Low-dielectric, nanoporous polyimide thin films prepared from block copolymer templating

Abstract

In this paper, a new method to the preparation of low-dielectric nanoporous polyimide (PI) films was addressed, based on the self-assembly structures of PS-b-P4VP/poly(amic acid) (PAA, precursor of PI) blends. It is found the microphase-separation structure of PS-b-P4VP/PAA is a precondition of the formation of nanoporous structures, which could be achieved by solvent annealing. Nanoporous PI films with spherical pore size of ~11 nm were obtained by thermal imidization followed by the removal of the PS-b-P4VP block copolymer. The porosity of the nanoporous PI films could be controlled by the weight fraction of the PS-b-P4VP block copolymer. The dielectric properties of the nanoporous PI films were studied, and it was found that the introduction of nanopores could effectively reduce the dielectric constant from 3.60 of dense PI films to 2.41 of nanoporous PI films with a porosity of 26%, making it promising in microelectronic devices. The fabrication method described here could be extended to other polymer systems.