Layered substrate, method for fabrication of layered substrate and method for growing epitaxial layer with the layered substrate

Abstract

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

Description

[Technical Field]

[0001] The present invention relates to a layered substrate, a method for manufacturing a layered substrate, and a method for epitaxial layers comprising a layered substrate. [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 sublimation growth, 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 the 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 substrates for the epitaxial growth process is essential to grow the highest quality crystals possible.

[0005] Several factors influence the growth of epitaxial layers using epitaxial processes, such as chemical vapor deposition (CVD) processes in reactors. The factors discussed below are particularly important with respect to CVD processes. However, those skilled in the art will recognize that epitaxial processes may have the same or similar limitations. The epitaxial process may be a vapor phase epitaxial growth (VPE) process, of which common types of VPE include metalorganic vapor phase epitaxial growth (MOVPE) and CVD processes, molecular beam epitaxial growth (MBE), liquid phase epitaxial growth (LPE), and hydride vapor phase epitaxy (HVPE).

[0006] In particular, temperature distribution within processes such as CVD processes is important for controlling the deposition of epitaxial layers. The temperature distribution within the substrate determines the rate of vapor transport and deposition. Optimizing the substrate temperature profile helps achieve uniform deposition of the epitaxial layer and minimize defects.

[0007] For example, other effects that have a significant impact on CVD processes include: · precursor gas flow rate and composition; · Quality of the substrate surface before epitaxial growth; · The influence of the growth rate of the epitaxial layer on its crystalline quality and uniformity; · Control of various process parameters such as pressure, gas flow rate, substrate temperature, deposition rate, etc.; Annealing treatment performed after epitaxial growth.

[0008] Taking the above considerations into account, EP 4,074,870 proposes an asymmetric substrate that allows the growth of high-quality epitaxial layers, however this solution does not compensate for variations in substrate temperature. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent No. 4,074,870 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in view of the drawbacks and shortcomings of the prior art and aims to provide an improved substrate bonding to a reactor that eliminates or at least mitigates the above drawbacks and shortcomings of the related prior art.

[0011] 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.

[0012] In particular, the problem is solved by a layered substrate. The layered substrate includes a heat-spreading substrate containing polycrystalline material in addition to a single-crystal growth layer. This allows for the growth of high-quality epitaxial layers. The temperature-leveling effect of the multilayer substrate reduces growth non-uniformity, which enhances the quality of the epitaxial layers and the electronic components produced therefrom. These epitaxial layers have reduced thermal stress and therefore improved geometry. These epitaxial layers also contain fewer impurities, dislocations, local polytype changes, and stacking faults. [Means for solving the problem]

[0013] A first aspect relates to a layered substrate for growing an epitaxial layer in a growth direction in a reactor. The layered substrate includes a monocrystalline growth layer having a growth surface for growing the epitaxial layer and an opposing heat spreader-facing surface for coupling the growth layer to a heat spreader substrate. The layered substrate further includes a heat spreader substrate having a growth-layer-facing surface for coupling to the heat spreader-facing surface and an opposing mounting surface for mounting the heat spreader substrate to the reactor. The heat spreader substrate includes a polycrystalline material having thermally bonded grains deposited in the growth direction, the deposited grains thermally coupling hot spots of the reactor to the mounting surface.

[0014] The first aspect facilitates smoothing out temperature profiles having bonded hot spots within a layered substrate at the mounting surface such that the temperature profile at the growth surface is smoother, thereby improving the quality of the epitaxial layer.

[0015] A second aspect relates to the substrate of the first aspect, wherein the monocrystalline growth layer has a thickness in the growth direction of ≥ 10 μm and / or ≤ 100 μm, and / or a thickness in the growth direction of ≥ 250 μm and / or ≤ 500 μm. Optionally, the layered substrate has a diameter with a radial dimension perpendicular to the growth direction of ≥ 150 mm, preferably ≤ 200 mm and / or ≤ 300 mm.

