Methods are described for forming “air gaps” between adjacent metal lines on patterned substrates. The common name “air gap” will be used interchangeably with the more technically accurate “gas pocket” and both reflect a variety of pressures and elemental ratios. The air gaps are produced within narrow gaps between copper lines while wide gaps retain dielectric material. Retention of the dielectric material within the wide gaps enables formation of a desirable planar top surface. Using a hardmask layer and a selective dry-etch process enables a wet processing step to be avoided right before the formation of the air gaps. The air gaps can have a dielectric constant approaching one, favorably reducing interconnect capacitance compared with typical low-k dielectric materials.