Micromorphology of sputtered aluminum thin films: A fractal analysis

In this article, the surface analyses of topography, microstructure and mechanical behavior of Al thin films sputtered on glass are presented to understand the influence of varying low substrate temperatures at high radio-frequency (RF) power. The films were prepared by RF magnetron sputtering process at different substrate temperatures of 55oC, 65oC, and 95oC and at a constant RF power of 350 W. The topography, microstructure and mechanical properties were characterized by atomic force microscope (AFM), field emission scanning electron microscope (FESEM) and nanoindentation method respectively. The results revealed that at a higher substrate temperature of 95oC the microstructure consists of dense and globular dominant aluminum structures and higher interface width (roughness) as compared to the other temperatures. Nanoindentation results showed that films deposited at 95oC exhibited the highest values of average hardness and elastic moduli and a lowest maximum depth of displacement. A fractal analysis on the topography and surface microstructure revealed a decrease of the fractal dimension with the increase in substrate temperature and that the films exhibited a mono-fractal behavior at all the substrate temperatures investigated in the present study. A description based on the sputtering theory for the monofractal nature of the aluminum films is provided.