The Impact of HC1 Precleaning and Sulfur Passivation on the Al2O3/Ge Interface in Ge Metal-Oxide-Semiconductor Capacitors

Surface treatment for Ge substrates using hydrogen chlorine cleaning and chemical passivation are investigated on AuTi/Al2O3/Ge metal-oxide-semiconductor capacitors.After hydrogen chlorine cleaning,a smooth Ge surface almost free from native oxide is demonstrated by atomic force microscopy and x-ray photoelectron spectroscopy observations.Passivation using a hydrogen chlorine solution is found to form a chlorine-terminated surface,while aqueous ammonium sulfide pretreatment results in a surface terminated by Ge-S bonding.Compared with chlorine-passivated samples,the sulfur-passivated ones show less frequency dispersion and better thermal stability based on capacitance-voltage characterizations.The samples with HCl pre-cleaning and (NH4 )2S passivation show less frequency dispersion than the HF pre-cleaning and (NH4)2S passivated ones.The surface treatment process using hydrogen chlorine cleaning followed by aqueous ammonium sulfide passivation demonstrates a promising way to improve gate dielectric/Ge interface quality.