Multi-gate transistors and methods of forming the same

A semiconductor structure, comprising:

• a first source/drain feature and a second source/drain feature disposed over a substrate;
• a plurality of channel members extending between the first source/drain feature and the second source/drain feature, wherein each of the plurality of channel members comprises a semiconductor layer sandwiched between two cap layers along a direction perpendicular to the substrate;
• and
• a gate structure wrapping around each of the plurality of channel members,
• wherein the gate structure is in direct contact with the semiconductor layer and the two cap layers of each of the plurality of channel members.

A method, comprising:

• depositing a buffer layer over a substrate;
• forming a stack on the buffer layer, wherein the stack comprises:
• a plurality of channel layers,
• a plurality of sacrificial layers interleaving the plurality of channel layers, and
• at least one cap layer disposed between each of the plurality of channel layers and an adjacent one of the plurality of sacrificial layers;
• forming a fin-shaped structure from the stack, the buffer layer and the substrate, the fin-shaped structure comprising a channel region and a source/drain region,
• forming a dummy gate stack over the channel region of the fin-shaped structure;
• depositing a gate spacer layer over the dummy gate stack;
• recessing the source/drain region to form a source/drain trench that exposes sidewalls of the plurality of channel layers and the plurality of sacrificial layers;
• selectively and partially recessing the plurality of sacrificial layers and a portion of the at least one cap layer to form a plurality of inner spacer recesses;
• forming a plurality of inner spacer features in the plurality of inner spacer recesses;
• forming a source/drain feature in the source/drain trench;
• removing the dummy gate stack;
• selectively removing the plurality of sacrificial layers to release the plurality of channel layers in the channel region as a plurality of channel members;
• and
• forming a gate structure around each of the plurality of channel members,
• wherein a composition of the at least one cap layer is different from a composition of the plurality of channel layers or a composition of the plurality of sacrificial layers.