Nanoscale topography, surface charge variation and defect correlation in 2–8 nm thick functional alumina films

In the nanometric regime, alumina films are often deposited by ALD methods yet in industrial applications, sputtered films thinner than 40 nm are used and research into those is sparse. Here, we investigated the nanoscale topography and the electrical properties of films less than 10 nm thick deposited by direct RF magnetron sputtering. Alumina films deposited on Si appeared to be uniform and topographically defect free as evaluated by TEM and AFM. However, their composition varied as a function of thickness as measured by XPS. The films were non-stoichiometric as Al content increased with film thickness. While SSRM measured current profiles did not highlight leakage sites or voids in the films, KPFM measured local charge fluctuations across the films deposited on Si and Au surfaces. The density of fluctuation sites decreased with an increase of alumina thickness. An electrodeposition method identified insulation weak spots in the alumina where Cu growths formed on the alumina surface. The growth mechanisms were investigated by TEM and EDX. The density of growths decreased with increased alumina thickness. Defects in the deposited alumina film are expected to be due to its nonstoichiometric nature causing charge variations, which weaken the films electrical insulating capability.