Method to recess cobalt for gate metal application

A method of forming a semiconductor structure comprising:

• providing a structure comprising a gate cavity exposing a portion of a semiconductor material portion, wherein a gate spacer surrounds the gate cavity;
• forming a material stack comprising, from bottom to top, a gate dielectric, a work function metal and a cobalt gate electrode within the gate cavity;
• recessing the cobalt gate electrode, wherein the recessing the cobalt gate electrode is performed by repeating steps of oxidizing the cobalt gate electrode utilizing an oxidizing agent to form a cobalt oxide layer on a surface of a remaining portion of the cobalt gate electrode and removing the cobalt oxide layer utilizing a chemical wet etch that is performed under an oxygen environment having an oxygen concentration of less than 10,000 ppm;
• recessing the work function metal;
• recessing the gate dielectric;
• and
• forming a gate cap above the recessed cobalt gate electrode to completely fill the gate cavity.

A method of forming a semiconductor structure comprising:

• providing a structure comprising a gate cavity exposing a portion of a semiconductor material portion, wherein a gate spacer surrounds the gate cavity;
• forming a material stack comprising, from bottom to top, a gate dielectric, a work function metal and a cobalt gate electrode within the gate cavity, wherein the work function metal comprises TiN;
• recessing the cobalt gate electrode, wherein the recessing the cobalt gate electrode is performed by repeating steps of oxidizing the cobalt gate electrode utilizing an oxidizing agent to form a cobalt oxide layer on a surface of a remaining portion of the cobalt gate electrode and removing the cobalt oxide layer utilizing a chemical wet etch;
• recessing the work function metal, wherein the recessing of the work function metal comprises using a H2O2 solution that is heated to a temperature above 70° C. or an SC-1 solution containing a mixture of H2O2 and an ammonia-derived base, wherein the ammonia-derived base comprises NH4OH or quaternary NH4OH, and the SC-1 solution is heated to a temperature above 70° C.;
• recessing the gate dielectric;
• and
• forming a gate cap above the recessed cobalt gate electrode to completely fill the gate cavity.