In this study, the etching characteristics of Al2O3 thin films were investigated using an ICP (inductively coupled plasma) of BCl3/Ar gas mixture. The etch rate of Al2O3 thin films as well as the SiO2/Al2O3 etch selectivity were measured as functions of BCl3/Ar mixing ratio (0∼100% Ar) at a constant gas pressure (10 mTorr), total gas flow rate (40 sccm), input power (800 W) and bias power (100 W). The behavior of the Al2O3 etch rate was shown to be quite typical for ion-assisted etch processes with a dominant chemical etch pathway. To analyze the etching mechanism using DLP (double langmuir probe), OES (optical emission spectroscopy) and surface analysis using XPS (x-ray photoelectron spectroscopy) were carried out.