Arrangement for growing sic volume monocrystal and growing method

Abstract

To provide an arrangement for growing a SiC volume monocrystal and a growing method.SOLUTION: An arrangement comprises: a susceptor 100 for absorbing electromagnetic energy, the susceptor for heating a cavity; and an insulator surrounding the susceptor, the insulator for thermally insulating the susceptor from the exterior of the arrangement. The insulator comprises: a thermal insulation wall 202 surrounding the susceptor in a growth direction Y and a circumferential direction C, the thermal insulation wall for reducing heat transfer in a radial direction from the susceptor to the exterior outside the arrangement, the radial direction being perpendicular to the growth direction; and a thermally conductive layer 210 disposed between the susceptor and the thermally insulation wall, the thermally conductive layer having thermal conductivity higher than that of the thermally insulation wall, in order to distribute heat on the thermally conductive layer. The thermally heat conductive layer is spaced apart from the susceptor to reduce heat transfer to the insulator from the susceptor triggered by thermal conduction. The thermally conductive layer is disposed on the thermally insulation wall, and increases the reflectivity of the insulator.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present application relates to an apparatus and a growth method for growing a SiC bulk single crystal.

Background Art

[0002] Silicon carbide (SiC) is used as a semiconductor material for high-frequency components and special light-emitting semiconductor components, including being used as a starting material for power semiconductor components, due to its excellent physical, chemical, electrical, and optical properties. For these components, SiC substrates having a large substrate diameter (200 mm or more) and high quality, such as those described in U.S. Patent No. 8,747,982 B2, are required.

[0003] Using a suitable starting material, SiC single crystals are grown by, for example, a physical vapor deposition (PVT) process as disclosed in, for example, U.S. Patent No. 8,865,324 B2. The crystal is then sliced into SiC substrates using a wire saw or a similar slicing technique, and the surface is then refined using multi-step polishing steps. In subsequent epitaxy processes, thin single crystal layers (e.g., SiC, GaN) are first deposited on the SiC substrate. The properties of these layers and the resulting devices depend on the quality of the SiC substrate.

[0004] The growth of SiC crystals is a very energy-intensive and thus expensive process. Any energy savings with the same or larger crystals results in an improvement in the economic efficiency of the resulting electrical components. For example, it has been proposed to use heat insulation materials as described in German Patent Application Publication No. 10 2009 004 751 B4. In this way, energy can be saved and the quality can be guaranteed.

[0005] At the same time, the deterioration of quality in crystal growth leads to huge costs. In order to achieve a high yield in crystal growth, it is necessary to be able to use starting materials and auxiliary materials, especially thermal insulation materials, of consistent quality that meet high requirements such as cleanliness, temperature stability, and transparency to electromagnetic fields.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0007] From the above viewpoints, the purpose is to reduce costs and save energy. At the same time, in order to guarantee quality, it is an object to select materials that enable setting a defined temperature profile (consistent for each growth). For the growth of high-quality SiC crystals, furthermore, it is an object that a defined temperature profile dominates in the growth setup. Another object is to use materials that can be used at high temperatures. A further object is that the materials can be used under vacuum conditions and can meet the requirements of cleanliness.

[0008] At least one of these objects is solved by the subject matter of the independent claims. Advantageous embodiments are solved by the dependent claims.

[0009] According to a general aspect, it is proposed to optimize the surface of the thermal insulation material. More specifically, thermal insulation materials that can be used for crystal growth applications usually have a wavy surface and structures with various densities. This has a two-fold adverse effect on crystal growth.

[0010] More specifically, typically, the fiber-based microstructure results in a surface with strong undulations and voids. This leads to a suboptimal and non-uniform return of energy to the susceptor due to the suboptimal reflection of thermal radiation from the insulation to the surface. Instead, the insulation gets hot because it is not possible due to undesirable absorption or due to the susceptor's direct backscattering to the insulation surface which is disadvantageous. In regions of low fiber density (large voids), much of the radiant energy from the crucible is absorbed by the insulation, while in regions of high fiber density (small voids), less radiant energy is absorbed.

[0011] These localized hot spots in the insulation create undesirable temperature inhomogeneities, which can randomly and uncontrollably affect the growing temperature field and potentially have an adverse effect on the quality of the grown crystal. This problem is further exacerbated by the way the insulation is produced. The gradual inhomogeneities associated with the production in the insulation due to fiber agglomeration or depletion in the insulation also result in the hot spots in the insulation described above, which are also difficult to control and dominate.

[0012] In summary, recent insulations affect crystal growth in two ways, namely, the insufficient return of heat to the susceptor due to thermal radiation caused by the surface structure, and the insufficient homogeneity of the temperature field due to fiber inhomogeneities and the formation of hot spots in the insulation.

[0013] By optimizing the insulation surface, the crystal yield and quality are improved by making the hot spots in the insulation uniform (and further improving the homogeneity for each growth) and by increasing the reflectivity (energy efficiency) of the insulation surface to the susceptor.

[0014] The inventors have found that both drawbacks can be substantially eliminated by surface treatment of the insulation, in particular by coating, infiltrating, and / or lining the surface of the insulation with foil. More specifically, coating, infiltration, and foil lining increase the return of energy to the susceptor, and the insulation effect can be significantly homogenized. The heat radiation hitting the susceptor from the optimized insulation surface can be directly and directionally reflected back to the susceptor along the entire length of the insulation. In addition, coating, infiltration, and foil lining each have a higher thermal conductivity than the original insulation, so they can compensate for the temperature inhomogeneity (hot spots) in the axial direction of the insulation.

[0015] The increase in thermal conductivity slightly increases the energy absorption, but since the electromagnetic coupling is usually higher in such materials, this effect is more than compensated for by the improvement in homogeneity and its effect on the crystals formed.

