Methods for Seeded Crystal Components and SiC Single Crystal Ingot Growth

Abstract

This invention discloses a seed crystal assembly and a method for growing SiC single-crystal ingots. The invention relates to a seed crystal assembly for growing single-crystal ingots in a physical vapor transport (PVT) process. Furthermore, the invention relates to a method for manufacturing bulk SiC crystals in a physical vapor transport growth system. The seed crystal assembly includes a base structure connectable to a crucible, the base structure having a base diameter through a central axis of the seed crystal assembly and a base height along the central axis, and a single-crystal seed crystal designed for growing a single-crystal ingot on a growth surface. The single-crystal seed crystal is attached to the base structure, the seed crystal having a seed crystal diameter across the central axis and a seed crystal height along the central axis, wherein at a growth temperature between 2000°C and 2600°C, the specific thermal conductivity of the base structure differs from that of the seed crystal by less than or equal to 25%.

Description

Technical Field

[0001] This invention relates to a seed crystal assembly for growing single-crystal ingots in a physical vapor transport (PVT) process. Furthermore, this invention relates to a method for manufacturing bulk SiC crystals in a physical vapor transport growth system. Background Technology

[0002] Due to its outstanding physicochemical and electrical properties, silicon carbide is particularly used as a semiconductor substrate material for power semiconductor devices, radio frequency components, and various special light-emitting semiconductor devices. Bulk SiC crystals with ideal purity and defect-free quality are required as the basis for these products.

[0003] As is known in the art, bulk SiC crystals are typically produced using physical vapor deposition techniques, particularly sublimation methods. This process requires temperatures exceeding 2000°C. Physical vapor transport (PVT) is essentially a sublimation and recondensation process in which the source material and seed crystal are placed in a growth furnace with the source material at a temperature higher than the seed crystal, causing the source material to sublimate and the vapor phase to diffuse and deposit onto the seed crystal to form a single crystal. Examples of the PVT process are disclosed in US8865324 B2.

[0004] To fabricate wafer-like substrates, bulk silicon carbide crystals need to be cut using tools such as diamond wire saws. The surface is then refined through subsequent multi-stage polishing steps. For the fabrication of electronic components, thin single-crystal layers (such as SiC or GaN) are epitaxially deposited onto the polished wafer. The properties of these layers, and therefore the properties of the electronic components manufactured from them, are decisively dependent on the quality of the underlying SiC substrate.

[0005] Significant negative impacts on the quality of SiC substrates are caused by stresses in the lattice that may occur during crystal growth. These stresses can lead to bending (bowing, warping) of SiC substrates produced from bulk SiC crystals or dislocations, particularly in the basal plane (so-called BPDs, or basal plane dislocations), which can be caused by relaxation of tension in the lattice.

[0006] During the growth of silicon carbide crystals, stress may be caused by a variety of factors, including: stress applied by the seed crystal assembly, thermal stress generated by the temperature gradient required for crystal growth, mechanical stress generated between the crucible wall and the crystal during crystal growth, and thermal stress formed during the cooling process after growth.

[0007] In order to gradually reduce stress balance during the growth of SiC single crystals, all contributing components must be considered, and improvements and remedies must be found for each individual cause.

[0008] In particular, this disclosure aims to reduce the negative impact of the seed and retainer system (hereinafter also referred to as the seed assembly) on the stress balance during the SiC single crystal growth process. It should be noted that the principles of this disclosure can also be applied to improve the bulk crystal quality of single crystals other than silicon carbide. However, in the following text, SiC is always given as an example.

[0009] In traditional processes, silicon carbide single-crystal seeds are typically fixed to a graphite seed holder using an adhesive bonding method. This seed holder provides support for the seed crystal within the growth apparatus through its contact surfaces. Figure 2 This mounting is illustrated by a sliding support on the support surface of the crucible. Alternatively, the seed crystal holder can also be clamped axially or radially within the growth assembly. Axial and radial clamping are respectively located in... Figure 3 and Figure 4 As shown in the figure, the bonding process itself, the connection between the two heterogeneous materials in the seed slab-seed system, and the geometric abrupt change in the transition zone from the edge of the silicon carbide seed to the contact surface of the seed slab, all contribute to the non-uniform heat dissipation of the entire seed slab-seed system.

