Graphite seed crystal holder and method for surface treatment thereof

Abstract

A graphite seed crystal holder and its surface treatment method are disclosed. The seed crystal holder has a conical structure with a taper of 10° to 15°, and is made of isostatically pressed graphite. A receiving groove is provided in the central area of ​​the upper surface of the seed crystal holder. A heat-insulating pad is installed in the receiving groove. The conical structure of the seed crystal holder, the receiving groove, and the heat-insulating pad are used together to control the radial temperature gradient at the solid-liquid growth interface. The method involves: polishing the sidewalls of the seed crystal holder; ultrasonically cleaning for a set time and drying; preparing a precursor solution by mixing resin and ethanol at a volume ratio of 1:1; uniformly coating the precursor solution onto the sidewall surface; heating to solidify the coating layer into a hard resin layer; sealing and curing the edges of the graphite paper; inserting the heat-insulating pad into the receiving groove; bonding the graphite paper and SiC seed crystal to the seed crystal holder using high-temperature adhesive; and completing the final in-situ carbonization during the crystal growth heating process to form a dense and smooth carbon layer. This invention avoids the problem of crystal cracking.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a graphite seed crystal holder and its surface treatment method. Background Technology

[0002] Solution growth is a crystal growth technique conducted under near-thermodynamic equilibrium conditions. Its temperature gradient is much lower than that of physical vapor transport (PVT), effectively reducing thermal stress during crystal growth and thus significantly decreasing crystal defects, providing a technological possibility for preparing higher-quality SiC crystals. However, solution growth of SiC crystals still faces core technical challenges that urgently need to be addressed: solution adhesion easily occurs at the bonding site between the seed crystal and the graphite seed holder (mainly concentrated on the crystal side, such as...). Figure 1 As shown in the diagram, when the crystal is placed in the air during the cooling stage of crystal growth or after growth is completed, the adhering solution releases stress, causing the crystal to crack and making it unsuitable for subsequent processing, resulting in serious product defects. Therefore, effectively suppressing or even eliminating solution adhesion on the crystal side is a key bottleneck in the solution-grown high-quality, intact, crack-free SiC crystals.

[0003] In traditional solution-based SiC crystal growth, the seed crystal is typically directly bonded to the surface of a graphite seed support without any special treatment. During crystal growth, due to the solution climbing effect, a large amount of solution accumulates on the sides of the graphite seed support and at the interface between the seed crystal and the support. After crystal growth, the difference in cooling rate and thermal expansion coefficient between the accumulated solution, the graphite seed support, and the grown crystal easily leads to crystal cracking. Furthermore, after the accumulated solution solidifies, it undergoes oxidation and deliquescence reactions in normal air, releasing stress and further causing crystal cracking. To address the shortcomings of existing technologies, it is urgent to innovate the seed crystal-graphite support structure to effectively control the radial temperature gradient at the solid-liquid growth interface and reduce internal crystal stress. Simultaneously, a surface treatment method that can effectively suppress and eliminate solution adhesion to the crystal sides is needed. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a graphite seed crystal holder and its surface treatment method. This seed crystal holder has a simple structure and low manufacturing cost. It can effectively control the radial temperature gradient at the solid-liquid growth interface, reduce internal stress in the crystal, and avoid crystal cracking. This method can effectively suppress or even eliminate solution adhesion and impurity crystal nucleation on the crystal side, solving the crystal cracking problem caused by the release of external stress from the solidified solution during SiC crystal growth using solution methods.

[0005] To achieve the above objectives, the present invention provides a graphite seed crystal holder, characterized in that it comprises: The seed crystal holder body has a conical structure with a taper of 10° to 15° and is made of isostatic graphite; a receiving groove is provided in the central area of ​​the upper surface of the seed crystal holder body. The edge sealing coating is applied to the sidewall of the seed crystal holder body. The edge sealing coating is one of high-purity TaC coating, SiC coating, BN coating, and dense carbon layer. An insulating pad, wherein the insulating pad is adapted to be installed in a receiving groove, and the material is graphite soft felt and / or graphite hard felt. The conical structure, receiving groove, edge sealing coating, and heat insulation pad of the seed crystal holder body are used together to regulate the radial temperature gradient at the solid-liquid growth interface.

