Crucible and method for manufacturing silicon carbide single crystal
The crucible design with a graphite bottom and flipable polycrystalline silicon carbide wall addresses contamination and impurity issues, reducing costs and enhancing silicon carbide crystal quality.
Patent Information
- Application Number
- JP2024011917
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-01-30
- Publication Date
- 2025-08-12
AI Technical Summary
Conventional graphite crucibles used in silicon carbide single crystal growth suffer from carbon atom contamination, impurity introduction, and changes in solution zone shape and temperature distribution, leading to high costs and reduced crystal quality.
A crucible design combining a graphite bottom with a polycrystalline silicon carbide wall that can be flipped for self-repair, maintaining consistent solution flow and temperature distribution.
Reduces production costs by 30-90% and improves crystal quality by preventing impurity introduction and maintaining stable growth conditions.
Smart Images
Figure 2025117190000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to the technical field of silicon carbide production, and in particular to a crucible and a method for producing silicon carbide single crystals by liquid phase techniques. [Background technology]
[0002] In the conventional liquid-phase method for growing silicon carbide single crystals, it is common to use a graphite crucible as a reaction vessel and a carbon atom source, and a silicon carbide wafer as a seed crystal. Polycrystalline silicon and cosolvent are placed in the graphite crucible as growth raw materials, and the seed crystal is fixed on a seed crystal holder at the top. The seed crystal is then pulled up and grown using the top-seeded solution growth (TSSG) method. Summary of the Invention [Problem to be solved by the invention]
[0003] At this time, the bottom of the graphite crucible, which is in a relatively high temperature state, melts and enters the solution as carbon atoms. The reaction equation is C(S) → C(L). The seed crystal area, which is in a relatively low temperature state, absorbs carbon atoms and grows into silicon carbide single crystals. At the same time, excess carbon atoms freely nucleate on the graphite crucible wall, which is also in a low temperature, and become silicon carbide polycrystals containing numerous impurities. This polycrystalline area grows quickly, and if it grows for a long time, it changes the shape of the solution zone, causing the flow and temperature distribution to deviate from the initial state. [Means for solving the problem]
[0004] The crucible disclosed in this specification is a crucible for pulling silicon carbide single crystals. The crucible includes a crucible bottom and a first crucible wall. The crucible bottom is made of graphite. The first crucible wall is made of polycrystalline silicon carbide and has a cylindrical shape with a central axis. The first crucible wall is separably connected to an upper portion of the crucible bottom. The first crucible wall includes a first end face located on one side of the central axis and a second end face located on the other side of the central axis. The first crucible wall is configured to be changeable between a first state in which the first end face is connected to the crucible bottom and a second state in which the second end face is connected to the crucible bottom.
[0005] In the technology described herein, a crucible is designed to combine polycrystalline silicon carbide and graphite materials. In the technology described herein, the graphite material serves as the crucible bottom to supply carbon to the growth system, and the polycrystalline silicon carbide material serves as the first crucible wall to surround the solution. When using the crucible described herein, the first crucible wall does not need to be frequently replaced, and self-repair of the first crucible wall can be achieved by changing the orientation of the first crucible wall, significantly reducing the cost of growing silicon carbide by a liquid phase method.
[0006] The crucible is designed with a first crucible wall made of polycrystalline silicon carbide. The first crucible wall surrounds the melted solution. During the crystal growth process, a dissolution reaction, represented by the reaction formula SiC(S) → Si(L) + C(L), occurs in the high-temperature area of the first crucible wall. A precipitation reaction, represented by the reaction formula Si(L) + C(L) → SiC(S), occurs in the low-temperature area of the first crucible wall. These two processes are inverse to each other. Therefore, by switching between the first and second states and then flipping the first crucible wall upside down for use in the next crystal growth, the first crucible wall can self-repair. This suppresses changes in the shape of the solution zone, allowing for consistent solution flow and temperature distribution. [Brief explanation of the drawings]
[0007] In order to more clearly describe the embodiments or technical solutions of the present invention, the drawings that need to be used to describe the embodiments or technical solutions are briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained based on these drawings without any creative efforts. [Figure 1] 1 is a schematic cross-sectional view of a crystal growth apparatus 100 according to a first embodiment. [Figure 2] 1 is a flow chart illustrating a method for growing silicon carbide single crystals. [Figure 3] FIG. 2 is a schematic diagram showing the structure of a crucible. [Figure 4] FIG. 2 is a schematic diagram showing the structure of a crucible. [Figure 5] FIG. 2 is a schematic diagram showing the structure of a crucible. [Figure 6] FIG. 1 is a schematic diagram showing a crucible of Example 2. [Figure 7] FIG. 10 is a schematic diagram showing a crucible of Example 3. DETAILED DESCRIPTION OF THE INVENTION
[0008] In order to help those skilled in the art better understand the technical solutions described in this specification, the technical solutions of the embodiments of this specification will be clearly and comprehensively described below in conjunction with the drawings of the embodiments of this specification. Obviously, the described embodiments are only some of the embodiments of the technology described herein, but are not all of the embodiments. Based on the embodiments of this specification, all other embodiments that can be obtained by those skilled in the art without any creative efforts should fall within the protection scope of the technology described herein.
