Metal gate structures and methods for forming thereof

A method for forming a metal gate structure on a substrate having a feature formed in a high k dielectric layer, comprising:

• depositing a first layer within the feature atop the dielectric layer, wherein the first layer is a barrier layer;
• depositing a second layer within the feature atop the first layer, wherein the second layer acts as a work function layer and a wetting layer to form a nucleation layer for a subsequently deposited layer;
• and
• depositing a third layer comprising aluminum (Al) within the feature atop the second layer to fill the feature, wherein the third layer forms a metal gate electrode.

A metal gate structure comprising:

• a first layer disposed within a feature formed in a dielectric layer of a substrate;
• a second layer comprising cobalt or nickel disposed above the first layer within the feature;
• and
• a third layer comprising a metal disposed above the second layer within the feature, wherein the third layer fills the feature, wherein at least one of the first or second layers forms a wetting layer to form a nucleation layer for a subsequently deposited layer, wherein one of the first, second, or third layers forms a work function layer, and wherein the third layer forms a gate electrode.

A metal gate structure, comprising:

• a first layer disposed within a feature formed in a dielectric layer of a substrate, wherein the first layer is a barrier layer;
• a second layer disposed above the first layer within the feature, wherein the second layer is a work function layer and a wetting layer to form a nucleation layer for a subsequently deposited layer;
• and
• a third layer comprising aluminum disposed above the second layer within the feature, wherein the third layer forms a gate electrode.