Single crystal production method, single crystal production apparatus, and crucible

Abstract

The present application is to solve the technical problem of reducing the generation of foreign crystals in a solution. The solution to the technical problem of the present application is to provide a single crystal manufacturing method including: a first heating process of heating a solution in such a manner that the temperature of the solution in contact with the side surface of a crucible is higher than the temperature of the solution in contact with the bottom surface of the crucible; and a second heating process of heating the solution in such a manner that the temperature of the solution in contact with the bottom surface of the crucible is higher than the temperature of the solution in contact with the side surface of the crucible, the first heating process and the second heating process being capable of being switched alternately.

Description

Technical Field

[0001] This invention relates to a technology for manufacturing single crystals formed from silicon carbide, a single crystal manufacturing apparatus and a crucible, and to an effective technology applicable, for example, to single crystal manufacturing technology using a solution method. Background Technology

[0002] Japanese Patent No. 5746362 (Patent Document 1) discloses a technique for controlling the carbon supersaturation of the crystal surface by switching the temperature gradient in the solution during the growth of a single crystal.

[0003] Japanese Patent Application Publication No. 2018-184324 (Patent Document 2) discloses a technique for heating the bottom surface of a crucible for an extended period of time.

[0004] Japanese Patent Application Publication No. 2-217388 (Patent Document 3) describes a technique for heating a crucible using a side heater and a bottom heater.

[0005] Japanese Patent Application Publication No. 2012-136388 (Patent Document 4) discloses a technology concerning an induction heating device having an upper coil portion disposed around an upper storage chamber and a lower coil portion disposed around a lower storage chamber.

[0006] Japanese Patent Application Publication No. 7-25694 (Patent Document 5) discloses a technology concerning a crucible having a protrusion extending from the bottom surface.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 5746362

[0010] Patent Document 2: Japanese Patent Application Publication No. 2018-184324

[0011] Patent Document 3: Japanese Patent Application Publication No. 2-217388

[0012] Patent Document 4: Japanese Patent Application Publication No. 2012-136388

[0013] Patent Document 5: Japanese Patent Application Publication No. 7-25694 Summary of the Invention

[0014] The technical problem that the invention aims to solve

[0015] For example, an inverter circuit can be used as a circuit to control the electric motors included in automobiles or home appliances. Power semiconductor devices, such as power MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) and IGBTs (Insulated-Gate Bipolar Transistors), can be used in this inverter circuit.

[0016] For such power semiconductor devices, in addition to requirements such as high withstand voltage, low on-state resistance and low switching losses are also required. Among them, the mainstream of existing power semiconductor devices is the field-effect transistor formed on a semiconductor substrate with silicon as the main component, but this power semiconductor device has approached the limit of theoretical performance.

[0017] In this regard, semiconductor devices including field-effect transistors formed on semiconductor substrates with a bandgap larger than that of silicon (hereinafter referred to as wide bandgap power semiconductor devices) have attracted attention.

[0018] The reason is that a large band gap means high insulation breakdown strength, thus making it easier to achieve high withstand voltage.

[0019] Furthermore, when the semiconductor material itself has high dielectric breakdown strength, the withstand voltage can be ensured even if the drift layer that maintains the withstand voltage is thinned. Therefore, for example, by thinning the drift layer and increasing the impurity concentration, the on-state resistance of the power semiconductor device can be reduced.

[0020] In other words, wide-bandgap power semiconductor devices offer a satisfactory balance between improved withstand voltage and reduced on-state resistance, which are trade-offs. Therefore, wide-bandgap power semiconductor devices are highly anticipated as semiconductor devices capable of achieving high performance.

[0021] Semiconductor materials with a larger band gap than silicon include silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and diamond. The following discussion focuses on silicon carbide.

[0022] Silicon carbide single crystals (hereinafter referred to as silicon carbide single crystals) can be manufactured, for example, by using a solution method. The solution method is a method in which a silicon carbide single crystal is manufactured by bringing a seed crystal mounted on the front end of an axle into contact with a solution containing carbon and silicon contained in a crucible, growing the silicon carbide single crystal on the seed crystal, and pulling the axle.

[0023] In the solution method, minimizing the formation of impurities within the solution contained in the crucible is crucial. This is because impurities are aggregates of granular silicon carbide, for example, approximately 1 mm to 3 mm in size. Once these impurities adhere to the seed crystal, the crystallization growing on the seed crystal will not form a single crystal. Therefore, in the solution method, from the perspective of growing silicon carbide single crystals on the seed crystal, it is desirable to reduce the formation of impurities within the solution.

[0024] Technical solutions for solving technical problems

[0025] One embodiment of the single crystal manufacturing method includes: (a) a step of bringing the lower surface of the seed crystal into contact with a solution containing carbon and silicon contained in a crucible by moving the seed crystal at its front end axially downward; and (b) a step of growing a single crystal formed of silicon carbide on the lower surface of the seed crystal.

[0026] The single crystal manufacturing method includes: (c1) a first heating step of heating the solution in such a way that the temperature of the solution in contact with the side of the crucible is higher than the temperature of the solution in contact with the bottom of the crucible; and (c2) a second heating step of heating the solution in such a way that the temperature of the solution in contact with the bottom of the crucible is higher than the temperature of the solution in contact with the side of the crucible, wherein the first heating step and the second heating step can be switched alternately.

[0027] One embodiment of the single crystal manufacturing apparatus allows for the placement of a crucible containing a solution of carbon and silicon within a container. Furthermore, the single crystal manufacturing apparatus includes: a base disposed inside the container; a first heating section for heating the crucible disposed on the base; a second heating section for heating the base; and a control section for controlling the electrical power supplied to the first heating section and the electrical power supplied to the second heating section.

[0028] The control unit alternately switches between a first action and a second action. The first action adjusts the electrical power supplied to the first heating unit and the electrical power supplied to the second heating unit in such a way that the temperature of the solution in contact with the side of the crucible is higher than the temperature of the solution in contact with the bottom of the crucible. The second action adjusts the electrical power supplied to the first heating unit and the electrical power supplied to the second heating unit in such a way that the temperature of the solution in contact with the bottom of the crucible is higher than the temperature of the solution in contact with the side of the crucible.

[0029] One embodiment of the crucible is capable of holding a solution containing carbon and silicon. The crucible has a main body for holding the solution and a heat transfer section protruding from the bottom of the main body.

[0030] Invention Effects

[0031] One implementation method can reduce the formation of impurities in the solution. Attached Figure Description

[0032] Figure 1 This is a diagram showing the configuration of a single crystal manufacturing apparatus according to an embodiment.

[0033] Figure 2 This diagram illustrates the dimensions of the main components of both the base and the crucible.

[0034] Figure 3 This diagram is used to illustrate the operation of a single crystal manufacturing apparatus.

[0035] Figure 4 This diagram is used to illustrate the operation of a single crystal manufacturing apparatus.

[0036] Figure 5 This diagram illustrates an example of switching between the first and second actions performed using the control unit.

[0037] Figure 6 It is a graph showing the temperature distribution of the solution achieved through the first action.

[0038] Figure 7 It is a graph showing the temperature distribution of the solution achieved through the second action.

[0039] Figure 8 This is another example of switching between the first and second actions.

[0040] Figure 9 This is a diagram illustrating an example of a configuration where the bottom surface of the crucible is heated.

[0041] Figure 10 This diagram illustrates the configuration in which the bottom surface of the crucible is heated in the embodiment.

[0042] Figure 11 (a) is a schematic diagram showing the power supplied to the first coil when power is continuously supplied to the first coil, and (b) is a schematic diagram showing the power supplied to the second coil when power is continuously supplied to the second coil.

[0043] Figure 12 (a) is a schematic diagram showing the power supplied to the first coil when the power is supplied intermittently to the first coil, and (b) is a schematic diagram showing the power supplied to the second coil when the power is supplied intermittently to the second coil.

[0044] Figure 13 This is a block diagram showing the configuration of the heating section in the embodiment.

[0045] Figure 14 (a) is a schematic diagram showing the power supplied to the first coil when the power is supplied intermittently to the first coil, and (b) is a schematic diagram showing the power supplied to the second coil when the power is supplied intermittently to the second coil.

[0046] Figure 15 (a) is a schematic diagram showing the power supplied to the first coil when the power is supplied intermittently to the first coil, and (b) is a schematic diagram showing the power supplied to the second coil when the power is supplied intermittently to the second coil.

[0047] Figure 16 This is a diagram showing the power supply current supplied to the first coil during the experiment.

[0048] Figure 17 This is a diagram showing the power supply current supplied to the second coil during the experiment.

[0049] Figure 18 This is a cross-sectional view of a crucible containing a solidified solution when heated from the side.

[0050] Figure 19 This is a cross-sectional view of a crucible containing a solidified solution when heated from the bottom.

[0051] Figure 20 This is a cross-sectional view of the crucible containing the solidified solution during the heating switching process.

[0052] Symbol Explanation

[0053] 10: Container; 11: Base; 12: Crucible; 12a: Heat transfer section; 13a: Insulation component; 13b: Insulation component; 13c: Insulation component; 14a: Coil; 14b: Coil; 15: Crucible lid; 15a: Cylindrical component; 15b: Connecting component; 16: Crystal holding shaft; 16a: Finned structure; 17: Thermocouple; 18: Crucible holding shaft; 20: Solution; 25a: Heating section; 25b 30: Heating unit; 40: Seed crystal; 50: Silicon carbide single crystal; 100: Single crystal manufacturing apparatus; 200a: First commercial power supply; 200b: Second commercial power supply; 201a: First AC / DC converter; 201b: Second AC / DC converter; 202a: First inverter; 202b: Second inverter; 203a: First transformer; 203b: Second transformer; 210: Control unit. Detailed Implementation

[0054] In all the accompanying drawings used to describe the embodiments, the same reference numerals are used to denote the same parts in principle, and repeated descriptions are omitted. Furthermore, even in top views, section lines are sometimes used for ease of understanding.

