Low dielectric constant silica films with ordered nanoporous structure

In this paper, a novel route to prepare low-k nanoporous SiO2 films is reported. Silicate sols are prepared with the precursor Si(OC2H5)4 and surfactant cetyltrimethyl ammonium bromide (CTAB) catalyzed by hydrochloric acid. The films are derived from dip-coating process. The refractive index and dielectric constant are measured with an ellipsometer and impedance analysis apparatus, which are smaller than 1.15 and 2.5 respectively. XRD and TEM patterns show that silica films derived from a mole ratio of CTAB/TEOS of 0.10 or 0.15 have typical mesoporous structures with a period of 5 nm and a pore size of 4 nm. A drag-wipe test shows that films with ordered porous structure have much better mechanical properties than those with disordered porosity. And hydrophobicity of silica films can be achieved by HMDS treatment and the contact angle of water to the surface of hydrophobic films can be up to 140°.