SiC crystal seed crystal protection method for reducing particles based on double-layer quartz vessel and nitrogen cavity coating

Abstract

The invention relates to the technical field of semiconductor material preparation and crystal growth, discloses a SiC crystal seed crystal protection method for reducing particles based on double-layer quartz vessel and nitrogen cavity coating, and aims to solve the problems of particle pollution and poor surface microscopic perfection of seed crystals in the SiC crystal growth process. The protection method is characterized by comprising the following steps: preparing a double-layer quartz vessel and dynamically capturing particles; seed crystal plasma pre-cleaning and gradient thermal field coating are carried out; and positive pressure inert atmosphere pollution-free integrated transfer and sealing are realized. According to the scheme, the initial surface perfectness of the silicon carbide seed crystal can be remarkably improved, and the forming probability of defects such as microtubules, dislocation and stacking faults is reduced, so that a large-size and high-quality silicon carbide single crystal ingot is obtained.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material preparation and crystal growth technology. Specifically, it relates to a method for protecting SiC crystal seed crystals by reducing particles based on a double-layer quartz dish and nitrogen cavity coating. Background Technology

[0002] In the technological landscape of the modern semiconductor industry, third-generation wide-bandgap semiconductor materials, represented by silicon carbide (SiC), have become core supporting materials in key fields such as power electronics, new energy vehicles, rail transportation, and 5G communications due to their superior performance under extreme conditions such as high voltage, high frequency, and high temperature. The preparation of silicon carbide single crystals, especially the stable growth of large-size, high-quality single crystals, is the cornerstone of the entire industry chain. In mainstream crystal growth processes such as physical vapor transport (PVT), the seed crystal, as a template guiding crystal orientation and determining the initial crystallization quality, has a decisive influence on the defect density, electrical properties, and yield of the final ingot due to its own quality and the microenvironment state during the initial growth stage. Therefore, the protection and pretreatment technology of seed crystals has always been the focus of research and optimization in this field.

[0003] Early technological practices primarily focused on establishing a stable and controllable macroscopic growth environment. For example, precise control of the crucible structure, insulation system, and gas flow field aimed to create a suitable temperature gradient and stable mass transfer rate within the growth chamber, which to some extent promoted the increase in silicon carbide crystal size and improved growth efficiency. During this stage, the industry generally used crucibles made of materials such as quartz or graphite as raw material carriers and employed conventional methods such as resistance heating to pre-treat seed crystals with coatings to prevent oxidation or decomposition at high temperatures. These technological solutions effectively solved the fundamental feasibility problem of crystal growth during a specific historical period, laying the foundation for the initial application of silicon carbide materials. For instance, the solution disclosed in patent document CN113445122B, through its refined thermal field control design, aims to optimize the growth conditions of large-size crystals, demonstrating continuous exploration in the control of the macroscopic process environment. Similarly, the patent document with publication number CN114395803B proposes a structural solution for local protection to address the specific problem that seed crystal edges are prone to sublimation and decomposition due to thermal stress concentration. These are all beneficial attempts to solve specific problems within the existing technical framework.

[0004] However, as downstream applications place increasingly stringent demands on the performance of silicon carbide devices, especially in the pursuit of lower defect densities and larger effective wafer areas, the aforementioned technical paths based on macroscopic control and local optimization are gradually revealing their inherent limitations. A deep-seated technical contradiction is becoming increasingly prominent: there is an inherent conflict between the increasingly stringent macroscopic process conditions (such as higher growth temperatures and longer holding times) required to achieve larger crystal sizes and longer growth cycles, and the high-cleanliness and high-stability environment required to ensure the initial microscopic perfection of the seed crystal surface. The reason for this is that as crystal growth processes evolve towards extreme conditions exceeding 2000 degrees Celsius and lasting for hundreds of hours, the microscopic particle contamination problem, which was originally considered a secondary influencing factor, is dramatically amplified and evolves into a bottleneck restricting crystal quality. In such a harsh thermochemical environment, the physical friction between the inner wall of a traditional single-layer quartz dish and the silicon carbide raw material powder, as well as the trace volatilization and precipitation of the dish's own material at high temperatures, will inevitably generate micron- or even nano-sized particulate impurities. These particles, under the disturbance of airflow within the growth chamber, easily migrate and adhere to the surface of the seed crystal, becoming the direct source of fatal crystal defects such as microtubules, dislocations, and stacking faults. Therefore, the crucible itself transforms from a passive "container" into an active "source of contamination."

[0005] Meanwhile, this contradiction is also reflected in the seed crystal coating protection stage. Traditional coating processes, whether due to insufficient uniformity in heating methods or lax control of the purity of the protective atmosphere, often result in protective films with uneven thickness, impure composition, or microscopic defects. In the past, these minor imperfections might have been tolerable, but in the current pursuit of near-perfect crystals, any initial surface unevenness or chemical contamination will be replicated and amplified layer by layer during the long growth process, ultimately leading to large-area lattice defects. Existing technologies, such as the solutions disclosed in the aforementioned patents, either focus on thermal field control while neglecting the suppression of source particulate contamination, or focus on the local structural protection of the seed crystal without providing a global, high-purity surface treatment solution. These solutions are essentially repairs and improvements within the existing process framework, failing to fundamentally break the negative feedback chain of "macroscopic growth conditions deteriorating the microscopic surface environment."

[0006] Therefore, how to systematically suppress the generation of particulate impurities in the process chamber from the source while meeting the high temperature and long cycle process requirements for large-scale crystal growth, and combine this with a seed crystal surface treatment technology that can guarantee purity and uniformity at the atomic scale, so as to completely break the inherent contradiction between macroscopic growth conditions and microscopic surface quality, has become a key challenge and a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for protecting SiC crystal seeds by reducing particles, which can systematically suppress micro-particle contamination from multiple dimensions such as the source of particle generation, the transport path and the pretreatment of the seed crystal surface, thereby significantly improving the microscopic perfection of the initial surface of silicon carbide (SiC) seed crystals without sacrificing the macroscopic growth process conditions, and breaking the inherent contradiction between macroscopic growth conditions and microscopic surface quality.

[0008] To achieve the aforementioned objectives, this invention provides a method for protecting SiC crystal seed crystals by reducing particles, based on a double-layer quartz dish and nitrogen chamber coating. The method comprises a series of precisely defined and organically linked process steps, specifically including: the preparation of the double-layer quartz dish and the construction of a dynamic particle trapping system; a high-purity seed crystal coating step based on plasma pre-cleaning and gradient thermal field deposition; and a contamination-free integrated transfer and sealing step based on positive pressure inert atmosphere protection. Through the synergistic effect of these steps, an initial environment of ultra-high cleanliness, from the macroscopic container to the microscopic surface, is constructed for the seed crystal before the start of physical vapor transport (PVT) crystal growth.

