Solventiess polyimide films by vapor deposition

Abstract

Vapor deposition polymerization (VDP) has been employed for the preparation of polyamic acid/imide films using a conventional thin film evaporator with a novel source design. The process utilizes the coevaporation of the dianhydride and diamine precursors. Control of source effusion rates permit film stoichiometry to be held to better than 1 mol %. Infrared, electron spectroscopy for chemical analysis (ESCA), and thermogravimetric analysis (TGA) results are consistent with the interpretation that the VDP films produced are polyamic acid curable to polyimide. The weight average molecular weight of the polyimide as determined by low angle light scattering (LALS) technique is 13 000, in agreement with the value estimated from the measured percent elongation at break point. Lift-off tests showed that vapor deposited polyimide is more resistant to hydrolitic attack at the silicon interface than spin coated Dupont RC5878. Dielectric constant (e - 2.91) and dissipation factor (tan δ - 0.008) are lower than those reported for commercial materials. Index of refraction measurements show a lesser degree of anisotropy for VDP polyimide than spin coated films, which may be important in reducing interfacial stress. Finally, a complete dry process utilizing this VDP technique for the fabrication of submicron polyimide patterns was demonstrated. © 1986, American Vacuum Society. All rights reserved.