Synthesis of model Al-Al2O3 multilayer systems with monolayer oxide thickness control by circumventing native oxidation

Abstract

A hybrid thin film deposition system was built by combining physical vapor deposition (PVD) with atomic layer deposition (ALD) without breaking high vacuum, which was achieved by a chamber-in-chamber design. The vacuum is better than 1 × 10−5 Pa during the entire sample transfer process between the ALD and PVD chambers. The Al-Al2O3 multilayers synthesized by the PVD-ALD integrated system consist of ALD Al2O3 sublayers between pure PVD Al sublayers. The Al2O3 sublayers, with incremental thickness of 1 nm from 1 to 10 nm, effectively interrupted the grain growth of the ~250 nm thick Al sublayers. Native surface oxide formation on the PVD deposited pure Al sublayers was circumvented by keeping the substrate in high vacuum between processing steps. The pure Al sublayers are constituted of equiaxed grains with no epitaxial or texture relationship with the neighboring layers. The Al grain boundaries are parallel to the film growth direction and extend the height of each Al sublayer, to form a brick-and-mortar type microstructure. In this system, ALD allows precise control of the thickness of each ultrathin Al2O3 layer, to thicknesses below the native surface oxide thickness of pure Al, and avoids further natural oxidation through the low-oxygen environment of the PVD-ALD system.