Method and structure for air gap inner spacer in gate-all-around devices

Abstract

A method includes providing a structure having a substrate and a fin. The fin has first and second layers of first and second different semiconductor materials. The first layers and the second layers are alternately stacked over the substrate. The structure further has a sacrificial gate stack engaging a channel region of the fin and gate spacers on sidewalls of the sacrificial gate stack. The method further includes etching a source/drain (S/D) region of the fin, resulting in an S/D trench; partially recessing the second layers exposed in the S/D trench, resulting in a gap between two adjacent layers of the first layers; and depositing a dielectric layer over surfaces of the gate spacers, the first layers, and the second layers. The dielectric layer partially fills the gap, leaving a void sandwiched between the dielectric layer on the two adjacent layers of the first layers.