[0055] <Research on Improvement>

[0056] In the case of growing silicon carbide single crystals using solution methods, a supersaturated state needs to be created in the solution to induce crystal precipitation. Therefore, in solution methods for growing silicon carbide single crystals, a temperature gradient is formed in the solution to create this supersaturated state. In this case, a high-temperature region and a low-temperature region are formed in the solution, with the supersaturated state achieved in the low-temperature region. Therefore, by creating a temperature gradient in the solution so that the region of the solution in contact with the seed crystal is a low-temperature region that achieves the supersaturated state, crystal growth on the seed crystal is possible.

[0057] When a crystal with the same structure and orientation as the seed crystal grows on the surface of the seed crystal, the desired silicon carbide single crystal grows from the seed crystal as the starting point. Conversely, even if crystals grow on the surface of the seed crystal, crystals with structures or orientations different from those of the seed crystal are called impurities. Once these impurities form on the seed crystal surface, they will hinder the growth of the silicon carbide single crystal. Therefore, in solution processing, from the viewpoint of enabling the growth of silicon carbide single crystals on the seed crystal, it is desirable to reduce the number of impurities generated in the solution.

[0058] In addition, regarding impurities, besides those directly generated on the surface of the seed crystal, there are also impurities that grow by having their nuclei suspended in the solution and attached to the seed crystal, generated on the side wall or bottom of the crucible.

[0059] Such impurities become a major obstacle to the growth of silicon carbide single crystals starting from the seed crystal, thus it is desirable to suppress their adhesion to the seed crystal. In other words, it is generally permissible for impurities to form on the sidewalls or bottom of the crucible itself, rather than on the seed crystal. However, once the impurities formed on the sidewalls or bottom of the crucible become gigantic, a portion of the gigantic impurities will separate, increasing the risk of suspension in the solution. Therefore, to reduce the number of impurities suspended in the solution and attached to the seed crystal, it is desirable to suppress the gigantification of impurities formed on the sidewalls or bottom of the crucible. Furthermore, the gigantification of impurities formed on the sidewalls or bottom of the crucible becomes a major factor leading to a reduction in the amount of raw material available for the growth of silicon carbide single crystals on the seed crystal and a decrease in the growth rate of silicon carbide single crystals.

[0060] Therefore, when growing silicon carbide single crystals using a solution method, it is necessary to suppress the growth of impurities formed on the sidewalls or bottom of the crucible. Therefore, in this embodiment, a method is implemented that can reduce the amount of impurities formed in the solution and suppress the growth of impurities formed on the sidewalls or bottom of the crucible.

[0061] The technical concept of this embodiment of the method will be explained below.

[0062] <Basic Ideas of Implementation>

[0063] As described above, in the solution-based growth of silicon carbide single crystals, a supersaturated state needs to be created in the solution to induce crystal precipitation. To create this supersaturation, a temperature gradient is formed in the solution. Therefore, in the solution contained in the crucible, high-temperature and low-temperature regions coexist; crystals precipitate in the low-temperature regions but not in the high-temperature regions. Thus, it can be assumed that, for example, if the low-temperature region where crystals precipitate becomes a high-temperature region, the precipitated crystals will redissolve (insight).

[0064] The inventors of this invention, taking into account this insight, conceived of a basic idea that can reduce the formation of impurities in the solution and suppress the enlargement of impurities formed on the sidewalls or bottom of the crucible. Therefore, this basic idea will be explained below.

[0065] The basic idea behind this embodiment is to switch between the high-temperature and low-temperature regions contained in the crucible, thereby transforming the low-temperature region where impurities precipitate into a high-temperature region and dissolving the precipitated impurities. Using this principle, the continued precipitation of impurities can be suppressed, resulting in a reduction in impurities and prevention of their enlargement.

[0066] Specifically, if we assume that the impurities are formed primarily on the sidewalls or bottom of the crucible, the basic idea of ​​this embodiment can be understood as follows: a first heating step that heats the solution in a manner that makes the temperature of the solution in contact with the side of the crucible higher than the temperature of the solution in contact with the bottom of the crucible; and a second heating step that heats the solution in a manner that makes the temperature of the solution in contact with the bottom of the crucible higher than the temperature of the solution in contact with the side of the crucible, alternating between the first heating step and the second heating step.

[0067] Based on this basic idea, in the first heating process, impurities precipitate on the bottom surface of the crucible, while those precipitated on the sides of the crucible dissolve. Conversely, in the second heating process, the impurities precipitated on the bottom surface of the crucible dissolve, while those precipitate on the sides of the crucible. As a result, by alternating between the first and second heating processes, impurity precipitation ceases. Therefore, by utilizing this basic idea, it is possible to reduce impurities and suppress their enlargement. The following describes a single-crystal manufacturing technology that specifically embodies this basic idea.

[0068] <Composition of Single Crystal Manufacturing Equipment>

[0069] Figure 1 This is a diagram showing the configuration of the single crystal manufacturing apparatus 100 according to this embodiment.

[0070] exist Figure 1In this single crystal manufacturing apparatus 100, there is a container 10. The interior space of the container 10 is filled with, for example, argon gas. In addition, a heat insulation member 13c is provided inside the container 10, and a base 11 capable of rotating in the horizontal direction is arranged inside the heat insulation member 13c. The container 10 is made of, for example, an iron-based material such as SUS.

[0071] Alternatively, as an argon filling structure, a quartz tube can be inserted between the heat insulation component 13c and the coil 14a, and between the heat insulation component 13c and the coil 14b, and the upper and lower ends of the quartz tube can be sealed by flanges, thereby filling the structure with argon.

[0072] Next, a crucible 12 is placed on the base 11. This crucible 12 is made of graphite, for example, and contains a high-temperature solution 20 containing silicon (Si) inside. Specifically, the crucible 12 has a main body capable of containing the solution 20 containing carbon and silicon and a heat transfer section 12a protruding from the bottom of the main body.

[0073] Regarding the crucible 12 configured in this way, the heat transfer section 12a can also function as a "foot," so it can be said that the heat transfer section 12a also has the secondary function of stabilizing and uprighting the crucible 12. The heat transfer section 12a is configured to contact the base 11 on which the crucible 12 can be placed. For example... Figure 1 As shown, the base 11 includes a first region R1 that contacts the heat transfer part 12a, a second region R2 that is surrounded by the first region R1, and a third region R3 that surrounds the first region R1. A heat insulation member 13a is provided in contact with the second region R2, and a heat insulation member 13b is provided in contact with the third region R3.

[0074] The base 11 is connected to a crucible holding shaft 18 that holds the base 11. This crucible holding shaft 18 is configured to be movable in the vertical direction and to rotate clockwise or counterclockwise. Thus, the base 11 mounted on the crucible holding shaft 18 and the crucible 12 disposed on the base 11 can move vertically using the crucible holding shaft 18 and can rotate horizontally. Furthermore, the crucible holding shaft 18 has a hollow internal structure, allowing the insertion of a thermocouple or radiation thermometer for temperature measurement.

[0075] Furthermore, a coil through which a high-frequency current flows is provided on the outer periphery of the container 10 of the single crystal manufacturing apparatus 100, and the crucible 12 is heated by induction heating based on the high-frequency current flowing in the coil. Specifically, the single crystal manufacturing apparatus 100 has a heating section 25a and a heating section 25b. The heating section 25a is configured to heat the crucible 12 by flowing a high-frequency current through a coil 14a located opposite the side of the crucible 12, utilizing the resulting induction heating phenomenon. In other words, the coil 14a functions as the heating section 25a for heating the crucible 12, thus... Figure 1 In the diagram, the coil 14a is also labeled as a heating element 25a. On the other hand, the heating element 25b is configured to heat the base 11 by circulating a high-frequency current through the coil 14b, which is positioned opposite the base 11 supporting the crucible 12, utilizing the resulting induction heating phenomenon. Furthermore, the crucible 12 is heated through heat conduction from the heated base 11. Specifically, heat is transferred from the heated base 11 to the heat transfer element 12a, and then from the heat transfer element 12a to the crucible 12 (main body), thus heating the crucible 12. In this way, the heating element 25b is configured to indirectly heat the crucible 12 via the base 11 by circulating a high-frequency current through the coil 14b, which is positioned opposite the base 11 supporting the crucible 12, utilizing the resulting induction heating phenomenon. Therefore, the coil 14b functions as the heating element 25b for heating the crucible 12, and thus... Figure 1 In the diagram, the heating element 25b is also marked on the coil 14b. Additionally, in... Figure 1 Although not shown in the figure, coils 14b and 14a are configured such that cooling water can flow through them.

[0076] Thus, in the single crystal manufacturing apparatus 100, the crucible 12 is configured to not only be heated by the heating section 25a, but also to be heated by heat conduction from the base 11 heated by the heating section 25b. It can be said that the heat transfer section 12a of the crucible 12 has the function of conducting heat from the base 11 heated by the heating section 25b to the main body.

[0077] In order to facilitate heating of the base 11 using the heating element 25b, the thickness of the base 11 is increased, thereby enlarging the portion opposite to the coil 14b. The base 11 could also be integrated with the crucible 12, but considering that the crucible 12 needs to be replaced each time a silicon carbide single crystal is manufactured, and that the manufacturing cost of an integrated product is high, it is desirable for the base 11 and crucible 12 to be constructed separately. In the case of separate construction of the base 11 and crucible 12, it can be configured such that only the heat transfer element 12a of the crucible 12 is disposed on the base 11, or the base 11 can be constructed in a manner that allows the heat transfer element 12a to be embedded into the base 11.

