Manufacturing method of silicon carbide single crystal and manufacturing apparatus of silicon carbide single crystal

Abstract

To make a good shape of a growth surface of a SiC singly crystal.SOLUTION: In a SiC single crystal manufacturing method by a gas supply method in which a SiC raw material gas 20 is supplied to grow a SiC single crystal 3 on a seed crystal 2, the raw material gas 20 is introduced to a heating vessel 12 through a first gas inlet port 7 arranged below the seed crystal 2 after the seed crystal 2 is arranged on a pedestal 13. Then, the heating vessel 12 is heated to 2,000°C or more to thermally decompose the raw material gas 20, which is supplied to the seed crystal 2 to glow the SiC single crystal 3. Furthermore, while the heating vessel 12 is heated to 2,000°C or more, an etching gas 23 is injected to a growth surface of the SiC single crystal 3 from a second gas inlet port 8 having a gas outlet port 8a projected to the pedestal 13 side from the first gas inlet port 7, and a local etching for reducing a height difference of the growth surface is performed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method and apparatus for producing silicon carbide (hereinafter referred to as SiC) single crystal. [Background technology]

[0002] A conventional gas growth method is known in which SiC source gas is supplied to the growth surface of a seed crystal made of SiC single crystal, and SiC single crystal is grown on the seed crystal. In this gas growth method, SiC single crystal is produced by introducing, in addition to the SiC source gas, dopant gases such as N2 (nitrogen), which acts as a dopant to adjust the crystal's resistivity.

[0003] In the production of SiC single crystals, if the in-plane temperature and gas distribution on the growth surface cannot be properly adjusted, the growth surface of the SiC single crystal will have a concave or convex shape, resulting in a large difference in height on the growth surface, which will increase the internal stress of the SiC single crystal and cause crystal cracking.

[0004] As a technique for solving such problems, Patent Document 1 proposes a method of equipping a reaction vessel with a tapered section and controlling the gas flow so that the SiC source gas is sprayed intensively onto the center of the growth surface of the SiC single crystal. Also proposed is a method of controlling the shape of the SiC single crystal by optimizing the structure of the components around the SiC single crystal, surrounding the growth surface with a heat insulating material, and adjusting the temperature distribution on the growth surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-132088 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even if the variation in the growth distribution of SiC single crystals is slight, the height difference on the growth surface will cumulatively increase over time if the SiC single crystal is grown for a long period of time. This problem is difficult to solve by methods such as controlling the flow of gas blown onto the growth surface of the SiC single crystal or adjusting the temperature distribution on the growth surface by optimizing the structure of the components surrounding the SiC single crystal, and it is an obstacle to growing long SiC single crystals.

[0007] An object of the present disclosure is to provide a method and apparatus for producing a SiC single crystal that can improve the shape of the growth surface of the SiC single crystal. [Means for solving the problem]

[0008] A first aspect of the present disclosure is a method for producing a SiC single crystal by a gas supply method in which a SiC source gas (20) is supplied to grow a SiC single crystal (3) on a seed crystal (2), the method comprising: placing the seed crystal (2) on a pedestal (13) disposed in a hollow heating vessel (12) that forms a growth space for the SiC single crystal; introducing the raw material gas into the heating vessel through a first gas inlet (7) disposed below the seed crystal; heating the heating vessel to 2000°C or higher to thermally decompose the source gas and supplying the decomposed source gas to the seed crystal to grow the SiC single crystal; The method includes at least one of: providing a second gas inlet (8) having a gas outlet (8a) that protrudes closer to the base than the first gas inlet; introducing a carrier gas (21) that also functions as an etching gas from the first gas inlet while heating the heating vessel to 2000°C or higher; and spraying an etching gas (23) from the second gas inlet against the growth surface of the silicon carbide single crystal to perform local etching that reduces differences in elevation on the growth surface.

[0009] In this way, the etching gas is sprayed onto the growth surface of the SiC single crystal, allowing the growth surface of the SiC single crystal to be locally etched. This allows the protrusion amount of the growth surface of the SiC single crystal to be controlled, making the protrusion amount small and preferably controlling the growth surface to be a flat surface. This makes it possible to improve the shape of the growth surface of the SiC single crystal.

[0010] A second aspect of the present disclosure is a SiC single crystal manufacturing apparatus using a gas supply method in which a SiC source gas (20) is supplied to grow a SiC single crystal (3) on a seed crystal (2), the apparatus comprising: a first gas inlet (7) for supplying the raw material gas to the seed crystal from below; a hollow heating vessel (12) for thermally decomposing the supply gas and for forming a growth space for the SiC single crystal; a heat insulating material (11) arranged around the heating container; a base (13) disposed in the heating vessel and on which the seed crystal is placed; a vacuum vessel (10) that accommodates the heating vessel, the heat insulating material, and the base; a heating device (15) for heating the heating container; a gas exhaust port (9) for exhausting exhaust gas containing unreacted gas from the supply gas supplied to the seed crystal from the growth space to the outside of the vacuum vessel; The apparatus further includes a second gas inlet (8) having a gas outlet (8a) protruding further toward the pedestal than the first gas inlet, and for spraying an etching gas (23) onto the growing surface of the SiC single crystal.

