Seed crystal for producing sic single crystal ingot, composite for producing sic single crystal ingot, sic single crystal ingot, method for producing sic single crystal ingot, and method for producing sic-bonded substrate

Abstract

To provide a seed crystal for producing an SiC single crystal ingot capable of suppressing generation of voids in the ingot caused by the seed crystal, a composite for producing the SiC single crystal ingot, the SiC single crystal ingot, a method for producing the SiC single crystal ingot, and a method for producing an SiC bonded substrate.SOLUTION: A seed crystal for producing a SiC single crystal ingot, comprising a laminated structure of a SiC single crystal layer that serves as a base for growing a SiC single crystal, and a SiC polycrystalline layer that supports the SiC single crystal layer.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a seed crystal for producing a SiC single crystal ingot, a composite for producing a SiC single crystal ingot, a SiC single crystal ingot, a method for producing a SiC single crystal ingot, and a method for producing a SiC bonded substrate. [Background technology]

[0002] Silicon carbide (hereinafter sometimes referred to as "SiC") is a wide bandgap semiconductor with a wide bandgap of 2.2 to 3.3 eV, and due to its excellent physical and chemical properties, it has been researched and developed as an environmentally resistant semiconductor material. In recent years, SiC has attracted attention as a material for power devices such as high-voltage, high-output electronic devices and high-frequency electronic devices, as well as short-wavelength optical devices in the blue to ultraviolet wavelength range, and research and development into this material has been intensified. However, the difficulty of producing high-quality large-diameter single crystals of SiC has hindered the practical application of SiC devices to date.

[0003] To solve this problem, sublimation recrystallization methods (e.g., the Lely process or the modified Lely process) have been developed, which use a SiC single crystal substrate as a seed crystal for sublimation recrystallization. In the modified Lely process for growing bulk SiC single crystals, a SiC sublimation source is placed in a crucible, a seed crystal made of a SiC single crystal is attached to the crucible lid, and the source material is sublimated to grow a SiC single crystal on the seed crystal by recrystallization of the SiC. After growing a roughly cylindrical SiC bulk single crystal (hereinafter sometimes referred to as a "SiC single crystal ingot"), it is typically cut to a thickness of approximately 300 to 600 μm and then subjected to processes such as grinding, lapping, and chemical mechanical polishing to produce a SiC single crystal substrate.

[0004] In the process of growing a SiC single crystal, a SiC seed crystal is fixed to a pedestal with an adhesive. A carbon adhesive containing an organic solvent is often used as the adhesive (see, for example, Patent Document 2). During the process of curing the carbon adhesive to fix the SiC seed crystal to the pedestal, a gas containing the organic solvent as a main component is generated from the heated carbon adhesive, which can form a void at the interface between the pedestal and the SiC seed crystal. When a SiC single crystal is grown in a high-temperature environment using the modified Lely process with a void formed between the pedestal and the SiC seed crystal, macro-defects (voids) form in the SiC seed crystal from the void. These voids can extend from the low-temperature side to the high-temperature side, sometimes reaching the SiC single crystal during growth. If the voids extend to the point where the macro-defects reach the SiC single crystal, the adhesion at the interface between the SiC seed crystal and the pedestal decreases, and the SiC single crystal ingot itself may peel off during growth. Furthermore, even if the SiC single crystal ingot containing the SiC seed crystal does not peel off, the grown SiC single crystal ingot will contain macro defects and be of reduced quality.

[0005] Patent Document 3 discloses a SiC seed having a SiC crystal body having a pair of parallel surfaces and a single buried protective layer provided between the pair of parallel surfaces of the SiC crystal body, the buried protective layer being made of carbon and having no gaps when viewed from one side of the pair of parallel surfaces. Patent Document 3 also provides a SiC seed for growing SiC single crystals in which, by using such a SiC seed and fixing the SiC seed with an adhesive, macro-defects generated from vacancies formed between the pedestal and the SiC seed are less likely to extend, and a method for producing a SiC single crystal ingot using the same. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-15401 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-193494 [Patent Document 3] Patent Publication No. 2021-75427 [Non-patent literature]

[0007] [Non-Patent Document 1] Wellmann P, Neubauer G, Fahlbusch L, Salamon M and Uhlmann N 2015 Cryst. Res. Technol. 50 2-9 Summary of the Invention [Problem to be solved by the invention]

[0008] In Patent Document 3, to address the problem of macrodefects generated from vacancies formed between the pedestal and the SiC seed extending, an embedded protective layer made of a high-temperature resistant carbide such as carbon, TaC, or NbC is formed on the SiC single crystal serving as the seed crystal. However, by embedding dissimilar materials such as carbon and carbides, which have thermal expansion coefficients significantly different from those of the SiC single crystal, in the SiC single crystal, thermal stress caused by the embedded protective layer occurs during the growth process of the SiC single crystal ingot, and there is a possibility that new macrodefects will occur due to cracks or thermal strain in the SiC single crystal ingot itself.

[0009] Furthermore, the formation of the buried protective layer may cause warping of the SiC seed crystal surface, which may lead to the generation of voids between the pedestal and the SiC seed, making it impossible to suppress the extension of macro-defects. Therefore, while controlling the warping of the SiC seed crystal is necessary while forming the buried protective layer, this control is difficult, so very precise control is required in the formation of the buried protective layer, which may result in a low production yield of the SiC seed crystal. As a result, the production cost of the SiC seed crystal increases in order to prepare a SiC seed crystal with a practical buried protective layer.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a seed crystal for producing a SiC single crystal ingot that can suppress the generation of voids in the ingot due to the seed crystal, a composite for producing a SiC single crystal ingot, a SiC single crystal ingot, a method for producing a SiC single crystal ingot, and a method for producing a SiC bonded substrate. [Means for solving the problem]

[0011] In order to solve the above problems, the seed crystal for producing a SiC single crystal ingot of the present invention has a layered structure including a SiC single crystal layer that serves as a base for growing a SiC single crystal, and a SiC polycrystalline layer that supports the SiC single crystal layer.

