Layered seed, method for fabrication of layered seed and method for growing volume mono crystal with the layered seed

Abstract

To provide a layered seed, a method for fabrication of the layered seed and a method for growing a volume mono crystal with the layered seed.SOLUTION: The present disclosure relates to a layered seed for growing a volume mono crystal by gas phase growth in a direction of growth (Y) in a crucible (1200). The layered seed comprises a monocrystalline growing layer (110) having a growing surface (112) for growing the volume mono crystal and an opposing heat spreader facing surface (114) for coupling the growing layer (110) to a heat spreader layer (140). The layered seed further comprises the heat spreader layer (140) having a growing layer facing surface (144) for coupling to the heat spreader facing surface (114) and an opposing mounting surface (142) for mounting the heat spreader layer (140) to the crucible (1200), wherein the heat spreader layer (140) comprises a polycrystalline material having thermally coupled grains (146) that are piled in the direction of growth (Y), the piled grains (146) being for equalizing hot spots of the crucible thermally coupled to the mounting surface (142).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a layered seed, a method for producing a layered seed, and a method for growing a volumetric single crystal with a layered seed. [Background technology]

[0002] Semiconductor materials such as silicon carbide (SiC) are commonly used in the manufacture of electronic components. SiC is a compound semiconductor that forms the basis of power electronics components, for example in the automotive and green energy sectors.

[0003] Using appropriate source materials, volumetric single crystals are typically grown by vapor phase epitaxy, a process known as physical vapor deposition (PVT). Substrates are then machined from the grown volumetric single crystals, for example using a multi-wire saw, and the surface is then refined using multiple polishing steps. In a subsequent epitaxial process, thin single-crystal layers (e.g., SiC, GaN) are deposited on the substrate. The properties of these layers and the devices fabricated from them depend crucially on the quality of the SiC substrate.

[0004] The basic principle of single crystal growth is based on the sublimation of the starting material and the subsequent transport of the species (SiC, Si2C, SiC2) in the gas phase to a seed where the material is deposited and a volumetric single crystal grows. The quality of the seed is crucial to ensure a low defect density in the growing crystal. Substrates are then produced from the bulk single crystal. Due to the increasing demand for high-quality substrates for the production of electrical components, the use of high-quality seeds for the growth process is essential to grow the highest quality crystals possible.

[0005] Several factors influence the growth of single crystals using sublimation processes such as the PVT process. The factors discussed below are particularly important with respect to the PVT process. However, those skilled in the art will recognize that other sublimation processes, such as gradient freeze, horizontal Bridgman, vapor-liquid-solid (VLS), chemical vapor transport (CVT), zone melting, and laser-heated floating zone (LHFZ), may have the same or similar limitations.

[0006] In this application in particular, the temperature distribution within the PVT system is important for controlling crystal growth. The temperature gradient between the source material and the seed crystal determines the rate of vapor transport and deposition. Optimizing the temperature profile helps achieve uniform crystal growth and minimize defects.

[0007] Another factor is the quality and orientation of the seed crystal, which plays a key role in determining the quality and orientation of the grown single crystal. The seed crystal provides a template for crystal growth, and any defects, stress, or misorientation in the seed crystal can propagate into the growing crystal. Therefore, it is important to select a high-quality seed crystal with the desired crystallographic orientation.

[0008] Other effects that significantly affect the PVT process include: The pressure in the PVT system, which affects vapor transport and deposition kinetics; The purity of the starting material, which directly affects the quality of the resulting single crystals; · The composition of the gas atmosphere in the PVT system, which affects the crystal growth rate and defect formation; Control of various process parameters, such as heating rate, cooling rate, growth time, and seed crystal rotation speed, which can affect crystal growth kinetics and morphology; and The design and material of the crucible used to contain the seed material also influences crystal growth.

[0009] Based on the above considerations, European Patent No. 1,200,651 proposes lateral support of the seed to enable the growth of high-quality crystals. However, this solution has several drawbacks. For example, the lateral support stresses the seed, reducing its quality. Furthermore, support materials, including metals, have different thermal properties than the seed material, thus affecting the temperature gradient within the crucible. Furthermore, support materials can contaminate the gas atmosphere within the PVT system and alter the pressure within the PVT system. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] European Patent No. 1,200,651 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in view of the drawbacks and shortcomings of the prior art, and aims to provide an improved seed bonding to a crucible that eliminates or at least mitigates the above drawbacks and shortcomings of the related prior art.

[0012] This object is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0013] In particular, the problem is addressed by a layered seed. The layered seed includes a heat spreader layer containing polycrystalline material in addition to the monocrystalline growth layer. This allows for the growth of high-quality SiC single crystals, from which high-quality SiC substrates can be manufactured. The temperature-leveling effect of the multilayer seed reduces growth nonuniformity. This increases the quality of the crystals and the wafers produced from them. These wafers have reduced thermal stress and therefore improved geometry. These wafers also contain fewer impurities, dislocations, local polytype changes, and stacking faults. [Means for solving the problem]

[0014] A first aspect relates to a layered seed for growing a volumetric single crystal in a growth direction in a crucible by vapor deposition, e.g., sublimation growth or high-temperature chemical vapor deposition (HTCVD). The layered seed includes a single-crystal growth layer having a growth surface for growing the volumetric single crystal and an opposing heat spreader-facing surface for coupling the growth layer to the heat spreader layer. The layered seed further includes a heat spreader layer having a growth-layer-facing surface for coupling to the heat spreader-facing surface and an opposing mounting surface for attaching the heat spreader to the crucible. The heat spreader layer includes a polycrystalline material having thermally bonded grains deposited in the growth direction, the deposited grains being for equalizing hot spots in the crucible thermally coupled to the mounting surface.

