Copper electrodeposition in fine recesses requires the use of several additives to induce a strongly accelerated deposition rate inside recesses. This leads to so-called bottom-up filling for fine recesses, induced by curvature-enhanced accelerator coverage. Here we show that more of the additives are incorporated in the deposit when this mechanism is active by studying the impurity concentrations with time-of-flight scanning ion mass spectroscopy in specially prepared samples with a high density of recesses. The undesired higher copper resistivity for small dimensions, induced by this incorporation, results in a reduction of the expected surface-scattering induced deviation from Matthiessen's rule. (c) 2005 The Electrochemical Society.