Structural characteristic and thermal stability of nanoporous SiO2 low-k thin films prepared by sol–gel method with catalyst HF

In this paper, hydrofluoric acid (HF) was used as catalyst in sol–gel method to prepare nanoporous silica thin film with ultra-low dielectric constant (k). The introduction of HF not only produced the Si–F bonds, which has the lower polarizability deriving from the least electronegative of fluorine ion, but also adjusted the speed of sol–gel reaction. The microstructure morphologies of the films catalyzed using HCl and HF were compared by FE-SEM. The results of N2 adsorption and desorption further confirmed the FE-SEM morphologies and indicated that the suited introduction of HF as catalyst increased the porosity and reduced the pore size distribution (about 10 nm). The differences among samples, which were catalyzed with different acids and different dosage, were also investigated by FTIR. All these results indicated that the film deposited using HF as catalyst exhibited better structural and dielectric properties, which appear to be a promising low-k material for IMD application.