[0009] The first end face and the second end face may have a flat surface perpendicular to the central axis, and the crucible bottom may have a flat surface configured to be able to come into close contact with the first end face and to be able to come into close contact with the second end face.
[0010] The first crucible wall may include a first spiral groove located on one side of the central axis and a second spiral groove located on the other side of the central axis. The first spiral groove and the second spiral groove may have the same shape. The crucible bottom may include a crucible bottom spiral groove capable of threadably engaging with the first spiral groove and the second spiral groove.
[0011] The first crucible wall includes a cylindrical first flange disposed on the outer periphery of the first end face and protruding from the first end face toward the central axis, and a cylindrical second flange disposed on the outer periphery of the second end face and protruding from the second end face toward the central axis. A first spiral groove is formed on the inner periphery of the first flange. A second spiral groove is formed on the inner periphery of the second flange. The crucible bottom has a disk shape centered on the central axis, and a crucible bottom spiral groove may be formed on the outer peripheral side surface of the crucible bottom.
[0012] The first crucible wall may have a first engagement portion disposed on the first end face and a second engagement portion disposed on the second end face. The first engagement portion and the second engagement portion may have the same shape. The crucible bottom may have a crucible bottom engagement portion engageable with both the first engagement portion and the second engagement portion.
[0013] The first and second engagement portions may be formed as ring-shaped protrusions centered on the central axis, and the crucible bottom engagement portion may be formed as a groove centered on the central axis.
[0014] The first end surface and the second end surface may have a first tapered surface and a second tapered surface formed by a conical surface centered on the central axis. The first tapered surface and the second tapered surface may have the same shape. The crucible bottom may have a crucible bottom tapered surface parallel to the first tapered surface and the second tapered surface. The crucible bottom tapered surface may be configured to be able to come into close contact with the first tapered surface and also be configured to be able to come into close contact with the second tapered surface.
[0015] The crucible may further include a second crucible wall. The second crucible wall may have a cylindrical shape sharing a central axis with the first crucible wall and be separably connected to an upper portion of the first crucible wall. In the first state, the lower end surface of the second crucible wall may be connected to a second end surface of the first crucible wall. In the second state, the lower end surface of the second crucible wall may be connected to a first end surface of the first crucible wall.
[0016] The crucible may further include a crucible lid disposed on the upper end surface of the second crucible wall.
[0017] The polycrystalline silicon carbide that forms the first crucible wall may have a porosity of 1% or less and a purity of greater than 99.95%.
[0018] The polycrystalline silicon carbide used to make the first crucible wall has a porosity of 1% or less to prevent the first crucible wall from being melted through, and a purity of greater than 99.95% to prevent impurities from being mixed into the solution. The polycrystalline silicon carbide is made by pressureless sintering and can withstand high temperatures of 2000°C or higher.
[0019] The graphite constituting the bottom of the crucible may have a porosity in the range of 1% to 10% and a purity of more than 99.95%.
[0020] If the porosity is too high, the bottom of the crucible will be easily melted through, causing the hot solution to leak out and damage the growth system. If the porosity is too low, the carbon dissolution rate at the bottom of the crucible will be slow, resulting in slow crystal growth. Furthermore, to avoid impurities from being mixed into the solution, it is preferable that the purity of the isotropic graphite be higher than 99.95%.
[0021] One embodiment of the present specification is a method for producing a silicon carbide single crystal using a crucible. The crucible includes a crucible bottom and a first crucible wall. The crucible bottom is made of graphite. The first crucible wall is made of polycrystalline silicon carbide and has a cylindrical shape with a central axis. The first crucible wall is detachably connected to an upper part of the crucible bottom. The first crucible wall includes a first end face located on one side of the central axis and a second end face located on the other side of the central axis. The first crucible wall is configured to be changeable between a first state in which the first end face is connected to the crucible bottom and a second state in which the second end face is connected to the crucible bottom. A first growth step in which crystal growth is performed in the first state and a second growth step in which crystal growth is performed in the second state are alternately repeated.
[0022] In the first growth step, if the crystal growth time exceeds a predetermined first time, the state may be changed from the first state to the second state after the first growth step is completed. In the subsequent first growth step, if the crystal growth time exceeds a second time that is greater than the first time, the state may be changed from the second state to the first state after the first growth step is completed. In the subsequent second growth step, if the crystal growth time exceeds the second time, the state may be changed from the first state to the second state after the second first growth step is completed.
[0023] The method may further include a step of exchanging the crucible bottom between the first and second growth steps, or between the second and first growth steps.
