Effects of grain growth on dynamic surface scaling during the deposition of Al polycrystalline thin films

Abstract

Evolution of surface structure during the growth of sputter-deposited polycrystalline Al films is studied by means of atomic force microscopy and dynamic scaling by power spectral density and image variography analyses. We incorporate the effects of grain growth based on quantitative measurements of grain size, morphology, and texture orientation through transmission electron microscopy and x-ray diffraction pole figure texture measurements. Temporal regimes of early surface smoothing followed by roughening are explained by the effects of grain-boundary grooves and grain growth during deposition. Three distinct surface morphologies described as flat grains, hillocks, and ridges develop during film growth. The ridges are periodic structures with constant spacing during growth that form along 〈110〉 directions on vicinal (111)-oriented grains and are due to spontaneous development and growth of steps along 〈110〉 directions induced by the Schwoebel-barrier mechanism. The spacing of ridge structures and the well-characterized median grain size correspond to characteristic dimensions that define transitions between regimes of combinations of physical processes responsible for surface evolution. We found a surface-diffusion-dominated anomalous scaling growth mode $(\ensuremath{\alpha}g1)$ at short length scales and a nonlinear KPZ type mode $(\ensuremath{\alpha}\ensuremath{\approx}0.35)$ at longer length scales.