High-temperature polyimide nanofoams for microelectronic applications

Foamed polyimides have been developed in order 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 block copolymers consisting of thermally stable and thermally labile blocks, the latter being the dispersed phase. Foam formation is effected by thermolysis of the thermally labile block, leaving pores of the size and shape corresponding to the initial copolymer morphology. Nanofoams prepared from a number of polyimides as matrix materials were investigated as well as from a number of thermally labile polymers. The foams were characterized by a variety of experiments including TEM, SAXS, WAXD, DMTA, density measurements, refractive index measurements and dielectric constant measurements. Thin film foams, with high thermal stability and low dielectric constants approaching 2.0, can be prepared using the copolymer/nanofoam approach.