[0024] In the first and second growth steps, polycrystalline silicon carbide may be deposited on the upper part of the inner wall of the first crucible to form a protruding portion protruding inward, and a recessed portion may be formed by eroding the lower part of the inner wall of the first crucible. In the first and second growth steps, the temperature profile in the vertical direction of the crucible may be adjusted so that the protruding amount of the protruding portion and the recessed amount of the recessed portion are approximately the same. [Example]
[0025] <Configuration of Crystal Growth Apparatus 100 and Crucible 10> FIG. 1 shows a cross-sectional schematic diagram of a crystal growth apparatus 100 of this embodiment. The crystal growth apparatus 100 mainly comprises a crucible 10, a solution 5, a support shaft 7, and a seed crystal 8. The crucible 10 is a crucible used to grow silicon carbide single crystals by a liquid phase method. The crucible 10 has a crucible bottom 1, a crucible wall 2, and a crucible lid 6. The crucible bottom 1, the crucible wall 2, and the crucible lid 6 correspond in size. The crucible bottom 1 and the crucible wall 2 are separably assembled.
[0026] The crucible wall 2 includes a first crucible wall 3 and a second crucible wall 4. The first crucible wall 3 and the second crucible wall 4 have a common central axis CA and have a cylindrical shape.
[0027] The first crucible wall 3 has a first end face E1 located on one side of the central axis CA and a second end face E2 located on the other side of the central axis CA. The first end face E1 and the second end face E2 each have planes P1 and P2 perpendicular to the central axis CA. The first crucible wall 3 also has a first flange F1 and a second flange F2. The first flange F1 is disposed on the outer periphery of the first end face E1 and is a cylindrical portion protruding from the first end face E1 in the direction of the central axis (+z direction). The second flange F2 is disposed on the outer periphery of the second end face E2 and is a cylindrical portion protruding from the second end face E2 in the direction of the central axis (-z direction). A first spiral groove G1 is formed on the inner periphery of the first flange F1. A second spiral groove G2 is formed on the inner periphery of the second flange F2. The first spiral groove G1 and the second spiral groove G2 have the same shape.
[0028] The crucible bottom 1 has a disk shape centered on the central axis CA. A flat surface BP is formed on the surface of the crucible bottom 1. The flat surface BP is configured to be able to come into close contact with the flat surface P1 of the first end face E1 and also to be able to come into close contact with the flat surface P2 of the second end face E2. A crucible bottom spiral groove BG is formed on the outer peripheral side surface of the crucible bottom 1. The crucible bottom spiral groove BG is capable of threaded engagement with the first spiral groove G1 and also capable of threaded engagement with the second spiral groove G2. In the example of FIG. 1, the crucible bottom spiral groove BG is engaged with the first spiral groove G1. As a result, the first crucible wall 3 is separably connected to the upper part of the crucible bottom 1. Furthermore, the flat surface P1 of the first crucible wall 3 and the flat surface BP of the crucible bottom 1 are in close contact with each other, thereby ensuring a seal at the connection between the first crucible wall 3 and the crucible bottom 1.
[0029] The first crucible wall 3 and the crucible bottom 1 are threadedly connected. During use, the high temperature growth environment causes the graphite and silicon carbide to expand, tightening the thread gap, providing an excellent sealing effect and preventing the solution from leaking.
[0030] The lower end surface of the second crucible wall 4 has a plane LP perpendicular to the central axis CA. The plane LP is configured to be able to come into close contact with the plane P1 of the first end face E1 and also with the plane P2 of the second end face E2. A second crucible wall spiral groove WG is formed on the outer peripheral side surface of the second crucible wall 4. The second crucible wall spiral groove WG is capable of threaded engagement with the first spiral groove G1 and also with the second spiral groove G2. In the example of FIG. 1, the second crucible wall spiral groove WG is engaged with the second spiral groove G2. This allows the second crucible wall 4 to be detachably connected to the upper part of the first crucible wall 3. Furthermore, the flat surface P2 of the first crucible wall 3 and the flat surface LP of the second crucible wall 4 are in close contact with each other, ensuring a seal at the connection between the first crucible wall 3 and the second crucible wall 4. The central axes CA of the first crucible wall 3 and the second crucible wall 4 are aligned with each other. When assembled in this manner, they can be easily separated, and no additional sealing process is required for the second crucible wall 4 and the first crucible wall 3 during use.
[0031] Here, a state in which the first end face E1 is connected to the crucible bottom 1 and the second end face E2 is connected to the lower end face of the second crucible wall 4 is defined as a first state. A state in which the second end face E2 is connected to the crucible bottom 1 and the first end face E1 is connected to the lower end face of the second crucible wall 4 is defined as a second state. Crucible 10 is configured so that its state can be changed between the first state and the second state.
[0032] The crucible 10 contains a solution 5. The liquid level of the solution 5 is approximately the same as the height of the upper end surface of the first crucible wall 3. A crucible lid 6 is placed on the upper end surface of the second crucible wall 4. The crucible lid 6 has an opening 6a corresponding to the central axis CA. A support shaft 7 is inserted into the opening 6a. The support shaft 7 is rotatable around the central axis CA and is movable in the vertical direction (z direction). A seed crystal 8 is attached to the lower surface of the support shaft 7.
