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

Abstract

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

Description

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

[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.

[0002] 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.

[0003] International Publication No. 2017 / 056691

[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 placed 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.

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

[0006] [Outline of Embodiments of the Present Disclosure] First, an outline of embodiments of the present disclosure will be described. In the crystallographic descriptions in this specification, individual orientations are represented by [ ], collective orientations by < >, individual planes by ( ), and collective planes by {}. A negative crystallographic index is usually represented by placing a "-" (bar) above the number, but in this specification, a negative crystallographic index 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 silicon carbide epitaxial substrate manufacturing apparatus according to (1) or (2) above, the source gas supply unit may include a silicon-containing gas supply unit and a carbon-containing gas supply unit.

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

[0011] (5) In the silicon carbide epitaxial substrate manufacturing apparatus 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 silicon carbide epitaxial substrate manufacturing apparatus 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 pipe unit, a second ammonia gas pipe connecting the second ammonia gas supply unit and the main pipe unit, and a source gas pipe connecting the source gas supply unit and the main pipe unit. Each of the connection unit between the first ammonia gas pipe and the main pipe unit and the connection unit between the second ammonia gas 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.

[0014] (8) The silicon carbide epitaxial substrate manufacturing apparatus according to (1) or (7) above may include a third ammonia gas supply unit connected to the main pipe 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 section, a second piping section, a third piping section, a dilution gas supply section, a carrier gas supply section, and a raw material gas supply section. A silicon carbide substrate is placed in the chamber. The main piping section is connected to the chamber. The first piping section is connected to the ammonia gas supply section. The second piping section connects the first piping section to the main piping section. The third piping section connects the first piping section 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 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 section, a second piping section, a third piping section, 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 section is connected to the ammonia gas supply section. The second piping section connects the first piping section to the main piping section. The third piping section connects the first piping section to the main piping section. The first flow rate control section is disposed on the second piping. The second flow rate control section is disposed on 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 maximum flow rate of the second flow rate control section 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 (9) or (10) above may include a source gas pipe connecting the source gas supply unit and the main pipe unit. The connection between the second pipe and the main pipe unit and the connection between the third pipe and the main pipe unit may each be located closer to the chamber than the connection between the source gas pipe and the main pipe unit.

[0018] (12) In the silicon carbide epitaxial substrate manufacturing apparatus 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 silicon carbide epitaxial substrate manufacturing apparatus 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: forming a buffer layer by epitaxial growth on a silicon carbide substrate using ammonia gas supplied from a first ammonia gas supply unit; forming a drift layer by epitaxial growth on the buffer layer using ammonia gas supplied from a second ammonia gas supply unit; and forming ammonia gas at a concentration higher than that at ammonia gas supplied from the second ammonia gas supply unit.

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

[0022] (16) In the method for manufacturing a silicon carbide epitaxial substrate according to (14) or (15), the silicon carbide substrate may have a main surface in contact with the buffer layer. The main surface may be a plane inclined at an angle of 6 degrees 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, details of the embodiment 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 schematically showing the configuration of a silicon carbide epitaxial substrate 100 according to this embodiment. Fig. 2 is a cross-sectional view schematically showing the configuration 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 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, orientation flat 3 and arc-shaped portion 4.

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

[0029] 1 , orientation flat 3 is linear when viewed in a direction from silicon carbide epitaxial layer 20 toward silicon carbide substrate 10. Arc-shaped portion 4 is continuous with orientation flat 3. Arc-shaped portion 4 is also arc-shaped. A notch may be provided instead of orientation flat 3. In this case, first direction 101 is the 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> direction 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> direction 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 refers to 100 mm or 101.6 mm (4 inches x 25.4 mm / inch). 6 inches refers to 150 mm or 152.4 mm (6 inches x 25.4 mm / inch). 8 inches refers to 200 mm or 203.2 mm (8 inches x 25.4 mm / inch). 10 inches refers to 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 Figure 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] 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, the (0001) plane. Third main surface 8 may be, for example, a plane inclined at an angle of 6 degrees 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 degrees or less, or may be 3 degrees 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 drift layer 14 is set to second thickness T2. Second thickness T2 may be greater than first thickness T1. Second thickness T2 is, for example, 5 μm or greater. Second thickness T2 may be, for example, 10 μm or greater, 30 μm or greater, or 50 μm or greater. Second thickness T2 may be 100 μm or less, or 80 μm or less.

