A method for recycling of silicon carbide crystal growth residual waste

Abstract

The present application relates to the technical field of silicon carbide crystal growth, and particularly relates to a recycling method for residual waste after silicon carbide crystal growth, comprising the following steps: step one, free carbon oxidation, free carbon is subjected to oxidation treatment in an oxidation atmosphere to generate gaseous carbon dioxide; step two, agglomeration directional oxidation, carbonized silicon is oxidized into silicon oxide powder by directional oxygen oxidation combined with physical oscillation; step three, heat preservation layer regeneration, the heat preservation layer micropore participates in carbonized silicon and generates silicon oxide by external directional oxygen oxidation; step four, waste separation and purification, the recycled powder is subjected to particle size grading, and high-purity silicon carbide powder and silicon oxide powder are obtained through electric selection and acid pickling; step five, raw material resynthesis, the recycled silicon carbide powder is doped in different proportions, and is mixed into unblended silicon powder and carbon powder according to a process proportion, and is subjected to secondary synthesis in a silicon carbide raw material synthesis path. The technical problems of difficult cleaning of the growth furnace and low waste recovery rate are solved.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide crystal growth technology, and in particular to a method for recycling residual waste after silicon carbide crystal growth. Background Technology

[0002] SiC, as a novel semiconductor material, possesses advantages such as a large bandgap, high breakdown voltage, high thermal conductivity, high electron saturation drift velocity, and low dielectric constant, making it a promising candidate for applications in the electrical field. Currently, the main method for SiC crystal preparation in China is the physical vapor transport method (PVT). The principle involves heating a high-temperature region and adjusting the temperature to cause SiC powder to volatilize into gaseous components. This establishes a temperature gradient within the crucible, allowing for the crystallization of silicon carbide single crystals in the seed crystal region, ultimately resulting in large-size silicon carbide single crystals.

[0003] However, in actual use, after silicon carbide crystal growth, clumps that are difficult to clean will form on the side wall of the growth furnace, and silicon carbide crystals will also penetrate into the insulation layer. These clumps cannot be recovered and are not conducive to multiple crystal growth cycles. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by introducing oxygen to oxidize the difficult-to-clean silicon carbide residue in the growth furnace at high temperature into easily cleanable silicon oxide for removal and recycling, thereby solving the technical problems of difficult cleaning inside the growth furnace and low waste recovery rate.

[0005] To address the above technical issues, the following technical solution is adopted:

[0006] A method for recycling residual waste after silicon carbide crystal growth includes the following steps:

[0007] Step 1: Oxidation of free carbon. Free carbon is oxidized in an oxidizing atmosphere to produce gaseous carbon dioxide.

[0008] Step 2, directional oxidation of agglomerates: silicon carbide agglomerates are oxidized into silicon oxide powder by directional oxygenation combined with physical vibration.

[0009] Step 3: Regeneration of the insulation layer. External directional oxygen is introduced to oxidize the micropores of the insulation layer, which then participate in silicon carbide formation and generate silicon oxide.

[0010] Step 4: Waste separation and purification. The recovered powder is classified by particle size and then separated by electrostatic separation and weak acid washing to obtain high-purity silicon carbide powder and silicon oxide powder.

[0011] Step 5: Raw material resynthesis. The recovered silicon carbide powder is mixed in different proportions with unmixed silicon powder and carbon powder according to the process ratio, and then a second synthesis is carried out in the silicon carbide raw material synthesis line.

[0012] Preferably, in the free carbon oxidation step, excess oxygen is introduced into the crucible, and the temperature is raised to 600-800℃ at 5℃ / min and held for 2 hours, with an oxygen concentration greater than 10%.

[0013] Preferably, the agglomeration-oriented oxidation step includes the following steps:

[0014] A. Heat the crucible to 1100-1200℃ and hold for 15 minutes;

[0015] B. Move the oxygen nozzle close to the sidewall of the agglomerate and continuously spray oxygen at multiple points;

[0016] C. Rolling the surface silica promotes silica shedding and deep silicon carbide oxidation.

[0017] Preferably, the insulation layer regeneration step includes the following steps:

[0018] a. While step A is being performed, the reflective layer inside the insulation layer opens to heat the insulation layer.

[0019] b. Adjust the opening ratio of the insulation layer to the maximum, and at the same time introduce oxygen from the outer layer of the insulation layer;

[0020] c. The silicon carbide in the gaps of the insulation layer is oxidized into silicon oxide and collected;

[0021] Preferably, the waste separation and purification step includes the following steps:

[0022] ①. After step one, the remaining silicon carbide at the bottom of the crucible is recovered and crushed and sieved again.

[0023] ②. The mixed powder of silicon dioxide and silicon carbide formed in steps two and three is pulverized and ground to D. 50 ≤10μm, then the powder is classified by airflow according to density, and then silicon carbide and silicon oxide are further separated by high voltage electric separation, and silicon oxide is output;

[0024] ③ Silicon carbide is acid-washed with a carbonic acid solution to remove metallic impurities. The carbonic acid solution is obtained by passing the carbon dioxide produced in steps one, two, and three into an aqueous solution containing carbonic anhydrase.

