Effective Work Function Modulation by As Implantation in Metal Gate Stacks.

Abstract

The impact of As implantation through TiN/TaN/HfO2, TiN/HfO2, TiN/TaN/SiON and TiN/SiON metal gate stacks on the effective WF was investigated. The effective WF was estimated based on the flatband voltage (VFB) shift for one dielectric thickness. The As implantation at 20 KeV influences the VFB shift for TiN/TaN/HfO2 by a maximum of 600 mV at an implanted dose of 5E15 cm-2. The shift in VFB is correlated to the As pile-up at the TaN-HfO2 interface, as evidenced by SIMS profile. The increasing dose of As ions resulted in an increase in VFB shift compared to un-implanted gate stack. This was related to the increase in As concentration at the TaN-HfO2 interface. It is suggested that As ions introduced as impurities at the interface of the gate electrode and the gate dielectric could induce interface dipole contributing to the work function of the gate stack resulting in a flat band voltage shift.