Sublimation system and method of growing at least one single crystal

Abstract

The present invention relates to a system and method for growing a bulk semiconductor single crystal, more specifically, based on physical vapor transport, for growing a bulk semiconductor single crystal, such as silicon carbide. The sublimation system comprises a crucible (102) having a longitudinal axis (120) and a side wall (116) extending along the longitudinal axis (120); the crucible comprises a fixing means for at least one seed crystal (110) and at least one raw material compartment (104) for receiving raw material (108); and a heating system formed to generate a temperature field around the circumference of the crucible along the longitudinal axis of the crucible, wherein the crucible (102) comprises at least one first thermal radiation cavity (118) arranged opposite the fixing means and adjacent to the raw material compartment (104), and the sides of the first thermal radiation cavity (118) are all closed.

Description

Technology 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 Technology

[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 for the growth of bulk SiC single crystals, particularly for commercial purposes. SiC substrates are produced by cutting pieces from bulk SiC crystals (e.g., using wire saws) and finishing the surface of the pieces through a series of polishing steps. The finished SiC substrates are used in the manufacture of semiconductor components, such as in epitaxial processes, where a thin single-crystal layer of a suitable semiconductor material (e.g., SiC, GaN) is deposited onto the SiC substrate. The properties of the deposited monolayer and the components produced therefrom depend critically on the quality and homogeneity of the base substrate. For this reason, the excellent physical, chemical, electrical, and optical properties of SiC make it the preferred semiconductor substrate material for power device applications.

[0004] PVT is essentially a crystal growth method involving the sublimation of a suitable source material and re-condensation in a seed crystal where the formation of a single crystal occurs. The source material and the seed crystal are placed inside a growth structure, and the source material is sublimated by heating. Then, the sublimated vapor diffuses in a controlled manner due to a temperature field having a gradient set between the source material and the seed crystal, precipitates into the seed phase, and grows as a single crystal.

[0005] Conventional PVT-based growth systems generally utilize induction or resistance heating systems to sublimate raw materials. In both cases, the core of the PVT-based growth system is the so-called reactor. A growth structure, which essentially includes a crucible and a fixing means for seed crystals and is traditionally made of graphite and carbon materials, is placed inside the reactor and heated by induction coils arranged outside the reactor or by resistance heaters arranged outside or inside the reactor. The temperature within the growth structure is measured by one or more pyrometers or one or more thermocouples installed near the top of the growth structure. The vacuum-sealed reactor is evacuated by one or more vacuum pumps, and an inert or doping gas is supplied through one or more gas supplies to create a controlled gas (gas-mixed atmosphere). All process parameters (pressure, temperature, gas flow, etc.) can be adjusted, controlled, and stored by a computer-operated system controller that communicates with all relevant components (e.g., inverter, pyrometer, vacuum control valve, mass flow control (MFC), and pressure gauge).

[0006] In the case of an induction heating PVT system, the reactor typically comprises one or more glass tubes that are optionally cooled with water and provided with flanges at both ends to seal the interior of the reactor against the atmosphere. An example of such an induction heating PVT system is described in patent US 8,865,324 B2. FIG. 9 illustrates such a conventional induction heating PVT system (800).

[0007] The growth array (800) includes a growth crucible (802) comprising a SiC supply area (804) and a crystal growth area (806). For example, powdered SiC raw material (808), which is injected as a pre-finished starting material into the SiC supply area (804) of the growth crucible (802) before the start of the growth process, is located within the SiC supply area (804). The raw material (808) may also be densified or at least partially composed of a solid material to improve the density of the raw material (808).

[0008] A seed crystal (810) is provided on the inner wall facing the SiC supply area (804) of the growth crucible (802) on the crucible lid (812) within the crystal growth region (806). The bulk SiC single crystal to be grown is grown on the seed crystal (810) by being deposited from the SiC growth gas phase formed within the crystal growth region (806). The bulk SiC single crystal and the seed crystal (810) to be grown may have approximately the same diameter.

[0009] A growth crucible (802) including a crucible lid (812) may be fabricated from an electrically and thermally conductive graphite crucible material. An insulating material (not shown in the drawing) is arranged around it, which may include, for example, a foam-like graphite insulating material, and its porosity is particularly higher than that of the graphite crucible material.

[0010] An insulating growth crucible (802) may be constructed of a quartz glass tube and placed inside a tubular vessel (814) that forms an autoclave or reactor. An induction heating device in the form of a heating coil (816) is arranged around the vessel (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, specifically about 2200°C. The heating coil (816) inductively couples current into the electrically conductive crucible wall (so-called susceptor) of the growth crucible (802). This current flows as a circulating current in a peripheral direction within the substantially circular and hollow cylindrical crucible wall and heats the growth crucible (802) within the process. The susceptor may be made of graphite, TaC, WC, Ta, W, or other refractory metals. The primary purpose of the susceptor is to provide a heat source inside the crucible (802). When the susceptor is heated by induction, the surface of the susceptor reaches a high temperature, and that temperature is transferred into the interior of the crucible (802) through conduction and / or radiation.