[0033] <Examples of materials and dimensions of the crucible 10> The upper surface of the first crucible wall 3 and the liquid surface of the solution 5 are at the same height, typically 20 to 100 mm. The first crucible wall 3 surrounds the melted solution 5 and provides a heat source for the solution 5 by induction self-heating during crystal growth. The second crucible wall 4 is located above the first crucible wall 3 and is spaced apart from the crucible bottom 1. The height of the second crucible wall 4 is determined by the temperature field design of different crystal growth systems and is typically 40 to 200 mm. The second crucible wall 4 mainly surrounds the bulk raw materials in the solution 5 before they melt and provides a heat source for the solution 5 by induction self-heating during crystal growth.
[0034] The crucible bottom 1 is made of isotropic graphite. For example, the crucible bottom 1 has a thickness of 20 to 50 mm and a diameter of 80 to 300 mm. The isotropic graphite constituting the crucible bottom 1 preferably has a porosity of 1% to 10%. If the porosity exceeds this range, the crucible bottom 1 is more likely to be melted and penetrated, which may cause the high-temperature solution to leak and damage the crystal growth apparatus. On the other hand, if the porosity exceeds this range, the rate at which carbon dissolves in the crucible bottom 1 slows, resulting in slower crystal growth. Furthermore, to prevent impurities from being mixed into the solution 5, the purity of the isotropic graphite is preferably greater than 99.95%.
[0035] The first crucible wall 3 and the second crucible wall 4 are made of polycrystalline silicon carbide. The first crucible wall 3 and the second crucible wall 4 have a thickness of, for example, 20 to 50 mm. The outer diameter of the second crucible wall 4 is the same as the diameter of the crucible bottom 1. The inner diameters of the first flange F1 and the second flange F2 of the first crucible wall 3 are the same as the outer diameter of the second crucible wall 4 and the diameter of the crucible bottom 1. The polycrystalline silicon carbide constituting the first crucible wall 3 and the second crucible wall 4 preferably has a porosity of 1% or less. This prevents the first crucible wall 3 and the second crucible wall 4 from being melted through. The polycrystalline silicon carbide preferably has a purity of more than 99.95%. This makes it possible to prevent impurities from being mixed into the solution 5. Polycrystalline silicon carbide is produced by pressureless sintering and can withstand high temperatures of 2000°C or higher.
[0036] <Crystal growth method> A method for growing a silicon carbide single crystal by a liquid phase method will be described using the flowchart of Figure 2. In step S10, the initial assembly of crucible 10 is performed. Specifically, crucible bottom 1 and first crucible wall 3 are screwed together at room temperature, and first crucible wall 3 and second crucible wall 4 are screwed together at room temperature. This completes the assembly of crucible 10 shown in Figure 1.
[0037] The crystal growth process is carried out in steps S20 to S70. Each step will be described below. In step S20, a preparation process is carried out. Specifically, the crucible 10 is placed on a tray at the bottom of the crystal growth furnace, and a heat-insulating graphite felt is placed under the crucible. Polycrystalline silicon and a cosolvent are evenly placed in the crucible. The cosolvent is one or a combination of two or more of Ti, Cr, Sc, Ni, Al, Co, Mn, Mg, Ge, As, Dy, Y, Nb, Nd, and Fe. The crucible lid 6 is placed on top of the second crucible wall 4. Heat-insulating material is placed on top of the crucible wall 2 and the crucible lid 6. The seed crystal 8 is fixed to the support shaft 7. The crystal growth furnace is sealed, and the seed crystal 8 and crucible 10 are placed at a predetermined height.
[0038] In step S30, a heating and temperature-raising process is carried out. Specifically, the atmosphere inside the crucible 10 is evacuated, and then an inert gas is introduced as protection. The temperature inside the crucible is raised by heating with a heating component to a predetermined growth temperature (typically 1700 to 2000°C). This melts the polycrystalline silicon and cosolvent, forming a solution 5.
[0039] In step S40, a seed crystal contact step is performed. Specifically, after the temperature reaches the growth temperature, the position of the seed crystal 8 is lowered and brought into contact with the solution 5.
[0040] In step S50, a growth process is carried out. In the growth process, the seed crystal 8 is pulled upward at a constant speed based on the crystal growth rate.
[0041] In the growth step, the high-temperature zone of the solution 5 is controlled to be located at the bottom of the crucible 10. This allows the graphite at the bottom of the crucible 1 to melt, thereby supplying carbon to the solution 5. There may be various methods for positioning the high-temperature zone at the bottom of the crucible 10. For example, a method of placing a resistance heater at the bottom of the crucible 10 or a method of adjusting the position of a heating coil (not shown) may be used.
