Conducting atomic force microscopy study of silicon dioxide breakdown

Abstract

A summary is given of an experimental method used to obtain the local dielectric strength of thin insulators using atomic force microscopy with conducting tips. This technique is applied to 7-15 nm thick SiO2, films grown on either crystalline silicon or polysilicon substrates. The dielectric breakdown of the oxides over small areas (approx.5×10-16 m2) follows that observed in the intrinsic breakdown of conventional metal-oxide-semiconductor structures, with a maximum breakdown field of 13.2±0.8 MV/cm. On the polycrystalline samples variation in dielectric strength between individual grains can be observed, with the oxide over some grains breaking down entirely. A difficulty when working in air is that sample or tip contamination and induced growth of material under the tip lead to changes in either the effective barrier height or local material thickness which are not related to the SiO2 film. These effects are discussed in detail.