Method for manufacturing silicon carbide epitaxial substrate, device for manufacturing silicon carbide epitaxial substrate, method for manufacturing silicon carbide semiconductor device, and program

Abstract

This method for manufacturing a silicon carbide epitaxial substrate comprises the following steps. Using a first dopant gas that includes ammonia, a buffer layer is formed on a silicon carbide substrate by epitaxial growth. Using a second dopant gas, a drift layer is formed on the buffer layer by epitaxial growth. The nitrogen concentration of the buffer layer is at least 3 × 1018 cm−3.

Description

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

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

[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 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 a first dopant gas containing ammonia; and forming a drift layer by epitaxial growth on the buffer layer using a second dopant gas. The buffer layer has a nitrogen concentration of 3×10 18 cm -3 That's all.

[0005] FIG. 1 is a plan view schematic showing the configuration of a silicon carbide epitaxial substrate according to this embodiment. FIG. 2 is a cross-sectional view schematic taken along line II-II in FIG. 1 . FIG. 3 is a partial cross-sectional view schematic showing the configuration of an apparatus for manufacturing a silicon carbide epitaxial substrate according to this embodiment. FIG. 4 is a flow diagram generally showing a method for manufacturing a silicon carbide epitaxial substrate according to this embodiment. FIG. 5 is a cross-sectional view schematic showing the step of forming a first layer. FIG. 6 is a cross-sectional view schematic showing the step of forming a second layer. FIG. 7 is a cross-sectional view schematic showing the step of forming a body region. FIG. 8 is a cross-sectional view schematic showing the step of forming a source region. FIG. 9 is a cross-sectional view schematic showing the step of forming a trench in first main surface 1. FIG. 10 is a cross-sectional view schematic showing the step of forming a gate insulating film. FIG. 11 is a cross-sectional view schematic showing the step of forming a gate electrode and an interlayer insulating film. FIG. 12 is a cross-sectional view schematic showing the configuration of a silicon carbide semiconductor device according to this 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 method for manufacturing a silicon carbide epitaxial substrate according to the present disclosure includes the following steps: forming a buffer layer on a silicon carbide substrate by epitaxial growth using a first dopant gas containing ammonia; and forming a drift layer on the buffer layer by epitaxial growth using a second dopant gas. The nitrogen concentration in the buffer layer is 3×10 18 cm -3 That's all.

[0008] (2) According to the method for manufacturing a silicon carbide epitaxial substrate according to (1) above, the nitrogen concentration in the buffer layer is 5×10 18 cm -3 It may be more than that.

[0009] (3) In the method for manufacturing a silicon carbide epitaxial substrate according to (1) or (2) above, the second dopant gas may contain nitrogen gas.

[0010] (4) In the method for manufacturing a silicon carbide epitaxial substrate according to (1) or (2) above, each of the first dopant gas and the second dopant gas may contain ammonia gas.

[0011] (5) In the method for manufacturing a silicon carbide epitaxial substrate according to any one of (1) to (4) above, the buffer layer may have a thickness of 1 μm or more.

[0012] (6) In the method for manufacturing a silicon carbide epitaxial substrate according to any one of (1) to (5) above, the drift layer may have a thickness of 5 μm or more.

[0013] (7) In the method for manufacturing a silicon carbide epitaxial substrate according to any one of (1) to (5), the silicon carbide substrate may have a main surface in contact with the buffer layer, and the main surface may be a plane inclined at an angle of 6° or less with respect to the (0001) plane or the (000-1) plane.

[0014] (8) A method for manufacturing a silicon carbide epitaxial substrate according to the present disclosure includes the following steps: forming a first layer by epitaxial growth on a silicon carbide substrate using a first dopant gas containing ammonia; and forming a second layer by epitaxial growth on the first layer using a second dopant gas containing nitrogen, with the nitrogen concentration in the first layer being higher than the nitrogen concentration in the second layer.

