Semiconductor structure and method for manufacturing the same

A semiconductor structure, comprising:

• channel layers over a substrate;
• first inner spacers around over the channel layers;
• second inner spacers around under the channel layers;
• an isolation structure between the second inner spacers;
• first source/drain features over the channel layers;
• second source/drain features under the channel layers;
• a gate dielectric layer covering sidewalls of the channel layers, the first inner spacers, and the second inner spacers;
• a first work function layer on the gate dielectric layer;
• a second work function layer interfacing the first work function layer and the gate dielectric layer;
• and
• a metal material wrapping around the second work function layer.

A method for manufacturing a semiconductor structure, comprising:

• forming a channel layer over a substrate;
• forming a first inner spacer over the channel layer;
• forming a second inner spacer under the channel layer;
• forming a first source/drain feature over the channel layer and the first inner spacer;
• removing a portion of the channel layer between the first inner spacer and the second inner spacer;
• forming a gate dielectric layer wrapping around the channel layer;
• forming a first work function layer wrapping around the gate dielectric layer;
• forming a second work function layer wrapping around the first work function layer, wherein a top surface of the second work function layer is higher than a top surface of the first inner spacer;
• forming a metal material wrapping around the second work function layer;
• and
• forming a second source/drain feature under the channel layer and the second inner spacer.