Hydrogen ions drifting into underlying layers during HDP-CVD were successfully suppressed by the insertion of plasma deposited silicon oxynitride (p-SiOxNyHz) film, and the hydrogen-trapping mechanism was clarified. The hydrogen ions are trapped in bonding states, not in interstitial ones. After HDP-CVD undoped silicate glass (HDP-USG) film deposition on the p-SiOxNyHz film, the decrease of the dangling bonds in the p-SiOxNyHz film measured by ESR was much lower than the increase of the desorbed hydrogen concentration measured by TDS. These results suggest that new hydrogen-trapping sites are mainly generated from ESR-inactive bonds by drifted hydrogen ions and atomic hydrogen during HDP-CVD. (c) 2006 Elsevier B.V. All rights reserved.