Controllable preparation of ultra-low-dielectric nanoporous silica via inorganic–organic hybrid templates

Abstract

Four organic–inorganic hybrids were respectively synthesized via hydrosilylative addition reaction between octahydridosilsesquioxane (POSS) and linear dienes with different numbers of methylene groups, and well characterized by FTIR, ¹³C NMR and ²⁹Si NMR technologies. It is confirmed that the hybrids have well-defined three-dimensional network structures with POSS cages uniformly dispersed in the networks. The four hybrids were then used as templates to produce silica films through an optimized spin-coating and calcination process. N₂ sorption–desorption determination reveals that the silica films are nanoporous with a narrow pore distribution. Cross-section HRTEM images of the four films further confirm that the nanosize pores are evenly dispersed. SEM observation shows that the surfaces of the films are smooth and free of cracks or flaws. By altering the number of methylene groups of the dienes linking the POSS cages, pore size and porosity of the porous silica films are easily adjusted. After dehydroxylation treatment with trimethylchlorosilane (TMCS), the porous films show very low dielectric constants, which is closely related to the porosity of the film. This result reveals that the controllable preparation of low dielectric silica films has been achieved in this study.