Method for producing a silicon carbide single crystal, silicon carbide single crystal substrate and silicon carbide epitaxy substrate

Abstract

Silicon carbide single crystal substrate (100), wherein the silicon carbide single crystal substrate (100) has a diameter of not less than 100 mm, the silicon carbide single crystal substrate (100) has an oxygen concentration of no more than 1 × 10 17 cm -3 exhibits the silicon carbide single crystal substrate (100) has a dislocation density of no more than 2 × 10 4 cm -2 exhibits, and the silicon carbide single crystal substrate (100) has a stacking fault area ratio of no more than 2.0%.

Description

Technical area

[0001] The present invention relates to a method for producing a silicon carbide single crystal, a silicon carbide single crystal substrate and a silicon carbide epitaxial substrate. background

[0002] US 7 314 520 B2 (Patent Document 1) discloses a method for manufacturing a silicon carbide single crystal substrate having a diameter of not less than 76 mm.

[0003] Devices for explosion protection of high-temperature furnaces are known from KR 10 2014 0 120 787 A. Citation listPatent document

[0004] PTD 1: US 7 314 520 B2 Summary of the invention

[0005] In the present invention, a method for producing a silicon carbide single crystal comprises: preparing a chamber, a growth container, a source material, and a seed crystal, the chamber including a gas inlet, a gas outlet, a welding portion, and a water-cooling portion configured to cool a portion including at least the welding portion with water, the growth container being arranged in the chamber, the source material being arranged in the growth container, the seed crystal being arranged to face the source material in the growth container; and growing a silicon carbide single crystal on the seed crystal by sublimating the source material. During growth, a dew point of gas passing through the gas outlet is maintained at not more than -40°C.

[0006] In the present invention, a silicon carbide single crystal substrate has a diameter of not less than 100 mm, has an oxygen concentration of not more than 1 × 10 17 cm -3 has a dislocation density of not more than 2 × 10 4 cm -2 and has a stacking fault area ratio of not more than 2.0%. Short description of the characters Fig. 1 is a schematic plan view showing an exemplary silicon carbide single crystal substrate of the present invention. Fig. Figure 2 shows a graph illustrating an exemplary relationship between an oxygen concentration and the dislocation density and the stacking fault area ratio of the silicon carbide single crystal substrate. Fig.3 is a schematic cross-sectional view showing an exemplary configuration of a crystal growing apparatus not according to the invention. Fig. 4 shows a schematic cross-sectional view illustrating an exemplary embodiment of an epitaxial growth apparatus which is not part of the present invention. Fig. Figure 5 shows a schematic cross-sectional view along a VV line in Fig. 4. Fig. 6 is a flowchart schematically illustrating a method for producing a silicon carbide single crystal of the present invention. Fig. 7 shows a graph illustrating an exemplary relationship between an oxygen concentration of a grown crystal and a dew point of a growth atmosphere. Fig.8 is a schematic cross-sectional view illustrating an exemplary silicon carbide epitaxial substrate of the present invention. Fig. Figure 9 shows a schematic cross-sectional view showing an exemplary embodiment around a region IX in Fig. 3 shows. Fig. 10 is a schematic plan view illustrating an exemplary configuration of a window section. Description of Embodiments[Description of Embodiments of the Present Invention]

[0007] First, embodiments of the present invention are listed and described.

[0008] A crystal growing apparatus not forming part of the present invention comprises: a chamber having a gas inlet and a gas outlet; an exhaust pump connected to the gas outlet; a dew point instrument disposed between the gas outlet and the exhaust pump, the dew point instrument being configured to measure a dew point of gas passing through the gas outlet.

[0009] Typically, a vacuum gauge is attached to the crystal growth apparatus to adjust the degree of vacuum during crystal growth. Furthermore, crystal growth is performed under the flow of a gas, such as high-purity argon (Ar) gas. Consequently, no attention has been paid to the mixing of impurities from the atmosphere during growth. However, according to the inventor's research, oxygen is incorporated into a single crystal during growth, causing dislocations and stacking faults. In other words, when the amount of oxygen is large, two-dimensional nucleus growth is likely to occur, resulting in an increase in dislocations and stacking faults. Part of the oxygen incorporated into the single crystal results from a very small amount of moisture present during growth. This moisture cannot be detected with a vacuum gauge.Accordingly, the dew point instrument is attached to the crystal growth apparatus as described above to adjust the dew point in the chamber, thereby controlling the amount of oxygen to be incorporated into the single crystal. By reducing the amount of oxygen incorporated into the single crystal, the occurrence of two-dimensional nucleation can be suppressed. Accordingly, a single crystal with reduced dislocations and stacking faults can be grown.

[0010] The chamber here comprises: a welding section; and a water cooling section which is designed to cool a section comprising at least the welding section with water.

