How is polysilicon melted?

Polysilicon is a very important material with a wide range of applications in optoelectronics, semiconductors, solar energy, and other fields. The polysilicon melting process plays a crucial role in its quality and performance. The following describes the polysilicon melting process.

The main raw material for polysilicon is silicon dioxide (SiO2). First, silicon dioxide undergoes a reduction reaction to convert it into crude silicon. Typically, silicon dioxide and carbon powder are reduced in a high-temperature furnace to remove oxides from the silicon dioxide, resulting in crude silicon. Further refining then produces high-purity polycrystalline silicon.

Polycrystalline silicon is typically melted using either arc melting or vapor phase melting. Arc melting involves melting the crude silicon in an electric arc furnace, a device that uses electricity to heat highly conductive materials to high temperatures, causing them to melt. During the arc melting process, the crude silicon is melted by heating, then gradually cooled and solidified into polycrystalline silicon crystals. During the crystallization process, impurities in the crystals can be minimized through stirring and crystal pulling, resulting in high-purity polycrystalline silicon.

Vapor phase melting of polycrystalline silicon involves reacting a silicon-containing gas (usually silicon chloride SiCl₄) with hydrogen at high temperatures to form silicon. By controlling the temperature and gas flow, the silicon chunks are gradually deposited on a substrate, ultimately forming a single polycrystalline silicon crystal.

Another method is to smelt polysilicon using a solution process. This involves placing crude silicon in a sodium hydroxide solution, causing a chemical reaction at high temperature to produce polysilicon.

During the polysilicon smelting process, careful control of the reaction temperature, atmosphere, reaction time, reaction speed, and corresponding process parameters is crucial to ensure that the resulting polysilicon meets all requirements and technical specifications. Furthermore, maintenance and upkeep of production equipment are essential to ensure process stability and consistent process parameters.

Overall, the polysilicon smelting process is a complex system involving integrated energy, material, and process control. The comprehensive optimization of equipment and technology is essential to producing high-quality, high-purity polysilicon products.