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Improvement of Hydrogen Degradation in Pt/SrBi2Ta2-xNbxO9/Pt Capacitor

Published online by Cambridge University Press:  10 February 2011

Akira Furuya
Affiliation:
Silicon Systems Research Laboratories, NEC Corporation, 1120 Shimokuzawa, Sagamihara, Kanagawa 229–1198, Japan, furuya@mel.cl.nec.co.jp
Joe D. Cuchiaro
Affiliation:
Symetrix Corporation, 5055 Mark Dabbling Blvd, Colorado Springs, Colorado 80919, U.S.A., joe@symetrixcorp.com
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Abstract

Ferroelectric SrBi2(Ta1-xNbx)2O9 (SBTN) thin films are under evaluation for IC memory applications. It has been reported that SrBi2(Ta1-xNbx)2O9 has higher fatigue endurance and imprint resistance than other common ferroelectric materials such as lead zirconate titanate (PZT). One of the most important technical issues for integrating ferroelectric oxide materials into IC memory applications is the degradation of ferroelectric capacitor properties from the oxide reduction from hydrogen. Hydrogen annealing processes performed to terminate dangling bonds in silicon, or, elevated temperature processes, which dissociate hydrogen, are expected to reduce the ferroelectric oxide thereby degrading the dielectric properties. Therefore, in this work, we have investigated reducing degradation of Pt/SBTN/Pt capacitors due to hydrogen exposure by evaluating the compositional dependence of the Ta/Nb ratio and incorporating TiN as a hydrogen diffusion barrier. To investigate compositional dependence, the Pt/SBTN/Pt capacitors with the desired composition were fabricated from enhanced metal organic decomposition solutions that were spin deposited and delineated with a conventional patterning and etching techniques. Post annealing the samples in H2 (1%)-N2 ambient at 200°C for 10–60min, hysteresis and current-voltage measurements were conducted to evaluate any degradation to pre-anneal measurements. This experimental condition revealed that the best electrical characteristics were obtained with the Ta/Nb ratio of 1.5/0.5. Therefore, Pt/SBTN/Pt capacitors with a Ta/Nb ratio of 1.5/0.5 were evaluated using a TiN barrier and its effect characterized. After depositing a TiN film on the Pt/SBTN/Pt capacitors, the samples were annealed in H2 (5%)-N2 at 400°C for 10–60 min. The TiN was removed with NH4OH: H2O2: H2O = 1: 3: 1, respectively, at 60 - 70°C and the hysteresis and current-voltage characteristics of the capacitors measured. It was found that the degradation was extremely reduced by incorporating a TiN barrier. Moreover, the degradation effects decreased with increased density of the deposited TiN film. TiN densities greater than 3.8g/cm3 in these experiments kept the leakage current degradation to less than 10−6A/cm2 while the degradation in remanent polarization is less than 20%.

Type
Research Article
Copyright
Copyright © Materials Research Society 1999

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References

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