DYNAMIC SCALING EXPONENTS OF COPPER ELECTRODEPOSITS FROM SCANNING FORCE MICROSCOPY IMAGING - INFLUENCE OF A THIOUREA ADDITIVE ON THE KINETICS OF ROUGHENING AND BRIGHTENING

Changes in the topography of Cu electrodeposits grown on polycrystalli ne Cu substrates at low constant current density from still aqueous co ncentrated CuSO4 + H2SO4 solutions, at 298 K, were studied by scanning force microscopy (SFM) at different scale lengths (L) from the nanome ter level upward. The dynamic scaling theory applied to SFM images lea ds to exponents alpha = 0.87 +/- 0.06 and beta = 0.63 +/- 0.08, which are consistent with an interface growing under an unstable regime. For similar conditions, the addition of 1,3-diethyl-2-thiourea reduces th e average crystal size ([ds]) of electrodeposits leading to scaling ex ponents alpha = 0.86 +/- 0.06 and beta = 0.24 +/- 0.05 for L < [ds] an d a logarithmic dependence for the spatial and temporal evolution of t he interface for L > 3 mu m and t --> 0. In an additive-free plating b ath, the unstable growth regime appears to be originated by enhanced e lectrodeposition at protrusions due to curvature effects and further s ustained by the electric and concentration fields built up around the growing deposit. The presence of the additive hinders the development of instabilities driving the evolution of the growing interface to tha t predicted by the Edwards-Wilkinson growth model on the asymptotic li mit.