[0012] The thickness of the SiC single crystal layer may be 1 μm or more and 1 mm or less, the thickness of the SiC polycrystalline layer may be 500 μm or more and 5.0 mm or less, and the thickness of the seed crystal may be 501 μm or more and 6.0 mm or less.

[0013] The seed crystal of the present invention may further include a surface protection layer laminated on the SiC polycrystalline layer.

[0014] The SiC single crystal layer and the SiC polycrystalline layer may be laminated by directly bonding them together.

[0015] An adhesive layer may be provided between the SiC single crystal layer and the SiC polycrystalline layer.

[0016] The surface of the SiC polycrystalline layer facing the base may have a curvature radius of 56 m or more.

[0017] In order to solve the above problems, the composite for producing a SiC single crystal ingot of the present invention includes the seed crystal of the present invention and a pedestal bonded to the seed crystal.

[0018] The base may be a lid for a crucible.

[0019] In order to solve the above problems, the SiC single crystal ingot of the present invention comprises the seed crystal of the present invention and a SiC single crystal growth portion grown on the SiC single crystal layer.

[0020] In order to solve the above problems, the method for producing a SiC single crystal ingot of the present invention uses the seed crystal of the present invention.

[0021] The method for producing a SiC single crystal ingot of the present invention may include a growing step of growing a SiC single crystal on the SiC single crystal layer of the seed crystal by a sublimation recrystallization method.

[0022] The method may further include a step of attaching the seed crystal to a base prior to the growing step.

[0023] The method may further include a cutting step of cutting the SiC single crystal ingot obtained by the growing step.

[0024] In order to solve the above problems, the method for producing a SiC bonded substrate of the present invention includes a transfer step of transferring a SiC single crystal thin film from the SiC single crystal ingot sliced ​​in the slice step onto a SiC polycrystalline substrate. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide a seed crystal for producing a SiC single crystal ingot that can suppress the generation of voids in the ingot due to the seed crystal, a composite for producing a SiC single crystal ingot, a SiC single crystal ingot, a method for producing a SiC single crystal ingot, and a method for producing a SiC bonded substrate. [Brief explanation of the drawings]

[0026] [Figure 1A] FIG. 1 is a schematic perspective view of a seed crystal shown as an example of the seed crystal of the present invention. [Figure 1B] FIG. 2 is a schematic perspective view of a seed crystal provided with a surface protective layer. [Figure 2A]FIG. 1 is a schematic cross-sectional view of a SiC crystal growth apparatus before SiC single crystal growth by the modified Lely method. [Figure 2B] FIG. 1 is a schematic cross-sectional view of a SiC crystal growth apparatus after growth of a SiC single crystal ingot. [Figure 3] 1 is a flowchart showing an example of a method for manufacturing a SiC single crystal ingot using a seed crystal according to the present invention. [Figure 4] 1 is a schematic diagram of a SiC single crystal ingot and a SiC single crystal thin film cut out from the ingot, illustrating the definition of the void generation rate. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to this embodiment.

[0028] [Seed crystals for producing SiC single crystal ingots] The seed crystal of the present invention is a seed crystal that can be used for producing a SiC single crystal ingot by, for example, a sublimation recrystallization method, and has a laminated structure of a SiC single crystal layer and a SiC polycrystalline layer as described below.

[0029] <SiC single crystal layer> The SiC single crystal layer is a layer that serves as a base for growing the SiC single crystal, and can play the role of a seed for growing the SiC single crystal to form an ingot.

[0030] The thickness of the SiC single crystal layer is preferably 1 μm or more and 1 mm or less. A thickness within this range allows the layer to adequately function as a seed while also providing cost benefits. Considering the strength of the SiC single crystal layer, the thickness is more preferably 10 μm or more and 800 μm or less, and even more preferably 200 μm or more and 500 μm or less.

[0031] However, if the thickness of the SiC single crystal layer is thinner than 1 μm, for example, when it is used as a seed crystal in the production of ingots by the modified Lely process, there is a high risk that the SiC single crystal layer will be lost due to etch-back in the initial stage of crystal growth of the SiC single crystal. Furthermore, depending on the bonding method used to bond and stack the SiC single crystal layer and the SiC polycrystalline layer, a thicker SiC single crystal layer generally reduces warpage as a substrate and provides better shape controllability. However, if the thickness of the SiC single crystal layer is thicker than 1 mm, the cost benefits of using it as a seed crystal are not fully realized, so a thickness of 1 mm or less is desirable.

[0032] As the SiC single crystal for the SiC single crystal layer, for example, a SiC single crystal produced by the modified Lely process can be used. From the viewpoint of obtaining a high-quality SiC single crystal ingot, a high-quality SiC single crystal ingot can be effectively obtained by using a SiC single crystal produced by either a solution growth method, a high-temperature gas growth method, or a CVD method, or a combination of these methods.

