A method for producing a high-purity polycrystalline silicon carbide substrate
By using protective balloon milling and fluidized bed granulation technology to process powder in a nitrogen atmosphere, the oxidation problem of polycrystalline silicon carbide substrates was solved, enabling the preparation of high-purity and high-activity silicon carbide substrates and reducing production costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG FINE CERAMICS NEW MATERIALS CO LTD
- Filing Date
- 2025-11-10
- Publication Date
- 2026-07-24
AI Technical Summary
Existing methods for preparing polycrystalline silicon carbide substrates suffer from powder oxidation, resulting in poor sintering activity and low purity, as well as high production cycles and costs.
Using protective balloon milling and fluidized bed granulation technology, powder is processed in a nitrogen atmosphere to avoid oxidation, and high-purity polycrystalline silicon carbide substrates are prepared through isostatic pressing, debinding and SPS sintering processes.
It effectively removes oxides from the surface of the powder, improves sintering activity and purity, shortens the production cycle, and reduces process costs.
Smart Images
Figure CN121472998B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of silicon carbide substrate preparation technology, and particularly relates to a method for preparing a high-purity polycrystalline silicon carbide substrate. Background Technology
[0002] Substrates are fundamental carriers used in semiconductor, optoelectronic, and materials science fields for physical support, growth, or attachment of functional materials such as thin films and crystals. Silicon carbide possesses ultra-wide bandgap, high thermal conductivity, and high breakdown electric field strength, making it suitable for high-power and high-temperature environments. Therefore, silicon carbide substrates are highly suitable for power electronics and radio frequency devices.
[0003] While using monocrystalline silicon carbide (SiC) substrates exclusively is the best choice for semiconductor device fabrication or other applications, its high cost and significant processing expenses make it a costly endeavor. Monocrystalline SiC fabrication typically employs crystal growth techniques such as physical vapor transport (PVT) and total thermal solution sizing (TSSG), which have high technical barriers and equipment requirements, are complex and time-consuming, and significantly increase costs compared to polycrystalline SiC. To reduce costs, composite SiC substrates with polycrystalline SiC as the main component can be used, greatly reducing the amount of monocrystalline SiC required. First, a polycrystalline SiC substrate is prepared as the base layer, and then a thin layer of monocrystalline SiC is grown on top to form the composite SiC substrate. Wafers or functional semiconductor devices can then be grown on the monocrystalline SiC substrate. Furthermore, polycrystalline SiC substrates can also be used in CoWoS packaging technology as a replacement for silicon interposers.
[0004] Existing methods for preparing polycrystalline silicon carbide substrates mainly involve chemical vapor deposition (CVD), but its production cycle is too long, and the process cost is also relatively high compared to traditional methods such as powder metallurgy. Compared to this, existing methods for preparing polycrystalline silicon carbide substrates using powder metallurgy can significantly shorten the production cycle and reduce costs. However, due to the difficulty in sintering silicon carbide materials, and the inability to add additives to achieve high-purity silicon carbide substrates, nanoparticles are required to improve sintering activity. On the other hand, using nanoparticles introduces the problem of easy oxidation. Nanoparticles have a large specific surface area and easily adsorb oxygen from the air, leading to surface oxidation, which greatly affects sintering activity and purity.
[0005] For example, CN108558405B relates to a method involving: S1, mixing β-silicon carbide and α-silicon carbide, wherein β-silicon carbide accounts for 1-15% of the sum of the mass of β-silicon carbide and α-silicon carbide; S2, placing the raw material obtained in step S1 into a ball mill for mixing for 24 hours, then removing the powder, sieving it, and placing the powder into a mold for hot pressing and sintering. Although this method can achieve a silicon carbide product density of over 95% of the theoretical value by adding a small amount of β-silicon carbide powder to the α-silicon carbide powder, it cannot avoid surface oxidation and oxygen adsorption, affecting the final product performance.