[0011] A method for producing a silicon carbide single crystal: preparing a chamber, a growth container, a source material, and a seed crystal, the chamber including a gas inlet, a gas outlet, a welding portion, and a water-cooling portion configured to water-cool a portion including at least the welding portion, the growth container being disposed in the chamber, the source material being disposed in the growth container, the seed crystal being disposed to face the source material in the growth chamber; and growing a silicon carbide single crystal on the seed crystal by sublimating the source material. During growth, a dew point of gas passing through the gas outlet is maintained at not more than -40°C.

[0012] In the manufacturing process, the silicon carbide single crystal is grown by a sublimation process. The sublimation process is also referred to as a sublimation recrystallization process, a modified Lely process, or the like. By maintaining the dew point of the gas passing through the gas outlet at not more than -40°C as described above, the dew point of the atmosphere in the growth container can be maintained at not more than -40°C. By strictly controlling the humidity in the growth container in this way, the amount of oxygen to be incorporated into the single crystal can be reduced. By reducing the amount of oxygen to be incorporated into the single crystal, the occurrence of two-dimensional nucleus growth can be suppressed. Accordingly, dislocations and stacking faults in the silicon carbide single crystal can be reduced.

[0013] It is noted that the moisture that causes an increase in the dew point arises from the moisture that adheres when an element placed in the chamber is exposed to atmospheric air. Therefore, to obtain a dew point of no more than -40 °C, the moisture adhering to the element is desirably reduced in advance by sufficiently storing the element to be placed in the chamber in a low-dew point environment for a predetermined time or by heating and drying the element before growth, for example. Furthermore, no pinhole should appear at the welding point of the chamber.

[0014] During waxing, a dew point of the gas passing through the gas outlet is preferably kept at no more than -50 °C.

[0015] During waxing, a dew point of the gas passing through the gas outlet is preferably kept at no more than -60 °C.

[0016] During waxing, a dew point of the gas passing through the gas outlet is preferably kept at no more than -80 °C.

[0017] In the present invention, a silicon carbide single crystal substrate has a diameter of not less than 100 mm, an oxygen concentration of not more than 1 × 10 17 cm -3 , a dislocation density of not more than 2 × 10 4 cm -2 and a stacking fault area ratio of not more than 2.0%.

[0018] The oxygen concentration of not more than 1 × 10 17 cm -3 in the crystal indicates that two-dimensional nucleation was suppressed in the growth process. In the silicon carbide single crystal substrate with an oxygen concentration of not more than 1 × 10 17 cm -3 the dislocation density cannot exceed 2 × 10 4 cm -2and the stacking fault area ratio cannot exceed 2.0%. Here, the oxygen concentration cannot exceed 1 × 10 17 cm -3 This can be achieved by strictly controlling the humidity during crystal growth, e.g., using a dew-point instrument. The oxygen concentration in the substrate can be measured, for example, by SIMS (secondary ion mass spectrometry). Cesium (Cs) ions can be used for the primary ions of SIMS.

[0019] In the silicon carbide single crystal substrate described above, the dislocation density is not more than 2 × 10 4 cm -2The dislocation density can be measured as follows. First, molten potassium hydroxide (KOH) or the like is used to etch the silicon carbide single-crystal substrate. The temperature of the molten KOH is approximately 500 to 530°C, and the etching time is approximately 5 to 10 minutes. Next, the main surface of the silicon carbide single-crystal substrate is observed using an optical microscope or the like to count the number of etching pits. The dislocation density can be determined by dividing the number of etching pits by the area of ​​the main surface of the silicon carbide single-crystal substrate.

[0020] In the silicon carbide single crystal substrate, the stacking fault area ratio is not more than 2.0%. The stacking fault area ratio can be measured as follows. If the main surface of the silicon carbide single crystal substrate does not conform to the (0001) plane, the main surface is first polished to expose the (0001) plane on the main surface. Next, PL (photoluminescence) imaging, or PL imaging, is used to visualize stacking faults in the main surface. For an excitation light source, for example, a fourth harmonic wave (266 nm) of a YAG laser or the like can be used. The measurement environment can be room temperature. In a region with stacking faults, band edge emission is weaker than in a region without stacking faults. Using these properties, stacking faults can be visualized. By visualizing stacking faults in this way, areas of regions with stacking faults are measured.The stacking fault area ratio can be determined by dividing the total area of ​​the stacking fault regions by the area of ​​the main surface.

[0021] The diameter of the silicon carbide single crystal substrate cannot be smaller than 150 mm.

[0022] The diameter of the silicon carbide single crystal substrate cannot be smaller than 200 mm.

[0023] In the present invention, a silicon carbide epitaxial substrate comprises: the silicon carbide single crystal substrate mentioned in each of [7] to [9]; and an epitaxial layer disposed on the silicon carbide single crystal substrate and having an oxygen concentration of not more than 1 × 10 17 cm -3 has.

