Abstract: A method includes providing a substrate, forming a patterned hard mask layer over the substrate, etching the patterned hard mask layer to form a hole that penetrates the patterned hard mask layer, forming a barrier portion in the hole, removing the patterned hard mask layer, and forming a gate structure over the substrate. Formation of the gate structure includes forming a dielectric body portion on the substrate. The barrier portion that is thicker than the dielectric body portion adjoins one end of the dielectric body portion. The dielectric body portion and the barrier portion are collectively referred to as a gate dielectric layer. Formation of the gate structure further includes forming a gate electrode on the gate dielectric layer and forming gate spacers on opposite sidewalls of the gate electrode. During formation of the gate spacers, a portion of the barrier portion is removed to form a recessed corner.

Abstract: A semiconductor device includes a source/drain feature over a semiconductor substrate, channel layers over the semiconductor substrate and connected to the source/drain feature, a gate portion between vertically adjacent channel layers, and an inner spacer between the source/drain feature and the gate portion and between adjacent channel layers. The semiconductor device further includes an air gap between the inner spacer and the source/drain feature.