Patent ID: 7936025

Claim:
A MOS transistor structure comprising: a gate dielectric layer; and a gate electrode structure on the gate dielectric layer that comprises a first metallic layer having a first work function on top of the gate dielectric layer, wherein the first metallic layer has a first thickness from 10 to 25 angstroms, a second metallic layer having a second work function on the first metallic layer, wherein the second metallic layer has a second thickness that does not exceed 150 angstroms, wherein the second metallic layer has a conductivity and density of states higher than the first metallic layer, wherein the first work function is overcome by the second work function, and a third metallic layer on the second metallic layer, wherein the third metallic layer has a third thickness that does not exceed 50 angstroms; and a polysilicon layer on top of the third metallic layer, wherein the gate electrode structure has an overall work function, wherein the second metallic layer having the second work function sets the overall work function of the gate electrode structure, wherein the first metallic layer acts as a diffusion barrier between the gate dielectric layer and the second metallic layer and the third metallic layer acts as a silicidation barrier between the second metallic layer and the polysilicon layer, wherein first metallic layer includes zirconium added to titanium nitride or tantalum nitride.