[0016] More specifically, a first aspect relates to an apparatus for growing a SiC bulk single crystal in a cavity typically formed by a crucible in a growth direction by sublimation growth. Silicon carbide crystals are generally grown using the physical vapor transport (PVT) method, specifically sublimation. The growth starts from a seed crystal placed in the crucible, and the seed crystal grows in the growth direction within the crucible, thereby forming a larger SiC crystal. The growth is usually carried out within a crucible surrounding the cavity.

[0017] More specifically, an apparatus for growing a SiC bulk single crystal typically comprises a crucible, which is a container designed to withstand high temperatures and is used to hold materials at extreme temperatures, and the seed crystal and raw materials are placed within the cavity. Further, this apparatus includes a susceptor, which is a material that usually absorbs electromagnetic energy in the form of microwaves or high frequencies and converts it into heat. In short, the crucible functions as a high-temperature container for holding and processing materials, while the susceptor enhances the efficiency of the heating process, particularly in applications where microwave or high-frequency energy is utilized.

[0018] Hereinafter, the susceptor particularly refers to the combination of the crucible and the susceptor. This is an advantage for applications where accuracy, speed, and energy efficiency are of utmost importance. Alternatively, the growth apparatus can include a crucible in addition to the susceptor.

[0019] The container, namely the crucible or the susceptor which is an integral part of the crucible, has a cavity inside which a SiC bulk single crystal grows. The inner surface of the container faces the cavity. The outer surface of the container faces the heat insulator.

[0020] Advantageously, the container has a prism shape. A prism is a polyhedron that includes a bottom surface which is a polygon with n sides, a second bottom surface which is a parallel translation copy (exactly translated without rotation) of the first bottom surface, and n other surfaces that form side walls connecting the corresponding sides of the two bottom surfaces. In this way, a closed cavity is realized. This prism shape enables the SiC bulk single crystal to be easily taken out from the cavity, that is, parallel to the surfaces forming the side walls. Often, the container has a cylindrical shape, that is, the bottom surface has a circular cross-section.

[0021] Particularly, since the cost of the container is high, a shape that can be used several times is advantageous. Therefore, in particular, the prism shape, especially the cylindrical shape, is advantageous because the SiC bulk single crystal can be pulled out along the growth direction and the dead space in the cavity can be reduced.

[0022] According to a first aspect, a heat insulator surrounds the susceptor. Therefore, the heat insulator insulates the susceptor from the outside of the apparatus. The thermal insulator is a material specifically designed to reduce or prevent the transfer of heat between objects at different temperatures, that is, between the susceptor heated during growth and the outside which is at ambient temperature. Its main function is to impede the flow of thermal energy by conduction, convection, and radiation.

[0023] As used herein, the thermal insulator surrounds the surface of the susceptor, which means that the thermal insulator surrounds or encircles the outer portion of the susceptor and covers at least a part of the entire exterior thereof. In particular, the thermal insulator is in proximity to the susceptor.

[0024] Furthermore, according to a first aspect, the thermal insulator includes a thermal insulation wall that surrounds the susceptor in the growth direction and the circumferential direction. Thus, the thermal insulator extends two-dimensionally, i.e., in the growth direction, i.e., the longitudinal direction, and in the circumferential direction of the susceptor. As used herein, this means that the thermal insulator has dimensions or components that extend along the length (longitudinal direction) and around the perimeter (circumference).

[0025] The longitudinal direction often refers to the vertical dimension of an object considered along the main axis of the object, i.e., the growth direction of the SiC crystal. For example, in the case of a tube or cylinder, the longitudinal direction is the direction from one end to the other end.

[0026] The circumferential direction refers to the direction around the outer boundary or surface of the susceptor. In the case of a container having a cylindrical shape, the circumferential direction would be a circular path around the outside.

[0027] Therefore, a thermal insulation wall that extends in both the longitudinal and circumferential directions has features or dimensions that span both its length and the outer perimeter around the susceptor. For example, in the case of a cylindrical or tubular object with dimensions along the length and around the perimeter, the thermal insulator forms a hollow cylinder.

[0028] In particular, the thermal insulator can include additional segments for completely surrounding the susceptor for thermal insulation purposes. For example, if the susceptor has a cylindrical shape, the thermal insulator can include a thermal insulation bottom surface, i.e., a segment that extends in the radial dimension and the circumferential dimension.

[0029] From the above viewpoints, the thermal insulation wall according to the first aspect reduces the radial heat transfer from the susceptor to the outside of the device, and the radial direction is perpendicular to the growth direction.

[0030] In particular, in connection with the growth apparatus, the heat insulator extending in the longitudinal and circumferential directions is advantageous because the surface area defined by these two dimensions is usually the maximum surface area of the container. In addition, the temperature in the growth direction must be controlled particularly precisely. Furthermore, in the case of induction heating, the susceptor is usually heated in the circumferential direction, and thus a heat insulating wall surrounding the susceptor in the circumferential direction is particularly advantageous.

[0031] Furthermore, according to a first aspect, a heat conductive layer is disposed between the susceptor and the heat insulating wall, and the heat conductive layer has a higher thermal conductivity than the heat insulating wall in order to disperse heat in the heat conductive layer.

[0032] As used herein, a heat conductive layer is a material or coating designed to efficiently transfer heat. Its main purpose is to increase the thermal conductivity of the layer and facilitate the rapid and effective transfer of heat from one point to another in the layer.

[0033] Furthermore, according to a first aspect, the heat insulator includes a heat conductive layer, and the heat conductive layer is spaced apart from the susceptor to reduce heat transfer from the susceptor to the heat insulator caused by heat conduction.

[0034] Heat transfer can occur by various mechanisms, two of which are heat conduction and heat radiation. Heat conduction is a mode of heat transfer that occurs by direct microscopic interaction of particles within a material or between different materials in direct contact. In this process, thermal energy is transferred from a higher temperature region to a lower temperature region within the material without the overall movement of the material itself. Heat radiation includes the transfer of heat by electromagnetic waves such as infrared radiation. Unlike conduction, it does not require a material medium, and heat is transferred through a vacuum or a transparent medium.

