Crucible for producing SiC bulk single crystals and method for growing SiC bulk single crystals

Abstract

The invention relates to a crucible with a cavity for growing SiC bulk single crystals by sublimation growth in a growth direction (Y). The crucible comprises: an end wall (110) having a seed holder (112) for holding a SiC seed in the cavity, the end wall (110) extending in a direction (r) perpendicular to the growth direction (Y); a side wall (140) extending in the growth direction (Y), the side wall (140) preventing permeation of a dopant gas from the outside into the cavity, the dopant gas being used to dope the SiC bulk single crystal during the sublimation growth; and a diffusion region (114) that allows the dopant gas to permeate into the cavity from the outside, where the diffusion region (114) is located between the seed holder (112) and the edge (142) of the side wall (140).

Description

Background Art

[0001] The semiconductor material silicon carbide (SiC) is used for high-frequency components and for special light-providing semiconductor components due to its excellent physical, chemical, electrical, and optical properties, and is in particular also used as a starting material for power electronics semiconductor components. These components require SiC substrates, such as those discussed in U.S. Patent US 8,747,982 B2, which have a large substrate diameter (equal to or greater than 200 mm) and high quality. A bulk single crystal of SiC with a large diameter and high quality is the object of the present specification. Summary of the Invention

[0002] At least this object is solved by the independent claims. Advantageous embodiments are solved by the dependent claims.

[0003] More specifically, a single crystal is a material in which the crystal lattice of the entire sample is continuous and does not break at the edges of the sample, without grain boundaries. The absence of defects associated with grain boundaries can endow single crystals with unique properties, especially mechanical, optical, and electrical properties. These properties are used industrially for technical applications, especially for optics and electronics.

[0004] By using a suitable source material, a bulk single crystal of SiC can be grown, for example, by a physical vapor transport (PVT) process, which describes a vacuum deposition method that can be used to produce single crystals. PVT is characterized by the process in which the material changes from the condensed phase to the gas phase (i.e., the sublimated phase) and then returns to the thin-film condensed phase. The material is transported in the gas phase from the source region to the seed region. The most common PVT processes are sputtering and evaporation. Further details of the PVT process can be found, for example, in U.S. Patent US8,747,982B2.

[0005] A disk-shaped single crystal SiC substrate is cut out from the bulk single crystal of SiC, and then at least one epitaxial layer, which is also particularly made of SiC, is provided for it during the manufacture of the component. In a subsequent epitaxial process, a thin single crystal layer (such as SiC, GaN) can first be deposited on the SiC substrate. The quality of this epitaxial layer depends decisively on the local orientation of the single crystal substrate, in other words, on the SiC substrate cut out from the bulk single crystal of SiC. If a local deviation from the optimal orientation occurs in the crystal structure of the SiC substrate, this may propagate into the epitaxial layer. The epitaxial layer then also contains local defects, which may ultimately lead to poor performance of the final product, namely the semiconductor component.

[0006] As Figure 9 shown, the PVT crystal growth is carried out in a crucible 1100. The crucible is a container in which a material (such as SiC) can be subjected to a very high temperature (higher than 2000 °C) (such as a temperature that allows the sublimation of SiC). In particular, the crucible is made of a material that can withstand a temperature high enough to melt and / or sublime its contents.

[0007] As shown Figure 10 in FIG. 1, the crucible 1100 is placed in a tubular container 1200, which can be designed as quartz glass (suitable for induction heating described later) or stainless steel (suitable for resistance heating described later) and forms a reactor, which is the core of the device 2000. For example, the crucible is held by a bracket 1210 arranged in the tubular container 1200. The tubular container 1200 is a machine for performing processes that require elevated temperatures and pressures relative to ambient pressure and / or temperature.

[0008] Actual crystal growth occurs in the reactor. The growth structure includes a spacer 1300 arranged around the crucible.

[0009] The walls of the crucible may include materials such as graphite and carbon. These materials allow the crucible to heat SiC to a growth temperature above 2000 °C.

[0010] In particular, for growing a bulk single crystal of SiC, a SiC seed 1114 is arranged at a seed holder 1112, which is arranged at the end wall 1110 of the crucible before the start of growth. More specifically, the SiC seed 1114 is arranged in the crystal growth region 1124 of the growth crucible 1100, which is preferably completely enclosed, especially during at least the growth period.

[0011] Powdery SiC source material is introduced into the SiC storage region 1120 of the growth crucible. The boundary of the SiC storage region 1120 at the start of the growth process is indicated by a thick dashed line 1122. The boundary is, for example, a wall made of porous graphite. During growth, by sublimation of the powdery SiC source material and by transporting the sublimated gaseous components into the crystal growth region 1124 (i.e., along the Y-axis), a SiC growth gas phase is generated there, and a bulk single crystal of SiC having a central longitudinal axis along the Y-axis grows by deposition from the SiC growth gas phase onto the SiC seed 1114.

[0012] For growing a bulk single crystal of SiC, a temperature distribution along the Y-axis as shown Figure 11 in FIG. 2 is achieved in the crucible. In particular, the dashed line 1130 indicates the highest temperature in Figure 10 and Figure 11 FIG. 2. In particular, the highest temperature is located in the middle of the SiC storage region 1120.

[0013] As shown Figure 10 in FIG. 3, heating can be provided by an induction coil 1400 placed outside the tubular container 1200. In particular, the induction coil 1400 has a radius R along the radial axis R coilThey are arranged in a circumferential direction. Alternatively, according to a solution not shown, the resistance heater can be placed inside the reactor 1200.

