Nobuhiro Fukuda

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 2.0xa0N/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 8.0xa0N/m even after heat treatment at 150°C in air for 3xa0days. Moreover, the adhesion strength of the Cu/ITO/BPDA-PDA film was maintained over 4.0xa0N/m even after heat treatment at 150°C in air for 3xa0days.

Effect of a metallic interfacial layer on peel strength deterioration between a Cu thin film and a polyimide substrate

The peel strength of a copper (Cu) thin film deposited on a polyimide (PI) substrate deteriorates after heat treatment at 150u2009°C in air. The deterioration involves Cu2O microparticles (10–100 nm) penetrating the PI substrate, both the substrate and film being oxidized. To prevent this penetration and oxidation, we introduced an interfacial layer (vanadium, titanium, or cobalt) at the interface between the Cu thin film and PI substrate. Both titanium and cobalt interfacial layers were effective as barriers against the penetration of Cu2O particles. The quality of the interfacial layers (e.g., quantity of dislocations) influenced their effectiveness. By annealing the cobalt interfacial layers at 280u2009°C for 1 h in a vacuum before sputter deposition of a Cu thin film, we succeeded in keeping the peel strength between the Cu thin film and the PI substrate above 0.1 N/m even after heat treatment of the laminate at 150u2009°C for three days.

Changes in the adhesion strength between copper thin films and polyimide substrates after heat treatment

The adhesion strength between a copper (Cu) thin film and a polyimide [pyromellitic dianhydride-oxydianiline (PMDA-ODA)] substrate is reduced by heat treatment at 150°C in air. In this work, we determined the changes in adhesion strength between Cu films and polyimide substrates using Auger electron spectroscopy (AES), attenuated total reflection Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The analysis showed that the weak boundary layer (WBL) shifted towards the Cu interface as the heat treatment time was increased. To confirm this shift, we looked at two other polyimide substrates: biphenyl dianhydride-p-phenylene diamine (BPDA-PDA) and biphenyl dianhydride-oxydianiline (BPDA-ODA). Comparing the adhesion strength for the Cu thin film, the adhesion strength was high for the Cu/PMDA-ODA and Cu/BPDA-ODA laminates, but very low for the Cu/BPDA-PDA laminate. One of the possible reasons for this behavior could be that the ether moiety between the two benzene rin...

Changes in the Peeled Surfaces of Copper Thin Films Deposited on Polyimide Substrates After Heat Treatment

Abstract Peel strength between a copper (Cu) thin film and a polyimide (pyromellitic dianhydride-oxydianiline, or PMDA-ODA) substrate is reduced by heat treatment at 150°C in air. In this work, we investigated the peel strength, the morphology of the interface between Cu films and polyimide substrates using optical microscopy and electron microscopy, and chemical change of the interface using Auger electron spectroscopy (AES) and micro X-ray photoelectron spectroscopy (XPS). The analysis showed that CuO “lumps” were present on the peeled surface of PMDA-ODA after heat treatment at 150°C in air. The peeled surfaces of other polyimide substrates were also analyzed: biphenyl dianhydride-para phenylene diamine (BPDA-PDA) and biphenyl dianhydride-oxydianiline (BPDA-ODA). CuO lumps were present on the peeled surface of BPDA-ODA after the heat treatment, but not that of BPDA-PDA. Compared with the adhesion strength for the Cu thin film, the adhesion strength was high for the Cu/PMDA-ODA and Cu/BPDA-ODA laminates...