[0035] Thus, by spacing the susceptor away from the heat insulator, usually more effective heat conduction is reduced, and heat transfer can be described by thermal radiation, especially since the device is used under vacuum conditions. Thus, by separating the heat conduction layer from the susceptor, the heat conduction layer can contribute to heat insulation. However, the larger the space, the larger the overall device. Since the device usually operates under vacuum conditions, space should be saved.

[0036] For example, the susceptor and the heat conduction layer are separated, i.e., spaced apart, by a distance of 0.1 mm or more, preferably 0.5 mm or more, and more preferably 1 mm or more in the radial direction. Additionally or alternatively, the susceptor and the heat conduction layer are separated by a distance of 5 cm or less, preferably 1 cm, and more preferably 5 mm in the radial direction.

[0037] Furthermore, according to a first aspect, the heat conduction layer is disposed on the heat insulating wall, thereby reducing the undulation of the heat insulator and increasing the reflectivity of the heat insulator.

[0038] The term undulation in the context of reflectivity refers to variations or irregularities on the reflective surface of a material or object. Undulation can affect the way light or electromagnetic waves interact with the surface and the resulting reflection characteristics. In particular, undulation often appears as surface roughness on a reflective material. Microscopic irregularities or fluctuations on the surface can cause scattering and diffusion of the reflected light. The degree of undulation or roughness can affect the specular reflection (mirror-like reflection) and diffuse reflection (scattering reflection) characteristics of the surface. Generally, the greater the value of undulation, the lower the reflection.

[0039] Thus, by reducing the undulation of the heat insulator, the reflectivity of the surface is increased, and the amount of thermal radiation that is reflected or scattered back to the susceptor (and absorbed by the susceptor) increases, thereby reducing the loss due to thermal radiation.

[0040] In other words, the heat conduction layer can increase the return of energy to the susceptor and significantly homogenize the heat insulation effect. The heat radiation hitting the optimized heat insulation material surface from the susceptor can be directly and directionally reflected back towards the susceptor over the entire length of the heat insulation material. Furthermore, the higher thermal conductivity of the heat conduction layer balances the temperature inhomogeneity (hot spots) in the axial direction of the heat insulation material. The increase in thermal conductivity slightly increases the energy absorption, but since the electromagnetic coupling is usually higher in such materials, this effect is fully compensated by the improvement in homogeneity and its effect on the generated crystals.

[0041] Advantageously, the susceptor has a higher absorbency than the heat conduction layer. For example, the absorption varies based on the different types of materials used for the susceptor and the heat insulation material.

[0042] According to a second aspect, the thermal conductivity ratio of the heat conduction layer to the thermal conductivity of the heat insulation wall is 10 or more. Advantageously, the ratio is 14 or more. More advantageously, the ratio is 18 or more.

[0043] The thermal conductivity ratio refers to the ratio of the thermal conductivity of one material, i.e., the thermal conductivity of the heat conduction layer, to the thermal conductivity of another material, i.e., the thermal conductivity of the heat insulation wall.

[0044] Thermal conductivity may vary with temperature, so it should be noted that when comparing materials here, the temperature relevant to a specific application is considered. Here, the reference temperature is considered to be the temperature at which the SiC bulk single crystal grows and is in the range of 2000°C to 2400°C. In particular, the exact temperature may vary depending on the specific SiC polytype (e.g., 4H-SiC, 6H-SiC) desired, the growth parameters, and the equipment used in the PVT process. In particular, a medium temperature of 2200°C is considered relevant to the thermal conductivity.

[0045] In addition, different materials may have anisotropic thermal conductivities, i.e., it means that the conductivity may vary depending on the direction, i.e., the circumferential direction and the growth direction. In such cases, an intermediate anisotropic thermal conductivity is considered appropriate.

[0046] The higher the thermal conductivity, the better the heat can be dispersed. This is important, for example, when local hot spots in the insulation material cause undesirable temperature inhomogeneities, which can have an uncontrolled impact on the growing temperature field and negatively affect the quality of the grown crystal. This aspect is further exacerbated by the way the insulation material is produced. The gradual inhomogeneities related to the production in the insulation material due to fiber agglomeration or depletion in the insulation material further result in the described hot spots in the insulation material, which are also difficult to control and dominate, and thus the thermal conductivity of the thermal conduction layer is very important.

[0047] According to a third aspect, in addition to any of the preceding aspects, the thermal conduction layer is disposed, i.e., arranged, on the insulation wall by at least one of coating, permeating, and backing the insulation wall with foil. Thereby, the thermal conduction layer and the insulation wall can be brought particularly close to each other, and as a result, the heat conduction between the insulation wall and the thermal conduction layer increases. Thereby, the heat generated at the hot spot of the insulation wall is efficiently dispersed in the thermal conduction layer, thereby reducing the influence of the heat hot spot.

[0048] To optimize the thermal conductivity, these layers are usually applied as thin and uniform layers. This ensures a tight interface between the layers and minimizes the thermal resistance.

[0049] In particular, surface coatings and penetrations can be applied to reduce undulations and improve reflection characteristics. Reflective coatings are designed, for example, to maximize reflection by reducing surface irregularities. These coatings are very important in applications where precise control of the reflected light is essential. Surface penetration is related to the process by which substances enter or soak into the surface of a material.

[0050] According to a fourth aspect, in addition to the third aspect, a thermal conduction layer is disposed on the heat insulation wall by coating and / or penetrating a metal carbide. The metal carbide coating has excellent hardness, wear resistance, and high-temperature stability. Preferably, the metal (carbide) includes a heat-resistant metal carbide. These heat-resistant metal carbides are selected based on the specific requirements of the application, taking into account factors such as heat resistance, wear resistance, and chemical compatibility. The coating method and the penetration method can include thermal spraying, physical vapor deposition, or chemical vapor deposition, depending on the material and the desired properties. In particular, these can be deposited on the heat-insulating material from both the gas phase and the solution, and at that time, a homogeneous and smooth surface can be produced.

