Fluorinated nanoporous SiO2 films with ultra-low dielectric constant

Fluorinated nanoporous silica (denoted as SiO₂:F) thin films with low dielectric constant were prepared by a sol-gel method and spin coating technique. The leakage current densities of the SiO₂:F thin films were 10⁻⁸ and 3 × 10⁻⁶ A/cm² respectively for the as-deposited films and for those subjected to annealing at a temperature of 450 °C. These currents are more than one order of magnitude lower than those of the common SiO₂ films. Photoluminescent results showed strong blue-light emission and a small blue shift in the SiO₂:F films that were related to the increment of the porosity. The dielectric properties were also characterized and the k value of the annealed SiO₂:F film was found to be about 1.67. The hole size in the films is small and the size distribution is uniform for the annealed SiO₂:F samples due to the effects of fluorination. The underlying mechanism for fluorination is discussed in this paper.