The reactive ion etching(RIE) properties of $Al_2O_3$ films prepared by PECVD were investigated $Al_2O_3$ films were found to be 2 to 3 orders more stable than the Si or $SiO_2$ in RIE environment.
The etch rate of the $Al_2O_3$ increased with decrease of pressure and increase of RF power, but the rate was independent of the fluoride atom concentration measured by the Ar actinometry.
Also the result showed that $H_2$ addition to $CF_4$ plasma gives more anisotropic etch profile than $O_2$ addition and the anisotropy of the etching could be predicted using the ratio between the RIE rate and the etch rate of substrate floated in the plasma.
The $Al_2O_3$ thin films were proved in this study to be an outstanding etch mask material because the film is very stable in the RIE environment and easy to remove.
