Replacement metal gate stack for diffusion prevention

A method of forming a semiconductor structure, the method comprising:

• depositing a gate dielectric layer lining a recess of a gate structure formed on a substrate, a first portion of the gate dielectric layer covering sidewalls of the recess and a second portion of the gate dielectric layer covering a bottom of the recess;
• depositing a protective layer above the gate dielectric layer, the protective layer substantially filling the recess;
• recessing the protective layer selectively to the gate dielectric layer, wherein a top surface of the protective layer is below of the recess;
• recessing the first portion of the gate dielectric layer until a top of the first portion of the gate dielectric layer is approximately coplanar with the top surface of the protective layer, wherein the protective layer protects the second portion of the gate dielectric layer while recessing the first portion of the gate dielectric layer;
• removing the protective layer;
• depositing a conductive barrier above the recessed first portion of the gate dielectric layer;
• depositing a metal gate above the conductive barrier;
• and
• forming a capping layer above the metal gate, wherein the conductive barrier separates the capping layer from the recessed first portion of the gate dielectric layer.