[0010] For high-quality silicon carbide single crystals to grow, a key prerequisite is that the predetermined temperature gradient (especially the radial temperature gradient at the growth interface) must not be disturbed or altered by non-uniform heat dissipation. When unpredictable temperature gradients and temperature deviations occur on the seed crystal surface, they will immediately induce local lattice stress in the silicon carbide seed crystal, ultimately leading to a decrease in the quality of the generated single crystal.

[0011] These stresses, occurring during crystal growth and the subsequent cooling phase, can remain within the crystal or partially relax by generating basal plane dislocations. Residual stresses can cause bending deformation (bowing, warping) in silicon carbide substrates processed from single-crystal ingots. Dislocations also have a degrading effect on the quality of SiC substrates produced from single-crystal ingots.

[0012] Known seed crystal components are illustrated, for example, in patents US6723166 B2 or US9590046 B2. According to US6723166 B2, by laterally covering the seed crystal seat, the seed crystal seat system is designed to both protect the seed crystal seat from excessive silicon carbide crystal growth and promote the deposition of low-defect silicon carbide crystals on the seed crystal surface. However, practical experience shows that this structure easily leads to uneven thermal coupling, which in turn induces stress and dislocation defects in the silicon carbide crystal.

[0013] Furthermore, US patent 9590046 describes a growth structure design that reconciles the difference in thermal expansion coefficients (bimetallic effect) between silicon carbide and graphite by allowing the seed slab-seed system to bend. This design prevents the bond layer from peeling off. However, bending of the seed slab-seed system can also induce uncontrollable stresses and dislocations in the crystal. When the grown single-crystal ingot is cut into SiC substrates, these stresses can cause the single-crystal wafers to bend and warp (resulting in bowing and warping). Since subsequent epitaxial processes require SiC substrates to have low bowing and warping values, excessive bowing and warping will directly lead to the scrapping of the SiC substrate.

[0014] Therefore, there is still a need for an improved seed crystal assembly and a method for growing at least one SiC single crystal ingot in a physical vapor transport (PVT) growth system that overcomes the problems of existing systems and results in single crystal ingots with improved quality. Summary of the Invention

[0015] This objective is achieved through the subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0016] This disclosure provides a seed crystal assembly for growing single-crystal ingots in a physical vapor transport (PVT) process. The seed crystal assembly includes a base structure connectable to a crucible and a single-crystal seed. The base structure has a base diameter passing through a central axis of the seed crystal assembly and a base height along the central axis. The single-crystal seed is designed to grow a single-crystal ingot on a growth surface. The single-crystal seed is attached to the base structure and has a seed diameter across the central axis and a seed height along the central axis. At a growth temperature between 2000°C and 2600°C, the specific thermal conductivity of the base structure differs from that of the seed crystal by less than or equal to 25%. For example, at a growth temperature between 2000°C and 2600°C, the specific thermal conductivity of the base structure differs from that of the seed crystal by less than or equal to 20%, preferably by 15%.

[0017] By choosing such materials, mechanical stress on the seed crystal can be avoided during the heating process, resulting in a crystal lattice with far fewer defects than when using conventional seed crystal components.

[0018] To improve the uniformity of temperature distribution at the growth boundary surface, the seed crystal can form a step on the base structure, the step having a diameter smaller than that of the base structure. This allows for improved heat dissipation, resulting in the desired temperature distribution. For example, the diameter of the seed crystal can be at least 2 mm smaller than the diameter of the base structure, and further, the diameter of the seed crystal can be no more than 10 mm smaller than the diameter of the base structure. Considering the diameter ratio, the ratio of the base diameter to the seed crystal diameter can be in the range of 1.05 to 1.2.

[0019] According to another example of this disclosure, the base structure has a first height along the central axis of the seed crystal assembly, wherein the seed crystal has a second height along the central axis, and wherein the base height is at least 1 mm greater than the seed crystal height. For example, the base height is no more than 5 mm greater than the seed crystal height. When considering the ratio of the two heights, the ratio of the base height to the seed crystal height can advantageously be in the range between 1.0 and 2.0.

