A multi-component flux system and method for liquid-phase growth of silicon carbide single crystals

Abstract

This invention belongs to the field of crystal growth technology, and particularly relates to a multi-component flux system and method for liquid-phase growth of silicon carbide single crystals. The system consists of Si, Cr, Al, M1, M2, and M3, where M1 is selected from La, Ce, Pr, and Nd; M2 is selected from Ge and Sn; and M3 includes a first functional group (Fe, Co, Ni, Sc, Y) and / or a second functional group (Ti, V, Mn, Cu, Zn, Zr). Through the synergistic effect of each component, carbon dissolution mass transfer, melt properties, and solid-liquid interface stability are regulated, improving crystal surface morphology, crystal quality, and effective usable area.

Description

Technical Field

[0001] This invention belongs to the field of crystal growth technology, and particularly relates to a multi-component flux system and method for growing silicon carbide single crystals by liquid phase method. Background Technology

[0002] Silicon carbide (SiC), as a third-generation wide-bandgap semiconductor material, possesses excellent properties such as a wide bandgap, high breakdown field strength, high thermal conductivity, and high electron saturation drift velocity. It shows great promise in high-power, high-frequency, high-voltage, and high-temperature applications such as new energy vehicles, AI data center power systems, high-voltage power transmission, rail transportation, and photovoltaic inverters. High-quality, large-size, low-defect-density SiC single-crystal substrates are key fundamental materials for fabricating high-performance SiC-based power devices and radio-frequency devices.

[0003] Currently, the physical vapor transport (PVT) method is the main industrial method for preparing SiC single crystals. This method is technically mature and has a high degree of industrialization, but it typically requires crystal growth at a high temperature of approximately 2200℃, which presents problems such as high growth temperature, high energy consumption, and difficulty in obtaining heavily doped p-type 4H-SiC substrates. Liquid-phase growth of SiC single crystals has become a widely studied crystal growth technique in recent years. Compared with the PVT method, the liquid-phase method generally has a lower growth temperature (approximately 1800℃), near-equilibrium growth conditions, and better defect repair capabilities, which are beneficial for reducing dislocation density and improving crystal quality.

[0004] In the liquid phase growth process, the composition of the flux system directly affects the solubility of carbon in the melt, solute transport behavior, melt viscosity, surface tension, interfacial wettability, relative supersaturation distribution, and the stability of the crystal growth interface. Therefore, the design of the flux system is one of the key technologies for growing high-quality SiC single crystals in the liquid phase method.

[0005] Current liquid-phase methods for growing silicon carbide single crystals typically employ Si-Cr, Si-Fe, Si-Ni, Si-Ti, Si-Cr-Al, and Si-Cr-Al-Ce systems as fluxes. Among these, Cr, Fe, Ni, and Ti can enhance the solubility of carbon in Si-based melts; Al can regulate melt properties, improve interfacial wetting behavior, and act as a p-type dopant; rare earth elements such as Ce play a role in reducing melt viscosity, increasing carbon solubility, and improving solute transport.

[0006] However, as the size of SiC single crystals increases, the difficulty of controlling the thermal, flow, and concentration fields during crystal growth also increases accordingly. Existing fluxing agents still struggle to simultaneously achieve high carbon solubility, stable solute transport, and good solid-liquid interface stability. Particularly during the liquid-phase growth of large-size SiC single crystals, the radial temperature difference and temperature fluctuations at the crystal edges tend to increase, leading to temperature gradient changes and localized relative supersaturation fluctuations at the crystal edges. This results in uneven solute supply near the growth interface and increases the tendency for interfacial instability defects such as macrostep clustering, trenches, solvent inclusions, microcracks, and multi-point nucleation. These defects affect the crystal surface morphology quality and reduce the effective usable area of ​​the crystal.

[0007] Furthermore, existing cosolvent systems often involve the simple addition of components with single functions, lacking the ability to synergistically regulate melt properties, solute transport, interfacial kinetics, and step structure evolution. For example, in high-temperature growth environments above approximately 1900℃, local temperature fluctuations, component segregation, and changes in supersaturation can induce changes in the polymorphic stability of SiC, increasing the risk of crystal transformation or polymorphic inclusions. Therefore, it is necessary to develop a multi-component cosolvent system suitable for liquid-phase SiC single crystal growth that, while maintaining high carbon dissolution capacity, can improve melt flow properties and surface properties, regulate the local relative supersaturation distribution near the growth interface, stabilize the solid-liquid growth interface, and reduce the tendency for interfacial instability defects to occur in the edge regions of large-size crystals. This would improve the surface morphology of SiC single crystal growth, enhance crystal quality, reduce defect density, and increase the effective usable area and yield of large-size crystals. Summary of the Invention

[0008] To address the problem that existing co-solvent systems in the liquid-phase growth of silicon carbide single crystals struggle to simultaneously achieve optimal performance in terms of carbon dissolution capacity, solute transport capacity, melt property control, and solid-liquid interface stability, this application discloses a multi-component co-solvent system and method for liquid-phase silicon carbide single crystal growth, involving a six-component co-solvent system of Si-Cr-Al-M1-M2-M3. This co-solvent system further introduces M1, M2, and M3 elements into the Si-Cr-Al base system. Through the synergistic effect between these components, it achieves comprehensive control over carbon dissolution and mass transfer behavior, melt surface and flow properties, local relative supersaturation distribution, and solid-liquid growth interface stability.

[0009] To achieve the above objectives, the first technical solution of this application discloses a multi-component flux system for liquid-phase growth of silicon carbide single crystals, which is composed of Si, Cr, Al, M1, M2 and M3, and the atomic percentage of each component is as follows:

[0010] Si 35-60 at.%, Cr 35-55 at.%, Al 0.5-10 at.%, M1 0.5-12 at.%, M2 0.1-10 at.%, M3 0.1-8 at.%; and the sum of the atomic percentages of each component is 100 at.%.