[0015] (9) According to the method for manufacturing a silicon carbide epitaxial substrate according to (8) above, the nitrogen concentration in the first layer is 3×10 18 cm -3 It may be more than that.

[0016] (10) According to the method for manufacturing a silicon carbide epitaxial substrate according to any one of (1) to (9) above, the silicon carbide epitaxial substrate may have a diameter of 200 mm or more.

[0017] (11) A method for manufacturing a silicon carbide semiconductor device according to the present disclosure includes the steps of preparing a silicon carbide epitaxial substrate using the method for manufacturing a silicon carbide epitaxial substrate described in any one of (1) to (10) above, and forming an electrode on the silicon carbide epitaxial substrate.

[0018] (12) A silicon carbide epitaxial substrate manufacturing apparatus according to the present disclosure includes a chamber in which a silicon carbide substrate is placed, a main piping section connected to the chamber, an ammonia gas supply section connected to the main piping section, a nitrogen gas supply section connected to the main piping section, a carrier gas supply section connected to the main piping section, and a raw material gas supply section connected to the main piping section.

[0019] (13) A silicon carbide epitaxial substrate manufacturing apparatus according to the present disclosure includes a chamber in which a silicon carbide substrate is placed, an ammonia gas supply unit connected to the chamber, a nitrogen 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.

[0020] (14) In the silicon carbide epitaxial substrate manufacturing apparatus according to (12) or (13), the ammonia gas supply unit may contain ammonia gas diluted with hydrogen gas, and the nitrogen gas supply unit may contain nitrogen gas diluted with hydrogen gas.

[0021] (15) In the silicon carbide epitaxial substrate manufacturing apparatus according to (13) or (14), the carrier gas supply unit may contain hydrogen gas.

[0022] (16) In the silicon carbide epitaxial substrate manufacturing apparatus according to any one of (13) to (15) above, the carrier gas supply unit may contain argon gas.

[0023] (17) In the silicon carbide epitaxial substrate manufacturing apparatus according to any one of (13) to (16) above, the upper limit of the flow rate of the nitrogen gas supplied from the nitrogen gas supply unit may be 200 sccm or less when converted into a flow rate of nitrogen gas with a concentration of 100%.

[0024] (18) A program executed by a computer for controlling a silicon carbide epitaxial substrate manufacturing apparatus according to the present disclosure causes the computer to execute the steps of epitaxially growing a buffer layer on a silicon carbide substrate using a first dopant gas containing ammonia, and epitaxially growing a drift layer on the buffer layer using a second dopant gas. The nitrogen concentration in the buffer layer is 3×10 18 cm -3 That's all.

[0025] (19) In the program according to (18), the nitrogen concentration in the buffer layer is 5×10 18 cm -3 It may be more than that.

[0026] (20) In the program according to (18) or (19), the second dopant gas may contain nitrogen gas.

[0027] (21) In the program according to (18) or (19), the second dopant gas may include ammonia gas.

[0028] (22) In the program according to any one of (18) to (21) above, the buffer layer may have a thickness of 1 μm or more.

[0029] (23) In the program according to any one of (18) to (22) above, the drift layer may have a thickness of 5 μm or more.

[0030] (24) In the program according to any one of (18) to (23), the silicon carbide substrate may have a first main surface in contact with the buffer layer, and the first 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.

[0031] (25) A program executed by a computer for controlling an apparatus for manufacturing a silicon carbide epitaxial substrate according to the present disclosure causes the computer to perform the steps of epitaxially growing a first layer on a silicon carbide substrate using a first dopant gas containing ammonia, and epitaxially growing a second layer on the first layer using a second dopant gas containing nitrogen, wherein the nitrogen concentration in the first layer is higher than the nitrogen concentration in the second layer.

[0032] (26) In the program according to (25), the nitrogen concentration in the first layer is 3×10 18 cm -3 It may be more than that.

[0033] (27) In the program according to any one of (18) to (26) above, the silicon carbide epitaxial substrate may have a diameter of 200 mm or more.

