Dielectric etch capabilities of a high density plasma etcher have been investigated for the Damascene etch. Here, the patterning of vias, pads, and interconnects by the selective etch stop film approach was evaluated. In particular, the role of fluorocarbon polymer film was studied in etch lag effects and differential dielectric etch (oxide versus nitride). The result shows that the highly selective etch relies on the selective deposition and fluorine scavenging. This article provides the physical insights for the success of the differential dielectric etch. While the investigation is under the Damascene etch, the fundamental understanding can be applied to any highly selective etching of oxide versus nitride.