[0025] Preferably, the raw material resynthesis step includes the following steps:

[0026] (1) The used silicon carbide raw material is crushed and screened, and silicon carbide powder with a particle size of less than 0.18 mm is screened out using an 80-mesh nylon screen and collected.

[0027] (2) The silicon carbide powder synthesized by the high temperature self-propagating method is crushed and screened. Silicon carbide powder with a particle size of less than 0.18 mm is screened out using an 80-mesh nylon screen and collected.

[0028] (3) Mix high-purity carbon powder and high-purity silicon powder in an atomic molar ratio of 1:1 for 8 hours using a mixer at a speed of 30 revolutions per minute.

[0029] (4) The collected silicon carbide fine powder and the mixed silicon carbide powder are mixed at a mass ratio of 1:9 and mixed for 4 hours at a speed of 30 revolutions per minute using a mixer.

[0030] (5) Loading the furnace: The mixed raw materials are loaded into the crucible and then loaded into the furnace.

[0031] (6) Raw material synthesis.

[0032] Preferably, the (6) raw material synthesis includes the following steps:

[0033] I. Gas washing; The furnace chamber pressure is evacuated to <1×10-4Pa using a vacuum pump and maintained at this pressure for 4 hours. Ar is then introduced to pressurize the furnace chamber to 60kPa~80kPa and maintain the pressure for 1h~3h minutes.

[0034] II. Second gas washing; The furnace chamber pressure is evacuated to <1×10-4Pa using a vacuum pump and maintained at this pressure for 4 hours. Ar is then introduced to pressurize the furnace chamber to 60kPa~80kPa and maintain the pressure for 2h~5h minutes.

[0035] III. Heating: Under a pressure of 50 kPa to 800 kPa, raise the temperature to 600°C to 800°C at a heating rate of 1°C / min to 10°C / min, and hold for 1 to 2 hours. Continue heating, controlling the temperature at 1300°C to 1400°C, and use a mechanical pump to evacuate the system, holding for 5 to 7 hours. This condition achieves maximum impurity removal from the silicon carbide powder. Raise the temperature to 2200°C within 2 to 3 hours and hold for 15 to 25 hours. This is the high-temperature self-propagating synthesis method for silicon carbide powder.

[0036] IV. Cool down, keep the furnace chamber pressure constant at 2kPa~20kPa, adjust the flow rate of gas introduced through the graphite pipe to maintain the argon flow rate at 200sccm~800sccm and cool down; when the temperature drops to room temperature, directly introduce argon into the furnace chamber to atmospheric pressure, open the furnace door and take out the raw material;

[0037] V. Raw material post-processing: The extracted silicon carbide is crushed, screened, washed, dried, and packaged.

[0038] Preferably, the oxidation mechanism involved in step two is located inside the growth furnace and is used for directional control of oxygen output;

[0039] The oxidation mechanism includes two sets of sealing covers that are horizontally slidably connected to both sides of the crucible, a cover plate that is vertically slidably connected to the top of the crucible, an air outlet set on the edge of the cover plate, a control frame that is vertically slidably connected to the cover plate, an air jet ring that is rotatably connected to the control frame, multiple sets of grinding wheels that are evenly arranged around the control frame, and multiple sets of ball bearings that are evenly arranged around the paint spraying ring.

[0040] The heat preservation mechanism involved in step three is set on the outside of the crucible and is used to dynamically control the collection and dissipation of heat radiation.

[0041] The separation mechanism involved in step four is located at the bottom of the growth furnace and is used to separate and purify the waste.

[0042] Preferably, the heat preservation mechanism includes a reflective component disposed on the outside of the crucible and a heat insulation component disposed on the outside of the reflective component. The reflective component includes multiple sets of reflective sheets rotatably connected around the crucible, a roller disposed at the lower part of each set of reflective sheets, a reflective film wound on the roller, and a control rod rotatably connected to the upper part of the reflective sheets, with one end of the reflective film fixedly connected to the control rod.

[0043] The insulation component includes a fixed layer, multiple sets of adjustment layers rotatably connected to the outside of the fixed layer and arranged from top to bottom, a lifting ring vertically slidably connected to the outside of the adjustment ring, and an air jet port provided on the inner side of the lifting ring.

[0044] As another preferred embodiment, the separation mechanism includes a feeding platform vertically slidably connected to the bottom of the crucible, multiple sets of ball mills arranged around the feeding platform, an airflow separator arranged inside the ball mills, an electrostatic separator arranged above the airflow separator, and an acid washing chamber arranged inside the airflow separator.

