Seed crystal holding member and single crystal manufacturing apparatus equipped with same

Abstract

To provide a seed crystal holding member having a higher heat transfer coefficient than a lid part made of graphite and a single crystal production apparatus equipped with the same.SOLUTION: A seed crystal holding member 10 is used in a single crystal production apparatus for growing a crystal on a seed crystal to produce a single crystal ingot. The seed crystal holding member for holding a seed crystal is made of a carbon material and has cavity layers H at the positions overlapping with the seed crystal, when viewing from the direction superimposing the seed crystal on the seed crystal holding member when the seed crystal is held by the seed crystal holding member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a seed crystal holder and a single crystal manufacturing apparatus equipped with the same. [Background technology]

[0002] Silicon carbide (SiC) has a dielectric breakdown field that is one order of magnitude larger than that of silicon (Si) and a band gap that is three times larger. SiC also has properties such as a thermal conductivity that is about three times higher than that of Si. For these reasons, SiC is expected to be used in power devices, high-frequency devices, high-temperature operating devices, and other applications.

[0003] Sublimation is a widely known method for producing SiC single crystals. In this method, a sublimation source material contained in a source material container is heated to 2000°C or higher to sublimate the source material, generating a sublimation gas. This sublimation gas is then supplied to a seed crystal made of SiC single crystal, which has been cooled to a temperature several tens to several hundreds of degrees Celsius lower than that of the source material container, whereby the sublimation gas is recrystallized on the seed crystal to grow a SiC single crystal. To reduce the costs associated with crystal growth, there is a demand for faster crystal growth. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-5159 Summary of the Invention [Problem to be solved by the invention]

[0005] In the crucible where SiC single crystals are grown, the temperature of the SiC seed crystal is controlled to be lower than the temperature of the source material surface in order to recrystallize the source gas on the surface of the SiC seed crystal. To increase the crystal growth rate, a large temperature difference between the source material surface and the seed crystal surface is desirable at the start of crystal growth, and a large temperature difference between the source material surface and the grown single crystal surface is desirable during crystal growth. For example, if heat removal from the seed crystal can be increased, this temperature difference can be increased. Heat removal from the seed crystal can be increased by forming the member to which the seed crystal is fixed using a material with high thermal conductivity. However, because the temperature of the seed crystal exceeds 2000°C, graphite has traditionally been used as the member to which the seed crystal is fixed, and materials other than graphite are not commonly used. Furthermore, while it is possible to increase heat removal by making the lid thinner, it is difficult to do so from the perspective of strength.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a seed crystal holder having a higher thermal conductivity than a graphite member, and a single crystal manufacturing apparatus including the same. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following means.

[0008] A seed crystal holding member according to a first aspect of the present invention is a seed crystal holding member made of a carbon material and configured to hold a seed crystal in a single crystal manufacturing apparatus for manufacturing a single crystal ingot by growing a crystal on the seed crystal, and has a hollow 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.

[0009] In the seed crystal holding member according to the above aspect, the length of the hollow layer in the direction in which the seed crystal and the seed crystal holding member overlap each other may be longer than 15 mm.

[0010] The seed crystal holder according to the above aspect may include a plurality of the hollow layers.

[0011] In the seed crystal holding member according to the above aspect, the carbon material may be graphite.

[0012] The seed crystal holding member according to the above aspect may include a base for fixing the seed crystal, and the base may be a portion that comes into contact with the seed crystal.

[0013] The seed crystal holder according to the above aspect may be a lid of a crucible used in a single crystal manufacturing apparatus for manufacturing a SiC single crystal ingot by sublimation.

[0014] A single crystal manufacturing apparatus according to a second aspect of the present invention includes a crucible comprising the lid according to the above aspect and a crucible body.

[0015] The seed crystal holder according to the above aspect may be used when producing a SiC single crystal ingot using a solution process.