[0014] Induction heating is the process of heating a conductive material through electromagnetic induction. An electromagnetic field is generated inside the coil by the current passing through the inductor 1400 to directly heat the material in the SiC storage area 1120 and / or to heat the side wall 1140 of the crucible to indirectly heat the SiC in the storage area. The side wall 1140 of the crucible extends along the growth direction (i.e., the Y-axis) with a radius R sidewall It extends along the circumferential direction. The spacer 1300 thermally insulates the crucible and the cavity formed inside the crucible.

[0015] The temperature can be measured by one or more pyrometers not shown or by one or more thermocouples. In particular, the temperature is measured in the cavity formed by the reactor 1200 but outside the crucible. The vacuum-sealed reactor 1200 can be evacuated via one or more vacuum pumps not shown through the outlet 1500. In addition, an inert gas and / or a doping gas (such as nitrogen) can be supplied to the system via one or more gas supply lines 1600, and the pressure in the system can be measured and controlled by a pressure sensor not shown.

[0016] Process parameters such as pressure, temperature, and gas flow can be set, controlled, and archived through computerized system control. The equipment control system communicates with all components involved (such as converters, pyrometers, vacuum control valves, mass flow controllers (MFCs) for providing doping gases, and pressure sensors).

[0017] As described above, the SiC single crystal or the substrate produced therefrom should have high quality for subsequent epitaxial processes. For this purpose, it should be ensured that a doping gas such as nitrogen is present in the growth space in a controlled manner throughout the growth period and can be incorporated into the lattice of the grown SiC single crystal. Uneven doping gas concentration during growth and thus uneven incorporation into the single crystal result in increased waste during processing into the SiC substrate. More specifically, doping gases such as nitrogen affect the brittleness of the SiC single crystal. Uneven incorporation of the doping gas, especially nitrogen, into the lattice results in cracks during crystal processing or wafer waste due to excessive bow and warp values of the SiC substrate. As used herein, the bow and warp of semiconductor wafers and substrates are measures of wafer flatness.

[0018] The doping gas can be introduced into the system by two different methods: using a gas-permeable growth crucible or a gas-impermeable growth crucible, with the gas-permeable crucible being more commonly used.

[0019] When using a gas-permeable growth apparatus, the gas supply lines for the inert gas and dopant gas controlled by the MFC typically lead to the reactor chamber, and there is a concentration equilibrium between the reactor chamber and the nitrogen content inside the growth crucible. The following problems exist in this process: The gas permeability of the crucible and the diffusion of nitrogen vary with temperature. For example, due to the temperature-dependent pore expansion in graphite, the concentration in the crucible changes during the duration of growing a bulk single crystal of SiC, as the growth is usually carried out with a temperature ramp to compensate for effects such as powder depletion. Growing a bulk single crystal of SiC with a temperature ramp also results in different nitrogen incorporation into the lattice, as this also occurs as a function of temperature.

[0020] This has the following effect: The varying nitrogen concentration during the growth period leads to the aforementioned development-reducing factors of crystal cracks and poor geometric values (bending and / or warping).

[0021] Given the above, the problem lies in uniformly and controllably supplying nitrogen into the crystal growth space of the crucible. With the increase in crystal diameter (200 mm and larger) and the associated increase in the size of the growth apparatus, considering these problems, a new solution is necessary. At the same time, the PVT process requires vacuum-sealed framework conditions in terms of process conditions and materials used.

[0022] Existing solutions propose providing a gas-permeable crucible, such as a crucible made of graphite. The nitrogen content in the reactor is controlled, for example, by the MFC and selectively introduced into the reactor. In this solution, the growth crucible located in the reactor has a certain permeability such that nitrogen can diffuse from the reactor into the growth crucible. However, it is generally not possible to control the nitrogen content in the crucible, which follows the temperature-dependent diffusion law. Similarly, the incorporation of nitrogen (in the growth space of the crucible) into the SiC lattice follows a temperature-dependent law, and it is not possible to influence the nitrogen incorporation mechanism in any other way. Due to the permeability of the crucible, the gaseous components of the source material (compounds containing Si and C) can also enter the reactor by diffusion along the radial temperature gradient from the crucible. There they deposit on cooler areas, such as in the spacers or reactor walls, resulting in aging and wear.

[0023] Alternatively, a gas-impermeable crucible can be used, such as a crucible made entirely of TaC. In this design, nitrogen gas must be fed directly, for example through a pipe, into the gas-impermeable crucible, which results in a significantly increased process workload and significantly higher manufacturing costs. If the dopant nitrogen is not supplied internally via an additional gas feed, it is not possible to manufacture N-doped SiC crystals therein, which are used in power electronic devices. Additionally, it is disadvantageous that pre-treatment-related impurities present in the crucible, such as water, Na, Ca, etc., which enter the crucible, for example, during the preparation of the crucible with the source material and seed before placing the crucible in the reactor, cannot be removed from the system by diffusion through the crucible wall during a bake out step under vacuum at the start of the process. However, the advantage of this design is that the gaseous components of the source material do not enter the reactor by diffusion along the radial temperature gradient from the crucible and cause isolation aging or reactor wear.

[0024] The object of the present invention is in particular to provide a solution for the crucible that allows for the provision of a doping gas with a constant concentration. In particular, the temperature influence caused by the temperature ramp should be avoided. Another object is to minimize the process complexity, for example by providing a pipe for directly supplying nitrogen gas into a cavity formed in the crucible. Additionally, the influence of interfering materials in the crucible should be avoided.

