Sub-200-nm-diameter cylindrical silicon nanopillars with high aspect ratio (40:1) fabricated by SF6/C4F8-modulated ICP-RIE

Abstract

Vertical silicon nanopillars are essential for vertical gate-all-around transistors in advanced integrated circuit. However, achieving high aspect ratios with precise dimensional control remains a key fabrication challenge. In this work, cylindrical silicon nanopillars with diameters below 200 nm, smooth and vertical sidewalls are developed using SF₆/C₄F₈ gas mixture within an Inductively Coupled Plasma Reactive Ion Etching system. The etching rate, sidewall angle, and structural morphology of nanopillars are analyzed under the impact of C₄F₈ gas flow, pressure, source power, and bias power. The single-step continuous etching approach utilizing SF₆/C₄F₈ gas mixture involves three mechanisms: fluorocarbon passivating film deposition produced by CF_x radicals, directional ion bombardment that removes passivation layer, and isotropic etching driven by F∗ radicals. By optimizing etching parameters, vertically aligned cylindrical Si nanopillars with height up to 8.3 μm and aspect ratio of 40:1 are produced, exhibiting excellent diameter uniformity. This research contributes valuable insights into SF₆/C₄F₈ plasma etching dynamics and highlights its potential for advanced applications involving silicon nanopillars.