[0006] In this invention, by using a conical structure with a taper of 10° to 15° on the seed crystal holder body, combined with an insulating pad (graphite soft felt and / or graphite hard felt) within the recess, the radial temperature distribution of the seed crystal holder can be actively adjusted, gradually reducing the radial temperature gradient. This results in larger SiC crystals with lower internal stress. An edge-sealing coating is applied to the sidewalls of the seed crystal holder body. This edge-sealing coating is one of high-purity TaC, SiC, BN, or dense carbon layers, which effectively suppresses and eliminates solution adhesion and impurity crystal nucleation on the crystal side, solving the crystal cracking problem caused by the release of external stress from the solidified solution. Compared to conventional graphite seed crystal holders, the seed crystal holder in this invention can effectively control the radial temperature gradient at the solid-liquid growth interface, reducing internal stress within the crystal during growth.

[0007] This seed crystal holder has a simple structure and low manufacturing cost. It can effectively control the radial temperature gradient at the solid-liquid growth interface, reduce internal stress in the crystal, and avoid crystal cracking.

[0008] Furthermore, in order to effectively control the radial temperature gradient at the solid-liquid growth interface, the thermal expansion coefficient of the seed crystal holder body is consistent with that of silicon carbide.

[0009] Furthermore, in order to ensure the thermal field optimization effect of the insulation pad, the insulation pad is a combination of graphite soft felt and graphite hard felt, with the graphite soft felt close to the side of the seed crystal and the graphite hard felt close to the bottom of the receiving groove.

[0010] The present invention also provides a surface treatment method for graphite seed crystal holders, comprising the following steps: S1: Polish the sidewalls of the seed crystal holder body to achieve a surface roughness of micron level; S2: Place the polished seed crystal holder body in anhydrous ethanol for ultrasonic cleaning for a set time, and then dry it; S3: Mix the resin and ethanol at a volume ratio of 1:1 and stir until homogeneous to obtain a precursor solution; S4: The precursor solution is uniformly coated on the sidewall surface, with a coating thickness of 10-30 μm; S5: Place the coated seed crystal holder in an oven and heat it at 80-200℃ for 1 hour to cure the coating and form a hard resin layer. S6: The edges of the graphite paper used to bond the SiC seed crystals are sealed. The sealing process involves coating the graphite paper edges with the precursor solution or graphite adhesive obtained in S3 and curing it in the manner described in S5. S7: An insulating pad is inserted into the receiving groove of the seed crystal holder body. The graphite paper with edge sealing treatment and the SiC seed crystal are bonded to the seed crystal holder body with high temperature adhesive to form a graphite seed crystal holder. The final in-situ carbonization is completed by the crystal growth heating process to form a dense and smooth carbon layer.

[0011] Furthermore, to ensure the carbonization effect, the crystal growth heating process in S7 is as follows: the graphite seed crystal holder is placed in the silicon carbide crystal growth furnace and heated from room temperature to 1000°C under vacuum or inert atmosphere, so that the resin layer is carbonized in situ during the heating process.

[0012] Furthermore, to ensure the polishing effect, in S1, 2000# sandpaper is used to polish the sidewalls of the seed crystal holder body.

[0013] Furthermore, to ensure the cleaning effect, the time is set to 20 minutes in S2.

