The etching properties of aluminum oxide thin films deposited by PECVD were studied in $CCl_4$ and $CF_4$ plasma. The etch properties of aluminum oxide are different in each plasma environments. The etch rate of aluminum oxide in $CCl_4$ plasma is about 1 order higher than in $CF_4$ plasma. It was thought that this difference of etch rate in each plasma result from that of etch mechanism. Therefore the etch mechanism of aluminum oxide in each plasma was investgated using Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS) and Optical Emission Spectroscopy (OES). The OES proved that F, CF, $CF_2$ radicals in $CF_4$ plasma and CCl, Cl radicals in $CCl_4$ plasma did not affect the etch rate of aluminum oxide films dominantly. The surface analysis of aluminum oxide etch by $CF_4$ and $CCl_4$ plasma using XPS, AES proved that the etch product of aluminum oxide in $CF_4$ plasma in $AIF_x$ and the that of aluminum oxide in $CCl_4$ is $AIF_x$. The vapour of $AIF_x$ is higher than that of AlClx therefore etch rate of aluminum oxide in $CCl_4$ plasma is higher than in $CF_4$ plasma. additionally tha etch mask application of aluminum oxide films was studied.
