Quartz crucible coating and preparation method thereof

Abstract

The invention relates to a quartz crucible coating and a preparation method thereof.The coating is of a double-layer composite structure and comprises a substrate layer and a functional layer, the substrate layer is composed of 40-65 vol% of polycrystalline silicon powder (the particle size D50 ranges from 1 micrometer to 5 micrometers) and 35-60 vol% of nanometer silica sol, and the functional layer covers the surface of the substrate layer and is composed of 50-70 vol% of polycrystalline silicon powder, 20-35 vol% of nanometer silica sol and 5-15 vol% of calcium fluoride powder (the particle size D90 is smaller than 0.5 micrometer). The preparation method comprises the following steps: preparing a substrate layer slurry and a functional layer slurry, sequentially coating the inner wall of a crucible with the slurry, drying, and sintering in an inert atmosphere according to a three-step temperature control program to finally form a coating with the thickness of 180-300 microns and the porosity of 8-15 vol%; the coating structure can avoid pollution of silicon nitride or silicon carbide particles, has excellent demolding performance, thermal stability and adhesive force, further improves the service life of a crucible and the purity of a silicon ingot, and meets the requirements of an advanced semiconductor process for cleanliness and reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quartz crucible coating preparation, in particular to a quartz crucible coating and a preparation method thereof. BACKGROUND

[0002] The evolution of semiconductor silicon components has always been closely related to the technological progress of integrated circuit process nodes. In recent years, with the continuous advancement of 7 nm, 5 nm and even more advanced processes, the device structure is becoming increasingly complex, and the critical dimension is continuously shrinking, which puts higher requirements on silicon components in terms of material purity, structural uniformity, particle control and plasma compatibility.

[0003] In core processes such as etching, traditional equipment generally uses ceramic materials such as alumina as the cavity, baffle and other key components. However, there are significant differences in dielectric properties and electrical conductivity between ceramic materials and silicon wafers, which easily cause plasma instability and micro-discharge phenomena at the edge of the wafer, resulting in a decrease in device yield. In contrast, silicon components based on high-purity single-crystal silicon or polycrystalline silicon perform better in plasma control and particle defect suppression due to their high consistency with wafers in physical and electrical properties, and have gradually become the mainstream choice in advanced etching equipment.

[0004] According to the different requirements of cleanliness and service life in application scenarios, silicon components are currently roughly divided into two material systems: high-purity zone melting single-crystal silicon components are widely used in high-end logic devices and advanced nodes below 5 nm, while polycrystalline silicon components produced by ingot casting are mostly selected for mature nodes above 28 nm or general power devices to balance performance and cost. However, in the polycrystalline silicon ingot casting process, quartz crucibles are generally used as smelting containers, and Si3N4 and other materials are coated on the inner wall to assist in demolding and prevent interfacial reactions between the crucible and molten silicon.

[0005] Although the Si3N4 coating has good lubricity and demolding performance, it still has the following technical bottlenecks in the high-temperature molten silicon environment: 1. Nitrogen source pollution problem: Si3N4 is prone to partial decomposition under high temperature and low oxygen conditions, and the generated Si-N active species can diffuse into the molten silicon, forming silicon nitride particle impurities with a size of about 0.1-1 μm after crystallization, affecting the purity of the silicon ingot and the yield of subsequent wafer preparation.

[0006] 2. Side reactions caused by carbon sources: To further improve the lubricity, some preparation routes introduce graphite or B2O3-graphite composite materials as coating components. However, graphite is prone to react with molten silicon above 1500°C to form silicon carbide (SiC) particles, which are not easy to remove and can seriously interfere with subsequent chemical mechanical polishing (CMP) and plasma etching processes.

[0007] III. Interfacial thermal stress and adhesion problem: there is a large difference in the thermal expansion coefficient between the traditional coating material and quartz and molten silicon, which can easily cause the coating to peel off, crack and other failure phenomena in thermal cycling. In addition, poor wettability and large adhesion often lead to difficult silicon ingot demolding, increasing the risk of breakage and loss during the production process.

[0008] Under the increasingly stringent requirements of advanced manufacturing, the existing quartz crucible inner wall coating system based on nitride or graphite materials has been difficult to meet the multiple demands of low particles, high purity, reusability and environmentally friendly manufacturing. In order to improve the quality of silicon ingots, reduce pollution sources, improve process compatibility and overall economy, it is urgent to develop a new type of crucible inner wall coating material and its preparation process without nitrogen and carbon source, good thermal stability, excellent wettability and reasonable interfacial stress matching, so as to solve the core problems of particle pollution, demolding difficulty and structural failure existing in the prior art. SUMMARY

[0009] One of the technical problems to be solved by the present application is to provide a quartz crucible coating to solve the problems of conventional coating of nitride or carbide particle pollution, easy cracking and peeling of the coating, difficult demolding and poor thermal stability in the prior art.

[0010] To overcome the defects of the prior art, the present application provides a quartz crucible coating, which comprises a double-layer composite structure composed of a base layer and a functional layer. The composition of the base layer includes polycrystalline silicon powder and nano-silica sol, the volume fraction of the polycrystalline silicon powder is 40-65 vol%; the volume fraction of the nano-silica sol is 35-60 vol% based on dry SiO2; The functional layer is covered on the surface of the base layer, and the composition of the functional layer includes polycrystalline silicon powder, nano-silica sol and calcium fluoride powder, the volume fraction of the polycrystalline silicon powder is 50-70 vol%, the volume fraction of the nano-silica sol is 20-35 vol% based on dry SiO2, and the volume fraction of the calcium fluoride powder is 5-15 vol%.