[0034] [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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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).

[0045] 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.

[0046] 2 , silicon carbide epitaxial layer 20 has buffer layer 11 (first layer 11) and drift layer 14 (second 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The nitrogen concentration of the buffer layer 11 is 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:

[0052] 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:

[0053] 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.

[0054] 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.

[0055] 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.

[0056] (Apparatus for manufacturing silicon carbide epitaxial substrate) Figure 3 is a partial cross-sectional schematic diagram showing the configuration of an apparatus for manufacturing silicon carbide epitaxial substrate 100 according to this embodiment. As shown in Figure 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), an induction heating coil (not shown), and control device 9.

[0057] 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.

[0058] 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 may be made of silicon carbide, for example. 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.

[0059] 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.

[0060] 3 , manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 includes a first dopant gas supply unit 231, a second dopant gas supply unit 232, a carrier gas supply unit 234, a source gas supply unit 233, a first dopant gas pipe 251, a second dopant gas pipe 252, a source gas pipe 253, and a carrier gas pipe 254. Each of first dopant gas supply unit 231, second dopant gas supply unit 232, carrier gas supply unit 234, and source gas supply unit 233 is connected to chamber 201.

[0061] The first dopant gas supply unit 231 is connected to the main pipe unit 207. The first dopant gas pipe 251 connects the first dopant gas supply unit 231 and the main pipe unit 207. The second dopant gas supply unit 232 is connected to the main pipe unit 207. The second dopant gas pipe 252 connects the second dopant gas supply unit 232 and the main pipe unit 207.

[0062] 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.

[0063] The first dopant gas supply unit 231 is an ammonia gas supply unit 231 configured to be able to supply ammonia gas. The first dopant gas supply unit 231 may be filled with diluted ammonia gas. Specifically, the first dopant gas supply unit 231 may contain ammonia gas diluted with hydrogen gas. The concentration of ammonia gas in the first dopant gas supply unit 231 is, for example, 1%. The concentration of ammonia gas in the first dopant 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.

[0064] The second dopant gas supply unit 232 is a nitrogen gas supply unit 232 configured to be able to supply nitrogen gas. The second dopant gas supply unit 232 may be filled with, for example, diluted nitrogen gas. Specifically, the second dopant gas supply unit 232 may contain nitrogen gas diluted with hydrogen gas. The upper limit of the flow rate of the nitrogen gas supply unit is, for example, 200 sccm.

[0065] The second dopant gas supply unit 232 may be an ammonia gas supply unit configured to be able to supply ammonia gas. The second dopant gas supply unit 232 may be filled with, for example, diluted ammonia gas. Specifically, the second dopant gas supply unit 232 may contain ammonia gas diluted with hydrogen gas. When the second dopant gas supply unit 232 contains ammonia gas, the concentration of the ammonia gas in the second dopant gas supply unit 232 is, for example, 0.1%. The concentration of the ammonia gas in the first dopant gas supply unit 231 may be, for example, 0.01% or more, 0.05% or more, 1% or less, or 0.2% or less.

[0066] The concentration of ammonia gas in the first dopant gas supply unit 231 may be higher than the concentration of ammonia gas in the second dopant gas supply unit 232. Specifically, the concentration of ammonia gas in the first dopant 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 dopant gas supply unit 232. The concentration of ammonia gas in the first dopant 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 dopant gas supply unit 232.

[0067] 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.

[0068] 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).

[0069] The connection between the first dopant gas pipe 251 and the main pipe section 207 is referred to as a first connection section 261. The connection between the second dopant 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.

[0070] 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.

[0071] The 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. The first flow rate control unit 241 controls the flow rate of gas flowing through the first dopant gas pipe 251. The second flow rate control unit 242 controls the flow rate of gas flowing through the second dopant gas pipe 252. The third flow rate control unit 243 controls the flow rate of gas flowing through the source 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).

