Formation of cylindrical silicon dioxide and silicon nitride nanopillars through alternating gas etching using inductively coupled plasma reactive ion etching

Abstract Combining the complementary characteristics of silicon nitride (Si 3 N 4 ) and silicon dioxide (SiO 2 ), double-layer nanopillars can be an effective etching mask for metallic substrates by enhancing the selectivity and process stability. The steepness of these nanopillars critically ensures the fidelity of the transferred profile, directly influencing the quality of the fabricated nanostructures. Here, we present an alternating gas etching (AGE) approach, implemented via inductively coupled plasma reactive ion etching, to fabricate Si 3 N 4 /SiO 2 double-layer nanopillars on metal substrates. To avoid oxidation of the underlying metal, oxygen—widely used in SF 6 -based etching—is excluded from the process chemistry. Instead, Ar is introduced to supplement SF 6 , where SF 6 drives the chemical etching of Si 3 N 4 and/or SiO 2 , and Ar facilitates the physical etching to remove reaction by-products. However, conventional SF 6 /Ar co-etching yields insufficient steepness due to incomplete by-product removal. We introduce an additional etching step by employing Ar + ion bombardment, which efficiently removes the weakly bounded by-products formed in the prior step. Repetition of a two-step AGE cycle (step 1: SF 6 with/without Ar chemical etching; step 2: Ar-only physical etching) enabled continuous, high-fidelity etching of nanopillars with steep sidewalls. This method provides a continuous and controllable dry etching route for high-aspect-ratio nanostructures, with strong potential for integration into advanced semiconducting processes.