Nonuniform silicon oxidation and application for the fabrication of aperture for near-field scanning optical microscopy

In this letter, a technological approach for the fabrication of a miniature aperture for near-field scanning optical microscopy using silicon micromachining technology is described. The aperture with diameter sizes from 10 to 500 nm at the apex of a SiO₂ tip on a Si cantilever is fabricated using a "Low temperature Oxidation & Selective Etching" technique. The SiO₂ tip is formed by nonuniform Si wet oxidation at 950 °C with a thickness of about 1 μm. The aperture is created by selective etching SiO₂ in a buffered-HF (50% HF:40% NH₄F, 9cc:100cc) solution at 36 °C using a thin chromium (Cr) layer deposited on the oxidized sample as a mask. Using the fabricated probe, atomic force microscopy and corresponding near-field scanning optical microscopy images of 300 nm diameter latex spheres on mica substrate are obtained.