Silicon nitride crystal based on physical vapor transport method and preparation method thereof

Abstract

The invention discloses a silicon nitride crystal based on a physical vapor transport method and a preparation method thereof, and the preparation method comprises the following steps: laying silicon nitride powder as a raw material at the bottom of a graphite crucible, fixing a seed crystal on a top cover of the crucible, placing the device in single crystal growth equipment, vacuumizing, heating to 1000-1300 DEG C, filling nitrogen to 800-1000 mbar, and preserving heat for 1-3 hours, the method comprises the following steps of: heating to the temperature of between 1,600 and 2,000 DEG C, inhibiting the decomposition of silicon nitride, continuously heating to the temperature of between 1,600 and 2,000 DEG C, adjusting the air pressure in equipment to 100 to 300 mbar, and promoting the silicon nitride to be decomposed into silicon steam and nitrogen. And controlling the temperature of a seed crystal area to be 1500-1700 DEG C and the axial temperature gradient to be 10-50 DEG C / cm, so that Si and N substances in a gas phase are crystallized on the surface of the seed crystal to generate a silicon nitride crystal. And after the crystal grows, filling inert gas and slowly cooling to room temperature to finally prepare the complete silicon nitride crystal. The preparation method disclosed by the invention is accurate in process and high in crystal quality, and the prepared silicon nitride crystal has the particle size of more than 500 microns and the purity of more than 5N, and is suitable for the field of application of high-end materials.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon nitride crystal preparation, and in particular to a silicon nitride crystal based on a physical vapor transport method and a preparation method thereof. Background Art

[0002] Silicon nitride (Si3N4) is a highly promising advanced ceramic material. It is widely used in aerospace, electronic components, high-temperature mechanical parts, and metallurgical refractory materials due to its high strength, high hardness, high wear resistance, excellent high temperature resistance, and corrosion resistance. In addition, silicon nitride is also a wide-bandgap semiconductor (5.3eV) that exhibits excellent stability in high-radiation environments and high-temperature conditions, making it particularly suitable for the manufacture of high-end optical devices, electronic devices, and power devices. However, the large-scale preparation of silicon nitride crystals, especially the preparation of high-purity, large-size single crystals, still faces many challenges.

[0003] In the prior art, the preparation methods of silicon nitride are mainly divided into two categories: powder synthesis and crystal growth: Powder synthesis method: Common methods include direct nitridation, carbon thermal reduction and chemical vapor reaction. Although these methods can achieve the synthesis of silicon nitride, the resulting products are mostly granular or powdered materials with particle sizes ranging from nanometers to micrometers, which is difficult to meet the requirements for the size, purity and performance of silicon nitride crystal materials in practical applications. For example, patent CN104891455A describes a method for preparing nano silicon nitride by reacting silicon tetrachloride with lithium nitride. Although the reaction is relatively efficient, the silicon tetrachloride used in the process is highly toxic and there are environmental pollution problems. In addition, the resulting materials are mostly granular and difficult to further process into large-sized crystals;

[0004] Crystal growth method: Crystal growth is one of the key technologies for preparing high-purity, large-size silicon nitride. At present, crystal growth usually adopts high-temperature and high-pressure synthesis method or chemical vapor deposition (CVD). Among them, the high-temperature and high-pressure method can produce silicon nitride crystals with higher hardness and strength, but the equipment of this method is complex and costly, and the crystal growth process is difficult to control, resulting in crystal size and purity that cannot meet the requirements of high-end applications. Although the CVD method has better purity control, its crystal growth rate is slow and the equipment is expensive, which is not suitable for industrial large-scale production.

[0005] The current method for preparing silicon nitride crystals faces the following major technical bottlenecks: Raw material limitation: Silicon tetrachloride, silicate, etc. are commonly used as raw materials in existing processes. These materials are either toxic or introduce impurities, making it difficult for the product purity to meet the requirements. In addition, some reaction raw materials are expensive, which increases the preparation cost; process complexity: The existing high temperature and high pressure method, CVD method, etc. have high equipment requirements, high energy consumption, and complex processes, which limits the feasibility of large-scale industrial production; crystal size limitation: Due to the high difficulty of control during the growth process, the size of silicon nitride crystals prepared by existing methods is mostly small, which cannot meet the needs of scenes such as high-performance optical windows and high-power electronic device substrates; environmental pollution problems: Some processes use highly toxic solvents or chemicals (such as silicon tetrachloride, organic solvents, etc.), which may release harmful gases (such as hydrogen chloride and hydrogen fluoride) during the reaction process, causing pollution to the environment, and requiring additional waste gas treatment equipment, further increasing production costs.

