Multiple gate field-effect transistors having various gate oxide thicknesses and methods of forming the same

Abstract

A semiconductor device includes a first transistor located in a first region of a substrate and a second transistor located in a second region of the substrate. The first transistor includes first channel members vertically stacked above the substrate and a first gate structure wrapping around each of the first channel members. The first gate structure includes a first interfacial layer. The second transistor includes second channel members vertically stacked above the substrate and a second gate structure wrapping around each of the second channel members. The second gate structure includes a second interfacial layer. The second interfacial layer has a first sub-layer and a second sub-layer over the first sub-layer. The first and second sub-layers include different material compositions. A total thickness of the first and second sub-layers is larger than a thickness of the first interfacial layer.