Investigating doping effects on high-κ metal gate stack for effective work function engineering

• La, Al or Mg in high-κ metal gate stack induce shifts in effective work function.
• Roll-off adds to effective work function shift for La and Mg and is opposite for Al.
• Shift in effective work function is identified as a dipole at SiO2/high-κ interface.
• Interfacial Hf substitution by La and Mg shifts work function towards N+.
• Interfacial Hf substitution by Al shifts work function towards P+ levels.

The impact of additives (La, Al and Mg) at the SiO2/high-κ interface has been investigated through ab initio simulations and electrical measurements. Various gate stacks with additive below or the above high-κ dielectric are compared. Combination of capacitance versus gate bias measurement and internal photon emission is performed to demonstrate that the threshold voltage shift is related to a dipole formation at the SiO2/high-κ interface. The respective roles of aluminum and lanthanum are clearly identified as well as their sensitivity to roll-off. Impact of additive on metal gate function is studied. Finally, ab initio enables an analysis of the dipole formation with additive at the SiO2/HfO2 interface.