Method for controlling growth of silicon carbide grains

Abstract

The invention relates to a method for controlling growth of silicon carbide crystal grains, which comprises the following steps: mixing a carbon source and a silicon source, and reacting on a deposition plate through gas phase transmission under a protective atmosphere to generate the silicon carbide crystal grains. The crystal form, the size and the quantity of the crystal grains can be regulated and controlled through the raw material ratio, the temperature system and the reaction times. According to the method, single-crystal or polycrystal silicon carbide can be obtained at low cost, the obtained silicon carbide crystal grains are high in purity and wide in size coverage range, the growth speed of the silicon carbide crystal is high in the growth process, and a new idea for silicon carbide crystal growth control is provided for the silicon carbide industry.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically relating to a method for controlling the growth of silicon carbide grains, which is particularly suitable for the large-scale preparation of high-performance silicon carbide single crystals or polycrystalline particles. Background Technology

[0002] Silicon carbide is an excellent non-oxide ceramic material with both structural and functional properties, characterized by high temperature resistance, corrosion resistance, oxidation resistance, high mechanical strength, and excellent thermal conductivity. As a semiconductor material, it also possesses core advantages such as wide bandgap, high breakdown field strength, and high saturated electron drift rate, making it irreplaceable in modern industrial high-performance devices and structural components. However, the large-scale preparation of high-quality silicon carbide grains has been limited by inherent defects in existing technologies, mainly in the following two aspects: On the one hand, the mainstream physical vapor transport (PVT) method requires the sublimation and recrystallization of silicon carbide raw materials at extreme high temperatures above 2200℃. This places extremely high demands on the high-temperature resistance and stability of the reaction chamber, heating elements, and insulation system, resulting in complex and expensive specialized equipment and enormous energy consumption during the production process. This method is mainly used for growing bulk single crystals and is difficult to flexibly prepare discrete single crystals or polycrystalline particles with controllable morphology and size, making it less economical.

[0003] On the other hand, high-temperature chemical vapor deposition (HT-CVD) uses special gases such as silane (SiH4) and propane (C3H8) as reaction sources. These gases are highly toxic and explosive, requiring complex safety protection and exhaust gas treatment systems for their storage, transportation, and use. This not only significantly increases equipment investment and operating costs but also poses serious safety hazards. Furthermore, the core advantage of this technology lies in thin film epitaxial growth, making it impossible to control the morphology and size of discrete grains.

[0004] Therefore, existing technologies, due to excessively high equipment and energy costs, poor process safety, and insufficient product controllability, are insufficient to meet the industrial demand for a simple, economical, safe, and controllable method for silicon carbide grain preparation. Developing a silicon carbide grain growth technology based on safe and inexpensive raw materials, with a simple process and easily adjustable parameters, has become crucial for promoting the development of the silicon carbide industry. Summary of the Invention

[0005] This invention aims to solve the problems of high cost, poor safety, difficulty in controlling grain shape and size, and insufficient purity in existing silicon carbide preparation technologies, and provides a silicon carbide grain growth method that is simple, low-cost, and has strong product controllability.

[0006] To achieve the above objectives, the present invention provides a method for controlling silicon carbide grain growth, comprising the following steps: 1) Raw material mixing: The carbon source and silicon source are mixed evenly according to a preset ratio to obtain the raw materials for silicon carbide grain growth; 2) Silicon carbide grain growth: The raw material is placed in a sagger for silicon carbide grain growth and spread evenly. After covering it with a deposition plate, the sagger is placed in a high-temperature furnace. Silicon carbide grains are synthesized under a protective atmosphere according to a segmented heating-holding regime, so that silicon carbide grains are formed and grown on the deposition plate. After cooling, silicon carbide grains are obtained.

[0007] Furthermore, the carbon source is an organic carbon source composed only of four elements: C, H, O, and N.

[0008] Furthermore, the silicon source is selected from one or more of silicon carbide, elemental silicon, silicon monoxide, silicon dioxide, and silicon nitride.

[0009] Furthermore, the mixing method described in step 1) is any one of dry ball milling, wet ball milling, or spray granulation.

[0010] Furthermore, when using wet ball milling, the dispersion medium added during the mixing process is ethanol.

