Abstract
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 non-stoichiometric nature causing charge variations, which weaken the films electrical insulating capability.
Highlights
Alumina (Al2O3) is a material used as a functional layer in a range of CMOS and micro/nano-electromechanical system (M/NEMS) applications
We investigated the correlation between the composition, surface topography, and the electrical properties of ultra-thin Al2O3 films deposited on 200 mm diameter substrates by direct radio frequency (RF) magnetron sputtering
Thinner films are likely to have increased numbers of defects compromising the functionality of the film for its target application
Summary
Alumina (Al2O3) is a material used as a functional layer in a range of CMOS and micro/nano-electromechanical system (M/NEMS) applications. A significant drawback is that sputtering is a challenging technique for the deposition of ultra-thin films due to different growth mechanisms This may increase nucleation spots and columnar grain growth [15], leading to pinhole formation and other defects in the film. Electrodeposition (ED) has been employed recently as a possible way to evaluate defects in ultra-thin films including composition, topography and thickness that correlates to a change in electrical properties such as conductivity. The challenge in controlling defects and maintaining good insulating properties is increased as the substrate areas become larger This is in particular is a challenge for industrial scale processing where substrates may be up to 300 mm in diameter [15]. We investigated the correlation between the composition, surface topography, and the electrical properties of ultra-thin Al2O3 films deposited on 200 mm diameter substrates by direct RF magnetron sputtering. Energy dispersive x-rays (EDX) technique was used to determine the composition of the electrodeposited copper and to identify the growth mechanisms
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