A method for forming a radio frequency area of an integrated circuit are provided. The method includes forming a buried oxide layer over a substrate, and an interface layer is formed between the substrate and the buried oxide layer. The method also includes etching through the buried oxide layer and the interface layer to form a deep trench, and a bottom surface of the deep trench is level with a bottom surface of the interface layer. The method further includes forming an implant region directly below the deep trench and forming an interlayer dielectric layer in the deep trench.