[0024] The oxygen concentration of not more than 1 × 10 17 cm -3indicates that two-dimensional nucleation growth was suppressed during epitaxial growth. Consequently, dislocation and stacking faults in the epitaxial layer can be reduced, as in the silicon carbide single-crystal substrate.

[0025] According to the above description, a silicon carbide single crystal substrate and a silicon carbide epitaxial substrate are provided, in each of which dislocation and stacking faults are reduced. [Details of the embodiment of the present invention]

[0026] Although the following describes one embodiment (hereinafter referred to as "the present embodiment") of the present invention in detail, the present embodiment is not limited thereto. In the description below, the same or corresponding elements are denoted by the same reference numerals and will not be described repeatedly. Regarding the crystallographic notations in the present specification, a single orientation is represented by [ ], a group orientation is represented by < >, a single plane is represented by ( ), and a group plane is represented by {}. Although a plane with a negative crystallographic index is normally expressed by "-" (overbar) above a number, a negative crystallographic index is indicated by a minus sign in front of the number in the present specification. [First embodiment: silicon carbide single crystal substrate]

[0027] A first embodiment is directed to a silicon carbide single crystal substrate. Fig.1 shows a schematic plan view illustrating an exemplary silicon carbide single crystal substrate according to the present embodiment. A silicon carbide single crystal substrate 100 has a diameter of not less than 100 mm. The diameter of the silicon carbide single crystal substrate 100 may be not less than 150 mm or not less than 200 mm. It can be considered that the probability of dislocations and stacking faults increases with larger diameters. Accordingly, it is considered that the effect of reducing dislocations and stacking faults in the present embodiment is more pronounced with larger diameters. The upper limit of the diameter is not specifically limited. The upper limit of the diameter may be, for example, 250 mm. The thickness of the silicon carbide single crystal substrate 100 is not specifically limited. The thickness of the silicon carbide single crystal substrate 100 is, for example,not less than 100 µm and not larger than 10 mm.

[0028] The polytype of the silicon carbide single crystal substrate 100 is desirably 4H-SiC because 4H-SiC is superior to other polytypes in electron mobility, dielectric strength, and the like. The silicon carbide single crystal substrate 100 is obtained by dicing a silicon carbide single crystal ingot. The silicon carbide single crystal substrate 100 may have a main surface 101 corresponding to a (0001) plane or (000-1) plane, or a plane inclined at a predetermined angle relative to the (0001) plane or (000-1) plane. When a main surface 101 corresponds to the plane inclined relative to the (0001) plane or (000-1) plane, the plane may be inclined in a <11-20> direction. An inclination angle relative to the (0001) or (000-1) plane is also called a "displacement angle." For example, the displacement angle cannot be less than 1° or greater than 8°. The upper limit of the displacement angle can be 7°, 6°, or 5°.The lower limit of the displacement angle can be 2° or 3°.

[0029] The silicon carbide single crystal substrate 100 according to the present embodiment has an oxygen concentration of not more than 1 × 10 17 cm -3 It is assumed that the occurrence of two-dimensional nucleation is caused by growing the silicon carbide single crystal so that it has an oxygen concentration of not more than 1 × 10 17 cm -3 is suppressed and consequently there is a reduction in dislocation and stacking faults. Fig. Figure 2 shows a graph plotting the result of an investigation of the relationship between oxygen concentration and dislocation density and stacking fault area ratio in the silicon carbide single crystal substrate 100 manufactured by the present inventor using the sublimation method. A specific numerical value of each point in Fig. 2 is shown in Table 1. [Table 1] oxygen concentration Dislocation density Stacking fault area ratio cm -3 cm -2 % 1 × 10 15 1 × 10 4 0 1 × 10 15 1 × 10 4 0 1 × 10 15 2 × 10 4 1 1 × 10 15 3 × 10 4 5 1 × 10 15 1 × 10 5 10

[0030] In each of Fig. 2 and Fig. 7, “Exponent 10” is denoted by “E+00”. In Fig. 2 and Fig. 7, for example, represents “E+17” “10 17 “ In Fig. 2, the horizontal axis represents the oxygen concentration, the vertical axis on the right represents the dislocation density, and the vertical axis on the left represents the stacking fault area ratio.

