Which of the following processes is used in order to fabricate polysilicon?
To determine which process is used to fabricate polysilicon, we can explore the methods commonly employed in the industry.
One of the primary processes used in the manufacturing of polysilicon is the Siemens process. This method involves the following steps:
1. Purification of Silicon: Initially, impure metallurgical-grade silicon (MG-Si) is placed in a reactor where it is heated to a high temperature, typically above 1000°C, to remove impurities such as metallic elements and oxygen. This purification step is crucial to obtain high-quality polysilicon.
2. Trichlorosilane (TCS) Production: The purified silicon is then reacted with hydrogen chloride (HCl) gas, forming trichlorosilane (SiHCl3). This reaction typically takes place at a temperature of about 300-350°C.
3. Deposition: The trichlorosilane produced in the previous step is then further heated at a higher temperature, typically around 1100-1200°C, resulting in the decomposition of trichlorosilane into pure silicon and hydrogen gas. The silicon is deposited onto a heated silicon rod known as a "seed" or "chuck," which gradually grows into a large polysilicon crystal.
It is important to note that while the Siemens process is a widely used method, there are other processes for polysilicon fabrication as well. These include the Fluidized Bed Reactor (FBR) process, the Modified Siemens process, and the Upgraded Metallurgical Grade (UMG) process.
To identify which process is used in a particular situation, it is essential to refer to specific manufacturing procedures, industry standards, or manufacturer documentation.