Sublimation system and method for growing at least one single crystal

Abstract

To provide a system and method for growing bulk semiconductor single crystals, more specifically, for growing bulk semiconductor single crystals such as silicon carbide based on physical gas-phase transport. [Solution] The sublimation system comprises a crucible (102) having a longitudinal axis (120) and side walls (116) extending along the longitudinal axis (120), wherein the crucible (102) comprises fixing means for at least one seed crystal (110) and at least one raw material compartment (104) for containing raw materials (108), and a heating system formed to generate a temperature field around the circumference of the crucible and along the longitudinal axis of the crucible, wherein the crucible (102) comprises at least one first thermal radiation cavity (118) located opposite the fixing means and adjacent to the raw material compartment (104), and the first thermal radiation cavity (118) is closed on all sides thereof.

Description

【Technical Field】 【0001】 The present invention relates to a system and method for growing bulk semiconductor single crystals, more specifically, for growing bulk semiconductor single crystals such as silicon carbide based on physical vapor transport. 【Background Art】 【0002】 Silicon carbide (SiC) is widely used as a semiconductor substrate material for electronic components in a wide range of applications such as power electronics, radio frequency, and light-emitting semiconductor components. 【0003】 Physical vapor transport (PVT) is generally used, especially for commercial purposes, to grow bulk SiC single crystals. SiC substrates are manufactured by cutting slices from bulk SiC crystals (e.g., using a wire saw) and finishing the slice surfaces in a series of polishing steps. The finished SiC substrates are used in the manufacture of semiconductor components in an epitaxial process or the like, where a thin single crystal layer of a suitable semiconductor material (e.g., SiC, GaN) is deposited on the SiC substrate. The properties of the deposited monolayer and the components manufactured therefrom are critically dependent on the quality and homogeneity of the underlying substrate. For this reason, the excellent physical, chemical, electrical, and optical properties of SiC make it a preferred semiconductor substrate material for power device applications. 【0004】 PVT is basically a crystal growth method involving sublimation of a suitable raw material followed by re-solidification onto a seed crystal, where single crystal formation occurs on the seed crystal. The raw material and the seed crystal are placed inside the growth structure, and the raw material is sublimated by heating. The sublimated vapor then diffuses in a controlled manner due to a temperature field having a gradient set between the raw material and the seed crystal, and deposits on the seed and grows as a single crystal. 【0005】 Conventional PVT-based growth systems generally utilize either an induction heating system or a resistance heating system to sublimate the raw materials. In both cases, the core of the PVT-based growth system is a so-called reactor. Essentially comprising a crucible and means for fixing seed crystals, the growth structure, conventionally made from graphite and carbon materials, is placed inside the reactor and heated by either an induction coil located outside the reactor or a resistance heater located outside or inside the reactor. The temperature inside the growth structure is measured by one or more pyrometers or thermocouples placed near the overture of the growth structure. The vacuum-sealed reactor is evacuated by one or more vacuum pumps and supplied with inert gas or doped gas via one or more gas supplies to create a controlled gas (gas mixture atmosphere). All process parameters (pressure, temperature, gas flow rate, etc.) can be adjusted, controlled, and stored by a computer-operated system controller, which communicates with all relevant components (e.g., inverter, pyrometer, vacuum control valve, mass flow control (MFC), and pressure gauge). 【0006】 In induction-heated PVT systems, the reactor typically includes one or more glass tubes, which are sometimes cooled with water and have flanges at both ends to seal the inside of the reactor to the atmosphere. An example of such an induction-heated PVT system is described in U.S. Patent No. 8,865,324(B2). Figure 9 shows such a conventional induction-heated PVT system 800. 【0007】 The growth mechanism 800 comprises a growth crucible 802, which includes a SiC supply region 804 and a crystal growth region 806. Powdered SiC raw material 808 is poured into the SiC supply region 804 of the growth crucible 802 as a pre-processed starting material before the start of the growth process, and is placed, for example, in the SiC supply region 804. The raw material 808 may be densified or composed of at least partially solid material in order to increase the density of the raw material 808. 【0008】 The seed crystal 810 is provided on the inner wall of the growth crucible 802, facing the SiC supply region 804, within the crystal growth region 806, for example, on the lid 812 of the crucible. The bulk SiC single crystal to be grown grows on the seed crystal 810 by deposition from the SiC growth gas phase formed within the crystal growth region 806. The growing bulk SiC single crystal and the seed crystal 810 may have approximately the same diameter. 【0009】 The growth crucible 802, including the crucible lid 812, may be manufactured from a conductive and heat-conductive graphite crucible material. A thermal insulator (not shown in the figure) is placed around it, which may include, for example, a porosity of a cellular graphite insulating material, the porosity of which is particularly higher than that of the graphite crucible material. 