[0031] According to the presentation in Fig. 2, the dislocation density and the stacking fault area ratio decrease with decreasing oxygen concentration. The dislocation density and the stacking fault area ratio are abruptly reduced when the oxygen concentration is increased from 1 × 10 19 cm -3 to 1 × 10 17 cm -3As a result, the dislocation density and the stacking fault area ratio are stable at low values. As can be seen from Fig. 2, the silicon carbide single crystal substrate 100 can have a dislocation density of not more than 2 × 10 4 cm -2 and a stacking fault area ratio of not more than 2.0% by controlling the oxygen concentration such that the oxygen concentration is not more than 1 × 10 17 cm -3 A smaller oxygen concentration is more preferred. The oxygen concentration is preferably not greater than 1 × 10 16 cm -3 and more preferably not larger than 1 × 10 15 cm -3 By reducing the oxygen concentration, the dislocation density can be 1 x 104 cm-2 or less. Furthermore, the stacking fault area ratio cannot be greater than 1% with decreasing oxygen concentration. [Silicon carbide epitaxial substrate]

[0032] According to the present embodiment, a silicon carbide epitaxial substrate is also provided. Fig. 8 is a schematic cross-sectional view illustrating an exemplary configuration of a silicon carbide epitaxial substrate according to the present embodiment. As shown in Fig. 8, a silicon carbide epitaxial substrate 1000 comprises the silicon carbide single crystal substrate 100 and an epitaxial layer 1001 disposed on the silicon carbide single crystal substrate 100. According to the above description, the silicon carbide single crystal substrate 100 has a diameter of not less than 100 mm, has an oxygen concentration of not more than 1 x 10 17 cm -3 has a dislocation density of not more than 2 × 10 4 cm -2 and has a stacking fault area ratio of not more than 2.0%.

[0033] The epitaxial layer 1001 is a silicon carbide single-crystal layer epitaxially grown on a main surface 101 of the silicon carbide single-crystal substrate 100. A property of the silicon carbide single-crystal substrate 100 is transferred to the epitaxial layer 1001. However, if a large amount of oxygen is present, two-dimensional nucleation may also occur in the epitaxial growth, leading to an increase in dislocations and stacking faults. Accordingly, in order to obtain an epitaxial layer 1001 with fewer dislocations and stacking faults in the silicon carbide single-crystal substrate 100, the oxygen concentration of the epitaxial layer 1001 must also be no greater than 1 x 10 17 cm -3. The oxygen concentration of the epitaxial layer 1001 can also be measured by SIMS, as in the silicon carbide single-crystal substrate 100. A lower oxygen concentration of the epitaxial layer 1001 is more preferable because dislocation and stacking faults can be reduced. The oxygen concentration of the epitaxial layer 1001 is preferably not greater than 1 × 10 16 cm -3 and more preferably not larger than 1 × 10 15 cm -3 .

[0034] The epitaxial layer 1001 may, for example, comprise nitrogen as a dopant. The nitrogen concentration of the epitaxial layer 1001 is, for example, not less than 1 × 10 14 cm -3 and not larger than 1 × 10 16 cm -3The thickness of the epitaxial layer 1001 is, for example, not less than 1 µm. The thickness of the epitaxial layer 1001 cannot be less than 10 µm or less than 20 µm. Furthermore, the thickness of the epitaxial layer 1001 is, for example, not greater than 200 µm. The thickness of the epitaxial layer cannot be greater than 150 µm or greater than 100 µm. [Second Embodiment: Crystal Growing Apparatus]

[0035] A second embodiment of the present invention is directed to a crystal growth apparatus. The crystal growth apparatus of the present invention includes: a single crystal growth apparatus for growing a single crystal using the sublimation method; an epitaxial growth apparatus for growing an epitaxial layer on a substrate using vapor-phase epitaxy such as CVD (chemical vapor deposition); and the like. [Single crystal growth device]

[0036] Fig. 3 shows a schematic cross-sectional view illustrating an exemplary configuration of the single crystal growth apparatus according to an embodiment not according to the invention. An arrow 91 in Fig. 3 represents a flow path of the gas. According to the illustration in Fig.3, a crystal growing apparatus 50 includes a chamber 20 having a gas inlet 21 and a gas outlet 22. The chamber 20 may be formed, for example, of stainless steel or the like. The gas outlet 22 is connected to an exhaust pump 30 through an outlet pipe 32. A dew point instrument 40 is arranged on the outlet pipe 32. The dew point instrument 40 is arranged between the gas outlet 22 and the exhaust pump 30 in the outlet pipe 32. The dew point of the gas passing through the gas outlet 22 is measured by the dew point instrument 40. The dew point measured by the dew point instrument 40 can be regarded as a dew point in the chamber 20. To suppress deterioration of the dew point instrument 40, a filter (not shown) may be arranged between the gas outlet 22 and the dew point instrument 40.

[0037] The dew point instrument 40 can be any dew point instrument as long as the dew point instrument can measure a dew point within a range of 0°C to -80°C. For example, the "EAX-TX-100" provided by Michell Instruments or the like can be used. Alternatively, a dew point instrument with a precision and measurement range equivalent to that of the EAX-TX-100 can be used.