[0045] The beneficial effects of this invention are:

[0046] (1) In this invention, by setting a free carbon oxidation step, oxygen is introduced into the growth furnace and kept at a high temperature, so that the excess carbon particles generated after the crystal growth in the silicon carbide waste can be completely oxidized. Within the temperature gradient in which free carbon can be oxidized, silicon carbide is not easy to be oxidized. This ensures that the carbon particles are completely oxidized into carbon dioxide and removed, while ensuring that no new impurities are mixed into the residual silicon carbide.

[0047] (2) In this invention, by setting a block directional oxidation step, the hard silicon carbide blocks formed on the inner sidewall of the growth furnace are first subjected to overall high-temperature oxidation, and then physical knocking is used to knock the local blocks. On the one hand, the surface blocks are quickly removed, and on the other hand, the deep silicon carbide blocks are contacted with oxygen and oxidized, thus ensuring the cleaning efficiency of the sidewall blocks.

[0048] (3) In this invention, through the heat insulation layer regeneration step, a reflective layer with dynamically adjustable reflection angle and a heat insulation layer with dynamically adjustable porosity are set. By using the reflective layer and the heat insulation layer, it is easy to establish an axial temperature gradient in the crucible. By controlling the temperature dissipation and cooperating with the external input of oxygen, the silicon carbide crystals in the micropores of the heat insulation layer are oxidized and removed, thereby realizing the regeneration of the heat insulation layer and improving the service life of the heat insulation layer.

[0049] (4) In this invention, by setting up a waste separation and purification step, the carbon dioxide generated in the previous oxidation process is recycled and reused. The carbon dioxide is made into carbonic acid, and the recycled silicon carbide is acid-washed with carbonic acid to remove metal impurities in silicon carbide, which is then recycled and costs are reduced.

[0050] In summary, this equipment has the advantages of being green and environmentally friendly, and is especially suitable for the field of silicon carbide crystal growth. Attached Figure Description

[0051] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments 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.

[0052] Figure 1 This is a schematic diagram of the structure of a growth furnace used in a method for recycling residual waste after silicon carbide crystal growth.

[0053] Figure 2 This is a schematic diagram of the internal structure of the growth furnace.

[0054] Figure 3 This is a schematic diagram of the oxidation mechanism.

[0055] Figure 4 This is a cross-sectional schematic diagram of the oxidation mechanism.

[0056] Figure 5 This is a schematic diagram of the control frame's working status.

[0057] Figure 6 This is a schematic diagram showing the location of the reflective layer.

[0058] Figure 7 This is a schematic diagram of the reflective layer.

[0059] Figure 8 This is a schematic diagram of the working state of the reflective layer.

[0060] Figure 9 This is a schematic diagram of the insulation layer.

[0061] Figure 10 This is a schematic diagram of the separation mechanism.

[0062] Figure 11 This is a schematic diagram of a method for recycling waste materials remaining after silicon carbide crystal growth. Detailed Implementation

[0063] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0064] Example 1

[0065] like Figure 11 As shown, a method for recycling residual waste after silicon carbide crystal growth includes the following steps:

[0066] Step 1: Oxidation of free carbon. Free carbon is oxidized in an oxidizing atmosphere to produce gaseous carbon dioxide.

[0067] Step 2, directional oxidation of agglomerates: silicon carbide agglomerates are oxidized into silicon oxide powder by directional oxygenation combined with physical vibration.

[0068] Step 3: Regeneration of the insulation layer. External directional oxygen is introduced to oxidize the micropores of the insulation layer, which then participate in silicon carbide formation and generate silicon oxide.

[0069] Step 4: Waste separation and purification. The recovered powder is classified by particle size and then separated by electrostatic separation and weak acid washing to obtain high-purity silicon carbide powder and silicon oxide powder.

[0070] Step 5: Raw material resynthesis. The recovered silicon carbide powder is mixed in different proportions with unmixed silicon powder and carbon powder according to the process ratio, and then a second synthesis is carried out in the silicon carbide raw material synthesis line.

[0071] In the free carbon oxidation step, excess oxygen is introduced into the crucible, and the temperature is increased to 600-800℃ at 5℃ / min and held for 2 hours, with an oxygen concentration greater than 10%.

[0072] In this embodiment, free carbon in the waste is removed by high-temperature oxidation. By controlling the temperature and oxygen concentration, the free carbon is fully reacted without oxidizing the residual silicon carbide, resulting in carbon dioxide instead of carbon monoxide.

[0073] The agglomeration-oriented oxidation step includes the following steps:

[0074] A. Heat the crucible to 1100-1200℃ and hold for 15 minutes;

[0075] B. Move the oxygen nozzle close to the sidewall of the agglomerate and continuously spray oxygen at multiple points;

[0076] C. The roller 16 moves along the side wall to roll the surface silica, promoting silica shedding and deep silicon carbide oxidation.

[0077] In this embodiment, the temperature of the crucible is further increased to reach the temperature range for silicon carbide oxidation, thereby achieving silicon carbide oxidation. The physical crushing of the roller 16, combined with the airflow impact generated by the oxygen injection from the oxygen nozzle, promotes the rapid shedding of silicon oxide and accelerates the oxidation of deep silicon carbide.