[0011] M1 is selected from one or more of La, Ce, Pr, and Nd;

[0012] M2 is selected from one or more of Ge and Sn;

[0013] M3 includes a first functional group and / or a second functional group, wherein the first functional group is selected from one or more of Fe, Co, Ni, Sc, and Y, and the second functional group is selected from one or more of Ti, V, Mn, Cu, Zn, and Zr.

[0014] Preferably, the total content of the elements in the first functional group is 0.5-8 at.%.

[0015] Preferably, the total content of the elements in the second functional group is 0.1-6 at.%.

[0016] Preferably, M1 is Ce, M2 is Ge, and M3 contains Co.

[0017] Preferably, the content of Si is 40-50 at.%, the content of Cr is 40-50 at.%, the content of Al is 1-5 at.%, the content of M1 is 2-8 at.%, the content of M2 is 1-5 at.%, and the content of M3 is 1-5 at.

[0018] The second technical solution of this application discloses a method for growing silicon carbide single crystals by liquid phase, using the multi-component flux system described in the first technical solution, including the following steps:

[0019] Weigh out Si, Cr, Al, M1, M2 and M3 raw materials according to the preset atomic percentage and place them in a crucible;

[0020] Heating is performed under a protective atmosphere or vacuum to melt the components and form a flux melt.

[0021] The heat treatment allows the melt to dissolve the carbon source and reach a saturated or near-saturated state suitable for silicon carbide growth;

[0022] Silicon carbide seed crystals are brought into contact with the melt for crystal introduction, and the growth temperature, temperature gradient, seed crystal rotation speed and growth time are controlled to enable silicon carbide to grow epitaxially on the surface of the seed crystals in the liquid phase.

[0023] After growth is complete, the temperature is lowered and the crystals are removed.

[0024] Furthermore, the growth temperature is 1650-2000℃.

[0025] Furthermore, the growth temperature is 1750-1950℃.

[0026] Furthermore, the silicon carbide seed crystal is a 4H-SiC seed crystal, and the growth crystal plane is the C plane.

[0027] Furthermore, the carbon source is a graphite crucible.

[0028] Beneficial effects:

[0029] This invention introduces three types of functional regulating elements, M1, M2, and M3, into the Si-Cr-Al basic cosolvent system. Utilizing the synergistic effect of multiple components, it achieves comprehensive regulation of carbon dissolution and mass transfer behavior, melt surface and flow properties, local relative supersaturation distribution, and the stability of the solid-liquid growth interface, yielding the following beneficial effects:

[0030] (1) Improve the solubility and mass transfer capacity of carbon in the melt. M1 elements (one or more of La, Ce, Pr, and Nd) and some M3 elements with strong carbon affinity can improve the equilibrium solubility and effective dissolution capacity of carbon in the flux melt, enhance the supply capacity of carbon source to the solid-liquid interface during growth, and thus help improve the growth rate of silicon carbide crystals.

[0031] (2) Reduce local relative supersaturation and its fluctuations. M1 element can improve the equilibrium solubility of carbon in the melt. While maintaining a certain carbon concentration supersaturation, it controls the relative supersaturation at the growth interface within a relatively low or stable range, which helps to reduce the sudden changes in relative supersaturation caused by local concentration fluctuations and reduce the tendency of two-dimensional nucleation, multi-point nucleation and interface instability.

[0032] (3) Improve melt flowability and solute transport uniformity. The first functional group M3 elements (one or more of Fe, Co, Ni, Sc, Y) can regulate the viscosity, surface tension, density and temperature response characteristics of the flux melt, improve the natural convection and Marangoni convection state inside the melt, promote the uniform transport of carbon source and dopant components near the growth interface, and reduce local solute enrichment or depletion.

[0033] (4) Improve the growth quality of large-size crystal edge regions. By controlling the melt flowability and interfacial dynamics behavior through the first functional group M3 element, the risk of interfacial instability caused by radial temperature difference, temperature gradient abrupt change and flow field disturbance in the crystal edge region can be reduced, and defects such as macrostep clustering, grooves, solvent inclusions and multi-point nucleation in the edge region can be reduced.

[0034] (5) Improve crystal stability. M2 elements (one or more of Ge and Sn) can regulate the Si activity and interfacial wetting behavior in the Si-based flux melt, change the relative chemical environment of Si / C in the melt, and thus regulate the dissolution-precipitation driving force of SiC at the solid-liquid interface; at the same time, combined with the suppression of local relative supersaturation fluctuations, it is beneficial to maintain the stability of the target SiC crystal form (such as 4H-SiC) during liquid phase growth and reduce the risk of polytype inclusions or crystal transformation.

[0035] (6) Reduce the tendency of step faceting and dislocation extension. The second functional group M3 elements (one or more of Ti, V, Mn, Cu, Zn, and Zr) can regulate the faceting behavior of the side of the step on the growth surface of silicon carbide, improve the stability of the side of the step, and help to regulate the interaction between through-screw dislocations and faceted steps, thereby reducing the tendency of through-screw dislocations to extend along the growth direction.

[0036] (7) Improve the effective usable area and yield of crystals. Due to the reduction of defects in the crystal edge region, the improvement of surface morphology, and the reduction of inclusions and polycrystalline defects, the present invention can improve the effective usable area of ​​large-size silicon carbide single crystals, thereby improving the crystal processing yield and device manufacturing yield. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a growth morphology diagram of Example 1;

[0039] Figure 2 This is a step flow topography diagram of Example 3;

[0040] Figure 3 This is a growth morphology diagram of Example 4;

[0041] Figure 4 The images show the growth morphology (left) and step flow morphology (right) of Example 5.

