In this study, we changed the input parameters (gas mixing ratio, RF power, DC bias voltage, and process pressure), and then monitored the effect on TiN etch rate and selectivity with <TEX>$SiO_2$</TEX>. When the RF power, DC-bias voltage, and process pressure were fixed at 700 W, - 150 V, and 15 mTorr, the etch rate of TiN increased with increasing <TEX>$CF_4$</TEX> content from 0 to 20 % in <TEX>$CF_4$</TEX>/Ar plasma. The TiN etch rate reached maximum at 20% <TEX>$CF_4$</TEX> addition. As RF power, DC bias voltage, and process pressure increased, all ranges of etch rates for TiN thin films showed increasing trends. The analysis of x-ray photoelectron spectroscopy (XPS) was carried out to investigate the chemical reactions between the surfaces of TiN and etch species. Based on experimental data, ion-assisted chemical etching was proposed as the main etch mechanism for TiN thin films in <TEX>$CF_4$</TEX>/Ar plasma.