[0025] According to a general example, a diffusion region with a specific arrangement that allows the doping gas to penetrate from the outside into the cavity solves this problem. More specifically, the diffusion region according to the general example is located between the impermeable seed holder at the end wall and the edge of the impermeable side wall.

[0026] In particular, the diffusion region defined above is only arranged in the region that experiences the smallest temperature gradient during the cultivation cycle. Considering that the temperature of the diffusion region is almost constant during the cultivation cycle, the amount of doping gas in the crucible cavity is constant, and thus, the control of the incorporation of the doping gas into the lattice is improved.

[0027] The permeability of the cultivation crucible with respect to the doping gas is changed by coating and / or infiltration, such that the side walls (i.e., the radial boundaries) of the cultivation crucible in the region of the source zone and the growth space become almost impermeable to the doping gas. At the same time, the seed holder arranged at the end wall of the cultivation crucible provides a barrier for the entry of nitrogen gas over its entire area.

[0028] This leads to the design of a growth crucible, where the diameter of the crucible is larger than the diameter of the inserted SiC seed and / or a diffusion gap is formed between the edges of the end wall and the side wall. The resulting doping gas ring between the outer SiC seed diameter and the inner crucible diameter and / or the resulting doping gas diffusion gap serves as a doping gas diffusion surface and / or a doping gas diffusion gap within the growth device according to the invention.

[0029] More specifically, a first aspect relates to a crucible with a cavity for growing a bulk single crystal of SiC by sublimation growth in a growth direction.

[0030] The description of the crucible refers to the above description. In particular, the crucible forms a cavity inside it, in which the bulk single crystal of SiC grows. The inner surface of the crucible faces the cavity. The outer surface of the crucible faces the above-mentioned reactor, i.e., is surrounded by the chamber formed by the reactor.

[0031] Advantageously, the crucible has a prismatic shape. A prism is a polyhedron that includes an n-sided polygonal base, a second base that is a translation copy (rigidly moved without rotation) of the first base, and n other faces that form the side walls, where the n other faces connect the corresponding sides of the two bases. Thus, a closed cavity is achieved. This prismatic shape enables the bulk single crystal of SiC to be easily removed from the cavity, i.e., parallel to the faces forming the side walls. Generally, the crucible has a cylindrical shape, i.e., the base has a circular cross-section.

[0032] It is noted that a geometry that can be used multiple times is advantageous because the cost of treating / coating the side walls, which will be described later, is high. Therefore, in particular, the geometry of a prism, especially that of a cylinder, is advantageous because the bulk single crystal of SiC can be extracted along the growth direction and the dead space in the cavity can be reduced.

[0033] The description of the bulk single crystal of SiC refers to the above description. The description of sublimation growth refers to the above description. In particular, in the case where the cylinder has a prismatic shape, the growth direction is perpendicular to the extension direction of the base, i.e., parallel to the direction of the faces forming the side walls.

[0034] According to the first aspect, the crucible includes an end wall, such as the first base in a prismatic shape. The end wall includes a seed holder for holding the SiC seed in the cavity. The seed holder and the SiC seed are hereinafter referred to as the holder-seed unit. The holder-seed unit reduces the permeability of the end wall to the doping gas. In particular, considering the growing bulk single crystal of SiC and the increasing thickness, the permeability is reduced. In other words, at least a part or only a part of the end wall is at least impermeable to the doping gas.

[0035] The seed holder can be formed, for example, from polycrystalline SiC. The thermal expansion coefficients of the two components of the holder-seed unit, i.e., the thermal expansion coefficients of the seed holder and the SiC seed, are very similar to each other, so that the force effect on the SiC seed caused by the temperature of the seed holder is particularly small. However, other holder materials are basically possible, for example, graphite materials.

[0036] The end wall extends perpendicular to the growth direction. This enables the easy extraction of the bulk single crystal of SiC after growth, i.e., the translation of the end wall with the holder-seed unit along the growth direction. In particular, in the case where the crucible has a cylindrical shape, the end wall extends in the radial direction.

[0037] Furthermore, according to the first aspect, the crucible includes a side wall extending in the growth direction. For example, in the case where the crucible has a cylindrical shape, the side wall forms a cylindrical surface surrounding the growth direction along the circumferential direction and extending in the growth direction. In this case, the crucible may additionally have a bottom wall opposite to the end wall, so that the cavity is closed. However, the bottom wall can have any shape for closing the cavity of the crucible.

[0038] Furthermore, the side wall is designed to prevent the doping gas from penetrating from an external source into the cavity. Penetration (also known as permeation) is the penetration of a penetrant (such as a fluid of a doping gas) through a part such as the wall or contact area of the crucible. It is directly related to the concentration gradient of the penetrant, the intrinsic permeability of the material, and the mass diffusivity of the material. The penetration process involves the diffusion of molecules (called penetrants) through an interface (such as the side wall). Penetration works through diffusion; the penetrant will move through the interface from a high concentration to a low concentration. Preventing penetration means that the amount of penetrant passing through this part of the side wall is negligible (or at least less) compared to another part (i.e., the diffusion region described later).

[0039] The doping gas can dope the material. Doping is the intentional introduction of impurities into an intrinsic semiconductor (i.e., the bulk single crystal of SiC) to modulate its electrical, optical, and structural properties. The doped material is called an extrinsic semiconductor.

