Fluorination mechanisms of $Al2O3$ and $Y2O3$ surfaces irradiated by high-density $CF4∕O2$ and $SF6∕O2$ plasmas

Fluorination of $Al2O3$ and $Y2O3$ surfaces was investigated by irradiating high-density, helicon-wave $CF4∕O2$ and $SF6∕O2$ plasmas. The $Al2O3$ surface bombarded by high-flux positive ions of the $CF4∕O2$ plasma was fluorinated significantly. On contrast, $Y2O3$ was less fluorinated than $Al2O3$ when they were irradiated by the same $CF4∕O2$ plasma. The analysis of the $Al2O3$ surface irradiated by the $CF4∕O2$ plasma suggests that the fluorination is triggered by reactions between fluorocarbon deposit and Al–O bonding with the assistance of ion bombardment. On the other hand, irradiation of the $SF6∕O2$ plasma induced less significant fluorination on the $Al2O3$ surface. This suggests a lower reaction probability between sulfur fluoride deposit and Al–O bonding. The difference in the fluorination of the $Al2O3$ and $Y2O3$ surfaces induced by the irradiations of the $CF4∕O2$ and $SF6∕O2$ plasmas is understood by comparing the bonding energies of C–O, S–O, Al–O, and Y–O.