MECHANICAL STABILITY OF Ir ELECTRODES USED FOR STACKED SrBi₂Ta₂O₉ FERROELECTRIC CAPACITORS

ABSTRACT

A simplified TiAlN\Ir bottom electrode (BE) has been applied for the integration of stacked SrBi₂Ta₂O₉ (SBT) ferroelectric capacitors on W-plugs. In order that the W-plugs are less exposed to oxygen during the high thermal budget used for the SBT crystallization (700°C/1 h), the implementation of low O₂ partial pressures was investigated. The optimization of the annealing conditions (O₂ flow) was attained by using planar TiAlN\Ir\ SBT FeCAP's. It was found that the optimal O₂ content was ∼20 ppm (∼10⁻³ Torr), attaining polarization values (P_r) as high as 7 μ C/cm². Higher O₂ partial pressures leads to SBT with inferior ferroelectric characteristics (Pr ∼ 3 μ C/cm² in full O₂ atmosphere), which correlated well with the formation of IrO₂ at the Ir-SBT interface. If patterned TiAlN\ Ir BE structures are used and SBT is crystallized at the optimal O₂ partial pressure, the system is no longer stable due to extended lateral oxidation of the TiAlN film, buckling of the Ir film and subsequent W-plug oxidation. These results will be explained taking into consideration the combination of high tensile stress in the SBT and the Ir films when annealed in atmospheres close to pure N₂.

Keywords:

• Ferroelectrics
• Iridium
• SBT
• stacked capacitors

ACKNOWLEDGMENTS

Partial financial support provided by EC through the IST Fleur Project IST-2000-30153.