Nanoporous polyimide films from polyimide-aliphatic polyester or polyimide-aliphatic polycarbonate copolymers

Abstract

We have explored polyimide foams created using a block copolymer approach as part of our research efforts to obtain thin film dielectric layers with very low dielectric constants for use in microelectronic devices. In these systems the pore sizes are in the nanometer range thus the term `nanofoam'. The polyimide foams are prepared from phase separated block copolymers consisting of thermally stabile and thermally labile blocks, the latter being the dispersed phase. Foam formation is effected by thermolysis of the labile block leaving pores the size and shape corresponding to the initial copolymer morphology. Polyimide nanofoams generated from thermolysis of polyimide-aliphatic polyester and polyimide-aliphatic polycarbonate copolymers were investigated. The aliphatic co-blocks were synthesized by ring opening polymerization of the cyclic monomers, such as ε-caprolactone, valerolactone, trimethylene carbonate, and L-lactide. The aliphatic blocks were designed in such a way as to allow for incorporation into polyimide copolymers. The foams were characterized by a variety of techniques including, TEM, SAXS, WAXD, DMTA, density and refractive index measurements.