This study investigates how the chemistry of the single (O-2, N-2, and H-2) and mixed gas sources (N-2/H-2), and the plasma-related operating conditions affects etching and (or) passivation of siloxane-based polymer (HOSP) films. Plasmas generated using inadequate power sources and an H-2-dominating chemistry induced the breakdown of carbonaceous species and over-crosslinking of the HOSP films, sharply degrading the films' dielectric constant (k) and insulating characteristics. However, properly adjusting the power/energy deposition and shifting the mixed gas toward the N-2-dominant regime generated an N-2/H-2 plasma that acted positively to protect the films from O-2 plasma damage and retard copper diffusion during thermal annealing. X-ray photoelectron and absorption spectroscopies, along with depth-profiling secondary ion mass analysis, indicated that the passivation effect was due to the formation of a surface nitride-based layer that contained implanted nitrogen atoms of various chemical bonding states including Si-N, C-N, and O-N. The synergistic effect of the mixed N-2/H-2 gases in the plasma passivation of HOSP films is discussed in terms of previous studies of plasma etching of low-k films and ion nitriding. (C) 2003 The Electrochemical Society.