Metal gate electrode of a field effect transistor

A method of fabricating a metal gate electrode of a field effect transistor comprising:

• forming a dielectric layer over a substrate comprising an isolation region surrounding an active region, wherein the dielectric layer is over the active region;
• forming an opening in the dielectric layer;
• filling the opening, wherein filling the opening comprises filling the opening with a high-dielectric-constant material, a conformal first metal material over the high-dielectric-constant material, and a capping layer over the first metal material;
• planarizing the capping layer to expose the high-dielectric-constant material;
• partially removing the first metal material and capping layer in the opening using a wet etching process, the first metal material having a maximum thickness ranging from about 1.5 nanometers (nm) to 45 nm;
• fully removing the remaining capping layer in the opening using a wet etching process in a solution comprising NH4OH and diluted HF;
• depositing a second metal material in the opening over the remaining first metal material.

A method of fabricating a metal gate electrode of a field effect transistor comprising:

• forming a dielectric layer over a substrate comprising an isolation region surrounding an active region, wherein the dielectric layer is over the active region;
• forming an opening in the dielectric layer;
• forming a metal electrode in the opening, forming the metal electrode comprises:
• forming a lower portion formed of a first metal material, wherein the lower portion has a recess, a bottom portion and sidewall portions, wherein each of the sidewall portions has a first width;
• and
• forming an upper portion, wherein the upper portion has a protrusion and a bulk portion, wherein the bulk portion has a second width, wherein the protrusion extends into the recess, wherein a ratio of the second width to the first width is from about 5 to 10, and the upper portion comprises a second metal material surrounding a signal metal, the signal metal having a substantially constant width.