[0040] According to a first aspect, during sublimation growth, a doping gas is used to dope a bulk single crystal of SiC. More specifically, in the SiC growth gas phase, a doping substance is provided. The doping gas (also referred to as the doping substance) is, for example, nitrogen (N), aluminum (Al), vanadium (V), and / or boron (B). The doping substance is supplied in gaseous or solid form. For example, doping metals or metalloids such as Al, V, and B are provided in solid form, for example, in a crucible with source materials. Additionally or alternatively, the metal and / or metalloid can be provided in gaseous form and can enter by diffusing through the crucible. Advantageously, the bulk single crystal of SiC is an n-doped SiC crystal with nitrogen. However, another doping is also basically possible. Advantageously, the polytype of SiC is 4H. 4H is particularly advantageous for use in power electronic devices. However, another SiC polytype is also basically possible.

[0041] To provide the doping gas, according to a first aspect, a diffusion region is provided that allows the doping gas to penetrate from the outside into the cavity. More specifically, the diffusion region is located between the edge of the seed holder and the sidewall. More specifically, the edge of the sidewall abuts the end wall. Thus, during the growth stage, the diffusion region is arranged at a position where it experiences a smaller temperature change than, for example, the sidewall, which is close to the heated SiC storage region. Further details of the temperature distribution are referred to the above descriptions of Figure 10 and Figure 11 The above description. Examples of the implementation of the diffusion region are discussed below in other aspects.

[0042] According to a second aspect, in addition to the first aspect, the sidewall comprises or consists of a material for preventing the penetration of the doping gas, and the material comprises at least one of the following: graphite with a density equal to or greater than 1.8 g / cm 3 , vitreous carbon, and refractory metal carbides. As used herein, refractory metal carbides can withstand high temperatures during the PCT process. According to an advantageous aspect, the material comprises graphite with a density equal to or greater than 1.85 g / cm 3 . Additionally or alternatively, the material comprises graphite with a density equal to or less than 1.95 g / cm 3 . The density of the graphite is controlled by using a process such as isostatic pressing. Thereby, graphite with a density lower than that of natural graphite can be achieved. Advantageously, the sidewall comprises or consists of a combination of the aforementioned materials. Thereby, the material of the sidewall can prevent the penetration of gas. This avoids the process step of coating the sidewall. Thus, the penetration rate of the crucible can be adjusted by the infiltration process.

[0043] As used herein, graphite is a crystalline form of elemental carbon.

[0044] As used herein, vitreous carbon (commonly referred to as glassy carbon or vitreous carbon) is a non-graphitizable or non-graphitized carbon that combines the properties of glass and ceramics with those of graphite. The most important properties are high temperature resistance, hardness, low density, low electrical resistance, low friction, low thermal resistance, extreme chemical erosion resistance, and impermeability to gases and liquids.

[0045] As used herein, carbides or refractory metal carbides generally describe compounds composed of carbon and refractory metals.

[0046] According to a third aspect, in addition to any of the foregoing aspects, the sidewall includes a layer on at least one of the inner surface and the opposite outer surface for preventing the penetration of doping gases, and the inner surface faces the cavity. Thus, the penetration rate of the crucible can be adjusted by a coating process.

[0047] It is noted that, as discussed with reference to a prismatic geometry that can be used multiple times, it is advantageous to provide a crucible with a layer because the cost of treating / coating the sidewall is cheaper than using a crucible made of or including graphite. Thus, in particular, a prismatic geometry, especially a cylindrical geometry, in combination with a layer is advantageous.

[0048] Advantageously, according to a fourth aspect in addition to the third aspect, the layer includes at least one of the following: photoresist, graphitized sugar layer, TaC, WC, and Ta4HfC5. These materials can be applied as thin films, from solutions, or from the gas phase. These layers are more stable in terms of temperature and chemical properties and are more airtight than graphite.

[0049] Advantageously, according to a fifth aspect in addition to the third or fourth aspect, the layer has a thickness equal to or greater than 0.5 μm, preferably the thickness is equal to or greater than 1 μm, and even more preferably the thickness is equal to or greater than 2 μm. Optionally, wherein the maximum thickness is equal to or less than 5 μm.

[0050] According to a sixth aspect, in addition to any of the foregoing aspects, the sidewall includes a layered structure for preventing the penetration of doping gases, and the layered structure includes alternating first and second layers. In the case of a cylindrical shape, each layer forms a cylindrical surface. At least two layers of a first material and two layers of a second material are provided. Advantageously, the first layer includes graphite and the second layer includes a refractory metal carbide.

[0051] According to a seventh aspect, in addition to any of the foregoing aspects, the end wall includes a diffusion region. For example, in the case of a circular end wall, the diffusion region forms an annular ring around the seed holder.

[0052] According to this example, the diameter of the crucible is larger than the diameter of the inserted seed holder. The resulting dopant gas-permeable diameter between the outer seed holder diameter and the inner crucible diameter serves as the dopant gas diffusion surface within the cultivation device according to the first example.

[0053] As the diameter of the seed holder used increases, the size of the diffusion region can also be adjusted by adjusting the growth crucible so that the amount of dopant gas corresponding to the volume of the growing crystal and the desired doping level is available.

[0054] According to the eighth aspect appended to the seventh aspect, the area of the diffusion region relative to the inner surface of the end wall is equal to or greater than 20% and equal to or less than 40%, and the inner surface of the end wall faces the cavity. This is particularly applicable to SiC bulk single crystals with a diameter greater than 200 mm perpendicular to the growth direction. The inventors have found that these ratios are sufficient to provide the necessary permeation ratio.

[0055] According to the ninth aspect, appended to any of the foregoing aspects, the crucible further includes a sealing element for sealing the contact area between the edge of the end wall and the side wall, thereby controlling (e.g., reducing) the permeation of dopant gas through the contact area.

