Recent studies have shown that sputter deposited amorphous NixNb1−x (60≤×≤75) alloy films are effective diffusion barriers for operation at temperatures up to 6(X) °C[1]. The thermal stability of the amorphous films has been established on Si and GaAs substrates and may be modified by interactions wilji polycrystalline metal overlayer films. In the current work a detailed microstructural examination by cross-sectional TEM was performed on the annealing behavior of 50 nm polycrystalline Cu films on amorphous Ni60Nb40. Specifically, the development of grooves at the intersection of grain boundaries in the Cu film with both the free surface and the amorphous Ni60Nb40 base was monitored to evaluate the low temperature interfacial diffusion processes. Based upon measurements of the groove dimensions and dihedral angle during vacuum annealing at 450 °C, the surface diffusion coefficient of Cu was determined as 7.4 × 10-20 m2/sec and the surface energy for Cu derived from groove kinetics was in good agreement with other reported determinations. In addition, the grain boundary grooves that were present at the Cu/amorphous Ni60Nb40 interface in the as-deposited condition were observed to be eliminated during annealing. Again, by following the kinetics of groove healing the interfacial diffusivity was determined to be of the order of 10-28m2/sec at 500 °C and the interfacial energy for the amorphous film/Cu surface was estimated to be ≥ 340 mJ/cm2. The benefits of utilizing amorphous Ni-Nb alloys as underlays to retard thermal grooving and electromigration failure in copper arc discussed.