[0009] Specifically, the preparation of the double-layer quartz dish and the construction of the particle dynamic capture system aim to fundamentally suppress particles generated by the physical interaction between the silicon carbide raw material and the inner wall of the crucible, and to actively remove particles precipitated from the crucible material itself at high temperatures. This step specifically includes the following sub-steps:

[0010] First, a double-layer quartz dish assembly is provided. The double-layer quartz dish assembly consists of an inner quartz dish and an outer quartz dish nested coaxially. The inner quartz dish is made of high-purity fused silica, and its surface in contact with the silicon carbide raw material powder is chemically and mechanically polished, with the surface roughness Ra controlled to be no greater than 0.08 micrometers. To further enhance its chemical inertness at high temperatures and reduce particle adhesion, an amorphous silicon nitride (Si3N4) thin film with a thickness of 50 to 80 nanometers is deposited on the inner surface of the inner quartz dish using low-pressure chemical vapor deposition (LPCVD).

[0011] Secondly, a set of spiral microchannels is etched onto the outer surface of the inner quartz dish using femtosecond laser precision machining technology. The spiral microchannels originate at the center of the bottom of the inner quartz dish and extend to the upper edge of the dish wall in an Archimedean or logarithmic spiral trajectory. The cross-sectional shape of the microchannels is rectangular, with a width and depth of 0.5 mm. The outer quartz dish is also made of high-purity fused silica, and its inner diameter matches the outer diameter of the inner quartz dish. When the outer quartz dish is fitted over the inner quartz dish, its inner wall completely seals the spiral microchannels, thus forming a closed spiral gas flow network that runs through the entire outer wall of the dish. The inner and outer quartz dishes are connected and sealed by a precision-machined graphite or silicon carbide ceramic sealing ring along the upper edge, forming an annular gap with a constant thickness of 1.5 mm. This gap is defined as the "Interstitial Gas Chamber."

[0012] Furthermore, a dynamic particle capture and gas purification circulation system connected to the spiral microchannel is constructed. The graphite or silicon carbide ceramic sealing ring is equipped with a gas inlet and a gas outlet, respectively connected to the end and start points of the spiral microchannel. The gas outlet is connected to an external closed-loop gas purification circuit via a high-temperature resistant ceramic pipe. The gas purification circuit consists of an oil-free diaphragm pump, a cryogenic cold trap downstream of the diaphragm pump, an ultra-low penetration air filter (ULPA filter) downstream of the cryogenic cold trap, and a mass flow controller downstream of the filter, connected in series. The cryogenic cold trap is cooled by liquid nitrogen, maintaining an operating temperature of -196 degrees Celsius to capture and solidify highly volatile impurities in the gas stream. The ULPA filter has a filtration accuracy of no less than 99.99995% for particles with a diameter of 0.12 micrometers. The mass flow controller is responsible for precisely controlling the gas flow rate in the circuit. The final output of the purification circuit is connected to the gas inlet on the sealing ring via another ceramic pipe. During crystal growth, high-purity argon gas (99.999% purity) is introduced into this closed-loop circuit, and a constant flow rate of 50 standard cubic centimeters per minute (sccm) is set using a mass flow controller. The diaphragm pump drives the high-purity argon gas to continuously circulate between the spiral microchannel and the external purification circuit. As the circulating gas flows within the microchannel, it continuously purges and carries away tiny particles that may precipitate from the quartz dish material or permeate from the main growth chamber. The carried particles enter the purification circuit with the gas and are efficiently captured and removed by the cryogenic cold trap and ULPA filter. The purified high-purity argon gas is then reinjected into the microchannel through the inlet, thus forming a dynamic and continuous particle capture and removal mechanism. Simultaneously, the pressure in the interlayer gas chamber is maintained 50 to 100 Pascals higher than the operating pressure of the main growth chamber, forming a positive pressure barrier that physically prevents particles from the main growth chamber from intruding into the interior of the double-layer quartz dish structure.

[0013] Furthermore, the high-purity seed crystal coating step based on plasma pre-cleaning and gradient thermal field deposition aims to prepare a dense, uniform, stress-free protective film on the seed crystal surface that is highly matched to the substrate lattice, providing an atomically flat and chemically pure template for subsequent homoepitaxial growth. This step is performed in a separate, dedicated high-cleanliness coating chamber, which is completely physically isolated from the PVT crystal growth furnace. This step specifically includes the following sub-steps:

[0014] First, in-situ plasma pre-cleaning of the seed crystal is performed. The silicon carbide seed crystal to be treated is fixed on a graphite base and placed into the coating chamber. The coating chamber is constructed of 316L stainless steel with electrolytically polished inner walls and is equipped with a heating jacket capable of heating the chamber to 400 degrees Celsius for baking and degassing. The chamber is then evacuated to 10... -7 A high vacuum state was established, followed by the introduction of 99.9999% pure nitrogen gas. The pressure inside the chamber was stabilized at 100 Pascals using a mass flow controller. A showerhead-shaped radio frequency electrode was positioned above the seed crystal. A 13.56 MHz radio frequency power supply applied 50 watts to this electrode, exciting the generation of low-temperature nitrogen plasma in the vicinity of the seed crystal surface. This plasma was then used to physically bombard and chemically clean the seed crystal surface for 180 seconds, thoroughly removing any residual organic matter, adsorbed oxide molecules, and microparticles that might be present on the surface.

