High-Resolution Direct Laser Writing Nanolithography Enabled by Oxidation-Mediated Corrosion Selectivity in N-Doped Sb Heat-Mode Resists

Abstract

Direct laser writing lithography provides a maskless and cost-effective approach to nanofabrication, yet its resolution is fundamentally limited by optical diffraction. This work demonstrates sub-diffraction-limit nanolithography and dry etching using nitrogen (N)-doped antimony (Sb) thin films. The NSb film acts as a positive-tone resist, achieving a development selectivity of 6.1 in tetramethylammonium hydroxide. Electrochemical measurements reveal that the thermally exposed film exhibits a higher corrosion current, lower potential, and lower charge transfer resistance compared to the as-deposited film, corresponding to an increased corrosion rate. This selectivity is primarily due to the formation of Sb crystal phase and higher degree of oxidation in the exposed film, which renders it more prone to corrosion. In contrast, the uniform dispersion of N and Sb atoms in the as-deposited film helps suppress the oxidation and dissolution of Sb to some extent. By confining the heat conduction within the heat affected zone, high-resolution nanostructures with a minimum feature size of 60 nm and a minimum period of 160 nm have been realized in NSb thin film. Moreover, the NSb film shows excellent etching resistance, with a maximum Si‑to‑film etching selectivity of 34.0 under SF6/O2 plasma. The etched Si structures display steep sidewalls and low line-edge roughness. This etching selectivity is attributed to the formation of non‑volatile SbOx and SbFx compounds under SF6/O2 plasma, which protect the NSb film from further etching while Si is readily removed. Finally, a Si nanohole array is fabricated to demonstrate an anti‑reflection function, highlighting its potential for use in photovoltaic solar cells.