[0016] The seed crystal holder according to the above aspect may be used when producing a SiC single crystal ingot using a gas method. [Effects of the Invention]

[0017] The seed crystal holder of the present invention has a higher thermal conductivity than conventional members, and therefore enables high-speed growth of SiC single crystal ingots. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a cross-sectional view showing a seed crystal holder according to one embodiment of the present invention. [Figure 2] 1A and 1B are diagrams showing an example of a seed crystal holder having a hollow layer in a pedestal, in which (a) is an exploded cross-sectional view of the pedestal before fabrication, and (b) is a cross-sectional view of the pedestal after fabrication. [Figure 3] 1A and 1B are diagrams showing another example of a seed crystal holder having a hollow layer in a pedestal, in which (a) is an exploded cross-sectional view of the pedestal before fabrication, and (b) is a cross-sectional view of the pedestal after fabrication. [Figure 4]1A and 1B are diagrams showing another example of a seed crystal holder having a hollow layer in a pedestal, in which (a) is an exploded cross-sectional view of the pedestal before fabrication, and (b) is a cross-sectional view of the pedestal after fabrication. [Figure 5] 1 is a cross-sectional view showing a single crystal manufacturing apparatus according to an embodiment of the present invention. [Figure 6] FIG. 6 is an enlarged schematic cross-sectional view of only the cover portion of the single crystal manufacturing apparatus shown in FIG. 5. [Figure 7] FIG. 10 is a schematic cross-sectional view showing an example of a lid portion of a type that does not have a base. [Figure 8] The results of a temperature distribution simulation (temperature difference tes in the height direction of the SiC single crystal and temperature difference te1 in the height direction of the pedestal) are shown, with (a) showing the results of an embodiment and (b) showing the results of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that in the following embodiments, identical or equivalent parts may be designated by the same reference numerals in the drawings. Furthermore, the drawings used in the following description may show characteristic parts enlarged for the sake of clarity, and the dimensional ratios of each component may not necessarily be the same as in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications can be made within the scope of the effects of the present invention. A configuration shown in one embodiment may also be applied to other embodiments.

[0020] (Seed crystal holding member) Fig. 1 is a cross-sectional schematic diagram showing a seed crystal holder according to one embodiment of the present invention. To facilitate understanding, Fig. 1 illustrates a seed crystal S. In the figure, the direction in which the seed crystal S and the seed crystal holder 10 overlap is the z direction, the plane perpendicular to the z direction is the xy plane, and the x and y directions are perpendicular to each other. This also applies to the subsequent figures.

[0021] The seed crystal holding member 10 shown in Figure 1 has a pedestal 11 as a seed crystal holding portion to which the seed crystal S is fixed, and the pedestal 11 has a hollow layer H (H1, H2) at a position overlapping with the seed crystal S when viewed in a plane from the z direction. The seed crystal holding member 10 is a member made of a carbon material for holding a seed crystal S in a single crystal production apparatus that produces a single crystal ingot by growing a crystal on the seed crystal S. By using a seed crystal S made of silicon carbide 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.

[0022] 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 thereof has a diameter approximately the same as that of the disk-shaped seed crystal.

[0023] 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 screws. The seed crystal holding member 10 includes a base and a support member, but may also consist of only a support member. When the seed crystal holding member 10 consists of only a 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 on the support member.

[0024] The seed crystal holding member 10 has two hollow layers (cavities), but may have one, or three or more. 2 to 4 show examples of seed crystal holding members having a hollow layer and how to make them.

[0025] As an example, the seed crystal holder shown in Figure 2 can be made by preparing a pedestal body 111A with a countersunk portion 111Aa, stacking cylinders 111B and disks 111C alternately on the bottom surface 111Aaa of the countersunk portion 111Aa to assemble a pedestal 111 having a hollow layer, and connecting the pedestal 111 to the support member 12 (see Figure 1). In the example shown in Figure 2, the umbrella portion 111Ab enables the pedestal 111 to be stably connected to the support member 12. Figure 2(a) is an exploded cross-sectional schematic diagram of the pedestal before fabrication, and (b) is a cross-sectional view of the pedestal after fabrication.

[0026] Although FIG. 2 shows an example in which there are two cylinders 111B and two disks 111C (cylinders 111Ba, 111Bb and disks 111Ca, 111Cb), there may be three or more of each, or one of each. The cylinder 111B and the disk 111C may be connected to the inner surface of the countersunk hole 111Aa with, for example, a carbon adhesive or with screws. Also, the cylinder 111B and the disk 111C may be connected to each other with, for example, a carbon adhesive or with screws.