[0016] The second aspect facilitates leveling the temperature profile by selecting appropriate parameters for thickness and diameter, thereby improving the quality of the epitaxial layer.

[0017] In the third aspect, the median particle size D50 is 3 μm or more and 80 μm or less, and preferably D50 is 3 μm or more and 50 μm or less, and the number of particles deposited on the heat spreader substrate in the heat generation direction is 3 or more and 163 or less, and preferably 5 or more and 163 or less.

[0018] The third aspect facilitates smoothing the temperature profile by selecting grain parameters, thereby improving the quality of the epitaxial layer.

[0019] A fourth aspect relates to the substrate 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 substrate 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 leveling the temperature profile by selecting the seed layer material, thereby improving the quality of the epitaxial layer.

[0021] A fifth aspect is a substrate according to any of the preceding aspects, wherein the heat spreader substrate 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 leveling of the temperature profile by doping the heat spreader substrate with impurities, thereby improving the quality of the epitaxial layer.

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

[0024] The sixth aspect, for the same reasons as the fifth aspect, improves the quality of the epitaxial layer and facilitates a leveling of the temperature profile by adding particularly high mass impurities to the grain boundaries.

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

[0026] The seventh aspect is advantageous for the same reasons as the fifth and sixth aspects, in particular, by adding a certain amount of impurity to the heat spreader substrate, it becomes easier to level the temperature profile, thereby improving the quality of the epitaxial layer.

[0027] An eighth embodiment relates to a substrate according to any of the preceding embodiments, wherein the angle between the crystallographic axis (110) of the monocrystalline growth layer and the surface normal (112) 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°.

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

[0029] A ninth aspect relates to a substrate according to any of the preceding aspects, wherein the growth surface comprises a silicon surface, a Si surface, preferably the growth surface is a Si surface.

[0030] The ninth aspect mitigates the effect of the temperature profile by using the Si face to improve growth, thereby improving the quality of the epitaxial layer.

[0031] A tenth aspect relates to the substrate of any of the preceding aspects, further comprising a connection layer between the single crystal growth layer and the heat spreader substrate, 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 equalizing the temperature profile by combining multi-layer substrates, thereby improving the quality of the epitaxial layer.

[0033] An eleventh aspect relates to a method for producing a layered substrate for growing epitaxial layers in a growth direction in a reactor, comprising: providing a single crystal growth layer having a growth surface for growing an epitaxial layer and an opposing heat spreader-facing surface for bonding the growth layer to a heat spreader substrate; providing a heat spreader substrate having a growth layer facing surface for bonding to the heat spreader facing surface and an opposing mounting surface for mounting the heat spreader to a reactor; the heat spreader substrate includes a thermally coupled polycrystalline material deposited in a growth direction, the deposited grains equalizing hot spots of a reactor thermally coupled to the 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 level the temperature profile for the same reasons as the first to tenth aspects.

[0035] A twelfth aspect relates to a method according to the eleventh aspect, in which 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 substrate. The twelfth aspect facilitates equalizing the temperature profile through uniform thermal coupling between multiple layers, thereby improving the quality of the epitaxial layer.

[0036] A thirteenth aspect relates to a method for growing an epitaxial layer in a growth direction, comprising: a step of mounting a layered substrate according to any one of the first to tenth aspects or a layered substrate produced according to the eleventh or twelfth aspects in a reactor; and growing an epitaxial layer on the single crystal growth layer by an epitaxial process.

[0037] For the same reasons as the first to twelfth aspects, the thirteenth aspect improves the quality of the epitaxial layer by leveling the temperature profile.

[0038] A fourteenth aspect relates to the method of the thirteenth aspect, wherein the mounting surface of the heat spreader substrate is attached to the reactor.

[0039] For the same reasons as the first to twelfth aspects, the fourteenth aspect improves the quality of the epitaxial layer by leveling the temperature profile.

[0040] A fifteenth aspect relates to a method according to any of the thirteenth or fourteenth aspects, wherein the epitaxial layer is grown by chemical vapor deposition, and optionally, growing comprises heating the layered substrate to a temperature of 1500°C or more and / or 2000°C or less.

