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 from the codeposit to form a porous structure. In a preferred embodiment, the codeposition is carried out by plasma enhanced chemical vapor deposition. After codeposition, the codeposit is exposed to a selective silicon removal reagent that can preferentially remove the silicon in the codeposit, leaving behind a porous structure. Repeated execution of the codeposition and the selective silicon removal steps build up thickness of the porous film. 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 general method is also advantageous for forming other porous films for other applications.