[0020] According to another advantageous example of this disclosure, the surface of the substrate structure opposite the seed crystal includes a passivation layer comprising at least one of a carbonaceous layer, a refractory metal layer, and a graphite layer. This passivation layer on the back surface of the substrate structure prevents components from evaporating from the substrate structure. For example, in the case where the substrate structure is formed of SiC, the passivation layer can prevent the evaporation of SiC at elevated growth temperatures.

[0021] The advantageous similarity in thermal conductivity between the seed crystal and the seed crystal base (also known as the base structure) can be achieved by a seed crystal assembly formed by at least two parts joined together or by a seed crystal assembly formed as a single integral part.

[0022] For example, seed crystal components can be manufactured by vertical etching or grinding.

[0023] According to another aspect of this disclosure, a method for growing at least one SiC single crystal ingot in a physical vapor transport (PVT) growth system is provided, the method comprising the following steps:

[0024] SiC powder source material is arranged in the source material compartment.

[0025] At least one seed crystal assembly according to any one of the preceding claims is arranged in a growth chamber, wherein the seed crystal comprises a SiC seed crystal, and wherein the source material chamber is connected to the growth chamber for providing sublimated gaseous components to the growth chamber.

[0026] An elevated temperature between 2000°C and 2600°C is applied to produce a sublimated gaseous component, which generates a SiC growth phase at the SiC seed crystal, thereby forming a SiC bulk single crystal ingot at the SiC seed crystal.

[0027] Advantageously, the seed crystal assembly is mounted at the growth system by means of a freely suspended support, or the seed crystal assembly is mounted at the growth system by means of a clamping support. Attached Figure Description

[0028] The accompanying drawings, incorporated in and forming part of this specification, illustrate several embodiments of the invention. These drawings, together with the specification, serve to explain the principles of the invention. The drawings are for illustrative purposes only, showing preferred and alternative examples of how the invention can be made and used, and should not be construed as limiting the invention to the embodiments shown and described. Furthermore, several aspects of the embodiments may be formed individually or in different combinations to create a solution according to the invention. Further features and advantages will become apparent from the following more specific description of various embodiments of the invention, as illustrated in the accompanying drawings, wherein like reference numerals denote like elements, and wherein:

[0029] Figure 1 A schematic cross-sectional view of a PVT growth apparatus is shown;

[0030] Figure 2 A schematic cross-sectional view of a seed crystal assembly supported on a support surface is shown.

[0031] Figure 3 A schematic cross-sectional view of a seed crystal assembly supported by an axial clamping device is shown.

[0032] Figure 4 A schematic cross-sectional view of a seed crystal assembly supported by a radial clamping device is shown.

[0033] Figure 5 A schematic cross-sectional view of the seed crystal assembly, which is formed as an integral part, is shown.

[0034] Figure 6 A schematic cross-sectional view of the seed crystal assembly, including individual sections, is shown.

[0035] Figure 7 A schematic cross-sectional view of the seed crystal assembly is shown, illustrating the temperature field at the growth interface;

[0036] Figure 8 A schematic cross-sectional view of a seed crystal assembly according to another example is shown;

[0037] Figure 9 A schematic cross-sectional view of a seed crystal assembly according to another example is shown;

[0038] Figure 10 A schematic cross-sectional view of a seed crystal assembly according to another example is shown. Detailed Implementation

[0039] The invention will now be described in more detail with reference to the accompanying drawings. Please refer to the following description first. Figure 1The invention demonstrates a growth apparatus 100 for preparing bulk silicon carbide single crystals 102 (also known as single crystal ingots or bulk single crystals) by sublimation growth. The apparatus includes a growth crucible 104, inside which are a silicon carbide storage region 106 and a crystal growth region 108. Powdered silicon carbide source material 110 is placed in the silicon carbide storage region 106, which is pre-prepared starting material loaded into the silicon carbide storage region 106 of the growth crucible 104 before the growth process begins.

[0040] A SiC seed crystal 112, extending axially into the crystal growth region 108, is disposed in the region opposite the SiC storage region 106 of the crucible end wall 116 of the growth crucible 104. The SiC seed crystal 112 is particularly a single crystal. Reference will be made below. Figures 2 to 10 The structure and arrangement of the crucible 104 are described in more detail.

