Plasma etching of As2S3 films for optical waveguides

Abstract

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.