Dry etching of SrBi₂Ta₂O₂ thin films for FRAM applications

Dry etching of SrBi₂Ta₂O₉ (SBT) thin films were carried out in a planar type inductively coupled plasma (ICP) etching system with Cl₂-based discharges. Etch rate was quite dependent of plasma parameters, and ion-enhanced chemical etching was a dominant mechanism for SBT etching. Compared to Cl₂/Ar plasmas, Cl₂/NF₃/Ar and Cl₂/NF₃/O₂/Ar plasmas resulted in a substantial increase in etch rates and better surface morphologies of etched surface. The Cl₂/NF₃/O₂/Ar plasma chemistry showed a maximum etch rate of ∼ 1600 Å/min at 5 mTorr, 700 W ICP power and 150 W rf chuck power. Addition of O₂ into the Cl₂/NF₃/Ar mixture played an important role in compensating oxygen depletion during the ICP etching and resulted in smooth surface. Electrical properties of the SBT films were quite dependent of plasma chemistries, but Cl₂/NF₃/O₂/Ar showed overall the best P-E hysteresis loop with remnant polarization (2Pr) = 12.3 mC/cm² and coercive field (Ec) = 41.9 V/cm.