US Patent 11664280 Semiconductor devices with backside air gap dielectric

A semiconductor structure has a frontside and a backside. The semiconductor structure includes an isolation structure at the backside; one or more transistors at the frontside, wherein the one or more transistors have source/drain electrodes; two metal plugs through the isolation structure and contacting two of the source/drain electrodes from the backside, wherein the two metal plugs and the isolation structure form sidewalls of a trench; and a dielectric liner on the sidewalls of the trench, wherein the dielectric liner partially or fully surrounds an air gap within the trench.