Fabrication of high-aspect-ratio SiO2 nanopillars by Si thermal oxidation for metalenses in the visible region

We propose a fabrication method of metalenses in the visible region with high-aspect-ratio SiO2 nanopillars by thermal oxidation of Si nanopillars. We first evaluated the expansion of the nanopillars in width due to thermal oxidation, which affects the phase shift on metalenses. Next, considering expansion due to thermal oxidation and processing errors, a metalens pattern was fabricated, and the pillar width distribution was measured. The highest aspect ratio was 8.7. Finally, the focusing of the fabricated reflective metalens was confirmed, which indicates that the proposed method can fabricate metalenses in the visible region with SiO2 nanopillars including transmissive metalens.