Etching characteristics and mechanisms of SrBi2Ta2O9 thin films in CF4/Ar and Cl2/Ar inductively coupled plasmas

We investigated etching mechanism of the SrBi2Ta2O9 (SBT) thin films using Cl2/Ar and CF4/Ar plasmas. The investigations were carried out through the analysis of the influence of gas mixing ratio on etch rate, plasma parameters and volume and surface chemistries. In both gas mixtures, increasing the Ar mixing ratio leads to an increase of the SBT etch rate, which reaches a maximum value at 80% Ar. The maximum etch rates are 970 and 1100 Å/min for Cl2/Ar and CF4/Ar plasmas, respectively. CF4/Ar plasma exhibits higher electron temperature but lower electron density while for Cl2/Ar plasma, these parameters are more sensitive to gas composition. The increase of Ar content in both gas mixtures causes monotonic changes of fluxes for all kinds of active species. Simplified description of ion-assisted etching mechanism indicates that a combination of physical sputtering and chemical etching activated by ion bombardment can account for the experimental data explaining the appearance of etch rate maximum as well as the differences in SBT etch rate in Cl2/Ar and CF4/Ar plasmas.