[0006] Chinese patent application with publication number CN104891455A discloses a method for preparing silicon nitride nanomaterials, which mainly comprises placing a mixture of silicon tetrachloride and lithium nitride in a special stainless steel reactor and sealing it, placing it in a resistance crucible furnace for heating, washing the product with alcohol, acid and water until it is neutral, separating and drying to obtain silicon nitride nanomaterials, but this method uses silicon tetrachloride as a raw material to prepare silicon nitride, and silicon tetrachloride is very harmful to the human body and easily causes environmental pollution; Patent CN108059133A discloses a nano silicon nitride and a preparation method thereof, which method comprises ball milling silicate to obtain powdered silicate, and uniformly mixing it with magnesium powder, magnesium chloride and ammonium chloride to obtain a mixture, and then heating the obtained mixture to 800-1000°C at a heating rate of 8-20°C / min and keeping it warm for 6-18h, and then acid washing it after cooling to obtain nano silicon nitride, but the nano silicon nitride particles prepared by the ball milling method are uneven and the size is mostly nanometer-level.

[0007] In summary, the current preparation methods of silicon nitride crystals are still difficult to achieve a comprehensive balance of high purity, large size and low cost. These technical defects have limited the application of silicon nitride crystals in many fields. Therefore, it is urgent to develop a new preparation method based on environmentally friendly raw materials, simplify the process flow, and effectively improve the purity and size of the crystals to meet the growing market demand and application requirements of high-end technologies. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for preparing silicon nitride crystals based on physical vapor transport method, so as to solve the problems of low crystal purity, small size, uneven size, easy cracking and low growth efficiency existing in the conventional preparation methods in the prior art.

[0009] In order to overcome the above defects of the prior art, the present invention provides a method for preparing silicon nitride crystals based on physical vapor transport method, characterized in that it comprises the following steps: S1: Raw material preparation: Select silicon nitride powder as the raw material for growing silicon nitride crystals, spread the silicon nitride powder on the bottom of a graphite crucible, and fix the seed crystal on the top cover of the graphite crucible; S2: vacuum treatment, placing the graphite crucible containing the silicon nitride raw material after the treatment in step S1 into a single crystal growth device, and vacuum treatment is performed on the inside of the single crystal growth device; S3: Temperature-raising decomposition treatment of silicon nitride: the interior of the single crystal growth equipment after the treatment in step S2 is heated to 1000-1300°C, and nitrogen is charged into the equipment for the first time, and the equipment is kept warm and pressurized for the first time for 1-3 hours to inhibit the decomposition of silicon nitride; then the interior of the single crystal growth equipment is heated to 1600-2000°C, and then the equipment is kept warm and pressurized for the second time to gradually decompose the silicon nitride powder into silicon vapor and nitrogen; S4: crystal growth: controlling the temperature of the seed crystal region on the top cover of the graphite crucible after the treatment in step S3 to 1500-1700° C., so that Si and N substances in the gas phase crystallize on the surface of the seed crystal to form silicon nitride crystals; S5: Cooling: After the crystal growth is completed, the equipment is filled with inert gas to normal pressure, and the temperature is slowly lowered to room temperature to obtain a complete silicon nitride crystal.