[0011] Compared with the prior art, the quartz crucible coating has the following advantages: the coating of the application adopts a double-layer composite structure composed of a base layer and a functional layer, the base layer is composed of 40-65 vol% of polycrystalline silicon powder and 35-60 vol% of nano silicon sol, the homogeneity of the silicon powder and the molten silicon is utilized to realize thermal expansion matching, the thermal stress of the interface is reduced, meanwhile, the nano silicon sol forms a continuous SiO2 glass phase network in the sintering process, coats the silicon powder particles and is tightly combined with the quartz crucible, the adhesion and thermal shock stability are significantly enhanced; the functional layer is composed of 50-70 vol% of polycrystalline silicon powder, 20-35 vol% of nano silicon sol and 5-15 vol% of calcium fluoride powder, after sintering, the calcium fluoride migrates to the surface at high temperature to form a CaF2 wetting barrier film, which effectively improves the contact angle of the crucible surface to the molten silicon, reduces the adhesion, and realizes smooth demolding; in the structure of the application, the polycrystalline silicon powder and the silicon sol cooperatively form a Si-SiO2-CaF2 composite structure, which not only has good thermal stability and mechanical strength, but also avoids the problem of pollution caused by nitrogen source or carbon source particles of the traditional nitride or graphite coating at high temperature. Through the above design, the application changes the traditional single-layer coating of Si3N4 or graphite into a double-layer homogeneous coating system of "polycrystalline silicon powder-silicon sol base layer + polycrystalline silicon powder-calcium fluoride functional layer", and forms the synergistic effect of material intrinsic compatibility, chemical stability and surface wetting regulation, solves the core problems of coating pollution, demolding difficulty and thermal failure in the prior art, and realizes the goals of high purity, low particle, high demolding property and long service life of the quartz crucible in the polysilicon ingot casting process.

[0012] In a possible implementation, the particle size D 50 of the polycrystalline silicon powder in the base layer is 1-5 μm; the particle size D 90 of the calcium fluoride powder in the functional layer is less than 0.5 μm.

[0013] Compared with the prior art, by controlling the particle size of the polycrystalline silicon powder in the base layer to be in the range of 1-5 μm, the density and uniformity of the coating are significantly improved, the smaller particle size can effectively reduce the pore defects, improve the contact area between the coating and the inner wall of the crucible, and thus enhance the adhesion and overall mechanical strength of the coating; meanwhile, the ultra-fine calcium fluoride powder with a particle size D 90 less than 0.5 μm in the functional layer can be uniformly dispersed and migrated to the surface of the coating during the sintering process, forming a continuous and dense CaF2 wetting barrier film, which fully plays a role in reducing the interfacial tension of the molten silicon and improving the demolding property, and avoids the risks of surface roughness and local stress concentration caused by coarse particles.

[0014] In a possible implementation, the thickness of the quartz crucible coating is 180-300 μm, and the porosity is 8-15 vol%.

[0015] Compared with the prior art, by controlling the coating thickness in the range of 180-300 μm, the coating of the present application has sufficient mechanical strength and wear resistance, ensuring the structural stability during multiple furnace use, and avoiding the risk of thermal stress concentration and peeling caused by excessive thickness; and by further controlling the porosity in the range of 8-15 vol%, the coating density, barrier property and mechanical property are ensured, and the overall thermal expansion behavior of the coating is adjusted by retaining appropriate porosity, the volume stress difference in thermal cycling is relieved, and the thermal shock stability and adhesion durability are improved.

[0016] Another technical problem to be solved by the present application is to provide a preparation method of a quartz crucible coating, so as to solve the problems of poor slurry dispersibility, insufficient film uniformity, easy peeling and cracking of the coating, insufficient sintering densification and poor demolding performance in the preparation process of the conventional preparation method in the prior art.

[0017] To overcome the defects of the prior art, the present application provides a preparation method of a quartz crucible coating, comprising the following steps: S1: slurry preparation: S11: base layer slurry preparation: add polycrystalline silicon powder to water-ethanol mixed solvent, add dispersant for ball milling treatment, then further add silica sol for stirring and dispersing treatment, adjust the solid content of the slurry to 40-50 wt%, and obtain the base layer slurry; S12: functional layer slurry preparation: mix polycrystalline silicon powder and calcium fluoride powder, add water-ethanol mixed solvent and ball mill, then add silica sol for stirring and dispersing treatment, adjust the solid content of the slurry to 45-55 wt%, and obtain the functional layer slurry; S2: coating and drying: coat the base layer slurry on the inner wall of the crucible to form a base layer wet film, and perform drying treatment; then further coat the functional layer slurry on the surface of the base layer wet film to form a functional layer wet film, and perform drying treatment again; S3: high-temperature sintering: place the crucible coating obtained by the step S2 in an inert atmosphere, and perform the following three-step temperature control program: low-temperature impurity removal stage: heat the crucible coating to 500±10℃ for the first time, and perform the first heat preservation; high-temperature densification stage: heat the crucible coating to 1200±100℃ for the second time, and perform the second heat preservation; slow cooling and shaping stage: control the crucible coating to cool down to 600℃, and then naturally cool down to room temperature, and complete sintering.

