Nano-Architectural Silica Thin Films with Two-Dimensionally Connected Cagelike Pores Synthesized from Vapor Phase

Abstract

Novel mesostructured silica thin films were prepared on a Si substrate by a vapor-phase synthesis. Vapor of tetraethoxysilane (TEOS) was infiltrated into a surfactant film consisting of a poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) triblock copolymer. Nanophase transition from a lamellar structure to a two-dimensional cage structure of a silica−surfactant nanocomposite was found under vapor infiltration. The rearrangement into the cage structure implies high mobility of the silica−surfactant composites in solid phase. The silica thin films have two-dimensionally connected cagelike mesopores and are isotropic parallel to the film surface. The structure of pores of the films is advantageous for next-generation low-k films. The mesoporous structure has a large lattice parameter d of ∼102 Å, silica layer thickness of ∼58 Å, pillar diameter in the middle of ∼60 Å, pore size of ∼72 Å, BET surface area of ∼729 m²/g, and pore volume of ∼1.19 cm³/g. The films synthesized by the vapor infiltration show a lower concentration of residual Si−OH groups compared to the films prepared by a conventional sol−gel method. The films show high thermal stability up to 900 °C and high hydrothermal stability. This method is a simpler process than conventional sol−gel techniques and attractive for mass production of a variety of organic−inorganic composite materials and inorganic porous films.