[0056] The sealing of the end wall and the side wall and possibly also the bottom wall and the side wall (if the side wall is not designed as a "can") can be optimized by introducing a sealing element including or consisting of graphite, such that the effect of the dopant gas diffusion channels in the contact area is eliminated. Then the effect of the channels at the end wall and / or the end wall and the bottom wall can be ignored, and only the dopant gas diffusion via the diffusion region next to the seed holder can be considered.

[0057] According to the tenth aspect, appended to any of the foregoing aspects, the crucible further includes a fastening element for fastening the end wall to the side wall and thereby regulating the permeation rate of dopant gas through the contact area between the edge of the end wall and the side wall. Thus, the thickness of the diffusion gap arranged in the contact area can be defined, for example, by fixing the fastening element (e.g., a screw) with a defined torque.

[0058] According to the eleventh aspect, appended to the tenth aspect, during the growth of the SiC bulk single crystal, a gap is formed between the edge of the end wall and the side wall for the dopant gas to pass through. This makes the diameter of the seed holder the same as the inner diameter of the crucible. The diffusion region is achieved through the gap, which forms a dopant gas diffusion channel. The channel width can be defined by the gap remaining between the end wall and the side wall during the fastening of the fastening element (e.g., screwing with a defined torque), and if the side wall is not designed as a "can", the channel width can also be defined by the gap between the bottom wall and the side wall.

[0059] Advantageously, the gap is equal to or greater than 0.1 mm and equal to or less than 0.5 mm. The gap width is measured along the radial and / or longitudinal axis of the crucible. The gap surrounds the crucible in the circumferential direction, thereby forming an annular ring that connects the outer surface of the crucible to the inner surface of the crucible. This is particularly applicable to a bulk single crystal of SiC with a diameter greater than 200 mm perpendicular to the growth direction.

[0060] According to a twelfth aspect, in addition to any of the foregoing aspects, the crucible further includes a bottom wall, wherein the bottom wall extends perpendicular to the growth direction such that the bottom wall, together with the end wall and the side wall, encloses a cavity. This is a possible solution for enclosing the cavity.

[0061] In particular, according to a first example of the twelfth aspect, the bottom wall includes a second seed holder for holding a second SiC seed in the cavity, and the crucible includes a second diffusion region that allows a doping gas to permeate, and the second diffusion region is located between the second seed holder and a second edge of the side wall. For the description of the second seed holder, the second SiC seed, and the second diffusion region, reference is made to the description of the seed holder, the SiC seed, and the diffusion region above. This solution enables a dual-crystal design. For example, if a support is connected to the bottom wall, a gas-permeable isolation material is introduced between the support and the growth crucible such that a second doping diffusion region can also be achieved at this location. Alternatively, a perforated or porous support can be used.

[0062] Optionally, according to a second example of the twelfth aspect, the bottom wall is non-removably connected to the side wall to form a can that prevents the doping gas from permeating from the outside into the cavity. Optionally, the outer surface of the bottom wall is connected to a support for holding the crucible in the growth device, such that the support prevents the doping gas from permeating from the outside into the cavity through the bottom wall, and the outer surface faces the outside. The impermeable support obviates the need to render the bottom wall impermeable.

[0063] A thirteenth aspect relates to a growth device. The growth device includes a crucible according to any of the foregoing aspects, a reactor that forms a chamber, wherein the crucible is disposed in the chamber; and a gas inlet for supplying a doping gas to the chamber. The description of the reactor refers to the above description. The gas inlet can be, for example, a valve, a permeable membrane, etc.

[0064] Advantageously, the growth device of the thirteenth aspect further includes at least one heating element, wherein the heating element surrounds the side wall to inductively heat the side wall. The description of inductive heating refers to the above. Additionally or alternatively, the growth device further includes a gas outlet for connecting to a vacuum pump for reducing the pressure in the chamber. The description of the gas outlet refers to the description of the gas inlet. In particular, the gas outlet can be used to control the low pressure, i.e., the vacuum, in the reactor chamber. Further, through the outlet, bake out gases can be extracted, thereby reducing the contamination of the reactor.

[0065] The fourteenth aspect relates to a method for growing a bulk single crystal of SiC in a cavity by sublimation growth in a growth direction, the method comprising the following steps:

[0066] Providing at least one SiC seed in the cavity, wherein the SiC seed is arranged at an end wall, the end wall is provided with a seed holder for holding the SiC seed, and the end wall extends perpendicular to the growth direction;

[0067] Closing the cavity with a side wall extending in the growth direction, the side wall preventing doping gas from penetrating into the cavity from the outside, the doping gas being used to dope the bulk single crystal of SiC during sublimation growth; and

[0068] Doping the bulk single crystal of SiC with the doping gas, wherein the doping gas diffuses through a diffusion region, the diffusion region allowing the doping gas to penetrate into the cavity from the outside, and the diffusion region is located between the seed holder and the edge of the side wall.

[0069] For the description of the parts mentioned in the fourteenth aspect, reference is made to the description of the first to thirteenth aspects above. In particular, for example, two SiC seeds can be provided in the cavity. For the description of the two SiC seeds, reference is made to the above description.

[0070] The fifteenth aspect relates to a method, the method comprising the following steps:

[0071] Providing a crucible according to any one of the first to twelfth aspects or a growth device according to the thirteenth aspect, and

[0072] Growing a bulk single crystal of SiC by the method of the fourteenth aspect.