【0010】 A heat-insulated growth crucible 802 is placed inside a tubular container 814, which may be constructed as a quartz glass tube and form an autoclave or reactor. An induction heating device in the form of a heating coil 816 is placed around the container 814 to heat the growth crucible 802. The growth crucible 802 is heated by the heating coil 816 to a growth temperature exceeding 2000°C, particularly up to about 2200°C. The heating coil 816 inductively couples an electric current to the conductive crucible wall (so-called susceptor) of the growth crucible 802. This current flows substantially as a circulating current in the circular, hollow, cylindrical crucible wall, heating the growth crucible 802 in the process. The susceptor may be made from graphite, TaC, WC, Ta, W, or other heat-resistant metals. The primary purpose of the susceptor is to provide a heat source inside the crucible 802. When the susceptor is heated by induction, its surface reaches a high temperature, and that temperature is then transferred to the inside of the crucible 802 through conduction and / or radiation. 【0011】 As described above, the induction coil 816 is mounted on the outside of the glass tube 814 and is usually surrounded by a Faraday cage (not visible in the drawing) that forms an electromagnetic shield to block electromagnetic radiation. As shown in the example in Figure 9, the induction coil 816 may have equidistant windings. 【0012】 Furthermore, in conventional resistance-heated PVT systems, the heating resistance element is mounted inside the reactor. If the reactor is made of metal, heat-resistant metal, and / or graphite, it can be cooled with water or air. Examples of resistance-heated PVT systems are described in the published patent applications U.S. Patent Application Publication No. 2016 / 0138185(A1) and U.S. Patent Application Publication No. 2017 / 0321345(A1). 【0013】 For the growth of high-quality crystals, homogeneous heat bonding to the growth crucible in the radial direction is considered extremely important. By bonding heat as homogeneously as possible, the crystal should grow as homogeneously and symmetrically as possible. In particular, this should prevent the formation of threading screw dislocations (TSDs) and threading edge dislocations (TEDs), also known as step dislocations. Heterogeneous and asymmetrical heat distribution and the resulting heterogeneous and asymmetrical growth are advantageous for the formation of these dislocations. 【0014】 Therefore, a PVT growth system must heat the inside of the crucible in a temperature field as homogeneous as possible in the radial direction and provide a defined temperature gradient in the axial direction in order to set the driving force for the sublimated gas species to move toward the seed and growing single crystal. In known PVT systems, the reactor structure, usually made of graphite or equivalent material, is heated from the wall region to create a temperature gradient from the outside to the inside of the crucible. As a result, the conversion of the SiC raw material decreases from the outside to the inside. 【0015】 As a result, regions are created within the raw material area where the temperature is no longer sufficient for complete conversion, and only recrystallization of the raw materials occurs, thus no longer contributing to crystal growth. This effect is amplified by the transformation of the sintered SiC powder into a carbon sponge, which occurs due to the difference in partial pressure between silicon-rich and carbon-rich gas species. As the growth time increases, the carbon sponge loses its thermal conductivity and gradually begins to act as an insulator between the heater and the raw materials. To counteract this effect, the raw materials must be heated more intensely for further growth. Even then, unreacted material residue often remains. Therefore, unreacted or thermally insulated raw materials lead to a significantly reduced yield and, consequently, increased costs. 【0016】 As the crystal diameter increases, a continuous increase in reactor size and the number of crucibles introduced becomes necessary. Due to the effects described above, the effective utilization rate of the introduced raw materials decreases further as the reactor diameter increases. 【0017】 Because the partial pressures of the Si-containing gas species and the C-containing gas species are different, the chemical composition of the raw materials contributing to crystal growth changes. If the process described above means that new material is no longer available for crystal growth, the chemical composition of the gas phase also changes, which affects crystal growth and ultimately leads to a decrease in crystal quality. 【0018】 A decrease in the thermal conductivity or graphitization of the raw materials is unavoidable in the PVT method, because it is used for the economical production of SiC single crystals to produce crystals with large diameters or corresponding lengths. Reducing the negative effects of non-conversion of SiC-containing raw materials can be achieved, for example, by introducing localized heating elements. 【0019】 For example, according to Chinese Utility Model No. 210974929(U), it is known that a solid rod is inserted into the raw material storage section for this purpose. 【0020】 The insertion of this localized heating element prevents recrystallization of the raw materials at the lower end of the crucible base and increases heat conduction toward the center of the raw material storage section. As a result, a larger volume is heated more uniformly, and graphitization of the raw materials is locally reduced. In this document, heating of the crucible is made possible by induction coils. Therefore, the hottest point is at the outer edge of the crucible, and the rods inside the storage section act as an extension of the heating element by heat conduction, transporting heat axially and radially from the crucible walls toward the center of the powder storage section. 【0021】 The shape of such additional conductive heaters can vary considerably, as shown in Japanese Patent No. 6859800(B2). The types of geometric shapes shown in this document correspond to the same principles as those in Chinese Utility Model No. 210974929(U). According to Japanese Patent No. 6859800(B2), a cylinder is proposed that is open on one side and has a recess at its lower end located at least in the center of its bottom. In addition, a complementary conical component is introduced into this recess. 【0022】 According to Japanese Patent No. 6859800(B2), only the outer cylindrical wall is heated via induction heating or resistance heating, and the heat is transferred into the powder volume via an additional conical component. 【0023】 Another advantage of such a mechanism is that it allows for the removal of recrystallized raw materials from the bottom of the crucible, thereby improving the lifespan of the crucible material. 