[0041] like Figure 1 In the illustrated embodiment, the crucible end wall 116 is configured as the crucible lid for the growth crucible 104. However, this is not the only implementation. The silicon carbide bulk single crystal 102 to be grown is grown on the silicon carbide seed crystal 112 by deposition, which originates from the silicon carbide growth vapor phase 114 formed within the crystal growth region 108. The grown silicon carbide bulk single crystal 102 and the silicon carbide seed crystal 112 have approximately the same diameter. If there is a dimensional deviation, the seed crystal diameter of the silicon carbide seed crystal 112 is at most 10% smaller than the diameter of the silicon carbide bulk single crystal 102. However, there may be a gap between the inner side of the crucible side wall 118 and the grown silicon carbide bulk single crystal 102 and the silicon carbide seed crystal 112. Figure 1 The gap is not shown.

[0042] According to Figure 1 In one embodiment, the growth crucible 104, including the crucible lid 116, may include a material having a density of, for example, at least 1.75 g / cm³. 3 The material is a dense, electrically and thermally conductive graphite crucible. An insulating layer 10 is arranged around it. This layer comprises, for example, a foamed graphite insulating material with a porosity significantly higher than that of the graphite crucible material.

[0043] The thermally insulated growth crucible 104 can be placed inside a tubular container 122, which in this embodiment is designed as a quartz glass tube and forms an autoclave or reactor. To heat the growth crucible 104, an induction heating device in the form of a heating coil 124 can be arranged around the container 11. Of course, other suitable heating devices, such as resistance heaters, can also be used.

[0044] The growth crucible 104 is heated by heating coil 124 to a growth temperature greater than 2000°C, preferably between 2000°C and 2600°C, particularly to about 2200°C. Heating coil 124 inductively couples current into the conductive crucible sidewall 118 of the growth crucible 104. This current flows essentially as a circulating current within the circumferential direction of the circular and hollow cylindrical crucible sidewall 118, heating the growth crucible 104 in the process. If desired, the relative position between heating coil 124 and the growth crucible 104 can be axially changed, i.e., in the direction of the central longitudinal axis 126 of the grown SiC bulk single crystal 102, particularly to adjust the temperature or temperature distribution within the growth crucible 104, and optionally also to alter it.

[0045] The position of the heating coil 124, which can be axially changed during the growth process, is... Figure 1 The figure is indicated by double arrow 128. Specifically, the heating coil 124 is displaced to accommodate the growth process of the growing SiC bulk single crystal 102. The displacement preferably occurs downwards, in other words, in the direction of the SiC source material 110, and preferably for a length equal to the length of growth of the SiC bulk single crystal 102, for example, approximately 20 mm in total. For this purpose, the growth apparatus 100 includes correspondingly configured monitoring, control, and adjustment devices, not shown in more detail in the figure.

[0046] The SiC growth gas phase 114 in the crystal growth region 108 is supplied by the SiC source material 110. The SiC growth gas phase 114 contains at least Si, Si2C and SiC2 (i.e., SiC gaseous substances) gaseous components. The transport of the SiC source material 110 to the growth boundary surface 130 at the growing SiC bulk single crystal 102 occurs along the axial temperature gradient.

[0047] The axial temperature gradient, measured along the central longitudinal axis 126, is adjusted to at least 5 K / cm, preferably at least 10 K / cm, particularly at the growth boundary surface 130. The temperature within the growth crucible 104 decreases towards the growing SiC bulk single crystal 102. This can be achieved through various measures. Thus, axially varied heating can be provided by dividing the heating coil 124 into two or more axial sections (not shown in more detail).

[0048] Furthermore, for example, by corresponding axial positioning of the heating coil 124, a stronger heating effect can be achieved in the lower part of the growth crucible 104 than in the upper part. Additionally, the thermal insulation at the two axial crucible end walls can be different. For example... Figure 1As schematically shown, for this purpose, the insulation layer 120 at the lower crucible end wall can have a greater thickness than that at the upper crucible end wall. Furthermore, the insulation layer 120 adjacent to the upper crucible end wall 116 can have a central cooling opening 132 through which heat is dissipated, and this central cooling opening 132 is arranged around a central longitudinal axis 126. The central cooling opening 132 is located in... Figure 1 The middle is indicated by a dashed line.

