Oxide thickness mapping of ultrathin Al2O3 at nanometer scale with conducting atomic force microscopy

In this work, we introduce conducting atomic force microscopy (C-AFM) for t he quantitative electrical characterization of ultrathin Al2O3 films on a n anometer scale length. By applying a voltage between the AFM tip and the co nductive Co substrate direct tunneling currents in the sub pA range are mea sured simultaneously to the oxide surface topography. From the microscopic I-V characteristics the local oxide thickness can be obtained with an accur acy of 0.03 nm. A conversion scheme was developed, which allows the calcula tion of three-dimensional maps of the local electrical oxide thickness with sub-angstrom thickness resolution and nanometer lateral resolution from th e tunneling current images. Local tunneling current variations of up to thr ee decades are correlated with the topography and local variations of the e lectrical oxide thickness of only a few angstroms. (C) 2001 American Instit ute of Physics.