Semiconductor devices with enclosed void cavities

Abstract

Field effect devices and ICs with very low gate-drain capacitance Cgd are provided by forming a substantially empty void between the gate and the drain regions. For vertical FETS a cavity is etched in the semiconductor (SC) and provided with a gate dielectric liner. A poly-SC gate deposited in the cavity has a central fissure (empty pipe) extending through to the underlying SC. This fissure is used to etch the void in the SC beneath the poly-gate. The fissure is then closed by a dielectric plug formed by deposition or oxidation without significantly filling the etched void. Conventional process steps are used to provide the source and body regions around the cavity containing the gate, and to provide a drift space and drain region below the body region. The etched void between the gate and drain provides lower Cgd and Ron*Qg than can be achieved using low k dielectrics.