Using a modified atomic force microscope (AFM) with a conducting cantilever, we have investigated the dielectric strength of SiO2 gate oxide films. This has been achieved by spatially resolving the prebreakdown tunneling current flowing between the silicon substrate and tip. During AFM imaging a voltage ramp was applied to the tip at each image point so as to determine the local threshold voltage required to generate a small tunneling current in the oxide, without causing an irreversible electrical breakdown. For an oxide 12-nm thick this voltage was found to vary by more than a factor of 2.7 over an area of 0.14 μm2, with a maximum value of 40.5 V. This suggests that the breakdown strength of conventional metal-oxide-silicon capacitors may not be limited by the intrinsic dielectric strength of the oxide, but by imperfections or nonuniformities in the Si/SiO2 structure. By preventing irreversible oxide breakdown during scanning, we can image the dielectric properties of oxide films with a lateral resolution better than 20 nm.
We used local probe techniques to characterize electron beam ͑e-beam͒ induced changes in thin oxides on silicon. Primary effects of the 1 nm wide, 300 keV e beam included the formation of positive charges trapped in the SiO 2 , physical restructuring in the oxide, and deposition of carbonaceous compounds. Charges remained stable in thicker oxides ͑460 nm͒ and appeared as changes in the contact potential or microwave response with widths down to 100 nm. In thinner oxides ͑20 nm͒ the amount of charge was smaller and less stable; below 7 nm no charge was detected. Physical changes in the oxide, evident as a swelling of irradiated areas, accounted for the etching selectivity of these regions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.