JP7615636B2 - Seed crystal holding member and single crystal manufacturing apparatus equipped with the same - Google Patents

Description

The present invention relates to a seed crystal holding member and a single crystal manufacturing apparatus equipped with the same.

Silicon carbide (SiC) has an electric breakdown field one order of magnitude larger than silicon (Si) and a band gap three times larger. SiC also has properties such as a thermal conductivity that is about three times higher than Si. For this reason, SiC is expected to be used in power devices, high-frequency devices, high-temperature operating devices, and more.

The sublimation method is widely known as one of the methods for producing SiC single crystals. In this method, the sublimation raw material contained in the raw material container is heated to 2000°C or higher, causing the raw material to sublimate and generate sublimation gas, which is then supplied to a seed crystal made of SiC single crystal that is several tens to several hundreds of degrees Celsius lower than the raw material container, and the sublimation gas is recrystallized on the seed crystal to grow a SiC single crystal.

JP 2014-5159 A

In the crucible in which the SiC single crystal is grown, the temperature of the SiC seed crystal is controlled to be lower than the surface of the raw material in order to recrystallize the raw material gas on the surface of the SiC seed crystal. In the SiC single crystal during crystal growth, if the temperature gradient within the crystal is large, the thermal stress within the crystal increases. If the thermal stress is large, a problem occurs in that the basal plane dislocation density of the manufactured SiC single crystal increases. Furthermore, if the thermal stress exceeds a certain value, cracks may occur.
The temperature gradient in the crystal can be considered separately as the temperature gradient in the crystal growth direction and the temperature gradient in the radial direction. Regarding the temperature gradient in the crystal growth direction, if the heat removal from the seed crystal side can be reduced, the temperature gradient in the crystal growth direction can be reduced. If the member to which the seed crystal is fixed can be made of a material with low thermal conductivity, the heat removal from the seed crystal side can be reduced. However, since the temperature of the seed crystal reaches 2000°C or more, graphite has conventionally been used as the member to which the seed crystal is fixed, and materials other than graphite are not usually used.

The present invention was made in consideration of the above circumstances, and aims to provide a seed crystal holding member having a lower thermal conductivity than a graphite member, and a single crystal manufacturing device equipped with the same.

The present invention provides the following means to solve the above problems.

The seed crystal holding member according to the first aspect of the present invention is a seed crystal holding member made of a carbon material and used in a single crystal manufacturing apparatus for manufacturing a single crystal ingot by growing a crystal on a seed crystal, the seed crystal holding member having a thermal conductivity adjustment layer at a position overlapping with the seed crystal when viewed from the direction in which the seed crystal and the seed crystal holding member overlap when the seed crystal is held by the seed crystal holding member, the thermal conductivity adjustment layer being a hollow layer or made of a thermal conductivity adjustment material that is a material with a thermal conductivity different from that of the carbon material, and having a smaller thermal conductivity in the crystal growth axis direction than the carbon material.

The seed crystal holding member according to the above aspect may include a plurality of the thermal conductivity adjustment layers.

In the seed crystal holding member according to the above aspect, the carbon material may be graphite.

In the seed crystal holding member according to the above aspect, the thermal conductivity adjusting material may be made of a powder material.

In the seed crystal holding member according to the above embodiment, the powder material may be selected from the group consisting of graphite, tantalum carbide, tungsten carbide, niobium carbide, molybdenum carbide, hafnium carbide, and zirconium carbide.

In the seed crystal holding member according to the above aspect, the thermal conductivity adjusting material may be made of graphite fibers.

In the seed crystal holding member according to the above aspect, the thermal conductivity adjustment layer may be a hollow layer, and the length of the hollow layer in the crystal growth axis direction may be 15 mm or less.

The seed crystal holding member according to the above aspect may include a base for fixing the seed crystal, and the base may be the part that comes into contact with the seed crystal.

The seed crystal holding member according to the above aspect may be a lid of a crucible used in a single crystal manufacturing apparatus that produces a SiC single crystal ingot using a sublimation method.

