The aluminum-polyimide interface: An electron-induced vibrational spectroscopy approach

Abstract

Clean polyimide films spin-coated onto gold substrate have been fully characterized by high resolution electron energy loss spectroscopy (HREELS): 19 electron-induced vibrational bands could be resolved and assigned by comparison with IR spectroscopy. The attribution of these peaks constitutes a firm and necessary basis for the detailed study of the incipient interface formation with aluminum at room temperature. The metal being evaporated at a low rate from a Knudsen effusion cell, its equivalent coverage on the polymer could be monitored very efficiently and allowed a clear distinction between three reaction steps: (i) at an Al coverage below 4 × 1014 Al atom/cm2, the aluminum atoms interact only with the C=O carbonyl in the polymer to form a C-O-metal complex; (ii) between 4 and 10 × 1014 atom/ cm 2, no further Al "reaction& occurs, but the appearance of new CH and OH stretching bands is attributed to bond breaking in the polymer and diffusion of the residues towards the surface; (iii) after further metal evaporation, all the peaks reduce in intensity and the observation of a v( Al-O) [or v( Al-C) band] testifies the formation of an aluminum oxide (or carbide) at the surface. Although no dedicated theory can be invoked up to now for the interpretation of HREELS data collected with different electron impact energies and under different scattering geometries, the spectra measured from polyimide before and after aluminum condensation are consistent with a modification of the geometry of the polymer monomeric unit after bonding with the metallic atoms. The metallized polymer surface appears with an equal statistical spatial distribution of all the chemical groups. © 1988 American Institute of Physics.