Imaging by atomic force microscopy of the electrical properties difference of the facets of oxygen-ion-induced ripple topography in silicon

Atomic force microscopy (AFM) is used in tapping and contact mode in order to study the roughness created in the crater bottom during secondary ions mass spectrometry (SIMS) analysis in silicon, using O2+ primary ions without oxygen flooding. A characteristic topography is observed, where ripples develop with an increasing peak to peak height amplitude and a triangular section showing very flat facets. We use the conductive-AFM (C-AFM, also called tunneling AFM (TUNA) mode) to measure the current flowing through the oxide. We show that when a rather strong electric field is applied between the tip and the sample, one side of the ripples (facets hidden from the beam) exhibits a far more important leakage current than the other (facets facing the beam) at a given fixed voltage, suggesting that the corresponding areas are thinner or covered with a poorer insulator. This is a direct observation at a nanometer scale of the different nature of the materials covering both sides of the facets. The authors propose that over the studied surface (r.m.s. roughness∼30 nm), both facets are sufficiently oxidized to behave like an insulator