US Patent 11984351 Cavity in metal interconnect structure

An integrated circuit device includes a dielectric structure within a metal interconnect over a substrate. The dielectric structure includes a cavity. A first dielectric layer provides a roof for the cavity. A second dielectric layer provides a floor for the cavity. A material distinct from the first dielectric layer and the second dielectric layer provides a side edge for the cavity. In a central area of the cavity, the cavity has a constant height. The height may be selected to provide a low parasitic capacitance between features above and below the cavity. The roof of the cavity may be flat. A gate dielectric may be formed over the roof. The dielectric structure is particularly useful for reducing parasitic capacitances when employing back-end-of-line (BEOL) transistors.