[0041] The fifteenth aspect improves the quality of the epitaxial layer by leveling 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 combination-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] Schematic of growing an epitaxial layer on a substrate growth layer; and [Figure 5] FIG. 1 is a schematic diagram of growing an epitaxial layer on a growth layer of a substrate. DETAILED DESCRIPTION OF THE INVENTION

[0044] [Epitaxial growth] Epitaxial growth is the process by which a crystalline layer of one material (the epitaxial layer) grows on a crystalline substrate of another material (the growth surface of the substrate), maintaining a continuous crystal lattice structure between the two layers.

[0045] There are two main types of epitaxial growth: homoepitaxy and heteroepitaxy. In homoepitaxy, the epitaxial layer and the substrate are made of the same material, for example, growing a layer of silicon on a silicon substrate. In heteroepitaxy, the epitaxial layer and the substrate are made of different materials, for example, growing a layer of GaAs on a silicon (Si) substrate.

[0046] Epitaxial growth processes typically include techniques such as CVD and MBE. In CVD, gases containing the desired atoms or molecules are introduced into a reactor where they react and deposit on the growth surface of the substrate, forming an epitaxial layer. In MBE, individual atoms or molecules are precisely deposited on the substrate surface in a high-vacuum environment.

[0047] Epitaxial growth allows for the creation of thin films with controlled properties, such as electronic, optical, or magnetic properties. It is widely used in the semiconductor industry to manufacture integrated circuits, LEDs, solar cells, and other electronic devices. Precise control of the material properties and crystalline structure achieved by epitaxial growth is essential to achieving high-performance devices with the desired functionality.

[0048] The epitaxial step-flow model can describe the growth process. More specifically, the epitaxial step-flow model is a theoretical framework used to describe the growth mechanism of thin epitaxial layers during epitaxial growth processes. It specifically focuses on the growth of thin layers via the interaction of atomic steps and terraces with the influx and deposition gas species on the substrate growth surface.

[0049] In the epitaxial step-flow model, the process begins with the influx of materials and nucleation of deposition gas species on the substrate surface.

[0050] Once nucleated, steps and terraces grow through the addition of atoms or molecules from the vapor phase. In atomic steps, atoms are incorporated into the growing lattice. These steps propagate across the surface as atoms are added, advancing the growth front.

[0051] The epitaxial layer continues to grow as atoms are deposited on the surface and incorporated into the crystal lattice. This layer maintains a continuous crystal structure with the substrate, especially the same polytype in SiC epitaxial growth, resulting in epitaxial growth.

[0052] [Temperature distribution] As mentioned above, thermal gradients are important for crystalline quality. In particular, when growing epitaxial layers using CVD processes, the temperature gradient across the surface, which may be in the x and z directions perpendicular to the axis of growth, must be precisely controlled to produce high-quality epitaxial layers. Like the PVT process, the CVD process is also a high-temperature process performed at temperatures of approximately 1500 °C or higher. High-purity gases fed into the reactor are deposited on the growth surface of a substrate placed on a holder. The holder can be rotated to equalize the temperature distribution in the x and z directions.

[0053] Ideally, as shown in Figure 4, the epitaxial layer 400 has only one growth front on the growth layer 110 of the substrate. As shown in Figure 4, a Cartesian coordinate system is used to describe the arrangement of the crystalline cells in the growth layer; that is, they are arranged in a regular grid extending in the x and z directions. Perpendicular to the grid is the growth direction Y. The Cartesian coordinates x and z in Figures 4 and 5 are converted in Figures 1 to 3 into circular coordinates, i.e., the radial direction r and the circumferential direction C.

[0054] Thermal effects play an important role in the nucleation process within the epitaxial step-flow model. Temperature affects the kinetics of adsorption, desorption, and surface diffusion of atoms or molecules on the substrate surface. Specifically, higher temperatures generally result in increased mobility of atoms or molecules on the substrate surface, promoting the formation of larger nuclei and accelerating the nucleation rate. Furthermore, temperature also affects the density of nucleation sites on the substrate surface.