[0014] This invention provides a surface treatment method for graphite seed crystal holders that effectively inhibits and eliminates solution adhesion to the crystal sidewalls. First, high-precision grinding eliminates macroscopic irregularities and defects on the original graphite surface, providing a smooth and uniform substrate for subsequent coating, ensuring strong adhesion and eliminating the risk of bubbles or peeling. The micron-level smooth surface itself has low surface energy, which can initially inhibit solution wetting and climbing on the sidewalls. Second, ultrasonic cleaning thoroughly removes fine graphite dust, grease, and other contaminants generated during grinding, preventing impurities from affecting the coating curing quality and subsequent carbonization purity. Simultaneously, ultrasonic cleaning penetrates deep into micropores, ensuring a high level of cleanliness on the sidewall surface, which is beneficial for the uniform spreading of the resin solution. Next, using resin as the carbon source and ethanol as both solvent and diluent, a 1:1 ratio can be used to adjust the solution viscosity to a suitable level, facilitating coating and ensuring good fluidity, allowing penetration into microscopic depressions. Furthermore, the evaporation of ethanol leaves a uniform resin film, preventing the coating from being too thin due to excessive solvent or uneven due to insufficient solvent. Furthermore, controlling the coating thickness to 10–30 μm ensures a continuous and dense carbon layer after carbonization without being too thick, which could lead to cracking or peeling. The resulting uniform coating ensures consistent protective performance across the entire sidewall, preventing weak points from becoming channels for solution penetration. Additionally, heat curing allows for resin cross-linking, forming a hard, mechanically resistant resin layer that provides a stable precursor morphology for subsequent in-situ carbonization. The curing temperature can be adjusted within the range of 80–200°C to accommodate different resin systems while preventing premature carbonization due to excessively high temperatures. Then, edge sealing seals the capillary pores between the graphite paper layers, preventing the solution (such as melt or gaseous precursor) from seeping into the graphite paper edges during crystal growth, thus avoiding crystal cracking caused by solution entering the interior of the graphite paper. Using the same precursor solution or specialized graphite adhesive as the sidewall coating ensures material compatibility and a consistent curing process, simplifying the operation. Finally, the in-situ carbonization of the resin is completed using the heating process of the crystal growth furnace itself, eliminating the need for additional carbonization equipment or separate heat treatment steps, significantly simplifying the process and reducing costs. The dense and smooth carbon layer formed by in-situ carbonization is tightly bonded to the graphite matrix, with no interface defects, effectively preventing solution climbing and inhibiting heterogeneous nucleation of impurities on the sidewalls. Vacuum or inert atmosphere protection ensures that no oxide impurities are introduced during the carbonization process, resulting in high carbon layer purity, and the smooth surface further reduces solution wettability. This invention can effectively control the radial temperature gradient at the solid-liquid growth interface by utilizing the conical structure of the seed crystal holder, the receiving groove, the sidewall sealing coating of the seed crystal holder, the graphite paper sealing coating, and the heat insulation pad, keeping it at a low level.

[0015] This method can effectively suppress or even eliminate solution adhesion and impurity crystal nucleation on the crystal side, solving the problem of crystal cracking caused by the release of external stress from the solidification solution during the solution-grown SiC crystal process. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a graphite seed crystal holder in the prior art; Figure 2 This is a schematic diagram of the structure of the seed crystal support body in this invention.

[0017] In the diagram: 1. Seed crystal holder body, 2. Receiving groove, 3. Side wall. Detailed Implementation

[0018] The present invention will be further described below.

[0019] like Figure 2 As shown, the present invention provides a graphite seed crystal holder, characterized in that it comprises: The seed crystal holder body 1 has a conical structure with a taper of 10° to 15° and is made of isostatic graphite. A receiving groove 2 is provided in the central area of ​​the upper surface of the seed crystal holder body 1. The taper refers to the angle between the generatrix of the side of the seed crystal holder body 1 and the bottom surface of the seed crystal holder body 1.

[0020] The edge sealing coating is applied to the sidewall 3 of the seed crystal holder body 1. The edge sealing coating is one of high-purity TaC coating, SiC coating, BN coating, and dense carbon layer. An insulating pad, which is adapted to be installed in the receiving groove 2, is made of graphite soft felt and / or graphite hard felt. The conical structure of the seed crystal holder body 1, the receiving groove 2, the edge sealing coating, and the heat insulation pad are used together to regulate the radial temperature gradient at the solid-liquid growth interface, keeping it at a low level.

[0021] In this invention, by using a conical structure with a taper of 10° to 15° on the seed crystal holder body, combined with an insulating pad (graphite soft felt and / or graphite hard felt) within the recess, the radial temperature distribution of the seed crystal holder can be actively adjusted, gradually reducing the radial temperature gradient. This results in larger SiC crystals with lower internal stress. An edge-sealing coating is applied to the sidewalls of the seed crystal holder body. This edge-sealing coating is one of high-purity TaC, SiC, BN, or dense carbon layers, which effectively suppresses and eliminates solution adhesion and impurity crystal nucleation on the crystal side, solving the crystal cracking problem caused by the release of external stress from the solidified solution. Compared to conventional graphite seed crystal holders, the seed crystal holder in this invention can effectively control the radial temperature gradient at the solid-liquid growth interface, reducing internal stress within the crystal during growth.

[0022] This seed crystal holder has a simple structure and low manufacturing cost. It can effectively control the radial temperature gradient at the solid-liquid growth interface, reduce internal stress in the crystal, and avoid crystal cracking.

[0023] In order to effectively control the radial temperature gradient at the solid-liquid growth interface, the thermal expansion coefficient of the seed crystal support body 1 is consistent with that of silicon carbide.

