MECHANICAL STABILITY OF Ir ELECTRODES USED FOR STACKED SrBi2Ta2O9 FERROELECTRIC CAPACITORS

Abstract

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 (Pr) 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.