[0018] Compared with the prior art, the preparation method of the quartz crucible coating has the following advantages: in step S1, the synergistic effect of the water-ethanol mixed solvent system and the dispersant, combined with the ball milling and stirring dispersion process, is used to prepare a high-uniformity polysilicon powder-silica sol base layer slurry and a calcium fluoride functional layer slurry, so as to ensure the stability and wettability of the slurry; further, in step S2, the step-by-step coating and drying procedure is used to form a base layer with enhanced bonding force, and then cover the calcium fluoride functional layer, so as to ensure the interface continuity and the structural integrity of each layer; in step S3, the three-step temperature control sintering procedure of low-temperature impurity removal, high-temperature densification and slow cooling and shaping is set, so that the silica sol is vitrified to form a continuous amorphous SiO2 network structure at high temperature, effectively coats and connects the silicon powder particles, enhances the overall mechanical strength and adhesion of the coating, and at the same time, makes the calcium fluoride powder migrate and enrich on the surface of the coating to form a continuous wettability barrier film, greatly improves the demolding performance and reduces the interface adhesion. The method utilizes the multi-factor synergy of "slurry dispersion-layered coating-segmented sintering", solves the problems of existing Si3N4 or graphite coating system, such as easy production of nitride / carbide particle pollution, poor coating adhesion and easy falling off, and difficult demolding with molten silicon, and finally obtains a quartz crucible coating with stable structure, excellent wettability, good thermal matching, and multiple furnace reuse, which comprehensively improves the purity of silicon ingot and the casting yield, and meets the dual needs of cleanliness and cost control for advanced semiconductor material manufacturing.

[0019] In a possible implementation, in the step S11, the dispersant is polyvinyl alcohol or ammonium polymethacrylate, and the addition amount of the dispersant is 0.1-0.3 wt% of the total mass of the base layer slurry.

[0020] Compared with the prior art, by adding the dispersant, the agglomeration of the polysilicon powder is effectively reduced, the dispersion stability of the powder in the water-alcohol solvent is improved, and the problems of local concentration and sedimentation caused by agglomeration are avoided; wherein, the polyvinyl alcohol can form a hydrogen bond adsorption layer on the particle surface to enhance the flowability of the slurry, and the ammonium polymethacrylate can maintain stable dispersion of particles through electrostatic repulsion, both of which can significantly improve the uniformity and film forming quality of the slurry.

[0021] In a possible implementation, in the step S11 and the step S12, the water-ethanol mixed solvent is prepared by deionized water and anhydrous ethanol at a volume ratio of 7:3, and the stirring and dispersion treatment time is 1 hour, and the ball milling treatment time is 4-6 hours.

[0022] Compared with the prior art, the above technical scheme utilizes the synergistic effect of the polarity of water and the permeability of ethanol, and takes into account the powder dispersion efficiency and slurry wettability, wherein the deionized water provides a system polarity environment to stabilize the silica sol, and the ethanol reduces the surface tension and improves the penetration and wettability, thereby avoiding agglomeration and bubble entrainment; the further defined 1-hour stirring dispersion ensures uniform premixing of the slurry, and the 4-6-hour ball milling treatment fully breaks up the powder agglomerates and improves the slurry fineness, so that the coating slurry with uniform particle size distribution, excellent stability and appropriate viscosity is obtained.

[0023] In a possible implementation, in the step S11, the viscosity of the base layer slurry is 150-350 mPa·s, and in the step S12, the viscosity of the functional layer slurry is 200-400 mPa·s.

[0024] Compared with the prior art, the above technical scheme precisely controls the viscosity of the slurry, so that the base layer slurry has good fluidity and wettability in the range of 150-350 mPa·s, ensuring that the slurry can be uniformly spread and fully penetrate into the surface micropores of the quartz crucible during coating, so as to realize dense film formation and excellent adhesion; and the viscosity of the functional layer slurry is controlled in the range of 200-400 mPa·s, which can improve the suspension stability while ensuring the fluidity, preventing the high-density powder such as calcium fluoride from settling and stratifying during the coating process, and forming a uniform and continuous functional layer structure.

[0025] In a possible implementation, in the step S2, the wet film thickness of the base layer is 80-120 μm, and the wet film thickness of the functional layer is 100-180 μm.

[0026] Compared with the prior art, the above technical scheme precisely controls the coating wet film thickness, so that the thickness of 80-120 μm of the base layer ensures the density of the silicon powder-silica sol skeleton and the bonding strength with the crucible matrix, and avoids drying cracks and sintering peeling caused by excessive thickness; and the thickness of 100-180 μm of the functional layer ensures the enrichment and uniform distribution of calcium fluoride functional particles on the surface, forms a stable and continuous wetting barrier layer, and avoids the problems of coating peeling and thermal stress concentration caused by excessive thickness.

[0027] In a possible implementation, in the step S2, the coating method is one of spraying, brushing or dipping.

[0028] Compared with the prior art, the above technical scheme flexibly selects the spraying, brushing or dipping process, so that the coating method can be adjusted according to different crucible sizes, shapes and production line equipment conditions to achieve the best film formation uniformity and production efficiency, and the spraying method is suitable for large-scale automatic continuous production and can obtain a uniform and flat coating thickness distribution.