[0051] In particular, tantalum carbide (TaC), tungsten carbide (WC), and hafnium carbide (HfC) have been found to be advantageous considering their high melting points, wear resistance, and high hardness.

[0052] According to a fifth aspect, in addition to the third and fourth aspects, the thermal conduction layer is disposed on the heat insulation wall by attaching a foil to the heat insulation wall. The foil enables a technical effect similar to that of the coated surface or the penetrated surface. In particular, the foil can contain graphite or be made of graphite. Graphite foil is a thin flexible material made of layers of graphene sheets. It has unique properties due to the structure of graphite consisting of carbon atoms arranged in a hexagonal pattern. In particular, graphite foil is an excellent thermal conductor. Furthermore, graphite is chemically inert, which means that graphite is resistant to many corrosive substances. This property makes graphite foil suitable for use in harsh environments where it is feared to be exposed to extreme temperatures, such as in a growth apparatus.

[0053] Preferably, the foil contains exfoliated graphite. Exfoliated graphite refers to a form of graphite that has undergone a process called exfoliation, resulting in the expansion and separation of individual graphene layers. Exfoliated graphite exhibits anisotropy in thermal conduction due to its hierarchical structure. The thermal conductivity of exfoliated graphite depends greatly on the direction in which heat is transferred with respect to the plane of the graphene layers. The anisotropic thermal properties are the result of the difference between in-plane (within the plane) thermal conduction and out-of-plane (perpendicular to the plane) thermal conduction.

[0054] Therefore, anisotropic thermal conduction can be used to advantage in that the thermal conductivity parallel to the symmetry axis of the growth apparatus, i.e., the thermal conductivity in the growth direction, is higher, and thus it can be used to homogenize the temperature non-uniformity along the heat insulation material and provide a smooth surface for high reflection. In particular, the in-plane direction exhibits a higher thermal conductivity, i.e., a hexagonal pattern, as described above. Therefore, this is advantageous for homogenizing the non-uniformities and hot spots in the heat insulation material.

[0055] According to a sixth aspect, in addition to any of the preceding aspects, the heat insulating wall comprises or consists of felt. Felt is a versatile material that can be used for insulation by a fibrous structure that creates a network of air pockets that resist the flow of heat.

[0056] Advantageously, the felt can comprise at least one of soft felt, hard felt, and a combination of soft and hard felt.

[0057] The felt that is advantageous for the device has a fiber-based microstructure that results in a surface with strong undulations and cavities. This results in a sub-optimal and non-uniform return of energy towards the susceptor due to sub-optimal reflection of thermal radiation from the heat insulating wall. Instead, the heat insulating wall gets hot due to undesirable absorption or because direct backscattering towards the susceptor is not possible for the heat insulating wall surface that is disadvantageous. In regions with low fiber density (large cavities), more of the radiant energy coming from the crucible is absorbed by the heat insulating wall, and in regions with high fiber density (small cavities), less radiant energy is absorbed. The adverse effects are compensated for by the heat conducting layer discussed above.

[0058] The heat insulating wall material can comprise or consist of short carbon fibers (hard felt) held together by a binder matrix and / or long carbon fibers (soft felt) integrated by needling.

[0059] The hard felt can be formed into a desired shape, such as a hollow cylinder, during the manufacturing process and then assumes a rigid shape. The soft felt is typically produced as a sheet mat having a thickness of about 5 mm to 25 mm. This mat can then be cut, rolled up as needed, and processed into a desired shape, such as a hollow cylinder, for example by sewing. For example, a hybrid solution where a soft felt mat is wound onto and fixed to a hard felt cylinder or where a soft felt mat is wound and surrounded by a hard felt cylinder is also conceivable.

[0060] According to a seventh aspect, in addition to the sixth aspect, the heat-insulating wall comprises or consists of a graphite heat-insulating material having short carbon fibers with a fiber length in the range between 1 mm and 10 mm and a fiber diameter in the range between 0.1 mm and 1 mm, and the short carbon fibers are joined by a resin, whereby a rigid felt is formed. Alternatively or additionally, the heat-insulating wall comprises a graphite heat-insulating material having long carbon fibers with a fiber length exceeding 10 (or 10 mm or more), and the long carbon fibers are joined by needling to form a soft felt.

[0061] According to an eighth aspect, in addition to any of the preceding aspects, the heat-insulating wall is formed by a hollow cylinder extending in the growth direction and the circumferential direction of the susceptor. For the shape of the hollow cylinder, refer to the above description. Advantageously, a plurality of coaxial hollow cylinder layers are stacked one inside the other, each cylinder layer having a different radius, and the cylinder having the smallest radius includes a heat-conducting layer on the inner surface facing the susceptor. Thus, different materials for different applications can be realized.

[0062] According to a ninth aspect, in addition to any of the preceding aspects, the ratio of the reflectivity ratio of the heat-conducting layer to the reflectivity ratio of the heat-insulating wall is 1.3 or more. The reflectivity ratio, also known as the reflectance ratio, is a measure comparing the amount of light or other electromagnetic radiation reflected by a surface to the amount incident on the surface. Thus, due to the higher reflectivity ratio of the heat-conducting layer, the heat-insulating properties of the heat-insulating object can be improved compared to an apparatus without the heat-conducting layer. Advantageously, the ratio is 1.4 or more. More preferably, the ratio is 1.5 or more.

[0063] According to a tenth aspect, in addition to any of the preceding aspects, the undulation height of the heat-conducting layer is 2 mm or less. Preferably, the undulation height of the heat-conducting layer is 1 mm or less. More preferably, the undulation height of the heat-conducting layer is 0.5 mm or less.

