Degradation of ferroelectric properties in integrated Pt/SrBi2Ta2O9/Pt capacitor by impurity diffusion from interlevel dielectric layer

The ferroelectric properties of integrated Pt/SrBi2Ta2O9 (SBT)/Pt capacitors with boron (B)- and phosphorus (P)-doped silicate glass (BPSG) as an interlevel dielectric layer were investigated. After annealing at 800 degreesC to densify the BPSG, a significant reduction in remanent polarization was observed. Both transmission electron microscopy and nanoprobe energy dispersive spectroscopy analysis showed bismuth (Bi) and P interdiffusion across the interface between the SBT and BPSG layers. This strongly suggests that Pt/SBT/Pt capacitor degradation results from Bi loss in the surface region of the SBT layer, which is induced by P diffusion into the SBT. The degradation in ferroelectric properties was prevented by inserting a thin undoped silicate glass (USG) layer between the SBT and the BPSG, which blocked P diffusion. From the USG thickness dependence of the remanent polarization, P-induced degradation was also verified. (C) 2002 American Institute of Physics.