[0055] Therefore, if the temperature distribution on the growth surface is not uniform, locally interrupted island growth in epitaxial islands 401, 402 can occur, as shown in FIG. 5. As the islands grow together, stresses and resulting defects are created in the crystal lattice. The defects can include, for example, dislocations and stacking faults. This reduces the yield of electrical components processed therefrom. For example, the defects can lead to higher leakage currents, preventing the components from carrying the desired voltage and current, or even destroying the components.

[0056] [Further improvements] It has been observed that even high-quality substrates, e.g., substrates with low dislocation density and low bending, can result in unexpectedly low quality when used in a subsequent epitaxy process, typically a type of CVD in which one or more single-crystalline layers of the same or different semiconductors are deposited (SiC on SiC, GaN on GaN, AlN on AlN, or GaN or AlN on SiC, or general homostructures or heterostructures). AlN on SiC, or general homostructures or heterostructures, can result in unexpectedly low quality grown layers.

[0057] Previously, the temperature distribution in the x- and z-planes described above with reference to Figures 4 and 5 has been compensated for by, for example, rotating the substrate and using materials with high thermal conductivity and low thermal mass for the substrate holder and chamber walls to minimize temperature gradients. Furthermore, thermal insulation layers can be applied to the chamber walls to reduce heat loss and improve temperature stability. Studies have shown that thermal coupling of the substrate to the reactor can result in local deviations from the desired temperature field at the mounting surface, where the heat is conducted to the growing surface.

[0058] These localized hot spots can increase the unwanted island growth shown in the top of Figure 5. In other words, the temperature distribution coupled to the mounting surface of the substrate affects the quality of the epitaxial layer. The technical problem to be solved is to optimize the temperature distribution on the growth surface of the substrate.

[0059] The inventors have therefore identified the possibility of providing improved substrates, improved manufacturing methods, and improved growth methods to avoid one or more of the above-mentioned drawbacks. The present invention relates to various solutions and variants for such improved seeds.

[0060] [Solution] Different implementations and variations are described below. The following disclosure has been facilitated by, and may be based, for example, at least in part on, the discussion and insights discussed above.

[0061] 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 substrate refers to a solid material upon which a thin film, layer, or pattern of another material is deposited or grown. It serves as a foundation or base upon which further material deposition or manufacturing processes occur. Substrates can be prepared with specific surface treatments, coatings, or patterns to optimize adhesion, promote nucleation, or control surface properties during subsequent deposition or manufacturing processes. Additionally, substrates may undergo cleaning and preparation steps to remove contaminants and ensure a pristine surface for material growth or deposition.

[0062] Furthermore, an epitaxial layer is a thin crystalline film grown on a surface by a process called epitaxy, as mentioned above. Epitaxy involves the deposition of atoms or molecules in a highly ordered manner, allowing the deposited material to acquire the crystalline structure and orientation of the underlying substrate. The main properties of an epitaxial layer are:

[0063] Crystalline structure: Epitaxial layers exhibit the same crystalline structure as the substrate on which they are grown. This ensures compatibility with the substrate and allows seamless integration into device structures. Orientation: The crystal lattice orientation of the epitaxial layer matches that of the substrate, resulting in a continuous, uniform lattice across the entire substrate surface. · Thickness control: Epitaxial growth techniques allow precise control over the thickness of the deposited layer, ranging from a few nanometers to several micrometers. · Doping: Epitaxial layers can be doped with specific impurities to change their electrical properties, such as carrier concentration and conductivity. · Surface smoothness: Epitaxial growth processes often result in smooth, defect-free surfaces, which are essential for high-performance semiconductor devices.

[0064] Additionally, a heat spreader is a component used to dissipate heat more effectively and uniformly across a surface. It is designed to transfer heat from heat-generating components, such as heaters near the edge walls, bonded to the mounting surface of the substrate and distribute it over the growing layer facing surface, thereby reducing localized hot spots on the edge walls.