[0072] The control device 9 is, for example, a computer. The control device 9 has, for example, a processor and a memory. The program is stored, for example, in the memory. The processor performs data processing by reading and executing the program stored in the memory. The program may be saved in a storage medium external to the control device 9. The control device 9 controls, for example, 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 control device 9 may control the temperature, pressure, etc. inside the chamber 201.

[0073] In the process of forming buffer layer 11, high-concentration ammonia gas is supplied to main piping section 207 using first dopant gas piping 251 and first dopant gas supply section 231. In the process of forming drift layer 14, nitrogen gas or low-concentration ammonia gas is supplied to main piping section 207 using second dopant gas piping 252 and second dopant gas supply section 232.

[0074] 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.

[0075] The first dopant gas supply unit 231 is connected to the first dopant 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 dopant 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.

[0076] The second dopant gas supply unit 232 is connected to the second dopant 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 dopant 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.

[0077] 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.

[0078] (Method for Manufacturing Silicon Carbide Epitaxial Substrate) Next, a method for manufacturing silicon carbide epitaxial substrate 100 according to this embodiment will be described.

[0079] 4 is a flow diagram schematically showing a method for manufacturing silicon carbide epitaxial substrate 100 according to this embodiment. As shown in FIG. 4, the method for manufacturing silicon carbide epitaxial substrate 100 according to this embodiment includes a step (S10) of forming first layer 11 and a step (S20) of forming second layer 14.

[0080] 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.

[0081] Next, silicon carbide substrate 10 is placed in chamber 201 of manufacturing apparatus 250 for silicon carbide epitaxial substrate 100. Specifically, silicon carbide substrate 10 is placed inside chamber 201 in a state where it is placed on holder 210.

[0082] Next, a step (S10) of forming first layer 11 is performed. FIG. 5 is a cross-sectional schematic diagram showing the step of forming first layer 11. First layer 11 is, for example, buffer layer 11. As shown in FIG. 5 , 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 to form buffer layer 11 on silicon carbide substrate 10.

[0083] 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.

[0084] In forming the buffer layer 11, ammonia gas supplied from the first dopant gas supply unit 231 is used as the dopant gas. As described above, the first dopant gas supply unit 231 contains ammonia gas diluted with hydrogen gas. The concentration of the ammonia gas in the first dopant 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 with hydrogen gas to a concentration of 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, 0.1 sccm or more and 2.0 sccm or less.

[0085] As described above, buffer layer 11 is formed by epitaxial growth on silicon carbide substrate 10 using first dopant gas. The first dopant gas contains ammonia gas. The first dopant gas is supplied from first dopant gas supply unit 231.

[0086] The thickness of buffer layer 11 is, for example, 2 μm or more. The thickness of buffer layer 11 may be, for example, 3 μm or more, or 5 μm or more. The thickness of buffer layer 11 may be, for example, 10 μm or less, or 8 μm or less.

[0087] The nitrogen concentration of the buffer layer 11 is 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:

[0088] Next, a step (S20) of forming second layer 14 is performed. Fig. 6 is a schematic cross-sectional view showing the step of forming second layer 14. Second layer 14 is, for example, drift layer 14. As shown in Fig. 6, drift layer 14 is formed on buffer layer 11 by epitaxial growth.

[0089] 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.

[0090] In forming the drift layer 14, nitrogen gas or ammonia gas supplied from the second dopant gas supply unit 232 is used as the dopant gas. When the second dopant gas supply unit 232 contains nitrogen gas, the flow rate of the nitrogen gas supplied to the chamber 201 is controlled using the second flow rate control unit 242. For example, the nitrogen gas may be undiluted and have a concentration of 100%. The nitrogen gas may also be diluted with hydrogen gas. The flow rate of the nitrogen gas, converted into the flow rate of nitrogen gas with a concentration of 100%, is, for example, 200 sccm or less.

[0091] When the second dopant gas supply unit 232 contains ammonia gas diluted with hydrogen gas, the concentration of the ammonia gas in the second dopant 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 to 200 sccm. 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 to 0.2 sccm.

