Reactive Ion Etching of $Y_{2}O_{3}$ films applying F-, Cl- and Cl/Br-based Inductively Coupled Plasmas

Reactive ion etching of yttrium oxide thin films was investigated using $CF_{4}/O_{2}, BCl_{3}, HBr$ and $Cl_{2}$ inductively coupled plasmas. For all gas combinations, with the exception of $Cl_{2}$, the etch rate was found to be similar, indicating a primarily physical etch process, enhanced in $Cl_{2}$ by an additional chemical-etching component. The highest observed etch rate was 53 nm/min in $Cl_{2}$, suitable for controlled etching of optical ridge waveguide structures several hundred nm in height. Overall, the surface quality of the etched $Y_{2}O_{3}$ films was the highest after etching in $CF_{4}/O_{2}$ plasmas, indicating a trade-off in etch rate and film quality between the various process gases. Preliminary selectivity measurements show that Ni is a suitable material for etch-masking of high resolution structures in $Y_{2}O_{3}$