Yttrium–scandium oxide as high-k gate dielectric for germanium metal–oxide–semiconductor devices

The feasibility of employing yttrium?scandium oxide (YScOx) as high-k gate dielectrics for germanium-metal?oxide?semiconductor (MOS) devices has been investigated. The composition and chemical structures of the film were studied using x-ray photoelectron spectroscopy (XPS). Conduction and valence band discontinuities at YScOx/Ge (1?0?0) interfaces were also determined by measuring the O 1s photoelectron energy loss and valence band spectra. Indeed, high-k (YScOx)/Ge MOS characteristics, exhibiting fairly good electrical characteristics, especially low leakage current density and low density of interface states, have been achieved due to the formation of stable Y-Sc-germanate at the interface. The effects of various scandium oxide (ScO) concentrations in YScOx on the electrical characteristics are also reported. It has been demonstrated that higher ScO concentration in YScOx may cause Vfb to shift to its even lower positive value even if considering hysteresis while it causes degradation in interfacial properties. Besides, the effects of several annealing treatments have been investigated in order to optimize the process conditions. This work suggests that ScO concentration up to 50% in YScOx along with post-metallization annealing treatment at 500 ?C will be the key to ensure reasonable electrical performance of Ge MOS devices.