Semiconductor device and forming method thereof

Abstract

Semiconductor devices and methods of forming the same are provided. An exemplary method includes forming a superlattice structure over a substrate, the superlattice structure comprising an upper portion separated from a lower portion by an insulation layer, wherein the insulation layer comprises a crystalline metal oxide, patterning the superlattice structure to form a fin protruding from the substrate, forming a dummy gate stack over a first portion of the fin, recessing a second portion of the fin not covered by the dummy gate stack to form a source / drain trench, forming a first source / drain feature in the source / drain trench and coupled to the lower portion of the superlattice structure, forming a second source / drain feature in the source / drain trench and coupled to the upper portion of the superlattice, and replacing the dummy gate stack by a gate structure.