Effect of ion bombardment on in-plane texture, surface morphology, and microstructure of vapor deposited Nb thin films

Niobium films were deposited by physical vapor deposition (PVD) and ion-beam-assisted deposition (IBAD) using ion energies of 0, 250, 500 and 1000 eV, and $R$ ratios (ion-to-atom arrival rate ratio) of 0, 0.1, and 0.4 on (100) silicon, amorphous glass, and (0001) sapphire substrates of thickness 50–1000 nm. Besides a {110} fiber texture, an in-plane texture was created by orienting the ion beam with respect to the substrate. The in-plane texture as measured by the degree of orientation was strongly dependent on both ion-beam energy and the $R$ ratio. In fact, the degree of orientation in the films followed a linear relationship with the energy per deposited atom, $E_n.$ The grain structure was columnar and the column width increased with normalized energy. The surface morphology depended on both the normalized energy of the ion beam and the film thickness. All films had domelike surface features that were oriented along the ion-beam incident direction. The dimension of these features increased with normalized energy and film thickness. Surface roughness also increased with normalized energy and film thickness, with the root-mean-square roughness increasing from 1.6 nm for the PVD sample (100 nm thick) to 36.7 nm for the IBAD film (1000 eV, $\text{R=0.4,}$ 800 nm thick). Both the surface morphology evolution and in-plane texture development in these films were the result of the different ion sputter rates among differently oriented grains.