Structures and dielectric properties of thin polyimide films with nano-foam morphology

Thin polyimide films with dispersed nano-foam morphology have been prepared for the purpose of obtaining low dielectric polymer insulators for microelectronic applications. They were obtained by utilizing micro phase-separated triblock copolymers where the thermally stable polyimide matrix component was derived from pyromellitic dianhydride (PMDA) with 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3F) and a thermally labile poly(propylene oxide)(PO) component comprised the outside block of the ABA triblock architecture. TEM studies show that the initial irregular nanoscale phase-separated morphology of polyimide triblock copolymers are mostly maintained in the final nano-foam films upon thermal decomposition of the dispersed PO component. The nano-foam polyimide films exhibit significantly lower dielectric constants ε′ (e.g., 2.3 at 19% porosity) as compared with ε′≊2.9 for the homopolymer, as predicted by Maxwell-Garnett theory, with the nano-pore structures remaining stable at 350°C. © 1996 American Institute of Physics.