Adhesion Enhancement of Thin Film Metals onto Polyimide Substrates by Bias Sputtering

Abstract

The adhesion of thin film metals deposited by bias sputtering has been studied. Al, Cr, Ta, and Ti thin films have been deposited onto polyimide substrates using DC magnetron sputter. RF bias of 0 ~ 400 watt was applied to the substrate during DC sputtering. The adhesion was evaluated using a 90 degree peel test. The peel adhesion strength was low when the RF bias was not applied during sputtering. However, it increased with RF bias power in all specimens. Scanning electron microscopy and Auger depth profile indicated that polyimide cohesive failure occurred during peeling and heavy deformation was observed in the metal films peeled from polyimide substrates when RF bias was applied during deposition. Cross-sectional transmission electron microscopy showed the thin implanted layer of metals in the polyimide interface. The implantation layer was likely formed due to the RF bias to the substrate. This implantation effect can explain the adhesion enhancement by bias sputtering.