[0078] These heating sections 25a and 25b are controlled by the control unit 50. That is, the single crystal manufacturing apparatus 100 has a control unit 50 that controls the electrical power supplied to the heating section 25a and the electrical power supplied to the heating section 25b. For example, the power supply for supplying electrical power to the heating section 25a and the power supply for supplying electrical power to the heating section 25b are separate power supplies, and the control unit 50 is configured to be able to control the heating sections 25a and 25b with different power supplies separately.

[0079] The control unit 50 is configured to alternately switch between a first operation and a second operation. The first operation adjusts the electrical power supplied to the heating unit 25a and the heating unit 25b in such a way that the temperature of the solution 20 in contact with the side surface of the crucible 12 is higher than the temperature of the solution 20 in contact with the bottom surface of the crucible 12. The second operation adjusts the electrical power supplied to the heating unit 25a and the heating unit 25b in such a way that the temperature of the solution 20 in contact with the bottom surface of the crucible 12 is higher than the temperature of the solution 20 in contact with the side surface of the crucible 12.

[0080] The solution 20 contained in the crucible 12, heated by heating sections 25a and 25b, reaches a high temperature, causing the graphite (C) constituting the crucible 12 to dissolve. Therefore, the solution 20 contains carbon and silicon. The crucible 12 is fitted with a crucible lid 15, which has a cylindrical component 15a and a connecting component 15b connected to the cylindrical component 15a. The connecting component 15b functions to fix and support the cylindrical component 15a, for example, it is configured to contact the crucible 12.

[0081] Furthermore, the single crystal manufacturing apparatus 100 is provided with a crystal holding shaft 16 that is movable in the vertical direction. This crystal holding shaft 16 can also be configured, similarly to the crucible holding shaft 18, to rotate clockwise or counterclockwise. In other words, the presence or absence of a rotation mechanism in the crystal holding shaft 16 and the crucible holding shaft 18 is optional.

[0082] A seed crystal formed of silicon carbide is mounted at the front end of the crystal holding shaft 16. Figure 1 (Not shown in the figure). Additionally, the crystal holding shaft 16 has a finned structure 16a mounted intersecting the extending direction of the crystal holding shaft 16. Furthermore, the interior of the crystal holding shaft 16 is a hollow structure, into which a thermocouple 17 for measuring the temperature near the seed crystal is inserted. Temperature measurement near the seed crystal can also be performed by using a radiation thermometer with a measuring diameter smaller than the inner diameter of the crystal holding shaft 16 at the upper end of the crystal holding shaft 16, instead of inserting the thermocouple 17.

[0083] Furthermore, the control unit 50 of the single crystal manufacturing apparatus 100 is also configured to control the crystal holding shaft 16, which has a finned structure 16a, to move vertically. Specifically, the control unit 50 is configured to control the crystal holding shaft 16, which has a finned structure 16a, to move vertically through the interior of the cylindrical member 15a. The control unit 50 is configured to move the crystal holding shaft 16, with the seed crystal at its front end, downward so that the lower surface of the seed crystal contacts the surface of the solution 20 contained in the crucible 12, and is configured such that after the lower surface of the seed crystal contacts the surface of the solution 20, moving the crystal holding shaft 16 upward allows a single crystal formed of silicon carbide to grow on the lower surface of the seed crystal. For example, in Figure 1 The diagram illustrates a silicon carbide single crystal 40 grown on the lower surface of a seed crystal. The seed crystal only needs to be in contact with the solution 20, and it is particularly desirable for it to be in contact with the surface of the solution 20.

[0084] Furthermore, one configuration involves growing a single crystal of silicon carbide on the lower surface of the seed crystal by moving the crystal holding axis 16 upward. This is one example; alternatively, it could be configured to grow the single crystal of silicon carbide on the lower surface of the seed crystal while the crystal holding axis 16 is stopped (maintained), or it could be configured to grow the single crystal of silicon carbide on the lower surface of the seed crystal by moving the crystal holding axis 16 downward. This configuration considers the possibility of the surface of solution 20 descending due to evaporation, for example. That is, when the surface of solution 20 recedes due to evaporation, single crystal growth can be reliably achieved by moving the crystal holding axis 16 downward while simultaneously growing the single crystal.

[0085] The single crystal manufacturing apparatus 100 is constructed as described above.

[0086] Figure 2 This is a diagram illustrating the dimensions of the main parts of the base 11 and the crucible 12.

[0087] For example, Figure 2 The dimensions of the main parts shown are as follows.

[0088] (1)

[0089] (2)

[0090] (3)

[0091] (4)

[0092] (5) "T1" = 100mm;

[0093] (6) “T2” = 80mm;

[0094] (7) "T3" = 30mm;

[0095] (8) "T4" = 250mm;

[0096] (9) “A1” = 90mm;

[0097] (10)

[0098] <Variation Example 1>

[0099] exist Figure 1 In the single crystal manufacturing apparatus 100 shown, an example is illustrated where the heating section 25b that heats the base 11 utilizes the induction heating phenomenon generated by the flow of a high-frequency current in the coil 14b. However, the heating section 25b that heats the base 11 is not limited to this. For example, it may also be composed of a resistance heater disposed below the base 11.

[0100] However, when the heating section 25b is composed of a resistance heater, "holes" need to be provided in the insulation material to accommodate the pair of wires used to energize the resistance heater. Especially in the case of a configuration where the crucible 12 rotates, a circumferential opening needs to be provided in the insulation material to accommodate the pair of wires. As a result, it may be difficult to ensure the high-temperature retention characteristics of the crucible 12. Therefore, from the viewpoint of improving the insulation effect of the insulation material and simplifying the configuration of the single crystal manufacturing apparatus 100, it is desirable that the heating section 25b, which heats the base 11, be made of... Figure 1 The diagram shows the structure of an induction heater that utilizes the phenomenon of induction heating.

[0101] <Operation of Single Crystal Manufacturing Equipment (Single Crystal Manufacturing Method)>

[0102] Next, the operation of the single crystal manufacturing apparatus 100 will be explained.

[0103] Figure 3 and Figure 4 This diagram is used to illustrate the operation of the single crystal manufacturing apparatus 100.

[0104] exist Figure 3 First, the control unit 50 lowers the crystal holding shaft 16, on which the seed crystal 30 is mounted, at its front end. As a result, the seed crystal 30 mounted on the crystal holding shaft 16 passes through the interior of the cylindrical member 15a of the crucible cover 15 and comes into contact with the surface of the carbon and silicon-containing solution 20 contained in the crucible 12. At this time, the fin structure 16a mounted on the crystal holding shaft 16 is positioned opposite the inner wall of the cylindrical member 15a.

[0105] Next, in Figure 4In the process, the control unit 50 slowly raises the crystal holding shaft 16. As a result, the silicon carbide single crystal 40 grows on the lower surface of the pulled seed crystal 30. At this time, the fin structure 16a mounted on the crystal holding shaft 16 moves while maintaining its position relative to the inner wall of the cylindrical member 15a. Then, as crystal growth continues, the lifting action of the crystal holding shaft 16 continues. On the other hand, when crystal growth ends, the control unit 50 further lifts the crystal holding shaft 16, isolating the silicon carbide single crystal 40 from the solution 20. This ends the growth of the silicon carbide single crystal 40. At this time, the fin structure 16a mounted on the crystal holding shaft 16 remains positioned relative to the inner wall of the cylindrical member 15a.

[0106] As described above, silicon carbide single crystals can be manufactured by operating the single crystal manufacturing apparatus 100. The description includes a method of isolating the silicon carbide single crystal 40 from the solution 20 by further pulling the crystal holding axis 16, thereby ending crystal growth. However, this method is not limited to this; for example, the silicon carbide single crystal 40 can also be isolated from the solution 20 and crystal growth can be ended by lowering the crucible holding axis 18 instead of the crystal holding axis 16.

[0107] <<Control Department Operations>>

[0108] As described above, silicon carbide single crystals are manufactured using a "solution method" in the single crystal manufacturing apparatus 100. In this embodiment, the single crystal manufacturing method involves alternating between a first heating step and a second heating step. The first heating step heats the solution 20 such that the temperature of the solution 20 in contact with the side surface of the crucible 12 is higher than the temperature of the solution 20 in contact with the bottom surface of the crucible 12. The second heating step heats the solution 20 such that the temperature of the solution 20 in contact with the bottom surface of the crucible 12 is higher than the temperature of the solution 20 in contact with the side surface of the crucible 12.

[0109] In this embodiment, these processes are implemented by controlling the heating section 25a and the heating section 25b using the control unit 50 of the single crystal manufacturing apparatus 100. Specifically, the control unit 50 alternately switches between a first operation and a second operation. The first operation adjusts the electrical power supplied to the heating section 25a and the heating section 25b to make the temperature of the solution 20 in contact with the side surface of the crucible 12 higher than the temperature of the solution 20 in contact with the bottom surface of the crucible 12. The second operation adjusts the electrical power supplied to the heating section 25a and the heating section 25b to make the temperature of the solution 20 in contact with the bottom surface of the crucible 12 higher than the temperature of the solution 20 in contact with the side surface of the crucible 12.

[0110] For example, when the control unit 50 performs the first operation, the temperature of the solution 20 in contact with the side surface of the crucible 12 is the temperature at which the impurity crystals dissolve, while the temperature of the solution 20 in contact with the bottom surface of the crucible 12 becomes the temperature at which the impurity crystals precipitate. Conversely, when the control unit 50 performs the second operation, the temperature of the solution 20 in contact with the bottom surface of the crucible 12 is the temperature at which the impurity crystals dissolve, while the temperature of the solution 20 in contact with the side surface of the crucible 12 becomes the temperature at which the impurity crystals precipitate.

[0111] Therefore, by repeating the alternation between the first and second actions, the precipitated impurities can be redissolved, resulting in the precipitation of impurities ceasing, reducing the number of impurities, and suppressing the enlargement of impurities.

[0112] Figure 5 This diagram illustrates an example of switching between the first and second actions performed using the control unit 50.

