Methods are described for forming and treating a flowable silicon-carbon-and-nitrogen-containing layer on a semiconductor substrate. The silicon and carbon constituents may come from a silicon-and-carbon-containing precursor while the nitrogen may come from a nitrogen-containing precursor that has been activated to speed the reaction of the nitrogen with the silicon-and-carbon-containing precursor at lower deposition temperatures. The initially-flowable silicon-carbon-and-nitrogen-containing layer is ion implanted to increase etch tolerance, prevent shrinkage, adjust film tension and/or adjust electrical characteristics. Ion implantation may also remove components which enabled the flowability, but are no longer needed after deposition. Some treatments using ion implantation have been found to decrease the evolution of properties of the film upon exposure to atmosphere.