[0042] The growth process has a temperature field distribution in the vertical direction (z direction) in which the temperature at the top of the solution 5 is low and the temperature at the bottom is high. Due to this temperature field distribution, the inner wall of the first crucible wall 3 made of polycrystalline silicon carbide is inevitably eroded locally at the bottom in the high-temperature region, while polycrystalline silicon carbide grows locally at the top in the low-temperature region. Therefore, as the crystal growth progresses, as shown in FIG. 3, a protrusion 3p is formed on the inner wall of the upper part of the first crucible wall 3, and a depression 3r is formed on the inner wall of the lower part of the first crucible wall 3. The protrusion 3p is a portion that protrudes inward due to the precipitation of polycrystalline silicon carbide. The depression 3r is a portion that is recessed due to erosion. Furthermore, as the crystal growth progresses, the bottom of the crucible bottom 1 becomes thinner (see region R1). Furthermore, since carbon atoms are uniformly nucleated in the protruding portion 3p, the grown polycrystalline silicon carbide is of high quality and essentially free from impurities.
[0043] By rationally adjusting the vertical temperature field distribution, the amount of polycrystalline silicon carbide generated on the upper side of the first crucible wall 3 and the amount of polycrystalline silicon carbide eroded on the lower side of the first crucible wall 3 can be controlled to be approximately equal. That is, the vertical temperature field distribution of the crucible can be adjusted so that the protrusion amount and protrusion profile of the protrusion portion 3p and the recess amount and recess profile of the recess portion 3r are equivalent. This enables the inner wall of the first crucible wall 3 to return to a vertical state (initial state) during self-repair, as described below. Methods for adjusting the temperature field distribution include, for example, adjusting the relative positions of the crucible 10 and the induction coil (not shown), adjusting the shape of the thermal felt on the outside of the crucible 10, and adjusting the heating frequency of the induction coil.
[0044] In step S60, it is determined whether the amount of crystal growth has reached a predetermined amount. If the determination is negative (S60: NO), the process returns to step S50, where crystal growth continues. On the other hand, if the determination is positive (S60: YES), the process proceeds to step S65.
[0045] In step S65, a cooling step is performed. Specifically, the seed crystal 8 is pulled up and separated from the liquid surface, and then the heating components are turned off. In step S70, a furnace opening step is performed. Specifically, the furnace chamber is opened, and the crystal is removed.
[0046] In step S80, it is determined whether it is necessary to turn the first crucible wall 3 upside down. Specifically, it is determined whether the amount of protrusion of the protrusion 3p or the amount of erosion of the recess 3r exceeds a predetermined amount. Various methods for this determination may be used. In this embodiment, it is determined that turning the crucible upside down is necessary when the total usage time of the crucible 10 after assembly exceeds a predetermined time. If turning the crucible upside down is not necessary (S80: NO), the process returns to step S20, and the next crystal growth is performed. On the other hand, if turning the crucible upside down is necessary (S80: YES), the process proceeds to step S100.
[0047] In step S100, a new crucible bottom 1 is prepared. In step S110, the first crucible wall 3 is removed from the used crucible 10. The removed first crucible wall 3 is then inverted upside down and joined to the new crucible bottom 1. The removed second crucible wall 4 is joined to the upper surface of the inverted first crucible wall 3. That is, when the used crucible 10 is in the first state (a state in which the first end face E1 is connected to the crucible bottom 1 and the second end face E2 is connected to the second crucible wall 4), the second end face E2 is connected to the new crucible bottom 1 and the first end face E1 is connected to the second crucible wall 4. When the used crucible 10 is in the second state (a state in which the second end face E2 is connected to the crucible bottom 1 and the first end face E1 is connected to the second crucible wall 4), the first end face E1 is connected to the new crucible bottom 1 and the second end face E2 is connected to the second crucible wall 4. As a result, as shown in FIG. 4, the protrusion 3p is positioned at the bottom of the first crucible wall 3 and the recessed portion 3r is positioned at the top of the first crucible wall 3.
[0048] Then, the process returns to step S20, and the next crystal growth step is performed. In the next crystal growth step, the recessed portion 3r located in the upper part of the first crucible wall 3 is gradually repaired by being filled with newly formed polycrystalline silicon carbide (see arrow A1 in FIG. 5). Furthermore, the protruding portion 3p located in the lower part of the first crucible wall 3 is eroded, and the amount of protrusion gradually decreases (see arrow A2 in FIG. 5). As a result, by continuing to use the crucible 10, the inner wall of the first crucible wall 3 can eventually return to the vertical state (initial state) as shown in FIG. 5. In other words, the first crucible wall 3 made of polycrystalline silicon carbide can self-repair.
[0049] After the self-repair is completed, if the use of the crucible 10 continues, a protrusion 3p is formed on the upper inner wall of the first crucible wall 3, and a recess 3r is formed on the lower inner wall of the first crucible wall 3, as shown in FIG. 3. If it is determined that the total usage time of the crucible 10 after being turned upside down has exceeded a predetermined time (S80: YES), the crucible bottom 1 is replaced with a new one (S100), and the first crucible wall 3 is turned upside down (S110). Then, the process returns to step S20, and the next crystal growth process is performed. Since the process is repeated from this point onward, a description thereof will be omitted.
