MECHANICAL STABILITY OF Ir ELECTRODES USED FOR STACKED SrBi 2 Ta 2 O 9 FERROELECTRIC CAPACITORS

Author: LISONI J.   JOHNSON J.   EVERAERT J.   GOUX L.   MEEREN H.   PARASCHIV V.   WILLEGEMS M.   MAES D.   HASPESLAGH L.   WOUTERS D.   CAPUTA C.   ZAMBRANO R.  

Publisher: Taylor & Francis Ltd

ISSN: 1058-4587

Source: Integrated Ferroelectrics, Vol.81, Iss.1, 2006-11, pp. : 37-45

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Abstract

A simplified TiAlNIr bottom electrode (BE) has been applied for the integration of stacked SrBi 2 Ta 2 O 9 (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 O 2 partial pressures was investigated. The optimization of the annealing conditions (O 2 flow) was attained by using planar TiAlNIr SBT FeCAP's. It was found that the optimal O 2 content was ∼20 ppm (∼10 −3 Torr), attaining polarization values (P r ) as high as 7 μ C/cm 2 . Higher O 2 partial pressures leads to SBT with inferior ferroelectric characteristics (Pr ∼ 3 μ C/cm 2 in full O 2 atmosphere), which correlated well with the formation of IrO 2 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 .