[0064] The waviness height refers to the vertical distance between the highest peak and the lowest valley of the surface profile within the specified sampling length. It is a measure of the amplitude of the unevenness or undulations present on the surface. Unlike roughness, waviness generally represents fluctuations with longer wavelengths in the surface profile. The waviness height is defined by the unevenness having a frequency lower than that related to roughness. These unevennesses often occur over a longer distance of the surface. Therefore, the waviness height is more appropriate than surface roughness for defining surface characteristics, considering radiation at a temperature of 2000 °C which results in longer wavelengths, i.e., wavelengths in the micrometer range, being more important than shorter wavelengths, i.e., wavelengths in the nanometer range. The waviness height can be measured using techniques such as profilometry or interferometry. Generally, the smaller the waviness height, the higher the reflectivity.

[0065] According to the eleventh aspect, in addition to any of the preceding aspects, the thickness ratio of the radial thickness of the heat conduction layer to the radial thickness of the heat insulation wall is 1 / 10 or less, preferably 1 / 15 or less, more preferably 1 / 20 or less.

[0066] The thin heat conduction layer reduces the influence on the heat insulation characteristics of the heat insulation wall. When the coating / penetration / foil is thick, an excessive amount of electromagnetic radiation is already coupled to the coating and heats the heat insulation material quite significantly, so the heat insulation material deteriorates considerably. At the same time, the coupling of energy to the susceptor is too little, which means it is more difficult to bring the device to the desired temperature.

[0067] Furthermore, apart from the pure heat insulation effect, in the case of induction heating described below, the electromagnetic field of the coil must not couple to the heat insulation material and heat the heat insulation material itself. The heat insulation material must be permeable to the electromagnetic field and ensure the lowest possible loss so that the energy can directly couple to the growth susceptor (which can be part of the crucible) and heat the internal raw material. Therefore, a thin heat conduction layer is particularly advantageous for induction heating.

[0068] A typical thickness of the heat insulation wall is 5 mm or more, more preferably 1 cm. Further, the thickness of the heat insulation wall is 15 cm or less, preferably less than 10 cm, more preferably less than 5 cm.

[0069] According to a twelfth aspect, in addition to any of the preceding aspects, the heat insulator further includes at least one heat insulation cover for covering the susceptor.

[0070] There are two different positions for the use of the heat insulation material in the SiC growth setup. On the one hand, the heat insulation material is arranged under and above the growth susceptor. On the other hand, a hollow single-part or multi-part heat insulation cylinder is placed above the susceptor, and they surround the susceptor in the circumferential direction and the longitudinal direction extending radially.

[0071] A thirteenth aspect relates to a system including an apparatus according to any of the preceding aspects. This system includes an induction heater, where the induction heater surrounds the heat insulator, a resistance heater, where the resistance heater is surrounded by the heat insulator, a reactor for accommodating the apparatus, and at least one of a vacuum pump for evacuating the system, particularly the reactor.

[0072] Thus, heating is performed by at least one of an induction coil installed outside the reactor or a resistance heater installed inside the reactor. Additionally, the apparatus can be placed inside the reactor, and actual crystal growth is performed inside the reactor. The apparatus for growth includes different graphite and heat insulation materials and seeds and raw materials placed inside a cavity formed inside the reactor, i.e., inside the crucible. Generally, this apparatus includes carbon-based materials because carbon-based materials can withstand high temperatures and, at the same time, are not a source of impurities for SiC crystals.

[0073] The thermal insulation is intended to ensure that as little as possible of the energy introduced into the susceptor is released to the outside, and that as much as possible of the energy available for heating the susceptor is utilized. The device consisting of the susceptor and the thermal insulation is preferably accommodated in a reactor in an intergas atmosphere of less than 50 mbar. In accordance with the laws of radiation, the susceptor emits a part of the induced energy outward towards the thermal insulation. As discussed above, the thermal insulation is usually positioned away from the susceptor, and therefore the heat transfer from the susceptor to the thermal insulation is mainly due to thermal radiation.

[0074] Additionally, the device can include devices for measuring temperature, such as pyrometers, thermocouples, etc. The vacuum-sealed reactor can be evacuated by one or more vacuum pumps. Further, the system can supply an inert gas and / or a doping gas (e.g., nitrogen) via one or more gas supply lines, and the pressure of the system can be measured and controlled. All process parameters (pressure, temperature, gas flow rate, …) can be set, monitored, and stored by a computer control system controller. The system control communicates with all relevant components (e.g., inverter, pyrometer, vacuum control valve, MFC, pressure gauge).

[0075] A fourteenth aspect relates to a method for growing a SiC bulk single crystal in a growth direction by sublimation growth within a cavity, the method comprising providing a SiC seed crystal and a SiC raw material within the cavity, and heating the susceptor to grow a SiC bulk single crystal within the cavity, and insulating the susceptor with a thermal insulation, the thermal insulation being a thermal insulation wall surrounding the susceptor in the growth direction (Y) and the circumferential direction, the thermal insulation wall being for reducing the radial (r) heat transfer from the susceptor to the outside of the device, the radial direction (r) being perpendicular to the growth direction (Y), and A heat conduction layer disposed between the susceptor and the heat insulating wall, wherein the heat conduction layer has a higher thermal conductivity than the heat insulating wall in order to disperse heat in the heat conduction layer, the heat conduction layer comprises The heat conduction layer is spaced apart from the susceptor to reduce heat transfer from the susceptor to the heat insulator caused by heat conduction, and the heat conduction layer is disposed on the heat insulating wall, thereby reducing the undulation of the heat insulator and increasing the reflectivity of the heat insulator. steps comprises

[0076] For an explanation of this method, refer to the explanations of the above-described aspects 1 to 13. In particular, the same terms are used, such as cavity, susceptor, heat insulator, heat insulating wall, and heat conduction layer. Therefore, the explanation of the terms used in this method is omitted. In particular, this method can be implemented by using any of the devices of the above-described aspects 1 to 13.