[0011] In this way, the second gas inlet dedicated to introducing the etching gas is provided, enabling local etching of the growth surface of the SiC single crystal. This allows the protrusion amount of the growth surface of the SiC single crystal to be controlled, making the protrusion amount small and preferably controlling the growth surface to be a flat surface. This makes it possible to improve the shape of the growth surface of the SiC single crystal.

[0012] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of a SiC single crystal manufacturing apparatus according to a first embodiment. [Figure 2A] FIG. 2 is a diagram showing the state of the growth surface of a SiC single crystal before the introduction of etching gas. [Figure 2B] FIG. 1 shows the state of the growth surface of a SiC single crystal one hour after the introduction of etching gas. [Figure 3] FIG. 10 is a diagram showing the relationship between the H 2 flow rate and etching time and the etching amount at the center position of the growth surface of a SiC single crystal. [Figure 4] FIG. 4 is a cross-sectional view of a SiC single crystal manufacturing apparatus according to a second embodiment. [Figure 5] 10A and 10B are diagrams illustrating changes in the position of the gas outlet. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, identical or equivalent parts will be denoted by the same reference numerals.

[0015] (First embodiment) The SiC single crystal manufacturing apparatus according to this embodiment is used to grow a long SiC single crystal by a gas supply method to manufacture a SiC single crystal ingot. This SiC single crystal manufacturing apparatus realizes a method for manufacturing a SiC single crystal that can improve the shape of the growth surface.

[0016] First, a SiC single crystal manufacturing apparatus 1 according to this embodiment will be described with reference to Fig. 1. This SiC single crystal manufacturing apparatus 1 is installed with the up-down direction of the page in Fig. 1 facing the top-to-bottom direction, and supplies a SiC raw material gas to the surface of a seed crystal 2 made of a SiC single crystal substrate, causing a SiC single crystal 3 to grow on the surface of the seed crystal 2. Specifically, the SiC single crystal manufacturing apparatus 1 is equipped with a gas supply unit 4, various supply gas sources 5, an etching gas source 6, first and second gas inlets 7 and 8, a gas outlet 9, a vacuum vessel 10, a heat insulating material 11, a heating vessel 12, a pedestal 13, a rotary pulling mechanism 14, and a heating device 15.

[0017] The gas supply unit 4 is provided below the SiC single crystal manufacturing apparatus 1, and introduces a raw material gas 20 containing various gases that serve as SiC raw materials from various supply gas sources 5, a carrier gas 21, and a dopant gas 22 into the SiC single crystal manufacturing apparatus 1. In addition, the gas supply unit 4 also introduces an etching gas 23 into the SiC single crystal manufacturing apparatus 1.

[0018] The gas supply unit 4 includes a source gas supply unit 4a that supplies a source gas 20, a carrier gas supply unit 4b that supplies a carrier gas 21, a dopant gas supply unit 4c that supplies a dopant gas 22, and an etching gas supply unit 4d that supplies an etching gas 23. Although not shown, each of these gas supply units 4a to 4d is configured with components that form a supply path. The source gas supply unit 4a introduces source gas 20 from a source gas source 5a (described later) into the SiC single crystal manufacturing apparatus 1. The carrier gas supply unit 4b introduces carrier gas 21 from a carrier gas source 5b (described later) into the SiC single crystal manufacturing apparatus 1. The dopant gas supply unit 4c introduces dopant gas 22 from a dopant gas source 5c (described later) into the SiC single crystal manufacturing apparatus 1. The etching gas supply unit 4d introduces etching gas 23 from an etching gas source 6 (described later) into the SiC single crystal manufacturing apparatus 1.

[0019] The various supply gas sources 5 supply gases including a SiC raw material gas into the SiC single crystal manufacturing apparatus 1 from below the seed crystal 2 placed on the pedestal 13. In this embodiment, the various supply gas sources 5 are configured to include a raw material gas source 5a, a carrier gas source 5b, and a dopant gas source 5c. A first gas inlet 7 is provided at the bottom 10a of a vacuum vessel 10 (described later), and the various gases supplied from the various supply gas sources 5 are supplied to the first gas inlet 7 through the respective gas supply units 4a to 4c, and are introduced from the first gas inlet 7 into the SiC single crystal manufacturing apparatus 1. The first gas inlet 7 is, for example, cylindrical, and its central axis is aligned with the center of the seed crystal 2.

[0020] The source gas source 5a supplies a source gas 20 containing a SiC source gas containing Si and C, for example, a mixed gas of a silane-based gas such as silane and a hydrocarbon-based gas such as propane. The carrier gas source 5b supplies a carrier gas 21 such as an inert gas such as Ar or He, or H2 that also functions as an etching gas. The dopant gas source 5c supplies a dopant gas 22 such as N2. Although not shown, each of these gas sources 5a to 5c is equipped with a heating device that controls the temperature and a flow rate control device that controls the flow rate of the respective supply gas, and the temperature and flow rate of each supply gas can be controlled according to the growth status of the SiC single crystal 3.