[0033] <SiC polycrystalline layer> The SiC polycrystalline layer supports the SiC single crystal layer and can act as a handle member to protect the SiC single crystal layer when handling the seed crystal. It also serves to ensure the seed crystal has a certain thickness and strength, which are required for the seed crystal.

[0034] It is believed that the SiC polycrystalline layer does not contribute to the extension of voids from the pedestal interface, preventing the generation of voids. For this reason, a seed crystal having a laminated structure of a SiC single crystal layer and a SiC polycrystalline layer can more effectively improve the yield of SiC single crystal wafers than when only a SiC single crystal layer is used as a seed crystal, as voids do not reach the SiC single crystal ingot.

[0035] Although the details of the void generation mechanism are still under investigation, when a single SiC seed crystal is used, the crystal erodes in a geometrically specific manner, possibly propagating along threading dislocations and strain lines inherent in the single crystal. Based on this hypothesis, the SiC polycrystalline layer is composed of countless crystalline particles, densely deposited with a random orientation, which presumably prevents voids from extending within the crystal due to a certain order, making void generation, i.e., backside sublimation, less likely. Furthermore, the presence of SiC polycrystalline particles at the bonding surface between the pedestal and the SiC polycrystalline layer improves the adhesion of the carbon adhesive compared to when the SiC single crystal is bonded to the pedestal, potentially suppressing the formation of an interfacial void layer, which is the starting point for void generation.

[0036] Furthermore, by providing the seed crystal with a SiC polycrystalline layer, the SiC seed crystal acts as a heat sink during crystal growth of the SiC single crystal ingot, and the latent heat generated at the surface of the SiC seed crystal can be removed as effectively as or more effectively than when only a SiC single crystal layer is used as the seed crystal, thereby suppressing the occurrence of thermal distortion. Furthermore, this heat removal effect can also suppress the occurrence of an extreme temperature gradient between the growth interface of the SiC single crystal and the seed crystal, which is thought to contribute to a reduction in the rate of void occurrence.

[0037] Furthermore, since the ratio of the SiC single crystal layer to the seed crystal thickness can be reduced by the thickness of the SiC polycrystalline layer, which is cheaper than the SiC single crystal, the cost of the seed crystal and the manufacturing cost of the SiC single crystal ingot can be reduced. Note that the thickness of the SiC polycrystalline layer may be thicker or thinner than that of the SiC single crystal layer.

[0038] The polycrystalline SiC layer may be made of polycrystalline SiC with an average grain size of 0.1 μm to 10 μm as viewed from the bonding surface where the single-crystal SiC layer is bonded. This average grain size is common for polycrystalline SiC and is not difficult to obtain.

[0039] The thickness of the SiC polycrystalline layer is preferably 500 μm or more and 5.0 mm or less. The heat of solidification of the SiC sublimation gas is generated on the growth surface of the SiC single crystal ingot. If the thickness of the SiC polycrystalline layer is within this range, this heat of solidification can be effectively removed, and the effects of thermal strain originating from the bonding interface between the graphite pedestal and the SiC polycrystalline layer, which occurs during the growth of the SiC single crystal ingot, for example, can be reduced. Furthermore, if the thickness is within this range, the seed crystal will not fall due to its own weight during the growth of the SiC single crystal ingot. Considering ease of handling and strength as a handle member, the thickness of the SiC polycrystalline layer is more preferably 1 mm or more and 4 mm or less, and even more preferably 1.5 mm or more and 3 mm or less.

[0040] The thicker the SiC polycrystalline layer, the more effectively it can remove the heat of solidification and reduce the effects of thermal distortion, but it is also more susceptible to the effects of gravity. Therefore, if the thickness is greater than 5 mm, the adhesive layer bonding the SiC polycrystalline layer to the pedestal may not be able to withstand the weight of the SiC polycrystalline layer during the temperature rise before the growth of the SiC single crystal ingot or during the early stages of growth, causing the seed crystal to fall. Furthermore, if the SiC polycrystalline layer is less than 500 μm thick, it may be less easy to handle as a handle member or may not have sufficient strength.

[0041] The polycrystalline SiC used in the polycrystalline SiC layer may be a compact mainly composed of polycrystalline SiC, and there are no particular limitations on the manufacturing method thereof. Examples of manufacturing methods for polycrystalline SiC include atmospheric pressure sintering using a sintering aid, atmospheric pressure sintering, hot pressing, hot isostatic pressing (HIP), chemical vapor deposition (CVD), and reaction sintering (RS).

[0042] If the thickness ranges of the SiC single crystal layer and the SiC polycrystalline layer are as described above, the seed crystal having a layered structure of these preferably has a thickness of 501 μm or more and 6.0 mm or less.

[0043] In the seed crystal of the present invention, the SiC single crystal layer and the SiC polycrystalline layer may be laminated by being directly bonded to each other. For example, as described in Patent Document 1, a method is employed in which a thick SiC single crystal substrate is bonded to a SiC polycrystalline layer using a delamination technique (also known as Smart Cut (registered trademark)) by ablation of hydrogen atoms, and then the SiC single crystal layer is separated and a thin SiC single crystal layer is transferred to the SiC polycrystalline layer, thereby obtaining a seed crystal in which the SiC single crystal layer and the SiC polycrystalline layer are directly bonded to each other.

[0044] In the seed crystal of the present invention, an adhesive layer may be provided between the SiC single crystal layer and the SiC polycrystalline layer. For example, by adopting an indirect bonding method using an adhesive containing polycarbosilane as a main component and SiC filler, and bonding the SiC single crystal layer and the SiC polycrystalline layer with the adhesive, a seed crystal having an adhesive layer between the SiC single crystal layer and the SiC polycrystalline layer can be obtained.

