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.