[0027] As an example, the seed crystal holding member shown in Figure 3 can be made by preparing a pedestal body 211A with a counterbore 211Aa and a female thread 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 pedestal 211 having a hollow layer, and connecting pedestal 211 to support member 12 (see Figure 1). In the example shown in Figure 3, pedestal 211 can be stably connected to support member 12 by umbrella portion 211Ab. (a) is an exploded cross-sectional schematic diagram of the pedestal before fabrication, and (b) is a cross-sectional view of the pedestal after fabrication.

[0028] In the case of the base shown in FIG. 3, the position can be easily adjusted, and adjustments may be made to aim for a desired thermal conductivity calculated by simulation or the like.

[0029] In the example shown in FIG. 3, an example in which there are two disks 211B is shown, but there may be three or more disks, or there may be one disk.

[0030] As an example, the seed crystal holder shown in Figure 4 can be made by preparing a pedestal body 311A ​​with a countersunk portion 311Aa, stacking a disk 311B with a support portion on its underside on the bottom surface 311Aaa of the countersunk portion 311Aa to assemble a pedestal 311 having a hollow layer, and connecting the pedestal 311 to the support member 12 (see Figure 1). In the example shown in Figure 4, the umbrella portion 311Ab enables the pedestal 311 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.

[0031] In the example shown in FIG. 4, three disks 311B (disks 311Ba, 311Bb, 311Bc) with support portions on their lower surfaces are shown, but there may be four or more, or just one. The disks 311Ba, 311Bb, and 311Bc may be connected to the inner surface of the countersunk hole 311Aa with, for example, a carbon adhesive or screws. Also, the disks 311Ba, 311Bb, and 311Bc may be connected to each other with, for example, a carbon adhesive or screws.

[0032] The seed crystal holder 10 is made of a carbon material, but it is permissible for it to contain impurities as long as it is of a purity sufficient for use in producing a SiC single crystal ingot. The carbon material constituting the seed crystal holder 10 is preferably graphite. In the sublimation method, solution method, and gas method used to manufacture SiC single crystal ingots, the seed crystal is heated to a high temperature of 2000°C or higher. Graphite has an extremely high sublimation temperature of 3550°C and can withstand the high temperatures during growth.

[0033] The pedestal 11 has a cavity layer that extends in a direction parallel to the xy plane, which is perpendicular to the z direction in which the pedestal 11 and the seed crystal S overlap. In the cavity layer, heat moves by radiation, which makes the heat move faster than when heat moves by thermal conduction. Therefore, it is possible to increase the thermal conductivity compared to a graphite seed crystal holder that does not have a cavity layer. Heat moves in the pedestal 11 by radiation in the cavity layer and by thermal conduction in areas other than the cavity layer (portions made of graphite). However, the emissivity of ordinary graphite is 0.7 to 0.9, which is smaller than the 1 of an ideal blackbody. This means that when heat transfers through a cavity layer, the amount of radiation from the high-temperature side of the cavity layer is approximately 10 to 30% less than that of an ideal blackbody, and even in the opposite, low-temperature side, the amount of absorption is 10 to 30% less than that of an ideal blackbody. Because heat transfer in the base is vertical, a cavity layer with a small height may have a slower heat transfer rate than thermal conduction. Specifically, in the case of graphite with an emissivity of 0.8, if the height (length) of the cavity layer is greater than 15 mm, heat transfer within the cavity layer will be faster than heat transfer by thermal conduction. Since the emissivity varies depending on the material and surface condition of the graphite, once the carbon material constituting the seed crystal holding member is determined, it can be confirmed by conducting a few experiments whether the thermal conductivity of the seed crystal holding member will be higher or lower than that of a seed crystal holding member that does not have a hollow layer. The thermal conductivity of the base 11 referred to here is the apparent thermal conductivity of the base 11, which is a combination of heat transfer by radiation and heat conduction.

[0034] In the case of a graphite seed crystal holder that does not have a hollow layer, its thermal conductivity is approximately 30 to 40 W / mK. In contrast, in the case of pedestal 11 that has a graphite hollow layer, its thermal conductivity can be made greater than 30 to 40 W / mK. The degree to which the thermal conductivity is increased can be adjusted by the configuration of the cavity layer.

