Plasma etching of As₂S₃ films for optical waveguides

Chalcogenide glasses are good candidate materials for ultra-fast non-linear optic devices. In this work, we present the photolithographic process and the plasma etching of arsenic tri-sulphide (As₂S₃) film. The films were deposited on thermally oxidized silicon substrates by ultra-fast pulsed laser deposition. To protect As₂S₃ film from photo-resist developer, thin resist layer ∼100-200 nm was remained on the UV exposed area by controlling resist development time. After removing the protective layer in oxygen plasma, As₂S₃ waveguides were patterned in inductively coupled plasma reactive ion etching (ICP-RIE) system using CF₄-O₂ gas mixture. We investigated the etch rate and the etch selectivity to photo-resist of As₂S₃ as a function of bias power, induction power, operating pressure, and gas flow rate ratio of CF₄ and O₂. The film is mainly etched by the chemical reaction with fluorine radicals. The content of oxygen in the plasma determines the etched sidewall profiles and nearly vertical profile was obtained at high oxygen content plasma.