SiBN ternary and SiOBN quaternary films prepared by rf-plasma and/or ECR-plasma CVD have been proposed, and this paper evaluates the relationship between film structure and dielectric constant as well as the other film properties. The SiBN films contain Si-N and B-N bonds, and the dielectric constant of the SiBN films reduces with increasing proportion of B-N bonds in the films. The SiBN films are less hygroscopic than BN films and they are therefore more stable. For the SiOBN films, the effects of oxygen doping on the dielectric constant and on breakdown strength are discussed in terms of the film composition and bonding configuration. The dielectric constant decreases with increasing oxygen atomic ratio and reaches a minimum when the amount of oxygen is equal to the amount of silicon. The effectiveness of this low-dielectric-constant material as an interlay-er is confirmed in actual VLSIs with planarized two-level metallization using the SiBN interlayer.