【0024】 Another known method for optimizing the reaction of raw materials is described in Japanese Patent No. 6501494(B2). In this method, a combination of two additional disc-shaped components (a heating element and a heating aid) is placed beneath a structure filled with raw materials. Since the diameter of the heating element is significantly smaller than the diameter of the heating aid, the resulting diameter difference is compensated for by installing a thermal insulating material. 【0025】 The enlarged diameter of the heating element allows the induction coil to couple more efficiently, thus heating more than the auxiliary heating element and crucible. Due to heat conduction, the heating element acts as a resistance heater, transporting heat locally to the center, thereby reducing or even preventing recrystallization of the raw materials. [Prior art documents] [Patent Documents] 【0026】 [Patent Document 1] US Patent No. 8,865,324(B2) [Patent Document 2] U.S. Patent Application Publication No. 2016 / 0138185 (A1) Specification [Patent Document 3] U.S. Patent Application Publication No. 2017 / 0321345 (A1) Specification [Patent Document 4] Chinese Utility Model Patent No. 210974929 (U) Specification [Patent Document 5] Japanese Patent No. 6859800 (B2) Specification [Patent Document 6] Japanese Patent No. 6501494 (B2) Specification [Summary of the Invention] 【0027】 The present invention has been made in view of the drawbacks and inconveniences of the prior art, and its object is to provide a system for growing a single crystal of a semiconductor material by physical vapor transport (PVT), and a method for manufacturing a single crystal of a semiconductor material with improved single crystal quality and cost-effectiveness by more efficiently using the raw materials used. 【0028】 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. 【0029】 The present invention is based on the idea that improved heating efficiency can be achieved by using not only heat conduction but also heat radiation in an additional and spatially controlled manner to heat the raw material section. 【0030】 Specifically, the basic problem of graphitization of raw materials is reduced according to the known solution described above by introducing a local heater based on the principle of heat conduction. This physical principle such as thermoelectricity is explained by Fourier's law (Equation 1), where dQ / dt is the heat power (also called heat flux), λ is the thermal conductivity, A is the area through which heat flows, d is the distance of the temperature difference, and ΔT is the temperature difference between the high-temperature surface and the low-temperature surface. 【0031】 [Number] 【0032】 The goal of the optimization described above for existing solutions is to significantly reduce the temperature difference between the walls and the center of structures that are typically made of graphite. 【0033】 In contrast, this disclosure is based on the idea of ​​circumventing the constraints of heat conduction by using thermal radiation. Radiative thermal power is described by the Stefan-Boltzmann law (Equation 2), where ε is the emissivity of the radiating surface, σ is the Stefan-Boltzmann constant, A is the surface area, and T is the (absolute) temperature of the radiator: 【0034】 【number】 【0035】 The Stefan-Boltzmann law states that the radiant power of an object in thermal equilibrium is proportional to the fourth power of its absolute temperature and directly proportional to its surface area. 【0036】 Figure 11 shows a comparison of the heat flux generated by heat conduction (curve 1001) and the heat flux generated by thermal radiation (curve 1002), both of which are functions of temperature. Mark 1003 highlights the temperature range in which crystal growth is generally carried out in the PVT process. Under the described temperature conditions, it is clear that heat transport via radiation is dominant over conduction. This is also demonstrated by the relationship of thermal power expressed in equations 1 and 2. As stated above, the thermal power due to radiation is T 4 While thermal power increases linearly, thermal power via thermal conduction increases only linearly. Therefore, especially when growing single-crystal SiC Booleans, heat transport via radiation is far more effective than heat transport via conduction, as seen in the conventional systems discussed so far, within the temperature range relevant to PVT growth. 【0037】 To benefit from thermal radiation for more efficient and radially uniform heating of the raw material compartment, this disclosure therefore proposes using at least one radiating cavity to transport heat from the outside of the crucible to the center of the raw material compartment. 【0038】 More specifically, the present disclosure provides a sublimation system for growing at least one single crystal of a semiconductor material by sublimation growth, the sublimation system comprising a crucible having a longitudinal axis and side walls extending along the longitudinal axis, the crucible comprising a fixing means for at least one seed crystal and at least one raw material compartment for containing raw materials. A heating system is formed to generate a temperature field around the circumference of the crucible and along the longitudinal axis of the crucible, the crucible comprising at least one first thermal radiation cavity located opposite the fixing means and adjacent to the raw material compartment, the first thermal radiation cavity being closed on all sides thereof. 【0039】 The inventors of this disclosure have discovered that by using cavities of a specified design, the raw material (usually powder) can be heated more uniformly in the radial direction during the growth process, thus resulting in more efficient conversion. Due to these additionally introduced cavities, more efficient heat transport occurs by radiation, which leads to heat being conducted more efficiently towards the center of the structure (axis of symmetry or longitudinal axis). This increases the surface area for heating the raw material, thereby improving the efficiency of heat transport into the raw material, which decreases during growth. 