Helmet structures for semiconductor interconnects

Interconnect structures are disclosed. An example includes conductive traces over a first dielectric layer, dielectric helmet structures over top surfaces of the conductive traces, and a second dielectric layer over the helmet structures. Spaces between adjacent ones of conductive traces are devoid of material. A bottom surface of the second dielectric layer is between top surfaces of the dielectric structures and bottom surfaces of the helmet structures, or co-planar with the top surface of the helmet structures, but the airgap extends above tops of the conductive traces. Another example includes a dielectric adjacent to upper sections but not lower sections of conductive traces, so as to provide airgaps between adjacent lower sections. Alternatively, a first dielectric material is adjacent the upper sections and a second compositionally different dielectric material is adjacent the lower sections. In either case, the sidewalls of the upper sections of the interconnect features may include scalloping.