Metal gates and manufacturing methods thereof

A semiconductor structure, comprising:

• a high-k metal gate structure (HKMG) over a channel region of a semiconductor layer formed over a substrate, the HKMG comprising:
• an interfacial layer disposed over the substrate,
• a high-k dielectric layer disposed over the interfacial layer, wherein the high-k dielectric layer and the interfacial layer have different widths, and
• a gate electrode disposed over and in physical contact with the high-k dielectric layer, wherein a width of a bottom surface of the gate electrode is less than a width of a top surface of the high-k dielectric layer, and wherein the gate electrode comprises a metal layer and a work function layer extending along a bottom surface and a sidewall surface of the metal layer, the metal layer comprises a shape of a trapezoid in a cross-section view;
• a source/drain feature disposed over the substrate and adjacent the HKMG;
• and
• a silicide layer in contact with the source/drain feature,
• wherein a portion of the silicide layer is disposed below a top surface of the source/drain feature.

A semiconductor structure, comprising:

• a high-k metal gate structure (HKMG) disposed over a channel region of a semiconductor layer formed over a substrate, the HKMG including:
• a high-k dielectric layer, and
• a gate electrode disposed over the high-k dielectric layer, wherein the gate electrode has a bottom surface physically in contact with the high-k dielectric layer and a top surface opposite the bottom surface, wherein, in a cross-section view, the top surface spans a first width, and the bottom surface spans a second width greater than the first width;
• gate spacers extending along a sidewall surface of the gate electrode and physically contacting a portion of a top surface of the high-k dielectric layer;
• source/drain features adjacent the HKMG and comprising a top surface and a sidewall surface above the semiconductor layer;
• and
• a silicide layer extending along the sidewall surface of the source/drain features.