[0029] In one possible implementation, the conditions of the three-step temperature control procedure in step S3 include: a low-temperature impurity removal stage: the crucible coating is heated to 500±10°C at a rate of 2–4°C / min, and is held for 60±5 min; a high-temperature densification stage: the crucible coating is continuously heated to a target temperature of 1100–1300°C at a rate of 3–5°C / min, and is held for 120±30 min, so as to cause the glass transition of SiO2 in the nano-silica sol and form a continuous amorphous network structure, thereby coating the polycrystalline silicon powder and calcium fluoride particles, enhancing the overall densification, bonding force and corrosion resistance of the coating, and at the same time, the calcium fluoride can migrate to the surface to form a wetting barrier layer at the temperature zone, thereby improving the demolding performance; a slow-cooling shaping stage: the crucible coating is cooled to 600°C at a rate of 1–2°C / min, and is then naturally cooled to room temperature.

[0030] Compared with the prior art, in the low-temperature impurity removal stage, the residual moisture, organic dispersant and low-temperature volatile substances in the slurry are removed at a temperature of 500±10°C and a rate of 2–4°C / min for 60±5 min, so as to avoid the foaming, bulging or micro-cracking of the coating caused by rapid heating; in the high-temperature densification stage, the glass transition of SiO2 in the nano-silica sol is caused at a temperature of 1100–1300°C and a rate of 3–5°C / min for 120±30 min, so as to form a continuous amorphous network structure, thereby coating the polycrystalline silicon powder and calcium fluoride particles, enhancing the overall densification, bonding force and corrosion resistance of the coating, and at the same time, the calcium fluoride can migrate to the surface to form a wetting barrier layer at the temperature zone, thereby improving the demolding performance; in the slow-cooling shaping stage, the temperature is cooled to 600°C at a rate of 1–2°C / min, so as to avoid the thermal stress concentration and coating cracking caused by high-temperature quenching, and further stabilize the microstructure of the coating and release the residual stress, and the above-mentioned three-step temperature control procedure cooperatively realizes a continuous transition process from impurity removal, glass transition densification to stable shaping, and finally the prepared coating has a dense structure, no cracks, firm adhesion, excellent thermal stability, corrosion resistance and demolding performance, and comprehensively solves the technical problems of coating particle pollution, falling and short service life in the background art. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 FIG. 1 is a coating cross-sectional morphology diagram of Example 1; Figure 2 FIG. 2 is a coating cross-sectional morphology diagram of Comparative Example 1; Figure 3 FIG. 3 is an infrared image of the silicon ingot of Example 1; Figure 4 FIG. 4 is an infrared image of the silicon ingot of Comparative Example 1. DETAILED DESCRIPTION

[0032] First, those skilled in the art should understand that these embodiments 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 adjust them as needed in order to adapt to specific application occasions.

[0033] The present application provides a quartz crucible coating, comprising a double-layer composite structure composed of a base layer and a functional layer: The composition of the base layer comprises 40-65 vol% of polysilicon powder and 35-60 vol% of nano-silicon sol. In the structure, the silicon powder is homologous to the material of molten silicon, which is used to provide thermal expansion matching. The silicon sol forms a continuous SiO2 network after sintering to coat and connect the silicon powder particles, enhances the bonding force of the coating and the inner wall of the quartz crucible, and constructs a dense "homogeneous skeleton layer", effectively blocking the diffusion of impurities such as Fe, Na and Al to the silicon ingot, and improving the purity.

[0034] The functional layer is covered on the surface of the base layer and is composed of 50-70 vol% of polysilicon powder, 20-35 vol% of nano-silicon sol and 5-15 vol% of calcium fluoride powder. The calcium fluoride powder migrates and enriches to the surface in the range of 900-1450℃ to form a continuous wetting barrier film of CaF2, which can effectively improve the contact angle of the crucible surface to the molten silicon, reduce the adhesion, and improve the demolding property. At the same time, the Si-SiO2-CaF2 composite structure formed by the silicon powder and the silicon sol cooperatively provides excellent thermal stability and thermal shock resistance, avoiding cracking or peeling of the functional layer during the ingot casting process.

[0035] Compared with the prior art, the coating of the present application has the following advantages: the traditional silicon nitride or graphite-based coating system is changed to a full silicon-based + calcium fluoride composite coating system, a double-layer design of "homogeneous silicon skeleton + CaF2 functional enrichment" is adopted, and the thermal matching property and chemical stability of the silicon powder and the surface migration and wetting effect of the calcium fluoride are utilized to cooperatively solve the problems of: (1) pollution of nitrogen source and carbon source, avoiding injection of silicon nitride and silicon carbide particles; (2) insufficient thermal stability and adhesion of the coating, realizing strong bonding and thermal shock resistance; (3) demolding difficulty, reducing the adhesion of the coating and the silicon ingot interface by the CaF2 functional layer, and ensuring the complete demolding of the silicon ingot.

[0036] As a preferred scheme, in the base layer, the particle size D 50 of the polysilicon powder is 1-5 μm; and in the functional layer, the particle size D 90 of the calcium fluoride powder is less than 0.5 μm.

[0037] As a preferred scheme, the thickness of the quartz crucible coating is 180-300 μm, and the porosity is 8-15 vol%.