[0006] Therefore, it is still necessary to develop a method for preparing high-purity polycrystalline silicon carbide substrates. Summary of the Invention
[0007] To address the shortcomings of current technologies, this invention proposes a method for preparing high-purity polycrystalline silicon carbide substrates. By protecting the ball mill, oxidation caused by the powder coming into contact with oxygen during ball milling is avoided. At the same time, the powder is treated and granulated in a nitrogen atmosphere using a fluidized bed granulation method, which effectively removes the oxygen adsorbed on the powder surface during the nitriding process. This solves the problems of difficult sintering and densification due to the easy oxidation of nano-silicon carbide and the low purity of the product.
[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:
[0009] A method for preparing a high-purity polycrystalline silicon carbide substrate includes the following steps:
[0010] S1. Protective Ball Milling: While stirring, add silicon carbide powder to the degassed water and mix evenly to form a silicon carbide slurry; continue stirring the slurry and heating it, while simultaneously blowing nitrogen gas into it. After boiling again, stop heating and continue blowing nitrogen gas until the slurry cools down; after cooling, change to blowing a mixture of ammonia and nitrogen gas into the silicon carbide slurry and stirring until the solution pH reaches 9-11; then add the silicon carbide slurry to the ball mill jar after removing the air and ball mill;
[0011] S2. Fluidized bed granulation: The slurry after ball milling in step S1 is sprayed into a fluidized bed. The sprayed material droplets are dried by high-temperature nitrogen to form particles, which then "boil" and fluidize in the bed. After cooling, a binder solution is sprayed into the fluidized bed at a uniform speed to allow the binder to fully mix with the silicon carbide particles and form granulated powder. The granulated powder is then removed and stored under nitrogen protection.
[0012] S3. Isostatic pressing: The granulated powder is isostatically encapsulated under a nitrogen atmosphere, and then isostatically pressed.
[0013] S4. Debinding: The green body after isostatic pressing in step S3 is placed under vacuum conditions and heated to debind, thus obtaining a silicon carbide green body.
[0014] S5, SPS sintering: The silicon carbide green body from step S4 is pretreated by heating to remove the nitrogen gas adsorbed on the green body, and then SPS sintering is performed to obtain a ceramic sample.
[0015] S6. Machining: The sintered ceramic sample is machined to obtain the required silicon carbide substrate.
[0016] In some specific implementation schemes, in step S1, the degassed water is obtained by boiling distilled water for 10-20 minutes to remove dissolved oxygen from the water.
[0017] Preferably, the mass ratio of silicon carbide powder to degassed water is 1:(0.9-2).
[0018] More preferably, the slurry is stirred and heated while nitrogen is bubbled into it. After boiling again for 2-10 minutes, heating is stopped and nitrogen is bubbled into it until the slurry cools to below 50°C.
[0019] In some specific implementation schemes, in step S1, the silicon carbide powder is high-purity nano-β silicon carbide powder with a particle size of 20-600 nm and a purity of not less than 99.95%.
[0020] Preferably, in step S1, the mass ratio of silicon carbide grinding balls in the ball mill jar to silicon carbide powder in the slurry is 1:(1.5-2.5).
[0021] In some specific implementation schemes, in step S2, the slurry after ball milling in step S1 is sprayed into a fluidized bed and fluidized at a temperature of 300-600℃ under a nitrogen atmosphere for 0.5-3 hours.
[0022] In some specific implementation schemes, in step S2, after fluidization for 0.5-3 hours, the temperature is lowered to 80-150°C, and then the binder solution is uniformly sprayed into the fluidized bed.
[0023] In some specific implementations, in step S2, the binder solution is a PMMA solution; preferably, the mass concentration of the PMMA solution is 1-6%. The higher the PMMA solution concentration, the more sufficient the binder, and the easier it is for the granulated particles to form large particles with a higher particle density, but this will prolong the drying time; the lower the PMMA solution concentration, the higher the proportion of fine powder in the granulated powder, and the worse the overall flowability of the granulated powder.
[0024] In some specific implementations, in step S3, the isostatic pressure is 20-80 MPa, and the pressure is maintained for 10-20 minutes.
[0025] In some specific implementations, in step S4, the green blank after isostatic pressing in step S3 is placed under vacuum conditions and kept at 200-300℃ for 2-6 hours, and then kept at 350-450℃ for 1-3 hours to obtain a silicon carbide blank.
