Insights into thermal diffusion of germanium and oxygen atoms in HfO_2/GeO_2/Ge gate stacks and their suppressed reaction with atomically thin AlO_x interlayers

摘要

The thermal diffusion of germanium and oxygen atoms in HfO_2/GeO_2/Ge gate stacks was comprehensively evaluated by x-ray photoelectron spectroscopy and secondary ion mass spectrom-etry combined with an isotopic labeling technique. It was found that ~(18)O-tracers composing the GeO_2 underlayers diffuse within the HfO_2 overlayers based on Fick's law with the low activation energy of about 0.5 eV. Although out-diffusion of the germanium atoms through HfO_2 also proceeded at the low temperatures of around 200 ℃, the diffusing germanium atoms preferentially segregated on the HfO_2 surfaces, and the reaction was further enhanced at high temperatures with the assistance of GeO desorption. A technique to insert atomically thin AlO_x interlayers between the HfO_2 and GeO_2 layers was proven to effectively suppress both of these independent germanium and oxygen intermixing reactions in the gate stacks.