[0038] The application also provides a preparation method of the quartz crucible coating, comprising the following steps: S1: slurry preparation: S11: base layer slurry preparation: polycrystalline silicon powder is added into a water-ethanol mixed solvent, a dispersant is added for ball milling treatment, then silica sol is further added for stirring and dispersing treatment, and the solid content of the slurry is adjusted to 40-50 wt% to obtain the base layer slurry; S12: functional layer slurry preparation: polycrystalline silicon powder is mixed with calcium fluoride powder, a water-ethanol mixed solvent is added and ball milling treatment is performed, then silica sol is added for stirring and dispersing treatment, and the solid content of the slurry is adjusted to 45-55 wt% to obtain the functional layer slurry; S2: coating and drying: The base layer slurry is coated on the inner wall of the crucible to form a base layer wet film, and drying treatment is performed; Then the functional layer slurry is further coated on the surface of the base layer wet film to form a functional layer wet film, and drying treatment is performed again; S3: high-temperature sintering: The crucible coating obtained by the step S2 is placed in an inert atmosphere, and the following three-step temperature control procedure is performed: Low-temperature impurity removal stage: the crucible coating is heated to 500±10℃ for the first time, and the first heat preservation is performed; High-temperature densification stage: the crucible coating is heated to 1200±100℃ for the second time, and the second heat preservation is performed; Slow cooling and shaping stage: the crucible coating is controlled to cool to 600℃, and then naturally cooled to room temperature, and the sintering is completed.

[0039] The above preparation method of the application can obtain a double-layer coating system with stable structure, smooth surface and firm adhesion, the total thickness of the prepared coating is 180-300 µm, and the overall porosity is controlled to be 8-15 vol%. The contact angle of the surface of the functional layer after sintering is large, so that the silicon ingot is easy to demold.

[0040] The coating preparation method provided by the application has the following advantages: It is completely free of nitrogen source and carbon source, and silicon nitride and silicon carbide particles are avoided from being implanted at the root; The high proportion of silica sol in the first layer significantly enhances the bonding force between the coating and the crucible and improves the thermal shock resistance; Calcium fluoride in the second functional structure migrates to form a wetting barrier film, improving the demolding property; The preparation process is compatible with existing spraying, brushing or dipping equipment, and is simple to operate and easy to promote in batches; The whole system has low raw material cost and strong industrial availability, and is suitable for replacing existing nitride or graphite-based coating system for semiconductor-grade or high-end photovoltaic-grade silicon ingot casting.

[0041] As a preferred scheme, in the step S11, the dispersant is polyvinyl alcohol or ammonium polymethacrylate, and the addition amount of the dispersant is 0.1-0.3 wt% of the total mass of the base layer slurry; and the silica sol is nano-silica sol.

[0042] As a preferred scheme, in the step S11 and the step S12, the water-ethanol mixed solvent is prepared by deionized water and anhydrous ethanol at a volume ratio of 7:3, and the stirring and dispersing treatment time is 1 hour, and the ball milling treatment time is 4-6 hours.

[0043] As a preferred scheme, in the step S11, the viscosity of the base layer slurry is 150-350 mPa·s, and in the step S12, the viscosity of the functional layer slurry is 200-400 mPa·s.

[0044] As a preferred scheme, in the step S2, the wet film thickness of the base layer is 80-120 μm, and the wet film thickness of the functional layer is 100-180 μm.

[0045] As a preferred scheme, in the step S2, the coating method is one of spraying, brushing or dipping.

[0046] As a preferred scheme, in the step S3, the conditions of the three-step temperature control program include: low-temperature impurity removal stage: the crucible coating is heated to 500±10℃ at a speed of 2-4℃ / min, and the first heat preservation is performed for 60±5 min; high-temperature densification stage: the crucible coating is continuously heated to the target temperature of 1100-1300℃ at a speed of 3-5℃ / min, and the second heat preservation is performed for 120±30 min to promote the glassification of the silica sol to form a continuous network and realize the densification of the coating; slow cooling and shaping stage: the crucible coating is cooled to 600℃ at a speed of 1-2℃ / min, and then naturally cooled to room temperature.

[0047] The following will provide specific examples combined with specific data to further explain the technical solutions of the above-mentioned application: Example 1: The present embodiment provides a quartz crucible coating and a preparation method thereof, the quartz crucible coating is prepared by the preparation method, specifically, a double-layer coating is sprayed and silicon ingot casting is performed, and the preparation method comprises the following steps: S1: slurry preparation S11: Substrate layer slurry preparation High purity silicon powder (D 50 = 3 μm)300 g, added into 500 mL of mixed solvent of deionized water: ethanol = 7:3 (volume ratio), 1 g of polyvinyl alcohol (0.2 wt%) (PVA) was added as a dispersant, and the powder was fully and uniformly dispersed by ball milling for 5 h. Then, a nano-silica sol with a dry basis SiO2 content of 30 wt% (equivalent volume fraction of about 40 vol%) was added, stirred for 1 h, and the solid content was adjusted to 45 wt% and the viscosity was 280 mPa·s to obtain the substrate layer slurry.

