Mechanical stability of ir electrodes used for stacked SrBi2Ta2O9 ferroelectric capacitors

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 degrees C/1 h), the implementation of low O-2 partial pressures was investigated. The optimization of the annealing conditions (O-2 flow) was attained by using planar TiAlN\Ir\SBT FeCAP's. It was found that the optimal O-2 content was similar to 20 ppm (similar to 10(-3) Torr), attaining polarization values (P-r) as high as 7 mu C/cm(2). Higher O-2 partial pressures leads to SBT with inferior ferroelectric characteristics (Pr similar to 3 mu C/cm(2) in full O-2 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 O-2 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 N-2.