FEASIBILITY STUDIES ON A DISTILLATION CASCADE FOR PRODUCTION OF ULTRA-HIGH PURITY TRICHLOROSILANE

Abstract

Elemental silicon is the backbone of the electronics and the solar photovoltaics industry in the present times. This work examines the purification of a silicon precursor such that the total impurity content in it is limited to a few parts per million. Trichlorosilane (TCS) is one of the most important precursors in the production of electronics grade elemental silicon. This is because of the relative ease with which crude trichlorosilane, containing phosphorus, boron and heavy metal chlorides as impurities can be purified by a distillation cascade. The system appears to have ideal vapour-liquid equilibrium behaviour with constant relative volatilities over the temperature and pressure ranges of interest in this kind of separation. The performance of a distillation column cascade for this separation in the dynamic state has been studied in this work through simulation codes developed in-house. Both total reflux and continuous feed and product withdrawal modes of operation have been studied. These studies theoretically establish the conditions that are expected to yield ultra pure TCS. The most economical sequence of columns in the cascade has also been tentatively determined through simplified mathematical criteria.