[0011] Furthermore, the mixing ratio of the carbon source and silicon source satisfies a C / Si atomic ratio of 1:1 to 1:3. The ideal stoichiometric ratio of silicon carbide (SiC) is C:Si = 1:1 (atomic ratio). If the solid raw materials are mixed strictly according to this ratio, a direct solid-solid reaction will mainly occur at high temperatures, which can easily lead to the product sintering into blocks, coarsening of grains, and uncontrollable morphology, making it difficult to obtain discrete, independent grains. A moderate excess of Si results in a higher partial pressure of Si-based species in the gas phase, which can provide sufficient growth units for grain growth and significantly improve the growth rate; at the same time, the excess Si-based species will promote the fusion growth of adjacent grains, which is beneficial for obtaining larger polycrystalline SiC particles.

[0012] Furthermore, the materials of the sagger and the deposition plate are independently selected from carbon or silicon carbide.

[0013] Furthermore, the segmented heating-holding regime includes a decomposition stage, a nucleation stage, and a growth stage performed sequentially, with the parameters of each stage independently adjustable. The heating rate for the decomposition stage is 10-15℃ / min, the maximum temperature is 1100-1750℃, and the holding time is 0.5-1.5h; the heating rate for the nucleation stage is 5-10℃ / min, the maximum temperature is 1850-2100℃, and the holding time is 1-2h; the heating rate for the growth stage is 1-5℃ / min, the maximum temperature is 2100-2600℃, and the holding time is 1-4h. The decomposition stage safely and fully converts the solid raw material into an effective gas-phase reaction precursor and creates a clean reaction interface for subsequent stages. The heating rate in this stage is 10-15℃ / min. This rapid heating rate quickly overcomes the coking and decomposition temperature range of organic matter in the raw materials, reducing complex side reactions of intermediate products and promoting efficient and concentrated decomposition of the raw materials to generate target gaseous substances such as CO and SiO. The maximum temperature is 1100-1750℃, and the holding time is 0.5-1.5h. This temperature range ensures the thermodynamic feasibility of the reaction between silicon source and carbon to generate gaseous SiO. The purpose of holding the temperature is to allow the raw materials, especially bulk or large-particle silicon sources, sufficient time to complete the complete gasification reaction, ensuring a stable and uniform precursor gas phase partial pressure within the reaction chamber, and avoiding fluctuations in the supply of reactants in subsequent stages due to incomplete decomposition of the raw materials. The nucleation stage creates appropriate supersaturation conditions on the deposition plate, guiding the uniform and controllable formation of silicon carbide nuclei, laying the foundation for crystal growth. The heating rate is 5-10℃ / min, slower than in the decomposition stage. This slows down the heating rate to ensure the deposition plate reaches the target temperature gradually and uniformly, preventing excessive supersaturation of the gas phase due to sudden temperature changes, which could trigger explosive nucleation, generating too many small, disordered, or heterogeneous nuclei, and resulting in nucleation only in localized areas. The maximum temperature is 1850-2100℃, which is the temperature at which silicon carbide crystals can exist stably and is higher than in the decomposition stage. When the gas phase containing SiO and CO is transported to the relatively low-temperature deposition plate, the temperature decrease leads to an increase in its supersaturation, thus satisfying the thermodynamic driving force for nucleation. The selection of this temperature window is crucial; if the temperature is too low (<1850℃), the nucleation driving force is insufficient; if the temperature is too high (>2100℃), it approaches the growth temperature, which may cause nucleation and growth to occur rapidly simultaneously, resulting in a loss of control over the nucleus density. The holding time is controlled at 1-2 hours to provide a stable thermal environment, allowing the nuclei sufficient time to complete the evolution from critical nuclei to stable nuclei and control the final nucleus density. The longer holding time is beneficial for obtaining more uniform and complete crystal nuclei. The growth stage, based on the already formed nuclei, achieves rapid and controllable epitaxial growth of silicon carbide crystals through a continuous gas phase supply. The heating rate is 1-5℃ / min, a very slow heating process. Its core purpose is to maintain a stable and well-defined temperature gradient.This gradient is the core driving force propelling the continuous transport of gaseous materials (SiO, CO) from the high-temperature raw material region to the relatively low-temperature deposition plate. Rapid heating disrupts this gradient, affecting growth stability and crystal quality. The highest temperature is 2100-2600℃, and this high temperature is crucial for promoting rapid silicon carbide crystal growth. At this temperature, the surface atomic mobility is extremely high, allowing Si and C atoms adsorbed from the gas phase to quickly find the correct positions in the crystal lattice, achieving high-quality epitaxial growth. Simultaneously, the high temperature also helps suppress the formation of certain unfavorable crystal forms (such as non-cubic phases) and promotes the growth of thermodynamically stable phases.

