CONDUCTING ATOMIC-FORCE MICROSCOPY STUDY OF SILICON DIOXIDE BREAKDOWN

A summary is given of an experimental method used to obtain the local dielectric strength of thin insulators using atomic force microscopy w ith conducting tips. This technique is applied to 7-15 nm thick SiO2 f ilms grown on either crystalline silicon or polysilicon substrates. Th e dielectric breakdown of the oxides over small areas (similar to 5X10 -(16) m(2)) follows that observed in the intrinsic breakdown of conven tional 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 t he oxide over some grains breaking down entirely. A difficulty when wo rking in air is that sample or tip contamination and induced growth of material under the tip lead to changes in either the effective barrie r height or local material thickness which are not related to the SiO2 film. These effects are discussed in detail. (C) 1995 American Vacuum Society.