Gate all around transistor device and fabrication methods thereof

Abstract

Embodiments of the present disclosure includes a semiconductor device. The semiconductor device includes first suspended nanostructures vertically stacked over one another and disposed on a substrate, a first gate stack engaging the first suspended nanostructures, a first gate spacer disposed on sidewalls of the first gate stack, second suspended nanostructures vertically stacked over one another and disposed on the substrate, a second gate stack engaging the second suspended nanostructures, and a second gate spacer disposed on sidewalls of the second gate stack. A middle portion of the first suspended nanostructures has a first thickness measured in a direction perpendicular to a top surface of the substrate. A middle portion of the second suspended nanostructures has a second thickness measured in the direction. The second thickness is smaller than the first thickness.