In this piper we report on the electrochemical deposition of copper on TIN from pyrophosphate solution. We show that deposition occurs through the instantaneous nucleation of hemispherical clusters followed by diffusion-limited growth over a wide potential range. In this potential regime, the nucleus density increases exponentially with applied potential. The nucleus densities obtained from atomic force microscopy images are in the range of 10(8)-10(11) cm(-2),about two orders of magnitude larger than the highest nucleus density observed in fluoroborate solutions. Such high nucleus densities are essential in depositing continuous thin films because coalescence occurs at relatively low coverages. The near-neighbor distances follow Poisson distributions indicating that the nuclei are randomly distributed over the surface. (C) 2000 The Electrochemical Society. S0013-4651(00)04-091-X. All rights reserved.