[0048] S12: Functional layer slurry preparation Silicon powder 300 g and ultra-fine CaF2 powder 10 g (D 90 ≤ 0.3 μm)were mixed, and the same ratio of water-ethanol mixed solvent was added, and ball milling was performed for 6 h to ensure homogeneity. Then, a nano-silica sol with a dry basis SiO2 content of 25 wt% was added, stirred for 1 h, and the solid content was 50 wt% and the viscosity was 320 mPa·s to obtain the functional layer slurry.

[0049] S2: Coating and drying First, the substrate layer slurry was sprayed on the inner surface of the quartz crucible to form a substrate layer wet film with a thickness of about 100 μm, and dried at 60 °C under hot air conditions for 40 min; Then, the functional layer slurry was sprayed on the surface of the substrate layer wet film to form a functional layer wet film with a thickness of about 160 μm, and dried under the same conditions.

[0050] S3: High temperature sintering The above double-layer coated crucible after drying was placed in an Ar inert atmosphere and sintered according to the following procedure: Low temperature impurity removal stage: 2 °C / min to 500 °C, 1 h; High temperature densification stage: 4 °C / min to 1300 °C, 2 h; Slow cooling and shaping stage: 1.5 °C / min to 600 °C, natural cooling to room temperature.

[0051] Silicon ingot casting: The coated crucible was placed in a casting furnace, a 99.999% argon protective atmosphere was introduced, and high-purity polycrystalline silicon material was added. After heating, melting, crystallization, and annealing steps, the ingot was completed, and after cooling, demolding and detection were performed.

[0052] Performance test As Figure 1 , Figure 3 shown, Figure 1The double-layer composite coating structure prepared by the embodiment 1 of the present application is shown, and the interface fusion state of the base layer (silicon powder-silica sol) and the functional layer (silicon powder-fluoride calcium) is clearly presented. The silicon powder particles (D50=3 μm) are uniformly dispersed in the vitrified SiO2 network to form a dense skeleton. The thickness of the functional layer is about 160 μm, and the fluoride calcium particles (D90≤0.3 μm) are enriched on the surface to form a continuous wet film. The thickness of the base layer is about 100 μm, The total thickness of the coating is 260 μm, and the porosity is 10 vol%, which verifies the structural integrity and thermal expansion matching; Coating structure observation: no cracking, peeling or falling off on the surface; Demolding condition: the silicon ingot can be demolded integrally, and there is no obvious adhesion residue on the surface; Infrared flaw detection (IR) detection: the silicon ingot image is bright, and there is no obvious impurity particle, such as Figure 3 As shown, the infrared transmission image of the silicon ingot coated by the coating of the present application shows that the whole is bright and uniform, and there is no dark spot or impurity particle, which further proves that the double-layer structure of the present application effectively blocks the diffusion of impurities such as Fe, Na and Al, avoids nitride / carbide pollution, and meets the cleanliness requirements of semiconductor-grade silicon ingot.

[0053] Embodiment 2 The embodiment provides a quartz crucible coating and a preparation method thereof. The quartz crucible coating is prepared by the preparation method. The preparation method is basically the same as that in embodiment 1. The main difference from embodiment 1 is that the coating method is brushing, the ratio of the base layer to the functional layer is slightly different, and the other processes are basically the same. Specifically, the double-layer coating is brushed and silicon ingot casting is performed. The preparation method comprises the following steps: S1: slurry preparation S11: the ratio of the base layer slurry is: silicon powder (55 vol%) + silica sol (45 vol%, dry basis), and other conditions are the same as those in embodiment 1.

[0054] S12: the ratio of the functional layer slurry is: silicon powder (70 vol%) + silica sol (20 vol%, dry basis) + CaF2 (10 vol%), and the stability of the slurry is good after stirring. Other conditions are the same as those in embodiment 1.

[0055] S2: coating and drying The wet film of the base layer is brushed to 90 μm, and naturally dried for 45 min; The wet film of the functional layer is brushed to 150 μm, and naturally dried for 45 min.

[0056] S3: high-temperature sintering The sintering conditions are the same as those in embodiment 1.

[0057] Silicon ingot casting and detection The procedure is the same as in Example 1.

[0058] Performance test Total coating thickness 240 μm, porosity 9.0 vol%; Coating structure: no cracking or delamination; Demoulding effect: the silicon ingot was demoulded completely without sticking phenomenon; Infrared impurity detection: the image of the silicon ingot was transparent without obvious impurity particles.

[0059] Example 3: The present example provides a quartz crucible coating and a preparation method thereof, the quartz crucible coating is prepared by the preparation method, the preparation method is substantially the same as that in Example 1, the main difference from Example 1 is that the coating method is dip coating, and the slurry ratio is adjusted, specifically, the coating is prepared by the dip coating method and the ingot is cast, and the preparation method comprises the following steps: S1: slurry preparation S11: silicon powder (50 vol%) + silica sol (50 vol%, dry basis), solvent containing PMAA dispersant; other conditions are the same as in Example 1; S12: silicon powder (60 vol%) + CaF2(15 vol%) + silica sol (30 vol%, dry basis); other conditions are the same as in Example 1.

[0060] S2: coating and drying The crucible is immersed in the base layer slurry for 30 s, the wet film is 110 μm, and then dried; Then immerse in the functional layer slurry for 30 s, the wet film is 170 μm, and then dry.

[0061] S3: high-temperature sintering The high-temperature sintering conditions are the same as in Example 1.

