Inductively coupled plasma etching of graded-refractive-index layers of TiO₂ and SiO₂ using an ITO hard mask

Transparent dielectric layers with varying compositions of TiO₂ and SiO₂, and ITO are deposited on sapphire and Si substrates by using an RF sputter system. Inductively coupled plasma (ICP) reactive ion etching (RIE) of the ITO hard mask is examined under H₂, CH ₄, and Cl₂ chemical environments. The slope of the sidewall and the etch residue on the sidewall of the ITO hard mask are controlled by the flow rates of H₂, CH₄, and Cl ₂. ICP-RIE dry etch of TiO₂ and SiO₂ is investigated under fluorinated environments. Comparable etch rates of TiO ₂ and SiO₂ (ratio ≈ 2:1) and high selectivity 1 over ITO are found. Graded-refractive-index (GRIN) layers, made up of multiple dielectric layers of TiO₂ and SiO₂, are patterned to form cylindrical pillars by ICP etching using the ITO hard mask. Fluorine containing residues are identified on the TiO₂ and SiO₂ surfaces. Various etch chemistries are investigated to obtain smooth, vertical, and residue-free sidewalls of the GRIN pillars.