Synthesis and characterization of fluorinated benzoxazole polymers with high T-g and low dielectric constant

Next generation microelectronic packaging requirements are driving the need to produce increasingly lower dielectric constant materials while maintain ing high thermal stability and ease of processing. Efforts have focused on the synthesis and analysis of new polymers with the goals of high thermal s tability [degradation temperature (T-d) > 400 degrees C, low glass-transiti on temperature (T-g) > 350 degrees C], low water uptake (<1%), solubility i n selected organic solvents, dielectric constant less than 2.5, and low the rmal expansion coefficient. These stringent combined goals have been largel y achieved with flexible aromatic benzoxazole polymers. Intramolecular hydr ogen bonding between pendant hydroxyl groups and the double-bond nitrogen o f the benzoxazole has been exploited to increase the polymer T-g, whereas t he incorporation of perfluoroisopropyl units effectively decreases the diel ectric constant. Out-of-plane impedance measurements on films of materials in this family (38-134 mu m thick) have resulted in typical dielectric valu es of 2.1-2.5 at 1 MHz, depending on copolymer ratios and functionalization s. Results have been correlated with optical waveguide measurements of film s 4-mu m thick to determine film anisotropy and the high-frequency dielectr ic constant, and have been corroborated by in-plane interdigitated electrod e dielectric measurements on samples 0.75 mu m thick. Candidate materials e xhibited extremely low water uptake (0.2%) even after submersion in boiling water for several days. Dynamic mechanical analysis of the polymers enable d the determination of the influence of intermolecular hydrogen bonding on the T-g and loss tangent magnitude. Finally, the coefficient; of thermal ex pansion has been examined and correlated with copolymer constitution. (C) 2 000 John Wiley & Sons, Inc.