Polysilicon

Polysilicon, or polycrystalline silicon, is elemental silicon that consists of many small crystalline grains. It is distinct from monocrystalline silicon, which has a single crystal lattice, and from amorphous silicon, which lacks a long-range crystalline order. Polysilicon is highly pure and serves as a primary feedstock for semiconductor device fabrication and for photovoltaic solar cells.

Commercial production begins with metallurgical-grade silicon, which is refined to electronic-grade purity. A common route is the Siemens process, in which chlorosilanes are reduced with hydrogen at high temperature to deposit silicon on heated rods, forming polycrystalline ingots. Other methods include purification and deposition techniques such as chemical vapor deposition and fluidized bed reactors. The resulting material is sold in forms such as rods, chunks, or powder and is subsequently melted and cast into ingots or ribbons for wafer production.

Polysilicon wafers are used in two major markets. In the electronics industry, high-purity polysilicon is melted and grown into ingots for silicon wafers used in integrated circuits and other devices. In the solar industry, polysilicon is refined to solar-grade purity and cast into ingots or ribbons that are sliced into wafers for photovoltaic cells. Polysilicon wafers are typically processed into either multi-crystalline or mono-crystalline silicon during subsequent wafer production steps, influencing device performance and manufacturing costs.

Quality and purity levels vary by application, with electronic-grade polysilicon achieving higher purity standards than many solar-grade materials. The term “polysilicon” thus encompasses a range of high-purity silicon feedstocks central to both the microelectronics and renewable energy sectors.