[0015] The first aspect facilitates flattening the temperature profile having hot spots bonded within the layered seed at the attachment surface so that the temperature profile at the growth surface is smoother, thereby improving the quality of the volumetric single crystal.

[0016] A second aspect relates to the seed of the first aspect, wherein the single crystal growth layer has a thickness in the growth direction of 0.5 mm or more and / or 1.0 mm or less, and / or the heat spreader layer has a thickness in the growth direction of 0.5 mm or more and / or 3.0 mm or less. Optionally, the layered seed has a diameter with a radial dimension perpendicular to the growth direction of 155 mm or more, preferably 210 mm or more and / or 360 mm or less. The second aspect facilitates flattening the temperature profile by selecting appropriate parameters for thickness and diameter, thereby improving the quality of the volumetric single crystal.

[0017] A third aspect relates to the seed of any of the preceding aspects, wherein the median grain size D50 is 3 μm or more and / or 80 μm or less, preferably D50 is 3 μm or more and / or 50 μm or less, and optionally the number of grains deposited in the heat spreader layer in the growth direction is 167 or more and / or 1000 or less.

[0018] The third aspect facilitates flattening the temperature profile by selecting grain parameters, thereby improving the quality of the volumetric single crystal.

[0019] A fourth aspect relates to the seed of any of the preceding aspects, wherein the monocrystalline growth layer comprises a first material, the first material being at least one of Si, SiC, AlN, GaN, AlGaN, AlInN, and InN, and / or the crystalline grains of the heat spreader layer comprise a second material, the second material being at least one of Si, SiC, AlN, GaN, Al2O3, GaAs, and an oxide substrate. Optionally, the second material is the same as the first material, and the first material is at least one of Si, SiC, AlN, and GaN, or the first material is different from the second material. Optionally, the monocrystalline growth layer consists of the first material.

[0020] A fourth aspect facilitates flattening the temperature profile by selecting the seed layer material, thereby improving the quality of the volumetric single crystal.

[0021] A fifth aspect relates to a seed according to any of the preceding aspects, wherein the heat spreader layer includes a third material, the third material being a metal, and preferably the third material being at least one of Ti, Fe, W, Mo, and V.

[0022] The fifth aspect facilitates flattening the temperature profile by adding impurities to the heat spreader layer, thereby improving the quality of the volumetric single crystal.

[0023] A sixth aspect relates to a seed according to any of the preceding aspects, wherein the grains of the heat spreader layer include a second material, and the heat spreader layer includes a third material, the third material having a higher mass than the second material. Optionally, the heat spreader layer includes the third material at grain boundaries between adjacent grains.

[0024] The sixth aspect facilitates flattening the temperature profile for the same reasons as the fifth aspect, and in particular improves the quality of the volumetric single crystal by adding high mass impurities to the grain boundaries.

[0025] A seventh aspect relates to a seed according to any of the preceding aspects, wherein the heat spreader layer comprises a concentration of impurities, the concentration being equal to or greater than 5 ppm, more preferably equal to or less than 10 ppm and / or 1000 ppm.

[0026] The seventh aspect improves the quality of the volumetric single crystal, for the same reasons as the fifth and sixth aspects, particularly by adding a certain amount of impurities to the heat spreader layer, thereby making it easier to flatten the temperature profile.

[0027] An eighth embodiment relates to the seed of any of the preceding embodiments, wherein the angle between the crystal axis of the single-crystalline growth layer and the surface normal of the growth surface is greater than or equal to 0° and / or less than or equal to 8°, preferably the angle is greater than or equal to 2° and / or less than or equal to 6°.

[0028] The eighth aspect mitigates the effect of the temperature profile by allowing step growth, thereby improving the quality of the volumetric single crystal.

[0029] A ninth embodiment relates to the seed of any of the preceding embodiments, wherein the growth surface (112) comprises a carbon face, the C-face, preferably the growth surface is the C-face.

[0030] The ninth aspect facilitates mitigating the effect of the temperature profile by using the C-face to improve growth, thereby improving the quality of the volumetric single crystal.

[0031] A tenth aspect relates to a seed according to any of the preceding aspects, further comprising a connection layer between the single crystal growth layer and the heat spreader layer, the connection layer preferably comprising at least one of a phenolic resin, a novolac resin, and a sintered powder, preferably a sintered silicon powder.

[0032] The tenth aspect facilitates flattening the temperature profile by combining multiple layers, thereby improving the quality of the volumetric single crystal.

[0033] An eleventh aspect is a method for producing a layered seed for growing a volumetric single crystal by directional vapor deposition in a crucible, the method comprising the steps of: providing a single crystal growth layer having a growth surface for growing a volumetric single crystal and an opposing heat spreader-facing surface for bonding the growth layer to a heat spreader layer; providing the heat spreader layer with a growth layer facing surface that bonds to the heat spreader facing surface and an opposing mounting surface for mounting the heat spreader to the crucible; the heat spreader layer includes a polycrystalline material having thermally bonded grains deposited in a growth direction and deposited grains for equalizing hot spots of a crucible thermally bonded to a mounting surface; The surface facing the growth layer is connected to the surface facing the heat spreader.

[0034] The eleventh aspect makes it easy to flatten the temperature profile for the same reasons as the first to tenth aspects.

[0035] A twelfth embodiment relates to the method of embodiment 11, wherein the growth layer-facing surface is connected to the heat spreader-facing surface by at least one of a bonding step and a sintering step to form a connection layer between the single crystal growth layer and the heat spreader layer. The twelfth aspect facilitates flattening the temperature profile through uniform thermal bonding between multiple layers, thereby improving the quality of the volumetric single crystal.

