Poly(tetraflouro-p-xylylene), a low dielectric constant chemical vapor polymerized polymer

Abstract

A low dielectric constant polymer, poly(tetrafluoro-p-xylylene) (VT-4) was synthesized by a chemical vapor polymerization process using 4,5,7,8,12,13,15,16-octafluoro-[2.2]-paracyclophane as a precursor. The VT-4 polymer has a dielectric constant of 2.42 and a dielectric loss of 0.008 at 1 MHz, perpendicular to the plane of the film. Thermal stability of VT-4 satisfied the SEMATECH criteria, exhibiting an onset of degradation at 460 °C, and 1% weight loss at 480 °C in an argon environment. The x-ray diffraction data suggest a disordered semicrystalline polymer as-deposited (at ∼12 °C). The crystalline phase became more ordered due to a decrease in the d spacing from 4.850 to 4.594 Å and an increase in the percent crystallinity from 39% as-deposited to 66% after successive postdeposition anneals to 300 °C. Optical measurements showed a highly anisotropic thin film with ne @630 nm=1.601 and n0 @630 nm=1.471, progressively becoming more negatively birefringent after postdeposition anneals, reaching a plateau at ∼250 °C, due to the polymer chain becoming more conformationally ordered.