[0078] The insulation layer regeneration step includes the following steps:

[0079] a. While step A is being performed, the reflective layer inside the insulation layer opens to heat the insulation layer.

[0080] b. Adjust the opening ratio of the insulation layer to the maximum, and at the same time introduce oxygen from the outer layer of the insulation layer;

[0081] c. The silicon carbide in the gaps of the insulation layer is oxidized into silicon oxide and collected;

[0082] In this embodiment, by adjusting the porosity of the insulation layer and the reflection angle of the reflective layer, the inner side of the insulation layer can also be rapidly heated. At the same time, oxygen is introduced from the outside. The oxygen passes through the micropores of the insulation layer, oxidizing the silicon carbide and carrying it out of the micropores, thereby achieving the cleaning and regeneration of the insulation layer.

[0083] The waste separation and purification step includes the following steps:

[0084] ①. After step one, the remaining silicon carbide at the bottom of the crucible is recovered and crushed and sieved again.

[0085] ②. The mixed powder of silicon dioxide and silicon carbide formed in steps two and three is pulverized and ground to D. 50 ≤10μm, then the powder is classified by airflow according to density, and then silicon carbide and silicon oxide are further separated by high voltage electric separation, and silicon oxide is output;

[0086] ③ Silicon carbide is acid-washed with a carbonic acid solution to remove metallic impurities. The carbonic acid solution is obtained by passing the carbon dioxide produced in steps one, two, and three into an aqueous solution containing carbonic anhydrase.

[0087] Because silicon carbide and silicon oxide have significant differences in density and hardness, grinding can enrich silicon carbide into coarse powder and silicon oxide into fine powder. The coarse and fine powders are then initially separated by airflow, followed by further separation by high-voltage electrostatic separation. Finally, the carbon dioxide generated in the previous steps is converted into carbonic acid, which is used to acid wash the silicon carbide to remove metallic impurities, thus completing the recovery of silicon carbide.

[0088] The raw material resynthesis step includes the following steps:

[0089] (1) The used silicon carbide raw material is crushed and screened, and silicon carbide powder with a particle size of less than 0.18 mm is screened out using an 80-mesh nylon screen and collected.

[0090] (2) The silicon carbide powder synthesized by the high temperature self-propagating method is crushed and screened. Silicon carbide powder with a particle size of less than 0.18 mm is screened out using an 80-mesh nylon screen and collected.

[0091] (3) Mix high-purity carbon powder and high-purity silicon powder in an atomic molar ratio of 1:1 for 8 hours using a mixer at a speed of 30 revolutions per minute.

[0092] (4) The collected silicon carbide fine powder and the mixed silicon carbide powder are mixed at a mass ratio of 1:9 and mixed for 4 hours at a speed of 30 revolutions per minute using a mixer.

[0093] (5) Loading the furnace: The mixed raw materials are loaded into the crucible and then loaded into the furnace.

[0094] (6) Raw material synthesis.

[0095] The synthesis of raw materials (6) includes the following steps:

[0096] I. Gas washing; The furnace chamber pressure is evacuated to <1×10-4Pa using a vacuum pump and maintained at this pressure for 4 hours. Ar is then introduced to pressurize the furnace chamber to 60kPa~80kPa and maintain the pressure for 1h~3h minutes.

[0097] II. Second gas washing; The furnace chamber pressure is evacuated to <1×10-4Pa using a vacuum pump and maintained at this pressure for 4 hours. Ar is then introduced to pressurize the furnace chamber to 60kPa~80kPa and maintain the pressure for 2h~5h minutes.

[0098] III. Heating: Under a pressure of 50 kPa to 800 kPa, raise the temperature to 600°C to 800°C at a heating rate of 1°C / min to 10°C / min, and hold for 1 to 2 hours. Continue heating, controlling the temperature at 1300°C to 1400°C, and use a mechanical pump to evacuate the system, holding for 5 to 7 hours. This condition achieves maximum impurity removal from the silicon carbide powder. Raise the temperature to 2200°C within 2 to 3 hours and hold for 15 to 25 hours. This is the high-temperature self-propagating synthesis method for silicon carbide powder.

[0099] IV. Cool down, keep the furnace chamber pressure constant at 2kPa~20kPa, adjust the flow rate of gas introduced through the graphite pipe to maintain the argon flow rate at 200sccm~800sccm and cool down; when the temperature drops to room temperature, directly introduce argon into the furnace chamber to atmospheric pressure, open the furnace door and take out the raw material;

[0100] V. Raw material post-processing: The extracted silicon carbide is crushed, screened, washed, dried, and packaged.

[0101] In this embodiment, by setting three steps—free carbon oxidation, agglomerated directional oxidation, and insulation layer regeneration—the waste material inside the inner wall of the growth furnace and the insulation layer is recycled, thereby improving the waste recycling rate while ensuring the cleanliness of the growth furnace.