[0021] Although N2, which is an n-type dopant, is used as the dopant gas 22, other n-type dopants may be used, or a p-type dopant such as TMA (trimethylaluminum) may be introduced.

[0022] The etching gas source 6 supplies an etching gas 23 such as H2 that etches the growth surface of the SiC single crystal 3. In this embodiment, the etching gas source 6 introduces the etching gas 23 into the SiC single crystal manufacturing apparatus 1 from below the SiC single crystal 3, and guides it to the outer edge of the SiC single crystal 3, where it is sprayed. A second gas inlet 8 is disposed at a position different from the first gas inlet 7 on the bottom 10a of the vacuum chamber 10, which will be described later, and the second gas inlet 8 protrudes above the first gas inlet 7, that is, toward the pedestal 13. This brings the gas outlet 8a of the second gas inlet 8 closer to the SiC single crystal 3, making it easier to spray the etching gas 23 onto the growth surface of the SiC single crystal 3.

[0023] In this embodiment, second gas inlet 8 is cylindrical and extends linearly in the vertical direction, and etching gas 23 is blown out from below SiC single crystal 3 through its interior. The central axis of second gas inlet 8 is offset from the central axis of first gas inlet 7, and second gas inlet 8 is disposed on the outer periphery of first gas inlet 7. This results in a structure in which the flow of various gases supplied from first gas inlet 7 is less likely to be obstructed by second gas inlet 8. Second gas inlet 8 is disposed in a position corresponding to the outer edge of pedestal 13, that is, at least a portion of second gas inlet 8 overlaps with the outer edge of pedestal 13 when viewed from above, making it possible to locally blow etching gas onto the outer edge of the growth surface of SiC single crystal 3.

[0024] The gas outlet 9 discharges unreacted gas from the source gas 20 after being supplied to the seed crystal 2, the carrier gas 21, the dopant gas 22, and the like, as exhaust gas to the outside of the SiC single crystal manufacturing apparatus 1.

[0025] The vacuum vessel 10 is made of quartz glass or the like and has a hollow cylindrical shape, i.e., a cylindrical shape in this embodiment, allowing for the introduction and discharge of the source gas 20, carrier gas 21, and dopant gas 22. The vacuum vessel 10 also accommodates other components of the SiC single crystal manufacturing apparatus 1 and is configured such that the pressure in the interior space can be reduced by evacuation. As described above, the bottom 10a of the vacuum vessel 10 is provided with the first gas inlet 7 and the second gas inlet 8. The source gas 20, carrier gas 21, and dopant gas 22 are introduced into the SiC single crystal manufacturing apparatus 1 through the first gas inlet 7, and the etching gas 23 is introduced through the second gas inlet 8. A through-hole 10b is formed in the upper portion of the vacuum vessel 10, specifically in an upper position of the sidewall, and a gas outlet 9 is fitted into the through-hole 10b.

[0026] The heat insulating material 11 has a hollow cylindrical shape, which in this embodiment is a cylindrical shape, and is arranged coaxially with the vacuum vessel 10. The heat insulating material 11 has a cylindrical shape with a smaller diameter than the vacuum vessel 10 and is arranged inside the vacuum vessel 10 to suppress heat transfer from the space inside the heat insulating material 11 to the vacuum vessel 10. The heat insulating material 11 is made of, for example, graphite, but the surface may be coated with a high-melting-point metal carbide such as TaC (tantalum carbide) or NbC (niobium carbide) to make it less susceptible to thermal etching. A through-hole 11a is also formed in the upper part of the heat insulating material 11, specifically at a position corresponding to the through-hole 10b of the vacuum vessel 10, and the gas exhaust port 9 is fitted into this through-hole 11a.

[0027] The heating vessel 12 is a crucible serving as a reaction vessel that forms a growth space for the SiC single crystal 3. It has a hollow cylindrical shape, i.e., a cylindrical shape in this embodiment. The hollow portion of the heating vessel 12 forms a growth space for growing the SiC single crystal 3 on the surface of the seed crystal 2. The heating vessel 12 is made of, for example, graphite, but its surface may be coated with a high-melting-point metal carbide such as TaC or NbC to make it less susceptible to thermal etching. The heating vessel 12 is disposed to surround the pedestal 13. Exhaust gases, such as unreacted gases in the source gas 20, are guided toward the gas outlet 9 through spaces between the inner peripheral surface of the heating vessel 12 and the outer peripheral surfaces of the seed crystal 2 and the pedestal 13. The heating vessel 12 decomposes the SiC source gas in the source gas 20 from the source gas supply unit 4a before directing the source gas 20 to the seed crystal 2. In addition, a through hole 12a is also formed in the upper part of the heating container 12, specifically at a position corresponding to the through hole 10b of the vacuum container 10 and the through hole 11a of the insulating material 11, and a gas exhaust port 9 is fitted into this through hole 12a.