[0015] Next, a protective film is deposited under a gradient thermal field. After plasma cleaning, the RF power output is stopped, and a high-purity nitrogen atmosphere is maintained. Inside the coating chamber, a multi-zone independently controlled water-cooled electromagnetic induction heating coil is arranged around the seed crystal substrate. The geometry and turn distribution of the coil are precisely designed to establish a precise and controllable radial temperature gradient on the seed crystal, with a high temperature at the center and a low temperature at the edges. A dual-wavelength optical pyrometer is used to monitor the temperature at the center of the seed crystal in real time without contact, and this monitoring signal is used as feedback for the PID control loop to precisely regulate the current and frequency of each zone of the induction coil. After the heating program is started, the temperature at the center of the seed crystal is rapidly increased to 1850 degrees Celsius, while the temperature at the edge of the seed crystal is maintained at 1800 degrees Celsius by controlling the power of the coil zones, thus forming a stable radial temperature difference of 50 degrees Celsius. Around the seed crystal substrate, a ring-shaped crucible made of high-purity graphite is placed concentrically, containing tantalum carbide (TaC) powder with a particle size of 10 to 50 micrometers as the coating source material. At a high temperature of 1850 degrees Celsius, tantalum carbide powder sublimates to form gaseous TaC molecules. Due to the temperature gradient on the seed crystal surface, the gaseous TaC molecules, after adsorption on the seed crystal surface, exhibit surface migration behavior driven by the thermal gradient, preferentially migrating and accumulating towards the lower-energy central high-temperature region. This process greatly promotes the densification of the film and effectively releases the internal stress that may be caused by lattice mismatch. The entire deposition process lasts 600 seconds, ultimately forming a high-quality tantalum carbide protective film with a thickness of 200 nanometers, a thickness non-uniformity of less than ±5%, and high orientation selectivity on the seed crystal surface.

[0016] Furthermore, the contamination-free integrated transfer and sealing step based on positive pressure inert atmosphere protection aims to ensure that the surface of the perfectly coated seed crystal is not contaminated by any secondary particles or chemicals from the external environment during the transfer from the coating chamber to the double-layer quartz dish assembly in the PVT growth furnace. This step is achieved through a specially designed sealing and transfer module. This step specifically includes the following sub-steps:

[0017] First, a sealed transfer module is provided. This module is essentially a small, portable clean chamber made of lightweight alloy or stainless steel, integrating a piezoelectric ceramic-driven robotic arm capable of precise movement in three-dimensional space. The arm's end is equipped with grippers for grasping seed crystal substrates. The module features independent high-purity nitrogen (99.9999% purity) purging inlets and exhaust valves, and is equipped with standardized mechanical and vacuum interfaces.

[0018] Secondly, both the coating chamber and the top cover of the PVT growth furnace used to support the double-layer quartz dish assembly are equipped with highly airtight gate valves that match the interface of the sealed transfer module. At the start of the transfer operation, the sealed transfer module is first docked with and locked to the gate valve of the coating chamber. The dead zone between the module and the gate valve is then evacuated and repeatedly flushed with high-purity nitrogen. Subsequently, the gate valves of both the coating chamber and the transfer module are opened simultaneously. While maintaining a positive pressure nitrogen environment inside both the coating chamber and the transfer module, the robotic arm within the control module extends into the coating chamber, grasps the coated seed crystal and its base, and then retracts back into the module. Both gate valves are then closed. At this point, the perfectly coated seed crystal is safely sealed in a moving environment continuously protected by positive pressure high-purity nitrogen.

[0019] Finally, the sealed transfer module carrying the seed crystal is moved to the side of the PVT growth furnace and docked with, locked, and cleaned in the intermediate area of ​​the furnace top cover. Prior to this operation, the prepared double-layer quartz dish assembly and its particle dynamic capture system were installed and fixed below the PVT furnace top cover. Then, the valves on both the PVT furnace top cover and the transfer module are opened simultaneously. Under continuous positive pressure nitrogen protection, the robotic arm precisely places and fixes the seed crystal and its base onto the seed crystal rod at the top of the double-layer quartz dish assembly. The robotic arm retracts into the module, and both valves close. This completes the entire process of pollution-free transfer and sealing, from coating to final installation.

[0020] After completing all the above preparatory steps, the PVT growth furnace can be shut down, and the main heating program and main process gas system can be started, while the particle dynamic capture system of the double-layer quartz dish continues to operate. Since the seed crystal has an atomically clean surface covered by a perfect protective film, and the particle generation source in the entire growth container environment has been eliminated and the transport path has been cut off, the subsequent silicon carbide crystal growth process can be carried out under unprecedented ultra-high cleanliness initial conditions. This greatly reduces the probability of the formation of defects such as microtubes, dislocations, and stacking faults, providing a decisive guarantee for obtaining large-size, high-quality silicon carbide single crystal ingots. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall process of the method of the present invention.

[0022] Figure 2 This is a cross-sectional view of the structure of the double-layer quartz dish assembly in this invention.

[0023] Figure 3 This is a schematic diagram of the particle dynamic capture and gas purification circulation system in this invention.

[0024] Figure 4 This is a schematic diagram of the coating chamber structure used for high-purity coating of seed crystals in this invention.

[0025] Figure 5 This is a schematic diagram of the pollution-free integrated transfer process using a sealed transfer module in this invention.

[0026] The attached figures are labeled as follows: 1. Inner quartz dish; 2. Outer quartz dish; 3. Spiral microchannel; 4. Interlayer gas chamber; 5. Sealing ring; 10. Double-layer quartz dish assembly; 11. Oil-free diaphragm pump; 12. Cryogenic cold trap; 13. ULPA filter; 14. Mass flow controller; 20. Coating chamber; 21. Silicon carbide seed crystal; 22. Base; 23. Radio frequency electrode; 24. Induction heating coil; 25. Ring crucible; 30. Sealed transfer module; 31. Robotic arm; 32. Valve. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The embodiments described below are merely some embodiments of this invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] Reference Figures 1 to 5This application discloses a method for protecting SiC crystal seed crystals by reducing particles, based on a double-layer quartz dish and nitrogen chamber coating. This method aims to precisely control multiple aspects, including the source of particle generation, the transport path, and the ultimate cleanliness of the seed crystal surface, through a systematic, multi-stage synergistic process. This creates an unprecedentedly high-cleanliness initial environment for the silicon carbide (SiC) seed crystal before the start of physical vapor transport (PVT) growth, fundamentally suppressing crystal growth defects caused by microscopic particles. The core technical concept of this method lies in the organic integration of a dynamic particle capture system, a high-quality thin-film protective layer, and a pollution-free transfer process, forming a complete technical closed loop.

[0029] In a specific implementation scenario, the overall methodology of this invention can be decomposed into three logically progressive and technologically connected key technical modules: First, the preparation of a double-layer quartz dish and the construction of a particle dynamic capture system, the goal of which is to eradicate the particle source at the physical container level; second, the high-purity coating step of the seed crystal based on plasma pre-cleaning and gradient thermal field deposition, the goal of which is to coat the seed crystal body with an atomically perfect "armor"; and finally, the pollution-free integrated transfer and sealing step based on positive pressure inert atmosphere protection, the goal of which is to ensure that the clean state created by the first two steps is not lost when transferred to the final growth station.

