A method for filling gaps between structures includes forming a plurality of high aspect ratio structures adjacent to one another with gaps, forming a first dielectric layer on tops of the structures and conformally depositing a spacer dielectric layer over the structures. The spacer dielectric layer is removed from horizontal surfaces and a protection layer is conformally deposited over the structures. The gaps are filled with a flowable dielectric, which is recessed to a height along sidewalls of the structures by a selective etch process such that the protection layer protects the spacer dielectric layer on sidewalls of the structures. The first dielectric layer and the spacer dielectric layer are exposed above the height using a higher etch resistance than the protection layer to maintain dimensions of the spacer layer dielectric through the etching processes. The gaps are filled by a high density plasma fill.