US Patent 9911652 Forming self-aligned vias and air-gaps in semiconductor fabrication

Mandrel lines non-mandrel lines, and spacers are located in a structure having several layers. A spacer in the set of spacers comprises a structure formed above the top mask layer. A first trench is etched at a first location on a mandrel line through the top mask layer and stopping at the middle mask layer. A second trench is etched at a second location on a non-mandrel line through the top mask layer and stopping at the middle mask layer. A spacer material is removed from a structure resulting from the etching the trenches. Vias are formed in the first and second trenches. An air-gap is formed at a location of the spacer. The first via structure and a first portion of the bottom mask layer under the first via structure are removed and filled with a conductive metal.