[0065] A polycrystalline material is a type of solid material that is 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 crystal 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.

[0066] 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 and the objects may not be aligned.

[0067] 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 growing structure, connecting other layers, or dissipating heat.

[0068] [First Solution - Layered Substrate] 1 shows a layered substrate on which an epitaxial layer is grown by epitaxial growth in a direction of growth Y in a reactor according to one example of a general solution. In particular, the layered substrate includes a single-crystalline growth layer 110 and a heat spreader substrate 140.

[0069] The single crystal growth layer 110 has a growth surface 112 for growing an epitaxial layer and an opposing heat spreader-facing surface 114 for bonding the growth layer 110 to the heat spreader substrate 140 .

[0070] The heat spreader substrate 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 substrate to a reactor. Thermal coupling 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.

[0071] The heat spreader substrate 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.

[0072] 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.

[0073] As mentioned above, at grain boundaries 148, which are interfaces between two adjacent grains 146 in the polycrystalline heat spreader substrate 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.

[0074] Given a plurality of deposited grains 146, the deposited grains 146 equalize hot spots in the temperature profile 1212 of the reactor thermally coupled to the mounting surface 142, resulting in a balanced temperature profile 252. Notably, FIG. 1 illustrates a temperature profile without an overall temperature profile.

[0075] In other words, using a polycrystalline layer, e.g., a polycrystalline SiC layer, in combination with a single crystalline layer, e.g., a single crystalline SiC layer, as a layered substrate, i.e., as a layered substrate, has the advantage that thermal non-uniformities 1212 are compensated for by grain boundaries 148 in the polycrystalline substrate 140.

[0076] These non-uniformities 1212 can arise from non-uniformities in the materials used in the end walls or any substrate holder and epitaxial growth reactor, e.g., graphite, resulting in heat not reaching the growth layer 110 uniformly. The thermal coupling of the substrate to the end walls or optional substrate holder can also be negatively affected by unwanted thermal contact or contact loss, e.g., due to different thermal expansion of materials used in the crucible.

[0077] The mechanism for thermal leveling occurs via heat dissipation at the internal grain boundaries 148 of the polycrystalline substrate, 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.

[0078] [First implementation - board layer dimensions] According to the implementation of the first solution, various dimensions of the substrate can be taken into account. More specifically, as described above, the layered substrate includes a substrate layer whose thickness is small compared to its diameter. The thickness of the substrate 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.

[0079] The thickness of a layered substrate can affect several aspects of the epitaxial growth process and the resulting epitaxial layer. For example, thicker substrates tend to provide a more stable base for epitaxial growth, resulting in better thickness uniformity across the deposited layer. Thinner substrates may experience greater thickness variation due to surface irregularities and variations in growth conditions. Furthermore, thicker substrates can better accommodate strain induced by lattice mismatch between the epitaxial layer and the substrate material. Thinner substrates may experience greater strain, leading to defects or dislocations in the epitaxial layer. The thickness of the substrate can affect the growth rate and nucleation behavior of the epitaxial layer. Thicker substrates require longer deposition times to achieve the desired thickness, while thinner substrates may reach the desired thickness more quickly. Furthermore, thicker substrates may exhibit different thermal properties, such as thermal conductivity and heat capacity, compared to thinner substrates. These thermal properties can affect the temperature distribution and thermal stability during the epitaxial growth process. Finally, thicker substrates typically require more material and can be more expensive to manufacture compared to thinner substrates. Additionally, thicker substrates can result in greater material waste during the epitaxial growth process.

[0080] The total thickness of polycrystalline substrate 140 and single-crystalline layer 110 can be 350 μm to 500 μm.

[0081] For example, the thickness of the single crystal growth layer 110 can range from tens of micrometers to hundreds of micrometers, depending on the application. Thinner growth layers can be used for certain applications requiring precise control over crystal orientation or morphology, while thicker growth layers may be preferred for larger-scale production or to accommodate specific growth conditions. Preferably, the thickness of the growth layer 110 is 10 μm or greater. Additionally or alternatively, the thickness of the growth layer 110 is 100 μm or less.