【0040】 By selectively introducing at least one cavity that allows heat transport via radiation, a significantly lower temperature difference can be achieved within the system. This allows the highest temperature, typically found in the wall areas of the crucible structure, to be transported to the center of the crucible. A major advantage of this is that the raw materials available during the growth process are used much more efficiently. This also allows the raw materials to be heated more uniformly over a larger area, thus enabling the gas phase composition to remain constant for a longer period during the growth process, thereby avoiding quality degradation caused by a changing gas phase. 【0041】 The resulting advantage is a significant increase in the mass of raw materials available for crystal growth, thus enabling an increase in the length and quality of the grown single crystals. 【0042】 These advantages can be particularly well achieved when growing SiC single crystals. However, it is clear that the sublimation growth of other semiconductor crystals can also benefit from the principles of this disclosure. 【0043】 In a favorable example, at least one first thermal radiation cavity is bounded to the raw material compartment by a separation wall formed from the same material as the crucible's sidewalls. This allows for optimal mixed heat transfer by radiation and conduction. Advantageously, this separation wall is significantly thinner than the sidewalls, thereby allowing heat radiating through the thermal radiation cavity to enter the raw material compartment more easily. More specifically, at least one first thermal radiation cavity may be bounded to the raw material compartment by a separation wall that is thinner than the crucible's sidewalls and thinner than each wall that borders the rest of the first thermal radiation cavity. 【0044】 To achieve uniform radial heat transport within the raw material compartment, the geometry of the sublimation system may be selected such that the first heat radiation cavity has an inner diameter across its longitudinal axis that is larger than the inner diameter of the raw material compartment. 【0045】 In a further advantageous example, the first thermal radiation cavity has at least one protruding section extending along its longitudinal axis into the raw material compartment. Such a protrusion allows heat to be directed closer to the center of the raw material compartment. Furthermore, the surface area of ​​the heating area is enlarged, which increases heating efficiency. 【0046】 In a further advantageous example, at least one second thermal radiation cavity is located inside the raw material compartment, and at least one second thermal radiation cavity is separate from the first thermal radiation cavity. By adding further thermal radiation cavities, additional means can be provided for more precise control of the temperature field acting on the raw materials. 【0047】 For example, at least one second thermal radiation cavity may be annular in shape, with the central axis of the annulus coinciding with the longitudinal axis of the crucible. Furthermore, such annular second thermal radiation cavity may be combined with one or more protruding sections in the first thermal radiation cavity. Alternatively, multiple annular second thermal radiation cavities may be provided at several axial positions along the longitudinal axis of the sublimation system. 【0048】 According to a further advantageous example of this disclosure, at least one second thermal radiation cavity is bounded from the raw material compartment by an inclined separation wall that includes an angle with respect to the longitudinal axis. The inclined separation wall may be formed in the shape of a funnel and directed toward the center of the raw material compartment. In this case, more heat is transferred to the surrounding area by thermal radiation. 【0049】 Different cavity heater geometry can be used to fine-tune and / or control the heat distribution within the powder chamber with greater precision. Primarily, the geometry of the crucible and insulating structure (overall structure) optimizes the temperature distribution within the crystal growth space, thereby optimizing crystal growth. Furthermore, different cavity heater geometry can optimize the transformation of the powder separated from it. In other words, new additional parameters are created, which allow for independent influence on powder transformation without affecting the temperature distribution within the crystal growth area. 【0050】 Alternatively, at least one second thermal radiation cavity may be bounded to the raw material compartment by a conical separation wall. This allows the central region of the raw material compartment to be heated more efficiently. 【0051】 In a further advantageous example of the present disclosure, a solid column is provided in the first thermal radiation cavity, penetrating the first thermal radiation cavity in a direction along its longitudinal axis. In this exemplary solution, the central region of the raw material compartment is heated less by thermal radiation and more by thermal conduction. 【0052】 According to a further advantageous example of this disclosure, the heating system comprises an induction coil and / or resistance heating coil, operable to generate an electromagnetic field, at least partially surrounding the crucible. Both heating systems create a temperature field inside the crucible. Note that a distinction must be made between the radial temperature field and the axial temperature field. The radial field must be as homogeneous as possible, especially within the region of the growing crystal. A temperature gradient is required along the longitudinal axis. The axial temperature gradient is primarily the driving force for growth, i.e., because the seed is colder than the (powdered) raw material, transport of sublimated Si and C species can occur. 【0053】 It may be shown that the best results are achieved in a sublimation system in which at least one thermal radiation cavity has a volume equal to at least 1% to a maximum of 20% of the volume of the raw material compartment, more specifically, the at least one thermal radiation cavity has a volume equal to at least 1% to a maximum of 18%, preferably a maximum of 16%, of the volume of the raw material compartment. 