[0024] To ensure the thermal field optimization effect of the insulation pad, the insulation pad is a combination of graphite soft felt and graphite hard felt, with the graphite soft felt close to the side of the seed crystal and the graphite hard felt close to the bottom of the receiving groove 2.

[0025] The present invention also provides a surface treatment method for graphite seed crystal holders, comprising the following steps: S1: Polish the sidewall 3 of the seed crystal holder body 1 to make its surface roughness reach the micron level (roughness less than 1.6μm). S2: Place the polished seed crystal holder 1 in anhydrous ethanol for ultrasonic cleaning for a set time, and then dry it; S3: Mix the resin and ethanol at a volume ratio of 1:1 and stir until homogeneous to obtain a precursor solution; S4: The precursor solution is uniformly coated on the surface of sidewall 3, with a coating thickness of 10-30 μm; S5: Place the coated seed crystal holder 1 in an oven and heat it at 80-200℃ for 1 hour to cure the coating layer and form a hard resin layer. S6: The edges of the graphite paper used to bond the SiC seed crystals are sealed. The sealing process involves coating the graphite paper edges with the precursor solution or graphite adhesive obtained in S3 and curing it in the manner described in S5. This process is used to inhibit the solution from climbing into the graphite paper during crystal growth, thus preventing the crystals from cracking.

[0026] S7: An insulating pad is inserted into the receiving groove 2 of the seed crystal holder body 1. The edge-sealed graphite paper and SiC seed crystal are bonded to the seed crystal holder body 1 with high-temperature adhesive to form a graphite seed crystal holder. The final in-situ carbonization is completed by the crystal growth heating process, forming a dense and smooth carbon layer. In-situ carbonization requires no additional equipment and ultimately obtains a dense and smooth carbon layer to prevent solution climbing and impurity crystal nucleation.

[0027] To ensure the carbonization effect, the crystal growth heating process in S7 is as follows: the graphite seed crystal holder is placed in the silicon carbide crystal growth furnace and heated from room temperature to 1000°C under vacuum or inert atmosphere, so that the resin layer is carbonized in situ during the heating process.

[0028] To ensure the polishing effect, in S1, 2000# sandpaper is used to polish the side wall 3 of the seed crystal holder body 1.

[0029] To ensure effective cleaning, the time is set to 20 minutes in S2.

[0030] This invention provides a surface treatment method for graphite seed crystal holders that effectively inhibits and eliminates solution adhesion to the crystal sidewalls. First, high-precision grinding eliminates macroscopic irregularities and defects on the original graphite surface, providing a smooth and uniform substrate for subsequent coating, ensuring strong adhesion and eliminating the risk of bubbles or peeling. The micron-level smooth surface itself has low surface energy, which can initially inhibit solution wetting and climbing on the sidewalls. Second, ultrasonic cleaning thoroughly removes fine graphite dust, grease, and other contaminants generated during grinding, preventing impurities from affecting the coating curing quality and subsequent carbonization purity. Simultaneously, ultrasonic cleaning penetrates deep into micropores, ensuring a high level of cleanliness on the sidewall surface, which is beneficial for the uniform spreading of the resin solution. Next, using resin as the carbon source and ethanol as both solvent and diluent, a 1:1 ratio can be used to adjust the solution viscosity to a suitable level, facilitating coating and ensuring good fluidity, allowing penetration into microscopic depressions. Furthermore, the evaporation of ethanol leaves a uniform resin film, preventing the coating from being too thin due to excessive solvent or uneven due to insufficient solvent. Furthermore, controlling the coating thickness to 10–30 μm ensures a continuous and dense carbon layer after carbonization without being too thick, which could lead to cracking or peeling. The resulting uniform coating ensures consistent protective performance across the entire sidewall, preventing weak points from becoming channels for solution penetration. Additionally, heat curing allows for resin cross-linking, forming a hard, mechanically resistant resin layer that provides a stable precursor morphology for subsequent in-situ carbonization. The curing temperature can be adjusted within the range of 80–200°C to accommodate different resin systems while preventing premature carbonization due to excessively high temperatures. Then, edge sealing seals the capillary pores between the graphite paper layers, preventing the solution (such as melt or gaseous precursor) from seeping into the graphite paper edges during crystal growth, thus avoiding crystal cracking caused by solution entering the interior of the graphite paper. Using the same precursor solution or specialized graphite adhesive as the sidewall coating ensures material compatibility and a consistent curing process, simplifying the operation. Finally, the in-situ carbonization of the resin is completed using the heating process of the crystal growth furnace itself, eliminating the need for additional carbonization equipment or separate heat treatment steps, significantly simplifying the process and reducing costs. The dense and smooth carbon layer formed by in-situ carbonization is tightly bonded to the graphite matrix, with no interface defects, effectively preventing solution climbing and inhibiting heterogeneous nucleation of impurities on the sidewalls. Vacuum or inert atmosphere protection ensures that no oxide impurities are introduced during the carbonization process, resulting in high carbon layer purity, and the smooth surface further reduces solution wettability. This invention can effectively control the radial temperature gradient at the solid-liquid growth interface by utilizing the conical structure of the seed crystal holder, the receiving groove, the sidewall sealing coating of the seed crystal holder, the graphite paper sealing coating, and the heat insulation pad, keeping it at a low level.

