Molecular design of POSS core star polyimides as a route to low-κ dielectric materials

Star polyimides incorporating the polyhedralsilsesquioxane (POSS-NH2) unit were prepared by in situ curing of polyamic acid macromolecules with amino POSS, octa (aminopropylsilsesquioxane), for the molecular-level design of low dielectric constant (low-kappa) materials that can be used to manufacture integrated circuits. Octameric POSS-NH2 having restricted rotation by multiple point attachment to the polyimide backbone is shown to introduce free volume into the films, thereby lowering their dielectric constants. A process for synthesizing POSS-polyimide star nanocomposites is reported, comprising a step forming porous-type POSS and subsequent step with polyimide precursor. The POSS-NH2 containing polyimides exhibit a number of desirable properties including low-water absorption and high thermal stability. Systematic studies demonstrate that proper insertion of POSS into a polyimide backbone can give rise to a reduction in the material's dielectric constant while also improving its mechanical and thermal properties. (C) 2008 Elsevier B.V. All rights reserved.