Desorption kinetics of GeO from GeO2/Ge structure

Abstract

High-κ dielectrics on Ge have recently attracted much attention as a potential candidate to replace planar silicon transistors for sub-32-nm generations. However, the instability of the high-κ/Ge interface, especially the desorption of germanium monoxide (GeO), hampers the development of Ge-based devices. Therefore, the typical GeO2/Ge structure was chosen to investigate GeO desorption. In this contribution, we describe the desorption kinetics of GeO, including Ge/GeO2 interface reaction, the diffusion process during GeO desorption, the desorption activation energy of GeO, the different mechanisms of GeO desorption, and the active oxidation of Ge. Through annealing GeO2/Ge in an ultrahigh vacuum (UHV), direct evidence for the consumption of Ge substrate has been shown by atomic force microscopy (AFM) measurements of the consumption depth. By using thermal desorption spectroscopy (TDS) measurements and studying oxygen-18 isotope tracing, we have clarified that the GeO desorption is not caused by the GeO direct-diffusion process. Isothermal TDS measurements and morphology investigation have revealed a transition from a uniform desorption mechanism to a nonuniform one as GeO2 thickness was reduced. On the basis of the experimental results in this study, a GeO desorption model has been developed. For GeO desorption, about 2 eV of activation energy has been obtained from kinetic calculation on the basis of TDS analysis. Different from the UHV annealing, the active oxidation of Ge has been observed by AFM measurements under low oxygen partial pressures.