[0092] The concentration of ammonia gas in the first dopant gas supply unit 231 is higher than the concentration of ammonia gas in the second dopant gas supply unit 232. Specifically, the concentration of ammonia gas in the first dopant 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 dopant gas supply unit 232. The concentration of ammonia gas in the first dopant 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 dopant gas supply unit 232.

[0093] As described above, the drift layer 14 is formed by epitaxial growth on the buffer layer 11 using the second dopant gas. The second dopant gas is nitrogen gas or ammonia gas. The second dopant gas is supplied from the second dopant gas supply unit 232.

[0094] The thickness of the drift layer 14 is, for example, 5 μm or more. The thickness of the drift layer 14 may be, for example, 10 μm or more, 30 μm or more, or 50 μm or more. The thickness of the drift layer 14 may be, for example, 100 μm or less, or 80 μm or less. 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.

[0095] In another aspect, the ammonia gas supplied from the first dopant gas supply unit 231 and the ammonia gas supplied from the second dopant 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 dopant 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 dopant 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.

[0096] 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.

[0097] In another embodiment, ammonia gas supplied from the first dopant gas supply unit 231 and nitrogen gas supplied from the second dopant gas supply unit 232 may be used simultaneously in part or all of the step of forming the buffer layer 11, and nitrogen gas supplied from the second dopant gas supply unit 232 may be used in the step of forming the drift layer 14. That is, nitrogen gas supplied from the second dopant 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.

[0098] 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.

[0099] A program executed by a computer for controlling an apparatus for manufacturing a silicon carbide epitaxial substrate causes the computer to execute the steps of: epitaxially growing a buffer layer on a silicon carbide substrate using a first dopant gas containing ammonia (S10); and epitaxially growing a drift layer on the buffer layer using a second dopant gas (S20). The program causes the computer to execute the steps of epitaxially growing a first layer on the silicon carbide substrate using the first dopant gas containing ammonia (S10); and epitaxially growing a second layer on the first layer using a second dopant gas containing nitrogen (S20).

[0100] Specifically, the control device 9 controls the first flow rate control unit 241, the third flow rate control unit 243, and the fourth flow rate control unit 244 to introduce a first dopant gas, hydrogen gas, and source gas into the chamber 201 and form a first layer on the silicon carbide substrate. Next, the control device 9 controls the second flow rate control unit 242, the third flow rate control unit 243, and the fourth flow rate control unit 244 to introduce a second dopant gas, hydrogen gas, and source gas into the chamber 201 and form a second layer on the first layer.

[0101] The nitrogen concentration in the first layer (buffer layer) is controlled to be higher than the nitrogen concentration in the second layer (drift layer). The nitrogen concentration in the buffer layer is controlled to be 3×10 18 cm -3 The nitrogen concentration in the buffer layer may be controlled to be 5×10 or more. 18 cm -3 The thickness of the buffer layer may be controlled to be 1 μm or more. The thickness of the drift layer may be controlled to be 5 μm or more.

[0102] 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.

[0103] Since the ammonia gas serving as the nitrogen source is thermally decomposed in pre-heating 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, and as a result, the in-plane concentration distribution of nitrogen doped into the growing silicon carbide epitaxial layer also becomes uniform.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] Since the ammonia gas serving as the nitrogen source is thermally decomposed in pre-heating 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, and 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] (Method for Manufacturing Silicon Carbide Semiconductor Device) Next, a method for manufacturing silicon carbide semiconductor device 300 according to this embodiment will be described.

[0113] First, silicon carbide epitaxial substrate 100 according to this embodiment is prepared (see FIG. 6 ). Next, a step of forming a body region is performed. FIG. 7 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.

[0114] Next, a step of forming a source region is performed. FIG. 8 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.

[0115] 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.

[0116] 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.

[0117] Next, a step of forming trenches in the first main surface 1 is performed. FIG. 9 is a cross-sectional schematic diagram showing the step of forming trenches in the first main surface 1. As shown in FIG. 9, 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.

