Subfins replaced using backside dielectric formation

Abstract

Techniques are provided herein to form semiconductor devices that have their semiconductor subfins removed and replaced with one or more dielectric materials. A semiconductor device includes a gate structure around or otherwise on a semiconductor region. A lower end of the semiconductor material includes a subfin adjacent to a dielectric layer that acts as shallow trench isolation (STI) between semiconductor devices. A backside process may be performed to remove the bulk substrate and expose a bottom surface of the subfin. The subfin may then be removed from the backside to form backside recesses. A dielectric liner may be formed within the backside recesses and a dielectric fill may be formed within a remaining volume of the backside recesses. Replacing the subfins with dielectric materials may lower parasitic capacitance between the subfins and the gate electrodes as well as reduce parasitic current between adjacent source or drain regions.