[0077] Advantageously, according to the 15th aspect, in the method according to the 14th aspect, the heat conduction layer increases the reflectivity, and as a result, the thermal energy supplied to the susceptor during heating is reduced by 5% or more, preferably, the thermal energy supplied to the cavity is reduced by 10% or more. For example, the supplied energy is reduced by the means described with reference to any of aspects 2 to 12.

[0078] The present invention will next be illustrated in more detail by way of example, using advantageous aspects and with reference to the drawings. The described aspects are merely possible configurations. However, the above-described individual features may be provided independently of each other or may be omitted.

[0079] The accompanying drawings are incorporated herein and form a part of this specification to illustrate some embodiments of the present invention. These drawings, together with the description, serve to explain the principles of the present invention. The drawings are for the sole purpose of showing preferred and alternative examples of how the present invention can be practiced and used, and should not be construed as limiting the present invention to only the illustrated and described embodiments. Furthermore, some aspects of the embodiments can form solutions according to the present invention individually or in different combinations. Therefore, the embodiments described below can be considered alone or in any combination.

[0080] It should be noted that the described embodiments are merely possible configurations, and the individual features described above can be provided independently of each other or completely omitted when implementing the present invention. Further features and advantages will become apparent from the following more detailed description of various embodiments of the present invention as shown in the accompanying drawings in which like references refer to like elements.

Brief Description of the Drawings

[0081]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0082] The present invention will next be described with reference to the drawings, first with reference to FIG. 1, which shows a system 10 for growing a SiC bulk single crystal within a cavity 110. More specifically, FIG. 1 shows a system 10 including a susceptor 100, where a reactor 11 forms a chamber and the susceptor 100 is disposed within the chamber. Further, a thermal insulator 200 surrounds the susceptor 100. As discussed above, the susceptor 100 forms a crucible having a cavity for growing a SiC bulk single crystal. Alternatively, according to an example not shown, the susceptor 100 can be provided separately from the crucible.

[0083] The susceptor 100 is provided with a SiC seed crystal 120 and a SiC raw material 130 at a first end.

[0084] The thermal insulator 200 includes a thermal insulation wall 202 that surrounds the susceptor 100 in the growth direction Y and the circumferential direction C. In particular, as shown in the example of FIG. 2, the thermal insulation wall 202 forms a hollow cylinder extending in the growth direction Y and the circumferential direction C. The thermal insulation wall 202 reduces the heat transfer in the radial direction r from the susceptor 110 to the outside of the apparatus. In particular, the radial direction r is perpendicular to the growth direction Y.

[0085] Furthermore, the thermal insulator 200 includes two thermal insulation covers 204 for covering the susceptor. The thermal insulation covers 204 can be made of the same material as the thermal insulation wall 202.

[0086] According to one example, the thermal insulation wall 202 includes felt, for example, soft felt, hard felt, or a combination thereof. The hard felt is made of short carbon fibers having a fiber length in the range between 1 mm and 10 mm and a fiber diameter in the range between 0.1 mm and 1 mm, and the short carbon fibers are joined by a resin, thereby forming the hard felt. The soft felt includes long carbon fibers having a fiber length greater than 10 (or 10 mm or more), and the long carbon fibers are joined by needling to form the soft felt.

[0087] As shown in FIG. 1, the reactor 11 houses a device including a susceptor 100 and a heat insulator 200. A vacuum pump for evacuating the reactor 11 is not shown.

[0088] The system 10 can further include a heater (not shown) disposed within the reactor 11. For example, the system can include an induction heater, which can surround the heat insulator 200. Additionally or alternatively, although not shown, the system 10 can include a resistance heater, which is surrounded by the heat insulator 200.

[0089] The heat insulation wall 202 of FIG. 1 is schematically shown in FIG. 2. In particular, in the example shown in FIG. 2, the induction heater 300 heats the susceptor 100. Alternatively, resistance heating (not shown) may be performed. In other words, the susceptor 100 absorbs electromagnetic energy from the heater and is thereby heated, and thus the cavity surrounded by the susceptor 100 is heated.

[0090] As shown in FIG. 2, the heat insulation wall 202 is spaced apart from the susceptor 100 to reduce heat transfer from the susceptor 100 to the heat insulator caused by heat conduction. In other words, the heat transfer from the susceptor 100 to the heat insulation wall 202 is caused by radiation, which is described by the Stefan-Boltzmann law (1). Q = ε * σ * A * T^4 (1) In Equation (1), the radiator is described. Q is the radiation power, ε is the emissivity (material-dependent), σ is the Stefan-Boltzmann constant, A is the radiation area, and T is the absolute temperature of the radiator.

[0091] As shown in FIG. 2, the radiation 1 from the susceptor 100 is radiated to the heat insulation wall 202. Considering the undulations of the heat insulation wall 202, the reflected radiation 2 is not directed towards the wall of the susceptor 1100. Rather, the probability that the reflected radiation 2 interacts with the heat insulation wall 202 again is high, and thus the probability that the reflected radiation 2 is absorbed by the heat insulation wall 202 is high.

[0092] Instead, as shown in FIG. 3, a heat conduction layer 210 is disposed between the susceptor 100 and the heat insulating wall 202. For example, the heat conduction layer 210 is disposed on the heat insulating wall 202 by at least one of coating, permeating, and lining with foil the heat insulating wall 202.

[0093] As shown in FIG. 3, the heat conduction layer 210 reduces the undulation of the heat insulator and increases the reflectivity of the heat insulator. In particular, after the interaction with the surface of the heat conduction layer 210, the radiation 1 becomes the redirected radiation 3 directed toward the susceptor 100. Therefore, the probability that the radiation is redirected toward the susceptor 100 is increased. Therefore, the heat conduction layer 210 reduces the amount of the radiation power Q transferred from the susceptor 100 to the heat insulator 200. In particular, the redirection can include processes such as reflection and scattering.

