Surface roughness of sputter-deposited gold films: a combined x-ray technique and AFM study

Abstract

We applied grazing incidence x-ray specular and non-specular reflectivity (GIXR) and small-angle x-ray scattering (SAXS) to study the surface roughness of gold films on quartz glass substrates. Two model systems were prepared: one series of Au films was sputtered in Ar at 3×10−3mbar (Au1 films) and one in residual air at 3×10−1 mbar (Au2). The combined x-ray experiments showed that the Au1 films are compact and smooth, with-mean-square (rms) roughness values too low to be quantified by means of atomic force microscopy (AFM) or SAXS. The surfaces of film and substrate exhibit a strong cross correlation that is gradually lost with increasing film thickness. The surface height–height correlation functions are well described by a self-affine model. In contrast, as directly proved via AFM, the Au2 films consist of islands that are coarsening with increasing film thickness. The film surface showed no cross-correlation with the substrate surface at all. The SAXS curves from the Au2 films were attributed to a volume scattering effect, by interpreting the films in terms of a two-dimensional array of hard hemispheres. Copyright © 1999 John Wiley & Sons, Ltd.