[0011] As mentioned above, the induction coil (816) is mounted outside the glass tube (814) and is surrounded by a Faraday cage (not shown in the drawing) that forms an electromagnetic shield to shield electromagnetic radiation. As illustrated in the example of FIG. 9, the induction coil (816) can be wound with equidistant windings.

[0012] In addition, in conventional resistance heating PVT systems, a heating resistance element is mounted inside the reactor. If the reactor is made of metal, refractory metal and / or graphite, it can be cooled by water or air. Examples of resistance heating PVT systems are described in published patent applications US 2016 / 0138185 A1 and US 2017 / 0321345 A1.

[0013] For the growth of high-quality crystals, uniform radial coupling of heat into the growth crucible is considered very important. By coupling heat as uniformly as possible, the crystals must also grow as uniformly and symmetrically as possible. Above all, this must prevent the formation of threading screw dislocations (TSDs) and threading edge dislocations (TEDs), also known as step dislocations, which are favored by non-uniform, asymmetric heat distribution and associated non-uniform, asymmetric growth.

[0014] Ultimately, to establish the driving force for the sublimated gas seed to move to the growing single crystal, the PVT growth system must heat the interior of the crucible with a temperature field that is as uniform as possible in the radial direction and provide a temperature gradient defined in the axial direction. In conventional PVT systems, the reactor structure, usually made of graphite or similar material, is heated from the wall region, creating a temperature gradient from the outside to the inside of the crucible. Consequently, the conversion of the SiC raw material decreases from the outside to the inside.

[0015] Consequently, regions are created within the raw material compartment where the temperature is no longer sufficient for complete conversion and only recrystallization of the raw material occurs, no longer contributing to crystal growth. This effect is amplified by the conversion of sintered SiC powder into the carbon sponge due to the different partial pressures of silicon and carbon-rich gas species. As growth time increases, the carbon sponge reduces its thermal conductivity and increasingly acts as an insulator between the heater and the raw material. To counteract this effect, the raw material must be heated more intensely for further growth. Nevertheless, residues of unreacted material often remain. Therefore, unreacted or thermally isolated raw material significantly reduces yield and increases costs.

[0016] As the crystal diameter increases, a continuous increase in the reactor size and the crucible introduced is also required. Due to the effects described above, the effective utilization of the introduced raw material is further reduced due to the increased diameter of the reactor.

[0017] Due to different partial pressures of gas species containing Si and C, the chemical composition of the raw material contributing to crystal growth changes. If the process described above means that the new material can no longer be used for crystal growth, the chemical composition of the gas phase also changes, affecting crystal growth and thus leading to a loss of crystal quality.

[0018] Since this is used for the economical production of SiC single crystals to produce crystals with large diameters or corresponding lengths, a reduction in thermal conductivity or graphitization of the raw material is inevitable in the PVT process. The reduction of the negative effects of non-conversion of SiC-containing raw materials can be achieved, for example, by introducing local heating elements.

[0019] For example, Chinese Utility Model CN210974929U describes inserting a solid rod inside a raw material storage container for this purpose.

[0020] The insertion of this local heating element is intended to prevent recrystallization of the raw material at the bottom of the crucible and to increase heat conduction toward the center of the raw material reservoir. As a result, a larger volume is heated uniformly, and the graphitization of the raw material is locally reduced. In this document, the crucible can be heated by an induction coil. Thus, the hottest point is at the outer edge of the crucible, and the rod inside the reservoir acts as an extension of the heating element by heat conduction, transferring heat axially and radially from the walls of the crucible to the center of the powder reservoir.

[0021] As illustrated in Japanese Patent Specification JP6859800B2, the form of such additional conductive heaters may also vary. The geometric variation illustrated in this document corresponds to the same principle as Chinese Utility Model CN210974929U. According to JP6859800B2, a cylinder with one side open is proposed, having a recess at the bottom located within the central part of the bottom. Additionally, a complementary conical component is introduced into this recess.

[0022] According to patent specification JP6859800B2, only the outer cylinder wall is heated via induction or resistance heating, and the heat is conducted into the powder volume through an additional conical component.

[0023] Another advantage of this setup is the possibility of increasing the lifespan of the crucible material by removing the recrystallized raw material at the bottom of the crucible.

[0024] Another known approach for optimizing the reaction of raw materials is described in Japanese Patent JP6501494B2. In this case, a combination of two additional disc-shaped components (a heating element and a heating aid) is placed under a structure filled with raw materials. Since the diameter of the heating element is significantly smaller than that of the heating aid, the resulting difference in diameter is compensated for by installing an insulating material.