[0036] A thirteenth aspect relates to a method for growing a volumetric single crystal in a growth direction, the method comprising the steps of: A step of mounting the layered seed according to any one of the first to tenth aspects or the layered seed manufactured by the method according to the eleventh or twelfth aspects in a crucible; Growing a volumetric single crystal on the single crystal growth layer by a vapor deposition process.

[0037] For the same reasons as the first to twelfth aspects, the thirteenth aspect facilitates improvement of the quality of the volume single crystal by flattening the temperature profile.

[0038] A fourteenth aspect relates to the method according to aspect 13, wherein the heat spreader layer is attached to a seed holder in the crucible. Optionally, the attachment layer is glued or sintered to the seed holder. Optionally, the heat spreader layer is clamped by the seed holder.

[0039] The fourteenth aspect makes it easy to improve the quality of the volume single crystal by flattening the temperature profile for the same reasons as the first to twelfth aspects.

[0040] A fifteenth aspect relates to the method of any of the thirteenth or fourteenth aspects, wherein the volumetric single crystal is grown by physical vapor transport (PVT). Optionally, growing comprises heating the layered seed at a temperature of 2000°C or more and / or 2400°C or less.

[0041] The fifteenth aspect makes it easy to improve the quality of the volume single crystal by flattening the temperature profile for the same reasons as the first to twelfth aspects.

[0042] The accompanying drawings are incorporated into and form a part of the specification to illustrate several embodiments of the present invention. These drawings, together with the description, serve to explain the principles of the invention. The drawings are merely for the purpose of illustrating preferred and alternative examples of how the invention can be made and used, and are not to be construed as limiting the invention to only the embodiments shown and described. Moreover, several aspects of the embodiments may be formed individually or in different combinations-solutions in accordance with the present invention. The embodiments described below can thus be considered alone or in any combination thereof. Further features and advantages will become apparent from the following more particular description of various embodiments of the invention, as illustrated in the accompanying drawings, in which like references refer to like elements. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 1 is a schematic diagram of a layered seed according to one embodiment. [Figure 2] FIG. 10 is a further schematic side view of a layered seed according to one embodiment. [Figure 3] FIG. 10 is a further schematic side view of a layered seed according to one embodiment. [Figure 4] FIG. 1 is a schematic diagram of the growth sequence. [Figure 5] FIG. 1 is a schematic diagram of a layered seed. DETAILED DESCRIPTION OF THE INVENTION

[0044] [Vapor growth] Volumetric single crystals are grown by vapor deposition, e.g., sublimation growth. Figure 4 shows an exemplary sublimation growth system 1000, specifically a PVT crystal growth system implemented in a crucible 1200. The crucible is a container in which a material, e.g., SiC, can be exposed to very high temperatures (greater than 2000°C), e.g., temperatures that allow the SiC to sublimate. In particular, the crucible is made of a material that can withstand temperatures high enough to melt and / or sublimate its contents.

[0045] As shown in Figure 4, crucible 1200 is placed in a tubular vessel 1300, which may be made of quartz glass, and is surrounded by an induction heater 1400. Alternatively, the tubular vessel may be stainless steel and the heater may be a resistance heater. Together, the components form the reactor, which is the core of system 1000. Tubular vessel 1300 is a machine used to perform processes requiring elevated temperatures and pressures relative to ambient pressure and / or temperature.

[0046] The actual crystal growth takes place inside the crucible 1200. The walls of the crucible 1200 can be made of materials such as graphite and carbon, which allow the crucible 1200 to heat the growth material, e.g., SiC, to growth temperatures in excess of 2000°C.

[0047] In particular, to grow a SiC volumetric single crystal, a SiC seed crystal 1110 is placed on a seed holder 1120 that is placed on an end wall 1210 of a crucible 1200 before growth begins. More specifically, the SiC seed crystal 1110 is preferably placed in a crystal growth region 1250 of the growth crucible, which is fully closed at least during growth.

[0048] Powdered SiC source material is introduced into the storage region 1260 of the growth crucible. A thick dashed line 1255 indicates the boundary of the storage region 1260 at the start of the growth process. The boundary may be, for example, a porous graphite wall. During growth, a SiC growth vapor phase is generated therein by sublimation of the powdered SiC source material and by transport of the sublimated gas components into the crystal growth region 1250, and a SiC volumetric single crystal having a central longitudinal axis along the Y-axis grows by deposition of SiC onto the SiC seed crystal 1110, among other things.

[0049] To grow SiC bulk single crystals, a temperature distribution along the Y axis was realized in the crucible. In general, the highest temperature is usually in the reservoir region 1260, and the seed 1110 is at a lower temperature so that the gaseous material condenses.

[0050] 4, heating can be provided either by induction coils 1400 located on the outside of the tubular vessel 1200. In particular, the induction coils 1400 are arranged along the circumferential direction C. Alternatively, according to a solution not shown, a resistance heater can be placed inside the reactor 1300. Induction heating is a process of heating a conductive material by electromagnetic induction. The conductive material is heated by passing a current through an inductor 1400, creating an electromagnetic field within the coil that directly heats the material in the SiC storage region 1160 and / or indirectly heats the SiC in the storage region by heating the crucible sidewalls. The crucible sidewalls extend circumferentially along the growth direction, i.e., the Y-axis. A shielding material thermally insulates the crucible and the cavity formed within it. In particular, the metal seed holder mentioned above is heated by the induction coil and may therefore affect the temperature distribution.