[0073] The present invention will now be described in more detail in an exemplary manner using advantageous aspects and with reference to the accompanying drawings. The aspects described are only possible configurations. However, in these configurations, the various features described above can be provided independently of each other or can be omitted. Description of the Drawings

[0074] 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 specification, are used to explain the principles of the present invention. The drawings are only for the purpose of showing how to manufacture and use the preferred and alternative examples of the present invention, and should not be construed as limiting the present invention to the embodiments shown and described. In addition, several aspects of the embodiments can be considered separately or in different combinations to form solutions according to the present invention. Therefore, the embodiments described below can be considered separately or in any combination thereof.

[0075] The described embodiments are merely possible configurations, and it must be remembered that the various features described above can be provided independently of each other or can be completely omitted when implementing the present invention. As shown in the accompanying drawings, further features and advantages will become apparent from the following more detailed description of various embodiments of the present invention, in which like reference numerals denote like elements, and in which:

[0076] In the drawings:

[0077] Figure 1 is a crucible having an infiltrated side wall;

[0078] Figure 2 is a crucible having a coated side wall;

[0079] Figure 3 is a crucible having a coated and infiltrated side wall;

[0080] Figure 4 is a crucible for growing more than one SiC single crystal;

[0081] Figure 5 is a crucible having fastening elements;

[0082] Figure 6 is having a sealing element Figure 5 of details;

[0083] Figure 7 is having a diffusion channel Figure 5 of details;

[0084] Figure 8 is a flow chart for growing a SiC bulk single crystal;

[0085] Figure 9 is a cross-sectional view of a crucible;

[0086] Figure 10 is a crucible arranged in a reactor Figure 9 of a cross-sectional view; and

[0087] Figure 11 is Figure 10 of the temperature profile of the reactor. Detailed Description

[0088] Now referring to the drawings and first referring to Figure 1 to describe the present invention, Figure 1 similar to the above Figure 10 . More specifically, Figure 1 shows a growth apparatus 10 having a crucible and a reactor 200 forming a chamber, wherein the crucible is arranged in the chamber.

[0089] The crucible includes a cavity for growing a bulk single crystal of SiC (not shown) in the growth direction Y by sublimation growth. The crucible includes an end wall 110 having a seed holder 112 for holding a SiC seed (not shown) in the cavity. The end wall 110 extends perpendicular to the growth direction Y. In other words, the end wall 110 extends in the radial direction R. More specifically, a SiC seed (not shown) is disposed in the crystal growth region 124 of the growth crucible. In addition, the crucible includes a side wall 140 and a bottom wall 150 that extend in the growth direction Y. The end wall 110, the side wall 140, and the bottom wall 150 enclose the cavity for growing the bulk single crystal of SiC.

[0090] The powdered SiC source material is disposed in the SiC storage region 120 of the crucible. The boundary of the SiC storage region 120 at the start of the growth process is indicated by the thick dashed line 122. As described above, during growth, by sublimation of the powdered SiC source material and by transporting the sublimated gaseous components into the crystal growth region 124, i.e., along the Y-axis, a SiC growth gas phase is generated there, and a bulk single crystal of SiC having a central longitudinal axis along the Y-axis grows by deposition from the SiC growth gas phase onto the SiC seed.

[0091] The crucible is held by a support 210 in a reactor 200. In addition, an insulator 300 surrounds the crucible. The growth apparatus further includes an induction heater 400, a gas outlet 500, and a gas inlet 600.

[0092] In addition, the end wall 110 includes a diffusion region 114 that allows doping gas to penetrate from the outside into the cavity. The diffusion region 114 is located between the seed holder 112 and the edge 142 of the side wall 140. The edge 142 of the side wall 140 abuts the end wall 110. More specifically, the diffusion region forms an annular ring around the seed holder 112. According to this example, the area of the diffusion region relative to the inner surface of the end wall 110 that faces the cavity is equal to or greater than 20% and equal to or less than 40%. According to another example, the area of the diffusion region relative to the inner surface of the end wall 110 that faces the cavity is equal to or greater than 25% and equal to or less than 35%.

[0093] Therefore, the arrangement of the diffusion region 114 at the end wall 110 improves the control of the doping amount supplied into the cavity. In particular, the heater 400 specifically heats the SiC storage region 120, which undergoes high temperature variations, while the diffusion region 114 undergoes small temperature variations during the growth cycle. Therefore, the influence caused by the temperature-dependent penetration rate of the end wall 110 can be reduced.

[0094] In addition, the sidewall 140 is designed to prevent dopant gas from penetrating from the outside into the cavity, which is used to dope the SiC bulk single crystal during sublimation growth. According to Figure 1 the example shown, the sidewall 140 includes a material for preventing the penetration of dopant gas. In particular, the sidewall 140 is infiltrated with a material for preventing the penetration of dopant gas. The material includes at least one of, for example, the following: graphite, vitreous carbon, and metal carbide having a density equal to or greater than 1.8 g / cm 3 . Advantageously, the material includes graphite having a density equal to or greater than 1.85 g / cm 3 . Additionally or alternatively, the material contains graphite having a density equal to or less than 1.95 g / cm 3 . For example, the material includes graphite having a density equal to or less than 1.95 g / cm 3 and equal to or greater than 1.8 g / cm 3 , advantageously equal to or greater than 1.85 g / cm 3 .

[0095] Figure 2 An alternative of the sidewall 140 including a material for preventing the penetration of dopant gas is shown in Figure 2 and is Figure 1 substantially the same. Figure 2 differs from Figure 1 in the sidewall 140. According to Figure 2 the example shown, the sidewall 140 may include an insulating layer 146 on the inner surface and an insulating layer 144 on the opposite outer surface. Each of the layers 144 and 146 prevents the penetration of dopant gas. The inner surface faces the cavity. For example, the layer includes at least one of the following: photoresist, graphitized sugar layer, TaC, WC, and Ta4HfC5 or other refractory metal carbides and / or combinations thereof. According to the example, the layer has a thickness equal to or greater than 0.5 μm, preferably the thickness is equal to or greater than 1 μm, and even more preferably the thickness is equal to or greater than 2 μm. As a supplement or alternative, the maximum thickness is equal to or less than 5 μm.