[0014] Furthermore, steps 1) and 2) can be repeated 1-3 times. During the repetition, the parameters of the segmented heating-holding regime can be adjusted, and the final silicon carbide grain purity is >99%. Its crystal form, size and quantity are controlled by the raw material ratio, heating-holding regime parameters and the number of repetitions.

[0015] The beneficial effects of this invention are: The product boasts high purity and extremely low impurity residue. Through precise matching of organic carbon sources (containing only C, H, O, and N) with various types of silicon sources, combined with a high-temperature holding period of 1100-1750℃ during the decomposition stage, the raw material impurities (H, O, N, etc.) are fully volatilized without the need for inducing agents, thus avoiding the introduction of exogenous impurities. The final product has a purity >99%, with no residual free C, Si, N, etc., meeting the stringent purity requirements of high-performance semiconductor devices and structural ceramics.

[0016] With precise control over crystal form and size, it can adapt to various application scenarios. By adjusting the C / Si atomic ratio and nucleation stage parameters, it can flexibly prepare single-crystal silicon carbide or dense polycrystalline silicon carbide, covering different application scenarios of semiconductor devices (single crystal) and structural components (polycrystalline).

[0017] The process is highly safe and has no safety hazards. It eliminates the use of highly toxic and explosive gaseous raw materials such as silane and propane, which are relied upon by HT-CVD technology. Instead, it uses solid organic carbon sources (such as glucose and cellulose) and solid silicon sources (elemental silicon, silicon nitride, etc.) as reaction substrates. It does not require complex safety protection and exhaust gas treatment systems, thus avoiding the risks of explosion and poisoning during gas storage, transportation, and reaction processes from the source. The production process is safe and controllable.

[0018] This invention boasts high growth efficiency and rapid grain growth rate. Because it eliminates the need for inducing agents and synthesizes at high temperatures, the resulting silicon carbide grains exhibit higher purity. When synthesizing silicon carbide crystals using this invention, crystal growth is rapid, with the crystal size increasing by over 100 μm per hour during the growth stage. This invention eliminates the need to distinguish between high-temperature and low-temperature zones, requires precise regional temperature difference control, and eliminates the need for gas-phase guiding devices. The equipment structure is very simple, resulting in high reliability, stability, and low cost. Detailed Implementation

[0019] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0020] Example 1: step: Raw material mixing: The carbon source is glucose (containing only C, H and O), and the silicon source is elemental silicon powder, which is mixed at a C / Si atomic ratio of 1:1; wet ball milling is used, with ethanol added as the dispersion medium, and the mixture is ball milled at 150 r / min for 4 hours, and then dried and ground into powder.

[0021] Grain growth: The raw material is spread in a graphite sagger, covered with a graphite deposition plate, and placed in a high-temperature furnace. A three-stage process is performed under a protective atmosphere (argon). Decomposition stage: Heat to 1500℃ at 12℃ / min and hold for 1 hour; Nucleation stage: Heat to 1900℃ at a rate of 8℃ / min, and hold for 1.5h; Growth stage: Increase temperature to 2200℃ at 3℃ / min and hold for 2 hours; Cool to room temperature and collect the silicon carbide grains on the deposition plate.

[0022] Test results: Purity: 99.6%, ICP-MS analysis showed no free C or Si impurities; Crystal form: cubic phase SiC single crystal, XRD detection shows sharp characteristic peaks without impurity peaks, and regular hexahedral grain morphology; Size: Average particle size 800μm, measured by laser particle size analyzer, size uniformity RSD=5.2%.

[0023] Example 2: step: Raw material mixing: The carbon source is cellulose (containing only C, H and O), and the silicon source is silicon nitride (Si3N4), which is mixed at a C / Si atomic ratio of 1:3; dry ball milling is used, ball milling at 200 r / min for 3 hours, and grinding into powder.

