The properties of SiO2 film and the Si/SiO2 interface formed by remote plasma enhanced chemical vapor deposition with the addition of chlorine into SiH4–N2O have been investigated. With the chlorine addition, the deposition rate increased at low deposition temperatures but at temperatures above 150 °C, it decreased because of the desorption of surface halide species. Chlorine at the Si/SiO2 interface prevented further subcutaneous oxidation and formed strong, terminal site Si–Cl bonds which reduced the interface state density. The substitution reaction of O and H with Cl in the bulk oxide film leads to a disordered film structure and decreased hydrogen concentration. The surface roughness increased and the refractive index decreased with increased Cl2 addition. With chlorine addition of less than 6 vol %, the interface trap density (located at ∼Ev+0.3–0.4 eV) significantly decreased down to the 1–3×1011 eV cm2 level at the Si midgap. At high chlorine partial pressure and temperature, the local interface trap density (located at ∼Ev+0.7–0.8 eV) increased due to increased structural disorder resulting from breakage of the Si–O bond.