The single crystal manufacturing apparatus according to the second aspect of the present invention includes a crucible comprising the lid and the crucible body according to the above aspect.

The seed crystal holding member according to the above embodiment may be used when producing a SiC single crystal ingot using a solution process.

The seed crystal holding member according to the above embodiment may be used when producing a SiC single crystal ingot using a gas method.

The seed crystal holder of the present invention can reduce the temperature gradient in the growth axis direction of the SiC single crystal ingot during crystal growth, preventing the occurrence of cracks and making it possible to obtain a SiC single crystal ingot with a low basal plane dislocation density.

FIG. 2 is a schematic cross-sectional view showing a seed crystal holding member according to the first embodiment of the present invention. 1A and 1B are schematic cross-sectional views of the pedestal after fabrication; FIG. 1B is a schematic cross-sectional view of the pedestal after fabrication; 10A and 10B are schematic cross-sectional views of another example of a seed crystal holding member having a hollow layer in a pedestal, in which FIG. 10A is an exploded schematic cross-sectional view of the pedestal before fabrication, and FIG. 10B is a schematic cross-sectional view of the pedestal after fabrication. 10A and 10B are schematic cross-sectional views of another example of a seed crystal holding member having a hollow layer in a pedestal, in which FIG. 10A is an exploded schematic cross-sectional view of the pedestal before fabrication, and FIG. 10B is a schematic cross-sectional view of the pedestal after fabrication. FIG. 4 is a schematic cross-sectional view showing a seed crystal holding member according to a second embodiment of the present invention. 1 is a cross-sectional schematic diagram showing a single crystal manufacturing apparatus according to one embodiment of the present invention. FIG. 7 is an enlarged schematic cross-sectional view of only the cover portion of the single crystal production apparatus shown in FIG. 6. FIG. 13 is a schematic cross-sectional view showing an example of a lid portion that does not have a base. 1 shows the results of a simulation of temperature distribution (temperature difference t _es in the height direction of the SiC single crystal, and temperature difference t _e1 in the height direction of the pedestal), where (a) shows the results for Example 1, (b) shows the results for Example 2, and (c) shows the results for the comparative example.

The following describes an embodiment of the present invention with reference to the drawings. Note that in the following embodiments, parts that are identical or equivalent to each other may be given the same reference numerals in the drawings. Also, the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in making the features easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. Also, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them. Appropriate changes can be made within the scope of the effects of the present invention. The configuration shown in one embodiment can also be applied to other embodiments.

(Seed crystal holding member)
First Embodiment
Fig. 1 is a schematic cross-sectional view showing a seed crystal holding member according to a first embodiment of the present invention. In Fig. 1, a seed crystal S is illustrated to aid in understanding. In the figure, the direction in which the seed crystal S and the seed crystal holding member 10 overlap is the z direction, the plane perpendicular to the z direction is the xy plane, and the x direction and the y direction are perpendicular to each other. The same applies to the subsequent figures.

The seed crystal holding member 10 shown in FIG. 1 includes a pedestal 11 as a seed crystal holding portion to which a seed crystal S is fixed, and the pedestal 11 has hollow layers H (H1, H2, H3, H4) as thermal conductivity adjustment layers at a position overlapping with the seed crystal S when viewed in a plane from the z direction, and the thermal conductivity of the seed crystal holding member 10 in the crystal growth direction (z direction) is smaller than the thermal conductivity of the carbon material constituting the seed crystal holding member 10.
The seed crystal holding member 10 is a member made of a carbon material and used to hold a seed crystal S in a single crystal production apparatus that produces a single crystal ingot by growing a crystal on a seed crystal S. By using a seed crystal S made of silicon carbide (SiC) as the seed crystal S, a SiC single crystal ingot can be produced using the single crystal production apparatus equipped with the seed crystal holding member 10.

In this specification, the "seed crystal holding member" may or may not have a pedestal.
In this specification, the term "pedestal" refers to a part or member to which a seed crystal is fixed, and the fixing surface of the part or member has a diameter approximately equal to that of the seed crystal on the disk.