[0062] Performance test: total coating thickness 260 μm, porosity 10.5 vol%; The coating is dense without peeling; the silicon ingot is demoulded smoothly with a smooth surface; the infrared image of the silicon ingot is transparent without obvious impurity particles.

[0063] Comparative Example 1: The present comparative example provides a quartz crucible coating and a preparation method thereof, the quartz crucible coating is prepared by the preparation method, specifically, a conventional Si3N4 single layer coating is prepared, which is different from Example 1: the S3N4 single layer coating is used in Comparative Example 1, without the base layer-functional layer double layer structure, and without the polycrystalline silicon powder and calcium fluoride functional design, comprising the following steps: S1: slurry preparation Si3N4 powder (D 50≈ 2 μm)75 vol%, PVA aqueous solution was added as binder, and ball milling was performed for 4 h.

[0064] S2: Coating and drying The slurry was sprayed on the inner wall of the crucible to form a single layer coating (wet film thickness of about 200 μm), and dried.

[0065] S3: High-temperature sintering Sintering was performed at 1250 °C for 2 h under an argon atmosphere.

[0066] Silicon ingot casting: the method was the same as that in Example 1.

[0067] Performance Results: As shown in Figure 2 , Figure 4 , Figure 2 is a coating cross-sectional morphology diagram of Comparative Example 1, and the coating surface can be seen. The local residual silicon nitride particles of Comparative Example 1 (indicated by arrows in the figure) are easily decomposed into Si-N active impurities at high temperatures, enter the whole molten silicon coating uniformly, but the local residual silicon nitride in the inner wall of the crucible exists obvious impurity particles in infrared detection, and dark impurity particles (marked by red circles) can be seen in many places, showing that there is a risk of nitrogen source pollution, which seriously affects the purity of the silicon ingot and the subsequent device yield.

[0068] Comparative Example 2: Single-layer Si-SiO2-CaF2 coating without a base layer The present comparative example provides a quartz crucible coating and a preparation method thereof, and the quartz crucible coating is prepared by the preparation method, specifically, a single-layer Si-SiO2-CaF2 coating without a base layer is prepared, which is different from Example 1: a single-layer Si-SiO2-CaF2 coating is directly prepared without a base layer structure support, and the method comprises the following steps: S1: Preparation of slurry Silicon powder 65 vol% (D 50 = 3 μm), CaF2 powder 10 vol% (D 90 ≤ 0.5 μm), and dry silica sol 25 vol%, using a water-ethanol mixed solvent, stirring and ball milling.

[0069] S2: Coating and drying The slurry was sprayed on the inner wall of the crucible in one step, and the wet film thickness was 250 μm, and then dried.

[0070] S3: High-temperature sintering Sintering was performed at 1300 °C for 2 h.

[0071] Silicon ingot casting: the method was the same as that in Example 1.

[0072] Performance: Results: The coating was locally drummed, cracked, and had poor surface continuity. During the demolding process, the silicon ingot was locally stuck to the pot and had cracks. Impurity particles were visible in the infrared detection, indicating that the lack of a base layer led to insufficient adhesion and unstable structure.

[0073] As can be seen from the comparison of Examples 1-3 and Comparative Examples 1 and 2, the double-layer composite structure design of "silicon powder-silica sol base layer + silicon powder-fluoride calcium functional layer" used in the examples of the present application not only avoids the problem of nitrogen source pollution compared with the traditional Si3N4 single-layer coating used in Comparative Example 1, but also has stronger adhesion, no cracking or peeling after sintering, and significantly improved overall demolding performance. The infrared detection image of the silicon ingot obtained finally is transparent and free of impurity particles. Compared with the single-layer Si-SiO2-CaF2 coating without a base layer in Comparative Example 2, the present application effectively improves the adhesion and structural stability of the coating and the substrate by constructing a "homogeneous framework layer" in the base layer that matches the thermal expansion coefficient of the crucible material. The problems of coating drumming, cracking, difficult demolding, and silicon ingot damage in Comparative Example 2 are avoided. The technical principle lies in that the polycrystalline silicon powder in the base layer provides thermal matching with the molten silicon material, and the nanosilica sol is glassified to form a continuous SiO2 network during the sintering process, enhancing the density and adhesion of the coating. The calcium fluoride powder in the functional layer migrates to the surface to form a CaF2 wetting barrier film at high temperature, significantly reducing the interfacial adhesion between the coating and the molten silicon and improving the demolding performance. The synergistic effect of the two-layer structure not only ensures the mechanical strength and thermal shock resistance, but also takes into account smooth demolding and particle control, solving the core technical problems of nitride or carbide particle pollution, insufficient adhesion and easy peeling, difficult demolding, and poor thermal stability in traditional coating systems, achieving a significant extension of the service life of the crucible and an improvement in the purity and yield of the silicon ingot, and meeting the urgent needs of advanced semiconductor manufacturing for high cleanliness, reliability, and low-pollution ingot casting processes.

[0074] Secondly, through the comparison of Examples 1-3 and Comparative Examples 1 and 2, it is further illustrated that the double-layer structure of the present application is dense and uniform, completely avoiding the problem of particle residue in traditional coatings Figures 1-4 , Figure 1 , Figure 2 ), and the silicon ingot of the present application is free of impurity pollution, while nitride coatings can cause significant defects, further fully demonstrating the breakthrough progress of the present application in purity control, structural stability, and demolding performance.