[0045] <Seed crystal 3> 1A is a schematic perspective view of a seed crystal 3 shown as an example of the seed crystal of the present invention. The seed crystal 3 has a structure in which a SiC polycrystalline layer 1 and a SiC single crystal layer 2 bonded to the SiC polycrystalline layer 1 are stacked.

[0046] (SiC polycrystalline layer 1) The SiC polycrystalline layer 1 may be, for example, a layer formed of polycrystalline SiC deposited by CVD, and may be a disk-shaped layer having a thickness of 0.3 mm to 5.0 mm and a diameter of 4 to 8 inches. For example, it may be formed into a 6-inch disk-shaped layer having a thickness of about 1.5 mm. The SiC polycrystalline layer 1 may be made of 4H—SiC crystal, 6H—SiC crystal, or 3C—SiC crystal, or a mixture of these.

[0047] (SiC single crystal layer 2) The SiC single crystal layer 2 is, for example, 1 μm to 1 mm thick and disk-shaped with the same diameter as the SiC polycrystalline layer 1. For example, it is formed into a 6-inch disk shape with a thickness of about 350 μm. The SiC single crystal of the SiC single crystal layer 2 can be made of any of 4H—SiC crystal, 6H—SiC crystal, and 3C—SiC crystal. 1 inch is 25.4 mm.

[0048] For example, if surface a1 of SiC polycrystalline layer 1 is the surface that bonds with bonding surface a4 of SiC single crystal layer 2, then surface a2 opposite to surface a1 is the surface that does not bond with SiC single crystal layer 2, and when producing a SiC single crystal ingot by sublimation recrystallization, surface a2 is the surface that is attached to a graphite support base, crucible lid, etc. using an adhesive, etc. There is no particular difference between surface a1 and surface a2, and surface a2 may be the surface that bonds with bonding surface a4 of SiC single crystal layer 2, in which case surface a1 is the surface that does not bond with SiC single crystal layer 2, and surface a1 is the surface that is attached to a support base, etc.

[0049] The crystal orientation of the surface a3 of the SiC single crystal layer 2 is not particularly limited. For example, when a commercially available 4H—SiC single crystal substrate, such as a disc-shaped wafer with its main surface in the c-axis direction and a 4° off-angle in the {11-20} direction, is used as the SiC single crystal layer 2, it is desirable to designate the Si-face side as the opposite surface a4 and the C-face as the surface a3. That is, if the opposite surface a4 is the surface that bonds with the SiC polycrystalline layer 1, then the opposite surface a3 is the surface that does not bond with the SiC polycrystalline layer 1. When a SiC single crystal ingot is produced by sublimation recrystallization, the surface a3 is the surface from which the SiC single crystal ingot grows. Note that the surface a3 may also be the surface that bonds with the SiC polycrystalline layer 1. In this case, the opposite surface a4 is the surface that does not bond with the SiC polycrystalline layer 1, and the surface a3 is the surface from which the SiC single crystal ingot grows.

[0050] <Seed crystal 3a> The seed crystal of the present invention may further include a surface protective layer laminated on the SiC polycrystalline layer. Fig. 1B is a schematic perspective view of a SiC bonding seed crystal 3A having a surface protective layer 4 on the opposite surface a2 of the SiC polycrystalline layer 1. The surface protective layer 4 is preferably a protective film made of carbon, for example. For example, a method of forming the protective film may be used in which a photosensitive resist, which is an organic film, is applied to the SiC polycrystalline layer 1 and then carbonized. The surface b1 is the bonding surface between the surface protective layer 4 and the SiC polycrystalline layer 1, and the opposite surface b2 is the bonding surface to a base or the like.

[0051] (surface warping) In the seed crystal of the present invention, the warpage in the SiC polycrystalline layer preferably has a radius of curvature of 56 m or more. Specifically, the warpage in the SiC polycrystalline layer can be measured, for example, as the warpage of the surface facing the base, i.e., the opposite surface a2, which is the surface not bonded to the SiC single crystal layer 2 in FIG. 1A. Also, in FIG. 1B, the warpage of the opposite surface b2, which is the surface attached to the base or the like, can be measured. The radius of curvature can be measured using a laser interferometer or the like.

[0052] When the curvature radius of the warp is 56 m or more, it is possible to prevent the occurrence of gaps that may lead to the generation of voids in the bonding surface between the seed crystal and the pedestal. From the viewpoint of ensuring stronger adhesion between the seed crystal and the pedestal, the curvature radius of the warp is preferably 142 m or more, more preferably 187 m or more.

[0053] If the curvature radius of the warpage is less than 56 m, a gap may occur at the bonding surface between the seed crystal and the pedestal where the seed crystal does not come into contact with the pedestal, which may result in voids in the ingot caused by the seed crystal.

[0054] The seed crystal of the present invention is a structure in which a SiC single crystal and a SiC polycrystal are combined, and since these are the same material, they have almost the same thermal expansion coefficient, so the seed crystal does not warp due to the thermal process in the ingot manufacturing process. However, since warping of the seed crystal may occur due to the shaping of the seed crystal in the processing step in which the seed crystal is processed into the desired shape, it is important to appropriately control this warping.

[0055] The processing method required to shape the seed crystal is not particularly limited. For example, in the case of SiC polycrystal, a bulk molded body of SiC polycrystal is first obtained, and then a SiC polycrystalline layer is obtained through processing methods such as grinding using a diamond grinding wheel, polishing using a slurry containing diamond abrasive particles, and mechanical chemical polishing (CMP). Alternatively, after bonding SiC polycrystal with SiC single crystal to form a seed crystal, the shape of the SiC polycrystal may be controlled by a combination of the above processing methods.