[0038] A growth container 10, a resistance heater 2, and a thermal insulator 15 are arranged in the chamber 20. The growth container 10, the resistance heater 2, and the thermal insulator 15 are formed, for example, from graphite. The growth container 10 comprises a mounting means 3 and a receiving portion 4. The mounting means 3 is configured to hold a seed crystal 11. The seed crystal 11 is a silicon carbide single-crystal substrate with a polytype of 4H-SiC. The mounting means 3 also functions as a cover of a receiving portion 4. The receiving portion 4 has a cylindrical shape with a bottom. The receiving portion 4 can accommodate a source material 12. The source material 12 is, for example, a silicon carbide polycrystal powder. In the growth container 10, the source material 12 and the seed crystal 11 are aligned with each other.

[0039] In the crystal growth apparatus 50, a predetermined temperature gradient is formed by the resistance heater 2 in the growth container 10. Corresponding temperatures of the sections of the growth container 10 can be detected using a radiation thermometer (not shown). The resistance heater 2 and the thermal insulator 15 are provided with openings to allow the passage of light from each of the temperature-measuring sections of the growth container 10. The radiation thermometer receives the light from the growth container 10 through a window portion 23 (view port) provided in the chamber 20 to measure a temperature. As shown in Fig. 9 and Fig.10, below, the window portion 23 includes a window material 202 composed, for example, of quartz. Since the thermal insulator 15 is provided with an opening, heat circulates around the window portion 23. Accordingly, a weld portion 310 around the window portion 23 deteriorates, with the result that outside air and moisture are likely to enter the chamber 20 through the weld portion 310. Such an abnormality can also be detected by the dew point instrument 40.

[0040] Fig. Figure 9 shows a schematic cross-sectional view showing an exemplary embodiment around a region IX of Fig.3. The chamber 20 includes the welding section 310. Furthermore, the chamber 20 includes a water cooling section 320 configured to cool the welding section 310 with water. In other words, the chamber 20 includes the gas inlet 21, gas outlet 22, the welding section 310, and the water cooling section 320 configured to cool the welding section 310 with water.

[0041] The water cooling section 320 includes an outer wall 321, an inner wall 322, and a water flow path 323. The water flow path 323 is arranged between the outer wall 321 and the inner wall 322. Water can flow in the water flow path 323. Although only the periphery of the window section 23 in Fig. 9, the water cooling section 320 may extend to other sections not shown. In particular, the chamber 20 is configured to be partially or completely cooled with water.

[0042] The window portion 23 includes a cylinder portion 201, a window material 202, a flange 203, a screw 204, and an O-ring 205 (gasket). The cylinder portion 201 may be formed, for example, from stainless steel. The cylinder portion 201 is connected to the water-cooling portion 320 by the welding portion 310. The welding portion 310 is provided at a portion where the outer wall 321 contacts the cylinder portion 201 and formed at a portion where the inner wall 322 contacts the cylinder portion 201. The welding portion 310 is located at a boundary between the window portion 23 and the water-cooling portion 320 and is subject to strong heat circulation. This may, for example, cause a pinhole in the welding portion 310 on the inner wall 322 side, resulting in moisture entering the chamber 20 and deteriorating crystal quality.

[0043] The window material 202 and the flange 203 are integrated with the cylinder portion 201 by the fastening screw 204. The window material 202 may be a plate formed of quartz or the like. The flange 203 may be formed, for example, of stainless steel or the like. The O-ring 205 is arranged between the window material 202 and the cylinder portion 201. By the fastening screw 204, the O-ring 205 is compressed by the window material 202 and the cylinder portion 201, thereby sealing the window portion 201. The O-ring 205 may, for example, be formed of a metal such as copper, or may be formed of a rubber or the like with a predetermined thermal resistance.

[0044] Fig.10 is a schematic plan view showing an exemplary configuration of the window portion. The window material 202 and the flange 203 may, for example, have a circular planar shape. The window material 202 is exposed with respect to the center of the flange 203. Light from the heated growth container 10 exits the chamber 20 through the window material 202. In particular, the chamber 20 further includes the window portion 23 configured to allow light to pass therethrough, and the window portion 23 is connected to the water cooling portion 320 by the welding portion 310. This light is received by the radiation thermometer, thereby measuring the temperature of each portion of the growth container 10.

[0045] About the Fig.An inert gas, such as Ar gas, helium (He) gas, or nitrogen (N2) gas, is introduced into the gas inlet 21 shown in Figure 3. Naturally, the dew point of the introduced gas is desirably no greater than -40°C. The introduced inert gas is exhausted to the outside by the exhaust pump 30. The pressure in the growth container 10 can be adjusted according to a flow rate of the introduced gas and an exhaust capacity of the exhaust pump 30.