[0118] 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.

[0119] 9 , 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.

[0120] Next, a step of forming a gate insulating film is performed. FIG. 10 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.

[0121] Next, a step of forming a gate electrode is performed. FIG. 11 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] (Silicon Carbide Semiconductor Device) Next, the configuration of a silicon carbide semiconductor device 300 according to this embodiment will be described. FIG. 12 is a cross-sectional schematic diagram showing the configuration of the silicon carbide semiconductor device 300 according to this embodiment. As shown in FIG. 12 , 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] Next, the effects of 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.

[0134] Nitrogen gas or ammonia gas is used to dope nitrogen into a silicon carbide epitaxial layer. Nitrogen gas is chemically very stable compared to ammonia gas and is therefore less likely to be decomposed by heat. Nitrogen gas that is not completely decomposed accumulates in the chamber over time. Therefore, the nitrogen concentration tends to be higher in the later stages of epitaxial growth than in the early stages.

[0135] 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 higher than the nitrogen concentration in drift layer 14. If a large amount of nitrogen gas is used as a dopant gas when forming buffer layer 11, a large amount of nitrogen gas accumulates in the chamber. As a result, the nitrogen concentration in drift layer 14 formed on buffer layer 11 may vary in the thickness direction. Specifically, the nitrogen concentration in drift layer 14 may increase toward first main surface 1. In particular, when the nitrogen concentration in buffer layer 11 is high, the influence of the tendency for the nitrogen concentration in drift layer 14 to be higher in the later stages of epitaxial growth than in the early stages of epitaxial growth becomes significant.

[0136] Furthermore, in a silicon carbide semiconductor device having a body diode such as a MOSFET, when holes, which are minority carriers, move from the drift layer to the silicon carbide substrate, the energy generated when the holes and electrons recombine can cause basal plane dislocations to grow into stacking faults, increasing forward resistance. By forming a buffer layer with a high nitrogen concentration between the silicon carbide substrate and the drift layer, it is possible to prevent holes, which are minority carriers, from moving from the drift layer to the silicon carbide substrate. As a result, it is possible to prevent an increase in forward resistance.

[0137] In the method for manufacturing a silicon carbide epitaxial substrate 100 according to the present disclosure, a buffer layer 11 is formed by epitaxial growth on a silicon carbide substrate 10 using a first dopant gas containing ammonia. A drift layer 14 is formed by epitaxial growth on the buffer layer 11 using a second dopant gas. This prevents an increase in forward resistance in a silicon carbide semiconductor device 300 having a body diode. Furthermore, because the buffer layer containing a high concentration of nitrogen is not formed by introducing a large amount of nitrogen gas, residual nitrogen gas that has not been thermally decomposed is prevented from accumulating in the chamber. This prevents the nitrogen concentration of the drift layer 14 from varying in the thickness direction of the drift layer 14. In other words, this reduces the effect of the tendency for the nitrogen concentration in the drift layer 14 to be higher in the later stages of epitaxial growth than in the early stages of epitaxial growth.

[0138] According to the method for manufacturing silicon carbide epitaxial substrate 100 according to the present disclosure, the nitrogen concentration in buffer layer 11 is 5×10 18 cm -3 This can further prevent the forward resistance from increasing in silicon carbide semiconductor device 300 having a body diode.

[0139] According to the method for manufacturing silicon carbide epitaxial substrate 100 according to the present disclosure, the second dopant gas may contain nitrogen gas. The nitrogen concentration in drift layer 14 is lower than the nitrogen concentration in buffer layer 11. Therefore, even when the second dopant gas used in forming drift layer 14 contains nitrogen gas, the influence of the tendency for the nitrogen concentration in drift layer 14 to be higher in the later stage of epitaxial growth than in the early stage of epitaxial growth is small.