[0050] The time used for the judgment in step S80 can be adjusted based on the state of crucible 10. After the initial assembly, crucible 10 has the inner wall of first crucible wall 3 in a substantially vertical state (FIG. 1). Because the self-repair process described above is not required, the total usage time until it is necessary to turn it upside down is relatively short. On the other hand, after turning it upside down, crucible 10 has protrusion 3p located at the bottom of first crucible wall 3 and depression 3r located at the top of first crucible wall 3 (FIG. 4). Because the self-repair process described above is required, the total usage time until it is necessary to turn it upside down is relatively long.
[0051] From this, those skilled in the art can deduce the following: A new crucible 10 is assembled (S10). The crucible 10 is in a first state (a state in which the first end face E1 is connected to the crucible bottom 1 and the second end face E2 is connected to the second crucible wall 4). An initial first growth step is performed (S20 to S70). If the crystal growth time exceeds a predetermined first time (S80: YES), the first crucible wall 3 is turned upside down to change the state from the first state to a second state (S110). The second state is a state in which the second end face E2 is connected to the crucible bottom 1 and the first end face E1 is connected to the second crucible wall 4. Thereafter, an initial second growth step is performed (S20 to S70). If the crystal growth time exceeds a second time that is longer than the first time (S80: YES), the first crucible wall 3 is turned upside down to change the state from the second state to the first state (S110). Thereafter, a second first growth step is performed (S20 to S70). If the crystal growth time exceeds the second time (S80: YES), the first crucible wall 3 is turned upside down to change the state from the first state to the second state (S110). Thereafter, the same flow is repeated.
[0052] <Issues> The following describes the challenges of the conventional graphite crucible-based crystal growth method. Graphite crucibles are made from high-purity isotropic graphite blocks, which must be hollowed out from the center to create the crucible. This process wastes a large amount of raw material. To improve the growth rate of silicon carbide single crystals, a high-temperature zone in the solution is typically placed at the bottom of the crucible, and a low-temperature zone is placed at the seed crystal area, i.e., the top of the solution. At this time, the graphite crucible's bottom, which is relatively hot, melts and enters the solution as carbon atoms. The reaction is C(S) → C(L). The seed crystal area, which is relatively cold, absorbs carbon atoms and grows into silicon carbide single crystals. The reaction is Si(L) + C(L) → SiC(S). At the same time, the excess carbon atoms are free to nucleate on the graphite crucible walls at the same low temperature, forming polycrystalline silicon carbide containing many impurities, which grows at a faster rate than single-crystal silicon carbide.
[0053] This results in the following problems: (1) The graphite dissolution reaction and silicon carbide precipitation reaction are not reversible, making it impossible to achieve self-repair and reuse of the crucible. (2) Heterogeneous nucleation of polycrystalline particles often fails to firmly adhere to the wall. The impact of the solution flow causes them to detach from the wall and adhere to the surface of the growing single crystal, significantly affecting the quality of the grown single crystal. (3) This polycrystalline region grows rapidly, and over a long period of growth, the shape of the solution zone changes, causing the flow and temperature distribution to deviate from their initial state. (4) The presence of solvent impurities in this polycrystalline region increases the risk of crucible cracking during the cooling process due to differences in thermal expansion coefficients, resulting in the risk of high-temperature solution leakage. These factors make graphite crucibles used in liquid-phase growth processes almost unusable for subsequent use, resulting in high costs for growing silicon carbide crystals using the liquid-phase method.
[0054] To address the issues associated with graphite crucibles, such as their high cost, fragility, and difficulty in reuse, Chinese Patent Application CN114481317A describes a method for reducing costs by fabricating crucibles from non-graphite materials, such as quartz, corundum, tungsten, and molybdenum. Chinese Patent Application CN113322510A also describes a method for avoiding crucible cracking during the cooling process by using crucibles made of boron nitride, corundum, sapphire, or tantalum carbide. However, these methods result in unwanted impurities being introduced into the silicon carbide crystal during growth. Furthermore, the melting points of materials such as quartz, corundum, and sapphire overlap with the commonly used growth temperatures for liquid-phase methods, making the cost of fabricating crucibles from boron nitride, tantalum carbide, tungsten, or molybdenum extremely high.
[0055] Therefore, growing silicon carbide crystals by liquid phase growth using conventional graphite crucibles can be costly and affect the quality of the crystals, while using crucibles made from other materials can introduce new impurities and increase costs.
[0056] <Effects> In the technology of the present specification, the use of isotropic graphite as the crucible bottom 1 ensures a sufficient supply of carbon to the solution 5. Furthermore, the use of polycrystalline silicon carbide as the first crucible wall 3, which can be turned upside down, allows the first crucible wall 3 to have self-repairing properties. The first crucible wall 3 can be reused simply by replacing the crucible bottom 1, significantly reducing production costs. Furthermore, the manufacturing cost of the crucible bottom 1 is significantly lower than that of a conventional graphite crucible, reducing crucible costs by approximately 80% to 90% and total manufacturing costs by approximately 30%.
[0057] The technology of the present specification can repair the recessed portion 3r and reduce the protrusion amount of the protruding portion 3p by the self-repair function of the first crucible wall 3. Since it is possible to suppress changes in the shape of the solution zone, it is possible to maintain constant solution flow and temperature distribution.