[0026] In some specific implementations, in step S5, the heating pretreatment involves vacuum heating the silicon carbide blank from step S4 at 500-700°C for 1-2 hours to remove nitrogen adsorbed on the blank.
[0027] In some specific implementations, in step S5, the SPS sintering is carried out under vacuum conditions, with the temperature raised to 1800-2200℃ and the SPS sintering performed at a pressure of 40-100MPa for 10-60 minutes to obtain a ceramic sample.
[0028] Compared with the prior art, the present invention has the following beneficial effects:
[0029] This invention avoids oxidation caused by the powder coming into contact with oxygen by using protective balloon milling of the powder. At the same time, the powder is nitrided by fluidized bed granulation, which can effectively remove the oxygen adsorbed on the powder surface during the nitriding process. This can maintain the high sintering activity of nano-silicon carbide, making it easy to sinter and densify. It can also maintain the high purity of the raw materials and realize the preparation of high-purity polycrystalline silicon carbide substrates.
[0030] Compared with existing physical vapor transport methods and chemical vapor deposition methods for preparing polycrystalline silicon carbide substrates, this invention employs a simpler process technology, which greatly shortens the production cycle and reduces process costs. Attached Figure Description
[0031] Figure 1 This is a schematic flowchart of the preparation method of the present invention. Detailed Implementation
[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description, in conjunction with the accompanying drawings, provides a more comprehensive understanding of the vacuum chuck with gradient porosity, its manufacturing method, and its applications. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.
[0033] See Figure 1 An embodiment of the present invention provides a method for preparing a high-purity polycrystalline silicon carbide substrate, comprising the steps of protective balloon milling, fluidized bed granulation, isostatic pressing, debinding, SPS sintering, and machining.
[0034] In a specific example, a method for preparing a high-purity polycrystalline silicon carbide substrate includes the following steps:
[0035] S1. Protect the ball mill. Boil distilled water for 10-20 minutes to remove dissolved oxygen and obtain degassed water. Prepare silicon carbide powder and degassed water at a mass ratio of 1:(0.9-2). While stirring, evenly add silicon carbide powder to the degassed water and mix thoroughly to form a silicon carbide slurry. Continue stirring the slurry and heating it while blowing nitrogen into it. Boil again for 2-10 minutes, then stop heating and continue blowing nitrogen until the slurry cools to below 50°C. After cooling, blow a mixture of ammonia and nitrogen into the silicon carbide slurry and stir until the solution pH reaches 9-11. Add the grinding balls and silicon carbide slurry to the ball mill jar at a mass ratio of 1:2. Then, blow nitrogen into the ball mill jar to remove air. Finally, add the silicon carbide slurry to the ball mill jar and ball mill for 6-12 hours.
[0036] In this step, the degassed water and the protective balloon mill for the powder effectively prevent oxidation caused by contact between the powder and oxygen. Boiling the water removes dissolved oxygen, and then introducing a mixture of ammonia and nitrogen saturates the water, making it less likely for oxygen to dissolve. Simultaneously, adjusting the pH to 9-11 alters the surface charge state and charge density of the silicon carbide dispersed particles, improving the dispersibility of the silicon carbide.
[0037] In step S1, the silicon carbide powder is high-purity nano-β silicon carbide powder with a particle size of 20-600 nm and a purity of not less than 99.95%.
[0038] S2. Fluidized Bed Granulation. The slurry from ball milling in step S1 is added to a fluidized bed via spraying and fluidized at 300-600℃ under a nitrogen atmosphere for 0.5-3 hours. During this time, the material droplets are dried by the high-temperature nitrogen from bottom to top, forming particles that move in all directions within the bed, creating a phenomenon similar to boiling liquid. After fluidizing for 0.5-3 hours, the temperature is lowered to 80-150℃, and a binder solution is sprayed into the fluidized bed at a uniform rate to allow the binder to fully mix with the silicon carbide particles, forming granulated powder. The resulting granulated powder is then removed and stored under nitrogen protection.