[0040] Silicon carbide substrate 10 contains nitrogen (N) as an n-type impurity. The conductivity type of silicon carbide substrate 10 is n-type. Silicon carbide epitaxial layer 20 contains nitrogen as an n-type impurity. The conductivity type of silicon carbide epitaxial layer 20 is n-type. Specifically, buffer layer 11 and drift layer 14 each contain nitrogen as an n-type impurity. The nitrogen concentration of buffer layer 11 is higher than the nitrogen concentration of drift layer 14. The conductivity type of buffer layer 11 and 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 7×10 or more. 18 cm -3 It may be 9×10 or more. 18 cm -3 The nitrogen concentration of the buffer layer 11 may be, for example, 5×10 19 cm -3 It may be 1×10 or less. 19 cm -3 It may be the following:

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

[0043] Buffer layer 11 may be composed of a single layer, or may be composed of two or more layers with different nitrogen concentrations. Buffer layer 11 may have, for example, a first buffer region 7 and a second buffer region 6. First buffer region 7 is provided on a silicon carbide substrate. Second buffer region 6 is provided on 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 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, it is possible to suppress the occurrence of defects due to differences in the crystal lattice constants.

[0046] (Apparatus for Manufacturing Silicon Carbide Epitaxial Substrate) 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 horizontal CVD (Chemical Vapor Deposition) apparatus. Apparatus 250 for manufacturing silicon carbide epitaxial substrate 100 mainly includes chamber 201, heating element 203, quartz tube 204, holder 210, a heat insulator (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 from 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 rotatably supported by rotation shaft 209. Rotation of stage 206 causes holder 210 to rotate.

[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 balancing the amount of gas supplied and the amount of gas exhausted.

[0050] 3 , manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 includes first ammonia gas supply unit 231, second ammonia gas supply unit 232, carrier gas supply unit 234, raw material gas supply unit 233, first ammonia gas piping 251, second ammonia gas piping 252, raw material gas piping 253, and carrier gas piping 254. First ammonia gas supply unit 231, second ammonia gas supply unit 232, carrier gas supply unit 234, and raw material gas supply unit 233 are each connected to 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 pipe unit 207. The carrier gas pipe 254 connects the carrier gas supply unit 234 and the main pipe unit 207. The source gas supply unit 233 is connected to the main pipe unit 207. The source gas pipe 253 connects the source gas supply unit 233 and the main pipe 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 serves as a raw material for silicon carbide. Examples of the raw material gas include propane (C3H8) gas and silane (SiH4) 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] The connection between the first ammonia gas pipe 251 and the main pipe section 207 is referred to as a first connection section 261. The connection between the second ammonia gas pipe 252 and the main pipe section 207 is referred to as a second connection section 262. The connection between the source gas pipe 253 and the main pipe section 207 is referred to as a third connection section 263. The connection between the carrier gas pipe 254 and the main pipe section 207 is referred to as a fourth connection section 264.

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

[0060] Manufacturing apparatus 250 for 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. First flow rate control unit 241 controls the flow rate of gas flowing through first ammonia gas pipe 251. Second flow rate control unit 242 controls the flow rate of gas flowing through second ammonia gas pipe 252. Third flow rate control unit 243 controls the flow rate of gas flowing through source gas pipe 253. Fourth flow rate control unit 244 controls the flow rate of gas flowing through carrier gas pipe 254. Each control unit is, for example, an MFC (Mass Flow Controller).

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

[0062] Second Embodiment Next, a configuration of an apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to a second embodiment will be described. The apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the second embodiment differs from the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment mainly in that it does not have a second ammonia gas supply unit 232, but is otherwise similar to the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment. The following description will focus on the configuration that differs from the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment.

