Scanning probe microscopy — a tool for the investigation of high-k materials

Dielectricrferroelectric materials such as Ba Sr TiO BST., PbZr Ti O PZT., and SrBi Ta O SBT. are x 1yx 3 x 1yx3 2 2 9 currently being investigated for integration into high-density CMOS technology. In this study, the micromorphology of polycrystalline BST, PZT, and SBT films was imaged by atomic force microscopy AFM.. Electrical properties such as polarization of the crystallites as well as tunnelingrleakage 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 SBT films could be polarized by applying a voltage of a few volts between tip and film. Time and temperature stability of the polarization were studied in annealing experiments. As expected, polarization decreased faster with increasing temperature. C-AFM on BST and SBT showed enhancement of leakage currents in grains and grain boundary regions, especially in depressions between adjacent crystallites. In thin SBT films, sites of leakage current were frequently visible at the edges of steps of test patterns. The results achieved demonstrate that scanning probe microscopy SPM.techniques are a valuable tool for the elucidation of the microscopic properties of high-k materials. In particular, they are capable of revealing the defects and discontinuities of the films that affect capacitor performance and reliability due to, e.g., fatigue, imprint, and leakage currents, issues of key interest in product applications. q2000 Elsevier Science B.V. All rights reserved.