[0051] [Temperature distribution] As mentioned above, thermal gradients are important for crystal quality. In particular, when growing SiC single crystals using the PVT process, the temperature gradients in the axial (y) and radial (r) directions must be precisely controlled to produce high-quality single crystals.

[0052] For example, the axial temperature gradient Y from the SiC source material in the source region 1260 to the seed 1210 determines the growth rate. Furthermore, as discussed, for example, in U.S. Pat. No. 8,865,324 B2, the radial temperature gradient r can be set to form a convex crystal. This prevents the in-growth of edge defects that can occur when the growing crystal inevitably comes into contact with the walls of the growth crucible.

[0053] In particular, excessive convexity is detrimental to the quality of the SiC substrate produced therefrom, for example by increasing the dislocation density and increasing the value of curvature and warpage geometry due to thermal stresses introduced into the crystal.

[0054] For this purpose, the components of the growth crucible, in particular the crystal channel and end wall 1210, are manufactured with a defined geometric shape and made of a material with defined thermal properties, in particular with regard to heat conduction, in particular graphite. The crystal channel is a cylindrical arrangement attached at its end to the inside of a cylinder. A seed holder 1120 closes the crystal channel on the end of the crucible, where the end wall 1210, also called a lid, is placed to close the crucible. The crystal channel defines the maximum diameter the crystal can achieve. The porous membrane contains pores through which gas species emerging from the source compartment enter the crystal channel.

[0055] [Further improvements] In addition to the temperature distribution along the growth axes Y and r described above, studies have shown that the thermal coupling of the seed to the crucible 1200 results in local deviations from the desired temperature field at the attachment surface that are conducted to the growth surface.

[0056] It has been found that even with the most favorable thermal gradients along the radial axis r and the growth axis Y, the resulting crystals do not exhibit the expected quality. In particular, this has been found to be due to non-optimal thermal coupling of the seed 1110 to the growth structure, in particular to the end walls 1210.

[0057] More specifically, Figure 5 shows the seed holder 1120, the seed crystal 1110, and the connection layer 1130 between the seed holder 1120 and the seed crystal 1110 of Figure 4. In addition, Figure 5 shows the temperature distribution 1212 at the end wall 1210 of Figure 4 for a desired temperature distribution (not shown). As shown in Figure 5, this temperature distribution 1212 may have a non-uniform distribution in the radial direction r. This temperature distribution 1212 is connected to the seed holder 1120.

[0058] It has also been found that the temperature distribution 1212, as shown by the temperature profile 1252, results in local deviations from the desired temperature field at the growth surface, i.e., the phase boundary of the growing seed.

[0059] This can lead to localized island growth that can negatively impact the quality of the growing crystal. The coincidence of growth fronts due to island growth leads to a variety of defects, ranging from macroscopic features such as polytype changes and heterogeneous grains to microscopic defects such as dislocations and stacking faults, that degrade the quality of the resulting crystal.

[0060] In other words, the temperature distribution 1252 affects the quality of the volume single crystal. The technical problem to be solved is to optimize the temperature distribution 1252 on the growth surface of the seed.

[0061] The inventors have therefore found it possible to provide improved seeds, improved manufacturing methods and improved growth methods to avoid one or more of the drawbacks mentioned above. The present invention relates to various solutions and variants for such improved seeds.

[0062] [Solution] Different implementations and variations are described below. The following disclosure has been facilitated by, and may be based at least in part on, the discussion and insights discussed above.

[0063] It should be noted that, in general, many assumptions have been made herein to enable the principles underlying the present disclosure to be explained in a clear, concise, and understandable manner. However, these assumptions should be understood as merely examples made herein for illustrative purposes, which are not necessarily essential to the invention and therefore should not limit the scope of the disclosure. Those skilled in the art will recognize that the principles of the following disclosure and as set forth in the claims can be applied to different scenarios and in ways not explicitly described herein. For example, a seed is a small, specially prepared crystal used as a starting point in the process of growing a larger crystal with desired properties. It serves as a template for the new crystal to grow, aligning its lattice structure with that of the seed crystal. Typically, in SiC PVT growth, the seed has a diameter in the same range as the resulting crystal grown on it. In length, it is a small / short disk.

[0064] Furthermore, a volumetric single crystal refers to a single crystal structure that ideally extends through the entire volume of a material, without grain boundaries or defects that would disrupt the crystal lattice. In other words, it is a solid material that consists of a single, continuous crystal, rather than many smaller crystals (polycrystalline) or an amorphous structure. In a bulk single crystal, the atoms or molecules are arranged in a highly regular, repeating pattern throughout the material. This results in properties such as uniformity of mechanical, electrical, and optical properties in all directions, making monocrystals highly desirable for a variety of applications in electronics, optics, and materials science.

[0065] Additionally, a heat spreader is a component used to dissipate heat more effectively and evenly across a surface. It is designed to transfer heat away from heat-generating components, such as end walls 1210 coupled to a mounting surface, and distribute it over the growing layer facing surface, thereby reducing localized hot spots on the end walls 1210.

[0066] A polycrystalline material is a type of solid material composed of multiple crystal grains. Each crystal grain within the material has its own crystal structure, orientation, and lattice arrangement. These crystal grains are typically randomly oriented relative to one another, forming boundaries known as grain boundaries. Unlike monocrystalline materials, whose overall structure consists of a continuous lattice without grain boundaries, polycrystalline materials have distinct grains separated by these boundaries. Each grain may have slightly different physical and chemical properties due to variations in crystal orientation, defects, impurities, or processing conditions.

[0067] Additionally, deposited grains is used herein to describe multiple grains that are stacked on top of each other in a disordered or haphazard manner to form a layer. The arrangement may be irregular, with the objects not neatly aligned.