[0030] The first key technology module, namely the preparation of the double-layer quartz dish and the construction of the particle dynamic capture system, will now be described in detail in an engineering manner. This step is based on the recognition that in traditional PVT growth, the physical and chemical interactions between the silicon carbide raw material and the inner wall of the graphite or quartz crucible at high temperatures, as well as the precipitation of impurities and particle detachment of the crucible material itself at high temperatures, are the main sources of particulate contamination within the growth chamber. To suppress and actively remove these particles at their source, this invention designs and implements a sophisticated hardware system.

[0031] Specifically, refer to Figure 2This step begins with providing a double-layer quartz dish assembly 10. This assembly consists of an inner quartz dish 1 and an outer quartz dish 2, which are nested together coaxially. For the inner quartz dish 1, high-purity fused silica with a purity of not less than 99.998% is used, such as JGS-1 grade or equivalent quartz produced by Heraeus. This material has extremely low bubble and hydroxyl content, ensuring excellent chemical stability and extremely low impurity precipitation in subsequent high-temperature operating environments exceeding 2000 degrees Celsius. The inner surface of the inner quartz dish 1, which will directly contact the high-purity silicon carbide raw material powder, must undergo a rigorous surface treatment process. This process is chemical mechanical polishing (CMP), using an alkaline colloidal suspension based on nano-sized silica (SiO2) particles with a pH controlled at 10.5 ± 0.2, in conjunction with a polyurethane polishing pad. During the polishing process, the polishing head pressure was set to 4.0 psi, and the spindle and polishing disc rotation speeds were set to 60 rpm and 55 rpm, respectively. This process stably controls the arithmetic mean roughness Ra value of the inner surface of the inner quartz dish 1 to below 0.08 micrometers, preferably below 0.05 micrometers. This mirror-like surface finish significantly reduces mechanical friction and physical adhesion between the silicon carbide powder and the dish wall, thereby reducing frictional particles generated by minute displacements during loading or thermal cycling.

[0032] To further improve the performance of the inner surface of the inner quartz dish 1, a surface modification treatment is required after chemical mechanical polishing and thorough cleaning and drying. This treatment uses low-pressure chemical vapor deposition (LPCVD) technology to deposit an amorphous silicon nitride (Si3N4) film with a thickness between 50 and 80 nanometers on the inner surface of the dish. The LPCVD process is carried out in a dedicated tube furnace, with dichlorosilane (SiH2Cl2) and high-purity ammonia (NH3) as the reaction precursors. The specific process parameters are set as follows: furnace tube temperature 780 degrees Celsius, chamber working pressure 25 Pascals, dichlorosilane to ammonia flow ratio of 1:3, and total flow rate of 200 standard cubic centimeters per minute (sccm). Under these conditions, the deposition rate is approximately 2.5 nanometers per minute, and by precisely controlling the deposition time to 24 minutes, a silicon nitride film with a thickness of approximately 60 nanometers can be obtained. This dense silicon nitride film has extremely high chemical inertness and hardness. At high temperatures, it can effectively prevent impurities such as alkali metal ions in the quartz matrix from diffusing outward and form an interface that is more stable than the surface of pure quartz and less likely to react with silicon carbide raw materials, thereby minimizing the probability of generating chemically reactive particles.

[0033] Next, the outer surface of the inner quartz dish 1 is precision-machined. A precision machining system equipped with a ytterbium-doped fiber femtosecond laser with a wavelength of 1030 nm and a pulse width of 280 femtoseconds is used to etch a set of spiral microchannels 3 on the outer wall of the inner quartz dish 1. The geometric configuration of the spiral microchannels 3 can be a logarithmic spiral, designed according to r = a·e. b·θ The function form is given by θ, where a and b are constants and θ is the polar angle. This configuration ensures a relatively uniform linear velocity of the gas flowing within the channel. The microchannel originates at the bottom center of the inner quartz dish 1 and spirals upwards until it reaches near the upper edge of the dish wall. The cross-section of the channel is precisely machined into a rectangle, with its width and depth strictly controlled within 0.5 mm ± 0.01 mm. The characteristics of femtosecond laser cold processing ensure that there is no heat-affected zone, no microcracks, and no recast layer at the processing edge, ensuring the structural integrity and airtightness of the microchannel. After processing, it needs to be thoroughly cleaned with deionized water in a megasonic cleaning machine to remove any debris generated during processing.

[0034] The outer quartz dish 2 is also made of the same high-purity fused quartz material as the inner quartz dish 1. Its inner diameter is precision ground and polished to ensure a precise fit with the outer diameter of the inner quartz dish 1. When the outer quartz dish 2 is fitted onto the inner quartz dish 1 from the outside, its smooth inner wall completely seals the spiral microchannels 3 on the outer wall of the inner quartz dish 1, thus forming a closed, spiral gas transport network that extends beneath the entire outer surface of the dish. The inner quartz dish 1 and the outer quartz dish 2 are connected, positioned, and sealed by a specially designed sealing ring 5 along their upper edges. This sealing ring 5 is preferably made of high-purity isotropic graphite or densified silicon carbide ceramic, and its upper and lower surfaces are precisely fitted to the upper edge faces of the inner and outer quartz dishes, respectively, to form an airtight seal. After assembly, an annular gap with a thickness of 1.5 mm is formed between the outer wall of the inner quartz dish 1 and the inner wall of the outer quartz dish 2. This gap is defined as the interlayer gas chamber 4.

