Interface structure for channel mobility improvement in high-k metal gate stack

A high-k metal 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 hafnium based, high-k dielectric layer formed over the bi-layer interfacial layer;
• a metal gate conductor layer formed over the high-k dielectric layer;
• and
• a lanthanum dopant species diffused within the high-k dielectric layer and within the nitrogen deficient, oxygen rich second dielectric layer, forming a high-k lanthanum oxide therein, and wherein the nitrogen rich first dielectric layer serves to separate the high-k lanthanum oxide from the semiconductor substrate surface.

A method of forming gate stack structure for field effect transistor (FET) devices, the method comprising:

• forming a nitrogen rich first dielectric layer over a semiconductor substrate surface;
• forming a nitrogen deficient, oxygen rich second dielectric layer on the nitrogen rich first dielectric layer, the first and second dielectric layers defining, in combination, a bi-layer interfacial layer;
• forming a high-k dielectric layer over the bi-layer interfacial layer;
• forming a metal gate conductor layer over the high-k dielectric layer;
• and
• diffusing a work function adjusting dopant species within the high-k dielectric layer and within the nitrogen deficient, oxygen rich second dielectric layer, and wherein the nitrogen rich first dielectric layer serves to separate the work function adjusting dopant species from the semiconductor substrate surface.