【0054】 This disclosure further relates to a method for growing at least one single crystal of a semiconductor material by sublimation growth, wherein this method is A crucible is prepared having a longitudinal axis and side walls extending along the longitudinal axis, at least one seed crystal is fixed to a fixing means of the crucible, and raw materials are filled into at least one raw material compartment. This includes generating a temperature field along the longitudinal axis of the crucible around the circumference of the crucible using a heating system, At least a portion of the heat of the temperature field is coupled into the raw material compartment via thermal radiation through at least one first thermal radiation cavity, the first thermal radiation cavity being located adjacent to the raw material compartment on the opposite side of the fixing means, and the thermal radiation cavity being closed on all sides. 【0055】 According to an advantageous example of this disclosure, no temperature difference exceeding 20K, preferably exceeding 15K, and more preferably exceeding 10K occurs on the opposite side of the seed crystal, extending across the longitudinal axis, which has the highest temperature within the raw material compartment. 【0056】 The accompanying drawings are incorporated herein by reference and form part of this specification to illustrate several embodiments of the present invention. These drawings, together with the description, serve to illustrate the principles of the present invention. The drawings are intended solely to illustrate preferred and alternative examples of how the present invention may be made and used, and should not be construed as limiting the present invention to the embodiments illustrated and described. Furthermore, several aspects of the embodiments may, individually or in different combinations, form solutions according to the present invention. Thus, the following detailed embodiments may be considered individually or in any combination thereof. Further features and advantages will become apparent from a more detailed description of the various embodiments of the present invention illustrated in the accompanying drawings. In the accompanying drawings, similar reference numerals refer to similar elements. [Brief explanation of the drawing] 【0057】 [Figure 1] This is a schematic cross-sectional side view of a sublimation system according to the first example. [Figure 2] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 3] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 4] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 5] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 6] Figure 5 is a schematic top view of the sublimation system. [Figure 7] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 8] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 9] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 10] This is a schematic cross-sectional side view of a known sublimation system. [Figure 11]This diagram compares heat flux via heat conduction and heat flux via thermal radiation. [Modes for carrying out the invention] 【0058】 The present invention will now be described in detail with reference to the figures, starting with Figure 1. 【0059】 Figure 1 shows a sublimation system 100 according to a first example of this disclosure. Note that the term sublimation system is intended to encompass any system for growing at least one single crystal of a semiconductor material using sublimation growth. Preferably, the term refers to a physical vapor transport (PVT) system for growing a silicon carbide (SiC) volume single crystal, as described with reference to Figure 10. Furthermore, heating systems are not shown in Figures 1 to 9 because their specific structure is not important to the subject of this disclosure. 【0060】 The sublimation system 100 includes a growth crucible 102, which includes raw material compartments, in particular a SiC supply area 104 and a crystal growth area 106. Powdered SiC raw material 108 is injected into the SiC supply area 104 of the growth crucible 102 as a pre-processed starting material before the start of the growth process, and is placed, for example, in the SiC supply area 104. The raw material 108 may be densified or composed of at least partially solid material in order to increase the density of the raw material 108. 【0061】 The seed crystal 110 is provided in the crystal growth region 106, on the inner wall of the growth crucible 102 facing the SiC supply region 104, for example, on the lid 112 of the crucible. The bulk SiC single crystal to be grown grows on the seed crystal 110 by deposition from the SiC growth gas phase formed in the crystal growth region 106. The growing bulk SiC single crystal and the seed crystal 110 may have approximately the same diameter. If the diameter of the crystal channels is larger than the diameter of the seed crystal 110, the bulk SiC single crystal may have a larger diameter than the seed crystal 110. However, the usable low-defect diameter of the grown bulk SiC single crystal is usually the same as the diameter of the seed crystal. 【0062】 The growth crucible 102, including the crucible lid 112, may be manufactured from a conductive and heat-conductive graphite crucible material. A thermal insulator (not shown in the figure) is placed around it, which may include, for example, a porosity of a cellular graphite insulating material, the porosity of which is particularly higher than that of the graphite crucible material. 【0063】 In induction heating, the thermally insulated growth crucible 102 is placed inside a tubular container (not shown in Figure 1), which may be constructed as a quartz glass tube and form an autoclave or reactor. An induction heating device in the form of a heating coil (not shown in the figure) is placed around the container to heat the growth crucible 102. The heating coil generates the required temperature field by inductively coupling an electric current within the conductive crucible wall (susceptor) of the growth crucible 102. This current flows substantially as a circulating current within the circular, hollow, cylindrical crucible wall, heating the growth crucible 102 in the process. The susceptor can be made from graphite, TaC, WC, Ta, W, or other heat-resistant metals, and may be an integral part of the crucible 102 or a separate part close to the crucible wall. The primary purpose of the susceptor is to provide a heat source inside the crucible 102. When the susceptor is heated by induction, its surface reaches a high temperature, and that temperature is then transferred to the inside of the crucible 102 through conduction and / or radiation. 