[0035] The brilliance of this double-layered quartz dish assembly 10 lies in the fact that it is not only a static container, but also the core of a dynamic particle capture system. (Refer to...) Figure 3To achieve the dynamic capture function, a gas purification and circulation system connected to the spiral microchannel 3 needs to be constructed. Two through-type precision gas interfaces are machined on the sealing ring 5, one as a gas inlet and the other as a gas outlet. The gas outlet is connected to an external closed-loop gas purification circuit via a 6 mm outer diameter alumina ceramic tube. This purification circuit consists of a series of functional components connected in series: first, an oil-free diaphragm pump 11, such as the German KNF N 86KT.18 model, with a pump head made of polytetrafluoroethylene (PTFE), ensuring that no oil or metal particle contamination is introduced during gas delivery. After being pumped out from the diaphragm pump 11, the gas enters a cryogenic cold trap 12. The trap body is made of 316L stainless steel, with staggered baffles inside to increase the contact area and residence time between the gas and the cold wall. Externally, it is cooled by liquid nitrogen contained in a Dewar flask, ensuring that the operating temperature inside the trap is stably maintained at -196 degrees Celsius (77K). At this low temperature, highly volatile impurities such as water vapor and organic vapors that may be present in the gas flow, escaping from the quartz dish or the environment, will be efficiently condensed and captured. After leaving the cryogenic trap 12, the gas then enters an ultra-low penetration air filter (ULPA filter) 13. This filter uses U16 grade glass fiber filter media, and its single-pass filtration efficiency for even the most difficult-to-filter 0.12-micron particles is strictly guaranteed to be above 99.99995%, effectively intercepting any solid particles carried in the circulating gas. The ultra-purified gas after passing through the ULPA filter 13 then passes through a mass flow controller (MFC) 14, such as the Brooks Instruments SLA5850 series thermal MFC. This MFC is responsible for precise closed-loop control of the gas flow in the loop. The final output of the purification loop, i.e., the outlet of the MFC, is connected to the gas inlet on the sealing ring 5 through another alumina ceramic tube, thus completing the construction of the entire closed-loop loop.

[0036] Before and throughout the PVT crystal growth process, high-purity argon gas with a purity of up to 99.999% (5N grade) is introduced into this closed-loop circuit, and a constant flow rate of 50 sccm is set using a mass flow controller 14. Driven by an oil-free diaphragm pump 11, the high-purity argon gas enters from the gas inlet, flows through the entire spiral microchannel 3, and is then extracted from the outlet to enter the external purification circuit for regeneration, repeating the cycle continuously. This continuous circulating airflow acts like a "scavenger" for the walls of the double-layer quartz dish. Any tiny particles that might precipitate from the quartz material due to high temperatures, or particles that attempt to penetrate from the main growth chamber due to pressure fluctuations, are effectively swept away and carried away by this flowing argon gas. This contaminated argon gas then enters the purification circuit, where particulate matter is completely captured in the ULPA filter 13, and gaseous impurities are solidified and removed in the cryogenic cold trap 12. The purified ultrapure argon gas is returned to the microchannels, forming a dynamic, efficient, and continuous particle capture and removal mechanism. More importantly, by precisely controlling the overall pressure of the argon gas circuit, the pressure in the interlayer gas chamber 4 and the spiral microchannel 3 can always be 50 to 100 Pascals higher than the operating pressure of the PVT main growth chamber. This small positive pressure difference forms a robust gas barrier or "gas curtain," effectively preventing any particulate matter from entering the double-layer quartz dish structure from the environment within the main growth chamber, thus providing double protection against particulate contamination.

[0037] Now we turn to the second key technology module: the high-purity seed crystal coating step based on plasma pre-cleaning and gradient thermal field deposition. The purpose of this step is to perform ultimate cleaning of the silicon carbide seed crystal surface, which serves as the starting point for crystal growth, and to deposit a functional protective film on it. This protective film must possess high density, high uniformity, no macroscopic stress, and good lattice compatibility with the silicon carbide substrate, thus providing a near-perfect, atomically flat, and chemically pure template for subsequent homoepitaxial growth. To prevent cross-contamination, this step is performed in a separate, dedicated high-cleanliness coating chamber 20, which is physically isolated from the PVT crystal growth furnace.

[0038] Reference Figure 4 The main body of the coating chamber 20 is constructed of 316L stainless steel, and all its inner surfaces have undergone electrolytic polishing, resulting in a surface roughness Ra of less than 0.2 micrometers to reduce surface area and gas adsorption. The outer wall of the chamber is encased in a programmable heating jacket, which can bake the entire chamber to 400 degrees Celsius for thorough degassing before the process begins. The vacuum system consists of a magnetically levitated turbomolecular pump with a pumping speed of 1000 liters / second and an oil-free dry vortex backing pump, capable of pumping the chamber to an ultimate vacuum of 10... -7 Pascal's level.

[0039] Before coating, the silicon carbide seed crystal 21 undergoes an in-situ plasma pre-cleaning process. The silicon carbide seed crystal 21 to be treated, for example, a 4H-SiC wafer with a diameter of 150 mm and a (0001) silicon surface, is fixed to a base 22 also made of high-purity isotropic graphite using a high-purity graphite clasp. It is then fed into the coating chamber 20 through a load-locked vacuum chamber. After the chamber returns to a high vacuum state, high-purity nitrogen gas with a purity of 99.9999% (6N grade) is introduced, and the pressure inside the chamber is precisely stabilized at 100 Pascals using a mass flow controller. Approximately 50 mm above the seed crystal 21, a showerhead-shaped radio frequency electrode 23 is positioned, with numerous micropores distributed on it to ensure plasma uniformity. Energy from a 13.56 MHz radio frequency power supply is coupled to this electrode through a matching network, with the applied power set to 50 watts. This power generates a low-temperature, high-density nitrogen plasma near the seed crystal surface. The high-energy nitrogen ions and active nitrogen radicals in the plasma perform a continuous 180-second physical sputtering and chemical cleaning of the seed crystal surface. Physical sputtering effectively removes loosely attached microparticles from the surface, while the chemical reaction efficiently decomposes and removes any organic contaminants that may have remained from the pretreatment, as well as the extremely thin oxide layer (SiOx) naturally formed on the surface, ultimately exposing an atomically clean silicon carbide surface.

[0040] After plasma cleaning, the RF power output is immediately stopped, but a high-purity nitrogen atmosphere of 100 Pascals is maintained inside the chamber. The process then seamlessly transitions to the protective film deposition process under a gradient thermal field. Inside the coating chamber 20, a multi-zone independently controlled water-cooled electromagnetic induction heating coil 24 is arranged around the seed crystal base 22. This coil is designed with a three-zone structure: a central main coil, an intermediate ring coil, and an outer ring coil. Each zone is powered by an independent RF power supply with a frequency adjustable in the range of 100-200 kHz. This design allows for the establishment of a precisely controllable radial temperature gradient on the seed crystal 21. The temperature at the very center of the seed crystal 21 is monitored in real-time non-contact using a dual-wavelength optical pyrometer, and this reading is used as the feedback signal for the main PID control loop. After the heating program is initiated, the system first rapidly raises the temperature at the center of the seed crystal to 1850 degrees Celsius within 120 seconds and then stabilizes it at that temperature using the main PID loop. Meanwhile, by adjusting the power ratio of the coils in the middle and outer regions, a smooth linear temperature decrease is achieved from the center to the edge of the seed crystal. At the very edge of the 150 mm diameter seed crystal, the temperature is precisely controlled at 1800 degrees Celsius. This establishes a stable radial temperature difference of 50 degrees Celsius across the entire seed crystal surface, with a higher temperature at the center and a lower temperature at the edge.