[0056] [Method of manufacturing seed crystals] Next, an example of a method for producing a seed crystal of the present invention will be described using the seed crystal 3 shown in FIG. 1A. The seed crystal 3 can be produced by a bonding process in which a SiC polycrystalline layer 1 is bonded to a separately prepared SiC single crystal layer 2. These bonding methods are preferably those that provide a strong mechanical bond across the entire bonding surface, are thermally and chemically stable, and are simple to perform the bonding process. Examples of such bonding methods include those that do not involve the insertion of a dissimilar material as an intermediate layer. For example, from the perspective of bonding a SiC single crystal and a SiC polycrystal that have different morphologies, a direct bonding method may be used, in which bonding is performed without using an adhesive or a low-melting-point metal or other adhesive material.

[0057] An example of the direct bonding method is a method in which, as described in Patent Document 1, a delamination technique using hydrogen atom ablation (also known as Smart Cut (registered trademark)) is used to first bond a thick SiC single crystal substrate to a SiC polycrystalline layer 1, and then a thin plate of SiC single crystal is separated from the SiC single crystal substrate to form a thin plate-like SiC single crystal layer 2 on the SiC polycrystalline layer 1.

[0058] Alternatively, instead of direct bonding, a seed crystal can be produced by bonding a SiC polycrystalline layer and a SiC single crystal layer using an indirect bonding method with an adhesive layer. For example, an indirect bonding method using an adhesive containing polycarbosilane as the main component and SiC filler can be used to produce a seed crystal because it does not require an intermediate layer of a different material. Furthermore, after bonding the SiC polycrystalline layer and the SiC single crystal layer, a polishing step can be added to polish the surface of the SiC single crystal layer.

[0059] [Manufacturing method for SiC single crystal ingots] <Application process, growth process> Next, an example of a method for producing a SiC single crystal ingot of the present invention will be described. This production method uses the seed crystal of the present invention. When a sublimation recrystallization method is employed, a growth step of growing a SiC single crystal on the SiC single crystal layer of the seed crystal by this method may be included. Furthermore, the method may further include a bonding step of bonding the seed crystal to a pedestal prior to the growth step.

[0060] 3 is a flowchart showing an example of a method for manufacturing a SiC single crystal ingot using a seed crystal according to the present invention. Step S1 is a bonding step in which a SiC seed crystal is bonded to a pedestal. For example, a method may be used in which a surface protective layer is formed by applying an organic photosensitive resist to the bonding surface of the seed crystal, which is the surface on which the seed crystal is bonded to the pedestal, and then carbonizing the surface.

[0061] The pedestal may be made of graphite, and the method for attaching the seed crystal to the pedestal is not limited to this. For example, a carbon adhesive may be used, and a carbonized adhesive layer may be formed between the seed crystal and the pedestal by a firing treatment.

[0062] By attaching the seed crystal to the pedestal, a composite for producing a SiC single crystal ingot is obtained, which includes the seed crystal of the present invention and the pedestal bonded to the seed crystal. The pedestal can be a crucible lid.

[0063] In the growth process of step S2, the SiC single crystal is grown, for example, by the modified Lely method. FIG. 2A is a schematic cross-sectional view of the SiC crystal growth apparatus before the SiC single crystal is grown by the modified Lely method. The heating method of the SiC crystal growth apparatus 100 is not limited, and either high-frequency induction heating or resistance heating may be used. In the example shown in FIG. 2A, an example of the high-frequency induction heating method is shown.

[0064] Pedestal 5, to which seed crystal 3 is attached via surface protective layer 4, is fixed to graphite crucible lid 8, and graphite crucible lid 8 is held on top of graphite crucible 7 made of graphite. The method for holding components such as pedestal 5, graphite crucible 7, and graphite crucible lid 8 is not particularly limited as long as it does not cause misalignment during growth of the SiC single crystal ingot. For example, these components may be fixed using an adhesive containing a carbon filler, or the components may be fixed in place by structural design.

[0065] The seed crystal 3 may be fixed directly to the graphite crucible lid 8 via the surface protective layer 4 without using the pedestal 5, or may be fixed directly to the pedestal 5 without providing the surface protective layer 4, or may be fixed directly to the graphite crucible lid 8 without providing the surface protective layer 4.

[0066] The graphite crucible 7 is filled with SiC powder 9, which serves as a precursor for growing a SiC single crystal ingot. The form of the SiC powder 9 is not limited; for example, SiC powder formed by the Acheson method or CVD method, which has been crushed, cleaned, and classified, can be used. The graphite crucible 7 is equipped with a SiC sublimation gas transport unit 10 that transports sublimation gas generated from the SiC powder 9 to the seed crystal 3. The SiC crystal growth apparatus 100 may be provided with a tapered guide 11 to control the shape of the growing SiC single crystal ingot and the rectification of the SiC sublimation gas. The shape and holding method of the tapered guide 11 are not limited; for example, the diameter of the tapered guide 11 may increase at a constant rate from the top to the bottom of the graphite crucible 7, i.e., in the growth direction of the growing SiC single crystal ingot.