In general, "thermal conductivity" indicates the ease with which heat is transmitted from one end of an object to the other end, and is expressed in units of W/(m·K).
In this specification, the term "thermal conductivity of the seed crystal holding member" refers to the ease of heat transfer from one end to the other end of the seed crystal holding member in the crystal growth direction (z direction), and the unit is W/(m·K) as in the general "thermal conductivity". Here, for example, when the seed crystal holding member is a lid part of a crucible having a pedestal, the "one end" is the surface of the pedestal to which the seed crystal is fixed (reference numeral 20a in FIG. 6), and the other end is the surface of the lid part that does not have the pedestal (reference numeral 20b in FIG. 6). The "thermal conductivity of the seed crystal holding member" can be measured by a known method for measuring "thermal conductivity". For example, it can be measured by a laser flash method or the like.

In addition to the pedestal 11, the seed crystal holding member 10 further includes a support member 12 that is connected to the pedestal 11 and supports the pedestal 11. The pedestal 11 and the support member 12 can be connected to each other by, for example, a carbon adhesive or by screws.
The seed crystal holding member 10 includes a base and a support member, but may be configured to consist of only the support member. When the seed crystal holding member 10 is configured to consist of only the support member (in this case, the seed crystal holding member 10 coincides with the support member), the seed crystal is fixed to a predetermined position of the support member.

The seed crystal holding member 10 has a configuration having four hollow layers, but there is no limit to the number or size of the hollow layers as long as the thermal conductivity of the seed crystal holding member 10 in the crystal growth direction is smaller than the thermal conductivity of the carbon material that constitutes the seed crystal holding member 10.
2 to 4 show examples of seed crystal holders in which the thermal conductivity adjustment layer is a hollow layer and how to make them. By filling the hollow layer of the seed crystal holder shown in each figure with a thermal conductivity adjustment material, it is possible to make a seed crystal holder in which the thermal conductivity adjustment layer is made of the thermal conductivity adjustment material.

As an example, the seed crystal holding member shown in FIG. 2 can be made by preparing a pedestal body 111A with a countersunk 111Aa, stacking cylinders 111B and disks 111C alternately on the bottom surface 111Aaa within the countersunk 111Aa to assemble a pedestal 111 having a hollow layer, and connecting the pedestal 111 to the support member 12 (see FIG. 1). In the example shown in FIG. 2, the pedestal 111 can be stably connected to the support member 12 by the umbrella portion 111Ab. FIG. 2(a) is an exploded cross-sectional schematic diagram of the pedestal before fabrication, and (b) is a cross-sectional diagram of the pedestal after fabrication.

FIG. 2 shows an example in which there are four cylinders 111B and four disks 111C (cylinders 111Ba, 111Bb, 111Bc, and 111Bd, and disks 111Ca, 111Cb, 111Cc, and 111Cd), but there may be five or more of each, or three or less of each.
The cylinder 111B and the disk 111C may be connected to the inner surface of the countersunk portion 111Aa by, for example, a carbon adhesive or by screws. The cylinder 111B and the disk 111C may be connected to each other by, for example, a carbon adhesive or by screws.

In the seed crystal holding member shown in FIG. 2, after placing the cylinder 111Ba, it is filled with a thermal conductivity adjusting material, then the disk 111Ca is placed, the cylinder 111Bb is placed on top of that, it is filled with a thermal conductivity adjusting material, then the disk 111Cb is placed, and so on. By repeating this process, it is possible to create a seed crystal holding member whose thermal conductivity adjusting layer is made of a thermal conductivity adjusting material.

The seed crystal holding member shown in FIG. 3 can be made, for example, by preparing a pedestal body 211A with a countersunk hole 211Aa and a female thread cut on its inner surface 211Aaa, screwing a disk 211B having a male thread on its side so that it can be screwed into the female thread, assembling a pedestal 211 with a hollow layer, and connecting the pedestal 211 to the support member 12 (see FIG. 1). In the example shown in FIG. 3, the umbrella portion 211Ab allows the pedestal 211 to be stably connected to the support member 12. (a) is an exploded cross-sectional schematic diagram of the pedestal before fabrication, and (b) is a cross-sectional diagram of the pedestal after fabrication.