[0063] 4 is a partial cross-sectional schematic view showing the configuration of an apparatus 250 for manufacturing silicon carbide epitaxial substrate 100 according to the second embodiment. As shown in FIG. 4 , the apparatus 250 for manufacturing 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 source gas supply unit 233, a dilution gas supply unit 235, 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 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 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 fourth pipe 274 connects the third pipe 273 to the dilution gas supply unit 235. The connection between the fourth pipe 274 and the third pipe 273 is located between the connection between the first pipe 271 and the third pipe 273 and the connection 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. An exhaust valve 278 is provided on the fifth pipe 275. 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. The fifth connection section 265 and the sixth connection section 266 are each located closer to the chamber 201 than the third connection section 263. From another perspective, the fifth connection section 265 and the sixth connection section 266 may each be located downstream of the third connection section 263 in the direction of gas flow 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] Manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 has fifth flow rate control unit 245, sixth flow rate control unit 246, seventh flow rate control unit 247, and eighth flow rate control unit 248. Fifth flow rate control unit 245 controls the flow rate of gas flowing through second pipe 272. Sixth flow rate control unit 246 controls the flow rate of gas flowing through an upstream portion of third pipe 273. Sixth flow rate control unit 246 is provided upstream of a connection between third pipe 273 and fourth pipe 274. Seventh flow rate control unit 247 controls the flow rate of gas flowing through fourth pipe 274. Eighth flow rate control unit 248 controls the flow rate of gas flowing through a downstream portion of the third flow path. Eighth flow rate control unit 248 is provided downstream of a connection between third pipe 273 and fourth pipe 274. Each control unit is, for example, an MFC.

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

[0070] Third Embodiment Next, a configuration of an apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to a third embodiment will be described. The apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the third embodiment differs from the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment mainly in that it does not have a first ammonia gas supply unit 231, but is otherwise similar to the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment. The following description will focus on the configuration that differs from the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment.

[0071] 5 is a partial cross-sectional schematic view showing the configuration of manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the third embodiment. As shown in Fig. 5, manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the third embodiment includes chamber 201, second ammonia gas supply unit 232, main piping unit 207, carrier gas piping 254, source gas piping 253, first piping 271, second piping 272, third piping 273, first flow rate control unit 241, second flow rate control unit 242, carrier gas supply unit 234, and 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 to the main pipe unit 207. The third pipe 273 connects the first pipe 271 to the main pipe unit 207. The carrier gas pipe 254 connects the carrier gas supply unit 234 to the main pipe unit 207. The source gas pipe 253 connects the source gas supply unit 233 to 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 between the third pipe 273 and the main pipe section 207 is defined as a seventh connection section 267. The connection between the second pipe 272 and the main pipe section 207 is defined as an eighth connection section 268. The seventh connection section 267 and the eighth connection section 268 are each located closer to the chamber 201 than the third connection section 263. From another perspective, the seventh connection section 267 and the eighth connection section 268 may each be located downstream of the third connection section 263 in the direction of gas flow in the main pipe section 207. The seventh connection section 267 may be located closer to the chamber 201 than the eighth connection section 268.

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

[0076] Fourth Embodiment Next, a configuration of an apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to a fourth embodiment will be described. The apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the fourth embodiment differs from the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment mainly in that it has a third ammonia gas supply unit 236, but is otherwise similar to the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment. The following description will focus on the configuration that differs from the apparatus 250 for manufacturing a silicon carbide epitaxial substrate 100 according to the first embodiment.

[0077] 6 is a partial cross-sectional schematic view showing the configuration of manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the fourth embodiment. As shown in Fig. 6, manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 includes first ammonia gas supply unit 231, second ammonia gas supply unit 232, third ammonia gas supply unit 236, carrier gas supply unit 234, source gas supply unit 233, first ammonia gas piping 251, second ammonia gas piping 252, third ammonia gas piping 276, source gas piping 253, and carrier gas piping 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 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 pipe 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 pipe unit 207.

[0081] Manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 has 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 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 piping section 207 may be a single main piping or may be multiple main piping. The main piping section 207 may have, for example, a first main piping (not shown), a second main piping (not shown), and a third main piping (not shown). The carrier gas supply section and the silane gas supply section may be connected to, for example, the first main piping. The carrier gas supply section and the propane gas supply section may be connected to, for example, the second main piping. The carrier gas supply section and the ammonia gas supply section may be connected to, for example, the third main piping.

