Ultralow-k nanocrystalline silica films with an open porosity of 30-31% and a pore radius of 0.8-0.9 nm have been etched using oxygen free highly polymerizing fluorocarbon plasma. It is shown that such plasma allows minimization of plasma damage in comparison with standard oxygen containing CF4 based plasmas and provides in situ sealing of the pores by deposition of fluorocarbon polymers in the film. We also demonstrate that the resulting surface is well suited for the nucleation and growth of atomic layer deposited WCN films. Characterization of the etched low-k dielectric by various analytical instrumentations demonstrates feasibility of this approach for integration of ultralow-k dielectric films. (c) 2005 American Vacuum Society.