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

Dielectric/fenoelectric materials such as BaxSr1-xTiO3 (BST), PbZrxTi1-xO3 (PZT), and SrBi2Ta2O9 (SBT) are currently being investigated for integratio n into high-density CMOS technology. In this study, the micromorphology of polycrystalline BST, PZT, and SET films was imaged by atomic force microsco py (AFM). Electrical properties such as polarization of the crystallites as well as tunneling/leakage currents were measured by electrostatic force mi croscopy (EFM) and conductive atomic force microscopy (C-AFM), respectively . EFM images revealed that single crystallites of PZT and SET films could b e polarized by applying a voltage of a few volts between tip and film. Time and temperature stability of the polarization were studied in annealing ex periments. As expected, polarization decreased faster with increasing tempe rature. C-AFM on BST and SET showed enhancement of leakage currents in grai ns and grain boundary regions, especially in depressions between adjacent c rystallites. In thin SET films, sites of leakage current were frequently vi sible at the edges of steps of test patterns. The results achieved demonstr ate that scanning probe microscopy (SPM) techniques are a valuable tool for the elucidation of the microscopic properties of high-k materials. In part icular, they are capable of revealing the defects and discontinuities of th e films that affect capacitor performance and reliability due to, e.g., fat igue, imprint, and leakage currents, issues of key interest in product appl ications. (C) 2000 Elsevier Science B.V. All rights reserved.