A method includes providing a structure having two fins extending from a substrate and an isolation structure adjacent to lower portions of the fins; forming a cladding layer over the isolation structure and over top and sidewalls of the fins; recessing the isolation structure using the cladding layer as an etch mask to expose the substrate; after the recessing of the isolation structure, depositing a seal layer over the substrate, the isolation structure, and the cladding layer; forming a sacrificial plug over the seal layer and between the two fins; and depositing a dielectric top cover over the sacrificial plug and laterally between the two fins.