Al2O3/GeO2 stacked gate dielectrics formed by post-deposition oxidation of ultrathin metal Al layer directly grown on Ge substrates

A simple and effective method for fabricating high-quality Al2O3/GeO2 gate dielectrics is proposed. Direct deposition of ultrathin Al layers several angstroms thick on cleaned Ge surfaces followed by conventional dry oxidation was shown to form Al2O3/GeO2 stacked structures. Precise control of interface GeO2 growth was achieved due to low oxygen diffusivity in the Al2O3 layer. Experimental results demonstrated that, in addition to post-oxidation conditions, Al thickness is a crucial parameter for creating high-quality Ge-MOS interfaces and equivalent oxide thickness (EOT) scaling of the gate dielectrics. A correlation between electrical properties and atomic bonding features at the oxide interface was identified by multi-frequency capacitance–voltage (C–V) measurements and x-ray photoelectron spectroscopy observation. An EOT scaled down to 1.2 nm and an interface state density (Dit) in the lower half of the 1011 cm−2 eV−1 were achieved under the optimized fabrication conditions.