Properties of nanoporous silica thin films determined by high-resolution x-ray reflectivity and small-angle neutron scattering

• Published in: Journal of applied physics 2000-02, Vol.87 (3), p.1193-1200
• Main Authors: Wu, Wen-li, Wallace, William E., Lin, Eric K., Lynn, Gary W., Glinka, Charles J., Ryan, E. Todd, Ho, Huei-Min
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.371997

A new methodology based on a novel combination of a high-resolution specular x-ray reflectivity and small-angle neutron scattering has been developed to evaluate the structural properties of low-dielectric-constant porous silica thin films about one micrometer thick supported on silicon wafer substrates. To complement these results, film composition was determined by high-energy ion scattering techniques. For the example thin film presented here, the overall film density was found to be (0.55±0.01) g/cm3 with a pore wall density of (1.16±0.05) g/cm3 and a porosity of (53±1)%. The characteristic average dimension for the pores was found to be (65±1) Å. It was determined that (22.1±0.5)% of the pores had connective paths to the free surface. The mass fraction of water absorption was (3.0±0.5)% and the coefficient of thermal expansion was (60±20)×10−6/°C from room temperature to 175 °C. Lastly, model fitting of the specular x-ray reflectivity data indicated the presence of a thin surface layer with an increased electron density compared to the bulk of the film as well as an interfacial layer with a reduced electron density.