[0010] The present invention discloses a method for preparing silicon nitride crystals based on physical vapor transport, which has the following advantages over the prior art: the preparation method of the present invention realizes the growth of silicon nitride crystals through physical vapor transport (PVT), and ensures the stability of crystal growth by using step-by-step heating and precise temperature control, especially in the two-stage heating in the S3 stage (initial stage of 1000-1300°C and high temperature stage of 1600-2000°C) with suitable pressure conditions, which effectively inhibits the excessive decomposition of silicon nitride and provides a continuous nitrogen and silicon vapor source, thereby ensuring the high efficiency of the crystal growth process, and uses vacuum treatment (S2) to remove impurity gases in the growth equipment, and controls the nitrogen pressure inside the equipment during the high-temperature decomposition process to avoid the introduction of impurities, combined with precise control of the temperature in the seed crystal area (1500-1700°C), it is possible to obtain high-purity, high-quality silicon nitride crystals; in step S4, by precisely setting the regional temperature of the seed crystal area, a stable driving force for crystal growth is provided, so that the crystal is kept at the seed crystal temperature. The crystal surface is crystallized in a uniform and orderly manner, avoiding the problem of uneven growth caused by temperature fluctuations in the existing method. In step S5, inert gas protection and slow cooling process are adopted to avoid the accumulation of crystal thermal stress caused by too fast cooling speed, reduce the generation of cracks and defects, and ensure the integrity of the crystal. Compared with the prior art, the present invention abandons the use of volatile toxic gases in chemical vapor deposition (CVD), reduces environmental pollution through the pyrolysis and gas phase reaction process of physical vapor transport method, and has low equipment requirements, which is convenient for industrial promotion. The preparation method of the present invention selects silicon nitride powder as raw material, which is suitable for materials of various particle sizes. In summary, by realizing fine control of temperature, pressure and materials in each step S1-S5, and synergistically acting at the same time, combined with the characteristics of the PVT process, not only the problems of slow crystal growth rate, low purity and many cracks in the prior art are overcome, but also the crystal size and uniformity are significantly improved, which has broad practical application value and industrial prospects.

[0011] In a possible embodiment, in step S1, the seed crystal is one of silicon nitride, silicon carbide, silicon or aluminum nitride, and the particle size of the seed crystal is greater than 200um and the purity is greater than 5N; the particle size of the silicon nitride powder is 1-20um and the purity is greater than 5N Compared with the prior art, the above technical scheme adopts different seed crystal materials, which have a significant effect on the adsorption of Si and N components in the gas phase and the crystal growth rate. Silicon nitride, silicon carbide, silicon and aluminum nitride have good chemical compatibility and thermal stability, and can provide a stable crystal growth surface under high temperature and high pressure conditions. When silicon nitride is selected as a seed crystal, its chemical composition is exactly the same as the target crystal, which can avoid the introduction of impurities and provide good crystal matching. When silicon carbide, aluminum nitride or silicon is used as a seed crystal, these materials have high hardness and thermal conductivity, can work stably in a high temperature environment, and have a good guiding effect on the crystal growth interface. The above implementation method reduces the dependence on high specific conditions by flexibly selecting seed crystal materials, is suitable for large-scale production environments, and reduces the technical threshold and cost of crystal manufacturing.

[0012] In a possible implementation manner, in step S2, the vacuum treatment condition is: vacuuming until the pressure inside the single crystal growth device is 10 -3 -10 -6 Pa.

[0013] Compared with the prior art, the above technical solution can effectively reduce the interference of impurities and gases in the growth process of silicon nitride crystals by using a high vacuum environment. -3 -10 -6 The range of Pa can reduce the influence of moisture, oxygen and other gases in the air on the crystal growth process. This helps to avoid the formation of impurities on the crystal surface, ensure the purity of silicon nitride crystals and the perfection of the lattice structure, effectively solve the problems of improper impurity control and unstable growth in the crystal growth process in the prior art, directly improve the quality of silicon nitride crystals, and have a high industrial application value.

[0014] In a possible implementation, in step S3, the conditions for the first filling of nitrogen are: filling until the pressure in the equipment is 800-1000 mbar, and the first heat preservation and pressure maintenance time is 1-3 hours.

[0015] Compared with the prior art, the above technical solution aims to provide an inert atmosphere for the reaction environment by filling high-pressure nitrogen (800-1000mbar), while inhibiting the premature decomposition of silicon nitride powder under high temperature conditions. The presence of high-pressure nitrogen can stabilize the structure of silicon nitride and reduce the loss of silicon and nitrogen elements. The 1-3 hours of insulation time makes the temperature inside the equipment evenly distributed, and provides sufficient time for the pretreatment of the powder to ensure that the decomposition process of the material is controllable and efficient in the subsequent steps. It successfully solves the decomposition problem of silicon nitride powder in the heating stage, reduces material waste, and significantly improves the uniformity and stability of the crystal growth process.

[0016] In a possible implementation, in step S3, the second heat preservation and pressure maintenance condition is: maintaining the air pressure in the equipment at 100-300 mbar.

