Competitive growth of Ta nanopillars during glancing angle deposition: Effect of surface diffusion

Abstract

Periodic arrays of Ta nanopillars were grown onto patterned substrates by glancing angle sputter deposition at growth temperatures Ts ranging from 200to900°C. The Si substrates were patterned using a colloidal suspension of 260-nm-diameter silica spheres that was dispersed to form a two-dimensional close-packed monolayer. At low growth temperatures, Ts⩽500°C, nanopillars exhibit regular hexagonal arrays. However, the arrays randomize with increasing Ts and completely degrade at Ts=900°C. The transition to a less ordered film morphology is attributed to strong interpillar competition caused by the increasing adatom diffusion length with increasing Ts. The competitive growth mode leads to a decrease in the pillar number density (by 48%) and pillar separation (from 65nm to negligible), an increase in the average pillar width from 200to260nm, the accelerated growth of some pillars at the cost of others which die out (25%), and an increased probability (20%) for the merging of neighboring pillars.