[0067] The graphite crucible 7 and the graphite crucible lid are secured in place by a heat insulator 6 that covers the body, bottom, and lid from the outside. The heat insulator 6 is made of a material that can withstand the growth temperatures of SiC single crystal ingots, which are 2000°C to 2400°C, and is, for example, a molded heat insulator made of carbon felt or a molded body thereof. In the SiC crystal growth apparatus 100, the heat insulator 6 is housed in a cylindrical quartz tube 12, and a high-frequency coil 13 is attached to the outer periphery.

[0068] When growing SiC single crystal, a constant amount of argon gas as an inert gas is flowed into the graphite crucible 7, and the inside of the graphite crucible 7 is made into a reduced pressure atmosphere by a vacuum pump, and the graphite crucible 7 is heated in this state.

[0069] 2B is a schematic cross-sectional view of the SiC crystal growth apparatus after growing a SiC single crystal ingot. SiC single crystal growth section 14 is a SiC single crystal grown in the growth process, and SiC polycrystalline adhesion and growth section 15 is a SiC polycrystal that has regrown after sublimation gas generated from SiC powder raw material 9 adheres to graphite crucible lid 7 during the growth process.

[0070] As the growth process, instead of the modified Lely process, a sublimation recrystallization method derived from the modified Lely process may be used, such as any of the methods described in Non-Patent Document 1, including PVT (Physical Vapor Transport), M-PVT (Modified-PVT), CF-PVT (Continuous Feeding PVT), HT-CVD (High Temperature Chemical Vapor Deposition), H-CVD (Halogenated-CVD), and SS (Sublimation Sandwich).

[0071] An example of the SiC single crystal ingot obtained by the growth step is an ingot comprising the seed crystal 3 described in the present invention and the SiC single crystal growth portion 14 grown on the SiC single crystal layer 2.

[0072] <Cutting process> The method for producing a SiC single crystal ingot of the present invention may further include a cutting step of cutting at least a portion of the SiC single crystal ingot obtained in the growth step. The SiC single crystal can be cut by removing the SiC single crystal growth section 14 together with the graphite crucible lid 8 from the SiC crystal growth apparatus 100 and using a wire electric discharge machine or the like. Examples of the cut portion include the interface between the seed crystal 3 and the SiC single crystal growth section 14, the interface between the SiC polycrystalline layer 1 and the SiC single crystal layer 2, a desired portion of the SiC single crystal growth section 14, a desired portion of the graphite crucible lid 8, a desired portion of the SiC polycrystalline layer, or a desired portion of the surface protective layer 4. The SiC single crystal ingot can be cut by slicing these portions. In other words, the cutting step is a step of cutting at least a portion of the SiC single crystal ingot so as to be separate from at least a portion of the graphite crucible lid 8 that serves as the base. It is important to process the final SiC single crystal ingot so that it does not include the SiC polycrystalline adhesion and growth portion 15.

[0073] [Definition of void occurrence rate] Figure 4 is a schematic diagram of a SiC single crystal ingot and a SiC single crystal thin film cut from it, illustrating the definition of void occurrence rate. The SiC single crystal ingot shown in Figure 4 was obtained by slicing the interface between the SiC polycrystalline layer 1 and the SiC single crystal layer 2. This ingot was cut into wafers with a thickness of 400–600 μm using a wire saw. The front and back surfaces of the cut wafers were then ground and polished to a mirror finish on both sides to a thickness of 350 μm. The total number of wafers produced was defined as "N wafers." Each wafer was then subjected to transmitted light observation using white light to detect the presence or absence of voids. The number of void-free wafers was defined as "X wafers," and the number of wafers with voids was defined as "NX wafers." The void occurrence rate was then calculated as a percentage by dividing the number of void-containing wafers (NX) by the total number of wafers (N).

[0074] Voids have an in-plane diameter of several tens to several hundreds of micrometers. In the case of 4H-SiC and 6H-SiC single crystals, they have a hexagonal hollow structure reflecting the symmetry of the crystal structure. The length of voids in the growth direction of the SiC single crystal can reach several millimeters to several tens of millimeters, penetrating the surface of the SiC single crystal and eroding the SiC single crystal ingot. Voids are rarely observed in production-grade SiC single crystal wafers currently on the market. Since voids render a wafer unusable as a commercial SiC single crystal wafer once they contain a void-inducing region, voids directly affect the product yield of SiC single crystal ingots. Therefore, we defined the void occurrence rate by focusing on the presence or absence of voids in SiC single crystal wafers obtained from SiC single crystal ingots, rather than the area percentage occupied by voids per SiC single crystal wafer. A higher void occurrence rate corresponds to a lower product yield of SiC single crystal wafers.

[0075] [Manufacturing method for SiC bonded substrates] The method for producing a SiC bonded substrate of the present invention includes a transfer step of transferring a SiC single crystal thin film from the SiC single crystal ingot sliced ​​in the above-mentioned slice step onto a SiC polycrystalline substrate.

[0076] Specifically, a delamination technique using hydrogen atom ablation (also known as Smart Cut (registered trademark)) can be used, as described in Patent Document 1. One example of such a method is to first bond a SiC single crystal ingot to a SiC polycrystalline substrate (bonding step), then separate a thin plate of the SiC single crystal from the SiC single crystal ingot, and transfer the thin plate-shaped SiC single crystal substrate to the SiC polycrystalline substrate (transfer step).

[0077] The method for producing a SiC bonded substrate of the present invention may include, in addition to the above-mentioned bonding and transferring steps, a step of polishing the bonding surface, a step of implanting phosphorus ions, a step of implanting hydrogen ions, and the like. [Example]

[0078] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples in any way.

