Single step preparation of novel hydrophobic composite films for LOW-k applications

Composite films with low dielectric constants (k) containing micro- and mesopores are synthesized from precursor solutions for the preparation of mesoporous silica and ethanolic suspensions of silicalite-1 nanoparticles. The material contains silicalite-1 nanoparticles (include nanocrystals and nanoslabs/intermediates) embedded in a randomly oriented matrix of highly porous mesoporous silica. Micropores result from the incorporated silicalite-1 nanoparticles, while decomposition of the porogen F127 leads to additional mesopores. The porosity of the composite films increases from 9 to 60% with the increase in porogen loading, while in parallel the elastic modulus and hardness decrease. The elastic moduli of the films are in the range of 13-20 GPa. Hydrophobie surfaces of the composite films are obtained by introducing methyl triethoxysilane during the preparation of both precursor solutions, leading to the incorporation of-CH₃ groups in the final composite films. These methyl groups are stable up to at least 500°C. A low k value of approximately 2 is observed for films cured at 400°C in N₂ flow, which is ideal for removing templates without decomposing methyl groups. Due to the intrinsic hydrophobicity of the material, post-silylation is not required rendering the composite films attractive candidates for future low k materials.