[0041] A ring-shaped crucible 25, made of high-purity graphite (purity >99.995%), is concentrically placed around the seed crystal base 22. High-purity tantalum carbide (TaC) powder with a particle size distribution between 10 and 50 micrometers is uniformly distributed within the crucible as the source material for the coating. At a high temperature of 1850 degrees Celsius at the center of the seed crystal, the TaC powder within the ring-shaped crucible 25 undergoes vigorous sublimation, forming a gaseous flow of TaC molecules, which is transported towards the cooler seed crystal surface. Once the gaseous TaC molecules reach and adsorb onto the seed crystal surface, their subsequent surface diffusion and nucleation behavior are significantly influenced by this radial temperature gradient. According to thermodynamic principles, adsorbed atoms tend to migrate to lower energy locations, i.e., to regions with higher temperatures. This temperature-driven surface migration effect promotes the preferential aggregation and nucleation of TaC atoms in the high-temperature region at the center of the seed crystal, and their outward growth along the temperature gradient. This greatly promotes the densification of the film and the merging of island structures, effectively suppressing the formation of pores. Simultaneously, this directional migration process effectively releases internal stress that may accumulate due to the lattice mismatch (approximately 3.5%) between TaC and SiC, preventing film cracking or peeling. The entire deposition process is precisely controlled for 600 seconds. Under these conditions, a high-quality cubic TaC protective film with a thickness of 200 nm, a thickness non-uniformity of less than ±5% over the entire 150 mm diameter range, and high (111) orientation preference is finally formed on the surface of seed crystal 21. The protective film has a smooth surface, and its root mean square (RMS) roughness is less than 1 nm as measured by atomic force microscopy (AFM).

[0042] Finally, we move to the third key technology module: the contamination-free integrated transfer and sealing step based on a positive pressure inert atmosphere. This step acts as a bridge, ensuring that the carefully prepared seed crystals with a perfect protective film from the previous stage are not subjected to any secondary contamination from dust, moisture, or organic molecules in the ambient air during the transfer from the coating chamber 20 to the double-layer quartz dish assembly 10 in the PVT growth furnace. This task relies on a specially designed, movable sealing and transfer module 30.

[0043] Reference Figure 5The sealed transfer module 30 is essentially a small, portable cleanroom. Its housing is machined from lightweight 6061-T6 aluminum alloy, with an internal volume of approximately 10 liters. It integrates a robotic arm 31 capable of precise translation and rotation in XYZ three-dimensional space. The robotic arm is driven by a piezoelectric ceramic motor, achieving micron-level positioning accuracy and extremely smooth movement, avoiding vibrations and particles that may occur with traditional motors. The end of the robotic arm 31 is equipped with a gripper made of high-temperature resistant PEEK (polyetheretherketone) material for grasping the graphite seed crystal base 22, preventing metal-to-metal contact contamination. The module 30 itself features a high-purity nitrogen (99.9999%) purge inlet and an exhaust valve, and is equipped with a pressure sensor, enabling it to maintain an ultra-clean nitrogen environment slightly above atmospheric pressure (e.g., 100 Pascals positive pressure) at all times. At its opening for connection with the outside, there is a standardized KF or ISO flange interface, and a highly airtight valve 32 is integrated.

[0044] To achieve seamless connection, the loading and unloading port of the coating chamber 20 and the top cover of the PVT growth furnace used to support the double-layer quartz dish assembly 10 are both pre-installed with valves 32 of the same specifications that are fully matched with the interface of the sealing transfer module 30.

[0045] The transfer operation is performed according to the following strict procedure. First, the sealed transfer module 30 is moved to the side of the coating chamber 20 and mechanically docked with and locked to the valve of the coating chamber via its flange interface. After docking, a small "dead zone" space is formed between the two closed valves. This dead zone is evacuated using an auxiliary vacuum pump and then repeatedly flushed with high-purity nitrogen three times (Pump-Purge cycle) to thoroughly remove residual air from the space. After purification, high-purity nitrogen is introduced into the dead zone until its pressure is equal to the pressure inside the coating chamber and the transfer module. Subsequently, the program controls the simultaneous opening of the valves of the coating chamber and the transfer module. At this moment, the two chambers are connected in a common, controlled positive pressure high-purity nitrogen environment. The robotic arm 31 in the control module extends into the coating chamber 20, precisely moves to the seed crystal base 22, firmly grasps the base with its PEEK grippers, and then smoothly retracts into the module 30. Once the robotic arm has fully retracted, the two valves immediately close synchronously. Thus, the seed crystal 21 with a perfect TaC protective film is safely encapsulated in a movable, ultra-clean microenvironment continuously protected by positive pressure high-purity nitrogen.

[0046] Next, the sealed transfer module 30 carrying the seed crystal is transported to the PVT growth furnace. Prior to this, the prepared double-layer quartz dish assembly 10 and its particle dynamic capture system have been completely installed and fixed at the designated position below the PVT furnace top cover, and the seed crystal rod is ready. Subsequently, the docking, locking, dead zone purification, and valve opening processes described above are repeated to dock the sealed transfer module 30 with the valves on the PVT furnace top cover. After the two chambers are connected, the robotic arm 31 precisely moves the seed crystal and its base 22 to the predetermined position and securely places it on the seed crystal rod inside the PVT furnace. After completing the placement, the robotic arm retracts back into the module 30, and the two valves close. Thus, from the final cleaning and coating of the seed crystal to its final installation in the growth furnace, the entire process achieves a complete, uninterrupted, and contamination-free transfer and sealing under a positive pressure inert atmosphere.

[0047] After completing all the meticulous preparatory steps described above, the main furnace body of the PVT growth furnace can be shut down, the main heating system can be started to raise the temperature, and the main process gas can be introduced according to the preset process program. During this process, the particle dynamic capture system of the double-layer quartz dish remains operational, providing continuous cleanliness for the growth environment. Because the initial surface of the seed crystal has atomic-level cleanliness and is covered by a high-quality TaC protective film, and the main particle generation sources in the entire growth container environment have been fundamentally suppressed, and potential particle transport paths have been cut off by the active airflow, the subsequent silicon carbide crystal growth process can be started under unprecedentedly high cleanliness initial conditions. This ideal initial state greatly reduces the probability of the formation of fatal defects such as micropipes, screw dislocations, and stacking faults caused by microscopic particles, providing a decisive prerequisite for finally obtaining large-size, high-integrity, and low-defect-density electronic-grade silicon carbide single crystal ingots.