[0025] Due to the large diameter of the heating element, the induction coil can be combined more efficiently and thus can be heated more than the auxiliary heating element and the crucible. Due to heat conduction, the heating element thus acts as a resistance heater, transferring the temperature locally to the center and thus reducing or even preventing recrystallization of the raw material. The problem to be solved

[0026] The present invention was created in consideration of the shortcomings and disadvantages of the prior art, and aims to provide a system for growing single crystals of semiconductor materials using a physical vapor transport (PVT) method, and a method for improving single crystal quality and manufacturing in a cost-effective manner by utilizing the raw materials used more efficiently. means of solving the problem

[0027] This objective is addressed by the subject of the independent claim. Advantageous embodiments of the present invention are the subject of the dependent claim.

[0028] The present invention is based on the idea that improved heating efficiency can be achieved by using thermal radiation to heat raw material compartments in an additional and spatially controlled manner, in addition to thermal conduction.

[0029] In particular, the fundamental problem of graphitization of raw materials is reduced according to the aforementioned known solution by introducing a local heater based on the principle of heat conduction. This physical principle of heat conduction is explained by Fourier's law (Equation 1), where dQ / dt is heat quantity (also called heat power or heat flux), ε 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 hotter surface and the colder surface.

[0030] (1)

[0031] The objective of the optimization described above for the existing solution is to significantly reduce the temperature difference between the walls and the center of the structure made of ordinary graphite.

[0032] In contrast, the present disclosure is based on the idea of ​​circumventing the limitations of heat conduction by utilizing thermal radiation. The radiated heat quantity is described by the Stefan-Boltzmann law (Equation 2). Here, 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 radiating body.

[0033] (2)

[0034] The Stefan-Boltzmann law states that the amount of radiation emitted by an object in thermal equilibrium is proportional to the fourth power of its absolute temperature and directly proportional to its surface area.

[0035] FIG. 11 illustrates a comparison of the heat flux generated by thermal conduction (curve 1001) and thermal radiation (curve 1002) as a function of temperature. Along with indication (1003), the temperature range in which crystal growth is typically performed in the PVT process is highlighted. In the described temperature regime, it is evident that heat transfer via radiation is dominant over conduction. This is also explained by the relationship of heat quantities described in Equations 1 and 2. As mentioned, the heat quantity through radiation While heat increases with [variable], heat through thermal conduction increases only linearly. Therefore, as in the prior art systems considered so far, it can be seen that heat transfer through radiation instead of conduction is much more effective in the temperature range associated with PVT growth, especially when growing single-crystal SiC bowls.

[0036] In order to benefit from heat radiation for heating raw material compartments more efficiently and more uniformly in a radial direction, the present disclosure therefore proposes using at least one radiating cavity to transfer heat from the outside of the crucible to the center of the raw material compartment.

[0037] In particular, the present disclosure provides a sublimation system for growing at least one single crystal of a semiconductor material by a sublimation growth process, wherein the sublimation system comprises a crucible having a longitudinal axis and a sidewall extending along the longitudinal axis, and the crucible comprises fixing means for at least one seed crystal and at least one source material compartment for receiving a source material. A heating system is formed to generate a temperature field around the circumference of the crucible along the longitudinal axis of the crucible, and the crucible comprises at least one first heat radiation cavity arranged opposite the fixing means and adjacent to the source material compartment, wherein the sides of the first heat radiation cavity are all closed.

[0038] The inventors of the present invention have discovered that by using cavities with a defined design, raw materials (usually powders) can be heated more uniformly when viewed radially during the growth process, thereby resulting in more efficient transformation. Due to the additionally introduced cavities, more efficient heat transfer by radiation occurs, which leads to the fact that heat can be transferred more efficiently to the center of the structure (axis of symmetry or longitudinal axis). This increases the surface area for heating the raw materials and increases the efficiency of heat transfer into the raw materials, which decreases during growth.

[0039] By selectively introducing at least one cavity that enables heat transfer via radiation, the temperature difference of the system can be significantly reduced. This enables the transfer of the hottest temperature within the wall region of the introduced crucible structure to the center of the crucible. A significant advantage of this is that the raw materials available during the growth process can be utilized much more efficiently. This also enables the gaseous phase composition to be maintained constant for a longer period during the growth process because the raw materials can be heated more uniformly over a wider area, thereby preventing quality loss due to changes in the gaseous phase.

[0040] The resulting advantage is that the mass of raw material available for effective crystal growth increases significantly, and consequently, the length and quality of the grown single crystal can be increased.

[0041] These advantages can be particularly well utilized for the growth of SiC single crystals. However, it is clear that the sublimation growth of other semiconductor crystals can also benefit from the principles according to the present disclosure.

