Electrical, thermal and mechanical properties of polyimide thin films prepared by high-temperature vapor deposition polymerization

Abstract

Polyimide thin films were prepared on the whole surface of a substrate using a high-temperature vapor deposition polymerization method (VDP-H). In this method, pyromellitic dianhydride (PMDA) and oxydianiline (ODA), which are monomers of polyimides, are introduced into a process chamber from separate evaporation sources through inlet tubes. As the process chamber was kept at about 200 C, neither monomer could deposit on the substrate. Because the temperature of the substrate was higher than the evaporation temperature of the monomers, only polymerized films were deposited on the substrate. Infrared spectroscopy indicated that the VDP-H films were about 50% imidized. When the film thickness was less than I1 m, a uniform step coverage was observed, and above 2.5 pm a patterned surface was reduced to a planar surface. Film thickness was controlled by changing the amounts of monomers in the evaporation sources. The dielectric constant (E= 3.5), dissipation factor (tan 5 0.002), thermal characteristics (5% weight loss temperature= 551 C), and tensile strength (170 MPa) of the vDP-H films cured for 60 min at 300 C in vacuum were the same as those reported for Kapton® films. The modulus of elasticity (4.0 GPa) was larger than that of Kaptont®, and it was found that the VDP-H films showed less elongation than Kapton®.