[0017] Compared with the prior art, the above-mentioned technical scheme is adopted, and the second heat preservation and pressure holding conditions (100-300 mbar) correspond to the first heat preservation and pressure holding, aiming to create a suitable low-pressure environment for the decomposition reaction of silicon nitride. The lower pressure helps to accelerate the decomposition of silicon nitride powder, increase the volatilization rate of silicon vapor and nitrogen, and provide sufficient gas phase raw materials for subsequent crystal growth. Within the low pressure range of 100-300 mbar, the partial pressures of silicon vapor and nitrogen reach a balance, effectively avoiding decomposition inhibition caused by excessive pressure and gas loss caused by excessively low pressure, thereby ensuring the controllability of the reaction.

[0018] In a possible implementation, in step S4, the axial temperature gradient of the seed crystal region is 10-50° C. / cm.

[0019] Compared with the existing technology, the above technical solution optimizes the thermodynamic and kinetic conditions in the crystal growth process by precisely controlling the axial temperature gradient in the seed crystal area. A reasonable axial temperature gradient (10-50°C / cm) helps to form a stable thermal driving field on the seed crystal surface, prompting the Si and N atoms in the gas phase to migrate and deposit in a directional manner, providing a stable driving force for crystal growth, and allowing the crystal to crystallize in a uniform and orderly manner on the seed crystal surface, thereby ensuring the uniformity and orderliness of crystal growth and avoiding the problem of uneven growth caused by temperature fluctuations in the existing method.

[0020] In a possible implementation, in step S5, the inert gas is one or both of argon and nitrogen.

[0021] Compared with the prior art, the above technical solution uses argon and / or nitrogen as inert gas, effectively solving the gas contamination problem that may occur during the crystal cooling process in the prior art, and optimizing the cooling environment of the silicon nitride crystal. Through this improvement, the quality, purity and consistency of the silicon nitride crystal can be greatly improved, ensuring the stability and efficiency in the industrial production process.

[0022] In a possible implementation, in step S5, the cooling condition is furnace cooling to room temperature.

[0023] Compared with the existing technology, the above technical scheme can effectively reduce the defects caused by uneven cooling or too fast cooling through furnace cooling, further improve the purity and structural integrity of silicon nitride crystals, and significantly reduce the thermal stress and cracks caused by temperature difference, thereby improving the quality, stability and integrity of silicon nitride crystals, ensuring the high performance of silicon nitride crystals, and being suitable for large-scale industrial production.

[0024] Another technical problem to be solved by the present invention is that the silicon nitride crystal prepared by the above preparation method can solve the shortcomings of conventional silicon nitride crystals in the prior art in terms of particle size, purity and crystal quality.

[0025] In order to overcome the above defects of the prior art, the present invention provides a silicon nitride crystal obtained by the above preparation method, wherein the particle size of the silicon nitride crystal is greater than 500um and the crystal purity is greater than 5N.

[0026] Compared with the prior art, the silicon nitride crystal of the present application has the following advantages: During the growth process of the silicon nitride crystal of the present invention, the key parameters (temperature, pressure and thermal field distribution) are regulated by the physical vapor transport method to ensure the full gasification and transmission of the silicon nitride decomposition products and the orderly crystallization on the surface of the seed crystal. The final technical effect is to achieve a significant improvement in the quality of crystal growth, that is, silicon nitride crystals with larger particle size, higher purity and complete structure, which not only overcomes the limitations of the existing silicon nitride crystals in size and performance, but also provides high-quality material guarantees for the practical application of silicon nitride crystals in optoelectronic devices, high-performance ceramic materials and other fields. The silicon nitride crystal specifically includes the following technical advances:

[0027] Particle size optimization: By precisely controlling the temperature gradient of silicon nitride decomposition during heating and the thermal field distribution in the seed crystal region, the present invention can significantly increase the growth rate of the crystal, so that the particle size of the prepared silicon nitride crystal is greater than 500 μm, overcoming the problem of generally small crystal particle size in the prior art; High purity: Through the synergistic effects of vacuum evacuation and high-temperature decomposition of silicon nitride powder, gas phase transmission, and seed crystal deposition, the introduction of impurities is minimized. At the same time, with the inert gas cooling measures, silicon nitride crystals with a purity of >5N are finally obtained, which effectively solves the problem of low crystal purity caused by insufficient impurity control in traditional processes; Crystal integrity: Rationally design the temperature gradient of the seed crystal area (10-50℃ / cm), optimize the deposition conditions of the gas phase material, reduce the generation of internal crystal defects, and overcome the problems of many crystal cracks and structural defects in the existing technology; BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the surface of the silicon nitride crystal obtained in Example 1 of the present invention; Figure 2It is a reaction process diagram of the present invention. DETAILED DESCRIPTION

