In the above steps, there are two pollution problems that need to be solved: the capture of by-product CO₂ in the preparation of industrial silicon, and the recycling of the tail gas in the purification of SiHCl₃ from the gas mixture.

High purity polysilicon is obtained from the reduction of SiHCl₃. The reactions are as follows.

1. Main reaction: SiHCl₃ + H₂ = Si + 3HCl^↑,

2. Secondary reaction: 4SiHCl₃ = Si + 3SiCl₄ + 2H₂^↑.

Si obtained from reactions (1) and (2) is deposited to form high purity polysilicon. In this process, about 25 percent of trichlorosilane is converted into polysilicon, and the remainder into tail gas. A large amount of tail gas containing many useful materials such as H₂, HCl, SiHCl₃, and SiCl₄ is emitted from the reduction furnace. Moreover, the tail gas includes many erosive and toxic substances. The tail gas must be recycled, or else it will cause serious pollution and also increase costs.

Silicon tetrachloride (SiCl₄) is the main component in the tail gas. It is a highly corrosive and toxic liquid. About 8,000 tons of by-product SiCl₄ are produced in the production of 1,000 tons of polysilicon. Due to the expensive treatment cost of SiCl₄, most Chinese companies do not have such treatment equipments, which then makes tail gas treatment become the bottleneck in the manufacture of polysilicon.