In the case of the base shown in Figure 3, the position can be easily adjusted, and adjustments can be made to achieve the desired thermal conductivity calculated through simulation, etc.

In the example shown in FIG. 3, four discs 211B (discs 211Ba, 211Bb, 211Bc, and 211Bd) are used, but the number may be five or more, or three or less.

In addition, in the seed crystal holding member shown in FIG. 3, a thermal conductivity adjusting material is laid on the bottom surface of the countersunk 211Aa, then a disk 211Ba is placed, a thermal conductivity adjusting material is laid on top of that, then a disk 211Bb is placed, and so on. By repeating this process, a seed crystal holding member can be produced in which the thermal conductivity adjusting layer is made of the thermal conductivity adjusting material.

As an example, the seed crystal holding member shown in FIG. 4 can be made by preparing a pedestal body 311A with a countersunk 311Aa, stacking a disk 311B with a support portion on its underside on the bottom surface 311Aaa of the countersunk 311Aa to assemble a pedestal 311 having a hollow layer, and connecting the pedestal 311 to the support member 12 (see FIG. 1). In the example shown in FIG. 4, the pedestal 311 can be stably connected to the support member 12 by the umbrella portion 311Ab. (a) is an exploded cross-sectional schematic diagram of the pedestal before fabrication, and (b) is a cross-sectional diagram of the pedestal after fabrication.

In the example shown in FIG. 4, four disks 311B (disks 311Ba, 311Bb, 311Bc, and 311Bd) are provided with support portions on their lower surfaces. However, the number of disks may be five or more, or may be three.
The disks 311Ba, 311Bb, 311Bc, and 311Bd may be connected to the inner surface of the countersunk hole 311Aa with, for example, a carbon adhesive or with screws. Also, the disks 311Ba, 311Bb, 311Bc, and 311Bd may be connected to each other with, for example, a carbon adhesive or with screws.

In the seed crystal holding member shown in FIG. 4, a thermal conductivity adjusting material is laid on the bottom surface of the countersunk 311Aa, then a disk 311Ba with a support on its underside is placed, a thermal conductivity adjusting material is laid on top of that, and then a disk 311Bb with a support on its underside is placed, and so on. By repeating this process, a seed crystal holding member can be produced in which the thermal conductivity adjusting layer is made of the thermal conductivity adjusting material.

Heat transfer occurs by radiation in the cavity layers and by thermal conduction in non-cavity areas (areas made of carbon material). In base 11, in which cavity layers and carbon material layers are alternately arranged, heat transfer occurs by alternating radiation and thermal conduction.
Comparing the transfer of heat by conduction and the transfer of heat by radiation, it is considered that the transfer of heat is faster in radiation than in conduction because the heat transfer occurs by radiation. However, the emissivity of general graphite is 0.7 to 0.9, which is smaller than the 1 of an ideal black body. In other words, this means that when heat transfers through a hollow layer, the amount of radiation from the high-temperature side in the hollow layer is about 10 to 30% smaller than that of an ideal black body, and furthermore, even in the opposing part, which is the low-temperature side, the amount of absorption is 10 to 30% smaller than that of an ideal black body. Since the heat transfer in the pedestal part is vertical, a hollow layer with a certain height becomes a resistance to the heat transfer due to the above-mentioned influence, and as a result, it has a heat insulating effect. Specifically, in the case of graphite with an emissivity of 0.8, if the height of the hollow layer is 15 mm or less, the heat transfer in the hollow layer is slower than that by thermal conduction.
However, since the emissivity changes depending on the material and surface condition of the graphite, once the carbon material constituting the seed crystal holding member has been determined, it is possible to confirm by conducting a few experiments whether the thermal conductivity of the seed crystal holding member is greater or smaller than that of a seed crystal holding member that does not have a hollow layer.