[0029] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0030] like Figure 2 As shown, Figure 2 The present invention provides a method for preparing silicon nitride crystals based on a physical vapor transport method, comprising the following steps: S1: Raw material preparation: Select silicon nitride powder as the raw material for growing silicon nitride crystals, spread the silicon nitride powder on the bottom of a graphite crucible, and fix the seed crystal on the top cover of the graphite crucible; S2: vacuum treatment, placing the graphite crucible containing the silicon nitride raw material after the treatment in step S1 into a single crystal growth device, and vacuum treatment is performed on the inside of the single crystal growth device; S3: Temperature-raising decomposition treatment of silicon nitride: the interior of the single crystal growth equipment after the treatment in step S2 is heated to 1000-1300°C, and nitrogen is charged into the equipment for the first time, and the equipment is kept warm and pressurized for the first time for 1-3 hours to inhibit the decomposition of silicon nitride; then the interior of the single crystal growth equipment is heated to 1600-2000°C, and then the equipment is kept warm and pressurized for the second time to gradually decompose the silicon nitride powder into silicon vapor and nitrogen; S4: crystal growth: controlling the temperature of the seed crystal region on the top cover of the graphite crucible after the treatment in step S3 to 1500-1700° C., so that Si and N substances in the gas phase crystallize on the surface of the seed crystal to form silicon nitride crystals; S5: Cooling: After the crystal growth is completed, inert gas is filled into the equipment to normal pressure, and the temperature is slowly lowered to room temperature to obtain a complete silicon nitride crystal.

[0031] As a preferred solution, in step S1, the seed crystal is one of silicon nitride, silicon carbide, silicon or aluminum nitride, and the particle size of the seed crystal is greater than 200um and the purity is greater than 5N; the particle size of the silicon nitride powder is 1-20um and the purity is greater than 5N As a preferred solution, in step S2, the vacuum treatment condition is: vacuuming until the pressure inside the single crystal growth equipment is 10 -3 -10 -6 Pa.

[0032] As a preferred solution, in step S3, the conditions for the first filling of nitrogen are: filling until the pressure in the equipment is 800-1000 mbar, and the time for the first heat preservation and pressure maintenance is 1-3 hours.

[0033] As a preferred solution, in step S3, the conditions for the second heat preservation and pressure maintenance are: maintaining the air pressure in the equipment at 100-300 mbar.

[0034] As a preferred solution, in step S4, the axial temperature gradient of the seed crystal region is 10-50°C / cm.

[0035] As a preferred solution, in step S5, the inert gas includes one or both of argon and nitrogen.

[0036] As a preferred solution, in step S5, the cooling condition is furnace cooling to room temperature.

[0037] The present invention also provides silicon nitride crystals obtained by the above preparation method, wherein the particle size of the silicon nitride crystals is greater than 500um and the crystal purity is greater than 5N.

[0038] The following is a description and explanation of the above-mentioned technical solutions in combination with specific data: Example 1 This embodiment provides a silicon nitride crystal based on physical vapor transport and a preparation method thereof, wherein the silicon nitride crystal is prepared by physical vapor transport. The preparation method comprises the following steps:

[0039] S1: Raw material preparation Silicon nitride powder is selected as the raw material for growing silicon nitride crystals, the silicon nitride powder is evenly spread on the bottom of a graphite crucible, and silicon nitride particles with a particle size of 300-500um are fixed on the top cover of the graphite crucible as seed crystal materials. The particle size range of the silicon nitride powder is 1-5μm, and silicon nitride material is selected as the seed crystal to ensure good crystal matching during the growth process.

[0040] S2: Vacuum treatment The graphite crucible (containing silicon nitride powder and silicon nitride seed crystal) treated in step S1 is placed in the single crystal growth equipment, and the vacuum equipment is started to vacuum the inside of the single crystal growth equipment until the air pressure reaches 10 -4 Pa to remove impurity gases in the equipment.

[0041] S3: Silicon nitride heating decomposition treatment The single crystal growth equipment is heated to 1150°C, and nitrogen is filled into the equipment at the same time. The pressure is adjusted to 900 mbar and maintained for 2 hours to inhibit the decomposition of silicon nitride. Subsequently, the temperature is further heated to 1800°C and the pressure is adjusted to 200 mbar to cause the silicon nitride powder to gradually decompose into silicon vapor and nitrogen, providing a gas phase source for crystal growth.

