Early growth stages of sputter deposited Ag on native SiO 2

Abstract

We have presented the kinetic study of the very initial growth stages of an ultrathin film (40–150 Å) of Ag sputter deposited on a Si(0 0 1) substrate, covered by native oxide, using grazing incidence X-ray reflectivity (GIXR) technique and atomic force microscopy (AFM). We observe that the films consist of mounds with the presence of voids. The thickness ‘ d xray’ and the packing fraction ‘ η’ of the film as a function of growth time ‘ t’ follow a simple power law, d xray∼ t m and η∼ t n with the exponent m=0.58 and n=0.4 respectively. We have quantitatively determined that the voids between the mounds decrease at the initial growth stages with the increase in mound size. The mound size increases mainly by coalescence. The mound size increases radially as ∼ t z as a function of time. The radial growth exponent z crosses over from z>0.5 to 0.25 indicating two growth regimes. GIXR measurements reveal sublinear dependence of η on d and the AFM measurements show a cross over of the radial growth exponent. Both these indicate that at the initial stages, the lateral growth of the mound is dominant over the vertical growth hence reducing the voids.