The seed crystal holding member 10 is made of a carbon material, but it is acceptable for it to contain impurities as long as it has a purity sufficient for use in producing a SiC single crystal ingot.
The carbon material constituting the seed crystal holding member 10 is preferably graphite. In the sublimation method, solution method, and gas method used in the production of SiC single crystal ingots, the seed crystal is heated to a high temperature of 2000° C. or more. Graphite has an extremely high sublimation temperature of 3550° C., and can withstand the high temperatures during growth.

The pedestal 11 has a hollow layer that extends in a direction parallel to the xy plane perpendicular to the z direction in which the pedestal 11 and the seed crystal S overlap.
When the seed crystal holding member 10 does not have a pedestal 11, the support member 12 has a hollow layer at a position overlapping with the seed crystal when viewed from the z direction.

In the case of a graphite seed crystal holder that does not have a hollow layer, its thermal conductivity (i.e., the thermal conductivity of graphite) is about 30 to 40 W/m·K. In contrast, in the case of pedestal 11 that has a hollow layer made of graphite, its thermal conductivity can be made smaller than 30 to 40 W/m·K. At 2000 to 2400° C., which is near the growth temperature of SiC single crystal, the thermal conductivity of SiC single crystal is about 20 to 25 [W/(m·K)], and the thermal conductivity of graphite used in the crucible is about 30 to 40 [W/(m·K)].
The degree to which the thermal conductivity is reduced can be adjusted by the configuration of the cavity layer.

The base 11 and the seed crystal S are bonded to each other at a bonding surface 11a and a bonding surface Sa. In this case, the bonding at the bonding surfaces may be performed by fixing the base 11 and the seed crystal S via an adhesive.
The pedestal 11 includes parallel portions 11A, 11B1, 11B2, 11B3, and 11C extending substantially parallel to the bonding surface of the seed crystal S, in this order from the bonding surface Sa side of the seed crystal S, and further includes a side wall portion 11AA in a direction substantially perpendicular to the bonding surface of the seed crystal S. The hollow layer H1 is configured by being surrounded by the parallel portion 11A, the parallel portion 11B1, and the side wall portion 11AA, the hollow layer H2 is configured by being surrounded by the parallel portion 11B1, the parallel portion 11B2, and the side wall portion 11AA, the hollow layer H3 is configured by being surrounded by the parallel portion 11B2, the parallel portion 11B3, and the side wall portion 11AA, and the hollow layer H4 is configured by being surrounded by the parallel portion 11B3, the parallel portion 11C, and the side wall portion 11AA.

Methods for fixing the seed crystal to the pedestal 11 include, for example, fixing the outer periphery of the seed crystal with graphite claws, or attaching the seed crystal to the pedestal using a carbon adhesive.

As will be described in detail later, when the seed crystal holding member of the present invention is used as a crucible lid (hereinafter simply referred to as "lid") for the sublimation method, the lid (or base) dissipates less heat than a conventional graphite lid (or graphite base), and thermal stress within the single crystal during crystal growth is reduced more than in the past.

The seed crystal holding member of the present invention can be used as a member for holding a single crystal when producing a single crystal ingot using the sublimation method, solution method, or gas method.

Second Embodiment
FIG. 5 is a schematic cross-sectional view showing a seed crystal holder according to a second embodiment of the present invention.
The seed crystal holding member 10A shown in Figure 5 has a pedestal 111 as a seed crystal holding portion to which the seed crystal S is fixed, and the pedestal 111 has a thermal conductivity adjustment layer 13 (13A, 13B, 13C, 13D) at a position overlapping with the seed crystal S when viewed in a plane from the z direction, and the thermal conductivity of the seed crystal holding member 10A in the crystal growth direction is smaller than the thermal conductivity of the carbon material that constitutes the seed crystal holding member 10A.

