Photoluminescence method for detecting trace levels of iron in ultrapure silicon

A nondestructive technique is presented for the determination of trace leve ls of interstitial iron contamination in ultrapure silicon. This approach i s based on the well-known ability of iron to undergo a reversible pairing r eaction with boron near room temperature. A variety of float-zoned silicon samples with low concentrations of boron (similar to 10(11) cm(-3)) were su bjected to thermal annealing treatments to study changes in the apparent bo ron concentration as determined by the standard method of comparing the pho toluminescence intensity of the boron bound exciton to that of the free exc iton. Changes in the apparent boron concentration were attributed to the fo rmation or dissociation of iron-boron pairs, allowing us to estimate the in terstitial iron concentration in these samples. Remarkably, relatively mild thermal treatments can change the apparent boron concentration in some of these samples by up to a factor of ten. (C) 2001 American Institute of Phys ics.