The lower furnace body of a single crystal silicon growth furnace (SCGF) is a core support component in the single crystal silicon production process. Its interior is subjected to high temperatures and high purity requirements for extended periods. This environment is also exposed to chemicals such as volatiles from the silicon melt and residual reaction gases. Direct contact between these substances and the lower furnace body can easily cause corrosion damage. Anti-corrosion coatings are a key barrier protecting the lower furnace body. The lower furnace body is typically made of metal (such as stainless steel or heat-resistant steel). While possessing a certain degree of high-temperature resistance, they are susceptible to surface oxidation and intergranular corrosion in the presence of corrosive media such as silicon-based compounds such as SiCl₄ and SiH₄, as well as trace amounts of oxygen and water vapor at high temperatures. Anti-corrosion coatings, through their unique structure and material properties, effectively prevent chemical contact with the lower furnace body, ensuring long-term stable operation of the lower furnace body.
The anti-corrosion coating on the lower furnace body of a SGF first forms a dense physical barrier, preventing chemicals from penetrating the substrate surface. During the preparation process, high-quality corrosion-resistant coatings (such as ceramic coatings and specialty alloy coatings) are sprayed and sintered to form a non-porous or low-porosity film structure. This dense structure acts as a "protective shell," completely enveloping the substrate of the lower body of a single-crystal silicon growth furnace. When silicon volatiles and corrosive gases within the furnace diffuse onto the surface of the lower body, the dense coating directly blocks the permeation path of these chemicals, preventing them from contacting the metal substrate. This physically eliminates the conditions for corrosion reactions and reduces the potential for substrate erosion.
The chemical inertness of the coating material is the core advantage of the single-crystal silicon growth furnace's lower body in resisting chemical attack. The materials used for corrosion-resistant coatings (such as alumina ceramic, silicon nitride, and Hastelloy alloy coatings) are inherently chemically stable. Even under the high temperatures of a single-crystal silicon growth furnace, they are not susceptible to chemical reactions with silicon-based compounds or trace acids and bases within the furnace. For example, alumina ceramic coatings are not only high-temperature resistant but also resist attack by silicon volatiles such as SiCl₄, preventing the formation of easily detachable corrosion products due to chemical reactions. Special alloy coatings, on the other hand, form a stable oxide film using their alloying elements (such as chromium, nickel, and molybdenum). This prevents further spread of oxidative corrosion even in the presence of trace amounts of oxygen, ensuring a consistently stable surface condition on the SCSGF furnace body.
The strong bond between the corrosion-resistant coating and the SCSGF furnace body substrate further enhances the corrosion resistance. Before coating application, the SCSGF furnace body substrate undergoes rigorous pretreatment, including sandblasting, degreasing, and pickling. These steps remove impurities and oxide layers from the substrate surface, creating a rough surface texture and increasing the contact area between the coating and the substrate. Subsequent processes such as thermal spraying and vacuum sintering ensure a strong bond between the coating molecules and the substrate, preventing coating shedding caused by thermal expansion and contraction at high temperatures and mechanical vibration. Even during extended operation of a single crystal silicon growth furnace (SCSF), the coating remains firmly adhered to the substrate surface, providing continuous corrosion protection and preventing localized corrosion caused by coating flaking and substrate exposure.
The high-temperature stability of the anti-corrosion coating ensures it will not fail under the high-temperature operating conditions of a SSGF. During single crystal silicon production, temperatures within the furnace often reach temperatures exceeding 1400°C. Conventional coatings are susceptible to softening, decomposition, or structural damage at such high temperatures, losing their corrosion resistance. However, the corrosion-resistant coating on the SSGF's lower body is specially formulated and processed to provide exceptional high-temperature stability. Even under high-temperature conditions, the coating's crystal structure and chemical composition remain stable, maintaining its density and chemical inertness. This means that even under extended high-temperature conditions, the coating maintains its full protective properties, resisting corrosion from chemicals within the furnace and preventing damage to the SSGF's lower body due to high-temperature coating failure.
Anti-corrosion coatings can also reduce the extent of damage to the lower body of a single-crystal silicon growth furnace (SCGF) by inhibiting the spread of localized corrosion reactions. If the anti-corrosion coating on the lower body of a SGF develops minor scratches or localized damage, chemicals within the furnace could potentially enter the substrate through the damaged area, causing localized corrosion. In this situation, some anti-corrosion coatings (such as chromium-containing alloy coatings) can function through a "self-healing" mechanism. The chromium in the coating reacts with trace amounts of oxygen at the damaged area, forming a new oxide film that covers the damaged area and prevents further spread of the corrosion reaction. This property effectively controls the spread of localized corrosion, preventing small damage from developing into widespread corrosion, and extending the service life of the lower body of a SGF.
Based on the practical needs of single-crystal silicon production, the anti-corrosion coating on the lower body of a SGF not only protects against chemical attack but also ensures the purity of the single crystal silicon. If the lower body substrate is corroded, the resulting metal ions and oxidation products could be introduced into the silicon melt, affecting the purity and quality of the single crystal silicon. Anti-corrosion coatings prevent substrate corrosion and reduce impurity generation, ensuring high-purity production of single-crystal silicon. Furthermore, the coating's corrosion resistance reduces maintenance frequency and replacement costs for the lower furnace body of single-crystal silicon growth furnaces, avoiding downtime and maintenance caused by corrosion.this ensures the continuity and stability of the single-crystal silicon production process, providing reliable support for the supply of single-crystal silicon to the photovoltaic and semiconductor industries.
