The structure of Ta nanopillars grown by glancing angle deposition

Regular arrays of Ta nanopillars, 200 nm wide and 500 nm tall, were grown on SiO2 nanosphere patterns by glancing angle sputter deposition (GLAD). Plan-view and cross-sectional scanning electron microscopy analyses show dramatic changes in the structure and morphology of individual nanopillars as a function of growth temperature Ts ranging from 200 to 700 °C. At low temperatures, Ts ≤ 300 °C, single nanopillars develop on each sphere and branch into subpillars near the pillar top. In contrast, Ts ≥ 500 °C leads to branching during the nucleation stage at the pillar bottom. The top branching at low Ts is associated with surface mounds on a growing pillar that, due to atomic shadowing, develop into separated subpillars. At high Ts, the branching occurs during the nucleation stage where multiple nuclei on a single SiO2 sphere develop into subpillars during a competitive growth mode which, in turn, leads to intercolumnar competition and the extinction of some nanopillars.