[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 (the portion between the first flow rate control unit 241 and the chamber 201) may be connected to the carrier gas supply unit 234 via a 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 going through the main pipe unit 207. In this case, the second ammonia gas pipe 252 (the portion between the second flow rate control unit 242 and the chamber 201) may be connected to the carrier gas supply unit 234 via a flow rate control unit.

[0087] The source gas supply unit 233 is connected to the source gas pipe 253, but can also be connected to the chamber 201 without going through the main pipe unit 207. In this case, the source gas supply unit 233 (the portion between the third flow rate control unit 243 and the chamber 201) may 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 according to this embodiment will be described.

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

[0090] First, silicon carbide substrate 10 is prepared. A silicon carbide single crystal of polytype 4H is manufactured by, for example, sublimation. Next, silicon carbide substrate 10 is prepared by slicing the silicon carbide single crystal by, for example, a wire saw. Silicon carbide substrate 10 contains n-type impurities, for example, nitrogen. The conductivity type of silicon carbide substrate 10 is, for example, n-type. Next, mechanical polishing is performed on silicon carbide substrate 10. Next, chemical mechanical polishing is performed on 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 cross-sectional schematic diagram showing the step of forming buffer layer 11. As shown in FIG. 8 , buffer layer 11 is formed on silicon carbide substrate 10 by epitaxial growth. In the epitaxial growth, for example, silane (SiH 4 ) and propane (C 3 H 8 ) are used as source gases, and hydrogen (H 2 ) is used as a carrier gas. After the temperature of holder 210 reaches, for example, about 1600° C., source gases, dopant gas, and 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 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 silane gas supplied to the chamber 201 is adjusted to, for example, 46 sccm. The flow rate of silane gas may be, for example, 30 sccm or more and 60 sccm or less. The flow rate of propane gas supplied to the chamber 201 is adjusted to, for example, 14 sccm. The flow rate of propane gas may be, for example, 10 sccm or more and 20 sccm or less. The flow rate of hydrogen gas supplied to the chamber 201 is adjusted to, for example, 120 slm. The flow rate of hydrogen gas may be, for example, 100 slm or more and 150 slm or less.

[0094] In forming the buffer layer 11, 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 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, buffer layer 11 is formed on silicon carbide substrate 10 using ammonia gas supplied from first ammonia gas supply unit 231. Buffer layer 11 has a thickness of, for example, 1 μm or more. Buffer layer 11 has a nitrogen concentration of, for example, 3×10 18 cm -3 That's all.

[0096] Next, a step (S20) of forming drift layer 14 is performed. 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 silane gas supplied to the chamber 201 is adjusted to, for example, 115 sccm. The flow rate of silane gas may be, for example, 80 sccm or more and 150 sccm or less. The flow rate of propane gas supplied to the chamber 201 is adjusted to, for example, 37.5 sccm. The flow rate of propane gas may be, for example, 25 sccm or more and 50 sccm or less. The flow rate of hydrogen gas supplied to the chamber 201 is adjusted to, for example, 120 slm. The flow rate of hydrogen gas may be, for example, 100 slm or more and 150 slm or less.

[0098] In forming the drift layer 14, 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 ammonia gas diluted with hydrogen gas to a concentration of 0.1% 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 1x10 or more 17 cm -3 In this manner, silicon carbide epitaxial substrate 100 is manufactured.

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

[0102] This eliminates 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 suddenly.

[0103] 4 , in a part or all of the step 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 step 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 step of forming the buffer layer 11 and the step 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 eliminates 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 suddenly.

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

[0106] This eliminates 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 suddenly.

[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 reaching silicon carbide substrate 10 on which a silicon carbide epitaxial layer is formed.

[0108] Since the ammonia gas serving as the nitrogen source is thermally decomposed in preheating region 211 before reaching silicon carbide substrate 10, the in-plane distribution of nitrogen becomes uniform across the wide surface of silicon carbide substrate 10 where epitaxial growth is occurring. 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 disturbances in the gas flow.

[0110] Here, the preheating region 211 refers to 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 to ensure reliable pyrolysis even if the length of the chamber is somewhat short, and is preferably 1800° C. or lower from the viewpoint of thermal efficiency. For example, preheating region 211 can be the region from the end of chamber 201 to silicon carbide substrate 10 that is closest to the end of chamber 201. Preheating region 211 is preferably 50 mm or longer and 1000 mm or shorter.