[0096] Figure 3 Another alternative for adjusting the Figure 1 penetration rate of the sidewall 140 is shown in Figure 3 . According to Figure 2 the example shown, the sidewall 140 including an impermeable material further includes isolation layers 144 and 146. The description of the isolation layers refers to the description of

[0097] above. Figures 1 to 3 In the example disclosed with reference to

[0098] According to the reference Figures 1 to 3 In the disclosed example, the bottom wall 150 is impermeable to the doping gas. For example, the bottom wall 150 includes a material or layer similar to the side wall 140.

[0099] Additionally or alternatively, the support 210 is made of an impermeable material. More specifically, the outer surface of the bottom wall 150 is connected to the support 210. The support holds the crucible in the growth device 10. Thus, the support 210 can prevent the doping gas from penetrating from the outside through the bottom wall 150 into the cavity.

[0100] In addition, the bottom wall 150 can be non - removably connected to the side wall 140 to form a can. The can prevents the doping gas from penetrating from the outside into the cavity. Non - removable means that the bottom wall 150 and the side wall 140 are designed such that they cannot be removed without causing damage.

[0101] Figure 4 is shown in Figures 1 to 3 an alternative of the bottom wall 150. Figure 4 is almost the same as Figure 3 Figure 4 differs from Figure 3 in that the bottom wall 151 and the SiC storage area 121. In particular, in addition to Figures 1 to 3 the first crystal growth area 124 of Figure 4 a second crystal growth area 126 is provided. The first crystal growth area 124 is arranged at the first end in the crucible along the growth direction, and the second crystal growth area 126 is arranged at the opposite second end in the crucible along the growth direction. Thus, two crystals can be grown in one cycle.

[0102] Furthermore, the bottom wall 151 includes a second seed holder 152 for holding a second (not shown) SiC seed in the cavity, and the crucible includes a second diffusion area 154 for allowing the doping gas to penetrate, and the second diffusion area is located between the second seed holder 152 and the second edge of the side wall 148. In other words, the bottom wall 151 shown in Figure 4 is similar to the end wall 110 described above in Figures 1 to 3

[0103] Another aspect of the crucible is shown in Figure 5 In particular, Figure 5 is similar to Figures 1 to 3 and additionally includes at least one fastening element 170. The fastening element 170 fastens the end wall 110 to the side wall 140. For example, the fastening element 170 is a screw. By adjusting the torque, the penetration rate of the doping gas through the contact area 172 formed between the edge 142 of the end wall 110 and the side wall 142 can be adjusted. Figure 5 The example of​​Figure 4 The example shown. In particular, the bottom wall 151 can be fastened to the side wall 140 with fastening elements.

[0104] Figure 5 Details of are in Figure 6 and Figure 7 are shown. In particular, Figure 6 shows Figure 5 a crucible of, in which an additional sealing element 180 is provided. The sealing element seals the contact area 172 between the end wall 110 and the edge of the side wall 140. Thus, the sealing element 180 reduces the penetration of doping gas through the contact area 172. Alternatively, as Figure 7 shown, a gap 190 is formed between the edge of the end wall 110 and the side wall 140. The gap allows doping gas to be transferred from the outside into the cavity. This may be advantageous when the diameter of the seed holder 113 is as large (or almost as large) as the inner diameter of the crucible. For example, the gap is equal to or greater than 0.1 mm and equal to or less than 0.5 mm.

[0105] Although not shown with reference to the above Figures 1 to 6 shown, the side wall may include a layered structure for preventing the penetration of doping gas. The layered structure includes alternating first and second layers. For example, the first layer includes graphite and the second layer includes refractory metal carbide.

[0106] In Figure 8 is described a method for growing such a bulk single crystal of SiC by sublimation growth in the growth direction. According to the method, first in step S10, a SiC seed is provided in the cavity. The SiC seed is arranged at the end wall provided with a seed holder for holding the SiC seed. The end wall extends perpendicular to the growth direction. Additionally, SiC material is provided in a storage area formed in the cavity.

[0107] Then, in step S12, the method continues with closing the cavity. In particular, a side wall extending in the growth direction surrounds the cavity. The side wall prevents doping gas from penetrating from the outside into the cavity, and the doping gas is used for doping the bulk single crystal of SiC during sublimation growth.

[0108] Then, in step S14, the method continues with growing a bulk single crystal of SiC in the cavity. During growth, doping gas is provided to dope the bulk single crystal of SiC with the doping gas. The doping gas diffuses through a diffusion area that allows the doping gas to penetrate from the outside into the cavity, and the diffusion area is located between the seed holder and the edge of the side wall.

[0109] In particular, the method for growing a bulk single crystal of SiC in the cavity in the growth direction by sublimation growth uses any of the above crucibles, such as in Figures 1 to 7 As advantageously described above Figures 1 to 7The growth apparatus described in [reference] is used to grow bulk single crystal SiC.