[0049] SiC bulk single crystal 102 is grown in growth direction 134. Figure 1 In the example shown, the growth direction 134 is oriented from top to bottom, in other words, from the crucible lid 116 to the SiC storage region 106. The growth direction 134 extends parallel to the central longitudinal axis 126. Since the SiC bulk single crystals 102 grown in the illustrated embodiment are concentrically arranged within the growth apparatus 100, the central longitudinal axis 126 can also be allocated as a whole to the growth apparatus 100.

[0050] Furthermore, the SiC growth vapor phase 114 may also contain dopants, which, according to... Figure 1 Not shown in greater detail in the view, it is nitrogen (N2) in this example. Alternative or additional dopants, such as aluminum (Al), vanadium (V), and / or boron (B), are also possible. The dopants are provided either in gaseous form or via a subsequently pretreated SiC source material 110. In this example, the silicon carbide bulk single crystal 102 is n-type doped with nitrogen. Its crystal form may be, for example, 4H-SiC, but other dopants or different silicon carbide crystal forms may also be used.

[0051] Figures 2 to 4 A more detailed schematic illustration shows how the seed crystal assembly 136 can be attached to the sidewall 118 of the crucible 104. In these figures, the seed crystal assembly 136 is formed from a conventional seed crystal holder 138 (hereinafter also referred to as a base structure). However, reference... Figures 2 to 4 The explained mounting principles are intended for use with seeded assemblies according to this disclosure, and as referenced Figures 5 to 10 A more detailed description follows. In conventional designs, the seed substrate 138 is made of graphite. The connection between the seed substrate 138 and the single-crystal SiC seed 112 is typically achieved through an adhesive layer 140. (As...) Figure 2 As shown, the seed crystal holder 138 is supported on the support surface 142 of the crucible sidewall 118. Therefore, the seed crystal holder is slidable to compensate for thermal expansion.

[0052] According to such Figure 3 In the alternative example shown, the seed crystal assembly 136 is secured by an axial clamping support 144. This axial clamping support 144 applies a clamping force along the longitudinal axis 126 (see [link to example]). Figure 1The axial clamping support 144 may include an annular fixing device or a plurality of smaller fixing devices disposed around the circumference of the seed crystal holder 138. A combination of an annular fixing device and several smaller fixing devices is also possible.

[0053] In addition, such as Figure 4 As shown, the seed crystal assembly can also be mounted at the crucible via a radial clamping support 146. The radial clamping support 146 applies a radially inward force toward the center of the seed crystal holder 138. The radial clamping support 146 may include a plurality of clamping elements distributed around the circumference of the seed crystal holder 138. Alternatively, the radial clamping support 146 may also include a retractable annular clamping element.

[0054] Figure 5 A first example of a seed crystal assembly 136 according to this disclosure is shown. The object of this disclosure is to produce stress-reduced or stress-free crystals. To address this problem, the following is first proposed... Figure 5 The seed crystal / seed pedestal system shown is referred to as seed crystal assembly 136. According to this aspect of the present disclosure, seed crystal assembly 136 includes a seed crystal pedestal (also referred to as a base structure) 138 and a seed crystal 112, both of which are integrally formed of the same material (e.g., SiC).

[0055] By using such a three-dimensional SiC seed saddle system, the SiC seed lattice remains stress-free during crystal growth. This means that less stress and fewer dislocations can occur in the grown crystal during the growth process. This disclosure is based on the use of a seed saddle system with optimal heat dissipation. The saddle 138 can be manufactured by targeted shaping, particularly of monolithic SiC crystals, for example by molding or grinding, for support on the support surface 148 or for clamping in the growth apparatus 100 by radial or axial clamping action. (See reference...) Figure 7 Let's discuss specific dimensions in more detail.

[0056] As Figure 5 As an alternative to the overall design, the seed crystal assembly 136 can also be manufactured by joining two or more separate parts. For example... Figure 6 As shown, the seed substrate 138 and the seed crystal 112 can also be connected using at least two silicon carbide geometries to form the seed crystal assembly 136 via bonding or special bonding techniques. Importantly, the seed substrate (or base structure) 138 is made of a material with a thermal conductivity similar to that of the seed crystal 112. Specifically, at a growth temperature of 2000°C to 2600°C, the difference in thermal conductivity between the seed substrate 138 and the seed crystal 112 does not exceed 20%, preferably not more than 15%.

