Stress Measurements and Processing Optimization for Solution Derived SrBi2Ta2O9 Thin Films

The development of stress in the SrBi2Ta2O9 (SBT) films generated from a chemical solution deposition method was monitored during processing using wafer curvature measurements. Stress measurements of the entire Si/SiO2/Pt/SBT stack revealed an overall tensile stress of ∼536 MPa. The greatest increase in tensile stress was recorded for the anneal of the Pt bottom electrode and was due to the thermal expansion mismatch. Deposition of an amorphous SBT layer on the Pt, followed by a low temperature anneal (300°C), had little overall effect on the stress of the stack; however, upon crystallization, significantly more tensile stress was introduced into the stack. To further investigate the effect that stress has on the various electrical properties SBT films, wafers with different stress states were produced and SBT films deposited on them. Initial investigations indicate that SBT films on wafers with a higher tensile stress displayed improved ferroelectric hysteresis and switchable polarization.