[0094] Furthermore, the heat conduction layer 210 has a higher thermal conductivity than the heat insulating wall 202. Therefore, the remaining part of the heat absorbed by the heat conduction layer 210 is dispersed within the heat conduction layer 210 rather than being restricted by the heat insulating wall 202 as can be derived from Fourier's law (2). Q = λ * A * (dT / dx) (2) Here, Q is the transferred heat output, λ is the thermal conductivity of the material, A is the cross-sectional area through which the heat is transferred, and dT / dx is the temperature gradient along the direction of heat transfer.

[0095] Fourier's law describes here the mechanism of heat conduction related to the homogenization of the temperature inhomogeneity in the heat conduction layer 210 of the heat insulator 200, and Stefan-Boltzmann's law describes the heat transport by radiation that describes the return of energy from the heat conduction layer 210 of the heat insulator 200 to the susceptor 100.

[0096] Therefore, by selecting the thermal conductivity, the generation of hot spots in the heat insulation wall 202 is suppressed, and by providing the heat conduction layer 210 on the surface, the undulation is reduced. As a result, the return of energy from the heat insulator 200 to the susceptor 100 increases.

[0097] As further shown in the schematic FIG. 3, the heat insulation wall 202 is thicker than the heat conduction layer 210. In particular, the thickness ratio of the thickness in the radial direction r of the heat conduction layer 210 to the thickness in the radial direction r of the heat insulation wall 202 is 1 / 10 or less, preferably 1 / 15 or less, and more preferably 1 / 20 or less. The thinner the thickness, the lower the probability of absorption of electromagnetic radiation, that is, the field emitted by the induction heater 300 and the thermal radiation emitted by the susceptor 100.

[0098] According to an example, the thermal conductivity ratio of the thermal conductivity of the heat conduction layer 210 to the thermal conductivity of the heat insulation wall is 10 or more, preferably 14 or more, and more preferably 18 or more. The higher the thermal conductivity ratio, the more efficiently the heat is dispersed by the heat conduction layer 210.

[0099] According to one example, the heat conduction layer 210 is disposed on the heat insulation wall 202 by coating and / or infiltrating a metal carbide. As shown in FIG. 3, the grooves on the surface of the heat insulation wall 202 can be filled with a coating and / or infiltration material. In particular, the metal can contain or consist of at least one of heat-resistant metals such as TaC, WC, and HfC. Thereby, the undulation is reduced and the reflectivity of the heat insulator is increased.

[0100] According to another example, the heat conduction layer 210 is disposed on the heat insulation wall 202 by pasting a foil on the heat insulation wall 202. In particular, the foil contains graphite, such as exfoliated graphite. Thereby, the undulation is reduced and the reflectivity of the heat insulator is increased.

[0101] In particular, the undulation height of the heat conduction layer 210 is 2 mm or less, preferably 1 mm or less, and more preferably 0.5 mm or less. To measure the undulation height, the vertical distance between the highest peak and the lowest valley of the surface profile, that is, the vertical distance in the radial direction r, is determined within a specified sampling length, here, in particular, in the axial direction Y and / or the circumferential direction C.

[0102] According to another example, the reflectance of the reflectance ratio of the heat conduction layer to the reflectance ratio of the heat insulation wall is 1.3 or more, preferably 1.4 or more, and more preferably 1.5 or more.

[0103] A method of growing such a SiC single crystal in the growth direction Y by sublimation growth is described in FIG. 4. According to this method, in the first step S10, as shown in FIG. 1 for example, SiC seed crystals can be prepared in the cavity of the reactor. The SiC seed crystals can be arranged on the end wall provided with a seed holder for holding the SiC seed crystals. The end wall extends perpendicular to the growth direction. In addition, the SiC material may be prepared in a storage region formed in the cavity.

[0104] This method further includes a step S12 of insulating the susceptor using a heat insulator including a heat insulation wall and a heat conductive layer, as described above in FIG. 3 for example.

[0105] More specifically, the heat insulation wall is arranged to surround the susceptor in the circumferential direction C and the growth direction Y. The heat insulation wall is for reducing the heat transfer in the radial direction r from the susceptor to the outside of the apparatus. The radial direction r is perpendicular to the growth direction Y. Further, the heat insulator includes a heat conduction layer disposed between the susceptor and the heat insulating wall. The heat conduction layer has a higher thermal conductivity than the heat insulation wall in order to disperse heat in the heat conduction layer. In addition, the heat conduction layer is arranged to be separated from the susceptor in order to reduce the heat transfer from the susceptor to the heat insulator caused by heat conduction.

[0106] Furthermore, the process includes heating a susceptor to grow a single crystal of SiC in a volume within the cavity (step S14). In particular, the heat conduction layer is disposed on the heat insulating wall, thereby reducing the undulation of the heat insulator, and thus increasing the reflectivity of the heat insulator. During heating, the heat conductive layer redirects the radiation emitted from the susceptor back to the susceptor.

[0107] In particular, the heat conduction layer increases the reflectivity, and as a result, the thermal energy supplied to the susceptor during heating in S14 is reduced by 5% or more, and preferably, the thermal energy supplied to the cavity is reduced by 10% or more.

[0108] In particular, according to the example discussed with reference to the figures, the susceptor 100 forms a crucible. According to an example not shown, the susceptor can be provided separately from the crucible.

[0109] In particular, according to an example not shown, a plurality of coaxial hollow cylindrical layers are stacked with one inside the other, each cylindrical layer having a different radius, and the cylinder having the smallest radius includes a heat conduction layer on the inner surface facing the susceptor.

