Radioactivation Analysis of Phosphorus in Iodine

Abstract

AN important method in the preparation of pure silicon for semiconductor devices is the silicon iodide process¹. In this method silicon tetraiodide is formed from the elements and purified by fractional distillation before being decomposed by passage over a heated tantalum filament. We have found by radio-activation analysis² that the predominating N-type impurity in silicon produced by this method in our laboratory is phosphorus, and that its concentration seems to be largely independent of the phosphorus content of the ‘crude’ silicon. This could be explained if there was an appreciable phosphorus-level in the iodine used, as the mass ratio of silicon to iodine in the above reaction is about one to twenty. Therefore we developed the following method for estimating the phosphorus content of iodine.