[0042] S4: Crystal Growth The temperature of the seed crystal region is precisely controlled to 1600°C, and the axial temperature gradient of the region is controlled to 30°C / cm. This temperature gradient helps Si and N substances in the gas phase to crystallize on the surface of the seed crystal to form silicon nitride crystals. This process ensures the stability of crystal growth by controlling temperature and atmosphere, avoiding the problem of crystal unevenness caused by temperature fluctuations during the growth process.

[0043] S5: Cooling After the crystal growth is completed, the equipment is filled with inert gas (argon) to normal pressure and slowly cooled to room temperature. This cooling process controls the temperature drop rate by cooling with the furnace, reduces cracks and thermal stress caused by excessive cooling during the cooling process, and ensures the integrity of the crystal structure.

[0044] Silicon Nitride Crystal Characteristics The silicon nitride crystals prepared in this embodiment have the following characteristics: the crystal size is greater than 500 μm, the crystal purity is greater than 5N, the surface is smooth and has no obvious cracks, and has good mechanical properties and thermal stability. The electron microscope image is as follows: Figure 1 shown.

[0045] Example 2 This embodiment provides another silicon nitride crystal based on physical vapor transport method and a preparation method thereof. The silicon nitride crystal is prepared by physical vapor transport method, and the specific steps are as follows: S1: Raw material preparation Silicon nitride powder is selected as the raw material for silicon nitride crystal growth, the silicon nitride powder is evenly spread on the bottom of the graphite crucible, and a silicon carbide single crystal with a diameter of 250-450mm is fixed on the top cover of the graphite crucible as a seed crystal. The silicon nitride powder has a particle size range of 5-10μm, and the silicon carbide material is used as the seed crystal to obtain better crystal matching.

[0046] S2: Vacuum treatment Place the graphite crucible (containing silicon nitride powder and silicon carbide seed crystal) after the treatment in step S1 into the single crystal growth equipment, start the vacuum equipment to evacuate the inside of the single crystal growth equipment until the pressure reaches 10 -3 Pa to ensure that there are very few impurities in the growth environment.

[0047] S3: Silicon nitride heating decomposition treatment The single crystal growth equipment is heated to 1000°C and filled with nitrogen at a pressure of 800 mbar for 1 hour. The temperature is then further heated to 1600°C and the pressure is adjusted to 100 mbar to gradually decompose the silicon nitride powder into silicon vapor and nitrogen.

[0048] S4: Crystal Growth By precisely controlling the temperature of the SiC seed crystal region to 1500°C and setting the axial temperature gradient of the region to 10°C / cm, this temperature gradient ensures the orderly deposition of Si and N atoms in the gas phase, promotes uniform crystal growth, and prevents uneven growth.

[0049] S5: Cooling After the crystal growth is completed, nitrogen is filled into the equipment to normal pressure and the temperature is slowly cooled to room temperature. This cooling process uses furnace cooling to avoid cracks and stress concentration caused by excessive cooling, thereby maintaining the integrity of the silicon nitride crystal.

[0050] Silicon Nitride Crystal Characteristics The silicon nitride crystals prepared in this embodiment have a grain size greater than 500 μm, a purity greater than 5N, a smooth crystal surface without obvious cracks, and excellent thermal stability and corrosion resistance.

[0051] Example 3 This embodiment provides another method for preparing silicon nitride crystals based on physical vapor transport, wherein the silicon nitride crystals are prepared by physical vapor transport. The specific steps are as follows:

[0052] S1: Raw material preparation Silicon nitride powder is selected as the raw material for growing silicon nitride crystals, the silicon nitride powder is evenly spread on the bottom of a graphite crucible, and single crystal silicon with a diameter of 300-500 mm is fixed on the top cover of the graphite crucible as a seed crystal. The particle size range of the silicon nitride powder is 10-20 μm, and silicon material is used as a seed crystal to ensure good lattice matching during crystal growth.

[0053] S2: Vacuum treatment Place the graphite crucible (containing silicon nitride powder and silicon seed crystal) after the treatment in step S1 into the single crystal growth equipment, start the vacuum equipment to vacuum the inside of the single crystal growth equipment until the pressure reaches 10 -6 Pa to reduce the interference of ambient gas on crystal growth.