[0102] In detail, when the gas phase reaches the relatively low-temperature sidewall of the furnace or crucible with the gas flow, the gas temperature drops sharply. At the low-temperature wall surface, the supersaturation of the gas phase increases significantly, and the chemical reaction equilibrium is disrupted. These gas molecules lose stability. They directly undergo deposition reactions or condensation on the cooler wall material, forming solid Si-C compounds. Liquid silicon with a relatively high silicon content comes into contact with and reacts with solid carbon, ultimately forming a new SiC layer that adheres tightly to the original sidewall, forming a hard crust.

[0103] Simultaneously, in addition to flowing towards the sidewalls, some gaseous substances also enter (or diffuse) the edge areas of the insulation material along with the airflow. The insulation material has a porous structure, allowing these gas molecules to penetrate into its pore network. When they penetrate deep into the insulation material, the ambient temperature is significantly lower than the temperature required to maintain a gaseous state. In the relatively low-temperature and confined pore space, these gaseous substances undergo a direct gas-solid phase transition, transforming into solid microcrystals. Because these deposits occur deep within the pores, even in dead spaces, and the newly formed SiC nanocrystals firmly adhere to the fibers / pore walls of the insulation material, they form residues that are difficult to remove using conventional physical methods.

[0104] This application introduces oxygen into a growth furnace and uses high-temperature oxidation to oxidize residual silicon carbide into silicon oxide. During the oxidation of silicon carbide into silicon oxide, volume expansion occurs, and carbon dioxide is generated. The escaped carbon dioxide forms a porous structure inside the silicon oxide, which is harder and chemically inert than silicon carbide, making it easier to clean. This promotes the detachment of silicon carbide agglomerates on the sidewalls and the discharge of silicon carbide from inside the insulation layer.

[0105] Meanwhile, in silicon carbide PVT crystal growth, due to the high temperature in the later stage of crystal growth and the different evaporation temperatures of the silicon and carbon components in the gas phase of silicon carbide powder, an excess of carbon particles remain in the later stage of crystal growth. These carbon particles are removed by producing carbon dioxide through high-temperature oxidation.

[0106] Example 2

[0107] like Figures 1-10 As shown, components that are the same as or corresponding to those in Embodiment 1 are referred to using the same reference numerals as in Embodiment 1. For simplicity, only the differences from Embodiment 1 are described below. The difference between Embodiment 2 and Embodiment 1 is as follows:

[0108] Furthermore, such as Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 As shown, the oxidation mechanism 1 involved in step two is installed inside the growth furnace and is used for directional control of oxygen output;

[0109] The oxidation mechanism 1 includes two sets of sealing covers 11 that are horizontally slidably connected to the upper sides of the crucible, a cover plate 12 that is vertically slidably connected to the top of the crucible, an air outlet 13 located on the edge of the cover plate 12, a control frame 14 that is vertically slidably connected to the cover plate 12, an air jet ring 15 that is rotatably connected to the control frame 14, multiple sets of rollers 16 that are evenly arranged around the control frame 14, and multiple sets of ball bearings 17 that are evenly arranged around the paint spraying ring.

[0110] The heat preservation mechanism 2 involved in step three is set on the outside of the crucible and is used to dynamically control the collection and dissipation of heat radiation.

[0111] The separation mechanism 3 involved in step four is located at the bottom of the growth furnace and is used to separate and purify the waste.

[0112] In this embodiment, the growth furnace includes a crucible and an insulation layer. Silicon carbide is adhered to the side wall of the crucible. The growth furnace is equipped with an openable furnace lid. The furnace lid has a vertically movable support plate for crystal growth. A cover is fixed on the support plate. The cover plate 12 is vertically slidably connected to the furnace lid. The sealing cover 11 slides horizontally on both sides of the top of the crucible.

[0113] In detail, during crystal growth, the support plate moves down, and the sealing caps 11 on both sides slide and close together to form a seal. After the crystal growth is completed and the crystal is removed, the furnace lid is closed, and the control frame 14 enters the crucible. The cover plate 12 moves down and forms a seal with the closed lid again. After oxidation is completed, the control frame 14 continues to move down, and the air jet ring 15 on it rotates at the same time. As the control frame 14 moves down, the grinding wheel 16 on it rolls over the agglomerates on the sidewall surface, causing the agglomerates to crack. At the same time, multiple balls 17 are provided on the air jet ring 15. The balls 17 are set on the outside of the air jet ring 15 through a telescopic rod and a spring. When the air jet ring 15 rotates, the balls 17 squeeze and crush the agglomerates on the sidewall surface, thereby causing the surface agglomerates to fall off quickly, improving the cleanliness of the sidewall and avoiding a large amount of residue. The air jet ring 15 sprays oxygen, which on the one hand directly sprays oxygen onto the surface of the agglomerates, thereby promoting the contact between the inside of the agglomerates and oxygen, thus accelerating oxidation. On the other hand, the impact force of the airflow accelerates the falling off of the agglomerates.