[0042] Figure 5 This is a growth morphology diagram for Comparative Example 1. Detailed Implementation

[0043] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0044] The first embodiment of this application discloses a multi-component flux system for growing silicon carbide single crystals in a liquid phase method, comprising Si, Cr, Al, M1, M2, and M3. The atomic percentages of each component are: Si 35-60 at.%, Cr 35-55 at.%, Al 0.5-10 at.%, M1 0.5-12 at.%, M2 0.1-10 at.%, and M3 0.1-8 at.%, with the sum of the atomic percentages of each component being 100 at.%. Cr is a metallic element that helps improve the solubility of carbon in Si-based melts; Al is an element used to adjust melt properties and interfacial wetting behavior and can serve as a p-type dopant.

[0045] M1 is a rare earth element selected from one or more of La, Ce, Pr, and Nd. M1 can improve the solubility of carbon in the flux melt and enhance the melt's flow properties and solute transport behavior, thereby contributing to a stronger supply of carbon source to the solid-liquid growth interface during growth. In the liquid-phase growth of silicon carbide single crystals, the carbon concentration near the growth interface can be characterized by the following relationship:

[0046] ;

[0047] .

[0048] Where ΔC is the carbon supersaturation near the growth interface. It is the actual carbon concentration at the growth interface. ΔC represents the equilibrium carbon solubility of the melt near the growth interface at the growth temperature, while σ represents the relative supersaturation at the growth interface. Typically, ΔC is related to the precipitation driving force and growth rate of SiC at the solid-liquid interface, while the magnitude of σ controls processes such as two-dimensional nucleation and multi-point nucleation. When M1 is added, the carbon solubility of the melt increases. Due to convection, dissolved carbon from the crucible sidewalls and bottom wall is transported to the growth interface, resulting in a larger ΔC. Simultaneously, due to… With the increase of concentration, σ can be controlled within a relatively low or stable range while maintaining a certain ΔC. This helps to reduce abrupt changes in relative supersaturation caused by local concentration fluctuations, and decreases the tendency for two-dimensional nucleation and interfacial instability.

[0049] M2 is an element that controls Si activity, crystal stability, and step flow morphology, selected from one or more of Ge and Sn. Ge and Sn have good compatibility with Si-based melts and can adjust the composition and structure of the flux melt, Si activity, and interfacial wetting behavior, which helps to improve the contact state between the flux melt and the silicon carbide seed crystal, thereby controlling the microstructure of the step flow on the growth surface. During the liquid-phase growth of silicon carbide single crystals, the chemical potential difference of SiC precipitating from the liquid phase to the solid phase can be characterized by the following relationship:

[0050] .

[0051] Where Δμ is the chemical potential difference of SiC from the liquid phase to the solid phase, which reflects the driving force for silicon carbide precipitation; R is the gas constant; and T is the thermodynamic temperature of growth. and These represent the Si activity and C activity in the melt, respectively. It is the balance activity product.

[0052] In addition, the activity ratio of Si to C can be used to characterize the relative chemical environment in the melt:

[0053] ;

[0054] This represents the activity ratio of Si to C, and its variation may affect the stability and growth selectivity of different SiC crystal forms.

[0055] when When Si activity is changed, the equilibrium carbon activity and effective supersaturation at the interface corresponding to SiC precipitation also change accordingly. Therefore, under conditions of similar actual carbon concentration, by adjusting the Si activity, the dissolution-precipitation driving force of SiC at the solid-liquid interface can be controlled to a certain extent, and the propagation state, step distribution, and morphological stability of the growth surface step flow can be further affected. At the same time, changes in Si activity will change the relative chemical environment of Si / C in the melt, which is related to the SiC crystal form selection and crystal form stability.

[0056] Therefore, by introducing appropriate amounts of Ge and / or Sn, the Si activity, interfacial wettability, and SiC precipitation driving force in the Si-based flux melt can be adjusted, thereby helping to improve the uniformity of step advancement, reduce the tendency of abnormally wide steps and macrostep clustering, and help maintain the stability of the target SiC crystal form during liquid phase growth.

[0057] M3 refers to elements that regulate melt surface properties, flow properties, step structure, and interface stability, and is selected from one or more of Fe, Co, Ni, Sc, Y, Ti, V, Mn, Cu, Zn, and Zr. In this invention, element M3 is not simply selected as a single replacement element with completely equivalent effects, but rather is divided into different functional groups based on its influence on the properties of the flux melt, solute transport behavior, step growth structure, and solid-liquid growth interface stability. M3 may be composed of one or more elements from the first functional group and / or the second functional group.

[0058] The first functional group comprises fluidity and interfacial dynamics control elements, selected from one or more of Fe, Co, Ni, Sc, and Y. These elements are used to adjust the viscosity, surface tension, density, and temperature response characteristics of the flux melt, improve the natural convection and Marangoni convection state within the melt, and promote the uniform transport of carbon source and dopant components near the growth interface. This helps to reduce the adverse effects of local compositional fluctuations and temperature disturbances on the stability of the solid-liquid growth interface. By introducing these elements, the tendency for interfacial instability defects caused by uneven solute transport, such as macrostep clustering, trenches, solvent inclusions, and multi-point nucleation, can be reduced. They are particularly suitable for improving interfacial instability problems caused by temperature gradient changes, local relative supersaturation fluctuations, and uneven solute distribution in the edge regions of large-size silicon carbide crystals.

[0059] The second functional group comprises step faceting and dislocation behavior control elements, selected from one or more of Ti, V, Mn, Cu, Zn, and Zr. These elements are used to regulate the faceting behavior of the side surfaces of the silicon carbide growth surface, improve the stability of the step sides, and may help control the interaction between through-screw dislocations and faceted steps, thereby reducing the tendency of through-screw dislocations to extend along the growth direction. Preferably, the elements in the second functional group are added in low concentrations to reduce the risk of precipitation of metal carbides or carbon-containing complex phases.

