ammonia gas supply unit, each of the first ammonia gas supply unit and the second ammonia gas supply unit is a dopant gas supply unit.

12. 12. The method for manufacturing a silicon carbide epitaxial substrate according to claim 11, wherein a concentration of the ammonia gas in the first ammonia gas supply unit is five times or more higher than a concentration of the ammonia gas in the second ammonia gas supply unit.

13. the silicon carbide substrate has a main surface in contact with the buffer layer, 13. The method for producing a silicon carbide epitaxial substrate according to claim 11, wherein the main surface is a plane inclined at an angle of 6° or less with respect to a (0001) plane or a (000-1) plane.

14. A step of preparing a silicon carbide epitaxial substrate by using the method for producing a silicon carbide epitaxial substrate according to claim 11 or 12; and forming an electrode on the silicon carbide epitaxial substrate.

15. A step of preparing a silicon carbide epitaxial substrate by using the method for producing a silicon carbide epitaxial substrate according to claim 10; and forming an electrode on the silicon carbide epitaxial substrate.