Semiconductor device and manufacturing method thereof

A semiconductor device, comprising:

• a substrate;
• a semiconductor fin over the substrate;
• a shallow trench isolation (STI) structure laterally surrounding the semiconductor fin;
• a semiconductor layer crossing the semiconductor fin;
• a gate structure over the semiconductor fin, wherein the gate structure comprises:
• an interfacial layer over the semiconductor layer;
• a gate dielectric layer over the interfacial layer, wherein the semiconductor layer, the interfacial layer, and the gate dielectric layer are in contact with the STI structure;
• and
• a gate electrode over the gate dielectric layer;
• gate spacers on opposite sidewalls of the gate structure, wherein the semiconductor layer and the interfacial layer are in contact with the gate spacers;
• and
• source/drain structures on opposite sides of the gate structure.

A semiconductor device, comprising:

• a germanium substrate;
• a silicon cap over the germanium substrate;
• a gate structure over the silicon cap, wherein the gate structure comprises:
• an oxide layer over the silicon cap;
• a high-k dielectric layer over the oxide layer;
• and
• a gate electrode over the high-k dielectric layer;
• gate spacers on opposite sidewalls of the gate structure;
• and
• source/drain structures on opposite sides of the gate structure.