Interfacial roughness of sputtered multilayers: Nb/Si

Abstract

We have carried out studies of the interfacial roughness of a number of Nb/a-Si multilayers using cross-section transmission electron microscopy, wide-angle x-ray diffraction, and low-angle x-ray reflectivity and diffuse scattering. The multilayers studied were grown by sputtering in an Ar atmosphere at various pressures. The effect of the layer thickness and of the number of layers has also been studied. We observed a clear transition in the growth morphology when the sputtering pressure is raised above the thermalization pressure (≊9 mTorr) of the sputtered atoms. Both the mosaic of the Nb crystallites and the interface roughness increase dramatically when the Ar pressure exceeds 9 mTorr. The roughness of the various interfaces is strongly conformal and the samples with large roughness show a roughness that increases with deposited layer number. We discuss the quantitative extraction of these parameters from the x-ray data and the implications of these results for the physics of the deposition process.