[0024] Grain growth: The raw material is spread in a silicon carbide sagger, covered with a silicon carbide deposition plate, and placed in a high-temperature furnace. A three-stage process is performed under argon protection. Decomposition stage: Heat to 1750℃ at a rate of 15℃ / min, and hold for 1.5 hours; Nucleation stage: Increase temperature to 2100℃ at 10℃ / min and hold for 2 hours; Growth stage: Increase temperature to 2600℃ at 5℃ / min and hold for 4 hours; Cool to room temperature and collect the product.

[0025] Test results: Purity: 99.3%, with no free N or Si residue; Crystal form: dense polycrystalline SiC, XRD analysis shows that it is mainly cubic phase with good intergranular fusion; Size: Average particle size 2.5mm, meeting the requirements for large-size particles in structural ceramics.

[0026] Example 3: step: First reaction: Raw material mixing: Sucrose (containing only C, H, and O) is used as the carbon source, and silicon dioxide is used as the silicon source. They are mixed at a C / Si atomic ratio of 1:2 and then mixed evenly by spray granulation.

[0027] Grain growth: Graphite sagger and graphite deposition plate, under argon protection: Decomposition stage: Heat to 1100℃ at a rate of 10℃ / min, and hold for 0.5h; Nucleation stage: Increase temperature to 1850℃ at 5℃ / min and hold for 1 hour; Growth stage: Increase temperature to 2100℃ at a rate of 1℃ / min and hold for 1 hour; After cooling, preliminary grains were obtained (average grain size 300 μm).

[0028] Second reaction: Repeat the raw material mixing step (same as the first time), spreading the new raw material in a sagger containing the initial grains; Adjusting the three-stage system: Decomposition stage: Heat to 1600℃ at 12℃ / min and hold for 1 hour; Nucleation stage: Heat to 2000℃ at a rate of 7℃ / min, and hold for 1.5 hours; Growth stage: Increase temperature to 2400℃ at 4℃ / min and hold for 3 hours; Cool to room temperature and collect the product.

[0029] Test results: Purity: 99.5%; Crystal form: a mixture of single crystals and polycrystalline; Size: average particle size 1.8 mm.

[0030] Example 4: step: Raw material mixing: starch (containing only C, H, and O) is used as the carbon source, and elemental silicon and silicon dioxide are used as the silicon source, with a mass ratio of 1:1 and a C / Si atomic ratio of 1:1.5; wet ball milling (ethanol as the dispersion medium) is performed at 180 r / min for 5 h, followed by drying and grinding.

[0031] Grain growth: silicon carbide sagger and graphite deposition plate, under argon protection: Decomposition stage: Heat to 1600℃ at 13℃ / min and hold for 1 hour; Nucleation stage: Heat to 2000℃ at a rate of 9℃ / min, and hold for 1.5h; Growth stage: Increase temperature to 2300℃ at a rate of 2℃ / min and hold for 2.5 hours; The product is collected by cooling.

[0032] Test results: Purity: 99.4%; Crystal form: cubic single crystal SiC, with uniform grain morphology; Size: average grain size 1.2 mm.

[0033] Comparative Example 1: step: Except for mixing the carbon source and silicon source at a C / Si atomic ratio of 1:4, the other steps and parameters are completely consistent with those in Example 1.

[0034] Test results: Purity: 97.2%, with residual free Si impurities, content 2.5%; Crystal form: polycrystalline and disordered, XRD detection shows characteristic peaks of elemental Si, and amorphous regions exist between grains; Size: average particle size 650μm, RSD=18.3%, indicating large size dispersion; This shows that excessive Si leads to unreacted Si residue, which compromises purity and crystal form controllability, thus verifying the necessity of C / Si = 1:1-1:3.

[0035] Comparative Example 2: step: Except for mixing the carbon source and silicon source at a C / Si atomic ratio of 1:0.8, the remaining steps and parameters are completely consistent with those in Example 1.

[0036] Test results: Purity: 96.8%, with residual free carbon impurities, content 2.9%; Crystal form: a mixture of single crystals and free carbon, XRD detection shows amorphous carbon characteristic peaks, and carbon particles are attached to the surface of the grains; Size: average particle size 580μm, rough surface (free carbon causes uneven grain growth); visible excess C, free carbon cannot be completely volatilized.

