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. (C) 2008 Elsevier B.V. All rights reserved.