Properties of Sol–Gel Derived Thin Organoalkylenesiloxane Films

We have prepared film-forming solutions for the growth of dense and porous thin organoalkylenesiloxane (OAS) films based on copolymers of methyltrimethoxysilane and 1,2-bis(trimethoxysilyl)ethane (BTMSE) by a sol–gel process. The chemical composition and microstructure of the OAS films have been studied by IR spectroscopy and spectral ellipsometry in relation to the mole fraction of BTMSE and the water: methoxy groups ratio in solution. The results demonstrate that partial substitution of ethylene bridges for silicon–oxygen bonds in OAS leads to distortion of the regular ladder-like structure characteristic of polymethylsilsesquioxane films and the presence of residual silanol groups, which causes an increase in the dielectric permittivity k of the matrix material. The relative porosity in porous OAS films produced via evaporationinduced self-assembly has been shown to be determined by not only the amount of surfactant added but also the presence of a sufficient amount of silanol groups, participating in the attachment of surfactant molecules, in the matrix copolymer solution. In this connection, an important factor determining the structure of the OAS matrix and its pore structure is control over the amount of water involved in the cohydrolysis process. It has been shown that the samples with a relative porosity of 38% prepared from a film-forming solution containing 47 mol % BTMSE ( m = 0.7) and 30 wt % surfactant have k ≈ 2.3 and are potentially attractive materials for use as insulators in integrated circuits.