Spin-on-glass thin films prepared from a novel polysilsesquioxane by thermal and ultraviolet-irradiation methods

New dielectric films are prepared by both pyrolytic and photolytic conversi on of beta-chloroethyl-silsesquioxane (BCESSQ). Film thickness, refractive index, composition, density and morphology are characterized using a palett e of techniques including ellipsometry, Rutherford backscattering and forwa rd recoil spectrometry, X-ray reflectivity, and atomic force and electron m icroscopies. After annealing at 350 degrees C, BCESSQ films, initially 200 nm thick reach about 55% of their original thickness after 20 min. For film s heated in air for 4 h, the atom fractions of carbon and hydrogen monotoni cally decrease to 10 and 30%, respectively, as annealing temperature increa ses from 225 to 450 degrees C. The BCESSQ reactivity is reflected in the lo ss of chlorine at 400 degrees C. At 450 degrees C, the film density is 1.88 g/cm(3), or 84% of thermally-grown silicon oxide. Upon exposure to ultravi olet ozone radiation, films ranging from ca. 200 to 700 nm are found to con vert to ormosil films within 30 min. Surprisingly, the chlorine concentrati on is found to decrease more quickly than the hydrogen and carbon concentra tions, suggesting that the ormosil him evolves HCl leaving a vinyl group of Si-CH=CH2. This reaction pathway differs from the thermal case. For films prepared by pyrolytic and photolytic methods, atomic force and electron mic roscopy studies show that the surface is smooth and featureless, the bulk i s void free when view at a magnification of 50 000 x, and the ormosil/subst rate interface is continuous. (C) 1999 Elsevier Science S.A. All rights res erved.