We investigated the dry etching characteristics of TiN in TiN/A12O3: gate stack using a inductively coupled plasma system. TiN thin film is etched by BCI3/He plasma. The etching parameters are the gas mixing ratio, the RF power, the DC-bias voltages and process pressures. The highest etch rate is in BClilHe (25%:75%) plasma. The selectivity of TIN thin film to Al2O3 is pretty similar with BCI3/He plasma, The chemical reactions of the etched TiN thin films arc investigated by X - ray photoelectron spectroscopy, The intensities of the Ti 2p and the N is peaks are modified by BCl3: plasma, Intensity and binding energy of Ti and N could be changed due to a chemical reaction on the surface of TiN thin films. Also we investigated that the non volatile byproducts such as TiClx formed by chemical reaction with CI radicals on the surface of TiN thin films.