[0068] A layer is a specific thin structure that can be deposited on another structure or layer. A layer can be made of different materials and has a specific function, such as providing a growing structure, connecting other layers, or dissipating heat.

[0069] [First Solution - Layered Seeds] 1 shows a layered seed for growing a volumetric single crystal by vapor deposition in a crucible in the direction of growth Y according to one example in accordance with a general solution. In particular, the layered seed includes a single crystal growth layer 110 and a heat spreader layer 140.

[0070] The single crystal growth layer 110 has a growth surface 112 for growing a volume single crystal and an opposing heat spreader-facing surface 114 for bonding the growth layer 110 to the heat spreader layer 140 .

[0071] The heat spreader layer 140 has a growth layer-facing surface 144 for bonding to the heat spreader-facing surface 114 and an opposing mounting surface 142 for attaching the heat spreader to the crucible. Thermal bonding refers to the process by which two or more objects or systems come into contact with each other and exchange thermal energy. When objects are thermally coupled, a temperature difference can cause heat to flow between them. This results in a change in temperature of one or both of the objects until they reach thermal equilibrium.

[0072] The heat spreader layer 140 comprises a polycrystalline material having a plurality of thermally coupled grains 146 deposited in a growth direction Y. As shown in FIG. 1 , adjacent deposited grains 146 are separated by grain boundaries 148.

[0073] Also shown in Figure 1 is a phonon 300. A phonon is a quasiparticle in a crystal lattice of atoms or molecules that represents the vibrational energy of the lattice. More simply, a phonon is a unit of vibrational energy that propagates through solid materials in much the same way that a photon carries energy in a wave. Phonons carry thermal energy through a material by transferring vibrational energy from one atom to another.

[0074] As mentioned above, at grain boundaries 148, which are interfaces between two adjacent grains 146 in the polycrystalline heat spreader layer 140, the behavior of phonons 300 differs from their behavior within the grains 146. In particular, phonons 300 are scattered at the grain boundaries 148, which can result in phonon reflection, transmission, or conversion to other types of vibrational modes.

[0075] Given a plurality of deposited grains 146, the deposited grains 146 equalize hot spots in the temperature profile 1212 of the crucible 1200 thermally coupled to the mounting surface 142 into a balanced temperature profile 252. Notably, Figure 1 shows a temperature profile without an overall radial temperature profile. In other words, using a polycrystalline layer, e.g., a polycrystalline SiC layer, in combination with a monocrystalline layer, e.g., a monocrystalline SiC layer, as a layered seed, i.e., a multi-layer seed system, has the advantage that thermal non-uniformities 1212 are compensated for by grain boundaries 148 within the polycrystalline layer 140.

[0076] These non-uniformities 1212 can arise from non-uniformities in the materials used in the growth structure, such as graphite, resulting in heat not reaching the seed 110 uniformly. Thermal coupling to the seed holder 1120 can also be negatively affected by unwanted thermal contact or contact loss, for example, due to different thermal expansion of materials used in the crucible. The mechanism for thermal leveling is via heat dissipation at the internal grain boundaries 148 of the polycrystalline layer, e.g., a SiC wafer. The number of intersecting grains 146 in the polycrystalline layer 140 and the resulting grain boundaries 148 result in a uniform temperature field for the subsequent single crystal layer 110, e.g., a single crystal SiC layer.

[0077] [First implementation - layer dimensions] According to the implementation of the first solution, various dimensions of the layer can be taken into account. More specifically, as mentioned above, the layered seed includes a layer whose thickness is small compared to its diameter. The thickness of the layer is measured here in the growth direction Y. The diameter of the layer is measured in the radial direction r. The radial dimension is perpendicular to the growth direction Y.

[0078] For example, the thickness of the single crystal growth layer 110 can range from several hundred micrometers to several millimeters, depending on the application. Thinner seed crystals can be used for certain applications requiring precise control over crystal orientation or morphology, while thicker seed crystals may be preferred for larger-scale production or to accommodate specific growth conditions. The thickness of the seed layer 110 is preferably 0.5 mm or greater. Additionally or alternatively, the thickness of the seed layer 110 is 1.0 mm or less.

[0079] Furthermore, the thickness of the layered seed can have a constraint on the total thickness, which can be between a minimum of 1.5 mm and a maximum of 3.5 mm, which allows the optimal thickness of the heat spreader layer in the same growth direction Y to be greater than 0.5 mm. Additionally or alternatively, the thickness of the heat spreader layer can be 3.0 mm or less.

[0080] FIG. 2 illustrates a layered seed with a thinner heat spreader layer 140 compared to the heat spreader layer 140 in the layered seed illustrated in FIG. 3. Notably, FIGS. 2 and 3 illustrate temperature profiles without an overall radial temperature profile. In other words, the leveling effect of the heat spreader layer is proportional to the thickness of the heat spreader layer. As a result, thickening the layer increases the leveling effect. However, as discussed above, a radial temperature profile can couple to the layered seed, allowing for convex growth. Therefore, the thickness can be limited to allow for convex growth.

[0081] Furthermore, the layered seed can have a diameter of radial dimension r, which affects the diameter of the resulting volumetric single crystal. The volumetric single crystal can have a diameter of 150 mm or more, preferably 200 mm or more and / or 300 mm or less. The layered seed has a diameter 5 to 20% larger. In particular, the layered seed can have a diameter of 155 mm or more. Preferably, the layered seed has a diameter of 210 mm or more. Additionally or alternatively, the layered seed has a diameter of 360 mm or less.