[0035] The base 11 and the seed crystal S are bonded to each other at their respective bonding surfaces 11a and Sa. In this case, bonding at the bonding surfaces may be performed via an adhesive. The base 11 includes parallel portions 11A, 11B, and 11C extending substantially parallel to the bonding surface Sa 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 extending in a direction substantially perpendicular to the bonding surface of the seed crystal S. The hollow layer H1 is configured to be surrounded by the parallel portions 11A, 11B, and the side wall portion 11AA, and the hollow layer H2 is configured to be surrounded by the parallel portions 11B, 11C, and the side wall portion 11AA.

[0036] The seed crystal can be fixed to the pedestal 11 by, for example, fixing the outer periphery of the seed crystal with graphite claws or by attaching the seed crystal to the pedestal using a carbon adhesive.

[0037] 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 a sublimation method, the lid (or base) dissipates more heat than a conventional graphite lid (or graphite base), making it possible to increase the growth rate of a single crystal compared to conventional methods.

[0038] The seed crystal holder of the present invention can be used as a member for holding a single crystal when producing a single crystal ingot using a solution method or a gas method in addition to the sublimation method.

[0039] (single crystal manufacturing equipment) Figure 5 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 and y directions are perpendicular to each other. The single crystal manufacturing apparatus shown in Figure 5 is used when manufacturing a single crystal ingot by sublimation deposition. Figure 6 is an enlarged cross-sectional schematic diagram of only the lid 20 shown in Figure 5.

[0040] The single crystal manufacturing apparatus 1000 shown in Fig. 5 includes a crucible 100 consisting of a lid 20, which is an example of a seed crystal holding member of the present invention, and a crucible body 30. The crucible body 30 is provided with a heat insulating material (not shown) for keeping the crucible 100 warm, and a heating means 40 on its outer periphery. To facilitate understanding, Fig. 5 also illustrates a raw material M for single crystal growth and a seed crystal S. 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. Methods for fixing the SiC seed crystal to the pedestal 21 include, for example, fixing the outer periphery of the SiC seed crystal with graphite claws, or attaching the SiC seed crystal to the pedestal using a carbon adhesive.

[0041] The 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. The crucible 100 reaches high temperatures 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.

[0042] 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 made up of the pedestal 21 and a plate 22. The pedestal 21 corresponds to the pedestal 11 shown in FIG. 1, and the plate 22 corresponds to the support member 12 shown in FIG. 1. The seed crystal S is fixed to one surface (seed crystal side surface) 21a of the pedestal 21. By covering the crucible body 30 with the lid 20, the pedestal 21 faces the raw material M for single crystal growth contained in the crucible 100. By facing the raw material M for single crystal growth and the seed crystal S placed on the pedestal 21, the raw material gas can be efficiently supplied to the seed crystal S. The pedestal 21 and the portion 22 other than the pedestal 21 may be formed as an integral member or may be separate members.

[0043] The lid 20 (or base 21) has a cavity layer that extends in the x and y directions, and therefore has a higher thermal conductivity than a conventional graphite lid (or graphite base) that does not have a cavity layer. This is because heat moves by radiation in the cavity layer, which is faster than heat transfer by thermal conduction. In this configuration, heat transfer occurs by thermal radiation in the cavity layer and by thermal conduction in areas other than the cavity layer (portions made of graphite). The lid portion (or the base that is in contact with the seed crystal), which is an example of a seed crystal holding member of the present invention, has greater heat removal than conventional graphite lid portions (or graphite bases), and can achieve a higher single crystal growth rate than conventional ones.

[0044] 6, the cavity layer H has a rectangular cross section, but is not limited to a rectangular shape. Furthermore, the two cavity layers H1 and H2 have the same shape, but may have different shapes. Within the cavity, heat is transferred by radiation from the seed crystal at the bottom to the top, so the higher the cavity, the faster the heat transfer can be. It is also desirable that heat transfer from the pedestal to the seed crystal be uniform across the seed crystal surface. If there are areas of strong localized heat transfer, the shape of the growing crystal surface may become distorted or the surface may become excessively convex, leading to cracks. To achieve uniform heat transfer, the inner diameter of the cavity must be somewhat larger than the outer diameter of the pedestal, and it is desirable that the cross-sectional area of ​​the cavity be at least one-third of the cross-sectional area of ​​the pedestal. The cavity does not necessarily have to be cylindrical, and can be changed to create a desired temperature distribution depending on the surrounding environment. The cavity can also be doughnut-shaped, or it can be divided by a partition plate in the height direction (z direction).

