High-temperature polymers for advanced microelectronics

Several series of aromatic polyethers and polybenzoxazoles with high therma l stability and low dielectric constant were prepared and characterized. Th e polyethers were synthesized by nucleophilic aromatic displacement of fluo rine with phenoxides. In order to avoid strongly polar groups such as carbo nyl and sulfone, trifluoromethyl groups were used to activate the fluorine for displacement, An additional benefit of the presence of the trifluoromet hyl groups is the decreased dielectric constant, which fluorinated material s exhibit. This is attributed to two factors: the strong electronegativity of fluorine, resulting in very low polarizability of the C-F bonds, and the larger radius of a fluorine atom in comparison with a hydrogen atom, resul ting in increased free volume. Trifluoromethyl substituted terphenyl and quadriphenyl poly(arylether)s pre pared in this study exhibit decomposition temperatures far in excess of 500 degreesC, even in air, dielectric constants below three, and mechanical pr operties comparable to engineering plastics such as polycarbonate and highp erformance thermoplastics such as PEEK. Poly(benzoxazole)s were prepared with and without fluorine substituents. Si nce most of the poly(benzoxazole)s were insoluble, they were prepared via s oluble poly(hydroxyamide) precursors, which were converted to the final pol ymers by thermal treatment. These materials had dielectric constants as low as 2.69 and also decomposition temperatures far above 500 degreesC in air.