[0028] The pedestal 13 is a member for mounting the seed crystal 2. The pedestal 13 has a circular surface on which the disk-shaped seed crystal 2 is mounted, for example, and the central axis of the pedestal 13 is arranged coaxially with the central axis of the heating vessel 12 and the central axis of a shaft 14a of a rotary pulling mechanism 14 (described later). The pedestal 13 is made of, for example, graphite, but the surface may be coated with a high-melting-point metal carbide such as TaC or NbC to make it less susceptible to thermal etching. The seed crystal 2 is attached to one surface of the pedestal 13 facing the first gas inlet 7, and a SiC single crystal 3 is grown on the surface of the seed crystal 2. The pedestal 13 is connected to the shaft 14a on the surface opposite to the surface on which the seed crystal 2 is mounted. The pedestal 13 is rotated as the shaft 14a rotates, and can be pulled upward in the plane of the drawing as the shaft 14a is pulled up.

[0029] The rotary pull-up mechanism 14 rotates and pulls up the pedestal 13 via a shaft 14a made of a pipe or the like. In this embodiment, the shaft 14a is configured as a straight line extending vertically, with one end connected to the surface of the pedestal 13 opposite the surface to which the seed crystal 2 is attached, and the other end connected to the main body of the rotary pull-up mechanism 14. This shaft 14a is also made of, for example, graphite, but its surface may be coated with a high-melting-point metal carbide such as TaC or NbC to make it less susceptible to thermal etching. This configuration enables the rotation and pulling of the pedestal 13, the seed crystal 2, and the SiC single crystal 3, and allows the growth surface of the SiC single crystal 3 to have a desired temperature distribution, while also allowing the temperature of the growth surface to be adjusted to a temperature suitable for growth as the SiC single crystal 3 grows.

[0030] The heating device 15 is configured with a heating coil, such as an induction heating coil or a direct heating coil, and is arranged to surround the periphery of the vacuum vessel 10. In this embodiment, the heating device 15 is configured with an induction heating coil. Here, the heating device 15 is configured as a single component, but it may be divided into multiple components. In this case, it is preferable that the heating device 15 is configured so that the temperature of each target location can be independently controlled. For example, the heating device 15 can be disposed in a position corresponding to the position below the heating vessel 12 and in a position corresponding to the pedestal 13. In this case, the heating device 15 can independently and optimally control the temperature below the heating vessel 12 to heat and decompose the SiC source gas, and independently control the temperatures around the pedestal 13, the seed crystal 2, and the SiC single crystal 3 to temperatures suitable for crystal growth.

[0031] Thus configured is the SiC single crystal manufacturing apparatus 1. Next, a method for manufacturing a SiC single crystal 3 using the SiC single crystal manufacturing apparatus 1 according to this embodiment will be described.

[0032] First, the seed crystal 2 is attached to one surface of the pedestal 13. The seed crystal 2 is an off-substrate whose surface opposite the pedestal 13, i.e., the growth surface of the SiC single crystal 3, has a predetermined off-angle, such as 4° or 8°, relative to the (000-1) C-plane. The pedestal 13 and the seed crystal 2 are then placed in the heating vessel 12. The heating device 15 is then controlled to provide a desired temperature distribution. That is, the SiC source gas contained in the source gas 20 is thermally decomposed and supplied to the surface of the seed crystal 2, and the SiC source gas is recrystallized on the surface of the seed crystal 2, while the temperature distribution within the heating vessel 12 is such that the sublimation rate is higher than the recrystallization rate. This allows the temperature of the bottom of the heating vessel 12 to be elevated to 2000°C or higher, while the temperature of the surface of the seed crystal 2 is lower than that of the bottom of the heating vessel 12 and is suitable for recrystallization of the SiC single crystal 3. For example, the inside of the heating vessel 12 is set to an environment of 2000°C or higher, preferably 2500°C or higher in at least a portion thereof. For example, the temperature of the bottom of the heating vessel 12 is set to about 2800±100°C, and the temperature of the surface of the seed crystal is set to about 2500±100°C.

[0033] Furthermore, while the vacuum vessel 10 is maintained at a desired pressure, a source gas 20 containing a SiC source gas is introduced through the source gas supply unit 4a. As a result, the source gas 20 is supplied to the seed crystal 2 as shown by the arrows in FIG. 1 , and a SiC single crystal 3 is grown on the surface of the seed crystal 2 based on this gas supply.

[0034] Furthermore, carrier gas 21 is introduced through carrier gas supply unit 4b, and dopant gas 22 is introduced through dopant gas supply unit 4c. As a result, carrier gas 21 and dopant gas 22 are caused to flow inside heating vessel 12, and SiC single crystal 3 is doped with N contained in dopant gas 22.