[0045] In the single crystal production apparatus 1000, the lid part 20 is of a type that includes a pedestal 21 and fixes a seed crystal on the pedestal 21, but as shown in Fig. 7, the single crystal production apparatus may be of a type in which the lid part 20A does not include a pedestal and the seed crystal S is fixed to a part of the lid part 20A. In this type, a portion 22A corresponding to the plate 22 in Fig. 6 has a cavity layer H. [Example]

[0046] (Example) Figure 8(a) shows the results of a simulation of the temperature distribution near the pedestal (temperature difference in the height direction of the SiC single crystal and temperature difference in the height direction of the pedestal) for a single crystal manufacturing apparatus of the type shown in Figure 6, i.e., equipped with a lid provided with a pedestal having two cavity layers. Note that Figure 8(a) shows the results of an example, and (b) shows the results of a comparative example. The cross-sectional schematic diagrams shown do not show the characteristics of the example and comparative example. This simulation was performed using "Virtual Reactor," a vapor phase crystal growth analysis software manufactured by STR-Group Ltd. This simulation is widely used to simulate temperature distribution inside a furnace, and has been confirmed to have a high correlation with actual experimental results.

[0047] In the model of the single crystal manufacturing equipment used in the simulation, the pedestal was made of graphite, the height of the pedestal was 59 mm, the height of the two cavity layers was 22 mm each, and the height of the SiC single crystal was 53 mm.

[0048] As a result of the simulation, the temperature difference in the height direction of the SiC single crystal, t es (i.e., the difference between the temperature of the crystal growth surface of the SiC single crystal and the temperature of the bonding surface with the pedestal), and the temperature difference in the height direction of the pedestal, t e1 (i.e., the difference between the temperature of the bonding surface with the SiC single crystal and the temperature of the surface on the opposite side) was 90°C and 56°C, respectively (see FIG. 8(a)).

[0049] (Comparative Example) We simulated the temperature distribution near the pedestal of a conventional single crystal manufacturing apparatus equipped with a lid and a pedestal that does not have a cavity layer. The only difference from the model in Figure 8 is that the pedestal does not have a cavity layer, and the materials and dimensions were the same.

[0050] As a result of the simulation, the temperature difference in the height direction of the SiC single crystal, t es (i.e., the difference between the temperature of the crystal growth surface of the SiC single crystal and the temperature of the bonding surface with the pedestal), and the temperature difference in the height direction of the pedestal, t e1 (i.e., the difference between the temperature of the bonding surface with the SiC single crystal and the temperature of the surface on the opposite side) was 86°C and 69°C, respectively (see FIG. 8(b)).

[0051] The temperature difference t in the height direction of the SiC single crystal of the comparative example es The temperature difference in the height direction of the SiC single crystal of the example was t es The temperature difference in the height direction of the SiC single crystal was 90° C. In the example, the temperature difference in the height direction of the SiC single crystal was larger than in the comparative example, and therefore the growth rate of the single crystal could be increased. [Explanation of symbols]

[0052] 10 Seed crystal holding member 11, 111, 211, 311 pedestal 12 Support member 20, 20A lid part 21 Pedestal 22 Plate H, H1, H2 cavity layer 100 crucible 1000 Single crystal manufacturing equipment

Claims

1. A seed crystal holding member used 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 base for fixing a seed crystal is provided, a fixing surface of the base to which the seed crystal is fixed is disk-shaped; 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 pedestal has a plurality of hollow layers that are arranged side by side in the overlapping direction, Each of the plurality of cavity layers has a rectangular shape when viewed in a cross section in the overlapping direction, A seed crystal holding member, wherein the plurality of hollow layers are arranged symmetrically with respect to an axis passing through the center of the circle of the fixing surface.

2. The seed crystal holder according to claim 1 , wherein the length of the hollow layer in the direction in which the seed crystal and the seed crystal holder overlap is longer than 15 mm.

3. The seed crystal holder according to claim 1 , wherein the carbon material is graphite.

4. A seed crystal holding member described in any one of claims 1 to 3, wherein the base is the part that contacts the seed crystal.

5. 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.

6. A single crystal manufacturing apparatus comprising a crucible comprising the lid and crucible body according to claim 5.

7. The seed crystal holder according to claim 1 , which is used when producing a SiC single crystal ingot using a solution process.

Images