How trichlorosilane is made

Chip-grade silicon starts as a volatile liquid made by blowing hydrogen chloride over powdered silicon.

stations: 5
things upstream: 15
raw sources: 8
steps from the ground: 4

The short version

Trichlorosilane is made by passing hydrogen chloride gas over powdered metallurgical silicon at about 300 °C. Yields of 80 to 90 percent are possible. Distillation separates it from other chlorinated silicon by-products, and the purified liquid becomes the starting point for the ultrapure silicon used in chips.

Grind the silicon

Metallurgical grade silicon is milled to a powder. A fine powder reacts faster and more evenly.

Goes in
Metallurgical silicon
Blow in hydrogen chloride

In a heated reactor, hydrogen chloride gas is blown through the powder, turning silicon into trichlorosilane and releasing hydrogen.

about 300 °C

Goes in
Hydrochloric acid
Condense the vapors

The hot mix leaving the reactor is cooled until the chlorosilanes turn to liquid. The hydrogen stays a gas and is drawn off.
Distill away the by-products

Silicon tetrachloride, hexachlorodisilane and dichlorosilane are the main by-products. Distillation separates the trichlorosilane from them.
Store it dry

The colorless, volatile liquid is kept in sealed tanks away from moisture, because water breaks it down.

End of the lineTrichlorosilane Next it goes into polysilicon.

Worth repeating

Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry.
In water it rapidly decomposes to a siloxane polymer and gives off hydrochloric acid.
Silicon refined through purified trichlorosilane can end up with impurity levels below one part per billion.