[0058] In the technology of the present specification, by using graphite for the crucible bottom 1 and polycrystalline silicon carbide for the first crucible wall 3 and the second crucible wall 4, it is possible to prevent other impurities from being mixed into the crucible 10. This makes it possible to improve the purity and quality of the grown silicon carbide crystals.
[0059] In the technology of the present specification, polycrystalline silicon carbide is used for the first crucible wall 3. This allows the deposited polycrystalline silicon carbide to adhere more firmly to the wall surface than when a graphite crucible is used. Since the deposited polycrystalline silicon carbide can be prevented from peeling off the wall surface, the quality of the grown single crystal can be improved. Furthermore, since the thermal expansion coefficients of the wall surface and the precipitate can be made the same, it is possible to prevent the crucible from cracking. [Example]
[0060] 6 shows a crucible 10 of Example 2. The same components as those in Example 1 are denoted by the same reference numerals, and the description thereof will be omitted.
[0061] The first crucible wall 3 has a first engagement portion C1 disposed on the first end face E1 and a second engagement portion C2 disposed on the second end face E2. The first engagement portion C1 and the second engagement portion C2 are configured as ring-shaped protrusions centered on the central axis CA. The first engagement portion C1 and the second engagement portion C2 have the same shape.
[0062] A crucible bottom engagement portion CB is formed on the surface of the crucible bottom 1. The crucible bottom engagement portion CB is configured as a groove centered on the central axis CA. The crucible bottom engagement portion CB is capable of mating and engaging with the first engagement portion C1 and also with the second engagement portion C2. Furthermore, the flat surface P1 of the first crucible wall 3 and the flat surface BP of the crucible bottom 1 are in close contact with each other, ensuring a seal at the connection between the first crucible wall 3 and the crucible bottom 1.
[0063] A second crucible wall engaging portion CW is formed on the lower end surface of the second crucible wall 4. The second crucible wall engaging portion CW is configured as a groove centered on the central axis CA. The second crucible wall engaging portion CW is capable of mating and engaging with the first engaging portion C1 and also with the second engaging portion C2. Furthermore, the flat surface P2 of the first crucible wall 3 and the flat surface LP of the second crucible wall 4 are in close contact with each other, thereby ensuring a seal at the connection between the first crucible wall 3 and the second crucible wall 4. [Example]
[0064] 7 shows a crucible 10 of Example 3. The same components as those in Example 1 are denoted by the same reference numerals, and the description thereof will be omitted.
[0065] The first crucible wall 3 has a first tapered surface T1 disposed on the first end face E1 and a second tapered surface T2 disposed on the second end face E2. The first tapered surface T1 and the second tapered surface T2 are configured as conical surfaces centered on the central axis CA. The first tapered surface T1 and the second tapered surface T2 have the same shape.
[0066] A crucible bottom tapered surface TB is formed on the surface of the crucible bottom 1. The crucible bottom tapered surface TB is a surface parallel to the first tapered surface T1 and the second tapered surface T2. The crucible bottom tapered surface TB can come into close contact with both the first tapered surface T1 and the second tapered surface T2.
[0067] A second crucible wall tapered surface TW is formed on the surface of the lower end face of the second crucible wall 4. The second crucible wall tapered surface TW is a surface parallel to the first tapered surface T1 and the second tapered surface T2. The second crucible wall tapered surface TW can come into close contact with both the first tapered surface T1 and the second tapered surface T2.
[0068] The crucible 10 of Example 3 can be brought into contact with the tapered surface, and can be brought into close contact in a self-aligning manner by a vertical load, thereby improving the adhesion.
[0069] Although the present invention has been described in detail by combining preferred embodiments with reference to the drawings, the present invention is not limited thereto. Those of ordinary skill in the art of the present invention may make various equivalent modifications or substitutions to the embodiments of the present invention without departing from the spirit and essence of the present invention. These modifications or substitutions should be considered to be within the scope of the present invention. Modifications or substitutions that are easily thought up by those skilled in the art of the present invention should be considered to be within the scope of the present invention.
[0070] <Modification> The structure that separably connects the first crucible wall 3 and the second crucible wall 4 may be different from the structure that separably connects the first crucible wall 3 and the crucible bottom 1. Furthermore, the crucible 10 does not need to include the second crucible wall 4. In other words, as long as it includes at least the crucible bottom 1 and the first crucible wall 3, the technology described in this specification can be realized. [Explanation of symbols]
[0071] 1: Crucible bottom 2: Crucible wall 3: First crucible wall 4: Second crucible wall 10: Crucible 100: Crystal growth apparatus CA: Central axis E1: First end surface E2: Second end surface
Claims
1. A crucible for pulling silicon carbide single crystals, The crucible comprises a crucible bottom and a first crucible wall; the crucible bottom is made of graphite; the first crucible wall is made of polycrystalline silicon carbide and has a cylindrical shape with a central axis; The first crucible wall is detachably connected to an upper portion of the crucible bottom, the first crucible wall has a first end surface located on one side of the central axis and a second end surface located on the other side of the central axis, The state can be changed between a first state in which the first end surface is connected to the bottom of the crucible and a second state in which the second end surface is connected to the bottom of the crucible. crucible.
