EFFECT OF DOSE STOICHIOMETRY ON THE STRUCTURE OF VAPOR-DEPOSITED POLYIMIDE THIN-FILMS

PMDA-ODA polyimide thin films can be formed by vapor co-deposition of the precursor molecules PMDA (pyromellitic dianhydride) and ODA (4,4'- oxydianiline) if the resulting polyamic acid film is heated to a 473 t o 573 K cure step. We have used laser Raman spectroscopy to study how dose composition, dose rate, and substrate temperature influence the p roperties of the resulting polyimide films. We find that only doses wi th excess PMDA produce high quality films. Doses with 1:1 stoichiometr y or excess ODA produce thermally unstable films that contain imine bo nds; these films decompose below 575 K. Dosing onto substrates below 3 15 K produces the polyamic acid precursor of polyimide. At higher subs trate temperatures, films with high defect densities or decomposed fil ms are produced. The equilibrium vapor pressures of ODA and PMDA are r eported.