[0112] Next, a silicon carbide semiconductor manufacturing apparatus is disclosed, which is a silicon carbide epitaxial substrate manufacturing apparatus 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 silicon carbide substrate 10 on which a silicon carbide epitaxial layer is formed.

[0113] Since the ammonia gas serving as the nitrogen source is thermally decomposed in preheating region 211 before reaching silicon carbide substrate 10, the in-plane distribution of nitrogen becomes uniform across the wide surface of silicon carbide substrate 10 where epitaxial growth is occurring. 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 disturbances in the gas flow.

[0115] Here, the preheating region 211 refers to 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 to ensure reliable pyrolysis even if the length of the chamber is somewhat short, and is preferably 1800° C. or lower from the viewpoint of thermal efficiency. For example, preheating region 211 can be the region from the end of chamber 201 to silicon carbide substrate 10 that is closest to the end of chamber 201. Preheating region 211 is preferably 50 mm or longer and 1000 mm or shorter.

[0117] (Method for Manufacturing Silicon Carbide Semiconductor Device) Next, a method for manufacturing 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. The thickness of body region 113 is, 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 the source region. Specifically, n-type impurities such as phosphorus are ion-implanted into the body region 113. This forms a source region 114 having n-type conductivity. The thickness of the source region 114 is, for example, 0.4 μm. The concentration of the n-type impurity contained in the source region 114 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 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 activation annealing time is, for example, about 30 minutes. The atmosphere of the activation annealing is, for example, an Ar atmosphere.

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

[0123] Next, thermal etching is performed on the recesses. Thermal etching can be performed, for example, by heating the first main surface 1 with the mask 117 formed thereon in an atmosphere containing a reactive gas having at least one type of halogen atom. The at least one type of halogen atom includes at least one of chlorine (Cl) atoms and fluorine (F) atoms. The atmosphere can include, for example, Cl2, BCl3, SF6, or CF4. For example, thermal etching is performed using a mixed gas of chlorine gas and oxygen gas as the reactive gas, with the heat treatment temperature set to, for example, 700°C or higher and 1000°C or lower. The reactive gas may contain a carrier gas in addition to the above-mentioned chlorine gas and oxygen gas. Examples of the carrier gas that can be used include nitrogen gas, argon gas, and helium gas.

[0124] 12 , trenches 106 are formed in the first main surface 1 by thermal etching. The trenches 106 are defined by side surfaces 123 and a bottom surface 124. The side surfaces 123 are 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. Next, the mask 117 is removed from the first main surface 1.

[0125] Next, a step of forming a gate insulating film is performed. FIG. 13 is a schematic cross-sectional view 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 oxygen-containing atmosphere at a temperature of, for example, 1300° C. or higher and 1400° C. or lower. This forms gate insulating film 115 that is in contact with drift layer 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 the step of forming a gate electrode and an interlayer insulating film. The gate electrode 127 is formed inside the trench 106 so as to be in contact with the gate insulating film 115. The gate electrode 127 is disposed inside 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 by, for example, a low pressure chemical vapor deposition (LPCVD) method.

[0127] Next, an interlayer insulating film 126 is formed. The interlayer insulating film 126 is formed so as to cover the gate electrode 127 and to be in contact with the gate insulating film 115. The interlayer insulating film 126 is formed by, for example, chemical vapor deposition. The interlayer insulating film 126 is made of, for example, a material containing silicon dioxide. Next, the interlayer insulating film 126 and part of the gate insulating film 115 are etched so as to form openings over the source region 114 and the contact region 118. As a result, the contact region 118 and the source region 114 are exposed from the gate insulating film 115.

[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 containing 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 maintained at a temperature of 900° C. or higher and 1100° C. or lower for about 5 minutes. This causes at least a portion of the source electrode 116 to be silicided. This forms the source electrode 116 in ohmic contact with the source region 114.

[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 drain electrode 120 is carried out. First, silicon carbide substrate 10 is polished at second main surface 2. Next, drain electrode 120 is formed. Drain electrode 120 is formed so as to be in contact with silicon carbide substrate 10 at second main surface 2. In this manner, silicon carbide semiconductor device 300 according to the present embodiment is manufactured.

