Roughness evolution of Nb films with thickness

The morphology of Nb films with thickness ranging between 10 and 1000 nm de posited by rf sputtering and the electron cyclotron resonance (ECR) techniq ue was investigated by scanning probe microscopy (SPM). The roughness of th e films increases with increasing thickness following a power law with an e xponent of 0.26 and 0.6 for conventional sputtering and the ECR technique r espectively. Firm surface features evaluated by the autocorrelation functio n of the SPM images show a similar dependence on the thickness with an expo nent of 0.25 independent of the deposition system. Evolution of Nb film mor phology deposited by rf sputtering is compatible with a surface diffusion-d riven growth process where desorption is negligible, while films deposited by the ECR technique show a more complex behaviour.