[0075] In the description of the application, the description of the terms "one embodiment", "some embodiments", "in this embodiment", "specific example", or "some examples" and the like means that the specific features, mechanisms, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the description, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0076] The above description is merely a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A coating for a quartz crucible, characterized by, The quartz crucible coating comprises a double-layer composite structure composed of a base layer and a functional layer. The base layer comprises polycrystalline silicon powder and nano-silicon sol, wherein the volume percentage of the polycrystalline silicon powder is 40-65 vol%, and the volume percentage of the nano-silicon sol (calculated based on dry SiO2) is 35-60 vol%. The functional layer is coated on the surface of the base layer, and the functional layer comprises polycrystalline silicon powder, nano-silicon sol and calcium fluoride powder, wherein the volume percentage of the polycrystalline silicon powder is 50-70 vol%, the volume percentage of the nano-silicon sol (calculated based on dry SiO2) is 20-35 vol%, and the volume percentage of the calcium fluoride powder is 5-15 vol%.

2. The quartz crucible coating according to claim 1, wherein In the substrate layer, the particle size D of the polycrystalline silicon powder 50 The particle size D of the calcium fluoride powder in the functional layer is 1–5 μm. 90 <0.5μm.

3. The quartz crucible coating according to claim 1, wherein The thickness of the quartz crucible coating is 180-300 μm, and the porosity is 8-15 vol%.

4. A method of producing the coating of a quartz crucible according to any one of claims 1 to 3, characterized in that The method comprises the following steps: S1: Preparation of slurry: S11: Preparation of base layer slurry: polycrystalline silicon powder is added to a water-ethanol mixed solvent, a dispersant is added for ball milling treatment, then nano-silicon sol is further added for stirring and dispersing treatment, and the solid content of the slurry is adjusted to 40-50 wt% to obtain the base layer slurry; S12: Preparation of functional layer slurry: polycrystalline silicon powder and calcium fluoride powder are mixed, added to a water-ethanol mixed solvent and subjected to ball milling treatment, then nano-silicon sol is added for stirring and dispersing treatment, and the solid content of the slurry is adjusted to 45-55 wt% to obtain the functional layer slurry; S2: Coating and drying: The base layer slurry is coated on the inner wall of the crucible to form a base layer wet film, and drying treatment is performed; Then, the functional layer slurry is further coated on the surface of the base layer wet film to form a functional layer wet film, and drying treatment is performed again; S3: High-temperature sintering: The crucible coating obtained by the step S2 is placed in an inert atmosphere, and the following three-step temperature control program is performed: Low-temperature impurity removal stage: the crucible coating is heated to 500±10℃ for the first time, and the first heat preservation is performed; High-temperature densification stage: the crucible coating is heated to 1200±100℃ for the second time, and the second heat preservation is performed; Slow cooling and shaping stage: the crucible coating is controlled to cool to 600℃, and then naturally cooled to room temperature, and the sintering is completed.

5. The method of claim 4, wherein the coating is applied by a method selected from the group consisting of: plasma spraying, physical vapor deposition, chemical vapor deposition, and sol-gel coating. In the step S11, the dispersant is polyvinyl alcohol or polyammonium methacrylate, and the addition amount of the dispersant is 0.1-0.3 wt% of the total mass of the base layer slurry.

6. The method of claim 4, wherein the coating is applied by a method selected from the group consisting of: plasma spraying, physical vapor deposition, chemical vapor deposition, and sol-gel coating. In the steps S11 and S12, the water-ethanol mixed solvent is prepared by deionized water and anhydrous ethanol in a volume ratio of 7:3, and the stirring and dispersing treatment time is 1 hour, and the ball milling treatment time is 4-6 hours.

7. The method of claim 4, wherein the coating is applied by a method selected from the group consisting of: plasma spraying, physical vapor deposition, chemical vapor deposition, and sol-gel coating. In the step S11, the viscosity of the base layer slurry is 150-350 mPa·s, and in the step S12, the viscosity of the functional layer slurry is 200-400 mPa·s.

8. The method of claim 4, wherein the coating is applied by a method selected from the group consisting of: plasma spraying, physical vapor deposition, chemical vapor deposition, and sol-gel coating. In the step S2, the thickness of the base layer wet film is 80-120 μm, and the thickness of the functional layer wet film is 100-180 μm.

9. The method of claim 4, wherein the coating is applied by a method selected from the group consisting of: plasma spraying, physical vapor deposition, chemical vapor deposition, and sol-gel coating. In the step S2, the coating method is one of spraying, brushing or dipping.

10. The method of claim 4, wherein the coating is applied by a method selected from the group consisting of: plasma spraying, physical vapor deposition, chemical vapor deposition, and sol-gel coating. In the step S3, the conditions of the three-step temperature control program include: Low-temperature impurity removal stage: the crucible coating is heated to 500±10°C at a rate of 2-4°C / min, and the first holding is performed for 60±5 min; High-temperature densification stage: the crucible coating is continuously heated to the target temperature of 1100-1300°C at a rate of 3-5°C / min, and the second holding is performed for 120±30 min, so as to promote the glassification of the silica sol to form a continuous network and realize the densification of the coating; Slow cooling and shaping stage: the crucible coating is cooled to 600°C at a rate of 1-2°C / min, and then naturally cooled to room temperature.

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