[0132] (Silicon Carbide Semiconductor Device) Next, the configuration of a silicon carbide semiconductor device 300 according to this embodiment will be described. FIG. 15 is a cross-sectional schematic diagram 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 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 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 its bottom surface 124, and in contact with the drift layer 14, the body region 113, and the source region 114 at its side surfaces 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 surfaces 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 at the second main surface 2.

[0138] Next, the effects of the apparatus 250 for manufacturing silicon carbide epitaxial substrate 100, the method for manufacturing silicon carbide epitaxial substrate 100, and the method for manufacturing 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, which has triple bonds. Therefore, the flow rate of ammonia gas required to achieve the same nitrogen concentration is significantly smaller than the flow rate of nitrogen gas.

[0140] Furthermore, 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 more times or 100 or more times 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. A flow rate controller (MFC) has a limit to the range of gas flow rates that can be flowed. Therefore, it has been difficult to accurately control the flow rates of ammonia gas required to form buffer layer 11 and the flow rate of ammonia gas required to form drift layer 14 using a single flow rate controller (MFC).

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

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

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

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

[0145] According to manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the present disclosure, first pipe 271 is connected to the ammonia gas supply unit. Second pipe 272 connects first pipe 271 to main pipe unit 207. Third pipe 273 connects first pipe 271 to main pipe unit 207. Dilution gas supply unit 235 is connected to third pipe 273. Carrier gas supply unit 234 is connected to main pipe unit 207. Source gas supply unit 233 is connected to main pipe unit 207.

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

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

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

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

[0150] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0151] REFERENCE SIGNS LIST 1 First main surface 2 Second main surface 3 Orientation flat 4 Arc-shaped portion 5 Outer periphery 6 Second buffer region 7 First buffer region 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 First 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 region 119 Source wiring 120 Drain electrode 123 Side surface 124 Bottom surface 126 Interlayer insulating film 127 Gate electrode 201 Chamber 203 Heating element 204 Quartz tube 205 Inner wall surface 206 Stage 207 Main piping section 208 Gas exhaust port 209 Rotating shaft 210 Holder 211 Preheating area 231 First ammonia gas supply section 232 Second ammonia gas supply section 233 Raw material gas supply section 234 Carrier gas supply section 235 Dilution gas supply section 236 Third ammonia gas supply section 241 First flow rate control section 242 Second flow rate control section 243 Third flow rate control section 244 Fourth flow rate control section 245 Fifth flow rate control section 246 Sixth flow rate control section 247 Seventh flow rate control section 248 Eighth flow rate control section 249 Ninth flow rate control section 250 Manufacturing apparatus 251 First ammonia gas piping 252 Second ammonia gas piping 253 Raw material gas piping 254 Carrier gas piping 261 First connection section 262 Second connection section 263 Third connection section 264 Fourth connection section 265 Fifth connection section 266 Sixth connection part 267 Seventh connection part 268 Eighth connection part 269 Ninth connection part 271 First pipe 272 Second pipe 273 Third pipe 274 Fourth pipe 275 Fifth pipe 276 Third ammonia gas pipe 278 Exhaust valve 300 Silicon carbide semiconductor device A Center T1 First thickness T2 Second thickness W1 Maximum diameter

Claims

1. An apparatus for manufacturing a silicon carbide epitaxial substrate, comprising: a chamber in which a silicon carbide substrate is placed; a main piping section connected to the chamber; a first ammonia gas supply section connected to the main piping section; a second ammonia gas supply section connected to the main piping section; a carrier gas supply section connected to the main piping section; and a source gas supply section connected to the main piping section, wherein a concentration of ammonia gas in the first ammonia gas supply section is higher than a concentration of ammonia gas in the second ammonia gas supply section.

2. An apparatus for manufacturing a silicon carbide epitaxial substrate, comprising: a chamber in which a silicon carbide substrate is placed; a first ammonia gas supply unit connected to the chamber; a second ammonia gas supply unit connected to the chamber; a carrier gas supply unit connected to the chamber; and a source gas supply unit connected to the chamber, wherein 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.

3. The silicon carbide epitaxial substrate manufacturing apparatus according to claim 1 or 2, wherein the source gas supply unit has a silicon-containing gas supply unit and a carbon-containing gas supply unit.