[0035] Then, the rotary pulling mechanism 14 rotates the pedestal 13, the seed crystal 2, and the SiC single crystal 3 via the shaft 14a while pulling them up in accordance with the growth rate of the SiC single crystal 3. This keeps the height of the growth surface of the SiC single crystal 3 almost constant, and enables the temperature distribution of the growth surface to be controlled with good controllability.

[0036] As described above, even if there is only a slight variation in the growth distribution of the SiC single crystal 3, the height difference on the growth surface will cumulatively increase over time if the SiC single crystal 3 is grown for a long period of time, hindering the lengthening of the SiC single crystal 3. For this reason, etching gas 23 is introduced while maintaining a temperature of 2000°C or higher, for example, the temperature during crystal growth, or carrier gas 21 containing H is introduced to suppress the height difference on the growth surface of the SiC single crystal 3. In this case, the following two methods can be used to introduce the etching gas 23.

[0037] (1) During the growth of the SiC single crystal 3, the supply of various gases, such as the source gas 20, from the first gas inlet 7 is stopped to stop the growth of the SiC single crystal 3, and only the etching gas 23 is introduced. At this time, a carrier gas 21 containing H may be used from the first gas inlet 7, simultaneously with or instead of the etching gas 23, to etch the center of the SiC single crystal 3. (2) During the growth of the SiC single crystal 3, the supply of various gases, such as the source gas 20, from the first gas inlet 7 is continued to grow the SiC single crystal 3, while the etching gas 23 is introduced. Either of these methods (1) and (2) can prevent the SiC single crystal 3 from becoming excessively convex during growth. Furthermore, a combination of (1) and (2) may be used.

[0038] The introduction of the etching gas 23 or the carrier gas 21 containing H in the method (1) may be performed at any timing during the growth of the SiC single crystal 3, or may be performed at regular intervals. The regular intervals may be at regular time intervals, or may be at intervals determined in accordance with the growth amount of the SiC single crystal 3, for example, such that the time interval for introducing the etching gas 23 becomes shorter as the growth amount increases.

[0039] For example, the SiC raw material in the unreacted gas may adhere to and clog the gas outlet 9, but it is advisable to measure the time required for clogging in advance by experiment or the like, and introduce the etching gas 23 or the carrier gas 21 containing H at a timing shorter than the time required for clogging. In this way, clogging of the gas outlet 9 due to adhesion of the SiC raw material can be suppressed, and long growth of the SiC single crystal 3 can be further facilitated.

[0040] Furthermore, as the SiC single crystal 3 grows, three-dimensional nuclei may flow into the growth surface, and polycrystallization may occur from the three-dimensional nuclei. Therefore, even if three-dimensional nuclei flow in, it is preferable to introduce the etching gas 23 or the carrier gas 21 containing H at a time interval shorter than the time required from the flow of the three-dimensional nuclei to polycrystallization so that the three-dimensional nuclei can be removed before polycrystallization occurs.

[0041] If both the blocking of gas outlet 9 and the three-dimensional nucleus inflow are taken into consideration, etching gas 23 or carrier gas 21 containing H may be introduced before the shorter of the time required before gas outlet 9 is blocked or the time required from the three-dimensional nucleus inflow to polycrystallization has elapsed. Furthermore, if a device capable of monitoring the growth surface of SiC single crystal 3 is provided, etching gas 23 or carrier gas 21 containing H may be introduced at the timing when the occurrence of three-dimensional nucleus inflow is detected.

[0042] On the other hand, when introducing the etching gas 23 in method (2), the timing of introduction can be set depending on the gas supply conditions from the first gas inlet 7 and the temperature distribution on the growth surface of the SiC single crystal 3. In this case, it is preferable to make the temperature of the growth surface of the SiC single crystal 3 higher than before the introduction of the etching gas 23. For example, the temperature of the growth surface of the SiC single crystal 3 is set to be about 50 to 100°C higher when the etching gas 23 is introduced than before the introduction of the etching gas 23. This allows etching to dominate, making it possible to prevent the SiC single crystal 3 from becoming excessively convex during growth.

[0043] For example, as shown in FIG. 2A, when a SiC single crystal 3 was produced that was large enough to produce a 6-inch wafer, the protrusion of the convex shape before the introduction of etching gas 23, i.e., the protrusion of the crystal center relative to the crystal periphery, was 10 mm. In this case, the growth of SiC single crystal 3 was stopped, and then the introduction of etching gas 23 was started. The protrusion of the convex shape was checked one hour after the start of the introduction of etching gas 23, and as shown in FIG. 2B, the protrusion had decreased to 5 mm. Note that FIG. 2B is an example of the case where only carrier gas 21 containing H2 was used, so the center of SiC single crystal 3 was etched, but if etching gas 23 were used, the periphery of SiC single crystal 3 would be locally etched.

