The etching mechanism of ZrO 2 thin films in BCl 3 /Ar plasma was investigated using a combination of experimental and modeling methods. It was found that an increase in the Ar mixing ratio causes the non-monotonic behavior of the ZrO 2 etch rate which reaches a maximum of 41.4nm/min at about 30–35% Ar. Langmuir probe measurements and plasma modeling indicated the noticeable influence of a BCl 3 /Ar mixture composition on plasma parameters and active species kinetics that results in non-linear changes of both densities and fluxes for Cl, BCl 2 and BCl2+. From the model-based analysis of surface kinetics, it was shown that the non-monotonic behavior of the ZrO 2 etch rate can be associated with the concurrence of chemical and physical pathways in ion-assisted chemical reaction.