[0039] In this fluidized bed granulation process, by continuously blowing flowing nitrogen gas over the surface of the nanoparticles, the oxygen adsorbed on the surface of the nanoparticles can be gradually replaced with nitrogen gas.
[0040] In step S2, the adhesive solution is a PMMA solution, for example, a PMMA solution with a mass concentration of 1-6%. This adhesive solution can be completely removed in subsequent steps.
[0041] S3. Isostatic pressing. Under a nitrogen atmosphere, the granulated powder from step S2 is isostatically encapsulated and then isostatically pressed; the isostatic pressing pressure is 20-80 MPa, and the pressure is held for 10-20 minutes.
[0042] In this step, the specific surface area of the green body after isostatic pressing is greatly reduced compared to that of nanoparticles, allowing it to be loaded into the furnace in air.
[0043] S4. Debinding. Place the green body after isostatic pressing in step S3 under vacuum conditions and hold it at 200-300℃ for 2-6 hours, then hold it at 350-450℃ for 1-3 hours to obtain a silicon carbide green body.
[0044] In step S4, there are two heat preservation sections. The first heat preservation section causes PMMA to decompose and generate volatile MMA monomers, while the second heat preservation section further decomposes its residues, thus reducing carbon residue.
[0045] S5, SPS sintering. The silicon carbide green body from step S4 is vacuum-held at 500-700℃ for 1-2 hours to remove the nitrogen gas adsorbed on the green body; the temperature is then raised to 1800-2200℃, and SPS sintering is carried out under vacuum conditions at 40-100MPa pressure for 10-60 minutes to obtain the ceramic sample.
[0046] S6. Machining. The sintered ceramic sample is machined to obtain the required silicon carbide substrate.
[0047] Those skilled in the art will understand that the method of the present invention can prepare high-purity polycrystalline silicon carbide substrates, and can also be used to make other forms of high-purity polycrystalline silicon carbide products, which should also be within the scope of protection of the present invention.
[0048] The present invention will be further explained and illustrated below through more specific embodiments, but these do not constitute any limitation.
[0049] Example 1
[0050] S1: Protective Ball Milling. Boil distilled water for 15 minutes to remove dissolved oxygen and obtain degassed water. Prepare β-silicon carbide powder with a particle size of 50 nm and a purity of 99.99% at a mass ratio of 1:1 with the degassed water. While stirring, evenly add silicon carbide powder to the degassed water and mix thoroughly to form a silicon carbide slurry. Continue stirring the slurry and heating it while blowing nitrogen gas into it. After boiling again for 5 minutes, stop heating and continue blowing nitrogen gas until the slurry cools to below 50°C. After cooling, blow a mixture of ammonia and nitrogen gas at a mass ratio of 1:1 into the silicon carbide slurry and stir until the solution pH is around 10. Add the grinding balls to the ball mill jar at a mass ratio of silicon carbide grinding balls to silicon carbide powder in the slurry of 1:2. Then, blow nitrogen gas into the ball mill jar to remove air. Subsequently, add the silicon carbide slurry to the ball mill jar and ball mill for 10 hours.
[0051] S2: Fluidized bed granulation. The slurry after ball milling in step S1 is added to a fluidized bed by spraying and fluidized at 500°C under a nitrogen atmosphere for 3 hours. After that, the temperature is lowered to 100°C, and a PMMA solution with a mass concentration of 4% is sprayed into the fluidized bed at a uniform rate to allow the PMMA solution to mix thoroughly with the silicon carbide particles to form granulated powder. The obtained granulated powder is then removed and stored under nitrogen protection.
[0052] S3: Isostatic pressing. The granulated powder from step S2 is isostatically encapsulated under a nitrogen atmosphere, followed by isostatic pressing. The isostatic pressing pressure is 40 MPa, and the pressure is held for 15 minutes.
[0053] S4: Debinding. The green body after isostatic pressing in step S3 is placed under vacuum and held at 280°C for 3 hours, then held at 400°C for 2 hours to obtain a silicon carbide green body.
