Stable SiN-BN ternary films were prepared by hybrid-plasma-enhanced chemical vapour deposition using silane (SiH4), diborane (B2H6) and ammonia (NH3) as source gases. In addition to the decomposition of the source gases using an RF plasma, the NH3 gas was excited using a microwave plasma; this caused the N-H bond number in the SiN-BN films to greatly decrease, while the Si-N and B-N bonds increased. When the distortion in the chemical bond structure surrounding the boron atom was improved, the stability of the B-rich SixByNz:H and BNx:H films was remarkably improved.