In situ surface cleaning on a Ge substrate using TMA and MgCp₂ for HfO₂-based gate oxides

Comparative studies of the in situ surface cleaning effect on Ge substrates using trimethyl aluminum (TMA) and dicyclopentadienyl magnesium (MgCp₂) were performed. The surface cleaning process is the direct exposure of either a TMA or MgCp₂ precursor on a Ge surface prior to the deposition of a HfO₂ gate dielectric. Also, we studied a HfO₂/Al₂O₃ and MgO bilayer on uncleaned Ge using the same precursors for comparison with surface treatment. From the correlation of chemical composition, line profile, atomic scale imaging and electrical evaluation, MgCp₂ was the most effective method for reducing Ge diffusion into the HfO₂ dielectric layer via the efficient surface cleaning process. MgCp₂ cleaning produces thermally-stable Ge oxides while TMA cleaning reduces all types of Ge sub-oxides. As a result, the process can form a thermally-stable interface layer primarily composed of Ge³⁺, leading to better electrical properties than TMA.