【0064】 As described above, in the case of induction heating, the coil is mounted on the outside of the glass tube and is usually surrounded by a Faraday cage (not visible in Figure 1) to block electromagnetic radiation. In the case of resistance heating, the coil, or another suitable heating means such as a heating plate, is mounted inside the reactor and also in thermal insulation, and is therefore in close contact with the crucible 102. The principle of this disclosure is applicable to both heating techniques. Thus, the coil is more broadly referred to as the heating means below and encompasses both induction heating and resistance heating (or a combination thereof). 【0065】 The temperature field created inside the crucible 102 is radially symmetrical with respect to the central axis 120 and has a gradient that promotes the growth of single crystals in the direction along the central axis 120. 【0066】 As shown in Figure 1, the crucible 102 is provided with a heating base 114 in the region adjacent to the raw material compartment 104 on the opposite side of the seed crystal 110. The heating base and side walls 116 are heated by a heating means during single crystal growth. According to this disclosure, a first thermal radiation cavity 118 is located on the opposite side of the seed crystal 110, adjacent to the raw material compartment 104, and the first thermal radiation cavity 118 is closed on all sides. During operation, the first thermal radiation cavity 118 is filled with a working gas that surrounds and fills the crucible 102. Typically, this is a mixture of an inert gas and a dopant, which diffuses through the walls of the first thermal radiation cavity 118 into the inner volume of the first thermal radiation cavity 118 according to the system pressure. 【0067】 The first thermal radiation cavity 118 is separated from the raw material compartment 104 by a separation wall 122. This separation wall 122 is manufactured from the same material as the rest of the crucible 102. 【0068】 According to this disclosure, the first thermal radiation cavity 118 transports heat from the heating base 114 to the separation wall 122 via thermal radiation. Since the separation wall 122 is relatively thin, heat easily passes into the raw material compartment 104, heating the raw material 108 uniformly in the radial direction. 【0069】 A portion of the side wall 116 of the crucible 102 that borders the first heat radiation cavity 118 is formed by an annular bordering structure 124. Thus, it is possible to make the first heat radiation cavity 118 have a diameter that is different from that of the raw material compartment 104 and that crosses the longitudinal axis 120. In the illustrated example, the first heat radiation cavity 118 extends further than the raw material compartment 104 in the direction crossing the longitudinal axis. This makes it possible for the raw material 108 to be heated more efficiently across the entire diameter of the raw material compartment 104. 【0070】 Particularly effective heating of the raw material 108 can be achieved by providing a first heat radiation cavity 118 having an internal volume corresponding to at least 1% of the internal volume of the raw material compartment 104. Specifically, at least one heat radiation cavity 118 should have a volume equal to at least 1% to a maximum of 20% of the volume of the raw material compartment 104, and more specifically, at least one first heat radiation cavity 118 may have a volume equal to at least 1% to a maximum of 18%, preferably a maximum of 16%, of the volume of the raw material compartment 104. 【0071】 The raw material compartment 104 is typically separated from the crystal growth chamber by a porous membrane. Therefore, the volume of the raw material compartment 104 is geometrically defined, even by the decreasing amount of raw material. Furthermore, when using solidified powder or solid raw materials (e.g., polycrystalline or ceramic SiC), a clear boundary is provided if necessary, even without a membrane. When SiC powder is converted to graphite sponge, the original volume remains. 【0072】 Figure 2 shows another example of the sublimation system 100 according to this disclosure, having a first thermal radiation cavity 118 of a different shape. Note that the remaining features of the sublimation system 100 correspond to the features of the sublimation system 100 shown in Figure 1. 【0073】 As shown in Figure 2, the first heat radiation cavity 118 has a central protruding section 126, which extends into the raw material section 104 along the longitudinal axis 120. Such a protrusion allows heat to be directed closer to the center of the raw material section. Furthermore, the surface area of ​​the heating area is enlarged, which increases the heating efficiency. The separation wall 122 is also relatively thin in the area of ​​the protruding section 126 in order to facilitate heat transport into the raw material 108. 【0074】 Figure 3 shows another example of the sublimation system 100 according to this disclosure, in which a second thermal radiation cavity 128 is provided in addition to the first thermal radiation cavity 118. Note that the remaining features of the sublimation system 100 correspond to the features of the sublimation system 100 shown in Figure 1. 【0075】 In the example shown in Figure 3, the second thermal radiation cavity 128 extends from the side wall 116 of the crucible 102 into the inner volume of the raw material compartment 104. Along the longitudinal axis 120, the second thermal radiation cavity 128 may be positioned axially, for example, approximately in the middle of the raw material compartment 104. The second thermal radiation cavity 128, as illustrated in Figure 3, is, for example, annular in shape and has a second separation wall 130 with approximately the same thickness as the first separation wall 122. The second thermal radiation cavity 128 guides heat from the side wall 116 into the raw material 108 via thermal radiation. Thus, the second thermal radiation cavity 128 allows for a localized influence on the temperature acting on the raw material 108. 