Effect of an interfacial layer on adhesion strength deterioration between a copper thin film and polyimide substrates

Abstract

Copper (Cu) was sputtered onto a polyetheretherketon (PEEK) film and onto three types of polyimide (PI) films; pyromellitic dianhydride-oxydianiline (PMDA-ODA), biphenyl dianhydride- para-phenylene diamine (BPDA-PDA) and biphenyl dianhydride-oxydianiline (BPDA-ODA). All films were pre-treated with oxygen plasma. We measured the adhesion strength between the Cu thin film and these polymer substrates and found that Cu/PMDA-ODA, Cu/BPDA-ODA and Cu/PEEK laminates showed strong adhesion, but Cu/BPDA-PDA laminate showed weak adhesion. These results show that the ether moiety between the two benzene rings in ODA (oxydianiline) would play an important role in the adhesion between a Cu thin film and a PI substrate. Furthermore, we found that the adhesion strength of the Cu/BPDA-PDA laminate could be significantly improved by a nickel (Ni) interfacial layer. Adhesion strength between a Cu thin film and a PMDA-ODA polyimide substrate is reduced from 10.0 to 2.0 N/m by heat treatment at 150°C in air. We introduced an interfacial layer of indium-tin-oxide (ITO) between the PI and Cu (Cu/ITO/PI) in order to prevent the oxidation of Cu and PI. The adhesion strength of the Cu/ITO/PMDA-ODA film was about 8.0 N/m even after heat treatment at 150°C in air for 3 days. Moreover, the adhesion strength of the Cu/ITO/BPDA-PDA film was maintained over 4.0 N/m even after heat treatment at 150°C in air for 3 days.