Sputter removal of thin overlayers of Cu on Si was studied using 10 keV O+2primary ions at near‐normal incidence. The decay length &lgr;, which characterizes the exponential fall‐off of the Cu signal, was found to depend upon the carrier type, the dopant concentration, the polarity and strength of the electric field above the (ntype) samples, and the intensity of light directed at the (ptype) samples, the &lgr; values varying between 0.4 and 2.2 &mgr;m. A similar dependence on sample and bombardment parameters was observed for the ion‐induced electron emission coefficient &ggr; which ranged from 0.05 to 3 electrons/O+2ion. The results suggest that the internal electrical field strength established in the ion‐bombarded sample is largely determined by the effective rate of electron emission. The field strength across the oxide controls the transport of positively charged Cu impurities through this region and thus also determines the Cu removal rate.