Atomic Force Microscopy (AFM) has been demonstrated to be one of the most powerful tools for nanoelectronic fabrication and characterization. However, AFM grown SiO2 has not been yet used as the gate dielectric, and its electrical behavior remains still unknown. After a topographic characterization, in this paper the conduction modes of AFM grown gate oxide (AFM-GOX) MOS structures are studied from measurements of their current-voltage (IV) characteristics. The results are compared to those obtained for thermally grown SiO2 (T-GOX), which is used as quality reference. Two types of structures have been used to study the conduction through AFM-GOX: a) MOS capacitors with polysilicon deposited gate, for standard electrical characterization and b) MOS structures without deposited gate, because the conductive AFM tip acts as gate terminal, for Conductive-AFM (C-AFM) measurements. Qualitatively, the fabrication process of the poly-Si gated structures consisted of: a field oxidation of the Si wafers, opening of windows in the field oxide to reach the substrate, then AFM oxidation was performed (4nm thick oxide), and as a last step a polysilicon gate was deposited. For the reference structures, AFM gate oxidation process was replaced by thermal oxidation with thickness of 3.5 and 4.5nm. The substrate was n-type Si.
The standard electrical characterization, reveals that the dielectric breakdown of T-GOX happens at higher voltage than for AFM-GOX. Moreover, the current level through AFM GOX at voltages below the breakdown value is several orders of magnitude larger than that measured at same voltages for thermal oxides. These differences could be caused by defects introduced during the AFM oxidation, performed in ambient air. However, a comparison between the IV curves of AFM-GOX and T-GOX measured by C-AFM shows that at a nanometer scale both oxides behave similarly.