Interfacial Reaction Mechanisms in Al2O3/Ge Structure by Oxygen Radical Process

Abstract

We have investigated the impacts of the oxygen radical process on the interfacial structures and electrical properties of Al2O3/Ge structures to clarify the interfacial reaction mechanisms. At a low process temperature, the oxygen radical process can introduce oxygen atoms to the Al2O3/Ge interface without a thermally activated process in spite of the high barrier property of the oxygen diffusion for the Al2O3 layers. In addition, the oxygen radical process at a low process temperature can relatively suppress the diffusion of Ge atoms from the Ge substrate or GeO molecules from the Al2O3/Ge interface to the surface of the Al2O3 layer. However, at a high process temperature, Ge atoms and/or GeO molecules actively diffuse into the Al2O3 layer during the oxygen radical process as well as the O2 thermal annealing, and the diffusion changes the depth distribution of Ge oxides in the Al2O3/Ge structure. From the analysis of the electrical properties of MOS capacitors, the interface state density (Dit) of the Al2O3/Ge structure decreases not with increasing thickness of the Ge oxide interlayer but with the amount of Ge oxide near the Al2O3/Ge interface. The increase in the amount of the Ge oxide distributed in the Al2O3 layer induces the increase in the capacitance equivalent thickness (CET). The diffusion of Ge into the Al2O3 layer with a high process temperature causes the unexpected increase in CET. Therefore, the oxygen radical process at low temperature effectively decreases Dit of Al/Al2O3/Ge MOS capacitors without increasing CET.