[0046] When the temperature and pressure in the growth container 10 meet predetermined conditions, the source material 12 sublimates and is redeposited on the seed crystal 11. Consequently, a silicon carbide single crystal 13 is grown on the seed crystal 11. In the crystal growth apparatus 50, the dew point of the gas passing through the gas outlet 22 can be measured and monitored by the dew point instrument 40. Consequently, the silicon carbide single crystal 13 can be grown while suppressing the admixture of oxygen resulting from a very small amount of moisture. By suppressing the amount of oxygen incorporated into the silicon carbide single crystal 13, the occurrence of two-dimensional nucleus growth can be suppressed. As a result, dislocations and stacking faults in the silicon carbide single crystal 13 are reduced. [Epitaxy growth device]

[0047] Fig.Figure 4 shows a schematic cross-sectional view illustrating an exemplary embodiment of an epitaxial growth apparatus that is not part of the invention. A crystal growth apparatus 200 shown in Fig. 4 and Fig. 5 is shown, represents a hot-wall CVD device of the lateral type. According to the illustration in Fig. 4, the crystal growing apparatus 200 includes heating elements 152, a thermal insulator 153, a quartz tube 154, and an induction heating coil 155. The heating element 152, the thermal insulator 153, and the quartz tube 154 are arranged in the chamber 120.

[0048] According to the presentation in Fig.4, two heating elements 152 are provided. Each heating element 152 has a semi-cylindrical hollow structure with a curved portion 157 and a flat portion 156. The two flat portions 156 are arranged facing each other. A space surrounded by the two flat portions 156 serves as a reaction chamber 150. A flat portion 156 is provided with a recess. A substrate holder 160 is provided in the recess. The substrate holder 160 is configured to hold a silicon carbide single-crystal substrate 100. Furthermore, the substrate holder 160 can be rotated. According to the above description, the silicon carbide single-crystal substrate 100 has a diameter of not less than 100 mm and an oxygen concentration of not more than 1 × 10 17 cm -3 , a dislocation density of not more than 2 × 10 4 cm -2 and a stacking fault area ratio of not more than 2.0%.

[0049] The thermal insulator 153 is provided to surround the outer peripheral portions of the heating elements 152. The reaction chamber 150 is thermally insulated from the outside by the thermal insulator 153. The quartz tube 154 is provided to surround the outer peripheral portion of the thermal insulator 153. The induction coil 155 is wound around the outer peripheral portion of the quartz tube 154. When an alternating current is applied to the induction heating coil 155, the heating elements 152 are inductively heated. In this way, the temperature in the reaction chamber 150 can be controlled. For example, when growing the epitaxial layer 1001, the temperature in the reaction chamber 150 is approximately 1,500 to 1,700°C.

[0050] Fig. Figure 5 shows a schematic cross-sectional view along a line VV in Fig. 4. An arrow 92 in Fig.5 illustrates a gas flow path. A chamber 120 has a gas inlet 121 and a gas outlet 122. The gas outlet 122 is connected to an exhaust pump 130 via an outlet pipe 132. A dew point instrument 140 is arranged between the gas outlet 122 and the exhaust pump 130 in the outlet pipe 132. The dew point of the gas passing through the gas outlet 122 is measured by the dew point instrument 140. The dew point measured by the dew point instrument 140 can be considered a dew point in the chamber 120.

[0051] In the chamber 120, a source material gas and a carrier gas are introduced through an introduction tube 131. The dew points of these gases are also desirably not greater than (-40) °C. The source material gas includes silane (SiH4) gas, propane (C3H8) gas, and the like. The source material gas may include, for example, ammonia (NH3) gas or the like as a dopant gas. The carrier gas may be a hydrogen (H2) gas or the like. The ammonia gas in the source material gas is preferably thermally decomposed before being supplied to the reaction chamber 150 to improve the per-level uniformity of the carrier concentration in the epitaxial layer 1001. The ammonia gas may be thermally decomposed, for example, using a preheating structure 158. The preheating structure 158 may be an externally heated elongated tube, a chamber with an electric heating coil provided therein, or the like. For example, the temperature of the inner wall surface of the preheating structure 158 may be approximately 1.300 to 1,600 °C.

[0052] A pressure in the reaction chamber 150 is adjusted by the flow rates of the source material gas and the carrier gas and the exhaust power of the exhaust pump 130. For example, during the growth of the epitaxial layer, the pressure in the reaction chamber 150 is approximately 5 to 20 kPa.

[0053] The epitaxial layer 1001 can be grown in the crystal growth apparatus 200 while the dew point in the chamber 120 is measured and monitored. Accordingly, the amount of oxygen to be incorporated into the epitaxial layer 1001 can be controlled. By performing the epitaxial growth to achieve an oxygen concentration of not more than 1 × 10 17 cm -3 The occurrence of two-dimensional nucleus growth can be suppressed. Consequently, dislocations and stacking faults can also be reduced in the epitaxial layer 1001.