[0113] exist Figure 5 In this context, "A" represents the time period during which the first action is performed, while "B" represents the time period during which the second action is performed. Additionally, in... Figure 5 In the diagram, the solid line represents the electrical power (coil output) supplied to the coil 14a of the heating section 25a. The dashed line represents the electrical power (coil output) supplied to the coil 14b of the heating section 25b.

[0114] exist Figure 5 In this process, crystal growth occurs while switching between the first action (“A”) and the second action (“B”). That is to say, in... Figure 5 The example illustrates a process in which a silicon carbide single crystal 40 is grown on the lower surface of a seed crystal while the crystal holding axis 16 is moved upward (see reference). Figure 4 An example of repeatedly switching between the first and second actions.

[0115] For example, in the first operation, the electrical power supplied to coil 14a is high, while the electrical power supplied to coil 14b is low. This means that the heating amount on the side surface of crucible 12 is greater than the heating amount on the bottom surface of crucible 12, thereby achieving a temperature distribution where the temperature of the solution 20 in contact with the side surface of crucible 12 is higher than the temperature of the solution 20 in contact with the bottom surface of crucible 12. Conversely, in the second operation, the electrical power supplied to coil 14a is reduced, while the electrical power supplied to coil 14b is increased. This means that the heating amount on the bottom surface of crucible 12 is greater than the heating amount on the side surface of crucible 12, thereby achieving a temperature distribution where the temperature of the solution 20 in contact with the bottom surface of crucible 12 is higher than the temperature of the solution 20 in contact with the side surface of crucible 12.

[0116] In addition, Figure 5The example shown illustrates that the electrical power supplied to coil 14a is greater than the electrical power supplied to coil 14b, not only in the first operation but also in the second operation. However, depending on the configuration of crucible 12, in order to achieve a temperature distribution where the temperature of the solution 20 in contact with the bottom surface of crucible 12 is higher than the temperature of the solution 20 in contact with the sides of crucible 12, it is also conceivable that the electrical power supplied to coil 14a is less than the electrical power supplied to coil 14b. That is, in the second operation, as long as a temperature distribution where the temperature of the solution 20 in contact with the bottom surface of crucible 12 is higher than the temperature of the solution 20 in contact with the sides of crucible 12 can be achieved, the relationship between the magnitudes of the electrical power (or current) supplied to coil 14a and the electrical power (or current) supplied to coil 14b is not limited.

[0117] All components constituting the single crystal manufacturing apparatus 100 have heat capacity; therefore, the temperature distribution of the solution 20 will shift with a delay relative to changes in all control conditions, including the adjustment of the electrical power supplied to coils 14a and 14b respectively. The shift in the temperature distribution of the solution 20 is not necessarily limited to conditions suitable for single crystal growth.

[0118] For example, regarding the switching from the first action to the second action, when the migration time from the end of the first action condition to the point where the temperature distribution of solution 20 becomes constant due to the second action is taken as the first migration time, a temperature distribution that is different from the temperature distribution achieved by the first action and the temperature distribution achieved by the second action is realized within the first migration time.

[0119] Several methods can be considered to control the temperature distribution of solution 20 to the desired state during the first migration time. As a first example, there is a method that directly moves to the second action after the first action ends. This method can achieve the temperature distribution of solution 20 achieved in the second action in a short time, thus having the advantage of allowing silicon carbide single crystals to grow for a longer period under stable conditions, making it particularly effective in single crystal manufacturing devices with small heat capacity. Furthermore, compared to the second and third examples described later, the electrical power control conditions are simpler and clearer, making it feasible in single crystal manufacturing devices without complex control mechanisms, which is also an advantage.

[0120] As a second example, there is a method that slowly changes the electrical power supplied to coils 14a and 14b respectively between the end of the first operation and the start of the second operation to absorb the migration delay caused by heat capacity. This method has the advantage that the temperature distribution of the solution 20 during the first migration time can be changed quasi-stable, and the temperature distribution of the solution 20 can be substantially controlled by utilizing the electrical power supplied to coils 14a and 14b respectively. As a result, the first migration time is substantially consistent with the period between the end of the first operation and the start of the second operation; therefore, compared to the first example and the third example described later, it is easier to achieve a temperature distribution suitable for silicon carbide single crystal growth during the first migration time.

[0121] As a second example, the change in electrical power can be considered as follows: Figure 5 The method shown maintains a constant rate of change of electrical power from the end of the first operation to the start of the second operation. Alternatively, the rate of change of electrical power can be increased or decreased for one or more moments between the end of the first operation and the start of the second operation. Since coils 14a and 14b are characterized by being independently controllable, in the latter case, adjustments can be made such that the rate of change of electrical power in one coil is greater than in the first example, and the rate of change of electrical power in the other coil is smaller than in the first example.

[0122] As a third example, a method is as follows: during a certain period between the end of the first action and the start of the second action, the electrical power supplied to coil 14a is less than the electrical power supplied to coil 14a under the second action condition, while the electrical power supplied to coil 14b is greater than the electrical power supplied to coil 14b under the second action condition. This method is called overshoot, and it has the effect of eliminating the delay in state change caused by heat capacity. The advantage of using this overshoot power change method is that, in single-crystal manufacturing devices with large heat capacity, the temperature distribution of solution 20 achieved by the second action reaches a constant state earlier than in the first example.

[0123] Thus far, regarding the switching from the first action to the second action, an example has been given of a method for controlling the temperature distribution of the solution 20 within the first migration time to a desired state. Similarly, the same method can certainly be applied to the switching from the second action to the first action.

[0124] Figure 6 This is a graph showing the results of simulating the temperature distribution of solution 20 achieved through the first action. The simulation was performed using the software "CGSim|STR Japan Co., Ltd. <Crystal Growth Analysis Simulation Software> (str-soft.co.jp)".

[0125] exist Figure 6As can be seen from the diagram, the temperature (K) of the solution 20 in contact with the side of the crucible is higher than the temperature (K) of the solution 20 in contact with the bottom of the crucible. At this point, because the temperature of the solution 20 in contact with the side of the crucible is higher, impurities dissolve. On the other hand, because the temperature of the solution 20 in contact with the bottom of the crucible is lower, impurities are formed (precipitated).

[0126] Figure 7 This is a graph showing the results of simulating the temperature distribution of solution 20 achieved through the second action. Figure 7 As can be seen from the diagram, the temperature (K) of the solution 20 in contact with the bottom surface of the crucible is higher than the temperature (K) of the solution 20 in contact with the sides of the crucible. At this point, because the temperature of the solution 20 in contact with the bottom surface of the crucible is higher, impurity crystals dissolve. On the other hand, because the temperature of the solution 20 in contact with the sides of the crucible is lower, impurity crystals form (precipitate).

[0127] Therefore, when repeatedly switching between the first and second actions, Figure 6 The temperature distribution shown is Figure 7 The temperature distribution shown alternates. As a result, the precipitated impurities redissolve, and the precipitation of impurities cannot continue. Therefore, by using this embodiment, it is possible to reduce the amount of impurities and suppress the growth of impurities.

[0128] Next, the timing for switching between the first and second actions will be explained.

[0129] Ideally, the first and second actions should be switched when the size of the impurity crystal exceeds a predetermined size. This is because determining the switching timing in this way can effectively suppress the growth of the impurity crystal.

[0130] However, measuring the size of impurities during the manufacturing process of silicon carbide single crystals is extremely difficult. Therefore, a control method that switches between the first and second actions when the size of the impurities exceeds a specified size is impractical. Therefore, alternating between the first and second actions at predetermined time intervals is more feasible.

[0131] Here, in the case of alternating between the first action and the second action at a predetermined time interval, in order to effectively suppress the giantification of impurities, for example, it is possible to accumulate data representing the relationship between the time interval and the size of the impurities, construct a database, and set the optimal time interval based on the data accumulated in the database.

[0132] <Variation Example 2>

[0133] exist Figure 5The example described is switching between the first and second actions while crystal growth is being performed, but the example of switching between the first and second actions using the control unit 50 is not limited to this. For example, either the first or second action may be performed during the crystal growth stage after the seed crystal has come into contact with the surface of the solution, while the other of the first and second actions may be performed while the silicon carbide single crystal grown on the lower surface of the seed crystal has left the solution surface.

[0134] Figure 8 This is a diagram illustrating an example of switching between the first and second actions (Variation Example 2).

[0135] exist Figure 8 The example shown illustrates a scenario where crystal growth is stopped during the first action, while the second action is performed simultaneously with crystal growth. In other words, as an example of switching between the first and second actions using the control unit 50, the following approach could also be adopted. Figure 8 The switching action shown.

[0136] In this case, the following advantages can be obtained.

[0137] For example, in representing the temperature distribution of the solution produced by performing the first action. Figure 6 In the process, the surface temperature of the solution 20 in contact with the seed crystal increases.

[0138] In order to grow silicon carbide single crystals on the lower surface of the seed crystal, it is desirable for the surface temperature of the solution in contact with the seed crystal to be among the lowest temperatures in the solution's temperature distribution. This is because silicon carbide single crystals grow in a supersaturated state, and supersaturation is achieved in the low-temperature region. Considering this, the temperature distribution of the solution resulting from the first step may not be suitable for silicon carbide single crystal growth. This is because... Figure 6 In the temperature distribution shown, the low supersaturation slows down the crystal growth rate, and therefore may not be a suitable temperature distribution for crystal growth.

[0139] In contrast, the temperature distribution of the solution resulting from the second action is represented by... Figure 7 In this process, the surface temperature of the solution 20 in contact with the seed crystal decreases. Therefore, the temperature distribution of the solution resulting from the second action can be considered suitable for silicon carbide single crystal growth. That is, in the temperature distribution of the solution resulting from the second action, the high supersaturation accelerates the crystal growth rate, and as a result, compared with the temperature distribution of the solution resulting from the first action, it can be considered a temperature distribution suitable for crystal growth.