[0060] In one preferred embodiment, M3 is composed of one or more elements from a first functional group or a second functional group; in another preferred embodiment, M3 is composed of a combination of elements from the first functional group and the second functional group to achieve synergistic regulation of melt flow properties, step faceting behavior, dislocation behavior, wettability, and local relative supersaturation distribution.

[0061] In a preferred embodiment, the total content of the first functional group elements is 0.5-8 at.%; and the total content of the second functional group elements is 0.1-6 at.%. In a more preferred embodiment, the total content of the first functional group elements is 2-6 at.% and the total content of the second functional group elements is 0.3-4 at.%.

[0062] In a preferred embodiment, the content of each component in the co-solvent system is further limited to: Si 40-50 at.%, Cr 40-50 at.%, Al 1-5 at.%, M1 2-8 at.%, M2 1-5 at.%, M3 1-5 at.%.

[0063] In a preferred embodiment, M1 is Ce, M2 is Ge, and M3 contains Co (corresponding to claim 4). This embodiment corresponds to a Si:Cr:Al:Ce:Ge:Co ratio of 47:40:2:5:3:3, which can effectively improve melt flowability and interfacial stability while increasing carbon solubility.

[0064] The second embodiment of this application discloses a method for growing silicon carbide single crystals using the above-described six-element co-solvent system in a liquid phase, comprising the following steps:

[0065] (1) Weigh Si, Cr, Al, M1, M2 and M3 raw materials according to the preset atomic percentages, and place each raw material in a crucible; wherein the purity of each raw material is preferably 4N (99.99%) or higher, so as to reduce the adverse effects of impurities on crystal quality. Mix the weighed raw materials and place them in the crucible. The crucible can be an isostatic graphite crucible, which is used as both a melt container and a carbon source.

[0066] (2) Heating is performed under an inert atmosphere, vacuum, or protective atmosphere to melt the components and form a six-component flux melt; wherein the atmosphere can be Ar, He, or other inert or protective atmospheres, and the atmosphere pressure can be 0.1-1 atm. During the heating process, the components gradually melt and form a uniform six-component flux melt. The heating rate can be set according to the thermal characteristics of the equipment, and is usually controlled within a range that ensures uniform heating of the melt and avoids local overheating.

[0067] (3) After reaching the set temperature, maintain the temperature to allow the melt to dissolve the carbon source and reach a saturated or near-saturated state suitable for silicon carbide growth; wherein the set temperature can be 1800-1850℃, and the holding time can be about 30 min, to improve the uniformity of the melt composition and promote the dissolution of the carbon source. The carbon source can be the graphite crucible itself, or other high-purity carbon-containing materials that can provide carbon to the flux melt.

[0068] (4) The SiC seed crystal is brought into contact with the hexa-element flux melt for crystal introduction, and the growth temperature, melt axial temperature gradient, seed crystal rotation speed, and growth time are controlled to allow SiC to undergo liquid-phase epitaxial growth on the seed crystal surface; wherein the seed crystal can be selected from 3C-SiC, 4H-SiC, or 6H-SiC seed crystals; the growth crystal plane of the seed crystal can be the C plane, the Si plane, or a crystal plane with a preset deflection angle relative to the C plane or the Si plane. Preferably, the seed crystal is a 4H-SiC seed crystal, and the growth crystal plane is the C plane.

[0069] In a further embodiment, the bonding surface of the seed crystal can be subjected to hot-press carbonization treatment before crystal pulling. For example, after fixing the seed crystal to the graphite substrate with the Si surface as the bonding surface, it can be subjected to hot-press carbonization treatment at 600°C for 2-4 hours to promote the full carbonization of the adhesive and improve the fixation stability between the seed crystal and the graphite substrate.

[0070] After crystal seeding is completed, the crystal growth stage begins. The liquid phase growth temperature can be 1650-2000℃, preferably 1750-1950℃. During the crystal growth stage, SiC is liquid-phase epitaxially grown on the seed crystal surface by controlling the melt axial temperature gradient, seed crystal rotation speed, and growth time. The seed crystal rotation speed can be set to 120-150 rpm to enhance the uniformity of solute transport in the melt and reduce local concentration fluctuations. The seed crystal pulling speed can be linearly reduced from a higher value to a lower value with the growth time, for example, from 150 μm / h to 80 μm / h, or from 120 μm / h to 50 μm / h, to reduce local oversaturation fluctuations at the interface in the later stage and stabilize the interface step flow growth.

[0071] (5) After growth is complete, the crystal is cooled and removed for further processing or characterization. After crystal growth is complete, the crystal can be lifted out of the melt at a speed of 0.5 mm / min, and then cooled to room temperature at an average cooling rate of 80-100 ℃ / h to reduce thermal stress concentration and reduce the generation of cooling cracks. After the furnace temperature drops to room temperature, the crystal sample is removed.

[0072] By combining the above-described method steps with the hexa-component co-solvent system, the method of the present invention can achieve at least the following technical effects:

[0073] (1) Achieve stable liquid phase epitaxial growth. By synergistically controlling carbon solubility, melt properties and interface state through a six-element cosolvent system, and by optimizing process parameters such as seeding temperature, growth temperature, seed rotation speed and pulling speed, stable liquid phase epitaxial growth can be achieved on the seed surface, reducing interface disturbances during the growth process.

[0074] (2) Balancing high growth rate and low defect density. Since the cosolvent system improves carbon solubility and solute transport capacity, this method can improve the growth rate of SiC crystals while maintaining interface stability; at the same time, by controlling the relative supersaturation and improving interface stability, the generation of defects such as inclusions, polymorphism and polytype inclusions is effectively suppressed.

[0075] (3) Applicable to large-size crystal growth. By controlling the melt flowability and interfacial dynamics behavior through the first functional group M3 element, this method is particularly beneficial to improve the interfacial instability problem caused by radial temperature difference, temperature gradient abrupt change and flow field disturbance in the crystal edge region during the liquid phase growth of large-size (such as 6-inch) silicon carbide, and reduce defects such as macrostep clustering, grooves, inclusions and microcracks in the edge region.