4. The silicon carbide epitaxial substrate manufacturing apparatus according to any one of claims 1 to 3, wherein the concentration of ammonia gas in the first ammonia gas supply unit is at least five times the concentration of ammonia gas in the second ammonia gas supply unit.

5. The silicon carbide epitaxial substrate manufacturing apparatus according to any one of claims 1 to 4, wherein the second ammonia gas supply unit contains ammonia gas diluted with hydrogen gas.

6. The silicon carbide epitaxial substrate manufacturing apparatus according to any one of claims 1 to 5, wherein each of the first ammonia gas supply unit and the second ammonia gas supply unit contains ammonia gas diluted with hydrogen gas.

7. The apparatus for manufacturing a silicon carbide epitaxial substrate according to claim 1, comprising: 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, wherein each of the connection portion between the first ammonia gas pipe and the main piping unit and the connection portion between the second ammonia gas pipe and the main piping unit is located closer to the chamber than the connection portion between the raw material gas pipe and the main piping unit.

8. The silicon carbide epitaxial substrate manufacturing apparatus according to claim 1 or claim 7, further comprising a third ammonia gas supply unit connected to the main pipe unit.

9. An apparatus for manufacturing a silicon carbide epitaxial substrate, comprising: a chamber in which a silicon carbide substrate is placed; a main piping section connected to the chamber; an ammonia gas supply section; a first piping connected to the ammonia gas supply section; a second piping connecting the first piping and the main piping section; a third piping connecting the first piping and the main piping section; a dilution gas supply section connected to the third piping; a carrier gas supply section connected to the main piping section; and a raw material gas supply section connected to the main piping section.

10. An apparatus for manufacturing a silicon carbide epitaxial substrate, comprising: a chamber in which a silicon carbide substrate is placed; a main piping section connected to the chamber; an ammonia gas supply section; a first piping connected to the ammonia gas supply section; a second piping connecting the first piping and the main piping section; a third piping connecting the first piping and the main piping section; a first flow rate control section disposed on the second piping; a second flow rate control section disposed on the third piping; a carrier gas supply section connected to the main piping section; and a raw material gas supply section connected to the main piping section, wherein the maximum flow rate of the second flow rate control section is 10 times or more the maximum flow rate of the first flow rate control section.

11. A silicon carbide epitaxial substrate manufacturing apparatus as described in claim 9 or claim 10, further comprising a raw material gas pipe connecting the raw material gas supply unit and the main pipe unit, wherein the connection between the second pipe and the main pipe unit and the connection between the third pipe and the main pipe unit are each located closer to the chamber than the connection between the raw material gas pipe and the main pipe unit.

12. The silicon carbide epitaxial substrate manufacturing apparatus according to any one of claims 9 to 11, wherein the ammonia gas supply unit contains ammonia gas diluted with hydrogen gas.

13. The silicon carbide epitaxial substrate manufacturing apparatus according to any one of claims 1 to 12, wherein the carrier gas supply unit contains hydrogen gas.

14. A method for manufacturing a silicon carbide epitaxial substrate, comprising: forming a buffer layer by epitaxial growth on a silicon carbide substrate using ammonia gas supplied from a first ammonia gas supply unit; and forming a drift layer by epitaxial growth on the buffer layer using ammonia gas supplied from a second ammonia gas supply unit, wherein the concentration of the ammonia gas in the first ammonia gas supply unit is higher than the concentration of the ammonia gas in the second ammonia gas supply unit.

15. The method for producing a silicon carbide epitaxial substrate according to claim 14, wherein the concentration of ammonia gas in the first ammonia gas supply unit is at least five times the concentration of ammonia gas in the second ammonia gas supply unit.

16. The method for manufacturing a silicon carbide epitaxial substrate according to claim 14 or 15, wherein the silicon carbide substrate has a main surface in contact with the buffer layer, and the main surface is a plane inclined at an angle of 6 degrees or less with respect to the (0001) plane or the (000-1) plane.

17. A method for manufacturing a silicon carbide semiconductor device, comprising the steps of: preparing a silicon carbide epitaxial substrate using the method for manufacturing a silicon carbide epitaxial substrate according to any one of claims 14 to 16; and forming an electrode on the silicon carbide epitaxial substrate.

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