Impact of AlTaO Dielectric Capping on Device Performance and Reliability for Advanced Metal Gate/High-$k$ PMOS Application

摘要

We have investigated the effect of ultrathin Al–Ta-based capping layers on $hbox{HfO}_{2}$ and experimentally demonstrated that, with proper Al and Ta composition, an AlTaO capping layer is a good candidate dielectric for PMOSFET devices. Lower threshold voltage and significantly improved mobility were observed with AlTaO capping without degrading the dielectric properties. The addition of Ta in an AlTaO structure produces d-states in the $hbox{Al}_{2}hbox{O}_{3}$ matrix, resulting in an additional $V_{T}$ shift toward the PMOS band edge. This AlTaO capping layer not only modulates the device $V_{T}$ suitably for PMOS applications but also retards Al diffusion through the $hbox{HfO}_{2}$ layer, preventing Al-caused mobility degradation. Furthermore, the incorporation of a capping layer can improve reliability characteristics during the negative bias stress.