[0042] According to 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 sidewall of the crucible. This allows for optimal mixed heat transfer by radiation and conduction. Advantageously, this separation wall is significantly thinner than the sidewall, so that heat emitted through the thermal radiation cavity can more easily enter the raw material compartment. In particular, at least one first thermal radiation cavity may be bounded to the raw material compartment by a separation wall that is thinner than the sidewall of the crucible and thinner than the wall defining the boundary of the remaining side of the first thermal radiation cavity.

[0043] To achieve radially uniform heat transfer into the raw material compartment, the geometry of the sublimation system can be selected such that the first heat radiation cavity has an inner diameter across the longitudinal axis that is larger than the inner diameter of the raw material compartment.

[0044] According to an additional advantageous example, the first thermal radiation cavity has at least one protruding section extending into the raw material section along the longitudinal axis. This protrusion allows heat to be directed closer to the center of the raw material section. In addition, the heating area is widened, increasing heating efficiency.

[0045] According to a further advantageous example, at least one second thermal radiation cavity is arranged within the raw material compartment, and at least one second thermal radiation cavity is separated from the first thermal radiation cavity. By adding additional thermal radiation cavities, additional means for much more precisely tailoring the temperature field acting on the raw material may be provided.

[0046] For example, at least one second thermal radiation cavity may be ring-shaped, having a central axis of the ring that coincides with the longitudinal axis of the crucible. Additionally, this ring-shaped second thermal radiation cavity may be combined with one or more protruding sections in the first thermal radiation cavity. Furthermore, multiple ring-shaped second thermal radiation cavities may be provided at multiple axial positions along the longitudinal axis of the sublimation system.

[0047] According to an additional favorable example, at least one second thermal radiation cavity is bounded for the raw material compartment by a slanted partition wall that includes an angle with respect to the longitudinal axis. The slanted partition wall may also be formed in the shape of a funnel toward the center of the raw material compartment. In this case, more heat is transferred to the surrounding area by thermal radiation.

[0048] Different geometric shapes of the cavity heater are used for fine adjustment and / or fine control of the heat distribution within the powder chamber. Primarily, the geometry and insulation structure of the crucible (overall structure) serve to optimize the temperature distribution within the crystal growth space, and thus optimize crystal growth. Then, different shapes of the cavity heater can be separated from this to optimize powder conversion. That is, new additional parameters are created that can exert a separate influence on powder conversion without affecting the temperature distribution within the crystal growth region.

[0049] Alternatively, at least one second thermal radiation cavity may be bounded to the raw material compartment by a conical separating wall. Thus, the central region of the raw material compartment is heated more efficiently.

[0050] According to a further advantageous example of the present disclosure, the first thermal radiation cavity is provided with a rigid column protruding along the longitudinal axis of the first thermal radiation cavity. By this exemplary solution, the central region of the raw material compartment is heated less by thermal radiation and more by heat conduction.

[0051] According to a further advantageous example of the present disclosure, the heating system comprises an induction coil and / or a resistance heating coil operable to generate an electromagnetic field that at least partially surrounds the crucible. Both heating systems generate a temperature field inside the crucible. It should be noted that there must be a distinction between the radial and axial temperature fields. In particular, the radial field within the region of the growing crystal should be as uniform as possible. Along the longitudinal axis, a temperature gradient is required. The axial temperature gradient is primarily the driving force of growth. Since the seed is colder than the (powder) source, the transfer of sublimated Si and C species may occur.

[0052] More specifically, it can be seen that the best results were achieved with a sublimation system having an internal volume equal to at least 1% to a maximum of 20% of the volume of the raw material compartment, and at least one thermal radiation cavity has a volume of 1% or more and 18% or less of the volume of the raw material compartment, preferably 16% or less.

[0053] The present disclosure relates to a method for growing at least one single crystal of a semiconductor material by a sublimation growth process. The method comprises the following:

[0054] A step of providing a crucible having a longitudinal axis and a side wall extending along the longitudinal axis, fixing at least one seed crystal to a fixing means of the crucible, and filling raw material into at least one raw material compartment;

[0055] A step of generating a temperature field around the circumference of the crucible and along the longitudinal axis of the crucible by a heating system;

[0056] At least a portion of the heat from the temperature field is combined into the raw material compartment through heat radiation via at least one first heat radiation cavity arranged opposite the fixing means and adjacent to the raw material compartment, and the sides of the heat radiation cavity are all closed.