[0044] In this way, by introducing the etching gas 23 or the carrier gas 21 containing H, it is possible to suppress the difference in height of the growth surface of the SiC single crystal 3. Furthermore, if the growth is completed, by maintaining the heating vessel 12 at 2000°C or higher and flattening the growth surface of the SiC single crystal 3 before cooling the SiC single crystal 3, it is possible to suppress crystal cracking due to stress occurring when the SiC single crystal 3 is cooled.

[0045] The etching amount and etching time of the SiC single crystal 3 can be set according to the desired height difference of the growth surface. Specifically, it has been confirmed that the etching amount at the center position of the growth surface of the SiC single crystal 3 is proportional to the flow rate of the etching gas 23 or the carrier gas 21 containing H2 and the etching time. For example, when H2 is introduced as the etching gas 23 through a simulation, the relationship between the flow rate of H2 and the etching rate at the center position of the growth surface of the SiC single crystal is shown in Figure 3. In this calculation, the surface temperature of the seed crystal 2 is set to 2500°C.

[0046] The etching rate depends on the gas flow rate near the crystal. For example, by controlling the gas flow rate [m / s] near the SiC single crystal 3 to 2 m / s, the etching rate of the SiC crystal can be controlled to 5 mm / h, and in 1 hour, it is possible to etch 5 mm from the center of the SiC single crystal 3. Therefore, the introduction time of the etching gas 23 or the carrier gas 21 containing H2 and the etching time are set based on the expected protrusion amount of the convex shape when the etching gas 23 or the carrier gas 21 containing H2 is introduced and the etching amount at the center position of the growth surface of the SiC single crystal 3 so that the protrusion amount after etching is the desired amount. This makes it possible to control the protrusion amount after etching to the desired amount, for example, to 5 mm or less even if the center position of the growth surface of the SiC single crystal 3 protrudes slightly from the outer edge, preferably so that the growth surface is flat.

[0047] As described above, the manufacturing apparatus for SiC single crystal 3 according to this embodiment is provided with second gas inlet 8 that is dedicated to introducing etching gas 23, enabling local etching of the growth surface of SiC single crystal 3. This allows the protrusion amount of the growth surface of SiC single crystal 3 to be controlled and reduced, preferably so that the growth surface is flat. This makes it possible to improve the shape of the growth surface of SiC single crystal 3. As a result, it is possible to achieve a long SiC single crystal 3.

[0048] (Second embodiment) The second embodiment will be described. This embodiment is different from the first embodiment in that the configuration of the second gas inlet 8 is changed, but the rest is the same as the first embodiment, so only the differences from the first embodiment will be described.

[0049] As shown in FIG. 4 , in this embodiment, the second gas inlet 8 is not linear but includes a bent portion 8b bent midway in the vertical direction, and the gas outlet 8a of the second gas inlet 8 is eccentric with respect to a base 8c that is located on the bottom 10a side of the vacuum vessel 10. In other words, the second gas inlet 8 is configured such that the gas outlet 8a and the base 8c, which extend in the vertical direction, are connected by the bent portion 8b that is inclined with respect to the vertical direction. A rotation mechanism 30 is connected to the base 8c, and the base 8c can be rotated by the rotation mechanism 30. Specifically, the gas outlet 8a, the bent portion 8b, and the base 8c are tubular with a circular cross section, and the gas outlet 8a and the base 8c extend in the vertical direction, with the bent portion 8b inclined with respect to the vertical direction. The rotation mechanism 30 rotates the base 8c around a line extending in the vertical direction as a rotation axis, thereby rotating the bent portion 8b and the gas outlet 8a as well. Since the bent portion 8b is tilted in the vertical direction, the gas outlet 8a is made eccentric with respect to the base portion 8c. Therefore, when the base portion 8c is rotated as shown in FIG. 5, the position of the gas outlet 8a changes so as to revolve around the base portion 8c.

[0050] Therefore, by changing the position of gas outlet 8a, etching gas 23 can be sprayed locally at a desired position on the growth surface of SiC single crystal 3. This allows etching gas 23 to be sprayed only at a location that protrudes more than other locations, making it possible to further flatten the growth surface of SiC single crystal 3. Even if gas outlet 8a is located at a location displaced from the center of the growth surface of SiC single crystal 3, SiC single crystal 3 is rotated by rotary pull-up mechanism 14, so that etching gas 23 is sprayed over the entire area at the same distance from the center of the growth surface. Because the distribution of elevation differences within the growth surface is determined by the distance from the center of the growth surface, etching gas 23 can be sprayed in the same manner over the entire area at the same distance, resulting in uniform etching.

[0051] (Other embodiments) Although the present disclosure has been described based on the above-described embodiment, it is not limited to the embodiment and encompasses various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0052] That is, the elements constituting the above-described embodiments are not necessarily essential unless they are specifically stated as essential or are clearly considered essential in principle. Furthermore, when numerical values ​​such as the number, value, amount, and range of components are mentioned, the present disclosure is not limited to the specific number unless they are specifically stated as essential or are clearly limited to a specific number in principle. Similarly, when the shape, direction, positional relationship, etc. of components are mentioned, the present disclosure is not limited to the shape, direction, positional relationship, etc., unless they are specifically stated as essential or are clearly limited to a specific shape, direction, positional relationship, etc. in principle.

