Polycrystalline Ni thin films on nanopatterned Si substrates: From highly conformal to nonconformal anisotropic growth

Abstract

The growth of polycrystalline Ni thin films on nanorippled Si templates is investigated in situ by grazing incidence small angle x-ray scattering as well as ex situ by atomic force microscopy and cross-sectional transmission electron microscopy. The templates have been fabricated by low-energy ion sputtering which leads to the spontaneous formation of a periodic ripple pattern with about 35 nm periodicity and about 3 nm peak-to-peak height. Highly conformal growth of the Ni film is observed under normal incidence deposition with the film surface perfectly replicating the substrate morphology up to a film thickness of at least 120 nm. Grazing incidence deposition perpendicular to the ripple orientation leads to the formation of one-dimensional nanowires on one side of the ripples due to geometrical shadowing. At a film thickness of about 10 nm, a transition to anisotropic columnar growth with rapidly decreasing conformity is observed. In this regime, the nanowires act as growth seeds for the columns and further geometrical shadowing leads to a film consisting of rows of tilted columns.