Polycrystalline silicon is a crystalline form composed of silicon, consisting of numerous grain boundaries and grains. Compared to monocrystalline silicon, polycrystalline silicon has an irregular grain structure with multiple grain boundaries, resulting in poorer lattice continuity.
The raw material for polycrystalline silicon is silicon ore, primarily silicon dioxide (SiO2). It can be extracted from silicon ores such as quartz, quartz sand, and wollastonite. During the production process, the silicon ore is crushed and ground into powder, and then transformed into polycrystalline silicon blocks or rods as end products through smelting and crystallization processes.
The following is a typical polysilicon manufacturing process:
1. Raw material preparation: Silicon ore is processed through crushing, grinding and other steps to obtain powdered silicon material.
2. Furnace charge preparation: Silicon material is mixed with a reducing agent (usually metallurgical grade pure hydrogen) to form a furnace charge.
3. Furnace charge smelting: The furnace charge is added to the polycrystalline silicon furnace and smelted under high temperature conditions. In the molten state, the oxides in the silicon charge are reduced to generate pure silicon liquid.
4. Seed crystal growth: A thin seed crystal rod (usually monocrystalline or polycrystalline silicon) is drawn from the molten silicon and immersed in the furnace. By slowly increasing the temperature of the crystal rod and moving the crystal rod, the molten silicon is encouraged to crystallize on the crystal rod.
5. Polycrystalline silicon rod growth: The molten silicon on the surface of the rod gradually cools and solidifies to form a polycrystalline silicon rod. At this time, silicon atoms are arranged at multiple grain boundaries to form a polycrystalline structure.
6. Bar cutting: The polycrystalline silicon bar is cut into the required size and shape by means of machinery or cutting process to obtain the required polycrystalline silicon block.
7. Polycrystalline silicon block reprocessing: Polycrystalline silicon blocks can be further processed, such as grinding, polishing and etching, to obtain polycrystalline silicon wafers or other polycrystalline silicon products that meet the requirements.
8. It should be noted that the above is a typical polysilicon production process. In actual production, it may vary depending on the specific process equipment and product requirements.