[0057] According to a further advantageous example of the present disclosure, in a plane facing a seed crystal that extends across the longitudinal axis and has a maximum temperature within the raw material compartment, a temperature difference exceeding 20K does not occur, preferably a temperature difference exceeding 15K does not occur, and more preferably a temperature difference exceeding 10K does not occur. Effects of the invention

[0058] Included within this specification. Brief explanation of the drawing

[0059] The attached drawings are included in this specification and constitute part of the specification for describing various embodiments of the present invention. Together with the description, these drawings serve to explain the principles of the present invention. The drawings are intended only to illustrate preferred and alternative examples of how the present invention can be made and used, and should not be interpreted as limiting the present invention to the embodiments merely exemplifying and describing it. Furthermore, various aspects of the embodiments may form a solution according to the present invention (individually or in different combinations). Accordingly, the embodiments described below may be considered alone or in any combination thereof. Additional features and benefits will become apparent from the following more specific description of various embodiments of the present invention, as illustrated in the attached drawings, where similar reference numerals refer to similar elements. FIG. 1 is a schematic cross-sectional view of a sublimation system according to the first example. FIG. 2 is a schematic cross-sectional view of a sublimation system according to an additional example. FIG. 3 is a schematic cross-sectional view of a sublimation system according to an additional example. FIG. 4 is a schematic cross-sectional view of a sublimation system according to an additional example. FIG. 5 is a schematic cross-sectional view of a sublimation system according to an additional example. Figure 6 is a schematic plan view of a sublimation system according to Figure 5. FIG. 7 is a schematic cross-sectional view of a sublimation system according to an additional example. FIG. 8 is a schematic cross-sectional view of a sublimation system according to an additional example. FIG. 9 is a schematic cross-sectional view of a sublimation system according to an additional example. FIG. 10 is a schematic cross-sectional view of a known sublimation system. Figure 11 is a comparison of heat flux through heat conduction with heat flux through heat radiation. Specific details for implementing the invention

[0060] Now, the present invention will be described in more detail with reference to the drawings, and first with reference to FIG. 1.

[0061] FIG. 1 illustrates a sublimation system (100) according to a first example of the present invention. It should be noted that the term "sublimation system" is intended to encompass any system for growing at least one single crystal of a semiconductor material by a sublimation growth process. 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 FIG. 10. Additionally, since the specific structure of the heating system is not important to the gist of the present disclosure, the heating system is not illustrated in FIG. 1 through 9.

[0062] The sublimation system (100) includes a growth crucible (102) comprising a raw material compartment, in particular a SiC supply area (104) and a crystal growth area (106). Within the SiC supply area (104), powdered SiC raw material (108) is positioned, for example, into the SiC supply area (104) of the growth crucible (102) as a pre-finished starting material before the start of the growth process. The raw material (108) may also be densified or at least partially composed of a solid material to improve the density of the raw material (108).

[0063] Within the crystal growth region (106), a seed crystal (110) is provided on the inner wall facing the SiC supply region (104) of the growth crucible (102), for example, on the crucible lid (112). The bulk SiC single crystal to be grown is grown on the seed crystal (110) by being deposited from the SiC growth gas phase formed within 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 channel is larger than that of the seed crystal (110), the bulk SiC single crystal may also have a larger diameter than that of the seed crystal (110). However, the usable low-defect diameter of the grown bulk SiC single crystal is usually the same size as the diameter of the seed crystal.

[0064] A growth crucible (102) including a crucible lid (112) may be fabricated from an electrically and thermally conductive graphite crucible material. An insulating material (not shown in the drawing) is arranged around it, which may include, for example, a foamed graphite insulating material, and its porosity is particularly higher than that of the graphite crucible material.

[0065] In the case of induction heating, the insulating growth crucible (102) may be composed of a quartz glass tube and is placed inside a tubular vessel (not shown in FIG. 1) that forms an autoclave or reactor. An induction heating device in the form of a heating coil (not shown in the drawing) is arranged around the vessel to heat the growth crucible (102). The heating coil (116) generates the necessary temperature field by inductively coupling an electric current into the electrically conductive crucible wall (susceptor) of the growth crucible (102). This current flows substantially as a circulating current in the peripheral direction within the circular and hollow cylindrical crucible wall and heats the growth crucible (102) in the process. The susceptor may be made of graphite, TaC, WC, Ta, W, or other refractory 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, the surface of the susceptor reaches a high temperature, and that temperature is transferred into the interior of the crucible (102) through conduction and / or radiation.

[0066] As mentioned above, in the case of induction heating, the coil is mounted outside the glass tube and is usually surrounded by a Faraday cage (not shown in FIG. 1) to shield electromagnetic radiation. In the case of resistance heating, other suitable heating means, such as a coil or a heating plate, are mounted inside the reactor and within the insulation, in close contact with the crucible (102). The principles of the present disclosure are applicable to both heating technologies. Accordingly, the coil will be referred to more generally as a heating means and will include (encompass) resistance heating (or a combination thereof) as well as induction heating.

[0067] The temperature field generated inside the crucible (102) is radially symmetric about the central axis (120) and has a gradient that induces the growth of a single crystal in a direction along the central axis (120).

