Electrical characterization of gate oxides by scanning probe microscopies

Ballistic electron emission microscopy (BEEM) and non-contact atomic force microscopy (NC-AFM) are used to characterize SiO2 and Al2O3 layers grown on Si(100). The effective conduction band mass and its energy dispersion in SiO2 and an offset between Al2O3 and Si conduction bands of 2.78 eV were obtained with BEEM. NC-AFM was used to image electrons, and in some instances holes, trapped in the oxide layers near the surface and in the bulk of the oxide. Modeling of the tip–surface interaction supports the interpretation of image features arising from a single electron occupying a trap. The polarity of the trapped charge was deduced from Kelvin (potential difference) images that were simultaneously recorded with the topographic images.