Nanoscale gadolinium oxide capping layers on compositionally variant gate dielectrics

Metal gate work function enhancement using nanoscale (1.0 nm) $Gd2O3$ interfacial layers has been evaluated as a function of silicon oxide content in the $HfxSiyOz$ gate dielectric and process thermal budget. It is found that the effective work function tuning by the $Gd2O3$ capping layer varied by nearly 400 mV as the composition of the underlying dielectric changed from 0% to 100% $SiO2$⁠, and by nearly 300 mV as the maximum process temperature increased from ambient to $1000°C$⁠. A qualitative model is proposed to explain these results, expanding the existing models for the lanthanide capping layer effect.