[0054] S3: Silicon nitride heating decomposition treatment The single crystal growth equipment was heated to 1300°C, and nitrogen was filled into the equipment, the pressure was adjusted to 950mbar, and the temperature was kept for 3 hours. The temperature was then raised to 2000°C, and the pressure was adjusted to 300mbar, causing the silicon nitride powder to gradually decompose into silicon vapor and nitrogen.

[0055] S4: Crystal Growth The temperature of the silicon seed crystal region after the treatment in step S3 is controlled to be 1700° C., and the axial temperature gradient of the region is set to be 50° C. / cm. This ensures that Si and N substances in the gas phase can be uniformly deposited on the surface of the seed crystal, ensuring the stability and uniformity of crystal growth.

[0056] S5: Cooling After the crystal growth is completed, argon is filled into the equipment to normal pressure and cooled to room temperature with the furnace. By slowly cooling, the silicon nitride crystal is ensured to be crack-free and of good integrity.

[0057] Silicon Nitride Crystal Characteristics The silicon nitride crystals prepared in this embodiment have a grain size greater than 500 μm, a purity greater than 5N, a smooth surface without obvious cracks, and excellent crystal properties, and are suitable for high-end optoelectronics, power devices, and other high-end technology applications.

[0058] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0059] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for preparing silicon nitride crystals based on physical vapor transport, characterized in that: The following steps are involved: S1: Raw material preparation: Select silicon nitride powder as the raw material for growing silicon nitride crystals, spread the silicon nitride powder on the bottom of a graphite crucible, and fix the seed crystal on the top cover of the graphite crucible; S2: vacuum treatment, placing the graphite crucible containing the silicon nitride raw material after the treatment in step S1 into a single crystal growth device, and vacuum treatment is performed on the inside of the single crystal growth device; S3: Temperature-raising decomposition treatment of silicon nitride: the interior of the single crystal growth equipment after the treatment in step S2 is heated to 1000-1300°C, and nitrogen is charged into the equipment for the first time, and the equipment is kept warm and pressurized for the first time for 1-3 hours to inhibit the decomposition of silicon nitride; then the interior of the single crystal growth equipment is heated to 1600-2000°C, and then the equipment is kept warm and pressurized for the second time to gradually decompose the silicon nitride powder into silicon vapor and nitrogen; S4: crystal growth: controlling the temperature of the seed crystal region on the top cover of the graphite crucible after the treatment in step S3 to 1500-1700° C., so that Si and N substances in the gas phase crystallize on the surface of the seed crystal to form silicon nitride crystals; S5: Cooling: After the crystal growth is completed, inert gas is filled into the equipment to normal pressure, and a complete silicon nitride crystal is obtained after cooling.

2. The method for preparing silicon nitride crystal based on physical vapor transport method according to claim 1, characterized in that: In the step S1, the seed crystal is one of silicon nitride, silicon carbide, silicon or aluminum nitride, and the particle size of the seed crystal is greater than 200um and the purity is greater than 5N; the particle size of the silicon nitride powder is 1-20um and the purity is greater than 5N.

3. The method for preparing silicon nitride crystal based on physical vapor transport method according to claim 1, characterized in that: In step S2, the vacuum treatment condition is: vacuumizing until the pressure inside the single crystal growth equipment is 10 -3 -10 - 6 Pa.

4. The method for preparing silicon nitride crystal based on physical vapor transport method according to claim 1, characterized in that: In step S3, the conditions for the first filling of nitrogen are: filling until the pressure in the equipment is 800-1000 mbar, and the time for the first heat preservation and pressure maintenance is 1-3 hours.

5. The method for preparing silicon nitride crystal based on physical vapor transport method according to claim 1, characterized in that: In step S3, the second heat preservation and pressure maintenance condition is: maintaining the air pressure in the equipment at 100-300 mbar.

6. The method for preparing silicon nitride crystal based on physical vapor transport method according to claim 1, characterized in that: In the step S4, the axial temperature gradient of the seed crystal region is 10-50° C. / cm.

7. The method for preparing silicon nitride crystal based on physical vapor transport method according to claim 1, characterized in that: In the step S5, the inert gas is one or both of argon and nitrogen.

8. The method for preparing silicon nitride crystal based on physical vapor transport method according to claim 1, characterized in that: In the step S5, the cooling condition is to cool to room temperature in the furnace.

9. A silicon nitride crystal obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The particle size of the silicon nitride crystal is greater than 500um, and the crystal purity is greater than 5N.

Images