[0082] Thus, a layered seed can be used to grow crystals, from which substrates with diameters of approximately 150 mm, 200 mm, and 300 mm can be produced. The heat spreader layer can also have a larger diameter than the single crystal growth layer.

[0083] The thickness and / or diameter values ​​are particularly applicable to heat spreader layers that include or consist of SiC.

[0084] [Second implementation - grain size] According to a second implementation of the first solution, in addition to or instead of the thickness of the heat spreader layer 140 described in the first embodiment, parameters related to the grains 146 in the polycrystalline layer can be used as another control variable. The median grain size (D50) in a polycrystalline material refers to the size of the grains in the material's microstructure, where half of the grains are smaller and half are larger than the median grain size. The effect of the median grain size on a polycrystalline material is significant, affecting various mechanical, thermal, electrical, and optical properties.

[0085] For example, as discussed above, the presence of grain boundaries 148 can impede the propagation of phonons, thereby reducing the thermal conductivity of the material. The smaller the D50, the more grain boundaries there are, which typically indicates a higher leveling effect.

[0086] Furthermore, a smaller D50 tends to improve the mechanical properties of polycrystalline materials because smaller grains create more grain boundaries, which act as barriers to dislocation motion and increase the strength and hardness of the material. However, excessively small grains can also reduce ductility and toughness.

[0087] In particular, D50 may be 3 μm or greater. Additionally or alternatively, D50 may be 80 μm or less. Preferably, D50 is 50 μm or less. D50 values ​​are particularly applicable to heat spreader layers comprising or consisting of SiC.

[0088] For example, given the above parameters for thickness, D50 of 3 μm, the number of grains stacked in the growth direction Y in the heat spreader layer is 167 or more and / or 1000 or less.

[0089] [Third implementation - grain size] The above discussion is primarily based on the assumption that the monocrystalline growth layer and heat spreader layer are made of SiC. According to a third implementation, alternative materials can be used to produce high-quality crystals. The heat spreader layer and monocrystalline growth layer of the layered seed can form a homostructure or heterostructure. The main difference between a homostructure and a heterostructure is the composition of the semiconductor material within the layered seed. A homostructure consists of layers of the same semiconductor material, while a heterostructure consists of layers of different semiconductor materials. Each type of structure offers distinct advantages and is used in different semiconductor devices depending on the desired characteristics and functionality.

[0090] For example, homostructures are commonly used in devices such as bipolar junction transistors (BJTs) and metal-oxide-semiconductor field-effect transistors (MOSFETs). Here, device characteristics are optimized by adjusting the doping concentration or thickness of the same semiconductor material. Heterostructures enable the creation of novel electronic and optoelectronic devices with functionalities such as improved carrier confinement, bandgap engineering, and increased electron mobility.

[0091] The above discussion is based primarily on the assumption that the single-crystal growth layer and heat spreader layer contain SiC. Alternative materials can be used to produce high-quality crystals. The heat spreader layer and single-crystal growth layer of the layered seed can form a homostructure or heterostructure.

[0092] For example, the monocrystalline growth layer may include or consist of a first material, the first material being at least one of Si, SiC, AlN, GaN, AlGaN, AlInN, and InN.

[0093] Additionally or alternatively, the grains of the heat spreader layer include or consist of a second material, which is at least one of Si, SiC, AlN, GaN, Al2O3, GaAs, and an oxide substrate. An oxide substrate refers to a material, typically a crystalline structure, composed primarily of oxide. An oxide is a chemical compound containing at least one oxygen atom and one other element. As mentioned above, in the case of a homostructure, the second material is the same as the first material, for example, the homostructure material can be at least one of Si, SiC, AlN, and GaN.

[0094] As mentioned above, in the case of a heterostructure, the first material is different from the second material. For example, the heat spreader layer can include SiC, and the single-crystal growth layer can include any of Si, AlN, GaN, AlGaN, AlInN, and InN.

[0095] Polycrystalline SiC can be used as a heat spreader, forming heterostructures with single-crystal AlN to improve AlN single-crystal growth and providing a low lattice mismatch. Advantageously, polycrystalline Si can be used as an inexpensive and easily accessible heat spreader in conjunction with a single-crystal SiC layer to improve SiC single-crystal growth.

[0096] In particular, the single-crystal growth layer may consist of a first material or may contain a first material and some dopant atoms. Similarly, the heat spreader layer growth layer may consist of a second material or may contain a second material and some impurities. These dopant atoms and impurities may not be taken into account when defining the seed layer as a homostructure.

[0097] [Fourth Implementation - Impurity] According to a fourth implementation of the first solution, additional elemental impurities may be introduced into the polycrystalline layer. This can occur during the formation of the polycrystalline heat spreader layer. For example, impurities accumulate at grain boundaries due to grain boundary segregation, a phenomenon in which certain atoms or molecules preferentially accumulate or segregate at the boundaries between crystalline grains in a polycrystalline material. These impurities, also known as foreign atoms that accumulate at grain boundaries, can act as more effective scattering centers for phonons than the grain boundaries themselves due to their relatively high mass.

[0098] The heat spreader layer contains impurities, for example, at a concentration of 5 ppm or more, preferably 10 ppm and / or 1000 ppm or less.

[0099] For example, the grains of the heat spreader layer can include a second material, such as Si, SiC, AlN, GaN, Al2O3, GaAs, and oxide substrates. Additionally, the heat spreader layer can include impurities of a third material, such as a metal, such as Ti, Fe, W, Mo, and V. The third material has a greater mass than the second material, which scatters phonons more efficiently.