[0054] The silicon carbide epitaxial substrate 1000 can be manufactured as described above, comprising: a silicon carbide single crystal substrate 100; and an epitaxial layer 1001 disposed on the silicon carbide single crystal substrate 100 and having an oxygen concentration of not more than 1 × 10 17 cm -3 has. [Third Embodiment: Method for Manufacturing a Silicon Carbide Single Crystal]

[0055] A third embodiment is directed to a method for producing a silicon carbide single crystal. Fig. Figure 6 shows a flow chart schematically illustrating the manufacturing process. According to the illustration in Fig. 6, the manufacturing process includes a preparation step (S10) and a crystal growth step (S20). Each of these steps is described below. [Preparation step (S10)]

[0056] In the preparation step (S10), for example, the crystal growing device 50, which is Fig. 3, is prepared first. Specifically, the following are prepared: the chamber 20 having the gas inlet 21, the gas outlet 22, the welding section 310, and the water cooling section 320 configured to water-cool a section including at least the welding section 310; the exhaust pump 30 connected to the gas outlet 22; and a dew point instrument 40 disposed between the gas outlet 22 and the exhaust pump 30.

[0057] Furthermore, the growth container 10 is prepared in the preparation step (S10). Here, moisture adhering to the growth container 10 is desirably reduced in advance by storing the growth container 10 in a low-dew point environment for a predetermined time or by heating and drying the growth container 10.

[0058] Here, the low dew point environment refers to an environment with a dew point of no more than -40 °C. The predetermined time is approximately 1 to 48 hours.

[0059] Next, the seed crystal 11 and the source material 12 are arranged in the growth container 10. Also, for example, moisture adhering to the seed crystal 11 and the source material 12 is desirably reduced in advance by storing the seed crystal 11 and the source material 12 in a low-dew point environment for a predetermined time. In the growth container 10, the seed crystal 11 is arranged facing the source material 12. The seed crystal 11 can be adhered to a mount 3 using an adhesive, for example. In this case, it is desirable that the adhesive be heated to reduce moisture after adhesion. The diameter of the seed crystal 11 is selected depending on a target diameter of the silicon carbide single crystal 13. The diameter of the seed crystal 11 is, for example, not less than 100 mm.After the seed crystal 11 and the source material 12 are arranged in the growth container 10, the growth container 10 is arranged in the chamber 20. [Crystal growth step (S20)]

[0060] In the crystal growth step (S20), the source material 12 sublimates in the growth container 10, whereby the silicon carbide single crystal 13 is grown on the seed crystal 11.

[0061] The growth container 10 is heated by a resistance heater 2. In this case, the temperature around the seed crystal 11 is adjusted to approximately 2,000 to 2,300 °C, for example. Furthermore, a temperature around the source material 12 is adjusted to approximately 2,300 to 2,500 °C.

[0062] An inert gas, such as Ar gas, is introduced through the gas inlet 21. The introduced gas is discharged through the gas outlet 22 by the exhaust pump 30. The pressure in the chamber 20 is adjusted according to the flow rate of the introduced gas and the exhaust capacity of the exhaust pump 30. The dew point of the gas passing through the gas outlet 22 is monitored by the dew point instrument 40. In the present embodiment, the standby state is continued until the dew point of the gas passing through the gas outlet 22 is not greater than -40°C, while allowing the gas flow at the pressure maintained above a pressure at which the source material 12 begins to sublimate. After the dew point of the gas passing through the gas outlet 22 is not greater than -40°C, the pressure in the chamber 20 is reduced to not more than 5 kPa. Accordingly, the source material 12 begins to sublimate.The sublimed source material is in turn deposited on the seed crystal 11 and grows as the silicon carbide single crystal 13.

[0063] In the present embodiment, the dew point of the gas passing through the gas outlet 22 is always kept at not more than -40 °C during crystal growth. Fig. Fig. 7 shows a graph plotting the result of an investigation of a relationship between the oxygen concentration in the silicon carbide single crystal 13 grown by the present inventor using the sublimation method and the dew point of the gas passing through the gas outlet 22. A specific numerical value at each point in Fig. 7 is shown in Table 2. [Table 2] dew point oxygen concentration °C cm -3 0 1 × 10 18 -20 5 × 10 17 -40 2 × 10 17 -60 5 × 10 15 -80 1 × 10 14

[0064] In Fig.7, the horizontal axis represents the dew point in the chamber 20 during crystal growth, specifically the dew point of the gas passing through the gas outlet 22, whereas the vertical axis represents the oxygen concentration of the silicon carbide single crystal 13 after it has been grown. As shown in Fig. 7, the oxygen concentration decreases with decreasing dew point. In particular, the oxygen concentration decreases abruptly to no more than 1 × 10 17 cm -3 when the dew point is not more than -40 °C. By setting the oxygen concentration to not more than 1 × 10 17 cm -3 As described above, it is possible to suppress the occurrence of two-dimensional nucleus growth, which otherwise leads to an increase in dislocation and stacking faults. According to the illustration in Fig.7 and Table 2, the oxygen concentration can be reduced at a low dew point. Accordingly, it can be said that the dew point of the gas passing through the gas outlet 22 is preferably maintained at not more than -50°C in the crystal growth step (S20), preferably at not more than -60°C, and more preferably at not more than -80°C.

