This work examines the impact of the chemistry of the gas mixture (N-2/H-2) and the plasma-related operating conditions on etching and/or passivation of siloxane-based polymer (HOSP) films. Plasmas generated using an inadequate power source and an H-2-dominating chemistry tend to induce the removal of carbonaceous species and over-cross-linking from such a film's structure, sharply degrading the film's dielectric constant (k) and insulating capacity. Nonetheless, properly adjusting the operating power supply and shifting the gas mixture toward the N-2-dominant regime cause the N-2/H-2 plasma to outperform the commonly used NH3 and N-2 plasmas with respect to protecting the films against O-2 plasma damage, by forming a surface nitride layer. (C) 2002 The Electrochemical Society.