[0114] It should be noted that an air outlet 13 is provided at the edge of the bottom surface of the cover plate 12 to output oxygen downwards. By releasing oxygen downwards through the air outlet 13, the oxygen can quickly contact the clumps on the side wall surface, and at the same time blow the dust generated by the clumps falling off downwards, reducing the upward movement.

[0115] It is worth mentioning that an exhaust vent is provided in the middle of the cover plate 12 to control the gas concentration in the crucible, thereby removing the carbon dioxide produced by the oxidation reaction through the tube and utilizing it.

[0116] like Figure 6 , Figure 7 , Figure 8 , Figure 9 As shown, the heat preservation mechanism 2 includes a reflective component 21 disposed on the outside of the crucible and a heat insulation component 22 disposed on the outside of the reflective component 21. The reflective component 21 includes multiple sets of reflective sheets 211 rotatably connected around the crucible, a roller 212 disposed at the lower part of each set of reflective sheets 211, a reflective film 213 wound on the roller 212, and a control rod 214 rotatably connected to the upper part of the reflective sheets 211, with one end of the reflective film 213 fixedly connected to the control rod 214.

[0117] The insulation component 22 includes a fixed layer 221, multiple sets of adjustment layers 222 rotatably connected to the outside of the fixed layer 221 and arranged from top to bottom, a lifting ring 223 vertically slidably connected to the outside of the adjustment ring, and an air jet 224 provided on the inner side of the lifting ring.

[0118] In this embodiment, by setting a dynamically adjustable reflective layer and a heat insulation layer, the protection against heat radiation and the adjustment of the porosity are realized, so that the heat insulation layer can be better adapted to the heat distribution requirements in the crystal growth and waste recycling process.

[0119] In detail, during the crystal growth process, the heat inside the furnace exhibits a vertical temperature gradient. The heat source is located at the bottom of the furnace body and is powered by induction coils or resistance heaters, forming a high-temperature core area. The heat energy is transferred into the furnace cavity through thermal radiation and gas thermal convection.

[0120] The insulation layer set on the outside of the crucible can be divided into three layers: the innermost layer is a reflective layer, the middle layer is a high-density carbon felt, and the outermost layer is a soft graphite felt. The inner reflective layer is usually made of tantalum foil to reflect infrared radiation to the crucible.

[0121] The core purpose of the perforation design in the insulation layer is to establish an axial temperature gradient: the perforations form local heat dissipation channels, forcing heat to escape vertically, creating a temperature difference that decreases from the high-temperature raw material zone at the bottom to the low-temperature seed crystal zone at the top within the furnace, driving SiC vapor to diffuse and deposit towards the seed crystal. The porosity of the insulation layer is the percentage of the perforated area to the total surface area of ​​the insulation layer. A small porosity results in insufficient heat dissipation, a weak axial temperature gradient, slowed vapor phase transport, and a reduced crystal growth rate. Conversely, a high porosity leads to rapid heat dissipation, causing overcooling at the top, premature vapor phase deposition, and the formation of polycrystalline structures or inclusions. Therefore, an ideal porosity needs to be set.

[0122] Based on this, multiple sets of reflective components 21 are arranged on the outside of the crucible, and each set of reflective components 21 is equipped with multiple sets of reflective sheets 211. The angle of each reflective sheet 211 is controlled by a motor or other device, thereby concentrating thermal radiation towards the bottom of the crucible to assist in the formation of a temperature gradient. Since the angles of the reflective sheets 211 are different, a roller 212 is arranged on the reflective sheets 211. The roller 212 winds up a reflective film 213, and the outer end of the reflective film 213 is fixed to a control rod 214. The control rod 214 is rotatably positioned below... During crystal growth on reflector 211, reflector 211 rotates to a preset angle. At this time, control rod 214 is pressed against the reflector 211 below, pulling open reflective film 213. Reflective film 213 is used to seal the pores in the middle of each set of reflectors 211. When crystal growth is completed and the insulation layer is regenerated, reflector 211 opens, and control rod 214 rotates to fully open the pores in the middle of reflector 211, so that heat radiation can be released to heat the middle insulation layer, thereby causing the silicon carbide in the pores of the insulation layer to oxidize.

[0123] Meanwhile, there are openings inside the insulation layer outside the reflective layer. By setting the insulation layer as an inner and outer double layer, and the outer layer being set into multiple groups from top to bottom that can rotate around the center, the openings in the inner and outer layers align when rotated, thus connecting the openings and increasing the opening ratio; if they are not aligned, the opening ratio decreases. By setting multiple groups, different opening ratios can be presented at different locations, thereby achieving an axial temperature gradient.

[0124] A lifting ring 223 is installed outside the insulation layer. Inside the lifting ring 223 is an air outlet 13. The air outlet 13 outputs oxygen. The oxygen passes through the opening, oxidizes the silicon carbide in the opening, and uses the airflow to carry the oxide out.