The seed crystal holding member of the first embodiment is provided with a hollow layer serving as a thermal conductivity adjustment layer, whereas the seed crystal holding member of the second embodiment differs from the seed crystal holding member of the first embodiment in that the thermal conductivity adjustment layer is made of a thermal conductivity adjustment material, which is a material with a thermal conductivity different from that of the carbon material constituting the seed crystal holding member.
The seed crystal holder 10A shown in FIG. 5 is configured so that the hollow layer is filled with the thermal conductivity adjusting material, but may be configured so that a carbon material layer and a thermal conductivity adjusting layer are laminated in this order.

As the thermal conductivity adjusting material, various materials can be used as long as the thermal conductivity of seed crystal holding member 10A in the crystal growth direction is smaller than the thermal conductivity of the carbon material constituting seed crystal holding member 10A.
Examples of the thermal conductivity adjusting material include graphite fiber and high melting point metal carbides (tantalum carbide, tungsten carbide, niobium carbide, molybdenum carbide, hafnium carbide, zirconium carbide).

The thermal conductivity adjusting material may be a powder material. When the powder layer and the uniform continuum layer are made of the same material, the powder layer is less likely to conduct heat than the uniform continuum layer. Therefore, the seed crystal holding member 10A has a smaller thermal conductivity than a conventional seed crystal holding member that does not have a thermal conductivity adjusting layer.
Examples of the powder material include graphite powder and powder of high melting point metal carbide (tantalum carbide (TaC), tungsten carbide, niobium carbide, molybdenum carbide, hafnium carbide, zirconium carbide).
The seed crystal holding member 10A has four thermal conductivity adjustment layers, but there is no limit to the number or size of the thermal conductivity adjustment layers as long as the thermal conductivity of the seed crystal holding member 10A in the crystal growth direction is smaller than the thermal conductivity of the carbon material that constitutes the seed crystal holding member 10A.

(Single crystal manufacturing equipment)
Fig. 6 is a cross-sectional schematic diagram showing a single crystal manufacturing apparatus according to one embodiment of the present invention. In the figure, the direction connecting the crucible lid and the bottom of the crucible body is the z direction, the plane perpendicular to the z direction is the xy plane, and the x direction and the y direction are perpendicular to each other. The single crystal manufacturing apparatus shown in Fig. 6 is used when manufacturing a single crystal ingot by sublimation. Fig. 7 is an enlarged cross-sectional schematic diagram of only the lid 20 shown in Fig. 6.

The single crystal manufacturing apparatus 1000 shown in Fig. 6 includes a crucible 100 including a lid 20, which is an example of a seed crystal holding member of the present invention, and a crucible body 30. A heat insulating material (not shown) for keeping the crucible 100 warm and a heating means 40 are provided on the outer periphery of the crucible body 30. In Fig. 6, a raw material M for single crystal growth and a seed crystal S are also shown to aid in understanding. The raw material M for single crystal growth is accommodated in the lower part of the crucible body 30.
The seed crystal S is fixed to a pedestal 21 provided on the lid portion 20. Examples of a method for fixing the SiC seed crystal to the pedestal 21 include a method for fixing the outer periphery of the SiC seed crystal with graphite claws and a method for attaching the SiC seed crystal to the pedestal using a carbon adhesive.

Crucible 100 is a crucible for producing SiC single crystals by sublimation, and may be made of, for example, graphite or graphite coated with tantalum carbide. Crucible 100 becomes hot during growth. Therefore, it must be made of a material that can withstand high temperatures. As mentioned above, graphite has an extremely high sublimation temperature of 3550°C, and can withstand the high temperatures that occur during growth.

In the single crystal manufacturing apparatus 1000, a pedestal 21 protruding downward is provided at the center of the inside of the lid part 20, and the lid part 20 is composed of the pedestal 21 and a plate 22. The pedestal 21 corresponds to the pedestal 11 shown in Fig. 1 or the pedestal 1011 shown in Fig. 5, and the plate 22 corresponds to the support member 12 shown in Fig. 1 or Fig. 5.
The seed crystal S is fixed to one surface (seed crystal side surface) 21a of the pedestal 21. The pedestal 21 faces the single crystal growth raw material M contained in the crucible 100 by covering the crucible body 30 with the lid part 20. By facing the single crystal growth raw material M and the seed crystal S placed on the pedestal 21, it is possible to efficiently supply raw material gas to the seed crystal S. The pedestal 21 and the plate 22 may be configured as an integral member or may be separate members.

