Atomic Layer Densification of AlN Passivation Layer on Epitaxial Ge for Enhancement of Reliability and Electrical Performance of High-K Gate Stacks

The impact of atomic layer bombardment (ALB) on the aluminum nitride (AlN) passivation layer between the HfO2 gate dielectric and the n-type epitaxial germanium (Ge) was investigated. The ALB technique was performed with the layer-by-layer, in situ helium/argon plasma bombardment in each cycle of atomic layer deposition (ALD) of AlN. An increase in the film density and a decrease in nitrogen vacancies, as manifested by the X-ray reflection and X-ray spectroscopy, were observed in the AlN layer treated by the ALB process. The improvements in the AlN quality contribute to a reduction of the equivalent oxide thickness from 1.36 to 1.19 nm of the AlN/HfO2 gate stack, together with the suppression of the gate leakage current, the interfacial state density, and the slow trap density. The reliability tests reveal promising reliability of the AlN/HfO2 gate stack with a small flat-band voltage shift under the constant voltage stress and a high operation voltage of ∼2.4 V projected for a 10 years time-dependent-dielectric-breakdown lifetime. All of the results point that the ALB technique can effectively enhance the material/interface properties, electrical characteristics, and reliability of nanoscale devices, which is critical and beneficial to the next-generation high-speed and low-power nanoelectronics.