Modification of chemical vapor deposition low-k films upon sequential exposure to helium plasma and then ammonia plasma is characterized using various methods. The He plasma emits extreme ultraviolet (EUV) photons creating O-2 vacancies, which impacts surface reactive sites and induces localized chemical modifications in the first surface monolayers. The subsequent NH3 plasma treatment provides complete sealing of the low-k surface. The depth of the modification, which is a factor of merit of the sealing process, is limited because of the high absorption coefficient of silica-based low-k materials in the range of EUV emission. (C) 2007 The Electrochemical Society.