The lid 20 (or the base 21) has a thermal conductivity adjusting layer 33 (33A, 33B, 33C, 33D) that extends in the xy direction, and therefore has a smaller thermal conductivity than a conventional graphite lid (or a graphite base) that does not have a thermal conductivity adjusting layer. The thermal conductivity adjusting layer 33 is a cavity layer or a layer made of a thermal conductivity adjusting material that is a material with a thermal conductivity different from that of the carbon material that constitutes the lid 20.
The lid portion (or the base which is the portion in contact with the seed crystal), which is an example of a seed crystal holding member of the present invention, dissipates less heat than a conventional graphite lid portion (or a graphite base), and reduces thermal stress in the growing single crystal more than in the conventional method.

In the lid portion 20 shown in FIG. 7, the thermal conductivity adjustment layer 33 has a rectangular shape in cross section, but is not limited to a rectangular shape. In addition, the four thermal conductivity adjustment layers 33A, 33B, 33C, and 33D have the same shape, but may have different shapes.

In the single crystal manufacturing apparatus 1000, the lid portion 20 is a type that includes a pedestal 21 on which a seed crystal is fixed, but as shown in FIG. 8, the single crystal manufacturing apparatus may be of a type in which the lid portion 20A does not include a pedestal and the seed crystal S is fixed to a part of the lid portion 20A. In this type, the portion 22A that corresponds to the plate 22 in FIG. 8 has a thermal conductivity adjustment layer 33.

Example 1
9(a) shows the results of a simulation of the temperature distribution near the pedestal (the temperature difference in the height direction of the SiC single crystal and the temperature difference in the height direction of the pedestal) for a single crystal manufacturing apparatus of the type shown in FIG. 1, i.e., having a lid with a pedestal. Note that FIG. 9(a) shows the results of Example 1, (b) shows the results of Example 2, and (c) shows the results of a comparative example. The cross-sectional schematic diagrams shown do not show the characteristics of each example and comparative example.
This simulation was performed using the vapor phase crystal growth analysis software "Virtual Reactor" manufactured by STR-Group Ltd. This simulation is widely used to simulate the temperature distribution in a furnace, and has been confirmed to have a high correlation with actual experimental results. In order to reduce the calculation load, the simulation was performed only on the structure of half (half in the radial direction) of an arbitrary cross section passing through the central axis of the cylindrical crucible.

In the model of the single crystal manufacturing equipment used in the simulation, four cavity layers were used as the thermal conductivity adjustment layer. The base was made of graphite, and the height of the base (length in the z direction) was 59 mm, the height of the four cavity layers (length in the z direction) was 2 mm, and the height of the SiC single crystal (length in the z direction) was 53 mm. The thermal conductivity of graphite was 40 W/m·K.

As a result of the simulation, the temperature difference t _es in the height direction of the SiC single crystal (i.e., the difference between the temperature of the growth surface of the SiC single crystal and the temperature of the bonding surface with the pedestal) and the temperature difference t _e1 in the height direction of the pedestal (i.e., the difference between the temperature of the bonding surface with the SiC single crystal and the temperature of the surface opposite it) were 75°C and 99°C, respectively (see Figure 9(a)).