[0082] Furthermore, from layered substrate considerations, the optimum thickness of the heat spreader substrate in the growth direction Y of the same may be greater than 250 μm. Additionally or alternatively, the thickness of the heat spreader substrate may be less than or equal to 500 μm, preferably less than or equal to 490 μm.

[0083] FIG. 2 shows a layered substrate with a thin heat spreader substrate 140 compared to the heat spreader substrate 140 in the layered seed shown in FIG. 3. Notably, FIGS. 2 and 3 show a temperature profile without an overall temperature profile. In particular, in contrast to PVT growth in epi reactors, a highly uniform temperature profile is sought. This is particularly impossible, and therefore the need for a heat spreader exists, for example, where the substrate is mounted.

[0084] In other words, the leveling effect of the heat spreader substrate is proportional to the thickness of the heat spreader substrate. As a result, the leveling effect increases as the substrate becomes thicker. However, as described above, the temperature profile can be coupled to the layered substrate to modify the temperature profile, for example, to compensate for the coupling effect of the end walls of the optional holder. Therefore, the thickness can be limited to allow the temperature profile to propagate.

[0085] Additionally, the layered substrate may have a diameter in radial dimension r of 150 mm or more, preferably 200 mm or more and / or 300 mm or less. The thickness and / or diameter values ​​are particularly applicable to heat spreader substrates comprising or consisting of SiC.

[0086] [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 substrate 140 described in the first implementation, 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 polycrystalline materials is significant, affecting various mechanical, thermal, electrical, and optical properties.

[0087] 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.

[0088] 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.

[0089] In particular, D50 may be 3 μm or more. Additionally or alternatively, D50 may be 80 μm or less. Preferably, D50 is 50 μm or less. This D50 value is particularly applicable to heat spreader substrates containing or made of SiC.

[0090] For example, for a thickness between 250 μm and 490 μm and a D50 between 3 μm and 80 μm, the number of crystal grains stacked in the growth direction Y in the heat spreader substrate is between 3 and 163 and / or less. The number of crystal grains stacked in the growth direction Y in the heat spreader substrate is preferably 5 or more.

[0091] [Third implementation - grain size] The above discussion is primarily based on the assumption that the single-crystal growth layer and heat spreader substrate are made of SiC. According to a third implementation, alternative materials can be used to produce high-quality epitaxial layers. The single-crystal growth layers of the heat spreader substrate and layered substrate can form homostructures or heterostructures. The primary difference between homostructures and heterostructures is the composition of the semiconductor material within the layered substrate. Homostructures consist of layers of the same semiconductor material, while heterostructures consist 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.

[0092] For example, homostructures are commonly used in devices such as bipolar junction transistors (BJTs) and metal-oxide-semiconductor field-effect transistors (MOSFETs), where 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.

[0093] The above discussion is based primarily on the assumption that the single-crystal growth layer and the heat spreader substrate comprise SiC. Alternative materials can be used to produce high-quality epitaxial layers. The single-crystal growth layers of the heat spreader substrate and the layered substrate can form homostructures or heterostructures.

[0094] 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.

[0095] Additionally or alternatively, the grains of the heat spreader substrate include or are composed 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.

[0096] As mentioned above, in the case of a heterostructure, the first material is different from the second material. For example, the heat spreader substrate can include SiC, and the single crystal growth layer can include any of Si, AlN, GaN, AlGaN, AlInN, and InN.

[0097] 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.

[0098] In particular, the single-crystal growth layer can consist of a first material or can contain the first material and some dopant atoms. Similarly, the heat spreader substrate growth layer can consist of a second material or can contain the second material and some impurities. These dopant atoms and impurities may not be taken into account when defining the seed layer as a homostructure.

[0099] [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 substrate. 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. Due to their relatively high mass, these impurities, also known as foreign atoms, can act as more effective scattering centers for phonons than the grain boundaries themselves.