Claims

1. A crucible having a cavity for growing a SiC bulk single crystal by sublimation growth in a growth direction (Y), the crucible comprising: an end wall (110) having a seed holder (112) for holding a SiC seed in the cavity, the end wall (110) extending in a direction (r) perpendicular to the growth direction (Y); a side wall (140) extending in the growth direction (Y), the side wall (140) preventing a doping gas from penetrating into the cavity from the outside, the doping gas being used to dope the SiC bulk single crystal during the sublimation growth; and A diffusion region (114) allows the doping gas to penetrate from the outside into the cavity, wherein the diffusion region (114) is located between the seed holder (112) and an edge (142) of the side wall (140).

2. The crucible according to claim 1, wherein: The side wall (140) includes a material for preventing the penetration of dopant gas, wherein the material includes at least one of the following: a density equal to or greater than 1.8 g / cm 3 Graphite, glassy carbon and refractory metal carbide, optionally, wherein the material includes a density equal to or greater than 1.85g / cm 3 Graphite, and / or the material comprises a density equal to or less than 1.9 g / cm 3 of graphite.

3. The crucible according to any one of the preceding claims, wherein: The sidewall (140) includes a layer (144, 146) on at least one of an inner surface and an opposing outer surface, the layer being configured to prevent penetration of the dopant gas.

4. The crucible according to claim 3, wherein: The layer (144, 146) includes at least one of the following: a photoresist, a graphitized sugar layer, TaC, WC, and Ta4HfC5.

5. The crucible according to any one of claims 4 to 5, wherein Said layer (144, 146) has a thickness equal to or greater than 0.5 μm, preferably equal to or greater than 1 μm, even more preferably equal to or greater than 2 μm, optionally wherein the maximum thickness is equal to or less than 5 μm.

6. Crucible according to any one of the preceding claims, wherein The sidewall (140) comprises a layered structure for preventing penetration of dopant gas, the layered structure comprising alternating first and second layers, optionally wherein the first layer comprises graphite and the second layer comprises metal carbide.

7. The crucible according to any one of the preceding claims, wherein the end wall (110) comprises the diffusion zone (114), optionally wherein: The diffusion region (114) forms an annular ring around the seed holder.

8. The crucible according to claim 7, wherein: The diffusion region (114) has an area equal to or greater than 20% and equal to or less than 40% relative to the inner surface of the end wall (110), the inner surface of the end wall (110) facing the cavity. Advantageously, the diffusion region (114) has an area equal to or greater than 25% and equal to or less than 35% relative to the inner surface of the end wall (110).

9. The crucible according to any of the preceding claims, further comprising a sealing element (180) for sealing a contact area (172) between the end wall (110) and the edge (142) of the side wall (140), thereby reducing the penetration of the doping gas through the contact area (172).

10. The crucible according to any of the preceding claims, further comprising a fastening element (170) for fastening the end wall (110) to the side wall (140) so as to adjust the penetration rate of the dopant gas through the contact area (172) between the end wall (119) and the edge (142) of the side wall (140).

11. The crucible according to claim 10, wherein: During the growth of the SiC bulk single crystal, a gap (190) is formed between the end wall (110) and the edge (142) of the side wall (140), the gap (190) being used to allow doping gas to pass through, preferably wherein the gap is equal to or greater than 0.1 mm and equal to or less than 0.5 mm.

12. The crucible according to any one of the preceding claims, further comprising a bottom wall (150, 151), wherein The bottom wall (150, 151) extends in a direction (r) perpendicular to the growth direction (Y), so that the bottom wall, the end wall (110) and the side wall (140) surround the cavity together; wherein the bottom wall (151) comprises a second seed holder (152) for holding a second SiC seed crystal in the cavity, and the crucible comprises a second diffusion region (154) allowing the doping gas to penetrate, the second diffusion region (154) being located between the second seed holder (152) and a second edge (148) of the side wall (140); or wherein the bottom wall (150) is inseparably connected to the side wall (140) to form a can, which prevents the doping gas from penetrating into the cavity from the outside; optionally, wherein the outer surface of the bottom wall is connected to a bracket (210), which is used to hold the crucible in the growth device (10) and thereby prevent the doping gas from penetrating into the cavity from the outside through the bottom wall (150), and the outer surface faces outward.

13. A growing device (10), comprising: A crucible according to any one of the preceding claims; a reactor (200) forming a chamber, wherein the crucible is arranged in the chamber; and A gas inlet (600) for supplying the doping gas to the chamber; optionally, the growth device (10) further comprises at least one of a heating element (400) and a gas outlet (500), wherein the heating element surrounds the side wall (140) to inductively heat the side wall (140), and the gas outlet (500) is connected to a vacuum pump to reduce the pressure in the chamber.

14. A method of growing at least one SiC bulk single crystal in a cavity in a growth direction (Y) by sublimation growth, the method comprising the steps of: Providing a SiC seed crystal in the cavity, wherein the SiC seed crystal is arranged at an end wall (110), the end wall (110) is provided with a seed crystal holder (112) for holding the SiC seed crystal, and the end wall (110) extends in a direction (r) perpendicular to the growth direction (Y); closing the cavity with a side wall (140) extending in the growth direction (Y), the side wall (140) preventing a doping gas from penetrating into the cavity from the outside, the doping gas being used to dope the SiC bulk single crystal during the sublimation growth; and The SiC bulk single crystal is doped with the doping gas, wherein the doping gas diffuses through a diffusion region (114), the diffusion region (114) allowing the doping gas to penetrate from the outside into the cavity, the diffusion region (114) being located between the seed holder (112) and an edge (114) of the sidewall (110).

15. A method of growing at least one SiC bulk single crystal in a cavity in a growth direction by sublimation growth, the method comprising the steps of: providing a crucible according to any one of claims 1 to 12 or a growth device (10) according to claim 13, and The SiC bulk single crystal is grown according to the method of claim 14.

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