Abstract
The detrimental impact of iron on the nucleation and precipitation of interstitial oxygen 
has recently been reported from this laboratory and interpreted in terms of the different thermodynamical behavior of iron silicides 
and iron silicate 
. By varying the nucleation time of oxygen precipitation and adjusting different initial iron concentrations
in CZ silicon wafers we have found a threshold concentration of iron (about 
) above which the precipitation was impeded. Estimates, based on migrating interstitial oxygen 
and iron 
gave a threshold level of iron in the range of 
to 
. Scanning electron microscope (SEM) pictures provided compelling evidences that iron is retarding oxygen precipitation.