[0140] According to the method for manufacturing silicon carbide epitaxial substrate 100 according to the present disclosure, each of the first dopant gas and the second dopant gas may be ammonia gas, which can further reduce the effect of the tendency for the nitrogen concentration in drift layer 14 to be higher in the later stage of epitaxial growth than in the early stage of epitaxial growth.

[0141] According to the method for manufacturing silicon carbide epitaxial substrate 100 according to the present disclosure, buffer layer 11 may have a thickness of 1 μm or more, which can further prevent holes, which are minority carriers, from migrating from drift layer 14 to silicon carbide substrate 10. As a result, an increase in forward resistance can be further prevented.

[0142] In the method for manufacturing silicon carbide semiconductor device 300 according to the present disclosure, silicon carbide epitaxial substrate 100 is prepared using the method for manufacturing silicon carbide epitaxial substrate 100 according to the present disclosure. This makes it possible to prevent an increase in forward resistance in silicon carbide semiconductor device 300 having a body diode.

[0143] Manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the present disclosure includes ammonia gas supply unit 231 and nitrogen gas supply unit 232. This allows buffer layer 11 to be formed with an optimum ammonia gas concentration for forming buffer layer 11, and allows drift layer 14 to be formed with an optimum nitrogen gas concentration for forming drift layer 14. As a result, it is possible to improve the controllability of the nitrogen concentration in each of buffer layer 11 and drift layer 14.

[0144] In manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the present disclosure, ammonia gas supply unit 231 may contain ammonia gas diluted with hydrogen gas. Nitrogen gas supply unit 232 may contain nitrogen gas diluted with hydrogen gas. This further improves the controllability of the nitrogen concentration in each of buffer layer 11 and drift layer 14.

[0145] In manufacturing apparatus 250 for silicon carbide epitaxial substrate 100 according to the present disclosure, the upper limit of the flow rate of nitrogen gas supplied from nitrogen gas supply unit 232 may be 200 sccm or less when converted into a flow rate of nitrogen gas with a concentration of 100%. This reduces the effect of the nitrogen concentration in drift layer 14 tending to be higher in the later stage of epitaxial growth than in the early stage of epitaxial growth.

[0146] 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 rather than the above-described embodiments, and it is intended to include any modifications within the scope of the claims and meanings equivalent to the claims.

[0147] 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 First layer (buffer layer) 14 Second layer (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 dopant gas supply section (ammonia gas supply section) 232 Second dopant gas supply section (ammonia gas supply section or nitrogen gas supply section) 233 Source gas supply section 234 Carrier 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 250 Manufacturing apparatus 251 First dopant gas piping 252 Second dopant gas piping 253 Source gas piping 254 Carrier gas piping 261 First connection section 262 Second connection section 263 Third connection section 264 Fourth connection section 300 Silicon carbide semiconductor device A Center T1 First thickness T2 Second thickness W1 Maximum diameter

Claims

1. A method for fabricating a silicon carbide substrate using a first dopant gas containing ammonia to form a buffer layer by epitaxial growth, and a second dopant gas to form a drift layer by epitaxial growth on the buffer layer, wherein the nitrogen concentration in the buffer layer is 3×10 18 cm -3 This is the method for manufacturing a silicon carbide epitaxial substrate.

2. The nitrogen concentration in the buffer layer is 5×10 18 cm -3 The method for producing a silicon carbide epitaxial substrate according to claim 1 .

3. The method for producing a silicon carbide epitaxial substrate according to claim 1 or 2, wherein the second dopant gas includes nitrogen gas.

4. The method for producing a silicon carbide epitaxial substrate according to claim 1 or 2, wherein each of the first dopant gas and the second dopant gas includes ammonia gas.

5. The method for producing a silicon carbide epitaxial substrate according to any one of claims 1 to 4, wherein the buffer layer has a thickness of 1 µm or more.

6. The method for manufacturing a silicon carbide epitaxial substrate according to any one of claims 1 to 5, wherein the drift layer has a thickness of 5 µm or more.

