Diffusion of copper into polyimide deposited by ionized cluster beam

Abstract

Copper was deposited by sputtering on two types of polyimide (PI) films, one is fabricated by ionized cluster beam deposition (ICBD) and the other is Kapton, commercially available from DuPont. Diffusion properties of copper into these two polyimide films were investigated by x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. In addition, the packing densities of these PI films were measured by a rotational analyzer type ellipsometer. We found that PI films deposited by ICBD (ICB-PI) have a higher packing density than Kapton. We also found that less copper is diffused into ICB-PI than into Kapton, that is, PI by the ICB method blocks Cu diffusion into PI. The diffusion coefficient of Cu/ICB-PI is 2.45×10−17–2.8×10−15 cm2/s at 300–390 °C, the activation energy of Cu diffusion into ICB-PI is 1.75 eV and D0 for ICB-PI is 1.92×10−1 cm2/s. The Cu atoms diffuse into PI as a form of clusters.