[0079] [Comparative Example 1] <Production of SiC single crystal ingots> In Comparative Example 1, a SiC single crystal was used as the seed crystal, and a SiC single crystal ingot was produced by the modified Lely process. Specifically, a wafer-shaped SiC single crystal with a diameter of 6 inches and a thickness of 0.5 mm was used as the seed crystal, and a carbonized adhesive layer was formed by a firing process using a carbon adhesive. The seed crystal was then attached and fixed to a pedestal (attaching process). In the process of growing a SiC single crystal ingot by the modified Lely process (growth process), a high-frequency induction heating SiC single crystal growth apparatus was used. The growth temperature for growing the SiC single crystal ingot was set to 2300°C. While a constant amount of a mixed gas of argon gas as an inert gas and N gas as a dopant was flowed into the graphite crucible, the graphite crucible was heated in a reduced pressure atmosphere of 2.5 Torr using a vacuum pump, and the temperature inside the graphite crucible was raised to 2300°C. The growth time for the SiC single crystal ingot was 150 hours, and an ingot with an effective length of 15 mm was obtained. The effective length here refers to the growth thickness from the seed crystal surface at which a SiC single crystal ingot equivalent to the seed crystal diameter was obtained.

[0080] Comparative Example 2 An SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Comparative Example 1, except that the thickness of the seed crystal was 1 mm.

[0081] Comparative Example 3 An SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Comparative Example 1, except that the thickness of the seed crystal was 1.5 mm.

[0082] Comparative Example 4 An SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Comparative Example 1, except that the thickness of the seed crystal was set to 2 mm.

[0083] Comparative Example 5 An SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Comparative Example 1, except that the thickness of the seed crystal was set to 5 mm.

[0084] <Fabrication of SiC polycrystalline layer 1> A SiC polycrystalline film having a thickness of 2.0 to 5.5 mm was formed on the surface of a disk-shaped carbon base substrate by chemical vapor deposition (CVD) using a film-forming apparatus. Methylchlorosilane was used as the source gas, and hydrogen and nitrogen gases were used as the carrier gas. The growth temperature in this chemical vapor deposition method was 1400°C. The base substrate was then heated and removed by a combustion method in an air atmosphere at 1000°C, producing a disk-shaped SiC polycrystalline film having a diameter of 6 inches. The SiC polycrystalline film was ground using a surface grinder and polished using a double-sided polishing device to obtain a substrate that would become the SiC polycrystalline layer 1, and this substrate was used to produce the seed crystals 3 in Examples 1 to 7.

[0085] <Fabrication of SiC single crystal substrate> A 4H—SiC single crystal ingot was obtained by the same modified Lely process as in Comparative Example 1. The SiC single crystal ingot and SiC bonded seed crystal were then separated from the base, and a plurality of wafer-shaped SiC single crystals were cut out with a wire saw to a cut-out thickness of 0.7 to 5.2 mm, and the front and back surfaces were ground and polished. The crystal growth surface of the SiC single crystal ingot was the C-plane, and the bonding surface to the SiC polycrystalline layer 1 was the Si-plane. The C-plane was polished by CMP (Chemical Mechanical Polish) to obtain a plurality of SiC single crystal substrates, which were used to manufacture the seed crystals 3 in Examples 1 to 7.

[0086] [Example 1] <Preparation of seed crystal 3> The manufactured SiC polycrystalline layer 1 was bonded to a SiC single crystal substrate (bonding step). In the bonding step, a delamination technique using hydrogen atom ablation (also known as Smart Cut (registered trademark)) as described in Patent Document 1 was used to bond a thick SiC single crystal substrate to the SiC polycrystalline layer 1, followed by separation and transferring a thin SiC single crystal layer 2 to the SiC polycrystalline layer 1. This was followed by a polishing step in which the surface of the SiC single crystal layer 2 was polished, yielding a seed crystal 3 including the SiC polycrystalline layer 1 and the SiC single crystal layer 2. In the seed crystal 3 of Example 1, the SiC polycrystalline layer 1 had a thickness of 0.4 mm and the SiC single crystal layer 2 had a thickness of 0.1 mm.

[0087] <Production of SiC single crystal ingots> A SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Comparative Example 1, except that the seed crystal of Example 1 was used.

[0088] [Example 2] A SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Example 1, except that a seed crystal 3 having a SiC polycrystalline layer 1 with a thickness of 1.0 mm and a SiC single crystal layer with a thickness of 0.001 mm was used.

[0089] [Example 3] A SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Example 1, except that a seed crystal 3 having a SiC polycrystalline layer 1 with a thickness of 0.9 mm and a SiC single crystal layer with a thickness of 0.1 mm was used.

[0090] [Example 4] A SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Example 1, except that a seed crystal 3 having a SiC polycrystalline layer 1 with a thickness of 1.4 mm and a SiC single crystal layer with a thickness of 0.1 mm was used.

[0091] [Example 5] A SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Example 1, except that a seed crystal 3 having a SiC polycrystalline layer 1 with a thickness of 2.0 mm and a SiC single crystal layer with a thickness of 0.001 mm was used.

[0092] [Example 6] A SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Example 1, except that a seed crystal 3 having a SiC polycrystalline layer 1 with a thickness of 1.9 mm and a SiC single crystal layer with a thickness of 0.1 mm was used.

[0093] [Example 7] A SiC single crystal ingot having an effective length of 15 mm was produced in the same manner as in Example 1, except that a seed crystal 3 having a SiC polycrystalline layer 1 with a thickness of 4.9 mm and a SiC single crystal layer with a thickness of 0.1 mm was used.