[0140] As can be seen from the above, the temperature distribution of the solution produced by the first action may not be suitable for the growth of silicon carbide single crystals, while the temperature distribution of the solution produced by the second action can be said to be suitable for the growth of silicon carbide single crystals.

[0141] Therefore, as Figure 8 As shown, if crystal growth is stopped during the first action, while the second action is performed simultaneously with crystal growth, then silicon carbide single crystal growth can be achieved only under the temperature conditions suitable for silicon carbide single crystal growth. As a result, in Figure 8 In the modified example 2 shown, the advantage of being able to manufacture silicon carbide single crystals of excellent quality is obtained. On the other hand, in Figure 5 In the switching example shown, the first and second actions are performed alternately while crystal growth is being carried out, thus achieving the advantage of shortening the manufacturing time of silicon carbide single crystals.

[0142] Furthermore, regarding the switching time between the first and second actions, the method determined based on a pre-built database as described above can be considered. However, from the viewpoint of shortening the crystal growth time, it is desirable to make the implementation time of the first action shorter than that of the second action. As a suitable condition for obtaining a switching time that satisfies this objective, for example, the dissolution rate of impurities in the solution 20 in contact with the side of the crucible 12 during the first action is higher than the precipitation rate of impurities at the same location during the second action. As a method to satisfy this condition, it is possible to adjust the electrical power supplied to coils 14a and 14b respectively so that the temperature distribution of the solution 20 during the first action has a larger temperature gradient compared to that distribution during the second action.

[0143] In the first and second operations, it is not necessary to keep the electrical power supplied to the coil completely constant; it can be gradually reduced. The first and second operations in subsequent cycles do not necessarily have the exact same output power as the first cycle. For example, compared to the first cycle, it is possible to slightly reduce the output power, or only slightly reduce the power supplied to coil 14a. These methods take into account that as crystals grow, the amount of solution to be heated decreases, and in order to achieve the same temperature distribution as the first cycle, the electrical power supplied to the coil is reduced.

[0144] <Features of the Implementation Method>

[0145] Next, the features of this embodiment will be described.

[0146] The first feature of this embodiment is, for example Figure 5 and Figure 8As shown, alternating between a first action (“A”) and a second action (“B”), the first action adjusts the electrical power supplied to heating section 25a and heating section 25b to make the temperature of the solution 20 in contact with the side surface of crucible 12 higher than the temperature of the solution 20 in contact with the bottom surface of crucible 12, and the second action adjusts the electrical power supplied to heating section 25a and heating section 25b to make the temperature of the solution 20 in contact with the bottom surface of crucible 12 higher than the temperature of the solution 20 in contact with the side surface of crucible 12. Thus, for example, the temperature of the solution 20 in contact with the side or bottom surface of crucible 12 can be periodically changed between the temperature of impurity crystal precipitation and the temperature of impurity crystal dissolution. This means that the amount of precipitated impurities can be reduced, and the enlargement of impurities can be suppressed, thereby suppressing the quality degradation of silicon carbide single crystals caused by impurities.

[0147] Next, the second feature of this embodiment is, for example, Figure 1 As shown, the crucible 12 is provided with a heat transfer section 12a protruding from the bottom of the main body of the crucible 12.

[0148] The technical significance of this second feature will be explained below.

[0149] For example, in the second action of raising the temperature of the solution 20 in contact with the bottom surface of the crucible 12 to the temperature at which the impurity crystals dissolve, it is very important to raise the temperature of the bottom surface of the crucible 12 uniformly. This is because if the temperature of the bottom surface of the crucible 12 cannot be raised uniformly, even if the second action is performed, the probability of a low-temperature region where the impurity crystals do not dissolve will increase, and as a result, the impurity crystals cannot dissolve in that region.

[0150] As a configuration for heating the bottom surface of crucible 12, for example, Figure 9 The structure shown. In Figure 9 In this configuration, a crucible 12 is disposed on a base 11, and the base 11 is configured to be heated using induction heating from a heating section 25b including a coil 14b. In this case, heat from the heated base 11 is conducted to the bottom surface of the crucible 12, which is in direct contact with the base 11. However, in induction heating using the coil 14b, the outer portions of the crucible 12 are more easily heated than the central portion of the base 11. Therefore, in... Figure 9 In the configuration shown, the outer part of the bottom surface of the crucible 12 is mainly heated (see reference). Figure 9 (As indicated by the arrow), it is difficult to heat the central part of the bottom surface of crucible 12. That is, in Figure 9 In the configuration shown, it is difficult to make the temperature of the bottom surface of the crucible 12 rise uniformly.

[0151] In contrast, in this embodiment, such as Figure 1As shown, the crucible 12 is provided with a heat transfer portion 12a protruding from the bottom of the main body of the crucible 12. In this case, as... Figure 10 As shown, heat is preferentially conducted from the base 11, which has been heated by induction heating from the heating section 25b including the coil 14b, to the center of the bottom surface of the crucible 12 via the heat transfer section 12a. As a result, using this embodiment, the temperature of the bottom surface of the crucible 12 can be raised uniformly. In other words, the heat transfer section 12a has the function of preferentially inducing heat from the heated base 11 to the center of the bottom surface of the crucible 12.

[0152] From the perspective of improving the overall temperature uniformity of the bottom surface of crucible 12, for example, Figure 1 As shown, it is desirable to provide a heat insulation member 13a inside the heat transfer section 12a, and to provide a heat insulation member 13b in a manner that surrounds the heat transfer section 12a.

[0153] Furthermore, in order to ensure a uniform temperature rise at the bottom surface of the crucible 12, the location of the heat transfer section 12a is crucial. Taking this into consideration, for example... Figure 2 The dimensions of the main parts are shown.

[0154] In particular, from the viewpoint that the impurity crystals on the bottom surface of the crucible 12 are dissolved uniformly by raising the temperature of the entire bottom surface, it is very important that "L3" is smaller than "L1" and "L4" is larger than "L1" and smaller than "L2". With this configuration, it is possible to avoid the situation where the sides of the crucible 12 are preferentially heated.

[0155] <Further Research on Improvement>

[0156] For example, in this embodiment, such as Figure 1 The configuration shown is such that the crucible 12 is heated by induction heating generated by supplying electrical power to the coil 14a, and the base 11 is heated by induction heating generated by supplying electrical power to the coil 14b.

[0157] The feature of this embodiment is, for example, Figure 5 and Figure 8 As shown, the first action (“A”) and the second action (“B”) are alternately switched. The first action adjusts the electrical power supplied to coil 14a and coil 14b to make the temperature of the solution 20 in contact with the side of crucible 12 higher than the temperature of the solution 20 in contact with the bottom of crucible 12. The second action adjusts the electrical power supplied to coil 14a and coil 14b to make the temperature of the solution 20 in contact with the bottom of crucible 12 higher than the temperature of the solution 20 in contact with the side of crucible 12.

[0158] At this time, as Figure 5 and Figure 8As shown, in either the first operation (“A”) or the second operation (“B”), electrical power is supplied to both coil 14a and coil 14b. This means that in either the first operation (“A”) or the second operation (“B”), high-frequency current flows simultaneously in both coil 14a and coil 14b. Therefore, for example, the electromagnetic field generated by the high-frequency current flowing in coil 14a may adversely affect the circuit including coil 14b, and conversely, the electromagnetic field generated by the high-frequency current flowing in coil 14b may adversely affect the circuit including coil 14a. That is, in either the first operation (“A”) or the second operation (“B”), high-frequency current flows simultaneously in both coil 14a and coil 14b, so electromagnetic interference may occur, resulting in adverse effects such as circuit malfunction.

[0159] Therefore, in this embodiment, a method for suppressing the aforementioned adverse effects is implemented. The technical concept of this embodiment, which implements this method, will be explained below.

[0160] <Technical Concept of Implementation>

[0161] The technical concept of this embodiment is as follows: Instead of continuously supplying power to coils 14a and 14b, power is supplied intermittently to each coil. Based on this premise, the power supply is exclusively controlled so that the time periods for supplying power to coil 14a and coil 14b do not overlap. That is, the time periods for supplying power to coil 14a are the periods for not supplying power to coil 14b, and vice versa. Therefore, when power is supplied to one coil, power is not supplied to the other, thus preventing the simultaneous flow of high-frequency current in both coils. As a result, electromagnetic interference caused by the simultaneous flow of high-frequency current in both coils can be suppressed, thereby preventing circuit malfunctions.

[0162] For example, Figure 11 (a) is a schematic diagram showing the electrical power supplied to coil 14a when electrical power is continuously supplied to coil 14a. On the other hand, Figure 11 (b) is a schematic diagram showing the electrical power supplied to coil 14b when electrical power is continuously supplied to coil 14b. Specifically, Figure 11 (a) indicates in Figure 5 The electrical power supplied to coil 14a in the first action (“A”) Figure 11 (b) indicates that in Figure 5 The electrical power supplied to coil 14b in the first action (“A”). In this case, it can be known that... Figure 11 (a) and Figure 11 As shown in (b), both coil 14a and coil 14b are supplied with electrical power simultaneously. Therefore, it can be known that... Figure 11 (a) and Figure 11 In the configuration shown in (b), where electrical power is continuously supplied to coils 14a and 14b respectively, high-frequency current flows simultaneously in both coils 14a and 14b, thereby causing electromagnetic interference and potentially resulting in adverse effects such as circuit malfunction.

[0163] Among them, Figure 11 In (a), when electrical power is continuously supplied to coil 14a, the instantaneous electrical power P1H supplied to coil 14a is equal to the average electrical power <P1H> supplied to coil 14a. Similarly, in Figure 11 In (b), when power is continuously supplied to coil 14b, the instantaneous power supplied to coil 14b, P2L, is equal to the average power supplied to coil 14b, <P2L>.