[0076] (4) Maintaining crystal stability. By regulating the activity of Si through the M2 element and suppressing local relative supersaturation fluctuations, this method helps to maintain the stable growth of the target SiC crystal form (such as 4H-SiC) and reduce the risk of polymorphic inclusions or crystal transformations caused by local component segregation, temperature fluctuations and supersaturation changes during high-temperature liquid phase growth.

[0077] The technical means and effects of this application will be described in detail below through specific embodiments.

[0078] Example 1: Liquid-phase growth of silicon carbide single crystals

[0079] In this embodiment, a 4-inch zero-offset semi-insulating 4H-SiC wafer is used as the seed crystal, with the C-side as the crystal growth surface and the Si-side as the bonding surface, fixed to the graphite substrate. After the seed crystal is bonded, it undergoes hot-pressing carbonization treatment at 600℃ for 2 hours to promote full carbonization of the adhesive and improve the fixation stability between the seed crystal and the graphite substrate. During crystal growth, a six-component flux system of Si-Cr-Al-Ce-Ge-Co is used, with the atomic molar ratio of Si, Cr, Al, Ce, Ge, and Co being 47:40:2:5:3:3. An isostatic graphite crucible is used as the melt container and carbon source, with an inner diameter of 150 mm and a height of 90 mm, and the melt height is controlled to be 40 mm.

[0080] During the heating stage, the system temperature is held at 1800℃ for 30 min to improve the uniformity of the melt composition and promote carbon source dissolution. The seed crystal is then lowered to bring its growth surface into contact with the melt, thus initiating crystal growth. After crystal initiation, the crystal growth stage begins, maintaining the growth temperature at 1850℃ to ensure sufficient solute carbon concentration in the melt and maintain a stable supersaturated state. During the crystal growth stage, the maximum rotational speed of the seed crystal is set to 150 rpm to enhance the uniformity of solute transport in the melt and reduce local concentration fluctuations. Simultaneously, the seed crystal pulling speed decreases linearly from 150 μm / h to 80 μm / h with growth time. In this embodiment, the total crystal growth time is set to 72 h. After crystal growth is complete, the crystal is lifted from the melt at a speed of 0.5 mm / min, and then the cooling stage begins. During cooling, the system cools to room temperature at an average rate of 100℃ / h to reduce thermal stress concentration and minimize cooling crack formation. After the furnace temperature dropped to room temperature, the crystal sample and the growth crucible were removed, yielding a silicon carbide single crystal. Subsequently, industrial CT, EDS, Raman spectroscopy, and microscopic surface morphology analysis were used to characterize and analyze the inclusion defects, crystal form, and surface morphology of the crystal.

[0081] Test results show that obvious flux inclusion defects were detected inside the SiC crystal obtained in this embodiment. Surface morphology analysis ( Figure 1 The results showed that a uniform and fine concentric ring-shaped step flow structure existed in the central region of the crystal growth surface, while the surface of the crystal edge region was smooth, and no macroscopic trenches were observed. Further tests showed that the average width of the crystal surface steps was approximately 25 μm, and the maximum observed macrostep height did not exceed 1500 nm. Based on the sample thickness test results, the average growth rate of the crystal obtained in this embodiment was calculated to be approximately 153 μm / h, which is comparable to the crystal growth rate of the PVT method. Raman spectroscopy showed that the grown sample was 4H-SiC, with no other crystal forms present. Raman and elemental analysis of the precipitates in the crucible confirmed that they were SiC, indicating that no other solid phase precipitates were generated during crystal growth. KOH etching results showed that the TSD defect density of the grown crystal was 505 cm⁻¹. -2 .

[0082] Example 2: Liquid-phase growth of silicon carbide single crystals

[0083] The specific implementation parameters and operation methods of this embodiment are basically the same as those of Embodiment 1. The difference is that when the system temperature rises to 1800℃ and the holding time is 30 min, it is changed to holding time at 1850℃ for 30 min. The growth temperature of the crystal growth stage is increased from 1850℃ to 1920℃, while the other process conditions remain unchanged.

[0084] Test results show that the surface morphology of the sample obtained in this embodiment is basically the same as that in Example 1. Industrial CT test results show that no flux inclusion defects were detected inside the grown SiC crystal; Raman spectroscopy results show that the crystal form of the obtained crystal is 4H-SiC. Based on the sample thickness test results, the average growth rate of the crystal obtained in this embodiment reached approximately 197 μm / h, indicating that under this flux growth system, appropriately increasing the growth temperature can significantly improve the growth rate of SiC crystal. In addition, after testing the precipitates inside the crucible, it was confirmed that they were still SiC, and no other solid precipitates were detected, indicating that under the growth condition of 1920℃, this multi-component flux system can still maintain good melt stability. KOH corrosion results show that the TSD defect density of the grown crystal is 547 cm⁻¹. -2 .

[0085] Example 3: Liquid-phase growth of silicon carbide single crystals

[0086] In this embodiment, the specific implementation parameters and methods are the same as in Embodiment 2, but the growth formula is changed to Si:Cr:Al:Pr:Sn:(Ti:Fe) = 40:42:2:5:5:(2:4), while the other process conditions remain unchanged.

[0087] Test results show that the grown crystals exhibit a regular hexagonal shape, a smooth surface, and a uniform and fine step flow structure (as seen under a microscope) Figure 2 (As shown). Further testing showed that the average width of the crystal surface steps was reduced to 17 μm, and the maximum observed macrostep height did not exceed 3000 nm. Based on the sample thickness test results, the average growth rate of the crystal obtained in this example was calculated to be approximately 166 μm / h, slightly lower than that in Example 2. Raman testing showed that the grown sample was 4H-SiC, with no other crystal forms present. Raman and elemental analysis of the precipitates in the crucible confirmed that they were silicon carbide, indicating that no other solid precipitates were generated during crystal growth. After etching the sample, the defect density was measured, with the TSD density decreasing to 200 cm⁻¹. -2 This indicates that adding elements from the second and third functional groups can change the structure of the steps and achieve defect transformation.

