C-AFM characterization of the dependence of HfAlOx electrical behavior on post-deposition annealing temperature

The dependence of the electrical behavior of thin HfAlOx layers (5 nm) on post-deposition annealing temperature (T-A) has been studied at a nanometer scale using conductive atomic force microscopy (CAFM) and high resolution transmission electron microscopy (HR-TEM). Topography, current maps and current-voltage (I-V) characteristics have been collected by CAFM. Current maps show an increase in conduction inhomogeneity for samples exposed to T-A greater than or equal to 900 degreesC: spots with current about one order of magnitude larger than the background region are present. The dielectric layer structure also becomes more inhomogeneous: HR-TEM images reveal that for TA greater than or equal to 900 degreesC HfO2 grains appear on the HfAlOx layer, whereas for lower T-A the HfAlOx layer is homogeneous. Moreover, for T-A greater than or equal to 900 degreesC the high-k/Si interface becomes rougher. Therefore, the increase in conduction inhomogeneity for samples annealed above 800 degreesC is believed to be caused by the material transition from an amorphous to a poly(nano)crystalline structure combined with the increase of the high-k/SiO2 interface roughness. (C) 2004 Elsevier B.V. All rights reserved.