[0065] The embodiments disclosed herein are presented in all respects as illustrative and non-restrictive. The spirit of the present invention is defined by the claims, not by the embodiments described above. All modifications are intended to be equivalent in spirit and meaning to the terms of the claims. List of reference symbols

[0066] 2: resistance heater; 3: mounting means; 4: receiving section; 10: growth container; 11: seed crystal; 12: source material; 13: single crystal; 15, 153: thermal insulator; 20, 120: chamber; 21, 121: gas inlet; 22, 122: gas outlet; 23: window section (view port); 30, 130: exhaust pump; 32, 132: outlet pipe; 40, 140: dew point instrument; 50, 200: crystal growth device; 91, 92: arrow; 100: silicon carbide single crystal substrate; 101: main surface; 131: insertion tube; 150: reaction chamber; 152: heating element; 154: quartz tube; 155: induction heating coil; 156: Flat section; 157: Curved section; 158: Preheating structure; 160: Substrate holder; 201: Cylinder section; 202: Window material; 203: Flange; 204: Screw; 205: O-ring (gasket); 310: Welding section; 320: Water cooling section; 321: Outer wall; 322: Inner wall; 323: Water flow path; 1000: Silicon carbide epitaxial substrate; 1001: Epitaxial layer.

Claims

[1] Silicon carbide single crystal substrate (100), wherein the silicon carbide single crystal substrate (100) has a diameter of not less than 100 mm, the silicon carbide single crystal substrate (100) has an oxygen concentration of not more than 1 × 10 17 cm -3 has, the silicon carbide single crystal substrate (100) has a dislocation density of not more than 2 × 10 4 cm -2 and the silicon carbide single crystal substrate (100) has a stacking fault area ratio of not more than 2.0%. [2] The silicon carbide single crystal substrate (100) according to claim 1, wherein the diameter is not less than 150 mm. [3] The silicon carbide single crystal substrate (100) according to claim 1, wherein the diameter is not less than 200 mm. [4] The silicon carbide single crystal substrate (100) according to claim 1, wherein the oxygen concentration is not more than 1 × 10 16 cm-3 amounts. [5] The silicon carbide single crystal substrate (100) according to claim 1, wherein the oxygen concentration is not more than 1 × 10 15 cm -3 amounts. [6] The silicon carbide single crystal substrate (100) according to claim 4 or 5, wherein the dislocation density is not more than 1 × 10 4 cm -2 amounts. [7] The silicon carbide single crystal substrate (100) according to any one of claims 1 to 6, wherein the stacking fault area ratio is not more than 1.0%. [8] Silicon carbide epitaxial substrate (1000) comprising: the silicon carbide single crystal substrate (100) according to any one of claims 1 to 7; and an epitaxial layer (1001) disposed on the silicon carbide single crystal substrate (100) and having an oxygen concentration of not more than 1 × 10 17 cm -3 has. [9] A method for producing a silicon carbide single crystal (13), the method comprising: Preparing (S10) a chamber (20), a growth container (10), a source material (12), and a seed crystal (11), wherein the chamber (20) comprises a gas inlet (21), a gas outlet (22), a welding section (310), and a water cooling section (320) configured to cool a section comprising at least the welding section (310) with water, wherein the growth container (10) is arranged in the chamber (20), wherein the source material (12) is arranged in the growth container (10), wherein the seed crystal (11) is arranged such that it faces the source material (12) in the growth container (10); and growing a silicon carbide single crystal (13) on the seed crystal (11) by sublimating the source material (12), wherein a dew point of gas passing through the gas outlet (22) is maintained at not more than -40 °C during growth. [10] A method for producing the silicon carbide single crystal (13) according to claim 9, wherein a dew point of the gas passing through the gas outlet (22) during growth is maintained at not more than -50°C. [11] A method for producing the silicon carbide single crystal (13) according to claim 9, wherein a dew point of the gas passing through the gas outlet (22) during growth is maintained at not more than -60°C. [12] A method for producing the silicon carbide single crystal (13) according to claim 9, wherein a dew point of the gas passing through the gas outlet (22) during growth is maintained at not more than -80°C.

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