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We report the fabrication of very smooth NdBCO thin films deposited by d.c. magnetron sputtering using Nd rich target (EDX composition Nd/sub 1.12/Ba/sub 1.88/Cu/sub 3/O/sub 7-/spl delta//). Films characterized by critical temperature (R=0) higher than 90 K and maximum roughness lower than 2-3 nm on large areas are routinely obtained on SrTiO/sub 3/ non-vicinal substrates. STM studies performed in situ in UHV environment, show a 2D nucleation mechanism of the growth preserved up to a thickness higher than 100 nm. This is in contrast to the common observation of screw dislocations starting from 10-12 nm in c-axis ReBCO thin films, that gives rise to an increase of the roughness with thickness. We compare the growth modes, the superconducting, and the structural properties of our NdBCO thin films deposited by d.c. magnetron sputtering from stoichiometric and Nd-rich targets, on different kind of substrates. The experimental results are discussed in the framework of the role of Nd/Ba substitution in the properties of Nd/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 7-/spl delta// thin films.