Adhesion Improvement of Polyimide/Metal Interface by He/O2/NF3 Atmospheric Pressure Plasma

The surface of polyimide (PI) was modified with He/O2/NF3 dielectric barrier discharge generated by 13.56 MHz r.f. at atmospheric pressure in order to improve adhesion between metal (Cu/Cr) and PI. He/O2/NF3 plasma severely etched the surface of PI and formed many conical clusters of below 100 nm diameter on the PI surface. The surface roughness of PI was increased from 0.4 to 11 nm with r.f. power. X‐ray photoelectron spectroscopy (XPS) analysis showed that oxygen concentration was increased as much as the decrease of carbon concentration after plasma treatment. XPS analysis also showed that the component ratio of CO bonding, which is a hydrophilic functional group, was increased about 30% by the plasma treatment as compared with untreated PI. T‐peel test showed that peel strength was increased with r.f. power. The highest peel strength was 148 gf · nm−1, which was about 50 times as high as the peel strength obtained without plasma activation. It is more than two times as strong as the adhesion between the Cu/Cr film and PI substrate treated by O2 plasma. The surface morphology and chemical composition of the detached side of the PI treated by He/O2/NF3 plasma were similar to untreated PI.