[0057] The interface layer 150 can be formed using various techniques. The bonding of two SiC bodies or one SiC body to a heterogeneous material body can be primarily achieved by using carbon-based adhesives, or adhesives that form a carbon-rich bonding layer after curing. Examples include phenolic varnish resins, phenolic resins, photoresists, and other organic carbon-based molecules. Furthermore, in the case of bonding two SiC bodies, techniques utilizing adhesive forces can also be applied to connect the two SiC bodies. Another technique is diffusion bonding. Diffusion bonding is a high-temperature, high-pressure process in which the surfaces of two SiC components are pressed together and bonded through atomic diffusion. It does not use filler metals, making it highly reliable in applications where purity is critical.

[0058] Essentially, this disclosure provides a seed crystal assembly 136 with optimized heat transfer to maintain the seed crystal without (or at least with minimal) mechanical stress during high-temperature PVT processes. This aspect is particularly important at the beginning of single crystal growth and during the first growth interval.

[0059] By controlling the thickness and diameter of each of the seed crystal components 136, heat dissipation of the radial temperature gradient on the growth boundary surface 130 of the seed crystal 112 can be optimized. Specifically, by correctly selecting the height and diameter of the base structure 138 and the seed crystal 112, balanced heat dissipation can be achieved in the edge and central regions of the seed crystal. Figure 7 As shown, the seed crystal assembly 136 has a stepped structure, the seed crystal seat 138 has a first height H, and the seed crystal 112 has a second height h. The seed crystal seat 138 has, for example, a substantially circular profile with a diameter D, and the seed crystal is formed as a substantially circular step with a smaller diameter d. It should be noted that these geometric considerations also apply to the composite seed crystal assembly 136, and not only to it. Figure 5 An example of a single-piece formation is shown.

[0060] exist Figure 7 In the cross-sectional view, dashed line 152 represents the temperature distribution by showing the temperature on the seed assembly 136. As can be seen from this distribution, the temperature along the diameter d of the seed 112 remains constant for a considerable portion of the intact growth boundary surface 130. Therefore, the mechanical stress within the lattice of the seed 112 remains low. Furthermore, because the seed saddle 138 and the seed 112 are made of the same material, their thermal expansion characteristics are identical, further reducing any mechanical stress between the seed saddle 138 and the seed 112. By controlling the dimensions H / h and D / d, balanced heat dissipation can be achieved in the edge and central regions of the seed 112. This contrasts with the radial temperature field according to the prior art, in which only a non-equilibrium temperature field with a strong radial gradient can be achieved. Curve 153 shows the temperature distribution achievable when, for example, a conventional graphite seed saddle is used, with the SiC seed attached to the graphite seed saddle by an adhesive.

[0061] The diameters D and d, and the heights H and h, are selected to control optimal heat dissipation at the seed crystal 112, which is attributable to the radial temperature gradient. According to the invention, the geometry and material properties of the particularly peripheral transition region 164 of the seed crystal seat 138 allow for controlled heat dissipation in both the radial and axial directions. This results in a favorable temperature profile, symbolized by curve 152. In particular, the temperature can be kept constant over a much larger radial region.

[0062] Ideally, the ratio H / h is in the range of 1.0 to 2.0, and the ratio D / d is in the range of 1.05 to 1.20. The support surface 148 designed in this way also serves as a balancer for controlling heat transfer through the seed crystal assembly 136.

[0063] As described above, the conventional use of heterogeneous materials for the seed crystal and the seed crystal seat, due to bonding or clamping (according to the prior art), and the resulting interface, leads to discontinuities in heat dissipation in the axial direction of the seed crystal assembly, which can be avoided in the assembly according to this disclosure.

[0064] Uniform heat dissipation or avoiding hot spots in the edge or central region of the seed crystal means that the lattice or seed-seed system remains stress-free. Otherwise, the temperature-dependent coefficient of thermal expansion would cause localized, uneven expansion and / or compression of the seed crystal lattice, which would continue to penetrate into the growing crystal. The result would be strain-grown single crystal. This can be avoided by using the seed assembly 136 according to this disclosure.