[0100] The mass of an atom or molecule is usually measured in units of atomic mass (u). The atomic mass of an element, such as W = 183.84u, is usually listed in the periodic table. The mass of a molecule, such as SiC = 40.1u, is determined by adding up the atomic masses of all the atoms that make up the molecule. As mentioned above, the heat spreader layer includes a third material at the grain boundaries between adjacent grains, which further enhances phonon scattering.

[0101] [5th ​​Implementation - Growth Layer] As mentioned above, the growth layer contains or consists of a single-crystal material. A set of crystal axes can be used to describe a single crystal. The orientation of the crystal can be specified by the angle between these axes or by the orientation of a particular crystal plane or direction relative to an external reference frame.

[0102] For example, in a cubic crystal, which has three mutually perpendicular crystal axes of equal length, orientation can be described by specifying the angle between one of these axes and a reference axis.

[0103] Crystal orientation is crucial in a variety of scientific and technological applications, including crystal growth, materials science, semiconductor technology, and crystallographic studies. It plays an important role in determining the properties and behavior of crystals in various contexts.

[0104] According to a fifth implementation of the first solution, the angle between the crystal axis of the single-crystal growth layer and the surface normal of the growth plane is 0° or greater. Preferably, the angle is 2° or greater. As discussed, for example, in EP 1 200 651 B1, such an orientation, particularly greater than 0° and / or less than or equal to 8°, preferably less than or equal to 6°, facilitates the growth of high-quality crystals.

[0105] Additionally, the terms "C-face" and "Si-face" are commonly used in the context of crystal growth, particularly in semiconductor materials such as silicon carbide (SiC). These terms refer to specific crystal planes on the surface of a semiconductor crystal, and these planes have different properties and reactivities.

[0106] The C-face (carbon face) of a semiconductor crystal, such as SiC, refers to the surface plane composed primarily of carbon atoms. This surface plane tends to have a higher concentration of carbon atoms, which can affect the surface chemistry and reactivity of the crystal. The C-face exhibits different surface properties compared to other crystal faces, which can affect the growth and properties of thin films or other structures deposited on this surface. For example, growth of the desired 4H polytype is achieved on the carbon-terminated surface of a SiC wafer.

[0107] The Si-face of a semiconductor crystal, such as silicon carbide (SiC), refers to the surface plane composed primarily of silicon atoms. This surface plane tends to have a higher concentration of silicon atoms, which may affect the surface chemistry and reactivity differently than the C-face.

[0108] [Implementation 6 - Connection Layer] According to a sixth implementation of the first solution, as shown in Figure 1, the polycrystalline layer 140 can be bonded to the monocrystalline layer 110 by a connection layer 160. In this case, it is necessary to create a connection that is temperature stable up to approximately 2000°C to 2400°C.

[0109] According to a variant, the connection layer 160 comprises an organic compound such as a phenolic resin or a novolac resin. Additionally or alternatively, the connection layer 160 may comprise a sintered powder, preferably a sintered silicon powder.

[0110] Phenolic resins, also known as phenolic resins, are a type of thermosetting polymer derived from the reaction of phenol (or substituted phenols) with formaldehyde. Novolak resins, often simply called novolaks, are a type of thermosetting resin derived from the condensation reaction of phenol (or substituted phenols) with formaldehyde in the presence of an acid catalyst. Sintering can be used to connect or bond two layers of material together, especially in the context of powder metallurgy or ceramic processing. In particular, interlayer sintering involves placing a layer of powder between the two layers that need to be bonded. When the entire assembly is subjected to sintering conditions, the powder in the interlayer undergoes sintering, forming a bond between the adjacent layers.

[0111] 1, the polycrystalline layer 140 can be coupled to the seed holder 1120 by a connecting layer 1120. The connecting layer 1120 can be realized according to any of the variations described above in consideration of the connecting layer 160. Additionally or alternatively, the connecting layer 1120 can be omitted and the polycrystalline layer 140 is held by clamping it with the seed holder 1120.

[0112] [Second Solution - How to Make Layered Seeds] For example, a layered seed such as that shown in FIG. 1 can be produced by the following steps.

[0113] providing a single crystal growth layer 110 having a growth surface 112 for growing a volumetric single crystal and an opposing heat spreader-facing surface 114 for bonding the growth layer 110 to a heat spreader layer 140; providing a heat spreader layer 140 having a growth layer facing surface 144 for bonding to the heat spreader facing surface 114 and an opposing mounting surface 142 for mounting the heat spreader 140 to a crucible; wherein the heat spreader layer 140 comprises a polycrystalline material having thermally coupled grains 146 deposited in a growth direction Y and grains deposited to equalize hot spots of a crucible thermally coupled to a mounting surface 142; The growth layer-facing surface 114 is connected to the heat spreader-facing surface 144 .

[0114] For a description of the components, see the first solution above, especially the implementation.

[0115] In particular, the manufacturing method includes the connecting step discussed in the sixth implementation. Correspondingly, the method includes connecting the growth layer-facing surface to the heat spreader-facing surface by at least one of a bonding process and a sintering process to form a connecting layer between the single-crystal growth layer and the heat spreader layer.

[0116] [Third solution - How to grow volumetric single crystals] For example, a layered seed such as that shown in Figure 1 can be used in a method for growing a volumetric single crystal. The growth method includes the following steps:

[0117] Mounting a layered seed of the first or second solution in a crucible; A volume single crystal is grown on the single crystal growth layer by a vapor deposition process.

[0118] For a description of layered seeds, see the first and second solutions above, especially the implementation.

[0119] In particular, the method for growing a volumetric single crystal includes a mounting step of mounting the layered seed to a seed holder 1120 in a crucible, for example, as described in the sixth implementation of the first solution. For example, the mounting layer is glued or sintered to the seed holder. Additionally or alternatively, a heat spreader layer is clamped by the seed holder.

