Metal gates and manufacturing methods thereof

1. A method, comprising:

providing a semiconductor layer;

forming an interfacial layer over the semiconductor layer;

depositing a high-k dielectric layer over the interfacial layer;

forming a dummy gate electrode layer over the high-k dielectric layer;

patterning the dummy gate electrode layer, the high-k dielectric layer, and the interfacial layer, resulting in the interfacial layer having a width greater than a width of the high-k dielectric layer;

after the patterning, forming spacers along sidewalls of the dummy gate electrode, the high-k dielectric layer, and the interfacial layer;

forming source/drain features;

replacing the dummy gate electrode with a metal gate electrode to form a high-k metal gate structure;

after the depositing of the high-k dielectric layer and before the forming of the dummy gate electrode depositing a capping layer over the high-k dielectric layer;

performing a spike anneal process to the capping layer in a nitrogen environment; and

removing the capping layer before the replacing of the dummy gate electrode.

2. A method, comprising:

providing a semiconductor layer;

forming an interfacial layer over the semiconductor layer;

depositing a high-k dielectric layer over the interfacial layer;

forming a dummy gate electrode layer over the high-k dielectric layer;

patterning the dummy gate electrode layer, the high-k dielectric layer, and the interfacial layer, resulting in the interfacial layer having a width greater than a width of the high-k dielectric layer;

after the patterning, forming spacers along sidewalls of the dummy gate electrode, the high-k dielectric layer, and the interfacial layer;

forming source/drain features;

replacing the dummy gate electrode with a metal gate electrode to form a high-k metal gate structure;

after the depositing of the high-k dielectric layer and before the forming of the dummy gate electrode, depositing a capping layer over the high-k dielectric layer;

before the forming of the dummy gate electrode, depositing a silicon-containing capping layer over the capping layer;

performing a spike anneal process to the silicon-containing capping layer; and

removing the silicon-containing capping layer.

3. A semiconductor structure, comprising:

a high-k metal gate structure (HKMG) disposed over a channel region of a semiconductor layer that is disposed over a substrate, the HKMG including:

an interfacial layer disposed over the semiconductor layer, the interfacial layer having a first length along a first direction;

a high-k dielectric layer disposed over the interfacial layer, the high-k dielectric layer having a second length along the first direction, wherein the second length is less than the first length; and

an electrode disposed over the high-k dielectric layer, the electrode having a third length along the first direction, wherein the second length is greater than the third length, and wherein a distance between an outer edge of the electrode and an outer edge of the high-k dielectric layer is less than a distance between the outer edge of the electrode and an outer edge of the interfacial layer;

gate spacers disposed along sidewalls of the electrode, wherein bottom portions of the gate spacers contact a top surface of the high-k dielectric layer;

source/drain features disposed in the semiconductor layer on opposite sides of the HKMG; and

a contact plug disposed over each of the source/drain features.