A by-product mixture produced in a process for producing polycrystalline
silicon is made to react with chlorine to form tetrachlorosilane (STC)
distillate in a chlorination reaction vessel, and the tetrachlorosilane
(STC) distillate is made to react with hydrogen in a hydrogenation
reaction vessel to be converted into trichlorosilane (TCS). In the
chlorination step, methyl chlorosilanes having boiling points close to
TCS are hyper-chlorinated to be converted into hyper-chlorinated methyl
chlorosilanes having higher boiling points, which facilitates the
hyper-chlorinated methyl chlorosilanes to be separated into high
concentration, and inhibits carbon from contaminating the polycrystalline
silicon. A donor/acceptor eliminator is provided in the circulation cycle
for producing TCS, and accordingly there is no need to take out a
by-product produced in the process for producing TCS to the outside of
the system, which can highly purify the TCS.