[0053] For example, in each of the above embodiments, the second gas inlet 8 is configured as a circular tube with a circular cross section, but it does not have to be annular. Also, while only one second gas inlet 8 is provided, two or more may be provided. In such cases, it is preferable that they are arranged at equal intervals in the circumferential direction around the first gas inlet 7. However, when the gas outlets 8a of the second gas inlet 8 are configured to be movable to the center position of the growth surface of the SiC single crystal 3, as in the second embodiment, the gas outlets 8a may come into contact with each other, so it is preferable to control the rotation mechanism 30 to prevent them from coming into contact. Alternatively, the eccentricity of the gas outlets 8a with respect to the base 8c may be adjusted to prevent the gas outlets 8a from coming into contact with each other.

[0054] In the first embodiment, the source gas 20, the carrier gas 21, and the dopant gas 22 are introduced through the first gas inlet 7, but they may be introduced through different inlets. The introduction of the carrier gas 21 is optional, and only the source gas 20 and the dopant gas 22 may be introduced.

[0055] Furthermore, in the above-described first embodiment, the SiC single crystal manufacturing apparatus 1 has been described as being of an upflow type, in which the source gas 20 is supplied to the growth surface of the SiC single crystal 3, passes by the outer peripheral surface of the SiC single crystal 3 and beside the pedestal 13, and is then discharged further upward. However, the present invention is not limited to this, and may be of a return flow type, in which the source gas 20 is supplied to the growth surface of the SiC single crystal 3, and then returned in the same direction as the supply. Alternatively, the present invention may be of a side flow type, in which the source gas 20 is supplied to the growth surface of the SiC single crystal 3, and then is discharged in the outer peripheral direction of the heating vessel 12.

[0056] (Aspects of the present disclosure) The present disclosure described above can be understood from the following viewpoints, for example. [First viewpoint] A method for producing a silicon carbide single crystal by a gas supply method in which a silicon carbide source gas (20) is supplied to grow a silicon carbide single crystal (3) on a seed crystal (2), the method comprising: placing the seed crystal (2) on a pedestal (13) disposed in a hollow heating vessel (12) that forms a growth space for the silicon carbide single crystal; introducing the raw material gas into the heating vessel through a first gas inlet (7) disposed below the seed crystal; heating the heating vessel to 2000°C or higher to thermally decompose the source gas and supplying the decomposed source gas to the seed crystal to grow the silicon carbide single crystal; a second gas inlet (8) having a gas outlet (8a) protruding closer to the base than the first gas inlet, and the method for producing a silicon carbide single crystal includes at least one of: introducing a carrier gas (21) that also functions as an etching gas from the first gas inlet while heating the heating vessel to 2000°C or higher; and spraying an etching gas (23) from the second gas inlet against a growth surface of the silicon carbide single crystal to perform localized etching that reduces differences in elevation on the growth surface. [Second perspective] The method for producing a silicon carbide single crystal according to a first aspect, wherein, in the etching, H 2 is locally sprayed onto the growth surface as the etching gas. [Third Perspective] The method for producing a silicon carbide single crystal according to the first or second aspect, wherein, in the etching, the introduction of the etching gas is performed while the introduction of the source gas is stopped. [Fourth viewpoint] The method for producing a silicon carbide single crystal according to any one of the first to third aspects, wherein, in performing the etching, the introduction of the etching gas is performed while continuing the introduction of the source gas in the introduction of the source gas. [Fifth viewpoint] The method for producing a silicon carbide single crystal according to the third or fourth aspect, wherein the etching includes periodically introducing the etching gas. [Sixth viewpoint] A silicon carbide single crystal manufacturing apparatus using a gas supply method in which a silicon carbide source gas (20) is supplied to grow a silicon carbide single crystal (3) on a seed crystal (2), the apparatus comprising: a first gas inlet (7) for supplying the raw material gas to the seed crystal from below; a hollow heating vessel (12) for thermally decomposing the source gas and for forming a growth space for the silicon carbide single crystal; a heat insulating material (11) arranged around the heating container; a base (13) disposed in the heating vessel and on which the seed crystal is placed; a vacuum vessel (10) that accommodates the heating vessel, the heat insulating material, and the base; a heating device (15) for heating the heating container; a gas exhaust port (9) for exhausting exhaust gas containing unreacted gas of the source gas supplied to the seed crystal from the growth space to the outside of the vacuum vessel; a second gas inlet (8) having a gas outlet (8a) that protrudes further toward the base than the first gas inlet, and that sprays an etching gas (23) onto the growth surface of the silicon carbide single crystal; [Seventh viewpoint] the pedestal has a circular surface on which the seed crystal is placed, The silicon carbide single crystal manufacturing apparatus according to a sixth aspect, wherein the gas outlet of the second gas inlet is located at a position corresponding to an outer edge of one surface of the pedestal, and the etching gas is sprayed onto the outer edge portion of the growth surface. [Eighth viewpoint] the second gas inlet is disposed at a location on the bottom of the vacuum vessel different from the first gas inlet, and has a base (8c) extending in a vertical direction from the bottom, and a bent portion (8b) connecting the base and the gas outlet and inclining the bent portion with respect to the vertical direction to make the gas outlet eccentric with respect to the base, The silicon carbide single crystal manufacturing apparatus according to a sixth aspect further comprises a rotation device (30) that rotates the base to change the position of the gas outlet. [Explanation of symbols]