[0088] Example 4: Liquid-phase growth of silicon carbide single crystals

[0089] In this embodiment, a 6-inch non-biased semi-insulating 4H-SiC wafer is selected as the seed crystal, with the C-side as the crystal growth surface and the Si-side as the bonding surface, and fixed onto the graphite substrate. After bonding, a hot-pressing carbonization treatment is performed at 600℃ for 4 hours to carbonize the adhesive and improve the stability of the seed crystal fixation.

[0090] During the growth process, a six-component flux system of Si:Cr:Al:Nd:Sn:Co = 42:45:2:5:4:2 was used. The isostatic graphite crucible served as both the melt container and the carbon source. The crucible had an inner diameter of 210 mm and a height of 110 mm, and the melt height was controlled to be 45 mm.

[0091] During the heating stage, when the system temperature rises to 1820℃, the seed crystal is lowered to initiate crystal growth. After crystal initiation, the crystal growth stage begins, and the growth temperature is maintained at 1870℃ to ensure sufficient solute carbon concentration in the melt and maintain a stable supersaturated state. During the crystal growth stage, the seed crystal rotation speed is set to a maximum of 120 rpm to enhance the uniformity of solute transport in the melt and reduce local concentration fluctuations. Simultaneously, the seed crystal pulling speed linearly decreases from 120 μm / h to 50 μm / h with growth time to reduce later-stage local supersaturation fluctuations at the interface and stabilize the interface step flow growth. In this embodiment, the total crystal growth time is set to 72 h. After crystal growth is complete, the crystal is rapidly pulled away from the melt at a speed of 0.5 mm / min to reduce the risk of liquid residue and edge encapsulation during crystal detachment from the interface. Subsequently, the cooling stage begins, with the system cooling to room temperature at an average cooling rate of 80℃ / h to reduce thermal stress concentration and cooling crack formation. After the furnace temperature dropped to room temperature, the crystal sample was removed, and the defects of the inclusions inside the crystal and the surface morphology were characterized and analyzed by industrial CT and microscopic surface morphology analysis methods, respectively.

[0092] like Figure 3As shown, the sample characterization results indicate that the obtained crystal has a spherical appearance. Raman spectroscopy results show that the obtained crystal still maintains the 4H-SiC crystal form and no obvious crystal form transformation has occurred. However, severe step-like clustering and macroscopic groove-like defects appeared in the outer edge region of the crystal, indicating that as the crystal size increases, the melt's ability to stabilize the growth interface is insufficient, and the edge region is more significantly affected by radial temperature difference, edge heat loss, and local flow field disturbance. The abrupt temperature gradient in the edge region causes large fluctuations in local relative supersaturation, which easily induces two-dimensional nucleation, step coalescence, and macrostep clustering, leading to instability of the edge growth interface. Industrial CT test results further show that there are solvent inclusion defects in the inner edge region of the crystal, indicating that the surface morphology of the crystal edge has begun to deteriorate in the early or middle stage of growth, with uneven solute transport, abnormal step coalescence, and groove formation in local areas, resulting in some flux residues being trapped inside the crystal. In addition, the average crystal growth rate was measured to be approximately 137 μm / h. Meanwhile, silicon carbide precipitation was observed on the surface of the residual solid in the cooled crucible, indicating that the flux system has a tendency for local supersaturation during growth or cooling, and the solute concentration distribution and supersaturation control in the melt are still insufficient. KOH etching results showed that the TSD defect density of the grown crystal was 5352 cm⁻¹. -2 .

[0093] The above results indicate that although the Si-Cr-Al-Nd-Sn-Co hexa-component system can maintain the growth of 4H-SiC crystal form and obtain a certain growth rate, it is still difficult to fully suppress problems such as step clustering, grooves, inclusions and local supersaturation precipitation in the crystal edge region under 6-inch large-size liquid phase growth conditions. This shows that simply introducing Nd, Sn and Ga is not enough to achieve synergistic optimization of carbon solubility, melt flow properties and edge interface stability.

[0094] Example 5: Liquid-phase growth of silicon carbide single crystals

[0095] In this embodiment, a 6-inch non-biased semi-insulating 4H-SiC wafer was used as the seed crystal, with the C-side as the crystal growth surface and the Si-side as the bonding surface, and fixed to the graphite substrate. The seed crystal bonding, hot-pressing carbonization treatment, crucible structure, melt height, crystal pulling temperature, growth temperature, seed crystal rotation speed, pulling speed program, growth time, melt detachment method, cooling regime, and sample characterization method were all the same as in Example 4.

[0096] Unlike Example 4, this example uses a flux system of Si:Cr:Al:(Pr:Nd):Sn:Co=42:45:2:(3:2):2:4. This system further introduces Pr, an element from group M1, into the Si-Cr-Al-Nd-Sn-Co system. In this system, both Pr and Nd are rare earth element regulators with similar physicochemical properties. The combined addition of Pr and Nd can, to a certain extent, regulate the solubility of carbon in the flux melt and the solute transport behavior, helping to enhance the stability of the carbon source supply in the crystal edge region while maintaining a high carbon solubility. Simultaneously, compared to Example 4, this example increases the Co content. Co, as an M3 regulator element, can adjust the surface properties, flow properties, and interfacial dynamics of the flux melt, helping to improve the interaction between the melt and the solid-liquid growth interface. The synergistic effect of Pr, Nd, Sn and Co can improve the morphology and uniformity of growth steps to a certain extent, reduce the tendency of unstable growth steps, abnormally wide steps and macrostep clustering in the crystal edge region, and thus help improve the growth stability of large-size silicon carbide crystal edge regions.

