A low κ dielectric barrier/etch stop has been developed for use in copper damascene application. The film is deposited using methane, silane and argon as precursors in a HDP-CVD reactor. The film has a dielectric constant of 4.2 which is lower than the dielectric constant of conventional SiC or plasma silicon nitride (>7). Film characterization including physical, electrical, adhesion to ILD films, etch selectivity, and copper diffusion barrier properties show that this film is a better barrier than silicon nitride for low κ copper damascene interconnects. This film consists of a refractive index in the range of 1.7 to 1.8, a compressive stress of 1.0-1.5×109 dynes/cm2, and a leakage current of 5.0×10−10 A/cm2 at 1 MV/cm. When integrated in-situ with HDP-FSG, an effective dielectric constant of 3.5 can be achieved.