Explanation of Reference Numerals

[0110] 1 Radiation 2 Reflected Radiation 3 Redirected Radiation 10 System 11 Reactor 100 Susceptor 110 Cavity 120 Seed Crystal 130 SiC Raw Material 200 Heat Insulator 202 Heat Insulating Wall, Heat Conductive Wall 204 Heat Insulating Cover 210 Heat Conduction Layer 300 Induction Heater

Claims

1. An apparatus for growing a SiC bulk single crystal in a growth direction (Y) by sublimation growth within a cavity (110), comprising: a susceptor (100) for absorbing electromagnetic energy, the susceptor (100) being for heating the cavity (110); a heat insulator (200) surrounding the susceptor (100), the heat insulator (200) being for thermally insulating the susceptor (100) from the outside of the apparatus, the heat insulator (200) comprising: a heat insulating wall (202) surrounding the susceptor (100) in the growth direction (Y) and the circumferential direction (C), the heat insulating wall (202) being for reducing radial (r) heat transfer from the susceptor (100) to the outside of the apparatus, the radial direction (r) being perpendicular to the growth direction (Y); a heat conduction layer (210) disposed between the susceptor (100) and the heat insulating wall (202), the heat conduction layer (210) having a higher thermal conductivity than the heat insulating wall (202) for dispersing heat in the heat conduction layer (210); and the heat conduction layer (210) being spaced apart from the susceptor (100) to reduce heat transfer from the susceptor (100) to the heat insulator (200) caused by heat conduction, the heat conduction layer (210) being disposed on the heat insulating wall (202) so as to reduce undulation of the heat insulator (200) and increase reflectivity of the heat insulator (200); a heat insulator (200); and an apparatus.

2. The apparatus according to claim 1, wherein a thermal conductivity ratio of the thermal conductivity of the heat conduction layer (210) to the thermal conductivity of the heat insulating wall (202) is 10 or more, preferably 14 or more, and more preferably 18 or more.

3. The apparatus according to claim 1 or 2, wherein the heat conduction layer (210) is disposed on the heat insulating wall (202) by at least one of coating, permeating, and lining with foil.

4. The heat conduction layer (210) is disposed on the heat insulation wall (202) by coating and / or infiltrating a metal carbide, preferably, the metal carbide includes a heat-resistant metal carbide, and optionally, the heat-resistant metal carbide includes at least one of TaC, WC, and HfC. The apparatus according to claim 3.

5. The heat conduction layer (210) is disposed on the heat insulation wall (202) by pasting a foil on the heat insulation wall (202), preferably, the foil includes graphite, and optionally, the foil includes exfoliated graphite. The apparatus according to claim 3 or 4.

6. The heat insulation wall (202) includes felt, preferably, the heat insulation wall (202) includes at least one of soft felt and hard felt. The apparatus according to any one of claims 1 to 5.

7. The heat insulation wall (202) is short carbon fibers having a fiber length in the range between 1 mm and 10 mm and a fiber diameter in the range between 0.1 mm and 1 mm, the short carbon fibers being joined by a resin, thereby forming a hard felt, and short carbon fibers long carbon fibers having a fiber length exceeding 10, the long carbon fibers being joined by needling to form a soft felt, and long carbon fibers including a graphite heat insulating material including at least one of them. The apparatus according to claim 6.

8. The heat insulation wall (202) extends in the growth direction (Y) and is formed by a hollow cylinder surrounding the susceptor (100) in the circumferential direction (C), preferably, a plurality of coaxial hollow cylinder layers are stacked with one inside the other, each cylinder layer has a different radius, and the cylinder having the smallest radius includes the heat conduction layer (210) on the inner surface facing the susceptor (100). The apparatus according to any one of claims 1 to 7.

9. The reflectance of the reflectance ratio of the heat conduction layer (210) to the reflectance ratio of the heat insulation wall (202) is 1.3 or more, preferably, 1.4 or more, and more preferably, 1.5 or more. The apparatus according to any one of claims 1 to 8.

10. The undulation height of the heat conduction layer (210) is 2 mm or less, preferably, 1 mm or less, and more preferably, 0.5 mm or less. The apparatus according to any one of claims 1 to 9.

11. The thickness ratio of the thickness of the heat conduction layer (210) in the radial direction (r) to the thickness of the heat insulation wall (202) in the radial direction (r) is 1 / 10 or less, preferably 1 / 15 or less, and more preferably 1 / 20 or less. The apparatus according to any one of claims 1 to 10.

12. The apparatus according to any one of claims 1 to 11, wherein the heat insulator (200) further includes at least one heat insulation cover (204) for covering the susceptor (100).

13. A system (10) including the apparatus according to any one of claims 1 to 12, wherein the system (10) is an induction heater (300), the induction heater surrounds the heat insulator (200), an induction heater (300), a resistance heater, the resistance heater is surrounded by the heat insulator (200), a resistance heater, a reactor (11) for accommodating the apparatus, and at least one of a vacuum pump for exhausting the reactor (11).

14. A method for growing a SiC bulk single crystal in a growth direction (Y) by sublimation growth in a cavity (110), preparing a SiC seed crystal (120) and a SiC raw material (130) in the cavity (110); heating the susceptor (100) to grow the SiC bulk single crystal in the cavity (130); insulating the susceptor (100) with a heat insulator (200), the heat insulator (200) being a heat insulation wall (202) surrounding the susceptor (100) in the growth direction (Y) and the circumferential direction, the heat insulation wall (202) being for reducing the radial (r) heat transfer from the susceptor (100) to the outside of the apparatus, the radial direction (r) being perpendicular to the growth direction (Y), a heat insulation wall (202); a heat conduction layer (210) disposed between the susceptor (100) and the heat insulating wall, the heat conduction layer (210) having a higher thermal conductivity than the heat insulating wall for dispersing heat in the heat conduction layer (210), a heat conduction layer (210) and including. The heat conduction layer (210) is spaced apart from the susceptor (100) to reduce heat transfer from the susceptor (100) to the heat insulating material (200) caused by heat conduction, and the heat conduction layer (210) is disposed on the heat insulating wall (202), thereby reducing the undulation of the heat insulating material (200) and increasing the reflectivity of the heat insulating material (200). Steps and A method comprising.

15. The method according to claim 14, wherein the heat conduction layer (210) increases the reflectivity, and as a result, the heat energy supplied to the susceptor (100) during heating is reduced by 5% or more, preferably, the heat energy supplied to the cavity is reduced by 10% or more.

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