[0120] Additionally, in the sublimation growth section, various sublimation growth processes were discussed. For example, volumetric single crystals are grown by the physical vapor transport (PVT) process. As noted above, for sublimation growth processes, particularly PVT processes, growth involves heating a layered seed to a temperature above 2000°C and / or below 2400°C. [Explanation of symbols]

[0121] 110 Single crystal growth layer 112 Growth aspect 114 Heat spreader facing surface 140 Heat spreader layer 142 Mounting surface 144 Growth layer facing surface 146 Grain 148 Grain boundaries 160 Connection Layer 252, 1252 temperature profile 300 phonons 1000 Sublimation Growth System 1110 seed crystal 1120 Seed Holder 1130 Connection Layer 1200 crucible 1210 End wall 1212 Temperature Profile 1250 Growth area 1260 Storage Area 1300 Tubular containers 1400 induction heating

Claims

1. A layered seed for growing a volumetric single crystal by vapor phase growth in a growth direction in a crucible, said layered seed comprising: a single crystal growth layer having a growth surface for growing the volume single crystal and an opposing heat spreader-facing surface for coupling the growth layer to a heat spreader layer; a heat spreader layer having a growth layer-facing surface that bonds to the heat spreader-facing surface and an opposing mounting surface that mounts the heat spreader to the crucible; the heat spreader layer includes a polycrystalline material having thermally bonded grains deposited in the growth direction, the deposited grains for equalizing hot spots of the crucible thermally bonded to the mounting surface; A layered seed characterized by:

2. the single crystal growth layer has a thickness of 0.5 mm or more and / or 1.0 mm or less in the growth direction, and / or the heat spreader layer has a thickness of 0.5 mm or more and / or 3.0 mm or less in the growth direction; Optionally, the layered seed has a diameter of at least 155 mm, preferably at least 210 mm and / or at most 360 mm in radial dimension, said radial dimension perpendicular to the growth direction.

3. a median particle size, D50, of 3 μm or more and / or 80 μm or less, preferably D50 of 3 μm or more and / or 50 μm or less; Optionally, the number of grains deposited in said heat spreader layer in said growth direction is 167 or more and / or 1000 or less.

4. the single crystal growth layer includes a first material, the first material being at least one of SiC, AlN, GaN, AlGaN, AlInN, and InN; and / or the crystal grains of the heat spreader layer include a second material, the second material being at least one of SiC, AlN, GaN, Al2O3, GaAs, and an oxide substrate; Optionally, the second material is the same as the first material, and the first material is at least one of Si, SiC, AlN, and GaN, or the first material is different from the second material; Optionally, the single crystal growth layer is made of a first material.

5. 2. The seed of claim 1, wherein the heat spreader layer comprises a third material, the third material being a metal, and preferably the third material being at least one of Ti, Fe, W, Mo, and V.

6. the grains of the heat spreader layer include a second material, the heat spreader layer includes a third material, the third material having a higher mass than the second material; Optionally, said heat spreader layer comprises said third material at grain boundaries between adjacent grains; Optionally, the second material is at least one of SiC, AlN, GaN, Al2O3, GaAs, and an oxide substrate; Optionally, the third material is a metal, preferably the third material is at least one of Ti, Fe, W, Mo, and V. The seed of claim 1 .

7. the heat spreader layer includes a concentration of impurities, the concentration being at grain boundaries of 5 ppm or more and / or 100 ppm or less; Optionally, the impurities include a third material that is a metal, preferably the third material is at least one of Ti, Fe, W, Mo, and V. The seed of claim 1 .

8. 2. The seed of claim 1, wherein the angle between the crystal axis of the single crystal growth layer and the surface normal of the growth surface is greater than or equal to 0° and / or less than or equal to 8°, preferably greater than or equal to 2° and / or less than or equal to 6°.

9. The SiC-seed of claim 1, wherein the growth surface comprises a carbon face, a C-face, and preferably the growth surface is a C-face.

10. 1. A method for producing a layered seed for growing a volumetric single crystal by vapor phase epitaxy in a growth direction in a crucible, said method comprising the steps of: providing a single crystal growth layer having a growth surface for growing the volumetric single crystal and an opposing heat spreader-facing surface for coupling the growth layer to a heat spreader layer; providing the heat spreader layer with a growth layer facing surface that bonds to the heat spreader facing surface and an opposing mounting surface for mounting the heat spreader to the crucible; the heat spreader layer comprises a polycrystalline material having thermally bonded grains deposited in the growth direction, the deposited grains equalizing hot spots of the crucible thermally bonded to the mounting surface; connecting the growth layer-facing surface to the heat spreader-facing surface; A method characterized by:

11. 11. The method of claim 10, wherein the growth layer-facing surface is connected to the heat spreader-facing surface by at least one of a bonding process and a sintering process to form a connection layer between the single crystal growth layer and the heat spreader layer.

12. 1. A method for growing a volumetric single crystal in a growth direction, said method comprising: Mounting the layered seed of claim 1 or the layered seed produced by the method of claim 10 in a crucible; During growth, growing the volumetric single crystal on the single crystal growth layer by a vapor deposition process.

13. the heat spreader layer is attached to the seed holder within the crucible; Optionally, the mounting surface is bonded or sintered to the seed holder; 13. The method of claim 12, optionally wherein the heat spreader layer is clamped by the seed holder.

14. 13. The method of claim 12, wherein the volumetric single crystal is grown by physical vapor transport, PVT, and optionally, growing comprises heating the layered seed to a temperature of 2000°C or more and / or 2400°C or less.

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