[0068] As illustrated in FIG. 1, within an area facing the seed crystal (110) and adjacent to the raw material compartment (104), the crucible (102) includes a heating base (114). The heating base and sidewalls (116) are heated by a heating means during the growth of a single crystal. According to the present disclosure, a first thermal radiation cavity (118) is arranged facing the seed crystal (110) means and adjacent to the raw material compartment (104), and the sides of the first thermal radiation cavity (118) are all closed. 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 into the internal volume of the first thermal radiation cavity (118) through the walls of the first thermal radiation cavity (118) according to the system pressure.

[0069] The first heat radiation cavity (118) is separated from the raw material compartment (104) by a separating wall (122). This separating wall (122) is made of the same material as the rest of the crucible (102).

[0070] According to the present disclosure, the first heat radiation cavity (118) transfers heat toward the separation wall (122) through heat radiation from the heating base (114). Since the separation wall (122) is relatively thin, heat is easily transferred into the raw material compartment (104) and heats the raw material (108) in a radially uniform manner.

[0071] A portion of the side wall (116) of the crucible (102) defining the boundary of the first heat radiation cavity (118) is formed by a ring-shaped boundary-defining structure (124). Thus, it can be achieved that the first heat radiation cavity (118) may have a different diameter from the raw material section (104) across the longitudinal axis (120). In the illustrated example, the first heat radiation cavity (118) extends further across the longitudinal axis than the raw material section (104). This allows the raw material (108) to be heated more efficiently over the entire diameter of the raw material section (104).

[0072] It can be seen that particularly efficient heating of the raw material (108) can be achieved when 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) is provided. Specifically, at least one heat radiation cavity (118) should have a volume equal to at least 1% and up to 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 up to 18%, preferably up to 16%, of the volume of the raw material compartment (104).

[0073] The raw material compartment (104) is typically separated from the crystal growth chamber by a porous membrane. Thus, the volume of the raw material compartment (104) is geometrically defined even when the raw material is depleted. Additionally, when using solidified powder or solid raw material (e.g., polycrystalline or ceramic SiC), sharp demarcation is provided without a membrane if necessary. When the SiC powder is converted into a graphite sponge, the original volume is maintained.

[0074] FIG. 2 illustrates another example of a sublimation system (100) according to the present disclosure having a first thermal radiation cavity (118) of a different shape. It should be noted that the remaining features of the sublimation system (100) correspond to the features of the sublimation system (100) illustrated in FIG. 1.

[0075] According to FIG. 2, the first heat radiation cavity (118) has a central protruding compartment (126) that extends into the raw material compartment (104) along the longitudinal axis (120). This protrusion directs heat closer to the center of the raw material compartment. Additionally, it expands the surface of the heating area to improve heating efficiency. A separating wall (122) is also located within the area of ​​the relatively thin protruding compartment (126) to facilitate heat transfer into the raw material (108).

[0076] FIG. 3 illustrates another example of a sublimation system (100) according to the present disclosure, wherein a second thermal radiation cavity (128) is provided in addition to the first thermal radiation cavity (118). It should be noted that the remaining features of the sublimation system (100) correspond to the features of the sublimation system (100) illustrated in FIG. 1.

[0077] According to the example illustrated in FIG. 3, the second heat radiation cavity (128) extends from the side wall (116) of the crucible (102) into the internal volume of the raw material compartment (104). Along the longitudinal axis (120), the second heat radiation cavity (128) may be arranged at an axial position corresponding, for example, to the approximate center of the raw material compartment (104). As exemplarily illustrated in FIG. 3, the second heat radiation cavity (128) is, for example, ring-shaped, and the second separating wall (130) has approximately the same thickness as the first separating wall (122). The second heat radiation cavity (128) directs heat from the side wall (116) into the raw material (108) through heat radiation. Thus, the second heat radiation cavity (128) allows for a local influence on the temperature acting on the raw material (108).

[0078] According to a further advantageous example of the present disclosure, the first heat radiation cavity (118) may include one or more pillars (132) connecting the heating base to the separating wall (122). This example is illustrated in FIG. 4.

[0079] As illustrated in FIG. 4, a central column (132) is provided inside the first thermal radiation cavity (118). At the location of the column (132), heat is not transferred via thermal radiation, but rather via heat conduction through the column (132). Thus, a local reduction in the heat flux into the raw material compartment (104) is achieved.

[0080] As described above, other geometric structures serve to fine-tune the temperature within the powder by being separated as much as possible from the temperature distribution determined by the overall crucible geometric structure to enable optimal crystal growth. Optimized powder transformation can be achieved together with other geometric structures within the growth space.