[0164] In contrast, for example Figure 12 (a) is a schematic diagram showing the electrical power supplied to coil 14a when electrical power is supplied discontinuously to coil 14a. On the other hand, Figure 12 (b) is a schematic diagram showing the electrical power supplied to coil 14b when electrical power is supplied discontinuously. Specifically, Figure 12 (a) indicates in Figure 5 The electrical power supplied to coil 14a in the first action (“A”) Figure 12 (b) indicates that in Figure 5 The electrical power supplied to coil 14b in the first action 1 (“A”). In this case, as Figure 12 (a) and Figure 12 As shown in (b), the control is achieved by not supplying power to coil 14b while power is being supplied to coil 14a. In other words, it is known that when using... Figure 12 (a) and Figure 12 When the configuration shown in (b) involves discontinuous power supply to coils 14a and 14b, control can be achieved by not simultaneously supplying power to both coils 14a and 14b. Therefore, using... Figure 12 (a) and Figure 12 When the configuration shown in (b) involves discontinuous power supply to coils 14a and 14b, it is possible to prevent high-frequency current from flowing simultaneously in both coils 14a and 14b. Therefore, electromagnetic interference caused by the simultaneous flow of high-frequency current in both coils 14a and 14b can be suppressed, thereby suppressing adverse effects such as circuit malfunctions.

[0165] Among them, Figure 12 In (a), when power is discontinuously supplied to coil 14a, the instantaneous power supplied to coil 14a, P1H, is higher than the average power supplied to coil 14a, <P1H>. Similarly, in Figure 12 In (b), when power is discontinuously supplied to coil 14b, the instantaneous power supplied to coil 14b, P2L, is higher than the average power supplied to coil 14b, <P2L>. That is, when employing the technical concept of this embodiment, it is possible to prevent both coil 14a and coil 14b from simultaneously carrying high-frequency current; on the other hand, the instantaneous power supplied is higher than the average power supplied. However, considering that it can suppress electromagnetic interference caused by the simultaneous flow of high-frequency current in both coils, thereby suppressing circuit malfunctions, the technical concept of this embodiment has very significant technical importance.

[0166] <Specific Methods>

[0167] The following explains the specific ways in which the above technical ideas are embodied.

[0168] This embodiment is based on the premise that power is not continuously supplied to coils 14a and 14b, but rather discontinuously. It employs a method where the first inverter supplying power to coil 14a and the second inverter supplying power to coil 14b operate exclusively. That is, when the first inverter supplying power to coil 14a is turned on, the second inverter supplying power to coil 14b is turned off; conversely, when the second inverter supplying power to coil 14b is turned on, the first inverter supplying power to coil 14a is turned off. Thus, when power is supplied to one coil, power is not supplied to the other, thereby preventing the simultaneous flow of high-frequency current in both coils. As a result, electromagnetic interference caused by the simultaneous flow of high-frequency current in both coils can be suppressed, thereby preventing circuit malfunctions.

[0169] <<The Structure and Operation of the Heating Unit>>

[0170] Figure 13 This is a block diagram showing the configuration of the heating section in this embodiment.

[0171] Figure 13 Examples of the configurations of heating section 25a and heating section 25b are shown.

[0172] exist Figure 13In this configuration, the heating unit 25a is configured to include a first AC / DC converter 201a, a first inverter 202a, a first transformer 203a, and a coil 14a, and is controlled by a control unit 210. In this heating unit 25a, firstly, a signal representing the target output power <<P1>> (i.e., the target output signal) is input to the control unit 210. Then, the control unit 210 outputs a target inverter voltage <<Vi1>> to the first AC / DC converter 201a to achieve the input power PA to the first inverter 202a. Next, in the first AC / DC converter 201a, based on the target inverter voltage <<Vi1>> input from the control unit 210, the AC power from the first commercial power supply 200a is converted into DC power. Thus, the input power PA is output from the first AC / DC converter 201a to the first inverter 202a. Next, the input power PA from the first AC / DC converter 201a is input into the first inverter 202a, and the output power <P1> is output. Specifically, the first inverter 202a converts the DC current converted by the first AC / DC converter 201a into a high-frequency current (e.g., 10kHz). Then, the output voltage from the first inverter 202a is stepped down by the first transformer 203a, and a high-frequency current (output power <P1>) is supplied to the coil 14a. That is, in order to prevent leakage or arcing in the heating furnace, the voltage is reduced by the first transformer 203a, allowing a corresponding large current to flow in the coil 14a to heat the heating furnace. The control unit 210 controls the on / off state of the first inverter 202a. As a result, the coil 14a generates periods when power is supplied and periods when no power is supplied. Then, the crucible 12 is induction heated in the coil 14a based on the supplied output power <P1>. In this operation, the crucible 12 is heated by the heating unit 25a.

[0173] Furthermore, the heating unit 25b is configured to include a second AC / DC converter 201b, a second inverter 202b, a second transformer 203b, and a coil 14b, and is controlled by the control unit 210. In the heating unit 25b configured in this way, firstly, a signal as the target output power <<P2>> is input to the control unit 210. Then, the control unit 210 outputs a target inverter voltage <<Vi2>> to the second AC / DC converter 201b to achieve the input power PB to the second inverter 202b. Next, in the second AC / DC converter 201b, based on the target inverter voltage <<Vi2>> input from the control unit 210, the AC power from the second commercial power supply 200b is converted into DC power. Thus, the input power PB is output from the second AC / DC converter 201b to the second inverter 202b. Next, the input power PB from the second AC / DC converter 201b is input into the second inverter 202b, and the output power <P2> is output. Specifically, the DC current converted by the second AC / DC converter 201b is converted into a high-frequency current (e.g., 10kHz) using the second inverter 202b. Then, the output voltage from the second inverter 202b is stepped down by the second transformer 203b, and a high-frequency current (output power <P2>) is supplied to the coil 14b. That is, in order to prevent leakage or arcing in the heating furnace, the voltage is reduced by the second transformer 203b, allowing a corresponding large current to flow in the coil 14b to heat the heating furnace. The control unit 210 controls the on / off state of the second inverter 202b. As a result, the coil 14b generates periods when power is supplied and periods when no power is supplied. Then, the base 11 is inductively heated in the coil 14b based on the supplied output power <P2>. In this way, the base 11 is heated by the heating element 25b.

[0174] In this specific manner, power is not continuously supplied to coils 14a and 14b, but rather discontinuously. At this time, the control unit 210 controls the first inverter 202a and the second inverter 202b, causing them to operate exclusively. That is, when the first inverter 202a is turned on to supply power to coil 14a, the second inverter 202b is turned off to supply power to coil 14b, and vice versa. Thus, when power is supplied to one coil, power is not supplied to the other, preventing the simultaneous flow of high-frequency current in both coils. Consequently, electromagnetic interference caused by the simultaneous flow of high-frequency current in both coils can be suppressed, thereby preventing circuit malfunctions.

[0175] <<Specific waveform examples>>

[0176] Next, specific waveform examples will be explained.

[0177] Figure 14 (a) is a schematic diagram showing the electrical power supplied to coil 14a when electrical power is supplied discontinuously to coil 14a. On the other hand, Figure 14 (b) is a schematic diagram showing the electrical power supplied to coil 14b when electrical power is supplied discontinuously. Specifically, Figure 14 (a) indicates in Figure 5 The electrical power supplied to coil 14a in the first action (“A”) Figure 14 (b) indicates that in Figure 5 The electrical power supplied to coil 14b in the first action (“A”). Figure 14 The lower part of (a) also shows the current waveform flowing in coil 14a. Figure 14 The lower part of (b) also shows the current waveform flowing in coil 14b.

[0178] in, Figure 14 (a) and Figure 14 The symbols in (b) represent the following meanings.

[0179] P1H: Instantaneous power supply to coil 14a;

[0180] P2L: Instantaneous power supply to coil 14b;

[0181] <P1H>: Average electrical power supplied to coil 14a;

[0182] <P2L>: Average electrical power supplied to coil 14b;

[0183] fa: On / off switching frequency;

[0184] fs1: The frequency of the current flowing in coil 14a;

[0185] fs2: The frequency of the current flowing in coil 14b;

[0186] d1: The opening time ratio of coil 14a;

[0187] d2: The opening time ratio of coil 14b.

[0188] The relationship d1 + d2 < 1 holds true. That is, there exists a period during which both the first and second inverters are simultaneously turned off.

[0189] Figure 15 (a) indicates in Figure 5 The electrical power supplied to coil 14a in the second action (“B”) Figure 15 (b) indicates that in Figure 5 The electrical power supplied to coil 14b in the second action (“B”). Figure 15 The current waveform flowing in coil 14a is also shown in (a). Figure 15 The current waveform flowing in coil 14b is also shown in (b).

[0190] in, Figure 15 (a) and Figure 15 The symbols in (b) represent the following meanings.

[0191] P1L: Instantaneous power supply to coil 14a;

[0192] P2H: Instantaneous power supply to coil 14b;

[0193] <P1L>: Average electrical power supplied to coil 14a;

[0194] <P2H>: Average electrical power supplied to coil 14b;

[0195] fa: On / off switching frequency;

[0196] fs1: The frequency of the current flowing in coil 14a;

[0197] fs2: The frequency of the current flowing in coil 14b;

[0198] d3: The opening time ratio of coil 14a;

[0199] d4: The opening time ratio of coil 14b.

[0200] The relationship d3+d4<1 holds true. That is, there exists a period in time when both the first and second inverters are simultaneously turned off.