【0076】 According to a further advantageous example of this disclosure, the first thermal radiation cavity 118 may include one or more columns 132 connecting the heating base to the separation wall 122. This example is shown in Figure 4. 【0077】 As shown in Figure 4, a central column 132 is provided inside the first thermal radiation cavity 118. At the location of the column 132, heat is transported not by thermal radiation, but by heat conduction through the column 132. Thus, a localized reduction in the heat flux entering the raw material compartment 104 is achieved. 【0078】 As explained above, different geometric shapes play a role in fine-tuning the temperature within the powder, isolating it as much as possible from the temperature distribution determined by the global crucible geometry, in order to enable optimal crystal growth. Optimized powder transformation can be achieved with different geometric shapes within the growth space. 【0079】 Figures 5 and 6 show further modifications of the protruding section 126 of Figure 2 as a side view and a corresponding schematic top view. The sublimation system 100 of Figures 5 and 6 differs from that shown in Figure 2 in that, instead of only one central protruding section 126A extending into the raw material section 104, a second, exemplary annular protruding section 126B is also arranged around the central protruding section 126A. Similar to the geometry of Figure 2, the advantage of this solution can be seen in that it allows heat to be directed closer to the center of the raw material section. Furthermore, the surface area of ​​the heating area is enlarged, which increases heating efficiency. The separation wall 122 is also relatively thin in the areas of the protruding sections 126A and 126B in order to facilitate heat transport into the raw material 108. 【0080】 It is obvious that other shapes and numbers of one or more protruding sections 126 may be used if the desired heating pattern requires them. 【0081】 In either case, one or more protruding sections 126 are in direct communication with the rest of the first thermal radiation cavity 118. In other words, there is no distance or boundary wall separating the internal volume of one or more protruding sections 126 from the remaining internal volume of the first thermal radiation cavity 118. 【0082】 In contrast, the second thermal radiation cavity 128 shown in Figure 3 has an internal volume separated from the internal volume of the first thermal radiation cavity 118. Figure 7 shows a modified example of the second thermal radiation cavity 128. In this example, the second thermal radiation cavity 128 is annular in shape and has a separation wall inclined toward the raw material compartment. The second thermal radiation cavity 128 is formed by introducing a funnel-shaped second separation wall 130 (basically forming a frustocone) into the bottom region of the raw material compartment 104. The second thermal radiation cavity 128 is located adjacent to the first thermal radiation cavity 118, and the two cavities are separated from each other by a portion of the first separation wall 122. 【0083】 This arrangement has the advantage of allowing heat to be directed more efficiently into the raw material 108. In detail, the surrounding bottom region of the raw material compartment 104 can be heated by benefiting from thermal radiation. 【0084】 As explained above, different geometric shapes play a role in fine-tuning the temperature within the powder, isolating it as much as possible from the temperature distribution determined by the global crucible geometry, in order to enable optimal crystal growth. Optimized powder transformation can be achieved with different geometric shapes within the growth space. 【0085】 To improve the radiation mechanism in the middle of the raw material compartment 104 and, in addition, to reduce the amount of raw material placed in the central region of the raw material compartment, the second thermal radiation cavity 128 may be bounded by a conical second separation wall 130. An example of this is shown in Figure 8. 【0086】 As explained above, different geometric shapes play a role in fine-tuning the temperature within the powder, isolating it as much as possible from the temperature distribution determined by the global crucible geometry, in order to enable optimal crystal growth. Optimized powder transformation can be achieved with different geometric shapes within the growth space. 【0087】 In all the examples shown in Figures 1 to 8, the first thermal radiation cavity 118 is always shown to have an inner diameter larger than the inner diameter of the raw material compartment 104. In contrast, Figure 9 shows an example of a sublimation system 100, where the inner diameter of the first thermal radiation cavity 118 is smaller than the inner diameter of the raw material compartment 104. 【0088】 Therefore, the heat flux entering the central region of the raw material compartment 104 is higher than that entering the surrounding region of the raw material compartment 104, and the heat flux is provided through the annular boundary structure 124 via heat conduction. 【0089】 In summary, this disclosure is based on the idea of ​​using hollow cavities at various locations in the region opposite the seed crystal 110 in order to guide the heat flux into the raw material compartment 104 in a more defined and efficient manner. 【0090】 By selectively introducing cavities that enable heat transport via radiation, significantly lower temperature differences can be achieved within the system. Specifically, at least one cavity exists on at least one side of each diffusion-determining surface of the raw material, facing away from the crystal, in order to locally influence the temperature distribution in the raw material. 【0091】 This allows the highest temperatures, typically concentrated in the wall area of ​​the crucible, to be transported to the center of the structure. A major advantage of this is that the raw materials available during the growth process are used much more efficiently. This also allows the raw materials to be heated more uniformly over a larger area, enabling a more consistent gas phase composition for longer periods during growth, thereby avoiding quality degradation caused by changing gas phases. 【0092】 The resulting advantage is a significant increase in the mass of raw materials that can be effectively used for crystal growth, thus enabling increases in length and quality. 【0093】 Furthermore, please note that you may arbitrarily combine some or any part of the exemplary structures described above, as shown in Figures 1 to 9. [Explanation of symbols] 【0094】 100 Sublimation System, PVT System 102 Crucible 104 SiC supply area, raw material section 106 Crystal growth region 108 Ingredients 110 seed crystals 112 Crucible Lid 114 Heating base 116 Side walls of the crucible 118 The first thermal radiation cavity 120 center axis 122 (First) Separation Wall 124 Circular boundary structure 126, 126A, 126B Protruding section 128 Second thermal radiation cavity 130 Second separation wall 132 pillars 800 PVT system 802 Crucible 804 SiC supply area 806 Crystal growth region 808 Ingredients 810 seed crystals 812 Crucible Lid 814 Containers, reactors 816 Induction heating coil 1001 Heat flux via conduction 1002 Heat flux via radiation 1003 Temperature range associated with SiC growth

