Low temperature process and thin SBT films for ferroelectric memory devices

At crystallization temperatures of about 800 degreesC bismuth layered oxide SrBi2Ta2O9 (SBT) deposited by MOD develops good ferroelectric properties for use in FeRAM devices. But scaling down the film thickness of SET below 150 nm only shorts are measured at this crystallization temperature after top electrode deposition. Working Pt/SBT/Pt-capacitors are achieved by reducing the crystallization temperature. Also temperatures of 800 degreesC are too high for. integration of the SET module in a stacked capacitor architecture for high density memory devices. Therefore. a process is needed to reduce the crystallization temperature of SET, called "Low Temperature Process". In this work the electric properties of spin-on processed SET crystallized in a temperature window from 650 degreesC up to 800 degreesC are investigated. As shown by XRD: transition of the nonferroelectric Fluorite phase to the Aurivillius phase rakes place at approximately 625 degreesC. Increasing the crystallization temperature gives better crystallized SET films with bigger SET grains. However, film porosity is also increasing with temperature. Electrical results of stoichiometric variations of SET are presented. SEM pictures show that cluster formation is correlated with less film porosity at lower temperatures.