[0094] Table 1 shows the thickness of the seed crystals and the state of void generation in Examples 1 to 7 and Comparative Examples 1 to 5.

[0095] [Table 1]

[0096] [Results and Discussion] Effect of Seed Crystal Thickness: Comparative Examples 1 to 5 Comparative Examples 1 to 5 are examples in which crystal growth of SiC single crystals was performed using a conventional SiC single crystal as a seed crystal, and the void generation yield was evaluated. In all of Comparative Examples 1 to 5, the voids extended approximately 3 mm from near the interface between the seed crystal and the pedestal in the direction of crystal growth. Therefore, in Comparative Examples 1 to 4, the voids reached the ingot, but in Comparative Example 5, they did not reach the ingot and void extension stopped within the seed crystal.

[0097] Therefore, from the results of Comparative Examples 1 to 5, it can be seen that when a single SiC crystal is used as a seed crystal, the occurrence of voids cannot be essentially suppressed simply by increasing the thickness of the seed crystal. If the seed crystal is made thicker than 3 mm to prevent voids from reaching the ingot, the cost of the seed crystal in the production of the SiC single crystal ingot increases. Therefore, it was reaffirmed that costs cannot be reduced unless an attempt is made to increase the production yield of the SiC single crystal ingot by using a seed crystal with as thin a thickness as possible.

[0098] Effect of Using Seed Crystals of the Present Invention: Examples 1 to 7 In Examples 1, 3, 4, 6, and 7, the thickness of the SiC single crystal layer 2 was 0.1 mm and the thickness of the SiC polycrystalline layer 1 was 0.4, 0.9, 1.4, 1.9, and 4.9 mm, respectively, and the void generation rate was 0%. Regardless of the thickness of the SiC polycrystalline layer 1, the presence of the SiC polycrystals themselves prevented the generation of voids. It should be noted that the thickness of the SiC bonding seed crystal is preferably 1.0 mm or more, taking into account ease of attachment.

[0099] In Examples 2 and 5, the thickness of the SiC single crystal layer 2 was 0.001 mm and the thickness of the SiC polycrystalline layer 1 was 1.0 mm and 2.0 mm, respectively, and the void generation rate was 0% in both cases. Even when the thickness of the SiC single crystal layer 2 was 0.001 mm, it was possible to manufacture a SiC single crystal ingot without any problems and to suppress the generation of voids.

[0100] According to each embodiment, it is possible to provide a seed crystal for producing a SiC single crystal ingot, a composite for producing a SiC single crystal ingot, a SiC single crystal ingot, a method for producing a SiC single crystal ingot, and a method for producing a SiC bonded substrate, which are capable of suppressing the generation of voids in the ingot due to the seed crystal, and which also improve the production yield of the SiC single crystal ingot. [Explanation of symbols]

[0101] 1: SiC polycrystalline layer, 2: SiC single crystal layer, 3: seed substrate, 4: surface protection layer, 5: base, 6: heat insulating material, 7: graphite crucible, 8: graphite crucible lid, 9: SiC powder, 10: SiC sublimation gas transport part, 11: tapered guide, 12: quartz tube, 13: high frequency coil, 14: SiC single crystal growth section, 15: SiC polycrystalline adhesion growth section, 100: SiC crystal growth apparatus, a1: surface, a2: opposite surface, a3: surface, a4: joining surface, b1: surface, b2: opposite surface, S1: bonding step, S2: growth step

Claims

1. a SiC single crystal layer serving as a base for growing a SiC single crystal; a SiC polycrystalline layer supporting the SiC single crystal layer; A seed crystal for producing a SiC single crystal ingot, comprising the stacked structure.

2. the thickness of the SiC single crystal layer is 1 μm or more and 1 mm or less; The thickness of the SiC polycrystalline layer is 500 μm or more and 5.0 mm or less, The seed crystal according to claim 1 , wherein the seed crystal has a thickness of 501 μm or more and 6.0 mm or less.

3. The seed crystal according to claim 1 , further comprising a surface protection layer laminated on the SiC polycrystalline layer.

4. The seed crystal according to claim 1 , wherein the SiC single crystal layer and the SiC polycrystalline layer are laminated by direct bonding.

5. The seed crystal of claim 1 , further comprising an adhesive layer between the SiC single crystal layer and the SiC polycrystalline layer.

6. The seed crystal according to claim 1 , wherein the SiC polycrystalline layer has a warpage with a radius of curvature of 56 m or more.

7. The seed crystal according to claim 1; a base to which the seed crystal is bonded; A composite for producing a SiC single crystal ingot, comprising:

8. The seed crystal according to claim 1; a SiC single crystal growth portion grown on the SiC single crystal layer; A SiC single crystal ingot comprising:

9. A method for producing a SiC single crystal ingot using the seed crystal according to claim 1.

10. a bonding step of bonding the seed crystal to a base; a growth step of growing a SiC single crystal on the SiC single crystal layer of the seed crystal attached to the pedestal; The method for producing a SiC single crystal ingot according to claim 9, comprising:

11. The method for producing a SiC single crystal ingot according to claim 10, further comprising a cutting step of cutting at least a portion of the SiC single crystal ingot obtained by the growing step so as to be separate from at least a portion of the pedestal.

12. 12. A method for manufacturing a SiC bonded substrate, comprising a transfer step of transferring a SiC single crystal thin film from the SiC single crystal ingot sliced ​​in the slice step according to claim 11 onto a SiC polycrystalline substrate.

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