Claims

[Claim 1] A sublimation system for growing at least one single crystal of a semiconductor material by sublimation growth, wherein the sublimation system (100) is A crucible (102) having a longitudinal axis (120) and a side wall (116) extending along the longitudinal axis (120), wherein the crucible (102) comprises a fixing means for at least one seed crystal (110) and at least one raw material compartment (104) for containing raw materials (108), The system comprises a heating system formed around the circumference of the crucible to generate a temperature field along the longitudinal axis of the crucible, A sublimation system wherein the crucible (102) comprises at least one first thermal radiation cavity (118) located on the opposite side of the fixing means and adjacent to the raw material compartment (104), the first thermal radiation cavity (118) being closed on all sides. [Claim 2] The sublimation system according to claim 1, wherein the at least one first thermal radiation cavity (118) is bounded from the raw material compartment (104) by a first separation wall (122) formed from the same material as the side wall (116) of the crucible (102). [Claim 3] The sublimation system according to claim 1 or 2, wherein the first thermal radiation cavity (118) has an inner diameter across the longitudinal axis (120) that is larger than the inner diameter of the raw material compartment. [Claim 4] The sublimation system according to any one of claims 1 to 3, wherein the at least one first thermal radiation cavity (118) is bounded with respect to the raw material compartment (104) by a first separation wall (122) that is thinner than the side wall (116) of the crucible (102) and thinner than each wall (124, 114) that borders the remaining side of the first thermal radiation cavity (118). [Claim 5] The sublimation system according to any one of claims 1 to 4, wherein the first thermal radiation cavity (118) has at least one protruding section (126) extending into the raw material section (104) along the longitudinal axis (120). [Claim 6] The sublimation system according to any one of claims 1 to 5, wherein at least one second thermal radiation cavity (128) is located inside the raw material compartment (104), and the at least one second thermal radiation cavity (128) is separate from the first thermal radiation cavity (118). [Claim 7] The sublimation system according to claim 6, wherein the at least one second thermal radiation cavity (128) is annular in shape, and the central axis of the annular coincides with the longitudinal axis of the crucible. [Claim 8] The sublimation system according to claim 6 or 7, wherein the at least one second thermal radiation cavity (128) is bounded from the raw material compartment (104) by an inclined separation wall (130) that includes an angle with respect to the longitudinal axis (120). [Claim 9] The sublimation system according to claim 8, wherein the at least one second thermal radiation cavity (128) is bounded to the raw material compartment (104) by a cone-shaped separation wall (130). [Claim 10] The sublimation system according to any one of claims 1 to 9, wherein a solid column (132) is provided in the first thermal radiation cavity (118) in a direction along the longitudinal axis (120) and penetrates the first thermal radiation cavity (118). [Claim 11] The sublimation system according to any one of claims 1 to 10, wherein the heating system comprises an induction coil and / or a resistance heater operable to generate an electromagnetic field, at least partially surrounding the crucible (102). [Claim 12] The sublimation system according to any one of claims 1 to 11, wherein the at least one first thermal radiation cavity (118) has an internal volume equal to at least 1% to a maximum of 20% of the volume of the raw material compartment. [Claim 13] The sublimation system according to claim 12, wherein the at least one first thermal radiation cavity (118) has an internal volume equal to at least 1% to a maximum of 18%, preferably a maximum of 16%, of the volume of the raw material compartment. [Claim 14] A method for growing at least one single crystal of a semiconductor material by sublimation growth, A crucible (102) is prepared having a longitudinal axis (120) and a side wall (116) extending along the longitudinal axis (120), at least one seed crystal (110) is fixed to a fixing means of the crucible (102), and at least one raw material compartment (104) is filled with raw material (108), This includes generating a temperature field around the circumference of the crucible (102) along the longitudinal axis (120) of the crucible (102) using a heating system, A method wherein the heat of the temperature field is combined into the raw material compartment via thermal radiation through at least one first thermal radiation cavity (118), the first thermal radiation cavity (118) is located on the opposite side of the fixing means and adjacent to the raw material compartment (104), and the thermal radiation cavity (118) is closed on all sides thereof. [Claim 15] The method according to claim 12, wherein no temperature difference exceeding 20K, preferably exceeding 15K, more preferably exceeding 10K occurs on the opposite side of the seed crystal (110) that extends across the longitudinal axis (120) and has the highest temperature within the raw material section.

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