[0057] REFERENCE SIGNS LIST 1...SiC single crystal manufacturing apparatus, 2...seed crystal, 3...SiC single crystal, 4...gas supply section, 4a...raw material gas supply section, 4b...carrier gas supply section, 4c...dopant gas supply section, 4d...etching gas supply section, 5...various supply gas sources, 5a...raw material gas source, 5b...carrier gas source, 5c...dopant gas source, 6...etching gas source, 7...first gas inlet, 8...second gas inlet, 8a...gas outlet, 8b...bent section, 8c...base, 9...gas outlet, 10...vacuum vessel, 10a...bottom, 11...insulating material, 12...heating vessel, 13...pedestal, 14...rotation lifting mechanism, 15...heating device, 20...raw material gas, 21...carrier gas, 22...dopant gas, 23...etching gas, 30...rotation mechanism

Claims

1. A method for producing a silicon carbide single crystal by a gas supply method in which a silicon carbide source gas (20) is supplied to grow a silicon carbide single crystal (3) on a seed crystal (2), the method comprising: placing the seed crystal (2) on a pedestal (13) disposed in a hollow heating vessel (12) that constitutes a growth space for the silicon carbide single crystal; introducing the raw material gas into the heating vessel through a first gas inlet (7) disposed below the seed crystal; heating the heating vessel to 2000°C or higher to thermally decompose the source gas and supplying the decomposed source gas to the seed crystal to grow the silicon carbide single crystal; a second gas inlet (8) having a gas outlet (8a) protruding closer to the base than the first gas inlet, and the method for producing a silicon carbide single crystal includes at least one of: introducing a carrier gas (21) that also functions as an etching gas from the first gas inlet while heating the heating vessel to 2000°C or higher; and spraying an etching gas (23) from the second gas inlet against a growth surface of the silicon carbide single crystal to perform localized etching that reduces a difference in elevation of the growth surface.

2. In the etching, H is used as the etching gas. ２ The method for producing a silicon carbide single crystal according to claim 1 , wherein the growth surface is locally sprayed with a gas containing methyl methacrylate.

3. 3. The method for producing a silicon carbide single crystal according to claim 1, wherein, in the etching, the etching gas is introduced while the introduction of the source gas is stopped.

4. 3. The method for producing a silicon carbide single crystal according to claim 1, wherein, in the etching, the etching gas is introduced while the introduction of the source gas is continued in the introduction of the source gas.

5. 5. The method for producing a silicon carbide single crystal according to claim 4, wherein the etching gas is introduced periodically during the etching.

6. A silicon carbide single crystal manufacturing apparatus using a gas supply method in which a silicon carbide source gas (20) is supplied to grow a silicon carbide single crystal (3) on a seed crystal (2), comprising: a first gas inlet (7) for supplying the raw material gas to the seed crystal from below; a hollow heating vessel (12) for thermally decomposing the source gas and for forming a growth space for the silicon carbide single crystal; a heat insulating material (11) arranged around the heating container; a base (13) disposed in the heating vessel and on which the seed crystal is disposed; a vacuum vessel (10) in which the heating vessel, the heat insulating material, and the base are housed; A heating device (15) for heating the heating container; a gas exhaust port (9) for exhausting exhaust gas containing unreacted gas of the source gas supplied to the seed crystal from the growth space to the outside of the vacuum vessel; a second gas inlet (8) having a gas outlet (8a) protruding further toward the base than the first gas inlet, and for spraying an etching gas (23) onto the growth surface of the silicon carbide single crystal.

7. the pedestal has a circular surface on which the seed crystal is placed, 7. The silicon carbide single crystal manufacturing apparatus according to claim 6, wherein the gas outlet of the second gas inlet is located at a position corresponding to an outer edge of one surface of the pedestal, and the etching gas is sprayed onto the outer edge portion of the growth surface.

8. the second gas inlet is disposed at a location on the bottom of the vacuum vessel different from that of the first gas inlet, and has a base (8c) extending in a vertical direction from the bottom, and a bent portion (8b) connecting the base and the gas outlet and inclining the bent portion with respect to the vertical direction to make the gas outlet eccentric with respect to the base, 7. The silicon carbide single crystal manufacturing apparatus according to claim 6, further comprising a rotation device (30) that rotates the base to change the position of the gas outlet.

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