[0201] exist Figure 14 In order to make <P1H> and Figure 5 and Figure 8 The solid lines are consistent, and <P2L> is consistent with... Figure 5 and Figure 8 By using the same dotted lines, and setting "d1", "d2", "P1H", and "P2L", it is possible to achieve... Figure 5 and Figure 8 The first action (“A”). Similarly, in Figure 15 In order to make <P1L> and Figure 5 and Figure 8 The solid lines are consistent, and <P2H> is consistent with... Figure 5 and Figure 8 By using the same dotted lines, and setting "d3", "d4", "P1L", and "P2H", it is possible to achieve... Figure 5 and Figure 8 The second action (“B”).

[0202] In this embodiment, the power supply to coils 14a and 14b is intermittent. However, if the switching frequency fa is sufficiently short compared to the time constant of the furnace temperature change, the intermittent operation has no effect on the furnace temperature change. Furthermore, if the switching frequency of the first inverter 202a (the frequency fs1 of the current flowing in coil 14a) and the switching frequency of the second inverter 202b (the frequency fs2 of the current flowing in coil 14b) are sufficiently high compared to the switching frequency fa, induction heating can be achieved.

[0203] Based on the above explanation, as Figure 5 and Figure 8 As shown, when one coil has an output, the output of the other coil is not zero, but by performing... Figure 14 or Figure 15 The exclusive action shown can achieve Figure 5 and Figure 8 The output of the inverter 202a is controlled by the first inverter 202a supplying current to coil 14a and the second inverter 202b supplying current to coil 14b. Therefore, by operating the first inverter 202a supplying current to coil 14a and the second inverter 202b supplying current to coil 14b exclusively, malfunctions of the first inverter 202a or the second inverter 202b caused by electromagnetic interference can be avoided, resulting in stable operation. Thus, using this embodiment, electromagnetic interference can be suppressed, eliminating the need for magnetic shielding between coils 14a and 14b, and reducing the cost of the single-crystal manufacturing apparatus.

[0204] <Other characteristics>

[0205] Next, other features of this embodiment will be described.

[0206] In the single crystal manufacturing apparatus 100 of this embodiment, for example... Figure 1 As shown, the heating unit 25a includes a coil 14a disposed opposite to the side of the crucible 12 disposed on the base 11, and the heating unit 25b includes a coil 14b disposed opposite to the base 11 and located below the crucible 12 containing the solution 20. In this respect, another feature of this embodiment is that the coil 14b is disposed opposite to the base 11, which is disposed further below the solution 20 contained in the crucible 12.

[0207] Therefore, the heating unit 25b can heat the base 11 by utilizing the induction heating phenomenon generated by the flow of a high-frequency current in the coil 14b located opposite the base 11. Furthermore, the bottom surface of the crucible 12 can be heated by heat conduction from the heated base 11.

[0208] In detail, heat is transferred from the heated base 11 (heated by the heating section 25b) to the heat transfer section 12a, and then from the heat transfer section 12a to the crucible 12 (main body), thereby heating the bottom surface of the crucible 12 that is in contact with the solution 20. That is, the heating section 25b is configured to indirectly heat the bottom surface of the crucible 12 that is in contact with the solution via the base 11 by utilizing induction heating generated by a high-frequency current flowing through a coil 14b positioned opposite the base 11 that supports the crucible 12. Furthermore, in order to heat the bottom surface of the crucible 12 that is in contact with the solution 20 using the coil 14b located on the outer side of the heat insulation member 13c, the coil 14b is positioned opposite the base 11, which is positioned further below the solution 20 contained within the crucible 12.

[0209] As a result, based on this other feature, the base 11 is heated by the induction heating phenomenon generated by the high-frequency current flowing in the coil 14b, and the bottom surface of the crucible 12 in contact with the solution 20 can be indirectly heated through heat conduction from the heated base 11. In other words, the technical significance of this other feature is that, instead of directly heating the bottom surface of the crucible 12 in contact with the solution 20, the coil 14b (other feature) is positioned opposite the base 11, and the base 11 on which the crucible 12 is placed is heated instead of the crucible 12 itself. By adopting this configuration, the bottom surface of the crucible 12 is indirectly heated via the base 11.

[0210] <Further features>

[0211] As described above, the first feature of this embodiment is, for example, Figure 5 and Figure 8 The diagram shows alternating switching between a first action (“A”) and a second action (“B”). The first action adjusts the electrical power supplied to the heating section 25a and the heating section 25b to make the temperature of the solution 20 in contact with the side surface of the crucible 12 higher than the temperature of the solution 20 in contact with the bottom surface of the crucible 12. The second action adjusts the electrical power supplied to the heating section 25a and the heating section 25b to make the temperature of the solution 20 in contact with the bottom surface of the crucible 12 higher than the temperature of the solution 20 in contact with the side surface of the crucible 12.

[0212] Regarding this point, in this embodiment, there are further features in adjusting the electrical power supplied to the heating unit 25a and the electrical power supplied to the heating unit 25b. Specifically, the further feature is that, in order to achieve the first and second operations described above, the electrical power supplied to the heating unit 25a is different from the electrical power supplied to the heating unit 25b. In other words, the further feature is that the first and second operations described above are achieved solely by employing a configuration that makes the electrical power supplied to the heating unit 25a different from the electrical power supplied to the heating unit 25b. As a specific example, such as... Figures 5-8 As shown, when the first action is performed, the "first electrical power" supplied to the heating unit 25a is greater than the "second electrical power" supplied to the heating unit 25b. On the other hand, when the second action is performed, the "third electrical power" supplied to the heating unit 25a is greater than the "fourth electrical power" supplied to the heating unit 25b. At this time, the "first electrical power" is greater than the "third electrical power," and the "second electrical power" is less than the "fourth electrical power." Thus, in a specific example, the first action and the second action can be performed respectively.

[0213] Thus, based on further features, by simply making the electrical power supplied to the heating section 25a different from the electrical power supplied to the heating section 25b, the temperatures of the solutions 20 in contact with the side and bottom surfaces of the crucible 12 can be periodically varied between the temperature at which the impurity crystals precipitate and the temperature at which the impurity crystals dissolve. As a result, using this embodiment, the amount of precipitated impurities can be reduced, and the enlargement of impurities can be suppressed, thereby suppressing the quality degradation of silicon carbide single crystals caused by impurities.

[0214] <Verifying the effect using experimental results>

[0215] Next, based on actual experimental results rather than simulation results, this embodiment will be used to explain how it can reduce the formation of impurities in the solution.

[0216] The feature of this embodiment is, for example Figure 5 and Figure 8As shown, the first action (“A”) and the second action (“B”) are alternately switched. The first action adjusts the electrical power supplied to the heating section 25a and the electrical power supplied to the heating section 25b to make the temperature of the solution 20 in contact with the side of the crucible 12 higher than the temperature of the solution 20 in contact with the bottom of the crucible 12. The second action adjusts the electrical power supplied to the heating section 25a and the electrical power supplied to the heating section 25b to make the temperature of the solution 20 in contact with the bottom of the crucible 12 higher than the temperature of the solution 20 in contact with the side of the crucible 12.

[0217] Hereinafter, the first action (first heating process) described above will be referred to as "side heating," and the second action (second heating process) described above will be referred to as "bottom heating." In addition, the action of alternately switching between the first action and the second action (a feature of this embodiment) will be referred to as "heating switching."

[0218] Figure 16 This is a diagram showing the power supply current supplied to coil 14a during the experiment. Figure 16 In the diagram, the horizontal axis represents time (hours), while the vertical axis represents the value of the power supply current (A) supplied to coil 14a.

[0219] exist Figure 16 In the diagram, the solid line represents the relationship between power supply current and time during "side heating". The dashed line represents the relationship between power supply current and time during "bottom heating", and the dotted-dash line represents the relationship between power supply current and time during "heating switching".

[0220] Figure 17 This is a diagram showing the power supply current supplied to coil 14b during the experiment. Figure 17 In the diagram, the horizontal axis represents time (hours), while the vertical axis represents the value of the power supply current (A) supplied to coil 14a.

[0221] exist Figure 17 In the diagram, the solid line represents the relationship between power supply current and time during "side heating". The dashed line represents the relationship between power supply current and time during "bottom heating", and the dotted-dash line represents the relationship between power supply current and time during "heating switching".

[0222] In the above Figure 16 and Figure 17 The experiment was conducted under the conditions shown. The switching of the power supply current was timed as follows: side heating for 6 hours, switching for 10 minutes, bottom heating for 5 hours and 50 minutes, switching for 10 minutes, side heating for 5 hours and 50 minutes, switching for 10 minutes, and bottom heating for 5 hours and 50 minutes. Furthermore, after the solution contained in the crucible cooled and solidified, each crucible was cut to obtain a cross-sectional view. The experimental results are explained below using these cross-sectional views.

[0223] Figure 18This is a cross-sectional view of the crucible 12 containing the solidified solution 20 during "side heating". Figure 18 In the test, it was confirmed that no impurities were observed in region RA, located on the side of crucible 12, and the maximum dissolved size on the side of crucible 12 was approximately 3 mm. On the other hand, impurities of approximately 2 mm were observed in region RB, located on the bottom surface of crucible 12.

[0224] This can be qualitatively understood as follows: during "side heating", since the temperature of the solution 20 in contact with the side of the crucible 12 is higher than the temperature of the solution 20 in contact with the bottom of the crucible 12, the impurities on the side of the crucible 12 dissolve, while the impurities precipitate on the bottom of the crucible 12.

[0225] then, Figure 19 This is a cross-sectional view of the crucible 12 containing the solidified solution 20 during "bottom heating". Figure 19 In the test, large impurity crystals of approximately 5 mm in size were observed in region RA, located on the side of crucible 12. Conversely, no impurity crystals were observed in region RB, located on the bottom surface of crucible 12, with a maximum dissolved size of approximately 4 mm. Additionally, impurity crystals of approximately 1 mm in size were observed in region RC, located on the bottom surface of crucible 12.

