Properties of nanoporous organosilicate hybrid thin films with a bimodal pore size distribution

摘要

Low dielectric poly[methylsilsesquioxane-ran-trifluoropropylsilsesquioxane-ran-(2,4,6,8-tetramethyl-2,4,6,8-tetraethylenecyclotetrasiloxane)silsesquioxane]s (P[M-ran-TFP-ran-(TCS)]SSQs) having various compositions were synthesized using trifluoropropyl trimethoxysilane,methyl trimethoxysilane and 2,4,6,8-tetramethyl-2,4,6,8-tetra(trimethoxysilylethyl)cyclotetrasiloxane.The chemical composition of the polymers and the content of SiOH end-groups were controlled by adjusting the reaction conditions,and they were characterized by ~1H-NMR.The thermally decomposable trifluoropropyl groups on the P[M-ran-TFP-ran-(TCS)]SSQ backbone and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (CD) were employed as pore generators.The dielectric constants of the porous CD/P[M-ran-TFP-ran-(TCS)]SSQ films were in the range 2.0-2.7 (at 100 kHz) depending on the concentration of the porogens,and showed no change over 4 days under aqueous conditions.The pore size of the films showed a bimodal distribution,with diameters of ca 0.5-l.0nm for those originating from the trifluoropropyl groups and 1.7nm from the CD.The elastic modulus and hardness of the 30 vol% CD-blended film with a dielectric constant of 2.26 were 2.40 and 0.38 GPa,respectively,as determined by a nanoindenter.