<p>A method of forming an interconnect structure for a semiconductor device involving etching patterns of openings (18, 22) in a layer (12) of thermally decomposable filler material and forming either pillars (8) of dielectric 5 material or conductive interconnections in respective patterns of openings. The filler material is subsequently decomposed to form cavities (30) between the pillars and adjacent interconnections, so that air forms the dielectric material therebetween.</p>