2. the first end surface and the second end surface have a plane perpendicular to the central axis, the crucible bottom has a flat surface configured to be able to come into close contact with the first end surface and to come into close contact with the second end surface, The crucible of claim 1.
3. the first crucible wall includes a first spiral groove located on one side of the central axis and a second spiral groove located on the other side of the central axis; the first spiral groove and the second spiral groove have the same shape, the crucible bottom has a crucible bottom spiral groove capable of threadably engaging with the first spiral groove and capable of threadably engaging with the second spiral groove; The crucible of claim 1.
4. the first crucible wall includes a cylindrical first flange disposed on an outer periphery of the first end face and protruding from the first end face toward the central axis, and a cylindrical second flange disposed on an outer periphery of the second end face and protruding from the second end face toward the central axis, The first spiral groove is formed on the inner periphery of the first flange, The second flange has an inner periphery on which the second spiral groove is formed, the crucible bottom has a disk shape centered on the central axis, and the crucible bottom spiral groove is formed on the outer peripheral side surface of the crucible bottom; The crucible according to claim 3.
5. the first crucible wall includes a first engaging portion disposed on the first end surface and a second engaging portion disposed on the second end surface; The first engaging portion and the second engaging portion have the same shape, the crucible bottom has a crucible bottom engaging portion engageable with the first engaging portion and engageable with the second engaging portion; The crucible of claim 1.
6. the first engaging portion and the second engaging portion are configured with ring-shaped protrusions centered on the central axis, The crucible bottom engagement portion is configured with a groove centered on the central axis. The crucible according to claim 5.
7. the first end surface and the second end surface include a first tapered surface and a second tapered surface configured as a conical surface centered on the central axis, the first tapered surface and the second tapered surface have the same shape, the crucible bottom has a crucible bottom tapered surface parallel to the first tapered surface and the second tapered surface; the crucible bottom tapered surface is configured to be able to come into close contact with the first tapered surface and also to be able to come into close contact with the second tapered surface; The crucible according to claim 6.
8. the crucible further comprises a second crucible wall; the second crucible wall has a cylindrical shape that shares the central axis with the first crucible wall and is detachably connected to an upper portion of the first crucible wall; In the first state, a lower end surface of the second crucible wall is connected to the second end surface of the first crucible wall, The crucible of claim 1 , wherein in the second state, a lower end surface of the second crucible wall is connected to the first end surface of the first crucible wall.
9. The crucible of claim 8 , further comprising a crucible lid disposed on an upper end surface of the second crucible wall.
10. The polycrystalline silicon carbide constituting the first crucible wall has a porosity of 1% or less and a purity of more than 99.95%. The crucible of claim 1.
11. The graphite constituting the bottom of the crucible has a porosity in the range of 1% to 10% and a purity of more than 99.95%. The crucible of claim 1.
12. A method for producing a silicon carbide single crystal using a crucible, comprising: The crucible comprises a crucible bottom and a first crucible wall; the crucible bottom is made of graphite; the first crucible wall is made of polycrystalline silicon carbide and has a cylindrical shape with a central axis; The first crucible wall is detachably connected to an upper portion of the crucible bottom, the first crucible wall has a first end surface located on one side of the central axis and a second end surface located on the other side of the central axis, the first end surface is connected to the bottom of the crucible, and the second end surface is connected to the bottom of the crucible; and the first end surface is configured to be changeable between a first state in which the first end surface is connected to the bottom of the crucible and a second state in which the second end surface is connected to the bottom of the crucible; a first growth step of growing crystals in the first state and a second growth step of growing crystals in the second state are alternately repeated; A method for producing silicon carbide single crystals.
13. In the first growth step, if a crystal growth time exceeds a predetermined first time, after the first growth step is completed, the state is changed from the first state to the second state; In the subsequent first second growth step, if the crystal growth time exceeds a second time greater than the first time, the state is changed from the second state to the first state after the first second growth step is completed; In the second first growth step that is subsequently performed, if the crystal growth time exceeds the second time, the state is changed from the first state to the second state after the second first growth step is completed. The method for producing a silicon carbide single crystal according to claim 12.
14. The method further includes a step of replacing the crucible bottom between the first growth step and the second growth step, or between the second growth step and the first growth step. The method for producing a silicon carbide single crystal according to claim 12.
15. In the first growth step and the second growth step, polycrystalline silicon carbide is precipitated on an upper portion of the inner wall of the first crucible wall, thereby forming a protrusion protruding inward, and a lower portion of the inner wall of the first crucible wall is eroded, thereby forming a depression; In the first growth step and the second growth step, a temperature profile in the vertical direction of the crucible is adjusted so that a protrusion amount of the protrusion portion and a recess amount of the recess portion are approximately equal to each other. The method for producing a silicon carbide single crystal according to claim 12.