[0097] like Figure 4 As shown, the sample characterization results indicate that the obtained crystal is a 4H-SiC crystal. Microscopic surface morphology analysis results show that a certain macro-step distribution still exists in the edge region of the obtained crystal, but no obvious macro-groove defects were observed. Compared with Example 4, the degree of interfacial instability in the crystal edge region is reduced in this example, indicating that the synergistic introduction of Pr-Nd composite M1 control element, Sn control element, and high Co content element helps to improve the local relative supersaturation fluctuation and solute transport unevenness in the edge region, thereby reducing the tendency to generate groove defects. In addition, the average crystal growth rate was measured to be approximately 144 μm / h, which is slightly higher than that in Example 4. Some test results of this sample are shown in Figure 4. KOH corrosion results show that the TSD defect density of the grown crystal is 1022 cm⁻¹. -2 .

[0098] The above results indicate that by using the Si-Cr-Al-(Pr-Nd)-Sn-Co cosolvent system, the stability of step flow in the edge region of large-size silicon carbide crystals can be improved to a certain extent, the tendency of macroscopic trench defects can be reduced, and the stable growth of 4H-SiC crystal form can be maintained. This can be achieved through the combined regulation of carbon dissolution and solute transport behavior by Pr and Nd, the regulation of Si activity and step flow morphology by Sn, and the regulation of melt flowability and interfacial dynamics by Co.

[0099] Example 6: Liquid-phase growth of silicon carbide single crystals

[0100] This embodiment is basically the same as Embodiment 5, except that the crystal growth temperature is increased from 1870℃ to 1950℃. The seed crystal fixing method, flux composition, crucible structure, melt height, seed crystal rotation speed, pulling speed program, growth time, cooling regime and sample characterization method are all the same as in Embodiment 5.

[0101] Sample characterization results showed that the obtained crystal was still a 4H-SiC crystal, and no obvious crystal transformation or polymorphic inclusions were observed, indicating that the Si-Cr-Al-(Pr-Nd)-Sn-Co cosolvent system still helps maintain the stable growth of the 4H-SiC crystal form at higher growth temperatures. Compared with Example 5, when the growth temperature was increased to 1950℃, the carbon solubility and solute transport capacity in the melt were further enhanced, and the average crystal growth rate increased to about 168 μm / h. Microscopic surface morphology analysis results showed that the obtained crystal surface was relatively smooth, and the macrostep height decreased from about 12000 nm to about 3600 nm, indicating that appropriately increasing the growth temperature in this cosolvent system helps improve the uniformity of step advancement, reduce the degree of macrostep clustering, and improve the smoothness of the growth surface. KOH etching results showed that the TSD defect density of the grown crystal was 853 cm⁻¹. -2 .

[0102] The above results indicate that appropriately increasing the growth temperature in the Si-Cr-Al-(Pr-Nd)-Sn-Co cosolvent system can improve the crystal growth rate while maintaining the stability of the 4H-SiC crystal structure, and further improve the surface morphology. This demonstrates that the composite cosolvent system formed by Pr-Nd combined with the M1-controlled component, Sn-controlled component, and Co-controlled component can maintain a relatively stable step-flow growth state under higher temperature growth conditions, thus helping to balance a higher growth rate and better crystal surface quality.

[0103] Example 7: Liquid-phase growth of silicon carbide single crystals

[0104] In this embodiment, a 6-inch zero-offset semi-insulating 4H-SiC wafer was used as the seed crystal, with the C-plane as the growth surface. The seed crystal fixation, hot-pressing carbonization treatment, crucible structure, melt height, holding time, seed crystal rotation speed, pulling speed, and growth time were the same as in Example 2. The flux system used was Si:Cr:Al:(Pr:Nd):Sn:V = 42:45:2:(3:2):2:4.

[0105] After growth, the crystal was characterized using industrial CT, Raman spectroscopy, and microscopic surface morphology analysis. The results showed that the crystal was 4H-SiC, with no obvious flux inclusions detected. A continuous and uniform step-flow structure existed on the crystal surface, and no through-groove defects were observed in the edge region. The average growth rate was approximately 170 μm / h. The maximum height and width of the edge step structure were 5500 nm and 40 μm, respectively. Furthermore, the steps were faceted, and KOH etching revealed a TSD defect density of approximately 334 cm⁻¹ in the grown crystal. -2 The experimental results were lower than those of Example 6.

[0106] Comparative Example 1: Liquid-phase growth of silicon carbide single crystals

[0107] This comparative example uses a 4-inch non-biased semi-insulating 4H-SiC wafer as the seed crystal, with the C-side as the crystal growth surface and the Si-side as the bonding surface, fixed to a graphite substrate. After bonding, it undergoes hot-pressing carbonization treatment at 600℃ for 2 hours to carbonize the adhesive and improve the stability of the seed crystal.

[0108] The growth process was the same as in Example 1, using a Si:Cr:Al = 50:46:4 flux system. The isostatic graphite crucible served as both the melt container and the carbon source, with an inner diameter of 150 mm and a height of 90 mm. The melt height was controlled to be 40 mm.

[0109] During the heating stage, the system temperature was raised to 1800 °C and held for 30 min to improve the uniformity of the melt composition and promote the dissolution of the carbon source. The seed crystal was then lowered to bring its growth surface into contact with the melt, thus initiating crystal growth. After crystal initiation, the crystal growth stage commenced, with the growth temperature maintained at 1850 °C to ensure sufficient solute carbon concentration in the melt and maintain a stable supersaturated state. During the crystal growth stage, the maximum rotational speed of the seed crystal was set to 150 rpm, and the seed crystal pulling speed decreased linearly from 150 μm / h to 80 μm / h with growth time. The total crystal growth time was set to 72 h. After crystal growth was complete, the crystal was lifted from the melt at a speed of 0.5 mm / min and then cooled to room temperature at an average cooling rate of 100 °C / h.

