Patent ID: 8492852

Claim:
A gate stack structure for field effect transistor (FET) devices, comprising: a nitrogen rich first dielectric layer formed over a semiconductor substrate surface; a nitrogen deficient, oxygen rich second dielectric layer formed on the nitrogen rich first dielectric layer, the first and second dielectric layers forming, in combination, a bi-layer interfacial layer; a high-k dielectric layer formed over the bi-layer interfacial layer, wherein both the nitrogen rich first dielectric layer and the nitrogen deficient, oxygen rich second dielectric layer comprising the bi-layer interfacial layer have a lower dielectric constant than the high-k dielectric layer; a metal gate conductor layer formed over the high-k dielectric layer; and a work function adjusting dopant species diffused within the high-k dielectric layer and beyond the high-k dielectric layer and into the nitrogen deficient, oxygen rich second dielectric layer disposed below the high-k dielectric layer, and wherein the nitrogen rich first dielectric layer serves to separate the work function adjusting dopant species from the semiconductor substrate surface.