[0048] Example 1

[0049] This embodiment aims to specifically demonstrate the complete implementation process of the method of the present invention.

[0050] 1. Preparation and System Construction of Double-Layer Quartz Dishes: Heraeus JGS-1 grade quartz was used to fabricate an inner quartz dish 1 with an inner diameter of 180 mm and a height of 200 mm, and an outer quartz dish 2 with an inner diameter of 183 mm, an outer diameter of 190 mm, and a height of 200 mm. The inner surface of the inner dish was CMP polished using a colloidal silica polishing slurry with pH = 10.5, a pressure of 4.0 psi, and a rotation speed of 60 / 55 rpm for 30 minutes, resulting in a final surface roughness Ra of 0.045 μm. Subsequently, in an LPCVD furnace at 780 °C and 25 Pa, SiH2Cl2 and NH3 (flow ratio 1:3, total flow rate 200 sccm) were introduced and deposited for 24 minutes to obtain a 60 nm thick Si3N4 film. A 1030 nm femtosecond laser was used to etch logarithmic spiral microchannels 3 with a depth and width of 0.5 mm on the outer wall of the inner dish. The inner and outer quartz dishes are assembled using a high-purity graphite sealing ring 5 to form an interlayer gas chamber 4 and a closed microchannel. This assembly is then connected to a purification loop consisting of a KNF N86KT.18 diaphragm pump 11, a liquid nitrogen cryogenic trap 12, a U16 grade ULPA filter 13, and a Brooks SLA5850 mass flow controller 14.

[0051] 2. Seed Crystal Coating: Take a 150mm diameter 4H-SiC(0001) silicon seed crystal 21, fix it on the graphite substrate 22, and send it into the coating chamber 20. Evacuate the chamber to 5×10⁻⁶. -7 After passing through a nitrogen atmosphere of 100 Pa, 6N nitrogen gas was introduced to a pressure of 100 Pa. A 13.56MHz RF power supply with a power of 50W was then turned on to perform a nitrogen plasma cleaning of the seed crystal for 180 seconds. After cleaning, the three-zone induction heating coil 24 was activated to heat the center of the seed crystal to 1850℃, while the edges were controlled at 1800℃. Under a nitrogen atmosphere of 100 Pa, the TaC powder in the surrounding graphite crucible 25 sublimated and deposited for 600 seconds, ultimately obtaining a TaC protective film with a thickness of 200nm ± 8nm and an RMS roughness of 0.8nm on the seed crystal surface.

[0052] 3. Pollution-free transfer: The sealed transfer module 30 carrying the seed crystal is docked with the coating chamber 20. After performing a vacuum-rinse cycle, the valve 32 is opened, and the seed crystal base 22 is removed using the internal piezoelectric robotic arm 31. The valve is then closed. The module is transferred to the PVT growth furnace and docked with the furnace top cover valve. The purification and valve opening procedure is performed again. The seed crystal base is precisely placed on the seed crystal rod above the double-layer quartz dish assembly 10 already installed in the furnace, and the valve is closed.

[0053] 4. Crystal Growth and Result Analysis: Shut down the PVT furnace and start the crystal growth program. After growth is complete, perform defect analysis on the obtained SiC ingot.

[0054] Comparative Example 1

[0055] This comparative example uses the traditional PVT pretreatment method.

[0056] 1. Crucible preparation: Use a standard, unpolished, single-layer high-purity graphite crucible. Fill it with SiC raw material powder of the same specifications.

[0057] 2. Seed preparation: For 150mm 4H-SiC seed crystals of the same specifications, traditional chemical cleaning methods (such as RCA cleaning) were used, and then the crystals were directly mounted on the seed crystal rod. No protective film was deposited.

[0058] 3. Transfer process: The seed crystals are installed in a glove box within a Class 100 cleanroom. The assembled furnace top cover is then manually moved and installed onto the PVT furnace body. This process carries the risk of exposure to the glove box environment.

[0059] 4. Crystal Growth and Result Analysis: The PVT furnace was shut down, and crystal growth was performed using the exact same growth procedure as in Example 1. After growth, the obtained SiC ingot underwent the same defect analysis.

[0060] Results Comparison

[0061] The silicon carbide ingots with a diameter of 150 mm obtained in Example 1 and Comparative Example 1 were tested, and key performance indicators were quantitatively compared. The results are summarized in the table below:

[0062]

[0063] The data comparison in the table above clearly shows that Example 1, which utilizes the "Method for Protecting SiC Crystal Seeds Based on Double-Layer Quartz Dishes and Nitrogen Chamber Coating to Reduce Particles" disclosed in this invention, demonstrates significant superiority over Comparative Example 1, which uses a traditional method, in all key crystal quality indicators. The initial cleanliness of the seed crystal is improved by orders of magnitude, and the microtube density and basal plane dislocation density of the final silicon carbide ingot are significantly reduced, while the area ratio of the effective crystal region (yield) is greatly improved. These data fully demonstrate the effectiveness and advancement of the technical solution of this invention in preparing high-quality, large-size silicon carbide single crystals.

[0064] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating, characterized in that, The method includes the following steps: The preparation steps of the double-layer quartz dish and the construction steps of the particle dynamic capture system are used to suppress and actively remove particle sources inside the physical vapor transport growth container. A high-purity seed crystal coating step based on plasma pre-cleaning and gradient thermal field deposition is used to form a functional protective film on the seed crystal surface; and A pollution-free integrated transfer and sealing process based on a positive pressure inert atmosphere is used to transfer the coated seed crystal from the coating environment and install it into the growth container without pollution.

2. The method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 1, characterized in that, The specific steps for preparing the double-layer quartz dish and constructing the particle dynamic capture system include: A double-layer quartz dish assembly (10) is provided, consisting of an inner quartz dish (1) and an outer quartz dish (2) coaxially nested. A set of spiral microchannels (3) are processed on the outer wall surface of the inner quartz dish (1). When the outer quartz dish (2) is fitted onto the outside of the inner quartz dish (1), its inner wall completely seals the spiral microchannels (3), thereby forming a closed gas flow path network. The inner quartz dish (1) and the outer quartz dish (2) are connected and sealed by a sealing ring (5), forming an interlayer gas chamber (4) between them; A dynamic particle capture and gas purification circulation system is constructed and connected to the spiral microchannel (3). The system is used to drive the purified gas to continuously circulate within the spiral microchannel (3) to purge and carry particulate matter.