[0226] This can be qualitatively understood as follows: during “bottom heating”, since the temperature of the solution 20 in contact with the bottom surface of the crucible 12 is higher than the temperature of the solution 20 in contact with the side surface of the crucible 12, the impurities on the bottom surface of the crucible 12 dissolve, and even if impurities are generated, they are small-sized impurities, while large-sized impurities are more likely to precipitate on the side surface of the crucible 12.

[0227] then, Figure 20 This is a cross-sectional view of the crucible 12 containing the solidified solution 20 during the "heating switch". Figure 20 In the analysis, small-sized impurity crystals were observed in region RA on the side of crucible 12, with a maximum dissolution of approximately 1 mm on the side of crucible 12. Conversely, no impurity crystals were observed in region RB on the bottom surface of crucible 12, with a maximum dissolution of approximately 2 mm on the bottom surface. Additionally, approximately 1 mm of impurity crystals were observed in region RC on the bottom surface of crucible 12.

[0228] During the "heating switching," the process alternates between a first action that raises the temperature of the solution 20 in contact with the side surface of the crucible 12 to be higher than the temperature of the solution 20 in contact with the bottom surface of the crucible 12, and a second action that raises the temperature of the solution 20 in contact with the bottom surface of the crucible 12 to be higher than the temperature of the solution 20 in contact with the side surface of the crucible 12. Therefore, during the "heating switching," the temperatures of the solutions 20 in contact with the side and bottom surfaces of the crucible 12 can be periodically varied between the temperature of impurity crystal precipitation and the temperature of impurity crystal dissolution. Therefore, it can be qualitatively understood that: Figures 18-20 The experimental results show that, during the "heating switch", compared with "side heating" or "bottom heating", the amount of precipitated impurities can be reduced, the giantification of impurities can be suppressed, and the dissolution of crucible 12 can also be suppressed.

[0229] The experimental results above confirm that, compared with "side heating" and "bottom heating," "heating switching" can reduce the amount of precipitated impurities, suppress the growth of impurities, and further suppress the dissolution of crucible 12. Therefore, the experimental results demonstrate that the basic idea of ​​this embodiment is an effective technical concept in suppressing the quality degradation of silicon carbide single crystals caused by impurities (e.g., in obtaining silicon carbide single crystals without attached impurities).

[0230] The invention completed by the inventors has been specifically described above based on the embodiments, but the invention is not limited to the above embodiments, and various modifications can be made without departing from its spirit.

Claims

1. A method for manufacturing single crystals, characterized in that, include: (a) A process of bringing the lower surface of the seed crystal into contact with a solution containing carbon and silicon contained in a crucible by moving the seed crystal at the front end axially downward. and (b) A process of growing a single crystal of silicon carbide on the lower surface of the seed crystal. The single crystal manufacturing method includes: (c1) A first heating step of heating the solution in such a way that the temperature of the solution in contact with the side of the crucible is higher than the temperature of the solution in contact with the bottom of the crucible; and (c2) A second heating step of heating the solution in such a way that the temperature of the solution in contact with the bottom surface of the crucible is higher than the temperature of the solution in contact with the side surface of the crucible. The first heating process and the second heating process are switched alternately. In the first heating step, the temperature of the solution in contact with the side surface of the crucible is the temperature at which the impurity crystals dissolve, while the temperature of the solution in contact with the bottom surface of the crucible is the temperature at which the impurity crystals precipitate. In the second heating process, the temperature of the solution in contact with the bottom surface of the crucible is the temperature at which the impurity crystals dissolve, while the temperature of the solution in contact with the side surface of the crucible is the temperature at which the impurity crystals precipitate.

2. The single crystal manufacturing method as described in claim 1, characterized in that, The single crystal manufacturing apparatus for implementing the single crystal manufacturing method comprises: A first heating section heats the crucible by passing a high-frequency current through a first coil located opposite the side of the crucible; and A second heating element heats the base by passing a high-frequency current through a second coil positioned opposite the base supporting the crucible. In the first heating process, by adjusting the electrical power supplied to the first heating unit and the electrical power supplied to the second heating unit, the temperature of the solution in contact with the side surface of the crucible is made higher than the temperature of the solution in contact with the bottom surface of the crucible. In the second heating process, by adjusting the electrical power supplied to the first heating unit and the electrical power supplied to the second heating unit, the temperature of the solution in contact with the bottom surface of the crucible is made higher than the temperature of the solution in contact with the side surface of the crucible.

3. The single crystal manufacturing method as described in claim 1, characterized in that, In step (b), the first heating step and the second heating step are performed simultaneously by alternating between the first heating step and the second heating step.

4. The single crystal manufacturing method as described in claim 1, characterized in that, Either the first heating step or the second heating step is performed in step (b) after step (a), while the other of the first heating step or the second heating step is performed with the single crystal grown on the lower surface of the seed crystal removed from the surface of the solution.

5. The single crystal manufacturing method as described in claim 1, characterized in that, The alternation between the first heating process and the second heating process is carried out at a predetermined time interval.

6. The single crystal manufacturing method as described in claim 1, characterized in that, The single crystal manufacturing apparatus for implementing the single crystal manufacturing method comprises: A first coil is positioned opposite the side of the crucible; and The second coil is positioned opposite the base supporting the crucible. The first heating process and the second heating process each supply electrical power to the first coil and the second coil respectively in such a way that the time period for supplying electrical power to the first coil and the time period for supplying electrical power to the second coil do not overlap.

7. The single crystal manufacturing method as described in claim 1, characterized in that, The single crystal manufacturing apparatus for implementing the single crystal manufacturing method comprises: A first coil is disposed at a position opposite to the side surface of the crucible; A first inverter for supplying electrical power to the first coil; A second coil is disposed at a position opposite to the base supporting the crucible; A second inverter for supplying electrical power to the second coil; and A control unit that controls the operation of the first inverter and the second inverter. The first heating process and the second heating process are each performed by the exclusive operation of the first inverter and the second inverter using the control unit.

8. The single crystal manufacturing method as described in claim 2, characterized in that, The second coil is positioned opposite the base, which is located further below the solution contained in the crucible.

9. The single crystal manufacturing method as described in claim 2, characterized in that, In the first heating process, the first electrical power supplied to the first heating unit is greater than the second electrical power supplied to the second heating unit. In the second heating process, the third electrical power supplied to the first heating unit is greater than the fourth electrical power supplied to the second heating unit. The first electrical power is greater than the third electrical power. The second electrical power is less than the fourth electrical power.

10. A single crystal manufacturing apparatus, characterized in that, The single crystal manufacturing apparatus is capable of placing a crucible containing a solution of carbon and silicon inside a container. The single crystal manufacturing apparatus has the following features: A base disposed inside the container; A first heating section for heating the crucible disposed on the base; A second heating element that heats the base; and A control unit that controls the electrical power supplied to the first heating unit and the electrical power supplied to the second heating unit. The control unit alternately switches between the first action and the second action. The first action involves adjusting the electrical power supplied to the first heating unit and the electrical power supplied to the second heating unit in a manner that makes the temperature of the solution in contact with the side of the crucible higher than the temperature of the solution in contact with the bottom of the crucible. The second action involves adjusting the electrical power supplied to the first heating unit and the electrical power supplied to the second heating unit in a manner that makes the temperature of the solution in contact with the bottom surface of the crucible higher than the temperature of the solution in contact with the side surface of the crucible. In the first action, the temperature of the solution in contact with the side surface of the crucible is the temperature at which the impurity crystals dissolve, while the temperature of the solution in contact with the bottom surface of the crucible is the temperature at which the impurity crystals precipitate. In the second action, the temperature of the solution in contact with the bottom surface of the crucible is the temperature at which the impurity crystals dissolve, while the temperature of the solution in contact with the side surface of the crucible is the temperature at which the impurity crystals precipitate.

11. The single crystal manufacturing apparatus as described in claim 10, characterized in that, The first heating element induction heats the crucible. The second heating element performs induction heating on the base.

12. The single crystal manufacturing apparatus as described in claim 10 or 11, characterized in that, The crucible has: The main body for receiving the solution; and A heat transfer section protruding from the bottom of the main body. In the single crystal manufacturing apparatus, the crucible is heated by bringing the heat transfer section into contact with the base, utilizing heat conduction from the base, which has been heated by the second heating section, through the heat transfer section.

13. The single crystal manufacturing apparatus as described in claim 12, characterized in that, The base includes: The first region in contact with the heat transfer part; The second region surrounded by the first region; and The third region surrounding the first region. The single crystal manufacturing apparatus has a heat-insulating component that contacts at least one of the second region and the third region.

14. The single crystal manufacturing apparatus as described in claim 10, characterized in that, The first heating element includes a first coil. The second heating element includes a second coil. The first operation and the second operation of the control unit can each be performed by supplying power to the first coil and the second coil respectively in a manner that the time period for supplying power to the first coil and the time period for supplying power to the second coil do not overlap.

15. The single crystal manufacturing apparatus as described in claim 10, characterized in that, The first heating element includes: First coil; and A first inverter for supplying electrical power to the first coil. The second heating element includes: Second coil; and A second inverter for supplying electrical power to the second coil. The first action and the second action of the control unit can each be performed by the exclusive operation of the first inverter and the second inverter using the control unit.

16. The single crystal manufacturing apparatus as described in claim 10, characterized in that, The first heating element includes a first coil disposed at a position opposite to the side of the crucible, the crucible being disposed above the base. The second heating element includes a second coil disposed opposite to the base, the base being capable of housing the crucible containing the solution on top of it.

17. The single crystal manufacturing apparatus as described in claim 10, characterized in that, In the first operation performed using the control unit, the first electrical power supplied to the first heating unit is greater than the second electrical power supplied to the second heating unit. In the second operation performed using the control unit, the third electrical power supplied to the first heating unit is greater than the fourth electrical power supplied to the second heating unit. The first electrical power is greater than the third electrical power. The second electrical power is less than the fourth electrical power.

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