Poly(tetrafluoro-p-xylylene), a low dielectric constant chemical vapor polymerized polymer
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 die SEMATECH criteria, exhibiting an onset of degradation at 460 degrees C, and 1% weight loss at 480 degrees C in an argon environment. The x-ray diffraction data suggest a disordered semicrystalline polymer as-deposited (at similar to 12 degrees C). The crystalline phase became mon ordered due to a decrease in the d spacing from 4.850 to 4.594 Angstrom and an increase in the percent crystallinity from 39% as-deposited to 66% after successive postdeposition anneals to 300 degrees C. Optical measurements showed a highly anisotropic thin film with n(e) @630 nm=1.601 and n(0) @630 nm=1.471, progressively becoming more negatively birefringent after postdeposition anneals, reaching a plateau at similar to 250 degrees C, due to the polymer chain becoming more conformationally ordered. (C) 1998 American Institute of Physics.