[0125] like Figure 10 As shown, the separation mechanism 3 includes a feeding platform 31 vertically slidably connected to the bottom of the crucible, multiple sets of ball mills 32 arranged around the feeding platform 31, an airflow separator 33 arranged inside the ball mills 32, an electrostatic separator 34 arranged above the airflow separator 33, and an acid washing chamber 35 arranged inside the airflow separator 33.

[0126] In this embodiment, by setting up an electrostatic separator 34 and an acid washing chamber 35, the separation of silicon oxide and silicon carbide is achieved, and then the silicon carbide is purified.

[0127] In detail, the feeding platform 31 is located at the bottom of the crucible and can move up and down. After the free carbon oxidation step, the feeding platform 31 moves down and feeds the silicon carbide waste into the ball mill for crushing. Then it is collected, and after agglomerated directional peroxidation and insulation layer regeneration, the feeding platform 31 moves down again, so that the silicon oxide and silicon carbide above fall into the ball mill 32 below for crushing. Due to the difference in hardness between silicon oxide and silicon carbide, silicon oxide is enriched into fine powder and silicon carbide is enriched into coarse powder. It is output from the ball mill 32 to the air classifier 33. After passing through the air classifier 33, it is finely output to the electrostatic separator 34 for further precise separation. The obtained silicon carbide powder enters the acid washing chamber 35 and is washed with carbonic acid to remove metal impurities. It is then output together with silicon oxide for raw material synthesis.

[0128] It should be noted that the carbonic acid used for pickling is obtained from the carbon dioxide generated in steps one, two and three of the oxidation process. By passing carbon dioxide into an aqueous solution containing carbonic anhydrase, the carbonic acid can be prepared efficiently. Then, the carbonic acid is introduced into the pickling chamber 35 to pickle the silicon carbide.

[0129] It should be noted that since the oxidation mechanism 1, the heat preservation mechanism 2, and the separation mechanism 3 are all located inside the electromagnetic coil, the mechanical components inside the device need to be isolated and shielded to prevent damage caused by coil heating.

[0130] In the description of this invention, it should be understood that the terms "front and back", "left and right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0131] Of course, those skilled in the art should understand that the term "a" should be understood as "at least one" or "one or more". That is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple. The term "a" should not be understood as a limitation on the quantity.

[0132] The above description is merely a preferred 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 under the technical guidance of 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 recycling residual waste after silicon carbide crystal growth, characterized in that, Includes the following steps: Step 1: Oxidation of free carbon. Free carbon is oxidized in an oxidizing atmosphere to produce gaseous carbon dioxide. Step 2, directional oxidation of agglomerates: silicon carbide agglomerates are oxidized into silicon oxide powder by directional oxygenation combined with physical vibration. Step 3: Insulation layer regeneration. Silicon carbide is infiltrated into the micropores of the externally oriented oxygen-oxidizing insulation layer to generate silicon oxide. Step 4: Waste separation and purification. The recovered powder is classified by particle size and then separated by electrostatic separation and weak acid washing to obtain high-purity silicon carbide powder and silicon oxide powder. Step 5: Raw material resynthesis. The recycled silicon carbide powder is doped in different proportions and mixed with unmixed silicon powder and carbon powder according to the process ratio. Secondary synthesis is carried out in the silicon carbide raw material synthesis line. The agglomeration-oriented oxidation step includes the following steps: A. Heat the crucible to 1100-1200℃ and hold for 15 minutes; B. Move the oxygen nozzle close to the sidewall of the agglomerate and continuously spray oxygen at multiple points; C. Rolling the surface silica promotes silica shedding and deep silicon carbide oxidation; The insulation layer regeneration step includes the following steps: a. While step A is being performed, the reflective layer inside the insulation layer opens to heat the insulation layer. b. Adjust the opening ratio of the insulation layer to the maximum, and at the same time introduce oxygen from the outer layer of the insulation layer; c. The silicon carbide in the gaps of the insulation layer is oxidized into silicon oxide and collected; The oxidation mechanism (1) involved in step two is located inside the growth furnace and is used for directional control of oxygen output; The oxidation mechanism (1) includes two sets of sealing covers (11) that are horizontally slidably connected to both sides of the crucible, a cover plate (12) that is vertically slidably connected to the top of the crucible, an air outlet (13) set on the edge of the cover plate (12), a control frame (14) that is vertically slidably connected to the cover plate (12), an air jet ring (15) that is rotatably connected to the control frame (14), multiple sets of rollers (16) that are evenly arranged around the control frame (14), and multiple sets of ball bearings (17) that are evenly arranged around the paint spraying ring. The heat preservation mechanism (2) involved in step three is set on the outside of the crucible and is used to dynamically control the collection and dissipation of heat radiation; The separation mechanism (3) involved in step four is located at the bottom of the growth furnace and is used to separate and purify the waste material; The heat preservation mechanism (2) includes a reflective assembly (21) disposed on the outside of the crucible and a heat insulation assembly (22) disposed on the outside of the reflective assembly (21). The reflective assembly (21) includes multiple sets of reflective sheets (211) rotatably connected around the crucible, a roller (212) disposed at the lower part of each set of reflective sheets (211), a reflective film (213) wound on the roller (212), and a control rod (214) rotatably connected to the upper part of the reflective sheet (211), with one end of the reflective film (213) fixedly connected to the control rod (214). The insulation component (22) includes a fixed layer (221), multiple sets of adjustment layers (222) rotatably connected to the outside of the fixed layer (221) and arranged from top to bottom, a lifting ring (223) vertically slidably connected to the outside of the adjustment ring, and an air jet (224) provided on the inner side of the lifting ring.