Example 2
A simulation was performed using a model in which the thermal conductivity adjustment layer was made of a thermal conductivity adjustment material. The difference from Example 1 is that the thermal conductivity adjustment layer was made of one layer of thermal conductivity adjustment material with a height of 5 mm, rather than four layers of hollow layers with a height of 2 mm. The thermal conductivity of the thermal conductivity adjustment material was set to 2 W/m·K.
As a result of the simulation, the temperature difference t _es in the height direction of the SiC single crystal (i.e., the difference between the temperature of the growth surface of the SiC single crystal and the temperature of the bonding surface with the pedestal) and the temperature difference t _e1 in the height direction of the pedestal (i.e., the difference between the temperature of the bonding surface with the SiC single crystal and the temperature of the surface opposite it) were 60°C and 105°C, respectively (see Figure 9 (b)).

Comparative Example
The results of a simulation of the temperature distribution near the pedestal of a conventional single crystal manufacturing apparatus equipped with a lid having a pedestal without a cavity layer are shown in Fig. 9(b). The only difference from the model in Fig. 9(a) is that the pedestal does not have a cavity layer, and the materials and dimensions are the same.

As a result of the simulation, the temperature difference t _es in the height direction of the SiC single crystal (i.e., the difference between the temperature of the growth surface of the SiC single crystal and the temperature of the bonding surface with the pedestal) and the temperature difference t _e1 in the height direction of the pedestal (i.e., the difference between the temperature of the bonding surface with the SiC single crystal and the temperature of the surface opposite it) were 86°C and 69°C, respectively (see Figure 9 (c)).

In the comparative example, the temperature difference t _es in the height direction of the SiC single crystal was 86° C., whereas the temperature differences t _es in the height direction of the SiC single crystal in Examples 1 and 2 were 75° C. and 60° C., respectively. Since the temperature difference in the height direction of the SiC single crystal is smaller in the example than in the comparative example, it is possible to reduce thermal stress during crystal growth and to obtain a SiC single crystal ingot with a low basal plane dislocation density and no cracks.

REFERENCE SIGNS LIST 10, 10A Seed crystal holding member 11, 21, 111, 211, 311, 1011 Pedestal 12 Support member 13, 13A, 13B, 13C, 13D, 33, 33A, 33B, 33C, 33D Thermal conductivity adjustment layer 20, 20A Lid 21 Pedestal 22 Plate 30 Crucible body H, H1, H2, H3, H4 Hollow layer 100 Crucible 1000 Single crystal manufacturing apparatus

Claims (10)

A seed crystal holding member for use in a single crystal production apparatus for producing a single crystal ingot by growing a crystal on a seed crystal, the seed crystal holding member being made of a carbon material and holding the seed crystal,
a thermal conductivity adjustment layer at a position overlapping with the seed crystal when viewed from a direction in which the seed crystal and the seed crystal holding member overlap when the seed crystal is held by the seed crystal holding member;
the thermal conductivity adjustment layer is a layer of a plurality of cavities or is made of a powder material of a thermal conductivity adjustment material having a thermal conductivity different from that of the carbon material;
A seed crystal holder having a thermal conductivity in a crystal growth axis direction that is smaller than that of the carbon material. The seed crystal holder according to claim 1, wherein the carbon material is graphite. 2. The seed holder of claim 1 , wherein the powdered material is selected from the group consisting of graphite, tantalum carbide, tungsten carbide, niobium carbide, molybdenum carbide, hafnium carbide, and zirconium carbide. The seed crystal holder according to claim 1 , wherein the thermal conductivity adjusting material is made of graphite fiber. 3. The seed crystal holder according to claim 1, wherein the thermal conductivity adjustment layer is a cavity layer, and the length of the cavity layer in the crystal growth axis direction is 15 mm or less. The seed crystal holder according to claim 1 , further comprising a base for fixing a seed crystal, the base being a portion that comes into contact with the seed crystal. The seed crystal holder according to claim 1 , wherein the seed crystal holder is a lid of a crucible used in a single crystal manufacturing apparatus for manufacturing a SiC single crystal ingot by sublimation. A single crystal manufacturing apparatus comprising a crucible comprising the lid and the crucible body according to claim 7 . The seed crystal holder according to claim 1 , which is used when producing a SiC single crystal ingot by a solution process. The seed crystal holder according to claim 1 , which is used when producing a SiC single crystal ingot using a gas method.

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