[0054] S5: SPS sintering. The silicon carbide preform from step S4 was vacuum-held at 600℃ for 1 hour to remove adsorbed nitrogen from the ceramic. While maintaining vacuum conditions, the temperature was increased to 2000℃, and SPS sintering was performed at 60MPa pressure for 40 minutes to obtain the ceramic sample.
[0055] S6: Machining. The sintered ceramic sample is machined to obtain the desired silicon carbide substrate or other products.
[0056] Example 2
[0057] Compared to Example 1, the only change is as follows: the particle size of the silicon carbide powder used in step S2 is changed to 200 nm.
[0058] Example 3
[0059] Compared to Example 1, the only change is as follows: the particle size of the silicon carbide powder used in step S1 is changed to 500 nm.
[0060] Example 4
[0061] Compared to Example 1, only the following changes were made: the SPS sintering conditions in step S5 were changed, with the temperature set to 1900°C and the pressure to 50 MPa.
[0062] Comparative Example 1
[0063] Compared to Example 1, the only change is as follows: the particle size of the silicon carbide powder used in step S1 is changed to 2μm.
[0064] Comparative Example 2
[0065] Compared to Example 1, the following changes are made: the boiling degassing treatment is not performed in step S1. Specifically, β-silicon carbide powder with a particle size of 50 nm and a purity of 99.99% is prepared with distilled water at a mass ratio of 1:1. While stirring, silicon carbide powder is uniformly added to the distilled water, and the mixture is thoroughly mixed to form a silicon carbide slurry. A mixture of ammonia and nitrogen gas at a mass ratio of 1:1 is bubbled into the silicon carbide slurry and stirred until the solution pH reaches approximately 10. The grinding balls are added to the grinding jar at a mass ratio of 1:2 (silicon carbide grinding balls to silicon carbide powder in the slurry). Nitrogen gas is then introduced into the grinding jar to remove air. The silicon carbide slurry is then added to the grinding jar, and the mixture is ball-milled for 10 hours.
[0066] Comparative Example 3
[0067] Compared to Example 1, the following changes are made: Fluidized bed granulation is not used in step S2; instead, a closed-loop spray dryer is used for granulation. Specifically, in step S1, 5% by mass of PVA (based on the mass of silicon carbide powder) is added to the ball mill jar as a binder before ball milling. After ball milling, a closed-loop spray dryer is used for spray granulation. The inlet temperature of the drying tower is controlled at 190°C, and the outlet temperature is controlled at 90°C. Nitrogen is used as a protective gas.
[0068] The density of the silicon carbide substrate prepared by the above method was determined by Archimedes' displacement method and GB / T3850-2015 standard, and the purity of the silicon carbide substrate prepared by the above method was determined by glow discharge mass spectrometry and YS / T1600-2023 standard.
[0069] The performance parameters of the silicon carbide substrates in each embodiment and comparative example were measured as follows:
[0070] Table 1. Density and purity of silicon carbide substrates in each embodiment and comparative example.
[0071] Density (g / cm3) purity(%) Example 1 3.18 99.951 Example 2 3.12 99.941 Example 3 3.09 99.942 Example 4 2.98 99.953 Comparative Example 1 2.78 99.924 Comparative Example 2 2.88 99.622 Comparative Example 3 2.93 99.745
[0072] As can be seen from the comparison between Example 2, Example 3, Comparative Example 1 and Example 1, the particle size of silicon carbide powder in the raw material directly affects the sintering density. The smaller the particle size, the higher the sintering activity, and the higher the density of the silicon carbide substrate obtained after sintering.
[0073] Comparing Comparative Examples 2 and 3 with Example 1, it is evident that the lack of a boiling degassing step prevents the removal of oxygen from the distilled water. During ball milling, an oxidation reaction occurs on the surface of the silicon carbide powder, and the resulting silica cannot be removed in the subsequent nitriding treatment. This results in lower density and purity of the sintered silicon carbide substrate. The absence of the fluidized bed nitriding treatment also prevents the complete removal of oxygen adsorbed on the surface of the silicon carbide powder. During the subsequent heating and sintering process, silica is also generated, significantly affecting its sintering activity and resulting in lower density and purity of the sintered silicon carbide substrate.