[0100] The heat spreader substrate may, for example, contain a concentration of impurities that is greater than or equal to 5 ppm, preferably less than or equal to 10 ppm and / or 1000 ppm.

[0101] For example, the grains of the heat spreader substrate can include a second material, such as the materials mentioned above, e.g., Si, SiC, AlN, GaN, Al2O3, GaAs, and oxide substrates. Additionally, the heat spreader substrate can include impurities of a third material, e.g., the third material can be a metal such as Ti, Fe, W, Mo, and V. Because the third material has a larger mass than the second material, phonons are scattered more efficiently. Preferably, the third material aggregates at the grain boundaries.

[0102] 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 substrate includes a third material at the grain boundaries between adjacent grains, which further enhances phonon scattering.

[0103] [5th ​​Implementation - Layer Growth] 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.

[0104] 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.

[0105] 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.

[0106] According to a fifth implementation of the first solution, the angle between the crystal axis of the monocrystalline growth layer and the surface normal of the growth plane is 0° or greater. Preferably, this angle is 2° to 8°, preferably 6° or less. For example, as discussed in EP 1,200,651 B1, such an orientation, particularly an orientation greater than 0°, facilitates growth as a step-flow. In particular, EP 1,200,651 B1 relates to sublimation processes. However, as noted above, step-flow growth can occur in epitaxial processes.

[0107] 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.

[0108] 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.

[0109] The Si-face of a semiconductor crystal, such as silicon carbide (SiC), refers to a 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.

[0110] [Implementation 6 - Connection Layer] According to a sixth implementation of the first solution, as shown in Figure 1, the polycrystalline substrate 140 can be bonded to the monocrystalline layer 110 by a connection layer 160. In doing so, it is necessary to create a connection with temperature stability up to approximately 1500°C to 2300°C.

[0111] 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.

[0112] 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.

[0113] Alternatively, the polycrystalline substrate 140 can be held by any substrate holder, for example by providing an additional connecting layer. In particular, in the case of epitaxy, a substrate holder is not required. The layered substrate can be placed directly in a pocket of the reactor. This pocket can be seen as the substrate holder.

[0114] [Second Solution - Method for manufacturing layered substrates] For example, a layered substrate such as that shown in FIG. 1 can be fabricated by the following steps. providing a monocrystalline growth layer 110 having a growth surface 112 for growing an epitaxial layer and an opposing heat spreader-facing surface 114 for bonding the growth layer 110 to a heat spreader substrate 140; providing a heat spreader substrate 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 reactor; Here, the heat spreader substrate 140 comprises a polycrystalline material having thermally coupled grains 146 deposited in a growth direction Y and grains deposited to equalize hot spots in a thermally coupled reactor to a mounting surface 142. The growth layer-facing surface 114 is connected to the heat spreader-facing surface 144 .

[0115] For the description of the components, reference is made to the first solution described above, in particular the implementation.

[0116] 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 substrate.

[0117] [Third solution - growing epitaxial layers] For example, a layered substrate such as that shown in Figure 1 can be used in a method for growing an epitaxial layer. The growth method includes the following steps: Mounting a layered substrate in a crucible according to the first or second solution; Growing an epitaxial layer on the single crystal growth layer by an epitaxial process.

[0118] For the description of the layered substrate, reference is made to the first and second solutions described above, in particular the implementation.

[0119] In particular, the method for growing an epitaxial layer includes a step of attaching the layered substrate to the reactor, for example, by any substrate holder or pocket in the reactor, as described in the sixth implementation of the first solution. For example, the heat spreader substrate is clamped by the substrate holder or held in a pocket in the end wall of the reactor. Advantageously, the substrate holder comprises graphite.