3. The method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 2, characterized in that, The inner quartz dish (1) is made of high-purity fused silica. The surface of the inner quartz dish (1) that is in contact with the silicon carbide raw material powder is chemically and mechanically polished so that the surface roughness Ra value is no greater than 0.08 micrometers. Furthermore, on the inner surface of the inner quartz dish (1) that has undergone chemical and mechanical polishing, an amorphous silicon nitride film with a thickness of 50 nanometers to 80 nanometers is deposited by low-pressure chemical vapor deposition to enhance its chemical inertness at high temperatures and reduce particle adhesion.

4. The method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 2, characterized in that, The particle dynamic capture and gas purification circulation system includes an external closed-loop gas purification circuit. The gas purification circuit is composed of an oil-free diaphragm pump (11), a cryogenic cold trap (12) located downstream of the oil-free diaphragm pump (11), an ultra-low penetration air filter (13) located downstream of the cryogenic cold trap (12), and a mass flow controller (14) located downstream of the ultra-low penetration air filter (13) connected in series. The final output end of the purification circuit is connected to the gas inlet on the sealing ring (5), and the gas outlet on the sealing ring (5) is connected to the input end of the purification circuit.

5. The method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 4, characterized in that, During crystal growth, high-purity argon gas with a purity of 99.999% is introduced into the closed-loop gas purification circuit, and a constant flow rate of 50 standard cubic centimeters per minute is set by the mass flow controller (14); the cryogenic cold trap (12) is cooled by liquid nitrogen, and the operating temperature is maintained at -196 degrees Celsius to capture and solidify highly volatile impurities in the gas flow; the ultra-low penetration air filter (13) has a filtration efficiency of not less than 99.99995% for particles with a diameter of 0.12 micrometers. Furthermore, by adjusting the pressure of the circuit, the pressure in the interlayer gas chamber (4) is always 50 to 100 Pa higher than the working pressure of the main growth chamber grown by physical vapor transport method, so as to form a positive pressure physical barrier.

6. The method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 1, characterized in that, The seed crystal high-purity coating step based on plasma pre-cleaning and gradient thermal field deposition is performed in a separate coating chamber (20), and the step specifically includes: In-situ plasma pre-cleaning sub-step of seed crystal: The silicon carbide seed crystal (21) to be treated is placed in the coating chamber (20), high-purity nitrogen gas is introduced and the pressure in the chamber is stabilized at 100 Pascals, and a radio frequency power of 13.56 MHz is applied through a radio frequency electrode (23) to generate low-temperature nitrogen plasma, and the surface of the silicon carbide seed crystal (21) is subjected to physical bombardment and chemical reaction cleaning for 180 seconds using the nitrogen plasma to remove organic residues, adsorbed oxide molecules and micro particles on the surface; The protective film deposition sub-step under gradient thermal field: After the plasma pre-cleaning is completed, the silicon carbide seed crystal (21) is heated under the condition of maintaining a high-purity nitrogen atmosphere and a stable radial temperature gradient is established on its surface. At the same time, the tantalum carbide powder source material around it is sublimated, thereby depositing a tantalum carbide protective film on the surface of the silicon carbide seed crystal (21).

7. The method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 6, characterized in that, In the protective film deposition sub-step under the gradient thermal field: A set of water-cooled electromagnetic induction heating coils (24) with multiple independent control around the seed crystal base (22) is used to heat the center temperature of the silicon carbide seed crystal (21) and maintain it at 1850 degrees Celsius, while controlling the edge temperature of the silicon carbide seed crystal (21) to maintain it at 1800 degrees Celsius, thereby forming a stable radial temperature difference of 50 degrees Celsius. Around the seed crystal base (22), an annular crucible (25) containing tantalum carbide (TaC) powder with a particle size of 10 to 50 micrometers is placed concentrically as the source material; The entire deposition process lasted 600 seconds, and finally a tantalum carbide protective film with a thickness of 200 nanometers, a thickness non-uniformity of less than ±5%, and a high (111) orientation preference was formed on the surface of the silicon carbide seed crystal (21).

8. The method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 1, characterized in that, The pollution-free integrated transfer and sealing step based on positive pressure inert atmosphere protection is achieved through a sealing transfer module (30); the sealing transfer module (30) is a portable clean chamber made of lightweight alloy or stainless steel, which integrates a piezoelectric ceramic driven robotic arm (31) that can move precisely in three-dimensional space, and the module is equipped with an independent high-purity nitrogen purging inlet and exhaust valve, which can maintain a positive pressure inert atmosphere environment higher than atmospheric pressure inside.

9. A method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 8, characterized in that, On the loading and unloading port of the coating chamber (20) and the top cover of the physical vapor transport growth furnace used to carry the double-layer quartz dish assembly (10), there are valves (32) with high airtightness that match the interface of the sealing transfer module (30). The transfer process includes: docking the sealing transfer module (30) with the valves (32) of the coating chamber (20) and the top cover of the growth furnace respectively, and after each docking, evacuating the dead zone space between the two valves (32) and repeatedly rinsing and purifying it with high-purity nitrogen, and then opening the two valves (32) at the same time to connect the chamber.

10. A method for protecting SiC crystal seeds by reducing particles based on a double-layer quartz dish and nitrogen cavity coating according to claim 9, characterized in that, The specific operational sequence of the pollution-free integrated transfer and sealing steps is as follows: After the sealing transfer module (30) is connected to the valve (32) of the coating chamber (20) and purified, the two valves (32) are opened while maintaining a positive pressure nitrogen environment inside both chambers. The robotic arm (31) is then inserted into the coating chamber (20) to grab the coated silicon carbide seed crystal (21) and its base (22), and then retreats back into the sealing transfer module (30) and closes the two valves (32). The sealed transfer module (30) carrying the silicon carbide seed crystal (21) is moved to the side of the growth furnace, and after docking with the valve (32) on the top cover of the growth furnace and completing the purification, the two valves (32) are opened while maintaining a positive pressure nitrogen environment inside both chambers. The robotic arm (31) is then controlled to accurately place and fix the silicon carbide seed crystal (21) and its base (22) on the seed crystal rod on the top of the double-layer quartz dish assembly (10). Then the robotic arm (31) retracts into the sealed transfer module (30) and closes the two valves (32).

Images