[0074] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.
Claims
1. A method for preparing a high-purity polycrystalline silicon carbide substrate, characterized in that, Includes the following steps: S1. Protective Ball Milling: While stirring, add silicon carbide powder to the degassed water and mix evenly to form a silicon carbide slurry. The silicon carbide powder is high-purity nano-β silicon carbide powder. Continue stirring the slurry and heating it while blowing nitrogen gas into it. After boiling again, stop heating and continue blowing nitrogen gas until the slurry cools down. After cooling, blow a mixture of ammonia and nitrogen gas into the silicon carbide slurry and stir until the solution pH reaches 9-11. Then, add the silicon carbide slurry to the ball mill jar after removing the air and ball mill it. S2. Fluidized bed granulation: The slurry after ball milling in step S1 is sprayed into a fluidized bed. The sprayed material droplets are dried by high-temperature nitrogen to form particles, which then "boil" and fluidize in the bed. After cooling, a binder solution is sprayed into the fluidized bed at a uniform speed to allow the binder to fully mix with the silicon carbide particles to form granulated powder. The granulated powder is then removed and stored under nitrogen protection. S3. Isostatic pressing: The granulated powder is isostatically encapsulated under a nitrogen atmosphere, and then isostatically pressed. S4. Debinding: The green body after isostatic pressing in step S3 is placed under vacuum conditions and heated to debind, thus obtaining a silicon carbide green body. S5, SPS sintering: The silicon carbide green body from step S4 is pretreated by heating to remove the nitrogen gas adsorbed on the green body, and then SPS sintering is performed to obtain a ceramic sample. S6. Machining: The sintered ceramic sample is machined to obtain the required silicon carbide substrate.
2. The preparation method according to claim 1, characterized in that, In step S1, the degassed water is obtained by boiling distilled water for 10-20 minutes to remove dissolved oxygen. The mass ratio of silicon carbide powder to degassed water is 1:(0.9-2). Continue stirring and heating the slurry while blowing nitrogen into it. After boiling again for 2-10 minutes, stop heating and continue blowing nitrogen into it until the slurry cools to below 50°C.
3. The preparation method according to claim 1, characterized in that, In step S1, the silicon carbide powder has a particle size of 20-600 nm and a purity of not less than 99.95%. In step S1, the mass ratio of silicon carbide grinding balls in the ball mill jar to silicon carbide powder in the slurry is 1:(1.5-2.5).
4. The preparation method according to claim 1, characterized in that, In step S2, the slurry after ball milling in step S1 is sprayed into a fluidized bed and fluidized at a temperature of 300-600℃ under a nitrogen atmosphere for 0.5-3 hours.
5. The preparation method according to claim 4, characterized in that, In step S2, after fluidization for 0.5-3 hours, the temperature is lowered to 80-150℃, and then the binder solution is sprayed into the fluidized bed at a uniform speed.
6. The preparation method according to claim 1, 4, or 5, characterized in that, In step S2, the adhesive solution is a PMMA solution; the mass concentration of the PMMA solution is 1-6%.
7. The preparation method according to claim 1, characterized in that, In step S3, the isostatic pressure is 20-80 MPa, and the pressure is maintained for 10-20 minutes.
8. The preparation method according to claim 1, characterized in that, In step S4, the green blank after isostatic pressing in step S3 is placed under vacuum conditions and kept at 200-300℃ for 2-6 hours, and then kept at 350-450℃ for 1-3 hours to obtain a silicon carbide blank.
9. The preparation method according to claim 1, characterized in that, In step S5, the heating pretreatment involves vacuum heating the silicon carbide blank from step S4 at 500-700℃ for 1-2 hours to remove the nitrogen gas adsorbed on the blank.
10. The preparation method according to claim 1 or 9, characterized in that, In step S5, the SPS sintering is carried out under vacuum conditions, with the temperature raised to 1800-2200℃ and the SPS sintering performed at a pressure of 40-100MPa for 10-60 minutes to obtain a ceramic sample.