High etch selectivity for plasma etching SiO₂ with AlN and Al₂O₃ masks

SiO₂ has been etched with high etching selectivity to Al₂O₃ and AlN masks using inductively coupled plasma. This offers a possibility to use very thin masks for deep etching of glass for e.g. microfluidic devices. Furthermore, SiO₂ can be etched with very low etching selectivity to the mentioned masks, indicating a possibility to pattern the Al₂O₃ and AlN with SiO₂ or photoresist mask. A process based on a mixture of SF₆ and C₄F₈ was observed to etch SiO₂ with a rate of about 100 nm/min at 250 V bias (peak-to-peak) voltage, when Al₂O₃ and AlN had a zero etch rate. A process based on pure C₄F₈ was observed to etch Al₂O₃ and AlN with about 350 V bias, when SiO₂ etch rate was still zero.