Characteristics of poly(alkyl silsesquioxane) thin films prepared from chemically linked alkyl units

Poly(alkyl silsesquioxane), PASSQ, copolymers containing the different alkyl components were synthesized by sol–gel polymerization with a bridged alkoxysilane as a matrix component, and the potential applications of low-k films were verified using TGA, FT-IR, 13C and 29Si solid state NMR after pore forming process by the thermal decomposition. As the higher alkyl groups in PASSQ were decomposed, the lower refractive indices were achieved from 1.45 to 1.27 due to the formation of nanoporous in the film. In particular, the modulus for the three different PASSQ films were significantly higher than 3.8 GPa of the typical thin film of poly(methyl silsesquioxane). The enhanced moduli for the films are ascribed to the formation of rigid film structure by the introduction of bridged ethylene of BTMSE in spite of the porous structure. In addition, the partial decomposition of bridge ethylene groups was accompanied with the dominant occurrence of methyl silicon groups, which reduced the mechanical properties with microporous structure.