7. The method for manufacturing a silicon carbide epitaxial substrate according to any one of claims 1 to 6, wherein the silicon carbide substrate has a first main surface in contact with the buffer layer, and the first main surface is a plane inclined at an angle of 6° or less with respect to a (0001) plane or a (000-1) plane.

8. A method for manufacturing a silicon carbide epitaxial substrate, comprising: forming a first layer on a silicon carbide substrate by epitaxial growth using a first dopant gas containing ammonia; and forming a second layer on the first layer by epitaxial growth using a second dopant gas containing nitrogen, wherein the nitrogen concentration in the first layer is higher than the nitrogen concentration in the second layer.

9. The nitrogen concentration in the first layer is 3 x 10 18 cm -3 The method for producing a silicon carbide epitaxial substrate according to claim 8 .

10. A method for manufacturing a silicon carbide epitaxial substrate according to any one of claims 1 to 9, wherein the silicon carbide epitaxial substrate has a diameter of 200 mm or more.

11. 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 1 to 10; and forming electrodes on the silicon carbide epitaxial substrate.

12. 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 connected to the main piping section; a nitrogen 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.

13. An apparatus for manufacturing a silicon carbide epitaxial substrate, comprising: a chamber in which a silicon carbide substrate is placed; an ammonia gas supply unit connected to the chamber; a nitrogen 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.

14. The silicon carbide epitaxial substrate manufacturing apparatus according to claim 12 or 13, wherein the ammonia gas supply unit contains ammonia gas diluted with hydrogen gas, and the nitrogen gas supply unit contains nitrogen gas diluted with hydrogen gas.

15. The silicon carbide epitaxial substrate manufacturing apparatus according to any one of claims 12 to 14, wherein the carrier gas supply unit contains hydrogen gas.

16. The silicon carbide epitaxial substrate manufacturing apparatus according to any one of claims 12 to 15, wherein the carrier gas supply unit contains argon gas.

17. A silicon carbide epitaxial substrate manufacturing apparatus according to any one of claims 12 to 16, wherein the upper limit of the flow rate of the nitrogen gas supplied from the nitrogen gas supply unit is 200 sccm or less when converted into a flow rate of nitrogen gas with a concentration of 100%.

18. A program executed by a computer for controlling a silicon carbide epitaxial substrate manufacturing apparatus, the program causing the computer to execute: forming a buffer layer on a silicon carbide substrate by epitaxial growth using a first dopant gas containing ammonia; and forming a drift layer on the buffer layer by epitaxial growth using a second dopant gas, wherein the nitrogen concentration in the buffer layer is 3×10 18 cm -3 That's it, the program.

19. The nitrogen concentration in the buffer layer is 5×10 18 cm -3 The program according to claim 18.

20. The program according to claim 18 or claim 19, wherein the second dopant gas includes nitrogen gas.

21. The program according to claim 18 or 19, wherein the second dopant gas includes ammonia gas.

22. The program according to any one of claims 18 to 21, wherein the buffer layer has a thickness of 1 μm or more.

23. The program according to any one of claims 18 to 22, wherein the drift layer has a thickness of 5 μm or more.

24. The program according to any one of claims 18 to 23, wherein the silicon carbide substrate has a first main surface in contact with the buffer layer, and the first main surface is a plane inclined at an angle of 6° or less with respect to the (0001) plane or the (000-1) plane.

25. A program executed by a computer for controlling a silicon carbide epitaxial substrate manufacturing apparatus, the program causing the computer to execute the steps of: forming a first layer on a silicon carbide substrate by epitaxial growth using a first dopant gas containing ammonia; and forming a second layer on the first layer by epitaxial growth using a second dopant gas containing nitrogen, wherein the nitrogen concentration in the first layer is higher than the nitrogen concentration in the second layer.

26. The nitrogen concentration in the first layer is 3 x 10 18 cm -3 The program according to claim 25.

27. The program according to any one of claims 18 to 26, wherein the silicon carbide epitaxial substrate has a diameter of 200 mm or more.

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