C-AFM-based thickness determination of thin and ultra-thin SiO2 films by use of different conductive-coated probe tips

The influence of the probe tip type on the electrical oxide thickness result was researched for four differently coated conductive tip types using SiO2 (oxide) films with optical thickness of 1.7-8.3 nm. For this purpose, conductive atomic force microscopy (C-AFM) was used to measure more than 7200 current-voltage (IV) curves. The electrical oxide thickness was determined on a statistical basis from the IV-curves using a recently published tunnelling model for C-AFM application. The model includes parameters associated with the probe tip types used. The evolution of the tip parameters is described in detail. For the theoretical tip parameters, measured and calculated IV-curves showed excellent agreement and the electrical oxide thickness versus the optical oxide thickness showed congruent behaviour, independent of the tip type. However, differences in the electrical oxide thickness were observed for the different tip types. The theoretical parameters were modified experimentally in order to reduce these differences. Theoretical and experimental tip parameters were compared and their effect on the differences in the electrical oxide thickness is discussed for the different tip types. Overall, it is shown that the proposed model provides a comprehensive framework for determining the electrical oxide thickness using C-AFM, for a wide range of oxide thicknesses and for differently coated conductive tips.