2. The method for recycling residual waste after silicon carbide crystal growth according to claim 1, characterized in that, In the free carbon oxidation step, excess oxygen is introduced into the crucible, and the temperature is increased to 600-800℃ at 5℃ / min and held for 2 hours, with an oxygen concentration greater than 10%.

3. The method for recycling residual waste after silicon carbide crystal growth according to claim 1, characterized in that, The waste separation and purification step includes the following steps: ①. After step one, the remaining silicon carbide at the bottom of the crucible is recovered and crushed and sieved again; ②. The mixed powder of silicon dioxide and silicon carbide formed in steps two and three is pulverized and ground to D. 50 ≤10μm, then the powder is classified by airflow according to density, and then silicon carbide and silicon oxide are further separated by high voltage electric separation, and silicon oxide is output; ③ Silicon carbide is acid-washed with a carbonic acid solution to remove metallic impurities. The carbonic acid solution is obtained by passing the carbon dioxide produced in steps one, two, and three into an aqueous solution containing carbonic anhydrase.

4. The method for recycling residual waste after silicon carbide crystal growth according to claim 1, characterized in that, The raw material resynthesis step includes the following steps: (1) The used silicon carbide raw material is crushed and screened, and silicon carbide powder with a particle size of less than 0.18 mm is screened out using an 80-mesh nylon screen and collected; (2) The silicon carbide powder synthesized by the high temperature self-propagating method is crushed and sieved. Silicon carbide powder with a particle size of less than 0.18 mm is screened out using an 80-mesh nylon screen and collected. (3) Mix high-purity carbon powder and high-purity silicon powder in an atomic molar ratio of 1:1 for 8 hours using a mixer at a speed of 30 revolutions per minute; (4) The collected silicon carbide fine powder and the mixed silicon carbide powder are mixed at a mass ratio of 1:9 and mixed for 4 hours at a speed of 30 revolutions per minute using a mixer; (5) Loading the furnace: The mixed raw materials are loaded into the crucible and then loaded into the furnace; (6) Raw material synthesis.

5. A method for recycling residual waste after silicon carbide crystal growth according to claim 4, characterized in that, The synthesis of raw materials (6) includes the following steps: I. Gas scrubbing; furnace chamber pressure is reduced to <1×10 using a vacuum pump. -4 Pa, maintain at this pressure for 4 hours, then introduce Ar to pressurize the furnace cavity to 60 kPa~80 kPa, and maintain the pressure for 1 hour~3 hours; II. Second gas scrubbing; furnace chamber pressure is reduced to <1×10 using a vacuum pump. -4 Pa, maintain at this pressure for 4 hours, then introduce Ar to pressurize the furnace cavity to 60 kPa~80 kPa, and maintain the pressure for 2 hours~5 hours; III. Heating: Under a pressure of 50 kPa to 800 kPa, raise the temperature to 600°C to 800°C at a heating rate of 1°C / min to 10°C / min, and hold for 1 to 2 hours; continue heating, controlling the temperature at 1300°C to 1400°C, and use a mechanical pump to evacuate the air, holding for 5 to 7 hours, under which maximum impurity removal of the silicon carbide powder is achieved; raise the temperature to 2200°C within 2 to 3 hours, and hold for 15 to 25 hours; perform the high-temperature self-propagating synthesis of silicon carbide powder; IV. Cool down, keep the furnace chamber pressure constant at 2kPa~20kPa, adjust the flow rate of gas introduced through the graphite pipe to maintain the argon flow rate at 200sccm~800sccm and cool down; when the temperature drops to room temperature, directly introduce argon into the furnace chamber to atmospheric pressure, open the furnace door and take out the raw material; V. Raw material post-processing: The extracted silicon carbide is crushed, screened, washed, dried, and packaged.

6. A method for recycling residual waste after silicon carbide crystal growth according to claim 1, characterized in that, The separation mechanism (3) includes a feeding platform (31) vertically slidably connected to the bottom of the crucible, multiple sets of ball mills (32) arranged around the feeding platform (31), an airflow separator (33) arranged inside the ball mills (32), an electrostatic separator (34) arranged above the airflow separator (33), and an acid washing chamber (35) arranged inside the airflow separator (33).

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