A method is provided for forming a fluorinated silicate glass layer with HDP-CVD having a lower dielectric constant without compromising the mechanical properties of hardness and compressive stress. A gaseous mixture comprising a silicon-containing gas, an oxygen-containing gas, and a fluorine-containing gas is provided to a process chamber. The ratio of the flow rate of the fluorine-containing gas to the flow rate of the silicon-containing gas is greater than 0.65. A high-density plasma is generated from the gaseous mixture by applying a source RF power having a power density less than 12 W/cm2. A bias is applied to a substrate in the process chamber at a bias power density greater than 0.8 W/cm2 and less than 2.4 W/cm2. The fluorinated silicate glass layer is deposited onto the substrate using the high-density plasma.