[0065] Another aspect of this disclosure is the passivation on the rear side of the seed crystal component 136. Reference will now be made to... Figures 8 to 10 This aspect will be explained in detail. It should be noted that the accompanying drawings in this disclosure are not drawn to scale. For clarity, all thin layers are shown with exaggerated thicknesses.

[0066] Specifically, when the seed assembly 136 is formed by a SiC seed substrate system, a passivation layer 154 can be provided to prevent SiC evaporation. The passivation of the back side of the SiC seed substrate 138 can be performed in different ways.

[0067] First, the passivation layer can be formed as a coating from a fluid solution (e.g., phenolic varnish resin, phenolic resin, etc.). This solution is not shown in the accompanying drawings.

[0068] In addition, such as Figure 8As shown, foil 156 (e.g., made of expanded graphite) can be attached to the back side of seed substrate 138 via a suitable adhesive layer 158. Instead of graphite, foil 156 can also be formed of an optionally carburized refractory metal. The back side of seed substrate 138 can be provided with a refractory metal foil 156, such as tantalum, tungsten, niobium, molybdenum, rhenium, iridium, ruthenium, hafnium, or zirconium, or a mixture of one or more refractory metals, or one or more carburized refractory metal foils (e.g., TaC, WC, ...). Alternatively, the carburization of foil 156 can be performed after the foil 156 and the back side of seed substrate 138 are bonded.

[0069] In addition, such as Figure 9 As shown, the seed substrate 138 may also have graphite and / or (carburized) refractory metal foil disposed on the back side of the SiC seed substrate, with or without a pre-coated SiC seed substrate back side primarily coated with a carbonaceous compound (e.g., phenolic varnish, phenolic resin, or any suitable photoresist). To attach the foil to the back surface of the seed substrate, it can be secured by clamping the foil during assembly of the growth assembly 100. Figure 9 As shown, the passivation layer 154 may, for example, comprise two or more foils 156 alternating with the adhesive layer 158.

[0070] Another example of passivation layer 154 is in Figure 10 As shown in the example, a coating having a carbon-containing layer 160 is deposited directly onto the back surface 162 of the seed substrate 138. At least one foil 156, comprising graphite and / or a refractory metal, is deposited on the coating 160. When the foil 156 is held in place during assembly of the growth apparatus 100 by means of a crucible lid or any other suitable clamping device, no additional adhesive is required between the foils 156. Figure 10 The image shows two foils 156, but of course, more layers could be involved.

[0071] refer to Figures 8 to 10 Any suitable combination of the examples explained can be used to form a passivation layer 154 on the back surface 162 of the seed 138. It should also be noted that various passivation concepts can be used with the monolithic seed assembly 136 as well as any kind of multi-part seed assembly 136.

[0072] In summary, by utilizing the solution according to this disclosure, it is possible to reduce the stress generation that may arise from the interaction between the seed crystal 112 and the seed holder 138 during the growth of a single crystal (particularly silicon carbide crystal) by using a stepped seed assembly, wherein the seed holder 138 is made of a material with a thermal conductivity close to that of the seed crystal 112 itself. Advantageously, the seed holder 138 is made of the same material as the seed crystal 112 (e.g., SiC). The seed holder 138 can even be single-crystal like the seed crystal 112; in particular, the seed assembly 136 can be integrally formed as a single component.

[0073] This directly improves the quality and yield of SiC substrates relative to their use in downstream processes such as epitaxy, which requires SiC substrates to have low bending and / or warping as well as low base dislocation density.