[0120] Additionally, various epitaxial growth processes are discussed in the epitaxial growth section. For example, epitaxial layers may be grown by chemical vapor deposition (CVD) processes. As noted above, for epitaxial growth processes, particularly CVD processes, growing involves heating the layered substrate to temperatures above 1500°C and / or below 2300°C. [Explanation of symbols]

[0121] 110 Single crystal growth layer 112 Growth aspect 114 Heat spreader facing surface 140 Heat spreader board 142 Mounting surface 144 Growth layer facing surface 146 Grain 148 Grain Boundaries 160 Connection Layer 252, 1252 temperature profile 300 phonons 400 epitaxial layer 1212 Temperature Profile

Claims

1. 1. A layered substrate for growing an epitaxial layer in a growth direction in a reactor, said layered substrate comprising: a single crystal growth layer having a growth surface for growing the epitaxial layer and an opposing heat spreader-facing surface for coupling the growth layer to a heat spreader substrate; The heat spreader substrate has a growth layer-facing surface that is bonded to the heat spreader-facing surface, and an opposing mounting surface that attaches the heat spreader substrate to the reactor. and The heat spreader substrate includes a polycrystalline material having thermally bonded grains deposited in the growth direction, the deposited grains equalizing hot spots of the reactor thermally bonded to the mounting surface. A substrate characterized by:

2. the single-crystal growth layer has a thickness in the growth direction of 10 μm or more and / or 100 μm or less, and / or the heat spreader substrate has a thickness in the growth direction of 250 μm or more and / or 500 μm or less, Optionally, the layered substrate has a diameter of 150 mm or more, preferably 200 mm and / or 300 mm or less in radial dimension, said radial dimension perpendicular to said growth direction.

3. The median particle size D50 is 3 μm or more and / or 80 μm or less, preferably 3 μm or more and / or 50 μm or less, Optionally, the number of crystal grains deposited on the heat spreader substrate in the growth direction is ≧3 and / or ≦163, preferably ≧5 and / or ≦163.

4. the single crystal 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 substrate 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, a monocrystalline growth layer is formed of said first material.

5. 2. The substrate of claim 1, wherein the heat spreader substrate 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 substrate comprise a second material, the heat spreader substrate comprises a third material, the third material having a higher mass than the second material; Optionally, said heat spreader layer includes said third material at grain boundaries between adjacent grains; Optionally, the second material is at least one of Si, 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 substrate of claim 1 .

7. the heat spreader substrate includes a concentration of impurities, the concentration being greater than or equal to 5 ppm and / or less than or equal to 100 ppm; 2. The substrate of claim 1, wherein the impurities optionally include a third material that is a metal, preferably at least one of Ti, Fe, W, Mo, and V, and that agglomerates at grain boundaries.

8. 2. The substrate 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 0° or more and / or 8° or less, preferably 2° or more and / or 6° or less.

9. The substrate of claim 1 , wherein the growth surface comprises a silicon surface, a Si surface, and preferably the growth surface is a Si surface.

10. 1. A method for producing a layered substrate for growing epitaxial layers in a reactor in a growth direction, the method comprising: providing a single crystal growth layer having a growth surface for growing the epitaxial layer and an opposing heat spreader-facing surface for coupling the growth layer to a heat spreader substrate; providing the heat spreader substrate having a growth layer-facing surface for bonding to the heat spreader-facing surface and an opposing mounting surface for mounting the heat spreader to the reactor; the heat spreader substrate includes a polycrystalline material having thermally bonded grains deposited in the growth direction, the deposited grains equalizing hot spots of the reactor thermally coupled to the mounting surface; connecting the growth layer-facing surface to the heat spreader-facing surface.

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 substrate.

12. 1. A method for growing an epitaxial layer in a growth direction, comprising: Mounting a layered substrate according to claim 1 or a layered substrate produced by the method of claim 10 in a reactor; and growing the epitaxial layer on the single crystal growth layer by an epitaxial process.

13. The method of claim 12 , wherein the mounting surface of the heat spreader substrate is attached to the reactor.

14. The method of claim 12 , wherein the epitaxial layer is grown by chemical vapor deposition, and optionally, growing comprises heating the layered substrate to a temperature of 1500° C. or more and / or 2000° C. or less.

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