[0081] FIGS. 5 and 6 illustrate additional variations of the protruding section (126) of FIG. 2 in a side view and a corresponding schematic plan view. The sublimation system (100) of FIGS. 5 and 6 differs from that shown in FIG. 2 in that only a single central protruding section (126A) extends into the raw material section (104), but a second exemplary ring-shaped protruding section (126B) is arranged around the central protruding section (126A). As with the geometry of FIG. 2, the advantage of this solution can be seen in that heat can be directed closer into the center of the raw material section. Additionally, it improves heating efficiency by expanding the surface area of ​​the heating zone. A separating wall (122) is also located within the area of ​​the relatively thin protruding sections (126A, 126B) to facilitate heat transfer into the raw material (108).

[0082] It is clear that if the desired heating pattern requires this, any other shape and number of one or more protruding sections (126) can also be used.

[0083] In any case, one or more protruding sections (126) are in direct communication with the remainder of the first thermal radiation cavity (118). That is, no distance or boundary wall separates the internal volume of one or more protruding sections (126) from the internal volume of the remainder of the first thermal radiation cavity (118).

[0084] In contrast, the second heat radiation cavity (128) illustrated in FIG. 3 has an internal volume separated from the internal volume of the first heat radiation cavity (118). FIG. 7 illustrates a variation of the second heat radiation cavity (128). According to this example, the second heat radiation cavity (128) is ring-shaped with a separating wall inclined toward the raw material compartment. The second heat radiation cavity (128) is formed by introducing a funnel-shaped second separating wall (130) (essentially forming a frustum of a cone) into the bottom region of the raw material compartment (104). The second heat radiation cavity (128) is positioned adjacent to the first heat radiation cavity (118), and the two cavities are separated from each other by a portion of the first separating wall (122).

[0085] This arrangement has the advantage that heat can be transferred into the raw material (108) much more efficiently. In particular, the surrounding floor area of ​​the raw material compartment (104) can be heated by benefiting from heat radiation.

[0086] As described above, different geometric structures serve to fine-tune the temperature within the powder by being separated as much as possible from the temperature distribution determined by the overall crucible geometric structure to enable optimal crystal growth. Optimized powder transformation can be achieved with various geometric structures within the growth space.

[0087] To improve the radiation mechanism within the middle of the raw material compartment (104) and further reduce the amount of raw material placed within the central area of ​​the raw material compartment, the second thermal radiation cavity (128) may also be bounded by a conical second separating wall (130). An example of this is illustrated in FIG. 8.

[0088] As described above, various geometric structures serve to fine-tune the temperature of the powder by being separated as much as possible from the temperature distribution determined by the overall crucible geometric structure to enable optimal crystal growth. Optimized powder transformation can be achieved together with other geometric structures within the growth space.

[0089] In all examples illustrated in FIGS. 1 through 8, the first thermal radiation cavity (118) is always depicted as having an inner diameter larger than the inner diameter of the raw material compartment (104). In contrast, FIG. 9 illustrates an example of a sublimation system (100) in which the inner diameter of the first thermal radiation cavity (118) is smaller than the inner diameter of the raw material compartment (104).

[0090] Accordingly, the heat flow rate into the central region of the raw material section (104) is higher than the heat flow rate into the peripheral region of the raw material section (104) provided through the structure (124) which defines the ring-shaped boundary through heat conduction.

[0091] In summary, the present disclosure is based on the idea of ​​using hollow cavities at various locations in the region facing the seed crystal (110) to guide the heat flux into the raw material compartment (104) in a more defined and efficient manner.

[0092] By selectively introducing cavities that enable heat transfer via radiation, significantly lower temperature differences within the system can be achieved. In particular, at least one cavity exists on at least one side of an individual diffusion-determining surface of the raw material extending away from the crystal to locally influence the temperature distribution of the raw material.

[0093] This enables the transfer of the temperature, which is usually hottest in the wall region of the introduced crucible, to the center of the structure. A significant advantage of this is the much more efficient use of available raw materials during the growth process. This also allows the raw materials to be heated more uniformly over a wider area, thereby enabling the gas phase composition to be maintained constant for a longer period during cultivation and thus preventing quality loss due to changes in the gas phase.

[0094] The resulting advantage is that the mass of raw material that can be effectively used for crystal growth increases significantly, and thus not only the quality but also the length can be increased.

