Variations in the composition and bonds of boron carbon nitride (BCN) film caused due to an oxygen (O-2) plasma ashing process are investigated for a low dielectric constant (low-k) insulating film for next generation LSI devices. The O-2 plasma treatment is preformed for BCN samples with various C compositions. The etching rate of BCN films with an O-2 plasma decreases with increasing C composition. The reaction of O atoms is suppressed in the BCN film with a high C composition. B-N and B-C bonds with lower bond energies are easily broken by the O-2 plasma and replaced by the generation of B-O, N-O, and C-O bonds. The B-atom concentration for all samples is decreased significantly by the O-2 plasma treatment. Ion bombardment may play a more dominant role than the O-atom reaction in the etching of the BCN film. The existence of C-N bonds with a high bonding energy may suppress etching and incorporation of O atoms. (C) 2008 Published by Elsevier B. V.