In this paper we report on the electrochemical deposition of copper onto n-type silicon with a 30 nm TiN barrier film. We show that the mechanism of nucleation and growth is dependent on the applied potential. At potentials more negative than -0.35 V, instantaneous nucleation of hemispherical clusters is followed by diffusion-limited growth. In this potential regime, the nucleus density is essentially constant at about 5 x 10(8) cm(-2). At potentials more positive than -0.35 V, the nucleation and growth kinetics are more complex, and clusters consisting of several nuclei are formed. The cluster density decreases to about 2 x 10(5) cm(-2) at -0.05 V.