[0037] Comparative Example 3 step: The decomposition stage was skipped, and the temperature was directly increased from room temperature to 1900°C at a rate of 8°C / min. The remaining steps and parameters were exactly the same as in Example 1.

[0038] Test results: Purity: 95.1%, with residual O and H impurities, content 4.6%, from undecomposed groups of organic carbon source; Crystal form: severe polycrystalline defects, broadened XRD characteristic peaks, indicating oxygen doping defects; Size: average particle size 420μm, RSD=22.5%, incomplete decomposition of raw materials, and fluctuating supply of gaseous species; It is evident that the lack of a decomposition stage leads to the failure to remove raw material impurities and instability of gaseous species, highlighting the necessity of the decomposition stage in the three-stage process for purity and growth uniformity.

[0039] Comparative Example 4: step: The three-stage parameters were adjusted as follows: during the decomposition stage, the temperature was increased from 20°C / min to 1800°C; during the growth stage, the temperature was increased from 6°C / min to 2700°C; and the remaining steps and parameters were completely consistent with those in Example 2.

[0040] Test results: Purity: 98.1%, SiC partially sublimated, resulting in trace Si loss; Crystal form: Crystal transformation, from cubic phase to a mixture of cubic and hexagonal phases, with impurity peaks appearing in XRD; Size: Average particle size 1.8 mm, but grains are cracked; It can be seen that the temperature rise during the decomposition stage is >15℃ / min, and the growth temperature is >2600℃, leading to uncontrolled crystal form and grain defects.

[0041] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom remain within the scope of this invention.

Claims

1. A method for controlling the growth of silicon carbide grains, characterized in that, Includes the following steps: 1) Raw material mixing: The carbon source and silicon source are mixed evenly according to a preset ratio to obtain the raw materials for silicon carbide grain growth; 2) Silicon carbide grain growth: The raw material is placed in a sagger for silicon carbide grain growth and spread evenly. After covering it with a deposition plate, the sagger is placed in a high-temperature furnace. Silicon carbide grains are synthesized under a protective atmosphere according to a segmented heating-holding regime, so that silicon carbide grains are formed and grown on the deposition plate. After cooling, silicon carbide grains are obtained.

2. The method for controlling silicon carbide grain growth according to claim 1, characterized in that, The carbon source is an organic carbon source composed only of four elements: C, H, O, and N.

3. The method for controlling silicon carbide grain growth according to claim 1, characterized in that, The silicon source is selected from one or more of silicon carbide, elemental silicon, silicon monoxide, silicon dioxide, and silicon nitride.

4. The method for controlling silicon carbide grain growth according to claim 1, characterized in that, The mixing method described in step 1) is any one of dry ball milling, wet ball milling, or spray granulation.

5. The method for controlling silicon carbide grain growth according to claim 4, characterized in that, When using wet ball milling, the dispersion medium added during the mixing process is ethanol.

6. The method for controlling silicon carbide grain growth according to claim 1, characterized in that, The mixing ratio of the carbon source and the silicon source satisfies a C / Si atomic ratio of 1:1 to 1:

3.

7. The method for controlling silicon carbide grain growth according to claim 1, characterized in that, The materials of the sagger and the deposition plate are independently selected from either carbon or silicon carbide.

8. The method for controlling silicon carbide grain growth according to claim 1, characterized in that, The segmented heating-holding regime includes a decomposition stage, a nucleation stage, and a growth stage performed sequentially, and the parameters of the three stages are independently adjustable.

9. The method for controlling silicon carbide grain growth according to claim 8, characterized in that, The heating rate for the decomposition stage is 10-15℃ / min, the maximum temperature is 1100-1750℃, and the holding time is 0.5-1.5h; the heating rate for the nucleation stage is 5-10℃ / min, the maximum temperature is 1850-2100℃, and the holding time is 1-2h; the heating rate for the growth stage is 1-5℃ / min, the maximum temperature is 2100-2600℃, and the holding time is 1-4h.

10. The method for controlling silicon carbide grain growth according to claim 1, characterized in that, Steps 1) and 2) can be repeated 1-3 times. During the repetition, the parameters of the segmented heating-holding regime can be adjusted, and the final silicon carbide grain purity is >99%. Its crystal form, size and quantity are controlled by the raw material ratio, heating-holding regime parameters and the number of repetitions.