An investigation of etching mechanism of low-temperature SiO2 thin films in CF4/Ar/O-2 inductively coupled plasmas at constant input power (900 W) and bias power (200 W) was carried out. It was found that that the variations of Ar/O-2 mixing ratio (0-50 %) at constant 50 % CF4 fraction as well as the change in gas pressure (4-10 mTorr) resulted in non-monotonic SiO2 etching rates. The zero-dimensional plasma model with Langmuir probe diagnostics data provided the detailed information on formation-decay kinetics for plasma active species. The model-based analysis of etching kinetics showed that these effects were not connected with the non-monotonic change of fluorine atom density (as was found in several works for the binary CF4/O-2 system), but resulted from the decrease in reaction probability and with the transition from neutral-flux to ion-flux-limited regimes of ion assisted chemical reaction.