[0074] Figure label:

[0075] Figure label description

[0076] 100 growth device

[0077] 102 bulk single crystal

[0078] 104 Growth Crucible

[0079] 106 storage area; source material compartment

[0080] 108 crystal growth region; growth chamber

[0081] 110 source materials

[0082] 112 Seed Crystal

[0083] 114 Growth Gas Phase

[0084] 116 Crucible End Wall

[0085] 118 Crucible Side Wall

[0086] 120 insulation layer

[0087] 122 containers

[0088] 124 heating coil

[0089] 126 central vertical axis

[0090] Variable position of 128 heating coil

[0091] 130 growth boundary surface

[0092] 132 central cooling opening

[0093] 134 Growth direction

[0094] 136 Seed Crystal Module

[0095] 138 seed crystal base; base structure

[0096] 140 adhesive

[0097] 142 Crucible support surface

[0098] 144 Axial Clamping Support

[0099] 146 Radial clamping support

[0100] Support surface of 148 seed crystal module

[0101] 150-page interface

[0102] Temperature distribution of 152 seed crystal module 136

[0103] 153. Temperature curves of known graphite seed crystal seats.

[0104] 154 passivation layer

[0105] 156 foil (graphite, refractory metal)

[0106] 158 adhesive layer

[0107] 160 Coating with a carbon layer

[0108] Back surface of 162 seed crystal seat

[0109] 164 Transition Zone

[0110] H base structure height

[0111] h Seed crystal height

[0112] D Base structure diameter

[0113] d Seed crystal diameter

Claims

1. A seed crystal assembly for growing single-crystal ingots in a physical vapor transport (PVT) process, the seed crystal assembly comprising: A base structure, connectable to a crucible, the base structure having a base diameter across the central axis of the seed crystal assembly and a base height along the central axis. A single-crystal seed crystal, designed to grow the single-crystal ingot on the growth surface. The single-crystal seed crystal is attached to the base structure, the seed crystal having a seed crystal diameter across the central axis and a seed crystal height along the central axis, and At growth temperatures between 2000℃ and 2600℃, the difference between the specific thermal conductivity of the base structure and the specific thermal conductivity of the seed crystal is less than or equal to 25%.

2. The seed crystal assembly according to claim 1, wherein the seed crystal forms a step on the base structure, the step having a diameter smaller than the diameter of the base structure.

3. The seed crystal assembly according to claim 2, wherein the diameter of the seed crystal is at least 2 mm smaller than the diameter of the base structure.

4. The seed crystal assembly according to claim 2, wherein the diameter of the seed crystal is no more than 10 mm smaller than the diameter of the base structure.

5. The seed crystal assembly according to claim 1, wherein the ratio of the base diameter to the seed crystal diameter is in the range of 1.05 to 1.

2.

6. The seed crystal assembly according to claim 1, wherein the base height is at least 1 mm greater than the seed crystal height.

7. The seed crystal assembly according to claim 6, wherein the base height is no more than 5 mm greater than the seed crystal height.

8. The seed crystal assembly according to claim 1, wherein the ratio of the base height to the seed crystal height is in the range of 1.0 to 2.

0.

9. The seed crystal assembly according to claim 1, wherein at a growth temperature between 2000°C and 2600°C, the specific thermal conductivity of the base structure differs from that of the seed crystal by less than or equal to 20%, preferably by 15%.

10. The seed crystal assembly according to claim 1, wherein the back surface of the base structure opposite to the seed crystal includes a passivation layer, the passivation layer including at least one of a carbonaceous layer, a refractory metal layer, and a graphite layer.

11. The seed crystal assembly of claim 1, wherein the seed crystal assembly is formed of at least two components joined together.

12. The seed crystal assembly according to claim 1, wherein the seed crystal assembly is formed as an integral part.

13. The seed crystal assembly of claim 12, wherein the seed crystal assembly is manufactured by vertical etching or grinding.

14. A method for growing at least one SiC single crystal ingot in a physical vapor transport (PVT) growth system, the method comprising the following steps: SiC powder source material is arranged in the source material compartment. At least one seed crystal assembly according to any one of the preceding claims is arranged in a growth chamber, wherein the seed crystal comprises a SiC seed crystal, and wherein the source material chamber is connected to the growth chamber for providing sublimated gaseous components to the growth chamber. Applying a high temperature between 2000°C and 2600°C generates a sublimated gaseous component, which forms a SiC growth phase at the SiC seed crystal, thereby forming a SiC bulk single crystal ingot at the SiC seed crystal.

15. The method of claim 14, wherein the seed crystal assembly is mounted at the growth apparatus by means of a freely suspended support, or wherein the seed crystal assembly is mounted at the growth apparatus by means of a clamping support.

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