Impacts of postannealing ambient atmospheres on Pt/SrBi 2.2 Ta 2 O 9 /Pt capacitors
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o Yu National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China
Hui-Qin Ling and Di Wu Materials Science and Engineering Department, Nanjing University, Nanjing 210093, People’s Republic of China; National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China
Zhi-Guo Liu and Nai-Ben Ming National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China; Center for Advanced Studies in Science and Technology of Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China (Received 11 January 2001; accepted 26 September 2001)
SrBi2Ta2O9 (SBT) films were prepared on Pt/TiO2/SiO2/Si substrates at 750 °C in oxygen by the metalorganic decomposition method. SBT film capacitors were postannealed in Ar (N2) at 350–750 °C and then reannealed in O2 at 750 °C. Effects of annealing atmosphere on the structure, morphology, and ferroelectric properties have been investigated systematically. The composition analyses indicate Ar- or N2-annealing at 750 °C leads to Bi evaporation and oxygen loss. Above 550 °C 100% Ar or N2 postannealing, the remnant polarization decreases and the coercive field increases significantly. The subsequent O2 recovery can hardly rejuvenate the electrical properties. The result is different from that with the effective O2 recovery in forming gas processing (annealing in an atmosphere containing 5% hydrogen). The possible origin and mechanism is discussed and proposed.
I. INTRODUCTION
A SrBi2Ta2O9 (SBT) thin film has been known as a prime candidate for construction of nonvolatile ferroelectric memories due to excellent reliability properties, even with conventional Pt electrodes.1 However, there still remain several problems that impede the incorporation of the SBT films in microelectronic device fabrication. One drawback is its high-temperature processing, which is not comparable with traditional Si semiconductor processing. Some efforts have been made to eliminate it.2,3 Another important problem is the H2-induced degradation behavior of an SBT capacitor during the passivation or the interlayer dielectric processing.4 –6 Compared to Pb(ZrTi)O3 capacitors, SBT seems to suffer damage easily by a hydrogen-containing atmosphere, leading to a decrease in remnant polarization and resistance. Although the degradation properties can be rejuvenated by the following oxygen recovery, the cause of the damage and oxygen recovery is not well understood. Since the ferroelectric materials will be subjected to numerous 3526
J. Mater. Res., Vol. 16, No. 12, Dec 2001
hydrogen-containing environments during device fabrication, a thorough investigation of this phenomenon is very necessary. We have studied low-temperature (100–400 °C) forming gas (5% H2 and 95% N2) processing effects on SBT capacitors.7 To thoroughly elucidate the mechanism for hydrogen-related damage to the ferroelectric capacitors, in contrast, the postannealing work of SBT capacit
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