[0031] This method can effectively suppress or even eliminate solution adhesion and impurity crystal nucleation on the crystal side, solving the problem of crystal cracking caused by the release of external stress from the solidification solution during the solution-grown SiC crystal process.

Claims

1. A graphite seed crystal holder, characterized in that, include: Seed crystal holder body (1), the seed crystal holder body (1) has a conical structure with a taper of 10° to 15°, and its material is isostatic graphite; a receiving groove (2) is provided in the central area of ​​the upper surface of the seed crystal holder body (1). The edge sealing coating is applied to the sidewall (3) of the seed crystal holder body (1). The edge sealing coating is one of high-purity TaC coating, SiC coating, BN coating, and dense carbon layer. The heat insulation pad is adapted to be installed in the receiving groove (2), and its material is graphite soft felt and / or graphite hard felt. The conical structure, the receiving groove (2), the sealing coating and the heat insulation pad of the seed crystal holder body (1) are used together to regulate the radial temperature gradient of the solid-liquid growth interface.

2. The graphite seed crystal holder according to claim 1, characterized in that, The thermal expansion coefficient of the seed crystal holder body (1) is consistent with that of silicon carbide.

3. The graphite seed crystal holder according to claim 1, characterized in that, The insulation pad is a combination of graphite soft felt and graphite hard felt, with the graphite soft felt close to the side of the seed crystal and the graphite hard felt close to the bottom of the receiving groove (2).

4. A surface treatment method for a graphite seed crystal holder, characterized in that, Includes the following steps: S1: Polish the sidewall (3) of the seed crystal holder body (1) to make its surface roughness reach the micron level; S2: Place the polished seed crystal holder body (1) in anhydrous ethanol for ultrasonic cleaning for a set time, and then dry it; S3: Mix the resin and ethanol at a volume ratio of 1:1 and stir until homogeneous to obtain a precursor solution; S4: The precursor solution is uniformly coated on the surface of the sidewall (3) with a coating thickness of 10-30 μm; S5: Place the coated seed crystal holder body (1) in an oven and heat it at a temperature of 80-200℃ for 1 hour to solidify the coating layer and form a hard resin layer. S6: The edges of the graphite paper used to bond the SiC seed crystals are sealed. The sealing process involves coating the graphite paper edges with the precursor solution or graphite adhesive obtained in S3 and curing it in the manner described in S5. S7: Insert a heat-insulating pad into the receiving groove (2) of the seed crystal holder body (1), and bond the graphite paper with edge sealing treatment and the SiC seed crystal to the seed crystal holder body (1) with high temperature adhesive to form a graphite seed crystal holder. The final in-situ carbonization is completed by the crystal growth heating process to form a dense and smooth carbon layer.

5. The surface treatment method for a graphite seed crystal holder according to claim 4, characterized in that, In S7, the crystal growth heating process is as follows: The graphite seed crystal holder is placed in a silicon carbide crystal growth furnace and heated from room temperature to 1000°C under vacuum or inert atmosphere, so that the resin layer is carbonized in situ during the heating process.

6. The surface treatment method for a graphite seed crystal holder according to claim 4, characterized in that, In S1, the sidewall (3) of the seed crystal holder body (1) is polished using 2000# sandpaper.

7. The surface treatment method for a graphite seed crystal holder according to claim 4, characterized in that, In S2, the time is set to 20 minutes.

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