[0095] In addition, it should be noted that some or only parts of the exemplary structures described above according to FIGS. 1 to 9 may be arbitrarily combined with each other. Explanation of the symbols

[0096] Reference Number Explanation 100 Sublimation System; PVT System 102 Crucible 104 SiC supply area; raw material section 106 Crystal Growth Region 108 raw materials 110 Seed Decisions 112 Crucible Lid 114 Heating Base 116 Side wall of the crucible 118 First thermal radiation cavity 120 central axis 122 (1st) partition wall 124 Structure defining the boundary of a ring shape 126, 126A, 126B protruding sections 128 Second Column Radiation Co-existence 130 Second partition wall 132 pillars 800 PVT System 802 Crucible 804 SiC Supply Area 806 Crystal Growth Region 808 raw materials 810 Seed Decision 812 Crucible Lid 814 Vessel; Reactor 816 Induction Heating Coil 1001 Heat flux through conduction 1002 Heat flux through 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 a sublimation growth process, wherein the sublimation system (100) comprises: a crucible (102) having a longitudinal axis (120) and a side wall (116) extending along the longitudinal axis (120); the crucible comprises a fixing means for at least one seed crystal (110) and at least one raw material compartment (104) for receiving raw material (108); and a heating system formed to generate a temperature field around the circumference of the crucible along the longitudinal axis of the crucible, wherein the crucible (102) comprises at least one first thermal radiation cavity (118) arranged opposite the fixing means and adjacent to the raw material compartment (104), wherein the first thermal radiation cavity (118) has all sides closed, and a portion of the side wall (116) of the crucible (102) forms the boundary of the first thermal radiation cavity (118). A sublimation system comprising: at least one first heat radiation cavity (118) being formed from the same material as the side wall (116) of the crucible (102) and being bounded to a raw material compartment (104) by a first separating wall (122) that is thinner than the side wall (116) of the crucible (102) and thinner than a wall defining the boundary of the remaining side of the first heat radiation cavity (118); the first heat radiation cavity (118) having an inner diameter crossing the longitudinal axis (120) that is larger than the inner diameter of the raw material compartment; the first heat radiation cavity (118) having at least one protruding compartment (126) extending into the raw material compartment (104) along the longitudinal axis (120), and the at least one protruding compartment (126) communicating directly with the remainder of the first heat radiation cavity (118). Claim 2 A sublimation system according to claim 1, wherein at least one second heat radiation cavity (128) is arranged within the raw material compartment (104), and the at least one second heat radiation cavity (128) is separated from the first heat radiation cavity (118). Claim 3 In paragraph 2, the sublimation system, wherein the at least one second thermal radiation cavity (128) is ring-shaped having a central axis of the ring that coincides with the longitudinal axis of the crucible. Claim 4 In paragraph 2, the sublimation system is defined for the raw material compartment (104) by an inclined separation wall (130) that includes an angle with respect to the longitudinal axis (120). Claim 5 ◈Claim 5 was abandoned upon payment of the registration fee.◈ In claim 2, the sublimation system wherein at least one second thermal radiation cavity (128) is bounded with respect to the raw material compartment (104) by a conical separation wall (130). Claim 6 A sublimation system according to claim 1, wherein the first heat radiation cavity (118) is provided with a solid column (132) that protrudes the first heat radiation cavity (118) in a direction along the longitudinal axis (120). Claim 7 In claim 1, the heating system comprises an induction coil and / or resistance heater operable to generate an electromagnetic field that at least partially surrounds the crucible (102), a sublimation system. Claim 8 A sublimation system according to claim 1, 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 9 In claim 8, the sublimation system, wherein the at least one first thermal radiation cavity (118) has an internal volume equal to at least 1% to a maximum of 18% of the volume of the raw material compartment. Claim 10 A method for growing at least one single crystal of a semiconductor material by a sublimation growth process comprises: providing a crucible (102) having a longitudinal axis (120) and a side wall (116) extending along said longitudinal axis (120); fixing at least one seed crystal (110) to a fixing means of said crucible (102); and filling at least one raw material compartment (104) with raw material (108); and generating a temperature field around the circumference of said crucible (102) and along said longitudinal axis (120) of said crucible (102) by a heating system; wherein the heat of said temperature field is coupled into the raw material compartment via thermal radiation through at least one first thermal radiation cavity (118) arranged opposite to said fixing means and adjacent to said raw material compartment (104), said thermal radiation cavity (118) having all sides closed, and said of said crucible (102) A portion of the side wall (116) defines the boundary of the first heat radiation cavity (118), and at least one first heat radiation cavity (118) is formed from the same material as the side wall (116) of the crucible (102) and is defined for the raw material section (104) by a first separating wall (122) which is thinner than the side wall (116) of the crucible (102) and thinner than the wall defining the boundary of the remaining side of the first heat radiation cavity (118); the first heat radiation cavity (118) has an inner diameter crossing the longitudinal axis (120) which is larger than the inner diameter of the raw material section; the first heat radiation cavity (118) has at least one protruding section (126) extending into the raw material section (104) along the longitudinal axis (120), and the at least one protruding section (126) is directly connected to the remainder of the first heat radiation cavity (118). Method of connecting. Claim 11 A method according to claim 10, wherein a temperature difference exceeding 20K does not occur in a plane facing the seed crystal (110) which extends across the longitudinal axis (120) and has a maximum temperature within the raw material section. Claim 12 delete Claim 13 delete Claim 14 delete Claim 15 delete

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