[0110] After the crystal samples were extracted, they were characterized using Raman spectroscopy and microscopic surface morphology analysis. The results showed that the central region of the obtained crystal was relatively flat, but the edge region was significantly coarsened, and the crystal exhibited groove-like defects that almost spanned the entire growth surface. Raman spectroscopy confirmed that the obtained crystal was 4H-SiC, and the average growth rate of the grown crystal was 127 μm / h. These results indicate that the Si-Cr-Al ternary flux system is still insufficient to fully stabilize the growth interface at the crystal edge region during 4-inch 4H-SiC liquid-phase growth. The morphology of the grown crystal and some test results are plotted on [date / image / image]. Figure 5 .

[0111] Comparative Example 2: Liquid-phase growth of silicon carbide single crystals

[0112] The seed crystal type, seed crystal fixing method, flux composition, crucible structure, melt height, seed crystal rotation speed, pulling speed program, growth time, cooling regime, and sample characterization method of this comparative example are all the same as those of Comparative Example 1. The difference from Comparative Example 1 is that the holding temperature before crystal pulling is increased from 1800℃ to 1850℃, and the crystal growth temperature is increased from 1850℃ to 1900℃.

[0113] Sample testing results show that defects such as step clustering and macroscopic grooves still exist in the edge region of the obtained crystal. Raman spectroscopy results further indicate the presence of 6H-SiC polytype inclusions in the crystal edge region. The average growth rate of the grown crystal is 144 μm / h. These results indicate that for the Si-Cr-Al cosolvent system, simply increasing the growth temperature may improve solute supply and enhance the crystal growth rate, but it is still difficult to effectively suppress edge interface instability and may increase the risk of polytype inclusions.

[0114] Comparative Example 3: Liquid-phase growth of silicon carbide single crystals

[0115] The seed crystal type, seed crystal fixing method, crucible structure, melt height, seed crystal rotation speed, seeding temperature, growth temperature, pulling speed program, growth time, cooling regime, and sample characterization method in this comparative example are all the same as in Example 2. The difference from Example 2 is that the flux ratio in this comparative example is changed from Si:Cr:Al:Ce:Ge:Co = 47:40:2:5:3:3 to Si:Cr:Al:Ce:Co = 47:43:2:5:3, that is, the M2 element Ge is removed.

[0116] Experimental results show that the grown crystal is generally smooth, but macrostep-like clustering occurs at the crystal edges. Raman spectroscopy reveals the presence of 4H and 6H impurities at the crystal edges, indicating a crystal form transformation during growth. Furthermore, measurements of the crystal thickness show an average growth rate of approximately 184 μm / h.

[0117] The above results indicate that the absence of the M2 component alters the activity of Si / C elements in the melt, leading to a change in the crystal structure of the grown crystal. Furthermore, the non-uniform propagation of the step flow results in step-like clustering at the edges of the grown crystal, with the macrostep height reaching a maximum of 7000 nm and the step width exceeding 50 μm.

[0118] The experimental summary table for the above embodiments is shown in Table 1.

[0119] Table 1 Summary of Experimental Results

[0120] .

[0121] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A multi-component flux system for liquid-phase growth of silicon carbide single crystals, characterized in that, Composed of Si, Cr, Al, M1, M2, and M3, the atomic percentage of each component is as follows: Si 35-60 at.%, Cr 35-55 at.%, Al 0.5-10 at.%, M1 0.5-12 at.%, M2 0.1-10 at.%, M3 0.1-8 at.%; and the sum of the atomic percentages of all components is 100 at.%. M1 is selected from one or more of La, Ce, Pr, and Nd; M2 is selected from one or more of Ge and Sn; M3 includes a first functional group and / or a second functional group, wherein the first functional group is selected from one or more of Fe, Co, Ni, Sc, and Y, and the second functional group is selected from one or more of Ti, V, Mn, Cu, Zn, and Zr.

2. The multi-component co-solvent system according to claim 1, characterized in that, The total content of the elements in the first functional group is 0.5-8 at.%.

3. The multi-component co-solvent system according to claim 1, characterized in that, The total content of the elements in the second functional group is 0.1-6 at.%.

4. The multi-component co-solvent system according to claim 1, characterized in that, M1 is Ce, M2 is Ge, and M3 contains Co.

5. The multi-component co-solvent system according to claim 1, characterized in that, The content of Si is 40-50 at.%, the content of Cr is 40-50 at.%, the content of Al is 1-5 at.%, the content of M1 is 2-8 at.%, the content of M2 is 1-5 at.%, and the content of M3 is 1-5 at.

6. A method for growing silicon carbide single crystals using a liquid-phase method, characterized in that, The multi-component cosolvent system according to claim 1 includes the following steps: Weigh out Si, Cr, Al, M1, M2 and M3 raw materials according to the preset atomic percentage and place them in a crucible; Heating is performed under a protective atmosphere or vacuum to melt the components and form a flux melt. The heat treatment allows the melt to dissolve the carbon source and reach a saturated or near-saturated state suitable for silicon carbide growth; Silicon carbide seed crystals are brought into contact with the melt for crystal introduction, and the growth temperature, temperature gradient, seed crystal rotation speed and growth time are controlled to enable silicon carbide to grow epitaxially on the surface of the seed crystals in the liquid phase. After growth is complete, the temperature is lowered and the crystals are removed.

7. The method according to claim 6, characterized in that, The growth temperature is 1650-2000℃.

8. The method according to claim 6, characterized in that, The growth temperature is 1750-1950℃.

9. The method according to claim 6, characterized in that, The silicon carbide seed crystal is a 4H-SiC seed crystal, and the growth crystal plane is the C plane.

10. The method according to claim 6, characterized in that, The carbon source is a graphite crucible.

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