A processing method for depositing porous silica and doped silica films is provided. The method uses a cyclic scheme wherein each cycle comprises first codepositing silica with silicon, then selectively removing the silicon to form a porous structure. In a preferred embodiment, the codeposition is carried out by plasma enhanced chemical vapor deposition. The reagent feed stream comprises a mixture of codeposition reagents and a selective silicon removal reagent. RF power modulation is used to control the codeposition and the selective silicon removal steps with the later proceeds whenever the RF power is turned off or reduced to a low level. A porous film with highly uniform small pores and a desired porosity profile can be obtained with this method. This method is advantageous for forming a broad range of low-k dielectrics for semiconductor integrated circuit fabrication. The method is also advantageous for forming other porous films for other applications.