Characterization Of High-K Dielectric/Ferroelectric Materials: Capabilities Of Scanning Probe Microscopy (Spm)

Dielectric/ferroelectric materials such as BaxSr1-xTiO3 (BST), PbZrxTi1-xO3 (PZT) and SrBi2Ta2O9 (SBT) are currently being investigated for integration into high-density CMOS technology. In this study the microstructure of polycrystalline BST, PZT and SET films was imaged by atomic force microscopy (AFM). Electrical properties such as polarization of the crystallites as well as tunneling/leakage currents were measured by electrostatic force microscopy (EFM) and conductive atomic force microscopy (C-AFM), respectively. EFM images revealed that single crystallites of PZT and SET films can be polarized by applying a low voltage between tip and film. On some SET films incomplete polarization of local regions was observed which may be related to special growth orientations of crystallites. Tip stability and charge free surfaces are major parameters for determining the quality of the results. C-AFM studies on BST displayed extended regions separated by high leakage current boundaries, which may reflect stress effects in the films. C-AFM on SET showed enhancement of leakage currents in grains and grain boundary regions, especially in depressions between adjacent crystallites. The results achieved demonstrate that SPM techniques are a valuable tool for the elucidation of the microscopic properties of high-k materials revealing the defects and discontinuities of the films which affect capacitor performance and reliability via, e.g., fatigue, imprint and leakage currents, issues of key interest for product applications.